Michal Smetana: Nuclear Deviance. Stigma Politics and the Rules of the Nonproliferation Game.

This book examines the linkage between deviance and norm change in international politics. It draws on an original theoretical perspective grounded in the sociology of deviance to study the violations of norms and rules in the global nuclear non-proliferation regime. As such, this project provides a unique conceptual framework and applies it to highly salient issues in the contemporary international security environment. The theoretical/conceptual chapters are accompanied by three extensive case. studies: Iran, North Korea, and Indi

A computational study of using black-box QR solvers for large-scale sparse-dense linear least squares problems

Large-scale overdetermined linear least squares problems arise in many practical applications. One popular solution method is based on the backward stable QR factorization of the system matrix A . This article focuses on sparse-dense least squares problems in which A is sparse except from a small number of rows that are considered dense. For large-scale problems, the direct application of a QR solver either fails because of insufficient memory or is unacceptably slow. We study several solution approaches based on using a sparse QR solver without modification, focussing on the case that the sparse part of A is rank deficient. We discuss partial matrix stretching and regularization and propose extending the augmented system formulation with iterative refinement for sparse problems to sparse-dense problems, optionally incorporating multi-precision arithmetic. In summary, our computational study shows that, before applying a black-box QR factorization, a check should be made for rows that are classified as dense and, if such rows are identified, then A should be split into sparse and dense blocks; a number of ways to use a black-box QR factorization to exploit this splitting are possible, with no single method found to be the best in all cases

Dual variable methods for mixed-hybrid finite element approximation of the potential fluid flow problem in porous media

Mixed-hybrid finite element discretization of Darcy's law and the continuity equation that describe the potential fluid flow problem in porous media leads to symmetric indefinite saddle-point problems. In this paper we consider solution techniques based on the computation of a null-space basis of the whole or of a part of the left lower off-diagonal block in the system matrix and on the subsequent iterative solution of a projected system. This approach is mainly motivated by the need to solve a sequence of such systems with the same mesh but different material properties. A fundamental cycle null-space basis of the whole off-diagonal block is constructed using the spanning tree of an associated graph. It is shown that such a basis may be theoretically rather ill-conditioned. Alternatively, the orthogonal null-space basis of the sub-block used to enforce continuity over faces can be easily constructed. In the former case, the resulting projected system is symmetric positive definite and so the conjugate gradient method can be applied. The projected system in the latter case remains indefinite and the preconditioned minimal residual method (or the smoothed conjugate gradient method) should be used. The theoretical rate of convergence for both algorithms is discussed and their efficiency is compared in numerical experiments. Copyright © 2006, Kent State University

Actively controlled journal bearing enabling to expand limits of stability

The lecture deals with the stability of the movement of the journal inside the hydrodynamic plain bearings, which limits the operating rotational speed. The purpose of active vibration control using piezoactuators is to increase the limit of the rotor stable rotation speed and control the journal position. Besides theory it will be presented the results of testing the first prototype of this type of the bearings

Sparse stretching for solving sparse-dense linear least-squares problems

Large-scale linear least-squares problems arise in a wide range of practical applications. In some cases, the system matrix contains a small number of dense rows. These make the problem significantly harder to solve because their presence limits the direct applicability of sparse matrix techniques. In particular, the normal matrix is (close to) dense, so that forming it is impractical. One way to help overcome the dense row problem is to employ matrix stretching. Stretching is a sparse matrix technique that improves sparsity by making the least-squares problem larger. We show that standard stretching can still result in the normal matrix for the stretched problem having an unacceptably large amount of fill. This motivates us to propose a new sparse stretching strategy that performs the stretching so as to limit the fill in the normal matrix and its Cholesky factor. Numerical examples from real problems are used to illustrate the potential gains

SIMULATION STUDY OF THE NON-COLLOCATED CONTROL OF A CANTILEVER BEAM

This article deals with the simulation of the active vibration control of a cantilever beam. For these purposes, a lumped parameter model has been developed and the simplest controller has been designed to ensure the structural stability of the control loop. The controller is of a proportional velocity feedback type. The control loop can also be stable in the case of a very small inherent damping of the cantilever beam. The lumped-parameter model is based on the Euler-Bernoulli beam theory. The developed tools can be used to simulate the collocated and non-collocated active vibration control. Since this article is intended to study the behaviour of a non-collocated control system of the transducer is sensing the vibration of the free end of the beam, while the actuator force acts near the fixed end

Solving mixed sparse-dense linear least-squares problems by preconditioned iterative methods

The efficient solution of large linear least-squares problems in which the system matrix A contains rows with very different densities is challenging. Previous work has focused on direct methods for problems in which A has a few relatively dense rows. These rows are initially ignored, a factorization of the sparse part is computed using a sparse direct solver, and then the solution is updated to take account of the omitted dense rows. In some practical applications the number of dense rows can be significant and for very large problems, using a direct solver may not be feasible. We propose processing rows that are identified as dense separately within a conjugate gradient method using an incomplete factorization preconditioner combined with the factorization of a dense matrix of size equal to the number of dense rows. Numerical experiments on large-scale problems from real applications are used to illustrate the effectiveness of our approach. The results demonstrate that we can efficiently solve problems that could not be solved by a preconditioned conjugate gradient method without exploiting the dense rows

Actively Controlled Journal Bearings for Machine Tools

The advantage of journal hydrodynamic bearings is high radial load capacity and operation at high speeds. The disadvantage is the excitation of vibrations, called an oil whirl, after crossing a certain threshold of the rotational speed which depends on the radial bearing clearance, the viscosity of lubricating oil, and the rotor mass. A passive way of how to suppress vibrations consists of adjusting the shape of the bearing bushing. Vibrations can be suppressed using the system of active vibration damping with piezoactuators to move the bearing bushing in two directions. The displacement of the bearing bushing is actuated by two piezoactuators, which respond to the position of the bearing journal relative to the bearing housing. Two stacked linear piezoactuators are used to actuate the location of the bearing bushing. A pair of capacitive sensors senses the position of the journal or shaft. The system of the actively controlled journal bearings is the first functional prototype in the known up to now. It works with a cylindrical bushing which does not require special technology of manufacturing and assembly. This new bearing enables not only to damp vibrations but also serves to maintain the desired bearing journal position with an accuracy of micrometers