Statistical mechanics of hydrated electron recombination in liquid and supercritical water

The photochemical yield of hydrated electrons as a function of temperature in liquid and supercritical water is treated in terms of energy fluctuations of the medium. The geminate pair, consisting of a positive ion and a hydrated electron, is regarded as a H-like atom embedded in a completely relaxed dielectric continuum. If the local medium energy is larger than the ionization energy of this atom, the electron escapes its geminate partner. By making use of the classical theory of energy fluctuations, escape probability is described by a simple explicit function, the variable of which is a combination of temperature, relative permittivity, and specific heat. First our earlier calculations on the recombination of solvated electrons, produced by ionizing radiation in a number of polar liquids, are improved and then the theory is compared with the experimental results on temperature dependent electron survival by Kratz et al. [S. Kratz, J. Torres-Alcan, J. Urbanek, J. Lindner, and P. Vo?hringer, Phys. Chem. Chem. Phys. 12, 12169 (2010)]. Two adjustable parameters are needed to achieve reasonable quantitative agreement.     

Ab initio characterization of the Ne-I2 van der Waals complex: intermolecular potentials and vibrational bound states

A theoretical study of the potential energy surface and bound states is performed for the ground state of the NeI(2) van der Waals (vdW) complex. The three-dimensional interaction energies are obtained from ab initio coupled-cluster, coupled-cluster single double (triple)/complete basis set, calculations using large basis sets, of quadruple- through quintuple-zeta quality, in conjunction with relativistic effective core potentials for the heavy iodine atoms. For the analytical representation of the surface two different schemes, based on fitting and interpolation surface generation techniques, are employed. The surface shows a double-minimum topology for linear and T-shaped configurations. Full variational quantum mechanical calculations are carried out using the model surfaces, and the vibrationally averaged structures and energetics for the NeI(2) isomers are determined. The accuracy of the potential energy surfaces is validated by a comparison between the present results and the corresponding experimental data available. In lieu of more experimental measurements, we also report our results/predictions on higher bound vibrational vdW levels, and the influence of the employed surface on them is discussed.     

Computational study of the interaction of indole-like molecules with water and hydrogen sulfide

The characteristics of the interaction between water and hydrogen sulfide with indole and a series of analogs obtained by substituting the NH group of indole by different heteroatoms have been studied by means of ab initio calculations. In all cases, minima were found corresponding to structures where water and hydrogen sulfide interact by means of X-H···π contacts. The interaction energies for all these π complexes are quite similar, spanning from -13.5 to -18.8 kJ/mol, and exhibiting the stability sequence NH > CH(2) ≈ PH > Se ≈ S > O, for both water and hydrogen sulfide. Though interaction energies are similar, hydrogen sulfide complexes are slightly favored over their water counterparts when interacting with the π cloud. σ-Type complexes were also considered for the systems studied, but only in the case of water complexes this kind of complexes is relevant. Only for complexes formed by water and indole, a significantly more stable σ-type complex was found with an interaction energy amounting to -23.6 kJ/mol. Oxygen and phosphorous derivatives also form σ-type complexes of similar stability as that observed for π ones. Despite the similar interaction energies exhibited by complexes with water and hydrogen sulfide, the nature of the interaction is very different. For π complexes with water the main contributions to the interaction energy are electrostatic and dispersive contributing with similar amounts, though slightly more from electrostatics. On the contrary, in hydrogen sulfide complexes dispersion is by far the main stabilizing contribution. For the σ-type complexes, the interaction is clearly dominated by the electrostatic contribution, especially in the indole-water complex.     

Hydrophobicity of ionisable compounds studied by countercurrent chromatography

Countercurrent chromatography (CCC) is a liquid chromatography technique in which the stationary phase is also a liquid. The main chemical process involved in solute separation is partitioning between the two immiscible liquid phases: the mobile phase and the support-free liquid stationary phase. The octanol-water partition coefficients (P(o/w)) is the accepted parameter measuring the hydrophobicity of molecules. It is considered to estimate active principle partitioning over a biomembrane. It was related to the substance biological activity. CCC is able to work with an octanol stationary phase and an aqueous mobile phase. In this configuration, CCC is a useful and easy alternative to measure directly the P(o/w) of the molecules compared to other methods including the classical and tedious shake-flask method. Three ketones are used as model compounds to illustrate the CCC protocol of P(o/w) measurement. The focus of this work is put on ionisable molecules whose apparent P(o/w) is completely changed by ionization. β-Blockers, diuretics and sulfonamides are compound classes that were studied. Some of the experimentally determined P(o/w) coefficients of the molecular forms disagreed with calculated and experimental values available in the literature. The P(o/w) coefficients of the ionic forms and the acidity constants were also calculated using a theoretical model. Relationships between biological properties and hydrophobicity are also discussed.     

Low-level laser therapy improves skeletal muscle performance, decreases skeletal muscle damage and modulates mRNA expression of COX-1 and COX-2 in a dose-dependent manner

We tested if modulation in mRNA expression of cyclooxygenase isoforms (COX-1 and COX-2) can be related to protective effects of phototherapy in skeletal muscle. Thirty male Wistar rats were divided into five groups receiving either one of four laser doses (0.1, 0.3, 1.0 and 3.0 J) or a no-treatment control group. Laser irradiation (904 nm, 15 mW average power) was performed immediately before the first contraction for treated groups. Electrical stimulation was used to induce six tetanic tibial anterior muscle contractions. Immediately after sixth contraction, blood samples were collected to evaluate creatine kinase activity and muscles were dissected and frozen in liquid nitrogen to evaluate mRNA expression of COX-1 and COX-2. The 1.0 and 3.0 J groups showed significant enhancement (P < 0.01) in total work performed in six tetanic contractions compared with control group. All laser groups, except the 3.0 J group, presented significantly lower post-exercise CK activity than control group. Additionally, 1.0 J group showed increased COX-1 and decreased COX-2 mRNA expression compared with control group and 0.1, 0.3 and 3.0 J laser groups (P < 0.01). We conclude that pre-exercise infrared laser irradiation with dose of 1.0 J enhances skeletal muscle performance and decreases post-exercise skeletal muscle damage and inflammation.     

Estudio de la estabilidad y dispersión del problema de propagación de ondas sísmicas en 2-D utilizando el método de diferencias finitas generalizadas

This paper shows the solution to the problem of seismic wave propagation in 2-D using generalized finite difference (GFD) explicit schemes. Regular and irregular meshes can be used with this method.As we are using an explicit method, it is necessary to obtain the stability condition by using the von Neumann analysis. We also obtained the star dispersion formulas for the phase velocities for the P and S waves, as well as the ones for the group velocities.As the control over the irregularity in the mesh is very important in the application of this method, we have defined an index of irregularity for the star (IIS) and another for the cloud (IIC), analyzing its relationship with the dispersion and time step used in the calculations.     

OPTIMAL HARVESTING TIME OF FARMED AQUATIC POPULATIONS WITH NONLINEAR SIZE‐HETEROGENEOUS GROWTH

Abstract This paper examines the question of optimal harvesting time in a size‐heterogeneous farmed aquatic population, using a model reflecting the effect of population density on both overall mortality rate and individual growth. This analysis enables an optimal harvesting rule to be deduced. The results obtained are applied to shrimp culture in recirculation systems in Mexico. Numerical solutions are derived for different production scenarios. Assuming identical culture conditions, results are also obtained under the hypothesis of homogeneous population growth, the view traditionally taken in the relevant economic literature. The optimal harvesting times calculated tend to decrease with higher densities, although this rule fails under the size‐heterogeneous population model. In general, optimal harvesting times are overestimated when size‐homogeneity in the culture is assumed. Our analysis reveals that management predictions are significantly mistaken if the size‐heterogeneity phenomenon is not taken into account.     

Spectral deformation and Bäcklund transformation of constrained Willmore surfaces

The class of constrained Willmore surfaces in space-forms forms a Möbius invariant class of surfaces with strong links to the theory of integrable systems. This paper is dedicated to an overview on the topic. We define a spectral deformation, by the action of a loop of flat metric connections, and Bäcklund transformations, by applying a dressing action. We establish a permutability between spectral deformation and Bäcklund transformation and verify that all these transformations corresponding to the zero multiplier preserve the class of Willmore surfaces. We show that, for special choices of parameters, both spectral deformation and Bäcklund transformation preserve the class of constrained Willmore surfaces admitting a conserved quantity, and, in particular, the class of constant mean curvature surfaces in 3-dimensional space-forms.     

Measuring the spectrum of colored noise by dynamical decoupling

Decoherence is one of the most important obstacles that must be overcome in quantum information processing. It depends on the qubit-environment coupling strength, but also on the spectral composition of the noise generated by the environment. If the spectral density is known, fighting the effect of decoherence can be made more effective. Applying sequences of inversion pulses to the qubit system, we developed a method for dynamical decoupling noise spectroscopy. We generate effective filter functions that probe the environmental spectral density without requiring assumptions about its shape. Comparing different pulse sequences, we recover the complete spectral density function and distinguish different contributions to the overall decoherence.     

The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters

In the last decade, chemists have dedicated many efforts to investigate the coordination chemistry of N-heterocyclic carbenes (NHCs). Although most of that research activity has been devoted to mononuclear complexes, transition-metal carbonyl clusters have not escaped from these investigations. This critical review, which is focussed on the reactivity of NHCs (or their precursors) with transition-metal carbonyl clusters (mostly are of ruthenium and osmium) and on the transformations underwent by the NHC-containing species initially formed in those reactions, shows that the polynuclear character of these metallic compounds or, more precisely, the close proximity of one or more metal atoms to that which is or can be attached to the NHC ligand, is responsible for reactivity patterns that have no parallel in the NHC chemistry of mononuclear complexes (74 references).