Coarsening of Topological Defects in Oscillating Systems with Quenched Disorder

We use large scale simulations to study interacting particles in two dimensions in the presence of both an ac drive and quenched disorder. As a function of ac amplitude, there is a crossover from a low drive regime where the colloid positions are highly disordered to a higher ac drive regime where the system dynamically reorders. We examine the coarsening of topological defects formed when the system is quenched from a disordered low ac amplitude state to a high ac amplitude state. When the quench is performed close to the disorder-order crossover, the defect density decays with time as a power law with \alpha = 1/4 to 1/3. For deep quenches, in which the ac drive is increased to high values such that the dynamical shaking temperature is strongly reduced, we observe a logarithmic decay of the defect density into a grain boundary dominated state. We find a similar logarithmic decay of defect density in systems containing no pinning. We specifically demonstrate these effects for vortices in thin film superconductors, and discuss implications for dynamical reordering transition studies in these systems.Comment: 7 pages, 8 postscript figures; this extended version to appear in Phys. Rev.

Theoretical and experimental study of AC loss in HTS single pancake coils

The electromagnetic properties of a pancake coil in AC regime as a function of the number of turns is studied theoretically and experimentally. Specifically, the AC loss, the coil critical current and the voltage signal are discussed. The coils are made of Bi2Sr2Ca2Cu3O10/Ag (BiSCCO) tape, although the main qualitative results are also applicable to other kinds of superconducting tapes, such as coated conductors. The AC loss and the voltage signal are electrically measured using different pick up coils with the help of a transformer. One of them avoids dealing with the huge coil inductance. Besides, the critical current of the coils is experimentally determined by conventional DC measurements. Furthermore, the critical current, the AC loss and the voltage signal are simulated, showing a good agreement with the experiments. For all simulations, the field dependent critical current density inferred from DC measurements on a short tape sample is taken into account.Comment: 22 pages, 15 figures; contents extended (sections 3.2 and 4); one new figure (figure 5) and two figures replaced (figures 3 and 8); typos corrected; title change

New Stellar (n,γ)(n,\gamma) Cross Sections and The "Karlsruhe Astrophysical Database of Nucleosynthesis in Stars"

Since April 2005 a regularly updated stellar neutron cross section compilation is available online at http://nuclear-astrophysics.fzk.de/kadonis. This online-database is called the "Karlsruhe Astrophysical Database of Nucleosynthesis in Stars" project and is based on the previous Bao et al. compilation from the year 2000. The present version \textsc{KADoNiS} v0.2 (January 2007) includes recommended cross sections for 280 isotopes between $^{1}$H and $^{210}$Po and 75 semi-empirical estimates for isotopes without experimental information. Concerning stellar $(n,\gamma)$ cross sections of the 32 stable, proton-rich isotopes produced by the $p$ process experimental information is only available for 20 isotopes, but 9 of them have rather large uncertainties of $\geq$9%. The first part of a systematic study of stellar $(n,\gamma)$ cross sections of the $p$-process isotopes $^{74}$Se, $^{84}$Sr, $^{102}$Pd, $^{120}$Te, $^{130}$Ba, $^{132}$Ba, $^{156}$Dy, and $^{174}$Hf is presented. In another application \textsc{KADoNiS} v0.2 was used for an modification of a reaction library of Basel university. With this modified library $p$-process network calculations were carried out and compared to previous results.Comment: Proceedings "International Conference on Nuclear Data for Science and Technology 2007", Nice/ Franc

La secuencia malacológica de la cueva de Nerja (Málaga): excavaciones de 1982

[Resumen] Este trabajo es un avance al estudio de la malaco fauna de los niveles arqueológicos del Vestfbulo de la Cueva de Nerja (Málaga). En el describimos la estratigraffa obtenida en el sondeo efectuado en la última campaña de excavaciones de 1982 en el Vestíbulo, y estudiamos los diferentes moluscos que aparecieron, agrupándolos en cuatro conjuntos, entre los que destaca el bromatológico. Observamos grandes acumulaciones de conchas que llegan a formar auténticas capas bioclásticas, conchas que fueron utiIizadas por los habitantes de la Cueva de Nerja para su alimentación. Las culturas que aparecen representadas corresponden al Paleolftico Superior, Epipaleol1tico y Neolítico Inicial, por lo que estos moluscos están situados en el Pleistoceno Final y Holoceno Inicial. A partir de los datos obtenidos en anteriores excavaciones en otra sala de la Cueva, y de los que exponemos aquí, se puede observar una serie de variaciones ecológicas y climáticas muy significativas, fundamentalmente en la transición Pleistoceno-Holoceno.[Resumé] Dans ce travail nous présentons les premieres rèsuIta ts de l' etude de lamaIacofaune du VestibuIo de la Grotte de Nerja (Málaga). Nous y décrirons la stratigraphie obtenue dans le forage réalisé dans le Vestibulo au cours de la campagne de fouilles enteprise en 1982. Aussi nous y étudions es différents mol usques apparus et les groupant en quatre ensembles, parmi lesquels il fant signaler l'eQ. semble bromatologique. N ous avons observé de grandes accumulations de coqui Ilages qui peurent former une véritable couche bioclastique. Ces coquilles ont été employ"'ees par les habitants de la Grotte pour leur alimentation. Les cultures qui y sont représentées correspondent au Paléolithique Supérieur, Epipaléolithique et Néolithique Initial, raison par laqueLle ces molusques se situeraient au Pleistocene Final el Holocene Initial. Les données obtenues par des fouilles realisées précájelment dans une autre salle de la G ro'tte ainsi que celles qui font I'objet de notre étude, nous ont permis de constater 'une série d'importantes variations écologiques et cl imati"ques fonfamentalment lors de la transition Pleistocene - Holocen

Electron degeneracy and intrinsic magnetic properties of epitaxial Nb:SrTiO3_3 thin-films controlled by defects

We report thermoelectric power experiments in e-doped thin films of SrTiO$_3$ (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and non-linear Hall effect. Ab-initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this paper for tetragonally distorted e-doped STO thin films, is similarto that observed in LaAlO$_3$/STO interfaces and magnetic STO quantum wells.Comment: 5 pages, 5 figure

El computador en la clase de Matemáticas: desde lo dinámico y lo semiótico

En esta investigación se utilizó un enfoque que permitió explorar los conceptos propios del curso de ecuaciones diferenciales ordinarias, ofrecido para los estudiantes de la Facultad de Ingeniería de la Pontificia Universidad Javeriana, Cali, Colombia, considerando los modelos teóricos propuesto por Godino y Batanero; la propuesta de Vergnaud, y los esquemas de representación de Brown. Se utiliza el computador como “instrumento mediador” (soportado en las potencialidades del software MatLab) que favoreció trabajar con instancias de modelación de las ecuaciones diferenciales en contextos propios de la Ingeniería, desde una perspectiva dinámica de las ecuaciones y otra semiótica desde el diseño de actividades para los estudiantes