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81.
Dr. Fabio Denis Romero Alice Leach Dr. Johannes S. Möller Francesca Foronda Prof. Stephen J. Blundell Prof. Michael A. Hayward 《Angewandte Chemie (International ed. in English)》2014,53(29):7556-7559
A series of strontium vanadium oxide–hydride phases prepared by utilizing a low‐temperature synthesis strategy in which oxide ions in Srn+1VnO3n+1 (n=∞, 1, 2) phases are topochemically replaced by hydride ions to form SrVO2H, Sr2VO3H, and Sr3V2O5H2, respectively. These new phases contain sheets or chains of apex‐linked V3+O4 squares stacked with SrH layers/chains, such that the n=∞ member, SrVO2H, can be considered to be analogous to “infinite‐layer” phases, such as Sr1?xCaxCuO2 (the parent phase of the high‐Tc cuprate superconductors), but with a d2 electron count. All three oxide–hydride phases exhibit strong antiferromagnetic coupling, with SrVO2H exhibiting an antiferromagnetic ordering temperature, TN>300 K. The strong antiferromagnetic couplings are surprising given they appear to arise from π‐type magnetic exchange. 相似文献
82.
A reliable method for the measurement of different plasminogen activators is of great interest for both manufacturing and
clinical medicine. A one-step assay based on a thickness shear mode acoustic sensor has been developed for this purpose. Two
separate mixtures of substrates (fibrinogen and plasminogen) and enzymes (thrombin and the plasminogen activator) were mixed,
and placed on the acoustic sensor surface. During the assay, the resonant frequency of a quartz crystal oscillating in the
thickness shear mode was measured and used to find a characteristic clot dissolution time, from the sample addition to the
time at the maximum dissolution rate. Calibrations of the acoustic assay were done for tissue-type plasminogen activator (t-PA)
as well as for the other plasminogen activators: urokinase (u-PA); streptokinase (SK) and staphylokinase (SAK). All gave relative
standard deviations of about 12%. Since the same method was used for all of the activators, their activities were compared,
resolving the differences between their unit definitions. Linear relationships were found between urokinase and streptokinase
which activate plasminogen directly and between t-PA and staphylokinase which require fibrin as a cofactor. The relationship
between the groups was found to curve, indicating the difference between the two mechanisms. The acoustic method, therefore,
may be used as a rapid and cost-effective reference method for the standardization and comparison of different plasminogen
activators. 相似文献
83.
The synthesis of the Mn(II) phase 4H-Ba(0.5)Sr(0.5)MnO(2+delta) via the topotactic reduction of 4H-Ba(0.5)Sr(0.5)MnO(3-x) with the novel reducing agent LiH, is described. Neutron powder diffraction data show that oxide ions are deintercalated from the host structure in a disordered manner to yield "tetrahedral" MnO(4) coordination sites. Magnetic susceptibility and neutron powder diffraction data show that the title phase adopts a canted antiferromagnetically ordered state below T(N) = 355K, consistent with the strong magnetic coupling expected between d(5) centers. 相似文献
84.
Ba7Mn5Cr2O2O20 adopts a structure containing an ordered array of Mn(IV), Mn(II) and Cr(V) cations and exhibits complex magnetic behaviour at low temperature. 相似文献
85.
Acoustic communication channel capacity determines the maximum data rate that can be supported by an acoustic channel for a given source power and source/receiver configuration. In this paper, broadband acoustic propagation modeling is applied to estimate the channel capacity for a time-invariant shallow-water waveguide for a single source-receiver pair and for vertical source and receiver arrays. Without bandwidth constraints, estimated single-input, single-output (SISO) capacities approach 10 megabitss at 1 km range, but beyond 2 km range they decay at a rate consistent with previous estimates by Peloquin and Leinhos (unpublished, 1997), which were based on a sonar equation calculation. Channel capacities subject to source bandwidth constraints are approximately 30-90% lower than for the unconstrained case, and exhibit a significant wind speed dependence. Channel capacity is investigated for single-input, multi-output (SIMO) and multi-input, multi-output (MIMO) systems, both for finite arrays and in the limit of a dense array spanning the entire water column. The limiting values of the SIMO and MIMO channel capacities for the modeled environment are found to be about four times higher and up to 200-400 times higher, respectively, than for the SISO case. Implications for underwater acoustic communication systems are discussed. 相似文献
86.
In this study, we calculate the interaction energy of intrinsic point defects vacancies and interstitials) with screw dislocations in body-centered cubic iron. First (we calculate the dipole tensor of a defect in the bulk crystal using molecular statics. Using a formulation based on linear elasticity theory, we calculate the interaction energy of the defect and the dislocation using both isotropic and anisotropic strain fields. Second, we perform atomistic calculations using molecular statics methods to directly calculate the interaction energy. Results from these two methods are compared. We verify that continuum methods alone are unable to correctly predict the interactions of defects and dislocations near the core. Although anisotropic theory agrees qualitatively with atomistics far from the core, it cannot predict which dumbbell orientations are stable and any continuum calculations must be used with caution. Spontaneous absorption by the core of both vacancies and dumbbells is seen. This paper demonstrates and discusses the differences between continuum and atomistic calculations of interaction energy between a dislocation core and a point defect. 相似文献
87.
Reaction of the n = 3 Ruddlesden-Popper oxychloride Sr(4)Mn(3)O(7.5)Cl(2) with calcium hydride yields the topotactically reduced phase Sr(4)Mn(3)O(6.5)Cl(2). The deintercalation of oxide ions from the central MnO(1.5) layer of the starting phase is accompanied by a rearrangement of the anion lattice, resulting in a layer of composition MnO(0.5) in the reduced material, consisting of chains of MnO(4) tetrahedra connected by edge and corner sharing. Magnetization and low-temperature neutron diffraction data are consistent with antiferromagnetic coupling of manganese spins, but no long-range magnetic order is observed down to 5 K, presumably due to the large interlayer separation in the reduced phase. The influence of anion substitution on the structural selectivity of low-temperature reduction reactions is discussed. 相似文献
88.
The title compound is prepared from stoichiometric mixtures of La2O3, SrCO3, Ga2O3, and Fe2O3 (flowing Ar, 1300 °C, 80 h) and characterized by neutron powder diffraction and magnetic measurements. 相似文献
89.
The polarizability properties of π electron systems are treated by the self-consistent field method, as modified by Pople for application to conjugated molecules. An analytical treatment of the π electron configuration of substituted hydrocarbons deduces certain universal symmetry properties of this method, and contains the Hückel treatment of inductive substituents as a simplified special case. Whereas the usual Hückel theory derives results by approximate perturbation methods, the treatment given here is formally exact. In a later section s.c.f. polarizability coefficients, as calculated on an Elliott 402 digital computer, are given for benzene, naphthalene, anthracene and phenanthrene, and the predictions of chemical properties are shown to be in better agreement with experiment than predictions derived from Hückel theory. 相似文献
90.
Hayward R. Alker Jr. 《International Journal of Mathematical Education in Science & Technology》2013,44(2):139-155
The development of three positively evaluated social science computer simulations is reviewed as a basis for comments on current debates about the utility of social simulations: Colby's treatment of neurotic belief dynamics, the Abelson‐Bernstein simulation of fluoridation controversies and Alker's projected computer model of United Nations parliamentary diplomacy. In each case, the non‐analytical nature of the computer model is not due to unusual mathematical ineptitude but derived from evidence contradicting the empirical validity of more elegant formalizations employing, respectively, formal logics and graph theory, differential equation systems, game theory and statistical models. Several analytically challenging problems concerning validity assessment, the nature of deep structure, and the policy‐relevant performance characteristics of complex models are mentioned. Moral, political, philosophical and pedagogical issues derive from the empirically provisional nature of all simulation versions of frequently controversial social theories, the frequent mystification of mathematical/computerized ‘results’, and the uneven practical utility and accessibility of social simulations. Conflicts between the ethical perspectives of doctors, public officials, citizens and natural scientists are suggested in terms of a humanoid interpretation of complex simulation systems. The pedagogical use of mixed or complementary developmental, philosophical, mathematical and scientific approaches is advocated to minimize potential abuses of social simulation research. 相似文献