Hawking radiation for Dirac spinors on the RP^3 geon

We analyse the Hawking(-Unruh) effect for a massive Dirac spinor on the Z_2 quotient of Kruskal spacetime known as the RP^3 geon. There are two distinct Hartle-Hawking-like vacua, depending on the choice of the spin structure, and suitable measurements in the static region (which on its own has only one spin structure) distinguish these two vacua. However, both vacua appear thermal in the usual Hawking temperature to certain types of restricted operators, including operators with support in the asymptotic future (or past). Similar results hold in a family of topologically analogous flat spacetimes, where we show the two vacua to be distinguished also by the shear stresses in the zero-mass limit. As a by-product, we display the explicit Bogolubov transformation between the Rindler-basis and the Minkowski-basis for massive Dirac fermions in four-dimensional Minkowski spacetime.Comment: 23 pages, no figures, uses amsmath, amssymb, latexsym packages, replaced with version published in Phys.Rev.

Imprints of Spacetime Topology in the Hawking-Unruh Effect

The Unruh and Hawking effects are investigated on certain families of topologically non-trivial spacetimes using a variety of techniques. First we present the Bogolubov transformation between Rindler and Minkowski quantizations on two flat spacetimes with topology ${\R}^3\times{S^1}$ (M_0 and M_-) for massive Dirac spinors. The two inequivalent spin structures on each are considered. Results show modifications to the Minkowski space Unruh effect. This provides a flat space model for the Hawking effect on Kruskal and RP^3 geon black hole spacetimes which is the subject of the rest of this part. Secondley we present the expectation values of the stress tensor for massive scalar and spinor fields on $M_0$ and $M_-$, and for massive scalar fields on Minkowski space with a single infinite plane boundary, in the Minkowski-like vacua. Finally we investigate particle detector models. We investigate Schlicht's regularization of the Wightman function and extend it to an arbitrary spacetime dimension, to quotient spaces of Minkowski space, to non-linear couplings, to a massless Dirac field, and to conformally flat spacetimes. Secondly we present some detector responses, including the time dependent responses of inertial and uniformly accelerated detectors on $M_-$ and $M$ with boundary with motion perpendicular to the boundary. Responses are also considered for static observers in the exterior of the RP^3 geon and comoving observers in RP^3 de Sitter space, via those in the associated GEMS.Comment: PhD Thesis, 205 page

Innovation processes and industrial districts

In this survey, we examine the operations of innovation processes within industrial districts by exploring the ways in which differentiation, specialization, and integration affect the generation, diffusion, and use of new knowledge in such districts. We begin with an analysis of the importance of the division of labour and then investigate the effects of social embeddedness on innovation. We also consider the effect of forms of organization within industrial districts at various stages of product and process life, and we examine the negative aspects of embeddedness for innovation. We conclude with a discussion of the possible consequences of new information and communications technologies on innovation in industrial districts

A GIS Approach for Evaluating Municipal Planning Capability: Residential Built Form in Markham and Vaughan, Ontario

This research describes a methodology for measuring built form patterns using spatial data and GIS that is amenable to the study of large geographical areas. This methodology was used to investigate the capability of municipal planning to influence residential development. In the early 1990s, the Town of Markham, Ontario, Canada adopted a residential development philosophy inspired by New Urbanism. An adjacent municipality, the City of Vaughan, has employed a conventional development approach. By calculating several built form measures derived from the design prescriptions associated with New Urbanism, this study seeks to discern if Markham's adoption of an unconventional development philosophy has resulted in a residential built form distinct from that in Vaughan. Built form measures are calculated for both municipalities for two eras. Development from 1981 to 1995 represents the "before" or baseline configuration, while development from 1996 to 2003 is used to characterize built form created when Markham's New Urbanist-inspired approach was in force. Period over period comparisons are carried out for each municipality, as are within-period comparisons between municipalities. Findings indicate that development patterns are distinct in the two study periods. From the early period to the more recent, street networks take on a more grid-like organization while building lots and blocks become smaller. These changes are accompanied by an overall decline in accessibility to amenities. However, development patterns were found to be quite similar in both municipalities in the recent study period, exhibiting differences in degree, not in kind. The findings appear to indicate that planning's influence over residential built form is limited to moderately accelerating positive trends, and moderately retarding negative trends

Innovations en milieu de travail dans le secteur manufacturier au Québec

Sur la base d'un sondage téléphonique mené auprès de la direction des établissements manufacturiers de 50 employés et plus au Québec, cette contribution se penche sur la diffusion des innovations organisationnelles. Les résultats présentés sont organisés autour de cinq configurations de changements, se distinguant par une logique organisationnelle spécifique, à laquelle sont associées des performances économiques et sociales ainsi que des pratiques de gestion des ressources humaines et de relations de travail. Ils confirment l'émergence d'un nouveau paradigme technico-productif, sans qu'il soit possible de conclure à une véritable transformation du travail, étant donné la faible diffusion des configurations participatives, qui affichent néanmoins les meilleures performances, en s'appuyant sur les pratiques de ressources humaines et de relations de travail les plus novatrices

Causal particle detectors and topology

We investigate particle detector responses in some topologically non-trivial spacetimes. We extend a recently proposed regularization of the massless scalar field Wightman function in 4-dimensional Minkowski space to arbitrary dimension, to the massive scalar field, to quotients of Minkowski space under discrete isometry groups and to the massless Dirac field. We investigate in detail the transition rate of inertial and uniformly accelerated detectors on the quotient spaces under groups generated by $(t,x,y,z)\mapsto(t,x,y,z+2a)$, $(t,x,y,z)\mapsto(t,-x,y,z)$, $(t,x,y,z)\mapsto(t,-x,-y,z)$, $(t,x,y,z)\mapsto(t,-x,-y,z+a)$ and some higher dimensional generalizations. For motions in at constant $y$ and $z$ on the latter three spaces the response is time dependent. We also discuss the response of static detectors on the RP^3 geon and inertial detectors on RP^3 de Sitter space via their associated global embedding Minkowski spaces (GEMS). The response on RP^3 de Sitter space, found both directly and in its GEMS, provides support for the validity of applying the GEMS procedure to detector responses and to quotient spaces such as RP^3 de Sitter space and the RP^3 geon where the embedding spaces are Minkowski spaces with suitable identifications.Comment: 47 pages, 9 figure

Pre-Big Bang Scenario on Self-T-Dual Bouncing Branes

We consider a new class of 5-dimensional dilatonic actions which are invariant under T-duality transformations along three compact coordinates, provided that an appropriate potential is chosen. We show that the invariance remains when we add a boundary term corresponding to a moving 3-brane, and we study the effects of the T-duality symmetry on the brane cosmological equations. We find that T-duality transformations in the bulk induce scale factor duality on the brane, together with a change of sign of the pressure of the brane cosmological matter. However, in a remarkable analogy with the Pre-Big Bang scenario, the cosmological equations are unchanged. Finally, we propose a model where the dual phases are connected through a scattering of the brane induced by an effective potential. We show how this model can realise a smooth, non-singular transition between a pre-Big Bang superinflationary Universe and a post-Big Bang accelerating Universe.Comment: 18 pages, minor typos corrected, Sec. 2 expanded with more details on the self-T-dual background, Sec.4 and 5 revised accordingly. Version to appear on JCA

Microwave dielectric study of spin-Peierls and charge ordering transitions in (TMTTF)2_2PF6_6 salts

We report a study of the 16.5 GHz dielectric function of hydrogenated and deuterated organic salts (TMTTF)$_2$PF$_6$. The temperature behavior of the dielectric function is consistent with short-range polar order whose relaxation time decreases rapidly below the charge ordering temperature. If this transition has more a relaxor character in the hydrogenated salt, charge ordering is strengthened in the deuterated one where the transition temperature has increased by more than thirty percent. Anomalies in the dielectric function are also observed in the spin-Peierls ground state revealing some intricate lattice effects in a temperature range where both phases coexist. The variation of the spin-Peierls ordering temperature under magnetic field appears to follow a mean-field prediction despite the presence of spin-Peierls fluctuations over a very wide temperature range in the charge ordered state of these salts.Comment: 7 pages, 6 figure

Efficient linear combination for distant n-gram models

Colloque avec actes et comité de lecture. internationale.International audienceThe objective of this paper is to present a large study concerning the use of distant language models. In order to combine efficiently distant and classical models, an adaptation of the back-off principle is made. Also, we show the importance of each part of a history for the prediction. In fact, each sub-history is analyzed in order to estimate its importance in terms of prediction and then a weight is associated to each class of sub-histories. Therefore, the combined models take into account the features of each history's part and not the whole history as made in other works. The contribution of distant n-gram models in terms of perplexity is significant and improves the results by 12.8%. Making the linear combination depending on sub-histories achieves an improvement of $5.3\%$ in comparison to classical linear combination