3,312 research outputs found
Abundant Refractory Sulfur in Protoplanetary Disks
Sulfur is one of the most abundant elements in the Universe, with important
roles in astro-, geo-, and biochemistry. Its main reservoirs in planet-forming
disks have previously eluded detection: gaseous molecules only account for
\% of total elemental sulfur, with the rest likely in either ices or
refractory minerals. Mechanisms such as giant planets can filter out dust from
gas accreting onto disk-hosting stars. For stars above 1.4 solar masses, this
leaves a chemical signature on the stellar photosphere that can be used to
determine the fraction of each element that is locked in dust. Here, we present
an application of this method to sulfur, zinc, and sodium. We analyse the
accretion-contaminated photospheres of a sample of young stars and find
\% of elemental sulfur is in refractory form in their disks. The
main carrier is much more refractory than water ice, consistent with sulfide
minerals such as FeS
Energy- and flux-budget (EFB) turbulence closure model for the stably stratified flows. Part I: Steady-state, homogeneous regimes
We propose a new turbulence closure model based on the budget equations for
the key second moments: turbulent kinetic and potential energies: TKE and TPE
(comprising the turbulent total energy: TTE = TKE + TPE) and vertical turbulent
fluxes of momentum and buoyancy (proportional to potential temperature).
Besides the concept of TTE, we take into account the non-gradient correction to
the traditional buoyancy flux formulation. The proposed model grants the
existence of turbulence at any gradient Richardson number, Ri. Instead of its
critical value separating - as usually assumed - the turbulent and the laminar
regimes, it reveals a transition interval, 0.1< Ri <1, which separates two
regimes of essentially different nature but both turbulent: strong turbulence
at Ri<<1; and weak turbulence, capable of transporting momentum but much less
efficient in transporting heat, at Ri>1. Predictions from this model are
consistent with available data from atmospheric and lab experiments, direct
numerical simulation (DNS) and large-eddy simulation (LES).Comment: 40 pages, 6 figures, Boundary-layer Meteorology, resubmitted, revised
versio
Supersymmetric Deformations of Maximally Supersymmetric Gauge Theories
We study supersymmetric and super Poincar\'e invariant deformations of
ten-dimensional super Yang-Mills theory and of its dimensional reductions. We
describe all infinitesimal super Poincar\'e invariant deformations of equations
of motion of ten-dimensional super Yang-Mills theory and its reduction to a
point; we discuss the extension of them to formal deformations. Our methods are
based on homological algebra, in particular, on the theory of L-infinity and
A-infinity algebras. The exposition of this theory as well as of some basic
facts about Lie algebra homology and Hochschild homology is given in
appendices.Comment: New results added. 111 page
MTN-001: Randomized Pharmacokinetic Cross-Over Study Comparing Tenofovir Vaginal Gel and Oral Tablets in Vaginal Tissue and Other Compartments
Background: Oral and vaginal preparations of tenofovir as pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) infection have demonstrated variable efficacy in men and women prompting assessment of variation in drug concentration as an explanation. Knowledge of tenofovir concentration and its active form, tenofovir diphosphate, at the putative vaginal and rectal site of action and its relationship to concentrations at multiple other anatomic locations may provide key information for both interpreting PrEP study outcomes and planning future PrEP drug development. Objective: MTN-001 was designed to directly compare oral to vaginal steady-state tenofovir pharmacokinetics in blood, vaginal tissue, and vaginal and rectal fluid in a paired cross-over design. Methods and Findings: We enrolled 144 HIV-uninfected women at 4 US and 3 African clinical research sites in an open label, 3-period crossover study of three different daily tenofovir regimens, each for 6 weeks (oral 300 mg tenofovir disoproxil fumarate, vaginal 1% tenofovir gel [40 mg], or both). Serum concentrations after vaginal dosing were 56-fold lower than after oral dosing (p<0.001). Vaginal tissue tenofovir diphosphate was quantifiable in ≥90% of women with vaginal dosing and only 19% of women with oral dosing. Vaginal tissue tenofovir diphosphate was ≥130-fold higher with vaginal compared to oral dosing (p<0.001). Rectal fluid tenofovir concentrations in vaginal dosing periods were higher than concentrations measured in the oral only dosing period (p<0.03). Conclusions: Compared to oral dosing, vaginal dosing achieved much lower serum concentrations and much higher vaginal tissue concentrations. Even allowing for 100-fold concentration differences due to poor adherence or less frequent prescribed dosing, vaginal dosing of tenofovir should provide higher active site concentrations and theoretically greater PrEP efficacy than oral dosing; randomized topical dosing PrEP trials to the contrary indicates that factors beyond tenofovir's antiviral effect substantially influence PrEP efficacy. Trial Registration: ClinicalTrials.gov NCT00592124
Length of stay in asylum centres and mental health in asylum seekers: a retrospective study from Denmark
<p>Abstract</p> <p>Background</p> <p>The length of stay in asylum centres is generally mentioned as a possible health risk to asylum seekers. Medical staff working with asylum seekers has claimed that long lengths of stay in asylum centres might cause or aggravate mental disorders. We used records from a large, multiethnic group of asylum seekers to study if the incidence of mental disorders increased with length of stay.</p> <p>Methods</p> <p>The study population was asylum seekers in Danish asylum centres run by the Danish Red Cross. General medical care was provided by Red Cross staff who could refer selected cases to medical specialists. If an asylum seeker needed more than three specialist consultations for mental illness or five consultations for physical illness the referrals had to be approved by The Danish Immigration Service. Between July 2001 – December 2002 the Red Cross prospectively registered health related data on all new applications (n = 4516) to the Immigration Service regarding referrals to medical specialists. We used these records to analyse the association between length of stay in the asylum centres and overall rate of referral for mental disorders. Data was analysed using weighted linear regression.</p> <p>Results</p> <p>We found that referrals for mental disorders increased with length of stay in asylum centres in a large, multiethnic population of asylum seekers. The association was found in all the categories of psychiatric illness studied and for a majority of the nationality groups studied.</p> <p>Conclusion</p> <p>Length of stay in asylum centres was associated with an increase in referrals for mental disorders in a large, multiethnic group of asylum seekers. The present study supports the view that prolonged length of stay in an asylum centre is a risk factor for mental health. The risk of psychiatric illness among asylum seekers should be addressed by political and humanitarian means, giving prevention of illness the highest priority.</p
Growth dynamics and the evolution of cooperation in microbial populations
Microbes providing public goods are widespread in nature despite running the
risk of being exploited by free-riders. However, the precise ecological factors
supporting cooperation are still puzzling. Following recent experiments, we
consider the role of population growth and the repetitive fragmentation of
populations into new colonies mimicking simple microbial life-cycles.
Individual-based modeling reveals that demographic fluctuations, which lead to
a large variance in the composition of colonies, promote cooperation. Biased by
population dynamics these fluctuations result in two qualitatively distinct
regimes of robust cooperation under repetitive fragmentation into groups.
First, if the level of cooperation exceeds a threshold, cooperators will take
over the whole population. Second, cooperators can also emerge from a single
mutant leading to a robust coexistence between cooperators and free-riders. We
find frequency and size of population bottlenecks, and growth dynamics to be
the major ecological factors determining the regimes and thereby the
evolutionary pathway towards cooperation.Comment: 26 pages, 6 figure
Association of kidney function with inflammatory and procoagulant markers in a diverse cohort: A cross-sectional analysis from the Multi-Ethnic Study of Atherosclerosis (MESA)
Background: Prior studies using creatinine-based estimated glomerular filtration rate (eGFR) have found limited associations between kidney function and markers of inflammation. Using eGFR and cystatin C, a novel marker of kidney function, the authors investigated the association of kidney function with multiple biomarkers in a diverse cohort.
Methods: The Multi-Ethnic Study of Atherosclerosis consists of 6,814 participants of white, African-American, Hispanic, and Chinese descent, enrolled from 2000-2002 from six U.S.
communities. Measurements at the enrollment visit included serum creatinine, cystatin C, and six
inflammatory and procoagulant biomarkers. Creatinine-based eGFR was estimated using the fourvariable
Modification of Diet in Renal Disease equation, and chronic kidney disease was defined by an eGFR less than 60 mL/min/1.73 m2.
Results: Adjusted partial correlations between cystatin C and all biomarkers were statistically significant: C-reactive protein (r = 0.08), interleukin-6 (r = 0.16), tumor necrosis factor-a soluble
receptor 1 (TNF-aR1; r = 0.75), intercellular adhesion molecule-1 (r = 0.21), fibrinogen (r = 0.14), and factor VIII (r = 0.11; two-sided p less than 0.01 for all). In participants without chronic kidney disease,
higher creatinine-based eGFR was associated only with higher TNF-aR1 levels.
Conclusion: In a cohort characterized by ethnic diversity, cystatin C was directly associated with multiple procoagulant and inflammatory markers. Creatinine-based eGFR had similar associations with these biomarkers among subjects with chronic kidney disease.This research was supported by contracts N01-HC-95159 through N01-HC-95169 from the National Heart, Lung, and Blood Institute (NHLBI)
The Quantum Internet
Quantum networks offer a unifying set of opportunities and challenges across
exciting intellectual and technical frontiers, including for quantum
computation, communication, and metrology. The realization of quantum networks
composed of many nodes and channels requires new scientific capabilities for
the generation and characterization of quantum coherence and entanglement.
Fundamental to this endeavor are quantum interconnects that convert quantum
states from one physical system to those of another in a reversible fashion.
Such quantum connectivity for networks can be achieved by optical interactions
of single photons and atoms, thereby enabling entanglement distribution and
quantum teleportation between nodes.Comment: 15 pages, 6 figures Higher resolution versions of the figures can be
downloaded from the following link:
http://www.its.caltech.edu/~hjkimble/QNet-figures-high-resolutio
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