625 research outputs found
Charging of highly resistive granular metal films
We have used the Scanning Kelvin probe microscopy technique to monitor the
charging process of highly resistive granular thin films. The sample is
connected to two leads and is separated by an insulator layer from a gate
electrode. When a gate voltage is applied, charges enter from the leads and
rearrange across the sample. We find very slow processes with characteristic
charging times exponentially distributed over a wide range of values, resulting
in a logarithmic relaxation to equilibrium. After the gate voltage has been
switched off, the system again relaxes logarithmically slowly to the new
equilibrium. The results cannot be explained with diffusion models, but most of
them can be understood with a hopping percolation model, in which the
localization length is shorter than the typical site separation. The technique
is very promising for the study of slow phenomena in highly resistive systems
and will be able to estimate the conductance of these systems when direct
macroscopic measurement techniques are not sensitive enough.Comment: 8 pages, 7 figure
Evaluation of the Influence of Different Grades of Reinforcing Steel on the Seismic Performance of Concrete reinforced Frame Structures with Nonlinear Static Analysis
In this investigation, the elasto-plastic behavior and the seismic performance of concrete reinforced frame structures reinforced are evaluated by applying the Pushover method. This evaluation is done on several cases: with high ductility steel (Grade 40), conventional steel (Grade 60) and high strength steel (Grade 75). For the previous, the capacity curve graph obtained from the displacement coefficient method was used to measure the capacity of the structure. In addition, the performance of the structure for different levels of seismic design are evaluated with the resulting values of ductility and rigidity of each case. The results showed that reinforcing a structure with a Grade 40 reinforcing steel increases the energy dissipation capacity, and if reinforced with a Grade 75 reinforcing steel increases the strength capacity in the structure. Finally, the comparative result of the various cases are presented to demonstrate the influence of reinforcing steel on the plastic behavior of concrete reinforced frame structures
Domination by second countable spaces and Lindelöf Σ-property
AbstractGiven a space M, a family of sets A of a space X is ordered by M if A={AK:K is a compact subset of M} and KâL implies AKâAL. We study the class M of spaces which have compact covers ordered by a second countable space. We prove that a space Cp(X) belongs to M if and only if it is a Lindelöf ÎŁ-space. Under MA(Ï1), if X is compact and (XĂX)\Î has a compact cover ordered by a Polish space then X is metrizable; here Î={(x,x):xâX} is the diagonal of the space X. Besides, if X is a compact space of countable tightness and X2\Î belongs to M then X is metrizable in ZFC.We also consider the class Mâ of spaces X which have a compact cover F ordered by a second countable space with the additional property that, for every compact set PâX there exists FâF with PâF. It is a ZFC result that if X is a compact space and (XĂX)\Î belongs to Mâ then X is metrizable. We also establish that, under CH, if X is compact and Cp(X) belongs to Mâ then X is countable
Mocarts: a lightweight radiation transport simulator for easy handling of complex sensing geometries
In functional neuroimaging (fNIRS), elaborated sensing geometries pairing multiple light sources and detectors arranged over the tissue surface are needed. A variety of software tools for probing forward models of radiation transport in tissue exist, but their handling of sensing geometries and specification of complex tissue architectures is, most times, cumbersome. In this work, we introduce a lightweight simulator, Monte Carlo Radiation Transport Simulator (MOCARTS) that attends these demands for simplifying specification of tissue architectures and complex sensing geometries. An object-oriented architecture facilitates such goal. The simulator core is evolved from the Monte Carlo Multi-Layer (mcml) tool but extended to support multi-channel simulations. Verification against mcml yields negligible error (RMSE~4-10e-9) over a photon trajectory. Full simulations show concurrent validity of the proposed tool. Finally, the ability of the new software to simulate multi-channel sensing geometries and to define biological tissue models in an intuitive nested-hierarchy way are exemplified
Regions of Diversity 8, 9 and 13 contribute to Streptococcus pneumoniae virulence
<p>Abstract</p> <p>Background</p> <p><it>Streptococcus pneumoniae </it>is the leading cause of community-acquired pneumonia. Previously, using comparative genomic analyses, 13 regions of genomic plasticity have been identified in the <it>S. pneumoniae </it>genome. These "Regions of Diversity" (RDs) accounted for half the genomic variation observed amongst all pneumococci tested, moreover, were determined to encode a variety of putative virulence factors. To date, genes within 5 RDs have been unequivocally demonstrated to contribute to <it>S. pneumoniae </it>virulence. It is unknown if the remaining RDs also contribute to virulence.</p> <p>Results</p> <p>Using allelic exchange, we created <it>S. pneumoniae </it>mutants that were deficient in RD2, 5, 7, 8, 9, 12 and 13. Mutants deficient in RD8, 9 and 13 were attenuated in a mouse model of disease. RD8 is 40,358 nucleotides in length and encodes 37 genes. Using a panel of isogenic mutants, we determined that RD8b3 is the operon within RD8 that is responsible for virulence. Mice infected with mutants deficient in RD8, RD8b3, RD9 and RD13 had significantly less bacteria in the blood two days after intranasal challenge and improved survival over time versus mice infected with wild type. In all instances mutants colonized the nasopharynx at levels equivalent to wild type.</p> <p>Conclusion</p> <p>Genes within RD1, 3, 4, 6, and 10 have previously been shown to contribute to virulence. This study demonstrates that genes within RD8, 9 and 13 also contribute to virulence. The ability of mutants deficient in RD2, 5, 7, 8, 9, 12, and 13 to colonize the nasopharynx indicates that genes within these RDs are not required for asymptomatic carriage. Nonetheless, the observation that mutants deficient in RD8b3, 9 and 13 are attenuated indicates that genes within these loci are necessary for spread of the bacteria beyond the nasopharynx to normally sterile sites.</p
Weakly uniformly rotund Banach spaces
summary:The dual space of a WUR Banach space is weakly K-analytic
Analysis of seismic bidirectionality on response of reinforced concrete structures with irregularities of l-shaped plan and soft story
The seismic design of buildings is usually performed using one-way analysis for each of main axes independently. However, seismic events have fairly random behaviour and impose bidirectional solicitations on structures. In this work, the study of the response in structures subjects to earthquake loads with irregularity of l-shaped plan and soft story is carried out. For this, the linear time-story analysis (LTHA) of these has been carried out imposing seismic solicitations in two orthogonal directions. Thus, the structural response with incidence angle variations of 10 is obtained and compared with the response derived from the unidirectional analysis. Variations of up to 50% and 72% are obtained for model structures with l-shaped plan and soft story respectively
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