Bicrystalline magnetic lateral superlattices Sussiau, M.; Nguyen Van Dau, F.; Galtier, P. ...
Journal of magnetism and magnetic materials,
1997, 1997-1-00, Letnik:
165, Številka:
1
Journal Article
Recenzirano
We have studied the correlations between structural, magnetic and transport properties of bicrystalline lateral magnetic superlattices grown by molecular beam epitaxy on vicinal Si(111) substrates ...misoriented towards 112. The substrates were thermally pre-treated in order to activate the step bunching phenomena, which results in a laterally modulated surface topology with a period of ≈ 1000 Å and an amplitude up to 80 Å. 100 Å thick Co or FeNi magnetic layers grown on such substrates exhibit an in-plane uniaxial anisotropy with the easy axis parallel to the step direction. Transmission electron microscopy experiments reveal that this anisotropy can be associated with a lateral pseudo-periodic variation of the epitaxial relationship of the metallic layers. Magneto-resistance measurements on a 700 μm × 100 μm active area surprisingly reveal a single-domain behaviour with a magnetization reversal by rotation.
A practical synthesis of the anti-methicillin resistant Staphylococcus aureus cephem ...(6R-trans)-E-7-2,5-dichloro-4-3-(carboxymethyl)amino-3-oxo-1-propenylphenyl-thio-acetylamino-4-(2-carboxy-8-oxo-5-thia-1-azabicyclo-4.2.0oct-2-en-3-yl)methylthio-2,6-dimethyl-1-3-(4-methylmorpholino-4-yl)propyl-1-pyridinium, hydroxide, inner salt (BMS-247243) was developed. A process was developed for the interchange of the iodide counterion in 3a to chloride 3b that was essential for an efficient synthesis of the C-3 side chain 4-mercaptopyridone 6b. Use of catalytic Bu4NCl in the reaction of chlorocinnamide 14 with the Li-salt of methylthioglycolate formed the methyl ester of the C-7 side chain 12b in high yield. Reaction with the dianion of thioglycolic acid gave an increased level of the corresponding Michael addition byproduct that led to lower quality thermodynamic product 12b by the reverse reaction. Cephem nucleus 16 was acylated with the acid chloride of acid 12b in a biphasic system to circumvent the cumbersome workup involved in reactions mediated by carbodiimdes DCC or EDAC for the synthesis of diester 17. An unusual degradation product diacid 20 was obtained during the deprotection of diester 17 with TFA to amorphous diacid 19. Reaction of diacid 19 with 4-mercaptopyridone 6b formed BMS-247243 in moderate yield. Alternately, an efficient coupling of diester 17 with 4-mercaptopyridone 6b gave crystalline diester 21 with minimal (<1%) contamination of the double bond isomer 22. Double deprotection of diester 21 followed by crystallization furnished the double zwitterion BMS-247243 in high yield.
Synthesis of biaryl type systems, 11‐aryl/heteroarylnaphtho2,1‐bfurans 8‐11 has been described with a view to studying the conformational orientation of C‐11 aryl/heteroaryl groups. Synthesis of 8‐11 ...was accomplished by a two‐step sequence involving O‐alkylation of 2‐naphthol with appropriate halo‐ketones 2‐4, followed by cyclization of the resulting naphthoxy‐ketones 5‐7 with methanesulphonic acid. The structures of 8‐11 are based on detailed 2D NMR spectral analysis. The H8 in these compounds is not subject to significant anisotropic upfield shielding effects. The slightly upfield chemical shift of H8 in molecules 9‐11, relative to 8 has been correlated with the electron density at C17 and C8 positions. While molecular modeling indicated dihedral angle (φ) between the C11 aryl/heteroaryl groups and the naphthofuran plane to be in the range of 70–60° in 8‐10, a single X‐ray crystal structural analysis of 11‐(4′‐pyridyl)naphtho2,1‐bfuran 10 indicated (φ) of 64.36°. In view of significant deviations from the orthogonal oreintation, the absence of any significant anisotropic shielding in 8‐11 is not entirely unexpected.
The population of Tundra Swans (Cygnus columbianus columbianus) breeding on the lower Alaska Peninsula represents the southern extremity of the species' range and is uniquely nonmigratory. We used ...data on recaptures, resightings, and recoveries of neck-collared Tundra Swans on the lower Alaska Peninsula to estimate collar loss, annual apparent survival, and other demographic parameters for the years 1978– 1989. Annual collar loss was greater for adult males fitted with either the thinner collar type (0.34) or the thicker collar type (0.15) than for other age/sex classes (thinner: 0.10, thicker: 0.04). The apparent mean probability of survival of adults (0.61) was higher than that of immatures (0.41) and for both age classes varied considerably by year (adult range: 0.44–0.95, immature range: 0.25–0.90). To assess effects of permanent emigration by age and breeding class, we analyzed post hoc the encounter histories of swans known to breed in our study area. The apparent mean survival of known breeders (0.65) was generally higher than that of the entire marked sample but still varied considerably by year (range 0.26–1.00) and indicated that permanent emigration of breeding swans was likely. We suggest that reductions in apparent survival probability were influenced primarily by high and variable rates of permanent emigration and that immigration by swans from elsewhere may be important in sustaining a breeding population at and near Izembek National Wildlife Refuge.
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