222 research outputs found
Nonequilibrium entropy production for open quantum systems
We consider open quantum systems weakly coupled to a heat reservoir and
driven by arbitrary time-dependent parameters. We derive exact microscopic
expressions for the nonequilibrium entropy production and entropy production
rate, valid arbitrarily far from equilibrium. By using the two-point energy
measurement statistics for system and reservoir, we further obtain a quantum
generalization of the integrated fluctuation theorem put forward by Seifert
[PRL 95, 040602 (2005)].Comment: 4 pages, 1 figur
Limitations in Predicting the Space Radiation Health Risk for Exploration Astronauts
Despite years of research, understanding of the space radiation environment
and the risk it poses to long-duration astronauts remains limited. There is a
disparity between research results and observed empirical effects seen in human
astronaut crews, likely due to the numerous factors that limit terrestrial
simulation of the complex space environment and extrapolation of human clinical
consequences from varied animal models. Given the intended future of human
spaceflight, with efforts now to rapidly expand capabilities for human missions
to the moon and Mars, there is a pressing need to improve upon the
understanding of the space radiation risk, predict likely clinical outcomes of
interplanetary radiation exposure, and develop appropriate and effective
mitigation strategies for future missions. To achieve this goal, the space
radiation and aerospace community must recognize the historical limitations of
radiation research and how such limitations could be addressed in future
research endeavors. We have sought to highlight the numerous factors that limit
understanding of the risk of space radiation for human crews and to identify
ways in which these limitations could be addressed for improved understanding
and appropriate risk posture regarding future human spaceflight.Comment: Accepted for publication by Nature Microgravity (2018
Single ion heat engine with maximum efficiency at maximum power
We propose an experimental scheme to realize a nano heat engine with a single
ion. An Otto cycle may be implemented by confining the ion in a linear Paul
trap with tapered geometry and coupling it to engineered laser reservoirs. The
quantum efficiency at maximum power is analytically determined in various
regimes. Moreover, Monte Carlo simulations of the engine are performed that
demonstrate its feasibility and its ability to operate at maximum efficiency of
30% under realistic conditions.Comment: 5 pages, 3 figure
Lattice-Boltzmann model for axisymmetric thermal flows
In this brief report, a thermal lattice-Boltzmann (LB) model is presented for
axisymmetric thermal flows in the incompressible limit. The model is based on
the double-distribution-function LB method, which has attracted much attention
since its emergence for its excellent numerical stability. Compared with the
existing axisymmetric thermal LB models, the present model is simpler and
retains the inherent features of the standard LB method. Numerical simulations
are carried out for the thermally developing laminar flows in circular ducts
and the natural convection in an annulus between two coaxial vertical
cylinders. The Nusselt number obtained from the simulations agrees well with
the analytical solutions and/or the results reported in previous studies.Comment: 11 pages, 4 figure
Developing a Mobile Application‐Based Particle Image Velocimetry Tool for Enhanced Teaching and Learning in Fluid Mechanics: A Design‐Based Research Approach
A robust and intuitive understanding of fluid mechanics—the applied science of fluid motion—is foundational within many engineering disciplines, including aerospace, chemical, civil, mechanical, naval, and ocean engineering. In‐depth knowledge of fluid mechanics is critical to safe and economical design of engineering applications employed globally everyday, such as automobiles, aircraft, and sea craft, and to meeting global 21st century engineering challenges, such as developing renewable energy sources, providing access to clean water, managing the environmental nitrogen cycle, and improving urban infrastructure. Despite the fundamental nature of fluid mechanics within the broader undergraduate engineering curriculum, students often characterize courses in fluid mechanics as mathematically onerous, conceptually difficult, and aesthetically uninteresting; anecdotally, undergraduates may choose to opt‐out of fluids engineering‐related careers based on their early experiences in fluids courses. Therefore, the continued development of new frameworks for engineering instruction in fluid mechanics is needed. Toward that end, this paper introduces mobile instructional particle image velocimetry (mI‐PIV), a low‐cost, open‐source, mobile application‐based educational tool under development for smartphones and tablets running Android. The mobile application provides learners with both technological capability and guided instruction that enables them to visualize and experiment with authentic flow fields in real time. The mI‐PIV tool is designed to generate interest in and intuition about fluid flow and to improve understanding of mathematical concepts as they relate to fluid mechanics by providing opportunities for fluids‐related active engagement and discovery in both formal and informal learning contexts
Updating Photon-Based Normal Tissue Complication Probability Models for Pneumonitis in Patients With Lung Cancer Treated With Proton Beam Therapy
Purpose: No validated models for predicting the risk of radiation pneumonitis (RP) with proton beam therapy (PBT) currently exist. Our goal was to externally validate and recalibrate multiple established photon-based normal tissue complication probability models for RP in a cohort with locally advanced nonsmall cell lung cancer treated with contemporary doses of chemoradiation using PBT. Methods and Materials: The external validation cohort consisted of 99 consecutive patients with locally advanced nonsmall cell lung cancer treated with chemoradiation using PBT. RP was retrospectively scored at 3 and 6 months posttreatment. We evaluated the performance of the photon Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) pneumonitis model, the QUANTEC model adjusted for clinical risk factors, and the newer Netherlands updated QUANTEC model. A closed testing procedure was performed to test the need for model updating, either by recalibration-in-the-large (re-estimation of intercept), recalibration (re-estimation of intercept/slope), or model revision (re-estimation of all coefficients). Results: There were 21 events (21%) of ≥grade 2 RP. The closed testing procedure on the PBT data set did not detect major deviations between the models and the data and recommended adjustment of the intercept only for the photon-based Netherlands updated QUANTEC model (intercept update: –1.2). However, an update of the slope and revision of the model coefficients were not recommended by the closed testing procedure, as the deviations were not significant within the power of the data. Conclusions: The similarity between the dose-response relationship for PBT and photons for normal tissue complications has been an assumption until now. We demonstrate that the preexisting, widely used photon based models fit our PBT data well with minor modifications. These now-validated and updated normal tissue complication probability models can aid in individualizing selection of the most optimal treatment technique for a particular patient
Water induced sediment levitation enhances downslope transport on Mars
On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought
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