Konformationsanalysen von Modell-Tripeptiden: Der Einfluss von α,α-disubstituierten α-Aminosäuren auf die Sekundärstruktur. Teil I. NMR- und CD-Untersuchungen

Conformational Analysis of Tripeptide Models: The Influence of α,α-disubstituted α-Amino Acids on the Secondary Structure. NMR and CD Investigations The conformational properties of α,α-disubstituted α-amino acids are discussed on the basis of NMR, CD, X-ray, and molecular-mechanics studies on tripeptide models 1 . It is shown that different disubstituted amino acids do not exert the same influence on secondary-structure formation. Thus, the choice of substituents allows the construction and stabilisation of different conformations of oligopeptide chains.     

Pion chemical potentials in heavy-ion collisions: relativistic quantum molecular dynamic analysis

In the framework of relativistic quantum molecular dynamics we analyse pion chemical potentials in the hadron system produced in central heavy-ion collisions at the bombarding energiesE _lab/A=(1–2) GeV/nucl. We find that the equilibrium relations hold for chemical potentials of π^?, of π⁰, of π⁺ and pion energy spectra reach local thermal equilibrium. However, there is no chemical equilibrium. The pion chemical potentials are very large and decrease during the expansion stage.     

Dimension of eigenspaces of Schrödinger operators-local Birman-Schwinger bound

We prove an upper bound on the dimension of eigenspaces of Schrödinger operators with singular and long range potentials. Its relation to upper and lower bounds on the eigenvalues is discussed.     

Dynamics of learning and generalization in perceptrons with constraints

Depending on the kind of constraints imposed on the weights of a perceptron, learning can be a combinatorially hard problem. As an example of this type, I discuss a perception with binary weights comparing results obtained from replica theory, dynamic mean field theory and simulated annealing. Contrary to the replica calculation, dynamics yields information about the performance of a polynomial algorithm in a situation where the best solution cannot be found in polynomial time. I also discuss improved learning algorithms and results for finite size perceptrons.     

Determination of halogenated acetic acids and 2,2-dichloropropionic acid in water samples

Summary A new method is described for the determination of halogenated acetic acids and 2,2-dichloropropionic acid in slightly polluted water. The acids were extracted in a light-phase rotary perforator, derivatised with diazomethane and determined by GC-ECD and GC-MS. The standard deviations were in the range of 14.5–16.8%. Average recoveries were 82%, 92% and 79% for monochloro-, dichloro- and trichloroacetic acid, respectively. The extraction yields for the bromoacetic acids and dichloropropionic acid were in the range of 64–85%.