The Accuracy of Perturbative Master Equations

We consider open quantum systems with dynamics described by master equations that have perturbative expansions in the system-environment interaction. We show that, contrary to intuition, full-time solutions of order-2n accuracy require an order-(2n+2) master equation. We give two examples of such inaccuracies in the solutions to an order-2n master equation: order-2n inaccuracies in the steady state of the system and order-2n positivity violations, and we show how these arise in a specific example for which exact solutions are available. This result has a wide-ranging impact on the validity of coupling (or friction) sensitive results derived from second-order convolutionless, Nakajima-Zwanzig, Redfield, and Born-Markov master equations.Comment: 6 pages, 0 figures; v2 updated references; v3 updated references, extension to full-time and nonlocal regime

The Feeling of Color: A Haptic Feedback Device for the Visually Disabled

Tapson J, Gurari N, Diaz J, et al. The Feeling of Color: A Haptic Feedback Device for the Visually Disabled. Presented at the Biomedical Circuits and Systems Conference (BIOCAS), Baltimore, MD.We describe a sensory augmentation system designed to provide the visually disabled with a sense of color. Our system consists of a glove with short-range optical color sensors mounted on its fingertips, and a torso-worn belt on which tactors (haptic feedback actuators) are mounted. Each fingertip sensor detects the observed objectpsilas color. This information is encoded to the tactor through vibrations in respective locations and varying modulations. Early results suggest that detection of primary colors is possible with near 100% accuracy and moderate latency, with a minimum amount of training

The Field White Dwarf Mass Distribution

We revisit the properties and astrophysical implications of the field white dwarf mass distribution in preparation of Gaia applications. Our study is based on the two samples with the best established completeness and most precise atmospheric parameters, the volume-complete survey within 20 pc and the Sloan Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of the observed mass distributions with Monte Carlo simulations, but find that it is difficult to constrain independently the initial mass function (IMF), the initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the variation of the Galactic disk vertical scale height as a function of stellar age, and binary evolution. Each of these input ingredients has a moderate effect on the predicted mass distributions, and we must also take into account biases owing to unidentified faint objects (20 pc sample), as well as unknown masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS sample). Nevertheless, we find that fixed standard assumptions for the above parameters result in predicted mean masses that are in good qualitative agreement with the observed values. It suggests that derived masses for both studied samples are consistent with our current knowledge of stellar and Galactic evolution. Our simulations overpredict by 40-50% the number of massive white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a Salpeter IMF when we account for all biases. Furthermore, we find no evidence of a population of double white dwarf mergers in the observed mass distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA

Improving health literacy about Tuberculosis among drug users. A pilot randomized controlled trial

Introduction: Despite effective treatment, tuberculosis remains among the top-10 causes of death causing ~1.3 million deaths in 2017. Furthermore, tuberculosis infection rates have increased amongst excluded populations such as people misusing substances. Objectives and design: We conducted a two London sites pilot randomized controlled trial to test interventions, recruitment, attrition rates and assessment procedures of a parallel, three-arms controlled trial to assess the effectiveness of tuberculosis health literacy interventions among drug dependent (heroin, crack cocaine or heroin and crack cocaine) population in treatment. Results: Forty-two subjects were recruited to the pilot trial (response rate = 26%) and randomized to three interventions (1st: Information booklet; 2nd: Interactive seminar; 3rd: Interactive seminar + contingency management targeting tuberculosis-health-related action). Baseline and post-intervention tuberculosis knowledge scores were obtained and re-assessed at 2-months follow up. The overall attrition rate was 43%. The knowledge scale had good internal reliability (Cronbach’s α = 0.7). Statistically significant increases in knowledge scores (baseline to post-intervention = 5.9 points, baseline to follow-up = 4.3) were recorded for the whole sample (CI = 99%; p < 0.001 for both analysis), but no statistically significant differences between-groups were observed (p = 0.7). Half of participants in the contingency management group achieved their health-action targets. Conclusion: Health literacy interventions to increase knowledge about tuberculosis among drug users are feasible and achieve promising increases in knowledge and health-related actions but measures to prevent a high attrition rate in a large-scale trial must be introduced. The absence of difference between trial-group outcomes suggests low-intensity interventions may achieve knowledge gain too. Further investigation of contingency management to promote tuberculosis-related health behaviours is needed

Large periodic time variations of termination shock particles between ~0.5-20 mev and 6-14 mev electrons measured by the crs experiment on Voyager 2 as it crossed into the heliosheath in 2007: An example of freshly accelerated cosmic rays?

We have examined features in the structure of the heliosheath using the fine scale time variations of termination shock particles (TSP) between ~0.5 - 20 MeV and electrons between 2.5-14 MeV measured by the CRS instrument as the V2 spacecraft crossed the heliospheric termination shock in 2007. The very disturbed heliosheath at V2 is particularly noteworthy for strong periodic intensity variations of the TSP just after V2 crossed the termination shock (2007.66) reaching a maximum between 2007.75 and 2008.0. A series of 42/21 day periodicities was observed at V2 along with spectral changes of low energy TSP and the acceleration of 6-14 MeV electrons. Evidence is presented for the acceleration of TSP and electrons at the times of the 42/21 day periodicities just after V2 crossed the HTS. Spectra for TSP between 2-20 MeV and electrons between 2.5-14 MeV are derived for three time periods including the time of the HTS crossing. The energy spectra of TSP and electrons at these times of intensity peaks are very similar above ~3 MeV, with exponents of a power law spectrum between -3.0 and -3.6. The ratio of TSP intensities to electron intensities at the same energy is ~500. The electron intensity peaks and minima are generally out of phase with those of nuclei by ~1/2 of a 42 day cycle. These charge dependent intensity differences and the large periodic intensity changes could provide new clues as to a possible acceleration mechanism

Morphological stability of electromigration-driven vacancy islands

The electromigration-induced shape evolution of two-dimensional vacancy islands on a crystal surface is studied using a continuum approach. We consider the regime where mass transport is restricted to terrace diffusion in the interior of the island. In the limit of fast attachment/detachment kinetics a circle translating at constant velocity is a stationary solution of the problem. In contrast to earlier work [O. Pierre-Louis and T.L. Einstein, Phys. Rev. B 62, 13697 (2000)] we show that the circular solution remains linearly stable for arbitrarily large driving forces. The numerical solution of the full nonlinear problem nevertheless reveals a fingering instability at the trailing end of the island, which develops from finite amplitude perturbations and eventually leads to pinch-off. Relaxing the condition of instantaneous attachment/detachment kinetics, we obtain non-circular elongated stationary shapes in an analytic approximation which compares favorably to the full numerical solution.Comment: 12 page

Anomalous cosmic rays in the heliosheath

We report on Voyager 1 and 2 observations of anomalous cosmic rays in the outer heliosphere. The energy spectrum of anomalous cosmic ray helium as each spacecraft crossed the solar wind termination shock into the heliosheath remained modulated. Assuming the intensity gradient between the two spacecraft is purely radial, we find that radial gradients in the heliosheath of He with 11.6–22.3 MeV/nuc and with ∼61–73MeV/nuc∼61–73 MeV/nuc are 4.9±1.2%/AU4.9±1.2%/AU and 0.0±0.5%/AU,0.0±0.5%/AU, respectively. Strong temporal variations of the 11.6–22.3 MeV/nuc He intensity at both spacecraft were observed in 2005 just after Voyager 1 crossed the termination shock and while Voyager 2 was upstream. After 2006.0, the intensity variations are more moderate and likely due to a combination of spatial and temporal variations. As of early 2008, the anomalous cosmic ray He energy spectrum has unfolded to what may be a source spectrum. The spectrum at Voyager 2 remains modulated. We examine three recent models of the origin of anomalous cosmic rays in light of these observations

The early X-ray afterglows of optically bright and dark Gamma-Ray Bursts

A systematical study on the early X-ray afterglows of both optically bright and dark gamma-ray bursts (B-GRBs and D-GRBs) observed by Swift has been presented. Our sample includes 25 GRBs. Among them 13 are B-GRBs and 12 are D-GRBs. Our results show that the distributions of the X-ray afterglow fluxes ($F_{X}$), the gamma-ray fluxes ($S_{\gamma}$), and the ratio ($R_{\gamma, X}$) for both the D-GRBs and B-GRBs are similar. The differences of these distributions for the two kinds of GRBs should be statistical fluctuation. These results indicate that the progenitors of the two kinds of GRBs are the same population. Their total energy explosions are comparable. The suppression of the optical emissions from D-GRBs should results from circumburst but not their central engine.Comment: 10 pages, 3 figures, 1 table; accepted by ChJA

Discovery of the accretion-powered millisecond pulsar SWIFT J1756.9-2508 with a low-mass companion

We report on the discovery by the Swift Gamma-Ray Burst Explorer of the eighth known transient accretion-powered millisecond pulsar, SWIFT J1756.9-2508, as part of routine observations with the Swift Burst Alert Telescope hard X-ray transient monitor. The pulsar was subsequently observed by both the X-Ray Telescope on Swift and the Rossi X-Ray Timing Explorer Proportional Counter Array. It has a spin frequency of 182 Hz (5.5 ms) and an orbital period of 54.7 minutes. The minimum companion mass is between 0.0067 and 0.0086 solar masses, depending on the mass of the neutron star, and the upper limit on the mass is 0.030 solar masses (95% confidence level). Such a low mass is inconsistent with brown dwarf models, and comparison with white dwarf models suggests that the companion is a He-dominated donor whose thermal cooling has been at least modestly slowed by irradiation from the accretion flux. No X-ray bursts, dips, eclipses or quasi-periodic oscillations were detected. The current outburst lasted approximately 13 days and no earlier outbursts were found in archival data.Comment: 13 pages, 2 figures, accepted by Astrophysical Journal Letter

Monitoring Supergiant Fast X-ray Transients with Swift. Results from the first year

Swift has allowed the possibility to give Supergiant Fast X-ray Transients (SFXTs), the new class of High Mass X-ray Binaries discovered by INTEGRAL, non serendipitous attention throughout all phases of their life. We present our results based on the first year of intense Swift monitoring of four SFXTs, IGR J16479-4514, XTE J1739-302, IGR J17544-2619 and AX J1841.0-0536. We obtain the first assessment of how long each source spends in each state using a systematic monitoring with a sensitive instrument. The duty-cycle of inactivity is 17, 28, 39, 55% (5% uncertainty), for IGR J16479-4514, AX J1841.0-0536, XTE J1739-302, and IGR J17544-2619, respectively, so that true quiescence is a rare state. This demonstrates that these transients accrete matter throughout their life at different rates. AX J1841.0-0536 is the only source which has not undergone a bright outburst during our campaign. Although individual sources behave somewhat differently, common X-ray characteristics of this class are emerging such as outburst lengths well in excess of hours, with a multiple peaked structure. A high dynamic range (including bright outbursts) of 4 orders of magnitude has been observed. We performed out-of-outburst intensity-based spectroscopy. Spectral fits with an absorbed blackbody always result in blackbody radii of a few hundred meters, consistent with being emitted from a small portion of the neutron star surface, very likely the neutron star polar caps. We also present the UVOT data of these sources. (Abridged)Comment: Accepted for publication in MNRAS. 20 pages, 9 figures, 8 table