observer and global output feedback stabilisation for some mechanical systems the objective of the work is two fold a first part is devoted to the problem of constructing an observer to the practical system called overhead crane with the position as output in a second part the problem of global output feedback stabilisation is solved for a class of euler lagrange systems when the variables of velocity are the unmeasured part of the state the equations of these systems are non linear with respect to the velocities a new output feedback control scheme is proposed it relies on the determination of a change of coordinates which gives to the systems a triangular form to illustrate the approach it is applied to a two link manipulator

speed observation and position feedback stabilization of partially linearizable mechanical systems the problems of speed observation and position feedback stabilization of mechanical systems are addressed in this paper our interest is centered on systems that can be rendered linear in the velocities via a partial change of coordinates it is shown that the class is fully characterized by the solvability of a set of partial differential equations pdes and strictly contains the class studied in the existing literature on linearization for speed observation or control a reduced order globally exponentially stable observer constructed using the immersion and invariance methodology is proposed the design requires the solution of another set of pdes which are shown to be solvable in several practical examples it is also proven that the full order observer with dynamic scaling recently proposed by karagiannis and astolfi obviates the need to solve the latter pdes finally it is shown that the observer can be used in conjunction with an asymptotically stabilizing full state feedback interconnection and damping assignment passivity based controller preserving asymptotic stability

the asymptotic properties of nonparametric tests for comparing survival distributions the asymptotic distribution under alternative hypotheses is derived for a class of statistics used to test the equality of two survival distributions in the presence of arbitrary and possibly unequal right censoring the test statistics include equivalents to the log rank statistic the modified wilcoxon statistic and the class of rank invariant test procedures introduced by peto peto when there are equal censoring distributions and the hazard functions are proportional the sample size formula for the f test used to compare exponential samples is shown to be valid for the log rank test in certain situations the power of the log rank test falls as the amount of censoring decreases

a globally exponentially stable speed observer for a class of mechanical systems experimental and simulation comparison with high gain and sliding mode designs abstractit is shown in the paper that the problem of speed observation for mechanical systems that are partially linearisable via coordinate changes admits a very simple and robust exponentially s

the matching conditions of controlled lagrangians and ida passivity based control this paper discusses the matching conditions resulting from the controlled lagrangians method and the interconnection and damping assignment passivity based control ida pbc method both methods have been presented recently in the literature as means to stabilize a desired equilibrium point of an euler lagrange respectively hamiltonian system in the context of mechanical systems with symmetry the original controlled lagrangians method is reviewed and an interpretation of the matching assumptions in terms of the matching of kinetic and potential energy is given secondly both methods are applied to the general class of underactuated mechanical systems and it is shown that the controlled lagrangians method is contained in the ida pbc method the lambda method as described in recent papers for the controlled lagrangians method transforming the matching conditions a set of non linear pdes into a set of linear pdes is discussed the method is used to transform the matching conditions obtained in the ida pbc method into a set of quadratic and linear pdes finally the extra freedom obtained in the ida pbc method with respect to the controlled lagrangians method is used to discuss the integrability of the closed loop system explicit conditions are derived under which the closed loop hamiltonian system is integrable leading to the introduction of gyroscopic terms

modeling and adaptive tracking for a class of stochastic lagrangian control systems this paper focuses on the problem of modeling and adaptive tracking for a class of stochastic lagrangian control systems with unknown parameters by reasonably introducing random noise a method to construct stochastic lagrangian control systems is given under some milder assumptions an adaptive tracking controller is designed such that the mean square of the tracking error converges to an arbitrarily small neighborhood of zero by tuning design parameters the reasonability of assumptions and the efficiency of the controller are demonstrated by a mechanics model in random vibration environment

a general class of nonparametric tests for survival analysis tarone and ware 1977 biometrika 64 156 160 developed a general class of s sample test statistics for right censored survival data that includes the log rank and modified wilcoxon procedures subsequently many authors have considered two and s sample classes in detail in this paper a family of nonparametric statistics is shown to unify existing and generate new test statistics for the s greater than or equal to 2 sample s sample trend and single continuous covariate problems

stabilization of a class of underactuated mechanical systems via interconnection and damping assignment we consider the application of a formulation of passivity based control pbc known as interconnection and damping assignment ida to the problem of stabilization of underactuated mechanical systems which requires the modification of both the potential and the kinetic energies our main contribution is the characterization of a class of systems for which ida pbc yields a smooth asymptotically stabilizing controller with a guaranteed domain of attraction the class is given in terms of solvability of certain partial differential equations one important feature of ida pbc stemming from its hamiltonian formulation is that it provides new degrees of freedom for the solution of these equations using this additional freedom we are able to show that the method of controlled lagrangians in its original formulation may be viewed as a special case of our approach as illustrations we design asymptotically stabilizing ida pbcs for the classical ball and beam system and a novel inertia wheel pendulum

asymptotic properties of censored linear rank tests a conjecture of prentice is established which states that for censored linear rank test exact scores based on conditional expectations can be replaced by approximate scores obtained by evaluating the score function at an estimate of the survival function we show that under minimal conditions asymptotically equivalent tests are obtained when either the kaplan meier altshuler or moment estimator of the survival function is used asymptotic normality is also established for a general random censorship model under the null hypothesis and for contiguous alternatives this is used to calculate efficacies and when the censoring times are i i d an expression for the asymptotic relative efficiency is given which is a natural generalization of the one for classical uncensored linear rank tests 1 introduction prentice 1978 has constructed a general class of linear rank tests for a regression model with censored data his approach was to specify a score function for a classical linear rank test in the absence of censoring chernoff and savage 1958 hajek and sidak 1967 to construct all possible rankings of the unobserved uncensored values which were consistent with observed censored sample and then to assign to each observation the average of all possible scores it could have received in the absence of censoring giving equal weighting to each possible uncensored ranking except for a few special scoring functions notably logarithmic or power law scores these averages are unwieldy when there is appreciable censoring and prentice suggested that asymptotically equivalent tests might arise if the score function was evaluated at some suitable estimate of the survivor function this is well known to be true for uncensored data but requires further justification when censoring is present because the estimate of the survivor function is more complicated in this work we show that prentice s conjecture is true under minimal conditions and also we show that it remains true if prentice s moment estimator of the survivor function is replaced by either the kaplan meier estimator or altshuler s estimator asymptotic normality of these tests is established under a random censorship model for the null hypothesis and contiguous alternatives by martingale methods this is used to compute efficacies for a general random censorship model and asymptotic relative efficiencies for i i d potential censoring times where fully efficient linear rank tests exist asymptotic normality for general alternatives has been established in cuzick 1982 by more complicated methods

geometric criteria for the quasi linearization of the equations of motion of mechanical systems a linear transformation of velocity for a mechanical system is said to quasi linearize the equations of motion of the system if it eliminates all terms quadratic in the velocity it is well known that controller observer synthesis becomes tractable when the dynamics of a mechanical system are in quasi linearized form in this technical note we show that the quasi linearization property is equivalent to the property that the lie algebra of killing vector fields is pointwise equal to the tangent space to the configuration manifold with the riemannian metric induced by the mass tensor of the mechanical system a sufficient condition for this property is that the riemannian manifold be locally symmetric we further show that a necessary and sufficient condition for quasi linearizability on 2 d riemannian manifolds is that the scalar curvature is constant the above results extend the zero riemannian curvature condition that has been extensively applied since its introduction in 1992 moreover the local symmetricity condition and the constant scalar curvature condition can be easily verified using differentiation

higher order sliding mode observers with scaled dissipative stabilisers abstractthis paper proposes a global theoretically exact finite time convergent observer for a class of nonlinear systems which are not necessarily bounded input bounded state with respect to the unknown inputs with this aim a scaled dissipative stabiliser is suggested ensuring that the highest derivative of the output estimation error is independent from the stabiliser gains after this a higher order sliding mode differentiator with the gains adjusted to the upper bound of the unknown inputs is applied achieving finite time convergence

a new swing up law for the furuta pendulum in this paper the swing up problem for the furuta pendulum is solved applying fradkov s speed gradient sg method to a dimension 4 model of the system the new law is compared with the conventional astrom furuta strategy based on a dimension 2 model a comparative analysis including simulations and experiments whereby the advantages and effectiveness of the new law for swinging the pendulum up are shown is included

repeated significance testing in survival analysis using a litter matched design this paper shows that asymptotically a general class of linear rank procedures in a litter matched design form a gauss markov process over time this result is used to develop a procedure for repeated significance testing for time to response differences in litter matched studies in addition an important class of two sample linear rank procedures is shown to have uncorrelated increments over time an example is given using a litter matched cancer study empirical indications of the accuracy of a method for approximating multivariate normal critical values are also given

position feedback global tracking control of el systems a state transformation approach the contribution of this paper is a dynamic position feedback global tracking controller for fully actuated euler lagrange el systems the properties we show for the closed loop system are uniform stability and exponential convergence global in the initial tracking errors and semiglobal in the initial estimation errors the novelty of our approach is that our observer and control design are based on a new model for el systems which is linear in the immeasurable velocities this model is shown to fit robot manipulators we also provide some simulation results

immersion and invariance a new tool for stabilization and adaptive control of nonlinear systems a new method to design asymptotically stabilizing and adaptive control laws for nonlinear systems is presented the method relies upon the notions of system immersion and manifold invariance and in principle does not require the knowledge of a control lyapunov function the construction of the stabilizing control laws resembles the procedure used in nonlinear regulator theory to derive the invariant output zeroing manifold and its friend the method is well suited in situations where we know a stabilizing controller of a nominal reduced order model which we would like to robustify with respect to higher order dynamics this is achieved by designing a control law that asymptotically immerses the full system dynamics into the reduced order one we also show that in adaptive control problems the method yields stabilizing schemes that counter the effect of the uncertain parameters adopting a robustness perspective our construction does not invoke certainty equivalence nor requires a linear parameterization furthermore viewed from a lyapunov perspective it provides a procedure to add cross terms between the parameter estimates and the plant states finally it is shown that the proposed approach is directly applicable to systems in feedback and feedforward form yielding new stabilizing control laws we illustrate the method with several academic and practical examples including a mechanical system with flexibility modes an electromechanical system with parasitic actuator dynamics and an adaptive nonlinearly parameterized visual servoing application

a remark on the converging input converging state property suppose that an equilibrium is asymptotically stable when external inputs vanish then every bounded trajectory which corresponds to a control which approaches zero and which lies in the domain of attraction of the unforced system must also converge to the equilibrium this well known but hard to cite fact is proved and slightly generalized here

a relationship between two forms of linear rank procedures for censored data summary this paper gives a useful relationship between two popular classes of linear rank statistics for arbitrarily right censored data the relationship allows a linear rank procedure with certain optimal properties to be transformed into the form of a procedure having established asymptotic properties under proportional hazards alternatives

weighted log rank statistics for comparing two distributions summary the derivation of locally most powerful rank statistics for comparing two censored samples against parametric alternatives is reformulated for more general classes of alternatives a particular class is considered which includes the case of two weibull distributions differing in shape parameter

on output feedback stabilization of euler lagrange systems with nondissipative forces this paper provides a solution to the problem of output feedback stabilization of systems described by euler lagrange equations perturbed by nondissipative forces this class of forces appears in some applications where we must take into account the interaction of the system with its environment the nonlinear dependence on the unmeasurable part of the state and the loss of the fundamental passivity property render most of the existing results on stabilization of nonlinear systems unapplicable to this problem the technique we use consists of finding a dynamic output feedback controller and a nonlinear change of coordinates such that the closed loop can be decomposed as a cascade of an asymptotically stable system and an input to state stable system this should be contrasted with the well known passivity based technique that aims at a feedback interconnection of passive systems we believe this design methodology to be of potential applicability to other stabilization problems where passivity arguments are unapplicable

observers are unnecessary for output feedback control of lagrangian systems we address and solve some long standing yet well documented open problems on output feedback tracking control of euler lagrange systems with arbitrarily high relative degree this includes underactuated systems our main contribution is to establish a theoretical foundation for the use of so called dirty derivatives a common ad hoc replacement of unavailable state measurements such as generalized velocities whence obviating the the use of observers for the purpose of position feedback tracking control reminiscent of passivity based control for robot manipulators our control law is globally lipschitz and the controller dynamics is linear for relative degree two fully actuated lagrangian systems without dissipative forces friction and with bounded inertia matrix we establish uniform global asymptotic stability in closed loop furthermore we show that our control approach applies to lagrangian systems augmented by a chain of integrators relative degree m 2 systems the design method which is based on a recursive procedure in the spirit of backstepping control is intuitive as it exploits structural properties such as passivity and inherent input output stability as a corollary we solve an output feedback global tracking control problem for flexible joint robots but also for systems coupled with output feedback linearizable actuator dynamics in addition we discuss remaining open problems of fairly general interest in the realm of analysis and design of robust nonlinear systems

exact description of simple wave interactions in multicomponent chromatography nonlinear wave interaction processes for a quasilinear hyperbolic homogeneous system of first order partial differential equations multicomponent chromatography are investigated the wave analysis is worked out by extending to the present multicomponent case the leading ideas of a well established method of approach that was developed for solving initial value wave problems in terms of exact solutions to 2 2 hyperbolic homogeneous systems these interaction processes may model different situations concerning the separation of a mixture into its chemical components several numerical plots are also given in order to illustrate the behavior of the exact wave solutions arising from the analysis that is accomplished

two globally convergent adaptive speed observers for mechanical systems a globally exponentially stable speed observer for mechanical systems was recently reported in the literature under the assumptions of known or no coulomb friction and no disturbances in this note we propose and adaptive version of this observer which is robust vis a vis constant disturbances moreover we propose a new globally convergent speed observer that besides rejecting the disturbances estimates some unknown friction coefficients for a class of mechanical systems that contains several practical examples

brief paper a globally exponentially convergent immersion and invariance speed observer for mechanical systems with non holonomic constraints the problem of velocity estimation for general n degrees of freedom mechanical systems is of great practical and theoretical interest for unconstrained systems many partial solutions have been reported in the literature however even in this case the basic question of whether it is possible to design a globally convergent speed observer remains open in this paper an affirmative answer to the question is given for general mechanical systems with knon holonomic constraints by proving the existence of a 3n 2k 1 dimensional globally exponentially convergent speed observer an observer for unconstrained mechanical systems is obtained as a particular case of this general result instrumental for the construction of the speed observer is the use of the immersion and invariance technique in which the observer design problem is recast as a problem of rendering attractive and invariant a manifold defined in the extended state space of the plant and the observer

constructive immersion and invariance stabilization for a class of underactuated mechanical systems a constructive approach to stabilize a desired equilibrium for a class of underactuated mechanical systems which obviates the solution of partial differential equations is proposed the immersion invariance methodology is adopted with the main result formulated in the port hamiltonian framework for both model and target dynamics the procedure is applicable to mechanical systems with under actuation degree larger than one extending the results recently reported by some of the authors the approach is successfully applied to two benchmark examples and some basic connections with the interconnection and damping assignment passivity based control are revealed an additional contribution of this work is the identification of a class of mechanical systems whose mechanical structure remains invariant under partial feedback linearization

exact solutions describing soliton like interactions in a nondispersive medium when two solitons collide they interact locally but emerge unscattered from the interaction in this paper we show that there are certain media whose responses are governed by the nonlinear nondispersive wave equation in which any two pulses travelling in opposite directions interact nonlinearly for a finite time when they collide but then part unaffected by the interaction for these media thedependence of the wave speed on the amplitude of the disturbance although special is not pathological in fact by a suitable choice of the constants in the expression for the sound speed the responses of many real materials can be modeled a concise representation is obtained for the exact solution of the initial value problem in terms of the solution of a first order system of linear ordinary differential equations an explicit solution is found for piecewise linear initial data

a parameter estimation approach to state observation of nonlinear systems abstract a novel approach to the problem of partial state estimation of nonlinear systems is proposed the main idea is to translate the state estimation problem into one of estimation of constant unknown parameters related to the systems initial conditions the class of systems for which the method is applicable is identified via two assumptions related to the transformability of the system into a suitable cascaded form and our ability to estimate the unknown parameters the first condition involves the solvability of a partial differential equation while the second one requires some persistency of excitation like conditions the proposed observer is shown to be applicable to position estimation of a class of electromechanical systems for the reconstruction of the state of power converters and for speed observation of a class of mechanical systems

a note on the relation between two forms of linear rank statistics for right censored and grouped data we show that two forms of linear rank statistics for right censored and grouped data are equivalent in the case of no tied value among uncensored observations we provide some intuition about the equivalence

on some hyperbolic systems of temple class abstract the aim of this paper is the statement of a general class of temple systems of conservation laws that includes both the chromatography electrophoresis like systems and the 2 2 leroux system that we generalize to any dimension we show that this class actually belongs to the temple type and compute a complete set of strict riemann invariants in a generic situation as the property the integral curve of this eigenvector is a straight line is essentially a linear algebra property we aim to deduce the results with simple linear algebra hypothesis and arguments from the structure of the jacobian matrix

a reduction procedure for generalized riemann problems with application to nonlinear transmission lines generalized simple wave solutions to quasilinear hyperbolic nonhomogeneous systems of pdes are obtained through the differential constraint method these solutions prove to be flexible enough to solve generalized riemann problems where discontinuous initial data are involved within such a theoretical framework the governing model of nonlinear transmission lines is investigated throughout

brief paper full order observer design for a class of port hamiltonian systems we consider a special class of port hamiltonian systems for which we propose a design methodology for constructing globally exponentially stable full order observers using a passivity based approach the essential idea is to make the augmented system consisting of the plant and the observer dynamics to become strictly passive with respect to an invariant manifold defined on the extended state space on which the state estimation error is zero we first introduce the concept of passivity of a system with respect to a manifold by defining a new input and output on the extended state space and then perform a partial state feedback passivation which leads to the construction of the observer we then illustrate this observer design procedure on two physical examples the magnetic levitation system and the inverted pendulum on the cart system

total energy shaping control of mechanical systems simplifying the matching equations via coordinate changes total energy shaping is a controller design methodology that achieves asymptotic stabilization of mechanical systems endowing the closed loop system with a lagrangian or hamiltonian structure with a desired energy function that qualifies as lyapunov function for the desired equilibrium the success of the method relies on the possibility of solving two pdes which identify the kinetic and potential energy functions that can be assigned to the closed loop particularly troublesome is the partial differential equation pde associated to the kinetic energy which is nonlinear and inhomogeneous and the solution that defines the desired inertia matrix must be positive definite in this note we prove that we can eliminate or simplify the forcing term in this pde by modifying the target dynamics and introducing a change of coordinates in the original system furthermore it is shown that in the particular case of transformation to the lagrangian coordinates the possibility of simplifying the pdes is determined by the interaction between the coriolis and centrifugal forces and the actuation structure the examples of pendulum on a cart and furuta s pendulum are used to illustrate the results

a monte carlo study of some two sample rank tests with censored data abstract the powers of several nonparametric tests for the two sample problem with censored data are compared by simulation the tests studied include gehan s efron s and peto s and prentice s generalized wilcoxon tests along with the logrank test the test with the greatest power changes with the sample sizes censoring mechanism and distribution of the random variables the test that performed the best overall was the peto prentice generalized wilcoxon statistic with an asymptotic variance estimate

on the lambda equations for matching control laws we discuss matching control laws for underactuated systems we previously showed that this class of matching control laws is completely characterized by a linear system of first order partial differential equations for one set of variables lambda followed by a linear system of first order partial differential equations for the second set of variables widehat g widehat v here we derive a new first order system of partial differential equations that encodes all compatibility conditions for the lambda equations we give four examples illustrating different features of matching control laws the last example is a system with two unactuated degrees of freedom that admits only basic solutions to the matching equations there are systems with many matching control laws where only basic solutions are potentially useful we introduce a rank condition indicating when this is likely to be the case

hodograph transformation and differential constraints for wave solutions to 2 2 quasilinear hyperbolic nonhomogeneous systems the differential constraint method is used to work out a reduction approach to determine solutions in a closed form to the highly nonlinear hodograph system arising from 2 2 hyperbolic nonhomogeneous models these solutions inherit all of the features of the standard wave solutions obtainable via the classical hodograph transformation and in the meantime incorporate the dissipative effects induced on wave processes by the source like term involved in the governing equations within such a theoretical framework the problem of integrating the standard linear hodograph system associated with 2 2 homogeneous models is also revisited and a number of results obtained elsewhere of relevant interest in wave problems are recovered as a particular case along the lines of the proposed reduction approach different examples of 2 2 governing models are analysed thoroughly in order to highlight the flexibility of the provided solutions to describe hyperbolic dissipative wave processes

a globally exponentially stable tracking controller for mechanical systems using position feedback a solution to the problem of global exponential tracking of mechanical systems without velocity measurements is given in the technical note the proposed controller is obtained combining a redesign of the recently reported exponentially stable immersion and invariance velocity observer and a new state feedback passivity based controller which assigns to the closed loop a port hamiltonian structure with a desired energy function the result is applicable to a large class of mechanical systems including those with unbounded inertia matrix and possible presence of friction forces unlike previous results that rely on the presence exact knowledge and pervasiveness of these forces our design treats them as disturbances which are suitably compensated

global stabilization of nonlinear cascade systems abstract we present sufficient conditions for the global stabilizability of two cascade connected nonlinear systems these are based on general results concerning global asymptotic stability of triangular systems which are proved in the last section for polynomial systems in particular the stabilizing feedback is given explicitly

linear rank tests for the nonresponders problem with censored data summary in a two sample setting a two parameter mixture model is postulated for the treated patients where a proportion of the patients improve and the remaining proportion of nonresponders behave like the control patients the response is subject to random censoring censored data versions of linear rank statistics are developed in order to detect improvement due to treatment the tests are compared to standard tests such as the logrank test in terms of asymptotic relative efficiency empirical power and performance on real data

biometrika centenary survival analysis although papers relating to survival analysis have appeared in biometrika since the very first issue the current emphasis on the topic in this journal is fairly new especially as it relates to applications in biostatistics this survey traces the development of survival analysis throughout the twentieth century as reflected in the pages of biometrika focusing primarily on work published since 1980

canonical transformation and stabilization of generalized hamiltonian systems abstract this paper introduces generalized canonical transformations for generalized hamiltonian systems which convert a generalized hamiltonian system into another one and preserve the generalized hamiltonian structure of the original as in classical mechanics it is expected that canonical transformations will provide new insights and fundamental tools for both analysis and synthesis of those systems firstly the class of generalized canonical transformations and some of their properties are indicated secondly it is shown how to stabilize the generalized hamiltonian systems using canonical transformations in addition some examples illustrate how such transformations are utilized for control systems design

technical communique global output feedback tracking control for a class of lagrangian systems the problem of global tracking control without velocity measurement of the so called euler lagrange systems has been paid a lot of attention for the past several years in this note a nice property of one degree of freedom euler lagrange systems is highlighted which in particular allows us to obtain a new solution to the problem of tracking control for this class of systems the solution is under the form of a linear like observer based controller which gives fairly good results as illustrated in the simulation the method can be generalized to any system having the same property

rank tests for survival analysis a comparison by analogy with games several commonly used two sample linear rank tests for censored data have been shown to be closely linked in mathematical structure this pedagogical paper elucidates the relationships among the tests by introducing a videogame played between a boys team and a girls team with different rules of payment by the consecutive losers considered depending on the rule of payment the total amount of money the girls win as a team becomes the wilcoxon statistic the savage statistic or their generalizations under censoring

estimating regression parameters using linear rank tests for censored data a class of estimates for regression parameters in a linear model with right censored data is proposed these estimates are derived by using linear rank tests for right censored data as estimating equations they are shown to be consistent and asymptotically normal with covariance matrix for which estimates are proposed efficient estimates within this class are derived together with conditions when they are fully efficient 0 introduction the problem of estimating regression coefficients using ranks has received much attention in the literature for uncensored data and the results are summarized very nicely in hettmansperger 1984 there has also been some work with censored data for the two sample problem specifically louis 1981 considered estimation of a scale change between two distributions with the use of a log rank test whereas wei and gail 1983 generalize to other linear rank tests as well we shall consider the general problem of multiple linear regression and show how linear rank tests can be used as estimating equations the resulting linear rank estimates will be shown to be asymptotically normal with variances that can be estimated consistently we shall also look at the efficiency of these estimates under various situations

robust energy shaping control of mechanical systems the problem of robustness improvement vis a vis external disturbances of energy shaping controllers for mechanical systems is addressed in this paper first it is shown that if the inertia matrix is constant constant disturbances both matched and unmatched can be rejected simply adding a suitable integral action interestingly not at the passive output for systems with non constant inertia matrix additional damping and gyroscopic forces terms must be added to reject matched disturbances and moreover enforce the property of integral input to state stability with respect to matched disturbances the stronger property of input to state stability this time with respect to matched and unmatched disturbances is ensured with further addition of nonlinear damping finally it is shown that including a partial change of coordinates the controller can be significantly simplified preserving input to state stability with respect to matched disturbances

riemann problems and exact solutions to a traffic flow model within the theoretical framework of differential constraints method a nonhomogeneous model describing traffic flows is considered classes of exact solutions to the governing equations under interest are determined furthermore riemann problems and generalized riemann problems which model situations of interest for traffic flows are solved

the problem of a covariate time qualitative interaction in a survival study we introduce a test for the equality of two survival distributions against the specific alternative of crossing hazards although this kind of alternative is somewhat rare designing a test specifically aimed at detecting such departures from the null hypothesis in this direction leads to powerful procedures upon which we can call in those few cases where such departures are suspected furthermore the proposed test and an approximate version of the test are seen to suffer only moderate losses in power when compared with their optimal counterparts should the alternative be one of proportional hazards our interest in the problem is motivated by clinical studies on the role of acute graft versus host disease as a risk factor in leukemic children and we discuss the analysis of this study in detail the model we use in this work is a special case of the one introduced by anderson and senthilselvan 1982 applied statistics 31 44 51 we propose overcoming an inferential problem stemming from their model by using the methods of davies 1977 biometrika 64 247 254 1987 biometrika 74 33 43 backed up by resampling techniques we also look at an approach relying directly on resampling techniques the distributional aspects of this approach under the null hypothesis are interesting but practically its behaviour is such that its use cannot be generally recommended outlines of the necessary asymptotic theory are presented and for this we use the tools of martingale theory

distributed global output feedback control for a class of euler lagrange systems this paper investigates the distributed tracking control problem for a class of euler lagrange multiagent systems when the agents can only measure the positions in this case the lack of the separation principle and the strong nonlinearity in unmeasurable states pose severe technical challenges to global output feedback control design to overcome these difficulties a global nonsingular coordinate transformation matrix in the upper triangular form is first proposed such that the nonlinear dynamic model can be partially linearized with respect to the unmeasurable states and a new type of velocity observers is designed to estimate the unmeasurable velocities for each system then based on the outputs of the velocity observers we propose distributed control laws that enable the coordinated tracking control system to achieve uniform global exponential stability both theoretical analysis and numerical simulations are presented to validate the effectiveness of the proposed control scheme

dynamics and control of a class of underactuated mechanical systems this paper presents a theoretical framework for the dynamics and control of underactuated mechanical systems defined as systems with fewer inputs than degrees of freedom control system formulation of underactuated mechanical systems is addressed and a class of underactuated systems characterized by nonintegrable dynamics relations is identified controllability and stabilizability results are derived for this class of underactuated systems examples are included to illustrate the results these examples are of underactuated mechanical systems that are not linearly controllable or smoothly stabilizable

control of nonlinear underactuated systems in this paper we introduce a new method to design control laws for nonlinear underactuated systems our method produces an infinite dimensional family of control laws whereas most control techniques only produce a finite dimensional family these control laws each come with a natural lyapunov function the inverted pendulum cart is used as an example in addition we construct an abstract system that is open loop unstable and cannot be stabilized using any linear control law and demonstrate that our method produces a stabilizing control law 2000 john wiley sons inc

energy shaping of mechanical systems via pid control and extension to constant speed tracking in a recent contribution it was shown that a class of mechanical systems which contains many practical examples can be stabilized via energy shaping without solving partial differential equations the proposed controller consists of two terms a partial linearizing state feedback and a linear pid loop around two new passive outputs in this brief note we prove that the first admittedly non robust step can be obviated leaving only the linear pid a second contribution of the note is to propose a slight modification to the controller to go beyond regulation tasks being able to follow ramp references in the actuated coordinates

linear rank statistics for truncated data summary motivated by prentice s 1978 generalization of linear rank statistics for censored data we introduce a similar kernel for deriving linear rank statistics for truncated data they take very similar forms to those of prentice s statistics moreover we also show that they can be expressed equivalently in weighted log rank type forms thus providing natural variance estimators explicit forms corresponding to wilcoxon and log rank tests are obtained extensions to data subject to both left truncation and right censoring are provided

observer design for unilaterally constrained lagrangian systems a passivity based approach this paper addresses the problem of state estimation in nonlinear lagrangian dynamical systems with frictionless unilateral constraints using the position measurement as output the discontinuous velocity variable in such systems is modeled as a function of bounded variation so that zeno phenomenon is not ruled out since the derivative of such functions is represented with the lebesgue stieltjes measure the framework of measure differential inclusions mdis is used to describe the dynamics a class of estimators is proposed which also uses the framework of mdis and is shown to generate asymptotically converging state estimates the existence and uniqueness of solutions for the proposed estimators is rigorously proven the global stability of error dynamics is analyzed using the generalized lyapunov methods for functions of bounded variation as particular cases of our estimators we provide an explicit construction of a full order observer and a reduced order observer

three classes of censored data rank tests strengths and weaknesses under censoring summary nonparametric tests are useful when definite parametric alternatives are not available the behaviour under censoring of extensions of the tests is used to delineate three distinct classes of censored data rank tests asymptotically efficient approximately distribution free and approximately unbiased section 2 gives qualitative comparisons 3 gives some representative numerical comparisons the pitman efficiencies approximated by lee desu gehan 1975 from simulations with 50 observations in each group are shown to agree with asymptotic calculations 1 weighted log rank tests it is assumed that two samples of randomly censored observations are available that is that the true lifetimes yij have cumulative distribution functions f y i oj for j 1 n i i 1 2 that the censoring times cij have cumulative distribution functions h y i of and that the observable quantities are xij min yij c and dij xij yij where a denotes the indicator function of the set a it is assumed that 01 0 that f t 1 0 is continuous in 0 and that the null hypothesis is 61 02 0 the true value of 02 will be denoted by 0 and the functions f t i 0 and h t i 0 will be abbreviated to f and h survival distributions will be denoted by a bar so that f t 1 f t the hazard rates of f and f t 10 will be denoted by a and ao respectively the test statistics studied are functions of di t the number of deaths observed before time t in the ith sample ri t the number at risk at time t in the ith sample and aj an estimator of the cumulative hazard function for the ith sample these functions are defined formally by n i n i

new class of control laws for robotic manipulators part 1 non adaptive case a new class of exponentially stabilizing control laws for joint level control of robot arms is introduced it has recently been recognized that the non linear dynamics associated with robotic manip