Formation of low-temperature cirrus from H2SO4/H2O aerosol droplets

We present experimental results obtained with a differential scanning calorimeter (DSC) that indicate the small ice particles in low-temperature cirrus clouds are not completely solid but rather coated with an unfrozen H2SO4/H2O overlayer. Our results provide a new look on the formation, development, and microphysical properties of low-temperature cirrus clouds.     

Lidar Multiple Scattering in Water Droplet Clouds: Toward an Improved Treatment

Although it has long been recognized that the effects of photon multiple scattering generally need to be accounted for in the analysis of lidar cloud returns, this is a difficult problem and current approaches are still rudimentary. The multiple scattering process is controlled by the size of the lidar beamwidth and the distance to the cloud, which jointly determine the lidar footprint, but cloud microphysical content (i.e., particle size, concentration, and shape) exerts a strong influence on the range distribution and depolarization of the returned energy. Since clouds are inherently inhomogeneous with height, it is our premise that vertically homogeneous cloud simulations based on idealized particle size distributions lead to misleading results. We offer a more realistic approach based on the contents of growing water droplet clouds predicted by a sophisticated adiabatic cloud model, which are offered for use as new standard vertically-inhomogeneous cloud models. Lidar returned signal and depolarization profiles derived from our analytical double-scattering method are given for inter-comparison purposes.Presented at the 7th International Workshop on Multiple Scattering Lidar/Light Experiments (MUSCLE7), July 21–23 1994, Chiba, Japan.     

Etude de la fragmentation par impact électronique de dérivés du benzothiazole

Study of Electron-Impact Fragmentation of Benzothiazole Derivatives The mass spectra of eighteen substituted benzothiazoles are reported and discussed. All these compounds are thermodynamically stable and give an intense molecular ion, which undergoes different types of fragmentation depending on the nature of the substituent which is rarely eliminated directly. β-Cleavage with respect to the heterocyclic double bond is often observed. Specific ²H-, ¹³C-, ¹⁵N- and ³⁴S-labelling have been used in order to confirm the fragmentation patterns.     

Determination of Y, Zr and ultra-low Nb concentrations in geological material by multi-ion counting spark-source mass spectrometry (MIC-SSMS)

Precise concentrations of Zr, Y and Nb in the μg/g to ng/g range have been determined in rock samples using multi-ion counting spark-source mass spectrometry (MIC-SSMS). A high resolution method, combined with interference correction on ⁹¹Zr and ⁹³Nb for low concentration samples, was applied. An analytical precision of 2–5% for concentrations down to 0.020 μg/g and 10% for lower concentrations was attained. The detection limit is below 0.005 μg/g. By measuring international reference materials, the accuracy of the method was determined to be within about 10% of the recommended values. However, the accuracy of the final concentration is influenced by interference corrections, but the additional error is below 20%. The interference problem is most difficult for Al-rich samples (>15% Al₂O₃), as the interfering molecules are ⁴⁰Ca²⁷Al¹²C₂ ⁺ and ²⁷Al₃ ¹²C⁺. The accordance between ICP-MS and MIC-SSMS results is worse for low Nb concentrations in the ng/g range. Here, ICP-MS gives systematically lower values than MIC-SSMS. The reason for this discrepancy is not yet clear, but may be caused by Nb loss during chemical treatment of the samples prior to ICP-MS measurements. Received: 29 December 1998 / Revised: 19 April 1999 / Accepted: 21 April 1999     

Existenz von Holomorphiegebieten zu vorgegebener erster Bettischer Gruppe

Ohne Zusammenfassung     

Über Rungesche Paare komplexer Mannigfaltigkeiten

Ohne Zusammenfassung     

Determination of Y, Zr and ultra-low Nb concentrations in geological material by multi-ion counting spark-source mass spectrometry (MIC-SSMS)

Precise concentrations of Zr, Y and Nb in the μg/g to ng/g range have been determined in rock samples using multi-ion counting spark-source mass spectrometry (MIC-SSMS). A high resolution method, combined with interference correction on ⁹¹Zr and ⁹³Nb for low concentration samples, was applied. An analytical precision of 2–5% for concentrations down to 0.020 μg/g and 10% for lower concentrations was attained. The detection limit is below 0.005 μg/g. By measuring international reference materials, the accuracy of the method was determined to be within about 10% of the recommended values. However, the accuracy of the final concentration is influenced by interference corrections, but the additional error is below 20%. The interference problem is most difficult for Al-rich samples (>15% Al₂O₃), as the interfering molecules are ⁴⁰Ca²⁷Al¹²C₂ ⁺ and ²⁷Al₃ ¹²C⁺. The accordance between ICP-MS and MIC-SSMS results is worse for low Nb concentrations in the ng/g range. Here, ICP-MS gives systematically lower values than MIC-SSMS. The reason for this discrepancy is not yet clear, but may be caused by Nb loss during chemical treatment of the samples prior to ICP-MS measurements.