New results on ultrafast coherent excitation of molecular vibrations in liquids

Coherent Raman probe scattering experiments are performed to study dynamical processes of polyatomic liquids at 300 K. For single homogeneous transitions the dephasing timeT ₂ is readily obtained from time resolved investigations. Spectral studies show an interesting time dependent shift in scattered frequency. After the excitaiton the vibrating molecules are shown to relax freely with their resonance frequency. Multiple, equally spaced transitions exhibit a beating phenomenon which provides the dephasing time and the frequency interval between neighboring vibrational states. Inhomogeneously broadened systems do not allow a ready determination of the dephasing time by the present probing technique. Previous experiments on the subject have to be reconsidered.     

A partially mechanized system for the combustion of organic samples in a stream of oxygen with quantitative recovery of the trace elements

Summary A partially mechanized apparatus made of quartz (Trace-0-Mat) is described that permits the complete mineralization of up to 1 g of organic or biological solid samples. The combustion takes place in pure oxygen in a very small burning chamber (ca. 75 cm³) to subsequently determine metallic and nonmetallic trace elements (1 ng/g) with high reliability. The controllable incineration is started with an IR-radiator system. All volatile trace elements (e.g. Hg, Se, Te, As, Sb, I) are condensed together with the products of the combustion process in a cooling system filled with liquid nitrogen that is mounted on top of the burning chamber. Subsequent refluxing with a suitable acid in a quartz test tube mounted below the burning chamber collects both the volatilized elements from the cooled areas and nonvolatile elements in the ashing residue. The volume of the acid is about 2 ml.The recoveries of the elements following the decomposition process that takes 50–60 min for one sample was checked using 7 NBS-Standard Reference Materials for the elements B, Cr, Cu, Fe, Mn, Zn (ICP-emission spectrometry), Cd, Pb (ETA-AAS), Hg (AAS-cold vapor technique), As (AAS-hydride method) and Se (XRF). Very good agreement with the certified values was observed. This furnished evidence that this new and very general decomposition method is not only poor in blanks but also avoids substantially losses of the elements to be determined by volatilization, adsorption or even baking in the quartz surface. The easy handling of the apparatus offers the best premises for a reliable determination of trace elements in the g/g and ng/g range in most non-volatile organic matrices.

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Teilmechanisiertes System zur Verbrennung organischer Proben im Sauerstoffstrom mit quantitativer Wiedergewinnung der Spurenelemente

Zusammenfassung Ein teilmechanisiertes aus Quarz bestehendes System (Trace-0-Mat) wird beschrieben, das die vollständige Mineralisation fester organischer oder biologischer Proben bis zu Mengen von 1 g gestattet. Die Verbrennung findet dabei in reinem Sauerstoff in einer sehr kleinen Verbrennungskammer (etwa 75 cm³) statt, so daß anschließend die metallischen und nichtmetallischen Spurenelemente mit hoher Zuverlässigkeit bestimmt werden können. Die steuerbare Veraschung wird durch ein System von IR-Strahlern gestartet. Alle flüchtigen Spurenelemente (z. B. Hg, Se, Te, As, Sb, I) werden zusammen mit den Verbrennungsprodukten in einem Kühlsystem kondensiert, das mit flüssigem Stickstoff gefüllt und über der Verbrennungskammer angeordnet ist. Die sich an den gekühlten Flächen befindlichen flüchtigen sowie die in der Asche vorhandenen nichtflüchtigen Elemente werden durch Rückflußbehandlung mit einer kleinen Säuremenge (2 ml) gelöst und in einem Quarzglas unterhalb der Verbrennungskammer gesammelt.Die Wiederfindung der Elemente nach dem Aufschlußprozeß (50–60 min) wurde mit Hilfe von 7 NBS-Referenzmaterialien für folgende Elemente geprüft: B, Cr, Cu, Fe, Mn, Zn (ICP-Emissionsspektrometrie), Cd, Pb (ETA-AAS), Hg (AAS-Kaltdampftechnik), As (AAS-Hydridmethode) und Se (Röntgenfluorescenz). Es ergab sich sehr gute Übereinstimmung mit den zertifizierten Werten. Diese neue und sehr allgemein anwendbare Aufschlußmethode weist nicht nur geringe Blindwerte auf, sondern vermeidet auch wesentliche Verluste der zu bestimmenden Elemente durch Verflüchtigung, Adsorption oder Zusammenbacken an der Quarzoberfläche. Durch die einfache Handhabung der Apparatur ist eine zuverlässige Bestimmung von Spurenelementen im g/g- und ng/g-Bereich für die meisten nichtflüchtigen organischen Matrices gewährleistet.

     

Inhaltsstoffe des Osmanthus-Absolues. 1. Mitteilung: 2,5-Epoxy-megastigma-6,8-dien

Constituents of Osmanthus Absolute, Ist communication:2,5-Epoxy-megastigma-6,8-dienes Besides some further ionone derivatives we identified two new bicyclic oxacompounds ( 1a / 1b ) of the megastigmane type in the Osmanthus absolute. Isolation, special features of their spectral datas and synthesis starting from ethyl α-safranate are described. The synthetic pathway choosen allowed the additional identification of four substances occurring in the same natural substrate, because some synthetic by-products formed int he reaction sequence exhibited corresponding spectra and GLC. retention as the hitherto unknown components of the Osmanthus absolute.     

Resonant-cavity light-emitting diodes: quantum noise and spatial emission characteristics

We demonstrate the interplay between the intensity noise and the spatial emission characteristics of resonant-cavity light-emitting diodes. First, we find that the total aperture intensity noise exhibits a sub-shot noise behavior in a quite large pumping regime. Second, we investigate the angular, spectral, and spatial emission characteristics of the devices by controlling the shape and width of the angular intensity distribution via temperature detuning of the quantum well wavelength and the cavity resonance wavelength. Finally, the angular and aperture resolved intensity noise exhibit a super-shot noise behavior in contrast to that of the total emission. We explain this difference with anticorrelations between various radial components which increase with the temperature-tuned extension of the spatial emission. PACS 85.60.Jb; 42.50.L; 23.20.En     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Magnetic field enhanced coherence length in cold atomic gases

We study the effect of an external magnetic field on coherent backscattering of light from a cold rubidium vapor. We observe that the backscattering enhancement factor can be increased with B. This surprising behavior shows that the coherence length of the system can be increased by adding a magnetic field, in sharp contrast with usual situations. This is mainly due to the lifting of the degeneracy between Zeeman sublevels. We find good agreement between our experimental data and a full Monte Carlo simulation, taking into account the magneto-optical effects and the geometry of the atomic cloud.     

Isospin violation in e+ e- -->BB

The ratio of the B+ B- and B0B0 production rates in e+ e- annihilation is computed as a function of the B meson velocity and BB*pi coupling constant, using a nonrelativistic effective field theory.