固支方板对水中爆炸作用的动态响应研究

 分析研究了在装药水中爆炸产生的强冲击载荷作用下固支方板的塑性动力响应过程。通过对水中爆炸理论和板的大变形理论分析，应用能量原理和Lagrangian函数，推导出反映固支方板在冲击载荷作用下变形的最终挠度的解析解。水中爆炸对固边方板破坏的实验在自制的水箱中进行。对不同的装药重量和炸距情况下方板的变形情况进行了理论计算，并对实验结果和误差来源进行了分析。实验结果和理论结果具有较好的一致性。     

Orientation of Nd and Mn magnetic moments in a CMR Nd0.72Ba0.28MnO3 by X-ray magnetic circular dichroism

X-ray absorption and X-ray magnetic circular dichroism at Mn L_2,3- and Nd M_4,5-edges of a twinned Nd_0.72Ba_0.28MnO₃ single crystal have been performed versus temperature (between 10 and 300 K) and applied magnetic field (between 0 and 6.5 T). The results show that neodymium cations order below 70 K with the magnetic moments antiparallel to the manganese subnetwork in weak applied magnetic field (<1.5 T). For higher magnetic field, the neodymium moments turn parallel to the manganese ones showing that the antiferromagnetic exchange coupling between both subnetworks is weak. The presence of a metal–insulator transition below 70 K in the studied single crystal correlated to the magnetic ordering of neodymium cations can be understood on the basis of the cation mismatch introduced by barium substitution.     

Local electronic structures at selected sites of intermetallic perovskites Mn3MeX (Me=divalent metal,X=N,C)

Summary We have measured the XANES (X-ray absorption near edge structure) spectra on the manganese and metal MeK-edges of the intermetallic perowskites Mn₃MeX (X=N, Me=Mn, Cu, Zn, Ga, Sn; X=C, Me=Ga, Sn) to investigate the distribution on the partial density of the empty states. The information on the local electronic structure at the two differents sites, obtained from the spectra in the first 10 eV above the onset, is discussed in terms of one-electron band model. The relative shape changes in the spectra between the different compounds are explained by the different magnitude of hybridization between the electronic states of different atoms and/or the filling of the empty band by the electrons supplied by the substituted metal. Moreover, information about the local geometrical structure has been obtained from the (10÷50) eV range of the spectra.

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Riassunto La distribuzione della densità parziale degli stati vuoti nelle perovskiti intermetalliche Mn₃MeX (X=N, Me=Mn, Cu, Zn, Ga, Sn; X=C, Me=Ga, Sn) è stata studiata mediante spettroscopia XANES (X-ray absorption near edge structure) alle soglieK del Mn e del metallo Me. Le informazioni sulla struttura elettronica locale di entrambi i siti, ottenute dall’analisi dei primi 10 eV degli spettri XANES, sono discussed in termini di un modello proposto. Il cambiamento relativo della forma negli spetttri dei diversi composti è posto in relazione alla differente ibridizzazione tra stati di atomi diversi e/o dal riempimento degli stati della banda vuota con elettroni forniti dal metallo sostituente. Sono state anche ottenute informazioni sulla struttura geometrica locale analizzando gli spettri nell’intervallo da 10 a 50 eV.

     

Weak-disorder expansion for the Anderson model on a tree

We show how certain properties of the Anderson model of a tree are related to the solutions of a nonlinear integral equation. Whether the wave function is extended or localized, for example, corresponds to whether or not the equation has a complex solution. We show how the equation can be solved in a weakdisorder expansion. We find that, for small disorder strength , there is an energyE _c () above which the density of states and the conducting properties vanish to all orders in perturbation theory. We compute pertubatively the position of the lineE _c () which begins, in the limit of zero disorder, at the band edge of the pure system. Inside the band of the pure system the density of states and conducting properties can be computed perturbatively. This expansion breaks down nearE _c () because of small denominators. We show how it can be resummed by choosing the appropriate scaling of the energy. For energies greater thanE _c () we show that nonperturbative effects contribute to the density of states but we have been unable to tell whether they also contribute to the conducting properties.     

Chemistry at the Edge of Graphene

The selective functionalization of graphene edges is driven by the chemical reactivity of its carbon atoms. The chemical reactivity of an edge, as an interruption of the honeycomb lattice of graphene, differs from the relative inertness of the basal plane. In fact, the unsaturation of the p_z orbitals and the break of the π conjugation on an edge increase the energy of the electrons at the edge sites, leading to specific chemical reactivity and electronic properties. Given the relevance of the chemistry at the edges in many aspects of graphene, the present Review investigates the processes and mechanisms that drive the chemical functionalization of graphene at the edges. Emphasis is given to the selective chemical functionalization of graphene edges from theoretical and experimental perspectives, with a particular focus on the characterization tools available to investigate the chemistry of graphene at the edge.     

Additive Schwarz preconditioners for C0 interior penalty methods for the obstacle problem of clamped Kirchhoff plates

The discrete variational inequalities resulting from interior penalty methods for the obstacle problem of clamped Kirchhoff plates can be solved by the primal-dual active set algorithm. We develop and analyze additive Schwarz preconditioners for the auxiliary systems that appear in each iteration of the primal-dual active set algorithm. Numerical results corroborate our theoretical estimates.     

On the existence of weak solutions of anisotropic generally restrained plates

This paper presents investigations of free vibration of anisotropic plates of different geometrical shapes and generally restrained boundaries. The existence and uniqueness of weak solutions of boundary value problems and eigenvalue problems which correspond to the statical and dynamical behaviour of the mentioned plates is demonstrated. It is determined that when the plates have corner points formed by the intersection of edges free or elastically restrained against translation, the corresponding bilinear forms maintain the V – ellipticity property.     

A variational approach to free vibration analysis of shear deformable polygonal plates with variable thickness

This paper presents a simple and general variational approach for the study of the free vibration behaviour of polygonal isotropic plates with variable thickness. The Reissner-Mindlin plate theory is used to take into account the effects of shear deformation and rotary inertia in the analysis. Moreover, this theory allows obtaining greater accuracy of frequency coefficients corresponding to vibration higher modes, even for the thin plates.The governing eigenvalue equation is obtained employing the Ritz method. The plate geometry is approximated by using non-orthogonal triangular co-ordinates, while sets of independent polynomials, expressed in these co-ordinates, are employed to approximate the displacement and rotation fields. The developed algorithm allows obtaining approximated analytical solutions for plates with different aspect ratios, thickness variation and boundary conditions, including edges elastically restrained by both translational and rotational springs. Therefore, a unified program has been easily implemented. Convergence and comparison analyzes are carried out to verify the reliability and accuracy of the numerical solutions. Finally, sets of parametric studies are performed and the results are given in graphical and tabular form.     

Series solutions for a transversely loaded and completely clamped thick rectangular plate based on the three-dimensional theory of elasticity

Summary The bending of a thick rectangular plate with all the edges completely clamped is analyzed by the three-dimensional theory of elasticity. A partially distributed uniform load over the top face is dealt within the analysis. The boundary conditions of the completely clamped edges are prescribed by three-dimensional, exact conditions that three displacement components vanish at the faces. The stress distributions at the edges are minutely examined by making the best use of advantages of the exact analysis. The stress distributions for the case of a fully distributed uniform load are compared with those obtained by Reissner's theory. The values of deflections and internal forces for various thickness-length ratios are also presented. Accepted for publication 5 June 1997     

First-principles study of the sulfur K and L2,3 edges of transition metal disulfide monolayers,MS2 (M=Mo,W and Re)

By means of the energy loss near edge structure (ELNES) analysis, the electronic structures of layered transition metal disulfides were studied. In the framework of full potential linearized augmented plane wave method, ELNES spectra of sulfur K and L_2,3 edges of layered MoS₂, WS₂ and ReS₂ have been calculated at magic angle conditions, and compared with those of bulks and the only existing experimental fine structure. Compared to the bulks, the energy differences between the main peaks in sulfur K and L_2,3 edges of monolayers decrease due to the slightly larger bond lengths that it can be used as a fingerprint for monolayers. Sulfur K edges in monolayers include some main features originated from electron transition to p_z (π) and p_x+p_y (σ) states and their hybridization. The overall dispersions of the sulfur L_2,3 edges in all cases are similar to the d-symmetry density of states. The first two features in L_2,3 edge of bulks and monolayers can be attributed to electron transition of sulfur 2p to the both unoccupied 3s-like states of sulfur and 4d states of transition metal atoms. Due to the considerable amount of s states at the energy position of a shoulder like structure in L_2,3 edge of both bulks and monolayers, these structures can be assigned to the sulfur 2p electron transition to unoccupied sulfur 3s states. The other features at higher energies are due to the transition of sulfur 2p electrons to the d-symmetry states of sulfur. In addition, due to the considerable energy band gaps, it seems that the use of core–hole approximation is essential for accurate reproduction of ELNES features of transition metal disulfides.