34,793 research outputs found
Comparison between the Torquato-Rintoul theory of the interface effect in composite media and elementary results
We show that the interface effect on the properties of composite media
recently proposed by Torquato and Rintoul (TR) [Phys. Rev. Lett. 75, 4067
(1995)] is in fact elementary, and follows directly from taking the limit in
the dipolar polarizability of a coated sphere: the TR ``critical values'' are
simply those that make the dipolar polarizability vanish. Furthermore, the new
bounds developed by TR either coincide with the Clausius-Mossotti (CM) relation
or provide poor estimates. Finally, we show that the new bounds of TR do not
agree particularly well with the original experimental data that they quote.Comment: 13 pages, Revtex, 8 Postscript figure
3-hydroxykynurenine suppresses CD4+ T-cell proliferation, induces T-regulatory-cell development, and prolongs corneal allograft survival
Copyright © 2011 Association for Research in Vision and Ophthalmology. This article is available open access through the publisherâs website at the link below.Purpose. IDO (indoleamine 2,3-dioxygenase) modulates the immune response by depletion of the essential amino acid tryptophan, and IDO overexpression has been shown to prolong corneal allograft survival. This study was conducted to examine the effect of kynurenines, the products of tryptophan breakdown and known to act directly on T lymphocytes, on corneal graft survival.
Methods. The effects of kynurenines on T-cell proliferation and death, T-regulatory-cell development, and dendritic cell function, phenotype, and viability were analyzed in vitro. The effect of topical and systemic administration of 3-hydroxykynurenine (3HK) on orthotopic murine corneal allograft survival was examined.
Results. T-lymphocyte proliferation was inhibited by two of the four different kynurenines: 3HK and 3-hydroxyanthranilic acid (3HAA). This effect was accompanied by significant T-cell death. Neither 3HK nor 3HAA altered dendritic cell function, nor did they induce apoptosis or pathogenicity to corneal endothelial cells. Administration of systemic and topical 3HK to mice receiving a fully mismatched corneal graft resulted in significant prolongation of graft survival (median survival of control grafts, 12 days; of treated, 19 and 15 days, respectively; P < 0.0003). While systemic administration of 3HK was associated with a significant depletion of CD4+ T, CD8+ T, and B lymphocytes in peripheral blood, no depletion was found after topical administration.
Conclusions. The production of kynurenines, in particular 3HK and 3HAA, may be one mechanism (in addition to tryptophan depletion) by which IDO prolongs graft survival. These molecules have potential as specific agents for preventing allograft rejection in patients at high rejection risk.Fight for Sight and the Wellcome Trust
NMR Search for the Spin Nematic State in LaFeAsO Single Crystal
We report a 75-As single crystal NMR investigation of LaFeAsO, the parent
phase of a pnictide high Tc superconductor. We demonstrate that spin dynamics
develop a strong two-fold anisotropy within each orthorhombic domain below the
tetragonal-orthorhombic structural phase transition at T[TO]~156 K. This
intermediate state with a dynamical breaking of the rotational symmetry freezes
progressively into a spin density wave (SDW) below T[SDW]~142 K. Our findings
are consistent with the presence of a spin nematic state below T[TO] with an
incipient magnetic order.Comment: Revised manuscript accepted for publication in Phys. Rev. Let
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Dielectric spectroscopy study of thermally-aged extruded model power cables
âModelâ extruded power cables, having a much reduced geometry but using the same extrusion techniques and materials as full-sized cables, have been examined using dielectric spectroscopy techniques to study their thermal ageing effects. Cables insulated with homo-polymer XLPE and co-polymer of XLPE with micron-sized ethylene-butyl-acrylate (EBA) islands were studied by both frequency-domain and time-domain dielectric spectroscopy techniques after accelerated thermal ageing under 135°C for 60 days. In the frequency domain, a frequency response analyzer (FRA) was used to measure the frequency range from 10-4Hz to 1Hz at temperatures from 20°C to 80°C. In the time domain, a special charging/discharging current measurement system was developed to measure the frequencies from 10-1Hz to 102Hz. These techniques were chosen to cope with the extremely low dielectric losses of the model cables. The results are compared with those from new model power cables that were degassed at 80°C for 5 days. Thermal ageing was found to increase the low-frequency conductivity, permittivity and the discharging current. Both homo- and co-polymer cables have substantial increase of dielectric loss after ageing
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Optical fiber sensors for coal mine shaft integrity and equipment condition monitoring
Shaft is an important structure of mine. Deep mining increases mine pressure, induces shaft deformation and affects mine normal lifting. How to improve the inspection efficiency, reduce the maintenance cost and ensure the normal operation of the shaft is an important problem facing the mine. The paper introduces the optical fiber sensing technology to monitor the equipment status of the main shaft, puts forward the implementation scheme of the optical fiber monitoring of shaft deformation, and sets up a shaft equipment condition monitoring system based on the optical fiber sensing technology. It can realize equipment displacement monitoring, strain monitoring and vibration signal monitoring in the process of shaft operation. Comprehensive on-line monitoring of shaft running state can be realized, which opens up a new method for shaft deformation monitoring technology. Fiber optic sensing monitoring technology is of great significance to the safe operation of shaft
Design and Fabrication of Three-Dimensional Scaffolds for Tissue Engineering of Human Heart Valves
We developed a new fabrication technique for 3-dimensional scaffolds for tissue engineering of human heart valve tissue. A human aortic homograft was scanned with an X-ray computer tomograph. The data derived from the X-ray computed tomogram were processed by a computer-aided design program to reconstruct a human heart valve 3-dimensionally. Based on this stereolithographic model, a silicone valve model resembling a human aortic valve was generated. By taking advantage of the thermoplastic properties of polyglycolic acid as scaffold material, we molded a 3-dimensional scaffold for tissue engineering of human heart valves. The valve scaffold showed a deviation of only +/- 3-4% in height, length and inner diameter compared with the homograft. The newly developed technique allows fabricating custom-made, patient-specific polymeric cardiovascular scaffolds for tissue engineering without requiring any suture materials. Copyright (c) 2008 S. Karger AG, Base
Pion Polarizabilities and Volume Effects in Lattice QCD
We use chiral perturbation theory to study the extraction of pion
electromagnetic polarizabilities from lattice QCD. Chiral extrapolation
formulae are derived for partially quenched QCD, and quenched QCD simulations.
On a torus, volume dependence of electromagnetic observables is complicated by
SO(4) breaking, as well as photon zero-mode interactions. We determine finite
volume corrections to the Compton scattering tensor of pions. We argue,
however, that such results cannot be used to ascertain volume corrections to
polarizabilities determined in lattice QCD with background field methods.
Connection is lacking because momentum expansions are not permitted in finite
volume. Our argument also applies to form factors. Volume effects for
electromagnetic moments cannot be deduced from finite volume form factors.Comment: 5 figs., 19p
Transverse momentum dependence in the perturbative calculation of pion form factor
By reanalysing transverse momentum dependence in the perturbative calculation
of pion form factor an improved expression of pion form factor which takes into
account the transverse momentum dependenc in hard scattering amplitude and
intrinsic transverse momentum dependence associated with pion wave functions is
given to leading order, which is available for momentum transfers of the order
of a few GeV as well as for . Our scheme can be extended to
evaluate the contributions to the pion form factor beyond leading order.Comment: 13 pages in LaTeX, plus 3 Postscript figure
Finding the Origin of the Pioneer Anomaly
Analysis of radio-metric tracking data from the Pioneer 10/11 spacecraft at
distances between 20 - 70 astronomical units (AU) from the Sun has consistently
indicated the presence of an anomalous, small, constant Doppler frequency
drift. The drift can be interpreted as being due to a constant acceleration of
a_P= (8.74 \pm 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is
suspected that there is a systematic origin to the effect, none has been found.
As a result, the nature of this anomaly has become of growing interest. Here we
present a concept for a deep-space experiment that will reveal the origin of
the discovered anomaly and also will characterize its properties to an accuracy
of at least two orders of magnitude below the anomaly's size. The proposed
mission will not only provide a significant accuracy improvement in the search
for small anomalous accelerations, it will also determine if the anomaly is due
to some internal systematic or has an external origin. A number of critical
requirements and design considerations for the mission are outlined and
addressed. If only already existing technologies were used, the mission could
be flown as early as 2010.Comment: 21 SS pages, 4+1 figures. final changes for publicatio
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