Bloch Oscillation under a Bichromatic Laser: Quasi-Miniband Formation, Collapse, and Dynamical Delocalization and Localization

A novel DC and AC driving configuration is proposed for semiconductor superlattices, in which the THz AC driving is provided by an intense bichromatic cw laser. The two components of the laser, usually in the visible light range, are near but not exactly resonant with interband Wannier-Stark transitions, and their frequency difference equals the Wannier-Stark ladder spacing. Multi-photon processes with the intermediate states in the conduction (valence) band cause dynamical delocalization and localization of valence (conduction) electrons, and the corresponding formation and collapse of the quasi-minibands.Comment: 4 pages, 3 figure

Critical wave-packet dynamics in the power-law bond disordered Anderson Model

We investigate the wave-packet dynamics of the power-law bond disordered one-dimensional Anderson model with hopping amplitudes decreasing as $H_{nm}\propto |n-m|^{-\alpha}$. We consider the critical case ($\alpha=1$). Using an exact diagonalization scheme on finite chains, we compute the participation moments of all stationary energy eigenstates as well as the spreading of an initially localized wave-packet. The eigenstates multifractality is characterized by the set of fractal dimensions of the participation moments. The wave-packet shows a diffusive-like spread developing a power-law tail and achieves a stationary non-uniform profile after reflecting at the chain boundaries. As a consequence, the time-dependent participation moments exhibit two distinct scaling regimes. We formulate a finite-size scaling hypothesis for the participation moments relating their scaling exponents to the ones governing the return probability and wave-function power-law decays

Comisarías de familia: hacia la excelencia en la atención familiar.

Tablas, AnexosEl proceso de la Experiencia Profesional Dirigida, en la comisaria de familia de Fontibón, se genera a partir de la necesidad que evidencia la secretaria distrital de integración social, por optimizar los procesos solicitados por los ciudadanos de la capital, donde se busca una atención más ágil y diligente, con un sentido humano y cercano, ante las necesidades expuestas por los consultantes de la Comisaria. En tal sentido la experiencia profesional dirigida, propuesta por la Universidad Nacional Abierta y a Distancia “UNAD”, básicamente estuvo direccionada en tres (3) grandes fases o momentos, que se desarrollarían de forma consecutiva y complementaria entre sí. La primera fase de exploración se denominó como la Formulación Diagnostica, donde su principal objetivo tenía que ver con la construcción o elaboración del diagnóstico inicial de los componentes básicos desarrollados por la comisaria de familia de Fontibón. Para lograr este primer objetivo se inició un constante trabajo de reconocimiento, exploración y observación participante del funcionamiento y exigencias de la comisaria, facilitando de esta forma la inclusión al sistema de trabajo de la misma.No Abstrac

Dynamics of an electron in finite and infinite one dimensional systems in presence of electric field

We study,numerically, the dynamical behavior of an electron in a two site nonlinear system driven by dc and ac electric field separately. We also study, numerically, the effect of electric field on single static impurity and antidimeric dynamical impurity in an infinite 1D chain to find the strength of the impurities. Analytical arguments for this system have also been given.Comment: File Latex, 8 Figures available on reques

Effect of nonlinearity on the dynamics of a particle in dc field-induced systems

Dynamics of a particle in a perfect chain with one nonlinear impurity and in a perfect nonlinear chain under the action of dc field is studied numerically. The nonlinearity appears due to the coupling of the electronic motion to optical oscillators which are treated in adiabatic approximation. We study for both the low and high values of field strength. Three different range of nonlinearity is obtained where the dynamics is different. In low and intermediate range of nonlinearity, it reduces the localization. In fact in the intermediate range subdiffusive behavior in the perfect nonlinear chain is obtained for a long time. In all the cases a critical value of nonlinear strength exists where self-trapping transition takes place. This critical value depends on the system and the field strength. Beyond the self-trapping transition nonlinearity enhances the localization.Comment: 9 pages, Revtex, 6 ps figures include

An experiment on teaching coordination in a globally distributed software engineering class

The importance of planning and management skills in software development is very difficult to convey in software engineering courses. We present the synopsis of an assignment whose purpose is to demonstrate the significance of such skills, including effective communication, team coordi-nation and collaboration, and overall project planning. The assignment is organized in the context of a distributed software engineering course carried out in collaboration with 12 universities in South America, Europe and Africa. The assignment is a globally distributed contest issued before most development activities related to the course’s software project are performed, aiming at favor-ing the collaboration between students prior to project development. The contest does not involve any programming, and is not related to the project development activities. Instead, it consists of making teams in different countries compete in collaboratively solving a set of very simple tasks. The complexity of the activity is in team collaboration and coordination, and their lack is evident when the tasks are not correctly solved, or not solved in time. Despite the simplicity of the as-signment, students have found it useful in helping them understand the significance of management and planning challenges in distributed software development. Moreover, the assignment helped in team building, by creating a better team atmosphere and contributing in identifying team members better suited for management

First report of Phytophthora infestans self fertile genotypes in southern Brazil.

During the autumn of 2011 and 2012, leaf and stem samples of potato plants infected with P. infestans were collected in southern Brazil. Monosporangial isolates of P. infestans were obtained from the samples and mating types were determined. Each isolate was paired with the A2 and A1 mating types of P. infestans and self-paired on Petri plates containingV8 juice agar. After this, the plates were kept at 18°C in darkness for 20 days. Three isolates collected in Paraná State (municipalities of Ponta Grossa 25°12'26''S, 50°07'11''W; Contenda 25°38'52''S, 49°34'26''W; and Castro 24°51'50''S, 49°53'50''W) formed oospores when paired with both mating type isolates and also when self-paired

Exact Solution of an Evolutionary Model without Ageing

We introduce an age-structured asexual population model containing all the relevant features of evolutionary ageing theories. Beneficial as well as deleterious mutations, heredity and arbitrary fecundity are present and managed by natural selection. An exact solution without ageing is found. We show that fertility is associated with generalized forms of the Fibonacci sequence, while mutations and natural selection are merged into an integral equation which is solved by Fourier series. Average survival probabilities and Malthusian growth exponents are calculated indicating that the system may exhibit mutational meltdown. The relevance of the model in the context of fissile reproduction groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.