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

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

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»

MICROPLASTIC ACCUMULATION IN TERRESTRIAL GASTROPODS AND SOILS

Microplastics (MPs) have become an emerging threat to ecosystems across the world. Transport, impacts, and fates are grossly understudied, especially in terrestrial environments. Current research on MP bioaccumulation has focused mainly on aquatic organisms with little study of terrestrial organisms, including snails where data are nearly nonexistent. To address this, we collected and examined land snails and their surrounding soil for MP content in shell and tissue. From September 11, 2020, to October 25, 2021, cover boards were placed (n=30) along relatively undisturbed sites in hardwood, forested areas, and tall grasses in a Wildlife Management Area (WMA) in Oak Ridge Tennessee. A total of 150 individuals were collected and 2.2 lbs of soil per site was taken directly underneath coverboards. For comparison with a more disturbed habitat, 150 snails and soil were also collected on the University of Tennessee campus from March 1, 2022, to July 10, 2022. Snails were placed in 70% ethanol for analysis and digested for 24 hours using a 1:1 ratio of potassium hydroxide pellets and sodium hypochlorite for organic matter removal. Samples were vacuum filtered, air dried for 1 week and then examined via stereomicroscope. MP shape, color, and number were recorded, and samples were examined twice, independent of one another to ensure accurate MP counts. Two tests were performed if MPs could not be determined. The “hot needle test” causes plastics to deform and melt when exposed to heat, and the “spring test” to examine the physical characteristics of the MP. Results for the less disturbed WMA (Oak Ridge) showed total MP abundance at 214 particles in snails and 478 for soils. MP counts ranged from 0 to 6 per snail and 5 to 33 per soil sample. For campus (Knoxville), MP counts were higher, with a total of 270 particles in snails and 540 particles in soils. MP counts ranged from 0 to 8 per snail and 7 to 35 particles per soil sample. This study confirms the accumulation of MPs in land snails and indicates that higher human activity is associated with higher densities of MPs in both snails and soils

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

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