139,401 research outputs found
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
Pursuit-evasion differential games with deception or interrupted observation
No full textAbstractThree stochastic pursuit-evasion differential games involving two players, E (the evader) and P (the pursuer), moving in the plane are considered. In the first game [Game (a)], the case where E induces errors in P's measurements of the bearing β of E from P and controls the size and direction of these errors, is considered. In the second game [Game (b)], the case where P receives readings of two false targets, which are seen within the same range of P, but with different bearing angles, is considered. In the third game [Game (c)], the case where P observes the range r of E from P, but has interrupted observation of β, is considered. In Games (a) and (b) P applies Proportional Navigation guidance laws, and in Game (c) E applies a Line-of-Sight guidance law. In Game (a), sufficient conditions on optimal evasion-deception strategies for E are given, and the strategies are computed for several cases. In Game (c), sufficient conditions on weak optimal pursuit strategies for P are given. A procedure is suggested for computing weak suboptimal pursuit strategies, and these are computed for a variety of cases
La 'circunstancia' de 'Herederos y Pretendientes
No full textIn June 2010, the Ortega y Gasset Foundation hosted a Conference about the “Spanish Philosophical Transition” in order to debate the book of Francisco Vázquez, La filosofía española. Herederos y Pretendientes. Una lectura sociológica (1963-1990), recently published. This paper is the author’s response to criticism raised in the Conference and to published reviews received by this book. First, the author summarized the argument of Herederos y pretendientes. Secondly he responds and takes into account the most important objections against the book’s hypothesis and methodology. Finally the author evaluates the favorable judgments received by the book and suggests the limits of the historian’s task.Fundación Ortega y Gasset-Marañó
Control of the motion of nonholonomic systems
No full textDissertation (MSc (Applied SCience))--University of Pretoria, 2007.This dissertation deals with the control, guidance and stabilisation of nonlinear, non¬holonomic systems. It is shown that the kinematics of the system can be separated from the dynamics of the system by using successively two inverse dynamics type of transformations. This leads to a linear decoupled kinematical system, control strategies can then be developed that directly control the motion of the system. The method is applied to a system which is composed of a disk rolling on a plane, a controlled slender rod that is pivoted through its center of mass about the disk's center and two overhead rotors with their axes fixed in the upper part of the rod. Control strategies are designed under which the disk's inclination is stabilised about its vertical position and the disk's motion is able to asymptotically track any given smooth ground trajectory. The control strategy is shown to be stable in the presence parametric uncertainties. It was furthermore shown that the system is path controllable. Finally an extended inverse dynamics control law is introduced which deals directly with underactuated systems. An example of an articulated crane is solved using extended inverse dynamics control. Feasible control is used to ensure that the internal dynamics of the system remains bounded and that the crane reach its desired final position in a given time interval [O, tƒ].Electrical, Electronic and Computer Engineeringunrestricte
A stochastic two-target pursuit-evasion differential game with three players moving in a plane
No full textAbstractA stochastic version of a two-target homicidal chauffeur pursuit-evasion differential game between a player P on one side and players Q1 and Q2 on the other side is considered. This is used to model a dogfight between two very agile players, Q1 and Q2, and a much less maneuverable player P. Sufficient conditions on optimal strategies are derived. These conditions require the existence of a properly smooth solution to a nonlinear partial differential equation on a generalized torus in R4. By applying a finite-difference method, the equation is solved numerically, and optimal strategies are computed
Optimal control for a class of distributed parameter systems where the cost functions are norms
No full textAbstractSome problem in optimal control, for a class of linear distributed parameter systems, are posed. By using a theorem of approximation theory, a maximum principle, which is applicable to these optimal control problems, is given. It is shown, that for the problems posed in this paper, this maximum principle is an extension of Butkovskii's maximum principle and of Demyanov and Rubinov's theorem.In addition, two optimal control problems, in linear lumped parameter systems areposed. For these problems it is shown that the maximum principle given in this paper, is an extension of Pontryagin's maximum principle
Control of the motion of a disk rolling on a plane curve
No full textAbstractThis work deals with the control of the motion of a disk rolling without slipping on a curve located in the horizontal plane. The disk’s motion is driven by a pedalling torque and by using two overhead rotors. In addition, the case where the disk rolls on a plane curve with its plane vertical to the (X,Y)-plane, is discussed
Navigation and control of a trolley by using a dynamical model
No full textAbstractThis work deals with the guidance and control of the motion of a trolley. The trolley is composed from two rear wheels, each of them controlled separately, and from two front castor wheels (see Figure 1). Given N points Pi, i = 1, …, N in the horizontal plane, a finite time interval [0, tf], and a sequence of times τ1 = 0 < τ2 < ⋯ < τN = tƒ. Based on a dynamical model of the trolley, and by using the concept of path controllability, a control law for the trolley's rear wheels is derived, to steer the trolley's center (x,y) in such a manner that (x,y) will pass through Pi at the time τi, i = 1, …, N, respectively
Author self-citation in orthodontics is associated with author origin and gender.
No full textBACKGROUND
The aims of this bibliometric study were to determine author self-citation trends in high-impact orthodontic literature and to investigate possible association between self-citation and publication characteristics.
METHODS
Six orthodontic journals with the highest impact factor as ranked by 2017 Journal Citation Reports were screened for a full publication year (2018) for original research articles, reviews, and case reports. Eligible articles were scrutinized for article and author characteristics and citation metrics. Univariable and multivariable negative binomial regression was used to examine associations between self-citation incidence and publication characteristics.
RESULTS
Medians for author self-citation rate of the most self-citing authors and self-citations were 3.03% (range 0-50) and 1 (range 0-19), respectively. In the univariable analysis, there was no association between self-citation counts and study type (P = 0.41), article topic (P = 0.61), number of authors (P = 0.62), and rank of authors (P = 0.56). Author origin (P = 0.001), gender (P = 0.001) and journal (P = 0.05) were associated with self-citation counts and in the multivariable analysis only origin and gender remained strong self-citation predictors. Asian authors and females self-cited significantly less often than all other regions and male authors.
CONCLUSIONS
Authors in orthodontics do not self-cite at a frequency that suggests potential citation manipulation. Author origin and gender were the only variables associated with citations counts. More bibliometric research is necessary to draw solid conclusions about author self-citation trends in orthodontic literature
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