Space shuttle active-pogo-suppressor control design using linear quadratic regulator techniques

Two methods of active pogo suppression (stabilization) for the space shuttle vehicle were studied analytically. The basis for both approaches was the linear quadratic regulator, state space technique. The first approach minimized root-mean-square pump inlet pressure by using either fullstate feedback, partial-state feedback, or output feedback with a Kalman filter. The second approach increased the modal damping associated with the critical structural modes by using either full-state feedback or reconstructed state feedback. A number of implementable controls were found by both approaches. The designs were analyzed with respect to sensitivity, complexity, and controller energy requirements, as well as controller performance. Practical controllers resulting from the two design approaches tended to use pressure and flow as feedback variables for the minimum-rms method and structural accelerations or velocities for the modal control method. Both approaches are suitable for the design of active pogo-suppression controllers

An Eulerian Approach to the Analysis of Krause's Consensus Models

Abstract. In this paper we analyze a class of multi-agent consensus dynamical systems inspired by Krause’s original model. As in Krause’s, the basic assumption is the so-called bounded confidence: two agents can influence each other only when their state values are below a given distance threshold R. We study the system under an Eulerian point of view considering (possibly continuous) probability distributions of agents and we present original convergence results. The limit distribution is always necessarily a convex combination of delta functions at least R far apart from each other: in other terms these models are locally aggregating. The Eulerian perspective provides the natural framework for designing a numerical algorithm, by which we obtain several simulations in 1 and 2 dimensions

Stereoscopic Projection in Natural Colors

The projection of pictures on a screen in such a way that they shall show relief, like that given by a stereoscope, has been accomplished by two methods, one of which depends on the use of polarized light, and the other on the use of color-filters. The following is an account of a modification of the latter method, which enables us to see the projected picture in relief, and at the same time in the original colors. A signal lantern is used

The fission yeast FANCM ortholog directs non-crossover recombination during meiosis

Peer reviewedPostprin

On the dependence of the leak-rate of seals on the skewness of the surface height probability distribution

Seals are extremely useful devices to prevent fluid leakage. We present experimental result which show that the leak-rate of seals depend sensitively on the skewness in the height probability distribution. The experimental data are analyzed using the critical-junction theory. We show that using the top-power spectrum result in good agreement between theory and experiment.Comment: 5 pages, 9 figure

Environmental factors influencing incubation constancy and recess frequency in Gadwall (Anas strepera) in the prairie pothole region of North Dakota

I examined nest attendance patterns for 132 Gadwall (Anas strepera) females breeding in the prairie pothole region located in Towner County, North Dakota from May to July 2000 - 2001. Overall, Gadwall had a daily incubation constancy of 76.5 ± 10.8%, and daily recess frequency of 2.2 ± 1.1 with each recess lasting 179.8 ± 133.8 minutes. Unlike other waterfowl species, Gadwall increased incubation constancy and decreased recess frequency as daily high temperature increased and showed no change in constancy with precipitation. Gadwall incubation constancy did not fit the body-size hypothesis, as Gadwall have a lower incubation constancy compared to species smaller in size. This may be because Gadwall have the latest peak clutch initiation of all dabbling ducks, providing the advantage of dense nesting cover and warmer ambient temperature compared to earlier nesting species. Of the 132 females, 19 (14%) delayed nocturnal incubation resulting in a significant difference in incubation constancy (P= 0.001) and recess frequency (P = 0.001) from those that did not delay nocturnal incubation. However, components of the incubation rhythms, after the onset of nocturnal incubation were similar for both groups

The Emergence of Resilience in Disaster Research

The contribution describes the emergence and development of the resilience concept within socio-scientific disaster research. In addition to psychological approaches references are usually made to the ecosystem research of Holling (1973) and succeeding approaches for coupled Social-Ecological Systems (SES). But for disaster research rather the concept of vulnerability is a substantial precursor. Vulnerability research tries to take the naturalness out of so-called natural disasters. It dates back to the 1970ies and has its roots in poverty and famine research as well as Human Ecology (Sen 1982; Chambers/Conway 1991). In the perspective of vulnerability disasters originate from the interaction of natural or societal stressors with local unsafe conditions that are shaped by temporally and spatially distant social processes. Resilience entered the vulnerability paradigm as the capacity of social systems to cope with such perturbations. In the sequel the resilience concept became a distinct concept within disaster research focusing on everyday activities and the factors that prevent disasters or enable to cope with them. From the perspective of social resilience a variety of social practices prior, during and after disasters form adaption to prevent future disasters, situational coping strategies to processes of reconstruction, but also social and cultural interpretative patterns that make collective stress bearable come to the fore. Originating from the vulnerability concept the local potential to influence broader societal processes leading to disasters is addressed within the concept of social resilience