12,786 research outputs found
EMU Ag-Zn battery wet-life extension test
The Extravehicular Mobility Unit (EMU) silver/zinc (Ag/Zn) battery is an 11 cell battery of approximately 30 AH. The Ag/Zn battery is comprised of two 4-cell monoblocks and one 3-cell monoblock. A discussion of a wet-life extension test performed on the battery is given in viewgraph form
Permutations preserving divisibility
We give a proof of a theorem on the common divisibility of polynomials and permuted polynomials (over GF(2)) by a polynomial g(x)
Nonequilibrium Stationary States and Phase Transitions in Directed Ising Models
We study the nonequilibrium properties of directed Ising models with non
conserved dynamics, in which each spin is influenced by only a subset of its
nearest neighbours. We treat the following models: (i) the one-dimensional
chain; (ii) the two-dimensional square lattice; (iii) the two-dimensional
triangular lattice; (iv) the three-dimensional cubic lattice. We raise and
answer the question: (a) Under what conditions is the stationary state
described by the equilibrium Boltzmann-Gibbs distribution? We show that for
models (i), (ii), and (iii), in which each spin "sees" only half of its
neighbours, there is a unique set of transition rates, namely with exponential
dependence in the local field, for which this is the case. For model (iv), we
find that any rates satisfying the constraints required for the stationary
measure to be Gibbsian should satisfy detailed balance, ruling out the
possibility of directed dynamics. We finally show that directed models on
lattices of coordination number with exponential rates cannot
accommodate a Gibbsian stationary state. We conjecture that this property
extends to any form of the rates. We are thus led to the conclusion that
directed models with Gibbsian stationary states only exist in dimension one and
two. We then raise the question: (b) Do directed Ising models, augmented by
Glauber dynamics, exhibit a phase transition to a ferromagnetic state? For the
models considered above, the answers are open problems, to the exception of the
simple cases (i) and (ii). For Cayley trees, where each spin sees only the
spins further from the root, we show that there is a phase transition provided
the branching ratio, , satisfies
Improved version of the eikonal model for absorbing spherical particles
We present a new expression of the scattering amplitude, valid for spherical
absorbing objects, which leads to an improved version of the eikonal method
outside the diffraction region. Limitations of this method are discussed and
numerical results are presented and compared successfully with the Mie theory.Comment: 7 pages, postscript figures available on cpt.univ-mrs.fr, to appear
in J. Mod. Optic
General limit to non-destructive optical detection of atoms
We demonstrate that there is a fundamental limit to the sensitivity of
phase-based detection of atoms with light for a given maximum level of
allowable spontaneous emission. This is a generalisation of previous results
for two-level and three-level atoms. The limit is due to an upper bound on the
phase shift that can be imparted on a laser beam for a given excited state
population. Specifially, we show that no single-pass optical technique using
classical light, based on any number of lasers or coherences between any number
of levels, can exceed the limit imposed by the two-level atom. This puts
significant restrictions on potential non-destructive optical measurement
schemes.Comment: 7 pages, 1 figur
Calculation of model Hamiltonian parameters for LaMnO_3 using maximally localized Wannier functions
Maximally localized Wannier functions (MLWFs) based on Kohn-Sham
band-structures provide a systematic way to construct realistic, materials
specific tight-binding models for further theoretical analysis. Here, we
construct MLWFs for the Mn e_g bands in LaMnO_3, and we monitor changes in the
MLWF matrix elements induced by different magnetic configurations and
structural distortions. From this we obtain values for the local Jahn-Teller
and Hund's rule coupling strength, the hopping amplitudes between all nearest
and further neighbors, and the corresponding reduction due to the GdFeO_3-type
distortion. By comparing our results with commonly used model Hamiltonians for
manganites, where electrons can hop between two "e_g-like" orbitals located on
each Mn site, we find that the most crucial limitation of such models stems
from neglecting changes in the underlying Mn(d)-O(p) hybridization.Comment: 15 pages, 11 figures, 3 table
Bootstrapping six-gluon scattering in planar super-Yang-Mills theory
We describe the hexagon function bootstrap for solving for six-gluon
scattering amplitudes in the large limit of super-Yang-Mills
theory. In this method, an ansatz for the finite part of these amplitudes is
constrained at the level of amplitudes, not integrands, using boundary
information. In the near-collinear limit, the dual picture of the amplitudes as
Wilson loops leads to an operator product expansion which has been solved using
integrability by Basso, Sever and Vieira. Factorization of the amplitudes in
the multi-Regge limit provides additional boundary data. This bootstrap has
been applied successfully through four loops for the maximally helicity
violating (MHV) configuration of gluon helicities, and through three loops for
the non-MHV case.Comment: 15 pages, 3 figures, 2 tables; contribution to the proceedings of
Loops and Legs in Quantum Field Theory, 27 April - 2 May 2014, Weimar,
Germany; v2, reference adde
On the backreaction of frame dragging
The backreaction on black holes due to dragging heavy, rather than test,
objects is discussed. As a case study, a regular black Saturn system where the
central black hole has vanishing intrinsic angular momentum, J^{BH}=0, is
considered. It is shown that there is a correlation between the sign of two
response functions. One is interpreted as a moment of inertia of the black ring
in the black Saturn system. The other measures the variation of the black ring
horizon angular velocity with the central black hole mass, for fixed ring mass
and angular momentum. The two different phases defined by these response
functions collapse, for small central black hole mass, to the thin and fat ring
phases. In the fat phase, the zero area limit of the black Saturn ring has
reduced spin j^2>1, which is related to the behaviour of the ring angular
velocity. Using the `gravitomagnetic clock effect', for which a universality
property is exhibited, it is shown that frame dragging measured by an
asymptotic observer decreases, in both phases, when the central black hole mass
increases, for fixed ring mass and angular momentum. A close parallelism
between the results for the fat phase and those obtained recently for the
double Kerr solution is drawn, considering also a regular black Saturn system
with J^{BH}\neq 0.Comment: 18 pages, 8 figure
Surprises in the suddenly-expanded infinite well
I study the time-evolution of a particle prepared in the ground state of an
infinite well after the latter is suddenly expanded. It turns out that the
probability density shows up quite a surprising behaviour:
for definite times, {\it plateaux} appear for which is
constant on finite intervals for . Elements of theoretical explanation are
given by analyzing the singular component of the second derivative
. Analytical closed expressions are obtained for some
specific times, which easily allow to show that, at these times, the density
organizes itself into regular patterns provided the size of the box in large
enough; more, above some critical time-dependent size, the density patterns are
independent of the expansion parameter. It is seen how the density at these
times simply results from a construction game with definite rules acting on the
pieces of the initial density.Comment: 24 pages, 14 figure
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