2,004 research outputs found
About a possible 3rd order phase transition at T=0 in 4D gluodynamics
We revisit the question of the convergence of lattice perturbation theory for
a pure SU(3) lattice gauge theory in 4 dimensions. Using a series for the
average plaquette up to order 10 in the weak coupling parameter beta^{-1}, we
show that the analysis of the extrapolated ratio and the extrapolated slope
suggests the possibility of a non-analytical power behavior of the form
(1/\beta -1/5.7(1))^{1.0(1)}, in agreement with another analysis based on the
same asumption. This would imply that the third derivative of the free energy
density diverges near beta =5.7. We show that the peak in the third derivative
of the free energy present on 4^4 lattices disappears if the size of the
lattice is increased isotropically up to a 10^4 lattice. On the other hand, on
4 x L^3 lattices, a jump in the third derivative persists when L increases. Its
location coincides with the onset of a non-zero average for the Polyakov loop.
We show that the apparent contradiction at zero temperature can be resolved by
moving the singularity in the complex 1/\beta plane. If the imaginary part of
the location of the singularity Gamma is within the range 0.001< Gamma < 0.01,
it is possible to limit the second derivative of P within an acceptable range
without affecting drastically the behavior of the perturbative coefficients. We
discuss the possibility of checking the existence of these complex
singularities by using the strong coupling expansion or calculating the zeroes
of the partition function.Comment: 7 pages, 9 figures, contains a resolution of the main paradox and a
discussion of possible check
Critical Percolation in High Dimensions
We present Monte Carlo estimates for site and bond percolation thresholds in
simple hypercubic lattices with 4 to 13 dimensions. For d<6 they are
preliminary, for d >= 6 they are between 20 to 10^4 times more precise than the
best previous estimates. This was achieved by three ingredients: (i) simple and
fast hashing which allowed us to simulate clusters of millions of sites on
computers with less than 500 MB memory; (ii) a histogram method which allowed
us to obtain information for several p values from a single simulation; and
(iii) a new variance reduction technique which is especially efficient at high
dimensions where it reduces error bars by a factor up to approximately 30 and
more. Based on these data we propose a new scaling law for finite cluster size
corrections.Comment: 5 pages including figures, RevTe
Universal Formulae for Percolation Thresholds
A power law is postulated for both site and bond percolation thresholds. The
formula writes , where is the space
dimension and the coordination number. All thresholds up to are found to belong to only three universality classes. For first two
classes for site dilution while for bond dilution. The last one
associated to high dimensions is characterized by for both sites and
bonds. Classes are defined by a set of value for . Deviations
from available numerical estimates at are within and
for high dimensional hypercubic expansions at . The
formula is found to be also valid for Ising critical temperatures.Comment: 11 pages, latex, 3 figures not include
Critical Exponent for the Density of Percolating Flux
This paper is a study of some of the critical properties of a simple model
for flux. The model is motivated by gauge theory and is equivalent to the Ising
model in three dimensions. The phase with condensed flux is studied. This is
the ordered phase of the Ising model and the high temperature, deconfined phase
of the gauge theory. The flux picture will be used in this phase. Near the
transition, the density is low enough so that flux variables remain useful.
There is a finite density of finite flux clusters on both sides of the phase
transition. In the deconfined phase, there is also an infinite, percolating
network of flux with a density that vanishes as . On
both sides of the critical point, the nonanalyticity in the total flux density
is characterized by the exponent . The main result of this paper is
a calculation of the critical exponent for the percolating network. The
exponent for the density of the percolating cluster is . The specific heat exponent and the crossover exponent
can be computed in the -expansion. Since , the variation in the separate densities is much more rapid than
that of the total. Flux is moving from the infinite cluster to the finite
clusters much more rapidly than the total density is decreasing.Comment: 20 pages, no figures, Latex/Revtex 3, UCD-93-2
Counting Lattice Animals in High Dimensions
We present an implementation of Redelemeier's algorithm for the enumeration
of lattice animals in high dimensional lattices. The implementation is lean and
fast enough to allow us to extend the existing tables of animal counts,
perimeter polynomials and series expansion coefficients in -dimensional
hypercubic lattices for . From the data we compute formulas
for perimeter polynomials for lattice animals of size in arbitrary
dimension . When amended by combinatorial arguments, the new data suffices
to yield explicit formulas for the number of lattice animals of size
and arbitrary . We also use the enumeration data to compute numerical
estimates for growth rates and exponents in high dimensions that agree very
well with Monte Carlo simulations and recent predictions from field theory.Comment: 18 pages, 7 figures, 6 tables; journal versio
Site percolation and random walks on d-dimensional Kagome lattices
The site percolation problem is studied on d-dimensional generalisations of
the Kagome' lattice. These lattices are isotropic and have the same
coordination number q as the hyper-cubic lattices in d dimensions, namely q=2d.
The site percolation thresholds are calculated numerically for d= 3, 4, 5, and
6. The scaling of these thresholds as a function of dimension d, or
alternatively q, is different than for hypercubic lattices: p_c ~ 2/q instead
of p_c ~ 1/(q-1). The latter is the Bethe approximation, which is usually
assumed to hold for all lattices in high dimensions. A series expansion is
calculated, in order to understand the different behaviour of the Kagome'
lattice. The return probability of a random walker on these lattices is also
shown to scale as 2/q. For bond percolation on d-dimensional diamond lattices
these results imply p_c ~ 1/(q-1).Comment: 11 pages, LaTeX, 8 figures (EPS format), submitted to J. Phys.
Girls’ Game-Songs and Hip-Hop: Music Between the Sexes
This article explores connections between girls’ musical game-songs and commercial songs recorded by male artists over several decades in United States. Basing on analysis of game songs’ and interviews of African American women (collected during fieldworks conducted from 1994 to 2002), it describes how black girls, through their dance and singing games, experience a musical socialization and inhabit an African American musical aesthetics and a gendered blackness. Kyra Gaunt highlights the oral and kinetic veiled intertextuality existing between girls' musical games and black popular songs, to question the role of gender in the social construction of popular musical taste. Those insights into the social and distinctly gendered construction of taste in black popular songs (Rhythm n blues as well as hip-hop) shows how girls' musical play, in handclapping games, cheers, and double-dutch, are a local formation of a "popular" culture that is in constant dialogue with the mass-mediation of black male performances, engendering and sustaining certain musical and social relationships between the sexes, and between children and adults in African American communities.Cet article explore les connexions existant entre les jeux musicaux des petites filles et les chansons populaires enregistrées par des artistes masculins aux Etats-Unis durant les dernières décennies. En se basant sur l’analyse de chansons des petites filles et sur des interviews collectées auprès de femmes afro-américaines durant des enquêtes de terrain menées entre 1994 et 2002, il décrit comment les petites filles noires expérimentent, au travers des danses et des chansons contenues dans leurs jeux, une forme de socialisation musicale et d’apprentissage d’une identité noire de genre. Kyra D. Gaunt met en lumière l’intertextualité orale et kinétique existant de façon cachée entre les jeux des petites filles et les musiques populaires afro-américaines, pour interroger la place du genre dans la construction sociale du goût musical. Ces regards portés aux sources de la construction sociale du goût et de la division de genre dans les chansons populaires afro-américaines - qu’il s’agisse du Rythm’n’ blues ou du hip-hop -, démontrent comment les jeux des petites filles, par les claquements de main, les exclamations, les jargons auxquels ils donnent lieu, contribuent à la formation locale d’une culture « populaire ». En constant dialogue avec les performances d’artistes masculins médiatisés par l’industrie musicale, ils engendrent et renforcent dans les communautés afro-américaines certaines relations sociales et musicales se tissant entre les sexes, et entre les enfants et les adultes
Trypanosoma cruzi IIc: phylogenetic and phylogeographic insights from sequence and microsatellite analysis and potential impact on emergent Chagas disease.
Trypanosoma cruzi, the etiological agent of Chagas disease, is highly genetically diverse. Numerous lines of evidence point to the existence of six stable genetic lineages or DTUs: TcI, TcIIa, TcIIb, TcIIc, TcIId, and TcIIe. Molecular dating suggests that T. cruzi is likely to have been an endemic infection of neotropical mammalian fauna for many millions of years. Here we have applied a panel of 49 polymorphic microsatellite markers developed from the online T. cruzi genome to document genetic diversity among 53 isolates belonging to TcIIc, a lineage so far recorded almost exclusively in silvatic transmission cycles but increasingly a potential source of human infection. These data are complemented by parallel analysis of sequence variation in a fragment of the glucose-6-phosphate isomerase gene. New isolates confirm that TcIIc is associated with terrestrial transmission cycles and armadillo reservoir hosts, and demonstrate that TcIIc is far more widespread than previously thought, with a distribution at least from Western Venezuela to the Argentine Chaco. We show that TcIIc is truly a discrete T. cruzi lineage, that it could have an ancient origin and that diversity occurs within the terrestrial niche independently of the host species. We also show that spatial structure among TcIIc isolates from its principal host, the armadillo Dasypus novemcinctus, is greater than that among TcI from Didelphis spp. opossums and link this observation to differences in ecology of their respective niches. Homozygosity in TcIIc populations and some linkage indices indicate the possibility of recombination but cannot yet be effectively discriminated from a high genome-wide frequency of gene conversion. Finally, we suggest that the derived TcIIc population genetic data have a vital role in determining the origin of the epidemiologically important hybrid lineages TcIId and TcIIe
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