The dynamic analysis of circular plates and shallow spherical shells

In the investigation reported here an attempt has been made to study the influence of Berger's approximation on the non-linear transient response of circular plates and shallow spherical shells. The governing equations of motion obtained from Berger's approximation are solved by using the rapidly converging Chebyshev series spacewise and the Houbolt scheme for integration in the time domain. Results calculated when using Berger's approximation are compared with exact results. It is shown that Berger's method yields very accurate values for plates and shells under transient loading, in the case of immovable edge conditions.     

Mössbauer studies in disordered (NiFe)1−xCrx alloys

The variation of hyperfine field, isomer shift and Curie temperature with chromium concentration has been studied for the alloys (NiFe)_1?xCr_x for x = 0, 5, 10 and 15 at .%. The decrease in hyperfine field and isomer shift suggests an emptying of the majority spin d-band with increasing Cr concentration (reducing number of average 3d + 4s electrons per atom). The Curie temperature is also found to reduce rapidly with Cr concentration in agreement with magnetisation data. But the Curie temperatures as determined from Mössbauer spectra are considerably lower than those given by magnetisation studies and for the 10 and 15 at .% Cr concentrations the magnetic transition is spread out over a range of temperatures suggesting a mictomagnetic behaviour.     

Positron annihilation in annealed and quenched teflon and in sulphur

The value (τ₂) and the intensity (I₂) of the delayed component in the lifetime spectra of positrons annihilating in annealed and quenched teflon and in sulphur and crystex (polymer sulphur), at room temperature and at 77° K are reported. These data and the X-ray diffraction patterns for these materials are discussed in terms of the free volume model for the formation and quenching of positronium atoms in molecular materials.     

Quark Masses in Terms of Gauge Constants and Cabibbo Angle

Fritzsch type of mass matrices for the 2×2 case and appropriate Lagrangians enable the choice of Yukawa constants of the Lagrangians in terms of the gauge constants. The mass matrices for the four quarks are shown to be proportional to V_L. The Cabibbo angle is computed to be 13^∘36′.     

Total synthesis of the novel, biologically active epoxyquinone dimer (+/-)-torreyanic acid: a biomimetic approach

[reaction: see text] A total synthesis of the complex, biologically active, dimeric natural product (+/-)-torreyanic acid, which is composed of seven rings and laced with dense, variegated oxy-functionalization, has been accomplished from readily available allyl-substituted p-benzoquinone 8. Our synthetic stratagem involves crafting an epoxyquinone monomer for use in a biomimetic cascade process involving tandem a 6pi electrocyclization and a Diels-Alder dimerization.     

Electronic, e.p.r., cyclic voltammetric and biological activities of copper(II) complexes with macrocyclic ligands

Eight new macrocyclic ligands have been prepared by the reaction of the precursor diketone (benzil, glyoxal, diacetyl or 2,3-pentanedione) with a diamine (thiosemicarbazide or semicarbazide). Copper(II) complexes of these ligands have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility, i.r., u.v.–vis, ¹H-n.m.r., mass and e.p.r. spectral studies. Mass, n.m.r. and i.r. data indicate the condensation of the diamine and diketone and the whole molecular ion structure. g-Values are calculated for all of the complexes in polycrystalline form as well as in DMSO solution. Spin Hamiltonian values and bonding parameters have also been calculated which indicates that an unpaired electron is present in the orbital. The metal-ligand bonding parameters shows strong in-plane σ sigma and in-plane π bonding. The magnetic and spectral data indicate tetragonal geometry for all of the complexes except [CuH₂L⁴]Cl₂ and [CuH₂L⁴]Cl₂ which are square planar. From c.v. data reversible Cu^II/Cu^I couples are observed for these complexes. The macrocyclic complexes show more antibacterial and antiviral activity as compared to the ligands. The antibacterial activities of the compounds were tested against S. aureus, S. subtillis and E. coli.     

A study of damping in fiber-reinforced composites

Damping contributions from the viscoelastic matrix, interphase and the dissipation resulting from damage sites are considered to evaluate composite material damping coefficients in various loading modes. The paper presents the results of the FEM/Strain energy investigations carried out to predict anisotropic-damping matrix comprising of loss factors η₁₁, η₂₂, η₁₂ and η₂₃ considering the dissipation of energy due to fiber and matrix (two phase) and correlate the same with various micromechanical theories. Damping in three phase (i.e., fiber-interphase-matrix) composite is also calculated as an attempt to understand the effect of interphase. The contribution of energy dissipation due to sliding at the fiber-matrix interface is incorporated to evaluate its effect on η₁₁, η₂₂, η₁₂ and η₂₃ in fiber-reinforced composite having damage in the form of hairline debonding. Comparative studies of the various micromechanical theories/models with FEM/Strain energy method for the prediction of damping coefficients have shown consistency when both the effect of variable nature of stress and the fiber interaction is considered. Parametric damping studies for three phase composite have shown that the change in properties of fiber, matrix and interphase leads to a change in the magnitude of effectiveness of interphase, but the manner in which the interphase would affect the various loss factors depends predominately upon whether the hard or soft interphase is chosen. Analysis of the effect of damage on composite damping indicates that it is sensitive to its orientation and type of loading.     

Sparse matrix multiplications for linear scaling electronic structure calculations in an atom-centered basis set using multiatom blocks

A sparse matrix multiplication scheme with multiatom blocks is reported, a tool that can be very useful for developing linear-scaling methods with atom-centered basis functions. Compared to conventional element-by-element sparse matrix multiplication schemes, efficiency is gained by the use of the highly optimized basic linear algebra subroutines (BLAS). However, some sparsity is lost in the multiatom blocking scheme because these matrix blocks will in general contain negligible elements. As a result, an optimal block size that minimizes the CPU time by balancing these two effects is recovered. In calculations on linear alkanes, polyglycines, estane polymers, and water clusters the optimal block size is found to be between 40 and 100 basis functions, where about 55-75% of the machine peak performance was achieved on an IBM RS6000 workstation. In these calculations, the blocked sparse matrix multiplications can be 10 times faster than a standard element-by-element sparse matrix package.     

Synthesis and reactivity of enediynyl amino acids and peptides: a novel concept in lowering the activation energy of Bergman cyclisation by H-bonding and electrostatic interactions

Novel enediynyl amino acids and peptides 3 and 5-8 were synthesized and their thermal reactivity towards Bergman cyclization studied and compared with the earlier reported amino acid 4, which demonstrated, for the first time, the effect of H-bonding and electrostatic interactions in lowering the activation energy of Bergman cyclization.     

Synthesis of new,pyrene-containing,metal-chelating lipids and sensing of cupric ions

The syntheses of several saturated, pyrene-containing, metal-chelating lipids are described. These lipids are capable of strongly binding to transition metal ions employing the metal-chelating headgroup. The excimer-to-monomer ratio of the pyrene groups changes with addition of cupric ions to the liposomes. Three other transition metal ions (Zn(2+), Ni(2+), and Hg(2+)) did not cause any appreciable changes in the excimer-to-monomer ratio. [reaction--see text]