Temperature, pressure, and isotope effects on the structure and properties of liquid water: a lattice approach

We present a lattice model to describe the effect of isotopic replacement, temperature, and pressure changes on the formation of hydrogen bonds in liquid water. The approach builds upon a previously established generalized lattice theory for hydrogen bonded liquids [B. A. Veytsman, J. Phys. Chem. 94, 8499 (1990)], accounts for the binding order of 1/2 in water-water association complexes, and introduces the pressure dependence of the degree of hydrogen bonding (that arises due to differences between the molar volumes of bonded and free water) by considering the number of effective binding sites to be a function of pressure. The predictions are validated using experimental data on the temperature and pressure dependence of the static dielectric constant of liquid water. The model is found to correctly reproduce the experimentally observed decrease of the dielectric constant with increasing temperature without any adjustable parameters and by assuming values for the enthalpy and entropy of hydrogen bond formation as they are determined from the respective experiments. The pressure dependence of the dielectric constant of water is quantitatively predicted up to pressures of 2 kbars and exhibits qualitative agreement at higher pressures. Furthermore, the model suggests a--temperature dependent--decrease of hydrogen bond formation at high pressures. The sensitive dependence of the structure of water on temperature and pressure that is described by the model rationalizes the different solubilization characteristics that have been observed in aqueous systems upon change of temperature and pressure conditions. The simplicity of the presented lattice model might render the approach attractive for designing optimized processing conditions in water-based solutions or the simulation of more complex multicomponent systems.     

Numerical calculation of wall effect and ‘backflow’ on the Stokes force

We give numerical results on the modification of the drag force F_x exerted on a sphere positioned eccentrically and moving at very low Reynolds number, at constant velocity within and along a cylindrical tube. The numerical results computed by Lattice-Boltzmann method or by finite volume formulation are in good agreement with the experimental results obtained by Ambari et al. (J. Fluid Mech. 149 (1984) 235–253). In particular, they confirm the existence of a minimum of the force F_x away from the axis of the cylinder and a sharp increase when the sphere approaches the sidewall. To cite this article: T. Godin et al., C. R. Mecanique 330 (2002) 837–842.     

Observation of diffusion and tunneling recombination of dye-photoinjected electrons in ultrathin TiO2 layers by surface photovoltage transients

Surface photovoltage transients were used to monitor both the short time dynamics (>10 ns) and the spatial distribution of electrons photoinjected in thin (2-20 nm) TiO2 layers from dye molecules adsorbed at the surface. At low temperatures (100-250 K), the dynamics are governed exclusively by spatially dependent tunneling recombination, with a rate that varies with the distance from the surface x as exp(-2x/a), and an initial exponential distribution of photoinjected electrons, n0 exp(-x/b). This model is confirmed by the observation of power law decay in time t(-a/2b) with a ratio a/b = 0.28 +/- 0.04. The stability of cis-di(isothiocyanato)-N-bis(2,2'-bipyridine-4,4'-dicarboxy) ruthenium(II) (N3) dye molecules on TiO2 during treatment in a vacuum at high temperatures was proven. For high temperatures (250-540 K), the thickness dependence of the decays indicates that the dynamics of surface recombination are retarded by the diffusion of electrons toward the interior of the film. The implications for thin layer coating in dye-sensitized solar cells are discussed.     

Stability and electronic properties of Rh-doped ruthenium clusters and their interaction with NH3 molecule

The stability and electronic properties of the Rh-doped ruthenium clusters and their reactivity towards NH₃ molecule have been studied using DFT calculations with the BLYP-D3/SDD level of theory. The results show that the doping of Ru clusters with Rh atom improves the catalytic performances of pure Ru clusters, and the Ru₅Rh and Ru₇Rh clusters are assumed to be less reactive than their neighbours. The interaction of NH₃ with clusters exhibits that the Ru atoms are preferred adsorption sites for the NH₃ molecule, and the adsorption takes place between the Ru atom of clusters and the N atom of NH₃ molecule. The adsorption energies of NH₃ on Ru_nRh clusters are in the range of ?101.5 to ?218.4?kJ?mol^?1, suggesting a strong adsorption between both species. Upon adsorption process, the electronic properties of the Ru_nRh clusters were substantially changed. The variation of E_g (ΔE_g) for the Ru_nRh (n?≥?7) clusters is very important (ΔE_g?≥?55%), suggesting that these clusters are very sensitive to the NH₃ molecule. Hence, these clusters can be employed as nanosensors for the detection of the NH₃ gas.     

The Higgs sector of supersymmetric theories and the implications for high-energy colliders

One of the main motivations for low-energy supersymmetric theories is their ability to address the hierarchy and naturalness problems in the Higgs sector of the standard model. In these theories, at least two doublets of scalar fields are required to break the electroweak symmetry and to generate the masses of the elementary particles, resulting in a rather rich Higgs spectrum. The search for the Higgs bosons of supersymmetry and the determination of their basic properties is one of the major goals of high-energy colliders and, in particular, the LHC, which will soon start operation. We review the salient features of the Higgs sector of the minimal supersymmetric standard model and of some of its extensions and summarize the prospects for probing them at the LHC and at the future ILC. In memoriam of Julius Wess, 1934–2007.     

The modular class of a regular Poisson manifold and the Reeb class of its symplectic foliation

We show that, for any regular Poisson manifold, there is an injective natural linear map from the first leafwise cohomology space into the first Poisson cohomology space which maps the Reeb class of the symplectic foliation to the modular class of the Poisson manifold. A Riemannian interpretation of the Reeb class will give some geometric criteria which enables one to tell whether the modular class vanishes or not. It also enables one to construct examples of unimodular Poisson manifolds and others which are not unimodular. Finally, we prove that the first leafwise cohomology space is an invariant of Morita equivalence. To cite this article: A. Abouqateb, M. Boucetta, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Efficient UV-light photocatalytic activity of TiO2@Phosphogypsum composite synthesized by sol–gel method

Optical and Quantum Electronics - All optical multiband radio transceiver is designed using Polarization Modulators. Polarization Modulators have been gaining popularity in recent times as the...     

Reactivity of CO2 traps in aerogel–wollastonite composites

Synthetic wollastonite has been used as the active phase embedded into two different silica aerogel composites. These composites are different in respect of the route used for the synthesis of the wollastonite powder. Texture and composition of both types of composite have been characterized. In addition, several factors (pH, reaction time, CO₂ saturation, etc.) that could help to optimize the carbonation process at room temperature and pressure have been studied. Under the same conditions, both composites confirm previous results showing efficiencies as CO₂ sequesters between 80% and 100% in only 15 min of gas flow. The textural characteristics of the aerogel, together with the grain size of the synthetic wollastonite powder, not only increase the speed of the reaction, but also inhibit the appearance of a passivating layer on the surface of the wollastonite grains attacked by the CO₂. This is an outstanding feature as it insists on a cutting-edge challenge of the CO₂ research: its economical availability.