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921.
Evidence is presented that the superconductivity of La2 ?β Srβ CuO4 and La2CuO4+δ occurs via holes in the LaO planes, rather than in the CuO2 planes. 相似文献
922.
The linear discrepancy of a poset P is the least k such that there is a linear extension L of P such that if x and y are incomparable, then |hL(x)−hL(y)|≤k, whereas the weak discrepancy is the least k such that there is a weak extension W of P such that if x and y are incomparable, then |hW(x)−hW(y)|≤k. This paper resolves a question of Tanenbaum, Trenk, and Fishburn on characterizing when the weak and linear discrepancy of a poset are equal. Although it is shown that determining whether a poset has equal weak and linear discrepancy is -complete, this paper provides a complete characterization of the minimal posets with equal weak and linear discrepancy. Further, these minimal posets can be completely described as a family of interval orders. 相似文献
923.
Given an irrational 0<λ<1, we consider billiards in the table P λ formed by a \(\tfrac{1}{2}\times1\) rectangle with a horizontal barrier of length \(\frac{1-\lambda}{2}\) with one end touching at the midpoint of a vertical side. Let NE?(P λ ) be the set of θ such that the flow on P λ in direction θ is not ergodic. We show that the Hausdorff dimension of NE?(P λ ) can only take on the values 0 and \(\tfrac{1}{2}\), depending on the summability of the series \(\sum_{k}\frac{\log\log q_{k+1}}{q_{k}}\) where {q k } is the sequence of denominators of the continued fraction expansion of λ. More specifically, we prove that the Hausdorff dimension is \(\frac{1}{2}\) if this series converges, and 0 otherwise. This extends earlier results of Boshernitzan and Cheung. 相似文献
924.
A versatile synthesis of unsaturated seven-membered ring lactams has been developed. The sequence involves hydroamination of Baylis-Hillman acetate with amines, followed by intramolecular cyclocarbonylation reactions of the resulting allylamines. This process can tolerate a wide array of functional groups, and affords lactams in excellent yields. 相似文献
925.
A facile and selective palladium-catalyzed domino procedure has been developed for the preparation of 2-carbonylbenzo[b]thiophene derivatives from 2-gem-dihalovinylthiophenols. This protocol involves intramolecular C-S coupling/intermolecular carbonylation cascade sequences and allows access to various highly functionalized benzo[b]thiophenes in moderate yields. 相似文献
926.
A weight ring in type A is the coordinate ring of the GIT quotient of the variety of flags in ℂ
n
modulo a twisted action of the maximal torus in SL(n,ℂ). We show that any weight ring in type A is generated by elements of degree strictly less than the Krull dimension, which
is at worst O(n
2). On the other hand, we show that the associated semigroup of Gelfand–Tsetlin patterns can have an essential generator of
degree exponential in n. 相似文献
927.
Miller KM McCullough SM Lepekhina EA Thibau IJ Pike RD Li X Killarney JP Patterson HH 《Inorganic chemistry》2011,50(15):7239-7249
A series of metal-organic networks of CuSCN were prepared by direct reactions with substituted pyridine and aliphatic amine ligands, L. Thiocyanate bridging is seen in all but 1 of 11 new X-ray structures. Structures are reported for (CuSCN)L sheets (L = 3-chloro- and 3-bromopyridine, N-methylmorpholine), ladders (L = 2-ethylpyridine, N-methylpiperidine), and chains (L = 2,4,6-collidine). X-ray structures of (CuSCN)L(2) are chains (L = 4-ethyl- and 4-t-butylpyridine, piperidine, and morpholine). A unique N-thiocyanato monomer structure, (CuSCN)(3-ethylpyridine)(3), is also reported. In most cases, amine ligands are thermally released at temperatures <100 °C. Strong yellow-to-green luminescence at ambient temperature is observed for the substituted pyridine complexes. High solid state quantum efficiencies are seen for many of the CuSCN-L complexes. Microsecond phosphorescence lifetimes seen for CuSCN-L are in direct contrast to the nanosecond-lifetime emission of CuSCN. MLCT associated with pyridine π* orbitals is proposed as the excitation mechanism. 相似文献
928.
Reported are adsorption isotherms for guar and hydroxypropyl guar (HPG), with and without the presence of borate ions, onto surfactant free anionic polystyrene latex. Guar and HPG formed adsorbed monolayers on the hydrophobic latex. The presence of borate ions converted the nonionic guar and HPG into an anionic polyelectrolyte. However, there was no measurable influence of bound borate ions on the adsorption of guar or HPG onto anionic, hydrophobic latex. To underscore the unusual behavior of HPG-borate, a sample of HPG was oxidized to introduce carboxyl groups, and the adsorption of the carboxylated HPG onto anionic polystyrene was measured. Unlike HPG-borate, oxidized HPG did not adsorb onto negative polystyrene latex at neutral pH because of electrostatic repulsion. To explain the adsorption of negative HPG-borate onto negative latex, we proposed that as HPG-borate segments approach the latex surface, the negative electrostatic potential near the latex surface induces the detachment of the labile borate groups from HPG. 相似文献
929.
Ionic diamine rhodium complex (1) catalyzes the reductive N-cyclization of 2-vinylnitroarenes using carbon monoxide as a reducing agent to afford functionalized indoles. The catalytic system allows direct access to indoles with ester and ketone groups at the 2- or 3-position, in good yields. 相似文献
930.
More than 70 unique micro-hydrated structures of pyrimidine, ranging in size from 1 to 7 water molecules, have been characterized with the B3LYP density functional and the 6-311++G(2df,2pd) triple-ζ split-valence basis set. Explicitly correlated MP2-F12 single-point computations were performed on each structure with a correlation consistent triple-ζ basis set to estimate the relative and dissociation energies at the MP2 complete basis set (CBS) limit. Many of these new structures have significantly lower energies than those previously reported (by as much as 12.66 kcal?mol(-1)). For clusters with 1 and 2 water molecules, the MP2-F12 relative and dissociation energies are virtually identical to the corresponding CCSD(T)-F12 values. As the number of hydrating waters increases, the structures in which the water molecules are clustered together at one of the N atoms have lower energies than those where the water molecules are more distributed around the pyrimidine ring. Micro-hydrated structures that effectively extend the low-energy hydrogen-bonding motifs to both sides of the ring, as would be expected in the bulk phase, reproduce the experimentally observed vibrational frequency shifts of ν(1) and ν(8b) in very dilute aqueous pyrimidine solutions to within 1 cm(-1) . Micro-hydrated structures of pyrimidine in which water molecules are clustered together have lower energies than structures in which the water molecules are more evenly spread around the pyrimidine ring. 相似文献