180 resultados para Booster
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The current study examined the effects of a 15-minute daily physical activity break on the stress levels of white collar employees. An innovative group physical activity program, the Booster Break, was implemented in two worksites, both located in a large metropolitan area. One hundred sixteen participants were randomly assigned to one of three conditions; 43 participants were assigned to the Booster Break condition, 40 participants were assigned to an individual, computer-based physical activity condition, and 32 were assigned to a no-physical activity control condition. Self-report and objective measures were taken at baseline and after the completion of the intervention. There were no significant differences among conditions in perceived stress or blood pressure after the intervention. However, the data showed trends in the direction predicted with a decrease in perceived stress among Booster Break (change in perceived stress = -0.1) and computer prompt participants (change in perceived stress = -0.2) and an increase in perceived stress among the control group (change in perceived stress = 0.2). More research is recommended to fully understand the effects of worksite physical activity on stress.^
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La gestión de los residuos radiactivos de vida larga producidos en los reactores nucleares constituye uno de los principales desafíos de la tecnología nuclear en la actualidad. Una posible opción para su gestión es la transmutación de los nucleidos de vida larga en otros de vida más corta. Los sistemas subcríticos guiados por acelerador (ADS por sus siglas en inglés) son una de las tecnologías en desarrollo para logar este objetivo. Un ADS consiste en un reactor nuclear subcrítico mantenido en un estado estacionario mediante una fuente externa de neutrones guiada por un acelerador de partículas. El interés de estos sistemas radica en su capacidad para ser cargados con combustibles que tengan contenidos de actínidos minoritarios mayores que los reactores críticos convencionales, y de esta manera, incrementar las tasas de trasmutación de estos elementos, que son los principales responsables de la radiotoxicidad a largo plazo de los residuos nucleares. Uno de los puntos clave que han sido identificados para la operación de un ADS a escala industrial es la necesidad de monitorizar continuamente la reactividad del sistema subcrítico durante la operación. Por esta razón, desde los años 1990 se han realizado varios experimentos en conjuntos subcríticos de potencia cero (MUSE, RACE, KUCA, Yalina, GUINEVERE/FREYA) con el fin de validar experimentalmente estas técnicas. En este contexto, la presente tesis se ocupa de la validación de técnicas de monitorización de la reactividad en el conjunto subcrítico Yalina-Booster. Este conjunto pertenece al Joint Institute for Power and Nuclear Research (JIPNR-Sosny) de la Academia Nacional de Ciencias de Bielorrusia. Dentro del proyecto EUROTRANS del 6º Programa Marco de la UE, en el año 2008 se ha realizado una serie de experimentos en esta instalación concernientes a la monitorización de la reactividad bajo la dirección del CIEMAT. Se han realizado dos tipos de experimentos: experimentos con una fuente de neutrones pulsada (PNS) y experimentos con una fuente continua con interrupciones cortas (beam trips). En el caso de los primeros, experimentos con fuente pulsada, existen dos técnicas fundamentales para medir la reactividad, conocidas como la técnica del ratio bajo las áreas de los neutrones inmediatos y retardados (o técnica de Sjöstrand) y la técnica de la constante de decaimiento de los neutrones inmediatos. Sin embargo, varios experimentos han mostrado la necesidad de aplicar técnicas de corrección para tener en cuenta los efectos espaciales y energéticos presentes en un sistema real y obtener valores precisos de la reactividad. En esta tesis, se han investigado estas correcciones mediante simulaciones del sistema con el código de Montecarlo MCNPX. Esta investigación ha servido también para proponer una versión generalizada de estas técnicas donde se buscan relaciones entre la reactividad el sistema y las cantidades medidas a través de simulaciones de Monte Carlo. El segundo tipo de experimentos, experimentos con una fuente continua e interrupciones del haz, es más probable que sea empleado en un ADS industrial. La versión generalizada de las técnicas desarrolladas para los experimentos con fuente pulsada también ha sido aplicada a los resultados de estos experimentos. Además, el trabajo presentado en esta tesis es la primera vez, en mi conocimiento, en que la reactividad de un sistema subcrítico se monitoriza durante la operación con tres técnicas simultáneas: la técnica de la relación entre la corriente y el flujo (current-to-flux), la técnica de desconexión rápida de la fuente (source-jerk) y la técnica del decaimiento de los neutrones inmediatos. Los casos analizados incluyen la variación rápida de la reactividad del sistema (inserción y extracción de las barras de control) y la variación rápida de la fuente de neutrones (interrupción larga del haz y posterior recuperación). ABSTRACT The management of long-lived radioactive wastes produced by nuclear reactors constitutes one of the main challenges of nuclear technology nowadays. A possible option for its management consists in the transmutation of long lived nuclides into shorter lived ones. Accelerator Driven Subcritical Systems (ADS) are one of the technologies in development to achieve this goal. An ADS consists in a subcritical nuclear reactor maintained in a steady state by an external neutron source driven by a particle accelerator. The interest of these systems lays on its capacity to be loaded with fuels having larger contents of minor actinides than conventional critical reactors, and in this way, increasing the transmutation rates of these elements, that are the main responsible of the long-term radiotoxicity of nuclear waste. One of the key points that have been identified for the operation of an industrial-scale ADS is the need of continuously monitoring the reactivity of the subcritical system during operation. For this reason, since the 1990s a number of experiments have been conducted in zero-power subcritical assemblies (MUSE, RACE, KUCA, Yalina, GUINEVERE/FREYA) in order to experimentally validate these techniques. In this context, the present thesis is concerned with the validation of reactivity monitoring techniques at the Yalina-Booster subcritical assembly. This assembly belongs to the Joint Institute for Power and Nuclear Research (JIPNR-Sosny) of the National Academy of Sciences of Belarus. Experiments concerning reactivity monitoring have been performed in this facility under the EUROTRANS project of the 6th EU Framework Program in year 2008 under the direction of CIEMAT. Two types of experiments have been carried out: experiments with a pulsed neutron source (PNS) and experiments with a continuous source with short interruptions (beam trips). For the case of the first ones, PNS experiments, two fundamental techniques exist to measure the reactivity, known as the prompt-to-delayed neutron area-ratio technique (or Sjöstrand technique) and the prompt neutron decay constant technique. However, previous experiments have shown the need to apply correction techniques to take into account the spatial and energy effects present in a real system and thus obtain accurate values for the reactivity. In this thesis, these corrections have been investigated through simulations of the system with the Monte Carlo code MCNPX. This research has also served to propose a generalized version of these techniques where relationships between the reactivity of the system and the measured quantities are obtained through Monte Carlo simulations. The second type of experiments, with a continuous source with beam trips, is more likely to be employed in an industrial ADS. The generalized version of the techniques developed for the PNS experiments has also been applied to the result of these experiments. Furthermore, the work presented in this thesis is the first time, to my knowledge, that the reactivity of a subcritical system has been monitored during operation simultaneously with three different techniques: the current-to-flux, the source-jerk and the prompt neutron decay techniques. The cases analyzed include the fast variation of the system reactivity (insertion and extraction of a control rod) and the fast variation of the neutron source (long beam interruption and subsequent recovery).
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National Highway Traffic Safety Administration, Washington, D.C.
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Mode of access: Internet.
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Mode of access: Internet.
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Mode of access: Internet.
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Mode of access: Internet.
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In this work we explore optimising parameters of a physical circuit model relative to input/output measurements, using the Dallas Rangemaster Treble Booster as a case study. A hybrid metaheuristic/gradient descent algorithm is implemented, where the initial parameter sets for the optimisation are informed by nominal values from schematics and datasheets. Sensitivity analysis is used to screen parameters, which informs a study of the optimisation algorithm against model complexity by fixing parameters. The results of the optimisation show a significant increase in the accuracy of model behaviour, but also highlight several key issues regarding the recovery of parameters.
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This is a set of resources aimed at promoting the development of the skills required to successfully identify and generate organic mechanisms in order to demonstrate a good understanding of the underlying chemical principles. Students complete a task independently, and then mark their own work as they watch talking mark scheme videos where an expert explains how to get to the correct answers. Our research has shown that engagement with these resources is perceived to be highly beneficial by students, and leads to an increase in their confidence to tackle mechanistic problems. If you are a non-UK (or non-A-level) teacher, the terms AS and A2 may be meaningless to you, but the resources should still be useful for anyone studying organic reaction mechanisms. The worksheets are available in Word format, and you should feel free to edit these to meet the needs of your students and the course you are teaching. You can download the files individually by selecting them on the left and clicking download. Please watch the short briefing video on You Tube and read the teachers' notes carefully. Contact me on d.read@soton.ac.uk if you have and questions or comments. Additionally, I would like to thank Henry Pearson for suggesting the format of the alternative self-assessment proformas which you may choose to use with your students.
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Pipeline systems play a key role in the petroleum business. These operational systems provide connection between ports and/or oil fields and refineries (upstream), as well as between these and consumer markets (downstream). The purpose of this work is to propose a novel MINLP formulation based on a continuous time representation for the scheduling of multiproduct pipeline systems that must supply multiple consumer markets. Moreover, it also considers that the pipeline operates intermittently and that the pumping costs depend on the booster stations yield rates, which in turn may generate different flow rates. The proposed continuous time representation is compared with a previously developed discrete time representation [Rejowski, R., Jr., & Pinto, J. M. (2004). Efficient MILP formulations and valid cuts for multiproduct pipeline scheduling. Computers and Chemical Engineering, 28, 1511] in terms of solution quality and computational performance. The influence of the number of time intervals that represents the transfer operation is studied and several configurations for the booster stations are tested. Finally, the proposed formulation is applied to a larger case, in which several booster configurations with different numbers of stages are tested. (C) 2007 Elsevier Ltd. All rights reserved.
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This research aimed at determining spectrophotometrically (290 to 320nm) the in vitro Sun Protection Factor (SPF) of sunscreens developed with rutin (R) or succinate rutin (SR), in association or not with UVB filter. Formulations were developed based on phosphate-base O/W emulsions, with (B) or not (A) the presence of polyacrylamide/C13-14 isoparaffin/laureth-7 (PIL), in accordance with the following associations: (a) control; (b) 1.0 % SR; (c) 0.1 % R; (d) 7.5 % ethylhexyl methoxycinnamate (EHMC); (e) 7.5 % EHMC + 0.1 % RS; (0 7.5 % EHMC + 0.1 % R. It was verified a statistical significative elevation of the SPF from 13.93 +/- 0.02 (Af) to 16.63 +/- 0.27 (Bf) and also in relation to 15.53 +/- 0.14 (Bd). According to the results, the EHMC had distinct behavior depending on the presence of bioactive substance and viscosity agent, thus, rutin obtained better profile as a SPF booster in these experimental conditions with the presence of PIL.
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Rutin, one of the major flavonoids found in an assortment of plants, was reported to act as a sun protection factor booster with high anti-UVA defense, antioxidant, antiaging, and anticellulite, by improvement of the cutaneous microcirculation. This research work aimed at evaluating the rutin in vitro release from semisolid systems, in vertical diffusion cells, containing urea, isopropanol and propylene glycol, associated or not, according to the factorial design with two levels with center point. Urea (alone and in association with isopropanol and propylene glycol) and isopropanol (alone and in association with propylene glycol) influenced significant and negatively rutin liberation in diverse parameters: flux (g/cm2.h); apparent permeability coefficient (cm/h); rutin amount released (g/cm2); and liberation enhancement factor. In accordance with the results, the presence of propylene glycol 5.0% (wt/wt) presented statistically favorable to promote rutin release from this semisolid system with flux = 105.12 8.59 g/cm2.h; apparent permeability coefficient = 7.01 0.572 cm/h; rutin amount released = 648.80 53.01 g/cm2; and liberation enhancement factor = 1.21 0.07.