1,232 research outputs found
The complex X-ray spectrum of the isolated neutron star RBS1223
We present a first analysis of a deep X-ray spectrum of the isolated neutron
star RBS1223 obtained with XMM-Newton. Spectral data from four new monitoring
observations in 2005/2006 were combined with archival observations obtained in
2003 and 2004 to form a spin-phase averaged spectrum containing 290000 EPIC-pn
photons. This spectrum shows higher complexity than its predecessors, and can
be parameterised with two Gaussian absorption lines superimposed on a
blackbody. The line centers, E_2 ~ 2E_1, could be regarded as supporting the
cyclotron interpretation of the absorption features in a field B ~ 4 x 10**13
G. The flux ratio of those lines does not support this interpretation. Hence,
either feature might be of truly atomic origin.Comment: 4 pages, 1 figure, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
New Predictions for Neutrino Telescope Event Rates
Recent measurements of the small- deep-inelastic regime at HERA translate
to new expectations for the neutrino-nucleon cross section at ultrahigh
energies. We present event rates for large underground neutrino telescopes
based on the new cross section for a variety of models of neutrino production
in Active Galactic Nuclei, and we compare these rates with earlier cross
section calculations.Comment: Talk presented by I. Sarcevic at the VIth International Workshop on
Theoretical Aspects of Underground Physics, Toledo, Spain, September 17-21,
1995, 3 p
Muon and Muon Neutrino Fluxes from Atmospheric Charm
The charm contribution to the atmospheric fluxes of muons and muon neutrinos
may be enhanced by as much as a factor of 10 when one includes the
contributions of D->pi,K->leptons and folds in uncertainties in the charm cross
section and energy distribution. In the energy range considered here, from 100
GeV to 10 TeV, the charm contribution is small compared to the conventional
flux of muons and muon neutrinos.Comment: 3 pages, submitted to the Proceedings of the Fifth International
Workshop on Topics in Astroparticle and Underground Physics, Sept. 199
Fully differential W' production and decay at next-to-leading order in QCD
We present the fully differential production and decay of a W' boson, with
arbitrary vector and axial-vector couplings, to any final state at
next-to-leading order in QCD. We demonstrate a complete factorization of
couplings at next-to-leading order in both the partial width of the W' boson,
and in the full two-to-two cross section. We provide numerical predictions for
the contribution of a W' boson to single-top-quark production, and separate
results based on whether the mass of the right-handed neutrino (nu_R) is light
enough for the leptonic decay channel to be open. The single-top-quark analysis
will allow for an improved direct W' mass limit of 525-550 GeV using data from
run I of the Fermilab Tevatron. We propose a modified tolerance method for
estimating parton distribution function uncertainties in cross sections.Comment: 23 pages, revtex3, 13 ps fig
Secondary Decays in Atmospheric Charm Contributions to the Flux of Muons and Muon Neutrinos
We present a calculation of the fluxes of muons and muon neutrinos from the
decays of pions and kaons that are themselves the decay products of charmed
particles produced in the atmosphere by cosmic ray-air collisions. Using the
perturbative cross section for charm production, these lepton fluxes are two to
three orders of magnitude smaller than the fluxes from the decays of pions and
kaons directly produced in cosmic ray-air collisions. Intrinsic charm models do
not significantly alter our conclusions, nor do models with a charm cross
section enhanced in the region above an incident cosmic ray energy of 1 TeV.Comment: 14 pages, 4 figures, Latex, psfi
Under What Conditions Can Recursion Be Learned? Effects of Starting Small in Artificial Grammar Learning of Center-Embedded Structure
It has been suggested that external and/or internal limitations paradoxically may lead to superior learning, that is, the concepts of starting small and less is more (Elman,; Newport,). In this paper, we explore the type of incremental ordering during training that might help learning, and what mechanism explains this facilitation. We report four artificial grammar learning experiments with human participants. In Experiments 1a and 1b we found a beneficial effect of starting small using two types of simple recursive grammars: right-branching and center-embedding, with recursive embedded clauses in fixed positions and fixed length. This effect was replicated in Experiment 2 (N = 100). In Experiment 3 and 4, we used a more complex center-embedded grammar with recursive loops in variable positions, producing strings of variable length. When participants were presented an incremental ordering of training stimuli, as in natural language, they were better able to generalize their knowledge of simple units to more complex units when the training input “grew” according to structural complexity, compared to when it “grew” according to string length. Overall, the results suggest that starting small confers an advantage for learning complex center-embedded structures when the input is organized according to structural complexity
A Multi-Level Optimization Algorithm and a Ship Design Application
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97130/1/AIAA2012-5555.pd
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
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