38,236 research outputs found
Regions of the T cell receptor alpha and beta chains that are responsible for interactions with CD3.
The T cell antigen receptor consists of the Ti alpha/beta heterodimer which recognizes antigen, and the associated CD3 chains, thought to be involved in signal transduction. To understand the nature of the interaction between Ti and CD3, chimeric molecules which included the COOH-terminal segments of Ti alpha or beta linked to the extracellular segment of CD8, were transfected into a mutant T cell deficient in Ti beta chain expression and cell surface CD3. Both chimeric chains were required to express the chimeric Ti and to restore CD3 surface expression. CD8/Ti and CD3 cointernalized and coimmunoprecipitated. Stimulation of the chimeric receptor induced transmembrane signaling events and cell activation. These results demonstrate that the Ti alpha and beta COOH termini containing the transmembrane domains are sufficient for structural and functional coupling of Ti to CD3
Testing Higher-Order Lagrangian Perturbation Theory Against Numerical Simulations - 1. Pancake Models
We present results showing an improvement of the accuracy of perturbation
theory as applied to cosmological structure formation for a useful range of
quasilinear scales. The Lagrangian theory of gravitational instability of an
Einstein-de Sitter dust cosmogony investigated and solved up to the third order
in the series of papers by Buchert (1989, 1992, 1993a), Buchert \& Ehlers
(1993), Buchert (1993b), Ehlers \& Buchert (1993), is compared with numerical
simulations. In this paper we study the dynamics of pancake models as a first
step. In previous work (Coles \etal 1993, Melott \etal 1993, Melott 1993) the
accuracy of several analytical approximations for the modeling of large-scale
structure in the mildly non-linear regime was analyzed in the same way,
allowing for direct comparison of the accuracy of various approximations. In
particular, the ``Zel'dovich approximation'' (Zel'dovich 1970, 1973, hereafter
ZA) as a subclass of the first-order Lagrangian perturbation solutions was
found to provide an excellent approximation to the density field in the mildly
non-linear regime (i.e. up to a linear r.m.s. density contrast of ). The performance of ZA in hierarchical clustering models can be
greatly improved by truncating the initial power spectrum (smoothing the
initial data). We here explore whether this approximation can be further
improved with higher-order corrections in the displacement mapping from
homogeneity. We study a single pancake model (truncated power-spectrum with
power-index ) using cross-correlation statistics employed inComment: TeX, 18 pages excl.figures; contact [email protected] ;
[email protected] . submitted to Astron. & Astrophy
Detailed AGB evolutionary models and near infrared colours of intermediate-age stellar populations: Tests on star clusters
We investigate the influence of Asymptotic Giant Branch stars on integrated
colours of star clusters of ages between ~100 Myr and a few gigayears, and
composition typical for the Magellanic Clouds. We use state-of-the-art stellar
evolution models that cover the full thermal pulse phase, and take into account
the influence of dusty envelopes on the emerging spectra. We present an
alternative approach to the usual isochrone method, and compute integrated
fluxes and colours using a Monte Carlo technique that enables us to take into
account statistical fluctuations due to the typical small number of cluster
stars. We demonstrate how the statistical variations in the number of
Asymptotic Giant Branch stars and the temperature and luminosity variations
during thermal pulses fundamentally limit the accuracy of the comparison (and
calibration, for population synthesis models that require a calibration of the
Asymptotic Giant Branch contribution to the total luminosity) with star cluster
integrated photometries. When compared to observed integrated colours of
individual and stacked clusters in the Magellanic Clouds, our predictions match
well most of the observations, when statistical fluctuations are taken into
account, although there are discrepancies in narrow age ranges with some (but
not all) set of observations.Comment: 12 pages, 14 figures, accepted for publication in A&
The Role of Dust in Models of Population Synthesis
We have employed state-of-the-art evolutionary models of low and
intermediate-mass AGB stars, and included the effect of circumstellar dust
shells on the spectral energy distribution (SED) of AGB stars, to revise the
Padua library of isochrones (Bertelli et al. 1994). The major revision involves
the thermally pulsing AGB phase, that is now taken from fully evolutionary
calculations by Weiss & Ferguson (2009). Two libraries of about 600 AGB
dust-enshrouded SEDs each have also been calculated, one for oxygen-rich
M-stars and one for carbon-rich C-stars. Each library accounts for different
values of input parameters like the optical depth {\tau}, dust composition, and
temperature of the inner boundary of the dust shell. These libraries of dusty
AGB spectra have been implemented into a large composite library of theoretical
stellar spectra, to cover all regions of the Hertzsprung-Russell Diagram (HRD)
crossed by the isochrones. With the aid of the above isochrones and libraries
of stellar SEDs, we have calculated the spectro-photometric properties (SEDs,
magnitudes, and colours) of single-generation stellar populations (SSPs) for
six metallicities, more than fifty ages (from 3 Myr to 15 Gyr), and nine
choices of the Initial Mass Function. The new isochrones and SSPs have been
compared to the colour-magnitude diagrams (CMDs) of field populations in the
LMC and SMC, with particular emphasis on AGB stars, and the integrated colours
of star clusters in the same galaxies, using data from the SAGE (Surveying the
Agents of Galaxy Evolution) catalogues. We have also examined the integrated
colours of a small sample of star clusters located in the outskirts of M31. The
agreement between theory and observations is generally good. In particular, the
new SSPs reproduce the red tails of the AGB star distribution in the CMDs of
field stars in the Magellanic Clouds.Comment: Accepted for publication in MNRA
A parabolic free boundary problem with Bernoulli type condition on the free boundary
Consider the parabolic free boundary problem For a
realistic class of solutions, containing for example {\em all} limits of the
singular perturbation problem we prove that one-sided
flatness of the free boundary implies regularity.
In particular, we show that the topological free boundary
can be decomposed into an {\em open} regular set (relative to
) which is locally a surface with H\"older-continuous space
normal, and a closed singular set.
Our result extends the main theorem in the paper by H.W. Alt-L.A. Caffarelli
(1981) to more general solutions as well as the time-dependent case. Our proof
uses methods developed in H.W. Alt-L.A. Caffarelli (1981), however we replace
the core of that paper, which relies on non-positive mean curvature at singular
points, by an argument based on scaling discrepancies, which promises to be
applicable to more general free boundary or free discontinuity problems
Thermal equilibrium of two quantum Brownian particles
The influence of the environment in the thermal equilibrium properties of a
bipartite continuous variable quantum system is studied. The problem is treated
within a system-plus-reservoir approach. The considered model reproduces the
conventional Brownian motion when the two particles are far apart and induces
an effective interaction between them, depending on the choice of the spectral
function of the bath. The coupling between the system and the environment
guarantees the translational invariance of the system in the absence of an
external potential. The entanglement between the particles is measured by the
logarithmic negativity, which is shown to monotonically decrease with the
increase of the temperature. A range of finite temperatures is found in which
entanglement is still induced by the reservoir.Comment: 8 pages, 1 figur
Monitoring the Impact of Health Reform on Americans 50-64: Medicaid Expansion and Marketplace Implementation Increased Health Coverage
This survey shows that the share of 50- to 64-year-olds without health insurance fell between December 2013 and March 2014. In states that expanded their Medicaid programs, a greater share of previously uninsured adults gained coverage, particularly among groups that have traditionally faced barriers to obtaining it. The survey also found that the newly insured differed in key ways from those who reported being insured for all of the past 12 months. On average, more were low income, and more reported that they had had trouble paying medical bills. This paper is part of a series that looks at the experience of 50- to 64-year-olds during the first open enrollment period of the Affordable Care Act (ACA)
Laser Interferometer Gravitational-Wave Observatory beam tube component and module leak testing
Laser Interferometer Gravitational-Wave Observatory (LIGO) is a joint project of the California Institute of Technology and the Massachusetts Institute of Technology funded by the National Science Foundation. The project is designed to detect gravitational waves from astrophysical sources such as supernova and black holes. The LIGO project constructed observatories at two sites in the U.S. Each site includes two beam tubes (each 4 km long) joined to form an "L" shape. The beam tube is a 1.25 m diam 304 L stainless steel, ultrahigh vacuum tube that will operate at 1×10^–9 Torr or better. The beam tube was manufactured using a custom spiral weld tube mill from material processed to reduce the outgassing rate in order to minimize pumping costs. The integrity of the beam tube was assured by helium mass spectrometer leak testing each component of the beam tube system prior to installation. Each 2 km long, isolatable beam tube module was then leak tested after completion
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