571 research outputs found
The Effect of Large Amplitude Fluctuations in the Ginzburg-Landau Phase Transition
The lattice Ginzburg-Landau model in d=3 and d=2 is simulated, for different
values of the coherence length in units of the lattice spacing , using
a Monte Carlo method. The energy, specific heat, vortex density , helicity
modulus and mean square amplitude are measured to map the phase
diagram on the plane . When amplitude fluctuations, controlled by the
parameter , become large () a proliferation of vortex
excitations occurs changing the phase transition from continuous to first
order.Comment: 4 pages, 5 postscript (eps) figure
Ultraviolet Fixed Points in Gauge and SUSY Field Theories in Extra Dimensions
We consider gauge field theories in following the Wilson RG approach
and show that they possess the ultraviolet fixed points where the gauge
coupling is dimensionless in any space-time dimension. At the fixed point the
anomalous dimensions of the field and vertex operators are known exactly. These
fixed points are nonperturbative and correspond to conformal invariant
theories. The same phenomenon also happens in supersymmetric theories with the
Yukawa type interactions.Comment: LaTeX, 10pp. v2: Comments and references adde
From constructive field theory to fractional stochastic calculus. (II) Constructive proof of convergence for the L\'evy area of fractional Brownian motion with Hurst index
{Let be a -dimensional fractional Brownian motion
with Hurst index , or more generally a Gaussian process whose paths
have the same local regularity. Defining properly iterated integrals of is
a difficult task because of the low H\"older regularity index of its paths. Yet
rough path theory shows it is the key to the construction of a stochastic
calculus with respect to , or to solving differential equations driven by
.
We intend to show in a series of papers how to desingularize iterated
integrals by a weak, singular non-Gaussian perturbation of the Gaussian measure
defined by a limit in law procedure. Convergence is proved by using "standard"
tools of constructive field theory, in particular cluster expansions and
renormalization. These powerful tools allow optimal estimates, and call for an
extension of Gaussian tools such as for instance the Malliavin calculus.
After a first introductory paper \cite{MagUnt1}, this one concentrates on the
details of the constructive proof of convergence for second-order iterated
integrals, also known as L\'evy area
Physical Model for Plaque Action in the Tooth-Plaque-Saliva System
A physical model describing the interrelationships of demineralization, remineralization, plaque thickness, glucose levels, and plaque enzymatic activity was presented. Selection of constants and variations of the parameters were kept in the range of possible in vivo situations. The results of calculations were discussed and correlated with the results of in vivo studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66483/2/10.1177_00220345700490013001.pd
An exploratory study into the role and interplay of intrinsic and extrinsic cues in Australian consumers’ evaluations of fish.
This study explores the role and interplay of intrinsic and extrinsic cues when evaluating fish quality and in shaping consumers' attitudes toward fish consumption. A sensory analysis of nine different fish including five variants of barramundi was conducted to determine how consumers evaluated the fish on intrinsic cues. Focus groups were then conducted to explore the impact of extrinsic cues on attitudes and purchase intentions. While the sensory analysis revealed distinct differences between barramundi variants on intrinsic cues (notably taste), the focus groups revealed that, as a brand, barramundi is perceived much more favourably and consistently. Consumers used extrinsic cues, particularly country of origin, as surrogate indicators of quality. Aquaculture producers need to ensure intrinsic product quality and consistency, as while consumers use the extrinsic cue of "Australian grown" as a surrogate indicator of quality, as their familiarity and confidence with seafood grows, this overreliance on extrinsic cues may diminish
The relationship between biological and psychosocial risk factors and resting‐state functional connectivity in 2‐monthold Bangladeshi infants: A feasibility and pilot study
Childhood poverty has been associated with structural and functional alterations in the developing brain. However, poverty does not alter brain development directly, but acts through associated biological or psychosocial risk factors (e.g. malnutrition, family conflict). Yet few studies have investigated risk factors in the context of infant neurodevelopment, and none have done so in low‐resource settings such as Bangladesh, where children are exposed to multiple, severe biological and psychosocial hazards. In this feasibility and pilot study, usable resting‐state fMRI data were acquired in infants from extremely poor (n = 16) and (relatively) more affluent (n = 16) families in Dhaka, Bangladesh. Whole‐brain intrinsic functional connectivity (iFC) was estimated using bilateral seeds in the amygdala, where iFC has shown susceptibility to early life stress, and in sensory areas, which have exhibited less susceptibility to early life hazards. Biological and psychosocial risk factors were examined for associations with iFC. Three resting‐state networks were identified in within‐group brain maps: medial temporal/striatal, visual, and auditory networks. Infants from extremely poor families compared with those from more affluent families exhibited greater (i.e. less negative) iFC in precuneus for amygdala seeds; however, no group differences in iFC were observed for sensory area seeds. Height‐for‐age, a proxy for malnutrition/infection, was not associated with amygdala/precuneus iFC, whereas prenatal family conflict was positively correlated. Findings suggest that it is feasible to conduct infant fMRI studies in low‐resource settings. Challenges and practical steps for successful implementations are discussed
Nature of the quantum phase transitions in the two-dimensional hardcore boson model
We use two Quantum Monte Carlo algorithms to map out the phase diagram of the
two-dimensional hardcore boson Hubbard model with near () and next near
() neighbor repulsion. At half filling we find three phases: Superfluid
(SF), checkerboard solid and striped solid depending on the relative values of
, and the kinetic energy. Doping away from half filling, the
checkerboard solid undergoes phase separation: The superfluid and solid phases
co-exist but not as a single thermodynamic phase. As a function of doping, the
transition from the checkerboard solid is therefore first order. In contrast,
doping the striped solid away from half filling instead produces a striped
supersolid phase: Co-existence of density order with superfluidity as a single
phase. One surprising result is that the entire line of transitions between the
SF and checkerboard solid phases at half filling appears to exhibit dynamical
O(3) symmetry restoration. The transitions appear to be in the same
universality class as the special Heisenberg point even though this symmetry is
explicitly broken by the interaction.Comment: 10 pages, 14 eps figures, include
Community structures of actively growing bacteria shift along a north-south transect in the western North Pacific
Bacterial community structures and their activities in the ocean are tightly coupled with organic matter fluxes and thus control ocean biogeochemical cycles. Bromodeoxyuridine (BrdU), halogenated nucleoside and thymidine analogue, has been recently used to monitor actively growing bacteria (AGB) in natural environments. We labelled DNA of proliferating cells in seawater bacterial assemblages with BrdU and determined community structures of the bacteria that were possible key species in mediating biochemical reactions in the ocean. Surface seawater samples were collected along a north-south transect in the North Pacific in October 2003 and subjected to BrdU magnetic beads immunocapture and PCR-DGGE (BUMP-DGGE) analysis. Change of BrdU-incorporated community structures reflected the change of water masses along a north-south transect from subarctic to subtropical gyres in the North Pacific. We identified 25 bands referred to AGB as BrdU-incorporated phylotypes, belonging to Alphaproteobacteria (5 bands), Betaproteobacteria (1 band), Gammaproteobacteria (4 bands), Cytophaga-Flavobacterium-Bacteroides (CFB) group bacteria (5 bands), Gram-positive bacteria (6 bands), and Cyanobacteria (4 bands). BrdU-incorporated phylotypes belonging to Vibrionales, Alteromonadales and Gram-positive bacteria appeared only at sampling stations in a subtropical gyre, while those belonging to Roseobacter-related bacteria and CFB group bacteria appeared at the stations in both subarctic and subtropical gyres. Our result revealed phylogenetic affiliation of AGB and their dynamic change along with north-south environmental gradients in open oceans. Different species of AGB utilize different amount and kinds of substrates, which can affect the change of organic matter fluxes along transect
Numerical Portrait of a Relativistic Thin Film BCS Superfluid
We present results of numerical simulations of the 2+1d Nambu - Jona-Lasinio
model with a non-zero baryon chemical potential mu including the effects of a
diquark source term. Diquark condensates, susceptibilities and masses are
measured as functions of source strength j. The results suggest that diquark
condensation does not take place in the high density phase mu>mu_c, but rather
that the condensate scales non-analytically with j implying a line of critical
points and long range phase coherence. Analogies are drawn with the low
temperature phase of the 2d XY model. The spectrum of the spin-1/2 sector is
also studied yielding the quasiparticle dispersion relation. There is no
evidence for a non-zero gap; rather the results are characteristic of a normal
Fermi liquid with Fermi velocity less than that of light. We conclude that the
high density phase of the model describes a relativistic gapless thin film BCS
superfluid.Comment: 37 pages, 16 figure
Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates
We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor,
using high precision torsional oscillator and DC calorimetry techniques. Our
investigation focused on the onset of superfluidity at low temperatures as the
4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel
system were used to determine the superfluid density of films with transition
temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor
system probed the excitation spectrum of both non-superfluid and superfluid
films for temperatures down to 10 mK. Both sets of measurements suggest that
the critical coverage for the onset of superfluidity corresponds to a mobility
edge in the chemical potential, so that the onset transition is the bosonic
analog of a superconductor-insulator transition. The superfluid density
measurements, however, are not in agreement with the scaling theory of an onset
transition from a gapless, Bose glass phase to a superfluid. The heat capacity
measurements show that the non-superfluid phase is better characterized as an
insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript
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