1,882 research outputs found
Detection of Major River Bed Changes in the River Ebro (north-eastern Spain)
Detection of major river bed changes in River Ebro (northeastern Spain
Loss Compensation in Time-Dependent Elastic Metamaterials
Materials with properties that are modulated in time are known to display
wave phenomena showing energy increasing with time, with the rate mediated by
the modulation. Until now there has been no accounting for material
dissipation, which clearly counteracts energy growth. This paper provides an
exact expression for the amplitude of elastic or acoustic waves propagating in
lossy materials with properties that are periodically modulated in time. It is
found that these materials can support a special propagation regime in which
waves travel at constant amplitude, with temporal modulation compensating for
the normal energy dissipation. We derive a general condition under which
amplification due to time-dependent properties offsets the material
dissipation. This identity relates band-gap properties associated with the
temporal modulation and the average of the viscosity coefficient, thereby
providing a simple recipe for the design of loss-compensated mechanical
metamaterials
Coherence and synchronization in diode-laser arrays with delayed global coupling
The dynamics of a semiconductor-laser array whose individual elements are
coupled in a global way through an external mirror is numerically analysed. A
coherent in-phase solution is seen to be preferred by the system at
intermediate values of the feedback coupling strength. At low values of this
parameter, a strong amplification of the spontaneous emission noise is
observed. A tendency towards chaos synchronization is also observed at large
values of the feedback strength.Comment: 8 pages, LaTeX, 6 PS figures, to appear in International Journal of
Bifurcation and Chao
Density functional perturbation theory within non-collinear magnetism
We extend the density functional perturbation theory formalism to the case of
non-collinear magnetism. The main problem comes with the exchange-correlation
(XC) potential derivatives, which are the only ones that are affected by the
non-collinearity of the system. Most of the present XC functionals are
constructed at the collinear level, such that the off-diagonal (containing
magnetization densities along and directions) derivatives cannot be
calculated simply in the non-collinear framework. To solve this problem, we
consider here possibilities to transform the non-collinear XC derivatives to a
local collinear basis, where the axis is aligned with the local
magnetization at each point. The two methods we explore are i) expanding the
spin rotation matrix as a Taylor series, ii) evaluating explicitly the XC for
the local density approximation through an analytical expression of the
expansion terms. We compare the two methods and describe their practical
implementation. We show their application for atomic displacement and electric
field perturbations at the second order, within the norm-conserving
pseudopotential methods
Propriedades do solo e adsorção de fosfato
Poster apresentado no Congresso Ibérico da Ciência do Solo, que decorreu de 15 a 18 de Junho de 2004, em Bragança.Quantificar a capacidade de adsorção de fosfato, em solos ácidos de Portugal, através de propriedades mineralógicas e químicas.Programa PRODEP/01. Medida 2.5.3
Significado agronómico do P extraído pelo método de Olsen em solos ácidos de Portugal
Poster apresentado no Encontro Anual da Sociedade Portuguesa de Ciência do Solo, que decorreu em Castelo Branco de 29 de Junho a 1 de Julho de 2005.O objectivo deste trabalho foi o de avaliar o significado agronómico do P extraído pelo método de Olsen, num conjunto de 32 solos agrícolas, pertencentes às principais unidades de Portugal e na sua maioria ácidos
Dynamics of modal power distribution in a multimode semiconductor laser with optical feedback
The dynamics of power distribution between longitudinal modes of a multimode
semiconductor laser subjected to external optical feedback is experimentally
analyzed in the low-frequency fluctuation regime. Power dropouts in the total
light intensity are invariably accompanied by sudden activations of several
longitudinal modes. These activations are seen not to be simultaneous to the
dropouts, but to occur after them. The phenomenon is statistically analysed in
a systematic way, and the corresponding delay is estimated.Comment: 3 pages, 4 figures, revte
Evaluación de la maloclusión, alteraciones funcionales y hábitos orales en una población escolar: Tarragona y Barcelona
Fundamento: La etiología de la maloclusión puede ser multifactorial y difícil de clasificar durante el desarrollo del individuo. Los objetivos del estudio son conocer las características de la maloclusión y su posible relación con las alteraciones funcionales y los hábitos orales. Métodos: Se estudió a 1.270 individuos representativos de la población escolar de Cataluña; 596 niños y 674 niñas de entre 6 y 14 años. Se obtuvo información mediante registros clínicos y cuestionarios. Se trata de un estudio observacional descriptivo mixto transversal, llevado a cabo entre 2006 y 2007 a través de un muestreo no probabilística de conveniencia. Se ha realizado el calibrado de los examinadores. Resultados: Fueron incluidos 1051 escolares con una edad media de 9,32 años. El 72,8% presenta según Angle Clase I, 19,0% y 5,2% Clase II/1 y II/2 respectivamente y 2,9% Clase III. El hábito onicofagia fue el más frecuente con un 46,4%. El mayor nivel de limitación funcional fue la hipertrofia amigdalar con un 21,2%. Existe relación estadísticamente significativa entre maloclusión sagital y tipo de respiración y movilidad lingual y entre maloclusión horizontal y tiempo de succión digital y movilidad lingual (p<0,05). Conclusiones: El diagnóstico de alteraciones funcionales y de hábitos orales puede advertir de la presencia de maloclusión
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