142 research outputs found
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
Determinación de los parámetros de productividad en los procesos de carenamiento en un varadero mediano
Productivity parameters were determined in maintenance works of 16 ships in the slipways of ASTINAVE, a medium-size shipyard at Guayaquil, Ecuador, in the period between April 2008 and January 2009. Typical processes applied during ship maintenance, its units for evaluation and a classification chart are presented. With the registered time (Man-Hour, M-H), mean values, standard deviations and variation coefficients were calculated for each process. Mean value results for each work were: Plating replacement: 0.220 M-H/kg, Hull cleaning: 0.435 M-H/m2-machine, Painting: 0.027 M-H/m2-machine, Cathodic protection: 0.116 M-H/Kg, Thickness measurement: 0.030 M-H/test, Propulsion system: 130.92 M-H/line, Steering system: 54.89 M-H/line, Ship docking/undocking: 43.97 M-H/maneuver, Bottom Valves: 15.83 M-H/#valve, and, Fuel tank cleaning: 0.0093 M-H/gal.Se determinaron Parámetros de Productividad en los trabajos de mantenimiento de 16 embarcaciones en el varadero de ASTINAVE, en Guayaquil, Ecuador, en el periodo Abril 08 hasta Enero 2009. Se describen, definen las unidades para su evaluación y se clasifican los procesos típicos que se desarrollan para el mantenimiento de buques. Con los tiempos (hombres-hora) registrados se calcularon los valores medios, desviaciones estándar y Coeficiente de Variación de los parámetros de cada proceso. Los valores medios resultantes son: Cambio de planchaje 0.220 H-H/kg, Limpieza del Casco 0.435 H-H/m2-máq, Pintado 0.027 H-H/m2-máq, Protección catódica 0.116 H-H/Kg, Medición de espesores 0.030 H-H/prueba, Sistema de Propulsión 130.92 H-H/línea, Sistema de Gobierno 54.89 H-H/línea, Varada/Desvarada 43.97 H-H/maniobra, Válvulas de Fondo 15.83 H-H/#válv, y, Tanques de combustible 0.0093 H-H/gal
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
. We consider the critical case ().
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
Time evolution of the Partridge-Barton Model
The time evolution of the Partridge-Barton model in the presence of the
pleiotropic constraint and deleterious somatic mutations is exactly solved for
arbitrary fecundity in the context of a matricial formalism. Analytical
expressions for the time dependence of the mean survival probabilities are
derived. Using the fact that the asymptotic behavior for large time is
controlled by the largest matrix eigenvalue, we obtain the steady state values
for the mean survival probabilities and the Malthusian growth exponent. The
mean age of the population exhibits a power law decayment. Some Monte
Carlo simulations were also performed and they corroborated our theoretical
results.Comment: 10 pages, Latex, 1 postscript figure, published in Phys. Rev. E 61,
5664 (2000
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
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.
Computational and in vitro Pharmacodynamics Characterization of 1A-116 Rac1 Inhibitor: Relevance of Trp56 in Its Biological Activity
In the last years, the development of new drugs in oncology has evolved notably. In particular, drug development has shifted from empirical screening of active cytotoxic compounds to molecularly targeted drugs blocking specific biologic pathways that drive cancer progression and metastasis. Using a rational design approach, our group has developed 1A-116 as a promising Rac1 inhibitor, with antitumoral and antimetastatic effects in several types of cancer. Rac1 is over activated in a wide range of tumor types and and it is one of the most studied proteins of the Rho GTPase family. Its role in actin cytoskeleton reorganization has effects on endocytosis, vesicular trafficking, cell cycle progression and cellular migration. In this context, the regulatory activity of Rac1 affects several key processes in the course of the cancer including invasion and metastasis. The purpose of this preclinical study was to focus on the mode of action of 1A-116, conducting an interdisciplinary approach with in silico bioinformatics tools and in vitro assays. Here, we demonstrate that the tryptophan 56 residue is necessary for the inhibitory effects of 1A-116 since this compound interferes with protein-protein interactions (PPI) of Rac1GTPase involving several GEF activators. 1A116 is also able to inhibit the oncogenic Rac1P29S mutant protein, one of the oncogenic drivers found in sun-exposed melanoma. It also inhibits numerous Rac1-regulated cellular processes such as membrane ruffling and lamellipodia formation. These results deepen our knowledge of 1A-116 inhibition of Rac1 and its biological impact on cancer progression. They also represent a good example of how in silico analyses represent a valuable approach for drug development.Fil: González, Nazareno. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Oncología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cardama, Georgina Alexandra. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Oncología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Chinestrad, Patricio Manuel. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Farmacología Molecular; ArgentinaFil: Robles Valero, Javier. Universidad de Salamanca; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Rodríguez Fdez, Sonia. Universidad de Salamanca; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Lorenzo Martín, L. Francisco. Universidad de Salamanca; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Bustelo, Xosé R.. Universidad de Salamanca; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Lorenzano Menna, Pablo. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Farmacología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gomez, Daniel Eduardo. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Oncología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
The three-dimensional Anderson model of localization with binary random potential
We study the three-dimensional two-band Anderson model of localization and
compare our results to experimental results for amorphous metallic alloys
(AMA). Using the transfer-matrix method, we identify and characterize the
metal-insulator transitions as functions of Fermi level position, band
broadening due to disorder and concentration of alloy composition. The
appropriate phase diagrams of regions of extended and localized electronic
states are studied and qualitative agreement with AMA such as Ti-Ni and Ti-Cu
metallic glasses is found. We estimate the critical exponents nu_W, nu_E and
nu_x when either disorder W, energy E or concentration x is varied,
respectively. All our results are compatible with the universal value nu ~ 1.6
obtained in the single-band Anderson model.Comment: 9 RevTeX4 pages with 11 .eps figures included, submitted to PR
Latin American platform comparative critical analysis. Learning from the KASSA platforms' reports.
1 CD-ROM. Projeto DG-Research - Contract nº GOCE-CT-2004-505582
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