621 research outputs found
On hyperovals of polar spaces
We derive lower and upper bounds for the size of a hyperoval of a finite polar space of rank 3. We give a computer-free proof for the uniqueness, up to isomorphism, of the hyperoval of size 126 of H(5, 4) and prove that the near hexagon E-3 has up to isomorphism a unique full embedding into the dual polar space DH(5, 4)
Growth Velocities of Branched Actin Networks
The growth of an actin network against an obstacle that stimulates branching
locally is studied using several variants of a kinetic rate model based on the
orientation-dependent number density of filaments. The model emphasizes the
effects of branching and capping on the density of free filament ends. The
variants differ in their treatment of side vs. end branching and
dimensionality, and assume that new branches are generated by existing branches
(autocatalytic behavior) or independently of existing branches (nucleation
behavior). In autocatalytic models, the network growth velocity is rigorously
independent of the opposing force exerted by the obstacle, and the network
density is proportional to the force. The dependence of the growth velocity on
the branching and capping rates is evaluated by a numerical solution of the
rate equations. In side-branching models, the growth velocity drops gradually
to zero with decreasing branching rate, while in end-branching models the drop
is abrupt. As the capping rate goes to zero, it is found that the behavior of
the velocity is sensitive to the thickness of the branching region. Experiments
are proposed for using these results to shed light on the nature of the
branching process.Comment: 6 figure
Epstein-Barr Virus, High-Risk Human Papillomavirus and Abnormal Cervical Cytology in a Prospective Cohort of African Female Sex Workers
Background High-oncogenic-risk human papillomavirus (hrHPV) is necessary, although insufficient, to promote cervical cancer. Like HPV, Epstein-Barr virus (EBV) is a common pathogen with the capacity to promote epithelial neoplasms. We examined the association between cervical EBV, hrHPV, and cytology in female sex workers in Nairobi, Kenya. Methods Women (n = 332) with known cervical cytology and hrHPV mRNA results were evaluated for cervical EBV DNA by conventional polymerase chain reaction. Prevalence ratios (PRs) were calculated to assess the relationships between EBV, hrHPV, and cervical cytology. Prospective analyses used risk ratios and time-to-event analyses to determine the association of EBV with hrHPV clearance and with abnormal cytology outcomes. Results Baseline prevalence of hrHPV and EBV was 29% and 19%, respectively. Higher EBV prevalence was found among women with older age, HIV, hrHPV, abnormal cytology, Mycoplasma genitalium infection, smoking habits, younger age at sexual debut, and less frequent condom use. At baseline, women with EBV had a higher prevalence of hrHPV infection than did EBV-negative women (52% vs. 24%; HIV-adjusted PR [95% confidence interval], 1.8 [1.3-2.6]). Epstein-Barr virus-positive women had a higher prevalence than did EBV-negative women of high-grade precancer (15% vs. 2%) and abnormal cytology (37% vs. 15%), although HIV- and hrHPV-adjusted associations were not significant (high-grade precancer: PR, 2.0 [0.7-5.9]; abnormal cytology: PR, 1.4 [0.9-2.2]). In prospective analyses, a marginal association was observed between baseline EBV detection and delayed hrHPV clearance. Conclusions Our data support a possible role for EBV as a high-risk marker or cofactor for HPV-mediated cervical cancer development
Galaxy And Mass Assembly (GAMA): testing galaxy formation models through the most massive galaxies in the Universe
We have analysed the growth of Brightest Group Galaxies and Brightest Cluster Galaxies (BGGs/BCGs) over the last 3 billion years using a large sample of 883 galaxies from the Galaxy And Mass Assembly survey. By comparing the stellar mass of BGGs and BCGs in groups and clusters of similar dynamical masses, we find no significant growth between redshift z = 0.27 and 0.09. We also examine the number of BGGs/BCGs that have line emission, finding that approximately 65 per cent of BGGs/BCGs show Hα in emission. From the galaxies where the necessary spectroscopic lines were accurately recovered (54 per cent of the sample), we find that half of this (i.e. 27 per cent of the sample) harbour ongoing star formation with rates up to 10 M⊙ yr−1, and the other half (i.e. 27 per cent of the sample) have an active nucleus (AGN) at the centre. BGGs are more likely to have ongoing star formation, while BCGs show a higher fraction of AGN activity. By examining the position of the BGGs/BCGs with respect to their host dark matter halo, we find that around 13 per cent of them do not lie at the centre of the dark matter halo. This could be an indicator of recent cluster–cluster mergers. We conclude that BGGs and BCGs acquired their stellar mass rapidly at higher redshifts as predicted by semi-analytic models, mildly slowing down at low redshifts
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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