Cooperative Performance and Board of Director Characteristics: A Quantitative Investigation

Previous cooperative governance literature has relied primarily on qualitative data to recommend change. Using data provided by the USDA-Rural Business and Cooperative Services Agency (RBS) and collected from cooperative top managers we find statistical evidence that various board of director characteristics do affect a range of cooperative financial measures.governance, finance, Agribusiness,

Collective pairing of resonantly coupled microcavity polaritons

We consider the possible phases of microcavity polaritons tuned near a bipolariton Feshbach resonance. We show that, as well as the regular polariton superfluid phase, a "molecular" superfluid exists, with (quasi-)long-range order only for pairs of polaritons. We describe the experimental signatures of this state. Using variational approaches we find the phase diagram (critical temperature, density and exciton-photon detuning). Unlike ultracold atoms, the molecular superfluid is not inherently unstable, and our phase diagram suggests it is attainable in current experiments.Comment: paper (4 pages, 3 figures), Supplemental Material (7 pages, 8 figures

Universality in modelling non-equilibrium pattern formation in polariton condensates

The key to understanding the universal behaviour of systems driven away from equilibrium lies in the common description obtained when particular microscopic models are reduced to order parameter equations. Universal order parameter equations written for complex matter fields are widely used to describe systems as different as Bose-Einstein condensates of ultra cold atomic gases, thermal convection, nematic liquid crystals, lasers and other nonlinear systems. Exciton-polariton condensates recently realised in semiconductor microcavities are pattern forming systems that lie somewhere between equilibrium Bose-Einstein condensates and lasers. Because of the imperfect confinement of the photon component, exciton-polaritons have a finite lifetime, and have to be continuously re-populated. As photon confinement improves, the system more closely approximates an equilibrium system. In this chapter we review a number of universal equations which describe various regimes of the dynamics of exciton-polariton condensates: the Gross-Pitaevskii equation, which models weakly interacting equilibrium condensates, the complex Ginsburg-Landau equation---the universal equation that describes the behaviour of systems in the vicinity of a symmetry--breaking instability, and the complex Swift-Hohenberg equation that in comparison with the complex Ginsburg-Landau equation contains additional nonlocal terms responsible for spacial mode selection. All these equations can be derived asymptotically from a generic laser model given by Maxwell-Bloch equations. Such an universal framework allows the unified treatment of various systems and continuously cross from one system to another. We discuss the relevance of these equations, and their consequences for pattern formation.Comment: 19 pages; Chapter to appear in Springer&Verlag book on "Quantum Fluids: hot-topics and new trends" eds. A. Bramati and M. Modugn

Exact and approximate moment closures for non-Markovian network epidemics

Moment-closure techniques are commonly used to generate low-dimensional deterministic models to approximate the average dynamics of stochastic systems on networks. The quality of such closures is usually difficult to asses and the relationship between model assumptions and closure accuracy are often difficult, if not impossible, to quantify. Here we carefully examine some commonly used moment closures, in particular a new one based on the concept of maximum entropy, for approximating the spread of epidemics on networks by reconstructing the probability distributions over triplets based on those over pairs. We consider various models (SI, SIR, SEIR and Reed-Frost-type) under Markovian and non-Markovian assumption characterising the latent and infectious periods. We initially study two special networks, namely the open triplet and closed triangle, for which we can obtain analytical results. We then explore numerically the exactness of moment closures for a wide range of larger motifs, thus gaining understanding of the factors that introduce errors in the approximations, in particular the presence of a random duration of the infectious period and the presence of overlapping triangles in a network. We also derive a simpler and more intuitive proof than previously available concerning the known result that pair-based moment closure is exact for the Markovian SIR model on tree-like networks under pure initial conditions. We also extend such a result to all infectious models, Markovian and non-Markovian, in which susceptibles escape infection independently from each infected neighbour and for which infectives cannot regain susceptible status, provided the network is tree-like and initial conditions are pure. This works represent a valuable step in deepening understanding of the assumptions behind moment closure approximations and for putting them on a more rigorous mathematical footing.Comment: Main text (45 pages, 11 figures and 3 tables) + supplementary material (12 pages, 10 figures and 1 table). Accepted for publication in Journal of Theoretical Biology on 27th April 201

Lessons in Failure: The Rice Growers Association Cooperative

This empirical study investigates a large California cooperative's closure and identifies lessons learned that might be useful to other cooperatives. It was found that the cooperative's directors failed to effectively supervise management. In turn, management fell short of expectations to fully evaluate complex business decisions.Agribusiness,

Industry Leaders' Perspectives on Communicating the Cooperative Value Package

Communication, Cooperatives, Value Package, Agribusiness, Q13, P13,

Collective Dynamics of Bose--Einstein Condensates in Optical Cavities

Recent experiments on Bose--Einstein condensates in optical cavities have reported a quantum phase transition to a coherent state of the matter-light system -- superradiance. The time dependent nature of these experiments demands consideration of collective dynamics. Here we establish a rich phase diagram, accessible by quench experiments, with distinct regimes of dynamics separated by non-equilibrium phase transitions. We include the key effects of cavity leakage and the back-reaction of the cavity field on the condensate. Proximity to some of these phase boundaries results in critical slowing down of the decay of many-body oscillations. Notably, this slow decay can be assisted by large cavity losses. Predictions include the frequency of collective oscillations, a variety of multi-phase co-existence regions, and persistent optomechanical oscillations described by a damped driven pendulum. These findings open new directions to study collective dynamics and non-equilibrium phase transitions in matter-light systems.Comment: 5 pages, 5 figure

Quench dynamics of a disordered array of dissipative coupled cavities

We investigate the mean-field dynamics of a system of interacting photons in an array of coupled cavities in presence of dissipation and disorder. We follow the evolution of on an initially prepared Fock state, and show how the interplay between dissipation and disorder affects the coherence properties of the cavity emission and that these properties can be used as signatures of the many-body phase of the whole array.Comment: 8 pages, 10 figures, new reference adde