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 Baía 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 baía Tuiuiú, Pantanal, Mato Grosso do Sul. Foram realizadas coletas bimestrais, durante três anos, na baía Tuiuiú, meandro abandonado do rio Paraguai. Dos exemplares coletados foram retirados os tratos digestivos e o conteúdo foi homogeneizado e diluído 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 baía 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 detritívoros constituem a base da cadeia alimentar aquática na baía 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