Phonon-induced decoherence of the two-level quantum subsystem due to relaxation and dephasing processes

Phonon-related decoherence effects in a quantum double-well two-level subsystem coupled to a solid are studied theoretically by the example of deformation phonons. Expressions for the reduced density matrix at T=0 are derived beyond the Markovian approximation by means of explicit solution of the non-stationary Schrodinger equation for the interacting electron-phonon system at the initial stage of its evolution. It is shown that as long as the difference between the energies of the electron in the left and the right well greatly exceeds the energy of the electron tunneling between the minima of the double-well potential, decoherence is primarily due to dephasing processes. This case corresponds to a strongly asymmetric potential and spatially separated eigenfunctions localized in the vicinity of one or another potential minimum. In the opposite case of the symmetric potential, the decoherence stems from the relaxation processes, which may be either "resonant" (at relatively long times) or "nonresonant" (at short times), giving rise to qualitatively different temporal evolution of the electron state. The results obtained are discussed in the context of quantum information processing based on the quantum bits encoded in electron charge degrees of freedom.Comment: 20 pages, no figure

Tribocorrosion behavior of CoCrMo alloy for hip prosthesis as a function of loads: A comparison between two testing systems

Metal-on-metal (MOM) hip prosthesis bearings have enjoyed renewed popularity, but concerns remain with wear debris and metal ion release causing a negative response in the surrounding tissues. Further understanding into the wear and corrosion mechanisms occurring in MOM hips is therefore essential. The purpose of this study was to evaluate the tribocorrosion behavior, or interplay between corrosion and wear, of a low-carbon CoCrMo alloy as a function of loading. The tribocorrosion tests were performed using two tribometer configurations. In the first configuration, “System A”, a linearly reciprocating alumina ball slid against the flat metal immersed in a phosphate buffer solution (PBS). In the second configuration, “System B”, the flat end of a cylindrical metal pin was pressed against an alumina ball that oscillated rotationally, using bovine calf serum (BCS) as the lubricant and electrolyte. System B was custom-built to emulate in vivo conditions. The tribocorrosion tests were performed under potentiostatic conditions at −0.345 V, with a sliding duration of 1800 s and a frequency of 1 Hz. In System A the applied loads were 0.05, 0.5, and 1 N (138, 296 and 373 MPa, respectively) and in System B were 16, 32, and 64 N (474, 597, and 752 MPa, respectively). Electrochemical impedance spectroscopy (EIS) and polarization resistance were estimated. The total mass loss (Kwc) in the CoCrMo was determined. The mass loss due to wear (Kw) and that due to corrosion (Kc) were determined. The dominant wear regime for the CoCrMo alloy subjected to sliding changes from wear–corrosion to mechanical wear as the contact stress increases. An attempt was made to compare both system, in their tribochemical responses and formulate some insights in the total degradation processes. Our results also suggest that the proteins in the serum lubricant assist in the generation of a protective layer against corrosion during sliding. The study highlights the need of adequate methodology/guidelines to compare the results from different test systems and translating in solving the practical problems

Chronic Stroke Sensorimotor Impairment Is Related to Smaller Hippocampal Volumes: An ENIGMA Analysis

BACKGROUND: Persistent sensorimotor impairments after stroke can negatively impact quality of life. The hippocampus is vulnerable to poststroke secondary degeneration and is involved in sensorimotor behavior but has not been widely studied within the context of poststroke upper-limb sensorimotor impairment. We investigated associations between non-lesioned hippocampal volume and upper limb sensorimotor impairment in people with chronic stroke, hypothesizing that smaller ipsilesional hippocampal volumes would be associated with greater sensorimotor impairment. METHODS AND RESULTS: Cross-sectional T1-weighted magnetic resonance images of the brain were pooled from 357 participants with chronic stroke from 18 research cohorts of the ENIGMA (Enhancing NeuoImaging Genetics through Meta-Analysis) Stroke Recovery Working Group. Sensorimotor impairment was estimated from the FMA-UE (Fugl-Meyer Assessment of Upper Extremity). Robust mixed-effects linear models were used to test associations between poststroke sensorimotor impairment and hippocampal volumes (ipsilesional and contralesional separately; Bonferroni-corrected, P<0.025), controlling for age, sex, lesion volume, and lesioned hemisphere. In exploratory analyses, we tested for a sensorimotor impairment and sex interaction and relationships between lesion volume, sensorimotor damage, and hippocampal volume. Greater sensorimotor impairment was significantly associated with ipsilesional (P=0.005; β=0.16) but not contralesional (P=0.96; β=0.003) hippocampal volume, independent of lesion volume and other covariates (P=0.001; β=0.26). Women showed progressively worsening sensorimotor impairment with smaller ipsilesional (P=0.008; β=−0.26) and contralesional (P=0.006; β=−0.27) hippocampal volumes compared with men. Hippocampal volume was associated with lesion size (P<0.001; β=−0.21) and extent of sensorimotor damage (P=0.003; β=−0.15). CONCLUSIONS: The present study identifies novel associations between chronic poststroke sensorimotor impairment and ipsilesional hippocampal volume that are not caused by lesion size and may be stronger in women.Artemis Zavaliangos-Petropulu, PhD, Bethany Lo, BSc, Miranda R. Donnelly, MS, Nicolas Schweighofer, PhD, Keith Lohse, PhD, PStat, Neda Jahanshad, PhD, Giuseppe Barisano, MD, Nerisa Banaj, PhD, Michael R. Borich, PhD, Lara A. Boyd, PhD, Cathrin M. Buetefisch, MD, PhD, Winston D. Byblow, PhD, Jessica M. Cassidy, PhD, Charalambos C. Charalambous, PhD, Adriana B. Conforto, PhD, Julie A. DiCarlo, MSc, Adrienne N. Dula, PhD, Natalia Egorova-Brumley, PhD, Mark R. Etherton, MD, PhD, Wuwei Feng, MD, Kelene A. Fercho, PhD, Fatemeh Geranmayeh, PhD, Colleen A. Hanlon, PhD, Kathryn S. Hayward, PhD, Brenton Hordacre, PhD, Steven A. Kautz, PhD, Mohamed Salah Khlif, PhD, Hosung Kim, PhD, Amy Kuceyeski, PhD, David J. Lin, MD, Jingchun Liu, MD, Martin Lotze, MD, Bradley J. MacIntosh, PhD, John L. Margetis, OTD, Feroze B. Mohamed, PhD, Fabrizio Piras, PhD, Ander Ramos-Murguialday, PhD, Kate P. Revill, PhD, Pamela S. Roberts, PhD, Andrew D. Robertson, PhD, Heidi M. Schambra, MD, Na Jin Seo, PhD, Mark S. Shiroishi, MD, Cathy M. Stinear, PhD, Surjo R. Soekadar, MD, Gianfranco Spalletta, MD, PhD, Myriam Taga, PhD, Wai Kwong Tang, MD, Gregory T. Thielman, EdD, Daniela Vecchio, PhD, Nick S. Ward, MD, Lars T. Westlye, PhD, Emilio Werden, PhD, Carolee Winstein, PhD, PT, George F. Wittenberg, MD, PhD, Steven L. Wolf, PhD, Kristin A. Wong, MD, Chunshui Yu, MD, Amy Brodtmann, MD, PhD, Steven C. Cramer, MD, Paul M. Thompson, PhD, Sook-Lei Liew, PhD, OTR,

Saturation overshoot and hysteresis for twophase flow in porous media

Saturation overshoot and hysteresis for two phase flow in porous media are briefly reviewed. Old and new challenges are discussed. It is widely accepted that the traditional Richards model for twophase flow in porous media does not support non-monotone travelling wave solutions for the saturation profile. As a concequence various extensions and generalizations have been recently discussed. The review highlights different limits within the traditional theory. It emphasizes the relevance of hysteresis in the Buckley–Leverett limit with jump-type hysteresis in the relative permeabilities. Reviewing the situation it emerges that the traditional theory may have been abandoned prematurely because of its inability to predict saturation overshoot in the Richards limit