994 resultados para Nuclear physics


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Almost 450 nuclear power plants are currently operating throughout the world and supplying about 17% of the world’s electricity. These plants perform safely, reliably, and have no free-release of byproducts to the environment. Given the current rate of growth in electricity demand and the ever growing concerns for the environment, the US consumer will favor energy sources that can satisfy the need for electricity and other energy-intensive products (1) on a sustainable basis with minimal environmental impact, (2) with enhanced reliability and safety and (3) competitive economics. Given that advances are made to fully apply the potential benefits of nuclear energy systems, the next generation of nuclear systems can provide a vital part of a long-term, diversified energy supply. The Department of Energy has begun research on such a new generation of nuclear energy systems that can be made available to the market by 2030 or earlier, and that can offer significant advances toward these challenging goals [1]. These future nuclear power systems will require advances in materials, reactor physics as well as heat transfer to realize their full potential. In this paper, a summary of these advanced nuclear power systems is presented along with a short synopsis of the important heat transfer issues. Given the nature of research and the dynamics of these conceptual designs, key aspects of the physics will be provided, with details left for the presentation.

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Este volumen se ha desarrollado para cubrir la nueva especificación del Nivel Avanzado (AS) de Ciencia del año dos mil ocho y ha sido respaldado por el OCR. Los objetivos están claramente definidos, para que los estudiantes sepan exactamente qué es lo que necesitan aprender. Las preguntas de auto-evaluación y el modelo de examen al final de cada capítulo, ofrecen oportunidades para el estudio independiente. Viene con un CD-ROM que proporciona información adicional y enlaces a sitios web libres, llenos de actividades de aprendizaje electrónico para el avance de los alumnos que lo necesiten y fomentar así la ampliación del conocimiento . Física 2 permite a los alumnos aprender sobre:impulso; impulso y las leyes de Newton; movimiento circular; campos gravitacionales; oscilaciones; física térmica; gases ideales; campos eléctricos; campos magnéticos; inducción electromagnética; condensadores; estructura atómica; física nuclear; radiactividad; radiografías; métodos de diagnóstico en medicina; uso de la ecografía en la medicina; la naturaleza del universo; la evolución del universo. Tiene un glosario de palabras clave, respuestas a la autoevaluación e índice.

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Manual diseñado para ayudar al alumno a obtener el máximo provecho y garantizar que se cumplan los objetivos necesarios de As y A Level de Física. Teoría relevante es descrita en cada capítulo y se le acompaña ejemplos de trabajo. Al final de cada capítulo hay una serie de ejercicios de examen para los cuales hay respuestas y consejos. Los temas del libro son: la forma de abordar un cálculo, matemáticas esenciales (fracciones, porcentaje, ecuaciones, exponentes, logaritmos), unidades y dimensiones, mecánica (velocidad, aceleración y fuerza, trabajo y energía), oscilaciones y ondas, instrumentos ópticos (microscopio, telescopio), electricidad y magnetismo, física atómica y nuclear, astronomía (distancias de las estrellas, los planetas y sus órbitas).

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Esta guía contiene una revisión de todos los temas de física para el Programa del Diploma de Bachillerato Internacional (IB Diploma). Los temas del libro son: medidas experimentales y la evaluación interna, cinemática, fuerzas y movimiento, proyectiles, el movimiento armónico simple, ondas, el fenómeno de la onda, física térmica, termodinámica, corrientes eléctricas, el campo y el potencial, inducción electromagnética, física atómica y nuclear, fuentes de energía, radiación solar y el efecto greenhouse, el cambio climático, tecnologías para reducir el cambio climático, energías renovables, el poder nuclear, tecnología digital, astrofísica, comunicaciones, ondas electromagnéticas.

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Este libro ha sido escrito específicamente para el Cambridge IGCSE en la asignatura de enseñanza secundaria de física. Los temas del libro son: midiendo la longitud y el volumen, calculando la aceleración, masa, peso y gravedad, el momento de una fuerza, la ley de Hooke, conservación de la energía, la energía que nosotros usamos, las fuerzas y la teoría cinética, la temperatura, radiación, física de las ondas, electricidad y magnetismo, los campos magnéticos, la corriente en circuitos eléctricos, las fuerzas electromagnéticas, el átomo nuclear, radioactividad.

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An analytic method to evaluate nuclear contributions to electrical properties of polyatomic molecules is presented. Such contributions control changes induced by an electric field on equilibrium geometry (nuclear relaxation contribution) and vibrational motion (vibrational contribution) of a molecular system. Expressions to compute the nuclear contributions have been derived from a power series expansion of the potential energy. These contributions to the electrical properties are given in terms of energy derivatives with respect to normal coordinates, electric field intensity or both. Only one calculation of such derivatives at the field-free equilibrium geometry is required. To show the useful efficiency of the analytical evaluation of electrical properties (the so-called AEEP method), results for calculations on water and pyridine at the SCF/TZ2P and the MP2/TZ2P levels of theory are reported. The results obtained are compared with previous theoretical calculations and with experimental values

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Electrical property derivative expressions are presented for the nuclear relaxation contribution to static and dynamic (infinite frequency approximation) nonlinear optical properties. For CF4 and SF6, as opposed to HF and CH4, a term that is quadratic in the vibrational anharmonicity (and not previously evaluated for any molecule) makes an important contribution to the static second vibrational hyperpolarizability of CF4 and SF6. A comparison between calculated and experimental values for the difference between the (anisotropic) Kerr effect and electric field induced second-harmonic generation shows that, at the Hartree-Fock level, the nuclear relaxation/infinite frequency approximation gives the correct trend (in the series CH4, CF4, SF6) but is of the order of 50% too small

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The performance of the SAOP potential for the calculation of NMR chemical shifts was evaluated. SAOP results show considerable improvement with respect to previous potentials, like VWN or BP86, at least for the carbon, nitrogen, oxygen, and fluorine chemical shifts. Furthermore, a few NMR calculations carried out on third period atoms (S, P, and Cl) improved when using the SAOP potential

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A set of connections among several nuclear and electronic indexes of reactivity in the framework of the conceptual Density Functional Theory by using an expansion ofthe energy functional in terms of the total number of electrons and the normal coordinates within a canonical ensemble was derived. The relations obtained provided explicit links between important quantities related to the chemical reactivity of a system. This paper particularly demonstrates that the derivative of the electronic energy with respect to the external potential of a system in its equilibrium geometry was equal to the negative of the nuclear repulsion derivative with respect to the external potential

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The role of the tensor terms in the Skyrme interaction is studied for their effect in dynamic calculations where non-zero contributions to the mean-field may arise, even when the starting nucleus, or nuclei are even-even and have no active time-odd potentials in the ground state. We study collisions in the test-bed 16O-16O system, and give a qualitative analysis of the behaviour of the time-odd tensor-kinetic density, which only appears in the mean field Hamiltonian in the presence of the tensor force. We find an axial excitation of this density is induced by a collision.

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In this paper, we report results of a quantitative analysis of the effects of neutrons on DNA, and, specifically, the production of simple and double breaks of plasmid DNA in aqueous solutions with different concentrations of free-radical scavengers. The radiation damage to DNA was evaluated by electrophoresis through agarose gels. The neutron and gamma doses were measured separately with thermoluminescent detectors. In this work, we have also demonstrated usefulness of a new system for positioning and removing samples in channel BH#3 of the IEA-R1 reactor at the Instituto de Pesquisas Energeticas e Nucleares (Brazil) without necessity of interrupting the reactor operation. (C) 2010 Elsevier Ltd. All rights reserved.

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This paper describes a new mechanical samples positioning system that allows the safe placement and removal of biological samples for prolonged irradiation, in a nuclear reactor during full-power continuous operation. Also presented herein the materials of construction and operating principles. Additionally, this sample positioning system is compared with an existing pneumatic and automated transfer system, already available at the research reactors. The system consists of a mechanical arm with a claw, which can deliver the samples for irradiations without reactor shutdown. It was installed in the lEA-R1 research reactor at Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, Brazil, and for the past 5 years, the system has successfully operated and allowed the conducting of important experiments. As a result of its introduction, the facility has been in a position to positively respond to the increased demand in studies of biology, medicine, physics, engineering, detector/dosimeter calibrations, etc. It is one example of the appropriated technologies that save energy and resources. (C) 2010 Elsevier Ltd. All rights reserved.

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Using data taken by SELEX during the 1996-1997 fixed target run at Fermilab, we study the production of charmed hadrons on copper and carbon targets with Sigma(-), p, pi(-), and pi(+) beams. Parametrizing the dependence of the inclusive production cross section on the atomic number A as A(alpha), we determine alpha for D(+), D(0), D(s)(+), D(+)(2010), Lambda(+)(c), and their respective anti-particles, as a function of their transverse momentum p(t) and scaled longitudinal momentum x(F). Within our statistics there is no dependence of alpha on x(F) for any charm species for the interval 0.1 < x(F) < 1.0. The average value of alpha for charm production by pion beams is alpha(meson) = 0.850 +/- 0.028. This is somewhat larger than the corresponding average alpha(baryon) = 0.755 +/- 0.016 for charm production by baryon beams (Sigma(-), p).