258 research outputs found
Knowledge, management and intelligent decision support for protection scheme design and application in electrical power systems
The paper describes a research project carried out inconjunction with two major UK utilities, focusing on the introduction of knowledge management and intelligent decision support to the existing protection design and application processes operated within both companies. A brief overview is provided of the generic design process, and the development of the web-based Design Engineering Knowledge Application System (DEKAS). This system incorporates intelligent case based reasoning (CBR) functionality to address the knowledge management and decision support requirements of each company's design process. The perceived key benefits of DEKAS relating to the management and utilisation of the data, information and knowledge throughout the protection design process is also discussed
Hole Pockets in the Doped 2D Hubbard Model
The electronic momentum distribution of the two
dimensional Hubbard model is studied for different values of the coupling , electronic density , and temperature, using
quantum Monte Carlo techniques. A detailed analysis of the data on
clusters shows that features consistent with hole pockets at momenta appear as the system is doped away
from half-filling. Our results are consistent with recent experimental data for
the cuprates discussed by Aebi et al. (Phys. Rev. Lett. {\bf 72}, 2757 (1994)).
In the range of couplings studied, the depth of the pockets is maximum at , and it increases with decreasing temperature.
The apparent absence of hole pockets in previous numerical studies of this
model is explained.Comment: 11 pages, 4 postscript figures appended, RevTeX (version 3.0
Influence of next-nearest-neighbor electron hopping on the static and dynamical properties of the 2D Hubbard model
Comparing experimental data for high temperature cuprate superconductors with
numerical results for electronic models, it is becoming apparent that a hopping
along the plaquette diagonals has to be included to obtain a quantitative
agreement. According to recent estimations the value of the diagonal hopping
appears to be material dependent. However, the values for discussed
in the literature were obtained comparing theoretical results in the weak
coupling limit with experimental photoemission data and band structure
calculations. The goal of this paper is to study how gets renormalized as
the interaction between electrons, , increases. For this purpose, the effect
of adding a bare diagonal hopping to the fully interacting two dimensional
Hubbard model Hamiltonian is investigated using numerical techniques. Positive
and negative values of are analyzed. Spin-spin correlations, ,
vs , and local magnetic moments are studied for values
of ranging from 0 to 6, and as a function of the electronic density. The
influence of the diagonal hopping in the spectral function
is also discussed, and the changes in the gap present in the density of states
at half-filling are studied. We introduce a new criterion to determine probable
locations of Fermi surfaces at zero temperature from data obtained
at finite temperature. It appears that hole pockets at
may be induced for negative while a positive produces similar
features at and . Comparisons with the standard 2D
Hubbard () model indicate that a negative hopping amplitude appears
to be dynamically generated. In general, we conclude that it is very dangerous
to extract a bare parameter of the Hamiltonian from PES data whereComment: 9 pages (RevTex 3.0), 12 figures (postscript), files packed with
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Integrating constructive feedback in personalised e-learning
When using e-learning material some students progress readily, others have difficulties. In a traditional classroom the teacher would identify those with difficulties and direct them to additional resources. This support is not easily available within e-learning. A new approach to providing constructive feedback is developed that will enable an e-learning system to identify areas of weakness and provide guidance on further study. The approach is based on the tagging of learning material with appropriate keywords that indicate the contents. Thus if a student performs poorly on an assessment on topic X, there is a need to suggest further study of X and participation in activities related to X such as forums. As well as supporting the learner this type of constructive feedback can also inform other stakeholders. For example a tutor can monitor the progress of a cohort; an instructional designer can monitor the quality of learning objects in facilitating the appropriate knowledge across many learners
Astrophysical Axion Bounds
Axion emission by hot and dense plasmas is a new energy-loss channel for
stars. Observational consequences include a modification of the solar
sound-speed profile, an increase of the solar neutrino flux, a reduction of the
helium-burning lifetime of globular-cluster stars, accelerated white-dwarf
cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We
review and update these arguments and summarize the resulting axion
constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3
figure
Eureka and beyond: mining's impact on African urbanisation
This collection brings separate literatures on mining and urbanisation together at a time when both artisanal and large-scale mining are expanding in many African economies. While much has been written about contestation over land and mineral rights, the impact of mining on settlement, notably its catalytic and fluctuating effects on migration and urban growth, has been largely ignored. African nation-statesâ urbanisation trends have shown considerable variation over the past half century. The current surge in ânewâ mining countries and the slow-down in âoldâ mining countries are generating some remarkable settlement patterns and welfare outcomes. Presently, the African continent is a laboratory of national mining experiences. This special issue on African mining and urbanisation encompasses a wide cross-section of country case studies: beginning with the historical experiences of mining in Southern Africa (South Africa, Zambia, Zimbabwe), followed by more recent mineralizing trends in comparatively new mineral-producing countries (Tanzania) and an established West African gold producer (Ghana), before turning to the influence of conflict minerals (Angola, the Democratic Republic of Congo and Sierra Leone)
Low temperature electronic properties of Sr_2RuO_4 II: Superconductivity
The body centered tetragonal structure of Sr_2RuO_4 gives rise to umklapp
scattering enhanced inter-plane pair correlations in the d_{yz} and d_{zx}
orbitals. Based on symmetry arguments, Hund's rule coupling, and a bosonized
description of the in-plane electron correlations the superconducting order
parameter is found to be a orbital-singlet spin-triplet with two spatial
components. The spatial anisotropy is 7%. The different components of the order
parameter give rise to two-dimensional gapless fluctuations. The phase
transition is of third order. The temperature dependence of the pair density,
specific heat, NQR, Knight shift, and susceptibility are in agreement with
experimental results.Comment: 20 pages REVTEX, 3 figure
Fermi acceleration in astrophysical jets
We consider the acceleration of energetic particles by Fermi processes (i.e.,
diffusive shock acceleration, second order Fermi acceleration, and gradual
shear acceleration) in relativistic astrophysical jets, with particular
attention given to recent progress in the field of viscous shear acceleration.
We analyze the associated acceleration timescales and the resulting particle
distributions, and discuss the relevance of these processes for the
acceleration of charged particles in the jets of AGNs, GRBs and microquasars,
showing that multi-component powerlaw-type particle distributions are likely to
occur.Comment: 6 pages, one figure; based on talk at "The multimessenger approach to
unidentified gamma-ray sources", Barcelona/Spain, July 2006; accepted for
publication in Astrophysics and Space Scienc
Higher-Order Assembly of BRCC36-KIAA0157 Is Required for DUB Activity and Biological Function
BRCC36 is a ZnÂČâș-dependent deubiquitinating enzyme (DUB) that hydrolyzes lysine-63-linked ubiquitin chains as part of distinct macromolecular complexes that participate in either interferon signaling or DNA-damage recognition. The MPNâș domain protein BRCC36 associates with pseudo DUB MPNâ» proteins KIAA0157 or Abraxas, which are essential for BRCC36 enzymatic activity. To understand the basis for BRCC36 regulation, we have solved the structure of an active BRCC36-KIAA0157 heterodimer and an inactive BRCC36 homodimer. Structural and functional characterizations show how BRCC36 is switched to an active conformation by contacts with KIAA0157. Higher-order association of BRCC36 and KIAA0157 into a dimer of heterodimers (super dimers) was required for DUB activity and interaction with targeting proteins SHMT2 and RAP80. These data provide an explanation of how an inactive pseudo DUB allosterically activates a cognate DUB partner and implicates super dimerization as a new regulatory mechanism underlying BRCC36 DUB activity, subcellular localization, and biological function
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
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