Stratégies, espaces et territoires

L'initiative portée par ce numéro spécial est née du constat d'une faiblesse relative, dans les travaux académiques, du recours à la dimension spatiale pour appréhender et analyser les objets et les problématiques propres aux sciences de gestion en général et au management stratégique en particulier. Cette absence de référence explicite à l'espace contraste, de manière étonnante, avec la prégnance et le caractère structurant de cette dimension dans nombre des objets de recherche et également dans nombre des questions méthodologiques à l'étude dans nos champs disciplinaires.Espace - Territoire - Stratégie

L'espace et le territoire dans l'agenda de recherche en stratégie

La vitesse des échanges et des relations ouverte par les technologies de l'information et de la communication dissoud certaines contraintes temporelles par la connexion parallèle et simultanée d'une multitude d'acteurs. Certains blocages inhérents aux distances sont aussi modifiés puisqu'il devient possible d'échanger, de communiquer, et de concevoir ensemble dans des lieux différents. Pourtant, de manière paradoxale, ces nouvelles potentialités n'ont fait que renforcer la centralité de l'espace comme facteur structurant de la polarisation des activités autour de certains territoires, comme la Silicon Valley figure emblématique de ce nouveau monde des technologies de la communication. Même l'avénement du virtuel, qui permet des dédoublements temporels avec la vie quasi autonome d'avatars, impose une modélisation de l'espace. L'homme artificiel ou virtuel ne saurait exister sans un retour réflexif sur les espaces de l'homme. L'espace et le territoire se retrouvent ainsi aujourd'hui au coeur de renouveaux théoriques en sciences humaines et sociales. Ce renouveau s'est imposé pour affronter des questions aussi vastes et multiples que la mondialisation de l'économie, l'hypercroissance ou l'appauvrissement de certaines régions, le développement durable d'activités et de territoires, l'émergence de nouvelles entreprises globales sur la scène internationale issues de «nouveaux» pays, la répartition des activités d'innovation et de recherche et développement, les effets des transformations techniques sur l'organisation spatiale du système économique et social, -ou encore l'animation d'acteurs territoriaux aux intérêts disparates, etc... La stratégie et la gestion ne sauraient rester en marge de cet effort d'interrogation théorique et de proposition conceptuelle. Cela justifie de mener ici un effort de repérages des principaux enjeux reliants stratégies, espaces et territoires. Ce travail se fera en distinguant deux aspects. Dans un premier temps nous aborderons la dimension spatiale des stratégies des firmes et des organisations qui nécessite d'interroger conjointement la localisation des activités et le management stratégique des distances. Dans un second temps nous reviendrons sur le territoire comme stratégie d'organisation de l'espace. Il s'agit notamment d'interroger les formes d'organisation spatiales, les modes de coordination et enfin les modalités de gouvernance d'acteurs disparates.Stratégie - Espace - Territoire - Localisation - Gouvernance

Investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using laser Doppler anemometry

Laser Doppler anemometry (LDA) is used to investigate the flow inside an idealized urban canopy consisting of a staggered array of cubes with a 25% density immersed into an atmospheric boundary layer with a Reynolds number of δ+=32,300. The boundary layer thickness to cube height ratio (δ/h=22.7) is large enough to be representative of atmospheric surface layer in neutral conditions. The LDA measurements give access to pointwise time-resolved data at several positions inside the canopy (z=h/4, h/2, and h). Synchronized hot-wire measurements above the canopy (inertial region and roughness sublayer) are also realized to get access to interactions between the different flow regions. The wall-normal mean velocity profile and Reynolds stresses show a good agreement with available data in the literature, although some differences are observed on the standard deviation of the spanwise component. A detailed spectral and integral time scale analysis inside the canopy is then carried out. No clear footprint of a periodic vortex shedding on the sides of the cubes could be identified on the power spectra, owing to the multiple cube-to-cube interactions occuring within a canopy with a building density in the wake interference regime. Results also suggest that interactions between the most energetics scales of the boundary layer and those related to the cube canopy take place, leading to a broadening of the energy peak in the spectra within the canopy. This is confirmed by the analysis of coherence results between the flow inside and above the canopy. It is shown that linear interactions mechanisms are significant, but reduced compared to smooth-wall boundary-layer flow. To our knowledge, this is the first time such results are shown on the dynamics of the flow inside an urban canopy

Application of Laser Doppler Anemometry to estimate turbulent power spectra inside an urban canopy

International audienceIn the present contribution, we propose to make use of Laser Doppler Anemometry to investigate the dynamics of the flow inside an urban canopy immersed into a thick turbulent boundary layer. Previous studies dedicated to such flows (Castro et al. 2006; Reynolds and Castro 2008) have focused the core of their analysis on the roughness sublayer region or on the inertial region. In contrast, the region below the canopy interface have received little attention so far, and only mean velocity or Reynolds stresses data can be found in the literature. Indeed, getting access to the dynamics of the flow inside the canopy represents a real experimental challenge: the flow is turbulent, 3-dimensionnal, and due to the tight clearance, only non-intrusive laser-based techniques such as LDA or PIV can be used. In this contribution, for the first time, a spectral analysis of the flow is carried out inside the canopy region. This is made possible thanks to very thorough LDA measurements as well as the use of advanced post-processing algorithm to compute temporal power spectra. Indeed, LDA measurement yields non-equidistantly spaced data points, and standard FFT algorithms cannot be used. A detailed comparison of various algorithms is undertaken, and a slight improvement is proposed to reduce the impact of measurement noise. Finally, the power spectra inside the canopy are analyzed and the main implications on the flow dynamics are discussed

[La fortification et architectvre perspective et artifices de Iaques Perret ...]

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 2009Tít. y autor tomados del principio del textoPosiblemente impreso en el siglo XVIISign.: A-L\p1\sLas h. de grab. calc., a doble plana: "Thomas de Leu sculpsit

Total Break of the l-IC Signature Scheme

The original publication is available at www.springerlink.comInternational audienceIn this paper, we describe efficient forgery and full-key recovery attacks on the l-IC- signature scheme recently proposed at PKC 2007. This cryptosystem is a multivariate scheme based on a new internal quadratic primitive which avoids some drawbacks of previous multivariate schemes: the scheme is extremely fast since it requires one exponentiation in a finite field of medium size and the public key is shorter than in many multivariate signature schemes. Our attacks rely on the recent cryptanalytic tool developed by Dubois et al. against the SFLASH signature scheme. However, the final stage of the attacks require the use of Grobner basis techniques to conclude to actually forge a signature (resp. to recover the secret key). For the forgery attack, this is due to the fact that Patarin's attack is much more difficult to mount against l-IC. The key recovery attack is also very efficient since it is faster to recover equivalent secret keys than to forge

Application of Laser Doppler Anemometry to estimate turbulent power spectra inside an urban canopy

In the present contribution, we propose to make use of Laser Doppler Anemometry to investigate the dynamics of the flow inside an urban canopy immersed into a thick turbulent boundary layer. Previous studies dedicated to such flows (Castro et al. 2006; Reynolds and Castro 2008) have focused the core of their analysis on the roughness sublayer region or on the inertial region. In contrast, the region below the canopy interface have received little attention so far, and only mean velocity or Reynolds stresses data can be found in the literature. Indeed, getting access to the dynamics of the flow inside the canopy represents a real experimental challenge: the flow is turbulent, 3-dimensionnal, and due to the tight clearance, only non-intrusive laser-based techniques such as LDA or PIV can be used. In this contribution, for the first time, a spectral analysis of the flow is carried out inside the canopy region. This is made possible thanks to very thorough LDA measurements as well as the use of advanced post-processing algorithm to compute temporal power spectra. Indeed, LDA measurement yields non-equidistantly spaced data points, and standard FFT algorithms cannot be used. A detailed comparison of various algorithms is undertaken, and a slight improvement is proposed to reduce the impact of measurement noise. Finally, the power spectra inside the canopy are analyzed and the main implications on the flow dynamics are discussed