An asymptotic result and a stability criterion for linear nonautonomous delay difference equations

Linear delay difference equations with variable coefficients and constant delays are considered. By the use of an appropriate solution of the so called generalized characteristic equation, an asymptotic result is obtained and a stability criterion is established.     

A facile one‐pot synthesis of tetrahydropyrimidines part 3 Synthesis of [alkanediylbis(3‐alkyl/aralkyl/aryl‐3,6‐dihydropyrimidine‐1,5(2H)‐diyl)bis(arylmethanones) and [1,4‐phenylenebis(3‐phenyl‐3,6‐dihydropyrimidine‐1,5(2H)‐diyl)]bis(phenylmethanone)

A facile one‐pot synthetic strategy has been developed for novel [alkanediylbis(3‐alkyl/aralkyl/ aryl‐3,6‐dihydropyrimidine‐1,5(2H)‐diyl)]bis(arylmethanones) 2a‐c, 2e‐m and [1,4‐phenylenebis(3‐phenyl‐3,6‐dihydropyrimidine‐1,5(2H)‐diyl)]bis(phenylmethanone) 2d by refluxing enaminones 1a‐f in methanol with diamines and formaldehyde.     

Isolation of 3,4-dihydroxyphenylacetic acid produced from p-hydroxyphenylacetic acid by immobilized plant cells of Mucuna pruriens and its identification by liquid chromatography/mass spectrometry

A cell suspension culture originating from a Mucuna pruriens (L.) DC f. utilis (Wall ex Wight) Back cultivar was immobilized in calcium alginate. Biotransformation of p- hydroxyphenylacetic acid to 3,4-dihydroxyphenylacetic acid was done in a bubble-jar containing a suitable incubation medium. To obtain a sample suitable for combined liquid chromatography/mass spectrometry (l.c./m.s.), electrolytes, proteins and carbohydrates were removed from the medium by chromatography on Sephadex G-10 and Affigel-601 columns. Product formation and isolation were followed by high-performance liquid chromatography with electrochemical and u.v. detection, and by continuous u.v. detection. The identity of 3,4-dihydroxyphenylacetic acid was confirmed by l.c./m.s., which also detected an impurity or by-product not observed by electrochemical or u.v. detection.     

On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples. I. Determination of clenbuterol in urine

The potential of the direct coupling of solid-phase extraction (SPE) with mass spectrometry (MS) for the analysis of biological samples is demonstrated. For SPE a cartridge exchanger is used and the eluate is directly introduced into the mass spectrometer. This system has been investigated for the determination of clenbuterol in urine. With mixed-mode cartridges, a considerable ion suppression has been obtained. The mass spectrum at the elution time of clenbuterol is dominated by that of creatinine and adduct formation of clenbuterol and creatinine has been observed. The whole procedure including injection of 1 ml urine, washing and desorption has been developed with cartridges containing 8-microm C18-bonded silica. If only a single MS step is used, the selectivity and, therefore, the sensitivity are insufficient. The detection limit is about 100 ng/ml. However, with atmospheric pressure chemical ionisation and the tandem MS mode the detection limit has been decreased to about 2 ng/ml and the ion suppression is only about 10%. For the electrospray ionisation the detection limit is about 10-times higher and the ion suppression is less favourable. The repeatability for the SPE-MS-MS procedure was 6.5% at 10 ng/ml (n=5) and the difference between the response factors at 10 ng/ml and 100 ng/ml was only 2.5%. The MS behaviour of clenbuterol and the matrix under the present conditions is discussed.     

Analyse multielementaire instrumentale des phosphates marocains par photoactivation nucleaire

Photonuclear activation and high resolution gamma-ray spectrometry have been used to determine non-destructively the concentrations of 25 trace elements in Maroccan phosphate rock. The activation was simultaneously performed for phosphate samples and multielement standards in the bremsstrahlung beam of a linear electron accelerator at 18 and 30 MeV maximum energies. Gamma-ray spectra were recorded with a 79 cm³ Ge(Li) detector and a programmable analyzer IN 96. A detailed study of interferences was carried out. Limits of detection between 0.5 and 125 μg·g^?1 were obtained.     

Are Clusters Important in Understanding the Mechanisms in Atmospheric Pressure Ionization? Part 1: Reagent Ion Generation and Chemical Control of Ion Populations

It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.

Technical Reports: A Single-photon Counting Pixel Detector for Surface Diffraction Experiments

The intense flux delivered by third-generation synchrotron sources has opened up exciting new possibilities in surface diffraction (SD) studies [1–3]. Nonetheless, practical SD experiments are plagued by several technical problems. Because the crystalline surface is typically probed down to a depth of approximately 1 or 2 nm when using subcritical-angle incident X-ray beams, the scattering volume is only about 10^-12 cm³. This is further exacerbated by the fact that the most interesting information on the surface structure is generally obtained from those regions of diffraction features known as crystal truncation rods (CTRs) where scattering is weakest, i.e., in between Bragg peaks.     

Highly ordered hexatic phases with large spontaneous polarization

In this article the physical properties of hexatic phases of three substances MHPNBC, FOOPP and FNHPP have been studied by differential scanning calorimetry, texture observation and dielectric spectroscopy. Experimental results are discussed from the point of view of existing theories. It is interesting that two of the substances studied, the FOOPP and FNHPP, exhibit enhanced spontaneous polarization in the highly ordered SmI* phase and show a jump of the spontaneous polarization in the vicinity of the SmC*–SmI* transition. In the SmI* phase of FOOPP a very high value of spontaneous polarization of the order of 530?nC?cm^?2 was found. Based on the results obtained the macroscopic and microscopic properties of the hexatic phases are discussed.