58,707 research outputs found
Completion of evaluation of manufacturing processes for B/Al composites containing 0.2mm diameter boron fibers
Four fabricators produced a total of 54 B/1100 Al, B/6061 Al, and B/2024 Al panels for evaluation. The 8 ply unidirectional, 45 to 50 volume percent, panels were made using 0.20 mm diameter boron fibers which were obtained from a single supplier. Hot press consolidation was carried out in vacuum except for one set of dry woven tape panels which were hot pressed in air. A single testing contractor conducted nondestructive inspection, metallography, fractography and mechanical property tests. The mechanical property tests included 21 and 260 C tensile tests and 21 C shear tests. Panel quality, as measured by nondestructive evaluation, was generally good as were the 21 C tensile properties. The panels hot pressed in air delaminated in the shear tests. Shear strength values were lower in these panels. But tensile strengths were not affected by the delaminations because of the relation between the tensile loading direction and the delaminations. Composite tensile strength was found to be proportional to the volume percent boron and the aluminum matrix rather than to the tape used or fabrication technique. Suitability of these composites for 260 C service was confirmed by tensile tests
Configuration interaction in the helium continuum
Configuration interaction in helium continuum and autoionization level
Universal nonequilibrium signatures of Majorana zero modes in quench dynamics
The quantum evolution after a metallic lead is suddenly connected to an
electron system contains information about the excitation spectrum of the
combined system. We exploit this type of "quantum quench" to probe the presence
of Majorana fermions at the ends of a topological superconducting wire. We
obtain an algebraically decaying overlap (Loschmidt echo) for large times after the quench, with
a universal critical exponent =1/4 that is found to be remarkably
robust against details of the setup, such as interactions in the normal lead,
the existence of additional lead channels or the presence of bound levels
between the lead and the superconductor. As in recent quantum dot experiments,
this exponent could be measured by optical absorption, offering a new signature
of Majorana zero modes that is distinct from interferometry and tunneling
spectroscopy.Comment: 9 pages + appendices, 4 figures. v3: published versio
Logarithmic terms in entanglement entropies of 2D quantum critical points and Shannon entropies of spin chains
Universal logarithmic terms in the entanglement entropy appear at quantum
critical points (QCPs) in one dimension (1D) and have been predicted in 2D at
QCPs described by 2D conformal field theories. The entanglement entropy in a
strip geometry at such QCPs can be obtained via the "Shannon entropy" of a 1D
spin chain with open boundary conditions. The Shannon entropy of the XXZ chain
is found to have a logarithmic term that implies, for the QCP of the
square-lattice quantum dimer model, a logarithm with universal coefficient . However, the logarithm in the Shannon entropy of the transverse-field
Ising model, which corresponds to entanglement in the 2D Ising conformal QCP,
is found to have a singular dependence on replica or R\'enyi index resulting
from flows to different boundary conditions at the entanglement cut.Comment: 4 pages and 4 page appendix, 4 figure
Optimal Estimation of Several Linear Parameters in the Presence of Lorentzian Thermal Noise
In a previous article we developed an approach to the optimal (minimum
variance, unbiased) statistical estimation technique for the equilibrium
displacement of a damped, harmonic oscillator in the presence of thermal noise.
Here, we expand that work to include the optimal estimation of several linear
parameters from a continuous time series. We show that working in the basis of
the thermal driving force both simplifies the calculations and provides
additional insight to why various approximate (not optimal) estimation
techniques perform as they do. To illustrate this point, we compare the
variance in the optimal estimator that we derive for thermal noise with those
of two approximate methods which, like the optimal estimator, suppress the
contribution to the variance that would come from the irrelevant, resonant
motion of the oscillator. We discuss how these methods fare when the dominant
noise process is either white displacement noise or noise with power spectral
density that is inversely proportional to the frequency ( noise). We also
construct, in the basis of the driving force, an estimator that performs well
for a mixture of white noise and thermal noise. To find the optimal
multi-parameter estimators for thermal noise, we derive and illustrate a
generalization of traditional matrix methods for parameter estimation that can
accommodate continuous data. We discuss how this approach may help refine the
design of experiments as they allow an exact, quantitative comparison of the
precision of estimated parameters under various data acquisition and data
analysis strategies.Comment: 16 pages, 10 figures. Accepted for publication in Classical and
Quantum Gravit
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