571 research outputs found
Spin-dynamics simulations of the triangular antiferromagnetic XY model
Using Monte Carlo and spin-dynamics methods, we have investigated the dynamic
behavior of the classical, antiferromagnetic XY model on a triangular lattice
with linear sizes . The temporal evolutions of spin configurations
were obtained by solving numerically the coupled equations of motion for each
spin using fourth-order Suzuki-Trotter decompositions of exponential operators.
From space- and time-displaced spin-spin correlation functions and their
space-time Fourier transforms we obtained the dynamic structure factor for momentum and frequency . Below
(Kosterlitz-Thouless transition), both the in-plane () and the
out-of-plane () components of exhibit very strong
and sharp spin-wave peaks. Well above , and
apparently display a central peak, and spin-wave signatures are still seen in
. In addition, we also observed an almost dispersionless domain-wall
peak at high below (Ising transition), where long-range order
appears in the staggered chirality. Above , the domain-wall peak
disappears for all . The lineshape of these peaks is captured reasonably
well by a Lorentzian form. Using a dynamic finite-size scaling theory, we
determined the dynamic critical exponent = 1.002(3). We found that our
results demonstrate the consistency of the dynamic finite-size scaling theory
for the characteristic frequeny and the dynamic structure factor
itself.Comment: 8 pages, RevTex, 10 figures, submitted to PR
The Muonium Atom as a Probe of Physics beyond the Standard Model
The observed interactions between particles are not fully explained in the
successful theoretical description of the standard model to date. Due to the
close confinement of the bound state muonium () can be used as
an ideal probe of quantum electrodynamics and weak interaction and also for a
search for additional interactions between leptons. Of special interest is the
lepton number violating process of sponteanous conversion of muonium to
antimuonium.Comment: 15 pages,6 figure
Gene expression differences in relation to age and social environment in queen and worker bumble bees
Eusocial insects provide special insights into the genetic pathways influencing aging because of their long-lived queens and flexible aging schedules. Using qRT-PCR in the primitively eusocial bumble bee Bombus terrestris (Linnaeus), we investigated expression levels of four candidate genes associated with taxonomically widespread age-related pathways (coenzyme Q biosynthesis protein 7, COQ7; DNA methyltransferase 3, Dnmt3; foraging, for; and vitellogenin, vg). In Experiment 1, we tested how expression changes with queen relative age and productivity. We found a significant age-related increase in COQ7 expression in queen ovary. In brain, all four genes showed higher expression with increasing female (queen plus worker) production, with this relationship strengthening as queen age increased, suggesting a link with the positive association of fecundity and longevity found in eusocial insect queens. In Experiment 2, we tested effects of relative age and social environment (worker removal) in foundress queens and effects of age and reproductive status in workers. In this experiment, workerless queens showed significantly higher for expression in brain, as predicted if downregulation of for is associated with the cessation of foraging by foundress queens following worker emergence. Workers showed a significant age-related increase in Dnmt3 expression in fat body, suggesting a novel association between aging and methylation in B. terrestris. Ovary activation was associated with significantly higher vg expression in fat body and, in younger workers, in brain, consistent with vitellogenin's ancestral role in regulating egg production. Overall, our findings reveal a mixture of novel and conserved features in age-related genetic pathways under primitive eusociality
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
Measurement of the Ds lifetime
We report precise measurement of the Ds meson lifetime. The data were taken
by the SELEX experiment (E781) spectrometer using 600 GeV/c Sigma-, pi- and p
beams. The measurement has been done using 918 reconstructed Ds. The lifetime
of the Ds is measured to be 472.5 +- 17.2 +- 6.6 fs, using K*(892)0K+- and phi
pi+- decay modes. The lifetime ratio of Ds to D0 is 1.145+-0.049.Comment: 5 pages, 2 figures submitted to Phys. Lett.
Confirmation of the Double Charm Baryon Xi_cc+ via its Decay to p D+ K-
We observes a signal for the double charm baryon Xi_cc+ in the charged decay
mode Xi_cc+ -> p D+ K- to complement the previously reported decay Xi_cc+ ->
Lambda_c K- pi+ in data from SELEX, the charm hadro-production experiment
(E781) at Fermilab. In this new decay mode we observe an excess of 5.62 events
over an expected background estimated by event mixing to be 1.38+/-0.13 events.
The Poisson probability that a background fluctuation can produce the apparent
signal is less than 6.4E-4. The observed mass of this state is
(3518+/-3)MeV/c^2, consistent with the published result. Averaging the two
results gives a mass of (3518.7+/-1.7)MeV/c^2. The observation of this new weak
decay mode confirms the previous SELEX suggestion that this state is a double
charm baryon. The relative branching ratio Gamma(Xi_cc+ -> pD+K-)/Gamma(Xi_cc+
-> Lambda_c K- pi+) = 0.36+/-0.21.Comment: 11 pages, 6 included eps figures. v2 includes improved statistical
method to determine significance of observation. Submitted to PL
Comparison of midterm results of endovascular aneurysm repair for ruptured and elective abdominal aortic aneurysms
Objective: Endovascular aneurysm repair (EVAR) became an increasingly preferred modality for abdominal aortic aneurysm (AAA) repair both in elective AAA repair (el-EVAR) and EVAR of a ruptured AAA (r-EVAR) setting. Ruptured AAAs usually have more hostile anatomies and less time for planning. Consequently, more complications may arise after r-EVAR. The purpose of this study was to compare mi-term outcomes between r-EVAR and el-EVAR. Methods: A retrospective cohort analysis of patients undergoing EVAR from 2000 to 2015 at a tertiary institution was performed. Patients with previous aortic surgery, nonatherosclerotic AAA and isolated iliac aneurysms were excluded. In-hospital casualties or patients who were intraoperatively converted to open repair were also excluded. For the midterm outcome analysis, only patients with at least two postoperative examinations (a 30-day computed tomography scan and a second postoperative examination performed 6 months or later) were considered. The primary end point was freedom from aneurysm-related complications (a composite of type I or III endoleak, aneurysm sac growth, migration of more than 5 mm, device integrity failure, AAA-related death, late postimplant rupture, or AAA-related secondary intervention). Freedom from secondary interventions, neck-related events (defined as a composite of type IA endoleak, migration of more than 5 mm, or preemptive neck-related secondary intervention) and late survival were secondary end points. The impact of device instructions for use (IFU) compliance on neck events was also assessed. Results: The study included 565 patients (65 r-EVAR and 500 el-EVAR). Eighty-two patients were treated outside proximal neck IFU, 13 in the r-EVAR group (21.3%) and 69 (14.5%) in the el-EVAR (P =.16). During the index hospitalization, there were more complications (12.3% vs 3.2%; P =.001) and reinterventions (12.3% vs 2.8%; P <.001) in the r-EVAR group. After discharge, median clinical follow-up time was 4.3 years (interquartile range, 2.1-7.0 years) without differences between both groups. Five-year freedom from AAA-related complications was 53.9% in the r-EVAR group and 65.4% in the el-EVAR (P =.21). In multivariable analysis the r-EVAR group was not at increased risk for late complications (hazard ratio [HR], 0.94; 95% confidence interval [CI], 0.54-1.61; P =.81). Five-year freedom from neck-related events was 74% in r-EVAR and 82% in the el-EVAR group (P =.345). Patients treated outside neck IFU were at greater risk for neck-related events both in r-EVAR (HR, 6.5; 95% CI, 1.8-22.9; P =.004) and el-EVAR group (HR, 2.6; 95% CI, 1.5-4.5; P <.001). Freedom from secondary interventions at 5 years was 63.0% for r-EVAR and 76.9% for el-EVAR (P =.16). Survival at 5 years was 68.8% in the r-EVAR group and 73.3% in the el-EVAR group (P =.30). Conclusions: Durable and sustainable midterm outcomes were found for both r-EVAR and el-EVAR patients who survived the postoperative period. Patients treated out
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 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 fbâ1 of protonâproton 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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