100 research outputs found
Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers
We have investigated the electrical transport through strained
p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement
shift for diodes with different well width, the shift due to a central
potential spike in a well, and magnetotunnelling spectroscopy demonstrate that
the first two resonances are due to tunnelling through heavy hole levels,
whereas there is no sign of tunnelling through the first light hole state. This
demonstrates for the first time the conservation of the total angular momentum
in valence band resonant tunnelling. It is also shown that conduction through
light hole states is possible in many structures due to tunnelling of carriers
from bulk emitter states.Comment: 4 pages, 4 figure
Gapped and gapless short range ordered magnetic states with wavevectors in the pyrochlore magnet TbTiO
Recent low temperature heat capacity (C) measurements on polycrystalline
samples of the pyrochlore antiferromagnet TbTiO
have shown a strong sensitivity to the precise Tb concentration , with a
large anomaly exhibited for at K and no such
anomaly and corresponding phase transition for . We have grown single
crystal samples of TbTiO, with approximate
composition , and , where the single
crystal exhibits a large C anomaly at =0.45 K, but neither the
nor the single crystals display any such anomaly. We
present new time-of-flight neutron scattering measurements on the
and the samples which show strong
quasi-Bragg peaks at low
temperatures characteristic of short range antiferromagnetic spin ice (AFSI)
order at zero magnetic field but only under field-cooled conditions, as was
previously observed in our single crystal. These results show that
the strong quasi-Bragg peaks
and gapped AFSI state at low temperatures under field cooled conditions are
robust features of TbTiO, and are not correlated with the presence
or absence of the C anomaly and phase transition at low temperatures.
Further, these results show that the ordered state giving rise to the C
anomaly is confined to for
TbTiO, and is not obviously connected with
conventional order of magnetic dipole degrees of freedom.Comment: 7 pages, 3 figure
From Spin Glass to Quantum Spin Liquid Ground States in Molybdate Pyrochlores
We present new magnetic heat capacity and neutron scattering results for two
magnetically frustrated molybdate pyrochlores: oxide LuMoO
and oxynitride LuMoON. LuMoO
undergoes a transition to an unconventional spin glass ground state at K. However, the preparation of the corresponding oxynitride tunes
the nature of the ground state from spin glass to quantum spin liquid. The
comparison of the static and dynamic spin correlations within the oxide and
oxynitride phases presented here reveals the crucial role played by quantum
fluctuations in the selection of a ground state. Furthermore, we estimate an
upper limit for a gap in the spin excitation spectrum of the quantum spin
liquid state of the oxynitride of meV or
, in units of its antiferromagnetic Weiss
constant K.Comment: 8 pages, 9 figure
Extending enterprise architecture modeling languages: application to telecommunications service creation
Enterprise Engineering offers a global view on multiple concerns such as processes, stakeholders, supporting technology. This global view is sustained by Enterprise Architecture frameworks, languages, tools and standards. The current effort has been focused on general purpose Enterprise Architecture frameworks, modeling languages and tools, which allow describing a wide range of domains. While they are expressive enough at the business layer, at the technical layer, where more detail is needed to describe a domain specific system, such general purpose Enterprise Architecture Modeling Languages sometime lack the semantic strength required. The concepts present in the language are too abstract, they need refinement and specification. To provide the necessary specific semantic strength, this paper proposes an approach to extend Enterprise Architecture Modeling Languages with domain specificity. The proposed approach is a model-driven one, allowing a high degree of automation in the building of tools for the language extension. To better show its benefits, the approach is applied on the domain of Telecommunications, for defining an Enterprise Architecture Modeling Language extension for service creation. The so defined language and its associated tools are illustrated on an IP Multimedia Subsystem conferencing service example.Vanea Chiprianov, Yvon Kermarrec, Siegfried Rouvrai
Les orientations de valeur des enseignants d'éducation physique et sportive. Influence du sexe, de l'âge et de l'ancienneté
L'objet de cette étude est d'examiner l'influence du genre, de l'âge et de l'ancienneté sur les orientations de valeur d'enseignants d'éducation physique. Les orientations de valeur représentent un système de croyances qui guide les enseignants dans leurs choix de contenus. La version révisée de l'inventaire des orientations de valeur (VOI) a été utilisée pour recueillir les données de 157 enseignants travaillant dans différentes régions de France. Les scores totaux sur chacune des orientations de valeur ont été calculés et utilisés pour diviser les enseignants en deux groupes représentant des catégories de priorités forte et faible. Le test khi-deux a été utilisé pour examiner les données de genre, d'âge et d'ancienneté. Les résultats indiquent que 83 % des enseignants prennent des décisions sur les contenus à enseigner à travers au moins une orientation de valeurs. Il n'y a pas de différences significatives sur le genre, l'âge et, pour quatre orientations de valeur, sur l'ancienneté. Les priorités des enseignants pour le processus d'apprentissage évoluent au cours de leur carrière
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