Advanced control concepts

The problems of excess control devices and insufficient trim control capability on shuttle ascent vehicles were investigated. The trim problem is solved at all time points of interest using Lagrangian multipliers and a Simplex based iterative algorithm developed as a result of the study. This algorithm has the capability to solve any bounded linear problem with physically realizable constraints, and to minimize any piecewise differentiable cost function. Both solution methods also automatically distribute the command torques to the control devices. It is shown that trim requirements are unrealizable if only the orbiter engines and the aerodynamic surfaces are used

Simian immunodeficiency virus infection in wild-caught chimpanzees from Cameroon

Simian immunodeficiency viruses (SIVcpz) infecting chimpanzees (Pan troglodytes) in west central Africa are the closest relatives to all major variants of human immunodeficiency virus type 1 ([HIV-1]; groups M, N and O), and have thus been implicated as the source of the human infections; however, information concerning the prevalence, geographic distribution, and subspecies association of SIVcpz still remains limited. In this study, we tested 71 wild-caught chimpanzees from Cameroon for evidence of SIVcpz infection. Thirty-nine of these were of the central subspecies (Pan troglodytes troglodytes), and 32 were of the Nigerian subspecies (Pan troglodytes vellerosus), as determined by mitochondrial DNA analysis. Serological analysis determined that one P. t. troglodytes ape (CAM13) harbored serum antibodies that cross-reacted strongly with HIV-1 antigens; all other apes were seronegative. To characterize the newly identified virus, 14 partially overlapping viral fragments were amplified from fecal virion RNA and concatenated to yield a complete SIVcpz genome (9,284 bp). Phylogenetic analyses revealed that SIVcpzCAM13 fell well within the radiation of the SIVcpzPtt group of viruses, as part of a clade including all other SIVcpzPtt strains as well as HIV-1 groups M and N. However, SIVcpzCAM13 clustered most closely with SIVcpzGAB1 from Gabon rather than with SIVcpzCAM3 and SIVcpzCAM5 from Cameroon, indicating the existence of divergent SIVcpzPtt lineages within the same geographic region. These data, together with evidence of recombination among ancestral SIVcpzPtt lineages, indicate long-standing endemic infection of central chimpanzees and reaffirm a west central African origin of HIV-1. Whether P. t. vellerosus apes are naturally infected with SIVcpz requires further study

Option value: improving resource allocation efficiency

Measuring consumer benefits associated with a policy or a project in a world where prices and outcomes are known with certainty is, at least in theory, straightforward. Changes in consumer surplus provide an appropriate measure of a policy's contribution to consumer welfare. But, in a world where prices and outcomes are uncertain, there is a strong case for concluding that measuring expected consumer surplus alone is inadequate (Bishop, 1982), and in many natural resource situations, uncertainty is the rule rather than the exception. Option value is the adjustment, if any, that is made to expected consumer surplus when there is uncertainty about the demand or supply of an environmental asset. The concept of option value is based on Weisbrod's (1964) argument that consumers, uncertain about their future demands for a commodity, would be willing to pay something above expected consumer surplus to maintain an option to consume the commodity in the future. As we have noted, this additional ""payment"" is option value. While Weisbrod's argument suggests that option value is positive, this need not be the case. A variety of authors have proven that option value can take either sign, depending on the specific circumstances, and especially on the type of uncertainty involved. We begin with an overview of the origin of option value in economics and its relevance to decision making under uncertainty. The next chapter considers compensation tests and identifies an ex ante compensation test as being appropriate for uncertain situations. Option value is then located within a total value framework that includes use values and existence values. Uncertainty in both demand and supply is then shown to provide justification for considering option value as an adjustment that individuals make to allow for uncertainty. However, we will show that there are few situations where the sign of option value can be unambiguously established in theory. The final chapters of the publication describe how option value can be measured and incorporated into cost-benefit analysis.This research was supported by a grant from the Foundation for Research Science and Technology, It constitutes Project 2 in the Centre for Resource Management's research programme for 1990/91

Distinguishing between similar tubular objects using pulse reflectometry:a study of trumpet and cornet leadpipes

This paper considers the measurement of the internal radius of a number of similar, short, tubular leadpipes using pulse reflectometry. Pulse reflectometry is an acoustical technique for measuring the internal bore of a tubular object by analysing the reflections which occur when an acoustical pulse is directed into the object. The leadpipes are designed to form the initial, or lead, part of a trumpet or cornet and their internal radii differ by less than 0.1 mm between similar pipes. The ability of the reflectometer to detect these small differences, which are considered by players to produce a noticeable difference in the sound of an instrument, are investigated. It is seen that the pulse reflectometer is able to distinguish between leadpipes with different nominal radii varying by as little as 0.03 mm, demonstrating its potential in the study of musical instruments and showing that it can be used as a diagnostic tool by the instrument manufacturer to detect defects which are significant enough to acoustically alter performance. The absolute accuracy of the radius measurements is also considered at the end of the leadpipe, where the uncertainty is ±0.05 mm

Economic benefits of Mt. Cook National Park

Market and non-market valued decisions are associated with New Zealand's system of national parks. The use benefits of Mount Cook National Park are not priced by the market mechanism, whereas many of the inputs necessary to operate and maintain the Park are priced. Estimates of the economic benefits are relevant information when deciding upon the allocation of resources to, and within, a system of national parks. In 1984, the consumers' surplus for adult New Zealand visitors was about $2.2 million. An estimate of the net national benefits is given by the consumers' surplus obtained by New Zealand visitors, plus the net benefits associated with foreign visitors, less the cost of Park management and land rental. The net benefit of Mount Cook National Park, as it was in 1984, is likely to be positive, indicating that the benefits associated with the current use pattern of resources exceeds their opportunity cost to the nation. However, this result cannot be used to establish the optimality of current expenditure and management. Approximately 170,000 adults visited Mount Cook National Park over 1984; 29$58. These expenditures give rise to secondary economic benefits and create opportunities for regional development. Visitor expenditures in the Mackenzie Basin area are associated with $13.4 million of additional regional output,$6.8 million of additional regional income, and 196 jobs. These effects derive their significance from regional objectives; they are not indicators of the national benefits associated with Mount Cook National Park

\epsilon-regularity for systems involving non-local, antisymmetric operators

We prove an epsilon-regularity theorem for critical and super-critical systems with a non-local antisymmetric operator on the right-hand side. These systems contain as special cases, Euler-Lagrange equations of conformally invariant variational functionals as Rivi\`ere treated them, and also Euler-Lagrange equations of fractional harmonic maps introduced by Da Lio-Rivi\`ere. In particular, the arguments presented here give new and uniform proofs of the regularity results by Rivi\`ere, Rivi\`ere-Struwe, Da-Lio-Rivi\`ere, and also the integrability results by Sharp-Topping and Sharp, not discriminating between the classical local, and the non-local situations

Is there a credibility crisis in strategic management research? Evidence on the reproducibility of study findings

Recent studies report an inability to replicate previously published research, leading some to suggest that scientific knowledge is facing a credibility crisis. In this essay, we provide evidence on whether strategic management research may itself be vulnerable to these concerns. We conducted a study whereby we attempted to reproduce the empirical findings of 88 articles appearing in the Strategic Management Journal using data reported in the articles themselves. About 70% of the studies did not disclose enough data to permit independent tests of reproducibility of their findings. Of those that could be retested, almost one-third reported hypotheses as statistically significant which were no longer so and far more significant results were found to be non-significant in the reproductions than in the opposite direction. Collectively, incomplete reporting practices, disclosure errors, and possible opportunism limit the reproducibility of most studies. Until disclosure standards and requirements change to include more complete reporting and facilitate tests of reproducibility, the strategic management field appears vulnerable to a credibility crisis