ORCID Profile
0000-0002-5254-0012
Current Organisation
University of Adelaide
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Publisher: Springer Science and Business Media LLC
Date: 05-07-2016
Publisher: Elsevier
Date: 2018
Publisher: American Geophysical Union (AGU)
Date: 28-05-2019
DOI: 10.1029/2018RG000630
Abstract: Groundwater extraction is increasing rapidly in many areas of the world, causing serious impacts such as falling water tables, ground surface subsidence, water quality degradation, and reduction of stream baseflow on which many ecosystems depend. Methods for understanding and predicting the impacts of groundwater extraction generally lack detailed spatial and temporal knowledge of the subsurface hydrogeomechanical properties. This review provides a comprehensive understanding of Earth and atmospheric tides and their impact on subsurface pore pressure. First, we evaluate the global occurrence of Earth and atmospheric tides. Then, we illustrate their impact on the groundwater response and connect this with the theory of poroelasticity, which underpins quantitative analyses. Finally, we review methods that utilize these impacts to characterize groundwater systems and to quantify their hydrogeomechanical properties. We conclude by highlighting their potential as passive and low‐cost investigation techniques and by outlining the research and developments required to progress and make analyses readily available. Thus, hydrogeomechanical properties of subsurface systems could be obtained at unprecedented spatial and temporal resolution, adding additional value to commonly acquired groundwater and atmospheric pressure data.
Publisher: Elsevier BV
Date: 03-2021
DOI: 10.1016/J.BBR.2020.113067
Abstract: Adolescents are more likely than adults to develop chronic symptoms, such as impulsivity and difficulty concentrating, following a mild traumatic brain injury (mTBI) which may relate to disruption of pre-frontal cortex (PFC development). During adolescence the PFC is undergoing extensive remodelling, driving maturation of executive functions incorporating attention, motivation and impulse control. In part maturation of the PFC is driven by outgrowth of dopaminergic neurons to the PFC under the guidance of specific axonal targeting cues, including netrin-1. How a mTBI in adolescence may alter the expression of these axonal targeting cues, and the influence on PFC development is not yet known. As such the effects of mTBI in mid-adolescence on executive functioning in adulthood (12 weeks) were examined via the 5-choice serial reaction task in both male and female Sprague Dawley rats. Animals at p35 (n = 12-16 per group) were injured via weight drop (100 g from 0.75 m) and injury confirmed by a significant increase in righting reflex. Interestingly, while a mid-adolescence mTBI in females led to significantly higher omissions and decreased accuracy when task difficulty was high (stimulus duration 1 s), males had significantly increased premature response rate when the intertrial interval was varied. Examination of levels of TH, as a reflection of dopaminergic innervation, found no difference in either gender post-TBI in the PFC, but a significant increase in the limbic system (nucleus accumbens) in males, but not females, chronically post-TBI, suggesting an imbalance between the regions. The increase in TH was accompanied by a chronic reduction in netrin-1 within the nucleus accumbens in males only. Taken together, these results indicate that mTBI in adolescence leads to sex specific effects in different domains of PFC function in adulthood, which may relate to subtle alterations in the developmental trajectory of the mesocortical limbic pathway in males only.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-8665
Abstract: & & In situ quantification of subsurface hydro-geomechanical properties is challenging and requires significant effort. Evolving research illustrates that subtle harmonic components in groundwater head measurements caused by Earth and atmospheric tides can be utilised to explore groundwater systems with little effort compared to traditional investigations. One long standing problem has been that, for dominant tidal components, Earth and atmospheric tides occur at the same frequency which prevents the use of the groundwater response to their in idual forcing to infer subsurface properties. While Acworth et al. (2016) offered a way forward, their approach has assumptions that limit the applicability. Here, we illustrate an extended method that disentangles the borehole water level response and attributes magnitude and phase to their in idual drivers. As a result, we obtain in idual changes in harmonic properties of the drivers and their groundwater response ( litude ratio and phase shift) using borehole water level records from different locations. In conjunction with groundwater flow and poroelastic theory, these properties can be used to infer the state of confinement, quantify specific storage and hydraulic conductivity as well as barometric efficiency of the formation. Further, because the stresses imposed by Earth and atmospheric tides are volumetric and uniaxial, respectively, their in idual responses can be used to reveal strain anisotropy. Our new approach is passive, i.e. it only requires the measurements of atmospheric and groundwater pressure records, and can provide further insight into subsurface processes and properties using information hidden in standard pressure records.& & & & & & & & & Acworth, R. I., Halloran, L. J. S., Rau, G. C., Cuthbert, M. O., and Bernardi, T. L. ( 2016), An objective frequency domain method for quantifying confined aquifer compressible storage using Earth and atmospheric tides, Geophys. Res. Lett., 43, 11,671& #8211 ,678, doi:10.1002/2016GL071328.& &
Publisher: Elsevier BV
Date: 08-2017
DOI: 10.1016/J.BBI.2017.04.006
Abstract: A history of repeated concussion has been linked to the later development of neurodegeneration, which is associated with the accumulation of hyperphosphorylated tau and the development of behavioral deficits. However, the role that exogenous factors, such as immune activation, may play in the development of neurodegeneration following repeated mild traumatic brain injury (rmTBI) has not yet been explored. To investigate, male Sprague-Dawley rats were administered three mTBIs 5days apart using the diffuse impact-acceleration model to generate ∼100G. Sham animals underwent surgery only. At 1 or 5days following the last injury rats were given the TLR4 agonist, lipopolysaccharide (LPS, 0.1mg/kg), or saline. TLR4 activation had differential effects following rmTBI depending on the timing of activation. When given at 1day post-injury, LPS acutely activated microglia, but decreased production of pro-inflammatory cytokines like IL-6. This was associated with a reduction in neuronal injury, both acutely, with a restoration of levels of myelin basic protein (MBP), and chronically, preventing a loss of both MBP and PSD-95. Furthermore, these animals did not develop behavioral deficits with no changes in locomotion, anxiety, depressive-like behavior or cognition at 3months post-injury. Conversely, when LPS was given at 5days post-injury, it was associated acutely with an increase in pro-inflammatory cytokine production, with an exacerbation of neuronal damage and increased levels of aggregated and phosphorylated tau. At 3months post-injury, there was a slight exacerbation of functional deficits, particularly in cognition and depressive-like behavior. This highlights the complexity of the immune response following rmTBI and the need to understand how a history of rmTBI interacts with environmental factors to influence the potential to develop later neurodegeneration.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-3635
Abstract: & & Earth and atmospheric tides are prevalent across the land-surface and provide natural forcing to characterise the hydro-geomechanical confined subsurface by using their groundwater response. Since tides are harmonic, their in idual influences on the pressure head can be separated into complex components containing level or pressure magnitudes and phases. The approximated planar strain from Earth tides, and the uniaxial loading from atmospheric tides, allow the estimation of a wide range of values based on hydraulic and poroelastic relationships. With recent research advances, tidal analysis can be used to estimate hydro-geomechanical properties including specific storage, hydraulic conductivity, porosity, shear, Young& #8217 s and Bulk moduli, Skempton& #8217 s and Biot-Willis coefficients and undrained/drained Poisson& #8217 s ratios. This approach does not require any assumption on mineral grain compressibility for unconsolidated systems. However, consolidated materials currently require an a priori estimate of grain compressibility. We applied this method to pressure measurements from different geological settings. The estimated hydro-geomechanical properties comply with theoretically expected values except for Poisson& #8217 s ratio, which differs from laboratory values due to differing confining pressures, and comparatively low frequencies of the Earth and Atmospheric tide signals. However, these estimated values from in-situ data are likely more realistic of the natural hydrogeological response. We anticipate that, by developing methods that routinely can derive engineering geotechnical values through the monitoring of hydraulic head variations, the collection of groundwater pressures will become a priority for large civic excavations or construction, such as mining, in addition to environmental studies and regulatory compliance.& &
Publisher: Wiley
Date: 15-12-2020
No related grants have been discovered for Timothy McMillan.