2,166 research outputs found
Vector meson - mixing and their form factors in light-cone quark model
The vector meson - mixing is studied in two alternative
scenarios with different numbers of mixing angles, i.e., the one-mixing-angle
scenario and the two-mixing-angle scenario, in both the octect-singlet mixing
scheme and the quark flavor mixing scheme. Concerning the reproduction of
experimental data and the behavior of transition form factors,
one-mixing-angle scenario in the quark flavor scheme performs better than that
in the octet-singlet scheme, while the two-mixing-angle scenario works well for
both mixing schemes. The difference between the two mixing angles in the
octet-singlet scheme is bigger than that in the quark flavor scheme.Comment: 16 pages, 7 figures, final version to appear in PR
Phonon Bloch oscillations in acoustic-cavity structures
We describe a semiconductor multilayer structure based in acoustic phonon
cavities and achievable with MBE technology, designed to display acoustic
phonon Bloch oscillations. We show that forward and backscattering Raman
spectra give a direct measure of the created phononic Wannier-Stark ladder. We
also discuss the use of femtosecond laser impulsions for the generation and
direct probe of the induced phonon Bloch oscillations. We propose a gedanken
experiment based in an integrated phonon source-structure-detector device, and
we present calculations of pump and probe time dependent optical reflectivity
that evidence temporal beatings in agreement with the Wannier-Stark ladder
energy splitting.Comment: PDF file including 4 figure
Renormalization group analysis of the 2D Hubbard model
Salmhofer [Commun. Math. Phys. 194, 249 (1998)] has recently developed a new
renormalization group method for interacting Fermi systems, where the complete
flow from the bare action of a microscopic model to the effective low-energy
action, as a function of a continuously decreasing infrared cutoff, is given by
a differential flow equation which is local in the flow parameter. We apply
this approach to the repulsive two-dimensional Hubbard model with nearest and
next-nearest neighbor hopping amplitudes. The flow equation for the effective
interaction is evaluated numerically on 1-loop level. The effective
interactions diverge at a finite energy scale which is exponentially small for
small bare interactions. To analyze the nature of the instabilities signalled
by the diverging interactions we extend Salmhofers renormalization group for
the calculation of susceptibilities. We compute the singlet superconducting
susceptibilities for various pairing symmetries and also charge and spin
density susceptibilities. Depending on the choice of the model parameters
(hopping amplitudes, interaction strength and band-filling) we find
commensurate and incommensurate antiferromagnetic instabilities or d-wave
superconductivity as leading instability. We present the resulting phase
diagram in the vicinity of half-filling and also results for the density
dependence of the critical energy scale.Comment: 16 pages, RevTeX, 16 eps figure
Content-aware Traffic Engineering
Also appears as TU-Berlin technical report 2012-3, ISSN: 1436-9915Also appears as TU-Berlin technical report 2012-3, ISSN: 1436-9915Today, a large fraction of Internet traffic is originated by Content Providers (CPs) such as content distribution networks and hyper-giants. To cope with the increasing demand for content, CPs deploy massively distributed infrastructures. This poses new challenges for CPs as they have to dynamically map end-users to appropriate servers, without being fully aware of network conditions within an ISP as well as the end-users network locations. Furthermore, ISPs struggle to cope with rapid traffic shifts caused by the dynamic server selection process of CPs. In this paper, we argue that the challenges that CPs and ISPs face separately today can be turned into an opportunity. We show how they can jointly take advantage of the deployed distributed infrastructures to improve their operation and end-user performance. We propose Content-aware Traffic Engineering (CaTE), which dynamically adapts the traffic demand for content hosted on CPs by utilizing ISP network information and end-user location during the server selection process. As a result, CPs enhance their end-user to server mapping and improve end-user experience, thanks to the ability of network-informed server selection to circumvent network bottlenecks. In addition, ISPs gain the ability to partially influence the traffic demands in their networks. Our results with operational data show improvements in path length and delay between end-user and the assigned CP server, network wide traffic reduction of up to 15%, and a decrease in ISP link utilization of up to 40% when applying CaTE to traffic delivered by a small number of major CPs
Determination of the and Mixing Angle from the Pseudoscalar Transition Form Factors
The possible range of mixing angle is determined from the
transition form factors and with
the help of the present experimental data. For such purpose, the quark-flavor
mixing scheme is adopted and the pseudoscalar transition form factors are
calculated under the light-cone pQCD framework, where the transverse momentum
corrections and the contributions beyond the leading Fock state have been
carefully taken into consideration. We construct a phenomenological expression
to estimate the contributions to the form factors beyond the leading Fock state
based on their asymptotic behavior at and . By taking
the quark-flavor mixing scheme, our results lead to , where the first error coming from experimental
uncertainty and the second error coming from the uncertainties of the
wavefunction parameters. The possible intrinsic charm component in and
is discussed and our present analysis also disfavors a large portion of
intrinsic charm component in and , e.g. .Comment: 18 Pages, 3 figures. Several references added. To be published in
EPJ
A cytomegalovirus-based vaccine provides long-lasting protection against lethal Ebola virus challenge after a single dose
This is the author accepted manuscript. The final version is available fromElsevier via the DOI in this record.Ebola virus (Zaire ebolavirus; EBOV) is a highly lethal hemorrhagic disease virus that most recently was responsible for two independent 2014 outbreaks in multiple countries in Western Africa, and the Democratic Republic of the Congo, respectively. Herein, we show that a cytomegalovirus (CMV)-based vaccine provides durable protective immunity from Ebola virus following a single vaccine dose. This study has implications for human vaccination against ebolaviruses, as well as for development of a 'disseminating' vaccine to target these viruses in wild African great apes.We thank Dr U. Koszinowski (Max von Pettenkofer-Institute, Ludwig-Maximilians-University, Germany) for providing the pSMfr3 MCMV BAC, and Dr D. Court (NCI-Frederick, MD) for providing the lambda-based recombination system used to construct the original MCMV/ZEBOV-NPCTL construct. We appreciate K. Marshall (VGTI, OR) and J. Bailey (NIAID, MT) for their organization and coordination of animals used in the study. We also thank the members of Rocky Mountain Veterinary Branch (DIR, NIAID, NIH) for assistance with animal care. Finally, we thank Drs H. Ebihara (DIR, NIAID, NIH), A. Marzi (DIR, NIAID, NIH), P. Barry (University of California at Davis, CA), M. Cranfield (Mountain Gorilla Veterinary Project, Baltimore, MD) for insightful discussions. This study was supported by R21 (AI088442) and the Intramural Research Program of the NIAID, NIH; and University of Plymouth, School of Biomedical and Healthcare Sciences internal funding
Non-leptonic two-body decays of the Bc meson in light-front quark model and QCD factorization approach
We study exclusive non-leptonic two-body
decays with (pseudoscalar or vector meson) being factored out in QCD
factorization approach. The non-leptonic decay amplitudes are related to the
product of meson decay constants and the form factors for semileptonic
decays. As inputs in obtaining the branching ratios for a large set of
non-leptonic decays, we use the weak form factors for the semileptonic
decays in the whole kinematical region and the
unmeasured meson decay constants obtained from our previous light-front quark
model. We compare our results of the branching ratios with those of other
theoretical studies.Comment: 11 pages, 3 figures, minor corrections, version to appear in PR
Quark structure of pseudoscalar mesons
I review to which extent the properties of pseudoscalar mesons can be
understood in terms of the underlying quark (and eventually gluon) structure.
Special emphasis is put on the progress in our understanding of eta-eta'
mixing. Process-independent mixing parameters are defined, and relations
between different bases and conventions are studied. Both, the low-energy
description in the framework of Chiral Perturbation Theory and the high-energy
application in terms of light-cone wave functions for partonic Fock states, are
considered. A thorough discussion of theoretical and phenomenological
consequences of the mixing approach will be given. Finally, I will discuss
mixing with other states pi^0, eta(c), ...).Comment: 48 pages, 7 figures, using epsfig.st
Minimal Flavour Violation and Beyond
Starting from the effective-theory framework for Minimal Flavour Violation,
we give a systematic definition of next-to-minimal (quark) flavour violation in
terms of a set of spurion fields exhibiting a particular hierarchy with respect
to a small (Wolfenstein-like) parameter. A few illustrative examples and their
consequences for charged and neutral decays with different quark chiralities
are worked out in some detail. Our framework can be used as a model-independent
classification scheme for the parameterization of flavour structure from
physics beyond the Standard Model.Comment: 17 pages, no figures, phenomenological discussion extended,
references adde
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