Biosynthesis of tuberin and xanthocillin from tyrosine

(2S)-Tyrosine (5) is incorporated stereospecifically into tuberin (1) with retention of the 3-$\text{pro}$-S proton and incomplete retention of the 2-S proton; a parallel pathway to the xanthocillin (4) is apparent with stereospecific retention of the 3-$\text{pro}$-R proton of tyrosine; results of experiments with $\text{threo}$- and $\text{erythro}$-3-hydroxytyrosine in relation to tuberin biosynthesis are reported.     

Theory of the quantized Hall effect (III)

In the previous paper, we have demonstrated the need for a phase transition as a function of θ in the non-linear σ-model describing the quantized Hall effect. In this work, we present arguments for the occurrence of exactly such a transition. We make use of a dilute gas instanton approximation as well as present a more rigorous duality argument to show that the usual scaling of the conductivity to zero at large distances is altered whenever $\text{σ}{}_{\mathrm{xy}}{}^{\mathrm{(0)}}\text{≈}\text{1}\text{2}\text{ne}{}^2\text{/h}$, n integer. This then completes our theory of the quantized Hall effect.     

Simultaneous Amplification of Terahertz Difference Frequencies by an Injection-Seeded Semiconductor Laser Amplifier at 850 nm

Two-frequency operation of an 850 nm semiconductor optical amplifier was achieved by simultaneously injection seeding it with two diode lasers. The two frequencies could be independently amplified without strong interference when they were separated by more than 10 GHz, and the spectral purity was preserved by the amplification process. At frequency differences below 10 GHz, unbalanced two-frequency output was observed, which can be explained by a two-mode interaction driven by the refractive index modulation at the beat frequency. The laser system is suitable for the difference-frequency generation of coherent terahertz radiation in ultra-fast photoconductors or nonlinear optical media.     

Test sets for integer programs

In this paper I discuss various properties of the simplicial complex of maximal lattice free bodies associated with a matrixA. If the matrix satisfies some mild conditions, and isgeneric, the edges of the complex form the minimal test set for the family of integer programs obtained by selecting a particular row ofA as the objective function, and using the remaining rows to impose constraints on the integer variables.     

Quantitative determination of element distributions in silicon based thin film solar cells using SNMS

The determination of elemental distributions in thin film solar cells based on amorphous silicon using electron beam SNMS is possible by quantifying the measured ion intensities. The relative sensitivity factors (RSFs) for all elements measured have to be known. The RSFs have been determined experimentally using implantation and bulk standards with known concentrations of the interesting elements. The measured RSFs have been compared with calculated RSFs. The model used for the calculation of the RSFs takes into account the probability for electron impact ionization and the dwell time of the neutrals inside the postionization region. The comparison between measured and calculated RSF shows, that this model is capable to explain the RSFs for most elements. Differences between calculated and measured values can be explained by the formation of hydride and fluoride molecules (in case of H and F) and influences of the angular distribution of the sputtered neutrals in case of Al. The experimentally determined RSFs have been used for a quantification of depth profiles of the i-, buffer-, p- and front contact layers of a-Si solar cells.     

Dichroism of (CH3NH3)2CdCl4 in the farinfrared

The dielectric constant of (CH₃NH₃)₂ CdCl₄ has been measured as a function of temperature in the submillimeter range. Freshly grown samples with a wide domain structure at room temperature show a pronounced dichroism in this spectral range which is caused by the orientation of the molecules in the room temperature orthorhombic phase and their response to the electromagnetic wave.