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

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

"Dynamic equilibrium in a competitive credit market: Intertemporal contracting as insurance against rationing" (Appendix)

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

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

Market Discipline in Conglomerate Banks: Is an Internal Allocation of Cost of Capital Necessary as an Incentive Device?

This paper analyzes the optimal conglomeration of bank activities. We show that incentive problems in banking sometimes dictate integration of activities, but with perfect market discipline always push us away from integration/conglomeration. Ineffective market discipline could make conglomeration optimal, even if conglomeration further undermines market discipline. We also show that an internal allocation of the cost of capital could add effective `internal' discipline and improve on the outcome of conglomeration. The analysis is subsequently applied to the Barings debacle. This paper was presented at the Financial Institutions Center's October 1996 conference on "

Effect of compaction pressure on consolidation behaviour of unsaturated silty soil

The effect of compaction pressure on subsequent soil behaviour during isotropic consolidation has been investigated by conducting controlled-suction triaxial tests on samples of an unsaturated compacted silty soil. A comprehensive set of laboratory experiments was carried out in a double-walled triaxial apparatus on samples of unsaturated soil that were prepared using two different compaction pressures. The axis translation technique was used for creating the desired suctions in the samples. In the experiments, the soil samples were subjected to isotropic consolidation under constant suctions. The results show that different compaction pressures produce different fabrics in a soil and therefore affect the behaviour of the soil. The results also show that the value of yield stress and the location of the loading¿collapse (LC) yield curve are functions of soil fabric. Furthermore, it is shown that the slopes of normal consolidation lines for densely and loosely compacted samples differ in unsaturated conditions but are the same in saturated soils. A comparison is made between the behaviour of the dense and loose samples, and the difference in the behaviour is explained

Competition, risk neutrality and loan commitments

Credit;monetary economics