Optimal control problems with delay, the maximum principle and necessary conditions

In this paper we consider a rather general optimal control problem involving ordinary differential equations with delayed arguments and a set of equality and inequality restrictions on state- and control variables. For this problem a maximum principle is given in pointwise form, using variational techniques. From this maximum principle necessary conditions are derived, as well as a Lagrange-like multiplier rule. Details may be found in ref. [2], together with extensions to the Hamilton-Jacobi equation and free end point problems

Mass Transfer in a closed stirred gas/liquid contactor: Part 1: The mass transfer rate kLS

Liquid phase mass transfer rates kLS for the absorption of oxygen in tap water and in aqueous ionic solutions have been determined in two closed stirred tank contactors for a power input between 3 and 70 W/kg and (impeller diameter)f(tank diameter) ratios DifT of 0.3, 0.35 and 0.4. The contactors had diameters\ud of 0. I9 and 0.6 m. The dispersed phase fraction was 1% by volume in all experiments. The values of kLS were determined using two different techniques:\ud (1) a transient physical absorption method; and (2) the sulphite method

Transmission and quantification of verocytotoxin-producing Escherichia coli O157 in dairy cattle and calves

Data from a field study of 14 months duration in a naturally colonized dairy herd and data from an experiment with calves were used to quantify transmission of verocytotoxin-producing Escherichia coli (VTEC O157) in cattle. For the latter, two groups of 10 calves were randomly assigned and put out in one of two pastures. From each group, five animals were experimentally inoculated with 109 c.f.u. O157 VTEC and, considered infectious, put back in their group. Each of the susceptible contact calves became positive within 6 days of being reunited. The estimate of the basic reproduction ratio (R0) in the experiment was 7·3 (95% CI 3·92¿11·5), indicating that each infectious calf will infect seven other calves on average during an assumed infectious period of 28 days in a fully susceptible population. The R0 among dairy cows appeared to be about 10 times lower (0·70, 95% CI 0·48¿1·04). After the transmission experiment, six contact-infected animals that were shedding continuously during the experiment were housed in a tie stall during winter. After 40 days, all six tested negative for O157 VTEC. In June, after a period of 34 weeks in which the heifers remained negative, they were put out in a clean and isolated pasture to observe whether they started shedding again. On each pasture that was infected with O157 VTEC during the transmission experiment the previous summer, newly purchased susceptible calves were placed. None of the heifers or calves started shedding during 14 weeks, indicating that both the heifers and the previously contaminated pasture did not function as reservoir of O157 VTE

Using simulation to estimate the power of a badger vaccine trial

The aim of this study was to estimate the power of a badger vaccine field trial using simulation techniques. The effects of sample size, sensitivity and specificity of the diagnostic test, transmission rate between unvaccinated badgers, Vaccine Efficacy for Susceptibility (VES) and Vaccine Efficacy for Infectiousness (VEI) on study power were determined. The most striking result was the large effect of the specificity of the diagnostic test on study power. Sample size had a small effect on power. Study power increased with increasing transmission rate between non-vaccinated badgers. Changes in VES had a higher impact on power than changes in VEI. In summary, study power in group randomized trials depends not only on sample size but on many other parameters. In the current vaccine trial, power was highly dependent on the specificity of the diagnostic test. Therefore, it is critical that the diagnostic test used in the badger vaccine trial is optimized to maximise test specificity

On “Morality and Sex Change”

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90516/1/3561812.pd

Rental externality, tenure security, and housing quality

This paper considers two tenure modes—owner- and renter-occupied housing—and models the effect of the rental externality and tenure security on single-family housing quality. We show that both rental externality and tenure security reduce renter-occupied housing quality when the user’s utilization, which reduces the quality of the accommodation, and the owner’s maintenance, which raises quality, are substitutes. Using singlefamily housing data in Japan, we obtain empirical results that are consistent with theoretical predictions. These results indicate that conventional wisdom—that the quality of renter-occupied housing is lower than that of owner-occupied housing—is supported for single-family housing in Japan