The instantaneous slow flow of a visco-elastic fluid between two concentric spheres

Summary A theoretical analysis is made of the flow of an incompressible viscoelastic fluid contained between two concentric spheres when the outer sphere is moved instantaneously in a given direction, whilst the inner sphere remains at rest. The solution is developed by successive approximations, the first corresponding to the instantaneous slow flow of a Newtonian viscous fluid. By allowing the radius of the outer sphere to approach infinity, the result obtained can be used to give an approximate solution to the equations of motion of a visco-elastic fluid flowing slowly past a fixed sphere.     

A family of double-bowl pseudo metallocalix[6]arene discs

We report the synthesis and magnetic characterisation of a series of planar [M?] (M= Ni(II), Zn(II)) disc complexes [Ni?(OH)?(L?)?](NO?)? (1), [Ni?(OH)?(L?)?](NO?)?·2MeOH (2), [Ni?(OH)?(L?)?](NO?)?·3MeNO? (3), [Ni?(OH)?(L?)?](NO?)?·2MeCN (4), [Zn?(OH)?(L?)?](NO?)?·2MeOH·H?O (5) and [Zn?(OH)?(L?)?](NO?)?·3MeNO? (6) (where HL? = 2-iminomethyl-6-methoxy-phenol, HL? = 2-iminomethyl-4-bromo-6-methoxy-phenol). Each member exhibits a double-bowl pseudo metallocalix[6]arene topology whereby the individual [M?] units form molecular host cavities which are able to accommodate various guest molecules (MeCN, MeNO? and MeOH). Magnetic susceptibility measurements carried out on complexes 1 and 4 indicate weak exchange between the Ni(II) centres.     

A donor-stabilization strategy for the preparation of compounds featuring P=B and As=B double bonds

A new class of heavier group 15 compounds demonstrating multiple bonding with boron has been synthesized using a simple donor-stabilization protocol.     

Density functional theory (DFT)-based modified embedded atom method potentials: Bridging the gap between nanoscale theoretical simulations and DFT calculations

A density functional theory (DFT)-calculation scheme for constructing the modified embedded atom method (MEAM) potentials for face-centered cubic (fcc) metals is presented. The input quantities are carefully selected and a more reliable DFT approach for surface energy determination is introduced in the parameterization scheme, enabling MEAM to precisely predict the surface and nanoscale properties of metallic materials. Molecular dynamics simulations on Pt and Au crystals show that the parameterization empl...     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Numerical simulations of the discontinuous progression of cerebral aneurysms based on fluid-structure interactions study

Investigations into the characteristics of hemodynamics will provide a better understanding of the pathology of cerebral aneurysms for clinicians.In this work,a steady state discontinuous-growth model of the cerebral aneurysms was proposed.With the assumption of the fluid-structure interaction between the wall of blood vessel and blood,a fluid-structure coupling numerical simulation for this model was built using software ANSYS and CFX.The simulation results showed that as the aneurysm volume increased,a bl...