62 research outputs found

    Block-iterative projection methods for parallel computation of solutions to convex feasibility problems

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    AbstractAn iterative method is proposed for solving convex feasibility problems. Each iteration is a convex combination of projections onto the given convex sets where the weights of the combination may vary from step to step. It is shown that any sequence of iterations generated by the algorithm converges if the intersection of the given family of convex sets is nonempty and that the limit point of the sequence belongs to this intersection under mild conditions on the sequence of weight functions. Special cases are block-iterative processes where in each iterative step a certain subfamily of the given family of convex sets is used. In particular, a block-iterative version of the Agmon-Motzkin-Schoenberg relaxation method for solving systems of linear inequalities is derived. Such processes lend themselves to parallel implementation and will be useful in various areas of applications, including image reconstruction from projections, image restoration, and other fully discretized inversion problems

    Convergence and Perturbation Resilience of Dynamic String-Averaging Projection Methods

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    We consider the convex feasibility problem (CFP) in Hilbert space and concentrate on the study of string-averaging projection (SAP) methods for the CFP, analyzing their convergence and their perturbation resilience. In the past, SAP methods were formulated with a single predetermined set of strings and a single predetermined set of weights. Here we extend the scope of the family of SAP methods to allow iteration-index-dependent variable strings and weights and term such methods dynamic string-averaging projection (DSAP) methods. The bounded perturbation resilience of DSAP methods is relevant and important for their possible use in the framework of the recently developed superiorization heuristic methodology for constrained minimization problems.Comment: Computational Optimization and Applications, accepted for publicatio

    T Cells Specifically Targeted to Amyloid Plaques Enhance Plaque Clearance in a Mouse Model of Alzheimer's Disease

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    Patients with Alzheimer's disease (AD) exhibit substantial accumulation of amyloid-β (Aβ) plaques in the brain. Here, we examine whether Aβ vaccination can facilitate the migration of T lymphocytes to specifically target Aβ plaques and consequently enhance their removal. Using a new mouse model of AD, we show that immunization with Aβ, but not with the encephalitogenic proteolipid protein (PLP), results in the accumulation of T cells at Aβ plaques in the brain. Although both Aβ-reactive and PLP-reactive T cells have a similar phenotype of Th1 cells secreting primarily IFN-γ, the encephalitogenic T cells penetrated the spinal cord and caused experimental autoimmune encephalomyelitis (EAE), whereas Aβ T cells accumulated primarily at Aβ plaques in the brain but not the spinal cord and induced almost complete clearance of Aβ. Furthermore, while a single vaccination with Aβ resulted in upregulation of the phagocytic markers triggering receptors expressed on myeloid cells-2 (TREM2) and signal regulatory protein-β1 (SIRPβ1) in the brain, it caused downregulation of the proinflammatory cytokines TNF-α and IL-6. We thus suggest that Aβ deposits in the hippocampus area prioritize the targeting of Aβ-reactive but not PLP-reactive T cells upon vaccination. The stimulation of Aβ-reactive T cells at sites of Aβ plaques resulted in IFN-γ-induced chemotaxis of leukocytes and therapeutic clearance of Aβ

    The no-risk society

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    vi, 228 p.; 23 cm

    Note---Performance Evaluation of State-Owned Enterprises: A Process Perspective

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    State-Owned Enterprises (SOEs) have become important instruments of social and economic policy in industrialized mixed economies and in developing countries. The use of SOEs as instruments of public policy and the resulting clashes between these enterprises and private firms on the one hand and government and other controllers on the other, are causing concern. Public committees in different countries as well as international organizations have been searching for positive theory for guidance in handling the multitude of problems related to these enterprises. Theoretical models have made important contributions to the formalization of certain problems and the classification of the information needed to solve them. Unfortunately, these theoretical models have had little relevance for the solution of important real problems. Much of the research on SOEs is concerned with how these enterprises should behave, and what should be the product of their operations. Almost no research has been done on why SOEs function as they do. The paucity of knowledge about the operation of SOEs stems both from insufficient research effort, and from the concern of researchers with formal structures and products of these organizations and not with management behavior or with decision processes. The purpose of this paper is to call for research beyond the confines of traditional economics, using the tools of management science to obtain insights into the difficult but salient problems of SOEs.state-owned enterprises, performance evaluation, social control

    Performance and Autonomy in Organizations: Determining Dominant Environmental Components

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    The formulation of a strategy for an organization begins with identifying the opportunities and risks in the environment. A full and permanent search--or scanning--of all environmental forces is both too costly and intractable in terms of management time. Our findings indicate that managers do not try to identify all environmental forces. Identifying the dominant components of the environment focuses scanning efforts and saves energy and costs. Furthermore, our findings clearly point out that achievement of autonomy may be advanced by organizational performance. An optimal strategy for a manager seeking to increase autonomy would be to concentrate efforts on dominant environmental components. A spillover effect will generalize this autonomy.
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