Studies on the mixing of two non-axial jets in a confined passage — turbulence characteristics

The mean characteristics of the flow due to mixing of two non-axial plane jets in a confined passage, were reported previously by Manjunath et al. (Exp. Fluids 11 (1991), 17–24), as part I. In this paper, the turbulence characteristics of the flow are discussed. The various components of the Reynolds stress tensor are reported for the four inlet angles considered, viz., 15°, 30°, 45° and 60°. As expected from the mean flow field, the inlet angle influences the distribution of the various turbulence components through the relative size of the recirculation zones and the turbulence field is different for the smaller angles of 15° and 30° in comparison to those for 45° and 60°.     

Determination of Cd, Co, Cu, Fe and Ni at parts per billion level in high-purity gallium by graphite furnace atomic absorption spectrometry (GFAAS)

Summary The determination of Cd, Co, Cu, Fe and Ni in 6N gallium by GFAAS is reported. The analytes are extracted as pyrrolidine dithiocarbamates into methyl-iso-butyl-ketone (MIBK) in the presence of tartrate. The conditions of extraction, quantity of reagents required and the matrix interference aspects are discussed. The method offers one-step matrix removal and preconcentration, leading to low experimental blanks.     

Rh2(OAc)4-catalyzed reactions of alpha-diazoimides: a simple and novel synthesis of mono- and bis(2,3-fused perhydrooxazol-4-one) systems

Simply, trapping the intermediate isomünchnone 1,3-dipoles by the external oxygen nucleophiles resulted in new heterocyclic systems and the use of diols led to the formation of four carbon-oxygen bonds in a single operation which eventually delivered bis(2,3-fused perhydrooxazol-4-one) systems.     

Josephson voltage standard at National Physical Laboratory,New Delhi

A C Josephson effect is now used by several countries as the reference standard for the unit of d.c. voltage. This paper describes the work done at the National Physical Laboratory (NPL), New Delhi in the realization of the unit of volt based on the a.c Josephson effect. A voltage standard at 1 mV level using a Nb-Nb point contact junction has been established and the as-maintained volt based on a bank of standard cells has been intercompared against it using a 1:1000 voltage divider. The experimental set-up used in this comparison and the results of recent measurements are described. The overall uncertainty in assigning the value of emf to a standard cell is about 1 ppm. The as-maintained volt has been found to agree with the Josephson voltage within overall uncertainty.     

Minor alkaloids of Tylophora asthmatica: Revised structure of tylophorinidine

The structure of the phenolic alkaloid tylophorinidine, isolated from Tylophora asthmatica, has been shown to be 2. Two other minor alkaloids isolated from the plant have been shown to be d-septicine (11) and d-isotylocrebrine (14).     

Potential functions for hydrogen bond interactions

A careful comparison of the distribution in the (R, θ)-plane of all NH … O hydrogen bonds with that for bonds between neutral NH and neutral C=O groups indicated that the latter has a larger mean R and a wider range of θ and that the distribution was also broader than for the average case. Therefore, the potential function developed earlier for an average NH … O hydrogen bond was modified to suit the peptide case. A three-parameter expression of the form \(V_{hb} = V_{min} + p_1 \Delta ^2 + q_1 e^{p_3 \Delta } \theta ^2 \) , with △ = R - R_min, was found to be satisfactory. By comparing the theoretically expected distribution in R and θ with observed data (although limited), the best values were found to bep ₁ = 25,p ₃ = ? 2 andq ₁ = 1 × 10^?3, with R_min = 2·95 Å and V_min = ? 4·5 kcal/mole. The procedure for obtaining a smooth transition from V_hb to the non-bonded potential V_nb for large R and θ is described, along with a flow chart useful for programming the formulae. Calculated values of ΔH, the enthalpy of formation of the hydrogen bond, using this function are in reasonable agreement with observation. When the atoms involved in the hydrogen bond occur in a five-membered ring as in the sequence a different formula for the potential function is needed, which is of the form V_hb = V_min +p ₁△² +q ₁ x ² wherex = θ ? 50° for θ ≥ 50°, withp ₁ = 15,q ₁ = 0·002, R_min = 2· Å and V_min = ? 2·5 kcal/mole.     

Crystal and molecular structure of sarcosine

The crystal structure of sarcosine in pure form has been determined at low temperature (135 K). The crystals are othorhombic, space group P2(1)2(1)2(1) with unit cell dimensions a = 6.687(2) A, b = 7.899(3) A, c = 8.607(3) A. On the basis of 988 reflections with intensities larger than 3 sigma (I) the structure was refined to a conventional R-factor of 0.034 to give e.s.d. in bond lengths of 0.002 A and 0.2 degrees in angles. The molecule is extended and exists in the zwitterionic form. There is a small deviation from planarity in the alpha-amino acid group as well as in the main chain.