5,653 research outputs found
Ground-plane screening of Coulomb interactions in two-dimensional systems: How effectively can one two-dimensional system screen interactions in another?
The use of a nearby metallic ground-plane to limit the range of the Coulomb
interactions between carriers is a useful approach in studying the physics of
two-dimensional (2D) systems. This approach has been used to study Wigner
crystallization of electrons on the surface of liquid helium, and most
recently, the insulating and metallic states of semiconductor-based
two-dimensional systems. In this paper, we perform calculations of the
screening effect of one 2D system on another and show that a 2D system is at
least as effective as a metal in screening Coulomb interactions. We also show
that the recent observation of the reduced effect of the ground-plane when the
2D system is in the metallic regime is due to intralayer screening.Comment: 14 pages, 7 figures Accepted in PR
Enhancing music information retrieval by incorporating image-based local features
This paper presents a novel approach to Music Information Retrieval. Having represented the music tracks in the form of two dimensional images, we apply the "bag of visual words" method from visual IR in order to classify the songs into 19 genres. By switching to visual domain we can abstract from musical concepts such as melody, timbre and rhythm. We obtained classification accuracy of 46% (with 5% theoretical baseline for random classification) which is comparable with existing state-of-the-art approaches. Moreover, the novel features characterize different properties of the signal than standard methods. Therefore, the combination of them should further improve the performance of existing techniques
Walls talk: Microbial biogeography of homes spanning urbanization.
Westernization has propelled changes in urbanization and architecture, altering our exposure to the outdoor environment from that experienced during most of human evolution. These changes might affect the developmental exposure of infants to bacteria, immune development, and human microbiome diversity. Contemporary urban humans spend most of their time indoors, and little is known about the microbes associated with different designs of the built environment and their interaction with the human immune system. This study addresses the associations between architectural design and the microbial biogeography of households across a gradient of urbanization in South America. Urbanization was associated with households' increased isolation from outdoor environments, with additional indoor space isolation by walls. Microbes from house walls and floors segregate by location, and urban indoor walls contain human bacterial markers of space use. Urbanized spaces uniquely increase the content of human-associated microbes-which could increase transmission of potential pathogens-and decrease exposure to the environmental microbes with which humans have coevolved
An adaptive wavelet transformation filtering algorithm for improving road anomaly detection and characterization in vehicular technology
Accelerometers are widely used in modern vehicular technologies to automatically detect and characterize road anomalies such as potholes and bumps. However, measurements from an accelerometer are usually plagued by high noise levels, which typically increase the false alarm and misdetection rates of an anomaly detection system. To address this problem, we have developed in this paper an adaptive threshold estimation technique to filter accelerometer measurements effectively to improve road anomaly detection and characterization in vehicular technologies. Our algorithm decomposes the output signal of an accelerometer into multiple scales using wavelet transformation (WT). Then, it correlates the wavelet coefficients across adjacent scales and classifies them using a newly proposed adaptive threshold technique. Furthermore, our algorithm uses a spatial filter to smoothen further the correlated coefficients before using these coefficients to detect road anomalies. Our algorithm then characterizes the detected road anomalies using two unique features obtained from the filtered wavelet coefficients to differentiate potholes from bumps. The findings from several comparative tests suggest that our algorithm successfully detects and characterizes road anomalies with high levels of accuracy, precision and low false alarm rates as compared to other known methods
SmartEx: a case study on user profiling and adaptation in exhibition booths
An investigation into user profiling and adaptation with exhibition booth as a case study is reported. First a review of the field of exhibitions and trade fairs and a summary introduction to adaptation and profiling are given. We then introduce three criteria for the evaluation of exhibition booth: effectiveness, efficiency and affect. Effectiveness is related the amount of information collected, efficiency is a measurement of the time taken to collect the information, and affect is the perception of the experience and the mood booth visitors have during and after their visit. We have selected these criteria to assess adaptive and profiled exhibition booths, we call smart exhibition (SmartEx). The assessment is performed with an experiment with three test conditions (non-profiled/non adaptive, profiled/non-adaptive and profiled adaptive presentations). Results of the experiment are presented along discussion. While there is significant improvements of effectiveness and efficiency between the two-first test conditions, the improvement is not significant for the last test condition, for reasons explained. As for the affect, the results show that it has an under-estimated importance in people minds and that it should be addressed more carefully
Two qubit conditional quantum logic operation in a single self-assembled quantum dot
The four-level exciton/biexciton system of a single semiconductor quantum dot
acts as a two qubit register. We experimentally demonstrate an
exciton-biexciton Rabi rotation conditional on the initial exciton spin in a
single InGaAs/GaAs dot. This forms the basis of an optically gated two-qubit
controlled-rotation (CROT) quantum logic operation where an arbitrary exciton
spin is selected as the target qubit using the polarization of the control
laser.Comment: 4- pages, 4 figures, to be submitted to PR
The GREGOR Fabry-P\'erot Interferometer
The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light
instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio
del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated
mounting. Thanks to its large-format, high-cadence CCD detectors with
sophisticated computer hard- and software it is capable of scanning spectral
lines with a cadence that is sufficient to capture the dynamic evolution of the
solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet
Sun and sunspot observations. However, in the vector spectropolarimetric mode
the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode
extends from 530-860 nm with a theoretical spectral resolution R of about
250,000, whereas in the vector spectropolarimetric mode the wavelength range is
at present limited to 580-660 nm. The combination of fast narrow-band imaging
and post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales down to
about 50 km on the solar surface.Comment: 14 pages, 17 figures, 4 tables; pre-print of AN 333, p.880-893, 2012
(AN special issue to GREGOR
Restricted Isometries for Partial Random Circulant Matrices
In the theory of compressed sensing, restricted isometry analysis has become
a standard tool for studying how efficiently a measurement matrix acquires
information about sparse and compressible signals. Many recovery algorithms are
known to succeed when the restricted isometry constants of the sampling matrix
are small. Many potential applications of compressed sensing involve a
data-acquisition process that proceeds by convolution with a random pulse
followed by (nonrandom) subsampling. At present, the theoretical analysis of
this measurement technique is lacking. This paper demonstrates that the th
order restricted isometry constant is small when the number of samples
satisfies , where is the length of the pulse.
This bound improves on previous estimates, which exhibit quadratic scaling
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