397 research outputs found
Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions
Recent experiments with high-speed ions have investigated potential
deviations from the time-dilation predicted by special relativity (SR). The
main contribution of this article is to show that the SR predictions are
matched by the experimental results only when the transverse Doppler effect in
the observed emissions from the ions are neglected in the analysis. However,
the Doppler effect in the emission cannot be neglected because it is similar to
the time dilation effect. Thus, the article highlights the need to consider
Doppler emission effects when validating SR time dilation using high-speed ion
experiments.Comment: 3 pages, 3 figure
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Surficial geology and performance assessment for a Radioactive Waste Management Facility at the Nevada Test Site
At the Nevada Test Site, one potentially disruptive scenario being evaluated for the Greater Confinement Disposal (GCD) Facility Performance Assessment is deep post-closure erosion that would expose buried radioactive waste to the accessible environment. The GCD Facility located at the Area 5 Radioactive Waste Management Site (RWMS) lies at the juncture of three alluvial fan systems. Geomorphic surface mapping in northern Frenchman Flat indicates that reaches of these fans where the RWMS is now located have been constructional since at least the middle Quaternary. Mapping indicates a regular sequence of prograding fans with entrenchment of the older fan surfaces near the mountain fronts and construction of progressively younger inset fans farther from the mountain fronts. At the facility, the oldest fan surfaces are of late Pleistocene and Holocene age. More recent geomorphic activity has been limited to erosion and deposition along small channels. Trench and pit wall mapping found maximum incision in the vicinity of the RWMS to be less than 1.5 m. Based on collected data, natural geomorphic processes are unlikely to result in erosion to a depth of more than approximately 2 m at the facility within the 10,000-year regulatory period
Role of electrostatic interactions in amyloid beta-protein (Abeta) oligomer formation: A discrete molecular dynamics study
Pathological folding and oligomer formation of the amyloid beta-protein
(Abeta) are widely perceived as central to Alzheimer's disease (AD).
Experimental approaches to study Abeta self-assembly are problematic, because
most relevant aggregates are quasi-stable and inhomogeneous. We apply a
discrete molecular dynamics (DMD) approach combined with a four-bead protein
model to study oligomer formation of the amyloid beta-protein (Abeta). We
address the differences between the two most common Abeta alloforms, Abeta40
and Abeta42, which oligomerize differently in vitro. We study how the presence
of electrostatic interactions (EIs) between pairs of charged amino acids
affects Abeta40 and Abeta42 oligomer formation. Our results indicate that EIs
promote formation of larger oligomers in both Abeta40 and Abeta42. The Abeta40
size distribution remains unimodal, whereas the Abeta42 distribution is
trimodal, as observed experimentally. Abeta42 folded structure is characterized
by a turn in the C-terminus that is not present in Abeta40. We show that the
same C-terminal region is also responsible for the strongest intermolecular
contacts in Abeta42 pentamers and larger oligomers. Our results suggest that
this C-terminal region plays a key role in the formation of Abeta42 oligomers
and the relative importance of this region increases in the presence of EIs.
These results suggest that inhibitors targeting the C-terminal region of
Abeta42 oligomers may be able to prevent oligomer formation or structurally
modify the assemblies to reduce their toxicity.Comment: Accepted for publication at Biophysical Journa
Random Convex Hulls and Extreme Value Statistics
In this paper we study the statistical properties of convex hulls of
random points in a plane chosen according to a given distribution. The points
may be chosen independently or they may be correlated. After a non-exhaustive
survey of the somewhat sporadic literature and diverse methods used in the
random convex hull problem, we present a unifying approach, based on the notion
of support function of a closed curve and the associated Cauchy's formulae,
that allows us to compute exactly the mean perimeter and the mean area enclosed
by the convex polygon both in case of independent as well as correlated points.
Our method demonstrates a beautiful link between the random convex hull problem
and the subject of extreme value statistics. As an example of correlated
points, we study here in detail the case when the points represent the vertices
of independent random walks. In the continuum time limit this reduces to
independent planar Brownian trajectories for which we compute exactly, for
all , the mean perimeter and the mean area of their global convex hull. Our
results have relevant applications in ecology in estimating the home range of a
herd of animals. Some of these results were announced recently in a short
communication [Phys. Rev. Lett. {\bf 103}, 140602 (2009)].Comment: 61 pages (pedagogical review); invited contribution to the special
issue of J. Stat. Phys. celebrating the 50 years of Yeshiba/Rutgers meeting
Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV
We report the results of a study of color coherence effects in ppbar
collisions based on data collected by the D0 detector during the 1994-1995 run
of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8
TeV. Initial-to-final state color interference effects are studied by examining
particle distribution patterns in events with a W boson and at least one jet.
The data are compared to Monte Carlo simulations with different color coherence
implementations and to an analytic modified-leading-logarithm perturbative
calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters
Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL
Measurement of the photon-jet production differential cross section in collisions at \sqrt{s}=1.96~\TeV
We present measurements of the differential cross section dsigma/dpT_gamma
for the inclusive production of a photon in association with a b-quark jet for
photons with rapidities |y_gamma|< 1.0 and 30<pT_gamma <300 GeV, as well as for
photons with 1.5<|y_gamma|< 2.5 and 30< pT_gamma <200 GeV, where pT_gamma is
the photon transverse momentum. The b-quark jets are required to have pT>15 GeV
and rapidity |y_jet| < 1.5. The results are based on data corresponding to an
integrated luminosity of 8.7 fb^-1, recorded with the D0 detector at the
Fermilab Tevatron Collider at sqrt(s)=1.96 TeV. The measured cross
sections are compared with next-to-leading order perturbative QCD calculations
using different sets of parton distribution functions as well as to predictions
based on the kT-factorization QCD approach, and those from the Sherpa and
Pythia Monte Carlo event generators.Comment: 10 pages, 9 figures, submitted to Phys. Lett.
Limits on anomalous trilinear gauge boson couplings from WW, WZ and Wgamma production in pp-bar collisions at sqrt{s}=1.96 TeV
We present final searches of the anomalous gammaWW and ZWW trilinear gauge
boson couplings from WW and WZ production using lepton plus dijet final states
and a combination with results from Wgamma, WW, and WZ production with leptonic
final states. The analyzed data correspond to up to 8.6/fb of integrated
luminosity collected by the D0 detector in pp-bar collisions at sqrt{s}=1.96
TeV. We set the most stringent limits at a hadron collider to date assuming two
different relations between the anomalous coupling parameters
Delta\kappa_\gamma, lambda, and Delta g_1^Z for a cutoff energy scale Lambda=2
TeV. The combined 68% C.L. limits are -0.057<Delta\kappa_\gamma<0.154,
-0.015<lambda<0.028, and -0.008<Delta g_1^Z<0.054 for the LEP parameterization,
and -0.007<Delta\kappa<0.081 and -0.017<lambda<0.028 for the equal couplings
parameterization. We also present the most stringent limits of the W boson
magnetic dipole and electric quadrupole moments.Comment: 10 pages, 5 figures, submitted to PL
Measurement of three-jet differential cross sections d sigma-3jet / d M-3jet in p anti-p collisions at sqrt(s)=1.96 TeV
We present the first measurement of the inclusive three-jet differential
cross section as a function of the invariant mass of the three jets with the
largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96
TeV. The measurement is made in different rapidity regions and for different
jet transverse momentum requirements and is based on a data set corresponding
to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at
the Fermilab Tevatron Collider. The results are used to test the three-jet
matrix elements in perturbative QCD calculations at next-to-leading order in
the strong coupling constant. The data allow discrimination between
parametrizations of the parton distribution functions of the proton.Comment: 10 pages, 4 figures, 2 tables, submitted to Phys. Lett. B, corrected
chi2 values for NNPD
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