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Time-lapse resistivity imaging and self-potential monitoring of experimentally induced saline intrusion in coastal aquifer sands
No full textExcessive groundwater abstraction in coastal areas exacerbates saltwater intrusion (SWI), a widespread global issue. Characterization of mechanisms delivering saltwater to wells can assist in developing suitable SWI mitigation strategies for reducing the risk of groundwater degradation. This paper presents findings from hydrogeological monitoring, time-lapse electrical resistivity tomography (ERT) and self-potential (SP) measurements to investigate SWI under natural and artificially perturbed conditions in a quasi-homogeneous pristine coastal sand aquifer, affected by large tidal ranges (>2 m). Time-lapse ERT surveys conducted under undisturbed conditions identified an upper saline recirculation cell (IRC) beneath the intertidal zone, arising due to seawater infiltrating into an underlying ∼20 m thick sand sequence containing fresher groundwater, with resistivity variations noted between spring and neap tides. Measurements taken during a 69-h constant-rate pumping test, discharging at 10.2 L/s, revealed that pumping drew saline water from the IRC towards abstraction wells. This resulted in saltwater contributions to discharge increasing from 1.4 to 4.1 %, consistent with the decrease in resistivity detected in ERT profiles between 3 m and 7 m below surface. Over the same period, SP signals fell by between 20 and 30 mV with greater declines occurring at locations nearer to the high-water mark. Monitoring data suggest that these changes in SP are primarily due to saline water intrusion from the IRC, rather than pressure changes resulting from pumping. Research findings provide further evidence that SP monitoring could act as a key geophysical early warning parameter for SWI, while ERT data further highlight the potential for monitoring SWI in shallow coastal aquifers. This study also demonstrates that optimal groundwater abstraction strategies in tidal-influenced coastal aquifers can be achieved by targeting deeper zones
Structure of far-red allophycocyanin: stripped down and tuned up for low energy photosynthesis
No full textProcess-and-forward: deep joint source-channel coding over cooperative relay networks
No full textWe introduce deep joint source-channel coding (DeepJSCC) schemes for image transmission over cooperative relay channels. The relay either amplifies-and-forwards its received signal, called DeepJSCC-AF, or leverages neural networks to extract relevant features from its received signal, called DeepJSCC-PF (Process-and-Forward). We consider both half- and full-duplex relays, and propose a novel transformer-based model at the relay. For a half-duplex relay, it is shown that the proposed scheme learns to generate correlated signals at the relay and source to obtain beamforming gains. In the full-duplex case, we introduce a novel block-based transmission strategy, in which the source transmits in blocks, and the relay updates its knowledge about the input signal after each block and generates its own signal. To enhance practicality, a single transformer-based model is used at the relay at each block, together with an adaptive transmission module, which allows the model to seamlessly adapt to different channel qualities and the transmission powers. Simulation results demonstrate the superior performance of DeepJSCC-PF compared to the state-of-the-art BPG image compression algorithm operating at the maximum achievable rate of conventional decode-and-forward and compress-and-forward protocols, in both half- and full-duplex relay scenarios over AWGN and Rayleigh fading channels
Code, test and coverage evolution in mature software systems: changes over the past decade
No full textDespite the central role of test suites in the software
development process, there is surprisingly limited information on how code and tests co-evolve to exercise different parts of the codebase.
Ten years ago, the Covrig project examined the code, test, and coverage evolution in six mature open-source projects, spanning a combined development time of twelve years. In this study, we significantly expand the analysis to nine mature projects and a combined period of 78 years of development time. Our focus is on understanding how development practices have changed and how these changes have impacted the way in which software is tested.
We report on the co-evolution of code and tests; the adoption of CI, coverage, and fuzzing services; the changes to the overall code coverage achieved by developer test suites; the distribution of patch coverage across revisions; how different kinds of code changes impact coverage; and the occurrence and evolution of
flaky tests.
Our large-scale study paints a mixed picture in terms of how software development and testing have changed over the past ten years. While developers put more emphasis on software testing and the overall code coverage achieved by developer test suites has increased in most projects, coverage and fuzzing services are not widely adopted, many patches are still poorly tested, and the fraction of flaky tests has increased
A proper orthogonal decomposition (POD) and spectral proper orthogonal decomposition (SPOD) study on the effects of different momentum ratios and Reynolds number in a T-junction with an upstream elbow
No full textT-junctions are critical components within the primary circuit of pressurised water reactors (PWRs). They connect the pressuriser (PRZ), with the steam generator (SG), and the reactor pressure vessel (RPV). As such, it is crucial to have a mechanistic understanding of the turbulent fluid flow and thermal mixing within such T-junctions. Computational fluid dynamics (CFD) studies of flows within T-junctions usually involve understanding the effects of variations in momentum and Reynolds numbers on the turbulent flow structures and thermal mixing phenomena. In this paper, we utilise proper orthogonal decomposition (POD) and spectral proper orthogonal decomposition (SPOD) methods to analyse the complex flow structures arising from various test cases for a PWR T-junction with an upstream elbow.
The first aim is to compare the flow structures resulting from different momentum ratios and/or Reynolds numbers of the inlet branch flow to identify the dominant factor. These parameters are adjusted by varying the branch pipe diameter and inlet branch velocity. The final aim is to compare flow structures obtained using POD and SPOD analysis. While both methods produce explicable patterns, they reveal vastly different structures that can be interpreted differently.
Momentum ratios have traditionally guided engineering design optimization. Our findings indicate that altering the Reynolds number of the inlet branch flow can help avoid turbulent flow structures that may compromise the structural integrity of nuclear components in NPPs. While POD is widely used for fluid flow analysis, SPOD offers a more detailed examination of turbulent fluid flow structures
Life-cycle seismic resilience of deteriorating highway bridges under mainshock-aftershock sequences
No full textReinforced concrete highway bridges often experience seismic events coupled with progressive deterioration due to corrosion over their lifespan. In many cases, the seismic mainshocks are followed by significant aftershocks, causing cumulative damage that disrupts normal operations and delays the restoration of bridges. Current research however lacks detailed assessment of seismic resilience considering the effects of aftershocks and corrosion deterioration over the lifetime of bridges. This study proposes a methodology for evaluating the life-cycle seismic resilience of deteriorating structures under mainshock and aftershock (MS-AS) sequences. Three multi-span reinforced concrete highway bridges with different geometries are used as benchmarks. A suite of 80 pairs of ground motion sequences is selected for undertaking the resilience evaluations based on the seismic scenarios considered. The Park-Ang damage index is adopted for the purpose of quantifying the cumulative damage. Nonlinear dynamic analysis is used to provide detailed insights into the mechanisms through which the aftershocks affect the cumulative damage. Based on the results, time-dependent system fragility curves under MS-AS sequences are developed in conjunction with a cumulative damage capacity model for the bridge piers. The seismic resilience of the bridges is subsequently assessed under ground motion sequences at different service times, and the effects of aftershocks and corrosion-induced deterioration on the resilience are examined. Finally, the life-cycle seismic resilience of the deteriorating benchmark bridges under MS-AS sequences is evaluated using the suggested framework. It is shown that the influence of aftershocks on the cumulative damage depends on a number of inter-related factors, including the relative mainshock-aftershock intensity as well as the dynamic characteristics of the bridges. The findings highlight the merits of the proposed framework in evaluating the life-cycle seismic resilience of bridges for different hazard scenarios and deterioration conditions
Alkali halide aqueous solutions under pressure: a non-equilibrium molecular dynamics investigation of thermal transport and thermodiffusion
No full textThermal gradients induce thermodiffusion in aqueous solutions, a non-equilibrium effect arising from the coupling of thermal and mass fluxes. While thermal transport processes have garnered significant attention under standard conditions, thermal transport at high pressures and temperatures, typical of the Earth’s crust, has escaped scrutiny. Non-equilibrium thermodynamics theory and non-equilibrium molecular dynamics simulations provide an excellent means to quantify thermal transport under extreme conditions and establish a connection between the behaviour of the solutions and their microscopic structure. Here, we investigate the thermal conductivity and thermal diffusion of NaCl and LiCl solutions in the GPa pressure regime, targeting temperatures between 300 K and 1000 K at 1 molal concentration. We employ non-equilibrium molecular dynamics simulations along with the Madrid-2019 and TIP4P/2005 force fields. The thermal conductivity of the solutions increases significantly with pressure, and following the behaviour observed at standard pressure, the thermal conductivity is lower than that of pure water. The reduction in thermal conductivity is significant in the GPa pressure regime, ∼3% for 1 molal NaCl and LiCl solutions. We demonstrate that under GPa pressure conditions, the solutions feature thermophobic behaviour, with ions migrating towards colder regions. The pronounced impact of pressure is more evident in LiCl solutions, which display a thermophilic to thermophobic “transition” at pressures above 0.25 GPa. We discuss a correlation between the solution’s thermophobicity and the disruption of the water hydrogen bond structure at high pressure, where the water structure resembles that observed in simple liquids
Are vulnerable neighbourhoods left behind? Urban cooling disparities from greenspace inequality in Antananarivo, Madagascar
No full textThe escalation of urbanisation contributes significantly to urban heat in both affluent and impoverished neighbourhoods. Community thermal vulnerability is often characterised by socio-demographic composition, with little consideration as places where people are unequally exposed to greenspace and how they associate with cooling disparities. Combining land surface temperature, this Antananarivo case study employed greenspace exposure Gini coefficient to map the locations of vulnerable neighbourhoods and evaluate how their cooling effect differ from others. Results show that nearly 25 % neighbourhoods were unequal where values of exposure to greenspace is disproportionately higher in some of grid cells than others, raising vulnerability to urban heat. These vulnerable neighbourhoods exhibited an average 0.01 °C greater cooling effect compared to the rest of more equal neighbourhoods. Specifically, main cooling role for vulnerable neighbourhoods is agricultural land with a 1 % coverage increase leading to a 0.02–0.03 °C temperature reduction in the day. Comparatively, the cooling effect for equal neighbourhoods relies on non-agricultural greenspace with 1 % coverage increase resulting in a 0.01–0.02 °C temperature reduction at night. Meanwhile, cooling models from 2017 and 2022 identified greenspace thresholds of 62% and 78% existing in equal neighbourhoods, which estimated to reduce average 0.78 °C, 1.24 °C nighttime temperature to bring equal neighbourhoods who were experiencing the high temperature to a more comfortable range regardless of any other factors. However, there was no thresholds detected in vulnerable neighbourhoods. Cooling disparities between vulnerable and equal neighbourhoods is influenced by factors of urbanisation, topology conditions, vegetation canopy, land cover, and day-to-night land surface temperature variations. These cooling disparities also depicted the trajectory of how neighbourhoods evolve from being equal to becoming vulnerable. Our findings emphasise the contributions of equitable greenspace distributions to urban heat mitigation and adaptation, implicating cooling strategies for marginalised communities in Antananarivo and other urban centres across Africa and beyond
Boosting photon-number-resolved detection rates of transition-edge sensors by machine learning
No full textTransition-edge sensors (TESs) are very effective photon-number-resolving (PNR) detectors that have enabled many photonic quantum technologies. However, their relatively slow thermal recovery time severely limits their operation rate in experimental scenarios compared with leading non-PNR detectors. In this work, we develop an algorithmic approach that enables TESs to detect and accurately classify photon pulses without waiting for a full recovery time between detection events. We propose two machine-learning-based signal processing methods: one supervised learning method and one unsupervised clustering method. By benchmarking against data obtained using coherent states and squeezed states, we show that the methods extend the TES operation rate to 800 kHz, achieving at least a four-fold improvement, whilst maintaining accurate photon-number assignment up to at least five photons. Our algorithms will find utility in applications where high rates of PNR detection are required and in technologies that demand fast active feed-forward of PNR detection outcomes
Mode transforming vortex laser with optical levitation
No full textThe work in this thesis spans two primary fields of inquiry. The first focuses on the
development of a novel laser system capable of direct optical vortex (OV) emission, while
the second aims to demonstrate its application in the optical levitation of reflective hollow
microspheres.
We first present the non-standard use of a wedge-plate shearing interferometer (WPSI)
as a TEM00 Gaussian to LG01 OV mode conversion device. A detailed description of
its geometric configuration and interferometric process is presented. It gives an idealised
power conversion of 99.6 % in favour of the of the LG01 OV-mode. However, since the OV
is generated in its face-reflection, the incident power conversion is equal to only its Fresnel
reflectance. Power scaling potential is improved through intracavity use of the WPSI.
A unidirectional ring cavity was used with a 20:1 power imbalance in favour of clock-
wise propagation which enhanced incident power to enable watt-level OV output power
(1.15 W). The unconverted power is recycled back into the cavity. In this configuration
we demonstrate the generation of OV beams with high beam-quality (M2 = 1.94, 2.09) and
high LG01 mode-purity (97.8 %).
In the second part, we demonstrate the use of this system in optical levitation. This work
was motivated by the desire to levitate metallic (possible reflective) hollow-sphere (shells
with low internal refractive index) targets for experiments with high-intensity, high-energy
laser systems particularly in the generation of high-density plasmas, point X-ray sources,
and charged-particle acceleration. We demonstrate the optical levitation of shells 20 to
110 μm in diameter (masses of 25 ng to 230 ng) at long focal length (f = 40 mm) and
measure <5 μm spatial stability in air and low vacuum