ORCID Profile
0000-0002-2820-2304
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CSIRO
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Publisher: Springer Science and Business Media LLC
Date: 26-06-2021
Publisher: Springer Science and Business Media LLC
Date: 05-08-2023
Publisher: IOP Publishing
Date: 22-08-2018
Publisher: Springer Science and Business Media LLC
Date: 26-07-2013
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2010
Publisher: MDPI AG
Date: 12-04-2023
DOI: 10.3390/MA16083053
Abstract: This study aimed to clarify the effect of wire structure and alkaline elements in wire composition on metal transfer behavior in metal-cored arc welding (MCAW). A comparison of metal transfer in pure argon gas was carried out using a solid wire (wire 1), a metal-cored wire without an alkaline element (wire 2), and another metal-cored wire with 0.084 mass% of sodium (wire 3). The experiments were conducted under 280 and 320 A welding currents, observed by high-speed imaging techniques equipped with laser assistance and bandpass filters. At 280 A, wire 1 showed a streaming transfer mode, while the others showed a projected one. When the current was 320 A, the metal transfer of wire 2 changed to streaming, while wire 3 remained projected. As sodium has a lower ionization energy than iron, the mixing of sodium vapor into the iron plasma increases its electrical conductivity, raising the proportion of current flowing through metal vapor plasma. As a result, the current flows to the upper region of the molten metal on the wire tip, with the resulting electromagnetic force causing droplet detachment. Consequently, the metal transfer mode in wire 3 remained projected. Furthermore, weld bead formation is the best for wire 3.
Publisher: IOP Publishing
Date: 11-07-2018
Publisher: Institute of Electrical Engineers of Japan (IEE Japan)
Date: 2014
Publisher: IOP Publishing
Date: 04-04-2007
Publisher: Springer Science and Business Media LLC
Date: 13-01-2016
Publisher: Elsevier BV
Date: 10-2018
Publisher: IOP Publishing
Date: 27-04-2011
DOI: 10.1088/0022-3727/44/19/194009
Abstract: The development of a three-dimensional computational model of gas–metal arc welding is described. The wire electrode, arc plasma and weld pool are included in the computational domain self-consistently. The model takes into account the motion of the electrode, flow in the weld pool, deformation of the weld-pool surface and the influence of metal droplet transfer. Results are presented for welding of an aluminium alloy. The current density distribution at the interface between the arc and the weld pool is strongly dependent on the surface profile of the weld pool. This in turn affects the temperature distribution in the weld pool. The momentum transferred by the droplet affects the direction of flow in the weld pool, and together with the energy transfer, increases the weld-pool depth. The results demonstrate the importance of including the arc plasma in the computational domain. Fair agreement is found between a measured weld profile and the predictions of the model. Inclusion of the influence of metal vapour in the model is expected to improve the agreement.
Publisher: Springer Science and Business Media LLC
Date: 09-01-2020
Publisher: AIP Publishing
Date: 27-07-1998
DOI: 10.1063/1.121899
Abstract: A two-dimensional numerical model of the PLASCON™ plasma reactor is used to investigate the destruction of ozone-depleting substances in the reactor. The model includes electromagnetic, fluid dynamic and chemical kinetic phenomena. Calculated temperature, flow and species concentration fields within the plasma torch, the injection manifold and the reaction tube are presented for the case of the destruction of CFC-12 (CF2Cl2). Conversion of CFC-12 to CFC-13 (CF3Cl), a more stable ozone-depleting substance, is found to occur in the region close to the injection manifold, and to be unaffected by reaction tube geometry. CFC-13 is predicted to be the dominant ozone-depleting substance in the exhaust gas. The predictions of the model are found to be in good agreement with measurements of the exhaust gas composition.
Publisher: Elsevier BV
Date: 09-2006
Publisher: AIP Publishing
Date: 15-07-2009
DOI: 10.1063/1.3176983
Abstract: This paper focuses on the numerical research of the influence of electrode erosion on the arc behavior during opening process of low-voltage circuit breakers. The mathematical model of three-dimensional air arc plasma considering electrode erosion is built based on magnetic hydrodynamics. The mass fraction equation of copper vapor is introduced to the model on the basis of traditional mass, momentum, and energy balance equations. The influence of copper vapor on the thermodynamic and transport properties of the gas mixture is considered in this paper. The distributions of temperature field, gas flow field, and mass fraction of copper vapor in the arc chamber are simulated. The arc root displacements and arc voltage, which takes account of the influence of electrode erosion, are calculated. The simulation results indicate that the immobility time of both moving contact and stationary contact is much longer considering electrodes erosion. The calculated voltage of the arc column during arc motion considering erosion is smaller because of the change in the electrical conductivity of air-copper vapor mixtures. Except for the numerical investigation on the arc motion considering electrode erosion, the experiment work is also carried out to support the simulation work.
Publisher: Japan Welding Society
Date: 2013
DOI: 10.2207/QJJWS.31.5S
Publisher: Informa UK Limited
Date: 11-03-2015
Publisher: MDPI AG
Date: 09-2017
Publisher: Springer Science and Business Media LLC
Date: 17-09-2019
Publisher: IOP Publishing
Date: 27-03-2008
Publisher: IOP Publishing
Date: 22-03-2017
Publisher: Elsevier BV
Date: 2014
Publisher: Elsevier BV
Date: 10-2018
Publisher: IOP Publishing
Date: 14-07-1994
Publisher: AIP Publishing
Date: 11-2525
DOI: 10.1063/1.1144516
Abstract: A technique is presented by which the Fowler–Milne spectroscopic method can be applied to thermal plasmas containing two or more atomic elements. The technique requires the measurement of the emission coefficient for an atomic transition of each element. These values are normalized to the maximum emission coefficient for each transition in the respective single-element plasmas. Neither calibration of the sensitivity of the apparatus nor knowledge of atomic transition probabilities is required. The technique allows the relative concentration of the elements to be derived significantly more precisely than other spectroscopic methods. The technique is applied to the measurement of the radial profiles of temperature and composition of free-burning arcs in mixtures of argon and nitrogen. Significant demixing is observed, with the direction of the demixing depending on the relative concentrations of argon and nitrogen.
Publisher: Springer International Publishing
Date: 2017
Publisher: IOP Publishing
Date: 04-08-2006
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TC01808E
Abstract: A direct one-step nano-gold printing process from a HAuCl 4 solution precursor is demonstrated using an atmospheric-pressure plasma jet.
Publisher: American Chemical Society (ACS)
Date: 19-12-2023
Publisher: Elsevier BV
Date: 09-2006
Publisher: IOP Publishing
Date: 16-07-2014
Publisher: Elsevier BV
Date: 03-2008
Publisher: Springer Science and Business Media LLC
Date: 16-12-2020
DOI: 10.1038/S41586-020-03043-4
Abstract: The safe, highly effective measles vaccine has been recommended globally since 1974, yet in 2017 there were more than 17 million cases of measles and 83,400 deaths in children under 5 years old, and more than 99% of both occurred in low- and middle-income countries (LMICs) 1–4 . Globally comparable, annual, local estimates of routine first-dose measles-containing vaccine (MCV1) coverage are critical for understanding geographically precise immunity patterns, progress towards the targets of the Global Vaccine Action Plan (GVAP), and high-risk areas amid disruptions to vaccination programmes caused by coronavirus disease 2019 (COVID-19) 5–8 . Here we generated annual estimates of routine childhood MCV1 coverage at 5 × 5-km 2 pixel and second administrative levels from 2000 to 2019 in 101 LMICs, quantified geographical inequality and assessed vaccination status by geographical remoteness. After widespread MCV1 gains from 2000 to 2010, coverage regressed in more than half of the districts between 2010 and 2019, leaving many LMICs far from the GVAP goal of 80% coverage in all districts by 2019. MCV1 coverage was lower in rural than in urban locations, although a larger proportion of unvaccinated children overall lived in urban locations strategies to provide essential vaccination services should address both geographical contexts. These results provide a tool for decision-makers to strengthen routine MCV1 immunization programmes and provide equitable disease protection for all children.
Publisher: IOP Publishing
Date: 17-09-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2GC02299K
Abstract: This work demonstrates alternative green ammonia processing using nitrogen and water based non-thermal plasma without pure hydrogen supply which results in an enormous amount of CO 2 emission.
Publisher: Elsevier BV
Date: 10-2017
Publisher: American Physical Society (APS)
Date: 11-1993
Publisher: AIP Publishing
Date: 09-1991
DOI: 10.1063/1.349355
Abstract: The use of a novel nonaxisymmetric quadrupole ion trap for frequency standard applications is suggested. The properties of such an elongated trap are examined using a cold-ion-cloud model. It is shown that increasing the elongation of the trap, while keeping either the smallest dimension or the volume of the trap constant, substantially increases the ratio of the number of ions that can be stored to the magnitude of the second-order Doppler shift of the ions. This indicates that a frequency standard incorporating an elongated rf ion trap can achieve greater precision than one based on the currently favored circular rf or Paul trap.
Publisher: IOP Publishing
Date: 03-11-2010
DOI: 10.1088/0022-3727/43/43/430301
Abstract: Metal vapour has a significant, and in some cases dominant, influence in many applications of atmospheric-pressure plasmas, including arc welding, circuit interruption and mineral processing. While the influence of metal vapour has long been recognized, it is only recently that diagnostic and computational tools have been sufficiently well-developed to allow this influence to be more thoroughly examined and understood. Some unexpected findings have resulted: for ex le, that the presence of metal vapour in gas–metal arc welding leads to local minima in the temperature and current density in the centre of the arc. It has become clear that the presence of metal vapour, as well as having intrinsic scientific interest, plays an important role in determining the values of critical parameters in industrial applications, such as the weld penetration in arc welding and the extinction time in circuit breakers. In gas–tungsten arc welding, metal vapour concentrations are formed by evaporation of the weld pool, and are relatively low, typically at most a few per cent. Moreover, the convective flow of the plasma near the weld pool tends to direct the metal vapour plume radially outwards. In gas–metal arc welding, in contrast, metal vapour concentrations can reach over 50%. In this case, the metal vapour is produced mainly by evaporation of the wire electrode, and the strong downwards convective flow below the electrode concentrates the metal vapour in the central region of the arc. The very different metal concentrations and distributions in the two welding processes mean that the metal vapour has markedly different influences on the arc. In gas–tungsten arc welding, the current density distribution is broadened near the weld pool by the influence of the metal vapour on the electrical conductivity of the plasma, and the arc voltage is decreased. In contrast, in gas–metal arc welding, the arc centre is cooled by increased radiative emission and the arc voltage is increased. In low-voltage circuit breakers, metal vapour is formed by evaporation of the electrodes (runners) and the splitter plates, and can have a major influence on the dynamics of arc motion. While the influence of metal vapour on arcs is now understood in general terms, there are many unresolved questions. Areas in which improvements and new insights are required include: diagnostic techniques for measurements of arc properties in the presence of metal vapour, and understanding of the possible deviations from local thermodynamic equilibrium and their influence on such measurements measurements of the influence of metal vapour in circuit breakers, in which the arc occurs within a solid enclosure, and in gas–metal arc welding, in which the formation of metal droplets and arc instabilities can disrupt standard techniques determination of the concentration of metal vapour species in different types of arcs understanding of the relative importance of the different effects of metal vapour (such as increased radiation and electrical conductivity, and the rapid influx of relatively cold gas) on the arc for different configurations the influence of metal vapour on the electrode boundary and sheath regions the treatment of radiative and mass transport in computational models understanding and treatment of the vaporization, condensation and nucleation of metal species, and methods of incorporation of these processes in computational models. In this cluster issue, many of these and related issues are addressed. The twelve contributions cover gas–metal arc welding, gas–tungsten arc welding and low-voltage circuit breakers, and include both experimental and computational studies, in some cases with striking results. A review of the influence of metal vapour in welding arcs is followed by three accounts of spectroscopic measurements of gas–metal arc welding, which are difficult to perform and until recently have rarely been attempted. The application of spectroscopic techniques to determine Stark widths of spectral lines is discussed in a further contribution. Two papers address the calculation of important plasma data sets, in particular net radiative emission coefficients and diffusion coefficients, which are vital input for computational models. Four sophisticated computational modelling studies of the influence of metal vapour on gas–metal arc welding, gas–tungsten arc welding, and arc splitting in low-voltage circuit breakers are then presented. The final contribution describes the application of a multiscale computational model to investigate the important occupational health problem of the production of fume from the metal vapour produced in welding arcs. Overall, the papers presented give an overview of the state of the art of research into metal vapour in atmospheric-pressure arcs, and at the same time constitute real progress in this topical and important field.
Publisher: CSIRO Publishing
Date: 2020
DOI: 10.1071/WR19181
Abstract: Abstract ContextFenced reserves from which invasive predators are removed are increasingly used as a conservation management tool, because they provide safe havens for susceptible threatened species, and create dense populations of native wildlife that could act as a source population for recolonising the surrounding landscape. However, the latter effect might also act as a food source, and promote high densities of invasive predators on the edges of such reserves. AimsOur study aimed to determine whether activity of the feral cat is greater around the edges of a fenced conservation reserve, Arid Recovery, in northern South Australia. This reserve has abundant native rodents that move through the fence into the surrounding landscape. MethodsWe investigated (1) whether feral cats were increasingly likely to be detected on track transects closer to the fence over time as populations of native rodents increased inside the reserve, (2) whether native rodents were more likely to be found in the stomachs of cats caught close to the reserve edge, and (3) whether in idual cats selectively hunted on the reserve fence compared with two other similar fences, on the basis of GPS movement data. Key resultsWe found that (1) detection rates of feral cats on the edges of a fenced reserve increased through time as populations of native rodents increased inside the reserve, (2) native rodents were far more likely to be found in the stomach of cats collected at the reserve edge than in the stomachs of cats far from the reserve edge, and (3) GPS tracking of cat movements showed a selection for the reserve fence edge, but not for similar fences away from the reserve. ConclusionsInvasive predators such as feral cats are able to focus their movements and activity to where prey availability is greatest, including the edges of fenced conservation reserves. This limits the capacity of reserves to function as source areas from which animals can recolonise the surrounding landscape, and increases predation pressure on populations of other species living on the reserve edge. ImplicationsManagers of fenced conservation reserves should be aware that increased predator control may be critical for offsetting the elevated impacts of feral cats attracted to the reserve fence.
Publisher: IOP Publishing
Date: 26-11-2013
Publisher: Springer Science and Business Media LLC
Date: 20-03-2015
Publisher: AIP Publishing
Date: 15-05-1993
DOI: 10.1063/1.353840
Abstract: The numerical plasma torch model of D. A. Scott, P. Kovitya, and G. N. Haddad [J. Appl. Phys. 66, 5232 (1989)], in which both the arc and plume regions are included in the computational domain, has been extended to treat the effect of the mixing of the plasma gas with the ambient gas. Both laminar diffusion and turbulent mixing are considered. The predictions of the model are compared with laser-scattering measurements of the temperature distribution in the plume of a plasma torch, for the case in which the plasma gas is argon and the ambient gas is air at atmospheric pressure. Good agreement is found between the measurements and the predictions of the model. The rapid decay in plume temperature away from the exit of the torch nozzle is shown to be mainly due to cooling by air entrained by turbulent mixing. The K-ε turbulence model is found to adequately approximate the turbulence phenonema involved.
Publisher: IOP Publishing
Date: 02-08-2017
Publisher: Elsevier BV
Date: 07-1992
Publisher: IOP Publishing
Date: 03-10-2017
Publisher: Elsevier BV
Date: 02-2023
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2011
Publisher: IOP Publishing
Date: 26-08-2016
Publisher: Springer Science and Business Media LLC
Date: 09-12-2016
DOI: 10.1038/SREP38610
Abstract: Cold atmospheric-pressure plasma (CAP) is a relatively new method being investigated for antimicrobial activity. However, the exact mode of action is still being explored. Here we report that CAP efficacy is directly correlated to bacterial cell wall thickness in several species. Biofilms of Gram positive Bacillus subtilis , possessing a 55.4 nm cell wall, showed the highest resistance to CAP, with less than one log 10 reduction after 10 min treatment. In contrast, biofilms of Gram negative Pseudomonas aeruginosa , possessing only a 2.4 nm cell wall, were almost completely eradicated using the same treatment conditions. Planktonic cultures of Gram negative Pseudomonas libanensis also had a higher log 10 reduction than Gram positive Staphylococcus epidermidis. Mixed species biofilms of P. aeruginosa and S. epidermidis showed a similar trend of Gram positive bacteria being more resistant to CAP treatment. However, when grown in co-culture, Gram negative P. aeruginosa was more resistant to CAP overall than as a mono-species biofilm. Emission spectra indicated OH and O, capable of structural cell wall bond breakage, were present in the plasma. This study indicates that cell wall thickness correlates with CAP inactivation times of bacteria, but cell membranes and biofilm matrix are also likely to play a role.
Publisher: Springer International Publishing
Date: 2023
Publisher: Public Library of Science (PLoS)
Date: 26-10-2018
Publisher: Oxford University Press (OUP)
Date: 13-10-2014
DOI: 10.1093/CRJ/CLU019
Publisher: IOP Publishing
Date: 08-1989
Publisher: Wiley
Date: 21-11-2017
Publisher: Springer Science and Business Media LLC
Date: 25-10-2013
Publisher: IOP Publishing
Date: 05-07-2022
Abstract: In the synthesis of alloy nanoparticles (NPs) via arc evaporation and fast quenching, the composition of the synthesized NPs differs significantly from that of the precursor. The properties of the NPs formed following evaporation of a copper–nickel anode by a helium arc are investigated using a nucleation model coupled to the thermal and flow fields derived from a magneto-hydrodynamic simulation of the arc, and experimentally. Results are obtained for three different Cu:Ni precursor compositions, 10:90, 50:50 and 90:10 at%. The synthesized particles are spherical with different size distributions and have a higher concentration of Cu than the precursor in all three cases, in contrast to previous observations, but in accordance with the predictions of the model. Emission spectroscopic measurements of copper and nickel lines indicate that the concentration of atomic copper in the plasma region near the anode is much higher than that of the nickel, in accordance with the predictions of the model. The higher vapour pressure of copper compared to nickel, and its higher activity in the alloy precursor (anode), immersed in a self-consistent thermal and flow field maintained by the transferred arc are found to play a critical role. The thermodynamic, radiative and transport properties of the helium plasma contaminated with evaporated precursor are important in determining the thermal and flow fields.
Publisher: Japan Welding Society
Date: 2013
DOI: 10.2207/QJJWS.31.80
Publisher: AIP Publishing
Date: 10-04-2015
DOI: 10.1063/1.4917210
Abstract: The influence of copper vapor mixed in hot CO2 on dielectric breakdown properties of gas mixture at a fixed pressure of 0.4 MPa for a temperature range of 300 K–4000 K is numerically analyzed. First, the equilibrium composition of hot CO2 with different copper fractions is calculated using a method based on mass action law. The next stage is devoted to computing the electron energy distribution functions (EEDF) by solving the two-term Boltzmann equation. The reduced ionization coefficient, the reduced attachment coefficient, and the reduced effective ionization coefficient are then obtained based on the EEDF. Finally, the critical reduced electric field (E/N)cr is obtained. The results indicate that an increasing mole fraction of copper markedly reduces (E/N)cr of the CO2–Cu gas mixtures because of copper's low ionization potential and large ionization cross section. Additionally, the generation of O2 from the thermal dissociation of CO2 contributes to the increase of (E/N)cr of CO2–Cu hot gas mixtures from about 2000 K to 3500 K.
Publisher: Japan Welding Society
Date: 2008
DOI: 10.2207/QJJWS.26.111
Publisher: Springer Science and Business Media LLC
Date: 25-09-2018
Publisher: AIP Publishing
Date: 11-2011
DOI: 10.1063/1.3658812
Abstract: A two-dimensional magneto-hydrodynamic (MHD) model of an ablation-dominated capillary discharge is developed. Special attention is paid to the interaction between the plasma and the capillary in two-dimensional geometry. The mass exchange process is taken into account by adopting a kinetic ablation model and a revised deposition model. The momentum and energy exchange processes associated with the ablated and deposited mass are also considered. By solving this model, key plasma parameters are calculated and presented in the paper. It is shown that distinct two-dimensional features exist in the distribution of these plasma parameters. Further, the calculated temperature results are consistent with previously presented measurements
Publisher: Japan Welding Society
Date: 2013
DOI: 10.2207/QJJWS.31.14S
Publisher: IOP Publishing
Date: 18-06-2013
Publisher: AIP Publishing
Date: 05-2001
DOI: 10.1063/1.1345884
Abstract: The application of thermochemical modeling, chemical kinetic modeling, and computational fluid dynamic modeling to waste destruction by thermal plasmas is considered. Destruction of liquid and gaseous wastes in the PLASCON™ waste destruction process is used as an ex le. It is demonstrated that thermochemical calculation of the mixing temperature is a useful tool to predict the level to which wastes are destroyed however, chemical kinetic calculations are necessary to investigate the formation of byproducts in the process. Computational fluid dynamic modeling is required to obtain temperature and flow fields in two dimensions. When combined with chemical kinetics, composition fields can also be obtained. These points are illustrated using the ex les of chlorobenzene and chlorofluorocarbon destruction.
Publisher: IOP Publishing
Date: 28-05-2020
Publisher: IOP Publishing
Date: 07-12-1998
Publisher: Springer Science and Business Media LLC
Date: 09-05-2019
Publisher: IOP Publishing
Date: 14-04-1992
Publisher: IOP Publishing
Date: 05-07-2022
Abstract: The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by Journal of Physics D with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5–10 years.
Publisher: Informa UK Limited
Date: 09-2008
Publisher: IOP Publishing
Date: 07-05-2015
Publisher: Springer Science and Business Media LLC
Date: 26-09-2018
DOI: 10.1038/S41598-018-32692-9
Abstract: Adverse environmental conditions at planting, such as cold temperature or water limitation, can lead to a reduced level of seed germination and plant establishment for cotton. Cold atmospheric-pressure plasma (CAP) treatment of cotton seeds prior to planting may help alleviate this problem. CAP is ionised gas that has a range of biological activities due to the formation of a mix of reactive oxygen and nitrogen species (RONS), excited molecules, charged particles and UV photons. Our results show that a 27 minutes CAP treatment using air can significantly increase water absorption of the seed, and improve warm germination, metabolic chill test germination and chilling tolerance in cotton. We also observe that the beneficial effect of CAP treatment is long-lasting and stable as improved germination activity is still seen when treatment occurs 4 months before germination testing, suggesting that future large-scale industrial seed plasma treatments may still be effectively applied well (months) before the seed planting. We conclude that CAP treatment is a promising new tool for use in the cotton industry that has the potential to significantly improve plant establishment in a wider range of environmental conditions.
Publisher: AIP Publishing
Date: 16-03-1992
DOI: 10.1063/1.107324
Abstract: A method of determining the temperature of a thermal plasma by laser scattering, without frequency resolution of the scattered signal, is introduced. The method gives valid measurements of the gas temperature across the complete diameter of a free-burning argon arc, even in regions in which local thermodynamic equilibrium does not exist. The results show that the maximum temperature in a 100 A arc, with a 60° conical thoriated-tungsten cathode, is over 18 000 K, in agreement with our previous spectroscopic measurements.
Publisher: Springer Science and Business Media LLC
Date: 2002
Publisher: AIP Publishing
Date: 08-04-2013
DOI: 10.1063/1.4798596
Abstract: The dielectric breakdown properties of SF6–N2 mixtures were investigated at different concentrations of N2, 0.01–1.6 MPa, and 300–3000 K. The equilibrium compositions of different SF6–N2 mixtures at several gas pressures and temperatures up to 3000 K were first calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. The electron energy distribution function was then obtained using the composition data by Boltzmann equation analysis. It was found that adding N2 to SF6 gas can markedly reduce the kinetic energy of electrons at relatively high gas temperatures, which enhances the dielectric field strength. Finally, the critical reduced electric field (E/N)cr, defined as the value for which ionization is equal to attachment, of hot SF6–N2 mixtures was determined. The results indicate that in the gas temperature range around 2000–3000 K, increasing the concentration of N2 effectively enhances the (E/N)cr of SF6–N2 mixtures, and the (E/N)cr of SF6–N2 mixtures at a wide range of concentrations of N2 (5%, 50%, and 95%) are all higher than that of pure SF6 gas. Further, this trend exists at all the gas pressures considered (0.01–1.6 MPa).
Publisher: IOP Publishing
Date: 04-07-2019
Publisher: American Physical Society (APS)
Date: 18-11-2002
Publisher: Elsevier BV
Date: 06-09-2007
Publisher: IOP Publishing
Date: 14-07-1996
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2008
Publisher: CSIRO Publishing
Date: 2015
DOI: 10.1071/WR14193
Abstract: Context Automatically activated cameras (camera traps) and automated poison-delivery devices are increasingly being used to monitor and manage predators such as felids and canids. Maximising visitation rates to sentry positions enhances the efficacy of feral-predator management, especially for feral cats, which are typically less attracted to food-based lures than canids. Aims The influence of camera-trap placement and lures were investigated to determine optimal monitoring and control strategies for feral cats and other predators in two regions of semi-arid South Australia. Methods We compared autumn and winter capture rates, activity patterns and behaviours of cats, foxes and dingoes at different landscape elements and with different lures in three independent 6 km × 3 km grids of 18 camera-trap sites. Key results Neither visual, olfactory or audio lures increased recorded visitation rates by any predators, although an audio and a scent-based lure both elicited behavioural responses in predators. Cameras set on roads yielded an eight times greater capture rate for dingoes than did off-road cameras. Roads and resource points also yielded highest captures of cats and foxes. All predators were less nocturnal in winter than in autumn and fox detections at the Immarna site peaked in months when dingo and cat activity were lowest. Conclusions Monitoring and management programs for cats and other predators in arid Australia should focus on roads and resource points where predator activity is highest. Olfactory and auditory lures can elicit behavioural responses that render cats more susceptible to passive monitoring and control techniques. Dingo activity appeared to be inversely related to fox but not cat activity during our monitoring period. Implications Optimised management of feral cats in the Australian arid zone would benefit from site- and season-specific lure trials.
Publisher: IOP Publishing
Date: 14-08-2019
Publisher: Springer Science and Business Media LLC
Date: 22-03-2015
Publisher: IOP Publishing
Date: 18-11-2019
Publisher: Springer Science and Business Media LLC
Date: 17-07-2017
DOI: 10.1038/S41598-017-04963-4
Abstract: Cold atmospheric plasma has recently emerged as a simple, low-cost and efficient physical method for inducing significant biological responses in seeds and plants without the use of traditional, potentially environmentally-hazardous chemicals, fungicides or hormones. While the beneficial effects of plasma treatment on seed germination, disease resistance and agricultural output have been reported, the mechanisms that underpin the observed biological responses are yet to be fully described. This study employs Fourier Transform Infrared (FTIR) spectroscopy and emission spectroscopy to capture chemical interactions between plasmas and seed surfaces with the aim to provide a more comprehensive account of plasma−seed interactions. FTIR spectroscopy of the seed surface confirms plasma-induced chemical etching of the surface. The etching facilitates permeation of water into the seed, which is confirmed by water uptake measurements. FTIR of exhaust and emission spectra of discharges show oxygen-containing species known for their ability to stimulate biochemical processes and deactivate pathogenic microorganisms. In addition, water gas, CO 2 , CO and molecules containing −C(CH 3 ) 3 − moieties observed in FTIR spectra of the exhaust gas during plasma treatment may be partly responsible for the plasma chemical etching of seed surface through oxidizing the organic components of the seed coat.
Publisher: MDPI AG
Date: 26-01-2021
DOI: 10.3390/S21030810
Abstract: Surface-enhanced Raman spectroscopy (SERS) technology is an attractive method for the prompt and accurate on-site screening of illicit drugs. As portable Raman systems are available for on-site screening, the readiness of SERS technology for sensing applications is predominantly dependent on the accuracy, stability and cost-effectiveness of the SERS strip. An atmospheric-pressure plasma-assisted chemical deposition process that can deposit an even distribution of nanogold particles in a one-step process has been developed. The process was used to print a nanogold film on a paper-based substrate using a HAuCl4 solution precursor. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the gold has been fully reduced and that subsequent plasma post-treatment decreases the carbon content of the film. Results for cocaine detection using this substrate were compared with two commercial SERS substrates, one based on nanogold on paper and the currently available best commercial SERS substrate based on an Ag pillar structure. A larger number of bands associated with cocaine was detected using the plasma-printed substrate than the commercial substrates across a range of cocaine concentrations from 1 to 5000 ng/mL. A detection limit as low as 1 ng/mL cocaine with high spatial uniformity was demonstrated with the plasma-printed substrate. It is shown that the plasma-printed substrate can be produced at a much lower cost than the price of the commercial substrate.
Publisher: IOP Publishing
Date: 14-07-2017
Publisher: IOP Publishing
Date: 18-09-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4RA08187K
Abstract: Vertically-aligned carbon nanotube arrays treated with inductively-coupled plasmas demonstrate selective support of biofilms of Gram-negative and Gram-positive bacteria.
Publisher: Informa UK Limited
Date: 04-2008
Publisher: Elsevier BV
Date: 11-2006
Publisher: AIP Publishing
Date: 05-08-2013
DOI: 10.1063/1.4817370
Abstract: The dielectric breakdown properties of SF6–CF4 mixtures were investigated at different ratios of SF6, 0.01–1.6 MPa, and gas temperatures up to 3000 K. Initially, the equilibrium compositions of SF6–CF4 mixtures were calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. Then the electron energy distribution function was obtained based on those data by solving the Boltzmann equation under the zero-dimensional two-term spherical harmonic approximation. Finally, the critical reduced electric field strength (E/N)cr of SF6–CF4 mixtures, which is defined as the value for which total ionization reaction is equal to total attachment reaction, were determined and analyzed. The results confirm the superior breakdown properties of pure SF6 at relatively low gas temperatures. However, for higher gas temperatures (i.e., T & 2200 K at 0.4 MPa), the (E/N)cr in SF6–CF4 mixtures are obviously higher than that in pure SF6 and the values of (E/N)cr increase with the reduction of the ratio of SF6.
Publisher: IOP Publishing
Date: 16-05-2013
Publisher: IOP Publishing
Date: 16-05-2013
Publisher: IOP Publishing
Date: 27-10-2014
Publisher: Elsevier BV
Date: 04-2017
Publisher: Japan Welding Society
Date: 2013
DOI: 10.2207/QJJWS.31.9S
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 02-2002
Publisher: IOP Publishing
Date: 19-08-2016
Publisher: IOP Publishing
Date: 08-02-2016
DOI: 10.1088/0022-3727/49/10/105502
Abstract: This paper is devoted to the computation of the non-equilibrium composition of an SF 6 plasma, and determination of the dominant particles and reactions, at conditions relevant to high-voltage circuit breakers after current zero (temperatures from 12 000 K to 1000 K and a pressure of 4 atm). The non-equilibrium composition is characterized by departures from both thermal and chemical equilibrium. In thermal non-equilibrium process, the electron temperature ( T e ) is not equal to the heavy-particle temperature ( T h ), while for chemical non-equilibrium, a chemical kinetic model is adopted. In order to evaluate the reasonableness and reliability of the non-equilibrium composition, calculation methods for equilibrium composition based on Gibbs free energy minimization and kinetic composition in a one-temperature kinetic model are first considered. Based on the one-temperature kinetic model, a two-temperature kinetic model with the ratio T e / T h varying as a function of the logarithm of electron density ratio ( n e / <?MML n e max ?> ) was established. In this model, T * is introduced to allow a smooth transition between T h and T e and to determine the temperatures for the rate constants. The initial composition in the kinetic models is obtained from the asymptotic composition as infinite time is approached at 12 000 K. The molar fractions of neutral particles and ions in the two-temperature kinetic model are consistent with the equilibrium composition and the composition obtained from the one-temperature kinetic model above 10 000 K, while significant differences appear below 10 000 K. Based on the dependence of the particle distributions on temperature in the two-temperature kinetic model, three temperature ranges, and the dominant particles and reactions in the respective ranges, are determined. The full model is then simplified into three models and the accuracy of the simplified models is assessed. The simplified models reduce the number of species and reactions by a factor of about 2, while providing results that agree closely with the full model. Thus, the physicochemical processes of SF 6 arc can be characterized by relatively few species and reactions in each temperature range. It is noted that the simplified models can also be applied to a wide range of pressures, 1–16 atm, conditions which cover most circuit breaker applications. The simplified species and reactions will allow the computing time of multi-dimensional models, taking into account departures from both thermal and chemical equilibrium, to be decreased dramatically while capturing the main physicochemical processes in SF 6 arcs.
Publisher: Elsevier BV
Date: 12-2021
Publisher: IOP Publishing
Date: 04-07-2022
Abstract: This study presents a numerical model of the hybrid-stabilized argon–steam thermal DC plasma torch of a new design for generating an argon–steam plasma suitable for efficient abatement of persistent perfluorinated compounds. The model includes the discharge region and the plasma jet flowing to the surrounding steam atmosphere contained in a plasma-chemical chamber. Compared to previous studies, the torch had a smaller nozzle diameter (5.3 mm) and a reduced input power (20–40 kW) and arc current (120–220 A). The outlet region for the plasma jet extends to 20 cm downstream of the exit nozzle. Fluid dynamic and thermal characteristics together with diffusion of argon, hydrogen and oxygen species, and distribution of plasma species in the discharge and the plasma jet are obtained for currents from 120 to 220 A. The results of the calculations show that the plasma jet exhibits high spatiotemporal fluctuations in the shear layer between the plasma jet and colder steam atmosphere. The most abundant species in the plasma jet are hydrogen and oxygen atoms near the jet center, and molecules of H 2 , O 2 and OH in colder surrounding regions. Satisfactory agreement is obtained with measurements of the radial temperature and electron number density profiles near the jet center close to the nozzle exit.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2011
Publisher: AIP Publishing
Date: 11-2011
DOI: 10.1063/1.3657426
Abstract: Calculated thermophysical properties of nitrogen plasmas in and out of thermal equilibrium are presented. The cut-off of the partition functions due to the lowering of the ionization potential has been taken into account, together with the contributions from different core excited electronic states. The species composition and thermodynamic properties are determined numerically using the Newton–Raphson iterative method, taking into account the corrections due to Coulomb interactions. The transport properties including diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity are calculated using the most recent collision interaction potentials by adopting Devoto’s electron and heavy particle decoupling approach, expanded to the third-order approximation (second-order for viscosity) in the framework of Chapman–Enskog method. Results are presented in the pressure range of 0.1 atm–10 atm and in electron temperature range from 300 to 40 000 K, with the ratio of electron temperature to heavy-particle temperature varied from 1 to 20. Results are compared with those from previous works, and the influences of different definitions of the Debye length are discussed.
Publisher: IOP Publishing
Date: 05-05-2021
Abstract: As the widely implemented electrode material, graphite has the characteristic of sublimation by the thermal shock of the switching arc, and the produced carbon vapor is easy to condense into carbon powders and deposit in the switch. The impact of the type of dilution gas in a mixture of 20% oxygen and 80% dilution gas on the sublimation and oxidation characteristics of the graphite electrode is investigated. It is found that when nitrogen dilution gas was replaced by argon, the heat flux to the electrodes decreased, which led to a 63% reduction of graphite sublimation. At the same time, the cooling rate of the arc was slower in argon, which promotes oxidation of the carbon vapor. The residual solid carbon can be reduced by 70%–85% by using argon as the dilution gas. Consequently, it is demonstrated that the stability and working life of the switch could be increased by appropriate selection of the dilution gas.
Publisher: IOP Publishing
Date: 14-05-2009
Publisher: IOP Publishing
Date: 15-05-2017
Publisher: IOP Publishing
Date: 15-03-2017
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2010
Publisher: Sumart Processing Society for Minerals, Environment and Energy
Date: 2019
DOI: 10.7791/JSPMEE.8.219
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0SE01593H
Abstract: Optimizing and perceiving a nanosecond repetitively pulsed DBD plasma-assisted CH 4 activation technique under temperature-independent, catalyst-free conditions, combining experimental and numerical researches.
Publisher: American Society for Cell Biology (ASCB)
Date: 05-2014
Abstract: Atmospheric gas plasmas (AGPs) are able to selectively induce apoptosis in cancer cells, offering a promising alternative to conventional therapies that have unwanted side effects such as drug resistance and toxicity. However, the mechanism of AGP-induced cancer cell death is unknown. In this study, AGP is shown to up-regulate intracellular reactive oxygen species (ROS) levels and induce apoptosis in melanoma but not normal melanocyte cells. By screening genes involved in apoptosis, we identify tumor necrosis factor (TNF)–family members as the most differentially expressed cellular genes upon AGP treatment of melanoma cells. TNF receptor 1 (TNFR1) antagonist–neutralizing antibody specifically inhibits AGP-induced apoptosis signal, regulating apoptosis signal–regulating kinase 1 (ASK1) activity and subsequent ASK1-dependent apoptosis. Treatment of cells with intracellular ROS scavenger N-acetyl-l-cysteine also inhibits AGP-induced activation of ASK1, as well as apoptosis. Moreover, depletion of intracellular ASK1 reduces the level of AGP-induced oxidative stress and apoptosis. The evidence for TNF-signaling dependence of ASK1-mediated apoptosis suggests possible mechanisms for AGP activation and regulation of apoptosis-signaling pathways in tumor cells.
Publisher: IOP Publishing
Date: 09-1986
Publisher: Informa UK Limited
Date: 07-03-2014
Publisher: Optica Publishing Group
Date: 15-05-2007
DOI: 10.1364/AO.46.003133
Abstract: A method is developed for determining the optical properties of an optically rough coating on an opaque substrate from reflectance measurements. A modified Kubelka-Munk two- flux model is used to calculate the reflectance of the coating as a function of the refractive index, absorption coefficient, scattering coefficient, and thickness. The calculated reflectance is then fitted to measurements using a spectral projected gradient algorithm, allowing the optical properties to be obtained. The technique is applied to titanium dioxide coatings on a titanium substrate. Realistic values of refractive index and absorption coefficients are generally obtained. Quantities that are useful for solar water-splitting applications are calculated, including the depth profile of absorption and the proportion of the incident photon flux absorbed in the coating under solar illumination.
Publisher: American Physical Society (APS)
Date: 09-1995
Publisher: Springer Science and Business Media LLC
Date: 28-12-2017
Publisher: IOP Publishing
Date: 20-03-2018
Publisher: IOP Publishing
Date: 29-07-2020
Publisher: IOP Publishing
Date: 26-11-2014
Publisher: IOP Publishing
Date: 16-05-2013
Publisher: AIP Publishing
Date: 10-2014
DOI: 10.1063/1.4897371
Abstract: Diffusion coefficients play an important role in the description of the transport of metal vapours in gas mixtures. This paper is devoted to the calculation of four combined diffusion coefficients, namely, the combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient, and combined pressure diffusion coefficient in SF6-Cu mixtures at temperatures up to 30 000 K. These four coefficients describe diffusion due to composition gradients, applied electric fields, temperature gradients, and pressure gradients, respectively. The influence of copper fluoride and sulfide species on the diffusion coefficients is shown to be negligible. The effect of copper proportion and gas pressures on these diffusion coefficients is investigated. It is shown that increasing the proportion of copper generally increases the magnitude of the four diffusion coefficients, except for copper mole fractions of 90% or more. It is further found that increasing the pressure reduces the magnitude of the coefficients, except for the combined temperature diffusion coefficient, and shifts the maximum of all four coefficients towards higher temperatures. The results presented in this paper can be applied to the simulation of high-voltage circuit breaker arcs.
Publisher: Springer Science and Business Media LLC
Date: 07-03-2014
DOI: 10.1038/SREP04304
Publisher: Japan Welding Society
Date: 2009
DOI: 10.2207/QJJWS.27.4S
Publisher: IOP Publishing
Date: 15-12-2010
Publisher: IOP Publishing
Date: 12-12-2019
Publisher: Institute of Electronics, Information and Communications Engineers (IEICE)
Date: 08-2008
Publisher: IOP Publishing
Date: 06-12-190728635
Publisher: IOP Publishing
Date: 25-11-2019
Publisher: AIP Publishing
Date: 02-09-2022
DOI: 10.1063/5.0093568
Abstract: The gas mixture CO2–O2 has been considered as an insulation and arc-quenching medium in gas-insulated switchgears. In this paper, the dielectric breakdown properties of CO2–O2 mixtures at different O2 concentrations and gas pressures were studied theoretically by considering ion kinetics in a spatial–temporal growth avalanche model. A kinetic scheme that includes all the main reactions likely to occur in CO2–O2 mixtures is presented. An improved method to calculate the dielectric strength of the gas mixture is developed, based on an avalanche model that considers both spatial growth and temporal processes. Next, the reaction rates of ionization, attachment, detachment and ion conversion, the effective ionization Townsend coefficient αeff/N, and reduced critical electric field strength (E/N)cr in CO2–O2 mixtures at different mixing ratios and gas pressures are analyzed in detail. Finally, a pulsed Townsend experiment is performed to verify the validity and accuracy of the calculation method. Based on this, one detachment reaction rate is modified to yield more accurate results. Better consistency between the results and the experimental values supports the validity of the kinetic system, reaction rates, and the improved calculation method.
Publisher: American Chemical Society (ACS)
Date: 12-2020
Publisher: AIP Publishing
Date: 14-09-2013
DOI: 10.1063/1.4819212
Publisher: AIP Publishing
Date: 10-10-2017
DOI: 10.1063/1.5006635
Abstract: The thermodynamic properties and transport coefficients of C5F10O-CO2 gas mixtures, which are being considered as substitutes for SF6 in circuit breaker applications, are calculated for the temperature range from 300 K to 30 000 K and the pressure range from 0.05 MPa to 1.6 MPa. Special attention is paid on investigating the evolution of thermophysical properties of C5F10O-CO2 mixtures with different mixing ratios and with different pressures both the mixing ratio and pressure significantly affect the properties. This is explained mainly in terms of the changes in the temperatures at which the dissociation and ionization reactions take place. Comparisons of different thermophysical properties of C5F10O-CO2 mixtures with those of SF6 are also carried out. It is found that most of the thermophysical properties of the C5F10O-CO2 mixtures, such as thermal conductivity, viscosity, and electrical conductivity, become closer to those of SF6 as the C5F10O concentration increases. The composition and thermophysical properties of pure C5F10O in the temperature range from 300 K to 2000 K based on the decomposition pathway are also given. The calculation results provide a basis for further study of the insulation and arc-quenching capability of C5F10O-CO2 gas mixtures as substitutes for SF6.
Publisher: IOP Publishing
Date: 05-12-2020
Publisher: Springer International Publishing
Date: 2018
Publisher: IOP Publishing
Date: 25-11-2014
Publisher: IOP Publishing
Date: 29-08-2008
Publisher: IOP Publishing
Date: 17-01-2013
Publisher: AIP Publishing
Date: 10-2008
DOI: 10.1063/1.2996272
Abstract: The kinetics of the nucleation and growth of carbon nanotube and nanocone arrays on Ni catalyst nanoparticles on a silicon surface exposed to a low-temperature plasma are investigated numerically, using a complex model that includes surface diffusion and ion motion equations. It is found that the degree of ionization of the carbon flux strongly affects the kinetics of nanotube and nanocone nucleation on partially saturated catalyst patterns. The use of highly ionized carbon flux allows formation of a nanotube array with a very narrow height distribution of half-width 7 nm. Similar results are obtained for carbon nanocone arrays, with an even narrower height distribution, using a highly ionized carbon flux. As the deposition time increases, nanostructure arrays develop without widening the height distribution when the flux ionization degree is high, in contrast to the fairly broad nanostructure height distributions obtained when the degree of ionization is low.
Publisher: IOP Publishing
Date: 21-10-2004
DOI: 10.1088/0022-3727/37/20/010
Abstract: The formation of titanium nanoparticles from plasmas in mixtures of titanium tetrachloride, argon and hydrogen is examined using three approaches: chemical equilibrium calculations, chemical kinetic calculations and a nucleation-coupled model of particle formation coupled to chemical kinetic equations. The results indicate that production of solid titanium particles requires a non-equilibrium process, such as is obtained using a rapid quench of the plasma. It is calculated that titanium yields approaching 100% are possible for sufficiently large residence times at a high temperature, and sufficiently rapid quench rates. The residence time and quench rate conditions are less stringent for high ratios of argon to titanium tetrachloride in the initial gas mixture. Adding hydrogen to the gas mixture leads to less stringent residence time, but more stringent quench rate conditions.
Publisher: IOP Publishing
Date: 25-06-2014
Publisher: Elsevier BV
Date: 11-2010
Publisher: American Physical Society (APS)
Date: 12-1994
Publisher: No publisher found
Date: 2018
Publisher: IOP Publishing
Date: 05-12-2020
Publisher: Springer Science and Business Media LLC
Date: 12-12-2008
Publisher: MDPI AG
Date: 29-04-2019
DOI: 10.3390/MA12091397
Abstract: : The characteristics of the welding heat source for tandem narrow-gap gas metal arc welding are examined for different ternary shielding gas (Ar-CO2-He) compositions. Results of previous calculations of arc properties for bead-on-plate geometry are adapted to the narrow-gap geometry to predict these characteristics. The heat source concentration factor decreases and the maximum heat flux density increases as the helium content increases, which leads to an increased welding heat efficiency. Addition of CO2 up to around 10% also increases the heat efficiency. When the CO2 content exceeds 10%, the heat source concentration factor increases significantly and the heat efficiency decreases. The shielding gas composition also affects the heat source distribution. The heat source characteristics are applied to a computational fluid dynamic model of the weld pool to predict the weld shape, and the predictions are verified by experiment. The results indicate that the appropriate addition of helium to the shielding gas can increase the heat transferred to the peripheral regions of the arc and increase the sidewall penetration.
Publisher: Trans Tech Publications, Ltd.
Date: 05-01-2021
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.1016.1031
Abstract: Metal additive manufacturing based on powder bed fusion processes is increasingly important. However, highly transient physical phenomena that occur in these processes at different length scales are difficult to observe. Challenging and costly experiments are usually needed to obtain data for process understanding and improvement. Computational modelling of powder-bed fusion processes is therefore important from several points of view. These include better process understanding, optimisation of process parameters and component designs, prediction of component properties, qualification of components and to assist process control. Several physical processes have to be treated to develop a complete model, namely the raking of the powder bed surface, the transfer of energy from the laser or electron beam to the metal, the melting and solidification of the powder, the flow of liquid metal in the melt pool, the heat transfer from the melt pool to the surrounding powder and solid metal, the evolution of the microstructure, and the residual stress and deformation of the component. These processes occur at very different scales, and have to be treated using several different computational techniques. In addition, the interdependency of some of the processes has to be accounted for. This paper discusses the rationale for developing a complete model, progress in developing sub-models of the different physical processes, and the framework that is envisaged to combine the sub-models into a predictive model of the additive manufacturing process.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 1997
DOI: 10.1109/27.649574
Publisher: Elsevier BV
Date: 04-2012
Publisher: IOP Publishing
Date: 05-07-2022
Abstract: The high heat flux density of the DC arc often leads to severe anode ablation, which is a key factor limiting the wider use of the DC plasma torches. In this study, a series of comparative experimental studies are conducted with the goal of suppressing nitrogen arc anode ablation by combining argon shielding flow and anode structure. It is found that for the planar electrode structure, the use of argon shielding gas can alleviate the ablation of the anode by nitrogen arc to some extent. If a boron nitride channel is installed on the anode surface to constrain the argon shielding flow, the electrode ablation can be significantly reduced. The experimental results show that there is no significant ablation on the anode surface after 1 h of operation of the nitrogen arc device with an arc current of 100 A. Further analysis reveals that, on the one hand, argon shielding gas can extend the range of motion of the nitrogen arc root along the anode surface and increase the speed of arc root motion, which has the effect of expanding the time-averaged arc anode attachment area. On the other hand, argon shielding gas can also increase the size of the nitrogen arc root and decrease the temperature of the arc root. The use of constraining channels can effectively control the range of motion of the arc root along the anode surface and strengthen the influence of argon shielding gas. The combination of these effects can substantially suppress the anode ablation of the DC arc device.
Publisher: IOP Publishing
Date: 06-03-2023
Abstract: The perfluoronitrile C 4 F 7 N is considered a promising SF 6 -alternative in high-voltage gas-insulated apparatus, thanks to its high dielectric strength and low global warming potential. However, a complete and consistent set of electron-neutral collision cross-sections of C 4 F 7 N is still lacking, which hinders relevant plasma modeling. In this contribution, the available electron-neutral collision cross-sections of C 4 F 7 N are first compiled and assessed. The initial cross-sections are adjusted iteratively by the electron swarm method to determine a complete and self-consistent cross-section set of C 4 F 7 N for the first time. The set is validated by a systematic comparison of electron swarm parameters between Boltzmann equation analysis and experimental measurements in pure C 4 F 7 N as well as C 4 F 7 N/N 2 and C 4 F 7 N/Ar mixtures. The proposed cross-section set of C 4 F 7 N will be made available to the community in the LXCat database. It will be of particular importance for applications with an emphasis on the discharge mechanisms of this novel gas.
Publisher: Springer Science and Business Media LLC
Date: 18-05-2011
Publisher: Springer Science and Business Media LLC
Date: 22-02-2007
Publisher: IOP Publishing
Date: 19-07-2021
Publisher: Elsevier BV
Date: 12-2010
Publisher: Springer Science and Business Media LLC
Date: 08-2000
Publisher: Informa UK Limited
Date: 25-04-2022
Publisher: CSIRO Publishing
Date: 2019
DOI: 10.1071/WR18118
Abstract: Context Feral cats (Felis catus) impact the health and welfare of wildlife, livestock and humans worldwide. They are particularly damaging where they have been introduced into island countries such as Australia and New Zealand, where native prey species evolved without feline predators. Kangaroo Island, in South Australia, is Australia’s third largest island and supports several threatened and endemic species. Cat densities on Kangaroo Island are thought to be greater than those on the adjacent South Australian mainland, based on one cat density estimate on the island that is higher than most estimates from the mainland. The prevalence of cat-borne disease in cats and sheep is also higher on Kangaroo Island than the mainland, suggesting higher cat densities. A recent continental-scale spatial model of cat density predicted that cat density on Kangaroo Island should be about double that of the adjacent mainland. However, although cats are believed to have severe impacts on some native species on the island, other species that are generally considered vulnerable to cat predation have relatively secure populations on the island compared with the mainland. Aims The present study aimed to compare feral cat abundance between Kangaroo Island and the adjacent South Australian mainland using simultaneous standardised methods. Based on previous findings, we predicted that the relative abundance of feral cats on Kangaroo Island would be approximately double that on the South Australian mainland. Methods Standardised camera trap surveys were used to simultaneously estimate the relative abundance of feral cats on Kangaroo Island and the adjacent South Australian mainland. Survey data were analysed using the Royle–Nichols abundance-induced heterogeneity model to estimate feral cat relative abundance at each site. Key results Cat abundance on the island was estimated to be over 10 times greater than that on the adjacent mainland. Conclusions Consistent with predictions, cat abundance on the island was greater than on the adjacent mainland. However, the magnitude of this difference was much greater than expected. Implications The findings show that the actual densities of cats at local sites can vary substantially from predictions generated by continental-scale models. The study also demonstrates the value of estimating abundance or density simultaneously across sites using standardised methods.
Publisher: IOP Publishing
Date: 03-1991
Publisher: AIP Publishing
Date: 25-10-2019
DOI: 10.1063/1.5109131
Abstract: Iso-C4 perfluoronitrile (C4F7N) is one of the most promising alternatives to SF6 for use in power equipment, such as high-voltage circuit breakers, due to its excellent electrical properties and environmentally friendly characteristics. The use of SF6 is being reduced because of its high global warming potential. To describe the physical and chemical processes occurring in the arc plasma in circuit breakers, both local thermodynamic equilibrium (LTE) and nonlocal chemical equilibrium (LCE) conditions have to be considered. The plasma composition of the arc core region can be calculated under the assumption of LTE by the method of minimization of the Gibbs free energy. The plasma composition of the arc boundary region or during the arc ignition period is not in LTE or LCE, so the use of a chemical kinetic model that considers the effects of the energy barrier in chemical reactions is required. Calculations for both conditions are presented for C4F7N. To develop the chemical kinetic model, the complete decomposition pathway and transition states were first reexamined and further developed. Based on the decomposition pathway, the rate constants of reactions were obtained according to the variational transition state theory method. The results obtained for the two cases provide a reference for the systematic understanding of the decomposition characteristics of C4F7N gas and for related engineering applications.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 1999
DOI: 10.1109/27.763013
Publisher: AIP Publishing
Date: 19-08-2019
DOI: 10.1063/1.5117313
Abstract: Underwater electrical explosions of Cu wires were carried out on a microsecond time scale to produce underwater shock waves. Experimental results show that the radial density distribution of the water flow after restrike contains several oscillations, observed as ∼1 mm-spaced layers in the backlit streak images and laser shadowgraphs. The phenomenon is attributed to the partial reheating of the exploding product (EP) by an interior restrike arc, which stimulates a compression wave propagating back and forth radially in the EP. Simulations are used to support the interior breakdown scenario and to demonstrate that each reflection of the compression wave at the EP–water interface launches a weak shock into the water, forming a multilayer structure. As the surrounding metallic vapor is ionized due to radiation and thermal conduction from the arc, the highly conductive plasma channel continues to extend radially and launches the main compression wave, which drowns out the multilayers when the power injection is sufficiently high.
Publisher: Elsevier BV
Date: 2020
Publisher: American Physical Society (APS)
Date: 26-09-1994
Publisher: Springer Science and Business Media LLC
Date: 15-11-2022
Publisher: IOP Publishing
Date: 07-08-2000
Publisher: IOP Publishing
Date: 27-10-2014
Publisher: Institute of Electrical Engineers of Japan (IEE Japan)
Date: 2013
Publisher: American Chemical Society (ACS)
Date: 07-12-2018
Publisher: IOP Publishing
Date: 24-02-2017
Publisher: Elsevier BV
Date: 08-2020
Publisher: Springer Science and Business Media LLC
Date: 02-04-2014
Publisher: Elsevier BV
Date: 2021
Publisher: IEEE
Date: 02-2010
Publisher: Springer Science and Business Media LLC
Date: 27-02-2017
Publisher: Elsevier BV
Date: 11-2021
Publisher: Elsevier BV
Date: 03-2020
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2011
Publisher: IOP Publishing
Date: 11-03-2016
Publisher: CSIRO Publishing
Date: 2019
DOI: 10.1071/AN17008
Abstract: Beef cattle production is the major agricultural pursuit in the arid rangelands of Australia. Dingo predation is often considered a significant threat to production in rangeland beef herds, but there is a need for improved understanding of the effects of dingo baiting on reproductive wastage. We experimentally compared fetal/calf loss on baited and non-baited treatment areas within three northern South Australian beef herds over a 2–4-year period. At re-musters, lactation was used to determine the outcomes of known pregnancies. Potential explanatory factors for fetal/calf loss (dingo baiting, dingo activity, summer heat, cow age, seasonal conditions, activity of dingo prey and selected livestock diseases) were investigated. From 3145 tracked pregnancies, fetal/calf loss averaged 18.6%, with no overall significant effect of baiting. Fetal/calf loss averaged 27.3% for primiparous (first pregnancy) heifers and 16.8% for multiparous (2nd or later calf) cows. On average, dingo-activity indices were 59.3% lower in baited treatments than in controls, although background site differences in habitat, weather and previous dingo control could have contributed to these lower indices. The overall scale and timing of fetal/calf loss was not correlated with dingo activity, time of year, a satellite-derived measure of landscape greenness (normalised difference vegetation index), or activity of alternative dingo prey. Limited blood testing suggested that successful pregnancy outcomes, especially in primiparous heifers, may have been reduced by the livestock diseases pestivirus and leptospirosis. The percentage occurrence of cattle hair in dingo scats was higher when seasonal conditions were poorer and alternative prey less common, but lack of association between fetal/calf loss and normalised difference vegetation index suggests that carrion feeding, rather than calf predation, was the more likely cause. Nevertheless, during the fair to excellent prevailing seasons, there were direct observations of calf predation. It is likely that ground baiting, as applied, was ineffective in protecting calves, or that site effects, variable cow age and disease confounded our results.
Publisher: American Geophysical Union (AGU)
Date: 04-10-2012
DOI: 10.1029/2012JD017921
Publisher: IOP Publishing
Date: 26-08-2009
DOI: 10.1088/0957-4484/20/37/375702
Abstract: The generation of heat by clusters and arrays of gold nanoparticles under illumination is investigated theoretically. The nanoparticles are embedded in a homogeneous dielectric medium, and the finite thermal resistance at the interface between the nanoparticle and the medium is taken into account. An analytic solution is derived for the case of a single nanoparticle. The T-matrix method is used to calculate the energy absorption efficiency of groups of nanoparticles, taking into account their optical interactions. Heat transfer equations are developed that take into account thermal interactions between nanoparticles. The equations are solved numerically using the finite element software COMSOL. Periodic boundary conditions are applied to treat the thermal interactions between the nanoparticles for arrays of nanoparticles. Results are presented for illumination by a standard xenon flash l . The thermal resistance at the nanoparticle-medium interface is found to strongly influence the nanoparticle temperature, but to have negligible influence on the temperature of the dielectric medium after a few tens of nanoseconds of exposure to the flash l pulse. Optical interactions are found to be important if particle centres are separated by about twice the particle diameter or less. Thermal interactions between nanoparticles via the medium are found to be the dominant factor in determining the temperature increase in the dielectric medium. The maximum temperature increase is proportional to the volume fraction of the nanoparticles in the medium.
Publisher: Elsevier BV
Date: 08-2023
Publisher: MDPI AG
Date: 12-02-2022
DOI: 10.3390/MET12020326
Abstract: In plasma MIG welding, inert gas introduced from the torch nozzle is ionized in the upstream region of the MIG arc, which is termed “plasma”. This study aims to clarify the effect of the plasma on the metal-transfer process in the plasma MIG welding through numerical analysis. As a result, the plasma with a temperature of approximately 10,000 K was found to be formed around the wire tip. The MIG arc temperature around the wire tip was 11,000 K at the maximum, which was lower than that of the conventional MIG welding by approximately 1000 K. This difference was caused by the decreased current density around the wire tip due to the influence of the plasma. The droplet temperature was also decreased by 400 K due to this lower current density. The amount of the metal vapor evaporated from the droplet was decreased compared to that of the conventional MIG welding due to the lower droplet temperature. This might lead to a decrease in fume formation generally known in the plasma MIG welding. In the conventional MIG welding, the arc attachment was concentrated around the wire tip, leading to a higher current density. However, in the plasma MIG welding, the plasma transported to the surrounding of the wire tip increases the electric conductivity in that region, due to the influence of the metal vapor mixture. This leads to the dispersion of the arc attachment toward the wire root. Consequently, the current density in the plasma MIG welding was found to decrease compared with that of the conventional MIG welding. The lower current density in plasma MIG welding decreases the Lorenz force acting on the wire neck, thus delaying droplet detachment to make the droplet diameter larger and the metal transfer frequency smaller. The latter was about 20% of that in the conventional MIG welding.
Publisher: IOP Publishing
Date: 14-02-2008
Publisher: IOP Publishing
Date: 11-2017
Publisher: Springer Science and Business Media LLC
Date: 28-10-2012
Publisher: IOP Publishing
Date: 05-2022
Abstract: Plasma catalysis is gaining increasing interest for various applications, but the underlying mechanisms are still far from understood. Hence, more fundamental research is needed to understand these mechanisms. This can be obtained by both modelling and experiments. This foundations paper describes the fundamental insights in plasma catalysis, as well as efforts to gain more insights by modelling and experiments. Furthermore, it discusses the state-of-the-art of the major plasma catalysis applications, as well as successes and challenges of technology transfer of these applications.
Publisher: MDPI AG
Date: 04-2020
DOI: 10.3390/MA13071619
Abstract: This study aims to reduce the diffusible hydrogen content in deposited metal during gas metal arc welding (GMAW) and flux-cored arc welding (FCAW) which induces cold cracking. To achieve this, a novel welding torch with a dual gas nozzle has been developed. This special welding torch decreases the hydrogen source gas evaporated from a welding wire by the suction from the inner gas nozzle. In order to improve the suction efficiency of this evaporated gas, precise control of the suction gas flow is indispensable. In this paper, a simplified numerical simulation model of this process has been described. This model can take account of the evaporation of the hydrogen source gas from the wire while simulating the behavior of the shielding gas and the arc. Using this model, the effect of suction nozzle structure and torch operating conditions on suction gas flow pattern and suction efficiency was also investigated to understand the process mechanism. Furthermore, the diffusible hydrogen content in deposited metal was measured by chromatography as a validation step. Results show that some of the shielding gas introduced from a shielding nozzle was drawn inward and also branched into an upward flow that was sucked into the suction nozzle and a downward flow to a base metal. This branching height was defined as the suction limit height, which decisively governed the suction efficiency. As a result, in order to reduce the diffusible hydrogen, it was suggested that the suction limit height should be controlled towards below the wire position, where the evaporation rate of the hydrogen source gas peaks through optimization of the suction nozzle design and the torch operating conditions.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2009
Publisher: Springer Science and Business Media LLC
Date: 13-06-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2011
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2003
Publisher: IOP Publishing
Date: 15-01-2016
Publisher: Springer Science and Business Media LLC
Date: 06-1995
DOI: 10.1007/BF01459700
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2011
Publisher: Public Library of Science (PLoS)
Date: 26-06-2015
Publisher: IOP Publishing
Date: 24-09-2015
Publisher: IOP Publishing
Date: 15-01-2015
Publisher: Elsevier BV
Date: 08-2013
Publisher: Informa UK Limited
Date: 15-09-2014
Publisher: IOP Publishing
Date: 17-08-2020
Abstract: Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO 2 conversion into value-added chemicals and fuels, CH 4 activation into hydrogen, higher hydrocarbons or oxygenates, and NH 3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NO x removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over ‘conventional’ catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2014
Publisher: AIP Publishing
Date: 15-07-2010
DOI: 10.1063/1.3465316
Abstract: The properties of kinetic ablation models are considered in this paper. The widely used kinetic ablation model (model-K) only considers monatomic vapor. A revised model (model-Z) was introduced by taking into account the polyatomic vapor’s internal degrees of freedom, as well as the temperature dependence of the average particle mass. In this work, both temperature and pressure dependence of average particle mass and the specific heat ratio γ are taken into account, producing an improved version of model-Z (denoted model-Z∗). Ablation data calculated by model-K and model-Z∗ for two typical capillary materials are presented. Compared to model-K, model-Z∗ predicts an increased ablation rate at lower plasma temperature and higher plasma density, and a decreased rate for the opposite conditions. Finally, based on the plasma parameters in a typical discharge cycle, all three models are used to calculate the time-dependent ablation rate and the integrated ablated mass. It is found that the main difference between their results arises because of the different average particle masses near the wall surface, and model-Z∗ is the most accurate for the discharge cycle considered. Further, it is found that the ablation parameters are highly sensitive to the pressure, in particular, through the pressure dependence of average particle mass.
Publisher: Springer Science and Business Media LLC
Date: 13-02-2020
Publisher: Informa UK Limited
Date: 14-08-2015
Publisher: IOP Publishing
Date: 09-10-2001
Publisher: Springer International Publishing
Date: 2023
Publisher: Springer Science and Business Media LLC
Date: 29-03-2012
Publisher: Informa UK Limited
Date: 2012
Publisher: Elsevier BV
Date: 06-2014
DOI: 10.1016/J.IJANTIMICAG.2014.01.025
Abstract: Cold atmospheric pressure plasma (APP) is a recent, cutting-edge antimicrobial treatment. It has the potential to be used as an alternative to traditional treatments such as antibiotics and as a promoter of wound healing, making it a promising tool in a range of biomedical applications with particular importance for combating infections. A number of studies show very promising results for APP-mediated killing of bacteria, including removal of biofilms of pathogenic bacteria such as Pseudomonas aeruginosa. However, the mode of action of APP and the resulting bacterial response are not fully understood. Use of a variety of different plasma-generating devices, different types of plasma gases and different treatment modes makes it challenging to show reproducibility and transferability of results. This review considers some important studies in which APP was used as an antibacterial agent, and specifically those that elucidate its mode of action, with the aim of identifying common bacterial responses to APP exposure. The review has a particular emphasis on mechanisms of interactions of bacterial biofilms with APP.
Publisher: IOP Publishing
Date: 18-06-2019
Publisher: Begell House
Date: 2003
Publisher: IOP Publishing
Date: 02-07-2020
Publisher: Elsevier BV
Date: 08-2008
Publisher: IOP Publishing
Date: 18-08-2011
DOI: 10.1088/0022-3727/44/35/355207
Abstract: The calculated values of thermodynamic and transport properties of mixtures of carbon and argon, and carbon and helium, at high temperatures are presented in this paper. The thermodynamic properties are determined by the method of Gibbs free energy minimization, using standard thermodynamic tables. The transport properties including electron diffusion coefficients, viscosity, thermal conductivity and electrical conductivity are evaluated using the Chapman–Enskog method expanded up to the third-order approximation (second order for viscosity). Collision integrals are obtained using the most accurate cross-section data that could be located. The calculations, which assume local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30 000 K for different pressures between 0.1 and 10 atm. The results are compared with those of previously published studies. Good agreement is found for pure argon and helium. Larger discrepancies occur for carbon and mixtures of carbon and argon, and carbon and helium these are explained in terms of the different values of the collision integrals that were used. The results presented here are expected to be more accurate because of the improved collision integrals employed.
Publisher: IOP Publishing
Date: 02-07-2018
Publisher: IOP Publishing
Date: 19-04-2011
DOI: 10.1088/0022-3727/44/18/185205
Abstract: The paper presents a transient three-dimensional model of an anti-phase-synchronized pulsed tandem gas–metal arc welding process, which is used to analyse arc interactions and their influence on the gas shield flow. The shielding gases considered are pure argon and a mixture of argon with 18% CO 2 . Comparison of the temperature fields predicted by the model with high-speed images indicates that the essential features of the interactions between the arcs are captured. The paper demonstrates strong arc deflection and kinking, especially during the low-current phase of the pulse, in agreement with experimental observations. These effects are more distinct for the argon mixture with 18% CO 2 . The second part of the paper demonstrates the effects of arc deflection and instabilities on the shielding gas flow and the occurrence of air contamination in the process region. The results allow an improved understanding of the causes of periodic instabilities and weld seam imperfections such as porosity, spatter, heat-tint oxidation and fume deposits.
Publisher: Springer Science and Business Media LLC
Date: 28-10-2016
Publisher: IOP Publishing
Date: 09-10-2020
Abstract: Thermal and chemical nonequilibrium modelling is performed to investigate the plasma characteristics of a nitrogen arc. The arc plasma is coupled with the electrodes self-consistently in the computational domain. The self-consistent effective binary diffusion coefficient approximation treatment of diffusion and a generalized form of Ohm’s law are incorporated in the model. It is found the electric field has to undergo a reversal in front of the anode to preserve current conservation due to the strong diffusion current density. No field reversal is found in front of the cathode. The detailed chemical reaction processes are analyzed to understand the species density behaviour. Along the cathode surface, the maximum values of current density and heat flux density occur at the intersection of the flat tip and the conical surface. The distributions of different components of the current density and heat flux density change with the arc current. On the anode side, the electric field and diffusion components contribute to the current density, and have opposite signs and similar magnitudes on the axis, leading to an off-axis maximum of the current density. The electron condensation heat makes the largest contribution to the total heat flux in the high current density region, and the heavy-species contribution from the plasma becomes important in the arc fringe. The high heat flux and current density at the anode show that the nitrogen arc possesses excellent energy source properties for arc welding and other processes that require workpiece melting.
Publisher: IOP Publishing
Date: 10-01-2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2002
Publisher: Springer Science and Business Media LLC
Date: 02-05-2016
Publisher: Springer Science and Business Media LLC
Date: 30-05-2016
Publisher: Springer Science and Business Media LLC
Date: 2019
Publisher: IOP Publishing
Date: 14-10-2010
DOI: 10.1088/0022-3727/43/43/434009
Abstract: A gas tungsten arc (GTA) was modelled taking into account the contamination of the plasma by metal vapour from the molten anode. The whole region of GTA atmosphere including the tungsten cathode, the arc plasma and the anode was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of the shielding gas and metal vapour. The transient two-dimensional distributions of temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the molten pool as a function of time for a 150 A arc current at atmospheric pressure, both for helium and argon gases. It was shown that the thermal plasma in the GTA was influenced by iron vapour from the molten pool surface and that the concentration of iron vapour in the plasma was dependent on the temperature of the molten pool. GTA on high sulfur stainless steel was calculated to discuss the differences between a low sulfur and a high sulfur stainless steel anode. Helium was selected as the shielding gas because a helium GTA produces more metal vapour than an argon GTA. In the GTA on a high sulfur stainless steel anode, iron vapour and current path were constricted. Radiative emission density in the GTA on high sulfur stainless steel was also concentrated in the centre area of the arc plasma together with the iron vapour although the temperature distributions were almost the same as that in the case of a low sulfur stainless steel anode.
Publisher: IOP Publishing
Date: 03-11-2010
DOI: 10.1088/0022-3727/43/43/434008
Abstract: The most advanced numerical models of gas–metal arc welding (GMAW) neglect vaporization of metal, and assume an argon atmosphere for the arc region, as is also common practice for models of gas–tungsten arc welding (GTAW). These models predict temperatures above 20 000 K and a temperature distribution similar to GTAW arcs. However, spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to measurements of GTAW arcs, they have shown the presence of a central local minimum of the radial temperature distribution. This paper presents a GMAW model that takes into account metal vapour and that is able to predict the local central minimum in the radial distributions of temperature and electric current density. The influence of different values for the net radiative emission coefficient of iron vapour, which vary by up to a factor of hundred, is examined. It is shown that these net emission coefficients cause differences in the magnitudes, but not in the overall trends, of the radial distribution of temperature and current density. Further, the influence of the metal vaporization rate is investigated. We present evidence that, for higher vaporization rates, the central flow velocity inside the arc is decreased and can even change direction so that it is directed from the workpiece towards the wire, although the outer plasma flow is still directed towards the workpiece. In support of this thesis, we have attempted to reproduce the measurements of Zielińska et al for spray-transfer mode GMAW numerically, and have obtained reasonable agreement.
Publisher: MDPI AG
Date: 06-04-2022
DOI: 10.3390/APP12073679
Abstract: Wire arc additive manufacturing (WAAM) is the process by which large, metallic structures are built, layer-by-layer, using a welding arc to melt wire feedstock. In this process, the proper selection of the shielding gas plays a vital role in the achievement of structurally acceptable part geometries and quality surface finishes. In this study, the authors used either a ternary mix (He, Ar and CO2) or a binary mix (Ar and CO2) of shielding gases to deposit wall geometries using an open loop-controlled WAAM system developed at Oak Ridge National Laboratory’s Manufacturing Demonstration Facility. The binary blend produced a wider and shorter geometry, while the ternary blend resulted in a narrower build that was more equivalent to the CAD geometry. The data indicated that the binary blend provided a higher oxygen concentration in the weld as compared to that of the ternary blend. The results imply that the arc characteristics and heat input had a significantly higher impact on the weld penetration than the surface tension effect of surface active elements. This was further verified by developing and applying a high-fidelity computational fluid dynamics (CFD) model of the thermophysical properties of gas mixtures. The results from the model showed that, while the influence of increased oxygen concentration on the surface tension for the binary blend led to a deeper penetration, the ternary blend gave rise to heat flux to the workpiece.
Publisher: IOP Publishing
Date: 14-10-2010
DOI: 10.1088/0022-3727/43/43/434001
Abstract: Metal vapour is formed in arc welding processes by the evaporation of molten metal in the weld pool, and in the case of gas–metal arc welding, in the wire electrode and droplets. The presence of metal vapour can have a major influence on the properties of the arc and the size and shape of the weld pool. Previous experimental and computational works on the production and transport of metal vapour in welding arcs, in particular those relevant to gas–metal arc welding and gas–tungsten arc welding, are reviewed. The influence of metal vapour on the thermodynamic, transport and radiative properties of plasmas is discussed. The effect of metal vapour on the distributions of temperature, current density and heat flux in arcs is examined in terms of these thermophysical properties. Different approaches to treating diffusion of metal vapour in plasmas, and the production of vapour from molten metal, are compared. The production of welding fume by the nucleation and subsequent condensation of metal vapour is considered. Recommendations are presented about subjects requiring further investigation, and the requirements for accurate computational modelling of welding arcs.
Publisher: MDPI AG
Date: 08-05-2023
Abstract: Arc welding is a thermal plasma process widely used to join metals. An arc welding model that couples fluid dynamic and electromagnetic equations was initially developed as a research tool. Subsequently, it was applied to improve and optimise industrial implementations of arc welding. The model includes the arc plasma, the electrode, and the workpiece in the computational domain. It incorporates several features to ensure numerical accuracy and reduce computation time and memory requirements. The arc welding code has been refactored into commercial-grade Windows software, ArcWeld, to address the needs of industrial customers. The methods used to develop ArcWeld and its extension to new arc welding regimes, which used the Workspace workflow platform, are presented. The transformation of the model to an integrated software application means that non-experts can now run the code after only elementary training. The user can easily visualise the results, improving the ability to analyse and generate insights into the arc welding process being modelled. These changes mean that scientific progress is accelerated, and that the software can be used in industry and assist welders’ training. The methods used are transferrable to many other research codes.
Publisher: IOP Publishing
Date: 11-2006
Publisher: Elsevier BV
Date: 03-2021
Publisher: Springer Science and Business Media LLC
Date: 02-2020
Publisher: Japan Welding Society
Date: 2013
DOI: 10.2207/QJJWS.31.1S
Publisher: IOP Publishing
Date: 28-07-2020
Publisher: Springer Science and Business Media LLC
Date: 16-03-2017
Publisher: Elsevier BV
Date: 08-2021
Publisher: IEEE
Date: 02-2010
Publisher: IOP Publishing
Date: 24-02-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/C39950000347
Publisher: Elsevier BV
Date: 09-2020
Publisher: Springer Science and Business Media LLC
Date: 13-03-2017
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2010
Publisher: Springer Science and Business Media LLC
Date: 02-01-2021
Publisher: IOP Publishing
Date: 14-04-2011
DOI: 10.1088/0022-3727/44/17/174025
Abstract: In this paper, we review the recent progress in nanofabrication by thermal plasmas, and attempt to define some of the most important issues in the field. For synthesis of nanoparticles, the experimental studies in the past five years are briefly introduced the theoretical and numerical modelling works of the past 20 years are reviewed with some detailed explanations. Also, the use of thermal plasmas to produce nanostructured films and coatings is described. A wide range of technologies have been developed, ranging from chemical vapour deposition processes to new plasma spraying processes. We present an overview of the different techniques and the important physical phenomena, as well as the requirements for future progress.
Publisher: IOP Publishing
Date: 07-06-2012
DOI: 10.1088/0022-3727/45/25/253001
Abstract: Low-temperature plasma physics and technology are erse and interdisciplinary fields. The plasma parameters can span many orders of magnitude and applications are found in quite different areas of daily life and industrial production. As a consequence, the trends in research, science and technology are difficult to follow and it is not easy to identify the major challenges of the field and their many sub-fields. Even for experts the road to the future is sometimes lost in the mist. Journal of Physics D: Applied Physics is addressing this need for clarity and thus providing guidance to the field by this special Review article, The 2012 Plasma Roadmap . Although roadmaps are common in the microelectronic industry and other fields of research and development, constructing a roadmap for the field of low-temperature plasmas is perhaps a unique undertaking. Realizing the difficulty of this task for any in idual, the plasma section of the Journal of Physics D Board decided to meet the challenge of developing a roadmap through an unusual and novel concept. The roadmap was ided into 16 formalized short subsections each addressing a particular key topic. For each topic a renowned expert in the sub-field was invited to express his/her in idual visions on the status, current and future challenges, and to identify advances in science and technology required to meet these challenges. Together these contributions form a detailed snapshot of the current state of the art which clearly shows the lifelines of the field and the challenges ahead. Novel technologies, fresh ideas and concepts, and new applications discussed by our authors demonstrate that the road to the future is wide and far reaching. We hope that this special plasma science and technology roadmap will provide guidance for colleagues, funding agencies and government institutions. If successful in doing so, the roadmap will be periodically updated to continue to help in guiding the field.
Publisher: IOP Publishing
Date: 15-12-2020
Abstract: Non-thermal plasmas show great potential in low-temperature activation of methane (CH 4 ) owing to the abundant energetic active species. Motivated by the fact that the chemical reactions in plasma-based CH 4 conversion are dominated and regulated by the energetic electrons and various radicals, the temporal evolution of the electron energy distribution function (EEDF) and its relation to hydrogen (H) radical generation in an atmospheric-pressure CH 4 needle–plane discharge plasma have been investigated numerically. The simulations are carried out using one-dimensional particle-in-cell Monte-Carlo collision and fluid dynamic models. It can be shown that during the formation and development of the streamer, a characteristic time exists, before and after which the evolution characteristic of the EEDF is reversed. This is mainly attributed to the competition between the energies continuously obtained from the electric field and the increasingly strong inelastic collisions and fast-growing low-energy electron population. When the litude of the applied voltage is increased, the fraction of electrons with high enough energy to participate in dissociation or ionization reactions of CH 4 increases, leading to an increased H density. Besides, the characteristic time decreases exponentially, and the energy efficiency of the activation of CH 4 molecules is decreased. An appropriate electron energy distribution and H radical density should be chosen to ensure acceptable product selectivity and conversion rate without excessive energy consumption this will depend on the required products. The results presented in this work provide a partial theoretical basis for effectively optimizing the content of high-energy electrons and H radicals.
Publisher: IOP Publishing
Date: 14-11-2021
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2008
Publisher: Springer Science and Business Media LLC
Date: 20-04-2020
DOI: 10.1038/S41591-020-0807-6
Abstract: A double burden of malnutrition occurs when in iduals, household members or communities experience both undernutrition and overweight. Here, we show geospatial estimates of overweight and wasting prevalence among children under 5 years of age in 105 low- and middle-income countries (LMICs) from 2000 to 2017 and aggregate these to policy-relevant administrative units. Wasting decreased overall across LMICs between 2000 and 2017, from 8.4% (62.3 (55.1–70.8) million) to 6.4% (58.3 (47.6–70.7) million), but is predicted to remain above the World Health Organization’s Global Nutrition Target of % in over half of LMICs by 2025. Prevalence of overweight increased from 5.2% (30 (22.8–38.5) million) in 2000 to 6.0% (55.5 (44.8–67.9) million) children aged under 5 years in 2017. Areas most affected by double burden of malnutrition were located in Indonesia, Thailand, southeastern China, Botswana, Cameroon and central Nigeria. Our estimates provide a new perspective to researchers, policy makers and public health agencies in their efforts to address this global childhood syndemic.
Publisher: IOP Publishing
Date: 30-08-2017
Publisher: Elsevier BV
Date: 2020
Publisher: Elsevier BV
Date: 05-2020
Publisher: IOP Publishing
Date: 03-1986
Publisher: IOP Publishing
Date: 21-09-2018
Publisher: IOP Publishing
Date: 15-02-2018
Publisher: CSIRO Publishing
Date: 2007
DOI: 10.1071/CH06405
Abstract: Sol–gel chemistry and a templating technique were combined for the synthesis of vanadium/titanium oxides with controlled porous structure and various quantities of vanadium (0–9.7 at-%). The specific surface area of the porous vanadium/titanium oxides increased with increasing vanadium content to a maximum of 72 m2 g–1 at 6.6 at-% V, with a corresponding decrease in anatase crystal size (minimum of 12.4 nm), and c-axis lattice parameter (0.9475 nm). The optical band-gap decreased substantially from 3.10 eV for TiO2 to 2.53 eV on the addition of 9.7 at-% V. The adsorption capability of the oxides for aqueous methylene blue (pH ~6) increased significantly with increasing vanadium content (26.7 to 318.9 mg L–1 g–1 for 0 to 9.7 at-% V). The photodegradation of methylene blue was most efficient with the 0.9 at-% V-TiO2 s le for both UV and visible light irradiation.
Publisher: Wiley
Date: 29-06-2009
DOI: 10.1002/TEE.20435
Publisher: Springer Science and Business Media LLC
Date: 21-02-2017
Publisher: Elsevier BV
Date: 06-2020
Publisher: IOP Publishing
Date: 24-06-2021
Publisher: Springer Science and Business Media LLC
Date: 08-01-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2008
Publisher: IOP Publishing
Date: 25-05-2012
DOI: 10.1088/0022-3727/45/23/235202
Abstract: A modelling study is performed to investigate the plasma flow through the constrictor of medium-power arc-heated thrusters. The Roe scheme is employed to solve the governing equations, which take into account the effects of compressibility, Joule heating and the Lorentz force, as well as the temperature and pressure dependence of the gas properties. The modelling results show that the gas flow within the constrictor is choked by the combined effects of friction and arc heating. The computed total pressure drop within the constrictor due to friction and arc heating is about twice the dynamic head at the constrictor outlet. The effects of the arc current, inlet pressure and mass flow rate, and the constrictor length and diameter on the gas flow characteristics within the constrictor are presented and discussed. Further, it is shown that the choking effects caused by arc heating reduce the flow rate more strongly for argon and nitrogen working gases than for hydrogen working gas.
Publisher: IOP Publishing
Date: 23-06-2021
Abstract: The digital twin (DT) is a relatively new concept that is finding increased acceptance in industry. A DT is generally considered as comprising a physical entity, its virtual replica, and two-way digital data communications in-between. Its primary purpose is to leverage the process intelligence captured within digital models—or usually their faster-solving surrogates—towards generating increased value from the physical entities. The surrogate models are created using machine learning based on data obtained from the field, experiments and digital models, which may be physics-based or statistics-based. Anomaly detection and correction, and diagnostic closed-loop process control are ex les of how a process DT can be deployed. In the manufacturing industry, its use can achieve improvements in product quality and process productivity. Metal additive manufacturing (AM) stands to gain tremendously from the use of DTs. This is because the AM process is inherently chaotic, resulting in poor repeatability. However, a DT acting in a supervisory role can inject certainty into the process by actively keeping it within bounds through real-time control commands. Closed-loop feedforward control is achieved by observing the process through sensors that monitor critical parameters and, if there are any deviations from their respective optimal ranges, suitable corrective actions are triggered. The type of corrective action (e.g. a change in laser power or a modification to the scanning speed) and its magnitude are determined by interrogating the surrogate models. Because of their artificial intelligence (AI)-endowed predictive capabilities, which allow them to foresee a future state of the physical twin (e.g. the AM process), DTs proactively take context-sensitive preventative steps, whereas traditional closed-loop feedback control is usually reactive. Apart from assisting a build process in real-time, a DT can help with planning the build of a part by pinpointing the optimum processing window relevant to the desired outcome. Again, the surrogate models are consulted to obtain the required information. In this article, we explain how the application of DTs to the metal AM process can significantly widen its application space by making the process more repeatable (through quality assurance) and cheaper (by getting builds right the first time).
Publisher: IOP Publishing
Date: 27-09-2013
Publisher: Elsevier BV
Date: 1990
Publisher: IOP Publishing
Date: 28-10-2021
Publisher: AIP Publishing
Date: 03-2013
DOI: 10.1063/1.4794969
Publisher: AIP Publishing
Date: 20-01-2022
DOI: 10.1063/5.0083021
Abstract: Recently, C4F7N mixtures have attracted attention as a promising SF6 alternative due to their low global warming potential and excellent electrical performance. In this study, we introduce a newly built experimental setup for pulsed Townsend measurements as well as the physical model for the acquisition of electron swarm parameters. The effective ionization rate coefficients, electron drift velocity, and density-normalized longitudinal diffusion coefficients in C4F7N and its mixtures with CO2 and N2 were obtained. The reduced critical electric field for pure C4F7N at 100 Pa is determined to be 1002 Td, while it decreases with increasing pressure because of the effect of ion kinetics during the discharge process. C4F7N shows good synergism with CO2 and N2. To have a dielectric strength equivalent to that of SF6, the mixing ratio of C4F7N in its mixtures with CO2 and N2 should be 18% and 12%, respectively. The results provide fundamental data for modeling discharges in C4F7N and its mixtures.
Publisher: Wiley
Date: 08-07-2019
DOI: 10.1111/COBI.13366
Abstract: Compassionate conservation focuses on 4 tenets: first, do no harm in iduals matter inclusivity of in idual animals and peaceful coexistence between humans and animals. Recently, compassionate conservation has been promoted as an alternative to conventional conservation philosophy. We believe ex les presented by compassionate conservationists are deliberately or arbitrarily chosen to focus on mammals inherently not compassionate and offer ineffective conservation solutions. Compassionate conservation arbitrarily focuses on charismatic species, notably large predators and megaherbivores. The philosophy is not compassionate when it leaves invasive predators in the environment to cause harm to vastly more in iduals of native species or uses the fear of harm by apex predators to terrorize mesopredators. Hindering the control of exotic species (megafauna, predators) in situ will not improve the conservation condition of the majority of bio ersity. The positions taken by so-called compassionate conservationists on particular species and on conservation actions could be extended to hinder other forms of conservation, including translocations, conservation fencing, and fertility control. Animal welfare is incredibly important to conservation, but ironically compassionate conservation does not offer the best welfare outcomes to animals and is often ineffective in achieving conservation goals. Consequently, compassionate conservation may threaten public and governmental support for conservation because of the limited understanding of conservation problems by the general public.
Publisher: IOP Publishing
Date: 31-05-2000
Publisher: AIP Publishing
Date: 15-11-2006
DOI: 10.1063/1.2364623
Abstract: The temporal and spatial dependence of species densities in a pulse-modulated inductively coupled plasma (PM-ICP) in an argon-hydrogen mixture was investigated by means of numerical modeling, taking into account time dependence, two temperatures, and chemical nonequilibrium, and also through spectroscopic measurements. Conservation equations for mass, momentum, electron energy, heavy-species energy, each species, and the electromagnetic field were developed and solved self-consistently. The transient behavior of the mass fraction of each species was determined by including chemical kinetics source terms in the species conservation equations. Fourteen chemical reactions involving seven species (e, Ar, Ar+, H2, H2+, H, and H+) were considered. The transport properties were evaluated based on the local species densities using the first-order approximation of the Chapman-Enskog method. Time-resolved electron density profiles were obtained from measurements of the Stark broadening of the Hβ line (486.1nm), performed using an optical system positioned using a stepper motor. The investigations were conducted for a maximum power level of 11.7kW with a duty factor of 66.7% and at a pressure of 27kPa. Reasonable agreement was found between the predicted and measured electron densities. The electron density in the discharge region varied considerably over a pulse cycle, while the hydrogen atom density remained high throughout the cycle, and peaked in a region that has been experimentally demonstrated to have optimal efficiency for hydrogen doping of materials. The main mechanisms responsible for the production of the relevant species in the PM-ICP are discussed.
Publisher: IOP Publishing
Date: 14-08-2000
Publisher: IOP Publishing
Date: 18-09-2014
Publisher: Japan Welding Society
Date: 2013
DOI: 10.2207/QJJWS.31.41
Publisher: Springer Science and Business Media LLC
Date: 12-1994
DOI: 10.1007/BF01570207
Publisher: IOP Publishing
Date: 05-06-2018
Publisher: Springer Science and Business Media LLC
Date: 17-07-2018
Publisher: Springer Science and Business Media LLC
Date: 09-2004
Publisher: IOP Publishing
Date: 14-04-2011
Publisher: Elsevier BV
Date: 06-2021
Publisher: Elsevier BV
Date: 02-2017
Publisher: Japan Welding Society
Date: 2021
DOI: 10.2207/QJJWS.39.277
Publisher: IOP Publishing
Date: 14-10-2010
DOI: 10.1088/0022-3727/43/43/434012
Abstract: In order to clarify the fume formation mechanism in arc welding, a quantitative investigation based on the knowledge of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of a heterogeneous condensation model, a homogeneous nucleation model and a coagulation model has been developed and coupled with the GTA or GMA welding model. A series of processes from evaporation of metal vapour to fume formation from the metal vapour was totally investigated by employing this simulation model. The aim of this paper is to visualize the fume formation process and clarify the fume formation mechanism theoretically through a numerical analysis. Furthermore, the reliability of the simulation model was also evaluated through a comparison of the simulation result with the experimental result. As a result, it was found that the size of the secondary particles consisting of small particles with a size of several tens of nanometres reached 300 nm at maximum and the secondary particle was in a U-shaped chain form in helium GTA welding. Furthermore, it was also clarified that most part of the fume was produced in the downstream region of the arc originating from the metal vapour evaporated mainly from the droplet in argon GMA welding. The fume was constituted by particles with a size of several tens of nanometres and had similar characteristics to that of GTA welding. On the other hand, if the metal transfer becomes unstable and the metal vapour near the droplet diffuses directly towards the surroundings of the arc not getting into the plasma flow, the size of the particles reaches several hundred nanometres.
Publisher: IOP Publishing
Date: 14-10-2010
DOI: 10.1088/0022-3727/43/43/434011
Abstract: The influence of metal vapour on the arc behaviour during the arc-splitting process in the quenching chamber of a low-voltage circuit breaker is investigated numerically. A three-dimensional magnetohydrodynamic model of air arc plasma, taking into account the production of metal vapour from erosion of an iron splitter plate, is developed. An equation describing conservation of the iron vapour mass is added to the standard mass, momentum and energy conservation equations. The influence of the iron vapour on the thermodynamic and transport properties of the gas mixture is considered. The arc voltage, distributions of temperature, gas flow and mass fraction of iron vapour in the arc chamber are calculated. The formation of new arc roots on the splitter plate is examined. The simulation results indicate that this is strongly influenced by the presence of iron vapour from the splitter plate, due to the increased electrical conductivity in the arc root formation region. The consequences of this are dramatic. The presence of metal vapour causes the arc to attach first to the cathode side of the splitter plate, and electromagnetic forces then cause the arc on this side to move more rapidly than the arc on the anode side. The opposite occurs if metal vapour is neglected. High-speed photography of arc motion is used to confirm the arc motion predicted in the presence of metal vapour. Further, the calculated arc voltage taking into account metal vapour is lower than that calculated neglecting metal vapour, because of the increased electrical conductivity, and agrees much better with the measured voltage.
Publisher: Elsevier BV
Date: 05-2019
Publisher: IOP Publishing
Date: 20-08-2019
Location: Australia
No related grants have been discovered for Anthony Murphy.