63,801 research outputs found
- Correlation and Elliptic Flow Parameter of Charmed Mesons at RHIC Energy
We study the correlation between the trigger and the associated
on near and away sides in Au+Au collisions at GeV.
In the region of trigger momentum GeV/, the spectrum is
composed of thermal-shower and shower-shower recombinations in the frame work
of the recombination model. We consider the azimuthal anisotropy in the
quenched hard parton distribution and then calculate the elliptic flow
parameter of charmed mesons (, and ) for different
centralities.Comment: 17 pages, 6 figure
Pulsar slow glitches in a solid quark star model
A series of five unusual slow glitches of the radio pulsar B1822-09 (PSR
J1825-0935) were observed over the 1995-2005 interval. This phenomenon is
understood in a solid quark star model, where the reasonable parameters for
slow glitches are presented in the paper. It is proposed that, because of
increasing shear stress as a pulsar spins down, a slow glitch may occur,
beginning with a collapse of a superficial layer of the quark star. This layer
of material turns equivalently to viscous fluid at first, the viscosity of
which helps deplete the energy released from both the accumulated elastic
energy and the gravitation potential. This performs then a process of slow
glitch. Numerical calculations show that the observed slow glitches could be
reproduced if the effective coefficient of viscosity is ~10^2 cm^{2}/s and the
initial velocity of the superficial layer is order of 10^{-10} cm/s in the
coordinate rotating frame of the star.Comment: 5 pages, 5 figures, accepted for publication in MNRAS (Main Journal
Geodesics on Calabi-Yau manifolds and winding states in nonlinear sigma models
We conjecture that a non-flat -real-dimensional compact Calabi-Yau
manifold, such as a quintic hypersurface with D=6, or a K3 manifold with D=4,
has locally length minimizing closed geodesics, and that the number of these
with length less than L grows asymptotically as L^{D}. We also outline the
physical arguments behind this conjecture, which involve the claim that all
states in a nonlinear sigma model can be identified as "momentum" and "winding"
states in the large volume limit.Comment: minor corrections, 43 pages, to appear in frontiers in mathematical
physics. Frontiers in Physics, Dec 16, 201
The symmetry of large N=4 holography
For the proposed duality relating a family of N=4 superconformal coset models
to a certain supersymmetric higher spin theory on AdS_3, the asymptotic
symmetry algebra of the bulk description is determined. It is shown that,
depending on the choice of the boundary charges, one may obtain either the
linear or the non-linear superconformal algebra on the boundary. We compare the
non-linear version of the asymptotic symmetry algebra with the non-linear coset
algebra and find non-trivial agreement in the 't Hooft limit, thus giving
strong support for the proposed duality. As a by-product of our analysis we
also show that the W_infinity symmetry of the coset theory is broken under the
exactly marginal perturbation that preserves the N=4 superconformal algebra.Comment: 26 page
THE role of the technology acceptance model in information systems research: a case study
Explaining the factors that lead to use and acceptance of information technology (IT), both at individual and organizational levels, has been the focus of information systems (IS) researchers since 1970s. The Technology Acceptance Model (TAM) is known as such an explanatory model and has increasingly gained recognition due to its focus on theories of human behaviour. Although this model has faced with some criticism in terms of not being able to fully explain the social-technical acceptance of technology, it is still known as one of the best IS methodologies that contributes greatly to explaining it. This paper discusses, describes and explains TAM as one of the well-known information system research methodologies and attempts to demonstrate how this model can be applied in practice in IS research projects. TAM is widely used in different areas of IS studies such as e-commerce, e-business, multimedia and mobile commerce. This paper shows how TAM can be applied in an IS research project by referring to a case study conducted in the area of mobile banking in the UK. This paper aims to contribute to IS research by providing an informed criticism of TAM as well as a clear proposal on how to use it
Similarity-Aware Spectral Sparsification by Edge Filtering
In recent years, spectral graph sparsification techniques that can compute
ultra-sparse graph proxies have been extensively studied for accelerating
various numerical and graph-related applications. Prior nearly-linear-time
spectral sparsification methods first extract low-stretch spanning tree from
the original graph to form the backbone of the sparsifier, and then recover
small portions of spectrally-critical off-tree edges to the spanning tree to
significantly improve the approximation quality. However, it is not clear how
many off-tree edges should be recovered for achieving a desired spectral
similarity level within the sparsifier. Motivated by recent graph signal
processing techniques, this paper proposes a similarity-aware spectral graph
sparsification framework that leverages efficient spectral off-tree edge
embedding and filtering schemes to construct spectral sparsifiers with
guaranteed spectral similarity (relative condition number) level. An iterative
graph densification scheme is introduced to facilitate efficient and effective
filtering of off-tree edges for highly ill-conditioned problems. The proposed
method has been validated using various kinds of graphs obtained from public
domain sparse matrix collections relevant to VLSI CAD, finite element analysis,
as well as social and data networks frequently studied in many machine learning
and data mining applications
Reionization Through the Lens of Percolation Theory
The reionization of intergalactic hydrogen has received intense theoretical
scrutiny over the past two decades. Here, we approach the process formally as a
percolation process and phase transition. Using semi-numeric simulations, we
demonstrate that an infinitely-large ionized region abruptly appears at an
ionized fraction of ~0.1 and quickly grows to encompass most of the ionized
gas: by an ionized fraction of 0.3, nearly ninety percent of the ionized
material is part of this region. Throughout most of reionization, nearly all of
the intergalactic medium is divided into just two regions, one ionized and one
neutral, and both infinite in extent. We also show that the discrete ionized
regions that exist before and near this transition point follow a near-power
law distribution in volume, with equal contributions to the total filling
factor per logarithmic interval in size up to a sharp cutoff in volume. These
qualities are generic to percolation processes, with the detailed behavior a
result of long-range correlations in the underlying density field. These
insights will be crucial to understanding the distribution of ionized and
neutral gas during reionization and provide precise meaning to the intuitive
description of reionization as an "overlap" process.Comment: 16 pages, version accepted by MNRAS (conclusions unchanged from
original
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