Directionality in van der Waals Interactions: the Case of 4-Acetylbiphenyl Adsorbed on Au(111)

We report on a theoretical study of adsorption of 4-Acetylbiphenyl molecule and its diffusion properties in the main directions of the Au(111) surface. Structural changes of the molecule, which are induced by adsorption lead to stronger conjugation of the $\pi$-system. The molecule is adsorbed in a flat configuration on the surface with roughly the same binding energy along the [110] and [112] directions, in good agreement with experiments. Furthermore, the diffusion barriers imply an important directionality of the molecule-surface interactions. This is somewhat surprising because our calculations show that the prevailing interaction is the long-range molecule-surface van der Waals interaction. Despite of its weakness, the van der Waals interaction discriminates the preferential adsorption sites as well as imposes a molecular geometry that needs to be considered when rationalizing the diffusion barriers

Lenguajes de Scripting

Los lenguajes de scripting son una subcategoría de los lenguajes de programación. Este tipo de lenguajes son interpretados, es decir, que para ejecutar las instrucciones existe un programa o intérprete que se encarga de procesar cada una de las órdenes y producir los resultados deseados. Algunos ejemplos de este tipo de lenguajes son: JavaScript, Lisp, P. H. P., Python, Ruby, etc. En el otro caso, en los lenguajes que no son interpretadosexiste un compilador que toma esas instrucciones y genera un archivo ejecutable. Tenemos en esta categoría a C, C++, Java, Microsoft Visual Basic, etc. Recientemente hemos visto dos enguajes de scripting orientados a objetos que han tenido una gran acogida por la comunidad de programadores: Ruby y Groovy

Planar laser induced fluorescence for temperature measurement of optical thermocavitation

Pulsed laser-induced cavitation, has been the subject of many studies describing bubble growth, collapse and ensuing shock waves. To a lesser extent, hydrodynamics of continuous wave (CW) cavitation or thermocavitation have also been reported. However, the temperature field around these bubbles has not been measured, partly because a sensor placed in the fluid would interfere with the bubble dynamics, but also because the short-lived bubble lifetimes (∼70–200 µs) demand high sampling rates which are costly to achieve via infrared (IR) imaging. Planar laser-induced fluorescence (PLIF) provides a non-intrusive alternative technique to costly IR imaging to measure the temperature around laser-induced cavitation bubbles. A 440 nm laser sheet excites rhodamine-B dye to fluoresce while thermocavitation is induced by a CW 810 nm laser. Post-calibration, the fluorescence intensity captured with a high-speed Phantom Miro camera is correlated to temperature field adjacent to the bubble. Using shadowgraphy and PLIF, a significant decrease in sensible heat is observed in the nucleation site– temperature decreases after bubble collapse and the initial heated volume of liquid shrinks. Based on irradiation time and temperature, the provided optical energy is estimated to be converted up to 50% into acoustic energy based on the bubble's size, with larger bubbles converting larger percentages

Brane with variable tension as a possible solution to the problem of the late cosmic acceleration

Braneworld models have been proposed as a possible solution to the problem of the accelerated expansion of the Universe. The idea is to dispense the dark energy (DE) and drive the late-time cosmic acceleration with a five-dimensional geometry. Here, we investigate a brane model with variable brane tension as a function of redshift called chrono-brane. We propose the polynomial $\lambda=(1+z)^{n}$ function inspired in tracker-scalar-field potentials. To constrain the $n$ exponent we use the latest observational Hubble data from cosmic chronometers, Type Ia Supernovae from the full JLA sample, baryon acoustic oscillations and the posterior distance from the cosmic microwave background of Planck 2015 measurements. A joint analysis of these data estimates $n\simeq6.19$ which generates a DE-like or cosmological-constant-like term, in the Friedmann equation arising from the extra dimensions. This model is consistent with these data and can drive the Universe to an accelerated phase at late times.Comment: 7 pages, 6 figures, accepted for publication in Phys. Rev. D (Rapid Communication

Diseño estructural : unidad 4

1 archivo PDF (77 páginas) ; 2a ediciónSe ilustra el análisis del equilibrio de estructuras sujetas a distintos tipos de acciones

El efecto competitivo de las importaciones recientes en México

Uno de los beneficios esperados de un proceso de liberalización y apertura comercial es la imposición de restricciones al poder de fijación de precios que tienen los monopolios o los oligopolios internos. Es decir, la disminución de las barreras arancelarias y el desmantelamiento de las no tarifarias, como permisos de importación y precios oficiales de importación, y su sustitución por aranceles, puede aumentar la competencia efectiva y la potencial que enfrentan los productores locales. Algunos autores (Esposito y Esposito, 1971) sugieren incluso que la liberalización comercial puede ser utilizada para disminuir las presiones inflacionarias de los bienes manufactureros locales, gracias al efecto competitivo que debe ser mayor en las industrias más concentradas (De Rosa y Goldstein, 1981). El comportamiento competitivo de la industria local es reforzado también por los consumidores. En efecto, una apertura comercial modificará la estructura de sus preferencias, y cuando éstas se desplacen hacia los productos importados, la elasticidad-precio de la demanda de los bienes nacionales tiende a menos infinito y en consecuencia el precio interno debe tender a su costo marginal (Zeelemberg, 1986).

Regulation of primary production in the Gulf of California through interaction of large-scale and local ocean processes [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): The suppression of primary productivity observed in eastern boundary ecosystems of the Pacific during El Nino episodes does not occur throughout the Gulf of California. On the contrary, analysis of the modern siliceous phytoplankton record from annually layered sediments and compilation of available primary productivity measurements indicate that production is significantly increased in the central Gulf during El Nino years compared to anti-El Nino years. Integrated observations of biological and physical variability during the spring of 1983, under the influence of the strong El Nino, show that very high primary productivity occurred along the eastern margin of the central Gulf. This resulted from the upwelling of a nutrient rich source provided by the locally formed Gulf water mass originating in the northern Gulf. Lower productivity and phytoplankton biomass were associated with the anomalous penetration of Tropical Surface Water along the western side of the Gulf

Quantum state of the multiverse

A third quantization formalism is applied to a simplified multiverse scenario. A well defined quantum state of the multiverse is obtained which agrees with standard boundary condition proposals. These states are found to be squeezed, and related to accelerating universes: they share similar properties to those obtained previously by Grishchuk and Siderov. We also comment on related works that have criticized the third quantization approach.Comment: 15 pages, 2 figure