16,315 research outputs found
Conductance of nano-systems with interactions coupled via conduction electrons: Effect of indirect exchange interactions
A nano-system in which electrons interact and in contact with Fermi leads
gives rise to an effective one-body scattering which depends on the presence of
other scatterers in the attached leads. This non local effect is a pure
many-body effect that one neglects when one takes non interacting models for
describing quantum transport. This enhances the non-local character of the
quantum conductance by exchange interactions of a type similar to the
RKKY-interaction between local magnetic moments. A theoretical study of this
effect is given assuming the Hartree-Fock approximation for spinless fermions
in an infinite chain embedding two scatterers separated by a segment of length
L\_c. The fermions interact only inside the two scatterers. The dependence of
one scatterer onto the other exhibits oscillations which decay as 1/L\_c and
which are suppressed when L\_c exceeds the thermal length L\_T. The
Hartree-Fock results are compared with exact numerical results obtained with
the embedding method and the DMRG algorithm
Two-color discrete localized modes and resonant scattering in arrays of nonlinear quadratic optical waveguides
We analyze the properties and stability of two-color discrete localized modes
in arrays of channel waveguides where tunable quadratic nonlinearity is
introduced as a nonlinear defect by periodic poling of a single waveguide in
the array. We show that, depending on the value of the phase mismatch and the
input power, such two-color defect modes can be realized in three different
localized states. We also study resonant light scattering in the arrays with
the defect waveguide.Comment: 10 pages, 3 figures, published in PR
Core Representations of the Standard Fixed Tree Game
This paper discusses the core of the game corresponding to the standard fixed tree problem. We introduce the concept of a weighted constrained egalitarian solution. The core of the standard fixed tree game equals the set of all weighted constrained egalitarian solutions. The notion of home-down allocation is developed to create further insight in the local behavior of the weighted constrained egalitarian allocation. A similar and dual approach by the notion of down-home allocations gives us the class of weighted Shapley values. The constrained egalitarian solution is characterized in terms of a cost sharing mechanism.Cooperative game theory;tree games;core;weighted constrained egalitarian solution
Fano resonance in quadratic waveguide arrays
We study resonant light scattering in arrays of channel optical waveguides
where tunable quadratic nonlinearity is introduced as nonlinear defects by
periodic poling of single (or several) waveguides in the array. We describe
novel features of wave scattering that can be observed in this structure and
show that it is a good candidate for the first observation of Fano resonance in
nonlinear optics.Comment: 3 pages, 3 figures, submitted to Optics Letters, slightly revise
Diffusion in infinite and semi-infinite lattices with long-range coupling
We prove that for a one-dimensional infinite lattice, with long-range
coupling among sites, the diffusion of an initial delta-like pulse in the bulk,
is ballistic at all times. We obtain a closed-form expression for the mean
square displacement (MSD) as a function of time, and show some cases including
finite range coupling, exponentially decreasing coupling and power-law
decreasing coupling. For the case of an initial excitation at the edge of the
lattice, we find an approximate expression for the MSD that predicts ballistic
behavior at long times, in agreement with numerical results.Comment: 4 pages, 5 figures, submitted for publicatio
Enhanced Parallel Generation of Tree Structures for the Recognition of 3D Images
Segmentations of a digital object based on a connectivity
criterion at n-xel or sub-n-xel level are useful tools in image topological
analysis and recognition. Working with cell complex analogous of digital
objects, an example of this kind of segmentation is that obtained from
the combinatorial representation so called Homological Spanning Forest
(HSF, for short) which, informally, classifies the cells of the complex as
belonging to regions containing the maximal number of cells sharing the
same homological (algebraic homology with coefficient in a field) information.
We design here a parallel method for computing a HSF (using
homology with coefficients in Z/2Z) of a 3D digital object. If this object
is included in a 3D image of m1 × m2 × m3 voxels, its theoretical time
complexity order is near O(log(m1 + m2 + m3)), under the assumption
that a processing element is available for each voxel. A prototype implementation
validating our results has been written and several synthetic,
random and medical tridimensional images have been used for testing.
The experiments allow us to assert that the number of iterations in which
the homological information is found varies only to a small extent from
the theoretical computational time.Ministerio de Economía y Competitividad MTM2016-81030-
J'Marcuse : La tarea intelectual de Herbert Marcuse ante la sociedad unidimensional
El propósito de la ponencia es reconstruir el vínculo entre el derrotero teórico de Herbert Marcuse y su diagnóstico de la sociedad norteamericana. Más específicamente, el objetivo es comprender las versiones contrastantes de Estados Unidos que conviven en la obra del autor a la luz de su preocupación por el papel de la teoría crítica en los procesos de transformación social. En primer término, se examina el lugar preponderante que ocupa Estados Unidos en el estudio de las sociedades industriales avanzadas emprendido por Marcuse en El hombre unidimensional. En esta sección, se presta particular atención al problema de la vigencia de la teoría crítica en el marco de una sociedad que, como la norteamericana, parece capaz de fagocitar las fuerzas tendientes al cambio social. En segundo término, la ponencia analiza cómo la irrupción de nuevas corrientes contestatarias en la escena cultural y política norteamericana modificó la visión de Marcuse sobre los Estados Unidos, así como las reformulaciones conceptuales implicadas en ese viraje. Para finalizar, la deriva intelectual y política de Marcuse por Estados Unidos se coteja con la de Theodor W. Adorno, propiciando una reflexión acerca de sus modos contrastantes de comprender y ejercer la teoría crític
Effect of solute content and temperature on the deformation mechanisms and critical resolved shear stress in Mg-Al and Mg-Zn alloys
The influence of solute atoms (Al and Zn) on the deformation mechanisms and
the critical resolved shear stress for basal slip in Mg alloys at 298 K and 373
K was ascertained by micropillar compression tests in combination with
high-throughput processing techniques based on the diffusion couples. It was
found that the presence of solute atoms enhances the size effect at 298 K as
well as the localization of deformation in slip bands, which is associated with
large strain bursts in the resolved shear stress ()-strain
() curves. Deformation in pure Mg and Mg alloys was more homogeneous
at 373 K and the influence of the micropillar size on the critical resolved
shear stress was much smaller. In this latter case, it was possible to
determine the effect of solute content on the critical resolved shear stress
for basal slip in Mg-Al and Mg-Zn alloys
Bacterial Active Community Cycling in Response to Solar Radiation and Their Influence on Nutrient Changes in a High-Altitude Wetland
Indexación: Web of Science; Scopus.Microbial communities inhabiting high-altitude spring ecosystems are subjected to extreme changes in solar irradiance and temperature throughout the diel cycle. Here, using 16S rRNA gene tag pyrosequencing (cDNA) we determined the composition of actively transcribing bacteria from spring waters experimentally exposed through the day (morning, noon, and afternoon) to variable levels of solar radiation and light quality, and evaluated their influence on nutrient recycling. Solar irradiance, temperature, and changes in nutrient dynamics were associated with changes in the active bacterial community structure, predominantly by Cyanobacteria, Verrucomicrobia, Proteobacteria, and 35 other Phyla, including the recently described Candidate Phyla Radiation (e.g., Parcubacteria, Gracilibacteria, OP3, TM6, SR1). Diversity increased at noon, when the highest irradiances were measured (3.3-3.9 H', 1125 W m(-2)) compared to morning and afternoon (0.6-2.8 H'). This shift was associated with a decrease in the contribution to pyrolibraries by Cyanobacteria and an increase of Proteobacteria and other initially low frequently and rare bacteria phyla (< 0.5%) in the pyrolibraries. A potential increase in the activity of Cyanobacteria and other phototrophic groups, e.g., Rhodobacterales, was observed and associated with UVR, suggesting the presence of photo activated repair mechanisms to resist high levels of solar radiation. In addition, the percentage contribution of cyanobacterial sequences in the afternoon was similar to those recorded in the morning. The shifts in the contribution by Cyanobacteria also influenced the rate of change in nitrate, nitrite, and phosphate, highlighted by a high level of nitrate accumulation during hours of high radiation and temperature associated with nitrifying bacteria activity. We did not detect ammonia or nitrite oxidizing bacteria in situ, but both functional groups (Nitrosomona and Nitrospira) appeared mainly in pyrolibraries generated from dark incubations. In total, our results reveal that both the structure and the diversity of the active bacteria community was extremely dynamic through the day, and showed marked shifts in composition that influenced nutrient recycling, highlighting how abiotic variation affects potential ecosystem functioning.http://journal.frontiersin.org/article/10.3389/fmicb.2016.01823/ful
Enhancement of the advanced Fenton process (Fe0/H2O2) by ultrasound for the mineralization of phenol
In this study, a successful mineralization of phenol was achieved by means of coupling zero-valent iron (ZVI) particles, hydrogen peroxide and a short input of ultrasonic irradiation. This short sono-advanced Fenton process (AFP) provided a better performance of ZVI in a subsequent silent degradation stage, which involves neither extra cost of energy nor additional oxidant. The short input of ultrasound (US) irradiation enhanced the activity of the Fe0/H2O2 system in terms of the total organic carbon (TOC) removal. Then, the TOC mineralization continued during the silent stage, even after the total consumption of hydrogen peroxide, reaching values of ca. 90% TOC conversions over 24 h. This remarkable activity is attributed to the capacity of the ZVI/iron oxide composite formed during the degradation for the generation of oxidizing radical species and to the formation of another reactive oxidant species, such as the ferryl ion. The modification of the initial conditions of the sono-AFP system such as the ultrasonic irradiation time and the hydrogen peroxide dosage, showed significant variations in terms of TOC mineralization for the ongoing silent degradation stage. An appropriate selection of operation conditions will lead to an economical and highly efficient technology with eventual large-scale commercial applications for the degradation organic pollutants in aqueous effluents
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