Equivariant localization and completion in cyclic homology and derived loop spaces

We prove an equivariant localization theorem over an algebraically closed field of characteristic zero for smooth quotient stacks by reductive groups $X/G$ in the setting of derived loop spaces as well as Hochschild homology and its cyclic variants. We show that the derived loop spaces of the stack $X/G$ and its classical $z$-fixed point stack $\pi_0(X^z)/G^z$ become equivalent after completion along a semisimple parameter $[z] \in G//G$, implying the analogous statement for Hochschild and cyclic homology of the dg category of perfect complexes $\text{Perf}(X/G)$. We then prove an analogue of the Atiyah-Segal completion theorem in the setting of periodic cyclic homology, where the completion of the periodic cyclic homology of $\text{Perf}(X/G)$ at the identity $[e] \in G//G$ is identified with a 2-periodic version of the derived de Rham cohomology of $X/G$. Together, these results identify the completed periodic cyclic homology of a stack $X/G$ over a parameter $[z] \in G//G$ with the 2-periodic derived de Rham cohomology of its $z$-fixed points.Comment: Pre-publication version. 42 pages. Comments welcom

ac Losses in a Finite Z Stack Using an Anisotropic Homogeneous-Medium Approximation

A finite stack of thin superconducting tapes, all carrying a fixed current I, can be approximated by an anisotropic superconducting bar with critical current density Jc=Ic/2aD, where Ic is the critical current of each tape, 2a is the tape width, and D is the tape-to-tape periodicity. The current density J must obey the constraint \int J dx = I/D, where the tapes lie parallel to the x axis and are stacked along the z axis. We suppose that Jc is independent of field (Bean approximation) and look for a solution to the critical state for arbitrary height 2b of the stack. For c<|x|<a we have J=Jc, and for |x|<c the critical state requires that Bz=0. We show that this implies \partial J/\partial x=0 in the central region. Setting c as a constant (independent of z) results in field profiles remarkably close to the desired one (Bz=0 for |x|<c) as long as the aspect ratio b/a is not too small. We evaluate various criteria for choosing c, and we show that the calculated hysteretic losses depend only weakly on how c is chosen. We argue that for small D/a the anisotropic homogeneous-medium approximation gives a reasonably accurate estimate of the ac losses in a finite Z stack. The results for a Z stack can be used to calculate the transport losses in a pancake coil wound with superconducting tape.Comment: 21 pages, 17 figures, accepted by Supercond. Sci. Techno

Brokering Community–campus Partnerships: An Analytical Framework

Academic institutions and community-based organizations have increasingly recognized the value of working together to meet their different objectives and address common societal needs. In an effort to support the development and maintenance of these partnerships, a diversity of brokering initiatives has emerged. We describe these brokering initiatives broadly as coordinating mechanisms that act as an intermediary with an aim to develop collaborative and sustainable partnerships that provide mutual benefit. A broker can be an individual or an organization that helps connect and support relationships and share knowledge. To date, there has been little scholarly discussion or analysis of the various elements of these initiatives that contribute to successful community–campus partnerships. In an effort to better understand where these features may align and diverge, we reviewed a sample of community–campus brokering initiatives across North America and the United Kingdom to consider their different roles and activities. From this review, we developed a framework to delineate characteristics of different brokering initiatives to better understand their contributions to successful partnerships. The framework is divided into two parts. The first examines the different structural allegiances of the brokering initiatives by identifying their affiliation, principle purpose, and who received primary benefits. The second considers the dimensions of brokering activities in respect to their level of engagement, platforms used, scale of activity, and area of focus. The intention of the community campus engagement brokering framework is to provide an analytical tool for academics and community-based practitioners engaged in teaching and research partnerships. When developing a brokering initiative, these categories describing the different structures and dimensions encourage participants to think through the overall goals and objectives of the partnership and adapt the initiative accordingly

Deformation-Quantization of Complex Involutive Submanifolds

The sheaf of rings of WKB operators provides a deformation-quantization of the cotangent bundle to a complex manifold. On a complex symplectic manifold $X$ there may not exist a sheaf of rings locally isomorphic to a ring of WKB operators. The idea is then to consider the whole family of locally defined sheaves of WKB operators as the deformation-quantization of $X$. To state it precisely, one needs the notion of algebroid stack, introduced by Kontsevich. In particular, the stack of WKB modules over $X$ defined in Polesello-Schapira (see also Kashiwara for the contact case) is better understood as the stack of modules over the algebroid stack of deformation-quantization of $X$. Let $V$ be an involutive submanifold of $X$, and assume for simplicity that the quotient of $V$ by its bicharacteristic leaves is isomorphic to a complex symplectic manifold $Z$. The algebra of endomorphisms of a simple WKB module along $V$ is locally (anti-)isomorphic to the pull-back of WKB operators on $Z$. Hence we may say that a simple module provides a deformation-quantization of $V$. Again, since in general there do not exist globally defined simple WKB modules, the idea is to consider the algebroid stack of locally defined simple WKB modules as the deformation-quantization of $V$. In this paper we start by defining what an algebroid stack is, and how it is locally described. We then discuss the algebroid stack of WKB operators on a complex symplectic manifold $X$, and define the deformation-quantization of an involutive submanifold $V$ by means of simple WKB modules along $V$. Finally, we relate this deformation-quantization to that given by WKB operators on the quotient of $V$ by its bicharacteristic leaves.Comment: 11 page

Characteristic classes for curves of genus one

We compute the cohomology of the stack M_1 with coefficients in Z[1/2], and in low degrees with coefficients in Z. Cohomology classes on M_1 give rise to characteristic classes, cohomological invariants of families of curves of genus one. We prove a number of vanishing results for those characteristic classes, and give explicit examples of families with non-vanishing characteristic classes

The dynamics of z~1 clusters of galaxies from the GCLASS survey

We constrain the internal dynamics of a stack of 10 clusters from the GCLASS survey at 0.87<z<1.34. We determine the stack cluster mass profile M(r) using the MAMPOSSt algorithm of Mamon et al., the velocity anisotropy profile beta(r) from the inversion of the Jeans equation, and the pseudo-phase-space density profiles Q(r) and Qr(r), obtained from the ratio between the mass density profile and the third power of the (total and, respectively, radial) velocity dispersion profiles of cluster galaxies. Several M(r) models are statistically acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The total mass distribution has a concentration c=r200/r-2=4.0-0.6+1.0, in agreement with theoretical expectations, and is less concentrated than the cluster stellar-mass distribution. The stack cluster beta(r) is similar for passive and star-forming galaxies and indicates isotropic galaxy orbits near the cluster center and increasingly radially elongated with increasing cluster-centric distance. Q(r) and Qr(r) are almost power-law relations with slopes similar to those predicted from numerical simulations of dark matter halos. Combined with results obtained for lower-z clusters we determine the dynamical evolution of galaxy clusters, and compare it with theoretical predictions. We discuss possible physical mechanisms responsible for the differential evolution of total and stellar mass concentrations, and of passive and star-forming galaxy orbits [abridged].Comment: 12 pages, 7 figures. Version accepted for publication in A&A after minor modification