A comparison of single shot nanosecond and femtosecond polarization-resolved laser-induced breakdown spectroscopy of Al

Aluminum samples have been analyzed by femtosecond polarization-resolved laser-induced breakdown spectroscopy (fs-PRLIBS). We compare the obtained spectra with those obtained from nanosecond PRLIBS (ns-PRLIBS). The main specific features of fs-PRLIBS are that a lower plasma temperature leads to a low level of continuum and no species are detected from the ambient gas. Furthermore, signals obtained by fs-PRLIBS show a higher stability than those of ns-PRLIBS. However, more elements are detected in the ns-PRLIBS spectra.     

The attenuation of ultrasound in water-alcohol mixtures by the method of streaming

Experimental results on the attenuation of ultrasound in polar-polar liquid, that is, water-alcohol mixtures, by the method of streaming are presented. A comparative study of the results obtained by this method and those obtained by other methods has been made. Results of the present investigations agree well with those obtained by other workers. From the observed attenuation data, the bulk viscosity coefficients ‘b’ of the mixtures have been determined using Eckart's formalism on streaming.Satisfactory results could be obtained in the cases of water/methyl alcohol, and water/ethyl alcohol mixtures at all percentage compositions of mixtures but in the case of water/n-propyl alcohol satisfactory results could not be obtained at 5% to 40% mixture compositions. This observation bears the similarity with the cases of pure non-polar liquids. Here the observed results have been attempted to be explained, at least on the basis of relevant physical principles, in terms of dipole moment and dielectric constant.     

LEED analysis of solid phase epitaxy of Si

The LEED technique has been used to study the solid phase epitaxial growth of silicon. The crystalline quality of the film surface, the growth rate and the activation energy have been determined. A comparison of these results with those obtained by other authors has been made.     

Sonochemical hydrosilylation of 2-substituted cyclohexanones in the presence of Wilkinson complex

The sonochemical hydrosilylation of alkyl substituted cyclohexanones catalyzed by Rh (PPh3)3Cl is described. The application of ultrasonic irradiation during the reaction highly enhances the reaction rates and produces higher yields than those obtained in silent reactions. The stereoselectivity of the reaction has not been changed, the isomeric distribution, i.e. the cis/trans ratio of the 2-substituted cyclohexanols formed, is very close to those obtained in conventional stirred reactions.     

Flutter of a buckled plate as an example of chaotic motion of a deterministic autonomous system

For aeroelasticity of plates and shells, the equations of motion are well established. Results obtained by numerical time integration have been compared to those obtained by topological theories of dynamics and also from experiment. All of these suggest that chaotic self-excited oscillations may occur for this deterministic system.     

A uniform asymptotic integral representation for the fourth moment of the field of a wave propagating in a statistically homogeneous medium

In this paper, a uniform integral representation has been obtained for the fourth moment of the field of a wave propagating in a medium with random large-scale irregularities. The solution to the equation was obtained using a method of integral transformations and Maslov's complex WKB method. The representation obtained differs in its form from those reported thus far and in particular from those given by the method of two-scale expansions and the interference integral method. First, the paper considers the case of a plane wave incident on a layer with irregularities, followed by a treatment of the general case of an arbitrary source.     

Molecular relaxation behaviour of mixtures of some polar non-associative liquids

Molecular relaxation studies have been made on rigid polar solutes dibenzofuran and s-trioxane and their mixtures with benzophenone, ortho- and meta-dichlorobenzenes in the microwave region over a range of temperatures in dilute benzene solutions. The relaxation times and the thermodynamic parameters for the activated state have been determined using the measured dielectric data. The results obtained have been discussed in terms of the molecular motion of the system and are consistent with those of other rigid molecules studied previously. The results are also compared with the computed values obtained by employing a relation proposed by us earlier.     

Influence of molecular weight distribution of linear polymers on stress relaxation after steady flow

Stress relaxation after steady flow has been measured with a Weissenberg rheogoniometer for some samples of polystyrene and high-density polyethylene; the same samples have been characterized by column fractionation, gel permeation chromatography, and osmometry.

A method suggested by Menefee and Peticolas has been used to obtain the molecular weight distribution from relaxation data, and the results have been compared with those obtained through the solution measurements. The distributions obtained by the two methods, as represented by the cumulative Z distribution versus the logarithm of molecular weight, are very similar in shape; but, in the case of polyethylenes, the distributions obtained by stress relaxation are found shifted by a factor of 2 toward high molecular weights.     

激光等离子体的单频及双频加热

本文在导出激光等离子体电子、离子耦合方程的基础上求得了单频加热无穷行列特征矩阵的准确解;又求得了在双频加热情况下各种不稳振荡的阈值与增率,并与单频加热作了比较。     

Two photon ionization of alkali atoms

Two photon ionization cross-sections of the alkali atoms have been calculated by using Hartree-Fock-Slater wavefunctions and the results are compared with those obtained by Bebb using quantum defect method.     

Static,anharmonic and phonon properties of ND4I

A detailed investigation of the phonon dispersion and static and anharmonic properties has been carried out for ND₄I using an extended three-body force shell model (ETSM) developed by Singh and Chandra. The ETSM results for phonon dispersion show better agreement with the experimental data than those obtained from the deformation dipole and rigid shell models. Calculated values have also been obtained for some other properties.     

Small Angle X-Ray Scattering of Hematite Aggregates

Small angle X-ray scattering has been utilised to study the structure of hematite aggregates. The small angle X-ray scattering (SAXS) spectra obtained provided insight into structure of the hematite aggregates and the size of the primary particles. The structural analysis results obtained by SAXS are consistent with previous results obtained from static light scattering studies. Both techniques indicate that the mass fractal dimensions of hematite aggregates are markedly higher than those obtained for other particle systems.     

Magnetic properties of ferromagnetic VFe alloys near the critical concentration for ferromagnetism

Magnetic measurements on a series of FeV alloys in the composition range 29–35 at .% Fe have been interpreted in terms of a local environment model. Values for the moment and density of magnetic clusters have been determined. Good agreement is obtained between values obtained from Curie constants, and those estimated from the critical coefficients. The results may be understood in terms of a random distribution of solute atoms.     

Computer simulation study of the statistics of self-avoiding-walks on a dilute lattice

A computer simulation study of the statistics of linear polymers in a random medium, described by self-avoiding-walks (SAW) on a randomly (bond) dilute square lattice has been made. The “phase diagram”, giving the critical value of the average connective constant (average inverse fugacity associated with a monomer in an infinite polymer) as a function of the bond concentration, has been obtained enumerating exactly (and extrapolating) the number of (finite step) SAWs on randomly dilute (Monte Carlo sample) lattices. The “phase diagram”, so obtained, has been compared with those obtained using the Cayley tree approximation and the real space renormalization group technique.     

Characterization of mechanochemically synthesized imidazolates of Ag, Zn, Cd, and Hg: Solid state reactivity of nd cations

Silver, zinc, cadmium, and mercury imidazolates have been synthesized mechanochemically by milling imidazole and the metal oxides in an agate mortar. The reaction products were characterized by FTIR and XRPD techniques. The results obtained for the mechanochemical imidazolates have been compared with those obtained by precipitation reported in the literature. The mechanochemical Ag imidazolate has the same orthorhombic crystal structure as the precipitated one. The mechanochemical Zn imidazolate has a tetragonal structure with similar crystal parameters to those of Zn(Imz)₂H₂O, but no water molecules are present in the structure. This new anhydrous form is a polymorph of the one obtained by precipitation. The mechanochemical Cd imidazolate has a monoclinic structure which is the polymorph of the precipited orthorombic form. The mechanochemical Hg imidazolate presents a hexagonal structure which is a polymorph of the orthorombic structure obtained by precipitation. The influence of the nd¹⁰ electronic configuration of the cations on the mechanochemical reaction is discussed.     

Development of an analytical potential to include excited configurations

Excited configurations are very important in dense plasma physics. In this work we propose a new analytical potential for excited configurations obtained from another one for ground configuration. With this potential several atomic magnitudes have been calculated for ions in excited configurations analyzing what kind of excited configurations introduce more influences in those magnitudes. Using this potential, atomic data generated are satisfactorily compared with those obtained using other analytical potential using sophisticated self-consistent codes, and with others available in the bibliography.     

General electrical transport properties of polycrystalline multi-layered metallic thin films

We have derived, following the recent theoretical calculation of the electrical conductivity of multi-layered metallic thin films, a general solution of the electrical conductivity for those films with grain structures, since those structures give important contributions to the electrical transport properties of polycrystalline thin film. The temperature coefficients of resistivity have also been obtained.     

High-frequency EPR applications of open nonradiative resonators

A new class of open single-mode cavities, the nonradiative (NR) resonators, has recently been proposed in order to overcome the limitations of standard cylindrical cavities and Fabry-Perot resonators at millimeter wavelengths. This paper presents the first applications of a NR resonator in W-band pulsed electron paramagnetic resonance spectroscopy. It consists of a cylindrical cavity having a lateral aperture that represents about 35% of its total height. Electron-spin-echo measurements performed on different samples show that the signal-to-noise ratio and the optimal pulse length obtained with the proposed device are comparable to those obtained with the closed cavity used in the commercial W-band spectrometer, at both cryogenic and room temperature. Similar results have been obtained for paramagnetic species optically activated by means of an optical fiber inserted in the aperture of the resonator. The insertion losses estimated for the probe employed with the NR resonator are higher than those of the commercial probe, hence, demonstrating that the proposed cavity holds the promise of improved resonator performance.     

Protonation rate constants of proline

The rate constants for protonation reactions of proline positive ion and zwitterion have been measured using a modulated temperature chemical relaxation method. The results are contrasted with those obtained for amino acids.     

Polarization effects on the line-strength calculations of Er3+-doped LiNbO3

The polarized optical absorption of Er³⁺-doped LiNbO₃ has been obtained and analyzed within the framework of the Judd-Ofelt theory including polarization dependences. These results are compared with those obtained under unpolarized conditions. Fluorescence lifetimes for different Er³⁺ concentrations have also been measured in the temperature range 10–300 K.