2,527 research outputs found
Computation of Casimir Interactions between Arbitrary 3D Objects with Arbitrary Material Properties
We extend a recently introduced method for computing Casimir forces between
arbitrarily--shaped metallic objects [M. T. H. Reid et al., Phys. Rev.
Lett._103_ 040401 (2009)] to allow treatment of objects with arbitrary material
properties, including imperfect conductors, dielectrics, and magnetic
materials. Our original method considered electric currents on the surfaces of
the interacting objects; the extended method considers both electric and
magnetic surface current distributions, and obtains the Casimir energy of a
configuration of objects in terms of the interactions of these effective
surface currents. Using this new technique, we present the first predictions of
Casimir interactions in several experimentally relevant geometries that would
be difficult to treat with any existing method. In particular, we investigate
Casimir interactions between dielectric nanodisks embedded in a dielectric
fluid; we identify the threshold surface--surface separation at which
finite--size effects become relevant, and we map the rotational energy
landscape of bound nanoparticle diclusters
Fluctuating volume-current formulation of electromagnetic fluctuations in inhomogeneous media: incandecence and luminescence in arbitrary geometries
We describe a fluctuating volume--current formulation of electromagnetic
fluctuations that extends our recent work on heat exchange and Casimir
interactions between arbitrarily shaped homogeneous bodies [Phys. Rev. B. 88,
054305] to situations involving incandescence and luminescence problems,
including thermal radiation, heat transfer, Casimir forces, spontaneous
emission, fluorescence, and Raman scattering, in inhomogeneous media. Unlike
previous scattering formulations based on field and/or surface unknowns, our
work exploits powerful techniques from the volume--integral equation (VIE)
method, in which electromagnetic scattering is described in terms of
volumetric, current unknowns throughout the bodies. The resulting trace
formulas (boxed equations) involve products of well-studied VIE matrices and
describe power and momentum transfer between objects with spatially varying
material properties and fluctuation characteristics. We demonstrate that thanks
to the low-rank properties of the associatedmatrices, these formulas are
susceptible to fast-trace computations based on iterative methods, making
practical calculations tractable. We apply our techniques to study thermal
radiation, heat transfer, and fluorescence in complicated geometries, checking
our method against established techniques best suited for homogeneous bodies as
well as applying it to obtain predictions of radiation from complex bodies with
spatially varying permittivities and/or temperature profiles
Seawater Desalination for Municipal Water Production
This paper examines the optimal allocation of several inputs in the context of seawater desalination by reverse osmosis (RO) as a source of municipal (or commercial or industrial) water. A cost-minimization model is developed, a production function is estimated, and sensitivity analyses are conducted using the optimization model to investigate the effect of environmental conditions and economic factors on the optimal input portfolio and the cost of operating a modeled seawater desalination facility. The objectives of this paper are to better understand the effect on the seawater desalination facility’s costs and input portfolio from changes in water quality, membrane lifespan, daily operations schedule, and energy prices. Findings include that lower total facility costs are associated with warm-weather water quality parameters, longer membrane life, and mid-range daily operations schedule (14.265 hours/day). Under most conditions, an interruptible power supply regime reduces facility costs. Exceptions include when the interruptible power supply regime implies significant reductions in operating hours and the associated reduction in energy price is very small.water, production, seawater desalination, Resource /Energy Economics and Policy,
Astronomy in the Cloud: Using MapReduce for Image Coaddition
In the coming decade, astronomical surveys of the sky will generate tens of
terabytes of images and detect hundreds of millions of sources every night. The
study of these sources will involve computation challenges such as anomaly
detection and classification, and moving object tracking. Since such studies
benefit from the highest quality data, methods such as image coaddition
(stacking) will be a critical preprocessing step prior to scientific
investigation. With a requirement that these images be analyzed on a nightly
basis to identify moving sources or transient objects, these data streams
present many computational challenges. Given the quantity of data involved, the
computational load of these problems can only be addressed by distributing the
workload over a large number of nodes. However, the high data throughput
demanded by these applications may present scalability challenges for certain
storage architectures. One scalable data-processing method that has emerged in
recent years is MapReduce, and in this paper we focus on its popular
open-source implementation called Hadoop. In the Hadoop framework, the data is
partitioned among storage attached directly to worker nodes, and the processing
workload is scheduled in parallel on the nodes that contain the required input
data. A further motivation for using Hadoop is that it allows us to exploit
cloud computing resources, e.g., Amazon's EC2. We report on our experience
implementing a scalable image-processing pipeline for the SDSS imaging database
using Hadoop. This multi-terabyte imaging dataset provides a good testbed for
algorithm development since its scope and structure approximate future surveys.
First, we describe MapReduce and how we adapted image coaddition to the
MapReduce framework. Then we describe a number of optimizations to our basic
approach and report experimental results comparing their performance.Comment: 31 pages, 11 figures, 2 table
Factors Affecting Implementation of an Evidence-Based Practice in the VA: Illness Management and Recovery
Objective: Illness management and recovery (IMR) is an evidence-based practice that assists consumers in managing their illnesses and pursuing personal recovery goals. Although research has examined factors affecting IMR implementation facilitated by multifaceted, active roll-outs, the current study attempted to elucidate factors affecting IMR implementation outside the context of a research-driven implementation. Methods: Semi-structured interviews with 20 local recovery coordinators and 18 local IMR experts were conducted at 23 VA medical centers. Interviews examined perceived and experienced barriers and facilitators to IMR implementation. Data were analyzed via thematic inductive/deductive analysis in the form of crystallization/immersion. Results: Six factors differed between sites implementing IMR from those not providing IMR: awareness of IMR, importer-champions, autonomy-supporting leadership, veteran-centered care, presence of a sensitive period, and presence of a psychosocial rehabilitation and recovery center. Four factors were common in both groups: recovery orientation, evidence-based practices orientation, perceived IMR fit within program structure, and availability of staff time. Conclusions and Implications for Practice: IMR can be adopted in lieu of active implementation support; however, knowledge dissemination appears to be key. Future research should examine factors affecting the quality of implementation. (PsycINFO Database Record (c) 2016 APA, all rights reserved
Calculation of nonzero-temperature Casimir forces in the time domain
We show how to compute Casimir forces at nonzero temperatures with
time-domain electromagnetic simulations, for example using a finite-difference
time-domain (FDTD) method. Compared to our previous zero-temperature
time-domain method, only a small modification is required, but we explain that
some care is required to properly capture the zero-frequency contribution. We
validate the method against analytical and numerical frequency-domain
calculations, and show a surprising high-temperature disappearance of a
non-monotonic behavior previously demonstrated in a piston-like geometry.Comment: 5 pages, 2 figures, submitted to Physical Review A Rapid
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Emerging Areas of Nursing Science and PhD Education for The 21\u3csup\u3est\u3c/sup\u3e Century: Response to Commentaries
We respond to commentaries from the American Academy of Nursing, the American Association of Colleges of Nursing, and the National Institute of Nursing Research on our thoughts about integrating emerging areas of science into nursing PhD programs. We identify areas of agreement and focus our response on cross-cutting issues arising from cautions about the unique focus of nursing science and how best to proceed with incorporation of emerging areas of science into nursing PhD programs
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