Application of non-parametric geostatistical methods to the identification of aggregate deposits on the continental shelf

More than 1 400 samples were used in the assessment of the sand and gravel potential of the continental shelf north of Espinho (northern Portugal). This study deals primarily with the determination of the probabilities of the occurrence of some textural (gravel, sand, silt and clay contents) and chemical (carbonate content) parameters and of some textural groups, according to Nickless' (1973) classification. Sediment samples were collected between 1986 and 1989, during several cruises sponsored by the Portuguese Hydrographic Institute. For the purpose of the present study, a non-parametric geostatistical methodology was used on the whole set of samples, encompassing the following steps: a) a preliminary variography analysis based on the raw data, to determine structural features, such as trends, anisotropies and nested models; b) binary codification of the initial data, in ‘less than' or ‘equal to' specific cut-offs determined with economic criteria; c) calculation and modelling of variograms of this indicator; and d) application of indicator kriging to obtain probability (risk) maps. The results obtained by the application of the methodology to the two data groups (sediment texture and Nickless classification) were compared in order to characterise the aggregate deposits which could be economically exploited in the near future. This study should help decision-makers to define an exploitation strategy, to be implemented in the near future. However, this preliminary approach requires further studies, namely by using cross-variography procedures and conditional probabilities.Más de 1 400 muestras sedimentarias fueron utilizadas en la evaluación del potencial en gravas y arenas que se pueden explotar para áridos naturales y de trituración para la construcción y obras públicas. El presente estudio se atiene a la determinación de la probabilidad de ocurrencia de algunos parámetros texturales (contenido en gravas, en arena y en fango) y químicos (contenido en carbonatos) y de determinados grupos texturales, según la clasificación de Nickless (1973). Las muestras fueron recogidas entre 1986 y 1989 en el transcurso de diversas campañas oceanográficas realizadas por el Instituto Hidrográfico de la Marina Portuguesa. Se ha realizado un estudio de geoestadística no paramétrica incluyendo las siguientes etapas: a) variografía preliminar de los datos de base para identificar características estructurales (por ejemplo, tendencias, anisotropías y estructuras imbricadas); b) se codificaron los datos iniciales en formato binario, según valores inferiores a o iguales a un patamar específico determinado por un criterio económico; c) se calcularon y modelaron variogramas de esta indicatriz; y d) la indicatriz fue krijeada para obtener mapas de probabilidad o riesgo. La referida metodología fue aplicada sobre los dos tipos de datos (granulometría sedimentaria y clasificación de Nickless). Se compararon los resultados obtenidos para caracterizar los depósitos de gravas y arenas que pueden ser explotados en un futuro próximo. La presente aplicación pretende ayudar a los organismos decisorios a definir una futura estrategia de explotación. Sin embargo, éste es solamente un estudio preliminar. Se necesitan estudios más profundos, utilizando, por ejemplo, procedimientos de variografía cruzada y probabilidades condicionales.Instituto Español de Oceanografí

Quantum critical point in the spin glass-antiferromagnetism competition in Kondo-lattice systems

A theory is proposed to describe the competition among antiferromagnetism (AF), spin glass (SG) and Kondo effect. The model describes two Kondo sublattices with an intrasite Kondo interaction strength $J_{K}$ and an interlattice quantum Ising interaction in the presence of a transverse field $\Gamma$. The interlattice coupling is a random Gaussian distributed variable (with average $-2J_0/N$ and variance $32 J^{2}/N$) while the $\Gamma$ field is introduced as a quantum mechanism to produce spin flipping. The path integral formalism is used to study this fermionic problem where the spin operators are represented by bilinear combinations of Grassmann fields. The disorder is treated within the framework of the replica trick. The free energy and the order parameters of the problem are obtained by using the static ansatz and by choosing both $J_0/J$ and $\Gamma/J \approx (J_k/J)^2$ to allow, as previously, a better comparison with the experimental findings. The results indicate the presence of a SG solution at low $J_K/J$ and for temperature $T<T_{f}$ ($T_{f}$ is the freezing temperature). When $J_K/J$ is increased, a mixed phase AF+SG appears, then an AF solution and finally a Kondo state is obtained for high values of $J_{K}/J$. Moreover, the behaviors of the freezing and Neel temperatures are also affected by the relationship between $J_{K}$ and the transverse field $\Gamma$. The first one presents a slight decrease while the second one decreases towards a Quantum Critical Point (QCP). The obtained phase diagram has the same sequence as the experimental one for $Ce_{2}Au_{1-x}Co_{x}Si_{3}$, if $J_{K}$ is assumed to increase with $x$, and in addition, it also shows a qualitative agreement concerning the behavior of the freezing and the Neel temperatures.Comment: 11 pages, 3 figures, accepted for publication in J. Phys.

Utilização de infravermelho próximo para determinação das propriedades da madeira.

Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso

Caracterização por microscopia óptica e eletrônica de varredura de amostras da madeira de pínus submetidas à compressão axial.

EVINCI. Resumo 048

Redesign participativo do aplicativo móvel Agritempo: a importância da interação usuário-desenvolvedor.

Este trabalho apresenta o impacto da aplicação do DCU no processo de desenvolvimento de um aplicativo móvel para o produtor agrícola por meio de uma validação colaborativa

Photoassociative ionization of Na inside a storage ring

Motivated by recent interest in low dimensional arrays of atoms, we experimentally investigated the way cold collisional processes are affected by the geometry of the considered atomic sample. More specifically, we studied the case of photoassociative ionization (PAI) both in a storage ring where collision is more unidirectional in character and in a trap with clear undefinition of collision axis. First, creating a ring shaped trap (atomotron) we investigated two-color PAI dependence with intensity and polarization of a probing laser. The intensity dependence of the PAI rate was also measured in a magneto-optical trap presenting equivalent temperature and density conditions. Indeed, the results show that in the ring trap, the value of the PAI rate constant is much lower and does not show evidences of saturation, unlike in the case of the 3D-MOT. Cold atomic collisions in storage ring may represent new possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio

Ramsey fringes formation during excitation of topological modes in a Bose-Einstein condensate

The Ramsey fringes formation during the excitation of topological coherent modes of a Bose-Einstein condensate by an external modulating field is considered. The Ramsey fringes appear when a series of pulses of the excitation field is applied. In both Rabi and Ramsey interrogations, there is a shift of the population maximum transfer due to the strong non-linearity present in the system. It is found that the Ramsey pattern itself retains information about the accumulated relative phase between both ground and excited coherent modes.Comment: Latex file, 12 pages, 5 figure

Comportamento do Angiostrongylus costaricensis em planorbídeos

Some terrestrial mollusks are natural hosts of Angiostrongylus costaricensis. In the laboratory, this nematode can be maintained in certain planorbids, which are aquatic mollusks and intermediate hosts of Schistosoma mansoni. Mollusks can be infected with Angiostrongylus costaricensis by ingestion of or active penetration by the first-stage larvae. In this work we assessed the ability of Biomphalaria glabrata to attract first-stage larvae of A. costaricensis. Movement of the nematode larvae towards the mollusks was observed after 15 min, 30 min and 1 h. B. glabrata did not attract the first-stage larvae of A. costaricensis in any of the three intervals. The susceptibility of two populations of Biomphalaria tenagophila to infection by A. costaricensis was also determined. One population was genetically selected for the susceptibility to S. mansoni while the other was not. Third-stage larvae were recovered from the snails 30 days after exposure of the two populations to 120 first-stage larvae. All the mollusks were infected. However, a significantly higher number of third-stage larvae were recovered in mollusks not genetically selected.Alguns moluscos terrestres são hospedeiros naturais do Angiostrongylus costaricensis. No laboratório, esse nematódeo pode ser mantido em planorbídeos, que são moluscos aquáticos e hospedeiros intermediários do Schistosoma mansoni. Os moluscos podem ser infectados com A. costaricensis por ingestão ou por penetração ativa de larvas de primeiro estágio. Neste trabalho, testamos a habilidade de Biomphalaria glabrata em atrair larvas de primeiro estágio de A. costaricensis. A movimentação das larvas do nematódeo em direção aos moluscos foi observada após 15 minutos, 30 minutos e 1 hora. B. glabrata não atraiu as larvas de primeiro estágio de A. costaricensis nos três intervalos de tempo. Verificamos também a suscetibilidade de duas populações de Biomphalaria tenagophila à infecção por A. costaricensis. Uma população era selecionada geneticamente para a susceptibilidade ao S. mansoni, enquanto a outra não o era. Larvas de terceiro estágio foram recuperadas dos moluscos 30 dias após a exposição das duas populações a 120 larvas de primeiro estágio. Todos os moluscos estavam infectados. Entretanto, um número significativamente maior de larvas de terceiro estágio foi recuperado em moluscos não geneticamente selecionados.19920