1,561 research outputs found
Localization in disordered superconducting wires with broken spin-rotation symmetry
Localization and delocalization of non-interacting quasiparticle states in a
superconducting wire are reconsidered, for the cases in which spin-rotation
symmetry is absent, and time-reversal symmetry is either broken or unbroken;
these are referred to as symmetry classes BD and DIII, respectively. We show
that, if a continuum limit is taken to obtain a Fokker-Planck (FP) equation for
the transfer matrix, as in some previous work, then when there are more than
two scattering channels, all terms that break a certain symmetry are lost. It
was already known that the resulting FP equation exhibits critical behavior.
The additional symmetry is not required by the definition of the symmetry
classes; terms that break it arise from non-Gaussian probability distributions,
and may be kept in a generalized FP equation. We show that they lead to
localization in a long wire. When the wire has more than two scattering
channels, these terms are irrelevant at the short distance (diffusive or
ballistic) fixed point, but as they are relevant at the long-distance critical
fixed point, they are termed dangerously irrelevant. We confirm the results in
a supersymmetry approach for class BD, where the additional terms correspond to
jumps between the two components of the sigma model target space. We consider
the effect of random fluxes, which prevent the system localizing. We show
that in one dimension the transitions in these two symmetry classes, and also
those in the three chiral symmetry classes, all lie in the same universality
class
Effective QCD Partition Function in Sectors with Non-Zero Topological Charge and Itzykson-Zuber Type Integral
It was conjectured by Jackson et.al. that the finite volume effective
partition function of QCD with the topological charge coincides with the
Itzyskon-Zuber type integral for rectangular matrices. In the
present article we give a proof of this conjecture, in which the original
Itzykson-Zuber integral is utilized.Comment: 7pages, LaTeX2
Social correlates of cigarette smoking among Icelandic adolescents: A population-based cross-sectional study
BACKGROUND: Previous research has shown that between 80 and 90 percent of adult
smokers report having started smoking before 18 years of age. Several studies
have revealed that multiple social factors influence the likelihood of smoking
during adolescence, the period during which the onset of smoking usually occurs.
To better understand the social mechanisms that influence adolescent smoking, we
analyzed the relationship and relative importance of a broad spectrum of social
variables in adolescent smoking in Iceland, a Nordic country with high per-capita
income.
METHODS: We used cross-sectional data from 7,430 14- to 16 year-old
students (approximately 81% of all Icelanders in these age cohorts) in the 2006
Youth in Iceland study. The Youth in Iceland studies are designed to investigate
the role of several cognitive, behavioral, and social factors in the lives of
adolescents, and the data collected are used to inform the design,
implementation, and evaluation of substance use prevention programs that are
being developed by Icelandic social scientists, policy makers, and practitioners.
RESULTS: Our analysis revealed that friends' smoking behavior and attitude toward
smoking were strongly associated with adolescent smoking and other tobacco use,
as well as alcohol consumption during the previous 30 days. Main protective
factors were parent's perceived attitude toward smoking, the quantity of time
spent with parents, absence of serious verbal conflict between parents and
adolescents, and participation in physical activity. Family structure was related
to adolescent smoking to a small extent, but other background factors were not.
CONCLUSION: We conclude that multiple social factors are related to adolescent
smoking. Parents and other primary preventive agents need to be informed about
the complicated nature of the adolescent social world in order to maximize their
impact.Icelandic Alcohol and Drug Prevention CommitteeIcelandic Red CrossCity of ReykjavikSports and Recreational Committee of Reykjavik to the Icelandic Centre for Social Research and AnalysisIcelandic Centre for Research (RANNÍS)Publishe
Extremal Black Attractors in 8D Maximal Supergravity
Motivated by the new higher D-supergravity solutions on intersecting
attractors obtained by Ferrara et al. in [Phys.Rev.D79:065031-2009], we focus
in this paper on 8D maximal supergravity with moduli space
[SL(3,R)/SO(3)]x[SL(2,R)/SO(2)] and study explicitly the attractor mechanism
for various configurations of extremal black p- branes (anti-branes) with the
typical near horizon geometries AdS_{p+2}xS^{m}xT^{6-p-m} and p=0,1,2,3,4;
2<=m<=6. Interpretations in terms of wrapped M2 and M5 branes of the 11D
M-theory on 3-torus are also given.
Keywords: 8D supergravity, black p-branes, attractor mechanism, M-theory.Comment: 37 page
Nonnegatively curved homogeneous metrics obtained by scaling fibers of submersions
We consider invariant Riemannian metrics on compact homogeneous spaces G/H
where an intermediate subgroup K between G and H exists, so that the
homogeneous space G/H is the total space of a Riemannian submersion. We study
the question as to whether enlarging the fibers of the submersion by a constant
scaling factor retains the nonnegative curvature in the case that the
deformation starts at a normal homogeneous metric. We classify triples of
groups (H,K,G) where nonnegative curvature is maintained for small
deformations, using a criterion proved by Schwachh\"ofer and Tapp. We obtain a
complete classification in case the subgroup H has full rank and an almost
complete classification in the case of regular subgroups.Comment: 23 pages; minor revisions, to appear in Geometriae Dedicat
Microbial communities associated with wheat, canola and lentil seeds produced in Saskatchewan
Non-Peer ReviewedCereals, oilseeds and legumes are staple crops in the Canadian Prairies that significantly contribute to global food supply. Microbial communities naturally carried by seeds offer the potential of improving crop production and yield through protection against abiotic and biotic factors. In this study, we assessed five cultivars/lines of each crop grown under different conditions (location, year) in Saskatchewan to investigate factors responsible for the seed microbiome assemblage. Our data reveal that crop type represented the largest source of variation for both bacterial (30%) and fungal communities (47%), while environment explained an additional 10% and 15%, of the microbial community variance. Additionally, in every sample analyzed, a core microbiome was detected consisting of five bacterial and twelve fungal amplicon sequence variants . Increasing our knowledge of assembly and dynamics of the seed microbiota will lead to better strategies for manipulating the plant microbiome through breeding, inoculation, and crop production practices in order to assure sustainable agriculture systems
Multiscale Representations for Manifold-Valued Data
We describe multiscale representations for data observed on equispaced grids and taking values in manifolds such as the sphere , the special orthogonal group , the positive definite matrices , and the Grassmann manifolds . The representations are based on the deployment of Deslauriers--Dubuc and average-interpolating pyramids "in the tangent plane" of such manifolds, using the and maps of those manifolds. The representations provide "wavelet coefficients" which can be thresholded, quantized, and scaled in much the same way as traditional wavelet coefficients. Tasks such as compression, noise removal, contrast enhancement, and stochastic simulation are facilitated by this representation. The approach applies to general manifolds but is particularly suited to the manifolds we consider, i.e., Riemannian symmetric spaces, such as , , , where the and maps are effectively computable. Applications to manifold-valued data sources of a geometric nature (motion, orientation, diffusion) seem particularly immediate. A software toolbox, SymmLab, can reproduce the results discussed in this paper
Gauge theory of Faddeev-Skyrme functionals
We study geometric variational problems for a class of nonlinear sigma-models
in quantum field theory. Mathematically, one needs to minimize an energy
functional on homotopy classes of maps from closed 3-manifolds into compact
homogeneous spaces G/H. The minimizers are known as Hopfions and exhibit
localized knot-like structure. Our main results include proving existence of
Hopfions as finite energy Sobolev maps in each (generalized) homotopy class
when the target space is a symmetric space. For more general spaces we obtain a
weaker result on existence of minimizers in each 2-homotopy class.
Our approach is based on representing maps into G/H by equivalence classes of
flat connections. The equivalence is given by gauge symmetry on pullbacks of
G-->G/H bundles. We work out a gauge calculus for connections under this
symmetry, and use it to eliminate non-compactness from the minimization problem
by fixing the gauge.Comment: 34 pages, no figure
Iwasawa N=8 Attractors
Starting from the symplectic construction of the Lie algebra e_7(7) due to
Adams, we consider an Iwasawa parametrization of the coset E_7(7)/SU(8), which
is the scalar manifold of N=8, d=4 supergravity. Our approach, and the manifest
off-shell symmetry of the resulting symplectic frame, is determined by a
non-compact Cartan subalgebra of the maximal subgroup SL(8,R) of E_7(7). In
absence of gauging, we utilize the explicit expression of the Lie algebra to
study the origin of E_7(7)/SU(8) as scalar configuration of a 1/8-BPS extremal
black hole attractor. In such a framework, we highlight the action of a U(1)
symmetry spanning the dyonic 1/8-BPS attractors. Within a suitable
supersymmetry truncation allowing for the embedding of the Reissner-Nordstrom
black hole, this U(1) is interpreted as nothing but the global R-symmetry of
pure N=2 supergravity. Moreover, we find that the above mentioned U(1) symmetry
is broken down to a discrete subgroup Z_4, implying that all 1/8-BPS Iwasawa
attractors are non-dyonic near the origin of the scalar manifold. We can trace
this phenomenon back to the fact that the Cartan subalgebra of SL(8,R) used in
our construction endows the symplectic frame with a manifest off-shell
covariance which is smaller than SL(8,R) itself. Thus, the consistence of the
Adams-Iwasawa symplectic basis with the action of the U(1) symmetry gives rise
to the observed Z_4 residual non-dyonic symmetry.Comment: 1+26 page
Chern-Simons Field Theory and Completely Integrable Systems
We show that the classical non-abelian pure Chern-Simons action is related in
a natural way to completely integrable systems of the Davey-Stewartson
hyerarchy, via reductions of the gauge connection in Hermitian spaces and by
performing certain gauge choices. The B\"acklund Transformations are
interpreted in terms of Chern-Simons equations of motion or, on the other hand,
as a consistency condition on the gauge. A mapping with a nonlinear
-model is discussed.Comment: 11 pages, Late
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