17,492 research outputs found
Realistic calculations of nuclear disappearance lifetimes induced by neutron-antineutron oscillations
Realistic calculations of nuclear disappearance lifetimes induced by
neutron-antineutron oscillations are reported for oxygen and iron, using
antineutron nuclear potentials derived from a recent comprehensive analysis of
antiproton atomic X-ray and radiochemical data. A lower limit of 3.3 x 10E8 s
on the neutron-antineutron oscillation time is derived from the
Super-Kamiokande I new lower limit of 1.77 x 10E32 yr on the neutron lifetime
in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap
experiments using ultracold neutrons, are calculated from updated antinucleon
optical potentials at threshold, with results shown to be largely model
independent.Comment: version matching PRD publication, typos and references correcte
Energy dynamics in a simulation of LAPD turbulence
Energy dynamics calculations in a 3D fluid simulation of drift wave
turbulence in the linear Large Plasma Device (LAPD) [W. Gekelman et al., Rev.
Sci. Inst. 62, 2875 (1991)] illuminate processes that drive and dissipate the
turbulence. These calculations reveal that a nonlinear instability dominates
the injection of energy into the turbulence by overtaking the linear drift wave
instability that dominates when fluctuations about the equilibrium are small.
The nonlinear instability drives flute-like () density
fluctuations using free energy from the background density gradient. Through
nonlinear axial wavenumber transfer to fluctuations, the
nonlinear instability accesses the adiabatic response, which provides the
requisite energy transfer channel from density to potential fluctuations as
well as the phase shift that causes instability. The turbulence characteristics
in the simulations agree remarkably well with experiment. When the nonlinear
instability is artificially removed from the system through suppressing
modes, the turbulence develops a coherent frequency spectrum
which is inconsistent with experimental data
Canonical formulation of the embedded theory of gravity equivalent to Einstein's General Relativity
We study the approach in which independent variables describing gravity are
functions of the space-time embedding into a flat space of higher dimension. We
formulate a canonical formalism for such a theory in a form, which requires
imposing additional constraints, which are a part of Einstein's equations. As a
result, we obtain a theory with an eight-parameter gauge symmetry. This theory
becomes equivalent to Einstein's general relativity either after partial gauge
fixing or after rewriting the metric in the form that is invariant under the
additional gauge transformations. We write the action for such a theory.Comment: LaTeX, 17 page
The exp-log normal form of types
Lambda calculi with algebraic data types lie at the core of functional
programming languages and proof assistants, but conceal at least two
fundamental theoretical problems already in the presence of the simplest
non-trivial data type, the sum type. First, we do not know of an explicit and
implemented algorithm for deciding the beta-eta-equality of terms---and this in
spite of the first decidability results proven two decades ago. Second, it is
not clear how to decide when two types are essentially the same, i.e.
isomorphic, in spite of the meta-theoretic results on decidability of the
isomorphism.
In this paper, we present the exp-log normal form of types---derived from the
representation of exponential polynomials via the unary exponential and
logarithmic functions---that any type built from arrows, products, and sums,
can be isomorphically mapped to. The type normal form can be used as a simple
heuristic for deciding type isomorphism, thanks to the fact that it is a
systematic application of the high-school identities.
We then show that the type normal form allows to reduce the standard beta-eta
equational theory of the lambda calculus to a specialized version of itself,
while preserving the completeness of equality on terms. We end by describing an
alternative representation of normal terms of the lambda calculus with sums,
together with a Coq-implemented converter into/from our new term calculus. The
difference with the only other previously implemented heuristic for deciding
interesting instances of eta-equality by Balat, Di Cosmo, and Fiore, is that we
exploit the type information of terms substantially and this often allows us to
obtain a canonical representation of terms without performing sophisticated
term analyses
Detecting many-body entanglements in noninteracting ultracold atomic fermi gases
We explore the possibility of detecting many-body entanglement using
time-of-flight (TOF) momentum correlations in ultracold atomic fermi gases. In
analogy to the vacuum correlations responsible for Bekenstein-Hawking black
hole entropy, a partitioned atomic gas will exhibit particle-hole correlations
responsible for entanglement entropy. The signature of these momentum
correlations might be detected by a sensitive TOF type experiment.Comment: 5 pages, 5 figures, fixed axes labels on figs. 3 and 5, added
reference
Isotopic Scaling in Nuclear Reactions
A three parameter scaling relationship between isotopic distributions for
elements with Z has been observed that allows a simple description of
the dependence of such distributions on the overall isospin of the system. This
scaling law (termed iso-scaling) applies for a variety of reaction mechanisms
that are dominated by phase space, including evaporation, multifragmentation
and deeply inelastic scattering. The origins of this scaling behavior for the
various reaction mechanisms are explained. For multifragmentation processes,
the systematics is influenced by the density dependence of the asymmetry term
of the equation of state.Comment: 10 Pages, 2 Figure
Special K\"ahler-Ricci potentials on compact K\"ahler manifolds
A special K\"ahler-Ricci potential on a K\"ahler manifold is any nonconstant
function such that is a Killing vector field
and, at every point with , all nonzero tangent vectors orthogonal
to and are eigenvectors of both and
the Ricci tensor. For instance, this is always the case if is a
nonconstant function on a K\"ahler manifold of complex
dimension and the metric , defined wherever , is Einstein. (When such exists, may be called {\it
almost-everywhere conformally Einstein}.) We provide a complete classification
of compact K\"ahler manifolds with special K\"ahler-Ricci potentials and use it
to prove a structure theorem for compact K\"ahler manifolds of any complex
dimension which are almost-everywhere conformally Einstein.Comment: 45 pages, AMSTeX, submitted to Journal f\"ur die reine und angewandte
Mathemati
Preliminary studies for anapole moment measurements in rubidium and francium
Preparations for the anapole measurement in Fr indicate the possibility of
performing a similar measurement in a chain of Rb. The sensitivity analysis
based on a single nucleon model shows the potential for placing strong limits
on the nucleon weak interaction parameters. There are values of the magnetic
fields at much lower values than found before that are insensitive to first
order changes in the field. The anapole moment effect in Rb corresponds to an
equivalent electric field that is eighty times smaller than Fr, but the
stability of the isotopes and the current performance of the dipole trap in the
apparatus, presented here, are encouraging for pursuing the measurment.Comment: 16 pages, 6 figures. Accepted for publication in the J. Phys.
Analysis of plasma instabilities and verification of the BOUT code for the Large Plasma Device
The properties of linear instabilities in the Large Plasma Device [W.
Gekelman et al., Rev. Sci. Inst., 62, 2875 (1991)] are studied both through
analytic calculations and solving numerically a system of linearized
collisional plasma fluid equations using the 3D fluid code BOUT [M. Umansky et
al., Contrib. Plasma Phys. 180, 887 (2009)], which has been successfully
modified to treat cylindrical geometry. Instability drive from plasma pressure
gradients and flows is considered, focusing on resistive drift waves, the
Kelvin-Helmholtz and rotational interchange instabilities. A general linear
dispersion relation for partially ionized collisional plasmas including these
modes is derived and analyzed. For LAPD relevant profiles including strongly
driven flows it is found that all three modes can have comparable growth rates
and frequencies. Detailed comparison with solutions of the analytic dispersion
relation demonstrates that BOUT accurately reproduces all characteristics of
linear modes in this system.Comment: Published in Physics of Plasmas, 17, 102107 (2010
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