5,256 research outputs found
Asymptotic Level Spacing of the Laguerre Ensemble: A Coulomb Fluid Approach
We determine the asymptotic level spacing distribution for the Laguerre
Ensemble in a single scaled interval, , containing no levels,
E_{\bt}(0,s), via Dyson's Coulomb Fluid approach. For the
Unitary-Laguerre Ensemble, we recover the exact spacing distribution found by
both Edelman and Forrester, while for , the leading terms of
, found by Tracy and Widom, are reproduced without the use of the
Bessel kernel and the associated Painlev\'e transcendent. In the same
approximation, the next leading term, due to a ``finite temperature''
perturbation (\bt\neq 2), is found.Comment: 10pp, LaTe
Dirac monopole with Feynman brackets
We introduce the magnetic angular momentum as a consequence of the structure
of the sO(3) Lie algebra defined by the Feynman brackets. The Poincare momentum
and Dirac magnetic monopole appears as a direct result of this framework.Comment: 10 page
Phonon emission and arrival times of electrons from a single-electron source
In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy
Relativistic Dyson Rings and Their Black Hole Limit
In this Letter we investigate uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies with a toroidal shape. The corresponding
field equations are solved by means of a multi-domain spectral method, which
yields highly accurate numerical solutions. For a prescribed, sufficiently
large ratio of inner to outer coordinate radius, the toroids exhibit a
continuous transition to the extreme Kerr black hole. Otherwise, the most
relativistic configuration rotates at the mass-shedding limit. For a given
mass-density, there seems to be no bound to the gravitational mass as one
approaches the black-hole limit and a radius ratio of unity.Comment: 13 pages, 1 table, 5 figures, v2: some discussion and two references
added, accepted for publication in Astrophys. J. Let
Low-Temperature Properties of Two-Dimensional Ideal Ferromagnets
The manifestation of the spin-wave interaction in the low-temperature series
of the partition function has been investigated extensively over more than
seven decades in the case of the three-dimensional ferromagnet. Surprisingly,
the same problem regarding ferromagnets in two spatial dimensions, to the best
of our knowledge, has never been addressed in a systematic way so far. In the
present paper the low-temperature properties of two-dimensional ideal
ferromagnets are analyzed within the model-independent method of effective
Lagrangians. The low-temperature expansion of the partition function is
evaluated up to two-loop order and the general structure of this series is
discussed, including the effect of a weak external magnetic field. Our results
apply to two-dimensional ideal ferromagnets which exhibit a spontaneously
broken spin rotation symmetry O(3) O(2) and are defined on a square,
honeycomb, triangular or Kagom\'e lattice. Remarkably, the spin-wave
interaction only sets in at three-loop order. In particular, there is no
interaction term of order in the low-temperature series for the free
energy density. This is the analog of the statement that, in the case of
three-dimensional ferromagnets, there is no interaction term of order in
the free energy density. We also provide a careful discussion of the
implications of the Mermin-Wagner theorem in the present context and thereby
put our low-temperature expansions on safe grounds.Comment: 24 pages, 3 figure
Integration over matrix spaces with unique invariant measures
We present a method to calculate integrals over monomials of matrix elements
with invariant measures in terms of Wick contractions. The method gives exact
results for monomials of low order. For higher--order monomials, it leads to an
error of order 1/N^alpha where N is the dimension of the matrix and where alpha
is independent of the degree of the monomial. We give a lower bound on the
integer alpha and show how alpha can be increased systematically. The method is
particularly suited for symbolic computer calculation. Explicit results are
given for O(N), U(N) and for the circular orthogonal ensemble.Comment: 12 pages in revtex, no figure
Metalanguage in L1 English-speaking 12-year-olds: which aspects of writing do they talk about?
Traditional psycholinguistic approaches to metalinguistic awareness in L1 learners elicit responses containing metalanguage that demonstrates metalinguistic awareness
of pre-determined aspects of language knowledge. This paper, which takes a more ethnographic approach, demonstrates how pupils are able to engage their own focus of metalanguage when reflecting on their everyday learning activities involving written language. What is equally significant is what their metalanguage choices reveal about
their understanding and application of written language concepts
Anderson transitions in three-dimensional disordered systems with randomly varying magnetic flux
The Anderson transition in three dimensions in a randomly varying magnetic
flux is investigated in detail by means of the transfer matrix method with high
accuracy. Both, systems with and without an additional random scalar potential
are considered. We find a critical exponent of with random
scalar potential. Without it, is smaller but increases with the system
size and extrapolates within the error bars to a value close to the above. The
present results support the conventional classification of universality classes
due to symmetry.Comment: 4 pages, 2 figures, to appear in Phys. Rev.
Energy level statistics for models of coupled single-mode Bose--Einstein condensates
We study the distribution of energy level spacings in two models describing
coupled single-mode Bose-Einstein condensates. Both models have a fixed number
of degrees of freedom, which is small compared to the number of interaction
parameters, and is independent of the dimensionality of the Hilbert space. We
find that the distribution follows a universal Poisson form independent of the
choice of coupling parameters, which is indicative of the integrability of both
models. These results complement those for integrable lattice models where the
number of degrees of freedom increases with increasing dimensionality of the
Hilbert space. Finally, we also show that for one model the inclusion of an
additional interaction which breaks the integrability leads to a non-Poisson
distribution.Comment: 5 pages, 4 figures, revte
Functional dynamics of the folded ankyrin repeats of I kappa B alpha revealed by nuclear magnetic resonance.
Inhibition of nuclear factor kappaB (NF-kappaB) is mainly accomplished by IkappaB alpha, which consists of a signal response sequence at the N-terminus, a six-ankyrin repeat domain (ARD) that binds NF-kappaB, and a C-terminal PEST sequence. Previous studies with the ARD revealed that the fifth and sixth repeats are only partially folded in the absence of NF-kappaB. Here we report NMR studies of a truncated version of IkappaB alpha, containing only the first four ankyrin repeats, IkappaB alpha(67-206). This four-repeat segment is well-structured in the free state, enabling full resonance assignments to be made. H-D exchange, backbone dynamics, and residual dipolar coupling (RDC) experiments reveal regions of flexibility. In addition, regions consistent with the presence of micro- to millisecond motions occur periodically throughout the repeat structure. Comparison of the RDCs with the crystal structure gave only moderate agreement, but an ensemble of structures generated by accelerated molecular dynamics gave much better agreement with the measured RDCs. The regions showing flexibility correspond to those implicated in entropic compensation for the loss of flexibility in ankyrin repeats 5 and 6 upon binding to NF-kappaB. The regions showing micro- to millisecond motions in the free protein are the ends of the beta-hairpins that directly interact with NF-kappaB in the complex
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