1,720,957 research outputs found
Effects on the Rotation of a Body Containing a Freely Moving Mass Along an Axis
No full textIn this study, a wing system in three different coordinates, x, y and z, was established. The main purpose of this study was to investigate the possibility of increasing rotation of a vehicle in order to escape some dangerous conditions in a short time interval. The angular velocities of masses on the three coordinate axes were examined and the effect of their position on the angular velocity was investigated. The aim was to determine how the angular velocity is increased or decreased and if this occurs immediately by changing the location of the masses. Ultimately, the investigation of changing angular velocity instantaneously to prevent dangerous accidents was targeted by sudden rotation of the vehicle. Initially, the state of the angular velocity was studied when the masses are stationary because the moment of inertia does not play an important role. The result is that the angular velocities for the different masses will be the same value as their initial value. Also, it is assumed that there are no external forces such as gravity and friction. Therefore, our vehicle rotates at the same initial speed. Second, the effect on the angular velocities when some mass on each axis change position and move further down to the outer ends of the system was studied. In this case, 'some mass' means the mass on the axes in which the vehicle is not rotating. In other words, in order to rotate the vehicle about the x-axis, we need to know the positions of the y and z masses. Therefore, there are only two masses that play a role on the vehicle rotation. After setting the initial conditions it was obtained that when the position of the masses was altered, the angular velocities were seen to decrease based on our simulations using the Matlab program. Changing the position of the mass undeniably changes the moment of inertia which in turn cause the angular velocity to change and not stay at the same speed. The last simulation in this study was investigated for the condition when all the masses are not stationary. In this case, all three masses on their respective axes are moving. The respective distances of each mass from its initial starting point and its effect on the angular velocity as the masses moved further towards the outer ends of the system was examined. In the previous case only, movement of two of the three masses were simulated and its effect on angular velocity determined. The critical positioning of the three masses was expected to greatly affect the angular velocity considering that the positions of the mass can significantly alter the angular velocity. The change in positions were simulated in Matlab and it was observed that as the masses moved further outward the angular velocities decrease and reached a constant limit.M.S., Mechanical Engineering and Mechanics -- Drexel University, 201
COVARIANCE EQUIVALENT REALIZATIONS: DEVELOPMENT AND APPLICATIONS TO MODEL AND CONTROLLER REDUCTION
No full textThe controller design to meet the mission requirements of a large scale system typically involves two steps: (a) model reduction and (b) control design. This dissertation presents a theory to unify steps (a) and (b). Of particular interest will be partial realizations that preserve the steady state covariance of the uncontrolled variables of a higher order realization. The unification is achieved via the following steps. (1) First a reduced order model (of \u27Riccati-solvable\u27 dimension) is obtained which preserves the mean-squared values of every controlled variable (a desirable property since mission requirements are often given in terms of the root-mean-squared values of the controlled variables). (2) Based upon this reduced model, an optimal LQG controller is designed to meet the mission requirements. This determines the optimal control inputs. (3) Since the Riccati-solvable dimension may be larger than the order of the desired controller, a reduction of the LQG controller is now desired. The controller reduction problem aims at producing reduced order controllers that preserve the steady state covariance (in particular, the mean-squared values) of the optimal control inputs of step (2). Thus, the model reduction and the control design problems are unified by consistently using the mission requirements in all steps (1)-(3). The theory described herein offers a flexibility which is used to advantage to accommodate the different requirements of the model reduction and the controller reduction problems. Furthermore, the algorithm presented herein is easily applicable to both the model- and controller-reduction problems, thus permitting the use of the same software package for both the problems. In addition, this dissertation presents the mathematical properties of the reduced models and the reduced controllers that are produced by the theory. The proposed technique is applied to the design of a controller for a solar optical telescope which is representative of large scale systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Controller design via structural reduced modeling by FETM
Get PDFThe Finite Element-Transfer Matrix (FETM) method has been developed to reduce the computations involved in analysis of structures. This widely accepted method, however, has certain limitations, and does not address the issues of control design. To overcome these, a modification of the FETM method has been developed. The new method easily produces reduced models tailored toward subsequent control design. Other features of this method are its ability to: (1) extract open loop frequencies and mode shapes with less computations, (2) overcome limitations of the original FETM method, and (3) simplify the design procedures for output feedback, constrained compensation, and decentralized control. This report presents the development of the new method, generation of reduced models by this method, their properties, and the role of these reduced models in control design. Examples are included to illustrate the methodology
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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