6,063 research outputs found
Study of the 2-d CP(N-1) models at \theta=0 and \pi
We present numerical results for 2-d CP(N-1) models at \theta=0 and \pi
obtained in the D-theory formulation. In this formulation we construct an
efficient cluster algorithm and we show numerical evidence for a first order
transition for CP(N-1\geq 2) models at \theta = \pi. By a finite size scaling
analysis, we also discuss the equivalence in the continuum limit of the
D-theory formulation of the 2-d CP(N-1) models and the usual lattice
definition.Comment: 3 pages, 2 figures. Talk presented at Lattice2004(spin), Fermilab,
June 21-26, 200
Meron-Cluster Simulation of a Chiral Phase Transition with Staggered Fermions
We examine a (3+1)-dimensional model of staggered lattice fermions with a
four-fermion interaction and Z(2) chiral symmetry using the Hamiltonian
formulation. This model cannot be simulated with standard fermion algorithms
because those suffer from a very severe sign problem. We use a new fermion
simulation technique - the meron-cluster algorithm - which solves the sign
problem and leads to high-precision numerical data. We investigate the finite
temperature chiral phase transition and verify that it is in the universality
class of the 3-d Ising model using finite-size scaling.Comment: 21 pages, 6 figure
From Spin Ladders to the 2-d O(3) Model at Non-Zero Density
The numerical simulation of various field theories at non-zero chemical
potential suffers from severe complex action problems. In particular, QCD at
non-zero quark density can presently not be simulated for that reason. A
similar complex action problem arises in the 2-d O(3) model -- a toy model for
QCD. Here we construct the 2-d O(3) model at non-zero density via dimensional
reduction of an antiferromagnetic quantum spin ladder in a magnetic field. The
complex action problem of the 2-d O(3) model manifests itself as a sign problem
of the ladder system. This sign problem is solved completely with a
meron-cluster algorithm.Comment: Based on a talk by U.-J. Wiese, 6 pages, 12 figures, to be published
in computer physics communication
REE Zoning in Allanite Related to Changing Partition Coefficients During Crystallization: Implications for REE Behaviour in an Epidote-Bearing Tonalite
Allanite is present in most samples of the tonalitic Bell Island Pluton, with an average mode near 0.05 wt.%. Allanite occurs as cores in igneous epidote-clinozoisite and exhibits characteristic and consistent zoning patterns. REE-rich cores (All40–70) grade out towards epidote-clinozoisite with REE below electron microprobe detection limits. La, Ce and Pr contents are highest in the REE-rich cores of zoned crystals. Nd and Sm contents both initially increase as total REE decreases and are highest in intermediate zones. Y contents are generally low throughout, but tend to be highest in analyses with All5–20. The zoning behaviour exhibited by the allanite, specifically the rimward increases in Nd, Sm, and Y, cannot be accounted for by simple fractionation and are best explained by increases in allanite/melt partition coefficients (Kd values) for these elements during crystallization. We propose that the variation in Kd values reflects modification of the allanite structure with changing REE content. These modifications are manifested by changes in colour, extinction, and pleochroism within the zoned crystals and include changes in unit-cell volume and dimensions. The changes in Kd values are large enough to result in crossing REE patterns within single allanite crystals. Fractional crystallization of zoned allanite can have noticeable effects on LREE contents and La/Sm (and almost certainly La/Lu) in magmas. In the Bell Island pluton, 80% of La, but \u3c3% of Y is contained in allanite. Although some of the variation in the LREE chemistry of the pluton is attributable to statistical sampling error, much of it appears to reflect petrogenetic processes that controlled LREE abundance and, ultimately, allanite mode. One sample of Bell Island tonalite is depleted in LREE and has low La/Lu and La/Sm. These chemical features can be modelled by fractionation of zoned allanite
Green's Functions from Quantum Cluster Algorithms
We show that cluster algorithms for quantum models have a meaning independent
of the basis chosen to construct them. Using this idea, we propose a new method
for measuring with little effort a whole class of Green's functions, once a
cluster algorithm for the partition function has been constructed. To explain
the idea, we consider the quantum XY model and compute its two point Green's
function in various ways, showing that all of them are equivalent. We also
provide numerical evidence confirming the analytic arguments. Similar
techniques are applicable to other models. In particular, in the recently
constructed quantum link models, the new technique allows us to construct
improved estimators for Wilson loops and may lead to a very precise
determination of the glueball spectrum.Comment: 15 pages, LaTeX, with four figures. Added preprint numbe
Muon spin rotation studies of niobium for superconducting RF applications
In this work we investigate superconducting properties of niobium samples via
application of the muon spin rotation/relaxation (muSR) technique. We employ
for the first time the muSR technique to study samples that are cutout from
large and small grain 1.5 GHz radio frequency (RF) single cell niobium
cavities. The RF test of these cavities was accompanied by full temperature
mapping to characterize the RF losses in each of the samples. Results of the
muSR measurements show that standard cavity surface treatments like mild baking
and buffered chemical polishing (BCP) performed on the studied samples affect
their surface pinning strength. We find an interesting correlation between high
field RF losses and field dependence of the sample magnetic volume fraction
measured via muSR. The muSR line width observed in ZF-muSR measurements matches
the behavior of Nb samples doped with minute amounts of Ta or N impurities. An
upper bound for the upper critical field Hc2 of these cutouts is found.Comment: 20 pages, 14 figure
Association between electronic cigarette use and changes in quit attempts, success of quit attempts, use of smoking cessation pharmacotherapy, and use of stop smoking services in England: time series analysis of population trends
Objectives To estimate how far changes in the prevalence of electronic cigarette (e-cigarette) use in England have been associated with changes in quit success, quit attempts, and use of licensed medication and behavioural support in quit attempts.
Design Time series analysis of population trends.
Participants Participants came from the Smoking Toolkit Study, which involves repeated, cross sectional household surveys of individuals aged 16 years and older in England. Data were aggregated on about 1200 smokers quarterly between 2006 and 2015. Monitoring data were also used from the national behavioural support programme; during the study, 8 029 012 quit dates were set with this programme.
Setting England.
Main outcome measures Prevalence of e-cigarette use in current smokers and during a quit attempt were used to predict quit success. Prevalence of e-cigarette use in current smokers was used to predict rate of quit attempts. Percentage of quit attempts involving e-cigarette use was also used to predict quit attempts involving use of prescription treatments, nicotine replacement therapy (NRT) on prescription and bought over the counter, and use of behavioural support. Analyses involved adjustment for a range of potential confounders.
Results The success rate of quit attempts increased by 0.098% (95% confidence interval 0.064 to 0.132; P<0.001) and 0.058% (0.038 to 0.078; P<0.001) for every 1% increase in the prevalence of e-cigarette use by smokers and e-cigarette use during a recent quit attempt, respectively. There was no clear evidence for an association between e-cigarette use and rate of quit attempts (β 0.025; 95% confidence interval −0.035 to 0.085; P=0.41), use of NRT bought over the counter (β 0.006; −0.088 to 0.077; P=0.89), use of prescription treatment (β −0.070; −0.152 to 0.013; P=0.10), or use of behavioural support (β −0.013; −0.102 to 0.077; P=0.78). A negative association was found between e-cigarette use during a recent quit attempt and use of NRT obtained on prescription (β −0.098; −0.189 to −0.007; P=0.04).
Conclusion Changes in prevalence of e-cigarette use in England have been positively associated with the success rates of quit attempts. No clear association has been found between e-cigarette use and the rate of quit attempts or the use of other quitting aids, except for NRT obtained on prescription, where the association has been negative.
Study registration The analysis plan was preregistered (https://osf.io/fbgj2/)
Is prevalence of e-cigarette and nicotine replacement therapy use among smokers associated with average cigarette consumption in England? A time-series analysis
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