2,049 research outputs found
Dynamical solutions of a quantum Heisenberg spin glass model
We consider quantum-dynamical phenomena in the ,
infinite-range quantum Heisenberg spin glass. For a fermionic generalization of
the model we formulate generic dynamical self-consistency equations. Using the
Popov-Fedotov trick to eliminate contributions of the non-magnetic fermionic
states we study in particular the isotropic model variant on the spin space.
Two complementary approximation schemes are applied: one restricts the quantum
spin dynamics to a manageable number of Matsubara frequencies while the other
employs an expansion in terms of the dynamical local spin susceptibility. We
accurately determine the critical temperature of the spin glass to
paramagnet transition. We find that the dynamical correlations cause an
increase of by 2% compared to the result obtained in the spin-static
approximation. The specific heat exhibits a pronounced cusp at .
Contradictory to other reports we do not observe a maximum in the -curve
above .Comment: 8 pages, 7 figure
Correlation of creep rate with microstructural changes during high temperature creep
Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten
Induced Ginibre ensemble of random matrices and quantum operations
A generalisation of the Ginibre ensemble of non-Hermitian random square
matrices is introduced. The corresponding probability measure is induced by the
ensemble of rectangular Gaussian matrices via a quadratisation procedure. We
derive the joint probability density of eigenvalues for such induced Ginibre
ensemble and study various spectral correlation functions for complex and real
matrices, and analyse universal behaviour in the limit of large dimensions. In
this limit the eigenvalues of the induced Ginibre ensemble cover uniformly a
ring in the complex plane. The real induced Ginibre ensemble is shown to be
useful to describe statistical properties of evolution operators associated
with random quantum operations, for which the dimensions of the input state and
the output state do differ.Comment: 2nd version, 34 pages, 5 figure
Implicit Bias in Daily Perceptions and Legal Judgments
In today’s demonstration, we explored the audience’s positive and negative associations with blacks and whites. The demonstration is an adaptation of the Implicit Association Test (www.projectimplicit.net), a computer-based task designed to explore mental connections between various concepts. Participants were presented with a list of concepts (stereotypically black and white names, pleasant and unpleasant concepts) in a column down the middle of a screen along with the response categories (black/white or Pleasant/Unpleasant) along the left and right sides. When reading a word, participants were asked to categorize it by slapping the knee (left or right) that corresponds to the category displayed on the left or right side of the screen. Their task was to do this as fast as possible, correcting any mistakes before going forward, and raising their hand after completing the last word in the list. We then noted the amount of time for a critical mass of participants (approximately seventy-five percent) to complete each trial. In simple trials, either names or valenced words are displayed. In two critical trials, both names and valenced words were presented simultaneously in the middle of the screen. The trials differ based on the pairings of the response categories, and these trials tend to show a drastic difference in completion times. When participants were required to use the same hand to categorize black names and unpleasant words or white names and pleasant words, they tended to respond almost twice as quickly as when using the same hand to categorize black names and pleasant words or white names and unpleasant words. While there are individual differences among the respondents, the demonstration provided audible and visceral evidence of the trend. We then asked the audience to interrogate the methodological and cultural implications of the task, ultimately concluding that the test potentially reveals the fairly widespread implicit negative associations with blacks. With this working hypothesis, we next discussed the nature of racial bias and its implications for judgment in legal domains
Nonlinear oscillations of gas bubbles submerged in water: implications for plasma breakdown
Gas bubbles submerged in a dielectric liquid and driven by an electric field can undergo dramatic changes in both shape and volume. In certain cases, this deformation can enhance the distribution of the applied field inside the bubble as well as decrease the internal gas pressure. Both effects will tend to facilitate plasma formation in the gas volume. A practical realization of these two effects could have a broad impact on the viability of liquid plasma technologies, which tend to suffer from high voltage requirements. In this experiment, bubbles of diameter 0.4–0.7 mm are suspended in the node of a 26.4 kHz underwater acoustic standing wave and excited into nonlinear shape oscillations using ac electric fields with amplitudes of 5–15 kV cm ‚à Ã1 . Oscillations of the deformed bubble are photographed with a high-speed camera operating at 5130 frames s ‚à Ã1 and the resulting images are decomposed into their axisymmetric spherical harmonic modes, ##IMG## [http://ej.iop.org/images/0022-3727/45/41/415203/jphysd431220ieqn001.gif] { , using an edge detection algorithm. Overall, the bubble motion is dominated by the first three even modes l = 0, 2 and 4. Electrostatic simulations of the deformed bubble's internal electric field indicate that the applied field is enhanced by as much as a factor of 2.3 above the nominal applied field. Further simulation of both the pure l = 2 and l = 4 modes predicts that with additional deformation, the field enhancement factors could reach as much as 10–50.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98592/1/0022-3727_45_41_415203.pd
Two-Qubit Separabilities as Piecewise Continuous Functions of Maximal Concurrence
The generic real (b=1) and complex (b=2) two-qubit states are 9-dimensional
and 15-dimensional in nature, respectively. The total volumes of the spaces
they occupy with respect to the Hilbert-Schmidt and Bures metrics are
obtainable as special cases of formulas of Zyczkowski and Sommers. We claim
that if one could determine certain metric-independent 3-dimensional
"eigenvalue-parameterized separability functions" (EPSFs), then these formulas
could be readily modified so as to yield the Hilbert-Schmidt and Bures volumes
occupied by only the separable two-qubit states (and hence associated
separability probabilities). Motivated by analogous earlier analyses of
"diagonal-entry-parameterized separability functions", we further explore the
possibility that such 3-dimensional EPSFs might, in turn, be expressible as
univariate functions of some special relevant variable--which we hypothesize to
be the maximal concurrence (0 < C <1) over spectral orbits. Extensive numerical
results we obtain are rather closely supportive of this hypothesis. Both the
real and complex estimated EPSFs exhibit clearly pronounced jumps of magnitude
roughly 50% at C=1/2, as well as a number of additional matching
discontinuities.Comment: 12 pages, 7 figures, new abstract, revised for J. Phys.
Nonlinear statistics of quantum transport in chaotic cavities
Copyright © 2008 The American Physical Society.In the framework of the random matrix approach, we apply the theory of Selberg’s integral to problems of quantum transport in chaotic cavities. All the moments of transmission eigenvalues are calculated analytically up to the fourth order. As a result, we derive exact explicit expressions for the skewness and kurtosis of the conductance and transmitted charge as well as for the variance of the shot-noise power in chaotic cavities. The obtained results are generally valid at arbitrary numbers of propagating channels in the two attached leads. In the particular limit of large (and equal) channel numbers, the shot-noise variance attends the universal value 1∕64β that determines a universal Gaussian statistics of shot-noise fluctuations in this case.DFG and BRIEF
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