Stability, vibration and passive damping of partially restrained imperfect columns

A theoretical and experimental study of slender tubular columns for possible use in space structures is conducted in the presence of partial rotational end restraints. Explicit formulas are derived for computing the buckling load and the lowest natural frequency of perfectly straight uniform elastic members with rotational end restraints possessing linear moment-rotation characteristics. An exact solution in the form of a transcendental equation, and a numerical solution using second-order finite-differences are also presented. The presence of an initial imperfection is also incorporated into the numerical procedure. Vibration tests are conducted on an imperfect tubular steel member in the absence of an axial load. A damping concept consisting of a string-mass assembly is explored. Three passive damping configurations involving combinations of three lead shots were investigated. The three lead shot configurations provided considerably greater damping than the single lead shot

Experimental and analytical study of an inlet forebody for an airframe-integrated scramjet concept

Preliminary analytical and experimental inlet forebody investigations have been conducted at Mach numbers of 6.0 and 8.5. The forebody design concept consisted of a sharp-nosed right circular cone followed by elliptical cross sections. This concept resulted in swept isentropic compression which would allow swept cowl leading edges. Measurements were made to define the condition of the inviscid flow field developed by the forebody, including flow profiles in the vicinity of cowl leading-edge stations, and the three-dimensional boundary-layer effects. The investigation verified some of the expected differences between the predicted and the experimental results

Induction of Spawning in the Tropical Walking Catfish (Clarias Batrachus) by Controlling Water Level and Temperature

This experiment was carried out to confirm the role of water level and water temperature in inducing the spawning of tropical walking catfish. Mature males and females reared under 23 - 25 °C, were paired and induced to spawn by controlling water level and water temperature. Decreasing water level and returning it to its original level resulted in a low spawning rate (less than 6.7 %) at 23 °C. Decreasing water level with simultaneous increase in water temperature, followed by returning the respective levels to their originals gave high spawning rates (41.7 — 50 %); whereas the same treatment but without any water temperature decreased when the water level was returned to the initial level, gave a low spawning rate (16.7 %). Increasing water level only, failed to induce spawning. A high spawning rate was obtained also when changes in water level were carried out under high temperature of 28 °C. No fish spawned in the absence of the environmental stimulation. From the results, it is confirmed that water level and temperature play important roles in inducing spawning of tropical walking catfish. Changes in water temperature probably increase the sensitivity of fish to the change in water level. Prolonged exposure to high water temperature could also improve the sensitivity of fish

Wealth effects of supervisory goodwill litigation: A portfolio approach

Using a unique set of publicly-traded litigation certificates, we measure the wealth effects of (largely) unanticipated damage awards in the ongoing supervisory goodwill litigation between thrifts and the federal government. Estimating abnormal returns for portfolios of litigation certificates and retained supervisory goodwill claims, we find that the estimated net wealth effect of four litigation-related events between October 1998 and April 1999 was roughly twice as large for the portfolio of publicly-traded litigation certificates as for the portfolio of retained litigation claims. This disparity is puzzling given that the aggregate amount of supervisory goodwill in each portfolio was roughly equivalent. This study provides some evidence that financial markets do not always value assets and liability retained within firms efficiently

Towards a Semantic Gas Source Localization under Uncertainty

Towards a Semantic Gas Source Localization under Uncertainty.Communications in Computer and Information Science book series (CCIS, volume 855), doi:10.1007/978-3-319-91479-4_42This work addresses the problem of efficiently and coherently locating a gas source in a domestic environment with a mobile robot, meaning efficiently the coverage of the shortest distance as possible and coherently the consideration of different gas sources explaining the gas presence. The main contribution is the exploitation, for the first time, of semantic relationships between the gases detected and the objects present in the environment to face this challenging issue. Our proposal also takes into account both the uncertainty inherent in the gas classification and object recognition processes. These uncertainties are combined through a probabilistic Bayesian framework to provide a priority-ordered list of (previously observed) objects to check. Moreover the proximity of the different candidates to the current robot location is also considered by a cost function, which output is used for planning the robot inspection path. We have conducted an initial demonstration of the suitability of our gas source localization approach by simulating this task within domestic environments for a variable number of objects, and comparing it with an greedy approach.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech