33,195 research outputs found
Process reconstruction from incomplete and/or inconsistent data
We analyze how an action of a qubit channel (map) can be estimated from the
measured data that are incomplete or even inconsistent. That is, we consider
situations when measurement statistics is insufficient to determine consistent
probability distributions. As a consequence either the estimation
(reconstruction) of the channel completely fails or it results in an unphysical
channel (i.e., the corresponding map is not completely positive). We present a
regularization procedure that allows us to derive physically reasonable
estimates (approximations) of quantum channels. We illustrate our procedure on
specific examples and we show that the procedure can be also used for a
derivation of optimal approximations of operations that are forbidden by the
laws of quantum mechanics (e.g., the universal NOT gate).Comment: 9pages, 5 figure
Linear force and moment equations for an annular smooth shaft seal perturbed both angularly and laterally
Coefficients are derived for equations expressing the lateral force and pitching moments associated with both planar translation and angular perturbations from a nominally centered rotating shaft with respect to a stationary seal. The coefficients for the lowest order and first derivative terms emerge as being significant and are of approximately the same order of magnitude as the fundamental coefficients derived by means of Black's equations. Second derivative, shear perturbation, and entrance coefficient variation effects are adjudged to be small
Achievable efficiencies for probabilistically cloning the states
We present an example of quantum computational tasks whose performance is
enhanced if we distribute quantum information using quantum cloning.
Furthermore we give achievable efficiencies for probabilistic cloning the
quantum states used in implemented tasks for which cloning provides some
enhancement in performance.Comment: 9 pages, 8 figure
Management of erectile dysfunction post-radical prostatectomy
© 2015 Saleh et al.Radical prostatectomy is a commonly performed procedure for the treatment of localized prostate cancer. One of the long-term complications is erectile dysfunction. There is little consensus on the optimal management; however, it is agreed that treatment must be prompt to prevent fibrosis and increase oxygenation of penile tissue. It is vital that patient expectations are discussed, a realistic time frame of treatment provided, and treatment started as close to the prostatectomy as possible. Current treatment regimens rely on phosphodiesterase 5 inhibitors as a first-line therapy, with vacuum erection devices and intraurethral suppositories of alprostadil as possible treatment combination options. With nonresponders to these therapies, intracavernosal injections are resorted to. As a final measure, patients undergo the highly invasive penile prosthesis implantation. There is no uniform, objective treatment program for erectile dysfunction post-radical prostatectomy. Management plans are based on poorly conducted and often underpowered studies in combination with physician and patient preferences. They involve the aforementioned drugs and treatment methods in different sequences and doses. Prospective treatments include dietary supplements and gene therapy, which have shown promise with there proposed mechanisms of improving erectile function but are yet to be applied successfully in human patients
Atomic level micromagnetic model of recording media switching at elevated temperatures
An atomic level micromagnetic model of granular recording media is developed
and applied to examine external field-induced grain switching at elevated
temperatures which captures non-uniform reversal modes. The results are
compared with traditional methods which employ the Landau-Lifshitz-Gilbert
equations based on uniformly magnetized grains with assigned intrinsic
temperature profiles for and . Using nominal parameters
corresponding to high-anisotropy FePt-type media envisioned for Energy Assisted
Magnetic Recording, our results demonstrate that atomic-level reversal slightly
reduces the field required to switch grains at elevated temperatures, but
results in larger fluctuations, when compared to a uniformly magnetized grain
model.Comment: 4 pages, 5 figure
Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media
The results of micromagnetic simulations are presented which examine the
impact of thermal fluctuations on sweep rate dependent coercivities of both
single-layer and exchange-coupled-composite (ECC) perpendicular magnetic
recording media. M-H loops are calculated at four temperatures and sweep rates
spanning five decades with fields applied normal to the plane and at 45
degrees. The impact of interactions between grains is evaluated. The results
indicate a significantly weaker sweep-rate dependence for ECC media suggesting
more robustness to long-term thermal effects. Fitting the modeled results to
Sharrock-like scaling proposed by Feng and Visscher [J. Appl. Phys. 95, 7043
(2004)] is successful only in the case of single-layer media with the field
normal to the plane.Comment: 7 pages, 14 figure
About the screening of the charge of a proton migrating in a metal
The amount of screening of a proton in a metal, migrating under the influence
of an applied electric field, is calculated using different theoretical
formulations. First the lowest order screening expression derived by Sham
(1975) is evaluated. In addition 'exact' expressions are evaluated which were
derived according to different approaches. For a proton in a metal modeled as a
jellium the screening appears to be 15 +/- 10 %, which is neither negligible
not reconcilable with the controversial full-screening point of view of
Bosvieux and Friedel (1962). In reconsidering the theory of electromigration, a
new simplified linear-response expression for the driving force is shown to
lead to essentially the same result as found by Sorbello (1985), who has used a
rather complicated technique. The expressions allow for a reduction such that
only the scattering phase shifts of the migrating impurity are required.
Finally it is shown that the starting formula for the driving force of Bosvieux
and Friedel leads exactly to the zero-temperature limit of well-established
linear response descriptions, by which the sting of the controversy has been
removed.Comment: 14 pages, 5 figure
Periodic homogenization of a pseudo-parabolic equation via a spatial-temporal decomposition
Pseudo-parabolic equations have been used to model unsaturated fluid flow in
porous media. In this paper it is shown how a pseudo-parabolic equation can be
upscaled when using a spatio-temporal decomposition employed in the
Peszyn'ska-Showalter-Yi paper [8]. The spatial-temporal decomposition
transforms the pseudo-parabolic equation into a system containing an elliptic
partial differential equation and a temporal ordinary differential equation. To
strengthen our argument, the pseudo-parabolic equation has been given
advection/convection/drift terms. The upscaling is done with the technique of
periodic homogenization via two-scale convergence. The well-posedness of the
extended pseudo-parabolic equation is shown as well. Moreover, we argue that
under certain conditions, a non-local-in-time term arises from the elimination
of an unknown.Comment: 6 pages, 0 figure
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