Mesures ultrasonores et de transport dans le semimétal de Weyl NbP

Abstract: In recent years, physicists have discovered that the topological electronic structure of materials can have dramatic consequences on their properties. In a new variety of topological materials called Weyl semimetals, electrons behave as massless relativistic particles. These materials are in some sense a 3-dimensional equivalent to graphene. Many interesting magneto-electric effects, that could possibly be applicable to quantum technologies, have been predicted in Weyl semimetals and are still studied today. Theoretical and preliminary experiments have demonstrated that it is possible to probe the topological nature of these materials by measuring the speed at which acoustic waves travel through the material. This research technique allows us to probe the volume of the sample and to avoid certain errors associated with electrical conductivity measurements. In this project, we explore experimentally how the application of a magnetic field modifies the speed and absorption of sound in the Weyl semimetal NbP. We will show how applied magnetic fields have an anisotropic effect on the sound velocity and compare with previous results on the isostructural material TaAs. In contrast to what was observed in TaAs, our measurements do not show significant evidence of the chiral anomaly. The sound velocity measurements also exhibit quantum oscillations that allow us to characterize the Fermi surface of the material. We have also carried out transport measurements on the same material NbP as a complementary measurement of quantum oscillations.Ces dernières années, les physiciens ont découvert que la structure électronique topologique des matériaux peut avoir des conséquences dramatiques sur leurs propriétés. Dans une nouvelle variété de matériaux topologiques appelés semimétaux de Weyl, les électrons se comportent comme des particules relativistes sans masse. Ces matériaux sont en quelque sorte l'équivalent tridimensionnel du graphène. De nombreux effets magnéto-électriques intéressants, qui pourraient éventuellement s’appliquer aux technologies quantiques, ont été prédits dans les semimétaux de Weyl et sont encore étudiés aujourd’hui. Des expériences théoriques et préliminaires ont démontré qu’il est possible de sonder la nature topologique de ces matériaux en mesurant la vitesse à laquelle les ondes acoustiques se déplacent à travers le matériau. Cette technique de recherche permet de sonder le volume de l’échantillon et d’éviter certaines erreurs associées aux mesures de conductivité électrique. Dans ce projet, nous explorons expérimentalement comment l’application d’un champ magnétique modifie la vitesse et l’absorption du son dans le semi-métal de Weyl NbP. Nous montrerons comment les champs magnétiques appliqués ont un effet anisotrope sur la vitesse du son et nous comparerons avec les résultats précédents sur le matériau isostructural TaAs. Contrairement à ce qui a été observé dans le TaAs, nos mesures ne montrent pas de preuves significatives de l’anomalie chirale. Les mesures de vitesse du son présentent également des oscillations quantiques qui nous permettent de caractériser la surface de Fermi du matériau. Nous avons également effectué des mesures de transport sur le même matériel, le NbP, comme mesure complémentaire des oscillations quantiques

The Nitrate Time Bomb (NTB) Model: a simple but effective method to investigate the impacts of historical nitrate loading on long-term groundwater nitrate concentrations

Nitrate water pollution, which remains an international problem, can cause long-term environmental damage and threaten both the economy and human health. Agricultural land is the major source of nitrate water pollution. It can take decades for nitrate leached from the soil to discharge into freshwaters. However, this nitrate time lag in the groundwater system has generally been ignored within the water resource management in many countries including the UK. We present a nitrate time bomb (NTB) model to modelling nitrate processes in the groundwater system. Whilst NTB contains simplified conceptual models, it can represent the major nitrate and hydrogeological processes in the groundwater system at both national and catchment scales, such as spatio-temporal nitrate loading, low-permeability superficial deposits, dual-porosity unsaturated zones and nitrate dilution in aquifers. The NTB model has been successfully used to simulate annual nitrate concentrations from 1925 to 2150 in the major aquifers in Great Britain and four local aquifer zones in the Eden Catchment, England. Monte Carlo simulations were undertaken to analyse parameter sensitivity and calibrate the model using observed datasets. These results help decision makers to understand how the historical nitrate loading from agricultural land affects the evolution of groundwater quality due to the nitrate time lag in the groundwater system. This NTB approach will be particularly valuable to evaluate the long-term impact and timescale of land management scenarios and programmes of measures introduced to help deliver water quality compliance. This model requires relatively modest parameterisation and is readily transferable to other areas

The impacts of historical agricultural landuse on the nitrate concentration trend in the major aquifers in England and Wales

Agricultural land is the major source of nitrates in UK groundwater. Due to the long time-lag in the groundwater system, it could take decades for leached nitrate from the soil to discharge into freshwaters. This paper presents an approach to modelling groundwater nitrate at the national scale, to simulate the impacts of historical nitrate loading from agricultural land on the evolution of groundwater nitrate concentrations. The sensitivity of parameters was analysed using Monte Carlo simulations. The model was calibrated using national nitrate monitoring data. Time series of annual average nitrate concentrations along with annual spatially distributed nitrate concentration maps from 1925 to 2150 were generated for 28 selected aquifer zones in England and Wales. The results show that 16 aquifer zones have an increasing trend in nitrate concentration, while average nitrate concentrations in the remaining 12 are declining. These results help decision makers to understand how the historical nitrate loading from agricultural land affects the evolution of groundwater quality due to the nitrate time lag in the groundwater system. This approach will be particularly valuable to evaluate the long-term impact and timescale of land management scenarios and programmes of measures introduced to help deliver water quality compliance

How important is the unsaturated zone in the terrestrial nitrogen budget? [abstract]

Inputs of nitrogen to agricultural land have had significant effects on aquatic and marine ecosystems through eutrophication, algal blooms and habitat loss. In order to manage this problem, terrestrial nitrogen budgets at the national scale have been developed. However, explicit representation of nitrate transport in the subsurface is seldom considered. Using derived estimates of unsaturated zone travel time and nitrate loading at the base of the soil zone, we quantify the total mass of nitrate held in in the unsaturated zone of aquifers in the United Kingdom. In the unsaturated zone of moderate and highly productive aquifers of the UK this is estimated to have peaked in 2008 at 1400 kt N; substantially greater than previous approximations. Currently 70% of the nitrate mass in the unsaturated zone is in the Chalk, with the remainder split between the Permo-Triassic Sandstones, Oolitic Limestones and other less important aquifers. The UK unsaturated zone is now a source of nitrate and in 2014 we estimate the net nitrate flux from the unsaturated zone to groundwater and surface water to be approximately 70 kt N/a. The mass of nitrate in the unsaturated zone should be considered in future terrestrial nitrogen budgets to improve national scale ecosystem management

Food Shelf Friendly: Increasing the Nutritional Quality of Food Shelf Donations

Introduction: Food insecurity is a household-level economic and social condition of limited access to nutritionally adequate and safe food. Food banks provide a major source of sustenance for individuals experiencing food insecurity, many of whom deal with obesity, diabetes and hypertension, however, the nutritional contents of many donations to these operations fail to meet the dietary recommendations set forth by the USDA for individuals with many chronic health conditions. In the present economy there is increasing demand for the services of local food shelves, however, often these organizations are unable to sufficiently meet the needs of their clients with regard to quantity ,and perhaps more importantly, the nutritional quality and variety of food available. One cause of the lack of nutritionally rich donations is poor public education about the needs of the food shelf and its clients. This study seeks to determine if consumer education at the point of purchase can influence donation decisions to increase the quantity and improve the nutritional quality of items donated to the Chittenden Emergency Food Shelf in a sustainable and reproducible manner.https://scholarworks.uvm.edu/comphp_gallery/1034/thumbnail.jp

Novel in vitro and mathematical models for the prediction of chemical toxicity

The focus of much scientific and medical research is directed towards understanding the disease process and defining therapeutic intervention strategies. Whilst the scientific basis of drug safety has received relatively little attention, despite the fact that adverse drug reactions (ADRs) are a major health concern and a serious impediment to development of new medicines. Toxicity issues account for ~21% drug attrition during drug development and safety testing strategies require considerable animal use. Mechanistic relationships between drug plasma levels and molecular/cellular events that culminate in whole organ toxicity underpins development of novel safety assessment strategies. Current in vitro test systems are poorly predictive of toxicity of chemicals entering the systemic circulation, particularly to the liver. Such systems fall short because of 1) the physiological gap between cells currently used & human hepatocytes existing in their native state, 2) the lack of physiological integration with other cells/systems within organs, required to amplify the initial toxicological lesion into overt toxicity, 3) the inability to assess how low level cell damage induced by chemicals may develop into overt organ toxicity in a minority of patients, 4) lack of consideration of systemic effects. Reproduction of centrilobular & periportal hepatocyte phenotypes in in vitro culture is crucial for sensitive detection of cellular stress. Hepatocyte metabolism/phenotype is dependent on cell position along the liver lobule, with corresponding differences in exposure to substrate, oxygen & hormone gradients. Application of bioartificial liver (BAL) technology can encompass in vitro predictive toxicity testing with enhanced sensitivity and improved mechanistic understanding. Combining this technology with mechanistic mathematical models describing intracellular metabolism, fluid-­‐flow, substrate, hormone and nutrient distribution provides the opportunity to design the BAL specifically to mimic the in vivo scenario. Such mathematical models enable theoretical hypothesis testing, will inform the design of in vitro experiments, and will enable both refinement and reduction of in vivo animal trials. In this way, development of novel mathematical modelling tools will help to focus and direct in vitro and in vivo research, and can be used as a framework for other areas of drug safety science

Zirconia-titania-doped tantala optical coatings for low mechanical loss Bragg mirrors

The noise caused by internal mechanical dissipation in the high refractive index amorphous thin films in dielectric mirrors is an important limitation for gravitational wave detection. The objective of this study is to decrease this noise spectral density, which is linearly dependent on such dissipation and characterized by the loss angle of the Young’s modulus, by adding zirconia to titania-doped tantala, from which the current mirrors for gravitational wave detection are made. The purpose of adding zirconia is to raise the crystallization temperature, which allows the material to be more relaxed by raising the practical annealing temperature. The Ta, Ti and Zr oxides are deposited by reactive magnetron sputtering in an Ar:O2 atmosphere using radio-frequency and high power impulse plasma excitation. We show that thanks to zirconia, the crystallization temperature rises by more than 150◦C, which allows one to obtain a loss angle of 2.5 × 10−4 , that is, a decrease by a factor of 1.5 compared to the current mirror high-index layers. However, due to a difference in the coefficient of thermal expansion between the thin film and the silica substrate, cracks appear at high annealing temperature. In response, a silica capping layer is applied to increase the temperature of crack formation by 100◦C

The effect of the branched-chain amino acids on the in-vitro activity of bovine intestinal alkaline phosphatase

Branched-chain amino acids (BCAA) are used as nutritional support for patients with a range of conditions including liver cirrhosis and in-born errors of amino acid metabolism, and are commonly used “sports”/exercise supplements. The effects of the BCAA on the in-vitro activity of calf intestinal alkaline phosphatase (EC. 3.1.3.1) were studied. All three BCAA were found to be uncompetitive inhibitors of the enzyme with L-leucine being the most potent (Ki’ = 24.9mM) and L-valine, the least potent (Ki’ = 37mM). Mixed BCAA are able to act in combination to inhibit the enzyme. Given the important role of intestinal alkaline phosphatase in gut homeostasis, these findings have potential implications for those taking high levels of BCAA as supplements

Combined inhibition of p97 and the proteasome causes lethal disruption of the secretory apparatus in multiple myeloma cells.

Inhibition of the proteasome is a widely used strategy for treating multiple myeloma that takes advantage of the heavy secretory load that multiple myeloma cells (MMCs) have to deal with. Resistance of MMCs to proteasome inhibition has been linked to incomplete disruption of proteasomal endoplasmic-reticulum (ER)-associated degradation (ERAD) and activation of non-proteasomal protein degradation pathways. The ATPase p97 (VCP/Cdc48) has key roles in mediating both ERAD and non-proteasomal protein degradation and can be targeted pharmacologically by small molecule inhibition. In this study, we compared the effects of p97 inhibition with Eeyarestatin 1 and DBeQ on the secretory apparatus of MMCs with the effects induced by the proteasome inhibitor bortezomib, and the effects caused by combined inhibition of p97 and the proteasome. We found that p97 inhibition elicits cellular responses that are different from those induced by proteasome inhibition, and that the responses differ considerably between MMC lines. Moreover, we found that dual inhibition of both p97 and the proteasome terminally disrupts ER configuration and intracellular protein metabolism in MMCs. Dual inhibition of p97 and the proteasome induced high levels of apoptosis in all of the MMC lines that we analysed, including bortezomib-adapted AMO-1 cells, and was also effective in killing primary MMCs. Only minor toxicity was observed in untransformed and non-secretory cells. Our observations highlight non-redundant roles of p97 and the proteasome in maintaining secretory homeostasis in MMCs and provide a preclinical conceptual framework for dual targeting of p97 and the proteasome as a potential new therapeutic strategy in multiple myeloma