Antiferromagnetism of the FeNb and FeTa MU-phases

The magnetic structure of the antiferromagnetic FeNb and FeTa alloys has been investigated using a variety of techniques including susceptibility. Mössbauer and neutron diffraction measurements. Our results indicate a simple structure in which alternate Kagomé layers of Fe atoms have their moments oriented in opposite directions, approximately perpendicular to the plane of the layers. Positive Weiss temperatures confirm that the dominant nearest neighbour intra-layer interactions are ferromagnetic. Specific heat and low angle neutron scattering observations suggest extensive short-range order above T_N. The substantial non-magnetic contribution to the Mössbauer spectra is shown to result from ≈ 25% occupation of the high-coordination ‘A’ sites by Fe atoms with a similar proportion of the low-coordinationB2 Kagomé sites occupied by Nb. A structural neutron super lattice line too weak to have been observed in earlier work using X-rays suggests that the true μ-phase unit cell may be three times larger in dimensions than previously envisaged.     

The influence of wire width on the charge distribution of transverse domain walls and their stray field interactions

We present here a numerical study of the magnetostatic charge distribution of transverse Néel type domain wall in permalloy nanowires. The calculations indicate that not only is the distribution highly non-uniform within a given transverse wall but it also varies dramatically with respect to the wire width. The implications of this for magnetostatic domain wall pinning are analyzed by considering the stray field interaction between a wall and another extended magnetic body for a particular domain wall chirality, where two distinct depinning mechanisms are observed depending on the wire width.     

Introducing Differential Calculus

In this paper we discuss three ways of introducing calculus all based on concepts which students would either already know or which can be introduced without much difficulty at this stage of their mathematical training. The aim of this paper is to persuade teachers of mathematics that topics in ‘higher mathematics’, specifically calculus, can and should be presented to students in terms of concepts with which they are familiar.     

The kinetic effects of decreasing catalytic activity on a simple rate expression

When kinetics are studied for a catalyzed reaction, the active catalyst surface available affects the results. This article illustrates the effect of a progressively decreasing available surface on the heterogeneous kinetics of a gas‐phase reaction in a closed system. The present contribution focuses on the effect of simple mth order surface deactivation on a simple nth order kinetic expression. The basic analysis and general results are unchanged if more complex equations are used. It is shown that there are certain common anomalous characteristics of kinetic expressions involving deactivation. In particular, the apparent rate constant and the apparent order are usually dependent on both the actual and initial pressures of the reactant, and the reaction may not go to completion. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 7–16, 2000     

Controlled Synthesis,Characterization, and Flow Properties of Ethylene–Diene Copolymers

The flow response of branched entangled resins is dominated by the branching topology of the constituent molecules, a property that is not directly accessible using experimental analytical tools for industrially relevant complex resins. In this paper, the controlled terpolymerization of ethylene, 1,9‐decadiene, and either hexene or octene in a continuous stirred tank reactor with a metallocene catalyst, is reported. The synthesized samples are characterized extensively with various analytical tools and their rheological properties are measured with small amplitude oscillatory shear and start‐up uniaxial extension experiments. A model is developed for the polymerization process with the mass balance during synthesis providing strong constraints on the rate constants. In silico ensembles of molecules, generated via Monte Carlo sampling, are used to reproduce the experimental results. The computer model allows us to infer the detailed branching structure of the molecules and to predict the optimum range of reactor conditions for this synthesis.     

Resonant shattering of neutron star crusts

The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (SGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ～10{46}-10{47} erg of energy seconds before the merger of a NS-NS or NS-black-hole binary. Such properties are consistent with Swift/BAT detections of SGRB precursors, and we use the timing of the observed precursors to place weak constraints on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state.