Plasma loop and strapping field dynamics: reproducing solar eruptions in the laboratory

Coronal mass ejections (CMEs) are dramatic eruptions of large, plasma structures from the Sun. These eruptions are important because they can harm astronauts, damage electrical infrastructure, and cause auroras. A mysterious feature of these eruptions is that plasma-filled solar flux tubes first evolve slowly, but then suddenly erupt. One model, torus instability, predicts an explosive-like transition from slow expansion to fast acceleration, if the spatial decay of the ambient magnetic field exceeds a threshold.

We create arched, plasma filled, magnetic flux ropes similar to CMEs. Small, independently-powered auxiliary coils placed inside the vacuum chamber produce magnetic fields above the decay threshold that are strong enough to act on the plasma. When the strapping field is not too strong and not too weak, expansion force build up while the flux rope is in the strapping field region. When the flux rope moves to a critical height, the plasma accelerates quickly, corresponding to the observed slow-rise to fast-acceleration of most solar eruptions. This behavior is in agreement with the predictions of torus instability.

Historically, eruptions have been separated into gradual CMEs and impulsive CMEs, depending on the acceleration profile. Recent numerical studies question this separation. One study varies the strapping field profile to produce gradual eruptions and impulsive eruptions, while another study varies the temporal profile of the voltage applied to the flux tube footpoints to produce the two eruption types. Our experiment reproduced these different eruptions by changing the strapping field magnitude, and the temporal profile of the current trace. This suggests that the same physics underlies both types of CME and that the separation between impulsive and gradual classes of eruption is artificial.

Optimized condition for etching fused-silica phase gratings with inductively coupled plasma technology

Polymer deposition is a serious problem associated with the etching of fused silica by use of inductively coupled plasma (ICP) technology, and it usually prevents further etching. We report an optimized etching condition under which no polymer deposition will occur for etching fused silica with ICP technology. Under the optimized etching condition, surfaces of the fabricated fused silica gratings are smooth and clean. Etch rate of fused silica is relatively high, and it demonstrates a linear relation between etched depth and working time. Results of the diffraction of gratings fabricated under the optimized etching condition match theoretical results well. (c) 2005 Optical Society of America.

Fabrication of fused silica phase gratings with inductively coupled plasma technology

Inductively coupled plasma (ICP) technology is a new advanced version of dry-etching technology compared with the widely used method of reactive ion etching (RIE). Plasma processing of the ICP technology is complicated due to the mixed reactions among discharge physics, chemistry and surface chemistry. Extensive experiments have been done and microoptical elements have been fabricated successfully, which proved that the ICP technology is very effective in dry etching of microoptical elements. In this paper, we present the detailed fabrication of microoptical fused silica phase gratings with ICP technology. Optimized condition has been found to control the etching process of ICP technology and to improve the etching quality of microoptical elements greatly. With the optimized condition, we have fabricated lots of good gratings with different periods, depths, and duty cycles. The fabricated gratings are very useful in fields such as spectrometer, high-efficient filter in wavelength-division-multiplexing system, etc..

Experimental and theoretical studies of the electrothermal instability in a nonequilibrium plasma

Experimental and theoretical studies have been made of the electrothermal waves occurring in a nonequilibrium MHD plasma. These waves are caused by an instability that occurs when a plasma having a dependence of conductivity on current density is subjected to crossed electric and magnetic fields. Theoretically, these waves were studied by developing and solving the equations of a steady, one-dimensional nonuniformity in electron density. From these nonlinear equations, predictions of the maximum amplitude and of the half width of steady waves could be obtained. Experimentally, the waves were studied in a nonequilibrium discharge produced in a potassium-seeded argon plasma at 2000°K and 1 atm. pressure. The behavior of such a discharge with four different configurations of electrodes was determined from photographs, photomultiplier measurements, and voltage probes. These four configurations were chosen to produce steady waves, to check the stability of steady waves, and to observe the manifestation of the waves in a MHD generator or accelerator configuration.

Steady, one-dimensional waves were found to exist in a number of situations, and where they existed, their characteristics agreed with the predictions of the steady theory. Some extensions of this theory were necessary, however, to describe the transient phenomena occurring in the inlet region of a discharge transverse to the gas flow. It was also found that in a discharge away from the stabilizing effect of the electrodes, steady waves became unstable for large Hall parameters. Methods of prediction of the effective electrical conductivity and Hall parameter of a plasma with nonuniformities caused by the electrothermal waves were also studied. Using these methods and the values of amplitude predicted by the steady theory, it was found that the measured decrease in transverse conductivity of a MHD device, 50 per cent at a Hall parameter of 5, could be accounted for in terms of the electrothermal instability.

Thermodynamic and kinetic behavior of an argon plasma jet. Decomposition of nitric oxide between 1300 - 1750 degrees K in an argon plasma

In the first part of the study, an RF coupled, atmospheric pressure, laminar plasma jet of argon was investigated for thermodynamic equilibrium and some rate processes.

Improved values of transition probabilities for 17 lines of argon I were developed from known values for 7 lines. The effect of inhomogeneity of the source was pointed out.

The temperatures, T, and the electron densities, n_e , were determined spectroscopically from the population densities of the higher excited states assuming the Saha-Boltzmann relationship to be valid for these states. The axial velocities, v_z, were measured by tracing the paths of particles of boron nitride using a three-dimentional mapping technique. The above quantities varied in the following ranges: 10¹² ˂ n_e ˂ 10¹⁵ particles/cm³, 3500 ˂ T ˂ 11000 °K, and 200 ˂ v_z ˂ 1200 cm/sec.

The absence of excitation equilibrium for the lower excitation population including the ground state under certain conditions of T and n_e was established and the departure from equilibrium was examined quantitatively. The ground state was shown to be highly underpopulated for the decaying plasma.

Rates of recombination between electrons and ions were obtained by solving the steady-state equation of continuity for electrons. The observed rates were consistent with a dissociative-molecular ion mechanism with a steady-state assumption for the molecular ions.

In the second part of the study, decomposition of NO was studied in the plasma at lower temperatures. The mole fractions of NO denoted by x_NO were determined gas-chromatographically and varied between 0.0012 ˂ x_NO ˂ 0.0055. The temperatures were measured pyrometrically and varied between 1300 ˂ T ˂ 1750°K. The observed rates of decomposition were orders of magnitude greater than those obtained by the previous workers under purely thermal reaction conditions. The overall activation energy was about 9 kcal/g mol which was considerably lower than the value under thermal conditions. The effect of excess nitrogen was to reduce the rate of decomposition of NO and to increase the order of the reaction with respect to NO from 1.33 to 1.85. The observed rates were consistent with a chain mechanism in which atomic nitrogen and oxygen act as chain carriers. The increased rates of decomposition and the reduced activation energy in the presence of the plasma could be explained on the basis of the observed large amount of atomic nitrogen which was probably formed as the result of reactions between excited atoms and ions of argon and the molecular nitrogen.

Plasma inverse scattering theory

The object of this report is to calculate the electron density profile of plane stratified inhomogeneous plasmas. The electron density profile is obtained through a numerical solution of the inverse scattering algorithm.

The inverse scattering algorithm connects the time dependent reflected field resulting from a δ-function field incident normally on the plasma to the inhomogeneous plasma density.

Examples show that the method produces uniquely the electron density on or behind maxima of the plasma frequency.

It is shown that the δ-function incident field used in the inverse scattering algorithm can be replaced by a thin square pulse.

Relações sociais, atividade física de lazer e obesidade: evidências longitudinais

A influências das relações sociais na saúde vem sendo largamente investigada em diferentes contextos. No que concerne a influência das relações sociais na atividade física de lazer (AFL) e na obesidade, abordagens multidimensionais e longitudinais, são escassas. O primeiro artigo objetivou investigar o efeito de quatro dimensões do apoio social no engajamento, manutenção, tipo e tempo gasto na prática de AFL em adultos durante um período de dois anos de seguimento (1999-2001). Enquanto que o segundo artigo visou investigar o efeito de cinco indicadores das relações sociais sobre a obesidade e potenciais diferenças de sexo nesta associação, após nove anos de seguimento (1991-2000). Para o primeiro artigo, foram analisados dados longitudinais obtidos através de questionários autopreenchidos aplicados em 3.253 funcionários de uma universidade no Rio de Janeiro (Estudo Pró-Saúde). Enquanto que para o segundo artigo, dados longitudinais do Swedish Level of Living Survey (LNU) foram utilizados. Os resultados do primeiro artigo mostraram associações estatisticamente significativas (p<0,05) entre as dimensões de apoio social e AFL coletiva no grupo de engajamento. Além disso, a dimensão emocional/informação associou-se com o tempo em AFL (OR=2,0; IC95% 1,2-3,9). No grupo de manutenção, o apoio material associou-se com AFL coletiva (OR=1,8; IC95% 1,1-3,1) e a dimensão interação social positiva foi associado com o tempo gasto em AFL (OR=1,65; IC95% 1,1-2,7). Os resultados do segundo artigo mostraram que após o ajuste por fatores de confusão, a falta de apoio emocional (RR = 1,98; 95% IC 1,1-3,8) associou-se à incidência de obesidade entre os homens. Além disso, homens no nível mais baixo de IRS (índice de relações sociais) tiveram risco aumentado de desenvolver obesidade (RR = 2,22; 95% IC 1,1-4,4). Entre as mulheres o IRS não esteve significativamente associado com a obesidade. Contudo, um efeito protetor na obesidade para as mulheres que mudaram o estado civil de casada para nãocasada tenha sido encontrado (RR = 0,39; 95% IC 0,2-0,9). Ao que tange o primeiro artigo, conclui-se que todas as dimensões de apoio social influenciaram o tipo ou o tempo gasto em atividade física de lazer. No entanto, nossos resultados sugerem que o apoio social é mais importante no engajamento do que na situação de manutenção. Esse achado é importante, pois sugere que a manutenção da AFL deve estar associada a outros fatores além do nível individual de apoio social, como um ambiente adequado e políticas de saúde/sociais voltadas para a prática da AFL. Em relação ao segundo artigo, o presente estudo fornece evidências de uma associação inversa entre as relações sociais e a incidência de obesidade, evidenciando diferenças de sexo. Além disso, foi sugerido que preocupações com a imagem corporal entre mulheres poderia ser uma explicação para as diferenças de sexo.

Ecuaciones diferenciales ordinarias para estudiantes de Física

Conceptos fundamentales. - Ecuaciones de primer orden. - Ecuaciones de orden superior. - Sistemas de ecuaciones. - Transformación de Laplace. - Solución para series de ecuaciones lineales. - Métodos aproximados. - Teoría de la estabilidad. - Problemas de contorno de Sturm-Liouville. - Apéndice: Teoremas fundamentales. Métodos simbólicos. Resumen de métodos analíticos exactos. Definición y propiedades de algunas funciones. Tablas de transformadas de Laplace. Tablas de transformadas de Fourier. Soluciones y sugerencias para algunos ejercicios.

La investigación en antropología física. Una mirada al futuro

Desde su creación en 1976 la Sociedad Española de Antropología Física (SEAF) viene celebrando sus congresos bienales de forma ininterrumpida en distintas ciudades españolas. Estos encuentros, destinados a la discusión de los avances y resultados de las investigaciones bioantropológicas, suponen un foro de debate científico en el que participan investigadores de diversas áreas interesados en los estudios de Antropología Física, promoviendo la interacción entre especialistas e investigadores en formación. Asimismo, y dado el interés que esta disciplina despierta en la sociedad en general, la celebración de los Congresos de la SEAF permite mostrar las novedades acontecidas en el ámbito de la ciencia bioantropológica, facilitando la difusión del conocimiento más allá de la esfera académica. En este marco de reuniones científicas, los profesores del área de Antropología Física de la Facultad de Ciencia y Tecnología de la Universidad del País Vasco-Euskal Herriko Unibertsitatea (UPV/EHU) han sido los encargados de organizar el XVIII Congreso de la SEAF, celebrado en Bilbao durante los días 19 a 21 de junio de 2013. Este libro recoge las ponencias y principales comunicaciones presentadas en el XVIII Congreso, seleccionadas para su publicación y agrupadas en diferentes bloques temáticos que recogen algunas de los conocimientos actuales de la investigación bioantropológica: Ecología Humana, Biología Esquelética y Antropología Forense Paleoantropología y Primatología, y Diversidad Genética Humana. Se ha pretendido mostrar algunas de las cuestiones más relevantes actualmente y la proyección futura de la investigación en Antropología biológica, encaminada tanto al cuestionamiento de paradigmas (como la preponderancia de África en la evolución humana o la existencia de una única especie humana a partir del Pleistoceno Superior, entre otros), como a la comprensión de la relación fenotipo-genotipo, entre otras cuestiones de gran importancia para la reconstrucción de la historia evolutiva de nuestra especie. Sirvan las ponencias invitadas como ejemplo del nuevo enfoque de algunas áreas de la investigación en Antropología.

Panorámica de la práctica física y deportiva en Gipuzkoa

A lo largo de la historia, la actividad física ha tenido una importante presencia en el comportamiento diario de los seres humanos, siendo diferentes las funciones, interpretaciones y motivaciones de dicha práctica, pero siempre, asociadas a un carácter existencial. Este concepto ha ido evolucionando a lo largo del tiempo, identificándolo en sus inicios con una actividad condicionada y vinculada de forma significativa a la cultura propia de los pueblos que lo practicaban, hasta convertirse en un fenómeno de masas, con implicaciones sociológicas y económicas difíciles de explicar. En este sentido, se ha podido constatar que, durante los últimos años, ha existido un especial interés por parte de los organismos públicos para conocer y valorar la práctica deportiva en Gipuzkoa.