106,455 research outputs found
Lechner, Fred G.
No full textMemorial Statement for Professor Fred G. Lechner, who died in 1983. The memorial statements contained herein were prepared by the Office of the Dean of the University Faculty of Cornell University to honor its faculty for their service to the university
On the existence of local observables in theories with a factorizing S-matrix
No full textThe scaling limit of the two-dimensional Ising model above the critical temperature is considered as an example for relativistic quantum theories on two-dimensional Minkowski space exhibiting a factorizing S-matrix. In this model, a recently proposed criterion for the existence of local quantum field theories with a prescribed factorizing scattering matrix is verified, thereby establishing a new constructive approach to two-dimensional quantum field theory in a particular example. The existence proof is accomplished by analysing the nuclearity properties of certain specific subsets of fermionic Fock spaces, and yields as a byproduct also a verification of the energy nuclearity condition of Buchholz and Wichmann in models of free fermions in four spacetime dimensions
Polarization-free quantum fields and interaction
No full textA new approach to the inverse scattering problem proposed by Schroer, is applied to two-dimensional integrable quantum field theories. For any two-particle S-matrix S-2 which is analytic in the physical sheet, quantum fields are constructed which are localizable in wedge-shaped regions of Minkowski space and whose two- particle scattering is described by the given S-2. These fields are polarization-free in the sense that they create one-particle states from the vacuum without polarization clouds. Thus they provide examples of temperate polarization-free generators in the presence of nontrivial interaction
Yang–Baxter endomorphisms
No full textEvery unitary solution of the Yang–Baxter equation (R-matrix) in dimension (Formula presented.) can be viewed as a unitary element of the Cuntz algebra (Formula presented.) and as such defines an endomorphism of (Formula presented.). These Yang–Baxter endomorphisms restrict and extend to several other (Formula presented.) - and von Neumann algebras, and furthermore define a II (Formula presented.) factor associated with an extremal character of the infinite braid group. This paper is devoted to a detailed study of such Yang–Baxter endomorphisms. We discuss the relative commutants of the subfactors induced by Yang–Baxter endomorphisms, a new perspective on algebraic operations on R-matrices such as tensor products and cabling powers, the characters of the infinite braid group defined by R-matrices, and ergodicity properties. This also yields new concrete information on partial traces and spectra of R-matrices
Modular Nuclearity and Localization
No full textWithin the algebraic setting of quantum field theory, a condition is given which implies that the intersection of algebras generated by field operators localized in wedge-shaped regions of the two-dimensional Minkowski space is non-trivial; in particular, there exist compactly localized operators in such theories which can be interpreted as local observables. The condition is based on spectral (nuclearity) properties of the modular operators affiliated with wedge algebras and the vacuum state and is of interest in the algebraic approach to the formfactor program, initiated by Schroer. It is illustrated here in a simple class of examples
Vertical disintegration of production and the rise of market for brands
No full textThe emergence of a market for brands is a relevant economic phenomenon that creates entrepreneurial opportunities. In this research, we explore the relationship between the size of market for brands and the vertical disintegration of production, as antecedent of the rise of market for brands. We take an industry-level perspective and focus on trademark transactions in the US as the empirical setting for our analysis. The results uncover a positive relationship between the degree of industry vertical disintegration and the size of market for brands. We conclude with examples of how a market for brands creates entrepreneurial opportunities
Importance de l’écosystème entrepreneurial dans l’écosystème d’affaires de start-ups et facteurs explicatifs
No full textLes recherches sur les start-ups mettent en avant l’importance du
local et du réseau entrainant une vision en termes de proximité
géographique (le local) ou organisée (le réseau). En
correspondance, les développements théoriques concernant les
écosystèmes entrepreneuriaux et les écosystèmes d’affaires
permettent d’envisager de vastes ensembles d’acteurs
hétérogènes et interconnectés. Ces acteurs sont soit localisés dans
un territoire donné et favorisent la création d’entreprise
(écosystème entrepreneurial) ou a-territorialisés mais cruciaux
dans le développement de la jeune entreprise (écosystème
d’affaires). Partant de l’idée que tous les acteurs en lien avec les
start-ups font partie de leur écosystème d’affaires et que ceux
présents sur le territoire font partie de leur écosystème
entrepreneurial, nous nous intéressons au degré de
correspondance entre écosystème entrepreneurial et écosystème
d’affaires. Nous cherchons également à envisager quels facteurs
inhérents aux start-ups vont favoriser un recours comparativement
plus important à l’écosystème entrepreneurial en nous
interrogeant selon deux axes : stade de croissance et degré
d’innovation. A cette fin, nous avons étudié la situation de 165
start-ups de la région de Toulouse, située dans le Sud-ouest de la
France
Entrepreneurial ecosystems and actor legitimacy
No full textPurpose – This study contributes to a better understanding of the important actor-specific, micro-level legitimacy dimensions in dynamic entrepreneurial ecosystems (EEs).
Design/methodology/approach – Using an embedded case study approach and rich longitudinal data collected over 16 years within a French EE, the study analyzes the legitimacy gaining process of two actors coming from opposite founding conditions.
Findings – Three dimensions of legitimacy (3L) are necessary to be accepted as functional actors within EEs: institutional legitimacy (IL) refers to the EE’s acceptance of an actor as an institution active in the field of entrepreneurship; cultural legitimacy (CL) means that the actor is recognized as possessing and promoting values considered appropriate by the entrepreneurial community; relational legitimacy (RL) relates to the willingness of the entrepreneurial community to interact with the actor. These are complementary dimensions that members of EEs need to possess to acquire full legitimacy. Different paths are possible to achieve this full legitimacy.
Research limitations/implications – Replicating the study with a comparative approach including more actors could represent an interesting avenue for research.
Practical implications – This research provides insights into the underlying dimensions of legitimacy in EEs, how various actors gain legitimacy in such contexts and how this influences the dynamics of EEs. Originality/value – The results provide novel insights into the issue of legitimacy in EEs and legitimacy theory in general
Start-ups in entrepreneurial ecosystems: the role of relational capacity
No full textPurpose: Entrepreneurial ecosystems provide the context for start-ups to access resources. The authors investigate the reliance of start-ups on their entrepreneurial ecosystem and the driving factors behind the proportion of local actors (belonging to their entrepreneurial ecosystem) within their overall set of relationships (their business ecosystem). Recognizing the limited relational capacity of firms, the authors focus on three differentiating firm characteristics: size, age and innovation of firms. Design/methodology/approach: The authors developed a sample of 163 start-ups located in the entrepreneurial ecosystem of Toulouse, France. The authors investigated the characteristics of their relationship sets using regression analysis. Findings: The results confirm that age is inversely related to the proportion of a start-up's relationships located in its entrepreneurial ecosystem. More surprisingly, for older start-ups, the authors also highlight the presence of a moderating effect of the start-up's size on the relationship between its degree of innovation and the proportion of its relationships in its entrepreneurial ecosystem: Larger and more innovative start-ups appear to rely more on their local entrepreneurial ecosystem. Originality/value: This research increases the understanding of the characteristics driving the interactions of start-ups with their entrepreneurial ecosystems by adopting a relational capacity approach. The authors introduce digital methods as an innovative approach for uncovering firms' ecosystems. Finally, from a practical point of view, the research should provide public authorities seeking to promote the link between local resources and the development of innovative start-ups in their regions with interesting insights
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