Diamagnetic susceptibility of solid and liquid paraffins

Experimental values for the diamagnetic susceptibility of a series of mono-disperse n-paraffins ranging between 6 and 50 carbon atoms in the solid (melt and solution crystallized) and in the liquid state are reported. From the dependence of the molecular susceptibility, ScHM, on the molecular weight, information about the intermolecular interactions between adjacent chain molecules and on the arrangement of the methyl end-groups is obtained. The ScHM values of melt- and solution-crystallized paraffins are, within experimental error, indistinguishable from each other. For C₁₂H₂₆ and C₄₄H₉₀ the specific susceptibility ScHM /M rises at the melting point within a few °C and reaches a plateau which characterizes the liquid state II. For the paraffin C₂₄H₅₀ an intermediate plateau between the melting point and the final true liquid state is observed and is called liquid state I. After cooling below the melting point TM, the ScHM value of the equilibrium state can be obtained after a short time only from liquid state I, while from liquid state II days and weeks are needed for this. By combining this information with the observed ScHM values, it is concluded that in liquid state I a higher or smectic-like order exists similar to mesophases, well-known in liquid crystals, while in the real liquid state II this order is lost.     

Methyl 5-Deoxy-α and β-D-Xylofuranosides

Abstract

Synthesized from D-xylose, methyl 5-deoxy-α-D-xylofuranoside (1) and methyl 5-deoxy-β-D-xylofuranoside (2) were obtained in overall yields of 24 and 26 %, respectively. The key step in the synthesis was the separation of an anomeric mixture on a strong anion exchanger in OH^? form. NMR data and mass spectra of title compounds 1, 2, methyl 2,3-di-O-acetyl-5-deoxy-α-D-xylofuranoside (3), and methyl 2,3-di-O-acetyl-5-deoxy-β-D-xylofuranoside (4) are discussed. The conformations of 1 and 2 were established from the best fit between calculated and experimental coupling constants using Karplus equation.     

Numerical solution of a system of nonlinear differential equations with a nonlocal condition

Lithuanian Mathematical Journal -     

Ab initio calculations on the structure of the cyclopropenyl anion

Calculations at the SCF level and with inclusion of correlation were carried out on a portion of the potential ¹A′ state of the cyclopropenyl anion which was found to be nonplanar in its most stable geometry.     

Simulation of random processes with various probability density functions

Various relationships are derived for simulation of random processes with simple or composite probability density functions. Depending on the properties of the corresponding parameters the resulting process is either stationary or non-stationary. Practical digital simulation with the formulas derived is fast enough to be used in real time with computer controlled simulators.     

Determination of microgram amounts of bromide by coulometric argentimetry

Summary A method for determining microgram amounts of bromide by means of coulometric argentimetry has been developed. This method permits determination of 5–100g of bromide in a sample volume of up to 10 ml with errors from + 3 to + 0.4%. The optimum conditions for detection of silver ions by means of a microelectrode biamperometric system have been determined. From the influence of current densities on the course of titration the optimum conditions for the determination of bromide in the presence of chloride are described.

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Zusammenfassung Ein Verfahren zur coulometrisch-argentometrischen Bestimmung von Mikrogrammengen Bromid wurde ausgearbeitet. Es ermöglicht die Bestimmung von 5 bis 100g Bromid in Proben bis zu 10 ml mit einem Fehler von + 3 bis + 0,4%. Die optimalen Bedingungen für den Nachweis von Silberionen mit Hilfe eines biamperometrisehen Mikroelektrodensystems wurden ermittelt. Ausgehend von dem Einfluß der Stromdichte auf den Titrationsverlauf werden die besten Bedingungen für die Bestimmung von Bromid in Gegenwart von Chlorid angegeben.

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Résumé On a développé une méthode pour doser des quantités de bromure de l'ordre du microgramme par argentimétrie coulométrique. Cette méthode permet le dosage de 5 à 100g de bromure sur un volume échantillon allant jusqu'à 10 ml, avec des erreurs de + 3 à + 0,4%. On a déterminé les conditions optimales pour déceler les ions argent au moyen d'un système biampérometrique à micro-électrode. On décrit les conditions optimales du dosage des bromures en présence de chlorures à partir de l'influence des densités de courant en cours de titrage.

     

Abnormal reflecting mirror structures for intra-cavity Čerenkov second-harmonic generation

Abnormal reflecting mirror (ARM) structures, consisting of a corrugated optical waveguiding structure, can serve as a wavelength-selective end mirror in a laser cavity. The ARM structure shows, for each wavelength in a certain region, 100% reflection at a certain angle of incidence. In the vicinity of this angle the waveguide is resonantly excited, leading to strong enhancement of the optical field in the layer structure, which is interesting for efficient second-harmonic generation (SHG). In this paper, experimental results of a first prototype, exhibiting Čerenkov SHG, are reported. Received: 16 May 2001 / Revised version: 28 August 2001 / Published online: 30 October 2001