Coastal Groundwater Dynamics - Investigation of Using Geoelectrical and Hydrochemical Tools for Saline Intrusion Monitoring

<p>With over 65 % of the global population currently living in areas near a coast, increasing fresh groundwater demands within these areas, shifted precipitation patterns, and rising mean sea levels, increased seawater intrusion into coastal aquifers has become a major issue for groundwater resources in many coastal countries all around the world. Although there are many past studies researching the saline interface in affected aquifers from a modelling, laboratory or field perspective with different hydrological and geophysical approaches, little is known about real field dynamics over various time spans and in different geological settings. This PhD project aims at detecting and characterising seawater intrusion into a shallow coastal Holocene sand and gravel aquifer at New Zealand's west coast with respect to seasonally changing aquifer resistivity and hydrochemical tracers, as well as investigating resistivity and hydraulic property changes within a tidal time frame. Seawater mixing behaviour over different time spans was monitored with electrical resistivity tomography (ERT) over the course of two years, and additional hydrochemical sampling was carried out during the second year of the long-term seawater intrusion monitoring study. During two consecutive years, repeat ERT measurements were able to determine seasonal and shorter-term cycles in seawater mixing behaviour within the shallow coastal aquifer. There are strong indications that increasing urbanisation has a major influence on seasonal seawater intrusion patterns, and the dominant processes at the field locations were identified to be tied to the amount of freshwater available over the course of a year, as well as enhanced evapotranspiration / evaporation during summer. Hydrochemical data backed these observations and were also able to characterise seawater intrusion as a function of depth at the field location. Within the smaller tidal cycle investigations, similarly behaving parts of the aquifer could be identified from resistivity ratios and time series analyses. Varying amplitudes in resistivity changes led to the conclusion that saline mixing within a diurnal tidal cycle is strongly dependent on the recharge regime of the aquifer and decreases significantly for times during the year when recharge is continuous as opposed to times with little general recharge but intense, isolated rainfall events. In addition, tidal time series were used to qualitatively infer hydraulic properties of the aquifer and ultimately delineate preferential flow paths for seawater intrusion at the field site. The results of this project support findings of previous modelling, laboratory and short-term field studies, and put the concepts into a much broader time frame. For the first time the dynamics of seawater mixing in a shallow coastal sand aquifer were conclusively studied at the same location and within different time frames, and are thus of great value for sustainable groundwater management in the area of investigation and similar coastal environments.</p>

Coastal Groundwater Dynamics - Investigation of Using Geoelectrical and Hydrochemical Tools for Saline Intrusion Monitoring

<p>With over 65 % of the global population currently living in areas near a coast, increasing fresh groundwater demands within these areas, shifted precipitation patterns, and rising mean sea levels, increased seawater intrusion into coastal aquifers has become a major issue for groundwater resources in many coastal countries all around the world. Although there are many past studies researching the saline interface in affected aquifers from a modelling, laboratory or field perspective with different hydrological and geophysical approaches, little is known about real field dynamics over various time spans and in different geological settings. This PhD project aims at detecting and characterising seawater intrusion into a shallow coastal Holocene sand and gravel aquifer at New Zealand's west coast with respect to seasonally changing aquifer resistivity and hydrochemical tracers, as well as investigating resistivity and hydraulic property changes within a tidal time frame. Seawater mixing behaviour over different time spans was monitored with electrical resistivity tomography (ERT) over the course of two years, and additional hydrochemical sampling was carried out during the second year of the long-term seawater intrusion monitoring study. During two consecutive years, repeat ERT measurements were able to determine seasonal and shorter-term cycles in seawater mixing behaviour within the shallow coastal aquifer. There are strong indications that increasing urbanisation has a major influence on seasonal seawater intrusion patterns, and the dominant processes at the field locations were identified to be tied to the amount of freshwater available over the course of a year, as well as enhanced evapotranspiration / evaporation during summer. Hydrochemical data backed these observations and were also able to characterise seawater intrusion as a function of depth at the field location. Within the smaller tidal cycle investigations, similarly behaving parts of the aquifer could be identified from resistivity ratios and time series analyses. Varying amplitudes in resistivity changes led to the conclusion that saline mixing within a diurnal tidal cycle is strongly dependent on the recharge regime of the aquifer and decreases significantly for times during the year when recharge is continuous as opposed to times with little general recharge but intense, isolated rainfall events. In addition, tidal time series were used to qualitatively infer hydraulic properties of the aquifer and ultimately delineate preferential flow paths for seawater intrusion at the field site. The results of this project support findings of previous modelling, laboratory and short-term field studies, and put the concepts into a much broader time frame. For the first time the dynamics of seawater mixing in a shallow coastal sand aquifer were conclusively studied at the same location and within different time frames, and are thus of great value for sustainable groundwater management in the area of investigation and similar coastal environments.</p>

Numerical Simulations of Polymers at the Nanoscale

<p>In this thesis we study a variety of nanoscale phenomena in certain polymer systems using a combination of numerical simulation methods and mathematical modelling. The problems considered are: (a) the mixing behaviour of polymeric fluids in micro- and nanofluidic devices, (b) capillary absorption of polymer droplets into narrow capillaries, and (c) modelling the phase separation and self-assembly behaviour in polymer systems with freely deforming boundaries. These problems are significant in nanotechnological applications of polymer-based systems. First, the mixing behaviour of a polymeric melt over two parallely patternedslip surfaces is considered. Using molecular dynamics (MD) simulations, it is shown that mixing is enhanced when the polymer chain size is smaller than the wavelength of the chemical pattern of the surfaces. An off-set in the upper and lowerwall patterns improved themixing in the centre of the channel. Application of a sinusoidally varying body force in addition to the patterned-slip conditions is shown to enhance mixing further, compared to a constant body force case, with some limitations. Simulation findings for the constant body force cases are in qualitative agreement with the continuum theory of Pereira [1]. However, in the case of a sinusoidally varying body force our simulations do not agree with the continuum theory. We explain the reasons for the discrepancy between the two and point out the deficiencies in the continuum theory in predicting the correct behaviour. Second, the capillary phenomena of polymer droplets in narrow capillaries is studied using MD simulations. It is demonstrated that droplets composed of longer chains require wider tubes for absorption and this result is in agreement with our continuum modelling. The observed capillary dynamics deviate significantly from the standard Lucas-Washburn description thus questioning its validity at the nanoscale. The metastable states during the capillary absorption in some cases cannot be explained using the existing models of capillary dynamics. Lastly, the phase separation process in polymer blends between both confined and unconfined boundaries is studied using Smoothed Particle Hydrodynamics (SPH). The SPH technique has the advantage of not using a grid to discretize the spatial domain, which makes it appealing when dealing with problems where the spatial domain can change with time. The applicability of the SPH method in describing phase separation in these systems is demonstrated. In particular, its ability to model freely deforming polymer blends is shown.</p>

Numerical Simulations of Polymers at the Nanoscale

<p>In this thesis we study a variety of nanoscale phenomena in certain polymer systems using a combination of numerical simulation methods and mathematical modelling. The problems considered are: (a) the mixing behaviour of polymeric fluids in micro- and nanofluidic devices, (b) capillary absorption of polymer droplets into narrow capillaries, and (c) modelling the phase separation and self-assembly behaviour in polymer systems with freely deforming boundaries. These problems are significant in nanotechnological applications of polymer-based systems. First, the mixing behaviour of a polymeric melt over two parallely patternedslip surfaces is considered. Using molecular dynamics (MD) simulations, it is shown that mixing is enhanced when the polymer chain size is smaller than the wavelength of the chemical pattern of the surfaces. An off-set in the upper and lowerwall patterns improved themixing in the centre of the channel. Application of a sinusoidally varying body force in addition to the patterned-slip conditions is shown to enhance mixing further, compared to a constant body force case, with some limitations. Simulation findings for the constant body force cases are in qualitative agreement with the continuum theory of Pereira [1]. However, in the case of a sinusoidally varying body force our simulations do not agree with the continuum theory. We explain the reasons for the discrepancy between the two and point out the deficiencies in the continuum theory in predicting the correct behaviour. Second, the capillary phenomena of polymer droplets in narrow capillaries is studied using MD simulations. It is demonstrated that droplets composed of longer chains require wider tubes for absorption and this result is in agreement with our continuum modelling. The observed capillary dynamics deviate significantly from the standard Lucas-Washburn description thus questioning its validity at the nanoscale. The metastable states during the capillary absorption in some cases cannot be explained using the existing models of capillary dynamics. Lastly, the phase separation process in polymer blends between both confined and unconfined boundaries is studied using Smoothed Particle Hydrodynamics (SPH). The SPH technique has the advantage of not using a grid to discretize the spatial domain, which makes it appealing when dealing with problems where the spatial domain can change with time. The applicability of the SPH method in describing phase separation in these systems is demonstrated. In particular, its ability to model freely deforming polymer blends is shown.</p>

COVID-19 and shielding: Experiences of UK patients with lupus and related diseases

Objective The UK’s shielding guidance for the ‘clinically extremely vulnerable’ (CEV) commenced on 23 March 2020 in response to the COVID-19 pandemic. The purpose of this study was to explore the impact of the pandemic and shielding on patients with lupus and related systemic autoimmune rheumatic diseases (SARDs). Methods This was a mixed-methods cohort study (N = 111) including pre-lockdown baseline surveys (March 2020), follow-up surveys (June 2020), and in-depth interviews during July 2020 (N = 25). Results Most participants had a high level of anxiety regarding their mortality risk from COVID-19 and supported the shielding concept. Shielding allocations and communications were perceived as inconsistently applied and delivered. Over half of those not classified as CEV reported feeling abandoned, at increased risk and with no support. Shielding communications increased feelings of being ‘cared about’, yet also increased fear, and the ‘vulnerable’ labelling was perceived by some to damage social- and self-identity. Over 80% of those classified as CEV stated that the classification and subsequent communications had changed their social-mixing behaviour. Despite many negative impacts of COVID-19 and shielding/lockdown being identified, including isolation, fear and reduced medical care, the during-pandemic quantitative data showed increases in most measures of well-being (which was low at both timepoints) from pre-lockdown, including reductions in the impact of fatigue and pain (Ps &lt; 0.001). Conclusion Shielding classifications and communications were generally positively viewed, although perceived as inconsistently delivered and anxiety-provoking. More frequent positively-framed communication and wellbeing support could benefit all SARD patients. Slower-paced ‘lockdown’ lifestyles may confer health/wellbeing benefits for some people with chronic diseases.

Investigation on thermo-physical properties of liquid In-Tl alloy

This research explores mixing behaviour of liquid In – Tl system through thermodynamic and the structural properties on the basis of Complex Formation Model. The properties like surface tension and viscosity have been analyzed through simple statistical model and Moelwyn – Hughes equation. The interaction parameters are found to be positive, concentration independent and temperature dependent. Theoretical results are in a good agreement with the corresponding literature data which support homo-coordinating tendency in the liquid In-Tl alloy. BIBECHANA 18 (2021) 149-158