bluuebunny/crossref_metadata_2025_split huggingface dataset:
A gradient flow approach to the robust pole‐placement problem
Authors: Lam James , Van Wei‐Yong 
Published: July 2007

AbstractThis paper provides a computational procedure for a type of robust pole‐placement problem. By exploiting the differentiability nature of the objective function based on the Frobenius norm condition number, the minimization problem is formulated in terms of a gradient flow to which standard ODE numerical routines can be applied. It is shown that a minimum point exists for the objective function. The algorithm is efficient and faces no singularity problem with the resulting eigenvector matrix. A numerical example is used to illustrate the technique and comparison with other methods is made.
RobustH∞tracking: A game theory approach
Authors: de Souza C. E. , Shaked U. , Fu M. 
Published: July 2007

AbstractThis paper investigates the problem of finite‐time‐horizon robustH∞tracking, for linear continuous time‐varying systems, from the game theory point of view. Three tracking problems are considered, depending on whether the reference signal to be tracked is perfectly known in advance, measured on line, or previewed in a fixed interval of time ahead. No aprioriknowledge of a dynamic model for the reference signal is assumed, and the parameters of the system are not completely known. A game is defined where, given the specific information on the tracking signal, the controller plays against nature that can choose any initial condition, any bounded energy disturbance input and measurement noise, and any set of parameters in a prescribed bounded region. A standard quadratic pay‐off function is defined where the energy of the tracking error signal is weighted against the energy of the disturbance, the noise signal, and the Euclidean norm of the initial condition.Conditions for the existence of a saddle‐point equilibrium in this zero‐sum game are not easy to find. We, therefore, augment the state‐space description of the system to convert the parameter uncertainty into exogenous bounded energy signals. An augmented game is then defined on the new perfectly known system, and it is shown that its saddle‐point equilibrium solution, if it exists, guarantees a prescribedH∞‐norm performance of the tracker, in the original system, for all possible parameters.Necessary and sufficient conditions for the existence of a saddle‐point solution to the augmented game are determined.H∞‐tracking controllers, which guarantee the prescribed performance level for all possible parameters, are derived for both the state and the output feedback cases.
Control of wheeled mobile robots not satisfying ideal velocity constraints: A singular perturbation approach
Authors: D'andréa‐novel B. , Campion G. , Bastin G. 
Published: July 2007

AbstractWe propose in this paper a singular perturbation formulation for mechanical systems not exactly satisfying velocity constraints. We particularize to ‘wheeled mobile robots’ which do not satisfy ideal pure rolling and nonslipping constraints. We study the robustness of static‐state linearizing feedback laws which have been obtained to solve a point tracking problem in the ideal case when constraints were satisfied.
Energy methods for stability of bilinear systems with oscillatory inputs
Authors: Baillieul J. 
Published: July 2007

AbstractA large body of recent literature has been devoted to the topic of motions of mechanical systems forced by oscillatory inputs (see, for example, References 7, 12, 15, 17 and 29). A common feature in most of this work (with Reference 7 being the exception) is that the results apply principally to kinematic problems, and the equations of motion do not involve drift terms. The main object of study in this paper is the class of bilinear control systems with oscillatory (periodic) inputs. We shall show that included in this class are models of mechanical system dynamics which are obtained through a process of reduction and linearization about operating points. In particular, we study the stability of such systems under high‐frequency, periodic forcing. Theaveraged potentialis defined for linearizations of the systems on the (reduced) configuration space, and it is shown that stable motions of the forced system are associated with minimum values of this quantity. We use both classical averaging theory as well as a novel geometric argument to provide parallel but independent assessments of the use of theaveraged potentialin carrying out a stability analysis. A salient feature of the geometric approach is that we are able to justify the use of an energy‐like quantity to determine Lyapunov stability in conservative mechanical systems. This makes contact with a growing body of literature on the use of energy methods for stability and control design (e.g. References 7, 8, 18, 24, 26 and 27). We briefly describe the connection with previous work on the averaged potential.
On passivity‐based output feedback global stabilization of euler‐lagrange systems
Authors: Ortega Romeo , Loria Antonio , Kelly Rafael , Praly Laurent 
Published: July 2007

AbstractIt is well known that in systems described by Euler‐Lagrange equations the stability of the equilibria is determined by the potential energy function. Further, these equilibria are asymptotically stable if suitable damping is present in the system. These properties motivated the development of a passivity‐based controller design methodology which aims at modifying the potential energy of the closed loop and the addition of the required dissipation. To achieve the latter objective measurement of the generalized velocities is typically required. Our main contribution in this paper is the proof that damping injection without velocity measurement is possible via the inclusion of a dynamic extension provided the system satisfies a dissipation propggation condition. This allows us to determine a class of Euler‐Lagrange systems that can be globally asymptotically stabilized with dynamic output feedback. We illustrate this result with the problem of set‐point control of elastic joints robots. Our research contributes, if modestly, to the development of a theory for stabilization of nonlinear systems with physical structures which effectively exploits its energy dissipation properties.
The multi‐steeringN‐trailer system: A case study of goursat normal forms and prolongations
Authors: Tilbury D. , Sastry S. 
Published: July 2007

AbstractIn this paper, wheeled mobile robots towing trailers are used as examples of systems which can be converted into extended Goursat normal form. For some configurations of this class of systems, a prolongation of the Pfaffian system is necessary before the Goursat form can be achieved. The advantage of the Goursat form is that once the kinetic constraints are in this normal form, the point‐to‐point path planning problem can be solved in a straightforward way.
On the continuity and incremental‐gain properties of certain saturated linear feedback loops
Authors: Chitour Yacine , Liu Wensheng , Sontag Eduardo 
Published: July 2007

AbstractThis paper discusses various continuity and incremental‐gain properties for neutrally stable linear systems under linear feedback subject to actuator saturation. The results complement our previous ones, which applied to the same class of problems and provided finite‐gain stability.
Robust control of constrained systems via convex optimization
Authors: Sznaier Mario , Blanchini Franco 
Published: July 2007

AbstractA successful controller design paradigm must take into account both model uncertainty and design specifications. Model uncertainty can be successfully addressed using ℋ︁∞robust control theory. However, this framework cannot directly accommodate the realistic case where in addition to robustness considerations the system is subject to both time‐ and frequency‐domain specifications, such as bounds on the control action. In this paper we propose a design procedure, based upon the use of convex optimization, that takes explicitly into account both time‐ and frequency‐domain specifications. The main result of the paper is a new framework to address problems having both control and output constraints and model uncertainty. Additionally, the paper serves as a brief tutorial on the issues involved in addressing design problems with multiple design specifications via convex optimization.
Constrained stabilization of discrete‐time systems
Authors: Zheng Alex , Balakrishnan Ragu , Morari Manfred 
Published: July 2007

AbstractBased on the growth rate of the set of states reachable with unit‐energy inputs, we show that a discretetime controllable linear system is globally controllable to the origin with constrained inputs if and only if all of its eigenvalues lie in the closed unit disk. These results imply that the constrained Infinite‐Horizon Model Predictive Control algorithm is stabilizing for a sufficiently large number of control moves if and only if the controlled system is stabilizable and all its eigenvalues lie in the closed unit disk.In the second part of the paper, we propose an implementable Model Predictive Control algorithm and show that with this scheme a discrete‐time linear system withnpoles on the unit disk (with any multiplicity) can be globally stabilized if the number of control moves is larger thann. For pure integrator systems, this condition is also necessary. Moreover, we show that global asymptotic stability is preserved for any asymptotically constant disturbance entering at the plant input.
Discrete‐time reference governors and the nonlinear control of systems with state and control constraints
Authors: Gilbert Elmer G. , Kolmanovsky Ilya , Tan Kok Tin 
Published: July 2007

AbstractDiscrete‐time, linear control systems with specified pointwise‐in‐time constraints, such as those imposed by actuator saturation, are considered. The constraints are enforced by the addition of a nonlinear ‘reference governor’ that attenuates, when necessary, the input commands. Because the constraints are satisfied, the control system remains linear and undesirable response effects such as instability due to saturation are avoided. The nonlinear action of the reference governor is defined in terms of a finitely determined maximal output admissible set and can be implemented on‐line for systems of moderately high order. The main result is global in nature: if the input command converges to a statically admissible input and the initial state of the system belongs to the maximal output admissible set, the eventual action of the reference governor is a unit delay.
New algebraic criteria for absolute stability of nonlinear systems
Authors: Hsiao Feng‐Hsiag , Hsieh Jer‐Guang , Chang Jaion‐Shea 
Published: July 2007

AbstractIn this paper, new and simple algebraic criteria are derived via elementary proofs to provide easy sufficient conditions for the standard absolute stability problems of nonlinear systems, i.e. Lur'e problems. These criteria are equivalent to the famous graphical circle criteria and Popov criterion. By means of the Sturm theorem and the Euclidean division algorithm, a Routh‐Hurwitz‐like Sturm criterion is obtained. No graphical technique is needed. Only basic numerical manipulations are involved in the new criteria.
Loop recovery via ℋ︁∞‐modified complementary sensitivity recovery for non‐minimum phase plants
Authors: Saeki Masami 
Published: July 2007

AbstractIn order to recovery robust stability of a desirable state feedback system by output feedback, the desirable complementary function is approximated by a modified complementary function of the output feedback system by solving an ℋ︁∞ norm‐minimization problem. The modified complementary function is obtained by getting rid of non‐minimum phase factors from the complementary function. Numerical examples show the superiority of this method to LQG/LTR method and other methods.
Loop transfer recovery design via new observer‐based and css architecture‐based controllers
Authors: Chen Ben M. , Chen Ya‐Ling 
Published: July 2007

AbstractTwo new controller structures, namely the continuous‐time current‐type observer and current‐type CSS (Chen‐Saberi‐Sannuti) architecture‐based controllers, are considered in this paper for loop transfer recovery design for general non‐strictly proper non‐minimum phase systems. The proposed observer is structurally analogous to the current estimator of discrete‐time systems, while the proposed CSS architecture falls into the category of the controller structures developed recently by Chen, Saberi and Sannuti. The properties of these new structures are characterized. In particular, sets of necessary and sufficient conditions under which a target loop transfer function can be either exactly and/or asymptotically recovered by the abovementioned controllers are obtained. More importantly, the new current‐type observer balances the observer structures for continuous‐time and discrete‐time linear systems.
Robust stability analysis of systems with real parametric uncertainty: A global optimization approach
Authors: Psarris Polycarpos , Floudas Christodoulos A. 
Published: July 2007

AbstractThis paper presents an optimization framework for the robustness analysis of linear and nonlinear systems with real parameter uncertainty. For linear systems, a nonlinear programming formulation for the exact calculation of the stability margin is presented. The potential of decomposition‐based global optimization methods for the solution of this nonconvex problem is discussed. Next the concept of the stability margin is extended to a class of nonlinear systems. A nonlinear stability margin and a uniqueness margin are defined to address the effect of parametric uncertainty on the stability of a particular steady state, as well as on the number of steady states of the system. This analysis allows for the derivation of necessary and sufficient conditions for robust stability and robust uniqueness of the steady state of the system in the presence of parametric uncertainty.
A global stabilization theorem for planar nonlinear systems
Authors: Tsinias J. 
Published: July 2007

AbstractWe provide sufficient conditions for global stabilization of planar nonlinear systems by means of static and dynamic feedback laws. The results of the paper extend previous work on the same problem. Our approach uses some ideas from a recent paper of the author based on the well‐known Artstein theorem on stabilization as well as a recent result of Coron and Praly.
A new H∞ design methodology for the control of flexible structures: Application to a sight system
Authors: Coustal P. , Delebecque F. , Nikoukhah R. 
Published: July 2007

AbstractWe present an Hscr;∞ controller design methodology for flexible systems. We illustrate our approach using an example drawn from an industrial application. The proposed method avoids undesirable (lightly damped) pole‐zero cancellations and yields a low‐order controller, using a new formulation of the standard problem.
A comparison of bootstrap methods and an adjusted bootstrap approach for estimating the prediction error in microarray classification
Authors: Jiang Wenyu , Simon Richard 
Published: July 2007

AbstractThis paper first provides a critical review on some existing methods for estimating the prediction error in classifying microarray data where the number of genes greatly exceeds the number of specimens. Special attention is given to the bootstrap‐related methods. When the sample sizenis small, we find that all the reviewed methods suffer from either substantial bias or variability. We introduce a repeated leave‐one‐out bootstrap (RLOOB) method that predicts for each specimen in the sample using bootstrap learning sets of sizeln. We then propose an adjusted bootstrap (ABS) method that fits a learning curve to the RLOOB estimates calculated with different bootstrap learning set sizes. The ABS method is robust across the situations we investigate and provides a slightly conservative estimate for the prediction error. Even with small samples, it does not suffer from large upward bias as the leave‐one‐out bootstrap and the 0.632+ bootstrap, and it does not suffer from large variability as the leave‐one‐out cross‐validation in microarray applications. Copyright © 2007 John Wiley & Sons, Ltd.
Geographic‐based ecological correlation studies using supplemental case–control data
Authors: Haneuse S. , Wakefield J. 
Published: July 2007

AbstractIt is well known that the ecological study design suffers from a variety of biases that render the interpretation of its results difficult. Despite its limitations, however, the ecological study design is still widely used in a range of disciplines. The only solution to the ecological inference problem is to supplement the aggregate data with individual‐level data and, to this end, Haneuse and Wakefield (Biometrics2007;63:128–136) recently proposed a hybrid study design in which an ecological study is supplemented with a sample of case–control data. The latter provides the basis for the control of bias, while the former may provide efficiency gains. Building on that work, we illustrate the use of the hybrid design in the context of a geographical correlation study of lung cancer mortality from the state of Ohio. Focusing on epidemiological applications, we initially provide an overview of the use of ecological studies in scientific research, highlighting the breadth of current application as well as advantages and drawbacks of the design. We consider the interplay between the two sources of information in the design: ecological and case–control, and then provide details on a Bayesian spatial random effects model in the setting of the hybrid design. Issues of specification are addressed, as well as sensitivity to modeling assumptions. Further, an interesting feature of these data is that they provide an example of how the proposed design may be used to resolve the ecological fallacy. Copyright © 2007 John Wiley & Sons, Ltd.
Aufbau und Eigenschaften verschiedener ölfreier Vakuumpumpen für den Grob‐ und Feinvakuumbereich
Authors: Hablanian Mars H. 
Published: July 2007

AbstractThe development of high vacuum pumps and systems during the last 35 years can be characterized by a trend of gradual elimination of liquids exposed to vacuum environment. The need for high purity vacuum process equipment precipitated the development of new pumping techniques: iongettering pumps, turbomolecular pumps and cryopumps. During the last 5 years, a number of dry coarse‐vacuum pumps have been developed. Some are entirely oilfree, some still use lubricants at the seals separating the driving mechanism from the vacuum side. This review contains general design and performance characteristics of four classes of equipment: hermetically sealed pumps using bellows to isolate the driving mechanism, a variety of multistaged positive displacement blowers, pumping trains based on turbo‐drag pumps, and multistaged reciprocal piston pumps. It is entirely practical to achieve pressure of 105 to 106 while discharging to atmosphere. Despite a complete absence of conventional lubrication in some of these pumps, periods exceeding 10000 hours without maintenance are obtained, providing a viable technology for clean vacuum systems.
Entgasen in der Kunststoffaufbereitungstechnik
Authors: Kapfer Klaus 
Published: July 2007

AbstractPolymer Compounding is the link between polymer synthesis and the conversion to the final part. Besides well known processing tasks such as Melting, Mixing, Homogenisation and Pelletisation, the Devolatilisation of volatile components such as air, moisture, monomers, oligomers and solvents represents a major aspect of the compoundig technology. Increasing demands for cleaner polymer parts and requirements for less environmental impact will augment the importance of this process task in polymer compounding.
Carl Hoffmann (1844 – 1910), der Erfinder der Drehschieberpumpe
Authors: Reich G. 
Published: July 2007

AbstractDer gelernte Schlosser Carl Hoffmann aus Berlin war seit 1869 bei Siemens & Halske beschäftigt zunächst als Monteur und Dreher, dann als Werkstattleiter und Konstrukteur. Nach sehr erfolgreichen Arbeiten auf dem Gebiet der Generatoren und Elektromotoren wurde er zum Oberingenieur ernannt. Er beschäftigte sich weiter mit dem Problem, rotierende Geräte so auszuführen, daß diese unmittelbar von Elektromotoren angetrieben werden konnten. Im Rahmen dieser Tätigkeit entstanden ganze Reihen von rotierenden Pumpen für Flüssigkeiten und Gase, darunter auch die – heute als Drehschieberpumpe bezeichnete – wichtigste Vakuumpumpe. Der wesentliche Fortschritt bestand darin, daß er für rotierende Vakuumpumpen ein Rückschlagventil einführte. Diese Pumpen wurden ab 1905 von den Siemens‐Schuckert Werken in Berlin‐Charlottenburg, ab 1906 von Arthur Pfeiffer in Wetzlar und ab 1908 von Leybold in Köln (als Gaedesche Kapselpumpe) hergestellt.Daß Carl Hoffmann, der als Starkstromtechniker nie etwas mit Vakuumtechnik zu tun hatte, kaum bekannt wurde, mag daran liegen, daß angestellte Techniker nur selten publizierten.
Information on Surface Structure by Low Energy Electron Diffraction
Authors: Wedler Harald , Heinz Klaus 
Published: July 2007

AbstractIn den letzten Jahrzehnten ist die quantitative Bestimmung von Oberflächenstrukturen zu einem wichtigen und interessanten Gebiet der Festkörperphysik geworden. Eine der leistungsfähigsten Methoden dieser Oberflächenkristallographie ist die Beugung langsamer Elektronen (Low Energy Electron Diffraction = LEED). Mittels Analyse von LEED‐Bildern und ‐Intensitäten können Gestalt und Größe der Oberflächeneinheitszelle, der Ordnungszustand und der atomare Aufbau bestimmt werden. Hochentwickelte Videomeßtechniken erlauben eine schnelle und verläßliche Datenaufnahme. Die dynamische Analyse der Intensitäten, die die Vielfachstreuung der Elektronen berücksichtigt, liefert den strukturellen Aufbau der Oberfläche mit einer Genauigkeit von bis zu 10−12 m.
High Rate Aluminum Sputtering in Compact Disc Production
Authors: Lübbehusen Michael , Seiler Reiner , Sichmann Eggo 
Published: July 2007

AbstractEine etwa 55 nm dicke Aluminiumschicht verleiht der Compact Disc (CD) ihr typisch „silbriges”︁ Aussehen. Die Schicht dient als Reflektor für den Laserstrahl des Abspielgerätes.Heute können diese Schichten in Single Disc Coatern in nur 1,1 s durch einen DC‐Magnetron Sputterprozeß aufgebracht werden, obwohl das Polycarbonat, aus dem die CD im wesentlichen besteht, nur beschränkt temperaturbelastbar ist.Forderungen der Industrie nach Produktivität, Zuverlässigkeit, geringem Energieverbrauch, hoher Targetausnutzung und stets gleichbleibender Schichtqualität stellen besondere Anforderungen an das Design von Sputterquellen.
Integration von Mikromechanik und Elektronik
Authors: Biebl Markus 
Published: July 2007

AbstractDie Oberflächen‐Mikromechanik erlaubt die Herstellung komplexer mechanischer Strukturen mit Dimensionen im Mikrometer‐ Bereich. In diesem Artikel werden zunächst die Grundzüge der Technologie der Oberflächen‐Mikromechanik dargestellt. Die Adhäsion der Strukturen wird als Beispiel für zu lösende Probleme bei der Herstellung mikromechanischer Systeme aufgezeigt. Mikromechanischer Resonatoren als Teststrukturen zur Bestimmung mechanischer Parameter werden vorgestellt. Schließlich wird auf die kostengünstige monolithische Integration mit CMOS‐Elektronik eingegangen.