Showing papers by "Virginia Tech published in 1975"

The effects of temperature upon the toxicity of chemicals to aquatic organisms

Abstract: Although rather extensive bibliographies give the impression that there is a vast amount of literature on the effects of temperature on aquatic organisms, when one tries to apply this information to specific interactions, such as the effects of temperature changes on chemical toxicity to aquatic organisms, often very little of the evidence is applicable. Although the most useful information on this relationship has been acquired in laboratory situations even this body of literature (which forms the bulk of this paper) is not adequate to make any scientifically justifiable generalizations. Field data on this relationship is almost non-existent and it is unlikely that much will become available unless specific studies are initiated which are directed toward this end. This is equally true of the laboratory information although it seems more likely that this will be generated as a spinoff from other research activities. In order to develop water quality management programs for steam-electric power plants one should understand the relationship between temperature and the response of aquatic organisms to toxic chemicals. Not only do some power plants discharge chlorine and other similar materials as well as heated waste water but those that discharge the latter only may be located near discharges of toxic chemicals. Since temperature and chemical stress to aquatic organisms are most commonly discussed independently we felt a paper covering this relationship would be useful.

Acoustics of Aircraft Engine-Duct Systems

Abstract: Noise generated in aircraft engines is usually suppressed by acoustically treating the engine ducts. The optimization of this treatment requires an understanding of the transmission and attenuation of the acoustic waves. A critical review is presented of the state of the art regarding methods of determining the transmission and attenuation parameters and the effect on these parameters of (1) acoustic properties of liners, (2) the mean velocity, including uniform and shear profiles and nonparallel flow, (3) axial and transverse temperature gradients, (4) slowly and abruptly varying cross sections, and (5) finite-amplitude waves and nonlinear duct liners.

Application of Optimal Control Theory to Civil Engineering Structures

Abstract: Modern control theory has been successfully applied to control the motions of aerospace vehicles. An exploratory study is made herein to investigate the feasibility of applying such a theory to control the vibration of civil engineering structures under random loadings. It is assumed that random excitations to structures, such as wind loads and earthquakes, can be modeled by passing either a stationary Gaussian white noise or a nonstationary Gaussian shot noise through a filter. The performance index to be minimized consists of the covariances of both the structural responses and the control forces. Under these conditions, the optimal control law is a linear feedback control. The optimal control forces are obtained by solving a matrix Riccati equation. Applications of the optimal control to a multi-degree-of-freedom structure, under stationary wind loads and nonstationary earthquakes, are demonstrated. It is shown that significant reduction in covariances of the structural responses can be achieved by the use of an active control system.

An adaptive state estimation solution to the maneuvering target problem

Abstract: A new approach to tracking a maneuvering target is presented. Modeling the randomly varying target as a semi-Markov process and then incorporating the statistics into the design of an adaptive state estimator produced an estimation scheme that greatly reduced the large bias errors that usually appear when a target makes an unexpected, large-scale maneuver.

The Influence of Motion and Audio Cues on Driver Performance in an Automobile Simulator

Abstract: A highway driving simulator with a computer-generated visual display, physical motion cues of roll, yaw, and lateral translation, and velocity-dependent sound/vibration cues was used to investigate the influence of these cues on driver performance. Forty-eight student subjects were randomly allocated to six experimental groups. Each group of eight subjects experienced a unique combination of the motion and audio cues. The control group received a full simulation condition while each of the remaining five groups performanced with certain combinations of motion and sound deleated. Each driver generated nine minutes of continuous data from which five performance measures were derived. Results indicate that the performance measures of yaw, lateral, and velocity deviation are significantly affected by the deletion of cues. In support of the hypothesis that driver performance is augmented by the addition of motion cues, statistically significant negative correlations were obtained between the number of motion cues present and the measures of yaw and lateral deviation. With respect to motion and audio cues, recommendations are made regarding simulator design criteria.

Estimating the efficacy of a vote

Abstract: The efficacy of a vote by an individual citizen in an election may be defined roughly as the expected effect it has on the outcome of the election. This is a measure of how much that voter contributes to the decision making of the social system in which he is. A number of political scientists have rightly claimed that the efficacy of a vote is small when the electorate is large. We argue here that they have somewhat misdefined an important parameter of the problem and we strengthen their work by means of a Bayesian analysis. Many people derive personal utility from the act of voting quite apart from the efficacy of the vote as such. This analysis depends primarily on the voter's estimate of the probability that his vote will either produce or resolve a tie. The asymptotic form for this probability is quite different from one that has appeared in the literature. The probability is tabulated on the assumption of a beta prior and the problem of choosing the parameters in this distribution is analyzed.

On Estimating the Aboveground Weights of Tree Stands

Abstract: Simulated sampling of nine tree stands was used to compare estimated stand component weights with known weights based on complete harvest. On average, estimates based on regressions of logarithm weight on either logarithm tree diameter or on logarithm (diameter) squared x height overestimated weights of stems, branches, and leaves by approximately 3% when the inherent bias of such regressions was accounted for. Ninety-five percent confidence intervals based on random sampling encompassed the measured stand weights 79%-100% of the time. Similar confidence intervals using stratified random sampling based on tree diameter encompassed the measured stand weights only 44%-98% of the time. The small average bias in estimates of stand weights using logarithmic regressions is of minor importance compared with the variation in estimates among replicated samples. 21 references.

Successful Biocontrol of Musk Thistle by an Introduced Weevil, Rhinocyllus conicus

Abstract: Rhinocyllus conicus FroeL., a thistle head-feeding weevil introduced from France, successfully controlled Carduus nutans L. (musk thistle) at a Virginia release site (Pulaski Co.) 6 yr after the initial release of 100 adults m 1969. Thistle density was reduced by 95%. This is the 1st documented success of musk thistle control by the introduction of R. conicus . In 1974 and 1975, ca. 90% of the thistles were attacked by the weevil; over 10% of the terminal heads were aborted. The unaborted heads produced few viable seeds and only the later-blooming, smaller heads escaped severe infestation. Dispersal was only 1.6 km 3 yr after release, but after 6 yr both eggs and adults were detected 32 km from the original release site.

A Simple Method for Robust Regression

Abstract: Estimates of the parameters of a linear model are usually obtained by the method of ordinary least-squares (OLS), which is sensitive to large values of the additive error term. By dividing the sample into nonoverlapping subsamples and computing the trimmed means of OLS subsample regression coefficients, we obtain a simple, consistent and asymptotically normal initial estimate of the coefficients, which protects the analyst from large values of ∈ i which are often hard to detect using OLS on a model with many regressors. The technique is applied to the calculation of risk parameters in the capital asset pricing model for securities on the N. Y. Stock Exchange.

Metalloprotease from Bacillus thuringiensis

Abstract: Bacillus thuringiensis var. kurstaki was shown to produce an extracellular, metal chelator-sensitive protease during the early stages of sporulation. Protease production in nutrient broth was dependent upon supplementation with Mn2+ or Ca2+. The addition of Ca2+ was required for enzyme stabilization. Protease production occurred in nutrient broth supplemented with 7 × 10-3 M Ca2+, 5 × 10-4 M Mn2+, and 10-3 M Mg2+. The protease had optimum activity in the pH range 6.5 to 7.5. It was inhibited by chelating agents but not by a serine protease inhibitor. The culture supernatant and the partially purified protease lacked esterase activity. Partial purification of the enzyme (92.3 ×) by (NH4)2SO4 fractionation and starch adsorption yielded an enzyme whose molecular weight was estimated to be 37,500 by acrylamide gel-sodium dodecyl sulfate electrophoresis or 40,800 by sucrose density gradient centrifugation. In the presence of Ca2+, the partially purified enzyme retained 78% of its activity after heating at 70 C for 10 min but only 8% of its activity after heating at 80 C for 10 min.

Approximations to the Average Run Length in Cumulative Sum Control Charts

Abstract: An approximation to the average run length for cumulative sum control charts is derived using the analogy between this procedure and the sequential probability ratio test for normal observations. This approximation is also derived by using a Brownian motion approximation to the cumulative sum. The Brownian motion approximation does not require the normality assumption. The analytical expression for the average run length obtained from the approximation is then used to determine the optimal choice of parameters to minimize the average run length at a specified deviation flom control, subject to a fixed average run length when in control.

Selected characteristics, roles, goals, and satisfactions of department chairmen in state and land-grant institutions

Abstract: Chairmen at 38 state and land-grant institutions were found to be involved in three major roles: academic, administrative, and leadership. The academic role consists of duties of student involvement and research activities. Chairmen enjoy this role and report high emphasis on concurrent goals but feel frustrated in terms of time to pursue commensurate activities. The administrative role requires the majority of time and also contains some of the less desirable duties. In addition, administrative goals are seen as over-emphasized. The leadership role involves tasks related to academic personnel and program development. It is a major satisfaction realized by accepting the position of chairman. Developing abilities of faculty members and maintaining academic freedom are the two most important goals in this role. The respondents also made suggestions on changes and development programs which would improve their effectiveness.

Comparative study of Silurian and Recent deposit-fedding bivalve communities

Abstract: Two communities dominated by deposit-feeding bivalves are recognized in Quisset Harbor, Massachusetts. Interference with life position and sediment preconditioning restrict the distribution of some species. The Eel Grass Community, dominated by Nucula proxima, comprises primarily non-siphonate forms which live in fecal-pellet rich, high-water-content, oxygenated sediment. The sediment texture results from active burrowing. This soft, mobile sediment readily clogs the siphons of siphonate bivalves. The Channel Community, dominated by Yoldia limatula, comprises primarily siphonate forms which live in partly compacted, low-water-content muds. Each community is characterized by abundant surface, shallow, and deep feeding species. Competition for food has generated this distinct stratification in feeding depth of the dominant species with each community.Similar competitive relationships, affecting both species occurrence and trophic stratification, are apparent in three Silurian age deposit-feeding bivalve communities from the McAdam Brook Formation of Nova Scotia. A community dominated by four non-siphonate species inhabited soupy, high-water-content muds. A community dominated by three siphonate species lived in cohesive muds. A mixed community, dominated by four species, two non-siphonate and two siphonate species (the most abundant of which are present, but not as the most abundant forms, in the other communities), characterized the mid-way point of the ecotone between the other two communities.These deposit-feeding bivalve dominated communities have similar structural patterns although separated by 400 million years and despite environmental differences and evolutionary changes. Both response to physical factors, such as sediment character, and interspecific competition impose and maintain this type of community structure.

Husband-Wife Influence in Purchase Decisions-A Confirmation and Extension

Abstract: This article provides two kinds of information about the measurement of husband-wife influence in family decision making. First, confirmatory support is given to certain conclusions by Davis [4] in his study of alternative measures of relative spousal influence. Second, the article extends the application of multitrait-multimethod procedures to the stages or phases of the decision process to determine the commonality of perceived influence across spouses and how these phases interrelate. Limited information about ethnic variations in family decision behavior is also presented since only black families were included in the study. METHODOLOGY

Asymptotic analysis of deterministic and stochastic equations with rapidly varying components

Abstract: The asymptotic character of deterministic and stochastic equations whose solutions have a rapidly varying component is studied. Of particular interest is the class of problems for which the limiting behavior can be described in a contracted and simplified framework.

Hypersonic ionizing air viscous shock-layer flows over nonanalytic blunt bodies

Abstract: The equations which govern the viscous shock-layer flow are presented and the method by which the equations are solved is discussed The predictions of the present finite-difference method are compared with other numerical predictions as well as with experimental data The principal emphasis is placed on predictions of the viscous flowfield for the windward plane of symmetry of the space shuttle orbiter and other axisymmetric bodies which approximate the shuttle orbiter geometry Experimental data on two slender sphere-cones at hypersonic conditions are also considered The present predictions agreed well with experimental data and with the past predictions Substantial differences were found between present predictions and more approximate methods

The rationale of periodic markets

Abstract: The origin and persistence of periodic markets are explained in terms of the needs of producers, the traditional organization of time, inertia, and comparative advantage. Producers often wish to buy or sell in the marketplace on only one or two days per week in order not to disrupt their production schedule. The week customarily has days set aside for work, rest, ceremonies, and commerce; such temporal patterns may be ordained by civil or religious authorities. Authorities may fix market days and locations, although the initial stimuli for foundation are usually the development of social stratification, the division of labor, and long-distance trade. Both part-time trading and designation of special days for commerce encourage the foundation of periodic markets. After markets have been established, inertia and comparative advantage maintain periodicity long after daily operations would be economically feasible.