Synthesis of Novel Chiral C 2-symmetric Diaza-18-crown-6 Ether Derivatives and their Enantioselective Recognition of Amino Acid Derivatives

New chiral diaza-18-crown-6 ether derivatives, gt;5gt; and gt;6gt; were synthesized from (gt;Rgt;)-(-)-2-amino-1-bütanol. These chiral artificial receptors exhibit pronounced chiral recognition toward the enantiomers of gt;lgt;- and gt;dgt;- amino acid derivatives. The highest enantioselectivity was observed in the case of Trp-OMe·HCl (gt;Kgt;gt;gt;Dgt;gt;/gt;Kgt;gt;gt;Lgt;gt;=12.5).     

Efficient J=0-1 soft-X-ray lasing in neon-like ions at pump powers below 250 GW

2 . By using a 0.7% prepulse that precedes the main pulse by 5 ns and applying a total pump energy of 100 J or less, the J=0-1 lasing is at least one order of magnitude higher than the non-lasing background. For the 32.6-nm line of Ti, the 25.5-nm line of Fe, and the 23.1-nm line of Ni, gain coefficients of (±) 4.20.4cmgt;-1gt;, (±) 3.90.3cmgt;-1gt;, and (±) 3.60.6cmgt;-1gt;, respectively, were measured for 2.4-cm-long curved targets, resulting in gain–length products of ∼10. Angle-resolved spectra indicate a beam divergence of 3 mrad (FWHM), typically. The space-resolved spectra show that the J=0-1 lasing lines are emitted from an approximately 60-μm-wide (FWHM) plasma region, whereas the nearby continuum emission is produced in a considerably broader plasma region of ∼250 μm. Lasing at 25.5 nm in neon-like iron was observed at a pump power as low as 180 GW (∼9 TW/cmgt;2gt;), with, however, considerable shot-to-shot scatter in the absolute laser output. Received: 5 September 1997/Revised version: 10 November 1997     

Neutron diffraction investigation of MnAs under high pressure

Powdered MnAs has been investigated by neutron diffraction in a pressure cryostat, at hydrostatic pressures up to 13 kbar and temperatures down to 4.2 K. It has been found that in the orthorhombic MnP type structure, which under pressure is retained at low temperature, a spiral magnetic structure with propagation vector τgt;agt; = 0.125X2πX g>ag>gt;1gt; at 12.6 kbar is formed.     

Magnetic properties of transition metal substituted MnP

The magnetic properties of polycrystalline samples of gt;Mngt;gt;1?gt;tgt;gt;gt;Tgt;gt;gt;tgt;gt;gt;Pgt; (gt;Tgt; = gt;Vgt;, gt;Crgt;, gt;Fegt; and gt;Cogt; for 0.00 ≦ gt;tgt; ≦ 0.50) are studied by magnetic susceptibility, magnetization and neutron diffraction measurements. The magnetic phase diagrams of the Mngt;1?gt;tgt;gt;gt;Tgt;gt;gt;tgt;gt;P phases exhibit paramagnetic, ferromagnetic, helimagnetic and spin glass regions depending on temperature and substitution (gt;Tgt;, gt;tgt;). The concentrated spin glass regions observed in gt;Mngt;gt;1?gt;tgt;gt;gt;Vgt;gt;gt;tgt;gt;gt;Pgt; and gt;Mngt;gt;1?gt;tgt;gt;gt;Cogt;gt;gt;tgt;gt;gt;Pgt; (0.30 ≦ gt;tgt; ≦ 0.50) are believed to result from the disorder in the metal sublattice. The variation of the magnetic moment of the ordered Mngt;1?gt;tgt;gt;gt;Tgt;gt;gt;tgt;gt;P phases with the substitution (gt;Tgt;, gt;tgt;) is discussed.     

Lase action on resonant molecular flows through capillaries

New experimental results are reported pointing to the possibility of a laser control of the resonant gases transit through capillaries in the Knudsen and intermediate regimes.     

Absorption and photoluminescent measurements in indirect,nitrogen doped GaAs1−χPχ

The absorption and photoluminescent spectra of nitrogen doped GaAsgt;1?χgt;Pgt;χgt; epitaxial layers were studied in the alloy composition range 0.58 ? χ ? 0.77. The structure in the absorption and luminescent spectra are analysed.