11,437 research outputs found
Entanglement reciprocation between atomic qubits and entangled coherent state
Introducing classical fields, we can transfer entanglement completely from
discrete qubits into entangled coherent state. The entanglement also can be
retrieved from the continuous-variable state of the cavities to the atomic
qubits. Via postselection measure, atomic entangled state and entangled
coherent state can be mutual transformed fully.Comment: 5 pages, 3 fighres. accepted by J Phys
Density of states near the Mott-Hubbard transition in the limit of large dimensions
The zero temperature Mott-Hubbard transition as a function of the Coulomb
repulsion U is investigated in the limit of large dimensions. The behavior of
the density of states near the transition at U=U_c is analyzed in all orders of
the skeleton expansion. It is shown that only two transition scenarios are
consistent with the skeleton expansion for U<U_c: (i) The Mott-Hubbard
transition is "discontinuous" in the sense that in the density of states finite
spectral weight is redistributed at U_c. (ii) The transition occurs via a point
at U=U_c where the system is neither a Fermi liquid nor an insulator.Comment: 4 pages, 1 figure; revised version accepted for publication in Phys.
Rev. Let
Quantum Heisenberg antiferromagnet on low-dimensional frustrated lattices
Using a lattice-gas description of the low-energy degrees of freedom of the
quantum Heisenberg antiferromagnet on the frustrated two-leg ladder and bilayer
lattices we examine the magnetization process at low temperatures for these
spin models. In both cases the emergent discrete degrees of freedom implicate a
close relation of the frustrated quantum Heisenberg antiferromagnet to the
classical lattice gas with finite nearest-neighbor repulsion or, equivalently,
to the Ising antiferromagnet in a uniform magnetic field. Using this relation
we obtain analytical results for thermodynamically large systems in the
one-dimensional case. In the two-dimensional case we perform classical Monte
Carlo simulations for systems of up to sites.Comment: Submitted to Teoreticheskaya i Matematicheskaya Fizika (special issue
dedicated to the 90th anniversary of Professor Sergei Vladimirovich
Tyablikov
Peierls distorted chain as a quantum data bus for quantum state transfer
We systematically study the transfer of quantum state of electron spin as the
flying qubit along a half-filled Peierls distorted tight-binding chain
described by the Su-Schrieffer-Heeger (SSH) model, which behaves as a quantum
data bus. This enables a novel physical mechanism for quantum communication
with always-on interaction: the effective hopping of the spin carrier between
sites and connected to two sites in this SSH chain can be induced by
the quasi-excitations of the SSH model. As we prove, it is the Peierls energy
gap of the SSH quasi-excitations that plays a crucial role to protect the
robustness of the quantum state transfer process. Moreover, our observation
also indicates that such a scheme can also be employed to explore the intrinsic
property of the quantum system.Comment: 10 pages, 6 figure
MicroRNA-24 regulates vascularity after myocardial infarction
BACKGROUND: Myocardial infarction leads to cardiac remodeling and development of heart failure. Insufficient myocardial capillary density after myocardial infarction has been identified as a critical event in this process, although the underlying mechanisms of cardiac angiogenesis are mechanistically not well understood. METHODS AND RESULTS: Here, we show that the small noncoding RNA microRNA-24 (miR-24) is enriched in cardiac endothelial cells and considerably upregulated after cardiac ischemia. MiR-24 induces endothelial cell apoptosis, abolishes endothelial capillary network formation on Matrigel, and inhibits cell sprouting from endothelial spheroids. These effects are mediated through targeting of the endothelium-enriched transcription factor GATA2 and the p21-activated kinase PAK4, which were identified by bioinformatic predictions and validated by luciferase gene reporter assays. Respective downstream signaling cascades involving phosphorylated BAD (Bcl-XL/Bcl-2-associated death promoter) and Sirtuin1 were identified by transcriptome, protein arrays, and chromatin immunoprecipitation analyses. Overexpression of miR-24 or silencing of its targets significantly impaired angiogenesis in zebrafish embryos. Blocking of endothelial miR-24 limited myocardial infarct size of mice via prevention of endothelial apoptosis and enhancement of vascularity, which led to preserved cardiac function and survival. CONCLUSIONS: Our findings indicate that miR-24 acts as a critical regulator of endothelial cell apoptosis and angiogenesis and is suitable for therapeutic intervention in the setting of ischemic heart disease. [KEYWORDS: Animals, Apoptosis/drug effects, Arterioles/pathology, Capillaries/pathology, Cell Hypoxia, Cells, Cultured/drug effects/metabolism, Collagen, Drug Combinations, Drug Evaluation, Preclinical, Endothelial Cells/ metabolism/pathology, GATA2 Transcription Factor/biosynthesis/genetics, Gene Expression Profiling, Heart Failure/etiology, Heme Oxygenase-1/biosynthesis/genetics, Laminin, Male, Mice, Mice, Inbred C57BL, MicroRNAs/antagonists & inhibitors/genetics/ physiology, Myocardial Infarc
Accelerated Particle Swarm Optimization and Support Vector Machine for Business Optimization and Applications
Business optimization is becoming increasingly important because all business
activities aim to maximize the profit and performance of products and services,
under limited resources and appropriate constraints. Recent developments in
support vector machine and metaheuristics show many advantages of these
techniques. In particular, particle swarm optimization is now widely used in
solving tough optimization problems. In this paper, we use a combination of a
recently developed Accelerated PSO and a nonlinear support vector machine to
form a framework for solving business optimization problems. We first apply the
proposed APSO-SVM to production optimization, and then use it for income
prediction and project scheduling. We also carry out some parametric studies
and discuss the advantages of the proposed metaheuristic SVM.Comment: 12 page
POET: POlarimeters for Energetic Transients
POET (Polarimeters for Energetic Transients) is a Small Explorer mission
concept proposed to NASA in January 2008. The principal scientific goal of POET
is to measure GRB polarization between 2 and 500 keV. The payload consists of
two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of
polarization measurements in the energy range from 2-15 keV and a high energy
polarimeter (Gamma-Ray Polarimeter Experiment -- GRAPE) that will measure
polarization in the 60-500 keV energy range. Spectra will be measured from 2
keV up to 1 MeV. The POET spacecraft provides a zenith-pointed platform for
maximizing the exposure to deep space. Spacecraft rotation will provide a means
of effectively dealing with systematics in the polarization response. POET will
provide sufficient sensitivity and sky coverage to measure statistically
significant polarization for up to 100 GRBs in a two-year mission. Polarization
data will also be obtained for solar flares, pulsars and other sources of
astronomical interest
What Can the Accretion Induced Collapse of White Dwarfs Really Explain?
The accretion induced collapse (AIC) of a white dwarf into a neutron star has
been invoked to explain gamma-ray bursts, Type Ia supernovae, and a number of
problematic neutron star populations and specific binary systems. The ejecta
from this collapse has also been claimed as a source of r-process
nucleosynthesis. So far, most AIC studies have focussed on determining the
event rates from binary evolution models and less attention has been directed
toward understanding the collapse itself. However, the collapse of a white
dwarf into a neutron star is followed by the ejection of rare neutron-rich
isotopes. The observed abundance of these chemical elements may set a more
reliable limit on the rate at which AICs have taken place over the history of
the galaxy.
In this paper, we present a thorough study of the collapse of a massive white
dwarf in 1- and 2-dimensions and determine the amount and composition of the
ejected material. We discuss the importance of the input physics (equation of
state, neutrino transport, rotation) in determining these quantities. These
simulations affirm that AICs are too baryon rich to produce gamm-ray bursts and
do not eject enough nickel to explain Type Ia supernovae (with the possible
exception of a small subclass of extremely low-luminosity Type Ias). Although
nucleosynthesis constraints limit the number of neutron stars formed via AICs
to <0.1% of the total galactic neutron star population, AICs remain a viable
scenario for forming systems of neutron stars which are difficult to explain
with Type II core-collapse supernovae.Comment: Latex File, aaspp4 style, 18 pages total (5 figures), accepted by Ap
Exact calculation of spectral properties of a particle interacting with a one dimensional fermionic system
Using the Bethe ansatz analysis as was reformulated by Edwards, we calculate
the spectral properties of a particle interacting with a bath of fermions in
one dimension for the case of equal particle-fermion masses. These are directly
related to singularities apparent in optical experiments in one dimensional
systems. The orthogonality catastrophe for the case of an infinite particle
mass survives in the limit of equal masses. We find that the exponent
of the quasiparticle weight, is different for the two
cases, and proportional to their respective phaseshifts at the Fermi surface;
we present a simple physical argument for this difference. We also show that
these exponents describe the low energy behavior of the spectral function, for
repulsive as well as attractive interaction.Comment: 22 pages + 1 postscript figure, REVTE
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