Chemico-electromechanical coupling in microporous media

We determine the macroscopic transport properties of isotropic microporous media by volume-averaging the local Nernst-Planck and Navier-Stokes equations in nonisothermal conditions. In such media, the excess of charge that counterbalances the charge deficiency of the surface of the minerals is partitioned between the Gouy-Chapman layer and the Stern layer. The Stern layer of sorbed counterions is attached to the solid phase, while the Gouy-Chapman diffuse layer is assumed to have a thickness comparable to the size of the pores. Rather than using Poisson-Boltzmann distributions to describe the ionic concentrations in the pore space of the medium, we rely on Donnan distributions obtained by equating the chemical potentials of the water molecules and ions between a reservoir of ions and the pore space of the medium. The macroscopic Maxwell equations and the macroscopic linear constitutive transport equations are derived in the vicinity of equilibrium, assuming that the porous material is deformable. In the vicinity of thermodynamic equilibrium, the cross-coupling phenomena of the macroscopic constitutive equations of transport follow Onsager reciprocity. In addition, all the material properties entering the constitutive equations depend only on two textural properties, the permeability and the electrical formation factor.     

Antimicrobial and cytotoxic activities of leaves, twigs and stem bark of Scutia buxifolia Reissek

The antimicrobial and cytotoxic activities of the dichloromethane, ethyl acetate and butanolic fractions from the leaves, twigs and stem bark of Scutia buxifolia were evaluated using the broth microdilution method and the brine shrimp lethality method, respectively. Phytochemical analysis was performed by thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC). The antimicrobial results demonstrated that the strongest effect occurred with the butanol fraction from the twigs and the ethyl acetate fraction from the stem bark against Saccharomyces cerevisiae (minimal inhibitory concentration; MIC?=?62.5?μg?mL(-1)), whereas the ethyl acetate and butanolic fractions from the twigs and stem bark were effective against Pseudomonas aeruginosa and Staphylococcus aureus, with MIC values ranging from 125 to 500?μg?mL(-1). LD(50) values varied from 50.00?±?0.22 to 82.23?±?0.34?μg?mL(-1). Quercetin, quercitrin, isoquercitrin and rutin were identified by HPLC and may be partially responsible for the antimicrobial activities observed. This study reports for the first time the antimicrobial and cytotoxic activities of S. buxifolia leaves, twigs and stem bark.     

On the possible catalysis by single water molecules of gas-phase hydrogen abstraction reactions by OH radicals

The gas phase hydrogen abstraction reaction between OH and CY(2)XH, where X = H, F, OH, or NH(2) and Y = H, CH(3) or F, in the absence and presence of a single water molecule is investigated using both density function theory, B3LYP, and explicitly correlated coupled cluster theory, CCSD(T)-F12. We find that a single water molecule could have a catalytic effect at low temperatures possible in laboratory experiments, but does not seem to catalyze these reactions at 298 K, and will not play a role under relevant atmospheric conditions.     

High order harmonic generation from solid targets: Towards intense attosecond pulses

Experiments and computer simulations on high order harmonic generation (HOHG) from steep plasma gradients using intense femtosecond laser pulses are presented. The importance of the plasma scale length for the efficiency of HOHG is demonstrated. By changing the pump intensity and the target parameters the regime of HOHG can be switched from non-relativistic to relativistic. Simulations show that attosecond pulses should already be present in our experiments in both interaction regimes. Two-color driven harmonic generation is shown to provide a highly efficient way of attosecond pulse production.     

Timescales in the response of materials to femtosecond laser excitation

The interaction of ultrashort laser pulses with materials involves a number of special features that are different from laser–matter interaction for longer pulse durations. For femtosecond laser excitation the fundamental physical processes such as energy deposition, melting, and ablation are separated in time. By choosing proper time windows, the various processes can be investigated separately. We present selected examples of theoretical studies of free electron excitation in metals, timescales of different melting processes, and peculiarities of near-threshold ablation. Depending on the timescales and intensity ranges, the discussed processes are combined in an overall picture of possible pathways of the material from excitation to ablation. PACS 61.80.-x; 64.70.-p     

Adhesive interface interactions between primary aliphatic amine surface conditioners and polyamic ester/polyimide resins

The interface reactions of 3-aminopropyltriethoxysilane treated surfaces, with a polyamic alkyl ester/polyimide resin formed from pyromellitic dianhydride and oxydianiline, were defined by Fourier Transform Infrared (FTIR) analysis on the surface layers of germanium internal reflection plates. Adhesion between these interfacial layers is the result of chemical bonding, which apparently proceeds through initial amide formation between the amino function of the silylated surface and the alkyl ester group present in the polyamic ester. Heating results in diamide formation by a second alkyl, surface-bound amine displacing the aromatic polymer amine. Heating the more stable dialkyldiamide to 300°C imidizes both the polymer and the interfacial region, producing a strong laminate composite. Polymer scission at the aromatic amide linkages occurs in this adhesion process, bonding surface-bound alkyl amines to one end of a shortened polymer chain.     

Generation of isothermal density perturbations in the inflationary universe

It is shown that not only adiabatic perturbations of the density but also isothermal density perturbations are generated in the inflationary universe. The magnitude of isothermal perturbations can be sufficiently large for the subsequent galaxy formation. The spectrum of isothermal perturbations can differ considerably from a flat one.     

Characteristics of a hybridly mode-locked cw dye laser

We present experimental and theoretical results on the characteristics and random variations of subpicosecond pulses generated by a synchronously pumped cw dye laser with saturable absorber. The analysis of the power spectra indicates rapid fluctuations of the pulse duration of 40–50%, energy fluctuations of 3%, and a jitter of the repetition time of 0.1% corresponding to an absolute jitter of 12 ps. The latter is caused mainly by the temporal jitter of the pump laser. A mismatch of the lengths of the dye and the pump-laser cavity can result in a nonstationary mode-locking regime with a periodic change of the pulse parameters. The interpretation of the experimental results are supported by computer simulations of the pulse evolution process.