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101.
The design and synthesis of clusters possessing the same number of cores but different connection methods and properties have always been difficult. Herein, we used 2-pyridinaldehyde, 1,3-diamino-2-propanol, and Dy (ClO4)3·6H2O at room temperature (RT) to obtain the cluster [Dy4(L1)4(μ2-OH)4]·4ClO4− ( 1 , HL1 = 2-pyridinecarboxaldehyde-1,3-diamino-2-propanol) with square Dy4O8 cluster cores. Cluster 1 consisted of four Schiff base ligands (L1)−, four Dy(III) ions, four bridged (μ2-OH)−, and four free ClO4−. The ligand HL1 was formed by in situ Schiff base reaction with 2-pyridinecarbaldehyde and 1,3-diamino-2-propanol in the presence of Dy(III) ions. 2-Aldehyde-8-hydroxyquinoline, 1,3-diamino-2-propanol, and Dy (NO3)3·6H2O reacted at RT to yield a tetranuclear Dy(III) cluster [Dy4(L2)2(μ3-OH)2(NO3)4(EtOH)2]·2CH3CN ( 2 , H3L2 = 2-aldehyde-8-hydroxyquinoline-1,3-diamino-2-propanol) with butterfly-shaped Dy4O6 cluster core. Cluster 2 consisted of two ligands (L2)3−, four Dy(III) ions, two bridged μ3-OH, two end-group-coordinated ethanol molecules, and four bidentate-chelated NO3−. The in situ reaction of 2-aldehyde-8-hydroxyquinoline and 1,3-diamino-2-propanol under Dy(III) ion-assisted catalytic conditions provided the ligand H3L2. It is worth noting that the magnetic test showed that 1 is a typical single-molecule magnet (SMM), whereas 2 only showed a significant frequency dependence behavior. We considered Orbach and Raman processes (τ−1 = τ0−1 exp(−Ueff/kBT) + CTn) to fit 1 and 2 in the high-temperature range and obtained Ueff = 7.01 and 5.43 K and τ0 = 1.18 × 10−4 and 4.14 × 10−5 s, respectively. 相似文献
102.
Semi-rigid connections can often be a more economical solution for a framing system than one with either fully fixed connections or fully pinned ones. In view of the fact that the properties of such ductile and partial-strength connections are not known accurately, this paper presents a method for the obtention of both upper and lower bound responses of semi-rigid frames for possible variations in their moment-rotation properties. The latter are thus assumed to be known within some key upper and lower bound values, namely a constitutive law that is still deterministic but is described in terms of a so-called “interval” model. A mathematical programming approach is used to formulate and solve the problem. In particular, for each load level, a pair of nonstandard optimization problems known as interval mathematical programs with equilibrium constraints (or interval MPECs) are solved to provide the required bounds. A number of examples are provided to highlight the important effects of considering uncertainties in semi-rigid connection properties. 相似文献
103.
提出了一种基于力学转化模型的钢筋混凝土板柱节点抗冲切性能分析方法,该方法能够将传统弹性力学的研究问题用结构力学模型解决. 通过OpenSees (Open System for Earthquake Engineering Simulation)计算平台进行建模,根据数值分析和试验结果的对比,确定和验证模型中的关键参数. 结果表明,该数值模型能够很好模拟板柱节点的抗冲切性能,包括载荷-变形响应、刚度变化规律及变形分布规律等,为全面认识板柱节点的工作机理、受力特征及内力分布规律提供新的研究途径,同时为工程设计与实践提供理论指导. 相似文献
104.
105.
Franz Luef 《Expositiones Mathematicae》2018,36(2):221-227
We point out a link between the theorem of Balian and Low on the non-existence of well-localized Gabor–Riesz bases and a constant curvature connection on projective modules over noncommutative tori. 相似文献
106.
Sergiu I. Vacaru 《International Journal of Theoretical Physics》2009,48(7):1973-1999
We argue that the Einstein gravity theory can be reformulated in almost Kähler (nonsymmetric) variables with effective symplectic form and compatible linear connection uniquely defined by a (pseudo) Riemannian metric. A class of nonsymmetric theories of gravitation on manifolds enabled with nonholonomic distributions is considered. We prove that, for certain types of nonholonomic constraints, there are modelled effective Lagrangians which do not develop instabilities. It is also elaborated a linearization formalism for anholonomic noncommutative gravity theories models and analyzed the stability of stationary ellipsoidal solutions defining some nonholonomic and/or nonsymmetric deformations of the Schwarzschild metric. We show how to construct nonholonomic distributions which remove instabilities in nonsymmetric gravity theories. It is concluded that instabilities do not consist a general feature of theories of gravity with nonsymmetric metrics but a particular property of some models and/or unconstrained solutions. 相似文献
107.
Nonholonomic Ricci Flows, Exact Solutions in Gravity, and?Symmetric and Nonsymmetric Metrics 总被引:1,自引:1,他引:0
Sergiu I. Vacaru 《International Journal of Theoretical Physics》2009,48(2):579-606
We provide a proof that nonholonomically constrained Ricci flows of (pseudo) Riemannian metrics positively result into nonsymmetric
metrics (as explicit examples, we consider flows of some physically valuable exact solutions in general relativity). There
are constructed and analyzed three classes of solutions of Ricci flow evolution equations defining nonholonomic deformations
of Taub NUT, Schwarzschild, solitonic and pp-wave symmetric metrics into nonsymmetric ones. 相似文献
108.
This note fills a hole in the author’s previous paper “Ricci-flat holonomy: A classification”, by dealing with irreducible holonomy algebras that are subalgebras or real forms of C⊕spin(10,C). These all turn out to be of Ricci type. 相似文献
109.
Mahuya Datta 《Transactions of the American Mathematical Society》2003,355(9):3813-3824
Let be a principal bundle over a manifold of dimension . If , then we prove that every differential 4-form representing the first Pontrjagin class of is the Pontrjagin form of some connection on . 相似文献
110.