Theory of a Probe in a Strong Magnetic Field. AT(30-1)-1238-MATT 599

A kinetic approach is used to develop a theory of electrostatic probes in a fully ionized plasma in the presence of a magnetic field. A consistent asymptotic expansion is obtained assuming that the electron Larmor radius is small compared to the radius of the probe. The order of magnitude of neglected terms is given. It is found that the electric potential within the tube of force defined by the cross section of the probe decays non-mono tonic ally from the probe; this bump disappears at a certain probe voltage and the theory is valid up to this voltage. The transition region, which extends beyond plasma potential, is not exponential. The possible saturation of the electron current is discussed. Restricted numerical results are given; they seem to be useful for weaker magnetic fields down to the zero-field limit. Extensions of the theory a r e considered.

Electrostatic plasma instabilities excited by a high-frequency electric field. AT(30-1)-1238-MATT-669

An analysis of the electrostatic plasma instabilities excited by the application of a strong, uniform, alternating electric field is made on the basis of the Vlasov equation. A very general dispersion relation is obtained and discussed. Under the assumption W 2 O » C 2 pi. (where wO is the applied frequency and wpi the ion plasma frequency) a detailed analysis is given for wavelengths of the order of or large compared with the Debye length. It is found that there are two types of instabilities: resonant (or parametric) and nonresonant. The second is caused by the relative streaming of ions and electrons, generated by the field; it seems to exist only if wO is less than the electron plasma frequency wpe. The instability only appears if the field exceeds a certain threshold, which is found.

Ion-Ion correlations effect on nonlinear high-frequency plasma conductivity. AT(30-1)-1238-MATT-675

On the basis of the BBGKY hierarchy of equations an expression is derived for the response of a fully ionized plasma to a strong, high-frequency electric field in the limit of infinite ion mass. It is found that even in this limit the ionion correlation function is substantially affected by the field. The corrections to earlier nonlinear results for the current density appear to be quite ssential. The validity of the model introduced by Dawson and Oberman to study the response to a vanishingly small field is confirmed for larger values of the field when the eorrect expression for the ion-ion correlations i s introduced; the model by itself does not yield such an expression. The results have interest for the heating of the plasma and for the propagation of a strong electromagnetic wave through the plasma. The theory seems to be valid for any field intensity for which the plasma is stable.

La población musulmana de Valencia en 1238

La población musulmana de Valencia en 1238. En Al-Andalus, XVI. Madrid 1951

Las ventanas de la iglesia templaria de San Bautista de Burguillos del Cerro

La iglesia de San Juan Bautista de Burguillos del Cerro perteneció a la orden del Temple por la ayuda prestada a la corona en la reconquista de los territorios extremeños, desde 1238 hasta la disolución de la orden en 1312. Emplazada en la frontera de defensa del reino de León del avance almohade durante los siglos XII a XIII, incluye una qubba musulmana, fue iglesia hasta 1797 y luego cementerio hasta 1908. Destacan por su singularidad las ventanas angostas del ábside así como las ventanas de tracería ojival de la nave principal y los rosetones de la qubba convertida en capilla funeraria a fines del siglo XIV L'église de Saint-Jean Baptiste de Burguillos del Cerro devint la propriété de l'ordre du Temple grâce à l'aide fournie à la couronne dans la reconquête des territoires d’Estrémadure, depuis 1238 jusqu'à la dissolution de l'ordre en 1312. Installée à la frontière de la défense du royaume de Léon de la progression almohade pendant le XIIe et XIII siècles, elle comprend une qubba musulmane et est restée église jusqu'à 1797 et puis convertie en cimetière jusqu'à 1908. Soulignent par leur singularité les fenêtres étroites de l’abside ainsi que les fenêtres de remplage ogival de la nef principale et les rosaces de la qubba transformée en chapelle funéraire à la fin du XIVe siècle.