Diffusion of clusters down (1 1 1) aluminum islands

The key factor determining nucleation processes and faceting in homoepitaxial growth as well as texture competition is the mobility of adatoms and small clusters across step edges and facets. Using a combination of molecular dynamics and ab initio calculations, we investigate the mechanisms of small clusters (dimer and trimer) diffusion down the aluminum (1 1 1) surface. In this paper we report results of molecular dynamics studies. Our study shows that the clusters dissociate at the step-edge of compact islands. As a result, the clusters diffuse down the step by an exchange mechanism with a small or medium Schwoebel barrier. The mechanism of this down-diffusion/dissociation is discussed and the corresponding energetics are calculated using the molecular statics method. We find a large anisotropy between the barriers at the two types of 1 1 0 oriented steps.     

Dynamic stiffness analysis of laminated beams using a first order shear deformation theory

In this paper the exact vibration frequencies of generally laminated beams are found using a new method, including the effect of rotary inertia and shear deformations. The effect of shear in laminated beams is more significant than in homogenous beams, due to the fact that the ratio of extensional stiffness to the transverse shear stiffness is high. The exact dynamic stiffness matrix is derived, and then any set of boundary conditions including elastic connections, and assembly of members, can be solved as in the classical direct stiffness method for framed structures. The natural frequencies of vibration of a structure are those values of frequency that cause the dynamic stiffness matrix to become singular, and one can find as many frequencies as needed from the same matrix. In the paper several examples are given, and compared with results from the literature.     

Ru-Containing Polymeric Catalysts for Cellulose Conversion to Polyols

In this paper Ru-containing catalysts based on hypercrosslinked polystyrene (MN-270) and its functional analogues (MN-100 and MN-500) were studied for the first time in cellulose hydrolytic hydrogenation. The catalysts were characterized using transmission electron microscopy (TEM), high resolution TEM, and porosity measurements. Catalytic studies demonstrated that the catalyst containing 1.0 % Ru and based on MN-270 is the most active. The total yield of sorbitol and mannitol was 50 % on the average at 85 % cellulose conversion.     

Superconductor Stability Revisited: Impacts from Coupled Conductive and Thermal Radiative Transfer in the Solid

Standard stability calculations following the Stekly, adiabatic or dynamic stability models apply purely solid thermal conduction mechanism, derive predictions under (quasi-) stationary and adiabatic conditions and assume ideal (mostly centrosymmetric) location of disturbances. Instead, the present paper takes into account also thermal radiative heat transfer in the superconducting solid, pool boiling, and considers the impact of random location and intensity of disturbances on the stability problem. The analysis is based on interplay between Monte Carlo radiative transfer calculations and a rigorous Finite Element method to calculate the resulting transient temperature field and stability functions. The combined Monte Carlo/Finite Element method is applied to 1G filament and 2G thin-film-coated high temperature superconductors. Results are strongly different from solutions achieved with standard, solely solid conduction thermal transport. It is not realistic, even in thin films, to assume uniform conductor temperature under transient disturbances. This may have significant consequences for design and simulation of performance of superconducting fault current limiters. There are doubts whether superconducting fault current limiters under any operation conditions could work in either pure flux flow or Ohmic resistive states.     

Transport and recombination in solar cells: New perspectives

The functioning of the solar cells relies on the photo-generation of carriers in p–n junctions and their subsequent recombination in the quasi-neutral regions. A number of basic issues concerning the physics of the operation of solar cells still remain obscure. This paper reports on some unsolved basic problems, namely: a model of the recombination processes that does not contradict Maxwell's equations; the role played by space charges in the transport phenomena, and the formation of quasi-neutral regions under the presence of non-equilibrium photo-generated carriers. In this work, a new formulation of the theory that explains the underlying physical phenomena involved in the generation of a photo-e.m.f. is presented.     

Influence of Boundaries on Shear-driven Flow of Liquids in Open Cavities

In recent years, the development of two-phase flow cooling systems in micro-electronic as well as surface coating/patterning technologies, often based on thin films and liquid filled micro-enclosures, has renewed the interest in the classical problem of the cavity flow driven by a shear stress imposed at the gas-liquid boundary. In this paper, we study, numerically, the influence of the cavity geometry and boundaries on the three dimensional velocity field driven by a shear flow of inert gas. This study has been performed in the frame of the ESA sponsored Space Program on heat and mass transfer CIMEX-1 and it has to be considered as a contribution in the preparation of the Space experiment. The reference values for the flow parameters as well as the geometrical features encountered in the present paper target the main features of the CIMEX-1 experiment, although the main conclusions can be considered of general validity.     

Control of the fluorescence of dye-antibody conjugates by (2-hydroxypropyl)-β-cyclodextrin in fluorescence microscopy and flow cytometry

When proteins are conjugated to fluorescent organic dyes, fluorescence emission of the dye molecules is usually decreased, sometimes up to 50-70%. This quenching phenomenon has been acknowledged for decades, but as yet, there are no simple, practical methods to control the fluorescence of dyes conjugated to proteins, especially for dyes conjugated to immunoglobulins. Here, we report that the addition of (2-hydroxypropyl)-β-cyclodextrin (HPβCD) to dye-antibody conjugates can increase fluorescence up to 2.5-fold in cell imaging and flow analysis. This method may be an effective way to increase the sensitivity of detection of fluorescent organic labels used in immunology, histochemistry, and cell biology.     

Angular diagram of broadband emission of millimeter-sized water droplets exposed to gigawatt femtosecond laser pulses

We report on the experiments on the interaction of gigawatt femtosecond laser pulses with suspended millimeter-sized water droplets. The transparent droplets experienced laser-induced breakdown and explosive boiling up and emitted a broadband radiation. This radiation covers the spectral range from 450 to 1100?nm and consists of the spectrum of laser pulse scattered and transformed by the droplet due to self-phase modulation and plasma emission produced in water during photoionization. The droplet emission spectrum showed remarkable broadening at all viewing angles and is maximal in the direction of the laser exit from the droplet. The enlargement of the droplet results in additional spectral spreading of the emitted radiation. The depth and amount of laser pulse spectral self-transformations upon propagation through the water droplet are simulated by means of numerical calculations.