Hochdrucksynthese und Kristallstruktur von YbH2, 67

High Pressure Synthesis and Crystal Structure of YbH_2.67 Ytterbiumhydrides can be synthesized by reaction of ytterbium metal in hydrogen atmosphere above 600 K. The experiments were carried out in the pressure range from 200 to 3200 bar. X‐ray investigations on powdered samples and elastic neutron diffraction experiments on deuterated compounds led to a complete structure determination. YbH_2.67 is obtained at reaction pressures of 200, 1400 und 3200 bar. In contrast to reports in literature the deuterides crystallize with trigonal symmetry (P3¯1m, a = 6.344(1)Å, c = 9.002(1)Å, Z = 9) and not in the cubic crystal system. The composition YbD_2.67 was additionally checked by chemical analysis. The crystal structure can be described as a close packing of ytterbium atoms (stacking sequence …ABC…) in which all tetrahedral holes and 2/3 of the octahedral holes are occupied in an ordered manner by hydrogen. Magnetic susceptibility measurements are in agreement with literature data.     

Accurate parametrized variational calculations of the molecular electronic polarizability by NDDO‐based methods

The variational method for the calculation of the electronic polarizability of molecules within the NDDO‐based semiempirical MO methods MNDO, AM1, and PM3 was parametrized to improve its accuracy. A training set of 156 compounds was used to fit 34 parameters simultaneously for 12 elements using a simplex optimization. The resulting parameters were tested for a test set of 83 molecules and the calculated polarizabilities compared with the experimental data. For AM1, the RMS deviation between experimental and calculated polarizabilities was reduced from 2.99 (using the original variational treatment) to 0.70 ų for the test set and from 2.81 to 0.40 ų for the training set. MNDO and PM3 gave similar improvements. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 17–31, 1999     

Production of PHAs from agricultural waste material

Polyhydroxyalkanoates (PHAs) are biodegradable substitutes to fossil fuel plastics that can be produced from renewable raw materials such as saccharides, alcohols and low-molecular-weight fatty acids. They are completely degradable to carbon dioxide and water through natural microbiological mineralization. Consequently, neither their production nor their use or degradation have a negative ecological impact. By keeping closed the cycle of production and re-use, PHAs can enable at least part of the polymer-producing industry to switch from ecologically harmful end-of-the-pipe production methods towards sounder technologies. Up to now such polyesters have been produced biotechnologically from refined raw materials (e.g. glucose and sodium propionate), but they can as well be produced much cheaper from agricultural waste materials (e.g. molasses, maltose, glycerol phase from biodiesel production, whey), as long as these materials have a known composition and are available in appropriate quantities. Yield factors and specific rates for growth and PHA accumulation are shown for 3 strains of Alcaligenes latus for different agricultural waste carbon sources.     

Formation of a Special Intermediate during Phase Transformation of Zeolite NaA to Nepheline

In the process of phase transformation of zeolite NaA to nepheline under hydrothermal conditions a special intermediate occurs. This is due to the high reaction rate of nepheline formation in the presence of water molecules. Consequently, the usually observed amorphous material with high condensed silica does not occur as separate phase. – The intermediate which is formed due to the destruction of the long-range order of zeolite is significantly short-range ordered. The phase transformation process starts at the outer surface of zeolite crystals, thus generating a diffusion barrier for sorption uptake processes.     

Silicate Cross‐Linked Bio‐Nanocomposite Hydrogels from PEO and Chitosan

The compositions and the multi phase structures of bio‐nanocomposite hydrogels made from silicate cross‐linked PEO and chitosan are related to some of their physical and biological properties. The gels are injectable and self‐healing because the cross‐linking is physical and reversible under deformation. The presence of chitosan aggregates affects the viscoelastic properties and reinforces the hydrogel network. The chitosan adds advantageous properties to the hydrogel such as enhanced cell spreading and adhesion. In vitro biocompatibility data indicate that NIH 3T3 fibroblasts grow and proliferate on the bio‐nanocomposite hydrogel as well as on hydrogel films.

     

Acyl- und Alkylidenphosphane. XXV. Molekül- und Kristallstruktur des 1,2-Di(tert-butyl)-3-dimethylamino-1-thio-4-trimethylsilylsulfano-1λ5,2λ3-diphosphet-3-ens

Acyl- and Alkylidenephosphines. XXV. Molecular and Crystal Structure of 1,2-Di(tert-butyl)-3-dimethylamino-1-thio-4-trimethylsilylsulfano-1λ⁵, 2λ³-diphosphet-3-ene The title compound 1 formed in a nearly quantitative yield by decomposition of tert-butyl(N,N-dimethylthiocarbamoyl)trimethylsilylphosphine, crystallizes in the orthorhombic space group P2₁2₁2₁ with {a = 1067.3(1); b = 1077.1(1); c = 1924.6(5) pm; Z = 4} at +20°C. An X-ray structure determination (R_G = 0.038) shows two tert-butyl groups at a four- (P1) and a three-coordinate phosphorus atom (P2) to be placed on different sides of the four membered ring. Characteristic bond lengths as well as the angles at the atoms P1, P2, C3, and C4 inside the ring have already been given above.     

The compton spectrometer

This is the story about how knowledge of the Compton profile led to the technical development of a useful apparatus. It is also the story of interdisciplinary collaboration between condensed matter theorists and medical physicists.     

Reactive-ion-etch damage in GaAs processing evaluated by a microwave absorption technique

Through determination of magnetic field-dependent resistivity by electric microwave absorption (EMA), both mobility and carrier concentration of conducting layers in a semiconducting substrate may be evaluated. We have employed this method to study the extent of electric damage produced during standard GaAs plasma processing; various typical heterostructures were subjected to realistic reactive ion etch treatments and the changes in transport properties were examined by EMA. It was seen that predominantly chemical etch processes result in little substrate damage, whereas physical milling produces considerable degradation. Oxynitride etching was noted to be benign only at low voltages, whereas photoresist stripping was not seen to produce any measurable substrate damage.