Radiant Emission Characteristics of Diffuse Conical Cavities

Radiant-energy emission of diffuse conical cavitie

Thermal Radiation Absorption in Rectangular-Groove Cavities

Thermal radiation absorption in rectangular-groove cavitie

Absorption and Emission Characteristics of Diffuse Spherical Enclosures

The thermal radiation characteristics of spherical cavities are of practical interest in connection with the absorption of radiant energy for both space-vehicle and terrestrial applications. Also, spherical cavities are of potential use as sources of black-body energy. The purpose of this brief paper is to determine both the absorption and emission characteristics of spherical cavities which are diffuse reflectors and emitters

Inertial forces and the foundations of optical geometry

Assuming a general timelike congruence of worldlines as a reference frame, we derive a covariant general formalism of inertial forces in General Relativity. Inspired by the works of Abramowicz et. al. (see e.g. Abramowicz and Lasota, Class. Quantum Grav. 14 (1997) A23), we also study conformal rescalings of spacetime and investigate how these affect the inertial force formalism. While many ways of describing spatial curvature of a trajectory has been discussed in papers prior to this, one particular prescription (which differs from the standard projected curvature when the reference is shearing) appears novel. For the particular case of a hypersurface-forming congruence, using a suitable rescaling of spacetime, we show that a geodesic photon is always following a line that is spatially straight with respect to the new curvature measure. This fact is intimately connected to Fermat's principle, and allows for a certain generalization of the optical geometry as will be further pursued in a companion paper (Jonsson and Westman, Class. Quantum Grav. 23 (2006) 61). For the particular case when the shear-tensor vanishes, we present the inertial force equation in three-dimensional form (using the bold face vector notation), and note how similar it is to its Newtonian counterpart. From the spatial curvature measures that we introduce, we derive corresponding covariant differentiations of a vector defined along a spacetime trajectory. This allows us to connect the formalism of this paper to that of Jantzen et. al. (see e.g. Bini et. al., Int. J. Mod. Phys. D 6 (1997) 143).Comment: 42 pages, 7 figure

Long-Time Dynamics of Variable Coefficient mKdV Solitary Waves

We study the Korteweg-de Vries-type equation dt u=-dx(dx^2 u+f(u)-B(t,x)u), where B is a small and bounded, slowly varying function and f is a nonlinearity. Many variable coefficient KdV-type equations can be rescaled into this equation. We study the long time behaviour of solutions with initial conditions close to a stable, B=0 solitary wave. We prove that for long time intervals, such solutions have the form of the solitary wave, whose centre and scale evolve according to a certain dynamical law involving the function B(t,x), plus an H^1-small fluctuation.Comment: 19 page

Proposta conceitual de estudo para a integração e gerenciamento do uso de marcadores bioquímicos de contaminação ambiental.

Resumo: A agricultura sustentável prioriza o uso racional da terra e da biota. Para tanto, é necessária a compreensão da interação entre os insumos agrícolas e os ecossistemas. Porém, há carência de métodos de fácil acesso para a verificação de contaminação ambiental por muitos desses produtos, como os agrotóxicos e de suas misturas. A aplicação de métodos alternativos no monitoramento de áreas degradadas pode gerar vantagens econômicas quando comparados à implementação de protocolos de análise que utilizam métodos de alto custo que demandam maior tempo de análise. Uma vez que a saúde ambiental pode ser avaliada por meio de estudos com indicadores biológicos, a abordagem aqui apresentada objetiva discutir alguns aspectos a respeito do monitoramento de risco ambiental com organismos não-alvo sentinela, focando parâmetros bioquímicos. Tais parâmetros evidenciariam que o agrotóxico penetrou no organismo e ocasionou uma resposta a um efeito de acordo com a dose ou o tempo de exposição. Esses parâmetros poderão ser utilizados como indicadores biológicos bioquímicos em programas de monitoramento ambiental devido à identificação precoce de alterações. Os resultados obtidos de seu uso poderão ser utilizados para subsidiar políticas relacionadas ao gerenciamento de riscos ambientais. Abstract: Sustainable agriculture prioritizes the rational use of land and biota. For this, there is a need for understanding the interaction between the agriculture inputs and the ecosystems. However, there is a lack of easy access methods for verifying environmental contamination due to many of these products, such as pesticides and their mixtures. The application of alternative methods for monitoring degraded areas can generate economic advantages when compared to the implementation of protocols for analysis using high cost methods which demand a longer analysis time. Since environmental health can be accessed through studies using biomarkers, the approach presented here aims to discuss some aspects on the environmental risk monitoring with sentinel non-target organisms, focusing on biochemical parameters. Such parameters showed that the pesticide penetrated into the body and caused a response according to the dose or time of exposition

Root-soil rotation stiffness of Norway spruce ( Picea abies (L.) Karst) growing on subalpine forested slopes

Trees bend and break when exposed to external forces such as wind, rockfall, and avalanches. A common simplification when modelling the tree response to these forces is to simplify the system as a clamped beam which means that the stem deflection is related to the stem flexibility only. However, a certain part of the stem deflection originates from rotation of the root-soil plate. In this paper, we investigate this contribution to the overall stem deflection. Norway spruce (Picea abies (L.) Karst) trees were subjected to winching tests to analyse the anchorage mechanics of the tree. The tests were performed at two experimental sites with an average slope of 32 and 34° and one site with a nearly flat ground in subalpine forests near Davos, Switzerland, during the vegetation periods of 2003 and 2004. The trees were pulled downslope with a winch and the applied force, stem base rotation, and the angle of the applied force relative to the stem were recorded. After the tree had fallen over, stem diameter and branch mass were measured for every meter segment. These data were used to model the tree in the finite element software ANSYS®, which was used for calculating the rotational stem base moment as a␣function of stem base rotation. The root-soil rotation stiffness k root was defined as the secant stiffness calculated at 0.5° root-soil plate rotation. Young's modulus of elasticity E of the stem was iteratively changed until the correct stem rotation was obtained. The best correlation between k root and different tree characteristics was the squared diameter at breast height, DBH2. Not incorporating the normal forces due to weight of the overhanging masses from crown and stem resulted in a maximum underestimation for k root of approximately 14%. Thus, also the acting moment on the stem base will be underestimated causing the safety factor against uprooting to be overestimate

Hydrogen transport in superionic system Rb3H(SeO4)2: a revised cooperative migration mechanism

We performed density functional studies of electronic properties and mechanisms of hydrogen transport in Rb3H(SeO4)2 crystal which represents technologically promising class M3H(XO4)2 of proton conductors (M=Rb,Cs, NH4; X=S,Se). The electronic structure calculations show a decisive role of lattice dynamics in the process of proton migration. In the obtained revised mechanism of proton transport, the strong displacements of the vertex oxygens play a key role in the establishing the continuous hydrogen transport and in the achieving low activation energies of proton conduction which is in contrast to the standard two-stage Grotthuss mechanism of proton transport. Consequently, any realistic model description of proton transport should inevitably involve the interactions with the sublattice of the XO4 groups.Comment: 11 pages, 11 figures, to appear in Physical Review

Uso potencial da brita e argila na redução da toxicidade de efluentes da aquicultura contendo diflubenzuron.

Resumo: O crescimento acelerado da aquicultura no Brasil e no mundo vem a atender a uma demanda crescente por proteína animal. No entanto, este crescimento deve vir acompanhado da medidas de conservação dos recursos naturais, bem como a minimização dos impactos sobre a qualidade da água dos viveiros de criação e dos efluentes gerados por esta atividade. O presente estudo tem por objetivo avaliar a toxicidade do inseticida diflubenzuron (usado na piscicultura) sobre o organismo Artemia salina, após a filtragem com um sistema natural de tratamento de efluentes, utilizando como meios filtrantes a brita e a argila expandida. Os resultados obtidos indicam que a argila expandida foi mais eficiente na redução da toxicidade do que a brita. Embora ainda sejam necessários testes com outros organismos não alvo, sugere-se o uso da argila como filtro na saída dos viveiros para melhoria da qualidade da água do efluente

Magnetic-field dependence of dynamical vortex response in two-dimensional Josephson junction arrays and superconducting films

The dynamical vortex response of a two-dimensional array of the resistively shunted Josephson junctions in a perpendicular magnetic field is inferred from simulations. It is found that, as the magnetic field is increased at a fixed temperature, the response crosses over from normal to anomalous, and that this crossover can be characterized by a single dimensionless parameter. It is described how this crossover should be reflected in measurements of the complex impedance for Josephson junction arrays and superconducting films.Comment: 4 pages including 5 figures in two columns, final versio