Development of the vertebrate central nervous system: formation of the neural tube

The developmental process of neurulation involves a series of coordinated morphological events, which result in conversion of the flat neural plate into the neural tube, the primordium of the entire central nervous system (CNS). Failure of neurulation results in neural tube defects (NTDs), severe abnormalities of the CNS, which are among the commonest of congenital malformations in humans. In order to gain insight into the embryological basis of NTDs, such as spina bifida and anencephaly, it is necessary to understand the morphogenetic processes and molecular mechanisms underlying neural tube closure. The mouse is the most extensively studied mammalian experimental model for studies of neurulation, while considerable insight into underlying developmental mechanisms has also arisen from studies in other model systems, particularly birds and amphibians. We describe the process of neural tube formation, discuss the cellular mechanisms involved and highlight recent findings that provide links between molecular signaling pathways and morphogenetic tissue movements. Copyright © 2009 John Wiley & Sons, Ltd.     

The Role of Pressure Drop and Flow Redistribution on Modeling Mercury Control Using Sorbent Injection in Baghouse Filters

Abstract

A mathematical model based on simple cake filtration theory was coupled to a reviously developed two-stage mathematical model for mercury (Hg) removal using powdered activated carbon injection upstream of a bag-house filter. Values of the average permeability of the filter cake and the filter resistance extracted from the model were 4.4× 10^?13 m² and 2.5 ×10^?4 m^?1, respectively. The flow is redistributed during partial cleaning of the filter, with flows higher across the newly cleaned filter section. The calculated average Hg removal efficiency from the baghouse is lower because of the high mass flux of Hg exiting the filter in the newly cleaned section. The model shows that calculated average Hg removal is affected by permeability, filter resistance, fraction of the baghouse cleaned, and cleaning interval.     

ECONOMIC CONSIDERATIONS FOR SOLAR AND RENEWABLE ENERGY IN DEVELOPING COUNTRIES

High costs of all commercial (especially imported) fuels have had especially severe impacts on the developing nations and, within these, on the most disadvantaged regions and socio-economic groups. Improving the security of supply while stabilizing prices has become a major energy-economic need. For the less developed nations this particularly calls for greater indigenous energy production and improved regional supply without massive capital commitments. Solar and renewable sources have a critical part to play in this. Certain of these appear promising for immediate development. For the longer term their potentials are far greater — but economic acceptance requires changed evaluation methods. Les pays en développement, et parmi eux les régions et groupes socioéconomiques les plus défavorisés, ont fortement ressenti les incidences particulièrement graves de la hausse des prix des combustibles commerciaux (et plus spécialement, des combustibles importés). S'assurer plus attentivement de l'approvisionnement tout en contenant le niveau des prix est devenu un impératif de leur politique énergético-économique. En ce qui concerne ces pays, cet effort requiert en particulier une production plus abondante d'énergie locale et une amélioration des approvisionnements régionaux sans engagements de capitaux démesurés. Les sources d'énergie solaire et d'énergie de remplacement ont un rôle significatif à jouer dans ce domaine. Quelques-unes d'entre elles destinées à certaines utilisations semblent pouvoir être mises en valeur dans l'immédiat. A longue échéance, leur potentiel est encore d'une plus grande portée. Cependant, pour les rendre rentables, leur méthodes d'évaluation serait à repenser. El alto costo de los combustibles (especialmente los importados) ha tenido un impacto especialmente severo en los paises en desarrollo, particularmente en las regiones y los grupos socioeconómicos que se encuentran en situación desventajosa. Mejorar la seguridad del suministro procurando al mismo tiempo mantener los precios estables se ha convertido en una necesidad importante dentro de la economía de la energía. Para los paises menos desarrollados esto significa especialmente desarrollar recursos energéticos propios y mejorar el suministro regional sin comprometer capital en forma masiva. Los recursos renovables (energiá solar) tienen un rol de importancia crítica y algunos de ellos parecen promisorios para su desarrollo immediato. Para el largo plazo el potencial de estos recursos es mucho mas grande aún — pero su aceptación económica requiere todos de evaluación nuevos.     

Comparative analysis of inorganic elements in the muscle and liver of some fish species

Four fish species were collected: brown trout, grouper, spotted tail bass, and black crappie. Fish samples were thawed and dissected. The pieces of edible muscle and liver tissues were digested in a reagent-grade nitric acid, in a constant temperature shaking-water bath at 58°C. Thirteen inorganic elements were determined by flame atomic absorption.The significant findings of this report are that inorganic elements, mercury, iron, copper, zinc, chromium, and nickel with the exception of magnesium show elevated levels in the livers than in the muscles of all the four fish species. It seems magnesium concentration levels were consistantly higher in the muscles than in the livers of all four fish species. It is found that calculations of muscle-liver ratios indicate that ratios in the range of 0.5 are preliminary indicative of environmental static conditions, whereas ratios in the range of more than one are indicative of environmental improvement.