Individual and Collective Responsiveness to Climate Change: A Response to Dwyer

Commentaire / Commentary

De l'expérience collective à la découverte des cycles

C'est en avril 1980 que Jacques Lessard rassemble autour de lui quelques diplômés du Conservatoire d'art dramatique de Québec et jette les bases de ce qui allait devenir l'une des plus remarquables entreprises théâtrales du Québec des années 80. Le Théâtre Repère, tout comme le groupe Carbone 14, le Nouveau Théâtre expérimental, la troupe Omnibus, le Théâtre expérimental des femmes et le groupe La Veillée, s'inscrit dans ce que, faute d'appellation officielle, on pourrait qualifier de courant postmoderne. [...]

Intelligence collective et démocratie en Politique, III, 11

À l’heure où les limites du modèle de la démocratie représentative traditionnelle apparaissent de plus en plus évidentes, on a pu défendre, dans la littérature récente, un modèle sensiblement différent : celui d’une démocratie épistémique, tirant parti, par le mécanisme de la délibération inclusive, d’une forme d’intelligence collective qui serait disséminée à travers les agents d’une collectivité. Or, les partisans d’une telle approche se réclament souvent d’un argument qu’on trouve sous la plume d’Aristote en Politique, III, 11. L’objectif de cette étude est d’examiner la légitimité d’une telle filiation, en examinant de manière comparative les arguments modernes en faveur de la démocratie épistémique délibérative et le texte aristotélicien. Un tel travail permet de nuancer la portée du recours à Aristote dans les justifications épistémiques de la démocratie : d’une part, le mécanisme auquel songe Aristote dans le texte de la Politique ne saurait se ramener à une forme quelconque de délibération inclusive ; et, d’autre part, l’argument épistémique se trouve restreint par la mise en évidence des limites intrinsèques du régime démocratique. Plutôt que la source d’une position moderne en faveur de la démocratie, on trouverait alors chez Aristote l’occasion de penser le danger concret qui guette tout modèle délibératif : c’est-à-dire, la confiscation du débat public par une minorité de démagogues, qui empêche la collectivité de tirer parti de la diversité cognitive qu’elle contient.

Les peuples en tant qu’agents : l'agentivité collective de List et Pettit appliquée aux nations

Dans ce texte, je propose d’adapter la théorie de l’agentivité collective de List et Pettit de manière à considérer les nations comme des agents. Cet exercice pourrait ainsi conférer un argument supplémentaire aux théories des droits collectifs s’intéressant aux groupes nationaux puisque ces derniers pourront véritablement être reconnus comme des sujets de droits, capables d’autodétermination et de revendications morales. La théorie des droits collectifs de Seymour sera utilisée comme modèle à cet égard. Bien que le libéralisme politique dans lequel s’inscrit Seymour refuse de se prononcer sur des problèmes métaphysiques, il est intéressant d’ouvrir la possibilité conceptuelle que des groupes nationaux soient des agents à part entière. Pour ce faire, il faudra déterminer comment un agent national peut prendre des décisions et comment il peut subir des actions, en plus d’étudier ce que cela pourrait impliquer pour la responsabilité collective des nations.

Collective behavior of laser-produced plasma from a multicomponent YBa2Cu3O7 target in air

The dynamics of diffusion of electrons and ions from the laser-produced plasma from a multielement superconducting material, namely YBa2Cu3O7, using a Q-switched Nd:YAG laser is investigated by time-resolved emission-spectroscopic techniques at various laser irradiances. It is observed that beyond a laser irradiance of 2.6 \xC3\x97 1011 W cm-2, the ejected plume collectively drifts away from the target with a sharp increase in velocity to 1.25 \xC3\x97 106 cm s-1, which is twice its velocity observed at lower laser irradiances. This sudden drift apparently occurs as a result of the formation of a charged double layer at the external plume boundary. This diffusion is collective, that is, the electrons and ions inside the plume diffuse together simultaneously and hence it is similar to the ambipolar diffusion of charged particles in a discharge plasma

CH local mode overtone excitations in benzyl chloride—A conformational study

The CH local mode overtone spectrum of benzyl chloride in the visible and NIR regions studied by laser induced thermal lens and conventional NIR absorption is presented. The analysis shows that the −CH2Cl group is symmetrically oriented with respect to the benzene ring, thus finalizing one of the two possible conformational models predicted by electron diffraction studies. The aryl CH bonds have a slightly larger force constant than that in benzene.

Spin and density longitudinal response of quantum dots in the time-dependent local-spin-density approximation

The longitudinal dipole response of a quantum dot has been calculated in the far-infrared regime using local-spin-density-functional theory. We have studied the coupling between the collective spin and density modes as a function of the magnetic field. We have found that the spin dipole mode and single-particle excitations have a sizable overlap, and that the magnetoplasmon modes can be excited by the dipole spin operator if the dot is spin polarized. The frequency of the dipole spin edge mode presents an oscillation which is clearly filling factor (v) related. We have found that the spin dipole mode is especially soft for even-n values. Results for selected numbers of electrons and confining potentials are discussed.

Wave-vector dependence of spin and density multipole excitations in quantum dots

We have employed time-dependent local-spin density-functional theory to analyze the multipole spin and charge density excitations in GaAs-AlxGa1-xAs quantum dots. The on-plane transferred momentum degree of freedom has been taken into account, and the wave-vector dependence of the excitations is discussed. In agreement with previous experiments, we have found that the energies of these modes do not depend on the transferred wave vector, although their intensities do. Comparison with a recent resonant Raman scattering experiment [C. Schüller et al., Phys. Rev. Lett. 80, 2673 (1998)] is made. This allows us to identify the angular momentum of several of the observed modes as well as to reproduce their energies

Low energy excitations of double quantum dots in the lowest Landau level regime

We study the spectrum and magnetic properties of double quantum dots in the lowest Landau level for different values of the hopping and Zeeman parameters by means of exact diagonalization techniques in systems of N=6 and 7 electrons and a filling factor close to 2. We compare our results with those obtained in double quantum layers and single quantum dots. The Kohn theorem is also discussed.

Edge excitations and topological order in rotating Bose gas

The edge excitations and related topological orders of correlated states of a fast rotating Bose gas are studied. Using exact diagonalization of small systems, we compute the energies and number of edge excitations, as well as the boson occupancy near the edge for various states. The chiral Luttinger-liquid theory of Wen is found to be a good description of the edges of the bosonic Laughlin and other states identified as members of the principal Jain sequence for bosons. However, we find that in a harmonic trap the edge of the state identified as the Moore-Read (Pfaffian) state shows a number of anomalies. An experimental way of detecting these correlated states is also discussed.

Delocalization and fragmentation of collective modes in doped 4He drops

We have investigated the fragmentation of collective modes in doped 4He drops in the framework of a finite-range density-functional theory, as well as the delocalization of the impurity inside the cluster. Our results indicate that the impurity is gradually delocalized inside the drop as the size of the latter increases. As an example, results are shown in the case of Xe-4HeN systems up to N=112.

Collective dynamic properties in simple crystals: Influence of the structural disorder

Collective dynamic properties in Lennard-Jones crystals are investigated by molecular dynamics simulation. The study is focused on properties such as the dynamic structure factors, the longitudinal and transverse currents and the density of states. The influence on these properties of the structural disorder is analyzed by comparing the results for one-component crystals with those for liquids and supercooled liquids at analogous conditions. The effects of species-disorder on the collective properties of binary crystals are also discussed.

Absence of collective effects in Heisenberg systems with localized magnetic moments

Existence of collective effects in magnetic coupling in ionic solids is studied by mapping spin eigenstates of the Heisenberg and exact nonrelativistic Hamiltonians on cluster models representing KNiF3, K2NiF4, NiO, and La2CuO4. Ab initio techniques are used to estimate the Heisenberg constant J. For clusters with two magnetic centers, the values obtained are about the same for models having more magnetic centers. The absence of collective effects in J strongly suggests that magnetic interactions in this kind of ionic solids are genuinely local and entangle only the two magnetic centers involved.

The role of dynamical polarization of the ligand-to-metal charge transfer excitations in the ab initio determination of effective exchange parameters

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits us to suggest a variant of the difference dedicated configuration interaction (DDCI) method, presently one of the most accurate and reliable for the evaluation of magnetic effective interactions. This method treats the bridging ligand orbitals mediating the interaction at the same level than the magnetic orbitals and preserves the high quality of the DDCI results while being much less computationally demanding. The numerical accuracy of the new approach is illustrated on various systems with one or two magnetic electrons per magnetic center. The fact that accurate results can be obtained using a rather reduced configuration interaction space opens the possibility to study more complex systems with many magnetic centers and/or many electrons per center.