Model reduction for Space Station Freedom

Model reduction is an important practical problem in the control of flexible spacecraft, and a considerable amount of work has been carried out on this topic. Two of the best known methods developed are modal truncation and internal balancing. Modal truncation is simple to implement but can give poor results when the structure possesses clustered natural frequencies, as often occurs in practice. Balancing avoids this problem but has the disadvantages of high computational cost, possible numerical sensitivity problems, and no physical interpretation for the resulting balanced 'modes'. The purpose of this work is to examine the performance of the subsystem balancing technique developed by the investigator when tested on a realistic flexible space structure, in this case a model of the Permanently Manned Configuration (PMC) of Space Station Freedom. This method retains the desirable properties of standard balancing while overcoming the three difficulties listed above. It achieves this by first decomposing the structural model into subsystems of highly correlated modes. Each subsystem is approximately uncorrelated from all others, so balancing them separately and then combining yields comparable results to balancing the entire structure directly. The operation count reduction obtained by the new technique is considerable: a factor of roughly r(exp 2) if the system decomposes into r equal subsystems. Numerical accuracy is also improved significantly, as the matrices being operated on are of reduced dimension, and the modes of the reduced-order model now have a clear physical interpretation; they are, to first order, linear combinations of repeated-frequency modes

Aplicaciones didácticas de la metáfora cognitiva al aprendizaje del inglés para la ciencia y la tecnología

En las últimas décadas, el cognitivismo ha realizado una importante contribución al desarrollo de las competencias comunicativas de los estudiantes de lenguas extranjeras. Por una parte, ha ofrecido un soporte teórico mediante la determinación de los estilos y de las estrategias de aprendizaje para obtener, almacenar y utilizar la información (O´Malley, 1987; Chamot, 1990; O´Malley y Chamot, 1990). Por otra, ha proporcionado pruebas empíricas de que la percepción de la metáfora tiene un efecto positivo en la adquisición de lenguas y facilita el empleo de estrategias de extensión metafórica (Low, 2008; Littlemore, 2004). Este estudio propone un marco teórico para mejorar el proceso de enseñanza/aprendizaje que combina ambos aspectos, ya que asume que la metáfora es un componente fundamental de la cognición que posibilita la integración de conceptos nuevos en campos de conocimiento ya existentes. Por ello, con el propósito de crear recursos didácticos en los que se apliquen estrategias metafóricas, se ha elaborado un listado de metáforas de imagen y de metáforas conceptuales tomadas de la base de datos METACITEC. Se presenta la propuesta metodológica validada por los resultados de encuestas y por la observación en el aula

Space Station flexible dynamics under plume impingement

Assembly of the Space Station requires numerous construction flights by the Space Shuttle. A particularly challenging problem is that of control of each intermediate station configuration when the shuttle orbiter is approaching it to deliver the next component. The necessary braking maneuvers cause orbiter thruster plumes to impinge on the station, especially its solar arrays. This in turn causes both overall attitude errors and excitation of flexible-body vibration modes. These plume loads are predicted to lead to CMG saturation during the approach of the orbiter to the SC-5 station configuration, necessitating the use of the station RCS jets for desaturation. They are also expected to lead to significant excitation of solar array vibrations. It is therefore of great practical importance to investigate the effects of plume loads on the flexible dynamics of station configuration SC-5 as accurately as possible. However, this system possesses a great many flexible modes (89 below 5 rad/s), making analysis time-consuming and complicated. Model reduction techniques can be used to overcome this problem, reducing the system model to one which retains only the significant dynamics, i.e. those which are strongly excited by the control inputs or plume disturbance forces and which strongly couple with the measured outputs. The particular technique to be used in this study is the subsystem balancing approach which was previously developed by the present investigator. This method is very efficient computationally. Furthermore, it gives accurate results even for the difficult case where the structure has many closed-spaced natural frequencies, when standard modal truncation can give misleading results. Station configuration SC-5 is a good example of such a structure

Private Enforcement in the States

Scholarship on U.S. litigation and civil procedure has scarcely studied the role of private enforcement in the states. Over the past two decades, scholars have established that, almost uniquely in the world, the U.S. often relies on private parties rather than administrative agencies to enforce important statutory provisions. Take your pick of any area in American governance, and you will find private rights of action: environmental law, civil rights, employment discrimination, antitrust, consumer protection, business competition, securities fraud, and so on. In each of these areas, Congress has deliberately empowered private plaintiffs instead of, or in addition to, government agencies. Yet, despite the vast importance of private enforcement at the federal level, we have no account of how prevalent private rights of action are in state law. And this question is particularly pressing now that a number of states— triggered by the Texas abortion law S.B. 8—are using private enforcement to weaken constitutional rights. Is private enforcement a meaningful method of governance in the states or just at the federal level? Which political conditions lead to the adoption of state private enforcement? And why does it exist? In this Article, we conduct the first systematic empirical investigation of the hidden world of state private enforcement. Using computational linguistics and machine learning, we identify private-enforcement provisions across a unique dataset of all fifty states’ laws going back to 2003. Our results show that private enforcement is ubiquitous at the state level. Even by conservative estimates, there are more than 3,500 private-rights-of-action provisions in state law, ranging from traditional areas like antitrust and employment all the way to privacy violations, lawsuits against police, gravedigging, veterinary care, and waste disposal. Counterintuitively, private-enforcement provisions are expanding the most in an ideologically mixed group of small states like Utah, New Hampshire, Connecticut, Nebraska, and Wisconsin. One takeaway from these results is that state private enforcement is strikingly different from that of the federal system—it is sprawling, messy, and even chaotic. We also use our data to test conventional theories behind private-enforcement adoption. The most prominent one—the separation-of-powers theory—posits that Congress enacts private rights of action when the executive is controlled by another political party. Our empirical bottom line is that we broadly fail to find evidence in favor of any of the theories, including separation of powers. Regression analyses based on our best estimates of private-enforcement provisions do not yield a statistically meaningful relationship between divided government and private-enforcement adoption. And, while some of our measures for fee-shifting and damage clauses unearth some evidence pointing toward the separations-of-powers theory, our preferred measures of such clauses do not. We even find no correlation between an increased adoption of private enforcement and legislative control by either Democrats or Republicans. It appears the political economy of private enforcement in the states diverges radically from that of the federal government. With an eye toward future theorizing and empirical testing, we put forth three institutional differences between the states and federal government that may explain this divergence. And we sketch a future comparative research agenda focused on studying federal–state divergence. Reaffirming the central role that private enforcement plays in our system reveals the need to reorient civil procedure and incorporate state private rights of action more explicitly into its core teachings

Clemson Catalog, 1945-1947, Volume 22

https://tigerprints.clemson.edu/clemson_catalog/1102/thumbnail.jp

National Aeronautics and Space Administration (NASA)/American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program, 1993, volume 2

The JSC NASA/ASEE Summer Faculty Fellowship Program was conducted by Texas A&M University and JSC. The objectives of the program, which began nationally in 1964 and at JSC in 1965, are (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of participant's institutions; and (4) to contribute to the research objectives of the NASA centers. Each faculty fellow spent at least 10 weeks at JSC engaged in a research project in collaboration with a NASA/JSC colleague. A compilation of the final reports on the research projects completed by the faculty fellows during the summer of 1993 is presented

Aeronautical engineering: A special bibliography with indexes, supplement 38, December 1973

This special bibliography lists 473 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1973