Pulsed glow discharges for analytical applications

Non equilibrium plasmas such as glow discharges have become a commonly used tool in direct surface and interface analysis of solid materials. The application of pulsed glow discharges to material analysis has been studied by several research groups over the last 20 years. Two European projects, EMDPA and GLADNET currently work on the analytical applications of glow discharges, giving a particular attention to pulsed discharges. This review demonstrates the advantages of pulsed discharge operation by showing how the specific excitation and ionisation processes observed during the plasma ignition phase and the afterglow can be used for analytical applications.     

T1-weighting of Hahn echo-trains in the stray-field for deuterium: prospects for imaging using long echo-train summation

Hahn-echoes have been observed in stray-field gradients of 37.5 T/m and 74.5 T/m for deuterium in heavy water in a number of forms: liquid, ice, and coordinated in solid copper sulfate and silica gel. In the diamagnetic samples, the application of many pulses (>1000 or more) in long pulse-trains produced many sustained echoes. This lengthening of T_echo is caused by T₁-weighting of the components of the Hahn echo (even in the absence of spin-locking). In contrast, for the paramagnetic complex, the shortening of T₁ greatly reduces T_echo and only few echoes are obtained. A new protocol for stray field imaging is suggested when T₁ is long: long echo-train summation (LETS). The observed magnetisation is much greater for heavy ice than for heavy water because the line-width, and hence the thickness of the excited slice, is greater.     

Easy and efficient tuning of the photochromic properties of 1,2-bis[5′-methyl-2′-(2″-pyridyl)thiazolyl]perfluorocyclopentene

Photochromic properties of the tilted compound could be easily tuned by simple oxidation of the peripheral pyridine groups by mCBPA. The mono- and bis-oxidized dithiazolylethenes were found to display both solution and single crystalline state photochromisms.     

Gaussian Beam Construction for Adiabatic Perturbations

We construct wave packets concentrated near a single space-time trajectory of the semi-classical Hamiltonian for a Bloch electron in a crystal lattice subject to slowly varying external electric and magnetic fields. The use of an analog of the Gaussian beam Ansatz make it possible to construct packets for arbitrarily long finite times.      

REACTION OF p-NITROPHENYL p-TOLUENESULFONATE WITH NUCLEOPHILIC REAGENTS IN AQUEOUS ETHANOL

Abstract

The rate of nucleophilic reaction of anions and amines with p-nitrophenyltosylate has been determined in a 41% w/w ethanol-water mixture at 25°. For weakly basic amines, the reaction is general base and general acid catalyzed. Aldoximates and thiophenolate show an enhanced nucleophilicity compared to phenolates of same basicity. The results are interpreted in terms of charge and frontier controlled reactions.     

Azeotropy in Terpolymerization

This work deals with the determination of the various azeotropies in radical terpolymerization: unitary azeotropy (m_i = M_i); binary azeotropy (m_i/m_j. = M_i/M_j), and ternary or true azeotropy (M_j = m_j for j = 1, 2, 3). General analytical solutions are given which are easily handled by a computer. In addition, these calculations show the existence of pseudo-azeotropy where the deviation between polymer and monomer feed compositions is very small, not only at the beginning of the reaction, but also with increasing conversion.     

Quantitative analysis of five tobacco‐specific N‐nitrosamines in urine by liquid chromatography–atmospheric pressure ionization tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination of five total tobacco‐specific N‐nitrosamines (TSNA), including free and conjugated forms in urine. The limits of detection for 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol, N′‐nitrosonornicotine, 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone, N′‐nitrosoanatabine and N′‐nitrosoanabasine were 0.6, 0.6, 10.0, 0.4 and 0.4 pg/mL, respectively, with a linear calibration range of up to 20,000 pg/mL. Intra‐ and inter‐day precision for TSNA measurements ranged from 0.82 to 3.67% and from 2.04 to 7.73% respectively. For total TSNAs, the β‐glucuronidase amount was optimized for hydrolysis time and yield. Different liquid chromatography columns and mobile phases with different pH conditions were evaluated. The validated method was then applied to 50 smoker and 30 nonsmoker urine samples. Our results suggest that this sensitive and relatively simple analytical method is suitable for application to epidemiological investigations of health risks associated with the exposure to tobacco smoke or secondhand smoke in both smokers and nonsmokers. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Optical properties of 1.3 μm room temperature emitting InAs quantum dots covered by In0.4Ga0.6As/GaAs hetero-capping layer

Room temperature 1.3 μm emitting InAs quantum dots (QDs) covered by an In_0.4Ga_0.6As/GaAs strain reducing layer (SRL) have been fabricated by solid source molecular beam epitaxy (SSMBE) using the Stranski–Krastanov growth mode. The sample used has been investigated by temperature and excitation power dependent photoluminescence (PL), photoluminescence excitation (PLE), and time resolved photoluminescence (TRPL) experiments. Three emission peaks are apparent in the low temperature PL spectrum. We have found, through PLE measurement, a single quantum dot ground state and the corresponding first excited state with relatively large energy spacing. This attribute has been confirmed by TRPL measurements which allow comparison of the dynamics of the ground state with that of the excited states. Optical transitions related to the InGaAs quantum well have been also identified. Over the whole temperature range, the PL intensity is found to exhibit an anomalous increase with increasing temperatures up to 100 K and then followed by a drop by three orders of magnitude. Carrier’s activation energy out of the quantum dots is found to be close to the energy difference between each two subsequent transition energies. PACS 68.65.Ac; 68.65.Hb; 78.67.Hc