Effects of alkyl chain lengths of gallates upon their distribution and reactivity towards diphenylpicryl hydracil radicals in Triton X‐100 micellar solutions

The reactivity of ethyl‐, propyl‐ and octylgallate towards diphenylpicryl hydracil radicals has been measured in homogeneous solution (ethanol) and in Triton X‐100 micellar solutions. Similar reactivities were measured in homogeneous solutions, indicating that the length of the alkyl chain does not influence the reactivity of the phenolic groups. On the other hand, different reactivities were measured in micellar solutions, particularly at low (5 mM) surfactant concentrations. Data obtained at different surfactant concentrations allow estimation of partitioning of the gallates and their intramicellar bimolecular rate constant. The values obtained indicate that all the observed differences in reactivity are attributable to differences in substrate partitioning between the micellar and aqueous pseudophases. In fact, similar values of the intramicellar rate constants were obtained, suggesting that the average location of the reactive groups inside the micelles is independent of the solute alkyl chain length. Copyright © 2009 John Wiley & Sons, Ltd.     

A model for the stabilization of atomic hydrogen centers in borate glasses

A previously proposed model describing the trapping site of the interstitial atomic hydrogen in borate glasses is analyzed. In this model the atomic hydrogen is stabilized at the centers of oxygen polygons belonging to B–O ring structures in the glass network by van der Waals forces. The previously reported atomic hydrogen isothermal decay experimental data are discussed in the light of this microscopic model. A coupled differential equation system of the observed decay kinetics was solved numerically using the Runge Kutta method. The experimental untrapping activation energy of 0.7×10⁻¹⁹ J is in good agreement with the calculated results of dispersion interaction between the stabilized atomic hydrogen and the neighboring oxygen atoms at the vertices of hexagonal ring structures.     

The development of a user-oriented plasma spectroscopy application

This note provides a short historical perspective on our paper “SPECTRA—a model for K-shell spectroscopy” [1] (JQSRT 1984;32:91-101).     

Controlled remote implementation of partially unknown quantum operation

A protocol for controlled remote implementation of a partially unknown operation on an arbitrary quantum state is proposed. In this protocol, a task can be performed using a GHZ state shared among three distant parties: Alice, Bob and the controller Charlie. This protocol is also generalized to the multi-party control system based on sharing an N-qubit GHZ state. Supported by the Natural Science Youth Teacher Foundation of Xuzhou Institute of Technology, China (Grant No. XKY2007317)     

Time resolution of the bunch-shape detector with a thin-wire emission target

The time resolution of a new bunch-length detector based on the radio frequency (RF) scanning of the produced secondary electrons is calculated. A dedicated Monte-Carlo code by means of SIMION software is developed for accurate simulation of spread in the investigated secondary electrons transit times and image width. In calculation the initial energy distribution of electrons and the actual structure of accelerating and focusing electric fields were considered. It is shown that by using a thin-wire emission target a femtosecond time precision could be achieved using moderate applied voltages.     

A study of time over threshold (TOT) technique for plastic scintillator counter

A new charge measurement method, time over threshold (TOT), has been used in some gas detectors lately. Here TOT is studied for TOF system, made of plastic scintillator counter, which can simplify the electronics of the system. The signal characteristics are measured and analyzed with a high quality oscilloscope, including noise, pedestal, signal amplitude, total charge, rise time and the correlation between them. The TOT and charge are related and can be fitted by some empirical formula. The charge measurement resolution by TOT is given and this will help the design of TOF electronics.     

Monte-Carlo simulation of a compact gamma-ray detector using wavelength-shifting fibers coupled to a YAP scintillation crystal

The production and transportation of fluorescent light produced in wavelength-shifting fibers (WSFs) coupled to YAP scintillation crystal is simulated using the GEANT4 codes.An advantage of the wavelength-shifting fiber readout technique over a direct readout with a position-sensitive photo-sensor is the reduced requirement for position sensitive photomultiplier tube photocathode area.With this gamma-ray detector,the gamma camera is small and flexible and has larger effective field of view and low cost.Simulation results show that a) a mean 12 of photons per 59.5 keV gamma ray interaction is produced in the WSF located nearest to the incident gamma ray,and a spatial resolution of 3.6 mm FWHM is obtained,b)a mean 27 of photons per 140 keV gamma ray interaction is produced and a spatial resolution of 3.1 mm FWHM is obtained.Results demonstrate the feasibility of this concept of a compact gamma-ray detector based on wavelength-shifting fibers readout.However,since the very low photoelectron levels,it is very important to use a photon counting device with good single photo-electron response to readout the WSFs.