909 research outputs found
Trajectory of test particle around a slowly rotating relativistic star emitting isotropic radiation
We explored the motion of test particles near slowly rotating relativistic
star having a uniform luminosity. In order to derive the test particle's
equations of motion, we made use of the radiation stress-energy tensor first
constructed by Miller and Lamb \cite{ML96}. From the particle's trajectory
obtained through the numerical integration of the equations of motion, it is
found that for sufficiently high luminosity, "suspension orbit" exists, where
the test particle hovers around at uniform angular velocity in the same
direction as the star's spin. Interestingly, it turned out that the radial
position of the "suspension orbit" was determined by the luminosity and the
angular momentum of the star alone and was independent of the initial positions
and the specific angular momentum of the particle. Also found is that there
exist not only the radiation drag but also "radiation counter-drag" which
depends on the stellar radius and the angular momentum and it is this radiation
counter-drag that makes the test particle in the "suspension orbit" to hover
around at uniform angular velocity which is greater than that induced by the
Lense-Thirring effect (i.e., general relativistic dragging of inertial frame).Comment: 23 pages, 7 figures, to appear in Phys. Rev. D
Thermal depinning of a single superconducting vortex
Thermal depinning has been studied for a single vortex trapped in a superconducting thin film in order to determine the value of the superconducting order parameter and the superfluid density when the vortex depins and starts to move around the film. For the Pb film in Pb/Al/Al{sub 2}O{sub 3}/PbBi junction having a gold line, the vortex depins from the artificial pinning site (Au line) and reproducibly moves through the same sequence of other pinning sites before it leaves the junction area of the Pb film. Values of the normalized order parameter {triangle}/{triangle}{sub o} vary from {triangle}/{triangle}{sub o}=0.20 at the first motion of the vortex to {triangle}/{triangle}{sub o}=0.16 where the vortex finally leaves the junction. Equivalently, the value of the normalized superfluid density changes from 4% to 2.5% for this sample in this same temperature interval. For the Nb film in Nb/Al/Al{sub 2}O{sub 3}/Nb junction, thermal depinning occurs when the value of {triangle}/{triangle}{sub o} is approximately 0.22 and the value of {rho}{sub s}/{rho}{sub so} is approximately 5%. These values are about 20% larger than those of a Pb sample having a gold line, but the values are really very close. For the Nb sample, grain boundaries are important pinning sites whereas, for the Pb sample with a gold line, pinning may have been dominated by an array Pb{sub 3}AU precipitates. Because roughly the same answer was obtained for these rather different kinds of pinning site, there is a reasonable chance that this is a general value within factors of 2 for a wide range of materials
Quantisation of Conformal Fields in Three-dimensional Anti-de Sitter Black Hole Spacetime
Utilizing the conformal-flatness nature of 3-dim. Anti-de Sitter (AdS_3)
black hole solution of Banados, Teitelboim and Zanelli, the quantisation of
conformally-coupled scalar and spinor fields in this background spacetime is
explicitly carried out. In particular, mode expansion forms and propagators of
the fields are obtained in closed forms. The vacuum in this conformally-coupled
field theories in AdS_3 black hole spacetime, which is conformally-flat, is the
conformal vacuum which is unique and has global meaning. This point
particularly suggests that now the particle production by AdS_3 black hole
spacetime should be absent. General argument establishing the absence of real
particle creation by AdS_3 black hole spacetime for this case of conformal
triviality is provided. Then next, using the explicit mode expansion forms for
conformally-coupled scalar and spinor fields, the bosonic and fermionic
superradiances are examined and found to be absent confirming the expectation.Comment: 51 pages, Revtex, version to appear in Int. J. Mod. Phys.
Precision medicine approaches for diabetic kidney disease:opportunities and challenges
The prevalence of end-stage kidney disease (ESKD) continuously increases worldwide. The increasing prevalence parallels the growth in the number of people with diabetes, which is the leading cause of ESKD. Early diagnosis of chronic kidney disease (CKD) in patients with diabetes and appropriate intervention is important to delay the progression of kidney function decline and prevent ESKD. Rate of CKD progression and response to treatment varies among patients with diabetes, highlighting the need to tailor individual treatment. In this review, we describe recent advances and areas for future studies with respect to precision medicine in diabetic kidney disease (DKD). DKD is a multi-factorial disease that is subject in part to genetic heritability, but is also influenced by various exogenous mediators, such as environmental or dietary factors. Genetic testing so far has limited utility to facilitate early diagnosis, classify progression or evaluate response to therapy. Various biomarker-based approaches are currently explored to identify patients at high risk of ESKD and to facilitate decision-making for targeted therapy. These studies have led to discovery and validation of a couple of inflammatory proteins such as circulating tumour necrosis factor receptors, which are strong predictors of kidney disease progression. Moreover, risk and drug-response scores based on multiple biomarkers are developed to predict kidney disease progression and long-term drug efficacy. These findings, if implemented in clinical practice, will pave the way to move from a one-size-fits-all to a one-fit-for-everyone approach
Acceptability of Active Case Finding with a Seed-and-Recruit Model to Improve Tuberculosis Case Detection and Linkage to Treatment in Cambodia: A Qualitative Study
Background
With support of the national tuberculosis (TB) program, KHANA (a local non-governmental organization in Cambodia) has implemented an innovative approach using a seed-and-recruit model to actively find TB cases in the community. The model engaged community members including TB survivors as seed and newly diagnosed people with TB as recruiters to recruit presumptive TB cases in their social network in a snowball approach for screening and linkage to treatment. This study aimed to explore the acceptability of the active case finding with the seed-and-recruit model in detecting new TB cases and determine the characteristics of successful seeds.
Methods
This qualitative study was conducted in four provinces (Banteay Meanchey, Kampong Chhnang, Siem Reap, and Takeo) in Cambodia in 2017. Fifty-six in-depth interviews and ten focus group discussions (with a total of 64 participants) were conducted with selected beneficiaries and key stakeholders at different levels to gain insights into the acceptability, strengths, and challenges in implementing the model and the characteristics of successful seeds. Transcripts were coded and content analyses were performed.
Results
The seed-and-recruit active case finding model was generally well-received by the study participants. They saw the benefits of engaging TB survivors and utilizing their social network to find new TB cases in the community. The social embeddedness of the model within the local community was one of the major strengths. The success of the model also hinges on the integration with existing health facilities. Having an extensive social network, being motivated, and having good knowledge about TB were important characteristics of successful seeds. Study participants reported challenges in motivating the presumptive TB cases for screening, logistic capacities, and high workload during the implementation. However, there was a general consensus that the model ought to be expanded.
Conclusions
These findings indicate that the seed-and-recruit model is well-accepted by the beneficiaries and key stakeholders. Further studies are needed to more comprehensively evaluate the impacts and cost-effectiveness of the model for future expansion in Cambodia as well as in other resource-limited settings
Spin relaxation in mesoscopic superconducting Al wires
We studied the diffusion and the relaxation of the polarized quasiparticle
spins in superconductors. To that end, quasiparticles of polarized spins were
injected through an interface of a mesoscopic superconducting Al wire in
proximity contact with an overlaid ferromagnetic Co wire in the single-domain
state. The superconductivity was observed to be suppressed near the
spin-injecting interface, as evidenced by the occurrence of a finite voltage
for a bias current below the onset of the superconducting transition. The spin
diffusion length, estimated from finite voltages over a certain length of Al
wire near the interface, was almost temperature independent in the temperature
range sufficiently below the superconducting transition but grew as the
transition temperature was approached. This temperature dependence suggests
that the relaxation of the spin polarization in the superconducting state is
governed by the condensation of quasiparticles to the paired state. The spin
relaxation in the superconducting state turned out to be more effective than in
the normal state.Comment: 9 pages, 8 figure
Molecular dynamics simulation of the transport of small molecules across a polymer membrane
The transport of small molecules through a polymer membrane is modeled using the computer simulation technique of molecular dynamics (MD). The transport coefficient is derived from a combination of the excess free energy and the diffusion constant. Both properties are derived from MD simulations, applied to helium and methane in polydimethylsiloxane (PDMS). The diffusional process appears to have the character of a jump diffusion for methane and less so for helium. Jumps are allowed by fluctuations of the size and shape of holes. Experimental diffusion constants are well reproduced. The excess free energies, determined by a particle insertion method, are lower by 5-7 kJ/mol than experimental values. It is shown that, as a result of a higher solubility, methane has a higher permeability constant than helium, despite its lower diffusion constant
Order-alpha_s corrections to the quarkonium electromagnetic current at all orders in the heavy-quark velocity
We compute in order alpha_s the nonrelativistic QCD (NRQCD) short-distance
coefficients that match quark-antiquark operators of all orders in the
heavy-quark velocity v to the electromagnetic current. We employ a new method
to compute the one-loop NRQCD contribution to the matching condition. The new
method uses full-QCD expressions as a starting point to obtain the NRQCD
contribution, thus greatly streamlining the calculation. Our results show that,
under a mild constraint on the NRQCD operator matrix elements, the NRQCD
velocity expansion for the quark-antiquark-operator contributions to the
electromagnetic current converges. The velocity expansion converges rapidly for
approximate J/psi operator matrix elements.Comment: 35 pages, minor corrections, version published in Phys. Rev.
Mass Spectrometric Sampling of a Liquid Surface by Nanoliter Droplet Generation from Bursting Bubbles and Focused Acoustic Pulses: Application to Studies of Interfacial Chemistry
The complex chemistry occurring at the interface between liquid and vapor phases contributes significantly to the dynamics and evolution of numerous chemical systems of interest, ranging from damage to the human lung surfactant layer to the aging of atmospheric aerosols. This work presents two methodologies to eject droplets from a liquid water surface and analyze them via mass spectrometry. In bursting bubble ionization (BBI), droplet ejection is achieved via the formation of a jet following bubble rupture at the surface of a liquid to yield 250 μm diameter droplets (10 nL volume). In interfacial sampling by an acoustic transducer (ISAT), droplets are produced by focusing pulsed piezoelectric transducer-generated acoustic waves at the surface of a liquid, resulting in the ejection of droplets of 100 μm in diameter (500 pL volume). In both experimental methodologies, ejected droplets are aspirated into the inlet of the mass spectrometer, resulting in the facile formation of gas-phase ions. We demonstrate the ability of this technique to readily generate spectra of surface-active analytes, and we compare the spectra to those obtained by electrospray ionization. Charge measurements indicate that the ejected droplets are near-neutral (<0.1% of the Rayleigh limit), suggesting that gas-phase ion generation occurs in the heated transfer capillary of the instrument in a mechanism similar to thermospray or sonic spray ionization. Finally, we present the oxidation of oleic acid by ozone as an initial demonstration of the ability of ISAT-MS to monitor heterogeneous chemistry occurring at a planar water/air interface
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