5,864 research outputs found
Stochastic pumping of heat: Approaching the Carnot efficiency
Random noise can generate a unidirectional heat current across asymmetric
nano objects in the absence (or against) a temperature gradient. We present a
minimal model for a molecular-level stochastic heat pump that may operate
arbitrarily close to the Carnot efficiency. The model consists a fluctuating
molecular unit coupled to two solids characterized by distinct phonon spectral
properties. Heat pumping persists for a broad range of system and bath
parameters. Furthermore, by filtering the reservoirs' phonons the pump
efficiency can approach the Carnot limit
Two-Dimensional Conformal Models of Space-Time and Their Compactification
We study geometry of two-dimensional models of conformal space-time based on
the group of Moebius transformation. The natural geometric invariants, called
cycles, are used to linearise Moebius action. Conformal completion of the
space-time is achieved through an addition of a zero-radius cycle at infinity.
We pay an attention to the natural condition of non-reversibility of time arrow
in order to get a correct compactification in the hyperbolic case.Comment: 8 pages,AMS-LaTeX, 18 PS figures; v2--small corrections; v3--add two
coments on notations and multidimensional generalisation
A Unified Treatment of the Characters of SU(2) and SU(1,1)
The character problems of SU(2) and SU(1,1) are reexamined from the
standpoint of a physicist by employing the Hilbert space method which is shown
to yield a completely unified treatment for SU(2) and the discrete series of
representations of SU(1,1). For both the groups the problem is reduced to the
evaluation of an integral which is invariant under rotation for SU(2) and
Lorentz transformation for SU(1,1). The integrals are accordingly evaluated by
applying a rotation to a unit position vector in SU(2) and a Lorentz
transformation to a unit SO(2,1) vector which is time-like for the elliptic
elements and space-like for the hyperbolic elements in SU(1,1). The details of
the procedure for the principal series of representations of SU(1,1) differ
substantially from those of the discrete series.Comment: 31 pages, RevTeX, typos corrected. To be published in Journal of
Mathematical Physic
Coherent states and the quantization of 1+1-dimensional Yang-Mills theory
This paper discusses the canonical quantization of 1+1-dimensional Yang-Mills
theory on a spacetime cylinder, from the point of view of coherent states, or
equivalently, the Segal-Bargmann transform. Before gauge symmetry is imposed,
the coherent states are simply ordinary coherent states labeled by points in an
infinite-dimensional linear phase space. Gauge symmetry is imposed by
projecting the original coherent states onto the gauge-invariant subspace,
using a suitable regularization procedure. We obtain in this way a new family
of "reduced" coherent states labeled by points in the reduced phase space,
which in this case is simply the cotangent bundle of the structure group K.
The main result explained here, obtained originally in a joint work of the
author with B. Driver, is this: The reduced coherent states are precisely those
associated to the generalized Segal-Bargmann transform for K, as introduced by
the author from a different point of view. This result agrees with that of K.
Wren, who uses a different method of implementing the gauge symmetry. The
coherent states also provide a rigorous way of making sense out of the quantum
Hamiltonian for the unreduced system.
Various related issues are discussed, including the complex structure on the
reduced phase space and the question of whether quantization commutes with
reduction
Generic solutions for some integrable lattice equations
We derive the expressions for -functions and generic solutions of
lattice principal chiral equations, lattice KP hierarchy and hierarchy
including lattice N-wave type equations. -function of free fermions
plays fundamental role in this context. Miwa's coordinates in our case appear
as the lattice parameters.Comment: The text of the talk at NEEDS-93 conference, Gallipoli, Italy,
September-93, LaTeX, 8 pages. Several typos and minor errors are correcte
A systematic review of ICD complications in randomised controlled trials versus registries: is our 'real-world' data an underestimation?
Implantable cardioverter defibrillator (ICD) implantation carries a significant risk of complications, however published estimates appear inconsistent. We aimed to present a contemporary systematic review using meta-analysis methods of ICD complications in randomised controlled trials (RCTs) and compare it to recent data from the largest international ICD registry, the US National Cardiovascular Data Registry (NCDR). PubMed was searched for any RCTs involving ICD implantation published 1999-2013; 18 were identified for analysis including 6433 patients, mean follow-up 3 months-5.6 years. Exclusion criteria were studies of children, hypertrophic cardiomyopathy, congenital heart disease, resynchronisation therapy and generator changes. Total pooled complication rate from the RCTs (excluding inappropriate shocks) was 9.1%, including displacement 3.1%, pneumothorax 1.1% and haematoma 1.2%. Infection rate was 1.5%.There were no predictors of complications but longer follow-up showed a trend to higher complication rates (p=0.07). In contrast, data from the NCDR ICD, reporting on 356 515 implants (2006-2010) showed a statistically significant threefold lower total major complication rate of 3.08% with lead displacement 1.02%, haematoma 0.86% and pneumothorax 0.44%. The overall ICD complication rate in our meta-analysis is 9.1% over 16 months. The ICD complication reported in the NCDR ICD registry is significantly lower despite a similar population. This may reflect under-reporting of complications in registries. Reporting of ICD complications in RCTs and registries is very variable and there is a need to standardise classification of complications internationally
News from the Virasoro algebra
It is shown that the local quantum field theory of the chiral energy-
momentum tensor with central charge coincides with the gauge invariant
subtheory of the chiral current algebra at level 1, where the gauge
group is the global symmetry. At higher level, the same scheme gives
rise to -algebra extensions of the Virasoro algebra.Comment: 4 pages, Latex, DESY 93-11
parafermions from constrained WZNW theories
The conformal field theory based on the coset construction is
treated as the WZNW theory for the affine Lie algebra with the
constrained subalgebra.Using a modification of the generalized
canonical quantization method generators and primary fields of an extended
symmetry algebra are found for arbitrary d.Comment: 14 pages,latex,misprints in formulas 26,40,45 corrected,a reference
adde
Segal-Bargmann-Fock modules of monogenic functions
In this paper we introduce the classical Segal-Bargmann transform starting
from the basis of Hermite polynomials and extend it to Clifford algebra-valued
functions. Then we apply the results to monogenic functions and prove that the
Segal-Bargmann kernel corresponds to the kernel of the Fourier-Borel transform
for monogenic functionals. This kernel is also the reproducing kernel for the
monogenic Bargmann module.Comment: 11 page
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