6,218 research outputs found
An analysis of the effect of a particular class of PFM on noise inputs
Statistical analysis of pulse frequency modulation systems with white noise inpu
Collisional Effects on Nonlinear Ion Drag Force for Small Grains
The ion drag force arising from plasma flow past an embedded spherical grain
is calculated self-consistently and non-linearly using particle in cell codes,
accounting for ion-neutral collisions. Using ion velocity distribution
appropriate for ion drift driven by a force field gives wake potential and
force greatly different from a shifted Maxwellian distribution, regardless of
collisionality. The low-collisionality forces are shown to be consistent with
estimates based upon cross-sections for scattering in a Yukawa (shielded) grain
field, but only if non-linear shielding length is used. Finite collisionality
initially enhances the drag force, but only by up to a factor of 2. Larger
collisionality eventually reduces the drag force. In the collisional regime,
the drift distribution gives larger drag than the shift distribution even at
velocities where their collisionless drags are equal. Comprehensive practical
analytic formulas for force that fit the calculations are provided.Comment: Fig 1. corrected in this versio
Coating thermal noise of a finite-size cylindrical mirror
Thermal noise of a mirror is one of the limiting noise sources in the high
precision measurement such as gravitational-wave detection, and the modeling of
thermal noise has been developed and refined over a decade. In this paper, we
present a derivation of coating thermal noise of a finite-size cylindrical
mirror based on the fluctuation-dissipation theorem. The result agrees to a
previous result with an infinite-size mirror in the limit of large thickness,
and also agrees to an independent result based on the mode expansion with a
thin-mirror approximation. Our study will play an important role not only to
accurately estimate the thermal-noise level of gravitational-wave detectors but
also to help analyzing thermal noise in quantum-measurement experiments with
lighter mirrors.Comment: 13 pages, 4 figure
The incidence of sudden unexpected death in epilepsy (sudep) in south dublin and wicklow
Patients with epilepsy have a mortality rate higher than that of the general population. Some of this excess mortality is attributable to sudden unexpected death (SUDEP). We examined the incidence of this phenomenon both retrospectively and prospectively in the population of South Dublin and Wicklow over the period May 1992–1995. Cases were ascertained by examination of post-mortem registers of hospitals serving the area studied. Information on cases was sought from hospital records, general practitioners and families. Fifteen cases (10 male, five female) were identified resulting in an overall incidence rate of SUDEP of 1:680/year for the 3 years of the study. This is the only study of incidence of SUDEP conducted in Ireland and our results are in keeping with incidence rates elsewhere in Europe and the USA
Bivariate -distribution for transition matrix elements in Breit-Wigner to Gaussian domains of interacting particle systems
Interacting many-particle systems with a mean-field one body part plus a
chaos generating random two-body interaction having strength , exhibit
Poisson to GOE and Breit-Wigner (BW) to Gaussian transitions in level
fluctuations and strength functions with transition points marked by
and , respectively; . For these systems theory for matrix elements of one-body transition
operators is available, as valid in the Gaussian domain, with , in terms of orbitals occupation numbers, level densities and an
integral involving a bivariate Gaussian in the initial and final energies. Here
we show that, using bivariate -distribution, the theory extends below from
the Gaussian regime to the BW regime up to . This is well
tested in numerical calculations for six spinless fermions in twelve single
particle states.Comment: 7 pages, 2 figure
Excitations of a Bose-condensed gas in anisotropic traps
We investigate the zero-temperature collective excitations of a
Bose-condensed atomic gas in anisotropic parabolic traps. The condensate
density is determined by solving the Gross-Pitaevskii (GP) equation using a
spherical harmonic expansion. The GP eigenfunctions are then used to solve the
Bogoliubov equations to obtain the collective excitation frequencies and mode
densities. The frequencies of the various modes, classified by their parity and
the axial angular momentum quantum number, m, are mapped out as a function of
the axial anisotropy. Specific emphasis is placed upon the evolution of these
modes from the modes in the limit of an isotropic trap.Comment: 7 pages Revtex, 9 Postscript figure
Recommended from our members
A Stretch/Bend Method for In Situ Measurement of the Delamination Toughness of Coatings and Films Attached to Substrates
A stretch/bend method for the in situ measurement of the delamination toughness of coatings attached to substrates is described. A beam theory analysis is presented that illustrates the main features of the test. The analysis is general and allows for the presence of residual stress. It reveals that the test produces stable extension of delaminations, rendering it suitable for multiple measurements in a single test. It also provides scaling relations and enables estimates of the loads needed to extend delaminations. Finite element calculations reveal that the beam theory solutions are accurate for slender beams, but overestimate the energy release rate for stubbier configurations and short delaminations. The substantial influence of residual stress on the energy release rate and phase angle is highly dependent on parameters such as the thickness and modulus ratio for the two layers. Its effect must be included to obtain viable measurements of toughness. In a companion paper, the method has been applied to a columnar thermal barrier coating deposited onto a Ni-based super-alloy.Engineering and Applied Science
Limb bone scaling in hopping diprotodonts and quadrupedal artiodactyls
Bone adaptation is modulated by the timing, direction, rate, and magnitude of mechanical loads. To investigate whether frequent slow, or infrequent fast, gaits could dominate bone adaptation to load, we compared scaling of the limb bones from two mammalian herbivore clades that use radically different high-speed gaits, bipedal hopping and quadrupedal galloping. Forelimb and hindlimb bones were collected from 20 artiodactyl and 15 diprotodont species (body mass M 1.05 - 1536 kg) and scanned in clinical computed tomography or X-ray microtomography. Second moment of area (Imax) and bone length (l) were measured. Scaling relations (y = axb) were calculated for l vs M for each bone and for Imax vs M and Imax vs l for every 5% of length. Imax vs M scaling relationships were broadly similar between clades despite the diprotodont forelimb being nearly unloaded, and the hindlimb highly loaded, during bipedal hopping. Imax vs l and l vs M scaling were related to locomotor and behavioural specialisations. Low-intensity loads may be sufficient to maintain bone mass across a wide range of species. Occasional high-intensity gaits might not break through the load sensitivity saturation engendered by frequent low-intensity gaits
Undecidable properties of self-affine sets and multi-tape automata
We study the decidability of the topological properties of some objects
coming from fractal geometry. We prove that having empty interior is
undecidable for the sets defined by two-dimensional graph-directed iterated
function systems. These results are obtained by studying a particular class of
self-affine sets associated with multi-tape automata. We first establish the
undecidability of some language-theoretical properties of such automata, which
then translate into undecidability results about their associated self-affine
sets.Comment: 10 pages, v2 includes some corrections to match the published versio
Similar dissection of sets
In 1994, Martin Gardner stated a set of questions concerning the dissection
of a square or an equilateral triangle in three similar parts. Meanwhile,
Gardner's questions have been generalized and some of them are already solved.
In the present paper, we solve more of his questions and treat them in a much
more general context. Let be a given set and let
be injective continuous mappings. Does there exist a set such
that is satisfied with a
non-overlapping union? We prove that such a set exists for certain choices
of and . The solutions often turn out to be attractors
of iterated function systems with condensation in the sense of Barnsley. Coming
back to Gardner's setting, we use our theory to prove that an equilateral
triangle can be dissected in three similar copies whose areas have ratio
for
- …