Using non-linear magneto-optic techniques to characterise particulate recording media

The concept of using comparison between magneto-optic measurements taken in the linear and second-harmonic reflected fields to address problems attending the development of ultra-high-density recording media as the limits of thermal stability are approached is presented. It is shown how magneto-optical measurements made routinely in the linear reflected field to access many of the bulk characteristics of such media may, by operating in the second-harmonic field, be fruitfully extended. To illustrate the techniques being explored, reference is made to initial measurements on a longitudinal recording medium under continuing development at Coventry. This medium, already shown to support recording at linear densities in excess of 100 kfci, is based on cobalt particles around 10 nm in diameter. Received: 16 October 2001 / Revised version: 14 March 2002 / Published online: 29 May 2002     

Flow-induced crystallization by surface growth of polyethylene fibers

A series of experiments has been carried out investigating several features of the surface growth method for observing longitudinal growth of polyethylene fibers in Couette geometry. Attempts to obtain limiting steady-state takeup rates using a Teflon rotor were hampered by fiber breakage; however, maximum growth rates before breakage were found to be considerably higher than those observed in previous studies. Growth rates were also obtained using a static method, and for the Teflon rotor indicated above a critical concentration a linear growth rate equal to the stirrer velocity with rates essentially independent of temperature. With a silanized glass rotor, the same method gave much lower growth rates at comparable stirrer speeds and temperatures and showed a temperature dependence suggestive of a nucleation-controlled mechanism. The implications of these results for other studies of the mechanisms of growth by the surface method are also discussed.     

Fully coupled finite volume solutions of the incompressible Navier–Stokes and energy equations using an inexact Newton method

An inexact Newton method is used to solve the steady, incompressible Navier–Stokes and energy equation. Finite volume differencing is employed on a staggered grid using the power law scheme of Patankar. Natural convection in an enclosed cavity is studied as the model problem. Two conjugate-gradient -like algorithms based upon the Lanczos biorthogonalization procedure are used to solve the linear systems arising on each Newton iteration. The first conjugate-gradient-like algorithm is the transpose-free quasi-minimal residual algorithm (TFQMR) and the second is the conjugate gradients squared algorithm (CGS). Incomplete lower-upper (ILU) factorization of the Jacobian matrix is used as a right preconditioner. The performance of the Newton- TFQMR algorithm is studied with regard to different choices for the TFQMR convergence criteria and the amount of fill-in allowed in the ILU factorization. Performance data are compared with results using the Newton-CGS algorithm and previous results using LINPACK banded Gaussian elimination (direct-Newton). The inexact Newton algorithms were found to be CPU competetive with the direct-Newton algorithm for the model problem considered. Among the inexact Newton algorithms, Newton-CGS outperformed Newton- TFQMR with regard to CPU time but was less robust because of the sometimes erratic CGS convergence behaviour.     

On the remainder term in theN-dimensional Euler Maclaurin expansion

The form of the remainder term in theN-dimensional Euler Maclaurin expansion is investigated. A concise formalism is developed for handling expressions which are lengthy to state using conventional notation. Conditions under which an integral representation involving only derivatives of the same total order with conventional kernel functions exists for the remainder term are derived.Work performed in part under the auspices of the U. S. Atomic Energy Commission.Part of this work was carried out by both authors at the University of N.S.W., Kensington, N.S.W., Australia.     

An analysis of local flow effects in flow-induced orientation and crystallization

An analysis is presented of the effects of external flow kinematics on the so-called local flow in seeded, flow-induced crystallization and orientation. The flow field around a growing crystal or nucleation seed is modelled by the Stokes flow equations past a prolate ellipsoid of high aspect ratio. Exact solutions for various flow kinematics, worked out elsewhere by the singularity method, are applied here to the analysis of local gradients. The results show that along the symmetry axis of the spheroid, the extensional gradients which result for various free-stream velocity fields are primarily the result of the constant-velocity free-stream component. However, free-stream, extensional flow can significantly enhance the region of such high gradients. Along the symmetry plane of the spheroid, primarily shearing gradients result, with small extensional gradients occurring when the free-stream flow has extensional components. Results of chain extension and birefringence calculations are also presented and discussed.     

<Emphasis Type="Italic">N</Emphasis>-arachidonoyl glycine,an abundant endogenous lipid,potently drives directed cellular migration through GPR18, the putative abnormal cannabidiol receptor

Background  

Microglia provide continuous immune surveillance of the CNS and upon activation rapidly change phenotype to express receptors that respond to chemoattractants during CNS damage or infection. These activated microglia undergo directed migration towards affected tissue. Importantly, the molecular species of chemoattractant encountered determines if microglia respond with pro- or anti-inflammatory behaviour, yet the signaling molecules that trigger migration remain poorly understood. The endogenous cannabinoid system regulates microglial migration via CB₂ receptors and an as yet unidentified GPCR termed the 'abnormal cannabidiol' (Abn-CBD) receptor. Abn-CBD is a synthetic isomer of the phytocannabinoid cannabidiol (CBD) and is inactive at CB₁ or CB₂ receptors, but functions as a selective agonist at this G_i/o-coupled GPCR. N-arachidonoyl glycine (NAGly) is an endogenous metabolite of the endocannabinoid anandamide and acts as an efficacious agonist at GPR18. Here, we investigate the relationship between NAGly, Abn-CBD, the unidentified 'Abn-CBD' receptor, GPR18, and BV-2 microglial migration.     

Conservative methods for the Toda lattice equations

We are concerned with the numerical integration of the Todalattice equations by using different conservative methods. Numericalexperiments suggest that the global error for isospectral schemesdecreases exponentially with time but it is almost constantfor either symplectic or more general integrators. We providea theoretical explanation for these experimental findings.     

Dynamics of Dendrimeric Molecules Undergoing Simple Shear Flow: A Nonequilibrium Brownian Dynamics Study

Nonequilibrium Brownian dynamics (NEBD) simulations are used to model the dynamics of six generations of dendrimers undergoing shear flow. A coarse‐grained bead‐spring model is proposed, which incorporates springs with stretching and bending potentials. The bending constant is used as one of the primary independent variables to control the deformability of the molecules. Rheological and conformational properties, such as viscosity, normal stress differences, visco‐elastic moduli, flow birefringence, mean square radius of gyration, and degree of prolateness, are observed under both transient (startup and cessation of flow) and steady‐state conditions. Comparisons are made with the corresponding linear chain analogs of the same molecular weight. The model qualitatively describes many of the experimentally observed effects in these systems, most notably a Newtonian viscosity profile (no shear thinning) and a maximum in the dependence of the intrinsic viscosity on the molecular weight. The dendrimers are also characterized by negligible start‐up overshoots in the transient viscosity and birefringence.