1,412 research outputs found
Numerical study of axisymmetric vortex breakdowns
Axisymmetric flow of rotating stream analyzed to determine conditions allowing isolated vortex breakdown to develo
Polarization, directional distribution, and off-specular peak phenomena in light reflected from roughened surfaces
Surface roughness and incident angle effect on angular distribution, polarization, and specular peak of reflected thermal radiatio
Formality and informality in the summative assessment of motor vehicle apprentices: a case study
This article explores the interaction of formal and informal attributes of competence‐based assessment. Specifically, it presents evidence from a small qualitative case study of summative assessment practices for competence‐based qualifications within apprenticeships in the motor industry in England. The data are analysed through applying an adaptation of a framework for exploring the interplay of formality and informality in learning. This analysis reveals informal mentoring as a significant element which influences not only the process of assessment, but also its outcomes. We offer different possible interpretations of the data and their analysis, and conclude that, whichever interpretation is adopted, there appears to be a need for greater capacity‐building for assessors at a local level. This could acknowledge a more holistic role for assessors; recognise the importance of assessors’ informal practices in the formal retention and achievement of apprentices; and enhance awareness of inequalities that may be reinforced by both informal and formal attributes of assessment practices
Análise da estrutura fatorial dos Testes de Torrance em estudantes portugueses
In order to verify the factorial structures of the Torrance verbal and figural tests, two activities of each instrument were applied with 193 students from the 10th and 12th years of education in Portugal. We tried to demonstrate that the collinearity of the fluency and flexibility variables could create methodological artifacts that hinder the understanding of the internal structure underlying the test. The principal component analysis without control of collinearity indicated a solution composed of four basic factors that separeted activities. Controlling for collinearity, we found a new solution, which also contained four factors that, unlike the previous result, grouped variables with similar processes but of different activities. The verbal and figural content is also an important element in the factor structure. This new arrangement makes more sense with the theory that underlies the instruments separating the different processes and content which are being measured by the activities.Com a finalidade de verificar a estrutura fatorial dos testes de Torrance, duas atividades verbais e duas figurais foram aplicadas em 193
estudantes do 10º e 12º ano do ensino secundário de Portugal. Tentou-se demonstrar que a colinearidade das variáveis fluência e flexibilidade
podem criar artefatos metodológicos que dificultam o entendimento da estrutura interna subjacente ao teste. A análise fatorial dos
componentes principais, sem controle da colinearidade, indicou uma solução composta por quatro fatores que separam basicamente as
atividades. Controlando-se a colinearidade, encontrou-se uma nova solução, também composta por quatro fatores, que, diferentemente
da anterior, organizou variáveis com processos semelhantes, mas de diferentes atividades. O tipo de conteúdo, verbal e figural, mostrou-se
ainda um importante elemento na organização dos fatores. Esse novo arranjo fez mais sentido diante da teoria que embasa os instrumentos,
ao separar os diferentes processos e conteúdos por eles avaliados
Association between gene expression biomarkers of immunosuppression and blood transfusion in severely injured polytrauma patients.
From band insulator to Mott insulator in one dimension
We derive the phase diagram for the one-dimensional model of a ferroelectric
perovskite recently introduced by Egami, Ishihara and Tachiki [Science, {\bf
261}, 1307 (1993)]. We show that the interplay between covalency, ionicity and
strong correlations results in a spontaneously dimerized phase which separates
the weak-coupling band insulator from the strong-coupling Mott insulator. The
transition from the band insulator to the dimerized phase is identified as an
Ising critical point. The charge gap vanishes at this single point with the
optical conductivity diverging as . The spin
excitations are gapless above the second transition to the Mott insulator
phase.Comment: 4 pages LaTex (RevTex) and 1 postscript figure included by eps
Susceptibility of the one-dimensional, dimerized Hubbard model
We show that the zero temperature susceptibility of the one-dimensional,
dimerized Hubbard model at quarter-filling can be accurately determined on the
basis of exact diagonalization of small clusters. The best procedure is to
perform a finite-size scaling of the spin velocity , and to calculate
the susceptibility from the Luttinger liquid relation . We
show that these results are reliable by comparing them with the analytical
results that can be obtained in the weak and strong coupling limits. We have
also used quantum Monte Carlo simulations to calculate the temperature
dependence of the susceptibility for parameters that should be relevant to the
Bechgaard salts. This shows that, used together, these numerical techniques are
able to give precise estimates of the low temperature susceptibility of
realistic one-dimensional models of correlated electrons.Comment: 10 pages, latex, figures available from the authors. To appear in
Phys. Rev. B, Rapid Comm
Effects of Lattice and Molecular Phonons on Photoinduced Neutral-to-Ionic Transition Dynamics in Tetrathiafulvalene--Chloranil
For electronic states and photoinduced charge dynamics near the neutral-ionic
transition in the mixed-stack charge-transfer complex
tetrathiafulvalene--chloranil (TTF-CA), we review the effects of Peierls
coupling to lattice phonons modulating transfer integrals and Holstein
couplings to molecular vibrations modulating site energies. The former
stabilizes the ionic phase and reduces discontinuities in the phase transition,
while the latter stabilizes the neutral phase and enhances the discontinuities.
To reproduce the experimentally observed ionicity, optical conductivity and
photoinduced charge dynamics, both couplings are quantitatively important. In
particular, strong Holstein couplings to form the highly-stabilized neutral
phase are necessary for the ionic phase to be a Mott insulator with large
ionicity. A comparison with the observed photoinduced charge dynamics indicates
the presence of strings of lattice dimerization in the neutral phase above the
transition temperature.Comment: 9 pages, 7 figures, accepted for publication in J. Phys. Soc. Jp
Coulomb parameters and photoemission for the molecular metal TTF-TCNQ
We employ density-functional theory to calculate realistic parameters for an
extended Hubbard model of the molecular metal TTF-TCNQ. Considering both intra-
and intermolecular screening in the crystal, we find significant longer-range
Coulomb interactions along the molecular stacks, as well as inter-stack
coupling. We show that the long-range Coulomb term of the extended Hubbard
model leads to a broadening of the spectral density, likely resolving the
problems with the interpretation of photoemission experiments using a simple
Hubbard model only.Comment: 4 pages, 2 figure
Phase diagram of the Hubbard chain with two atoms per cell
We obtain the quantum phase diagram of the Hubbard chain with alternating
on-site energy at half filling. The model is relevant for the ferroelectric
perovskites and organic mixed-stack donor-acceptor crystals. For any values of
the parameters, the band insulator is separated from the Mott insulator by a
dimer phase. The boundaries are determined accurately by crossing of excited
levels with particular discrete symmetries. We show that these crossings
coincide with jumps of charge and spin Berry phases with a clear geometrical
meaning.Comment: 5 pages including 2 figures To be published in Phys. Rev. B (Rapid
Communications
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