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101.
We determine the pure global dimension of finite dimensional hereditary or radical-squared zero algebras over algebraically closed fields. The results are applied to algebras of dimension four and to the incidence algebras of critical ordered sets studied by Loupias. We further prove that the path algebra of an oriented cycle shares with Dedekind domains the Kulikov property (submodules of pure-projective modules are pure-projective). 相似文献
102.
Pavel Kratochvíl Dagmar Strakov Jií Podeva 《Journal of Polymer Science.Polymer Physics》1979,17(6):945-950
Interaction of nonidentical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by A24, the second virial coefficient for interaction of unlike species. This parameter is related to the compatibility of the two polymers in solution and is obtainable experimentally, e.g., by light scattering. With chemically markedly different polymers, A24 depends neither on the molecular weight of the polymers nor on the solvent and becomes characteristic of the polymer pair. For a mixture of two copolymers or of a homopolymer and a copolymer with similar compositions, A24 depends both on the solvent and on the molecular weight of polymers. Under such circumstances A24 ceases to be a quantity given only by the chemical structure of the two polymers; however, under suitable conditions it remains a sensitive function of the difference between the chemical nature of polymer components. 相似文献
103.
104.
Matthias Wanner Dagmar Gerthsen Stefan-Sven Jester Biprajit Sarkar Brigitte Schwederski 《Colloid and polymer science》2005,283(7):783-792
In the present study, effects of the treatment of citrate-reduced Au sols with NaCl, NaBr and Na2SO4 are described. The particles are characterized by transmission electron microscopy (TEM) and spectroscopic methods, suggesting an exchange of the citrate capping by the anions of the Na salts. Under electron beam exposure the capping of the NaCl- and NaBr-treated particles disappears. The specific electronic properties of the Na salt-treated particles are studied by electron absorption spectroscopy (EAS) and electron paramagnetic resonance (EPR). A discussion of the results in comparison with the spectroscopic responses from the original particles is given. A correlation between the data of EAS and EPR is found. The respective electron-withdrawing effect of the capping anions towards the Au core seems to be of considerable significance regarding the orbital situation around the Fermi level. 相似文献
105.
Enantiopure stannyl-[D1]methanol was converted to chloro-[D1]methylstannane under complete inversion of configuration using Ph3P/N-chlorosuccinimide in THF. It was transmetalated to stereospecifically give chloro-[D1]methyllithium (ee up to 98%). Its microscopic configurational stability was tested by performing tin-lithium exchange in the presence of benzaldehyde as the electrophile under various conditions. The macroscopic configurational stability was addressed by using the same electrophile but by adding it 30 s after the addition of MeLi used for transmetalation. Chloro-[D1]methyllithium is chemically very labile, however completely configurationally stable on both time scales up to the temperature of rapid decomposition (-78 degrees C). 相似文献
106.
Grycová L Hulová D Maier L Standara S Necas M Lemière F Kares R Dostál J Marek R 《Magnetic resonance in chemistry : MRC》2008,46(12):1127-1134
Adducts of the quaternary protoberberine alkaloids (QPA) berberine, palmatine, and coptisine were prepared with nucleophiles derived from pyrrole, pyrazole, imidazole, and 1,2,4-triazole. The products, 8-substituted 7,8-dihydroprotoberberines, were identified by mass spectrometry and 1D and 2D NMR spectroscopy, including (1)H--(15)N shift correlations at natural abundance. In addition, two adducts of QPA with chloroform and methanethiolate were characterized by using NMR data. Single-crystal X-ray structures of 8-pyrrolyl-7,8-dihydroberberine, 8-pyrazolyl-7,8-dihydroberberine, and 8-imidazolyl-7,8-dihydroberberine are also presented. 相似文献
107.
Civis S Babánková D Cihelka J Sazama P Juha L 《The journal of physical chemistry. A》2008,112(31):7162-7169
Large-scale plasma was created in gas mixtures containing carbon monoxide by high-power laser-induced dielectric breakdown (LIDB). The composition of the mixtures used corresponded to a cometary and/or meteoritic impact into the Earth's early atmosphere. A multiple-centimeter-sized fireball was created by focusing a single 85 J, 450 ps near-infrared laser pulse into the center of a 15 L gas cell. The excited reaction intermediates that formed in various stages of the LIDB plasma chemical evolution were investigated by optical emission spectroscopy (OES) with temporal resolution. Special attention was paid to any OES signs of molecular ions. However, carbon monoxide cations were registered only if their production was enhanced by Penning ionization, i.e., excess He was added to the CO. The chemical consequences of laser-produced plasma generation in a CO-N 2-H 2O mixture were investigated using high resolution Fourier-transform infrared absorption spectroscopy (FTIR) and gas chromatography (GC). Several simple inorganic and organic compounds were identified in the reaction mixture exposed to ten laser sparks. H 2 (18)O was used to avoid possible contamination. The large laser spark triggered more complex reactivity originating in carbon monoxide than expected, when taking into account the strong triple bond of carbon monoxide causing typically inefficient dissociation of this molecule in electrical discharges. 相似文献
108.
Lutz Dahlenburg Frank W. Heinemann Dagmar Kramer Ralf Menzel 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(3):m144-m146
In the structure of the title compound, [Ir2Cl3H2(C36H28P2)2]BF4·2CH2Cl2, the bimetallic cation features a confacial bioctahedral structure that is held together by three bridging chloride ions and is very close to C2 symmetric. The hydrides are in a syn orientation (trans to the same halide bridge), and the chelating bis(phosphine) atropisomers display a racemic (R,R)/(S,S) configuration. Because of the high trans‐bond‐weakening influence of the hydride ligands, the Ir—Cl bonds trans to Ir—H [2.5262 (7) and 2.5365 (7) Å] are significantly longer than those opposite the Ir—P linkages [2.4287 (7)–2.4672 (8) Å]. The Ir—P distances vary between 2.2464 (9) and 2.2565 (8) Å. This study illustrates the usefulness of sterically demanding biaryl‐based P2 ligands in the synthesis of halide‐bridged Ir2 complexes, which are valuable precursors of versatile catalysts for homogeneous C=O hydrogenation. 相似文献
109.
Bilanicová D Salis A Ninham BW Monduzzi M 《The journal of physical chemistry. B》2008,112(38):12066-12072
The present work shows that salt anions affect the activity of Pseudomonas cepacia lipase both in aqueous and in nonaqueous media (NAM) according to a Hofmeister series. The biocatalytic assay in water was the hydrolysis of p-nitrophenyl acetate, whereas the esterification between 1-hexyl-beta-D-galactopyranoside and palmitic acid was followed in an organic solvent. The solid lipase preparations to be used in NAM were obtained through lyophilization in the presence of concentrated solutions of Hofmeister salts (Na2SO4, NaH2PO4/Na2HPO4, NaCl, NaBr, NaI, NaSCN). Salts affect enzyme activity in organic media through two mechanisms: (1) enzyme protection during lyophilization; (2) enzyme activation during the reaction. At least in our case, the latter seems to be more important than the former. The decrease of the activation energy caused by the stabilization of the transition state due to "kosmotropic" anions might be the driving force of enzyme activation. According to the most recent findings, dispersion forces may be responsible of specific anion enzyme activation/deactivation in NAM. 相似文献
110.
Dagmar Medková Mariya Ptashnyk Werner Varnhorn 《Mathematical Methods in the Applied Sciences》2016,39(6):1621-1630
In this paper, we study the well‐posedness of a coupled Darcy–Oseen resolvent problem, describing the fluid flow between free‐fluid domains and porous media separated by a semipermeable membrane. The influence of osmotic effects, induced by the presence of a semipermeable membrane, on the flow velocity is reflected in the transmission conditions on the surface between the free‐fluid domain and the porous medium. To prove the existence of a weak solution of the generalized Darcy–Oseen resolvent system, we consider two auxiliary problems: a mixed Navier–Dirichlet problem for the generalized Oseen resolvent system and Robin problem for an elliptic equation related to the general Darcy equations. © 2016 The Authors Mathematical Methods in the Applied Sciences Published by John Wiley & Sons Ltd. 相似文献