323 research outputs found
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
No association between human herpesvirus 6 reactivation and cryptococcosis in human immunodeficiency virus-infected patients
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
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