Molecular dynamics of liquid acetone determined by depolarized Rayleigh and low-frequency Raman scattering spectroscopy

Slow to ultrafast dynamics of liquid acetone at variable temperature was investigated by depolarized Rayleigh and low-frequency Raman scattering spectroscopy, in the region 0-200 cm(-1). A detailed analysis was performed on the spectra and corresponding time responses, and a consistent view of the molecular dynamics of this dipolar solvent was obtained. The effects of temperature on the spectra were interpreted, and distinct dynamical processes identified. At very low frequencies, or long time scales, acetone dynamics is characterized by a slow diffusive reorientation obeying the Stokes-Einstein-Debye hydrodynamic theory only in the limit of subslip boundary conditions. An alternative model based on the microviscosity concept proved to be able to reproduce this correlation time and its temperature dependence. A comparative analysis of collective and single-molecule reorientational times, these latter estimated from intramolecular Raman spectra, led to an orientational correlation parameter g(2) of unity, which denotes a statistical disorder of molecular polarizability tensors. A fast local restructuring process is putatively responsible for an additional contribution at subpicosecond time scales often referred to as intermediate response in other molecular liquids. The high frequency portion of the dynamical susceptibility showed the signature of librational intermolecular motions, giving rise to an ultrafast decay of the time correlation function of polarizability anisotropy. The overall approach, which provided valuable information on dynamics, structure and molecular interactions of neat acetone, will be applied to acetone electrolytic solutions.     

Cyanoacetanilides Intermediates in Heterocyclic Synthesis. Part 2: Preparation of Some Hitherto Unknown Ketene Dithioacetal,Benzoazole and Pyridone Derivatives

Ketene dithioacetal 3 , aminopyrazole 5 , tetrazine 7 , benzoazole 9 and pyridone 11 , 12 , 13 and 16 derivatives were prepared from cyanoacetanilide 1 as a starting material.     

Mixed finite element methods for the Signorini problem with friction

In this article, we propose and study different mixed variational methods in order to approximate the Signorini problem with friction using finite elements. The discretized normal and tangential constraints at the contact interface are expressed by using either continuous piecewise linear or piecewise constant Lagrange multipliers in the saddle?point formulation. A priori error estimates are established and several numerical examples corresponding to the different choices of the discretized normal and tangential constraints are carried out. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006     

A finite-element approach in stream-tube method for solving fluid and solid mechanics problems

This paper presents a theoretical formulation in which the stream-tube method (STM) is examined through a variational approach for solving solid strain and fluid flow problems with finite elements. The analysis considers a reference domain, used as computational domain, related to the physical domain by an unknown transformation function to be determined numerically. Mass conservation is automatically verified by STM. The variational approach leads to eliminate the pressure in fluid problems and avoids to set up a mixed displacement–pressure procedure in the case of incompressible solids. Examples are given for fluid flows, applications and comparisons are also provided in the bending problem in elasticity.     

Effect of composition,thickness and temperature on non-linear I–V curves in vanadium phosphate glasses

Summary Glass layers of (V₂O₅)_1−x (P₂O₅) _x were prepared by melting appropriate mixtures of V₂O₅ and P₂O₅ powders. The measurements ofI–V characteristic curves show three regions of conduction, namely high-resistance state, turnover point with zero-differential resistance region (∂V/∂I=0) and differential negative-resistance region. The turnover point is strongly dependent on composition, sample thickness and temperature. It is found that the increase of the ratio of phosphorus/vanadium reduces conductance as well as it raises the field required to produce turnover behaviour. The data in the range up to the turnover point are discussed on the basis of an electrothermal process. Results of the negative-resistance state could be explained in terms of a hopping mechanism.     

Stability of multiobjective NLP problems with fuzzy parameters in the objectives and constraints functions

This paper deals with the stability of multiobjective nonlinear programming problems with fuzzy parameters in the objectives and constraints functions. These fuzzy parameters are characterized by fuzzy numbers. The existing results concerning the qualitative analysis of the notions (solvability set, stability sets of the first kind and of the second kind) in parametric nonlinear programming problems are reformulated to study the stability of multiobjective nonlinear programming problems under the concept of α-pareto optimality. An algorithm for obtaining any subset of the parametric space which has the same corresponding α-pareto optimal solution is also presented. An illustrative example is given to clarify the obtained results.     

Stark broadening of the overlapping 4471.48 Å HeI line in a plasma. II. Nonmarkovian and ion dynamic effects

The inclusion of a frequency-dependent collision operator in the line shape expression is investigated quantitatively for the 4471 Å overlapping HeI line. We compare at several electron densities frequency-independent (markovian) profiles with frequency-dependent (nonmarkovian) profiles taking into account incomplete electron-atom collisions. No significant discrepancies appear in the domain of validity of the impact approximations (|Δω| ? ωp_e), whereas for the far wings important differences may be found. At the extrema (two peaks, one dip) the nonmarkovian intensities prove to be the higher ones. For a modest electron density, the inclusion of ion dynamic shielding introduces more modifications then nonmarkovian effects. In the blue wing, the frequency-dependent profile lies below the frequency-independant profile in accord with the hydrogenic behavior for that part of the line shape in the presence of a large perturber density.     

Determination of the interference between the elements of a central-receiver solar system

Summary This work deals with the problem of determining the shadow and blocking effects between the rectangular heliostats of a central-receiver system for the utilization of solar energy. The type of approach followed is the McFee approach, suitably generalized. Indications are also given regarding the calculation of the density of radiation collected on a receiver assumed to be flat.

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Riassunto Questo lavoro affronta il problema della determinazione degli effetti di shadow e blocking tra eliostati rettangolari di un sistema a ricevitore centrale ai fini dello sfruttamento dell'energia solare. Il tipo di approccio seguíto è quello di McFee, opportunamente generalizzato. Si forniscono anche indicazioni per il calcolo della densità di radiazione raccolta sul ricevitore che qui è considerato piatto.

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Il presente lavoro è oggetto di un contratto di ricerca fra il CRTN, ENEL e l'Istituto di Fisica dell'Università di Milano.     

Acetate- and thiol-capped monodisperse ruthenium nanoparticles: XPS, XAS, and HRTEM studies

Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.