82,705 research outputs found
A measurement-based measure of the size of macroscopic quantum superpositions
Recent experiments claiming formation of quantum superposition states in near
macroscopic sys- tems raise the question of how the sizes of general quantum
superposition states in an interacting system are to be quantified. We propose
here a measure of size for such superposition states that is based on what
measurements can be performed to probe and distinguish the different branches
of the state. The measure allows comparison of the effective size for
superposition states in very different physical systems. It can be applied to a
very general class of superposition states and reproduces known results for
near-ideal cases. Comparison with a prior measure based on analy- sis of
coherence between branches indicates that significantly smaller effective
superposition sizes result from our measurement-based measure. Application to a
system of interacting bosons in a double-well trapping potential shows that the
effective superposition size is strongly dependent on the relative magnitude of
the barrier height and interparticle interaction.Comment: 21 pages, 20 figures. Accepted by Phys. Rev. A. Replaced old version
with accepted version. Significant changes and improvements, particularly to
section on 1-particle measurement
Quantum ballistic experiment on antihydrogen fall
We study an interferometric approach to measure gravitational mass of
antihydrogen. The method consists of preparing a coherent superposition of
antihydrogen quantum state localized near a material surface in the
gravitational field of the Earth, and then observing the time distribution of
annihilation events followed after the free fall of an initially prepared
superposition from a given height to the detector plate. We show that a
corresponding time distribution is related to the momentum distribution in the
initial state that allows its precise measurement. This approach is combined
with a method of production of a coherent superposition of gravitational states
by inducing a resonant transition using oscillating gradient magnetic field. We
estimate an accuracy of measuring the gravitational mass of antihydrogen atom
which could be deduced from such a measurement.Comment: arXiv admin note: text overlap with arXiv:1403.478
Extended active space CASSCF/MRSD CI calculations of the barrier height for the reaction: O + H2 yields OH + H
The convergence of the barrier height for the O + H2 yields OH + H reaction was studied as a function of the size of the active space and basis set completeness. The barrier height is rapidly convergent with respect to expansion of the active space. Addition of 2p yields 2p' correlation terms to the active space lowers the barrier to the O + H2 reaction by about 2.0 kcal/mole, but addition of 3d and other terms has little additional effect. Multireference singles and doubles contracted CI plus Davidson's correction calculations using a (5s5p3d2f1g/4s3p2d1f) basis set with a 5 sigma 2 pi active space lead to a barrier height of 12.7 kcal/mole. Including an estimate of the CI contraction error and basis set superposition error leads to 12.4 kcal/mole as the best estimate of the barrier height
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A Study of Static and Dynamic Mechanical Behavior of the Substrate in Ultrasonic Consolidation
A new 2-D FEM model is developed for a fundamental study of the time
dependent mechanical behavior of the substrate in ultrasonic consolidation. The simulation
shows that for a given vibration condition, the amplitude of contact friction stress and
displacement stabilize to a saturated state after certain number of ultrasonic cycles. With
the increased substrate height, the amplitude of contact frictional stress decreases, while
that of contact interface displacement increases. The energy density and transfer coefficient
at the contact interface with different substrate heights can be used as parameters to predict
the potential for ultrasonic bonding. The reason for the decrease in the frictional stress
and displacement at the contact interface for certain substrate height seems to be caused by
the complicated wave interference occurring in the substrate. A specific substrate geometry
generates a minimum strain state at the interface as a result of wave superposition. Such
minimum strain state is believed to have produced the “lack of bonding” defect.Mechanical Engineerin
Two-dimensional Gaussian processes applied to the determination of contact between lubricated rolling surfaces
The effectiveness of a lubricant film preventing metallic contact between two rolling surfaces (such as in ball bearings) as a function of surface roughness parameters was investigated. The parameters considered are the spectral moments of the two-dimensional surface obtained by superposition of the two rolling surfaces. The peak height distribution, estimation of one-dimensional profile spectral moments, and the estimation of two-dimensional surface moments from several profile measurements were considered. Also given is an asymptotic relation between the mean film thickness and contact occurrences
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