Axisymmetric pulse recycling and motion in bulk semiconductors

The Kroemer model for the Gunn effect in a circular geometry (Corbino disks) has been numerically solved. The results have been interpreted by means of asymptotic calculations. Above a certain onset dc voltage bias, axisymmetric pulses of the electric field are periodically shed by an inner circular cathode. These pulses decay as they move towards the outer anode, which they may not reach. As a pulse advances, the external current increases continuously until a new pulse is generated. Then the current abruptly decreases, in agreement with existing experimental results. Depending on the bias, more complex patterns with multiple pulse shedding are possible.Comment: 8 pages, 15 figure

Free boundary problems describing two-dimensional pulse recycling and motion in semiconductors

An asymptotic analysis of the Gunn effect in two-dimensional samples of bulk n-GaAs with circular contacts is presented. A moving pulse far from contacts is approximated by a moving free boundary separating regions where the electric potential solves a Laplace equation with subsidiary boundary conditions. The dynamical condition for the motion of the free boundary is a Hamilton-Jacobi equation. We obtain the exact solution of the free boundary problem (FBP) in simple one-dimensional and axisymmetric geometries. The solution of the FBP is obtained numerically in the general case and compared with the numerical solution of the full system of equations. The agreement is excellent so that the FBP can be adopted as the basis for an asymptotic study of the multi-dimensional Gunn effect.Comment: 19 pages, 9 figures, Revtex. To appear in Phys. Rev.

Emerging moralities and citizenship

El estudio de la obra de Arturo A. Roig pone en evidencia su carácter de “clásico" de la filosofía “nuestroamericana". En efecto, el filósofo ha instituido categorías nuevas, redefinido otras más tradicionales, explorado vías para enriquecer el acervo filosófico con saberes provenientes de otras formas discursivas, escritas o populares trasmitidas por el lenguaje oral, y formado un discipulado prestigioso. Esta producción en su integridad, aun los estudios sobre la Historia de las Ideas Latinoamericanas, fue concebida por su autor como ancilla emancipationis, una “filosofía del concernimiento" en términos de la Filosofía Intercultural. Como homenaje al Maestro Arturo A. Roig se comunica aquí un breve desarrollo teórico que incorpora las categorías de “a priori antropológico" y “moralidades emergentes", así como las redefiniciones de “ciudadanía" y “dignidad humana", a una investigación filosófica intercultural en curso sobre las “ciudadanías interculturales emergentes", resultante de las migraciones que constituyen el “fenómeno biopolítico mayor de nuestro tiempo"The study of Arturo A. Roig‟s work highlights his character as a “classic" of Our American philosophy. Indeed, the philosopher has instituted new categories, redefined more traditional ones, he has also explored new ways to enrich the philosophical wealth with the knowledge coming from other discursive forms, whether written or popular traditions transmitted orally, and he has built a prestigious discipleship. The totality of his production, even his studies on the History of Latin American Ideas, has been conceived as an ancilla emancipationis, “a philosophy of concern", as Intercultural Philosophy formulates it. Thus, as a homage to the Master Arturo A. Roig this contribution exposes a brief theoretical development incorporating as well the categories “anthropological a priori" and “emerging moralities", as the redefinitions of “citizenship" and “human dignity", to an actual philosophical enquiry on the “emerging intercultural citizenship" which results from the international migrations (“our time‟s greatest bio-political phenomenon").Fil: Bonilla, Alcira B.. Universidad de Buenos Aire

Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias

A standard drift-diffusion model of space charge wave propagation in semiconductors has been studied numerically and analytically under dc voltage bias. For sufficiently long samples, appropriate contact resistivity and applied voltage - such that the sample is biased in a regime of negative differential resistance - we find chaos in the propagation of nonlinear fronts (charge monopoles of alternating sign) of electric field. The chaos is always low-dimensional, but has a complex spatial structure; this behavior can be interpreted using a finite dimensional asymptotic model in which the front (charge monopole) positions and the electrical current are the only dynamical variables.Comment: 12 pages, 8 figure

Chapman-Enskog method and synchronization of globally coupled oscillators

The Chapman-Enskog method of kinetic theory is applied to two problems of synchronization of globally coupled phase oscillators. First, a modified Kuramoto model is obtained in the limit of small inertia from a more general model which includes ``inertial'' effects. Second, a modified Chapman-Enskog method is used to derive the amplitude equation for an O(2) Takens-Bogdanov bifurcation corresponding to the tricritical point of the Kuramoto model with a bimodal distribution of oscillator natural frequencies. This latter calculation shows that the Chapman-Enskog method is a convenient alternative to normal form calculations.Comment: 7 pages, 2-column Revtex, no figures, minor change

Magnetoswitching of current oscillations in diluted magnetic semiconductor nanostructures

Strongly nonlinear transport through Diluted Magnetic Semiconductor multiquantum wells occurs due to the interplay between confinement, Coulomb and exchange interaction. Nonlinear effects include the appearance of spin polarized stationary states and self-sustained current oscillations as possible stable states of the nanostructure, depending on its configuration and control parameters such as voltage bias and level splitting due to an external magnetic field. Oscillatory regions grow in size with well number and level splitting. A systematic analysis of the charge and spin response to voltage and magnetic field switching of II-VI Diluted Magnetic Semiconductor multiquantum wells is carried out. The description of stationary and time-periodic spin polarized states, the transitions between them and the responses to voltage or magnetic field switching have great importance due to the potential implementation of spintronic devices based on these nanostructures.Comment: 14 pages, 4 figures, Revtex, to appear in PR

Universality of the Gunn effect: self-sustained oscillations mediated by solitary waves

The Gunn effect consists of time-periodic oscillations of the current flowing through an external purely resistive circuit mediated by solitary wave dynamics of the electric field on an attached appropriate semiconductor. By means of a new asymptotic analysis, it is argued that Gunn-like behavior occurs in specific classes of model equations. As an illustration, an example related to the constrained Cahn-Allen equation is analyzed.Comment: 4 pages,3 Post-Script figure

La transformación del logos

RESUMEN: En este artículo no se intenta determinar con qué grado de justicia puede atribuírsele a María Zambrano el calificativo de «feminista»