Buckling of laminated plates - A simple finite element based on higher-order theory

A four-noded rectangular element with seven degrees of freedom at each node is developed for buckling analysis of laminated plate structures having any number of layers with a constant thickness of individual layers. The displacement model is so chosen that it can explain adequately the parabolic distribution of transverse shear stresses and the non-linearity of in-plane displacements across the thickness. A geometrical stiffness matrix is developed using in-plane stresses. A wide range of plates from thick to thin are examined under uniaxial loading conditions. The results are compared with the existing analytical and numerical solutions. The present formulations confirm its applicability for buckling analysis of a wide range of plates.     

Manifestation of diamagnetic chemical shifts of proton NMR signals by an anisotropic shielding effect of nitrate anions

A remarkable upfield shift of the py_α protons of complexed 2,2′-bipyridine in [cis-Pd(bpy)(NO₃)₂] is observed which is considered to originate from the anisotropic influence of suitably positioned coordinated nitrate anions around the Pd(II) centre of the molecule. A typical complexation-induced downfield shift is observed for the NH₂ protons in [cis-Pd(en)(NO₃)₂] where ‘en’ stands for ethylenediamine.     

Towards an enantiospecific total synthesis of garsubellin A and related phloroglucin natural products: the α-pinene approach

The first enantiospecific approach to garsubellin A and related phloroglucin natural product nemorosone, of contemporary interest from (−)-α-pinene, has been delineated. Through a series of stereospecific operations, the requisite stereochemistry of the prenyl groups has been secured. Kende cyclization has been employed as the key step to construct the functionalized bicyclo[3.3.1]nonane core.     

Silver-palladium nanodispersions in silicate matrices: highly uniform, stable, bimetallic structures

Ag-Pd nanobimetallic colloidal particles are prepared in a single step by a chemical reduction method. Organically modified aminosilicate is used as a supporting matrix as well as a stabilizing agent, to obtain very uniform, well-distributed bimetallic particles. These nanoparticles are found to be stable for several months in both the solid and the liquid phases. The structure of the bimetallic particles has been followed by X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The distribution and the particle size are determined by transmission electron microscope and X-ray diffraction studies. Polymerization and condensation of the support silicate material have been confirmed by Fourier transform infrared spectroscopy.     

Efficient synthesis of tertiary amines from secondary amines

Reliable N-alkylations of secondary amines have been developed. By using DIAD and TPP (or PS-TPP) a variety of secondary amines can be converted to the corresponding tertiary amines in good to excellent yields with diverse alkylhalides; no formation of quaternary amine salts are observed. These protocols are amenable to combinatorial chemistry libraries, and are also useful for the syntheses of secondary amines by an acid lysis of the cleavable tertiary amino resins.     

A study of structural and bonding variations in the homologous series [Mo(2)(CN)(6)(dppm)(2)](n-) (n = 2, 1, 0)

Reaction of Mo(2)Cl(4)(dppm)(2) (dppm = bis(diphenylphosphino)methane) with 6 equiv of [n-Bu(4)N][CN] or [Et(4)N][CN] in dichloromethane yields [n-Bu(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (1) and [Et(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (2), respectively. The corresponding one- and two-electron oxidation products [n-Bu(4)N][Mo(2)(CN)(6)(dppm)(2)] (3) and Mo(2)(CN)(6)(dppm)(2) (4)were prepared by reactions of 1 with the oxidant NOBF(4). Single-crystal X-ray structures of 2.2CH(3)CN, 3.2CH(3)CN.2H(2)O, and 4.2CH(3)NO(2) were performed, and the results confirmed that all three complexes contain identical ligand sets with trans dppm ligands bisecting the Mo(2)(mu-CN)(2)(CN)(4) equatorial plane. The binding of the bridging cyanide ligands is affected by the oxidation state of the dimolybdenum core as evidenced by an increase in side-on pi-bonding overlap of the mu-CN in going from 1 to 4. The greater extent of pi-donation into Mo orbitals is accompanied by a lengthening of the Mo-Mo distance (2.736(1) A in Mo(2)(II,II) (2), 2.830(1) A in Mo(2)(II,III) (3), and 2.936(1) A in Mo(2)(III,III) (4)). A computational study of the closed-shell members of this homologous series, [Mo(2)(CN)(6)(dppm)(2)](n)() (n = 2-, 0), indicates that the more pronounced side-on pi-donation evident in the X-ray structure of 4 leads to significant destabilization of the delta orbital and marginal stabilization of the delta() orbitals with respect to nearly degenerate delta and delta orbitals in the parent compound, 2. The loss of delta contributions combined with the reduced orbital overlap due to higher charges on molybdenum centers in oxidized complexes 3 and 4 is responsible for the observed increase in the length of the Mo-Mo bond.     

Study of approximate coupled cluster methods for first-order static properties

In this paper, we analyse the algebraic structure of the equations for calculating the first order static properties using several approximate versions of Coupled Cluster (CC) methods. In particular, the non-variational and the variational method using a CC wavefunction corresponding to an appropriately defined perturbed Hamiltonian as well as the simple expectation value expression using a CC stationary state are studied under different approximations. Two different models are proposed: (a) use of maximum overlap orbitals where the pertinent approximations are TT ₂, T ⁽¹⁾ T ₂ ⁽¹⁾, (b) use of Hartree-Fock orbitals and T(T ₁+T ₂), T ⁽¹⁾(T ₁ ⁽¹⁾ +T ₂ ⁽¹⁾ ) approximations. It is analytically shown that in both these models certain approximate versions of the methods under purview yield identical results for first order static properties.NCL Communication No. 3725     

A variational coupled cluster theory for closed shells using a propagator modification procedure

A general partial summation method for including arbitrary classes of diagrams to all orders in the coupled cluster based size consistent energy functional for closed shell states is developed. Since the various reduced density matrices which appear in the energy functional are essentially the time-independent analogues of the corresponding many body Green functions, it is possible to derive Dyson-like equations for these quantities. By expanding the associated proper self energy parts in terms of the T-amplitudes, one can carry out partial summations in the reduced density matrices and thus in energy. At a higher level, higher order terms in a proper self energy can also be generated by renormalizing the internal propagators in it, and considering only the irreducible self-energy terms.     

Electrophoretic dynamics of large DNA stars in polymer solutions and gels

We have developed a procedure for synthesizing large stable branched DNA structures that enables visualization via fluorescence microscopy. Using this procedure we have synthesized large DNA stars and observed their electrophoretic behavior in polymer solutions and gels. In dilute polyacrylamide solutions, the DNA stars move as random coils and appear to experience only brief collisions with the polymer chains in solution. The effect of polymer solution concentration on the electrophoretic mobility of stars in the dilute regime is found to be in good accord with predictions of the transient entanglement coupling (TEC) model. In semidilute polymer solutions, the star arms extend in the field direction and drag the core through the matrix. The star arms form several U-shaped conformations as they collide and engage with polyacrylamide chains. The U-shaped conformations occasionally evolve into J-shaped conformations as the star arms slide off the matrix chains they engage during electrophoretic migration. In concentrated polymer solutions, the arms of the star extend and form V-shaped structures with the core as the apex. The arms then pull the core through the matrix. These V-shaped conformations are much longer-lived than U-shaped ones and, unlike the latter, do not transform to J-shaped conformations. In polyacrylamide and agarose gels, where matrix entanglements are fixed, DNA stars become trapped when entanglements with matrix molecules prevent the core from being pulled through the matrix by the extended arms. This trapping was observed at all gel concentrations and electric fields studied.