572 research outputs found
Distinct claudin expression profiles of hepatocellular carcinoma and metastatic colorectal and pancreatic carcinomas
MMT Extremely Metal Poor Galaxy Survey I. An Efficient Technique to Identify Metal Poor Galaxies
We demonstrate a successful strategy for identifying extremely metal poor
galaxies. Our preliminary survey of 24 candidates contains 10 metal poor
galaxies of which 4 have 12+log(O/H)<7.65, some of the lowest metallicity blue
compact galaxies known to date. Interestingly, our sample of metal poor
galaxies have systematically lower metallicity for their luminosity than
comparable samples of blue compact galaxies, dIrrs, and normal star-forming
galaxies. Our metal poor galaxies share very similar properties, however, with
the host galaxies of nearby long-duration gamma-ray bursts (GRBs), including
similar metallicity, stellar ages, and star formation rates. We use H\beta to
measure the number of OB stars present in our galaxies and estimate a
core-collapse supernova rate of ~10^-3 yr^-1. A larger sample of metal poor
galaxies may provide new clues into the environment where GRBs form and may
provide a list of potential GRB hosts.Comment: Accepted to AJ, 8 pages using emulateap
Full orbital calculation scheme for materials with strongly correlated electrons
We propose a computational scheme for the ab initio calculation of Wannier
functions (WFs) for correlated electronic materials. The full-orbital
Hamiltonian H is projected into the WF subspace defined by the physically most
relevant partially filled bands. The Hamiltonian H^{WF} obtained in this way,
with interaction parameters calculated by constrained LDA for the Wannier
orbitals, is used as an ab initio setup of the correlation problem, which can
then be solved by many-body techniques, e.g., dynamical mean-field theory
(DMFT). In such calculations the self-energy operator \Sigma(e) is defined in
WF basis which then can be converted back into the full-orbital Hilbert space
to compute the full-orbital interacting Green function G(r,r',e). Using
G(r,r',e) one can evaluate the charge density, modified by correlations,
together with a new set of WFs, thus defining a fully self-consistent scheme.
The Green function can also be used for the calculation of spectral, magnetic
and electronic properties of the system. Here we report the results obtained
with this method for SrVO3 and V2O3. Comparisons are made with previous results
obtained by the LDA+DMFT approach where the LDA DOS was used as input, and with
new bulk-sensitive experimental spectra.Comment: 36 pages, 14 figure
Aharonov-Anandan Effect Induced by Spin-Orbit Interaction and Charge-Density-Waves in Mesoscopic Rings
We study the spin-dependent geometric phase effect in mesoscopic rings of
charge-density-wave(CDW) materials. When electron spin is explicitly taken into
account, we show that the spin-dependent Aharonov-Casher phase can have a
pronounced frustration effects on such CDW materials with appropriate electron
filling. We show that this frustration has observable consequences for
transport experiment. We identify a phase transition from a Peierls insulator
to metal, which is induced by spin-dependent phase interference effects.
Mesoscopic CDW materials and spin-dependent geometric phase effects, and their
interplay, are becoming attractive opportunities for exploitation with the
rapid development of modern fabrication technology.Comment: 5 pages, 6 figures, to appear in Phys.Rev.B(Aug.15, 1998
Charge Transport in Manganites: Hopping Conduction, the Anomalous Hall Effect and Universal Scaling
The low-temperature Hall resistivity \rho_{xy} of La_{2/3}A_{1/3}MnO_3 single
crystals (where A stands for Ca, Pb and Ca, or Sr) can be separated into
Ordinary and Anomalous contributions, giving rise to Ordinary and Anomalous
Hall effects, respectively. However, no such decomposition is possible near the
Curie temperature which, in these systems, is close to metal-to-insulator
transition. Rather, for all of these compounds and to a good approximation, the
\rho_{xy} data at various temperatures and magnetic fields collapse (up to an
overall scale), on to a single function of the reduced magnetization
m=M/M_{sat}, the extremum of this function lying at m~0.4. A new mechanism for
the Anomalous Hall Effect in the inelastic hopping regime, which reproduces
these scaling curves, is identified. This mechanism, which is an extension of
Holstein's model for the Ordinary Hall effect in the hopping regime, arises
from the combined effects of the double-exchange-induced quantal phase in
triads of Mn ions and spin-orbit interactions. We identify processes that lead
to the Anomalous Hall Effect for localized carriers and, along the way, analyze
issues of quantum interference in the presence of phonon-assisted hopping. Our
results suggest that, near the ferromagnet-to-paramagnet transition, it is
appropriate to describe transport in manganites in terms of carrier hopping
between states that are localized due to combined effect of magnetic and
non-magnetic disorder. We attribute the qualitative variations in resistivity
characteristics across manganite compounds to the differing strengths of their
carrier self-trapping, and conclude that both disorder-induced localization and
self-trapping effects are important for transport.Comment: 29 pages, 20 figure
Can One Trust Quantum Simulators?
Various fundamental phenomena of strongly-correlated quantum systems such as
high- superconductivity, the fractional quantum-Hall effect, and quark
confinement are still awaiting a universally accepted explanation. The main
obstacle is the computational complexity of solving even the most simplified
theoretical models that are designed to capture the relevant quantum
correlations of the many-body system of interest. In his seminal 1982 paper
[Int. J. Theor. Phys. 21, 467], Richard Feynman suggested that such models
might be solved by "simulation" with a new type of computer whose constituent
parts are effectively governed by a desired quantum many-body dynamics.
Measurements on this engineered machine, now known as a "quantum simulator,"
would reveal some unknown or difficult to compute properties of a model of
interest. We argue that a useful quantum simulator must satisfy four
conditions: relevance, controllability, reliability, and efficiency. We review
the current state of the art of digital and analog quantum simulators. Whereas
so far the majority of the focus, both theoretically and experimentally, has
been on controllability of relevant models, we emphasize here the need for a
careful analysis of reliability and efficiency in the presence of
imperfections. We discuss how disorder and noise can impact these conditions,
and illustrate our concerns with novel numerical simulations of a paradigmatic
example: a disordered quantum spin chain governed by the Ising model in a
transverse magnetic field. We find that disorder can decrease the reliability
of an analog quantum simulator of this model, although large errors in local
observables are introduced only for strong levels of disorder. We conclude that
the answer to the question "Can we trust quantum simulators?" is... to some
extent.Comment: 20 pages. Minor changes with respect to version 2 (some additional
explanations, added references...
Gene Targeting Implicates Cdc42 GTPase in GPVI and Non-GPVI Mediated Platelet Filopodia Formation, Secretion and Aggregation
Background: Cdc42 and Rac1, members of the Rho family of small GTPases, play critical roles in actin cytoskeleton regulation. We have shown previously that Rac1 is involved in regulation of platelet secretion and aggregation. However, the role of Cdc42 in platelet activation remains controversial. This study was undertaken to better understand the role of Cdc42 in platelet activation. Methodology/Principal Findings: We utilized the Mx-cre;Cdc42 lox/lox inducible mice with transient Cdc42 deletion to investigate the involvement of Cdc42 in platelet function. The Cdc42-deficient mice exhibited a significantly reduced platelet count than the matching Cdc42 +/+ mice. Platelets isolated from Cdc42 2/2, as compared to Cdc42 +/+, mice exhibited (a) diminished phosphorylation of PAK1/2, an effector molecule of Cdc42, (b) inhibition of filopodia formation on immobilized CRP or fibrinogen, (c) inhibition of CRP- or thrombin-induced secretion of ATP and release of P-selectin, (d) inhibition of CRP, collagen or thrombin induced platelet aggregation, and (e) minimal phosphorylation of Akt upon stimulation with CRP or thrombin. The bleeding times were significantly prolonged in Cdc42 2/2 mice compared with Cdc42 +/+ mice. Conclusion/Significance: Our data demonstrate that Cdc42 is required for platelet filopodia formation, secretion an
Large Scale Structure of the Universe
Galaxies are not uniformly distributed in space. On large scales the Universe
displays coherent structure, with galaxies residing in groups and clusters on
scales of ~1-3 Mpc/h, which lie at the intersections of long filaments of
galaxies that are >10 Mpc/h in length. Vast regions of relatively empty space,
known as voids, contain very few galaxies and span the volume in between these
structures. This observed large scale structure depends both on cosmological
parameters and on the formation and evolution of galaxies. Using the two-point
correlation function, one can trace the dependence of large scale structure on
galaxy properties such as luminosity, color, stellar mass, and track its
evolution with redshift. Comparison of the observed galaxy clustering
signatures with dark matter simulations allows one to model and understand the
clustering of galaxies and their formation and evolution within their parent
dark matter halos. Clustering measurements can determine the parent dark matter
halo mass of a given galaxy population, connect observed galaxy populations at
different epochs, and constrain cosmological parameters and galaxy evolution
models. This chapter describes the methods used to measure the two-point
correlation function in both redshift and real space, presents the current
results of how the clustering amplitude depends on various galaxy properties,
and discusses quantitative measurements of the structures of voids and
filaments. The interpretation of these results with current theoretical models
is also presented.Comment: Invited contribution to be published in Vol. 8 of book "Planets,
Stars, and Stellar Systems", Springer, series editor T. D. Oswalt, volume
editor W. C. Keel, v2 includes additional references, updated to match
published versio
Mass Transfer by Stellar Wind
I review the process of mass transfer in a binary system through a stellar
wind, with an emphasis on systems containing a red giant. I show how wind
accretion in a binary system is different from the usually assumed Bondi-Hoyle
approximation, first as far as the flow's structure is concerned, but most
importantly, also for the mass accretion and specific angular momentum loss.
This has important implications on the evolution of the orbital parameters. I
also discuss the impact of wind accretion, on the chemical pollution and change
in spin of the accreting star. The last section deals with observations and
covers systems that most likely went through wind mass transfer: barium and
related stars, symbiotic stars and central stars of planetary nebulae (CSPN).
The most recent observations of cool CSPN progenitors of barium stars, as well
as of carbon-rich post-common envelope systems, are providing unique
constraints on the mass transfer processes.Comment: Chapter 7, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Self-Similarity in General Relativity \endtitle
The different kinds of self-similarity in general relativity are discussed,
with special emphasis on similarity of the ``first'' kind, corresponding to
spacetimes admitting a homothetic vector. We then survey the various classes of
self-similar solutions to Einstein's field equations and the different
mathematical approaches used in studying them. We focus mainly on spatially
homogenous and spherically symmetric self-similar solutions, emphasizing their
possible roles as asymptotic states for more general models. Perfect fluid
spherically symmetric similarity solutions have recently been completely
classified, and we discuss various astrophysical and cosmological applications
of such solutions. Finally we consider more general types of self-similar
models.Comment: TeX document, 53 page
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