3,504 research outputs found
Kraichnan model of passive scalar advection
A simple model of a passive scalar quantity advected by a Gaussian
non-solenoidal ("compressible") velocity field is considered. Large order
asymptotes of quantum-field expansions are investigated by instanton approach.
The existence of finite convergence radius of the series is proved, a position
and a type of the corresponding singularity of the series in the regularization
parameter are determined. Anomalous exponents of the main contributions to the
structural functions are resummed using new information about the series
convergence and two known orders of the expansion.Comment: 21 page
Behavior of the anomalous correlation function in uniform 2D Bose gas
We investigate the behavior of the anomalous correlation function in two
dimensional Bose gas. In the local case, we find that this quantity has a
finite value in the limit of weak interactions at zero temperature. The effects
of the anomalous density on some thermodynamic quantities are also considered.
These effects can modify in particular the chemical potential, the ground sate
energy, the depletion and the superfluid fraction. Our predictions are in good
agreement with recent analytical and numerical calculations. We show also that
the anomalous density presents a significant importance compared to the
non-condensed one at zero temperature. The single-particle anomalous
correlation function is expressed in two dimensional homogenous Bose gases by
using the density-phase fluctuation. We then confirm that the anomalous average
accompanies in analogous manner the true condensate at zero temperature while
it does not exist at finite temperature.Comment: 15 pages, 3 figure
Sustained Id2 regulation of E proteins is required for terminal differentiation of effector CD8+ T cells.
CD8+ T cells responding to infection differentiate into a heterogeneous population composed of progeny that are short-lived and participate in the immediate, acute response and those that provide long-lasting host protection. Although it is appreciated that distinct functional and phenotypic CD8+ T cell subsets persist, it is unclear whether there is plasticity among subsets and what mechanisms maintain subset-specific differences. Here, we show that continued Id2 regulation of E-protein activity is required to maintain the KLRG1hi CD8+ T cell population after lymphocytic choriomeningitis virus infection. Induced deletion of Id2 phenotypically and transcriptionally transformed the KLRG1hi "terminal" effector/effector-memory CD8+ T cell population into a KLRG1lo memory-like population, promoting a gene-expression program that resembled that of central memory T cells. Our results question the idea that KLRG1hi CD8+ T cells are necessarily terminally programmed and suggest that sustained regulation is required to maintain distinct CD8+ T cell states
Mental Health, Bullying, and Victimization Among Chinese Adolescents
The purpose of this study was to examine if adolescents who experience anxiety or depression have higher levels of reported bullying victimization or perpetration than those who do not. Based on the existing research, we hypothesized that those who experienced moderate or severe depression and anxiety would have higher rates of bullying victimization and perpetration when compared to those who experienced mild or no depression. This study used an observational design, and data were collected from a convenience sample of adolescents in a large regional high school in an Eastern province of China. The final sample included 1481 adolescents aged 14–19 years who provided complete data for each of the study variables. Demographic data were collected through a four-item demographic survey, bullying perpetration and victimization data were collected using subscales from the Illinois Bully Scale, and anxiety and depression were measured using the Chinese version of the General Anxiety Disorder-7 scale and the Patient Health Questionnaire, respectively. Descriptive analyses, correlational analyses, and multivariate analysis of covariance were used to analyze the data. About 7.1% and 15.2% of participants reported moderate-to-severe depression or moderate-to-severe anxiety, respectively. Pairwise comparisons indicated that adolescents with no or mild depression had significantly lower bullying perpetration than those with moderate-to-severe depression, but those with no or mild anxiety had significantly higher perpetration than those with moderate-to-severe anxiety. There was no statistically significant difference in victimization among different anxiety or depression levels alone (all p-values ≥ 0.05). This is among the first studies to examine reported levels of bullying perpetration and victimization among adolescents experiencing anxiety and depression. The findings help to identify adolescents who experience moderate-to-severe levels of depression as an at-risk group for bullying perpetration, who should therefore be a focus of bullying intervention work
Fermionic construction of partition function for multi-matrix models and multi-component TL hierarchy
We use -component fermions to present -fold
integrals as a fermionic expectation value. This yields fermionic
representation for various -matrix models. Links with the -component
KP hierarchy and also with the -component TL hierarchy are discussed. We
show that the set of all (but two) flows of -component TL changes standard
matrix models to new ones.Comment: 16 pages, submitted to a special issue of Theoretical and
Mathematical Physic
Academic Stress, Physical Activity, Sleep, and Mental Health Among Chinese Adolescents
The purpose of this study was to examine the impacts of academic stress on physical activity and sleep, and subsequently their impacts on anxiety and depression. Methods: This cross-sectional study collected data from a convenience sample of 1533 adolescents in an eastern province in China. Surveys were used to collect data on academic stress, anxiety, depression, sleep, physical activity, and demographics. Descriptive statistics, correlation analysis, and path analysis were used to analyze data. Results: The participants reported about 6.77 ± 0.89 h of sleep per day and 1.62 ± 1.79 days of 60 min of physical activity each week. Academic stress was positively correlated with anxiety and depression, which were negatively correlated with physical activity and sleep. The path analysis showed that academic stress directly predicted anxiety (β = 0.54) and depression (β = 0.55), and hours of sleep (β = 0.024) and the number of days of 60 min physical activity (β = 0.014) mediated the relation. Conclusion: The results largely supported our hypotheses and supported the need to lessen academic stress experienced by Chinese adolescents, in effort to enhance mental health indices directly, and by allowing for engagement in health-related behaviors such as physical activity and sleep
Fermionic construction of partition functions for two-matrix models and perturbative Schur function expansions
A new representation of the 2N fold integrals appearing in various two-matrix
models that admit reductions to integrals over their eigenvalues is given in
terms of vacuum state expectation values of operator products formed from
two-component free fermions. This is used to derive the perturbation series for
these integrals under deformations induced by exponential weight factors in the
measure, expressed as double and quadruple Schur function expansions,
generalizing results obtained earlier for certain two-matrix models. Links with
the coupled two-component KP hierarchy and the two-component Toda lattice
hierarchy are also derived.Comment: Submitted to: "Random Matrices, Random Processes and Integrable
Systems", Special Issue of J. Phys. A, based on the Centre de recherches
mathematiques short program, Montreal, June 20-July 8, 200
Non-saturating large magnetoresistance in semimetals
The rapidly expanding class of quantum materials known as {\emph{topological
semimetals}} (TSM) display unique transport properties, including a striking
dependence of resistivity on applied magnetic field, that are of great interest
for both scientific and technological reasons. However, experimental signatures
that can identify or discern the dominant mechanism and connect to available
theories are scarce. Here we present the magnetic susceptibility (), the
tangent of the Hall angle () along with magnetoresistance in four
different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb and
TaSb, all of which exhibit non-saturating large MR. We find that the
distinctly different temperature dependences, and the values of
in phosphides and antimonates serve as empirical criteria to
sort the MR from different origins: NbP and TaP being uncompensated semimetals
with linear dispersion, in which the non-saturating magnetoresistance arises
due to guiding center motion, while NbSb and TaSb being {\it
compensated} semimetals, with a magnetoresistance emerging from nearly perfect
charge compensation of two quadratic bands. Our results illustrate how a
combination of magnetotransport and susceptibility measurements may be used to
categorize the increasingly ubiquitous non-saturating large magnetoresistance
in TSMs.Comment: Accepted for publication at Proc. Natl. Acad. Sci., minor revisions,
6 figure
The Razumov-Stroganov conjecture: Stochastic processes, loops and combinatorics
A fascinating conjectural connection between statistical mechanics and
combinatorics has in the past five years led to the publication of a number of
papers in various areas, including stochastic processes, solvable lattice
models and supersymmetry. This connection, known as the Razumov-Stroganov
conjecture, expresses eigenstates of physical systems in terms of objects known
from combinatorics, which is the mathematical theory of counting. This note
intends to explain this connection in light of the recent papers by Zinn-Justin
and Di Francesco.Comment: 6 pages, 4 figures, JSTAT News & Perspective
The role of orthogonal polynomials in the six-vertex model and its combinatorial applications
The Hankel determinant representations for the partition function and
boundary correlation functions of the six-vertex model with domain wall
boundary conditions are investigated by the methods of orthogonal polynomial
theory. For specific values of the parameters of the model, corresponding to
1-, 2- and 3-enumerations of Alternating Sign Matrices (ASMs), these
polynomials specialize to classical ones (Continuous Hahn, Meixner-Pollaczek,
and Continuous Dual Hahn, respectively). As a consequence, a unified and
simplified treatment of ASMs enumerations turns out to be possible, leading
also to some new results such as the refined 3-enumerations of ASMs.
Furthermore, the use of orthogonal polynomials allows us to express, for
generic values of the parameters of the model, the partition function of the
(partially) inhomogeneous model in terms of the one-point boundary correlation
functions of the homogeneous one.Comment: Talk presented by F.C. at the Short Program of the Centre de
Recherches Mathematiques: Random Matrices, Random Processes and Integrable
Systems, Montreal, June 20 - July 8, 200
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