6,487 research outputs found
Magnetic Sensors Based on Long Josephson Tunnel Junctions - An Alternative to SQUIDs
The properties of Josephson devices are strongly affected by geometrical
effects. A loop-shaped superconducting electrode tightly couples a long
Josephson tunnel junction with the surrounding electromagnetic field. Due to
the fluxoid conservation, any change of the magnetic flux linked to the loop
results in a variation of the shielding current circulating around the loop,
which, in turn, affects the critical current of the Josephson junction. This
method allows the realization of a novel family of robust superconducting
devices (not based on the quantum interference) which can function as a
general-purpose magnetic sensors. The best performance is accomplished without
compromising the noise performance by employing an in-line-type junction few
times longer than its Josephson penetration length. The linear (rather than
periodic) response to magnetic flux changes over a wide range is just one of
its several advantages compared to the most sensitive magnetic detectors
currently available, namely the Superconducting Quantum Interference Devices
(SQUID). We will also comment on the drawbacks of the proposed system and
speculate on its noise properties.Comment: 13 pages, 4 figure
Color space analysis for iris recognition
This thesis investigates issues related to the processing of multispectral and color infrared images of the iris. When utilizing the color bands of the electromagnetic spectrum, the eye color and the components of texture (luminosity and chromaticity) must be considered. This work examines the effect of eye color on texture-based iris recognition in both the near-IR and visible bands. A novel score level fusion algorithm for multispectral iris recognition is presented in this regard. The fusion algorithm - based on evidence that matching performance of a texture-based encoding scheme is impacted by the quality of texture within the original image - ranks the spectral bands of the image based on texture quality and designs a fusion rule based on these rankings. Color space analysis, to determine an optimal representation scheme, is also examined in this thesis. Color images are transformed from the sRGB color space to the CIE Lab, YCbCr, CMYK and HSV color spaces prior to encoding and matching. Also, enhancement methods to increase the contrast of the texture within the iris, without altering the chromaticity of the image, are discussed. Finally, cross-band matching is performed to illustrate the correlation between eye color and specific bands of the color image
Plasmons in Sodium under Pressure: Increasing Departure from Nearly-Free-Electron Behavior
We have measured plasmon energies in Na under high pressure up to 43 GPa
using inelastic x-ray scattering (IXS). The momentum-resolved results show
clear deviations, growing with increasing pressure, from the predictions for a
nearly-free electron metal. Plasmon energy calculations based on
first-principles electronic band structures and a quasi-classical plasmon model
allow us to identify a pressure-induced increase in the electron-ion
interaction and associated changes in the electronic band structure as the
origin of these deviations, rather than effects of exchange and correlation.
Additional IXS results obtained for K and Rb are addressed briefly.Comment: 5 pages, 4 figure
Kinetics of photoinduced matter transport driven by intensity and polarization in thin films containing azobenzene
We investigate the kinetics of photoinduced deformation phenomena in azobenzene-containing thin solid films. We show that a light intensity pattern and a light polarization pattern produce two distinct material transport processes whose direction and kinetics can be independently controlled. The kinetics of the intensity-driven deformation scales with the incoming light power while the kinetics of the polarization-driven mass transport scales with the amplitude of the electromagnetic field pattern. We conclude that these two processes are fully independent one from the other and originate from two different microscopic mechanisms
Bias deconstructed: Unravelling the scale dependence of halo bias using real space measurements
We explore the scale dependence of halo bias using real space
cross-correlation measurements in N-body simulations and in Pinocchio, an
algorithm based on Lagrangian Perturbation Theory. Recent work has shown how to
interpret such real space measurements in terms of k-dependent bias in Fourier
space, and how to remove the k-dependence to reconstruct the k-independent
peak-background split halo bias parameters. We compare our reconstruction of
the linear bias, which requires no free parameters, with previous estimates
from N-body simulations which were obtained directly in Fourier space at large
scales, and find very good agreement. Our reconstruction of the quadratic bias
is similarly parameter-free, although in this case there are no previous
Fourier space measurements to compare with. Our analysis of N-body simulations
explicitly tests the predictions of the excursion set peaks (ESP) formalism of
Paranjape et al. (2013) for the scale dependence of bias; we find that the ESP
predictions accurately describe our measurements. In addition, our measurements
in Pinocchio serve as a useful, successful consistency check between Pinocchio
and N-body simulations that is not accessible to traditional measurements.Comment: 13 pages, 9 figures; v3 -- Matches published versio
Defect formation in superconducting rings: external fields and finite-size effects
Consistent with the predictions of Kibble and Zurek, scaling behaviour has
been seen in the production of fluxoids during temperature quenches of
superconducting rings. However, deviations from the canonical behaviour arise
because of finite-size effects and stray external fields.
Technical developments, including laser heating and the use of long Josephson
tunnel junctions, have improved the quality of data that can be obtained. With
new experiments in mind we perform large-scale 3D simulations of quenches of
small, thin rings of various geometries with fully dynamical electromagnetic
fields, at nonzero externally applied magnetic flux. We find that the outcomes
are, in practice, indistinguishable from those of much simpler Gaussian
analytical approximations in which the rings are treated as one-dimensional
systems and the magnetic field fluctuation-free.Comment: 10 pages, 3 figures, presentation at QFS2012, to appear in JLT
Long Josephson Tunnel Junctions with Doubly Connected Electrodes
In order to mimic the phase changes in the primordial Big Bang, several
"cosmological" solid-state experiments have been conceived, during the last
decade, to investigate the spontaneous symmetry breaking in superconductors and
superfluids cooled through their transition temperature. In one of such
experiments the number of magnetic flux quanta spontaneously trapped in a
superconducting loop was measured by means of a long Josephson tunnel junction
built on top of the loop itself. We have analyzed this system and found a
number of interesting features not occurring in the conventional case with
simply connected electrodes. In particular, the fluxoid quantization results in
a frustration of the Josephson phase, which, in turn, reduces the junction
critical current. Further, the possible stable states of the system are
obtained by a self-consistent application of the principle of minimum energy.Comment: 34 pages, 9 figures, Phys. Rev. B April 201
Characterizing Diffused Stellar Light in simulated galaxy clusters
[Abridged] In this paper, we carry out a detailed analysis of the performance
of two different methods to identify the diffuse stellar light in cosmological
hydrodynamical simulations of galaxy clusters. One method is based on a
dynamical analysis of the stellar component. The second method is closer to
techniques commonly employed in observational studies. Both the dynamical
method and the method based on the surface brightness limit criterion are
applied to the same set of hydrodynamical simulations for a large sample about
80 galaxy clusters.
We find significant differences between the ICL and DSC fractions computed
with the two corresponding methods, which amounts to about a factor of two for
the AGN simulations, and a factor of four for the CSF set. We also find that
the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of
1.5-2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost
unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to
decrease from ~80 per cent in galaxy groups to ~60 per cent in rich clusters,
thus in excess of what found from observational analysis.
We identify the average surface brightness limits that yields the ICL
fraction from the SBL method close to the DSC fraction from the dynamical
method. These surface brightness limits turn out to be brighter in the CSF than
in the AGN simulations. This is consistent with the finding that AGN feedback
makes BCGs to be less massive and with shallower density profiles than in the
CSF simulations. The BCG stellar component, as identified by both methods, are
slightly older and more metal-rich than the stars in the diffuse component.Comment: 18 Pages, 15 figures. Matches to MNRAS published versio
Alimentação de Liposarcus anisitsi e Potamorhina squamoralevis, peixes abundantes na BaÃa Tuiuiú, Pantanal, Mato Grosso do Sul, Brasil.
Os grandes sistemas fluviais da América do Sul abrigam uma grande diversidade de espécies de peixes, que obtém o alimento nas mais diversas fontes. Este trabalho visou identificar e analisar a composição da dieta de Liposarcus anisitsi e Potamorhina squamoralevis, espécies abundantes na baÃa Tuiuiú, Pantanal, Mato Grosso do Sul. Foram realizadas coletas bimestrais, durante três anos, na baÃa Tuiuiú, meandro abandonado do rio Paraguai. Dos exemplares coletados foram retirados os tratos digestivos e o conteúdo foi homogeneizado e diluÃdo diversas vezes para facilitar a leitura e identificação dos itens alimentares que foi efetuada sob microscópio. As duas espécies apresentaram o detrito/sedimento como principal item alimentar. Além dos detritos, L. anisitsi ingeriu quantidades expressivas de restos de vegetais e algas. P. squamoralevis ingeriu quantidades significativas de algas e restos de vegetais são menos importantes na sua dieta. Também foram ingeridos outros itens, em menor proporção. Na baÃa Tuiuiú, P. squamoralevis e L. anisitsi podem ser classificados como espécies especializadas, uma vez que se alimentam principalmente de detrito/sedimento, com alguma tendência a generalistas, já que podem se alimentar também de outros itens alimentares associados a detritos. As espécies utilizam diferentes micro-hábitats na captura do alimento o que possibilita a sua coexistência. Devido à sua abundância e frequência de ocorrência, os peixes detritÃvoros constituem a base da cadeia alimentar aquática na baÃa Tuiuiú. The major river systems of South America have a great diversity of fish species, which feed on a great diversity of food sources. This study aimed to identify and analyze the composition of the feeding of Liposarcus anisitsi and Potamorhina squamoralevis, abundants in the Tuiuiú bay, Pantanal, Mato Grosso do Sul State. Samples were collected bimonthly during three years in the Tuiuiú bay, an oxbow lake the Paraguay river. From the specimens were taken the digestive tracts and the contents were homogenized and diluted several times to facilitate the reading and identification of food items that was performed under microscope. In both fish species, the detritus / sediment were the main food item. L. anisitsi ingested large amounts of plant debris and algae. P. squamoralevis ingested significant amounts of algae; plant remains are less important in the diet of this species. Other items were also eaten in smaller proportions. In the Tuiuiú bay, P. squamoralevis and L. anisitsi can be classified as specialized species, since they feed mainly on detritus / sediment, with some degree to generalism, since it can feed also on other food items. L. anisitsi and P. squamoralevis use different microhabitats to capture food which allow them to coexist. Due to its abundance and frequency of occurrence, detritus feeding fishes are the basis of the aquatic food chain in the Tuiuiú bay
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