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101.
Constantinos G. Efthymiou Constantina Papatriantafyllopoulou Nadia I. Alexopoulou Catherine P. Raptopoulou Roman Boča Jerzy Mrozinski Evangelos G. Bakalbassis Spyros P. Perlepes 《Polyhedron》2009
The reactions of 2-(hydromethyl)pyridine, hmpH, with Ni(O2CMe)2·4H2O in H2O, in the absence of counterions, have been investigated. The synthetic study has led to the two new complexes [Ni(O2CMe)2(hmpH)2] (1) and [Ni4(O2CMe)4(hmp)4(H2O)2] (2). Complex 1 can also be transformed into 2 by reacting with an excess of NaOH in H2O. The structures of 1 and 2·2.25H2O·0.5(1,4-dioxane) have been solved by single-crystal, X-ray crystallography. The octahedral NiII center in centrosymmetric 1 is coordinated by two 1.10 (Harris notation) MeCO2− groups and two N,O-chelating (1.11) hpmH ligands. The tetranuclear cluster molecule of 2·2.25H2O·0.5(1,4-dioxane) possesses a distorted cubane {Ni4(μ3-OR′)4}4+ core [R′ = (2-pyridyl)CH2–] with the NiII ions and the oxygen atoms from the 3.31 hmp− ligands occupying alternate vertices of the cube. Two 2.11 MeCO2− groups cap two opposite faces of the cube, while two 1.10 MeCO2− ions and two aqua ligands complete the octahedral coordination sphere of the metal centers. Characteristic IR bands for the two complexes are discussed in terms of the nature of bonding and the structures of the two complexes. The variable-temperature magnetic properties of 2 have been modeled with two J values, and reveal antiferromagnetic exchange interactions between the four NiII ions to give a diamagnetic ground state. 相似文献
102.
Gaoxiang Liu Zhaoguo Zhu Sandra M. Ciborowski Isuru R. Ariyarathna Evangelos Miliordos Kit H. Bowen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(23):7855-7859
Mass spectrometric analysis of the anionic products of interaction between platinum atomic anions, Pt?, and methane, CH4 and CD4, in a collision cell shows the preferred generation of [PtCH4]? and [PtCD4]? complexes and a low tendency toward dehydrogenation. [PtCH4]? is shown to be H?Pt?CH3? by a synergy between anion photoelectron spectroscopy and quantum chemical calculations, implying the rupture of a single C?H bond. The calculated reaction pathway accounts for the observed selective activation of methane by Pt?. This study presents the first example of methane activation by a single atomic anion. 相似文献
103.
Curved beam structures have been used in many civil, mechanical, aircraft, and aerospace constructions. The analysis is mainly based on solid and plate models due to the fact that traditional curved beam elements do not include nonuniform warping effects, especially in the dynamic analysis. In this article, independent warping parameters have been taken into account and the initial curvature effect is considered. Curved beam’s behavior becomes more complex, even for dead loading, due to the coupling between axial force, bending moments, and torque that curvature produces. In addition to these, the Isogeometric tools (b-splines or NURBS), either integrated in the Finite Element Method or in a Boundary Element–based Method called Analog Equation Method, have been employed in this contribution for the dynamic analysis of horizontally curved beams of open or closed (box-shaped) cross sections. Free vibration characteristics and responses of the stress resultants and displacements to moving loading have been studied. 相似文献
104.
Tolis EI Engelhardt LP Mason PV Rajaraman G Kindo K Luban M Matsuo A Nojiri H Raftery J Schröder C Timco GA Tuna F Wernsdorfer W Winpenny RE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(35):8961-8968
The synthesis and structural characterization of a nonanuclear FeIII cage complex is reported. The nine iron centers in [Fe9(mu3-O)4(O3PPh)3(O2CCMe3)13] lie on the vertices of an incomplete icosahedron, with the P atoms of triphenylphosphonate at the other three vertices. The paramagnetic core therefore describes a tridiminished icosahedron. Magnetic studies suggest an S=1/2 ground state for the molecule. Analysis of exchange paths and the susceptibility data point to the interpretation that the cluster can be divided into two nearly decoupled sections: an {Fe6O3} section, with an S=0 ground state, in which three oxo-centered triangles bound a central triangle that is not oxo-centered; and an {Fe3O} triangle with S=1/2. The analysis of the susceptibility data leads to a Heisenberg model based on three significant antiferromagnetic exchange interactions, with values of 173.7 cm-1 in the {Fe3O} triangle, and 30.9 and 19.1 cm-1 within the {Fe6O3} section, while the exchange between them is <1 cm-1. With these assignments, the theoretical low-temperature differential susceptibility is also in very good agreement with measurements up to 50 T. Magnetic measurements in the milli-kelvin range reveal striking hysteresis loops and magnetization reversals associated with a Landau-Zener-Stückelberg (LZS) transition as enhanced by the occurrence of a phonon bottleneck. 相似文献
105.
Evangelos Triantaphyllou 《Journal of Global Optimization》1994,5(1):69-94
This paper deals with the problem of identifying a hidden Boolean function : 0, 1' 0, 1 from positive and negative examples. This problem is of paramount importance in many real life applications of artificial intelligence. The method proposed in this paper is based on a branch-and-bound approach. This approach is an expansion of some earlier work (Triantaphyllouet al., 1994). Computational results, comparing the new method with one based on Karmakar's interior point method, suggest that the new method is very efficient. 相似文献
106.
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108.
Coupled cluster and multireference configuration approaches are employed to study the electronic and geometric structures of mono-coordinated complexes of lithium, sodium, and beryllium with nitric oxide and its isovalent NS, NSe, and NTe species. Ground and low-lying excited states were examined for both linear-bonded and side-bonded isomers. We show that the ionic M+NX− (M=Li, Na, Be and X=O, S, Se, Te) picture is a more natural representation and can account for the symmetry of the low−lying electronic states as Σ−, Δ, and Σ+, the smaller excitation energies and the larger binding energies for heavier X. An additional electron binds to the positively charged Li and Na terminal creating stable anions. The electron affinity (EA) of LiNX and NaNX species is in the 0.5–0.8 eV range. Despite the negative EA of beryllium and the very small EA of NO, the BeNO molecule has an EA of ~1.0 eV, which is increased to ~1.5 eV for the heavier BeNX species. This is attributed to the fact that the additional electron goes to the beryllium end for BeNO but to a π(MN) π*(NX) orbital of the rest species. Our accurate results contradict previous findings and serve as a guide for future experimental studies. © 2019 Wiley Periodicals, Inc. 相似文献
109.
A common approach for comparing the structures of biomolecules or solid bodies is to translate and rotate one structure with respect to the other to minimize the pointwise root-mean-square deviation (RMSD). We present a new, robust numerical algorithm that computes the RMSD between two molecules or all the mutual RMSDs of a list of molecules and, if desired, the corresponding rotation matrix in a minimal number of operations as compared to previous algorithms. The RMSD gradient can also be computed. We address the problem of symmetry, both in alignment (possible alternative alignments due to indistinguishable atoms) as well as geometry. In the latter case, it is possible to have degenerate superposition. A necessary condition is optimal superimposability to one's mirror image. Double (respectively, triple) degeneracy results in a one- (respectively, two)-parameter family of rotations leaving the superposition invariant. The software, frmsd , is freely available at http://www.ams.stonybrook.edu/~coutsias/codes/frmsd.tgz . © 2019 Wiley Periodicals, Inc. 相似文献
110.
Shear banding (SB) is manifested by the abrupt “demixing” of the flow into regions of high and low shear rate. In this paper, we first relate analytically the rheological parameters of the fluid with the range of shear rates and stresses of SB occurrence. For this, we accept that the origin of shear banding is constitutive, and adopt a non-linear viscoelastic expression able to accommodate the double-valuedness of the stress with flow intensity, under certain conditions. We then implement the model for the case of pressure driven flow through a cylindrical pipe; we derive approximate expressions for the velocity profile in the two-banded regions (core and outer annular), the overall throughput in the presence or absence of “spurt”, and the radial location limits of the shear rate discontinuity. 相似文献