5,752 research outputs found
Saddle Points and Stark Ladders: Exact Calculations of Exciton Spectra in Superlattices
A new, exact method for calculating excitonic absorption in superlattices is
described. It is used to obtain high resolution spectra showing the saddle
point exciton feature near the top of the miniband. The evolution of this
feature is followed through a series of structures with increasing miniband
width. The Stark ladder of peaks produced by an axial electric field is
investigated, and it is shown that for weak fields the line shapes are strongly
modified by coupling to continuum states, taking the form of Fano resonances.
The calculated spectra, when suitably broadened, are found to be in good
agreement with experimental results.Comment: 9 pages Revtex v3.0, followed by 4 uuencoded postscript figures,
SISSA-CM-94-00
Partition function of the eight-vertex model with domain wall boundary condition
We derive the recursive relations of the partition function for the
eight-vertex model on an square lattice with domain wall boundary
condition. Solving the recursive relations, we obtain the explicit expression
of the domain wall partition function of the model. In the
trigonometric/rational limit, our results recover the corresponding ones for
the six-vertex model.Comment: Latex file, 20 pages; V2, references adde
The eVALuate study: two parallel randomised trials, one comparing laparoscopic with abdominal hysterectomy, the other comparing laparoscopic with vaginal hysterectomy
OBJECTIVE: To compare the effects of laparoscopic hysterectomy
and abdominal hysterectomy in the abdominal trial, and
laparoscopic hysterectomy and vaginal hysterectomy in the
vaginal trial.
DESIGN: Two parallel, multicentre, randomised trials.
Setting 28 UK centres and two South African centres.
Participants 1380 women were recruited; 1346 had surgery;
937 were followed up at one year.
PRIMARY OUTCOME: outcome Rate of major complications.
RESULTS: In the abdominal trial laparoscopic hysterectomy was
associated with a higher rate of major complications than
abdominal hysterectomy (11.1% v 6.2%, P = 0.02; difference
4.9%, 95% confidence interval 0.9% to 9.1%) and the number
needed to treat to harm was 20. Laparoscopic hysterectomy
also took longer to perform (84 minutes v 50 minutes) but was
less painful (visual analogue scale 3.51 v 3.88, P = 0.01) and
resulted in a shorter stay in hospital after the operation (3 days
v 4 days). Six weeks after the operation, laparoscopic
hysterectomy was associated with less pain and better quality of
life than abdominal hysterectomy (SF-12, body image scale, and
sexual activity questionnaires).
In the vaginal trial we found no evidence of a difference in
major complication rates between laparoscopic hysterectomy
and vaginal hysterectomy (9.8% v 9.5%, P = 0.92; difference
0.3%, − 5.2% to 5.8%), and the number needed to treat to harm
was 333.We found no evidence of other differences between
laparoscopic hysterectomy and vaginal hysterectomy except
that laparoscopic hysterectomy took longer to perform (72
minutes v 39 minutes) and was associated with a higher rate of
detecting unexpected pathology (16.4% v 4.8%, P = < 0.01).
However, this trial was underpowered.
CONCLUSIONS: Laparoscopic hysterectomy was associated with a
significantly higher rate of major complications than abdominal
hysterectomy. It also took longer to perform but was associated
with less pain, quicker recovery, and better short term quality of
life. The trial comparing vaginal hysterectomy with laparoscopic
hysterectomy was underpowered and is inconclusive on the rate
of major complications; however, vaginal hysterectomy took less
time
Anomalous relaxation kinetics of biological lattice-ligand binding models
We discuss theoretical models for the cooperative binding dynamics of ligands
to substrates, such as dimeric motor proteins to microtubules or more extended
macromolecules like tropomyosin to actin filaments. We study the effects of
steric constraints, size of ligands, binding rates and interaction between
neighboring proteins on the binding dynamics and binding stoichiometry.
Starting from an empty lattice the binding dynamics goes, quite generally,
through several stages. The first stage represents fast initial binding closely
resembling the physics of random sequential adsorption processes. Typically
this initial process leaves the system in a metastable locked state with many
small gaps between blocks of bound molecules. In a second stage the gaps
annihilate slowly as the ligands detach and reattach. This results in an
algebraic decay of the gap concentration and interesting scaling behavior. Upon
identifying the gaps with particles we show that the dynamics in this regime
can be explained by mapping it onto various reaction-diffusion models. The
final approach to equilibrium shows some interesting dynamic scaling
properties. We also discuss the effect of cooperativity on the equilibrium
stoichiometry, and their consequences for the interpretation of biochemical and
image reconstruction results.Comment: REVTeX, 20 pages, 17 figures; review, to appear in Chemical Physics;
v2: minor correction
Semiclassical Analysis of the Wigner Symbol with One Small Angular Momentum
We derive an asymptotic formula for the Wigner symbol, in the limit of
one small and 11 large angular momenta. There are two kinds of asymptotic
formulas for the symbol with one small angular momentum. We present the
first kind of formula in this paper. Our derivation relies on the techniques
developed in the semiclassical analysis of the Wigner symbol [L. Yu and R.
G. Littlejohn, Phys. Rev. A 83, 052114 (2011)], where we used a gauge-invariant
form of the multicomponent WKB wave-functions to derive asymptotic formulas for
the symbol with small and large angular momenta. When applying the same
technique to the symbol in this paper, we find that the spinor is
diagonalized in the direction of an intermediate angular momentum. In addition,
we find that the geometry of the derived asymptotic formula for the
symbol is expressed in terms of the vector diagram for a symbol. This
illustrates a general geometric connection between asymptotic limits of the
various symbols. This work contributes the first known asymptotic formula
for the symbol to the quantum theory of angular momentum, and serves as a
basis for finding asymptotic formulas for the Wigner symbol with two
small angular momenta.Comment: 15 pages, 14 figure
Statistical mechanics of an ideal Bose gas in a confined geometry
We study the behaviour of an ideal non-relativistic Bose gas in a
three-dimensional space where one of the dimensions is compactified to form a
circle. In this case there is no phase transition like that for the case of an
infinite volume, nevertheless Bose-Einstein condensation signified by a sudden
buildup of particles in the ground state can occur. We use the grand canonical
ensemble to study this problem. In particular, the specific heat is evaluated
numerically, as well as analytically in certain limits. We show analytically
how the familiar result for the specific heat is recovered as we let the size
of the circle become large so that the infinite volume limit is approached. We
also examine in detail the behaviour of the chemical potential and establish
the precise manner in which it approaches zero as the volume becomes large.Comment: 13 pages, 2 eps figures, revtex
Towards a CPT Invariant Quantum Field Theory on Elliptic de Sitter Space
Consequences of Schr\"{o}dinger's antipodal identification on quantum field
theory in de Sitter space are investigated. The elliptic
identification provides observers with complete information. We show that a
suitable confinement on dimension of the elliptic de Sitter space guarantees
the existence of globally defined spinors and orientable
manifold. In Beltrami coordinates, we give exact solutions of scalar and spinor
fields. The CPT invariance of quantum field theory on the elliptic de Sitter
space is presented explicitly.Comment: 16 pages, some references have been added, the structure of paper
have been revised, accepted for publication in Int. J. Mod. Phys.
Free Energy of the Eight Vertex Model with an Odd Number of Lattice Sites
We calculate the bulk contribution for the doubly degenerated largest
eigenvalue of the transfer matrix of the eight vertex model with an odd number
of lattice sites N in the disordered regime using the generic equation for
roots proposed by Fabricius and McCoy. We show as expected that in the
thermodynamic limit the result coincides with the one in the N even case.Comment: 11 pages LaTeX New introduction, Method change
From non-degenerate conducting polymers to dense matter in the massive Gross-Neveu model
Using results from the theory of non-degenerate conducting polymers like
cis-polyacetylene, we generalize our previous work on dense baryonic matter and
the soliton crystal in the massless Gross-Neveu model to finite bare fermion
mass. In the large N limit, the exact crystal ground state can be constructed
analytically, in close analogy to the bipolaron lattice in polymers. These
findings are contrasted to the standard scenario with homogeneous phases only
and a first order phase transition at a critical chemical potential.Comment: 12 pages, 7 figures, revtex; v2: improved readability, following
advice of PRD referee; accepted for publicatio
Spacetime Encodings II - Pictures of Integrability
I visually explore the features of geodesic orbits in arbitrary stationary
axisymmetric vacuum (SAV) spacetimes that are constructed from a complex Ernst
potential. Some of the geometric features of integrable and chaotic orbits are
highlighted. The geodesic problem for these SAV spacetimes is rewritten as a
two degree of freedom problem and the connection between current ideas in
dynamical systems and the study of two manifolds sought. The relationship
between the Hamilton-Jacobi equations, canonical transformations, constants of
motion and Killing tensors are commented on. Wherever possible I illustrate the
concepts by means of examples from general relativity. This investigation is
designed to build the readers' intuition about how integrability arises, and to
summarize some of the known facts about two degree of freedom systems. Evidence
is given, in the form of orbit-crossing structure, that geodesics in SAV
spacetimes might admit, a fourth constant of motion that is quartic in momentum
(by contrast with Kerr spacetime, where Carter's fourth constant is quadratic).Comment: 11 pages, 10 figure
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