Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H(2) formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H(2) is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of ?(0) = 2 × 10(16) D-atoms cm(-2) per layer of H(2)O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D(2) formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous.     

Synthesis of silver nanoparticles and antimony oxide nanocrystals by pulsed laser ablation in liquid media

Pulsed laser ablation in liquid media (PLALM) is a prominent technique for the controlled fabrication of nanomaterials via rapid reactive quenching of ablated species at the interface between the plasma and liquid. Results on nanoparticles and nanocrystals formed by PLALM of silver (Ag) and antimony (Sb) solid targets in different liquid environments (Sodium Dodecyl Sulfate, distilled water) are presented. These experiments were done by irradiating solid targets of Ag and Sb with a nanosecond pulsed Nd:YAG laser output of wavelength 532 nm. Nanoparticles of silver and nanocrystals of antimony oxide (Sb₂O₃) obtained were characterized using UV-Vis spectrometry, Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), X-ray Energy Dispersion Analysis (EDAX) and X-ray diffractometry (XRD). The morphology of nanomaterials formed is studied as a function of surfactant environment. The silver nanoparticles obtained were spherical of size in the order of 10–35 nm in solution of SDS having different concentrations. In case of the Sb target, ablation was performed in two different molarities of SDS solution and distilled water. Nanocrystals of Sb₂O₃ in powder form having cubic and orthorhombic phases were formed in SDS solution and as fibers of nanocrystals of cubic Sb₂O₃ in distilled water.     

Zum Nachweis des Thoriums mit Alizarin S und seine Bestimmung am Ringofen nach Weisz

Zusammenfassung Zum Nachweis des Thoriums bewährte sich als Reagens eine wäßrige, perhydrol- und ammomumnitrathaltige Alizarin S-Lösung. Da Alizarin kein spezifisches Reagens für Thorium ist, wird ein Analysengang beschrieben, der sich zur Entfernung störender Substanzen aus Mineralen eignet. Das dabei erhaltene Thoriumnitrat kann am Ringofen quantitativ bestimmt werden.

---

Summary Aqueous alizarin S solution along with perliydrol and ammonium nitrate was found suitable for the detection of thorium. Since alizarin is not a specific reagent for thorium, an analytical procedure is described, which is suitable for the removal of interfering substances from minerals. The thorium nitrate obtained in this way can be determined quantitatively on the ring oven.

---

Résumé On a utilisé pour la recherche du thorium, une solution aqueuse d'alizarine S avec le perhydrol et le nitrate d'ammonium. Comme l'alizarine n'est pas un réactif spécifique du thorium, on a décrit un procédé d'analyse qui permet l'élimination des substances gênantes à partir des minéraux. On peut doser quantitativement le nitrate de thorium alors obtenu, à l'aide du four annulaire.

---

---

Wir danken an dieser Stelle dem Conselho Nacional de Pesquisas von Brasilien, der uns die Durchführung dieser Arbeiten ermöglicht hat.     

Sur des familles remarquables d'hypersurfaces isoparamétriques dans les espaces sphériques

Sans résumé     

Mikrochemie

Ohne Zusammenfassung     

Sur les représentations linéaires des groupes clos

Sans résumé     

Aromatische Aminoverbindungen

Ohne Zusammenfassung