Optical behaviour of VTE treated near stoichiometric LiNbO3 crystals

Near stoichiometric LiNbO₃ crystal wafers of thickness up to 2 mm were prepared by vapour transport equilibration technique (VTE) at various process temperatures. Crystals were characterised by measurement of the UV absorption edge, refractive index, second harmonic generation (SHG) efficiency, and conoscopy pattern analysis. The comparison of VTE treated crystals show that the blue shift in cut off wavelength occurred with the increasing process temperature (i.e. increasing Li/Nb ratio). The refractive indices were found decreasing with increasing process temperature of VTE samples. The SHG efficiency increases in the range of 1.98-2.3 times for the VTE processed samples with respected to congruent crystals. Conoscopy pattern reveals the optical homogeneity of the VTE treated crystal.     

A simple approach to intervalley transfer in electric field

Intervalley population transfer as a function of electric field has been investigated in a simple way assuming a Davydov type distribution. It has been shown that the current-voltage characteristics contain a region of negative differential conductivity and the threshold field is 3·5 kV/cm.The authors would like to thank Prof. P. C. Bhattacharya for his interest in this work. One of the authors (R.K.K) wishes to express his appreciation to the CNET, for his appointment as a Visiting Scientist, and to thank Dr. Palmier for helpful discussions.     

The effect of gamma-ray irradiation on the sorptive properties of hydrous SiO2 and ZrO2

The sorption capacities of hydrous SiO₂ and ZrO₂ for the Zn(ammine) ion have been observed to increase on irradiation with γ-rays, by ca. 4.1 and 3.8%, respectively. The rates of sorption increase differently in the irradiated exchangers, depending upon their characteristic natures; e. g. when the external concentration of the Zn(ammine) solution is 0.2M, the increase in the F value due to irradiation is more striking in the case of SiO₂ than for ZrO₂. On the other hand, at a lower external concentration of the Zn(ammine) solution (0.01M), the increase in the F value, particularly during the first five minutes, is more significant for ZrO₂.     

High spin isomer in151Sm

An investigation of the high spin isomer in¹⁵¹Sm was performed via the¹⁵⁰Nd(α, 3nγ) reaction at a projectile energy of 35 MeV. A newγ-transition, 693.6 keV was identified having an exponential delayed component. The transition feeds the 1912 keV state of the negative parity band built on theh _11/2 state. This transition was also observed in coincidence withγ-rays belonging to¹⁵¹Sm in theγ-γ coincidence experiment atE _α =37 MeV. A new isomeric state having energyE _x =2605.8 keV and half lifeT _1/2=23.1±3.5 ns is proposed.     

Effect of solvent upon CH...O hydrogen bonds with implications for protein folding

The series of CH...O bonds formed between CF(n)H(4-n) (n = 0-3) and water are studied by quantum calculations under vacuum and in various solvents, including aqueous environment. The results are compared with the OH...O bond of the water dimer in the same solvents. Increasing polarity of the solvent leads in all cases to a lessening of the H-bond interaction energy, in a uniform fashion such that the CH...O bonds all remain weaker than OH...O in any solvent. These H-bond weakenings are coupled to a shortening of the inter-subunit separation. The contraction of the covalent CH bond to the bridging proton is reduced as the solvent becomes more polar, and the blue shift of its stretching vibration is likewise diminished. A process is considered that simulates protein folding by starting from a pair of noninteracting subunits in aqueous solvent and then goes to a H-bonded pair within the confines of a protein environment. This process is found to be energetically more favorable for some of the CH...O H-bonds than for the nominally stronger conventional OH...O H-bond. This finding suggests that CH...O bonds can make important energetic contributions to protein folding, on par with those made by traditional H-bonds.     

Dislocation structure of coarse-plate perlite in carbon steel after cold and high-temperature strain

It is demonstrated that during cold plastic deformation of coarse-plate perlite in carbon steel, planar cementite defects play the key role in deformation transfer through interphase boundaries and promote dissolution of cementite plates. It is first established that the austenite substructure formed upon high-temperature deformation is inherited by cementite and ferrite components of perlite during the subsequent phase transformation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 18–27, August, 2004.     

Stoichiometric and catalytic reductive aldol cyclizations of alkynediones induced by Stryker's reagent

Conjugate reduction of alkynones by stoichiometric [(Ph(3)P)CuH](6) or catalytic [(Ph(3)P)CuH](6) and polymethyl-hydrosiloxane proceeds to cyclization by an aldol reaction with tethered ketones to generate [small beta]-hydroxyenones with good diastereoselectivity.     

Microbial desulfurization of different coals

Coal is the most important nonrenewable energy source of fossil origin. It is also the most common fuel in thermal power plants. However, during coal incineration in power plants, high sulfur content of coal poses serious environmental problems owing to sulfur dioxide emission. We studied the application of microbial methods for removal of sulfur from three types of high sulfur coals—two samples collected from Assam and Rajasthan in India and one from Libiaz, Poland. These coal samples were desulfurized using indigenous Acidithiobacillus sp. After investigation of the effect of various parameters, the conditions optimized for the maximum removal of total sulfur (91.87% for lignite, 63.13% for Polish coal, and only 9.44% for Assam coal) were as follows: initial pH of 1.5 (2.5 in the case of Assam coal), particle size of 45 μ, pulp density of 2% (w/v), incubation period of 30 d at −35°C in presence of 44.2 g/L of ferrous sulfate in the media with shaking at 140 rpm. Poor removal of sulfur in the case of Assam coal was owing to extensive precipitation of jarosites. In addition, the sulfur in Assam coal is mostly found in organic form, which is difficult to remove with Acidithiobacillus sp. The removal of sulfur from the three coal samples was demonstrated with photomicrographic studies.     

Material distribution across the interface of random and ordered island arrays

We grow single and twofold stacked island layers on patterned substrates and investigate the material distribution in and around the patterned area. For both layers a pronounced material depletion region occurs outside the pattern. The material gradients across the planar-patterned interface are symmetric in the first, but highly asymmetric in the second layer. We can describe these phenomena by simulations that take into account the surface curvature for the first and a strain-field modulated surface for the second layer.     

Plasma ion evolution in the wake of a high-intensity ultrashort laser pulse

Experimental investigations of the late-time ion structures formed in the wake of an ultrashort, intense laser pulse propagating in a tenuous plasma have been performed using the proton imaging technique. The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel. On the basis of extensive particle in cell simulations of the plasma evolution in the wake of the pulse, we interpret this pattern as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield.