13,384 research outputs found
The effects of surface finish and grain size on the strength of sintered silicon carbide
The effects of surface treatment and microstructure, especially abnormal grain growth, on the strength of sintered SiC were studied. The surfaces of sintered SiC were treated with 400, 800 and 1200 grit diamond wheels. Grain growth was induced by increasing the sintering times at 2050 C. The beta to alpha transformation occurred during the sintering of beta-phase starting materials and was often accompanied by abnormal grain growth. The overall strength distributions were established using Weibull statistics. The strength of the sintered SiC is limited by extrinsic surface flaws in normal-sintered specimens. The finer the surface finish and grain size, the higher the strength. But the strength of abnormal sintering specimens is limited by the abnormally grown large tabular grains. The Weibull modulus increases with decreasing grain size and decreasing grit size for grinding
An improved solar wind electron-density model for pulsar timing
Variations in the solar wind density introduce variable delays into pulsar
timing observations. Current pulsar timing analysis programs only implement
simple models of the solar wind, which not only limit the timing accuracy, but
can also affect measurements of pulsar rotational, astrometric and orbital
parameters. We describe a new model of the solar wind electron density content
which uses observations from the Wilcox Solar Observatory of the solar magnetic
field. We have implemented this model into the tempo2 pulsar timing package. We
show that this model is more accurate than previous models and that these
corrections are necessary for high precision pulsar timing applications.Comment: Accepted by ApJ, 13 pages, 4 figure
Self-consistent models of triaxial galaxies in MOND gravity
The Bekenstein-Milgrom gravity theory with a modified Poisson equation is
tested here for the existence of triaxial equilibrium solutions. Using the
non-negative least square method, we show that self-consistent triaxial
galaxies exist for baryonic models with a mild density cusp . Self-consistency is achieved for a wide range of central
concentrations, , representing
low-to-high surface brightness galaxies. Our results demonstrate for the first
time that the orbit superposition technique is fruitful for constructing galaxy
models beyond Newtonian gravity, and triaxial cuspy galaxies might exist
without the help of Cold dark Matter.Comment: 19 pages, 1 table, 7 figures, Accepted for publication in Ap
Tube choledochoureterostomy: A simple method for bile diversion
A technique of bile diversion by tube choledochoureterostomy has been devised for the purpose of studying the role of bile in the intestinal absorption of drugs. This method was used in six dogs. No technical difficulties or major complications developed, as are inevitable with alternative methods, including external fistula. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
Non-Markovian entanglement dynamics in coupled superconducting qubit systems
We theoretically analyze the entanglement generation and dynamics by coupled
Josephson junction qubits. Considering a current-biased Josephson junction
(CBJJ), we generate maximally entangled states. In particular, the entanglement
dynamics is considered as a function of the decoherence parameters, such as the
temperature, the ratio between the reservoir cutoff
frequency and the system oscillator frequency , % between
the characteristic frequency of the %quantum system of interest, and
the cut-off frequency of %Ohmic reservoir and the energy levels
split of the superconducting circuits in the non-Markovian master equation. We
analyzed the entanglement sudden death (ESD) and entanglement sudden birth
(ESB) by the non-Markovian master equation. Furthermore, we find that the
larger the ratio and the thermal energy , the shorter the
decoherence. In this superconducting qubit system we find that the entanglement
can be controlled and the ESD time can be prolonged by adjusting the
temperature and the superconducting phases which split the energy
levels.Comment: 13 pages, 3 figure
Numerical study of the one-dimensional quantum compass model
The ground state magnetic phase diagram of the one-dimensional quantum
compass model (QCM) is studied using the numerical Lanczos method. A detailed
numerical analysis of the low energy excitation spectrum is presented. The
energy gap and the spin-spin correlation functions are calculated for finite
chains. Two kind of the magnetic long-range orders, the Neel and a type of the
stripe-antiferromagnet, in the ground state phase diagram are identified. Based
on the numerical analysis, the first and second order quantum phase transitions
in the ground state phase diagram are identified.Comment: 6 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1105.211
Variational perturbation approach to the Coulomb electron gas
The efficiency of the variational perturbation theory [Phys. Rev. C {\bf 62},
045503 (2000)] formulated recently for many-particle systems is examined by
calculating the ground state correlation energy of the 3D electron gas with the
Coulomb interaction. The perturbation beyond a variational result can be
carried out systematically by the modified Wick's theorem which defines a
contraction rule about the renormalized perturbation. Utilizing the theorem,
variational ring diagrams of the electron gas are summed up. As a result, the
correlation energy is found to be much closer to the result of the Green's
function Monte Carlo calculation than that of the conventional ring
approximation is.Comment: 4 pages, 3 figure
Status Update of the Parkes Pulsar Timing Array
The Parkes Pulsar Timing Array project aims to make a direct detection of a
gravitational-wave background through timing of millisecond pulsars. In this
article, the main requirements for that endeavour are described and recent and
ongoing progress is outlined. We demonstrate that the timing properties of
millisecond pulsars are adequate and that technological progress is timely to
expect a successful detection of gravitational waves within a decade, or
alternatively to rule out all current predictions for gravitational wave
backgrounds formed by supermassive black-hole mergers.Comment: 10 pages, 3 figures, Amaldi 8 conference proceedings, accepted by
Classical & Quantum Gravit
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