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941.
We determine the values attained by the rank of the Gauss map of a projective model for a fixed algebraic variety in positive characteristic p. In particular, it is shown that any variety in p>0 has a projective model such that the differential of the Gauss map is identically zero. On the other hand, we prove that there exists a product of two or more projective spaces admitting an embedding into a projective space such that the differential of the Gauss map is identically zero if and only if p=2. 相似文献
942.
Hajime Kaji 《Mathematische Annalen》1985,273(1):163-176
943.
Kaoru Yamanouchi Hajime Watanabe Seiichiro Koda Soji Tsuchiya Kozo Kuchitsu 《Chemical physics letters》1984,107(3):290-294
Laser-induced fluorescence spectra of Ne- and Ar -aniline complexes were observed with a resolution of 0.04 cm?1. By a simulation analysis of the rotational structures, the distances between the rare-gas atom and the aromatic ring of aniline were found to be 3.35 ± 0.04 and 3.50 ± 0.04 A in the X?1A1 state of the Ne and Ar complexes, respectively, and about 0.05 A shorter when aniline was excited to the Ã1B2 state. 相似文献
944.
Sei-ichi Saito Yoji Umezawa Hajime Morishima Tomohisa Takita Hamao Umezawa Masatoshi Narita Masami Otsuka Susumu Kobayashi Masaji Ohno 《Tetrahedron letters》1982,23(5):529-532
An improved route to synthesize deglyco-bleomycin A2, the aglycon of bleomycin A2, aiming at the total synthesis of bleomycin is described. The new route is characterized by the stepwise elongation of the amino acid constituents and the use of a thiol ester obtained by aldol condensation. 相似文献
945.
The 7-endo radical cyclization of (bromomethyl)dimethylsilyl ethers derived from ethyl γ-hydroxy-α-methylenecarboxylates bearing a bulky γ-substituent such as isopropyl, cyclohexyl, and tert-butyl groups in tetrahydrofuran gave preferentially cyclic silyl ethers bearing the ethoxycarbonyl group anti to the γ-substituents in high yields. Treatment of the cyclic silyl ethers with silica gel gave acyclic ethyl γ-hydroxy-α-[2-(hydroxydimethylsilyl)ethyl]carboxylates. The reduction of the cyclization products with DIBAL followed by Tamao oxidation gave the corresponding acyclic triols. 相似文献
946.
Hanamoto T Koga Y Kido E Kawanami T Furuno H Inanaga J 《Chemical communications (Cambridge, England)》2005,(15):2041-2043
The palladium catalyzed cross-coupling reactions of aryl iodides and 5-tributylstannyl-4-fluoropyrazole prepared from fluoro(tributylstannyl)acetylene proceeded smoothly giving the corresponding 5-aryl-4-fluoropyrazole in good yields. 相似文献
947.
[reaction: see text] Cu(I) complexes of xanthane-based diphosphines were versatile catalysts for dehydrogenative alcohol silylation, exhibiting high activity and broad substrate scope. Highly selective silylation of 1-decanol over 2-decanol is possible even with a silylating reagent of small steric demand such as HSiMe(2)Ph or HSiEt(3). 相似文献
948.
Hashihayata T Sakoh H Goto Y Yamada K Morishima H 《Chemical & pharmaceutical bulletin》2002,50(3):423-425
A (2R,4S)-trans-disubstituted pyrrolidine ring system was constructed by employing iodine-mediated oxidative cyclization of (1R)-N-[1-(4-bromophenyl)-3-butenyl]acetamide 3 as a key step. The resulting diastereomeric mixture of (2R)-2-aryl-4-acetoxypyrrolidine 4 was stereoselectively converted to the side-chain of a novel ultrabroad-spectrum carbapenem 1, via (2R,4R)-2-aryl-4-hydroxypyrrolidine 7. 相似文献
949.
Development of a novel solid-phase extraction element for thermal desorption gas chromatography analysis 总被引:2,自引:0,他引:2
A novel solid-phase extraction element is developed for sorptive enrichment of dilute analytes from liquid samples with high extraction efficiencies due to its larger amounts of polydimethylsiloxane (PDMS) absorbent than the conventional syringe type of solid-phase microextraction (SPME). The extraction element is made of titanium (Ti) open tubular tube (30 mm x 1.2 mm i.d. x 1.6 mm o.d.) coated with a chemically bonded layer of PDMS (500 microm in thickness). The extraction element combined with thermal desorption-gas chromatography-mass spectrometry using a pyrolysis-gas chromatography-mass spectrometry system was used to extract and analyze a typical herbicide, bethrodine in water samples over a concentration range from 2.5 to 2.5 x 10(4) ng/l. Thus obtained calibration curve showed good linearity for the tested whole concentration range with regression coefficient of 0.992. Detection limit of 0.5 ng/l level was achieved and the reproducibility of the measurements for bethrodine at 10 ng/l level was found to be fairly good with relative standard deviation below 7.5%. 相似文献
950.
Guizhong Qi Yuu Nitto Akira Saiki Taketoshi Tomohiro Yuushou Nakayama Hajime Yasuda 《Tetrahedron》2003,59(52):10409-10418
Yb[C(SiMe3)3]2 initiates the living polymerization of methyl methacrylate (MMA) at −78°C to give the polymer with Mn of 51.0×104 (Mw/Mn=1.1) and high isotacticity (97%) in a quantitative yield. Mixing of the acetone solution of resulting polymer (Mn=16.3×104) with the acetone solution of syndiotactic poly(MMA) (Mn=15.7×104) prepared by the (C5Me5)2SmMe(THF) initiator produces desired stereocomplex in high yield bearing very high Tm whose tensile modulus is higher than the respective isotactic and syndiotactic poly(MMA)s. Yb[C(SiMe3)3]2 also generated isotactic (98%) poly[2-(dimethylamino)ethyl methacrylate] (DMEMA), and (C5Me5)2SmMe(THF) affords the syndiotactic (97%) polymer in high yields. The combination of isotactic poly(MMA)-block-poly(DMEMA) (97/3) and syndiotactic poly(MMA)-block-poly(DMEMA) (97/3) provides the amphiphathic stereocomplex. In sharp contrast to the catalysis of Yb[C(SiMe3)3]2 in toluene, the addition of THF or HMPA resulted in the formation of syndio-rich poly(MMA). 相似文献