24,169 research outputs found
A technique to investigate space maintenance tasks
Effects of space suit pressurization and weightlessness on performance decrement in space maintenance activit
Significance of zero modes in path--integral quantization of solitonic theories with BRST invariance
The significance of zero modes in the path-integral quantization of some
solitonic models is investigated. In particular a Skyrme-like theory with
topological vortices in (1+2) dimensions is studied, and with a BRST invariant
gauge fixing a well defined transition amplitude is obtained in the one loop
approximation. We also present an alternative method which does not necessitate
evoking the time-dependence in the functional integral, but is equivalent to
the original one in dealing with the quantization in the background of the
static classical solution of the non-linear field equations. The considerations
given here are particularly useful in - but also limited to - the one-loop
approximation.Comment: 16 pages, LaTe
Quantum Tunneling and Phase Transitions in Spin Systems with an Applied Magnetic Field
Transitions from classical to quantum behaviour in a spin system with two
degenerate ground states separated by twin energy barriers which are asymmetric
due to an applied magnetic field are investigated. It is shown that these
transitions can be interpreted as first- or second-order phase transitions
depending on the anisotropy and magnetic parameters defining the system in an
effective Lagrangian description.Comment: 18 pages, 7 figure
Intrinsic response time of graphene photodetectors
Graphene-based photodetectors are promising new devices for high-speed
optoelectronic applications. However, despite recent efforts, it is not clear
what determines the ultimate speed limit of these devices. Here, we present
measurements of the intrinsic response time of metal-graphene-metal
photodetectors with monolayer graphene using an optical correlation technique
with ultrashort laser pulses. We obtain a response time of 2.1 ps that is
mainly given by the short lifetime of the photogenerated carriers. This time
translates into a bandwidth of ~262 GHz. Moreover, we investigate the
dependence of the response time on gate voltage and illumination laser power
MinMax Radon Barcodes for Medical Image Retrieval
Content-based medical image retrieval can support diagnostic decisions by
clinical experts. Examining similar images may provide clues to the expert to
remove uncertainties in his/her final diagnosis. Beyond conventional feature
descriptors, binary features in different ways have been recently proposed to
encode the image content. A recent proposal is "Radon barcodes" that employ
binarized Radon projections to tag/annotate medical images with content-based
binary vectors, called barcodes. In this paper, MinMax Radon barcodes are
introduced which are superior to "local thresholding" scheme suggested in the
literature. Using IRMA dataset with 14,410 x-ray images from 193 different
classes, the advantage of using MinMax Radon barcodes over \emph{thresholded}
Radon barcodes are demonstrated. The retrieval error for direct search drops by
more than 15\%. As well, SURF, as a well-established non-binary approach, and
BRISK, as a recent binary method are examined to compare their results with
MinMax Radon barcodes when retrieving images from IRMA dataset. The results
demonstrate that MinMax Radon barcodes are faster and more accurate when
applied on IRMA images.Comment: To appear in proceedings of the 12th International Symposium on
Visual Computing, December 12-14, 2016, Las Vegas, Nevada, US
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