17,873 research outputs found
Environment-dependent dissipation in quantum Brownian motion
The dissipative dynamics of a quantum Brownian particle is studied for
different types of environment. We derive analytic results for the time
evolution of the mean energy of the system for Ohmic, sub-Ohmic and super-Ohmic
environments, without performing the Markovian approximation. Our results allow
to establish a direct link between the form of the environmental spectrum and
the thermalization dynamics. This in turn leads to a natural explanation of the
microscopic physical processes ruling the system time evolution both in the
short-time non-Markovian region and in the long-time Markovian one. Our
comparative study of thermalization for different environments sheds light on
the physical contexts in which non-Markovian dissipation effects are dominant.Comment: 10 pages, 6 figures, v2: added new references and paragraph
Multistep Measurement of Plantar Pressure Alterations Using Metatarsal Pads
Metatarsal pads are frequently prescribed for nonoperative management of metatarsalgia due to various etiologies. When appropriately placed, they are effective in reducing pressures under the metatarsal heads on the plantar surface of the foot. Despite the positive clinical reports that have been cited, there are no quantitative studies documenting the load redistribution effects of these pads during multiple step usage within the shoe environment. The objective of this study was to assess changes in plantar pressure metrics resulting from pad use. Ten normal adult male subjects were tested during a series of 400-step trials. Pressures were recorded from eight discrete plantar locations at the hindfoot, midfoot, and forefoot regions of the insole. Significant increases in peak pressures, contact durations, and pressure-time integrals were noted at the metatarsal shaft region with pad use (P ≤ .05). Statistically significant changes in metric values were not seen at the other plantar locations, although metatarsal pad use resulted in mild decreases in mean peak pressures at the first and second metatarsal heads and slight increases laterally. Contact durations decreased at all metatarsal head locations, while pressure-time integrals decreased at the first, second, third, and fourth metatarsal heads. A slight increase in pressure-time integrals was seen at the fifth metatarsal head. The redistribution of plantar pressures tended to relate not only to the dimensions of the metatarsal pads, but also to foot size, anatomic foot configuration, and pad location. Knowledge of these parameters, along with careful control of pad dimensions and placement, allows use of the metatarsal pad as an effective orthotic device for redistributing forefoot plantar pressures
Observation of Scarred Modes in Asymmetrically Deformed Microcylinder Lasers
We report observation of lasing in the scarred modes in an asymmetrically
deformed microcavity made of liquid jet. The observed scarred modes correspond
to morphology-dependent resonance of radial mode order 3 with their Q values in
the range of 10^6. Emission directionality is also observed, corresponding to a
hexagonal unstable periodic orbit.Comment: 4 pages, 6 figure
Dynamically stabilized decoherence-free states in non-Markovian open fermionic systems
Decoherence-free subspaces (DFSs) provide a strategy for protecting the
dynamics of an open system from decoherence induced by the system-environment
interaction. So far, DFSs have been primarily studied in the framework of
Markovian master equations. In this work, we study decoherence-free (DF) states
in the general setting of a non-Markovian fermionic environment. We identify
the DF states by diagonalizing the non-unitary evolution operator for a
two-level fermionic system attached to an electron reservoir. By solving the
exact master equation, we show that DF states can be stabilized dynamically.Comment: 11 pages, 3 figures. Any comments are welcom
Electronic and optical properties of LiBC
LiBC, a semiconducting ternary borocarbide constituted of the lightest
elements only, has been synthesized and characterized by x-ray powder
diffraction, dielectric spectroscopy, and conductivity measurements. Utilizing
an infrared microscope the phonon spectrum has been investigated in single
crystals. The in-plane B-C stretching mode has been detected at 150 meV,
noticeably higher than in AlB2, a non-superconducting isostructural analog of
MgB2. It is this stretching mode, which reveals a strong electron-phonon
coupling in MgB2, driving it into a superconducting state below 40 K, and is
believed to mediate predicted high-temperature superconductivity in hole-doped
LiBC [H. Rosner, A. Kitaigorodsky, and W. E. Pickett, Phys. Rev. Lett. 88,
127001 (2002)].Comment: 4 pages, 4 figure
analyses from a cross-sectional online survey
Objectives Opportunities for men having sex with men (MSM) to meet each other
have very much improved by new communication technologies. Meeting venue-based
characteristics can impact how many partners are met and how much sexual risk
is taken. We analysed the association between physical and virtual venues and
the risk for bacterial sexually transmitted infections (bSTIs) among
participants in an MSM online survey. Methods Data were collected during
2013/2014 with a survey targeting MSM living in Germany. The impact of the
meeting place with the last non-steady anal sex partner on diagnosis with a
bSTI in the previous year was analysed using bivariate and multivariate
regression analysis, taking into account self-reported HIV status, serostatus
communication, condom use, partner number, age and city size. Results The
study sample consisted of 8878 respondents (7799 not diagnosed with HIV; 1079
diagnosed with HIV). Meeting partners online was most common (62% HIV−/51%
HIV+), followed by sex venues (11% HIV−/25% HIV+); other venues were each
reported by 2–6% of the respondents. Venue-dependent proportions reporting
bSTIs in the recent year were 2–4 folds higher among men diagnosed with HIV.
In multivariate analysis, HIV status was the strongest predictor for bSTIs
(OR=5.0; 95% CI 2.8 to 8.7). Compared with meeting partners online, sex (OR
1.6; 95% CI 1.0 to 2.5) and social venues (OR 1.9; 95% CI 1.4 to 2.6) were
associated with increased bSTI risk for men not diagnosed with HIV, but the
risk when meeting partners by smartphone apps was only of borderline
significance (OR 1.5; 95% CI 0.9 to 2.3). For men diagnosed with HIV, bSTI
risk increased for sex venues (OR 1.5; 95% CI 1.1 to 2.1), and was lower for
non-gay/other venues (OR 0.2; 95% CI 0.1 to 0.5). Conclusions Venues are
connected to social-behavioural facets of corresponding sexual encounters, and
may be important arenas for differential HIV and STI education, treatment and
prevention
Active optical clock based on four-level quantum system
Active optical clock, a new conception of atomic clock, has been proposed
recently. In this report, we propose a scheme of active optical clock based on
four-level quantum system. The final accuracy and stability of two-level
quantum system are limited by second-order Doppler shift of thermal atomic
beam. To three-level quantum system, they are mainly limited by light shift of
pumping laser field. These limitations can be avoided effectively by applying
the scheme proposed here. Rubidium atom four-level quantum system, as a typical
example, is discussed in this paper. The population inversion between
and states can be built up at a time scale of s.
With the mechanism of active optical clock, in which the cavity mode linewidth
is much wider than that of the laser gain profile, it can output a laser with
quantum-limited linewidth narrower than 1 Hz in theory. An experimental
configuration is designed to realize this active optical clock.Comment: 5 page
Novel cyclic di-GMP effectors of the YajQ protein family control bacterial virulence
Bis-(3 ',5 ') cyclic di-guanylate (cyclic di-GMP) is a key bacterial second messenger that is implicated in the regulation of many critical processes that include motility, biofilm formation and virulence. Cyclic di-GMP influences diverse functions through interaction with a range of effectors. Our knowledge of these effectors and their different regulatory actions is far from complete, however. Here we have used an affinity pull-down assay using cyclic di-GMP-coupled magnetic beads to identify cyclic di-GMP binding proteins in the plant pathogen Xanthomonas campestris pv. campestris (Xcc). This analysis identified XC_3703, a protein of the YajQ family, as a potential cyclic di-GMP receptor. Isothermal titration calorimetry showed that the purified XC_3703 protein bound cyclic di-GMP with a high affinity (K-d similar to 2 mu M). Mutation of XC_3703 led to reduced virulence of Xcc to plants and alteration in biofilm formation. Yeast two-hybrid and far-western analyses showed that XC_3703 was able to interact with XC_2801, a transcription factor of the LysR family. Mutation of XC_2801 and XC_3703 had partially overlapping effects on the transcriptome of Xcc, and both affected virulence. Electromobility shift assays showed that XC_3703 positively affected the binding of XC_2801 to the promoters of target virulence genes, an effect that was reversed by cyclic di-GMP. Genetic and functional analysis of YajQ family members from the human pathogens Pseudomonas aeruginosa and Stenotrophomonas maltophilia showed that they also specifically bound cyclic di-GMP and contributed to virulence in model systems. The findings thus identify a new class of cyclic di-GMP effector that regulates bacterial virulence
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