52,951 research outputs found
Fatigue failure load indicator
An indicator for recording the load at which a fatigue specimen breaks during the last cycle of a fatigue test is described. A load cell is attached to the specimen which is alternately subjected to tension and compression loads. The output of the load cell which is proportional to the load on the specimen is applied to the input of a peak detector. Each time the specimen is subjected to a compression load, means are provided for applying a positive voltage to the rest of the peak detector to reset it. During the last cycle of the tension load the peak detector measures the maximum load on the specimen. Means are provided for disconnecting the load cell from the peak detector when there is a failure in the specimen
On the Uniqueness of Solution of Magnetostatic Vector‐potential Problems by Three‐dimensional Finite‐element Methods
In this paper, particular attention is paid to the impact of finite‐element approximation on uniqueness and to approximations implicit in finite element formulations from the uniqueness requirements standpoint. It is also shown that the flux density is unique without qualifications. The theoretical and numerical uniqueness of the magnetic vector potential in three‐dimensional problems is also given. This analysis is restricted to linear, isotropic media with Dirichlet Boundary conditions. As an interesting consequence of this analysis it is shown that, under usual conditions adopted in obtaining three‐dimensional finite‐element solutions, it is not necessary to specify div Ā in order that Ā be uniquely defined
Chiral Vortons and Cosmological Constraints on Particle Physics
We investigate the cosmological consequences of particle physics theories
that admit stable loops of current-carrying string - vortons. In particular, we
consider chiral theories where a single fermion zero mode is excited in the
string core, such as those arising in supersymmetric theories with a D-term.
The resulting vortons formed in such theories are expected to be more stable
than their non-chiral cousins. General symmetry breaking schemes are considered
in which strings formed at one symmetry breaking scale become current-carrying
at a subsequent phase transition. The vorton abundance is estimated and
constraints placed on the underlying particle physics theories from
cosmological observations. Our constraints on the chiral theory are
considerably more stringent than the previous estimates for more general
theories.Comment: minor corrections made. This version will appear in PR
Oscillation pressure device for dynamic calibration of pressure transducers
Method and apparatus for obtaining dynamic calibrations of pressure transducers. A calibration head (15), a flexible tubing (23) and a bellows (20) enclose a volume of air at atmospheric pressure with a transducer (11) to be calibrated subject to the pressure inside the volume. All of the other apparatus in the drawing apply oscillations to bellows (20) causing the volume to change thereby applying oscillating pressures to transducer (11) whereby transducer (11) can be calibrated
Reexamination of optimal quantum state estimation of pure states
A direct derivation is given for the optimal mean fidelity of quantum state
estimation of a d-dimensional unknown pure state with its N copies given as
input, which was first obtained by M. Hayashi in terms of an infinite set of
covariant positive operator valued measures (POVM's) and by Bruss and
Macchiavello establishing a connection to optimal quantum cloning. An explicit
condition for POVM measurement operators for optimal estimators is obtained, by
which we construct optimal estimators with finite POVM using exact quadratures
on a hypersphere. These finite optimal estimators are not generally universal,
where universality means the fidelity is independent of input states. However,
any optimal estimator with finite POVM for M(>N) copies is universal if it is
used for N copies as input.Comment: v3(journal version): title changed, presentation improve
Collisions of strings with Y junctions
We study the dynamics of Nambu--Goto strings with junctions at which three
strings meet. In particular, we exhibit one simple exact solution and examine
the process of intercommuting of two straight strings, in which they exchange
partners but become joined by a third string. We show that there are important
kinematical constraints on this process. The exchange cannot occur if the
strings meet with very large relative velocity. This may have important
implications for the evolution of cosmic superstring networks and non-abelian
string networks.Comment: 4 pages, 1 figure, uses revtex 4. Clarifying comments added to
correct a conceptual error, reference updated. Version accepted by Phys Rev
Letters, with additional references and minor change
A new numerical method to construct binary neutron star initial data
We present a new numerical method for the generation of binary neutron star
initial data using a method along the lines of the the Wilson-Mathews or the
closely related conformal thin sandwich approach. Our method uses six different
computational domains, which include spatial infinity. Each domain has its own
coordinates which are chosen such that the star surfaces always coincide with
domain boundaries. These properties facilitate the imposition of boundary
conditions. Since all our fields are smooth inside each domain, we are able to
use an efficient pseudospectral method to solve the elliptic equations
associated with the conformal thin sandwich approach. Currently we have
implemented corotating configurations with arbitrary mass ratios, but an
extension to arbitrary spins is possible. The main purpose of this paper is to
introduce our new method and to test our code for several different
configurations.Comment: 18 pages, 8 figures, 1 tabl
The stochastic Gross-Pitaevskii equation II
We provide a derivation of a more accurate version of the stochastic
Gross-Pitaevskii equation, as introduced by Gardiner et al. (J. Phys. B
35,1555,(2002). The derivation does not rely on the concept of local energy and
momentum conservation, and is based on a quasi-classical Wigner function
representation of a "high temperature" master equation for a Bose gas, which
includes only modes below an energy cutoff E_R that are sufficiently highly
occupied (the condensate band). The modes above this cutoff (the non-condensate
band) are treated as being essentially thermalized. The interaction between
these two bands, known as growth and scattering processes, provide noise and
damping terms in the equation of motion for the condensate band, which we call
the stochastic Gross-Pitaevskii equation. This approach is distinguished by the
control of the approximations made in its derivation, and by the feasibility of
its numerical implementation.Comment: 24 pages of LaTeX, one figur
Semiclassical Extremal Blackholes
Extremal black holes are studied in a two dimensional model motivated by a
dimensional reduction from four dimensions. Their quantum corrected geometry is
calculated semiclassically and a mild singularity is shown to appear at the
horizon.
Extensions of the geometry past the horizon are not unique but there are
continuations free from malevolent singularities. A few comments are made about
the relevance of these results to four dimensions and to the study of black
hole entropy and information loss.Comment: 16 pages, 2 figures upon request, CALT-68-1833 - (new version
corrects omissions in previous list of references
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