Cycles and 1-unconditional matrices

We characterize the 1-unconditional subsequences of the canonical basis (e_rc) of elementary matrices in the Schatten-von-Neumann class S^p . The set I of couples (r,c) must be the set of edges of a bipartite graph without cycles of even length 4<=l<=p if p is an even integer, and without cycles at all if p is a positive real number that is not an even integer. In the latter case, I is even a Varopoulos set of V-interpolation of constant 1. We also study the metric unconditional approximation property for the space S^p_I spanned by (e_rc)_{(r,c)\in I} in S^p .Comment: 29 pages. This new version computes explicitly certain unconditionality constants, shows how our results generalize Varopoulos' work on V-Sidon sets, investigates the metric unconditional approximation property in the same contex

Transfer of Fourier multipliers into Schur multipliers and sumsets in a discrete group

We inspect the relationship between relative Fourier multipliers on noncommutative Lebesgue-Orlicz spaces of a discrete group and relative Toeplitz-Schur multipliers on Schatten-von-Neumann-Orlicz classes. Four applications are given: lacunary sets; unconditional Schauder bases for the subspace of a Lebesgue space determined by a given spectrum, that is, by a subset of the group; the norm of the Hilbert transform and the Riesz projection on Schatten-von-Neumann classes with exponent a power of 2; the norm of Toeplitz Schur multipliers on Schatten-von-Neumann classes with exponent less than 1.Comment: Corresponds to the version published in the Canadian Journal of Mathematics 63(5):1161-1187 (2011

Free group automorphisms, invariant orderings and topological applications

We are concerned with orderable groups and particularly those with orderings invariant not only under multiplication, but also under a given automorphism or family of automorphisms. Several applications to topology are given: we prove that the fundamental groups of hyperbolic nonorientable surfaces, and the groups of certain fibred knots are bi-orderable. Moreover, we show that the pure braid groups associated with hyperbolic nonorientable surfaces are left-orderable.Comment: Published by Algebraic and Geometric Topology at http://www.maths.warwick.ac.uk/agt/AGTVol1/agt-1-15.abs.htm

The Good Temp

[Excerpt] The story of the explosion of temporary employment and the challenge to the permanent employment contract in the last half of the twentieth century has been told many times. Researchers from\u27\u27a variety of academic disciplines have written about it, as have activists who organize to help American workers maintain a decent standard of living and a modicum of dignity, and policy analysts who fear the degradation of the employment relationship that seems to be a foregone implication of temporary work. They have focused on different units of analysis: workers who desire permanent jobs but can\u27t find them, workers who have lost out as companies have downsized and restructured, businesses and their myriad reasons for using temporary workers as a solution to their profitability and competition problems, and the temporary help service industry (THS) itself. The Good Temp takes a different tack to explain these developments in labor market institutions and behaviors. Specifically, we look at how the THS industry in the United States reinvented temporary work in the second half of the twentieth century and examine how individual THS agencies continue to manufacture and market this reinvented product—the good temporary worker—today. It is a customized, historically specific make and model whose marketability rested on two selling points: that temporary employment could be a viable alternative to permanent employment and that the workers on whom the system of temporary employment relations depends could be as good as permanent workers and sometimes better. The historical and social construction of the good temp, we show, was embedded in THS-industry profitmaking strategies and relied on the diffusion of new norms about what constituted acceptable employment practice. Now entrenched, these norms underpin our current employment relations in the United States which many, if not most, of us experience as precarious and contingent, even when we have so-called permanent jobs

Modeling structural change in spatial system dynamics: A Daisyworld example

System dynamics (SD) is an effective approach for helping reveal the temporal behavior of complex systems. Although there have been recent developments in expanding SD to include systems' spatial dependencies, most applications have been restricted to the simulation of diffusion processes; this is especially true for models on structural change (e.g. LULC modeling). To address this shortcoming, a Python program is proposed to tightly couple SD software to a Geographic Information System (GIS). The approach provides the required capacities for handling bidirectional and synchronized interactions of operations between SD and GIS. In order to illustrate the concept and the techniques proposed for simulating structural changes, a fictitious environment called Daisyworld has been recreated in a spatial system dynamics (SSD) environment. The comparison of spatial and non-spatial simulations emphasizes the importance of considering spatio-temporal feedbacks. Finally, practical applications of structural change models in agriculture and disaster management are proposed

Lacunary matrices

We study unconditional subsequences of the canonical basis e_rc of elementary matrices in the Schatten class S^p. They form the matrix counterpart to Rudin's Lambda(p) sets of integers in Fourier analysis. In the case of p an even integer, we find a sufficient condition in terms of trails on a bipartite graph. We also establish an optimal density condition and present a random construction of bipartite graphs. As a byproduct, we get a new proof for a theorem of Erdos on circuits in graphs.Comment: 14 page