1,300 research outputs found
A committee machine gas identification system based on dynamically reconfigurable FPGA
This paper proposes a gas identification system based on the committee machine (CM) classifier, which combines various gas identification algorithms, to obtain a unified decision with improved accuracy. The CM combines five different classifiers: K nearest neighbors (KNNs), multilayer perceptron (MLP), radial basis function (RBF), Gaussian mixture model (GMM), and probabilistic principal component analysis (PPCA). Experiments on real sensors' data proved the effectiveness of our system with an improved accuracy over individual classifiers. Due to the computationally intensive nature of CM, its implementation requires significant hardware resources. In order to overcome this problem, we propose a novel time multiplexing hardware implementation using a dynamically reconfigurable field programmable gate array (FPGA) platform. The processing is divided into three stages: sampling and preprocessing, pattern recognition, and decision stage. Dynamically reconfigurable FPGA technique is used to implement the system in a sequential manner, thus using limited hardware resources of the FPGA chip. The system is successfully tested for combustible gas identification application using our in-house tin-oxide gas sensors
Casimir interaction between a sphere and a grating
We derive the explicit expression for the Casimir energy between a sphere and
a 1D grating, in terms of the sphere and grating reflection matrices, and valid
for arbitrary materials, sphere radius, and grating geometric parameters. We
then numerically calculate the Casimir energy between a metallic (gold) sphere
and a dielectric (fused silica) lamellar grating at room temperature, and
explore its dependence on the sphere radius, grating-sphere separation, and
lateral displacement. We quantitatively investigate the geometrical dependence
of the interaction, which is sensitive to the grating height and filling
factor, and show how the sphere can be used as a local sensor of the Casimir
force geometric features. To this purpose we mostly concentrate on separations
and sphere radii of the same order of the grating parameters (here of the order
of one micrometer). We also investigate the lateral component of the Casimir
force, resulting from the absence of translational invariance. We compare our
results with those obtained within the proximity force approximation (PFA).
When applied to the sphere only, PFA overestimates the strength of the
attractive interaction, and we find that the discrepancy is larger in the
sphere-grating than in the sphere-plane geometry. On the other hand, when PFA
is applied to both sphere and grating, it provides a better estimate of the
exact results, simply because the effect of a single grating is underestimated,
thus leading to a partial compensation of errors.Comment: 16 pages, 7 figure
Development of a SimpleProbe real-Time PCR Assay for rapid detection and identification of the US novel urethrotropic clade of Neisseria meningitidis ST-11 (US_NmUC)
Urethritis, or inflammation of the urethra, is one of the most common reasons men seek clinical care. Sexually transmitted pathogens including Neisseria gonorrhoeae are responsible for over half of the symptomatic urethritis cases in U.S. men. Recently, clinics in Indianapolis, Columbus, Atlanta, and other U.S. cities began to note increasing numbers of men presenting with urethritis and Gram-negative intracellular diplococci in their urethral smears who test negative for N. gonorrhoeae. Many of these discordant cases, which have periodically reached highs of more than 25% of presumed gonococcal cases in some sexually transmitted infection clinics in the U.S. Midwest, are infected with strains in a novel urethrotropic clade of Neisseria meningitidis ST-11 (US_NmUC). However, no cultivation-independent tests are available for the US_NmUC strains, and prior studies relied on microbial culture and genome sequencing to identify them. Here, we describe a PCR test that can identify the US_NmUC strains and distinguish them from commensal and invasive N. meningitidis strains as well as N. gonorrhoeae. Our SimpleProbe®-based real-time PCR assay targets a conserved nucleotide substitution in a horizontally acquired region of US_NmUC strain genomes. We applied the assay to 241 urine specimens whose microbial compositions had previously been determined by deep shotgun metagenomic sequencing. The assay detected the single US_NmUC positive case in this cohort, with no false positives. Overall, our simple and readily adaptable assay could facilitate investigation of the pathogenesis and epidemiology of the US_NmUC clade
First fringes with an integrated-optics beam combiner at 10 um - A new step towards instrument miniaturization for mid-infrared interferometry
Observations at mas-resolution scales and high dynamic range hold a central
place in achieving, for instance, the spectroscopic characterization of
exo-Earths or the detailed mapping of their protoplanetary disc birthplace.
Ground or space-based multi-aperture infrared interferometry is a promising
technique to tackle these goals. But significant efforts still need to be
undertaken to achieve a simplification of these instruments if we want to
combine the light from a large number of telescopes. Integrated-optics appears
as an alternative to the current conventional designs, especially if its use
can be extended to a higher number of astronomical bands. This article reports
for the first time the experimental demonstration of the feasibility of an
integrated-optics approach to mid-infrared beam combination for single-mode
stellar interferometry. We have fabricated a 2-telescope beam combiner
prototype integrated on a substrate of chalcogenide glasses, a material
transparent from 1 to 14 um. We have developed laboratory tools to characterize
the modal properties and the interferometric capabilities of our device. We
obtain fringes at 10 um and measure a mean contrast V=0.981 \pm 0.001 with high
repeatability over one week and high stability over 5h. We show experimentally
- as well as on the basis of modeling considerations - that the component has a
single-mode behavior at this wavelength, which is essential to achieve
high-accuracy interferometry. From previous studies, the propagation losses are
estimated to 0.5 dB/cm for such components. We also discuss possible issues
that may impact the interferometric contrast. The IO beam combiner performs
well at 10. We also anticipate the requirement of a better matching between the
numerical apertures of the component and the (de)coupling optics to optimize
the total throughput. The next step foreseen is the achievement of wide-band
interferograms.Comment: Accepted in A&A; 7 pages; 7 figure
Condensation of the atomic relaxation vibrations in lead-magnesium-niobate at
We present neutron diffraction, dielectric permittivity and photoconductivity
measurements, evidencing that lead-magnesium niobate experiences a diffuse
phase transformation between the spherical glass and quadrupole glass phases,
in the temperature interval between 400 K and 500 K, with the quadrupole phase
possessing extremely high magnitudes of dielectric permittivity. Our analysis
shows that the integral diffuse scattering intensity may serve as an order
parameter for this transformation. Our experimental dielectric permittivity
data support this choice. These data are important for the aplications desiring
giant dielectric responses, in a wide temperature intervals and not related to
electron's excitations.Comment: 6 figure
Risques géologiques et activité sismique dans la région d'Al Hoceima (Maroc) : Approche de la quantification des facteurs responsables du déclenchement des instabilités de terrain Geological hazards and seismic activity within the area of Al Hoceima (Morocco): Approach of quantifying factors responsible for the triggering of the ground instabilities
International audienceCe travail présente une étude des risques géologiques liés à l'activité sismique de la région d'Al Hoceima, Maroc. Cette étude a nécessité l'identification des modifications récentes enregistrées dans les formations géologiques, conséquentes de la crise sismique qu'a connue la région en 1994. L'analyse de ces phénomènes a permis de mettre en évidence les liens entre la sismicité et les instabilités de terrain. Un essai de quantification des facteurs responsables du déclenchement de ces instabilités a conduit à suggérer que la pente ainsi que la sismicité constituent les facteurs capitaux dans l'occurrence des mouvements de terrain. This work presents a study of the geological hazards caused by seismic activity within Al Hoceima region, Morocco. This study required the identification of recent geological modifications caused by the seismic crisis of 1994. The analysis undertaken revealed the existence of a good correlation between seismicity and the geological field data. Furthermore, an attempt of quantifying the triggering factors of land instabilities caused us to suggest that the slope and seismicity are the main factors in the studied area
Homogenization of the one-dimensional wave equation
We present a method for two-scale model derivation of the periodic
homogenization of the one-dimensional wave equation in a bounded domain. It
allows for analyzing the oscillations occurring on both microscopic and
macroscopic scales. The novelty reported here is on the asymptotic behavior of
high frequency waves and especially on the boundary conditions of the
homogenized equation. Numerical simulations are reported
Photothermal heterodyne imaging of individual nonfluorescent nanoclusters and nanocrystals
We introduce a new, highly sensitive, and simple heterodyne optical method
for imaging individual nonfluorescent nanoclusters and nanocrystals. A 2 order
of magnitude improvement of the signal is achieved compared to previous
methods. This allows for the unprecedented detection of individual small
absorptive objects such as metallic clusters (of 67 atoms) or nonluminescent
semiconductor nanocrystals. The measured signals are in agreement with a
calculation based on the scattering field theory from a photothermal-induced
modulated index of refraction profile around the nanoparticle
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