Design of cylindrical plastic pipe linings to resist buckling due to collapse pressures

Flexible (non-bonded) polymeric sewer linings are used extensively to renovate both gravity and pressure pipes. Linings for both types of pipe are subject to collapse pressures, and in the case of gravity pipes this is the dominant source of loading; the efficient design of linings to sustain collapse pressures is therefore an important problem. In this paper, the buckling of an ideal thinwalled elastic lining in a rigid cylindrical cavity is first presented as a simple closed form solution, and The effect of a representative small imperfection shown to be significant. The different types of imperfection that can be encountered in practical lined pipe systems are identified, and the situations in which each can arise are discussed. A generalised procedure for obtaining the structural imperfections in, and hence buckling capacities of, practical systems is then presented and two example applications are used to illustrate its application in specific situations

Objectivity, Proximity and Adaptability in Corporate Governance

Countries appear to differ considerably in the basic orientations of their corporate governance structures. We postulate the trade-off between objectivity and proximity as fundamental to the corporate governance debate. We stress the value of objectivity that comes with distance (e.g. the market oriented U.S. system), and the value of better information that comes with proximity (e.g. the more intrusive Continental European model). Our key result is that the optimal distance between management and monitor (board or shareholders) has a bang-bang solution: either one should capitalize on the better information that comes with proximity or one should seek to benefit optimally from the objectivity that comes with distance. We argue that this result points at an important link between the optimal corporate governance arrangement and industry structure. In this context, we also discuss the ways in which investors have "contracted around" the flaws in their own corporate governance systems, pointing at the adaptability of different arrangements.http://deepblue.lib.umich.edu/bitstream/2027.42/39651/3/wp266.pd

Getting more than a fair share: nutrition of worker larvae related to social parasitism in the Cape honey bee Apis mellifera capensis

Besides activation of ovaries and thelytokous reproduction of Cape workers, larval nutrition is an important aspect in parasitism of the African honey bee. When reared by workers of other subspecies, Cape larvae receive more food which is slightly more royal jelly-like. This results in worker-queen intermediates, with reduced pollen combs, enlarged spermathecae and higher numbers of ovarioles. The intermediates weigh more and develop faster than normal workers. The appearance of worker-queen intermediates probably affects parasitism of the African honey bee colonies by Cape workers. Different levels of larval nutrition resulting in less distinct caste differentiation may be important for the reproductive success of Cape workers in their own colonies. Similar processes, albeit less pronounced, may occur in colonies of other subspecies

Incommensurability and its Implications for Practical Reasoning, Ethics and Justice

If values conflict and rival human interests clash we often have to weigh them against each other. However, under particular conditions incommensurability prevents the assignment of determinable and impartial weights. In those cases an objective balance does not exist. The original thesis of this book sheds new light on aspects of incommensurability and its implications for public decision-making, ethics and justice. Martijn Boot analyzes a number of previously ignored or unrecognized concepts, such as ‘incomplete comparability’, ‘incompletely justified choice’, ‘indeterminateness’ and ‘ethical deficit’ – concepts that are essential for comprehending problems of incommensurability. Apart from problematic implications, incommensurability has also favourable consequences. It creates room for autonomous rational choices that are not dictated by reason. Besides, insight into incommensurability promotes recognition of different possible rankings of universally valid but sometimes conflicting human values. This book avoids unnecessary technical language and is accessible not only for specialists but for a large audience of philosophers, ethicists, political theorists, economists, lawyers and interested persons without specialized knowledge. Reviews This book is a rigorous treatment of a major question: Can there be rational decisions between options having incommensurable values? Challenging the view that incommensurability does not preclude rational choice, Boot details obstacles to choices between incommensurables and indicates how practical reasoning should accommodate them. In doing this he says much of value about justice, healthcare, punishment, and other major topics. – Robert Audi, John A. O'Brien Professor of Philosophy, University of Notre Dame It is hard to think of a more important practical question than whether there are irresoluble conflicts between values. Philosophers in recent years have made major advances in clarifying that question and developing answers to it, but their work is often technical. Martijn Boot is technically adept, but in this highly significant book makes his arguments in clear and engaging prose. He brings out the implications of incommensurability in various areas, as well as taking the debate forward on several fronts. – Roger Crisp, Professor of Moral Philosophy, St Anne's College, Oxfor

The Aim of a Theory of Justice

Amartya Sen argues that for the advancement of justice identification of ‘perfect’ justice is neither necessary nor sufficient. He replaces ‘perfect’ justice with comparative justice. Comparative justice limits itself to comparing social states with respect to degrees of justice. Sen’s central thesis is that identifying ‘perfect’ justice and comparing imperfect social states are ‘analytically disjoined’. This essay refutes Sen’s thesis by demonstrating that to be able to make adequate comparisons we need to identify and integrate criteria of comparison. This is precisely the aim of a theory of justice (such as John Rawls’s theory): identifying, integrating and ordering relevant principles of justice. The same integrated criteria that determine ‘perfect’ justice are needed to be able to adequately compare imperfect social states. Sen’s alternative approach, which is based on social choice theory, is incapable of avoiding contrary, indeterminate or incoherent directives where plural principles of justice conflict

All-optical three-dimensional electron pulse compression

We propose an all-optical, three-dimensional electron pulse compression scheme in which Hermite-Gaussian optical modes are used to fashion a three-dimensional optical trap in the electron pulse's rest frame. We show that the correct choices of optical incidence angles are necessary for optimal compression. We obtain analytical expressions for the net impulse imparted by Hermite-Gaussian free-space modes of arbitrary order. Although we focus on electrons, our theory applies to any charged particle and any particle with non-zero polarizability in the Rayleigh regime. We verify our theory numerically using exact solutions to Maxwell's equations for first-order Hermite-Gaussian beams, demonstrating single-electron pulse compression factors of $>10^{2}$ in both longitudinal and transverse dimensions with experimentally realizable optical pulses. The proposed scheme is useful in ultrafast electron imaging for both single- and multi-electron pulse compression, and as a means of circumventing temporal distortions in magnetic lenses when focusing ultrashort electron pulses.Comment: 21 pages, 7 figure

Dynamic equilibrium in a competitive credit market: Intertemporal contracting as insurance against rationing

Credit Markets;monetary economics

Credit Ratings as Coordination Mechanisms

In this paper, we provide a novel rationale for credit ratings. The rationale that we propose is that credit ratings can serve as a coordinating mechanism in situations where multiple equilibria can obtain. We show that credit ratings provide a "focal point" for firms and their investors. We explore the vital, but previously overlooked implicit contractual relationship between a credit rating agency and a firm. Credit ratings can help fix the desired equilibrium and as such play an economically meaningful role. Our model provides several empirical predictions and insights regarding the expected price impact of ratings changes, the discreteness in funding cost changes, and the effect of the focus of organizations on the efficacy of credit ratings.http://deepblue.lib.umich.edu/bitstream/2027.42/39841/3/wp457.pd