ORCID Profile
0000-0002-4306-5950
Current Organisation
New York University - Abu Dhabi Campus
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Publisher: American Astronomical Society
Date: 10-2023
Publisher: American Astronomical Society
Date: 17-10-2016
Publisher: American Astronomical Society
Date: 15-10-2014
Publisher: MDPI AG
Date: 22-08-2022
DOI: 10.3390/EN15166086
Abstract: In this paper, a thorough framework for multiobjective design optimization of switched reluctance motor (SRM) is proposed. Selection of stator and rotor pole embrace coefficients is an essential step in the SRM design process since it influences torque output and torque ripple in SRM. The problem of determining optimal pole embrace is formulated as a multi-objective optimization problem with the objective of optimizing average torque, efficiency and torque ripple, and response surface models were obtained based on the genetic aggregation method. The results obtained by genetic aggregation response surface (GARS) and the non-dominated genetic algorithm (NSGA-II) were validated with the finite element method (FEM) model of the initial SRM. The optimized model displayed better efficiency profile over a wide speed range. The initial and optimized models recorded maximum efficiencies of 85% and 94.05%, respectively, at 2000 rpm. The efficiency values of 93.97–94.05% were achieved for the three pareto optimal candidates. The findings indicate the viability of the suggested strategy and support the use of GARS and NSGA-II as useful methods for addressing SRM key challenges.
Publisher: American Astronomical Society
Date: 05-04-2019
Publisher: MDPI AG
Date: 29-06-2021
DOI: 10.3390/MATH9131526
Abstract: Friction-induced stick-slip vibrations are one of the major causes for down-hole drill-string failures. Consequently, several nonlinear models and control approaches have been proposed to solve this problem. This work proposes a dual-loop control strategy. The inner loop d s the vibration of the system, eliminating the limit cycle due to nonlinear friction. The outer loop achieves the desired velocity with a fast time response. The optimal tuning of the control parameters is carried out with a multi-method ensemble meta-heuristic, the Coral Reefs Optimisation algorithm with Substrate Layer (CRO-SL). It is an evolutionary-type algorithm that combines different search strategies within a single population, obtaining a robust, high-performance algorithm to tackle hard optimisation problems. An application ex le based on a real nonlinear dynamics model of a drill-string illustrates that the controller optimised by the CRO-SL achieves excellent performance in terms of stick-slip vibrations cancellation, fast time response, robustness to system parameter uncertainties and chattering phenomenon prevention.
Publisher: IEEE
Date: 22-08-2022
Publisher: American Astronomical Society
Date: 24-03-2015
Publisher: MDPI AG
Date: 29-11-2022
Abstract: This paper presents a method to extend the eigenstructure assignment based design of the Positive Position Feedback (PPF) d ing controller to the family of well-known second-order Positive Feedback Controllers (PFC) namely: (i) the Positive Velocity and Position Feedback (PVPF) and (ii) the Positive Acceleration Velocity and Position Feedback (PAVPF) using appropriate eigenstructure assignment. This design problem entails solving a set of linear equations in the controller parameters using Linear Matrix Inequalities (LMI) to specify a convex design constraint. These d ing controllers are popularly used in tandem with a tracking controller (typically an integrator) to deliver high-bandwidth nanopositioning performance. Consequently, the closed-loop performance of all three controllers (PPF, PVPF and PAVPF) employed in tandem with suitably gained integral tracking loops is thoroughly quantified via relevant performance metrics, using measured frequency response data from one axis of a piezo-stack actuated x-y nanopositioner.
Publisher: MDPI AG
Date: 30-12-2022
Abstract: Finding a reliable approach to detect bearing faults is crucial, as the most common rotating machine defects occur in its bearings. A convolutional neural network can automatically extract the local features of the mechanical vibration signal and classify the patterns. Nevertheless, these types of networks suffer from the extraction of the global feature of the input signal as they utilize only one scale on their input. This paper presents a method to overcome the above weakness by employing a combination of three parallel convolutional neural networks with different filter lengths. In addition, a bidirectional gated recurrent unit is utilized to extract global features. The CWRU-bearing dataset is used to prove the performance of the proposed method. The results show the high accuracy of the proposed method even in the presence of noise.
Publisher: IEEE
Date: 30-05-2021
Publisher: Oxford University Press (OUP)
Date: 21-02-2022
Abstract: Quasi-stationary density wave theory predicts the existence of an age gradient across the spiral arms with a phase crossing at the corotation radius. We have examined evidence for such age gradients using star formation history (SFH) maps derived from lightning, a spectral energy distribution fitting procedure, and by using spatially resolved stellar clusters. Three galaxies from the LEGUS survey were used to analyse the azimuthal offsets of spatially resolved stellar clusters. Kernel density estimation plots of azimuthal cluster distance offsets reveal prominent central peaks and secondary peaks on the positive side, relative to the density wave for NGC 5194 and NGC 5236. These secondary downstream peaks in the cluster distributions show overall evidence for an age gradient. NGC 628 shows secondary peaks on both sides of the density wave. The cluster distributions also show an increasing spatial spread with age, consistent with the expectation that they were born in the density wave. SFH maps of 12 nearby galaxies were analysed using spirality, a matlab-based code, which plots synthetic spiral arms over FITS images. The SFH maps reveal a gradual decrement (tightening) in pitch angles with increasing age. By analysing the pitch angle differences between adjacent age bins using the error function, the average of the probabilities shows a $69{{\\ \\rm per\\ cent}}\\pm 25{{\\ \\rm per\\ cent}}$ chance that the pitch angle values decrease (tighten) with increasing age. Thus, we see a tightening of the spiral pattern in galaxies, both when segregating stellar populations specifically by age or more generally by colour, as was shown in our previous studies.
Publisher: Oxford University Press (OUP)
Date: 21-12-2019
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2021
Publisher: American Astronomical Society
Date: 24-05-2019
Publisher: American Astronomical Society
Date: 15-05-2019
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2023
Publisher: American Astronomical Society
Date: 02-08-2016
Publisher: Oxford University Press (OUP)
Date: 29-04-2022
Abstract: The near-absence of compact massive quiescent galaxies in the local Universe implies a size evolution since z ∼ 2.5. It is often theorized that such ‘red nuggets’ have evolved into today’s elliptical (E) galaxies via an E-to-E transformation. We examine an alternative scenario in which a red nugget develops a rotational disc through mergers and accretion, say, at 1 ≲ z ≲ 2, thereby cloaking the nugget as the extant bulge/spheroid component of a larger, now old, galaxy. We have performed detailed, physically motivated, multicomponent decompositions of a volume-limited s le of 103 massive ($M_*/\\rm M_{\\odot } \\gtrsim 1\\times 10^{11}$) galaxies within 110 Mpc. Many less massive nearby galaxies are known to be ‘fast-rotators’ with discs. Among our 28 galaxies with existing elliptical classifications, we found that 18 have large-scale discs, and two have intermediate-scale discs, and are reclassified here as lenticulars (S0) and elliculars (ES). The local spheroid stellar mass function, size–mass diagram and bulge-to-total (B/T) flux ratio are presented. We report lower limits for the volume number density of compact massive spheroids, nc, Sph ∼ (0.17–$1.2) \\times 10^{-4}\\, \\rm Mpc^{-3}$, based on different definitions of ‘red nuggets’ in the literature. Similar number densities of local compact massive bulges were reported by de la Rosa et al. using automated two-component decompositions and their existence is now abundantly clear with our multicomponent decompositions. We find disc-cloaking to be a salient alternative for galaxy evolution. In particular, instead of an E-to-E process, disc growth is the dominant evolutionary pathway for at least low-mass ($1\\times 10^{10}\\lt M_*/\\rm M_{\\odot } \\lessapprox 4 \\times 10^{10}$) red nuggets, while our current lower limits are within an alluring factor of a few of the peak abundance of high-mass red nuggets at 1 ≲ z ≲ 2.
Publisher: IEEE
Date: 19-02-2023
Publisher: Crimean Astrophysical Observatory
Date: 02-12-2021
DOI: 10.31059/AAT.VOL3.ISS1.PP39-43
Abstract: For decades, astronomers have been investigating how the central supermassive black hole (BH) may govern the host galaxy’s properties and vice versa. Our work adds another step to this study. We have performed state-of-theart 2D modeling and multi-component photometric decompositions of the largest-to-date s le of galaxies with dynamically-measured black hole masses (MBH). The multi-component decomposition allows us to accurately extract the bulge (spheroid) stellar luminosity/mass and structural parameters (also for other galaxy components) and provides detailed galaxy morphologies. We investigated the correlations between MBH and various host galaxy properties, including the bulge (M*,sph) and total galaxy (M*,gal) stellar masses discussed here. Importantly, we analyzed the role of galaxy morphology in these correlations. Our work reveals that the BH scaling relations depend on galaxy morphology and thus depend on the galaxy’s formation and evolution physics. Here we discuss that in the MBH–M*,sph diagram, early-type galaxies (ETGs) with a disk, ETGs without a disk, and late-type galaxies (LTG-spirals) define distinct relations, with quadratic slopes but different zero-points. We also review the MBH–M*,gal relation, where ETGs and LTGs define different relations. Notably, the existence of the MBH–M*,gal relations enables one to quickly estimate MBH in other galaxies without going through the multi-component decomposition process to obtain M*,sph. The final morphology-dependent black hole scaling relations provide tests for morphology-aware simulations of galaxies with a central BH and hold insights for BH-galaxy co-evolution theories based on BH accretion and feedback.
Publisher: Springer Science and Business Media LLC
Date: 15-07-2028
DOI: 10.1007/S41114-022-00041-Y
Abstract: The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.
Publisher: Elsevier BV
Date: 07-2022
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.23
Abstract: Recent X-ray observations by Jiang et al. have identified an active galactic nucleus (AGN) in the bulgeless spiral galaxy NGC 3319, located just $14.3\\pm 1.1$ Mpc away, and suggest the presence of an intermediate-mass black hole (IMBH $10^2\\leq M_\\bullet/\\textrm{M}_{\\odot}\\leq 10^5$ ) if the Eddington ratios are as high as 3 to $3\\times10^{-3}$ . In an effort to refine the black hole mass for this (currently) rare class of object, we have explored multiple black hole mass scaling relations, such as those involving the (not previously used) velocity dispersion, logarithmic spiral arm pitch angle, total galaxy stellar mass, nuclear star cluster mass, rotational velocity, and colour of NGC 3319, to obtain 10 mass estimates, of differing accuracy. We have calculated a mass of $3.14_{-2.20}^{+7.02}\\times10^4\\,\\textrm{M}_\\odot$ , with a confidence of 84% that it is $\\leq $ $10^5\\,\\textrm{M}_\\odot$ , based on the combined probability density function from seven of these in idual estimates. Our conservative approach excluded two black hole mass estimates (via the nuclear star cluster mass and the fundamental plane of black hole activity—which only applies to black holes with low accretion rates) that were upper limits of ${\\sim}10^5\\,{\\textrm M}_{\\odot}$ , and it did not use the $M_\\bullet$ – $L_{\\textrm 2-10\\,\\textrm{keV}}$ relation’s prediction of $\\sim$ $10^5\\,{\\textrm M}_{\\odot}$ . This target provides an exceptional opportunity to study an IMBH in AGN mode and advance our demographic knowledge of black holes. Furthermore, we introduce our novel method of meta-analysis as a beneficial technique for identifying new IMBH candidates by quantifying the probability that a galaxy possesses an IMBH.
Publisher: IEEE
Date: 22-08-2022
Publisher: American Astronomical Society
Date: 12-2021
Abstract: Building upon three late-type galaxies in the Virgo cluster with both a predicted black hole mass of less than ∼10 5 M ⊙ and a centrally located X-ray point source, we reveal 11 more such galaxies, more than tripling the number of active intermediate-mass black hole candidates among this population. Moreover, this amounts to a ∼36 ± 8% X-ray detection rate (despite the sometimes high, X-ray-absorbing, H i column densities), compared to just 10 ± 5% for (the largely H i -free) dwarf early-type galaxies in the Virgo cluster. The expected contribution of X-ray binaries from the galaxies’ inner field stars is negligible. Moreover, given that both the spiral and dwarf galaxies contain nuclear star clusters, the above inequality appears to disfavor X-ray binaries in nuclear star clusters. The higher occupation, or rather detection, fraction among the spiral galaxies may instead reflect an enhanced cool gas/fuel supply and Eddington ratio. Indeed, four of the 11 new X-ray detections are associated with known LINERs or LINER/H ii composites. For all (four) of the new detections for which the X-ray flux was strong enough to establish the spectral energy distribution in the Chandra band, it is consistent with power-law spectra. Furthermore, the X-ray emission from the source with the highest flux (NGC 4197: L X ≈ 10 40 erg s −1 ) suggests a non-stellar-mass black hole if the X-ray spectrum corresponds to the “low/hard state”. Follow-up observations to further probe the black hole masses, and prospects for spatially resolving the gravitational spheres of influence around intermediate-mass black holes, are reviewed in some detail.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2021
Publisher: American Astronomical Society
Date: 17-12-2018
Publisher: American Astronomical Society
Date: 05-12-2019
Publisher: Elsevier BV
Date: 11-2023
Publisher: Oxford University Press (OUP)
Date: 08-06-2020
Abstract: The spiral arms spanning disc galaxies are believed to be created by density waves that propagate through galactic discs. We present a novel method of finding the co-rotation radius where the spiral arm pattern speed matches the velocities of the stars within the disc. Our method uses an image-overlay technique, which involves tracing the arms of spiral galaxies on images observed in different wavelengths. Density wave theory predicts that spiral arms observed from different wavelengths show a phase crossing at the co-rotation radius. For the purpose of this study, 20 nearby galaxies were analysed in four different wavelengths with pitch angle measurements performed by two independent methods. We used optical wavelength images (B band 440 nm), two infrared wavelength images provided by Spitzer (3.6 and 8 μm) and ultraviolet images from GALEX (1350, 1750 Å). The results were compared and verified with other records found in the literature. We then found rotation curve data for six of our galaxies and used our co-rotation radii estimates to measure the time that would elapse between star formation and moving to their observed positions in the B-band spirals. The average time lapse for this motion was found to be ∼50 Myr. The success of this new method of finding the co-rotation radius confirms density wave theory in a very direct way.
Publisher: American Astronomical Society
Date: 14-05-2013
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921310006307
Abstract: Work done to date on the SMBH mass function has brought to light some interesting puzzles, the best known of which is cosmic downsizing. The solution to this problem is based upon the methodology by which we determine SMBH masses, which comes mainly from studies of active galaxies. The most massive SMBHs cease to be active at earlier epochs than their less massive counterparts, thus leading to an apparent decrease in the SMBH mass function with time. The larger SMBHs should still be present in the local Universe, but they lie in quiescent galaxies. This lack of certainty reflects the biggest gap in the observational record – the mass of SMBHs in quiescent galaxies.
Publisher: Cambridge University Press (CUP)
Date: 03-2020
DOI: 10.1017/S1743921320001726
Abstract: Our multi-component photometric decomposition of the largest galaxy s le to date with dynamically-measured black hole masses nearly doubles the number of such galaxies. We have discovered substantially modified scaling relations between the black hole mass and the host galaxy properties, including the spheroid (bulge) stellar mass, the total galaxy stellar mass, and the central stellar velocity dispersion. These refinements partly arose because we were able to explore the scaling relations for various sub-populations of galaxies built by different physical processes, as traced by the presence of a disk, early-type versus late-type galaxies, or a Sérsic versus core-Sérsic spheroid light profile. The new relations appear fundamentally linked with the evolutionary paths followed by galaxies, and they have ramifications for simulations and formation theories involving both quenching and accretion.
Publisher: IOP Publishing
Date: 07-09-2022
Abstract: Dielectric elastomer actuators (DEAs) usually suffer from rate-dependent viscoelastic nonlinearity, which manifests as hysteresis in their deformation cycles, leading to huge challenges in their modeling and control. In this work, we propose a model-free, proxy-based, sliding-mode tracking control approach to mitigate viscoelastic nonlinearity, achieving high-precision tracking control of DEAs. To this end, we first investigate the viscoelastic nonlinearity of DEAs, revealing its asymmetric and rate-dependent characteristics. Then, by combining the benefits of the PID control for small positioning errors and sliding-mode control for large errors, a proxy-based, sliding-mode tracking controller (PBSMC) is established. Finally, the stability of the controller is analyzed. To verify the effectiveness of the controller, several experiments are conducted to demonstrate the performance of DEAs in tracking sinusoidal trajectories under different frequencies. The experimental results demonstrate that with the PBSMC, the DEA can precisely track sinusoidal trajectories within a frequency range of 0.1 Hz–4.0 Hz by effectively minimizing the effect of inherent viscoelastic nonlinearity. Compared with open-loop tracking performance, the proxy-based, sliding-mode controlled DEA shows a significant reduction in maximum tracking errors from 45.87% to 8.72% and in root-mean-square errors from 24.46% to 3.88%. The main advantages of the proxy-based, sliding-mode control are: (a) it adopts a model-free approach, avoiding the need for complex dynamic modeling (b) it can achieve high-precision tracking control of DEAs, thereby paving the way for the adoption of DEAs in several emerging applications.
Publisher: MDPI AG
Date: 20-09-2022
Abstract: Designers of Positive Feedback Controllers (PFCs) arbitrarily place poles into the left-hand half-plane of the complex plane without any detailed understanding of where to stop. This works aims to clearly demonstrate, via rigorous mathematical derivation, the conditions for which pole–placement becomes possible. It also highlights the design limits for the family of second–order PFCs—the most popular PFC group. To this end, the complete family of PFCs, namely, Positive Acceleration Velocity Position Feedback and its derivatives, are analysed in great depth with respect to pure d ing and also with respect to combined d ing and tracking applications. To showcase the practical value and validity of this work, experimental results on a piezoelectric nanopositioner are also presented and discussed.
Publisher: American Astronomical Society
Date: 12-2021
Abstract: Galaxies can grow through their mutual gravitational attraction and subsequent union. While orbiting a regular high-surface-brightness galaxy, the body of a low-mass galaxy can be stripped away. However, the stellar heart of the infalling galaxy, if represented by a tightly bound nuclear star cluster, is more resilient. From archival Hubble Space Telescope images, we have discovered a red, tidally stretched star cluster positioned ∼5″ (∼400 pc in projection) from, and pointing toward the center of, the post-merger spiral galaxy NGC 4424. The star cluster, which we refer to as “Nikhuli,” has a near-infrared luminosity of (6.88 ± 1.85) × 10 6 L ⊙, F 160 W and likely represents the nucleus of a captured/wedded galaxy. Moreover, from our Chandra X-ray Observatory image, Nikhuli is seen to contain a high-energy X-ray point source, with L 0.5 − 8 keV = 6.31 − 3.77 + 7.50 × 10 38 erg s −1 (90% confidence). We argue that this is more likely to be an active massive black hole than an X-ray binary. Lacking an outward-pointing comet-like appearance, the stellar structure of Nikhuli favors infall rather than the ejection from a gravitational-wave recoil event. A minor merger with a low-mass early-type galaxy may have sown a massive black hole, aided an X-shaped pseudobulge, and be sewing a small bulge. The stellar mass and the velocity dispersion of NGC 4424 predict a central black hole of (0.6–1.0) × 10 5 M ⊙ , similar to the expected intermediate-mass black hole in Nikhuli, and suggestive of a black hole supply mechanism for bulgeless late-type galaxies. We may potentially be witnessing black hole seeding by capture and sinking, with a nuclear star cluster the delivery vehicle.
Publisher: MDPI AG
Date: 17-10-2022
Abstract: We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 min per galaxy, assuming 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code’s results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the s le of nearby galaxies defined by DMS PPak. Spirality’s error bars overlapped 2DFFT’s error bars for 26 of the 30 galaxies. The two methods’ agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies’ spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our s le. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. All code is freely available.
Publisher: Elsevier BV
Date: 2021
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2021
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2021
Publisher: MDPI AG
Date: 08-05-2017
DOI: 10.3390/CRYST7050130
Publisher: Elsevier BV
Date: 05-2023
DOI: 10.1016/J.ISATRA.2022.10.028
Abstract: This paper presents a new Global Fast Non-singular Terminal Sliding Mode Controller (GFNTSMC) that delivers high-precision tracking of high-frequency trajectories when applied to a piezo-driven nanopositioner. The control scheme is realized by combing inverse hysteresis model and global fast non-singular terminal sliding mode compensation. The inverse Bouc-Wen hysteresis model is used to calculate the required hysteresis-compensating feedforward control voltage according to the reference signal. The key uniqueness of the proposed control strategy is it's red global fast convergence, achieved with high accuracy and high bandwidth. The stability of the reported GFNTSMC controller is proved with the Lyapunov theory. Its performance is verified through experimentally recorded tracking results, and its superiority over three benchmark control approaches, namely the Proportional-Integral-Derivative (PID), the Positive Position Feedback with integral action (PPF+I) and the conventional linear high-order sliding mode controller (LHOSMC) is demonstrated through comparative tracking error analysis. Its wide-band stability as well as its significant robustness to parameter uncertainty is also showcased.
Publisher: Springer Science and Business Media LLC
Date: 05-03-2021
DOI: 10.1007/S11465-020-0619-X
Abstract: Typically, the achievable positioning bandwidth for piezo-actuated nanopositioners is severely limited by the first, lightly-d ed resonance. To overcome this issue, a variety of open- and closed-loop control techniques that commonly combine d ing and tracking actions, have been reported in literature. However, in almost all these cases, the achievable closed-loop bandwidth is still limited by the original open-loop resonant frequency of the respective positioning axis. Shifting this resonance to a higher frequency would undoubtedly result in a wider bandwidth. However, such a shift typically entails a major mechanical redesign of the nanopositioner. The integral resonant control (IRC) has been reported earlier to demonstrate the significant performance enhancement, robustness to parameter uncertainty, guaranteed stability and design flexibility it affords. To further exploit the IRC scheme’s capabilities, this paper presents a method of actively shifting the resonant frequency of a nanopositioner’s axis, thereby delivering a wider closed-loop positioning bandwidth when controlled with the IRC scheme. The IRC d ing control is augmented with a standard integral tracking controller to improve positioning accuracy. And both d ing and tracking control parameters are analytically optimized to result in a Butterworth Filter mimicking pole-placement—maximally flat passband response. Experiments are conducted on a nanopositioner’s axis with an open-loop resonance at 508 Hz. It is shown that by employing the active resonance shifting, the closed-loop positioning bandwidth is increased from 73 to 576 Hz. Consequently, the root-mean-square tracking errors for a 100 Hz triangular trajectory are reduced by 93%.
Publisher: Elsevier BV
Date: 08-2021
Publisher: IEEE
Date: 22-11-2022
Publisher: Oxford University Press (OUP)
Date: 19-07-2017
Publisher: American Astronomical Society
Date: 20-06-2014
Publisher: Institution of Engineering and Technology (IET)
Date: 12-2020
Publisher: American Astronomical Society
Date: 06-03-2019
Publisher: Elsevier BV
Date: 2021
Publisher: American Astronomical Society
Date: 29-03-2012
Publisher: Elsevier BV
Date: 08-2022
Publisher: American Astronomical Society
Date: 06-11-2020
Publisher: American Astronomical Society
Date: 03-2022
Abstract: This paper is the fourth in a series presenting (galaxy morphology, and thus galaxy formation)-dependent black hole (BH) mass, M BH , scaling relations. We have used a s le of 119 galaxies with directly measured M BH and host spheroid parameters obtained from multicomponent decomposition of, primarily, 3.6 μ m Spitzer images. Here, we investigate the correlations between M BH and the projected (apparent) luminosity density μ , the projected stellar mass density Σ, and the de-projected (internal) stellar mass density ρ , for various spheroid radii. We discover the predicted M BH – μ 0,sph relation and present the first M BH – μ e ,sph and M BH – ρ e,int,sph diagrams displaying slightly different (possibly curved) trends for early- and late-type galaxies (ETGs and LTGs, respectively) and an offset between ETGs with (fast-rotators, ES/S0) and without (slow-rotators, E) a disk. The scatter about various M BH –〈Σ〉 R,sph (and 〈 ρ 〉 r ,sph ) relations is shown to systematically decrease as the enclosing aperture (and volume) increases, dropping from 0.69 dex when using the spheroid “compactness,” 〈Σ〉 1kpc,sph , to 0.59 dex when using 〈Σ〉 5kpc,sph . We also reveal that M BH correlates with the internal density, ρ soi,sph , at the BH’s sphere-of-influence radius, such that core-Sérsic (high Sérsic index, n ) and (low- n ) Sérsic galaxies define different relations with total rms scatters 0.21 dex and 0.77 dex, respectively. The M BH –〈 ρ 〉 soi,sph relations will help with direct estimation of tidal disruption event rates, binary BH lifetimes, and together with other BH scaling relations, improve the characteristic strain estimates for long-wavelength gravitational waves pursued with pulsar timing arrays and space-based interferometers.
Publisher: EDP Sciences
Date: 21-04-2017
DOI: 10.1051/0004-6361/201630061
Abstract: Aims. This work is the first stage of a c aign to search for intermediate-mass black holes (IMBHs) in low-luminosity active galactic nuclei (LLAGN) and dwarf galaxies. An additional and equally important aim of this pilot study is to investigate the consistency between the predictions of several popular black hole scaling relations and the fundamental plane (FP) of black-hole activity (FP-BH). Methods. We used well established X-ray and radio luminosity relations in accreting black holes, along with the latest scaling relations between the mass of the central black hole ( M BH ) and the properties of its host spheroid, to predict M BH in seven LLAGN, that were previously reported to be in the IMBH regime. Namely, we used the recently re-evaluated M BH − M sph ( M sph : spheroid absolute magnitude at 3.6 μ m) scaling relation for spiral galaxies, the M BH − n sph ( n sph : major axis Sérsic index of the spheroid component) relation, the M BH −PA (PA: spiral pitch angle) relation, and a recently re-calibrated version of the FP-BH for weakly accreting BHs, to independently estimate M BH in all seven galaxies. Results. We find that all LLAGN in our list have low-mass central black holes with log M BH / M ⊙ ≈ 6.5 on average, but that they are, most likely, not IMBHs. All four methods used predicted consistent BH masses in the 1 σ range. Furthermore, we report that, in contrast to previous classification, galaxy NGC 4470 is bulge-less, and we also cast doubts on the AGN classification of NGC 3507. Conclusions. We find that our latest, state-of-the-art techniques for bulge magnitude & Sérsic index computations and the most recent updates of the M BH − L sph , M BH − n sph , and M BH −PA relations and the FP-BH produce consistent results in the low-mass regime. We thus establish a multiple-method approach for predicting BH masses in the regime where their spheres of gravitational influence cannot be spatially resolved. Our approach mitigates against outliers from any one relation and provides a more robust average prediction. We will use our new method to revisit more IMBH candidates in LLAGN.
Publisher: MDPI AG
Date: 06-12-2022
Abstract: We present an analysis of the pitch angle distribution function (PADF) for nearby galaxies and its resulting black hole mass function (BHMF) via the well-known relationship between pitch angle and black hole mass. Our s le consists of a subset of 74 spiral galaxies from the Carnegie-Irvine Galaxy Survey with absolute B-band magnitude MB −19.12 mag and luminosity distance DL≤25.4 Mpc, which is an extension of a complementary set of 140 more luminous (MB≤−19.12 mag) late-type galaxies. We find the PADFs of the two s les are, somewhat surprisingly, not strongly dissimilar a result that may hold important implications for spiral formation theories. Our data show a distinct bimodal population manifest in the pitch angles of the Sa–Sc types and separately the Scd–Sm types, with Sa–Sc types having tighter spiral arms on average. Importantly, we uncover a distinct bifurcation of the BHMF, such that the Sa–Sc galaxies typically host so-called “supermassive” black holes (M•≳106M⊙), whereas Scd–Sm galaxies accordingly harbor black holes that are “less-than-supermassive” (M•≲106M⊙). It is amongst this latter population of galaxies where we expect fruitful bounties of elusive intermediate-mass black holes (IMBHs), through which a better understanding will help form more precise benchmarks for future generations of gravitational wave detectors.
Publisher: Zenodo
Date: 2018
Publisher: Springer International Publishing
Date: 07-10-2022
Publisher: IEEE
Date: 26-11-2022
Location: No location found
Location: United States of America
Location: United Arab Emirates
No related grants have been discovered for Benjamin Davis.