4,982 research outputs found
Enhancement of Photoemission on P-type GaAs using Surface Acoustic Waves
We demonstrate that photoemission properties of GaAs photocathodes (PCs) can
be altered by surface acoustic waves (SAWs) generated on the PC surface due to
dynamical piezoelectric fields of SAWs. Simulations with COMSOL indicate that
electron effective lifetime in p-doped GaAs may increase by a factor of 10x to
20x. It implies a significant, by a factor of 2x to 3x, increase of quantum
efficiency (QE) for GaAs PCs. Essential steps in device fabrication are
demonstrated, including deposition of an additional layer of ZnO for
piezoelectric effect enhancement, measurements of I-V characteristic of the SAW
device, and ability to survive high-temperature annealing.Comment: 5 pages, 4 figure
Optical versus video see-through mead-mounted displays in medical visualization
We compare two technological approaches to augmented reality for 3-D medical visualization: optical and video see-through devices. We provide a context to discuss the technology by reviewing several medical applications of augmented-reality research efforts driven by real needs in the medical field, both in the United States and in Europe. We then discuss the issues for each approach, optical versus video, from both a technology and human-factor point of view. Finally, we point to potentially promising future developments of such devices including eye tracking and multifocus planes capabilities, as well as hybrid optical/video technology
Wide-angle, off-axis, see-through head-mounted display
A 60-deg-field-of-view optical see-through head-mounted display (HMD) using off-axis optics has been designed for 3-D medical imaging visualization. Two basic on-axis optical design concepts for see-though HMDs are reviewed first, to motivate the design of an off-axis optical form. An off-axis design is then presented. Because HMDs are typically designed from the pupil of the eye to the miniature display, it is common to assess final performance according to the display characteristics. Such analysis, however, does not provide information that is easily translated into task-based performance metric. Therefore, we present an analysis of the performance of the design from a usability viewpoint. For this analysis, the optical system is ray-traced from the display to the eye. Three key measures of performance-accommodation, astigmatism, and chromatic blur-are presented over the field of regard using customized graphical output
A Requirement-centric Approach to Web Service Modeling, Discovery, and Selection
Service-Oriented Computing (SOC) has gained considerable popularity for implementing Service-Based Applications (SBAs) in a flexible\ud
and effective manner. The basic idea of SOC is to understand users'\ud
requirements for SBAs first, and then discover and select relevant\ud
services (i.e., that fit closely functional requirements) and offer\ud
a high Quality of Service (QoS). Understanding usersÂ’ requirements\ud
is already achieved by existing requirement engineering approaches\ud
(e.g., TROPOS, KAOS, and MAP) which model SBAs in a requirement-driven\ud
manner. However, discovering and selecting relevant and high QoS\ud
services are still challenging tasks that require time and effort\ud
due to the increasing number of available Web services. In this paper,\ud
we propose a requirement-centric approach which allows: (i) modeling\ud
usersÂ’ requirements for SBAs with the MAP formalism and specifying\ud
required services using an Intentional Service Model (ISM); (ii)\ud
discovering services by querying the Web service search engine Service-Finder\ud
and using keywords extracted from the specifications provided by\ud
the ISM; and(iii) selecting automatically relevant and high QoS services\ud
by applying Formal Concept Analysis (FCA). We validate our approach\ud
by performing experiments on an e-books application. The experimental\ud
results show that our approach allows the selection of relevant and\ud
high QoS services with a high accuracy (the average precision is\ud
89.41%) and efficiency (the average recall is 95.43%)
Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?
Intracellular transport processes driven by molecular motors can be described
by stochastic lattice models of self-driven particles. Here we focus on
bidirectional transport models excluding the exchange of particles on the same
track. We explore the possibility to have efficient transport in these systems.
One possibility would be to have appropriate interactions between the various
motors' species, so as to form lanes. However, we show that the lane formation
mechanism based on modified attachment/detachment rates as it was proposed
previously is not necessarily connected to an efficient transport state and is
suppressed when the diffusivity of unbound particles is finite. We propose
another interaction mechanism based on obstacle avoidance that allows to have
lane formation for limited diffusion. Besides, we had shown in a separate paper
that the dynamics of the lattice itself could be a key ingredient for the
efficiency of bidirectional transport. Here we show that lattice dynamics and
interactions can both contribute in a cooperative way to the efficiency of
transport. In particular, lattice dynamics can decrease the interaction
threshold beyond which lanes form. Lattice dynamics may also enhance the
transport capacity of the system even when lane formation is suppressed.Comment: 25 pages, 17 figures, 2 table
An approach to the synthesis of biological tissue
Mathematical phantoms developed to synthesize realistic complex backgrounds such as those obtained when imaging biological tissue, play a key role in the quantitative assessment of image quality for medical and biomedical imaging. We present a modeling framework for the synthesis of realistic tissue samples. The technique is demonstrated using radiological breast tissue. The model employs a two-component image decomposition consisting of a slowly, spatially varying mean-background and a residual texture image. Each component is synthesized independently. The approach and results presented here constitute an important step towards developing methods for the quantitative assessment of image quality in medical and biomedical imaging, and more generally image science
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Numerical simulations of the convective dilution process in helium-rich white dwarfs
The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018DB and DBA white dwarfs are generally believed to
be the result of a process by which a thin radiative hydrogen
atmosphere floating in diffusive equilibrium
on top of a helium envelope is eventually completely
diluted in the underlying more massive helium convection
zone that develops with cooling. However,
the observed hydrogen abundances in these objects
exceed by several orders of magnitude the predictions
obtained from such a scenario invoking diffusive
equilibrium, thus currently leaving the very existence
of DB and DBA white dwarfs unaccounted
for in any satisfactory way. We present here the results
of new numerical simulations aimed at improving
the modeling of this convective dilution process.
In particular, we show how DA white dwarfs can be
transformed into DB stars below 20,000 K, and more
importantly, we propose a model that predicts the
correct amount of hydrogen observed in DBA stars
without invoking any accretion mechanism, an alternative
model that has been proposed over the years
to account qualitatively for the presence of hydrogen
in the atmospheres of DBA stars.Astronom
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