Magnetocrystalline anisotropy of nickel

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Overlap Fermions on a 20420^4 Lattice

We report results on hadron masses, fitting of the quenched chiral log, and quark masses from Neuberger's overlap fermion on a quenched $20^4$ lattice with lattice spacing $a = 0.15$ fm. We used the improved gauge action which is shown to lower the density of small eigenvalues for $H^2$ as compared to the Wilson gauge action. This makes the calculation feasible on 64 nodes of CRAY-T3E. Also presented is the pion mass on a small volume ($6^3 \times 12$ with a Wilson gauge action at $\beta = 5.7$). We find that for configurations that the topological charge $Q \ne 0$, the pion mass tends to a constant and for configurations with trivial topology, it approaches zero possibly linearly with the quark mass.Comment: Lattice 2000 (Chiral Fermion), 4 pages, 4 figure

Control of Load and Profile in the Machine-Cutting of D-Shaped Tunnels: An Initial Investigation

Previous reports in this service (Research Reports 220 and 237) have been concerned only with the load-control of tunnelling machines producing tunnels of near-circular cross sectional profile. The investigations there reported were aimed primarily at improving the load control on such a machine currently operating at the N.C.B's Cadley Hill Colliery

Modelling of Coal and Mineral Extraction Processes

Mining involves the following fundamental operations: (a) The actual winning of the coal, stone or mineral ore from the underground seam of vein in which it naturally occurs, (b) The clearance of the material from several such sources in any one mine to some central point for the final operation, (c) The preparation of the extracted raw material for sale, involving perhaps washing, crushing and grading or blending according to lump size or composition.......

Case Studies in Computer Control

This document brings together under one cover details relating to the computer control of three vert different processes, these being (i) Longwall coal cutting (ii)Electric vehicle testing (iii) A pilot distillation column These applications all pose very interesting problems of process modelling and control systems design and provide a good test of modern control theory. It is chiefly for these reasons that the processes have formed the core of the author's research work over several years

The Wider Application of Multi-pass Systems Theory Part 1. Multi-Machine and Multi-Cell Systems

A general time-(distance-) domain representation of unidirectional multi-pass processes is presented which describes all previously identified examples 1. It is then shown that systems of multiple machines in which the signal flow is unidirectional can be simulated by the repeated simulation of a single machine and that such a procedure is described by the same general time-domain formulation. The stability of this multi-pass simulation sequence and hence, that of the multi-machine system, can therefore be investigated analytically using the frequency-response approach previously applied 1 to real-life-multi-pass processes. It is demonstrated how the approach can be applied also to discretised spatially-distributed processes, provided again that signal flow is unidirectional. The modelling and analysis techniques presented in this first paper are shown to be unsuitable, however, in the presence of either counterflow signals or feedback controllers which are not of a local nature and uniformly distributed along the process. The identification of these limitations is an important objective and provides the motivation and starting point for a companion paper in which the multi-pass systems approach is adapted to cope with this much wider class of processes

The Dynamic Behaviour of Packed and Tray-Type Binary Distillation Columns Described by Lumped-Parameter Models

Parametric transfer-function matrix (T.F.M) models are derived from the differential equations describing the variation of liquid and vapour compositions within symmetrical distillation columns separating binary mixtures. Both packed and tray-type columns are considered, the models developed having minimal order 6 and 4 respectively, (implying perfectly-stirred mixtures and minimum number of trays in each column section) so removing the complications introduced by spatial variations encountered in earlier studies 1,2 of longer columns. The T.F.M's obtained are are again shown to diagonal with the same choice of input and output vectors as were employed in the "long" column studies. Furthermore, the fundamental behavioural differences between packed and tray-type columns are again revealed using these low- order physical models as were demonstrated in the previous studies. In particular, the sign of the static gain of packed-columns, responding to total flow changes is again shown to be parameter-sensitive and the sign of the total-flow gain at high-frequency is shown to be the reverse of that for tray-type columns, so again causing nonminimum-phase behaviour in packed-columns in some circumstances. Because of their behavioural and parametric similarities, it is proposed that the minimal-order models developed in this report be used as a future basis for control system design studies for spatially-distributed and multi-tray columns in situations where travelling-wave phenomena are unimportant

Towards the Continuum Limit of the Overlap Quark Propagator in Landau Gauge

The properties of the momentum space quark propagator in Landau gauge are examined for the overlap quark action in quenched lattice QCD. Numerical calculations were done on two lattices with different lattice spacing $a$ and similar physical volumes to explore the quark propagator in the continuum limit. We have calculated the nonperturbative wavefunction renormalization function $Z(p)$ and the nonperturbative mass function $M(p)$ for a variety of bare quark masses and perform a simple linear extrapolation to the chiral limit. We find the behaviour of $Z(p)$ and $M(p)$ in the chiral limit are in good agreement between the two lattices.Comment: 3 pages, 2 figures, talk, Lattice2002(Chiral Fermion

Load Control of a 300 h.p. Tunnelling Machine: The Addition of Integral Control Action to Prevent Manually Created Overloads

Whereas a proportional-plus-derivative controller (designed in Research Reports 220 and 230)for the Cadley Hill tunnelling machine was shown to produce only small load errors in response to changes in rock hardness, errors resulting from excessive manual rate settings were not investigated. It is here proposed that effective integral action can be incorporated to eliminate such errors, which can be excessive because of the very wide range of rate settings available to the driver. Implementations using a d.c. blocking circuit in the rate feedback channel of ther N.C.B. controller are tested connected to the analogue simulator of the tunnelling machine and shown to be successful. Redesign of the existing printed circuits will, however, be necessary to achieve an overriding controller that is completely error free

Electrodynamic Simulation of Inertia Load

Dynamic response in most electromechanical motion control systems is dominated by the rate terms. The need to simulate load often arises in testing such systems or algorithms. This report addresses the issue of stability in dynamic inertia load simulation using coupled machines. A criterion limiting the simulated inertia is derived. No suitable scheme has however been identified to avoid violation of this stability criterion in trying to simulate arbitrarily large inertia load apart from recourse to DSP