Effects of geminal methyl groups on the tunnelling rates in the ring opening of cyclopropylcarbinyl radical at cryogenic temperature

CVT + SCT calculations on the rate of tunnelling at 20 K in the ring opening of cyclopropylcarbinyl radical, substituted with geminal methyl groups at a ring carbon (1b), have been performed. The calculations predict that, contrary to expectations based on the effect of mass on the rate of tunnelling, the geminal methyl substituents in 1b should make the rate of ring opening to 1,1-dimethyl-3-butenyl radical (2b) 10(4) times faster than the rate of ring opening of unsubstituted cyclopropylcarbinyl radical (1a) to 3-butenyl radical (2a) and almost 10(6) times faster than the rate of ring opening of 1b to 2,2-dimethyl-3-butenyl radical (2c). The reasons for these unexpected findings are discussed.     

Regio‐ and stereoselective synthesis of 1‐benzopyrano[2,3‐b]pyrrolo[2,3‐d]pyridines: A microwave‐accelerated intramolecular [3+2] cycloaddition reaction of azomethine ylide

Regio‐ and stereoselective syntheses of tetracyclic compounds having chromone, pyrrolidine, and piperidine rings have been accomplished by an intramolecular [3+2] cycloaddition reaction involving azomethine ylide. The reactions were carried out thermally as well as by irradiation with microwave. The latter process accelerates the reaction. The selectivities were investigated by density functional theory computation. J. Heterocyclic Chem., (2011).     

Development and validation of a liquid chromatography-tandem mass spectrometry method to determine ulifloxacin, the active metabolite of prulifloxacin in rat and rabbit plasma: application to toxicokinetic study

A simple, high‐throughput and specific high‐performance liquid chromatography–tandem mass spectrometry method has been developed and validated according to the FDA guidelines for quantification of ulifloxacin in rat and rabbit plasma. The analyte was separated on a Peerless basic C₁₈ column (33 × 4.6 mm, 3 µm) with an isocratic mobile phase of methanol–water containing formic acid (0.5%, v/v; 9:1, v/v) at a flow rate of 0.5 mL/min. The MS/MS detection was carried out by monitoring the fragmentation of m/z 350.500 → 248.500 for ulifloxacin and m/z 332.400 → 231.400 for ciprofloxacin (internal standard; IS) on a triple quadrupole mass spectrometer. The response to ulifloxacin was linear over the range 0.010–2.500 µg/mL in both plasma. The limit of detection and lower limit of quantification of ulifloxacin were determined in both species to be 0.0025 and 0.010 µg/mL, respectively. The method was successfully applied to quantitatively assess the toxicokinetics of ulifloxacin in rat and rabbit following a single 400 mg/kg (in rat) and 200 mg/kg (in rabbit) oral dose of the prulifloxacin. Copyright © 2010 John Wiley & Sons, Ltd.     

Stability of Charged Thin-Shell Wormholes in (2+1) Dimensions

In this paper we construct charged thin-shell wormholes in (2+1)-dimensions applying the cut-and-paste technique implemented by Visser, from a BTZ black hole which was discovered by Bañados, Teitelboim and Zanelli (Phys. Rev. Lett. 69:1849, 1992), and the surface stress are determined using the Darmois-Israel formalism at the wormhole throat. We analyzed the stability of the shell considering phantom-energy or generalised Chaplygin gas equation of state for the exotic matter at the throat. We also discussed the linearized stability of charged thin-shell wormholes around the static solution.     

Middle school students’ proportional reasoning in real life contexts in the domain of geometry and measurement

The purpose of this study was to examine middle school students’ proportional reasoning, solution strategies and difficulties in real life contexts in the domain of geometry and measurement. The underlying reasons of the difficulties were investigated as well. Mixed research design was adopted for the aims of the study by collecting data through an achievement test from 935 sixth, seventh and eighth grade students. The achievement test included real life problems that required proportional reasoning, and were related to the measurement of length, perimeter, area and volume concepts. In addition, task-based interviews were conducted on 12 of these students to collect more comprehensive data and to support the findings of the achievement test. Findings revealed that although students were mostly successful in giving correct answers, their reasoning lacked a clear argument of the direct and indirect proportional relationships between the variables and that they approached the problems by superficial characteristics of the problems.     

Branching random walks,stable point processes and regular variation

Using the theory of regular variation, we give a sufficient condition for a point process to be in the superposition domain of attraction of a strictly stable point process. This sufficient condition is used to obtain the weak limit of a sequence of point processes induced by a branching random walk with jointly regularly varying displacements. Because of heavy tails of the step size distribution, we can invoke a one large jump principle at the level of point processes to give an explicit representation of the limiting point process. As a consequence, we extend the main result of Durrett (1983) and verify that two related predictions of Brunet and Derrida (2011) remain valid for this model.     

Amorphous and nanocrystalline silicon made by varying deposition pressure in PECVD process

Silicon thin films are deposited using plasma enhanced chemical vapor deposition (PECVD) of silane, argon, hydrogen mixture at various pressures in the range of 2–8 Torr. Raman scattering shows these to be amorphous in the pressure range 6–8 Torr, and nanocrystalline in the range 2–4 Torr. The volume fraction of nanocrystals is estimated by fitting the Raman data to three peaks and is found to be ～75% for the films deposited at low pressure, density of states of these films was measured. It is observed that the electrical conduction in these films depends on the crystalline volume fraction (ρ), estimated from the laser Raman Spectroscopy. Temperature dependence electrical conductivity shows that at lower temperatures thermionic emission dominates for the films with lower ρ, whereas, hopping is the main conduction mechanism for the films having high ρ. The density of states is estimated from the space charge limited currents (SCLC) observed at high fields. Photoconductivity at room temperature is also measured. The amorphous films are found to be more photosensitive than the nanocrystalline one. In the context of these findings, changes in the properties of silicon from amorphous to nanocrystalline are described.