42,031 research outputs found
On finite complete rewriting systems and large subsemigroups
Let be a semigroup and be a subsemigroup of finite index in (that
is, the set is finite). The subsemigroup is also called a
large subsemigroup of . It is well known that if has a finite complete
rewriting system then so does . In this paper, we will prove the converse,
that is, if has a finite complete rewriting system then so does . Our
proof is purely combinatorial and also constructive.Comment: We have made major changes to the paper and simplified most of the
proof
Non-Langevin behaviour of the uncompensated magnetisation in nanoparticles of artificial ferritin
The magnetic behaviour of nanoparticles of antiferromagnetic ferritin has
been investigated by 57Fe Mossbauer absorption spectroscopy and magnetisation
measurements, in the temperature range 2.5K-250K and with magnetic fields up to
7T. Samples containing nanoparticles with an average number of Fe atoms ranging
from 400 to 2500 were studied. The value of the anisotropy energy per unit
volume was determined and found to be in the range 3-6 10**5 ergs/cm3, which is
a value typical for ferric oxides. By comparing the results of the two
experimental methods at large field, we show that, contratry to what is
currently assumed, the uncompensated magnetisation of the feritin cores in the
superparamagnetic regime does not follow a Langevin law. For magnetic fields
below the spin-flop field, we propose an approximate law for the field and
temperature variation of the uncompensated magnetisation which has so far never
been applied in antiferromagnetic systems. This approach should more generally
hold for randomly oriented antiferro- magnetic nanoparticles systems with weak
uncompensated moments.Comment: 11 pages, 11 figure
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A unified model of the electrical power network
Traditionally, the different infrastructure layers, technologies and management activities associated with the design, control and protection operation of the Electrical Power Systems have been supported by numerous independent models of the real world network. As a result of increasing competition in this sector, however, the integration of technologies in the network and the coordination of complex management processes have become of vital importance for all electrical power companies.
The aim of the research outlined in this paper is to develop a single network model which will unify the generation, transmission and distribution infrastructure layers and the various alternative implementation technologies. This 'unified model' approach can support ,for example, network fault, reliability and performance analysis. This paper introduces the basic network structures, describes an object-oriented modelling approach and outlines possible applications of the unified model
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Update of an early warning fault detection method using artificial intelligence techniques
This presentation describes a research investigation to access the feasibility of using an Artificial Intelligence (AI) method to predict and detect faults at an early stage in power systems. An AI based detector has been developed to monitor and predict faults at an early stage on particular sections of power systems. The detector for this early warning fault detection device only requires external measurements taken from the input and output nodes of the power system. The AI detection system is capable of rapidly predicting a malfunction within the system. Artificial Neural Networks (ANNs) are being used as the core of the fault detector. In an earlier paper [11], a computer simulated medium length transmission line has been tested by the detector and the results clearly demonstrate the capability of the detector. Today’s presentation considers a case study illustrating the suitability of this AI Technique when applied to a distribution transformer. Furthermore, an evolutionary optimisation strategy to train ANNs is also briefly discussed in this presentation, together with a ‘crystal ball’ view of future developments in the operation and monitoring of transmission systems in the next millennium
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Power system fault prediction using artificial neural networks
The medium term goal of the research reported in this paper was the development of a major in-house suite of strategic computer aided network simulation and decision support tools to improve the management of power systems. This paper describes a preliminary research investigation to access the feasibility of using an Artificial Intelligence (AI) method to predict and detect faults at an early stage in power systems. To achieve this goal, an AI based detector has been developed to monitor and predict faults at an early stage on particular sections of power systems. The detector only requires external measurements taken from the input and output nodes of the power system. The AI detection system is capable of rapidly predicting a malfunction within the system . Simulation will normally take place using equivalent circuit representation. Artificial Neural Networks (ANNs) are used to construct a hierarchical feed-forward structure which is the most important component in the fault detector. Simulation of a transmission line (2-port circuit ) has already been carried out and preliminary results using this system are promising. This approach provided satisfactory results with accuracy of 95% or higher
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Early warning fault detection using artificial intelligent methods
This paper describes a research investigation to access the feasibility of using an Artificial Intelligence (AI) method to predict and detect faults at an early stage in power systems. An AI based detector has been developed to monitor and predict faults at an early stage on particular sections of power systems. The detector for this early warning fault detection device only requires external measurements taken from the input and output nodes of the power system. The AI detection system is capable of rapidly predicting a malfunction within the system. Artificial Neural Networks (ANNs) are being used as the core of the fault detector. A simulated medium length transmission line has been tested by the detector and the results demonstrate the capability of the detector. Furthermore, comments on an evolutionary technique as the optimisation strategy for ANNs are included in this paper
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Today's problems with the evaluation methods of full lightning impulse parameters as described in IEC 60060-1
In this paper the present problems with the evaluation methods for lightning impulse parameters, as defined in IEC 60060-1, are described. Also the current practice of evaluation in many laboratories world-wide, that is obtained by a questionnaire, is presented. Some of the work performed up the present time and the initial conclusions are reported, then some recommendations are made for future work
Dynamics of Neural Networks with Continuous Attractors
We investigate the dynamics of continuous attractor neural networks (CANNs).
Due to the translational invariance of their neuronal interactions, CANNs can
hold a continuous family of stationary states. We systematically explore how
their neutral stability facilitates the tracking performance of a CANN, which
is believed to have wide applications in brain functions. We develop a
perturbative approach that utilizes the dominant movement of the network
stationary states in the state space. We quantify the distortions of the bump
shape during tracking, and study their effects on the tracking performance.
Results are obtained on the maximum speed for a moving stimulus to be
trackable, and the reaction time to catch up an abrupt change in stimulus.Comment: 6 pages, 7 figures with 4 caption
Pion Interferometry for Hydrodynamical Expanding Source with a Finite Baryon Density
We calculate the two-pion correlation function for an expanding hadron source
with a finite baryon density. The space-time evolution of the source is
described by relativistic hydrodynamics and the Hanbury-Brown-Twiss (HBT)
radius is extracted after effects of collective expansion and multiple
scattering on the HBT interferometry have been taken into account, using
quantum probability amplitudes in a path-integral formalism. We find that this
radius is substantially smaller than the HBT radius extracted from the
freeze-out configuration.Comment: 4 pages, 2 figure
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