Observed difference between the probabilities of recoilless resonance absorptionf′ and reemissionf″ of gamma-quanta in single crystals of Na2[Fe(CN)5NO]·2 H2O

The recoilless absorption probability factor,f, and recoilless reemission,f, both measured on Na₂[Fe(CN)₅NO]·2 H₂O single crystals using the black filter technique, were found to be different. Unexpectedly, the results found weref>f. In the calculation off, selfabsorption in the scatterer, non-ideality of the black filter and the influence of non-resonant scattering processes have all been taken into account. By varying the scattering geometry for the incoming and outgoing -beam relative to the crystallographic axes only a change in the reemitted valuesf _a, f_b, f_c could be detected because of the long lifetime of the excited nucleus (10^–7 s) relative to the lattice vibration frequencies (10¹² Hz).     

The complete matter sector in a three-generation compactification

We consider a Calabi-Yau compactification paradigm with three light generations and anR-symmetry. From a special form of the Tian-Yau manifold, we also construct a new three-generation model with markedly different phenomenology. Thecomplete spectrum of all light matter fields is obtained in a universal way and moreover in a physically suitable basis, allowing a straightforward analysis of all their couplings. Here we discuss all the renormalizable Yukawa couplings. This computation can equally well be repeated for all compactification models based on Calabi-Yau complete intersections in products of homogeneous spaces.     

Über die lokale Zetafunktion von Shimuravarietäten. Monodromiefiltration und verschwindende Zyklen in ungleicher Charakteristik

Ohne Zusammenfassung

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On the local zeta function of Shimura varieties. Monodromy filtration and vanishing cycles in unequal characteristic

     

The luminescence of Pr3+ in BaY4Si5O17

The cell constants of four new monoclinic compounds BaR₄X₅O₁₇ (R = Y, Gd; X = Si, Ge) are given. The luminescence of various RE activators in the silicates is reported. Pr³⁺-activated BaY₄Si₅O₁₇ shows efficient ultraviolet 5d → 4f emission and weak 4f → 4f emission (mainly red luminescence from the ¹D₂ level). The 5d → 4f emission is ascribed to Pr³⁺ on Y sites, the 4f → 4f emission to Pr³⁺ on Ba sites. Energy transfer from Pr³⁺ to Gd³⁺ has been observed. Gd³⁺ plays an intermediate role in the energy transfer from Pr³⁺ to Sm³⁺ and to Dy³⁺ in BaGd₄Si₅O₁₇. Upon activation with Tb³⁺ the silicates show characteristic green Tb³⁺ luminescence with a quantum efficiency of 75% for ultraviolet excitation.     

Matrix isolation infrared spectra of the complexes between methylacetate and water or hydrochloric acid

The hydrogen-bonded complexes between methylacetate (MeAc) and water or hydrochloric acid have been studied by infrared spectrometry in a low temperature Argon matrix. The ν_CO, ν_CC and ν_CC ional modes of MeAc show a splitting to the low and to the high frequency side of the free molecule. This suggests that water and HCl interact with the keto and ether oxygens. This conclusions is supported by the appearance of two main absorptions in the ν_HCl region. These results are discussed as a function of the gas-phase basicity of the two oxygen atoms, derived from the O(1s) core electron binding energies and from the ionization potentials.     

Determination of aminophenol isomers in water samples by extraction and thin-layer chromatography densitometry

A TLC densitometric method for the determination of the aminophenol isomers in water samples has been developed. The aminophenols are first extracted into chloroform-isoamylalcohol (1:2) mixture. The extracted aminophenols are separated on a TLC plate and visualized by spaying solution of 2,4,7-trintro-9-fluorenone in acetone. The colored spots are scanned for light absorption or reflection and the amount of each aminophenol is evaluated.     

Determination of mono-ortho substituted chlorobiphenyls by multidimensional gas chromatography and their contribution to TCDD equivalents

The mono-ortho chlorobiphenyls (CBs) 60, 74, 114, 123, 157, 167 and 189 were determined in Aroclor mixtures and aquatic organisms by multidimensional gas chromatography with electron capture detection (MDGC/ECD), using a combination of an Ultra 2 and an FFAP column. MDGC/ECD is recommended as the most suitable technique for direct determination of these CBs, without a liquid chromatographic (LC) pre-separation of mono-ortho CBs from the other CBs. Dependent, to some extent, on the stationary phase used, single-column determinations of these CBs easily yield too high results due to the presence of interferences. The contribution of the mono-ortho CBs studied to the total 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQs) from CBs in fish is highly dependent on the toxic equivalency factors (TEFs) used and varies between 0.02 and 22%. This contribution is mainly due to CBs 74, 114, 157 and 167 which may easily be determined by taking three heart-cuts and combining them into one MDGC/ECD run. The analytical error is negligible compared with the huge uncertainty of the TEFs. A need for more precise TEFs is emphasized.     

Use of chemiluminescence to the study of photostability of automotive coatings

Chemiluminescence (CL) imaging has been used to study the photodegradation of two automotive coatings, a melamine-crosslinked acrylic resin and an acrylic Polyurethane, as a function of artificial weathering time. Characteristics of the CL emission from coatings, the influence of light stabilizers and different types of sample were studied. The results indicate that the method is highly sensitive and can be used to measure photodegradation in unstabilized and stabilized coatings after only 48 h and 100–200 h of exposure, respectively. Measurements can be carried out on free clearcoats or on clearcoats applied on metallic panels. It is also possible to assess the degradation of individual layers in multiple-layer coating systems. Extrapolation to the failure time of coatings by CL is not yet achievable, but results show that the technique is useful for rapidly screening the relative performance of new coating formulations or light stabilizers added to clearcoats.     

Study of metal complexes of a tripodal hydroxypyridinone ligand by electrospray tandem mass spectrometry

The tripodal ligand N,N,N-tris[(1,hydroxy-2-pyridinon-6-yl)amide]propylamine was synthesized. It is composed of an anchor (nitrogen atom), a functional group (hydroxamate), and also a spacer of variable length defined by the number of methylene groups linking the anchor and the functional group. The characterization of this ligand in the presence of several divalent metal cations (Fe(II), Mn(II), Co(II) and Cu(II)), performed by electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS), allowed elucidation of oxidation states and also of different fragmentation patterns. The importance of the spacer length was studied in the case of the iron binary complex by comparing this ligand with another with a shorter spacer. In this way the stabilizing conditions, in which hydrogen bonds are implicated, were clarified.