Self-focusing of a Gaussian laser beam reflected from a thermocapillary liquid surface

Self-focusing of laser radiation reflected from the surface of liquid heavy hydrocarbons is reported. Close agreement of experimental data with theoretical previsions suggests that thermocapillarity is the main physical phenomenon involved. The focus appears at 40 cm of the sample surface after 1 s of irradiation at 350 mW.     

Interfacial energy and the law of corresponding states 2: associated fluids

A mesoscopic model for the liquid/vapor interface previously developed for nonpolar fluids [J. Phys. Chem. A 2003, 107, 875; 2003, 107, 883] is extended to the case of polar associated compounds. The interfacial energy is factorized in two terms: one corresponding to association depending on the hydrogen bonds density, the other corresponding to the nonpolar contribution. This last term is treated in the framework of the corresponding states formalism similar to the one used in the case of nonpolar fluids [J. Phys. Chem. B 2004, 108, 5951]. The model yields a generalized behavior of the association factor as a function of the dielectric constant for the treated fluids. The calculated surface tension shows a mean error of about 1% for seven compounds having different multivalent H-bond characters.     

On number system constructions

We investigate various number system constructions. After summarizing earlier results we prove that for a given lattice Λ and expansive matrix M: Λ → Λ if ρ(M ⁻¹) < 1/2 then there always exists a suitable digit set D for which (Λ, M, D) is a number system. Here ρ means the spectral radius of M ⁻¹. We shall prove further that if the polynomial f(x) = c ₀ + c ₁ x + ··· + c _k x ^k ∈ Z[x], c _k = 1 satisfies the condition |c ₀| > 2 Σ _i=1 ^k |c _i | then there is a suitable digit set D for which (Z ^k , M, D) is a number system, where M is the companion matrix of f(x). The research was supported by OTKA-T043657 and Bolyai Fellowship Committee.     

Is ammonia a better solvent than water for contact ion pairs?

The existence of a charge-transfer-to-solvent process when a KI contact ion pair (CIP) dissolved in supercritical water (SCW) is excited by UV light was confirmed by use of electronic structure calculations applied to molecular dynamics trajectories. We observed similar behavior with fluid density as that found for the KI-CIP in supercritical ammonia (SCA); nevertheless, there are some distinct features in the two supercritical solvents. First, the effect of the solvent field due to the molecules lying beyond the first solvation shell is very different in SCW compared with that observed in SCA; in SCW it actually has a destabilizing effect over the ground and excited states. Second, our results for the thermodynamic behavior of the CIP indicate that SCA is better solvent than SCW for this species. The differences found can be attributed to the solvent molecules surrounding the CIP and bridging the two ions; they shield more efficiently the ion pair from long-range solvent effects in SCA. The different behavior is partially attributed to a stronger solvent-solvent interaction in SCW than in SCA.     

Frequency analysis of diffusion in 1D systems with energy and spatial disorder

We have analyzed the frequency-dependent features of diffusive transport of mobile carriers by hopping in a disordered environment composed of varying energy barriers. We developed a simple approach based on the solution of the master equation for a gradient of concentration (chemical potential) under a sinusoidal perturbation. This method extends the well-known result of the steady state case, D = {1 / Γ}⁻¹, to the frequency domain. The results of our calculations are in agreement with the approximate analytical solution of the CTRW formalism. We are able to determine the onset of frequency-dependent diffusivity in terms of probabilities of highest energy barriers.     

Effect of Starvation and Shock Loads on the Biodegradation of 4-Chlorophenol in a Discontinuous Moving Bed Biofilm Reactor

The influence of starvation (defined as the period without substrate) and shock loads on the performance of a moving bed sequencing batch reactor degrading 4-chlorophenol (4CP) were investigated. The biomass was acclimated to biodegrade 100 mg/L of 4CP, and the colonization of the packing material was followed. Two starvation periods and two shock loads were studied. The degradation capacity of the suspended and the attached biomass present on the moving bed was also evaluated. The experiments showed that, after the starvation period, the specific degradation rate decreased from 30.5 to 28.5 and 20 mg 4CP/gVSS/h, when starvation periods of 24 and 48 h were applied, respectively. When two concentration peaks of 500 and 1,050 mg/L were applied, a loss of 6% and 8% on the specific degradation rate, respectively, was also observed. The moving bed thus showed great robustness against starvation periods and shock loads. Suspended biomass presented higher specific degradation rates, but attached biomass did not generate a metabolite that is inhibitory when it accumulates.     

Environmental monitoring of phenolic pollutants in water by cloud point extraction prior to micellar electrokinetic chromatography

Many aromatic compounds can be found in the environment as a result of anthropogenic activities and some of them are highly toxic. The need to determine low concentrations of pollutants requires analytical methods with high sensitivity, selectivity, and resolution for application to soil, sediment, water, and other environmental samples. Complex sample preparation involving analyte isolation and enrichment is generally necessary before the final analysis. The present paper outlines a novel, simple, low-cost, and environmentally friendly method for the simultaneous determination of p-nitrophenol (PNP), p-aminophenol (PAP), and hydroquinone (HQ) by micellar electrokinetic capillary chromatography after preconcentration by cloud point extraction. Enrichment factors of 180 to 200 were achieved. The limits of detection of the analytes for the preconcentration of 50-ml sample volume were 0.10 μg L⁻¹ for PNP, 0.20 μg L⁻¹ for PAP, and 0.16 μg L⁻¹ for HQ. The optimized procedure was applied to the determination of phenolic pollutants in natural waters from San Luis, Argentina. Figure Schematic representation of the cloud point extraction process.     

Laser Control of Zeolite Nucleation

Precursor solutions for the synthesis of zeolites are irradiated by means of a Nd‐YAG laser. These solutions are subsequently submitted to a hydrothermal treatment and the results analyzed by X‐ray diffraction and electron microscopy. Laser irradiation promotes the formation of silica nanoparticles that nucleate into zeolite (silicalite‐1), following a hydrothermal treatment. The average crystal size (in the 0.6–3.6 μm range) of the zeolite exponentially decreases as a function of laser irradiation time. In addition, a longer irradiation time results in a narrower crystal size distribution.     

Studies of Ciprofloxacin Encapsulation on Alginate/Pectin Matrixes and Its Relationship with Biodisponibility

Screening of ciprofloxacin (Cip) with selected biopolymers brings about 90% antibiotic interactions with a coacervate composed of alginate/high metoxylated pectin in 2:1 ratio. Fourier transform infrared spectroscopy analysis provides information about the nature of this interaction, revealing ionic and hydrophobic patterns among the molecules. Alginate/high methoxylated pectin gel microspheres developed by ionic gelation encapsulates 46.8?±?5.0% Cip. The gel matrix can release Cip in a sustained manner, releasing 42.7?±?0.2% in 2?h under simulated stomach pH conditions, and 83.3?±?1.1% Cip release in 80?mM phosphate at pH?=?7.40 (intestinal). The increase of sodium chloride from 50 to 200?mM implies a Cip release from 69.0?±?1.5% to 95.1?±?3.6% respectively in 2?h. Scanning electron microscopy revealed the cohesive effect of HM pectin over alginate molecules on the microsphere surface. Those results guarantee all Cip contained in the alginate/HM pectin microspheres could be released in an established kinetic profile along the gastrointestinal tract, avoiding the Cip undesirable side effects during absorption.     

Nearest level spacing statistics in open chaotic systems: generalization of the Wigner surmise

We investigate the nearest level spacing statistics of open chaotic wave systems. To this end we derive the spacing distributions for the three Wigner ensembles in the one-channel case. The theoretical results give a clear physical meaning of the modifications on the spacing distributions produced by the coupling to the environment. Based on the analytical expressions obtained, we then propose general expressions of the spacing distributions for any number of channels, valid from weak to strong coupling. The latter expressions contain one free parameter. The surmise is successfully compared with numerical simulations of non-Hermitian random matrices and with experimental data obtained with a lossy electromagnetic chaotic cavity.