5,163 research outputs found
Note on exponential families of distributions
We show that an arbitrary probability distribution can be represented in
exponential form. In physical contexts, this implies that the equilibrium
distribution of any classical or quantum dynamical system is expressible in
grand canonical form.Comment: 5 page
Random Hamiltonian in thermal equilibrium
A framework for the investigation of disordered quantum systems in thermal
equilibrium is proposed. The approach is based on a dynamical model--which
consists of a combination of a double-bracket gradient flow and a uniform
Brownian fluctuation--that `equilibrates' the Hamiltonian into a canonical
distribution. The resulting equilibrium state is used to calculate quenched and
annealed averages of quantum observables.Comment: 8 pages, 4 figures. To appear in DICE 2008 conference proceeding
Metric approach to quantum constraints
A new framework for deriving equations of motion for constrained quantum
systems is introduced, and a procedure for its implementation is outlined. In
special cases the framework reduces to a quantum analogue of the Dirac theory
of constrains in classical mechanics. Explicit examples involving spin-1/2
particles are worked out in detail: in one example our approach coincides with
a quantum version of the Dirac formalism, while the other example illustrates
how a situation that cannot be treated by Dirac's approach can nevertheless be
dealt with in the present scheme.Comment: 13 pages, 1 figur
Spectral Properties of the k-Body Embedded Gaussian Ensembles of Random Matrices for Bosons
We consider spinless Bosons distributed over degenerate
single-particle states and interacting through a -body random interaction
with Gaussian probability distribution (the Bosonic embedded -body
ensembles). We address the cases of orthogonal and unitary symmetry in the
limit of infinite matrix dimension, attained either as or as . We derive an eigenvalue expansion for the second moment of the
many-body matrix elements of these ensembles. Using properties of this
expansion, the supersymmetry technique, and the binary correlation method, we
show that in the limit the ensembles have nearly the same
spectral properties as the corresponding Fermionic embedded ensembles. Novel
features specific for Bosons arise in the dense limit defined as
with both and fixed. Here we show that the ensemble is not ergodic, and
that the spectral fluctuations are not of Wigner-Dyson type. We present
numerical results for the dense limit using both ensemble unfolding and
spectral unfolding. These differ strongly, demonstrating the lack of ergodicity
of the ensemble. Spectral unfolding shows a strong tendency towards
picket-fence type spectra. Certain eigenfunctions of individual realizations of
the ensemble display Fock-space localization.Comment: Minor corrections; figure 5 slightly modified (30 pages, 6 figs
Spectral Properties of the k-Body Embedded Gaussian Ensembles of Random Matrices
We consider spinless Fermions in degenerate single-particle
levels interacting via a -body random interaction with Gaussian probability
distribution and in the limit to infinity (the embedded -body
random ensembles). We address the cases of orthogonal and unitary symmetry. We
derive a novel eigenvalue expansion for the second moment of the Hilbert-space
matrix elements of these ensembles. Using properties of the expansion and the
supersymmetry technique, we show that for , the average spectrum has
the shape of a semicircle, and the spectral fluctuations are of Wigner-Dyson
type. Using a generalization of the binary correlation approximation, we show
that for , the spectral fluctuations are Poissonian. This is
consistent with the case which can be solved explicitly. We construct
limiting ensembles which are either fully integrable or fully chaotic and show
that the -body random ensembles lie between these two extremes. Combining
all these results we find that the spectral correlations for the embedded
ensembles gradually change from Wigner-Dyson for to Poissonian for .Comment: 44 pages, 3 postscript figures, revised version including a new proof
of one of our main claim
Nuclear Structure Calculations with Low-Momentum Potentials in a Model Space Truncation Approach
We have calculated the ground-state energy of the doubly magic nuclei 4He,
16O and 40Ca within the framework of the Goldstone expansion starting from
various modern nucleon-nucleon potentials. The short-range repulsion of these
potentials has been renormalized by constructing a low-momentum potential
V-low-k. We have studied the connection between the cutoff momemtum Lambda and
the size of the harmonic oscillator space employed in the calculations. We have
found a fast convergence of the results with a limited number of oscillator
quanta.Comment: 6 pages, 8 figures, to be published on Physical Review
Minimal long-term neurobehavioral impairments after endovascular perforation subarachnoid hemorrhage in mice
AbstractCognitive deficits are among the most severe and pervasive consequences of aneurysmal subarachnoid hemorrhage (SAH). A critical step in developing therapies targeting such outcomes is the characterization of experimentally-tractable pre-clinical models that exhibit multi-domain neurobehavioral deficits similar to those afflicting humans. We therefore searched for neurobehavioral abnormalities following endovascular perforation induction of SAH in mice, a heavily-utilized model. We instituted a functional screen to manage variability in injury severity, then assessed acute functional deficits, as well as activity, anxiety-related behavior, learning and memory, socialization, and depressive-like behavior at sub-acute and chronic time points (up to 1 month post-injury). Animals in which SAH was induced exhibited reduced acute functional capacity and reduced general activity to 1 month post-injury. Tests of anxiety-related behavior including central area time in the elevated plus maze and thigmotaxis in the open field test revealed increased anxiety-like behavior at subacute and chronic time-points, respectively. Effect sizes for subacute and chronic neurobehavioral endpoints in other domains, however, were small. In combination with persistent variability, this led to non-significant effects of injury on all remaining neurobehavioral outcomes. These results suggest that, with the exception of anxiety-related behavior, alternate mouse models are required to effectively analyze cognitive outcomes after SAH.</jats:p
Repository Software as a Platform for the Registry of Open Access Repositories
We have migrated the ROAR service to a repository software-based platform.
The goal of this project was to reduce the administrative overhead for us and improve the experience for users by enabling them to control and update their own records
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