933 research outputs found
Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad
The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions
Influence of contact angle on slow evaporation in two-dimensional porous media
We study numerically the influence of contact angle on slow evaporation in
two-dimensional model porous media. For sufficiently low contact angles, the
drying pattern is fractal and can be predicted by a simple model combining the
invasion percolation model with the computation of the diffusive transport in
the gas phase. The overall drying time is minimum in this regime and is
independent of contact angle over a large range of contact angles up to the
beginning of a transition zone. As the contact angle increases in the
transition region, the cooperative smoothing mechanisms of the interface become
important and the width of the liquid gas interface fingers that form during
the evaporation process increases. The mean overall drying time increases in
the transition region up to an upper bound which is reached at a critical
contact angle \Theta_c. The increase in the drying time in the transition
region is explained in relation with the diffusional screening phenomenon
associated with the Laplace equation governing the vapor transport in the gas
phase. Above \Theta_c the drying pattern is character- ized by a flat traveling
front and the mean overall drying time becomes independent of the contact
angle. Drying time fluctuations are studied and are found to be important below
\Theta_c, i.e., when the pattern is fractal. The fluctuations are of the same
order of magnitude regardless of the value of contact angle in this range. The
fluctuations are found to die out abruptly at \Theta_c as the liquid gas
interface becomes a flat front
A panel analysis of UK industrial company failure
We examine the failure determinants for large quoted UK industrials using a panel data set
comprising 539 firms observed over the period 1988-93. The empirical design employs data
from company accounts and is based on Chamberlainâs conditional binomial logit model,
which allows for unobservable, firm-specific, time-invariant factors associated with failure
risk. We find a noticeable degree of heterogeneity across the sample companies. Our panel
results show that, after controlling for unobservables, lower liquidity measured by the quick
assets ratio, slower turnover proxied by the ratio of debtors turnover, and profitability were
linked to the higher risk of insolvency in the analysis period. The findings appear to support
the proposition that the current cash-flow considerations, rather than the future prospects of
the firm, determined company failures over the 1990s recession
The influence of temperature in a capillary imbibition salt weathering simulation test on Mokattam limestone
Electrification of granular systems of identical insulators
Insulating particles can become highly electrified during powder handling,
volcanic eruptions, and the wind-blown transport of dust, sand, and snow.
Measurements in these granular systems have found that smaller particles
generally charge negatively, while larger particles charge positively. These
observations are puzzling, since particles in these systems are generally
chemically identical, and thus have no contact potential difference. We show
here that simple geometry leads to a net transfer of electrons from larger to
smaller particles, in agreement with these observations. We integrate this
charging mechanism into the first quantitative charging scheme for a granular
system of identical insulators, and show that its predictions are in agreement
with measurements. Our theory thus seems to provide an explanation for the
hitherto puzzling phenomenon of the size-dependent charging of granular systems
of identical insulators.Comment: 8 pages, 5 figures, published in Physical Review
Medical applicant general practice experience and career aspirations: a questionnaire study
Background: Increasing access to general practice work experience placements for school students
is a strategy for improving general practice recruitment, despite limited evidence and concerns
surrounding equity of access to general practice experiences.
Aims: To examine the association between undertaking general practice experience and the
perceptions of general practice as an appealing future career among prospective medical applicants.
To identify socioeconomic factors associated with obtaining general practice experience.
Design & setting: Cross-sectional questionnaire study in the UK.
Method: Participants were UK residents aged â„16 years and seriously considering applying to study
medicine in 2019/2020. They were invited to take part via the University Clinical Aptitude Test (UCAT).
Questionnaire data were analysed using a linear regression of general practice appeal on general
practice experience, adjusting for career motivations and demographics, and a logistic regression of
general practice experience on measures of social capital and demographics.
Results: Of 6391 responders, 4031 were in their last year of school. General practice experience
predicted general practice appeal after adjusting for career motivation and demographics (b = 0.37,
standard error [SE] = 0.06, P<0.00001). General practice experience was more common among
students at private (odds ratio [OR] = 1.65, 95% confidence interval [CI] = 1.31 to 2.08, P<0.0001) or
grammar schools (OR = 1.33, 95% CI = 1.02 to 1.72, P = 0.03) and in the highest socioeconomic group
(OR = 1.62, 95% CI = 1.28 to 2.05, P<0.0001), and less likely among students of âotherâ ethnicity (OR
= 0.37, 95% CI = 0.20 to 0.67, P = 0.0011).
Conclusion: Having general practice experience prior to medical school was associated with finding
general practice appealing, which supports its utility in recruitment. Applicants from more deprived
backgrounds were less likely to have had a general practice experience, possibly through lack of
accessible opportunities
Obesity challenges the hepatoprotective function of the integrated stress response to asparaginase exposure in mice
Obesity increases risk for liver toxicity by the anti-leukemic agent asparaginase, but the mechanism is unknown. Asparaginase activates the integrated stress response (ISR) via sensing amino acid depletion by the eukaryotic initiation factor 2 (eIF2) kinase GCN2. The goal of this work was to discern the impact of obesity, alone versus alongside genetic disruption of the ISR, on mechanisms of liver protection during chronic asparaginase exposure in mice. Following diet-induced obesity, biochemical analysis of livers revealed that asparaginase provoked hepatic steatosis that coincided with activation of another eIF2 kinase PKR-like endoplasmic reticulum kinase (PERK), a major ISR transducer to ER stress. Genetic loss of Gcn2 intensified hepatic PERK activation to asparaginase, yet surprisingly, mRNA levels of key ISR gene targets such as Atf5 and Trib3 failed to increase. Instead, mechanistic target of rapamycin complex 1 (mTORC1) signal transduction was unleashed, and this coincided with liver dysfunction reflected by a failure to maintain hydrogen sulfide production or apolipoprotein B100 (ApoB100) expression. In contrast, obese mice lacking hepatic activating transcription factor 4 (Atf4) showed an exaggerated ISR and greater loss of endogenous hydrogen sulfide but normal inhibition of mTORC1 and maintenance of ApoB100 during asparaginase exposure. In both genetic mouse models, expression and phosphorylation of Sestrin2, an ATF4 gene target, was increased by asparaginase, suggesting mTORC1 inhibition during asparaginase exposure is not driven via eIF2-ATF4-Sestrin2. In conclusion, obesity promotes a maladaptive ISR during asparaginase exposure. GCN2 functions to repress mTORC1 activity and maintain ApoB100 protein levels independently of Atf4 expression, whereas hydrogen sulfide production is promoted via GCN2-ATF4 pathway
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