80,108 research outputs found
Instrumentation for Millimeter-wave Magnetoelectrodynamic Investigations of Low-Dimensional Conductors and Superconductors
We describe instrumentation for conducting high sensitivity millimeter-wave
cavity perturbation measurements over a broad frequency range (40-200 GHz) and
in the presence of strong magnetic fields (up to 33 tesla). A Millimeter-wave
Vector Network Analyzer (MVNA) acts as a continuously tunable microwave source
and phase sensitive detector (8-350 GHz), enabling simultaneous measurements of
the complex cavity parameters (resonance frequency and Q-value) at a rapid
repetition rate (approx. 10 kHz). We discuss the principal of operation of the
MVNA and the construction of a probe for coupling the MVNA to various
cylindrical resonator configurations which can easily be inserted into a high
field magnet cryostat. We also present several experimental results which
demonstrate the potential of the instrument for studies of low-dimensional
conducting systems.Comment: 20 pages including fig
Managing healthcare workflows in a multi-agent system environment
Whilst Multi-Agent System (MAS) architectures appear to offer a more flexible model for designers and developers of complex, collaborative information systems, implementing real-world business processes that can be delegated to autonomous agents is still a relatively difficult task. Although a range of agent tools and toolkits exist, there still
remains the need to move the creation of models nearer to code generation, in order that the development path be more rigorous and repeatable. In particular, it is essential that complex organisational
process workflows are captured and expressed in a way that MAS can successfully interpret. Using a complex social care system as an exemplar, we describe a technique whereby a business process is
captured, expressed, verified and specified in a suitable format for a healthcare MAS.</p
On Superalgebras of Matrices with Symmetry Properties
It is known that semi-magic square matrices form a 2-graded algebra or
superalgebra with the even and odd subspaces under centre-point reflection
symmetry as the two components. We show that other symmetries which have been
studied for square matrices give rise to similar superalgebra structures,
pointing to novel symmetry types in their complementary parts. In particular,
this provides a unifying framework for the composite `most perfect square'
symmetry and the related class of `reversible squares'; moreover, the
semi-magic square algebra is identified as part of a 2-gradation of the general
square matrix algebra. We derive explicit representation formulae for matrices
of all symmetry types considered, which can be used to construct all such
matrices.Comment: 25 page
Resonant Tunneling in Truly Axial Symmetry Mn12 Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling
Magnetization measurements of a truly axial symmetry Mn12-tBuAc molecular
nanomagnet with a spin ground state of S = 10 show resonance tunneling. This
compound has the same magnetic anisotropy as Mn12-Ac but the molecules are
better isolated and the crystals have less disorder and a higher symmetry.
Hysteresis loop measurements at several temperatures reveal a well-resolved
step fine-structure which is due to level crossings of excited states. All step
positions can be modeled by a simple spin Hamiltonian. The crossover between
thermally assisted and pure quantum tunneling can be investigated with
unprecedented detail.Comment: 5 pages, 6 figure
Dynamics of axial separation in long rotating drums
We propose a continuum description for the axial separation of granular
materials in a long rotating drum. The model, operating with two local
variables, concentration difference and the dynamic angle of repose, describes
both initial transient traveling wave dynamics and long-term segregation of the
binary mixture. Segregation proceeds through ultra-slow logarithmic coarsening.Comment: 4 pages, 3 Postscript figures; submitted to PR
Electrodynamics of quasi-two-dimensional BEDT-TTF charge transfer salts
We consider the millimeter-wave electrodynamics specific to
quasi-two-dimensional conductors and superconductors based on the organic donor
molecule BEDT-TTF. Using realistic physical parameters, we examine the current
polarizations that result for different oscillating (GHz) electric and magnetic
field polarizations. We show that, in general, it is possible to discriminate
between effects (dissipation and dispersion) due to in-plane and interlayer ac
currents. However, we also show that it is not possible to selectively probe
any single component of the in-plane conductivity tensor, and that excitation
of interlayer currents is strongly influenced by the sample geometry and the
electromagnetic field polarization.Comment: 5 pages including 3 figures Minor correction to figure
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