Optical properties of silver colloidal centers in KCl crystals

The Ag colloidal centers in additively colored KCl: Ag crystals have been studied by optical and electron microscope methods. The transmission electron microscope studies reveal that the colloidal particles are spherical in shape and have a size distribution which can be described by the skewed zeroth order logarithmic distribution (ZOLD) function. The band shape of the experimental absorption spectra of colloidal particles agrees well with that calculated on the basis of Mie theory, if the optical constants are suitably modified and if the particle size distribution is taken into account. If the particle size is so small that the size distribution cannot be measured by electron microscope the optical absorption bands can be used to determine the size distribution parameters provided the distribution is well described by ZOLD, which in turn is used to calculate theoretical extinction bands.     

Generation of higher harmonics in laser plasma formed on the surface of a silver target

The results of investigation of the higher harmonics (from the 21st to the 61st order) of radiation of a femtosecond laser (793 nm, 48 fs) that are generated in silver plasma are presented. The changes in the shape and spectra of harmonics for different chirps of the laser radiation are studied. It is found that the wavelengths of harmonics generated in the region of the plateaulike distribution of the converted radiation intensity can be tuned. It is shown that the conditions of phase matching between harmonics and laser radiation are different for different modulations of the femtosecond pulse spectrum. The tuning range of the spectrum of the converted radiation in the region of lower harmonics, which lie in the beginning region of the plateau, is shown to amount to 0.8 nm.     

Cu(II) ion based 1D coordination polymer: Its thermal,fluorescence properties,Hirshfeld surface analysis and theoretical calculations

In this investigation, the reaction of [Cu(2,2′-bpy)(H₂O)₄][ClO₄]₂ with thiosemicarbazide (tsc) yielded [Cu(2,2′-bpy)(NCS)₂]_n frameworks, which has crystallized in noncentrosymmetric space group (Cc). The complex has been characterized by elemental analyses, FT-IR spectrum, powder X-ray diffraction analysis and single-crystal diffraction analysis. This complex is 1D polymer with high thermal stability and showing positive cotton effect. These results have provided some interesting insights into its nonlinear optical applications. Solid state fluorescence spectrum shows broad photoluminescence emission bands, which are assigned as the bands of intra-ligand charge transfer and MLCT (metal to ligand charge transfer) transitions. During investigation of various intermolecular interactions, both single crystal X-ray diffraction and Hirshfeld surface analysis give comparable results.     

EPR and optical absorption study of Cr-doped tetramethyl ammonium cadmium chloride single crystals

EPR study of Cr³⁺-doped tetramethyl cadmium chloride (TMCC) single crystals is carried out at room temperature. The crystal field and spin-Hamiltonian parameters are evaluated from the resonance line positions of different lines observed in the EPR spectra. The g and D parameter values are found to be g=1.9741±0.0002 and D=553±2×10⁻⁴ cm⁻¹, respectively. EPR data indicate that the site symmetry of Cr³⁺ ion in the crystal is distorted octahedron. Cr³⁺ ions enter the lattice substitutionally replacing Cd²⁺ sites and bind to the neighboring extra Cd vacancies necessary for charge compensation. The optical absorption spectra are measured in 195–925 nm wavelength range at room temperature. From optical study the energy values of different orbital levels are estimated. Further, the bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained to be B=722, C=2845, Dq=2043 cm⁻¹, h=1.015 and k=0.21.     

Dynamic correlation effects on drag resistivity of a symmetric electron–electron bilayer

We have studied the effect of dynamic electron correlations on Coulomb drag in a low density symmetric electron–electron bilayer. The drag resistivity is calculated considering the contribution from direct e–e scattering processes using the semi-classical Boltzmann approach, with the effective inter-layer interaction W₁₂(q, ω; T) determined within the ?wierkowski, Szyman?ki, and Gortel model, generalized to include the dynamics of electron correlations through the frequency-dependent intra- and inter-layer local-field correction (LFC) factors. In turn, the LFCs are obtained by extending the quantum Singwi, Tosi, Land, and Sjölander (qSTLS) approach to finite temperatures. At low temperatures (T ? 2 K), the calculated drag resistivity is found to agree nicely with the measurements by Kellogg et al., while it is somewhat overestimated at higher temperatures. The overestimation is seen to increase with decreasing density of electrons. However, there is found to be a marked improvement over the predictions of the conventional (i.e., static) STLS and random-phase approximation (RPA). It turns out that the inclusion of exchange-correlations in the RPA causes a red-shift in the bilayer plasmons which leads to an enhancement of drag resistivity. Our study demonstrates clearly the importance of including the dynamical nature of correlations to have a reasonable account of measured drag resistivity.     

Reproducible cavitation activity in water-particle suspensions

The study of cavitation inception in liquids rarely yields reproducible data, unless special control is taken on the cleanliness of the experimental environment. In this paper, an experimental technique is demonstrated which allows repeatable measurements of cavitation activity in liquid-particle suspensions. In addition, the method is noninvasive: cavitation bubbles are generated using a shock-wave generator, and they are photographed using a digital camera. The cavitation activity is obtained after suitable image processing steps. From these measurements, the importance of the particle's surface structure and its chemical composition is revealed, with polystyrene and polyamide particles generating the highest yields. Further findings are that cavitation nuclei become depleted with an increasing number of experiments, and the existence of nuclei with varying negative pressure thresholds. Finally, a decrease of the cavitation yield is achieved by prepressurization of the suspension-indicating that the cavitation nuclei are gaseous.     

Influence of electric field on the hydrogen bond network of methanol

The understanding of the structure of hydrogen (H) bonding liquids in electric (E) fields is important in the context of several areas of research, such as electrochemistry, surface science, and thermodynamics of electrolyte solutions. We had earlier presented a general thermodynamic framework for this purpose, and had shown that the application of E field enhances H-bond interactions among water molecules. The present investigation with methanol suggests a different result-the H-bond structure, as indicated by the average number of H bonds per molecule, goes through a maxima with increasing field strength. This result is explained based on the symmetry in the location of the H-bonding sites in the two types of molecules.     

Fréchet Embeddings of Negative Type Metrics

We show that every n-point metric of negative type (in particular, every n-point subset of L ₁) admits a Fréchet embedding into Euclidean space with distortion , a result which is tight up to the O(log log n) factor, even for Euclidean metrics. This strengthens our recent work on the Euclidean distortion of metrics of negative into Euclidean space. S. Arora supported by David and Lucile Packard Fellowship and NSF grant CCR-0205594. J.R. Lee supported by NSF grant CCR-0121555, NSF 0514993, NSF 0528414 and an NSF Graduate Research Fellowship.     

A nonparametric test for a two-sample scale problem based on subsample medians

A nonparametric test for the two-sample scale problem is proposed by considering the subsample medians of three observations. The proposed statistic has the advantage of not requiring the two distribution functions to have a common median, but rather requiring them to have any common quantile of order α,0≤α≤1 (not necessarily 1/2), which is assumed to be known. Pitman efficiency considerations indicate that the proposed test performs well relative to tests already existing in the literature for heavy tailed distributions.