Cavity flow past a slender pointed hydrofoil

A slender-body theory for the flow past a slender, pointed hydrofoil held at a small angle of Attack to the flow, with a cavity on the upper surface, has been worked out. The approximate solution valid near the body is seen to be the sum of two components. The first consists of a distribution of two-dimensional sources located along the centroid line of the cavity to represent the variation of the cross-sectional area of the cavity. The second component represents the crossflow perpendicular to the centroid line. It is found that over the cavity boundary which envelops a constant pressure region, the magnitude of the cross-flow velocity is not constant, but varies to a moderate extent. With this variation neglected only in the neighbourhood of the hydrofoil, the cross-flow is solved by adopting the Riabouchinsky model for the two-dimensional flow. The lift is then calculated by integrating the pressure along the chord; the dependence of the lift on cavitation number and angle of attack is shown for a specific case of the triangular plan form

Oblique Long Waves on Beach and Induced Longshore Current

This study considers the 3D runup of long waves on a uniform beach of constant or variable downward slope that is connected to an open ocean of uniform depth. An inviscid linear long-wave theory is applied to obtain the fundamental solution for a uniform train of sinusoidal waves obliquely incident upon a uniform beach of variable downward slope without wave breaking. For waves at nearly grazing incidence, runup is significant only for the waves in a set of eigenmodes being trapped within the beach at resonance with the exterior ocean waves. Fourier synthesis is employed to analyze a solitary wave and a train of cnoidal waves obliquely incident upon a sloping beach, with the nonlinear and dispersive effects neglected at this stage. Comparison is made between the present theory and the ray theory to ascertain a criterion of validity. The wave-induced longshore current is evaluated by finding the Stokes drift of the fluid particles carried by the momentum of the waves obliquely incident upon a sloping beach. Currents of significant velocities are produced by waves at incidence angles about 45 [degrees] and by grazing waves trapped on the beach. Also explored are the effects of the variable downward slope and curvature of a uniform beach on 3D runup and reflection of long waves

Hydromechanics of low-Reynolds-number flow. Part 5. Motion of a slender torus

In order to elucidate the general Stokes flow characteristics present for slender bodies of finite centre-line curvature the singularity method for Stokes flow has been employed to construct solutions to the flow past a slender torus. The symmetry of the geometry and absence of ends has made a highly accurate analysis possible. The no-slip boundary condition on the body surface is satisfied up to an error term of O(E^2 ln E), where E is the slenderness parameter (ratio of cross-sectional radius to centre-line radius). This degree of accuracy makes it possible to determine the force per unit length experienced by the torus up to a term of O(E^2). A comparison is made between the force coefficients of the slender torus to those of a straight slender body to illustrate the large differences that may occur as a result of the finite centre-line curvature

Lifetime Difference and Endpoint effect in the Inclusive Bottom Hadron Decays

The lifetime differences of bottom hadrons are known to be properly explained within the framework of heavy quark effective field theory(HQEFT) of QCD via the inverse expansion of the dressed heavy quark mass. In general, the spectrum around the endpoint region is not well behaved due to the invalidity of $1/m_Q$ expansion near the endpoint. The curve fitting method is adopted to treat the endpoint behavior. It turns out that the endpoint effects are truly small and the explanation on the lifetime differences in the HQEFT of QCD is then well justified. The inclusion of the endpoint effects makes the prediction on the lifetime differences and the extraction on the CKM matrix element $|V_{cb}|$ more reliable.Comment: 11 pages, Revtex, 10 figures, 6 tables, published versio

THE WELFARE EFFECTS OF BANNING TOURNAMENTS WHEN COMMITMENT IS IMPOSSIBLE: SOME RESULTS FROM THE BROILER SECTOR

We consider the implications of banning tournament contracts and replacing them with fixed performance standard contracts in a multi-period model where the principal cannot commit to future contract parameters. A ban cannot increase total surplus in a static model. In a dynamic model, however, a ban of tournaments can increase total surplus by mitigating the ratchet effect. Calibrating our model to published data from the broiler sector, we find that a ban on use of contemporaneous and lagged relative performance data does not improve total surplus under most circumstances but could increase total surplus in a few instances of low wealth and unitary relative risk aversion. A more enforceable, period-by-period ban is even less likely to be welfare enhancing and does not hinder the principal from redistributing a fixed compensation pool from low ability growers to high ability growers.Livestock Production/Industries,

Do the Selfish Mimic Cooperators? Experimental Evidence from Finitely-Repeated Labor Markets

Experimental studies have consistently shown that cooperative outcomes can emerge even in finitely repeated games. Such outcomes are justified by existing reputation building models, which suggest that cooperative outcomes can be sustained if some subjects have other-regarding preferences. While the existence of other-regarding preferences is typically used to justify experimental outcomes, we are unaware of empirical studies that explicitly examine the interaction between cooperators (those with other-regarding preferences) and selfish subjects in sustaining cooperation. In this paper, we classify subjects as either selfish or cooperative using simple social preference games and then test for behavioral differences between the two types in a finitely-repeated labor market with unenforceable worker effort. Theory predicts, and our data confirms, that (1) selfish players mimic the actions of cooperators when trading partners can track the individual reputation of past partners and (2) selfish and cooperative types act differently when individual reputations cannot be tracked.contracts, relational contracts, implicit contracts, market interaction, experimental economics, repeated transaction, social preferences, reputation, firm latitude, finitely-repeated games

AJAE Appendix: Tournaments, Fairness, and Risk

The material contained herein is supplementary to the article named in the title and published in the American Journal of Agricultural Economics, Volume 88, Number 3, August 2006.Research Methods/ Statistical Methods, Risk and Uncertainty,

AJAE Appendix: Contract Enforcement, Social Efficiency, and Distribution: Some Experimental Evidence

The material contained herein is supplementary to the article named in the title and published in the American Journal of Agricultural Economics, May 2007, Volume 89, Issue 2.Marketing,

Social Preferences and Relational Contracting: An Experimental Investigation

The form and regulation of contracts is of increasing importance to agricultural economists as farmers and agribusinesses increasing rely on contracts rather than markets to acquire inputs and sell outputs. We focus on the differences between the joint and individual surplus achievable under complete versus incomplete or relational contracts, where the latter are contracts that are not verifiable by a third party and must rely upon threat of termination in order to entice mutually satisfactory performance. Using an experimental market similar to Brown, Falk, and Fehr [Brown, M., A. Falk, and E. Fehr. Relational Contracts and the Nature of Market Interactions, Econometrica, 72 (2004):747-780] we replicate the general results found by these authors, including the qualitative findings that complete contracts dominate incomplete contracts in terms of social surplus generated and that incomplete contracts significantly deviate from the minimal levels of social surplus predicted by equilibrium models featuring purely self-interested agents. We extend the Brown, Falk, and Fehr results in a fundamental way: we explicitly link individual outcomes in relational contracts (e.g, surplus, prices, quality) to the nature of subjects' social preferences, which were measured by a separate experimental protocol that was implemented prior to the experimental trading session. We find subjects with other-regarding preferences enter into relational contracts that generate levels of social surplus similar to the surplus generated under complete contracts. Furthermore, subjects with other-regarding preferences tend to locate others with similar preferences and enter into long-term trading relationships that generate these higher surplus levels. We discuss the ramifications of the results for current regulatory efforts aimed at agricultural contracts.Marketing,