3,159 research outputs found
Siting Multiple Observers for Maximum Coverage: An Accurate Approach
The selection of the minimal number of observers that ensures the maximum visual coverage
over an area represented by a digital elevation model (DEM) have great interest in many
elds, e.g., telecommunications, environment planning, among others. However, this problem
is complex and intractable when the number of points of the DEM is relatively high. This
complexity is due to three issues: 1) the di culty in determining the visibility of the terrain
from one point, 2) the need to know the visibility at all points of the terrain and 3) the
combinatorial complexity of the selection of observers.
The recent progress in total-viewshed maps computation not only provides an e cient solu-
tion to the rst two problems, but also opens other ways to new solutions that were unthinkable
previously. This paper presents a new type of cartography, called the masked total viewshed
map, and provides optimal solutions for both sequential and simultaneous observers location.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
Effect of the spin-orbit interaction on the thermodynamic properties of crystals: The specific heat of bismuth
In recent years, there has been increasing interest in the specific heat
of insulators and semiconductors because of the availability of samples with
different isotopic masses and the possibility of performing \textit{ab initio}
calculations of its temperature dependence using as a starting point the
electronic band structure. Most of the crystals investigated are elemental
(e.g., germanium) or binary (e.g., gallium nitride) semiconductors. The initial
electronic calculations were performed in the local density approximation and
did not include spin-orbit interaction. Agreement between experimental and
calculated results was usually found to be good, except for crystals containing
heavy atoms (e.g., PbS) for which discrepancies of the order of 20% existed at
the low temperature maximum found for . It has been conjectured that
this discrepancies result from the neglect of spin-orbit interaction which is
large for heavy atoms (1.3eV for the valence electrons of
atomic lead). Here we discuss measurements and \textit{ab initio} calculations
of for crystalline bismuth (1.7 eV), strictly speaking a
semimetal but in the temperature region accessible to us ( 2K) acting as a
semiconductor. We extend experimental data available in the literature and
notice that the \textit{ab initio} calculations without spin-orbit interaction
exhibit a maximum at 8K, about 20% lower than the measured one. Inclusion
of spin-orbit interaction decreases the discrepancy markedly: The maximum of
is now only 7% larger than the measured one. Exact agreement is obtained
if the spin-orbit hamiltonian is reduced by a factor of 0.8.Comment: 4 pages, 3 figure
Diffusion in a class of exactly solvable non-harmonic potentials. Intrinsic effects induced by non-linearities
This paper deals with the problem of a particle that diffuses in a potential with a reflecting barrier and has a point of stable equilibrium and a point of unstable equilibrium. Based on the exact solutions obtained earlier for the Fokker-Planck equation of a class of these models, we analyze the behavior of the probability density, the mean path and the onset time which determines the transition from unimodal to bimodal probability densities. The study is made over different initial positions, two of them very close to the unstable point, which permits a clear comparison among the subsequent evolutions, and the observation of some intrinsic effects induced by non-linearities
Intersection of crisis loci in a driven nonlinearly damped oscillator
We report on a phenomenon observed in a driven nonlinearly damped oscillator when two control parameters, the frequency of the external excitation and the nonlinear damping coefficient, are varied simultaneously. An interior crisis locus and a boundary crisis locus, corresponding to two different chaotic attractors, intersect in a point of the parameter space. There exists an interchange in the type of crisis that each attractor suffers after crossing the intersection point
Spiral waves solutions in reaction-diffusion equations with symmetries. Analysis through specific models
Symmetries of nonlinear reaction-diffusion equations determine the existence of regular rotating spiral waves. They are only a consequence of kinetics processes and molecular diffusion. We prove the existence of these waves as invariant solutions of reaction-diffusion models with appropiate Lie point symmetries
Geminivirus C2 protein represses genes involved in sulphur assimilation and this effect can be counteracted by jasmonate treatment
Geminiviruses are plant viruses that infect a broad range of crops and cause extensive losses worldwide, having an important economic impact. C2, a multifunctional pathogenicity factor encoded by geminiviruses, has been recently shown to suppress the responses to jasmonates in the host plant, which might at least partially explain its well-established role in pathogenicity. Sulphur is one of the essential macro-elements for plant life, and is considered to have a role in plant defence, in a phenomenon named sulphur-induced resistance (SIR) or sulphur-enhanced defence (SED). In this work, we show that geminivirus C2 protein represses the expression of genes involved in the sulphur assimilation pathway in Arabidopsis, but, interestingly, this effect can be neutralized by exogenous jasmonate treatment. These preliminary results may raise the idea that geminiviruses might be affecting sulphur metabolism, and maybe counteracting SIR/SED, through the manipulation of the jasmonate signalling pathway, which would define a novel strategy in plant-virus interactions and may unveil SIR/SED as an important player in the plant defence against viruses.Ministerio de Ciencia y Innovación/FEDER AGL2007-66062-C02-02/AGR AGL2010-22287-CO2European Regional Development Fund (ERDF) BIO2010-15201Junta de AndalucÃa BIOÂ27
Coherent Radiation from Extensive Air Showers in the Ultra-High Frequency Band
Using detailed Monte Carlo simulations we have characterized the features of
the radio emission of inclined air showers in the Ultra-High Frequency band
(300 MHz - 3 GHz). The Fourier-spectrum of the radiation is shown to have a
sizable intensity well into the GHz frequency range. The emission is mainly due
to transverse currents induced by the geomagnetic field and to the excess
charge produced by the Askaryan effect. At these frequencies only a
significantly reduced volume of the shower around the axis contributes
coherently to the signal observed on the ground. The size of the coherently
emitting volume depends on frequency, shower geometry and observer position,
and is interpreted in terms of the relative time delays. At ground level, the
maximum emission at high frequencies is concentrated in an elliptical ring-like
region around the intersection of a Cherenkov cone with its vertex at shower
maximum and the ground. The frequency spectrum of inclined showers when
observed at positions that view shower maximum in the Cherenkov direction, is
shown to be in broad agreement with the pulses detected by the Antarctic
Impulsive Transient Antenna (ANITA) experiment, making the interpretation that
they are due to Ultra-High Energy Cosmic Ray atmospheric showers consistent
with our simulations. These results are also of great importance for
experiments aiming to detect molecular bremsstrahlung radiation in the GHz
range as they present an important background for its detection.Comment: 8 pages, 8 figure
Transient Transcriptional Regulation of the CYS-C1 Gene and Cyanide Accumulation upon Pathogen Infection in the Plant Immune Response
Cyanide is produced concomitantly with ethylene biosynthesis. Arabidopsis (Arabidopsis thaliana) detoxifies cyanide primarily through the enzyme b-cyanoalanine synthase, mainly by the mitochondrial CYS-C1. CYS-C1 loss of function is not toxic for the plant and leads to an increased level of cyanide in cys-c1 mutants as well as a root hairless phenotype. The classification of genes differentially expressed in cys-c1 and wild-type plants reveals that the high endogenous cyanide content of the cys-c1 mutant is correlated with the biotic stress response. Cyanide accumulation and CYS-C1 gene expression are negatively correlated during compatible and incompatible plant-bacteria interactions. In addition, cys-c1 plants present an increased susceptibility to the necrotrophic fungus Botrytis cinerea and an increased tolerance to the biotrophic Pseudomonas syringae pv tomato DC3000 bacterium and Beet curly top virus. The cys-c1 mutation produces a reduction in respiration rate in leaves, an accumulation of reactive oxygen species, and an induction of the alternative oxidase AOX1a and pathogenesis-related PR1 expression.We hypothesize that cyanide, which is transiently accumulated during avirulent bacterial infection and constitutively accumulated in the cys-c1 mutant, uncouples the respiratory electron chain dependent on the cytochrome c oxidase, and this uncoupling induces the alternative oxidase activity and the accumulation of reactive oxygen species, which act by stimulating the salicylic aciddependent signaling pathway of the plant immune systemEspaña MINECO BIO2010-15201Junta de AndalucÃa grant no. CVI-719
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