74,761 research outputs found
Neuromodulation: present and emerging methods.
Neuromodulation has wide ranging potential applications in replacing impaired neural function (prosthetics), as a novel form of medical treatment (therapy), and as a tool for investigating neurons and neural function (research). Voltage and current controlled electrical neural stimulation (ENS) are methods that have already been widely applied in both neuroscience and clinical practice for neuroprosthetics. However, there are numerous alternative methods of stimulating or inhibiting neurons. This paper reviews the state-of-the-art in ENS as well as alternative neuromodulation techniques-presenting the operational concepts, technical implementation and limitations-in order to inform system design choices
A Generative Model for Parts-based Object Segmentation
The Shape Boltzmann Machine (SBM) [1] has recently been introduced as a stateof-the-art model of foreground/background object shape. We extend the SBM to account for the foreground object’s parts. Our new model, the Multinomial SBM (MSBM), can capture both local and global statistics of part shapes accurately. We combine the MSBM with an appearance model to form a fully generative model of images of objects. Parts-based object segmentations are obtained simply by performing probabilistic inference in the model. We apply the model to two challenging datasets which exhibit significant shape and appearance variability, and find that it obtains results that are comparable to the state-of-the-art. There has been significant focus in computer vision on object recognition and detection e.g. [2], but a strong desire remains to obtain richer descriptions of objects than just their bounding boxes. One such description is a parts-based object segmentation, in which an image is partitioned into multiple sets of pixels, each belonging to either a part of the object of interest, or its background. The significance of parts in computer vision has been recognized since the earliest days of th
Did Earth-approaching asteroids 3551, 3908, or 4055 produce meteorites?
Orbital integrations show that Amor asteroid 3908 could have ejected one out of four plausible groups of meteorite producing fireballs during a collision in the asteroid belt. It was suggested by others that such a collision may also have split asteroids 3551 and 3908. A member of this group of fireballs is listed as one of the better possibilities for recovery
Novel Rubidium Poly-Nitrogen Materials at High Pressure
First-principles crystal structure search is performed to predict novel
rubidium poly-nitrogen materials at high pressure by varying the stoichiometry,
i. e. relative quantities of the constituent rubidium and nitrogen atoms. Three
compounds of high nitrogen content, RbN_{5}, RbN_{2}, and Rb_{4}N_{6}, are
discovered. Rubidium pentazolate (RbN5) becomes thermodynamically stable at
pressures above \unit[30]{GPa}. The charge transfer from Rb to N atoms enables
aromaticity in cyclo-N_{^{_{5}}}^{-} while increasing the ionic bonding in the
crystal. Rubidium pentazolate can be synthesized by compressing rubidium azide
(RbN3) and nitrogen (N2) precursors above \unit[9.42]{GPa}, and its
experimental discovery is aided by calculating the Raman spectrum and
identifying the features attributed to N_{^{_{5}}}^{-} modes. The two other
interesting compounds, RbN2 containing infinitely-long single-bonded nitrogen
chains, and Rb_{4}N_{6} consisting of single-bonded N_{6} hexazine rings,
become thermodynamically stable at pressures exceeding \unit[60]{GPa}. In
addition to the compounds with high nitrogen content, Rb_{3}N_{3}, a new
compound with 1:1 RbN stoichiometry containing bent N_{3} azides is found to
exist at high pressures
Nodal Domain Statistics for Quantum Maps, Percolation and SLE
We develop a percolation model for nodal domains in the eigenvectors of
quantum chaotic torus maps. Our model follows directly from the assumption that
the quantum maps are described by random matrix theory. Its accuracy in
predicting statistical properties of the nodal domains is demonstrated by
numerical computations for perturbed cat maps and supports the use of
percolation theory to describe the wave functions of general hamiltonian
systems, where the validity of the underlying assumptions is much less clear.
We also demonstrate that the nodal domains of the perturbed cat maps obey the
Cardy crossing formula and find evidence that the boundaries of the nodal
domains are described by SLE with close to the expected value of 6,
suggesting that quantum chaotic wave functions may exhibit conformal invariance
in the semiclassical limit.Comment: 4 pages, 5 figure
Deformable subreflector computed by geometric optics
Using a Cassegrainian geometry, the 64-meter antenna with its distorted paraboloidal reflecting surface is forced to produce a uniform phase wavefront by a pathlength-compensating subreflector. First, the computed distortion vectors at the joints or nodes of the main reflector structure supporting the surface panels are best fitted to a paraboloid. Second, the resulting residual distortion errors are used to determine a compensating subreflector surface by ray tracing using geometric optics principles. Third, the totally corrected subreflector surface is defined by the normal directions and distances to the surface of the original symmetric hyperboloid for the purpose of evaluation. Finally, contour maps of distortions of the paraboloid reflector and the compensating subreflector are presented. A field-measured check of the subreflector in focused position as computed by the described methodology is also presented for the antenna position at horizon look with the geometry at 45 degrees elevation
Graphene as a Novel Single Photon Counting Optical and IR Photodetector
Bilayer graphene has many unique optoelectronic properties , including a
tuneable band gap, that make it possible to develop new and more efficient
optical and nanoelectronic devices. We have developed a Monte Carlo simulation
for a single photon counting photodetector incorporating bilayer graphene. Our
results show that, conceptually it would be feasible to manufacture a single
photon counting photodetector (with colour sensitivity) from bilayer graphene
for use across both optical and infrared wavelengths. Our concept exploits the
high carrier mobility and tuneable band gap associated with a bilayer graphene
approach. This allows for low noise operation over a range of cryogenic
temperatures, thereby reducing the cost of cryogens with a trade off between
resolution and operating temperature. The results from this theoretical study
now enable us to progress onto the manufacture of prototype photon counters at
optical and IR wavelengths that may have the potential to be groundbreaking in
some scientific research applications.Comment: Conference Proceeding in Graphene-Based Technologies, 201
Concurrent Image Processing Executive (CIPE). Volume 1: Design overview
The design and implementation of a Concurrent Image Processing Executive (CIPE), which is intended to become the support system software for a prototype high performance science analysis workstation are described. The target machine for this software is a JPL/Caltech Mark 3fp Hypercube hosted by either a MASSCOMP 5600 or a Sun-3, Sun-4 workstation; however, the design will accommodate other concurrent machines of similar architecture, i.e., local memory, multiple-instruction-multiple-data (MIMD) machines. The CIPE system provides both a multimode user interface and an applications programmer interface, and has been designed around four loosely coupled modules: user interface, host-resident executive, hypercube-resident executive, and application functions. The loose coupling between modules allows modification of a particular module without significantly affecting the other modules in the system. In order to enhance hypercube memory utilization and to allow expansion of image processing capabilities, a specialized program management method, incremental loading, was devised. To minimize data transfer between host and hypercube, a data management method which distributes, redistributes, and tracks data set information was implemented. The data management also allows data sharing among application programs. The CIPE software architecture provides a flexible environment for scientific analysis of complex remote sensing image data, such as planetary data and imaging spectrometry, utilizing state-of-the-art concurrent computation capabilities
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