Phenylessigs?ure, ein neues Reagens auf Thorium

Ohne Zusammenfassung     

Quasistatic and dynamic functional properties of thin superelastic NiTi wires

2D/3D structures made from thin NiTi wires (d < 100μm) are currently considered for engineering applications in textile, medical or robotics fields. The development of such novel applications requires the knowledge of the thermomechanical behaviour of NiTi ultra thin wires in tension, torsion bending and combined loads, which might differ from that of thicker wires due to influence of texture, cold work and higher aspect ratio. To deal with this challenge, a new experimental testing approach presented in this paper has been developed. It includes thermomechanical tensile testing, combined tension-torsion testing and forced tensile vibrational testing realized on self-made testing rigs equipped with Peltier furnaces and in-situ electric measurement systems. The collected experimental datasets provide a basis upon which FEM implementable SMA models describing functional thermomechanical behaviours of 2D/3D NiTi wire structures (quasistatic and dynamic) are presently being constructed     

Manifestation of the stochastic resonance in submerged jets under an acoustic action

A phenomenon that is similar to the well-known stochastic resonance in nonlinear oscillators but is caused by the turbulence in a circular submerged jet under a harmonic acoustic action, rather than by noise, is considered. It is shown that, at a fixed distance from the nozzle, a variation of the initial turbulence level leads to a non-monotonic variation of the wave amplitude at the frequency of the acoustic action, namely, to the appearance of an amplitude maximum at a certain level of the initial turbulence. The qualitative explanation of the phenomenon consists in that the initial turbulence acts on the system in a way similar to that of external noise: it changes the effective parameters of the system and, in particular, shifts the spectral maxima, which is equivalent to a change in a certain “eigenfrequency.” Such a change in the effective parameters of the jet leads to a phenomenon similar to the stochastic resonance.     

Untersuchung von implantierten Schichten (N2+, CO+) von Werkzeugst?hlen mit dem AES-Verfahren

Summary The paper deals with the depth distribution of implanted elements from the surface, i.e., the concentration profile, studied by means of Auger electron spectroscopy. Results obtained in low carbon CrMoV tool steel implanted with N ₂ ⁺ or CO⁺ ions have been correlated with theoretical curves which were calculated by the LSS method for pure -iron.Low doses of implanted nitrogen (1.5 and 2.0 · 10¹⁷ ions/ cm²) exhibit no differences between measured concentration profiles and theoretical distribution, while a high dose (4.0 · 10¹⁷ ions/cm²) induced profile deformation together with sputtering of the material surface. By bombardment with carbon monoxide (1.5 – 4.0 · 10¹⁷ ions/cm²), these molecular ions are split after their incidence and carbon as well as oxygen atoms can move independently within the material. The position of the oxygen concentration profiles correspond to the theoretically found curves (the true heights of the profile being substantially lower), whereas the concentration profiles of carbon are very flat and of asymmetrical shape.     

Efficient Oligomerization of Aromatic Amino Acids Induced by Gaps in Four-Helix Bundles of DNA or RNA

The formation of peptides from amino acids is one of the processes associated with life. Because of the dominant role of translation in extant biology, peptide-forming processes that are RNA induced are of particular interest. We have previously reported the formation of phosphoramidate-linked peptido RNAs as the products of spontaneous condensation reactions between ribonucleotides and free amino acids in aqueous solution. We now asked whether four-helix bundle (4HB) DNA or RNA folding motifs with a single- or double-nucleotide gap next to a 5’-phosphate can act as reaction sites for phosphoramidate formation. For glycine, this was found to be the case, whereas phenylalanine and tryptophan showed accelerated formation of peptides without a covalent link to the nucleic acid. Free peptides with up to 11 tryptophan or phenylalanine residues were found in precipitates forming in the presence of gap-containing DNA or RNA 4HBs. Control experiments using motifs with just a nick or primer alone did not have the same effect. Because folded structures with a gap in a double helix are likely products of hybridization of strands formed in statistically controlled oligomerization reactions, our results are interesting in the context of prebiotic scenarios. Independent of a putative role in evolution, our findings suggest that for some aromatic amino acids an RNA-induced pathway for oligomerization exists that does not have a discernable link to translation.     

DoE-Driven Development of an Organocatalytic Enantioselective Addition of Acetaldehyde to Nitrostyrenes in Water**

The development of an enantioselective enamine-catalysed addition of masked acetaldehyde to nitroalkenes via a rational approach helped to move away from the use of chloroform. The presented research allows the use of water as a reaction medium, therefore improving the industrial relevance of a protocol to access very important pharmaceutical intermediates. Critical to the success is the use of chemometrics-assisted ‘Design of Experiments’ (DoE) optimisation during the development of the presented new synthetic approach, which allows to investigate the chemical space in a rational way.     

Bisoxazoline-Lewis acid-catalyzed direct-electron demand oxo-hetero-Diels-Alder reactions of N-oxy-pyridine aldehyde and ketone derivatives

A general catalytic oxo-hetero-Diels-Alder reaction for pro-chiral aldehyde and ketone N-oxy-pyridines is presented. The catalytic and asymmetric oxo-hetero-Diels-Alder reaction of electron-rich dienes with N-oxy-pyridine-2-carbaldehyde and ketone derivatives, catalyzed by chiral copper(II)-bisoxazoline complexes, gives optically active six-membered oxygen heterocycles in moderate to good yields and with excellent enantioselectivities.     

Ge clusters in Si matrix: structure and dynamics

We have determined by computer simulations, some structural properties of Ge clusters embedded in a Si crystalline host matrix for cluster sizes varying from 0.5 to 1.5 nm. In order to describe inter-atomic forces we have chosen a Valence Force Field (VFF) semi-empirical potential. Next we have calculated the density of vibrational states by diagonalization of the dynamical matrix defined with the same potential. The influence of the volume/interface ratio of Ge on the vibrational properties is discussed. Received 10 December 1998 and Received in final form 7 April 1999