684 research outputs found
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 (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 and , 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 and 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 auprÚs 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 ,
, ,
and some higher dimensional generalizations.
For motions in at constant and 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)PF salts
We report a study of the 16.5 GHz dielectric function of hydrogenated and
deuterated organic salts (TMTTF)PF. 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 in comparison to classical linear combination
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