28,806 research outputs found
Motion around a Monopole + Ring system: I. Stability of Equatorial Circular Orbits vs Regularity of Three-dimensional Motion
We study the motion of test particles around a center of attraction
represented by a monopole (with and without spheroidal deformation) surrounded
by a ring, given as a superposition of Morgan & Morgan discs. We deal with two
kinds of bounded orbits: (i) Equatorial circular orbits and (ii) general
three-dimensional orbits. The first case provides a method to perform a linear
stability analysis of these structures by studying the behavior of vertical and
epicyclic frequencies as functions of the mass ratio, the size of the ring
and/or the quadrupolar deformation. In the second case, we study the influence
of these parameters in the regularity or chaoticity of motion. We find that
there is a close connection between linear stability (or unstability) of
equatorial circular orbits and regularity (or chaoticity) of the
three-dimensional motion.Comment: 13 pages, 17 figures, to appear in MNRA
Boundary versus bulk behavior of time-dependent correlation functions in one-dimensional quantum systems
We study the influence of reflective boundaries on time-dependent responses
of one-dimensional quantum fluids at zero temperature beyond the low-energy
approximation. Our analysis is based on an extension of effective mobile
impurity models for nonlinear Luttinger liquids to the case of open boundary
conditions. For integrable models, we show that boundary autocorrelations
oscillate as a function of time with the same frequency as the corresponding
bulk autocorrelations. This frequency can be identified as the band edge of
elementary excitations. The amplitude of the oscillations decays as a power law
with distinct exponents at the boundary and in the bulk, but boundary and bulk
exponents are determined by the same coupling constant in the mobile impurity
model. For nonintegrable models, we argue that the power-law decay of the
oscillations is generic for autocorrelations in the bulk, but turns into an
exponential decay at the boundary. Moreover, there is in general a nonuniversal
shift of the boundary frequency in comparison with the band edge of bulk
excitations. The predictions of our effective field theory are compared with
numerical results obtained by time-dependent density matrix renormalization
group (tDMRG) for both integrable and nonintegrable critical spin- chains
with , and .Comment: 20 pages, 12 figure
Hamming distance and mobility behavior in generalized rock-paper-scissors models
This work reports on two related investigations of stochastic simulations
which are widely used to study biodiversity and other related issues. We first
deal with the behavior of the Hamming distance under the increase of the number
of species and the size of the lattice, and then investigate how the mobility
of the species contributes to jeopardize biodiversity. The investigations are
based on the standard rules of reproduction, mobility and predation or
competition, which are described by specific rules, guided by generalization of
the rock-paper-scissors game, valid in the case of three species. The results
on the Hamming distance indicate that it engenders universal behavior,
independently of the number of species and the size of the square lattice. The
results on the mobility confirm the prediction that it may destroy diversity,
if it is increased to higher and higher values.Comment: 7 pages, 9 figures. To appear in EP
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
Thermal diagnostic of the Optical Window on board LISA Pathfinder
Vacuum conditions inside the LTP Gravitational Reference Sensor must comply
with rather demanding requirements. The Optical Window (OW) is an interface
which seals the vacuum enclosure and, at the same time, lets the laser beam go
through for interferometric Metrology with the test masses. The OW is a
plane-parallel plate clamped in a Titanium flange, and is considerably
sensitive to thermal and stress fluctuations. It is critical for the required
precision measurements, hence its temperature will be carefully monitored in
flight. This paper reports on the results of a series of OW characterisation
laboratory runs, intended to study its response to selected thermal signals, as
well as their fit to numerical models, and the meaning of the latter. We find
that a single pole ARMA transfer function provides a consistent approximation
to the OW response to thermal excitations, and derive a relationship with the
physical processes taking place in the OW. We also show how system noise
reduction can be accomplished by means of that transfer function.Comment: 20 pages, 14 figures; accepted for publication in Class. Quantum Gra
Bayesian approach to fuse NDT data to find dynamic elastic modulus of granite stone
The main objective of the paper is to propose a criterion for combining NDT test data coming from sonic and ultrasonic tests to evaluate dynamic elastic modulus of granite stone. Bayesian updating allows us to combine initial information with new information to provide more realistic results. The paper fuses NDT test data gathered from sonic and ultrasonic tests having uncertainties in velocity, Poisson ratio and density values of granite stone under consideration using Bayesian statistics into a normal probabilistic distribution plot of dynamic elastic modulus. Many times especially in case of heritage buildings destructive tests count be performed because of minimum intrusion guidelines, so one has to rely on NDT test data to gain knowledge about the mechanical parameters of the building
Sound and light from fractures in scintillators
Prompted by intriguing events observed in certain particle-physics searches
for rare events, we study light and acoustic emission simultaneously in some
inorganic scintillators subject to mechanical stress. We observe
mechanoluminescence in , and ,
in various mechanical configurations at room temperature and ambient pressure.
We analyze how the light emission is correlated to acoustic emission during
fracture. For , we set a lower bound on the energy of
the emitted light, and deduce that the fraction of elastic energy converted to
light is at least
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