3,466 research outputs found
Wigner Crystal in One Dimension
A one--dimensional gas of electrons interacting with long--range Coulomb
forces () is investigated. The excitation spectrum consists
of separate collective charge and spin modes, with the charge excitation
energies in agreement with RPA calculations. For arbitrarily weak Coulomb
repulsion density correlations at wavevector decay extremely slowly and
are best described as those of a one--dimensional Wigner crystal. Pinning of
the Wigner crystal then leads to the nonlinear transport properties
characteristic of CDW. The results allow a consistent interpretation of the
plasmon and spin excitations observed in one--dimensional semiconductor
structures, and suggest an interpretation of some of the observed features in
terms of ``spinons''. A possible explanation for nonlinear transport phenomena
is given.Comment: 10 pages, RevTe
Foreground removal from WMAP 7yr polarization maps using an MLP neural network
One of the fundamental problems in extracting the cosmic microwave background
signal (CMB) from millimeter/submillimeter observations is the pollution by
emission from the Milky Way: synchrotron, free-free, and thermal dust emission.
To extract the fundamental cosmological parameters from CMB signal, it is
mandatory to minimize this pollution since it will create systematic errors in
the CMB power spectra. In previous investigations, it has been demonstrated
that the neural network method provide high quality CMB maps from temperature
data. Here the analysis is extended to polarization maps. As a concrete
example, the WMAP 7-year polarization data, the most reliable determination of
the polarization properties of the CMB, has been analysed. The analysis has
adopted the frequency maps, noise models, window functions and the foreground
models as provided by the WMAP Team, and no auxiliary data is included. Within
this framework it is demonstrated that the network can extract the CMB
polarization signal with no sign of pollution by the polarized foregrounds. The
errors in the derived polarization power spectra are improved compared to the
errors derived by the WMAP Team.Comment: Accepted for publication in Astrophysics & Space Scienc
Characterization of one-dimensional quantum channels in InAs/AlSb
We report the magnetoresistance characteristics of one-dimensional electrons
confined in a single InAs quantum well sandwiched between AlSb barriers. As a
result of a novel nanofabrication scheme that utilizes a 3nm-shallow wet
chemical etching to define the electrostatic lateral confinement, the system is
found to possess three important properties: specular boundary scattering, a
strong lateral confinement potential, and a conducting channel width that is
approximately the lithography width. Ballistic transport phenomena, including
the quenching of the Hall resistance, the last Hall plateau, and a strong
negative bend resistance, are observed at 4K in cross junctions with sharp
corners. In a ring geometry, we have observed Aharonov-Bohm interference that
exhibits characteristics different from those of the GaAs counterpart due to
the ballistic nature of electron transport and the narrowness of the conducting
channel width.Comment: pdf-file, 8 figures, to be published in Phys. Rev.
Stability analysis of agegraphic dark energy in Brans-Dicke cosmology
Stability analysis of agegraphic dark energy in Brans-Dicke theory is
presented in this paper. We constrain the model parameters with the
observational data and thus the results become broadly consistent with those
expected from experiment. Stability analysis of the model without best fitting
shows that universe may begin from an unstable state passing a saddle point and
finally become stable in future. However, with the best fitted model, There is
no saddle intermediate state. The agegraphic dark energy in the model by itself
exhibits a phantom behavior. However, contribution of cold dark matter on the
effective energy density modifies the state of teh universe from phantom phase
to quintessence one. The statefinder diagnosis also indicates that the universe
leaves an unstable state in the past, passes the LCDM state and finally
approaches the sable state in future.Comment: 15 pages, 12 figure
Investigating knowledge management factors affecting Chinese ICT firms performance: An integrated KM framework
This is an Author's Accepted Manuscript of an article published in the Journal of Information Systems Management, 28(1), 19 - 29, 2011, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/10580530.2011.536107.This article sets out to investigate the critical factors of Knowledge Management (KM) which are considered to have an impact on the performance of Chinese information and communication technology (ICT) firms. This study confirms that the cultural environment of an enterprise is central to its success in the context of China. It shows that a collaborated, trusted, and learning environment within ICT firms will have a positive impact on their KM performance
Novel multiple sclerosis susceptibility loci implicated in epigenetic regulation
We conducted a genome-wide association study (GWAS) on multiple sclerosis (MS) susceptibility in German cohorts with 4888 cases and 10,395 controls. In addition to associations within the major histocompatibility complex (MHC) region, 15 non-MHC loci reached genome-wide significance. Four of these loci are novel MS susceptibility loci. They map to the genes L3MBTL3, MAZ, ERG, and SHMT1. The lead variant at SHMT1 was replicated in an independent Sardinian cohort. Products of the genes L3MBTL3, MAZ, and ERG play important roles in immune cell regulation. SHMT1 encodes a serine hydroxymethyltransferase catalyzing the transfer of a carbon unit to the folate cycle. This reaction is required for regulation of methylation homeostasis, which is important for establishment and maintenance of epigenetic signatures. Our GWAS approach in a defined population with limited genetic substructure detected associations not found in larger, more heterogeneous cohorts, thus providing new clues regarding MS pathogenesis
Collective Animal Behavior from Bayesian Estimation and Probability Matching
Animals living in groups make movement decisions that depend, among other factors, on social interactions with other group members. Our present understanding of social rules in animal collectives is based on empirical fits to observations and we lack first-principles approaches that allow their derivation. Here we show that patterns of collective decisions can be derived from the basic ability of animals to make probabilistic estimations in the presence of uncertainty. We build a decision-making model with two stages: Bayesian estimation and probabilistic matching.
In the first stage, each animal makes a Bayesian estimation of which behavior is best to perform taking into account personal information about the environment and social information collected by observing the behaviors of other animals. In the probability matching stage, each animal chooses a behavior with a probability given by the Bayesian estimation that this behavior is the most appropriate one. This model derives very simple rules of interaction in animal collectives that depend only on two types of reliability parameters, one that each animal assigns to the other animals and another given by the quality of the non-social information. We test our model by obtaining theoretically a rich set of observed collective patterns of decisions in three-spined sticklebacks, Gasterosteus aculeatus, a shoaling fish species. The quantitative link shown between probabilistic estimation and collective rules of behavior allows a better contact with other fields such as foraging, mate selection, neurobiology and psychology, and gives predictions for experiments directly testing the relationship between estimation and collective behavior
A search for resonant production of pairs in $4.8\ \rm{fb}^{-1}p\bar{p}\sqrt{s}=1.96\ \rm{TeV}$
We search for resonant production of tt pairs in 4.8 fb^{-1} integrated
luminosity of ppbar collision data at sqrt{s}=1.96 TeV in the lepton+jets decay
channel, where one top quark decays leptonically and the other hadronically. A
matrix element reconstruction technique is used; for each event a probability
density function (pdf) of the ttbar candidate invariant mass is sampled. These
pdfs are used to construct a likelihood function, whereby the cross section for
resonant ttbar production is estimated, given a hypothetical resonance mass and
width. The data indicate no evidence of resonant production of ttbar pairs. A
benchmark model of leptophobic Z \rightarrow ttbar is excluded with m_{Z'} <
900 GeV at 95% confidence level.Comment: accepted for publication in Physical Review D Sep 21, 201
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
Search for New Particles Decaying to Dijets at CDF
We have used 106 pb^-1 of data collected with the Collider Detector at
Fermilab to search for new particles decaying to dijets. We exclude at the 95%
confidence level models containing the following new particles: axigluons and
flavor universal colorons with mass between 200 and 980 GeV/c, excited quarks
with mass between 80 and 570 GeV/c^2 and between 580 and 760 GeV/c^2, color
octet technirhos with mass between 260 and 480 GeV/c^2, W' bosons with mass
between 300 and 420 GeV/c^2, and E_6 diquarks with mass between 290 and 420
GeV/c^2.Comment: 18 pages, 4 figures, 1 table. Submitted to Physical Review D Rapid
Communications. Postscript file of paper is also available at
http://www-cdf.fnal.gov/physics/pub97/cdf3276_dijet_search_prd_rc.p
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