Preconcentration of rare earths in geological materials with ascorbic acid for their neutron activation analysis

The potential use of ascorbic acid as a complexing reagent in the separation and preconcentration of rare earth elements (REE) in geological materials in a suitable solid matrix has been demonstrated. Traces of REE from some USGS standard rock samples, viz., GSP-1, G-2, AGV-1 and PCC-1, have been separated after acid dissolution in two ways: (1) by ion exchange chromatography on Dowex 50×8 column and Na-ascorbate as eluent and (2) by direct complexation with ascorbic acid under specific experimental conditions. The separated REE were coprecipitated with the non isotopic diluent, calcium fluoride, before neutron activation analysis. Radiometric determinations showed that the overall recovery of REE in both cases was practically quantitative.     

Kinetics of the oxidation of sulphite by tetrachloroaurate(III)

Summary The reaction between sulphite and gold(III) in hydrochloric acid medium has been studied; an initial complex is formed prior to electron transfer. The reaction rate is inversely proportional to the hydrogen ion concentration and the reaction appears to proceed through the intermediate formation of a free radical which reacts with gold(III) to give the products. Evidence for the formation of dithionate together with sulphate is presented.     

A method of tunable high repetition-rate picosecond optical pulse generation using injection locking of laser diodes

A method of tunable, high repetition-rate optical pulse generation by using optical injection locking of semiconductor lasers has been described in this paper. This method utilizes the superposition of five coherent optical carriers obtained from the spectrum of optical phase modulation, which results in a sharp optical pulse. Theoretical calculations indicate that a pulse width of 1 ps and a repetition rate of 200 GHz can be achieved for a modulator drive frequency of 40 GHz. PACS 42.79.Sz; 42.79.Hp; 42.79.-e; 42.62.-b; 85.60.-q     

Mössbauer Studies on Nanocrystalline Diol Capped γ-Fe2O3

Nanocrystalline indium (nano-In) was prepared with different particle sizes by electrochemical deposition. The temperature dependence of the local electric field gradient (EFG) of nano-In was investigated in a temperature range of 20–300 K using the probe ¹¹¹In for perturbed γγ angular correlation (PAC) experiments. The temperature dependence of the EFG of nano-In can be described by a (1−BT ^3/2) dependence as in bulk-In. It is shown that the low temperature value of the EFG and the proportionality constant B vary systematically with particle size.     

Quantum yield of Cl* (2P1/2) production in the gas phase photolysis of CCl4 in the ultraviolet

In this paper, we have probed the dynamics of chlorine atom production from the gas phase photodissociation of carbon tetrachloride at 222 and 235 nm. The quantum yield, φ* of Cl* (²P_1/2) production has been determined by probing the nascent concentrations of both excited (²P_1/2) and ground state (²P_3/2) chlorine atoms by suitable resonance-enhanced multiphoton ionization (REMPI) detection schemes. Although at the photolysis wavelengths the absorption of carbon tetrachloride is weak, significant amounts of Cl* are produced. Surprisingly, the quantum yield of Cl* production does not follow the absorption spectrum closely, which gives rise to the possibility of an indirect dissociation mechanism present in CCl₄ along with direct dissociation at these ultraviolet wavelengths     

Calorific study of the smectic A—smectic C transition in TBBA

An a.c. calorimetric technique has been used to measure the heat capacity variation associated with the smectic A—smectic C transition in terephthal-bis-(4n)-butylaniline (TBBA). Contrary to expectations based on the recent observation of petransitional acoustic effects in the semectic-A phase, the heat capacity shows no evidence of critical fluctuations and can be well described by a Landau mean-field model.     

Symmetric scattering ine ±-H ionization collisions

Triple differential cross-sections for ionization of hydrogen atoms by electrons and positrons have been calculated for symmetric coplanar geometry following a multiple scattering method suggested and used earlier by the authors. Results show single binary peaks exactly at 45° and double binary peaks exactly at 135° for higher energies as are expected from an analysis of Briggs [3]. At lower energies there are certain deviations from these values. An analysis of scattering mechanism at peaks are also given. This supports Briggs’ explanation.     

Solitons at the critical density of negative ions in multicomponentplasmas

The derivation of solitary waves in generalized multicomponent plasmas shows that the negative ion introduces a critical density at which the characteristics of the solitons are studied. The soliton's behavior derived using the Korteweg-deVries (KdV) equation at the critical density shows that the nonlinearity of the wave vanishes. Thus the mode of study is augmented through a modified KdV equation. Using a higher-order equation involving quadratic and cubic nonlinearities, the transition of the KdV equation to a modified KdV equation along with the conservation of the Sagdeev potential, which is not affected by the negative ions, is studied in detail. The results are compared with experimental observations, especially those made by Y. Nakamura et al. (J. Plasma Phys., vol.33, p.237-48, 1985)     

Trans-bis(dimethylglyoximato) cobalt(III) complexes containing imidazole and thiocyanate as axial ligands

Imidazole(Im), benzimidazole(BzIm), morpholine (Morph) and their derivatives react with Co(CNS)₂ and dimethylglyoxime(DH₂) in ethanolic medium in presence of air to form a number of new cobalt(III) complexes of the type trans-[Co(DH)₂(L)(SCN)], which are characterised on the basis of electronic and IR spectra, NMR (¹H and ¹³C) and mass spectra as well as thermogravimetric (TG-DTA) and conductance measurements. The thiocyanate groups are S-bonded. The NMR observations suggest that in solution these compounds exist as mixtures of the neutral species [Co(DH)₂(L)(SCN)] and the salt [Co(DH)₂(SCN)₂]^? [Co(DH)₂(L)₂]⁺. The mass spectra does not show the molecular ion peak of the complex. The TG-DTA measurements show that the thermolysis of these complexes proceeds through polymeric intermediates giving CO₃O₄ as the end product.