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.     

Time-dependent analysis of tunneling effect in the formation of ultracold molecules via photoassociation of laser-cooled atoms

The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs₂ and attributed to the 0_g ^-(6s, 6p _3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling is an efficient mechanism for transferring the population to the inner well (R < 15a ₀), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a ³Σ⁺ _u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances, and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels a ³Σ⁺ _u(6s, 6s)↦0_g ^-(6s, 6p _3/2) photoassociation at detunings around 2.9 cm^-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation), or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”). In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control the population of the inner well and hence the formation of ultracold molecules in low vibrational levels. Received 19 April 2002 Published online 1st October 2002 RID="a" ID="a"e-mail: francoise.masnou@lac.u-psud.fr     

Analytical Chemistry for the life sciences

Summary A course on Analytical Chemistry for the life sciences currently conducted at the Chemistry Department of Chelsea College, London, is described. This course has three main components: Lectures on the analysis of materials of biological importance, practical experiments using both chemical and instrumental methods, and lectures from experts of other departments on specialized fields of application.

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Analytische Chemie für die Biowissenschaften

Zusammenfassung Ein Ausbildungsplan für Analytische Chemie wird beschrieben wie er gegenwärtig in der chemischen Abteilung des Chelsea College, London, für Biowissenschaftler in Anwendung ist. Die Ausbildung umfaßt folgende drei Teile: Vorlesungen über die Analyse von biologisch relevanten Materialien, Praktika in chemischen und instrumentellen Analysenmethoden und Vorlesungen von einschlägigen Experten über spezielle Anwendungsgebiete.

     

Numerische Auswertung chronometrischer Gerinnungsanalysen von Humanplasma

Zusammenfassung Aus kinetischen Überlegungen zum Ablauf der Blutgerinnung wird eine einfache Eichfunktion abgeleitet. Die Funktion dient zur Bestimmung der wirksamen Konzentration von Gerinnungsfaktoren aus der gemessenen Gerinnungszeit durch lineare Regressionsanalyse. Sie ist der empirischen Näherung durch doppeltlogarithmische Auftragung der Konzentration des Gerinnungsfaktors gegen die Gerinnungszeit in der Korrelation zwischen gemessenem und berechnetem Kurvenverlauf überlegen. Am Beispiel einer Fibrinogenbestimmung wird die Auswertung der gemessenen Gerinnungszeiten mit Hilfe dieser Funktion gezeigt.

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Numerical evaluation of chronometric human plasma coagulation tests

Summary From kinetic considerations on blood coagulation a simple calibration function is derived. The function can be used for the determination of effective concentrations of coagulation factors from measured coagulation time by linear regression analysis. Concerning the correlation between measured and calculated calibration plots the function shows more conformity than the empirical approach by bilogarithmic plotting of concentration vs. coagulation time. The numerical evaluation of measured coagulation time in a fibrinogen determination is presented as an example.

     

Comparison of calorimetric and IR-spectroscopic data for alcohols and alcoholic solutions

The heats of solution of alcohols in hexane can be considered as the energy necessary to break hydrogen bonds (H-bond). The amount of non H-bonded OH groups estimated from caloric data, are in good agreement with IR-spectroscopic data. Comparison of calorimetric and IR-spectroscopically determined H-bond energies permit the separation of intermolecular van der Waals effects from H-bond interactions. This separation shows that van der Waals interactions of alcohols or water should not be underestimated.