On the dynamics of a predator–prey model with nonconstant death rate and diffusion

The main goal of this paper is to describe the global dynamic of a predator–prey model with nonconstant death rate and diffusion. We obtain necessary and sufficient conditions under which the system is dissipative and permanent. We study the global stability of the nontrivial equilibrium, when it is unique. Finally, we show that there are no nontrivial steady state solutions for certain parameter configuration.     

On a finite element method for a compressible viscous flow in a MOCVD reactor

We propose a stable finite element method for approximating the flow of a chemically reacting gas mixture in an MOCVD (metal‐organic chemical vapor deposition) reactor. The flow is governed by the full compressible Navier‐Stokes equations extended by transport equations for the chemical species, the energy equations and the equation of state, together with boundary conditions providing information on the reactor geometry and experimental conditions. The equations form a semilinear system with a constraint for which the corresponding pressure term is not the Lagrangian multiplier. An application of our method to a real world model of growth of GaAs shows the consistency with experimental data. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005     

结构非线性分析中求解预定荷载水平的改进弧长法

本文对目前广泛应用于结构非线性分析之中的弧长法进行改进。改进后的弧长法除保持原有优点外，能够在自动跟踪结构非线性平衡路径的同时，进一步求得位于结构平衡睡径任一区段的任意预先指定的荷载水平及相应的变形。本文的方法可以推广应用于求解预先指定的应力或位移。数值算例表明了本文方法的计算精度、效率及可靠性。     

Orbital contributions to some two-electron properties

Analytical formulas are given for the orbital contributions to two-electron properties such as 〈r〉, with n = ?2, ?1, 1, 2, 3, and 4, for atomic systems in which orbitals are expanded as linear combinations of Gaussian functions. Numerical values for all possible contributions in the atoms Li to Ne have been calculated at the Hartree–Fock level. These quantities are compared and discussed to show what kind of information can be obtained from such quantities. The influence of the basis set size has also been considered.     

Cytoskeletal turnover and Myosin contractility drive cell autonomous oscillations in a model of Drosophila Dorsal Closure

Oscillatory behaviour in force-generating systems is a pervasive phenomenon in cell biology. In this work, we investigate how oscillations in the actomyosin cytoskeleton drive cell shape changes during the process of Dorsal Closure (DC), a morphogenetic event in Drosophila embryo development whereby epidermal continuity is generated through the pulsatile apical area reduction of cells constituting the amnioserosa (AS) tissue. We present a theoretical model of AS cell dynamics by which the oscillatory behaviour arises due to a coupling between active myosin-driven forces, actin turnover and cell deformation. Oscillations in our model are cell-autonomous and are modulated by neighbour coupling, and our model accurately reproduces the oscillatory dynamics of AS cells and their amplitude and frequency evolution. A key prediction arising from our model is that the rate of actin turnover and Myosin contractile force must increase during DC in order to reproduce the decrease in amplitude and period of cell area oscillations observed in vivo. This prediction opens up new ways to think about the molecular underpinnings of AS cell oscillations and their link to net tissue contraction and suggests the form of future experimental measurements.     

Crystal structure of hexacyano cobaltate(III) of caesium and tetramethylammonium: Cs[(Me)4N]2Co(CN)6

Summary The structure of a novel hexacyano cobaltate(III) of Cs and tetramethylammonium (TMA), Cs(TMA)₂Co(CN)₆, has been determined by single crystal x-ray diffraction using Patterson and Fourier techniques, and refined by least squares to R=0.053 for 126 independent reflections. The compound is cubic with a_o=12.592(2) Å, space group Fm3m, Z=4.There is a cubic network of Co–CN–Cs atoms with Co–C and C–N distances of 1.87(2) and 1.18(2) Å respectively. The bulky (TMA) cations occupy the cubic voids in this network. The C–N distance of (TMA) is 1.38(2) Å. The Me groups are oriented towards the Cs atoms and there is hindered rotation of the CH₃ groups. The Hatoms occupy positions at maximum distance from the C–N triple bonds, pointing to the faces of the octants of the unit cell.     

Evidence of Verwey transition in iron- and iron oxide-encapsulated carbon nanotubes

Magnetization measurements in two different samples of iron- and iron oxide-encapsulated carbon nanotubes are presented. The samples showed coercivity smaller than 1 kOe. The dependence of the coercivity with the temperature has an abrupt change at temperatures close to 125 K. In this temperature the ZFC and FC magnetization curves also present an abrupt change. This effect is attributed to a Verwey transition.     

Interfacial properties of Lennard-Jones chains by direct simulation and density gradient theory

We perform a series of molecular dynamics simulations of Lennard-Jones chains systems, up to tetramers, in order to investigate the influence of temperature and chain length on their phase separation and interfacial properties. Simulation results serve as a test to check the accuracy of a statistical associated fluid theory (soft-SAFT) coupled with the density gradient theory. We focus on surface tension and density profiles. The simulations allow us to discuss the success and limitations of the theory and how to estimate the only adjustable parameter, the influence parameter. This parameter is obtained by fitting the surface tension, and then used to obtain the density profiles in a predictive manner. A good agreement is found if the temperature dependence of this parameter is neglected.(c) 2004 American Institute of Physics.     

Antenna chemistry with metallic single-walled carbon nanotubes

We show that, when subjected to microwave fields, surfactant-stabilized single-walled carbon nanotubes (SWNTs) develop polarization potentials at their extremities that readily drive electrochemical reactions. In the presence of transition metal salts with high oxidation potential (e.g., FeCl3), SWNTs drive reductive condensation to metallic nanoparticles with essentially diffusion-limited kinetics in a laboratory microwave reactor. Using HAuCl4, metallic particles and sheaths deposit regioselectively at the SWNT tips, yielding novel SWNT-metal composite nanostructures. This process is shown to activate exclusively metallic SWNTs; a degree of diameter selectivity is observed using acceptors with different oxidation potentials. The reaction mechanism is shown to involve Fowler-Nordheim field emission in solution, where electric fields concentrate at the SWNT tips (attaining approximately 10(9) V/m) due to the SWNT high aspect ratio (approximately 1000) and gradient compression in the insulating surfactant monolayer. Nanotube antenna chemistry is remarkably simple and should be useful in SWNT separation and fractionation processes, while the unusual nanostructures produced could impact nanomedicine, energy harvesting, and synthetic applications.