Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p??<2.0 GeV/c the yield andp??-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

Secoandrostansäuren als enantiomere prostaglandin-analoga—I : 4- propyl-3,4-seco-androstan-3-säuren

Starting with 4-propyltestosterone syntheses of the enantiomeric tetrahydro-PGA₁ analogue 60 and its epimer 58 are described. Besides the isomer 56 the deoxy compound 28 as well as its noracid 35 were prepared as compounds closely related to 60. A key intermediate was the unsaturated acid 20.     

Secoandrostansäuren als enantiomere prostaglandin-analoga—II : 6-pentyl-4-nor-3,5-seco-androstan-3-säuren

A synthesis of the enantiomeric tetrahydro-PGA₁ analogue 48 is described. In addition the homoacid 50, its pentanor analogue 39 and its epimer 51, the 6-deoxy compounds 13 and 16 as well as the lactones 14, 53, 56 and 68 were prepared as compounds closely related to 48. Simple androstane derivatives served as starting materials for the syntheses. Key intermediates were 4, 32 and 63.     

Bulk single crystals of β-Ga2O3 and Ga-based spinels as ultra-wide bandgap transparent semiconducting oxides

In the course of development of transparent semiconducting oxides (TSOs) we compare the growth and basic physical properties bulk single crystals of ultra-wide bandgap (UWBG) TSOs, namely β-Ga₂O₃ and Ga-based spinels MgGa₂O₄, ZnGa₂O₄, and Zn_1-xMg_xGa₂O₄. High melting points of the materials of about 1800 -1930 °C and their thermal instability, including incongruent decomposition of Ga-based spinels, require additional tools to obtain large crystal volume of high structural quality that can be used for electronic and optoelectronic devices. Bulk β-Ga₂O₃ single crystals were grown by the Czochralski method with a diameter up to 2 inch, while the Ga-based spinel single crystals either by the Czochralski, Kyropoulos-like, or vertical gradient freeze / Bridgman methods with a volume of several to over a dozen cm³. The UWBG TSOs discussed here have optical bandgaps of about 4.6 - 5 eV and great transparency in the UV / visible spectrum. The materials can be obtained as electrical insulators, n-type semiconductors, or n-type degenerate semiconductors. The free electron concentration (n_e) of bulk β-Ga₂O₃ crystals can be tuned within three orders of magnitude 10¹⁶ - 10¹⁹ cm^?3 with a maximum Hall electron mobility (μ) of 160 cm²V^?1s^?1, that gradually decreases with n_e. In the case of the bulk Ga-based spinel crystals with no intentional doping, the maximum of n_e and μ increase with decreasing the Mg content in the compound and reach values of about 10²⁰ cm^?3 and about 100 cm²V^?1s^?1 (at n_e > 10¹⁹ cm^?3), respectively, for pure ZnGa₂O₄.     

Conformational analysis of flavonoids: Crystal and molecular structure of 3′,5′-dibromo-3-methyl-6,4′-dihydroxyflavone (1:2) triphenylphosphine oxide complex

Crystal structure determination and AM1 molecular orbital calculations were performed on the flavone, 3,5 — dibromo — 3 — methyl — 6,4 — dihydroxyflavone (EMD21388), crystallized as a (1:2) triphenylphosphine oxide (TPPO) co-crystal complex. This is also the first structural report of a 21 TPPO co-crystal complex with a flavone. The calculated molecular structure is in good agreement with the observed crystallographic conformation which shows that the angle between the benzopyrone and phenyl rings,, [C(3)-C(2)-C(1)-C(6)] is 49.1(8)°, compared with the geometry-optimized minimum energy angle of 46.0°. The barrier to rotation in this system is about 3.5 kcal/mol. Biochemical data for EMD 21388 show it is the most potent inhibitor of the enzyme iodothyronine deiodinase and is the strongest competitor for the binding of thyroxine to its serum transport protein transthyretin. This analysis reveals that the flavone can adopt a conformation that has structural homology with the thyroid hormone.     

Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p⊥<2.0 GeV/c the yield andp⊥-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

n‐type conductivity in sublimation‐grown AlN bulk crystals

AlN crystals grown by physical vapour‐phase transport in the presence of a SiC doping source possess n‐type conductivity. The net donor concentration attains up to mid 10¹⁷ cm^–3. The investigation reveals shallow donors forming an impurity band and acceptor‐like electron traps at about 0.5 eV below the conduction band edge. Thermal electron emission from these traps is responsible for the observed n‐type conductivity. The shallow donors are suggested to be due to Si atoms on Al sites. The majority of them is assumed to be compensated by deep acceptors in the lower half of the band gap. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)