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81.
82.
We analyze the effects of different coupling anisotropies in a spin-1/2 ladder on the electron spin resonance (ESR) shift. Combining a perturbative expression in the anisotropies with density matrix renormalization group computation of the short range correlations at finite temperature, we provide the full temperature and magnetic field evolution of the ESR paramagnetic shift. We show that for well chosen parameters the ESR shift can be in principle used to extract quantitatively the anisotropies and, as an example, discuss the material BPCB. 相似文献
83.
Accreditation and Quality Assurance - An emerging intervention in the area of dementia therapy is serious gaming. Serious gaming is understood as any meaningful use of computerized game whose chief... 相似文献
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85.
On the Dimorphism of Nd3Cl[SiO4]2 On reacting NdCl3, Nd2O3, and SiO2 (molar ratio: 1 : 4 : 6) at 850 °C in evacuated silica tubes, pale violet, hydrolysis resistant neodymium(III) chloride ortho‐silicate Nd3Cl[SiO4]2 can be obtained within seven days. If equimolar amounts of NaCl are added as flux, rod‐ or platelet‐shaped, transparent single crystals of two modifications accumulate simultaneously. The one with the higher density (A‐Nd3Cl[SiO4]2) crystallizes monoclinically (C2/c, no. 15; a = 1416.6(1), b = 638.79(6), c = 872.21(9) pm, β = 98.403(7)°; Vm = 117.55 cm3/mol, Z = 4), whereas the one with the lower density (B‐Nd3Cl[SiO4]2) exhibits orthorhombic symmetry (Pnma, no. 62; a = 709.36(7), b = 1815.7(2), c = 631.48(6) pm; Vm = 122.45 cm3/mol, Z = 4). Two crystallographically independent Nd3+ cations exist in each of both crystal structures, which in the A type are surrounded by nine (1 Cl– + 8 O2–) and ten (2 Cl– + 8 O2–), whilst those in the B type by only two times eight (1 Cl– + 7 O2– and 2 Cl– + 6 O2–) anions, respectively. Thereby all oxygen atoms of both forms represent members of discrete ortho‐silicate tetrahedra ([SiO4]4–). Although both crystal structures are built of alternating anionic double layers {(Nd1)2[SiO4]2}2– and cationic single layers {(Nd2)Cl}2+, there is a higher cross‐linkage of the building units in the A‐type lattice, where the cations are coordinated by three and four tetrahedra edges of ortho‐silicate anions, compared to only two times two of them in the B type. From this an about 4% higher density of Nd3Cl[SiO4]2 results for the A‐type structure (Dx = 5.55 g/cm3) in comparison with B‐type Nd3Cl[SiO4]2 (Dx = 5.33 g/cm3). 相似文献
86.
87.
NaPr9S2[SiO4]6: A Sulfide Silicate of Praseodymium with the Structure of Bromapatite NaPr9S2[SiO4]6 is obtained as pale green single crystals of hexagonal columnar shape from reactions of Pr, Pr6O11, S, SiO2 and NaCl (850°C, 7 d) in fused evacuated silica tubes. The crystal structure (hexagonal, P63/m, Z = 1, a = 981.05(4), c = 689.68(2) pm) corresponds with a modified bromapatite structure where orthosilicate ([SiO4]4?) and sulfide (S2?) anions provide coordination numbers of eight and nine to the two crystallographically different cations. These occupy the positions 4 f (Na+ together with Pr3+ in a molar ratio of 1:3) and 6h (Pr3+ only) to realize an average Ca5Br[PO4]3-type structure. 相似文献
88.
K. H. Althoff G. Anton B. Bock D. Bour R. Dostert P. Erbs T. Jahnen O. Kaul E. Kohlgarth B. Lücking D. Menze W. Meyer E. P. Schilling W. J. Schwille D. Sundermann W. Thiel D. Thiesmeyer 《Zeitschrift fur Physik C Particles and Fields》1989,43(3):375-380
At the Bonn 2.5 GeV electron synchrotron an angular distribution of the target asymmetry of the reaction γ+d↑→p+n has been measured at photon-lab-energies of 450 and 650 MeV and at proton-CM-angles between 25° and 155°. At 550 MeV the data of our previous run [1] have been improved. Using deuterated ammonia as material for the polarized deuteron target a maximum vector polarization of 44% could be achieved. At 450 and 650 MeV the data are consistent with a smooth sin 2Θ-like distribution. The evidence for a structure around 90° at 550 Mev remains. This might be due to the influence of a higher momentum state (like a dibaryon). The feasibility of measuring the tensor asymmetry of the deuteron photodisintegration with a polarized target has been shown for the first time. Data were taken in a short run for one kinematical setting. 相似文献
89.
Steven D. Dong Kurt Sundermann Karen M.J. Smith Joseph Petryka Fenghua Liu David C. Myles 《Tetrahedron letters》2004,45(9):1945-1947
A facile and efficient route to epothilone analogs has been developed from the natural product epothilone D (1). Degradation of 1 via an oxidative cleavage sequence provides acid intermediate 4 rapidly in six steps. From 4, a variety of epothilone analogs have been prepared utilizing ring-closing metathesis to reconstruct the trisubstituted-12,13-double bond. Using this approach, we report a number of epothilone analogs with varying C-15 aromatic side chains and C-14 allylic substitutions and their biological activities. 相似文献
90.
Schönecker B Zheldakova T Lange C Günther W Görls H Bohl M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(23):6029-6042
Copper(I) complexes incorporating the isomeric bidentate ligands IMPY (iminomethyl-2-pyridines) or AMPY (aminomethylene-2-pyridines) are quite unusual in their ability to bind and activate molecular oxygen. Using these complexes, hydroxylations of nonactivated CH, CH2, or CH3 groups in the gamma-position in relation to the imino-nitrogen atom, and with a specific orientation of one H atom with respect to the binuclear Cu-O species, can be achieved in synthetically useful yields. Through mechanistic studies employing conformationally well-defined molecules (for example, cyclic isoprenoids), coupled with solid-state X-ray structure analyses and force-field calculations, we postulate a seven-membered transition state for this reaction in which six atoms lie approximately in a plane. This plane is defined by the positions of the lone pairs on the nitrogen atoms, as well as the copper and the oxygen atoms. For a successful hydroxylation, one hydrogen atom should be located close to this plane. Prediction of the stereochemical course of these reactions is possible based on a simple geometrical criterion. The convenient introduction of IMPY and AMPY groups as auxiliaries into oxo and primary amino compounds and the simple hydrolysis after the hydroxylation procedure has allowed the synthesis of 3-hydroxy-1-oxo and 3-hydroxy-1-amino compounds. If desired, the 3-hydroxy-1-IMPY and -1-AMPY compounds can be reduced with NaBH4 to obtain 3-hydroxy-1-aminomethylpyridines. For a successful hydroxylation procedure, the method employed for the synthesis of the CuI complexes is very important. Starting either from CuI salts or from CuII salts with a subsequent reduction with benzoin/triethylamine may turn out to be the better way, depending on the ligand and the molecular structure. 相似文献