913 research outputs found
Condensation of Hard Spheres Under Gravity: Exact Results in One Dimension
We present exact results for the density profile of the one dimensional array
of N hard spheres of diameter D and mass m under gravity g. For a strictly one
dimensional system, the liquid-solid transition occurs at zero temperature,
because the close-pakced density, , is one. However, if we relax this
condition slightly such that , we find a series of critical
temperatures T_c^i=mgD(N+1-i)/\mu_o with \mu_o=const, at which the i-th
particle undergoes the liquid-solid transition. The functional form of the
onset temperature, T_c^1=mgDN/\mu_o, is consistent with the previous result
[Physica A 271, 192 (1999)] obtained by the Enskog equation. We also show that
the increase in the center of mass is linear in T before the transition, but it
becomes quadratic in T after the transition because of the formation of solid
near the bottom
Dynamics of Flux Tubes in Large N Gauge Theories
The gluonic field created by a static quark anti-quark pair is described via
the AdS/CFT correspondence by a string connecting the pair which is located on
the boundary of AdS. Thus the gluonic field in a strongly coupled large N CFT
has a stringy spectrum of excitations. We trace the stability of these
excitations to a combination of large N suppressions and energy conservation.
Comparison of the physics of the N=infinity flux tube in the {\cal N}=4 SYM
theory at weak and strong coupling shows that the excitations are present only
above a certain critical coupling. The density of states of a highly excited
string with a fold reaching towards the horizon of AdS is in exact agreement at
strong coupling with that of the near-threshold states found in a ladder
diagram model of the weak-strong coupling transition. We also study large
distance correlations of local operators with a Wilson loop, and show that the
fall off at weak coupling and N=infinity (i.e. strictly planar diagrams)
matches the strong coupling predictions given by the AdS/CFT correspondence,
rather than those of a weakly coupled U(1) gauge theory.Comment: 22 pages, 4 figures; v2: clarifications in section 5, 1 reference
added; v3: the final version (minor changes, 1 more reference added
B(d,s)-anti-B(d,s) mixing and Lepton Flavour Violation in SUSY GUTs: impact of the first measurements of phi(s)
In this work we re-examine the correlation between B(d,s)-anti-B(d,s) mixing
and Lepton Flavour Violation in the light of recent experimental measurements
in the system. We perform a generic SUSY analysis of the allowed down
squark mass insertion parameter space. In the SUSY GUT scenario this parameter
space is then used to make predictions for LFV branching ratios. We find that
the recent measurement for the CP phase excludes the lowest rates for
tau --> mu + gamma and provides a lower bound of ~ 3E-9 for tan beta = 10.
Future experimental improvements in the bound on tau --> mu + gamma and the
measurement of phi(s) will constitute a strong test of the SUSY GUT scenario.Comment: 8 pages, 7 jpeg figures using pdflatex. Version published in Nuclear
Physics
A cluster theory for a Janus fluid
Recent Monte Carlo simulations on the Kern and Frenkel model of a Janus fluid
have revealed that in the vapour phase there is the formation of preferred
clusters made up of a well-defined number of particles: the micelles and the
vesicles. A cluster theory is developed to approximate the exact clustering
properties stemming from the simulations. It is shown that the theory is able
to reproduce the micellisation phenomenon.Comment: 27 pages, 8 figures, 6 table
Liquid-Solid Transition of Hard Spheres Under Gravity
We investigate the liquid-solid transition of two dimensional hard spheres in
the presence of gravity. We determine the transition temperature and the
fraction of particles in the solid regime as a function of temperature via
Even-Driven molecular dynamics simulations and compare them with the
theoretical predictions. We then examine the configurational statistics of a
vibrating bed from the view point of the liquid-solid transition by explicitly
determining the transition temperature and the effective temperature, T, of the
bed, and present a relation between T and the vibration strength.Comment: 14 total pages, 4 figure
Phylogenomics using low-depth whole genome sequencing: a case study with the olive tribe
Species trees have traditionally been inferred from a few selected markers, and genome-wide investigations remain largely restricted to model organisms or small groups of species for which sampling of fresh material is available, leaving out most of the existing and historic species diversity. The genomes of an increasing number of species, including specimens extracted from natural history collections, are being sequenced at low depth. While these datasets are widely used to analyse organelle genomes, the nuclear fraction is generally ignored. Here we evaluate different reference-based methods to infer phylogenies of large taxonomic groups from such datasets. Using the example of the Oleeae tribe, a worldwide-distributed group, we build phylogenies based on single-nucleotide polymorphisms (SNPs) obtained using two reference genomes (the olive and ash trees). The inferred phylogenies are overall congruent, yet present differences that might reflect the effect of the distance to the reference on the amount of missing data. To limit this issue, the genome complexity was reduced by using pairs of orthologous coding sequences as the reference, thus allowing combining SNPs obtained using two distinct references. Concatenated and coalescence trees based on these combined SNPs suggest events of incomplete lineage sorting and/or hybridization during the diversification of this large phylogenetic group. Our results show that genome-wide phylogenetic trees can be inferred from low-depth sequence datasets for eukaryote groups with complex genomes, and histories of reticulate evolution. This opens new avenues for large-scale phylogenomics and biogeographic analyses covering both the extant and historic diversity stored in museum collections
Opportunities for selective reporting of harms in randomized clinical trials: Selection criteria for non-systematic adverse events
Background: Adverse events (AEs) in clinical trials may be reported in multiple sources. Different methods for reporting adverse events across trials or across sources for a single trial may produce inconsistent information about the adverse events associated with interventions. Methods: We compared the methods authors use to decide which AEs to include in a particular source (i.e., "selection criteria"), including the number of different types of AEs reported (i.e., rather than the number of events). We compared sources (e.g., journal articles, clinical study reports (CSRs)) of trials for two drug-indications - gabapentin for neuropathic pain and quetiapine for bipolar depression. Electronic searches were completed in 2015. We identified selection criteria and assessed how criteria affected AE reporting. Results: We identified 21 gabapentin and 7 quetiapine trials. We found 6 gabapentin CSRs and 2 quetiapine CSRs, all written by drug manufacturers. All CSRs reported all AEs without applying selection criteria; by comparison, no other source reported all AEs, and 15/68 (22%) gabapentin sources and 19/48 (40%) quetiapine sources reported using selection criteria. Selection criteria greatly affected the number of AEs reported. For example, 67/316 (21%) AEs in one quetiapine trial met the criterion "occurring in ≥2% of participants in any treatment group," while only 5/316 (2%) AEs met the criterion "occurring in ≥10% of quetiapine-treated patients and twice as frequent in the quetiapine group as the placebo group." Conclusions: Selection criteria for reporting AEs vary across trials and across sources for individual trials. If investigators do not pre-specify selection criteria, they might "cherry-pick" AEs based on results. Even if investigators pre-specify selection criteria, selective reporting will produce biased meta-analyses and clinical practice guidelines. Data about all AEs identified in clinical trials should be publicly available; however, sharing data will not solve all the problems identified in this study
Universality and the magnetic catalysis of chiral symmetry breaking
The hypothesis that the magnetic catalysis of chiral symmetry breaking is due
to interactions of massless fermions in their lowest Landau level is examined
in the context of chirally symmetric models with short ranged interactions. It
is argued that, when the magnetic field is sufficiently large, even an
infinitesimal attractive interaction in the appropriate channel will break
chiral symmetry.Comment: 24 pages, 6 figures, REVTeX. The final version with minor
corrections. To appear in Phys Rev D60 (1999
Electrochemical capacitance of a leaky nano-capacitor
We report a detailed theoretical investigation on electrochemical capacitance
of a nanoscale capacitor where there is a DC coupling between the two
conductors. For this ``leaky'' quantum capacitor, we have derived general
analytic expressions of the linear and second order nonlinear electrochemical
capacitance within a first principles quantum theory in the discrete potential
approximation. Linear and nonlinear capacitance coefficients are also derived
in a self-consistent manner without the latter approximation and the
self-consistent analysis is suitable for numerical calculations. At linear
order, the full quantum formula improves the semiclassical analysis in the
tunneling regime. At nonlinear order which has not been studied before for
leaky capacitors, the nonlinear capacitance and nonlinear nonequilibrium charge
show interesting behavior. Our theory allows the investigation of crossover of
capacitance from a full quantum to classical regimes as the distance between
the two conductors is changed
Bose-Einstein condensation in multilayers
The critical BEC temperature of a non interacting boson gas in a
layered structure like those of cuprate superconductors is shown to have a
minimum , at a characteristic separation between planes . It is
shown that for , increases monotonically back up to the ideal
Bose gas suggesting that a reduction in the separation between planes,
as happens when one increases the pressure in a cuprate, leads to an increase
in the critical temperature. For finite plane separation and penetrability the
specific heat as a function of temperature shows two novel crests connected by
a ridge in addition to the well-known BEC peak at associated with the
3D behavior of the gas. For completely impenetrable planes the model reduces to
many disconnected infinite slabs for which just one hump survives becoming a
peak only when the slab widths are infinite.Comment: Four pages, four figure
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