1,911 research outputs found
The strong Novikov conjecture for low degree cohomology
We show that for each discrete group G, the rational assembly map
K_*(BG) \otimes Q \to K_*(C*_{max} G) \otimes \Q is injective on classes dual
to the subring generated by cohomology classes of degree at most 2 (identifying
rational K-homology and homology via the Chern character). Our result implies
homotopy invariance of higher signatures associated to these cohomology
classes. This consequence was first established by Connes-Gromov-Moscovici and
Mathai.
Our approach is based on the construction of flat twisting bundles out of
sequences of almost flat bundles as first described in our previous work. In
contrast to the argument of Mathai, our approach is independent of (and indeed
gives a new proof of) the result of Hilsum-Skandalis on the homotopy invariance
of the index of the signature operator twisted with bundles of small curvature.Comment: 11 page
Internal Energy of the Potts model on the Triangular Lattice with Two- and Three-body Interactions
We calculate the internal energy of the Potts model on the triangular lattice
with two- and three-body interactions at the transition point satisfying
certain conditions for coupling constants. The method is a duality
transformation. Therefore we have to make assumptions on uniqueness of the
transition point and that the transition is of second order. These assumptions
have been verified to hold by numerical simulations for q=2, 3 and 4, and our
results for the internal energy are expected to be exact in these cases.Comment: 9 pages, 4 figure
Monte Carlo Study of an Extended 3-State Potts Model on the Triangular Lattice
By introducing a chiral term into the Hamiltonian of the 3-state Potts model
on a triangular lattice additional symmetries are achieved between the
clockwise and anticlockwise states and the ferromagnetic state. This model is
investigated using Monte Carlo methods. We investigate the full phase diagram
and find evidence for a line tricritical points separating the ferromagnetic
and antiferromagnetic phases.Comment: 6 pages, 10 figure
Localisation and colocalisation of KK-theory at sets of primes
Given a set of prime numbers S, we localise equivariant bivariant Kasparov
theory at S and compare this localisation with Kasparov theory by an exact
sequence. More precisely, we define the localisation at S to be KK^G(A,B)
tensored with the ring of S-integers Z[S^-1]. We study the properties of the
resulting variants of Kasparov theory.Comment: 16 page
Proof of Bose-Einstein Condensation for Dilute Trapped Gases
The ground state of bosonic atoms in a trap has been shown experimentally to
display Bose-Einstein condensation (BEC). We prove this fact theoretically for
bosons with two-body repulsive interaction potentials in the dilute limit,
starting from the basic Schroedinger equation; the condensation is 100% into
the state that minimizes the Gross-Pitaevskii energy functional. This is the
first rigorous proof of BEC in a physically realistic, continuum model.Comment: Revised version with some simplifications and clarifications. To
appear in Phys. Rev. Let
Normalized indices derived from visceral adipose mass assessed by MRI and their correlation with markers for insulin resistance and prediabetes
Visceral adipose tissue (VAT) plays an important role in the pathogenesis of insulin resistance (IR), prediabetes and type 2 diabetes. However, VAT volume alone might not be the best marker for insulin resistance and prediabetes or diabetes, as a given VAT volume may differently impact on these metabolic traits based on body height, gender, age and ethnicity. In a cohort of 1295 subjects from the Tübingen Diabetes Family Study (TDFS) and in 9978 subjects from the UK Biobank (UKBB), undergoing magnetic resonance imaging for quantification of VAT volume, total adipose tissue (TAT, in the TDFS), total abdominal adipose tissue (TAAT) in the UKBB, and total lean tissue (TLT), VAT volume and several VAT-indices were investigated for their relationships with insulin resistance and glycemic traits. VAT-related indices were calculated by correcting for body height (VAT/m: VAT/body height; VAT/m²: VAT/(body height)², and VAT/m³: VAT/(body height)³), TAT (%VAT), TLT (VAT/TLT) and weight (VAT/WEI), with closest equivalents used within the UKBB dataset. Prognostic values of VAT and VAT-related indices for insulin sensitivity, HbA1c levels and prediabetes/diabetes were analyzed for males and females. Males had higher VAT volume and VAT-related indices than females in both cohorts (p < 0.0001) and VAT volume has shown to be a stronger determinant for insulin sensitivity than anthropometric variables. Among the parameters uncorrected VAT and derived indices, VAT/m³ most strongly correlated negatively with insulin sensitivity and positively with HbA1c levels and prediabetes/diabetes in the TDFS (R² = 0.375/0.305 for females/males for insulin sensitivity, 0.178/0.148 for HbA1c levels vs. – e.g. – 0.355/0.293 and 0.144/0.133 for VAT, respectively) and positively with HbA1c (R² = 0.046/0.042) in the UKBB for females and males. Furthermore, VAT/m³ was found to be a significantly better determinant of insulin resistance or prediabetes than uncorrected VAT volume (p < 0.001/0.019 for females/males regarding insulin sensitivity, p < 0.001/< 0.001 for females/males regarding HbA1c). Evaluation of several indices derived from VAT volume identified VAT/m³ to most strongly correlate with insulin sensitivity and glucose metabolism. Thus, VAT/m³ appears to provide better indications of metabolic characteristics (insulin sensitivity and pre-diabetes/diabetes) than VAT volume alone
One-dimensional Kondo lattice at partial band filling
An effective Hamiltonian for the localized spins in the one-dimensional Kondo
lattice model is derived via a unitary transformation involving a bosonization
of delocalized conduction electrons. The effective Hamiltonian is shown to
reproduce all the features of the model as identified in various numerical
simulations, and provides much new information on the ferro- to paramagnetic
phase transition and the paramagnetic phase.Comment: 11 pages Revtex, 1 Postscript figure. To appear in Phys. Rev. Let
Hodge Theory on Metric Spaces
Hodge theory is a beautiful synthesis of geometry, topology, and analysis,
which has been developed in the setting of Riemannian manifolds. On the other
hand, spaces of images, which are important in the mathematical foundations of
vision and pattern recognition, do not fit this framework. This motivates us to
develop a version of Hodge theory on metric spaces with a probability measure.
We believe that this constitutes a step towards understanding the geometry of
vision.
The appendix by Anthony Baker provides a separable, compact metric space with
infinite dimensional \alpha-scale homology.Comment: appendix by Anthony W. Baker, 48 pages, AMS-LaTeX. v2: final version,
to appear in Foundations of Computational Mathematics. Minor changes and
addition
Free expansion of two-dimensional condensates with a vortex
We study the free expansion of a pancake-shaped Bose-condensed gas, which is
initially trapped under harmonic confinement and containing a vortex at its
centre. In the case of a radial expansion holding fixed the axial confinement
we consider various models for the interactions, depending on the thickness of
the condensate relative to the value of the scattering length. We are thus able
to evaluate different scattering regimes ranging from quasi-three-dimensional
(Q3D) to strictly two-dimensional (2D). We find that as the system goes from
Q3D to 2D the expansion rate of the condensate increases whereas that of the
vortex core decreases. In the Q3D scattering regime we also examine a fully
free expansion in 3D and find oscillatory behaviour for the vortex core radius:
an initial fast expansion of the vortex core is followed by a slowing down.
Such a nonuniform expansion rate of the vortex core may be taken into account
in designing new experiments.Comment: 10 pages, 4 figure
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