1,367 research outputs found
Fano resonances in a three-terminal nanodevice
The electron transport through a quantum sphere with three one-dimensional
wires attached to it is investigated. An explicit form for the transmission
coefficient as a function of the electron energy is found from the first
principles. The asymmetric Fano resonances are detected in transmission of the
system. The collapse of the resonances is shown to appear under certain
conditions. A two-terminal nanodevice with an additional gate lead is studied
using the developed approach. Additional resonances and minima of transmission
are indicated in the device.Comment: 11 pages, 5 figures, 2 equations are added, misprints in 5 equations
are removed, published in Journal of Physics: Condensed Matte
Property (T) and rigidity for actions on Banach spaces
We study property (T) and the fixed point property for actions on and
other Banach spaces. We show that property (T) holds when is replaced by
(and even a subspace/quotient of ), and that in fact it is
independent of . We show that the fixed point property for
follows from property (T) when 1
. For simple Lie groups and their lattices, we prove that the fixed point property for holds for any if and only if the rank is at least two. Finally, we obtain a superrigidity result for actions of irreducible lattices in products of general groups on superreflexive Banach spaces.Comment: Many minor improvement
Chaotic maps and flows: Exact Riemann-Siegel lookalike for spectral fluctuations
To treat the spectral statistics of quantum maps and flows that are fully
chaotic classically, we use the rigorous Riemann-Siegel lookalike available for
the spectral determinant of unitary time evolution operators . Concentrating
on dynamics without time reversal invariance we get the exact two-point
correlator of the spectral density for finite dimension of the matrix
representative of , as phenomenologically given by random matrix theory. In
the limit the correlator of the Gaussian unitary ensemble is
recovered. Previously conjectured cancellations of contributions of
pseudo-orbits with periods beyond half the Heisenberg time are shown to be
implied by the Riemann-Siegel lookalike
Probabilistic models of information retrieval based on measuring the divergence from randomness
We introduce and create a framework for deriving probabilistic models of Information Retrieval. The models are nonparametric models of IR obtained in the language model approach. We derive term-weighting models by measuring the divergence of the actual term distribution from that obtained under a random process. Among the random processes we study the binomial distribution and Bose--Einstein statistics. We define two types of term frequency normalization for tuning term weights in the document--query matching process. The first normalization assumes that documents have the same length and measures the information gain with the observed term once it has been accepted as a good descriptor of the observed document. The second normalization is related to the document length and to other statistics. These two normalization methods are applied to the basic models in succession to obtain weighting formulae. Results show that our framework produces different nonparametric models forming baseline alternatives to the standard tf-idf model
On multiplicities in length spectra of arithmetic hyperbolic three-orbifolds
Asymptotic laws for mean multiplicities of lengths of closed geodesics in
arithmetic hyperbolic three-orbifolds are derived. The sharpest results are
obtained for non-compact orbifolds associated with the Bianchi groups SL(2,o)
and some congruence subgroups. Similar results hold for cocompact arithmetic
quaternion groups, if a conjecture on the number of gaps in their length
spectra is true. The results related to the groups above give asymptotic lower
bounds for the mean multiplicities in length spectra of arbitrary arithmetic
hyperbolic three-orbifolds. The investigation of these multiplicities is
motivated by their sensitive effect on the eigenvalue spectrum of the
Laplace-Beltrami operator on a hyperbolic orbifold, which may be interpreted as
the Hamiltonian of a three-dimensional quantum system being strongly chaotic in
the classical limit.Comment: 29 pages, uuencoded ps. Revised version, to appear in NONLINEARIT
Numerical Study of Length Spectra and Low-lying Eigenvalue Spectra of Compact Hyperbolic 3-manifolds
In this paper, we numerically investigate the length spectra and the
low-lying eigenvalue spectra of the Laplace-Beltrami operator for a large
number of small compact(closed) hyperbolic (CH) 3-manifolds. The first non-zero
eigenvalues have been successfully computed using the periodic orbit sum
method, which are compared with various geometric quantities such as volume,
diameter and length of the shortest periodic geodesic of the manifolds. The
deviation of low-lying eigenvalue spectra of manifolds converging to a cusped
hyperbolic manifold from the asymptotic distribution has been measured by
function and spectral distance.Comment: 19 pages, 18 EPS figures and 2 GIF figures (fig.10) Description of
cusped manifolds in section 2 is correcte
Differential criterion of a bubble collapse in viscous liquids
The present work is devoted to a model of bubble collapse in a Newtonian
viscous liquid caused by an initial bubble wall motion. The obtained bubble
dynamics described by an analytic solution significantly depends on the liquid
and bubble parameters. The theory gives two types of bubble behavior: collapse
and viscous damping. This results in a general collapse condition proposed as
the sufficient differential criterion. The suggested criterion is discussed and
successfully applied to the analysis of the void and gas bubble collapses.Comment: 5 pages, 3 figure
The structure of molecular gas associated with NGC2264: wide-field 12CO and H2 imaging
We present wide-field, high-resolution imaging observations in 12CO 3-2 and
H2 1-0 S(1) towards a ~1 square degree region of NGC2264. We identify 46 H2
emission objects, of which 35 are new discoveries. We characterize several
cores as protostellar, reducing the previously observed ratio of
prestellar/protostellar cores in the NGC2264 clusters. The length of H2 jets
increases the previously reported spatial extent of the clusters. In each
cluster, <0.5% of cloud material has been perturbed by outflow activity. A
principal component analysis of the 12CO data suggests that turbulence is
driven on scales >2.6 pc, which is larger than the extent of the outflows. We
obtain an exponent alpha=0.74 for the size-linewidth relation, possibly due to
the high surface density of NGC2264. In this very active, mixed-mass star
forming region, our observations suggest that protostellar outflow activity is
not injecting energy and momentum on a large enough scale to be the dominant
source of turbulence.Comment: MNRAS accepte
Blood ties: ABO is a trans-species polymorphism in primates
The ABO histo-blood group, the critical determinant of transfusion
incompatibility, was the first genetic polymorphism discovered in humans.
Remarkably, ABO antigens are also polymorphic in many other primates, with the
same two amino acid changes responsible for A and B specificity in all species
sequenced to date. Whether this recurrence of A and B antigens is the result of
an ancient polymorphism maintained across species or due to numerous, more
recent instances of convergent evolution has been debated for decades, with a
current consensus in support of convergent evolution. We show instead that
genetic variation data in humans and gibbons as well as in Old World Monkeys
are inconsistent with a model of convergent evolution and support the
hypothesis of an ancient, multi-allelic polymorphism of which some alleles are
shared by descent among species. These results demonstrate that the ABO
polymorphism is a trans-species polymorphism among distantly related species
and has remained under balancing selection for tens of millions of years, to
date, the only such example in Hominoids and Old World Monkeys outside of the
Major Histocompatibility Complex.Comment: 45 pages, 4 Figures, 4 Supplementary Figures, 5 Supplementary Table
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