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581.
Heiko Lueken Klaus Handrick Helmut Schilder Johann W. Buchler Kiong-Lam Lay 《无机化学与普通化学杂志》1996,622(1):95-99
The magnetism of μ-oxo-bis[(5,15-dimethyl-2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III)] with bridge geometry d(Fe? O) = 1.752 Å and ?(Fe? O? Fe) = 178.6° can be explained in terms of antiferromagnetically exchange coupled iron(III)-3d5 pairs. The magnetochemical analysis in the temperature range 6K–295K on the basis of the isotropic Heisenberg model (spin Hamiltonian: ? = ?2J?1 · ?2 S1 = S2 = 5/2) leads to the exchange parameter J = ?125 cm?1. With regard to the Fe? O bond length the J value corresponds to the series of data observed for other μ-oxodiiron-porphyrins and -porphycenes. Compared to the spin-spin coupling in [Fe2Cl6O]2?, |J| is enhanced by ≈ 10%. 相似文献
582.
A straightforward synthesis of chiral aza-bis(oxazoline) (Azabox) ligands from commercially available amino alcohols is described. The new protocol allows access to previously reported Azabox ligands in considerably improved yields but also to new derivatives, including non-C2-symmetrical ones. 相似文献
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584.
An "easy-hard" phase transition is shown to characterize the multiprocessor scheduling problem in which one has to distribute the workload on a parallel computer such as to minimize the overall run time. The transition can be analyzed in detail by mapping it on a mean-field antiferromagnetic Potts model. The static phase transition, characterized by a vanishing ground state entropy, corresponds to a transition in the performance of practical scheduling algorithms. 相似文献
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587.
Vapour pressure is an important parameter for predicting the distribution of a substance in the environment. Therefore, the vapour pressure of the herbicide Triallate was determined using the Knudsen effusion technique. At least two polymorphic phases of Triallate were identified employing thermooptical and calorimetric methods. 相似文献
588.
589.
The system (Fe0.88Mn0.12
1–x
Al
x
has been investigated in a concentration range from 5 to 14 at.% Al. We applied Mössbauer spectroscopy in the temperature range from 4 up to 900 K and X-ray diffractometry at room temperature. The as-cast samples show a bcc phase for all concentrations and exhibit broadened six-line Mössbauer spectra typical for disordered alloys. The Mössbauer spectra during a high temperature treatment show dramatic changes. These are due to ordering processes appearing at temperatures above 700 K. As an example of the observed changes, we present results obtained for the alloy withx= 14 at.% Al. 相似文献
590.
Seeing surfaces: The brain's vision of the world 总被引:1,自引:0,他引:1
Surfaces of environmental objects are the key to understanding the visual experience of primates. Surfaces create structure in patterns of light available for sampling by visual systems, and delineate potential interactions that an animal can have with its environment, such as approaching goals, avoiding obstacles, grasping an object, or identifying members of a social group. Recent progress in modeling the perception of visual surfaces highlights the importance of feedforward and feedback connections in visual neural networks that segregate and group visual input into coherent regions related to corresponding surfaces in the visual world. Rich non-linear network dynamics in the brain underlie surface perception, including the detection, regularization, and grouping of visual boundaries between surfaces, the determination of “ownership” of a boundary by a closer surface that partially occludes a background, and the apprehension of a surface's visual quality, such as color or texture. Recent modeling efforts on these fronts are reviewed. 相似文献