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Metric enrichment, finite generation, and the path coreflection

Alexandru Chirvasitu (2024)

Archivum Mathematicum

We prove a number of results involving categories enriched over CMet, the category of complete metric spaces with possibly infinite distances. The category CPMet of path complete metric spaces is locally 1 -presentable, closed monoidal, and coreflective in CMet. We also prove that the category CCMet of convex complete metric spaces is not closed monoidal and characterize the isometry- 0 -generated objects in CMet, CPMet and CCMet, answering questions by Di Liberti and Rosický. Other results include...

Metric Entropy of Homogeneous Spaces

Stanisław Szarek (1998)

Banach Center Publications

For a precompact subset K of a metric space and ε > 0, the covering number N(K,ε) is defined as the smallest number of balls of radius ε whose union covers K. Knowledge of the metric entropy, i.e., the asymptotic behaviour of covering numbers for (families of) metric spaces is important in many areas of mathematics (geometry, functional analysis, probability, coding theory, to name a few). In this paper we give asymptotically correct estimates for covering numbers for a large class of homogeneous...

Metrics in the sphere of a C*-module

Esteban Andruchow, Alejandro Varela (2007)

Open Mathematics

Given a unital C*-algebra 𝒜 and a right C*-module 𝒳 over 𝒜 , we consider the problem of finding short smooth curves in the sphere 𝒮 𝒳 = x ∈ 𝒳 : 〈x, x〉 = 1. Curves in 𝒮 𝒳 are measured considering the Finsler metric which consists of the norm of 𝒳 at each tangent space of 𝒮 𝒳 . The initial value problem is solved, for the case when 𝒜 is a von Neumann algebra and 𝒳 is selfdual: for any element x 0 ∈ 𝒮 𝒳 and any tangent vector ν at x 0, there exists a curve γ(t) = e tZ(x 0), Z ∈ 𝒜 ( 𝒳 ) , Z* = −Z and ∥Z∥ ≤ π, such...

Monotone convolution semigroups

Takahiro Hasebe (2010)

Studia Mathematica

We study how a property of a monotone convolution semigroup changes with respect to the time parameter. Especially we focus on "time-independent properties": in the classical case, there are many properties of convolution semigroups (or Lévy processes) which are determined at an instant, and moreover, such properties are often characterized by the drift term and Lévy measure. In this paper we exhibit such properties of monotone convolution semigroups; an example is the concentration of the support...

Moore-Penrose inverses of Gram operators on Hilbert C*-modules

M. S. Moslehian, K. Sharif, M. Forough, M. Chakoshi (2012)

Studia Mathematica

Let t be a regular operator between Hilbert C*-modules and t be its Moore-Penrose inverse. We investigate the Moore-Penrose invertibility of the Gram operator t*t. More precisely, we study some conditions ensuring that t = ( t * t ) t * = t * ( t t * ) and ( t * t ) = t t * . As an application, we get some results for densely defined closed operators on Hilbert C*-modules over C*-algebras of compact operators.

Morita equivalence of groupoid C*-algebras arising from dynamical systems

Xiaoman Chen, Chengjun Hou (2002)

Studia Mathematica

We show that the stable C*-algebra and the related Ruelle algebra defined by I. Putnam from the irreducible Smale space associated with a topologically mixing expanding map of a compact metric space are strongly Morita equivalent to the groupoid C*-algebras defined directly from the expanding map by C. Anantharaman-Delaroche and V. Deaconu. As an application, we calculate the K⁎-group of the Ruelle algebra for a solenoid.

Morita equivalence of measured quantum groupoids. Application to deformation of measured quantum groupoids by 2-cocycles

Michel Enock (2012)

Banach Center Publications

In a recent article, Kenny De Commer investigated Morita equivalence between locally compact quantum groups, in which a measured quantum groupoid, of basis ℂ², was constructed as a linking object. Here, we generalize all these constructions and concepts to the level of measured quantum groupoids. As for locally compact quantum groups, we apply this construction to the deformation of a measured quantum groupoid by a 2-cocycle.

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