Small high-temperature nuclear reactors for space power

Criticality calculations for small, cylindrical, lithium cooled reactors for space power system

A Refined Neuronal Population Measure of Visual Attention

Neurophysiological studies of cognitive mechanisms such as visual attention typically ignore trial-by-trial variability and instead report mean differences averaged across many trials. Advances in electrophysiology allow for the simultaneous recording of small populations of neurons, which may obviate the need for averaging activity over trials. We recently introduced a method called the attention axis that uses multi-electrode recordings to provide estimates of attentional state of behaving monkeys on individual trials. Here, we refine this method to eliminate problems that can cause bias in estimates of attentional state in certain scenarios. We demonstrate the sources of these problems using simulations and propose an amendment to the previous formulation that provides superior performance in trial-by-trial assessments of attentional state

Molecular and mass spectroscopic analysis of isotopically labeled organic residues

Experimental studies aimed at understanding the evolution of complex organic molecules on interstellar grains were performed. The photolysis of frozen gas mixtures of various compositions containing H2O, CO, NH3, and CH4 was studied. These species were chosen because of their astrophysical importance as deducted from observational as well as theoretical studies of ice mantles on interstellar grains. These ultraviolet photolyzed ices were warmed up in order to produce refractory organic molecules like the ones formed in molecular clouds when the icy mantles are being irradiated and warmed up either by a nearby stellar source or impulsive heating. The laboratory studies give estimates of the efficiency of production of such organic material under interstellar conditions. It is shown that the gradual carbonization of organic mantles in the diffuse cloud phase leads to higher and higher visual absorptivity - yellow residues become brown in the laboratory. The obtained results can be applied to explaining the organic components of comets and their relevance to the origin of life

The Supreme Court as the Grand Mediator in Social Regulation of the Media - De Gustibus Non Disputandum Est: Or Are They

This article presents a study of administrative and statutory schemes designed to regulate various aspects of the media in considering broad questions of indecency, obscenity, and societal and parental controls over content in various forms of media broadcasting. The article then provides an important historical back-drop by referencing Burstyn v. Wilson (a 1950s case involving an alleged secular sacrilege ) and Pacifica Foundation (the George Carlin Filthy Words monologue case). It then turns to a discussion of the litigation and controversy spurred by passage of the Communications Decency Act of 1996 and the Child Online Protection Act of 1998 as the focus of congressional attention turned to regulating the Internet. In this context, the article discusses Reno v. ACLU and American Library Association v. United States, two cases which provided direct challenges to Congressional regulatory responses. This article concludes by noting important international implications of the attempts to place restrictions on the Internet, and offers several tentative conclusions by bringing to the forefront the debate on the use of filtering technology designed to provide controls and supervision over this new media

Field theory of the inverse cascade in two-dimensional turbulence

A two-dimensional fluid, stirred at high wavenumbers and damped by both viscosity and linear friction, is modeled by a statistical field theory. The fluid's long-distance behavior is studied using renormalization-group (RG) methods, as begun by Forster, Nelson, and Stephen [Phys. Rev. A 16, 732 (1977)]. With friction, which dissipates energy at low wavenumbers, one expects a stationary inverse energy cascade for strong enough stirring. While such developed turbulence is beyond the quantitative reach of perturbation theory, a combination of exact and perturbative results suggests a coherent picture of the inverse cascade. The zero-friction fluctuation-dissipation theorem (FDT) is derived from a generalized time-reversal symmetry and implies zero anomalous dimension for the velocity even when friction is present. Thus the Kolmogorov scaling of the inverse cascade cannot be explained by any RG fixed point. The beta function for the dimensionless coupling ghat is computed through two loops; the ghat^3 term is positive, as already known, but the ghat^5 term is negative. An ideal cascade requires a linear beta function for large ghat, consistent with a Pad\'e approximant to the Borel transform. The conjecture that the Kolmogorov spectrum arises from an RG flow through large ghat is compatible with other results, but the accurate k^{-5/3} scaling is not explained and the Kolmogorov constant is not estimated. The lack of scale invariance should produce intermittency in high-order structure functions, as observed in some but not all numerical simulations of the inverse cascade. When analogous RG methods are applied to the one-dimensional Burgers equation using an FDT-preserving dimensional continuation, equipartition is obtained instead of a cascade--in agreement with simulations.Comment: 16 pages, 3 figures, REVTeX 4. Material added on energy flux, intermittency, and comparison with Burgers equatio

Comparative environmental assessment of two materials suited to central tower CSP technology

Compatibility of containment materials with molten salt thermal storage media is a significant technical challenge for Concentrating Solar Power plants. Metal alloys in contact with molten salt must have a specific behavior, mechanical properties and resistance to degradation processes that allow them to operate at temperatures above 500 °C, being both respectful to the environment. Firstly, this study presents two types of specific materials to operate at raised temperatures in Concentrating Solar Power plants, particularly the central tower technology. The materials are AISI 347H stainless steel and the Ni-based alloy HRSA INCONEL 617. Then, a Life Cycle Assessment shows the influence and contribution to different impact categories from the elements that compose both metals, demonstrating that materials that provide better mechanical properties could have environmental shortcomings. This paper aims to contribute to an improved understanding of the environmental implications of these materials and which is the best choice in terms of sustainability. The results showed better environmental behavior in the AISI 347H case against INCONEL 617.Publicad

Life Cycle Assessment of heat transfer fluids in parabolic trough concentrating solar power technology

The majority of parabolic trough concentrating solar power plants consist of an indirect system where the heat transfer fluid (typically synthetic oil) exchanges energy with a secondary circuit which is connected to the power cycle. Synthetic oil has a technical limitation by the maximum operating temperature. This results in the search for new fluids. On the other hand, with the aim of having energy when there is no sun shining, it has increased the use of thermal storage. Thermal energy storage systems are composed of molten salts and presents higher operating temperatures than synthetic oil. Thus, direct systems, in which thermal storage and heat transfer fluid are unified and normally molten salts, emerge to improve the power cycle performance. To determine the future potential of direct systems, this paper evaluates the environmental damage of two types of molten salts and synthetic oil in order to decide whether the use of salts is better than synthetic oil, from an environmental point of view by using the Life Cycle Assessment (LCA) techniques. LCA results showed greater impacts in the syntheticoil case than the molten saltsPublicad

Influence of elemental composition in environmental impacts of steel

The environmental behavior of four steels was analyzed. In the operation phase of concentrating solar power plants, steels withstand high temperature because of its contact with molten salts. Hence, choosing the steel type for the molten salt tanks remains a great challenge. In the cold tank, carbon steel is usually used although an approach with low chromium content steel is being studied for these applications. Likewise, in high temperature applications, such as hot store tank, austenitic stainless steel is the most frequent choice. However, ferritic steel is being considered as a promising material in these applications. As many researchers studied the steel technical properties without considering their environmental damages, this work aimed to introduce the environmental aspects into the material choice by using the life cycle assessment technique. On one hand, the results showed the environmental adequacy of carbon steel against low chromium content steel. On the other hand, the results obtained in those steels suitable in high temperature application revealed significant environmental benefits from the ferritic steel instead of the austenitic steel

El pistachero II: Estudio fenológico y económico

10 páginas, tablas estadísticas y figuras.El pistachero es capaz de sobrevivir y dar frutos en situaciones adversas, intolerables para la mayor parte de los frutales. Sin embargo también tiene unos condicionamientos de medio bastantes específicos que limitan su posible área de cultivo, como son las necesidades en frío para cubrir adecuadamente su periodo de reposos invernal, la sincronía en la floración de machos y hembras para tener una buena polinización y sensibilidad a las heladas tardías de primavera. Con los resultados obtenidos en este trabajo y en el trabajo presentado en este VI Congreso de la SEAE “El pistachero I: Estudio de variedades en secano y en manejo ecológico”, se realiza un estudio de viabilidad económica. Se recomienda que a la hora de hacer una nueva plantación, se incluya en la misma diferentes variedades hembras y machos. Las variedades hembras con las que se han obtenido mejores resultados son: Avdat, Ashoury y Larnaka, y como polinizadores: C-especial, Askar, Nazar, Chico y Mateur. Las variedades recomendadas, tienen unas necesidades cercanas a las 1.000 horas-frío para el inicio de la actividad vegetativa y la floración es en la primera quincena de abril. En el estudio económico y considerando que sólo uno de cada tres años se obtiene producción, debido a problemas de heladas de primavera o por veceria, se pueden obtener una rentabilidad económica, a partir de los veinte años, superior a los 600 €, lo que le permite ser una buena alternativa para algunas zonas del secano españolPeer reviewe