Techniques for obtaining regional radiation budgets from satellite radiometer observations, phase 4 and phase 5

A scheme was developed which divides the earth-atmosphere system into 2060 elemental areas. The regions previously described are defined in terms of these elemental areas which are fixed in size and position as the satellite moves. One method, termed the instantaneous technique, yields values of the radiant emittance (We) and the radiant reflectance (Wr) which the regions have during the time interval of a single satellite pass. The number of observations matches the number of regions under study and a unique solution is obtained using matrix inversion. The other method (termed the best fit technique), yields time averages of We and Wr for large time intervals (e.g., months, seasons). The number of observations in this technique is much greater than the number of regions considered, and an approximate solution is obtained by the method of least squares

Techniques for computing regional radiant emittances of the earth-atmosphere system from observations by wide-angle satellite radiometers, phase 3

Radiometers on earth orbiting satellites measure the exchange of radiant energy between the earth-atmosphere (E-A) system and space at observation points in space external to the E-A system. Observations by wideangle, spherical and flat radiometers are analyzed and interpreted with regard to the general problem of the earth energy budget (EEB) and to the problem of determining the energy budget of regions smaller than the field of view (FOV) of these radiometers

Comment: Despite The Controversy Surrounding The Helms-Burton Act Its End Is Far From Becoming A reality

From the moment the Cuban Liberty and Democratic Solidarity Act, popularly known as the Helms-Burton Act,\u27 entered the 104th Congress it sparked a great deal of controversy domestically and internationally

Comentario: A Pesar De La Controversia Que Rodea La Ley Helms-Burton Su final Esta Lejos De Convertirse En Una Realidad

Desde el momento en que el Acta Por La Libertad Cubana y Solidaridad Democritica, popularmente conocido como la ley Helms-Burton,\u27 entr6 en el Congreso numero 104 este causo mucha controversia dom~sticamente e internacionalment

Arterial spin labelling: initial experience, clinical impact and difficulties

RESUMO O arterial spin labeling (ASL) é uma técnica de perfusão por ressonância magnética (RM) que usa os protões das moléculas de água do sangue arterial como marcador endógeno. As suas principais vantagens residem no facto de ser um método não invasivo, rápido e que dispensa a administração de contraste. Actualmente os seus resultados são reprodutíveis de modo robusto, o que o torna uma ferramenta cada vez mais utilizada na prática clínica. O objectivo deste trabalho é apresentar a nossa experiência inicial com o ASL, salientando os aspectos técnicos, as principais solicitações clínicas, os resultados obtidos e as dificuldades experimentadas. Métodos: Foi efectuada uma revisão dos exames realizados durante um período de oito meses, usando uma técnica de ASL pulsado, num aparelho de 3T. A avaliação dos mapas de perfusão foi realizada de modo qualitativo. Resultados: As principais indicações clínicas para a realização de ASL foram epilepsia, doenças neuro-degenerativas e tumores intra-parenquimatosos. Embora o ASL não tenha sido, em nenhum dos casos, a principal ferramenta diagnóstica, contribuiu, por vezes, com dados fisiológicos importantes para o diagnóstico e para a orientação terapêutica. Salientam-se os casos de doentes com múltiplas crises epilépticas nos quais foi possível identificar focos de hiperperfusão pós-ictal (cujos resultados foram concordantes com o SPECT). Destacam-se ainda casos de doenças neuro-degenerativas nos quais o ASL identificou áreas de hipoperfusão típicas das respectivas entidades nosológicas. As principais dificuldades estiveram relacionadas com o carácter qualitativo da avaliação e com a valorização clínica dos achados. Conclusão: O estudo da perfusão cerebral por ASL tem um potencial diagnóstico importante. Com este trabalho mostramos que, com uma aquisição rápida e pós-processamento simples, pode facilmente integrar os estudos de RM de rotina. Abstract Arterial spin labelling (ASL) is a MR perfusion technique that uses protons from water molecules of the arterial blood as an endogenous tracer. It is fast, non-invasive and does not require gadolinium administration. Due to the increasing robustness of the results, it is becoming an important clinical tool. In this article we present our initial experience with ASL, highlighting some technical aspects, the main clinical applications, some achieved results and most important difficulties. Methods: Review of the examinations performed during eight months, using a pulsating ASL technique in a 3T machine. Perfusion maps were evaluated qualitatively. Results: The most frequent clinical applications were epilepsy, neurodegenerative disorders and tumours. Although perfusion data from ASL had never been crucial for diagnosis, it still provided substantial information. We highlight two epileptic patients who had had recent seizures, in which ASL depicted distinct post-ictal hyperperfusion areas (with the results being confirmed by SPECT studies). The impact was also remarkable in patients with neurodegenerative disorders in which ASL depicted hypoperfusion areas, typical of each nosological entity. The main difficulties were related to the lack of quantitative evaluation and to the clinical interpretation of the results obtained. Conclusion: ASL perfusion studies have a great potential in several clinical conditions. In this article we show that, with a fast acquisition and easy post-processing, it can integrate routine MRI examinations

Collapse prediction and creep effects

The recent collapse of famous historical constructions attributed mainly to the time-dependent behaviour of masonry has driven the attention of the technical community over this issue. Numerical analyses in which units and mortar are individually represented have proven to be of great interest to understand the phenomena at the level of the masonry constituents. Nevertheless, before analysing the influence of long-term effects, it is important that numerical models are able to adequately reproduce the behaviour under short-term compression as it provides a solid basis to correctly capture the response under sustained stresses. Reproduction of short-term behaviour remains, however, unresolved in literature. A contribution is given in the present paper by considering a standard continuum model and a discrete particle model to represent units and mortar. The particle model has showed clear advantages. In addition, the results of an experimental investigation on the creep behaviour of regular ancient masonry including both short-term and long-term creep tests are provided together with a careful discussion of the results

Masonry compression : a numerical investigation at the meso-level

The analysis of masonry assemblages under compression using detailed modelling strategies in which units and mortar are modelled separately is a challenging task. Sophisticated standard non-linear continuum models, based on plasticity and cracking, are widely available to represent the masonry components but such models overestimate the experimental strength of masonry prisms under compression. Alternative modelling approaches are therefore needed. This paper focuses on the discussion and detailed analysis of a particle model consisting in a phenomenological discontinuum approach to represent the micro-structure of units and mortar. The micro-structure attributed to the masonry components is composed by linear elastic particles of polygonal shape separated by non-linear interface elements. All the inelastic phenomena occur in the interfaces and the process of fracturing consists of progressive bond-breakage. Clear advantages have been shown by the particle model, when compared to standard continuum models.Portuguese Foundation for Science and Technology - SFRH/BD/5002/2001

Validation of analytical and continuum numerical methods for estimating the compressive strength of masonry

The advances in computational mechanics witnessed in the last decades have made available a large variety of numerical tools. Sophisticated non-linear models are now standard in several finite element based programs. This paper addresses the ability of continuum numerical methods, based on plasticity and cracking, as well as on analytical methods to provide reliable estimations of masonry compressive strength. In addition, a discussion on the load transfer between masonry components is presented and special attention is given to the numerical failure patterns. The results found overestimate the experimental strength and peak strain. Alternative modelling approaches that represent the micro-structure of masonry components are therefore needed

Masonry micro-modelling adopting a discontinuous framework

Several continuous and discontinuous micro-modelling approaches for masonry assemblages are currently under investigation by the authors. The aim is to find a model that provides a suitable description of the material behaviour under compression. Firstly, the behaviour under short-term loading is being considered and, in a later stage, also long-term loading will be addressed. The present paper illustrates the recent advances in the research, focused on the assessment and application of a proposed discontinuous model to the simulation of uniaxial compression tests of masonry prisms. In this model, a fictitious micro-structure composed by linear elastic particles separated by non-linear interfaces is adopted to model units and mortar. The main results obtained and their critical discussion are given in the paper

Testing and modelling of masonry creep and damage in uniaxial compression

The problems related to the analysis of ancient constructions are gigantic due to the difficulties in characterizing the geometry, the materials, the sequence of construction, the existing damage and the building processes.A difficult aspect in the repair and strengthening of existing structures is the long term loading of masonry in compression. Safety assessment has been greatly influenced by the collapse of monumental buildings in the last decade, where creep behaviour and creep-fatigue interaction proved to be of relevance for massive masonry walls. Experimental tests on masonry creep have been recently carried out, together with numerical implementations. Both testing and numerical modelling of multi-leaf masonry walls need still more research.Experimental testing on the creep of regular ancient masonry together with numerical modelling is currently under investigation and is briefly addressed in the paper. In addition, a discussion of the load transfer between masonry components is given. This represents a contribution for understanding creep behaviour and load transfer mechanisms in multi-leaf walls.- (undefined