An experimental study of the properties of surface pressure fluctuations for separating turbulent boundary layers

Noise generated by helicopter and turbomachine rotors is a nuisance that designers would like to predict and to minimize within other design constraints. A key element for the noise calculation procedure is knowledge relating the flowfield structure to the surface pressure fluctuation structure. Surface pressure fluctuation data for zero-pressure-gradient and accelerating turbulent boundary layers were obtained. The zero-pressure-gradient turbulent boundary layers were examined with freestream velocities of 72 and 105 fps. Mean and fluctuation velocity profiles and streamwise velocity spectra and wavespeeds were obtained for momentum thickness Reynolds numbers up to 18000 for the zero-pressure-gradient case and up to 4000 for the favorable-pressure-gradient case. The wall shearing stress was estimated from a Clauser plot of the near wall data. It is clear that turbulent pressure fluctuations are produced by turbulent velocity fluctuations. Detailed simultaneous measurements of all of these fluctuations are needed to determine in more detail the structural relationships between velocity and pressure fields. Although some measurements were made for unseparated flows, none were made for separated flows

Valuation of Biodiversity for Use in New Product Research in a Model of Sequential Search

We develop a model of search in which a researcher chooses the size of sequential batches of samples to test. While earlier work has considered similar questions, the contribution of this paper is to use the search model to place a value on the marginal research opportunity. The valuation of such opportunities may be of little interest or relevance in many of the contexts in which search models are employed, but we apply our analysis to an area of considerable societal interest: the valuation of biological diversity for use in new product research. While data from which to make inferences are limited, we find that, using plausible estimates of relevant parameters, the value of biodiversity in these applications is negligible.

Tariff Liberalization, Wood Trade Flows, and Global Forests

This paper examines the question of the likely effects on global forests of a further reduction in wood products tariffs including both solid wood products and pulp and paper, as has been proposed to the World Trade Organization (WTO) by the Asia Pacific Economic Community (APEC). The tariff reductions would be an extension of the tariff reductions associated with the Uruguay Round (Federal Register 1999). The questions include both how international trade is likely to change in response to further tariff reduction and also the implications for timber harvests and forests generally of such trade liberalization in the various forest regions. The paper finds that the evidence suggests further reductions in tariffs on forest products are likely to generate only very modest increases in worldwide trade and production, and the increased harvest pressures on forests due to tariff reduction should be quite modest. The major countries likely to experience export and production increases are found largely in the northern hemisphere and are likely to be able to facilitate additional harvests with minimal effects on the forests due to the modest nature of the impact, new forest practices laws, new forest set-asides, and movement toward improved practices designed to achieve multifaceted sustainable forestry. Furthermore, there is little reason to expect that tariff reductions will significantly increase harvests from tropical forests. Earlier tariff reductions appear to have had minimal impacts on tropical harvests or exports. Nevertheless, tropical forests will remain under deforestation pressure due to land conversion objectives, commonly to provide additional agricultural lands.

Investments in Biodiversity Prospecting and Incentives for Conservation

There is considerable interest in biodiversity prospecting (the search for valuable new products from natural sources) as a conservation strategy. In an earlier paper, we have argued that the value of the marginal species (and, by extension, the incentives for the conservation of the habitat on which it is found) is small. In this paper, we show that investments in biodiversity prospecting are unlikely to increase incentives for conservation by much. If the value of the marginal species were appreciable, researchers ought already to have made investments to exploit it. If it is not, it is doubtful that additional investments will generate any substantial increase. It is important to be clear about our findings: we are not saying that none of the myriad uses of biodiversity is important. Quite to the contrary, we are saying that if biodiversity is important, more effective strategies for its conservation must be found.

An experimental study of surface pressure fluctuations in a separating turbulent boundary layer

Measurements of streamwise velocity fluctuation and surface pressure fluctuation spectra and wavespeeds are reported for a well-documented separating turbulent boundary layer. Because a portion of the acoustic pressure fluctuations is the same across the nominally two-dimensional turbulent flow, it is possible to decompose two microphone signals and obtain directly the turbulent flow contributions to the surface pressure spectra. The rms surface pressure fluctuation p' and spectra phi(omega) increase through the adverse pressure gradient attached flow region and the detached flow zone and scale on the maximum turbulent shearing stress tau(M); p'/tau(M) increases to the detachment location and decreases downstream due to the rapid movement of the pressure-fluctuation-producing motions away from the wall after the beginning of intermittent backflow. At lower frequencies for the attached flow phi(omega) is approximately omega to the -0.7 while phi(omega) is approximately omega to the -3 at higher frequencies. After the beginning of intermittent backflow, phi(omega) varies with omega at low frequencies and omega to the -3 at high frequencies; farther downstream the lower frequency range varies with omega to the 2.4. The surface pressure fluctuation celerity for the attached flow increases with frequency and agrees with the semi-logarithmic overlap equation of Panton and Linebarger. After the beginning of the separation process, the wavespeed decreases because of the oscillation of the instantaneous wavespeed direction and the streamwise coherence decreases drastically

The Deceptive \u27Right to Know\u27: How Pessimism Rewrote the First Amendment

In the decade of the 1940\u27s, particularly in the years just after World War II, freedom of the press, which had been newly elevated and protected by the Supreme Court in the 1930\u27s, began to suffer the corrosive effects of doubt about the strength of the American political system. Among the devastations of war was the failure of the intellectuals\u27 confidence in the mettle of the American citizenry. By the mid-1960\u27s, one consequence was clear: The first amendment no longer meant that the American press was expected to speak freely; it had begun to mean that much of what the press said had to be responsive to assumptions about those who might receive the communication. The idea of a public right to know had begun to undermine the solid foundations of press freedom. Since 1964, the Court has elevated the idea of a right to know to such an extent that the traditional imperative of a right to speak, developed so extensively by the Supreme Court in the 1930\u27s, can no longer be confidently assumed. Hollow rights have been advanced on behalf of consumers to justify governmental controls on press content. This article shows the origins of this wrongheaded theory of the first amendment in the intellectual ferment of the years immediately after World War II. It examines the evolution of Court thinking in three areas of press law: libel, broadcast regulation, and commercial speech

Density and composition of aquatic oligochaete populations in different farmers' ricefields

La densité et la composition des populations d'oligochetes aquatiques ont été estimées dans 32 rizières des Philippines et mises en relation avec les propriétés physico-chimiques des sols et les quantités d'agrochimiques utilisées. La distribution spatiale des organismes et les stratégies d'échantillonnage ont été déterminées à partir d'un échantillonnage de haute densité effectué dans une rizière de référence. Une faible diversité spécifique des organismes a été mise en évidence. Les espèces dominantes sont #Limnodrilus hoffmeisterii et #Branchiura sowerbii. La distribution spatiale des populations est de type contagieux et les densités varient de 0 à 35000 m-2 (Maximum = 620 kg P.F. ha-1). La densité moyenne des populations montre une corrélation positive avec la teneur en eau du sol, sa teneur en matière organique et la quantité d'engrais azoté épandue. Aucun effet des pesticides n'a pu être mis en évidence. (Résumé d'auteur