Smooth stabilisation of nonholonomic robots subject to disturbances

In this paper, we address the problem of stabilisation of robots subject to nonholonommic constraints and external disturbances using port-Hamiltonian theory and smooth time-invariant control laws. This should be contrasted with the commonly used switched or time-varying laws. We propose a control design that provides asymptotic stability of an manifold (also called relative equilibria)-due to the Brockett condition this is the only type of stabilisation possible using smooth time-invariant control laws. The equilibrium manifold can be shaped to certain extent to satisfy specific control objectives. The proposed control law also incorporates integral action, and thus the closed-loop system is robust to unknown constant disturbances. A key step in the proposed design is a change of coordinates not only in the momentum, but also in the position vector, which differs from coordinate transformations previously proposed in the literature for the control of nonholonomic systems. The theoretical properties of the control law are verified via numerical simulation based on a robotic ground vehicle model with differential traction wheels and non co-axial centre of mass and point of contact.

Robust estimation using the Huber function with a data-dependent tuning constant

Robust estimation often relies on a dispersion function that is more slowly varying at large values than the square function. However, the choice of tuning constant in dispersion functions may impact the estimation efficiency to a great extent. For a given family of dispersion functions such as the Huber family, we suggest obtaining the "best" tuning constant from the data so that the asymptotic efficiency is maximized. This data-driven approach can automatically adjust the value of the tuning constant to provide the necessary resistance against outliers. Simulation studies show that substantial efficiency can be gained by this data-dependent approach compared with the traditional approach in which the tuning constant is fixed. We briefly illustrate the proposed method using two datasets.

Effects of variance-function misspecification in analysis of longitudinal data

The approach of generalized estimating equations (GEE) is based on the framework of generalized linear models but allows for specification of a working matrix for modeling within-subject correlations. The variance is often assumed to be a known function of the mean. This article investigates the impacts of misspecifying the variance function on estimators of the mean parameters for quantitative responses. Our numerical studies indicate that (1) correct specification of the variance function can improve the estimation efficiency even if the correlation structure is misspecified; (2) misspecification of the variance function impacts much more on estimators for within-cluster covariates than for cluster-level covariates; and (3) if the variance function is misspecified, correct choice of the correlation structure may not necessarily improve estimation efficiency. We illustrate impacts of different variance functions using a real data set from cow growth.

Protein turnover in malnourished patients with cystic fibrosis: Effects of elemental and nonelemental nutritional supplements

To evaluate the relative efficacy of nonele-mental versus semielemental enteral supplements for nutritional rehabilitation of cystic fibrosis (CF) patients, whole-body protein turnover using the [15N]glycine method was studied in nine malnourished CF patients during enteral feedings, in a block design study compar-ing a semielemental formula (Criticare), a higher protein density but nonelemental formula (Traumacal) (T), and a nonelemental formula that had been modified to become isocaloric and isonitrogenous to the semielemental formula (modified Traumacal, MT). No significant differences in rates of protein synthesis or catabolism were observed comparing the three formulas. However the higher protein density nonelemental formula resulted in higher net protein deposition compared to the other two formulas (T + 0.42 g kg-110 h-1versus 0.33 g kg-110 h-1for Criticare and-0.59 g kg-110 h-1for MT), although this was significant (p < 0.05) for the MT versus T comparison only. This study lends support to the use of less expensive nonelemental formulas for the nutritional management of malnourished patients with CF. © 1990 Raven Press Ltd, New York.

Cyclosporin-responsive enteropathy and protracted diarrhea

We describe a child bom to unrelated parents who developed severe protracted secretory type diarrhea associated with subtotal villus atrophy and intestinal inflammation at the age of 19 months. No infectious, metabolic, or anatomical basis for this condition was identified and the child required total parenteral nutrition for a period of 18 months despite trials of special enteral formulas, steroids, and anti-inflammatory agents. This refractory “enteropathy” responded dramatically to the introduction of cyclosporin, with cessation of the secretory diarrhea, recovery from the enteropathy, and cessation of parenteral nutrition. The symptoms relapsed when cyclosporin was briefly discontinued and improved following reintroduction of this drug. This experience suggests a role for immune factors in the pathogenesis of the enteropathy in this case and that a trial of cyclosporin is worthy of consideration in similar cases. © 1990 Raven Press, Ltd., New York.

Working correlation structure misspecification, estimation and covariate design: Implications for generalised estimating equations performance

The method of generalised estimating equations for regression modelling of clustered outcomes allows for specification of a working matrix that is intended to approximate the true correlation matrix of the observations. We investigate the asymptotic relative efficiency of the generalised estimating equation for the mean parameters when the correlation parameters are estimated by various methods. The asymptotic relative efficiency depends on three-features of the analysis, namely (i) the discrepancy between the working correlation structure and the unobservable true correlation structure, (ii) the method by which the correlation parameters are estimated and (iii) the 'design', by which we refer to both the structures of the predictor matrices within clusters and distribution of cluster sizes. Analytical and numerical studies of realistic data-analysis scenarios show that choice of working covariance model has a substantial impact on regression estimator efficiency. Protection against avoidable loss of efficiency associated with covariance misspecification is obtained when a 'Gaussian estimation' pseudolikelihood procedure is used with an AR(1) structure.

Estimating equations for removal data analysis

We consider the problem of estimating a population size from successive catches taken during a removal experiment and propose two estimating functions approaches, the traditional quasi-likelihood (TQL) approach for dependent observations and the conditional quasi-likelihood (CQL) approach using the conditional mean and conditional variance of the catch given previous catches. Asymptotic covariance of the estimates and the relationship between the two methods are derived. Simulation results and application to the catch data from smallmouth bass show that the proposed estimating functions perform better than other existing methods, especially in the presence of overdispersion.

Gittins indices and constrained allocation in clinical trials

We explore the use of Gittins indices to search for near optimality in sequential clinical trials. Some adaptive allocation rules are proposed to achieve the following two objectives as far as possible: (i) to reduce the expected successes lost, (ii) to minimize the error probability at the end. Simulation results indicate the merits of the rules based on Gittins indices for small trial sizes. The rules are generalized to the case when neither of the response densities is known. Asymptotic optimality is derived for the constrained rules. A simple allocation rule is recommended for one-stage models. The simulation results indicate that it works better than both equal allocation and Bather's randomized allocation. We conclude with a discussion of possible further developments.

Aavan meren täällä puolen : Arkkityyppiset piirteet ja amerikkalaisvaikutteet suosituimmissa suomalaisissa molli-iskelmissä

What are the musical features that turn a song into a hit? The aim of this research is to explore the musical features of hit tunes by studying the 224 most popular Finnish evergreens from the 1930s to the 1990s. It is remarkable, that 80-90% of Finnish oldies are in a minor key, though parallel major keys have also been widely employed within single pieces through, for example, modulations. Furthermore, melodies are usually diatonic, staying mostly in the same key. Consequently, chromatically altered tones in the melody and short modulations in the bridge sections become more prominent. I have concentrated in particular on the melodic lines in order to find the most typical melodic formulas from the data. These analyzed melodic formulas play an important role, because they serve as leading phrases and punchlines in songs. Analysis has revealed three major melodic formulas, which most often appear in the melodic lines of hit tunes. All of these formulas share common thematic ground, because they originate from the triadic tonic chord. Because the tonic chord is the most conventional opening chord in the verse parts, it is logical that these formulas occur most often in verses. The strong dominance of these formulas is very much a result of the rhythmic flexibility they possess; for instance, they can be found in every musical style from waltz to foxtrot. Alongside the major formulas lies a miscellaneous group of other tonic-related melodic formulas. One group of melodic formulas consists of melodic quotations. These quotations appear in a different musical context, for instance in a harmonically altered form, and are therefore often difficult to recognize as such. Yet despite the contextual manipulation, the distinctive character of the cited melody usually remains the same. Composers have also made use of certain popular chord-progressions in order to create new but familiar-sounding melodies. The most important individual progression in this case is what is known as a "circle of fifths" and its shortened, prolonged and altered versions. Because that progression is harmonically strong, it is also a contrastive tool used especially in chorus parts and middle sections (AABA). I have also paid attention to ragtime and jazz influences, which can be found in harmony parts and certain melody notes, which extend, suspend or alter the accompaning chords. Other influences from jazz and ragtime in the Finnish evergreen are evident in the use of typical Tin Pan Alley popular song forms. The most important is the AABA form, which dominates over the data along with the verse/chorus-type popular song form. To briefly illustrate the main results, the basic concept of the hit tune can be traced back to Tin Pan Alley songs, whereas the major stylistic aspects, such as minor keys and musical styles, bear influences from Russian, Western European, and Finnish traditions.

Vapaata mielenjuoksua : Suomenkielisen freestyle-rapin ilmenemismuodot, estetiikka ja kompositio

The thesis is about Finnish freestyle-rap, a modern form of oral poetry producing improvised rap lyrics at the moment of performance. The research material consists of interviews with seven freestyle experts and a DVD from Finnish Rap Championships 2005 containing freestyle-rap. The thesis has three goals: describing the different variations or subgenres of freestyle, outlining the esthetics and register of freestyle, and examining the composition of freestyle. The research material acts a central role in the thesis but the theoretical framework is also wide: cornerstones are John Miles Foley's register analysis, oral formulaic theory and William Levelt's psycholinguistic theory on planning of speech. Freestyle is divided into three partially overlapping genres with slight variation in conventions. The genres are freestyle battle, cypher, and live freestyle. Freestyle's esthetics are composed of certain qualities and preferences: the rhyme is a syllabically repeating vocal rhyme. The rapping must be synchronised with the background rhythm and the rhyme comes in the end of the line. The lyrics must be somehow anchored to the surroundings and the moment of performance. The style of rapping, ie. flow, has to be personal one way or the other. Individual formulas are used to some extent in freestyle compostition. When planning the lines, all other content is subordinate to the rhyme, whose phonetic processing is the primary act in the planning of freestyle. This discovery sets Levelt's theory open to doubt.

Non-linear resonance in strings under narrow band random excitation, part I: Planar response and stability

Non-linear planar response of a string to planar narrow band random excitation is investigated in this paper. A response equation for the mean square deflection σ2 is obtained under a single mode approximation by using the equivalent linearization technique. It is shown that the response is triple valued, as in the case of harmonic excitation, if the centre frequency of excitation Ω lies in a certain specified range. The triple valued response occurs only if the excitation bandwidth β is smaller than a critical value βcrit which is a monotonically increasing function of the intensity of excitation. An approximate method of investigating the almost sure asymptotic stability of the solution is presented and regions of instability in the Ω-σ2 plane have been charted. It is shown that planar response can become unstable either due to an unbounded growth of the in-plane component of motion or due to a spontaneous appearance of an out-of-plane component.

Incompressible boundary layer for longitudinal flow over a cylinder with an applied magnetic field

The flow, heat and mass transfer problem for a steady laminar incompressible boundary layer flow in an electrically conducting fluid over a longitudinal cylinder with an applied magnetic field has been studied. The partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. The results are found to be strongly dependent on the magnetic field and dissipation parameter. The effect of the mass transfer is more pronounced on the skin friction than on the heat transfer. The results have been compared with those of the series solution, the asymptotic solution, the Glauert and Lighthill's solution, local similarity, local nonsimilarity and difference-differential methods. Good agreement is found with all of them, except with the results of the local similarity and series solution methods.

A novel approach to 6-DOF adaptive trajectory tracking control of an AUV in the presence of parameter uncertainties

In this paper, the trajectory tracking control of an autonomous underwater vehicle (AUVs) in six-degrees-of-freedom (6-DOFs) is addressed. It is assumed that the system parameters are unknown and the vehicle is underactuated. An adaptive controller is proposed, based on Lyapunov׳s direct method and the back-stepping technique, which interestingly guarantees robustness against parameter uncertainties. The desired trajectory can be any sufficiently smooth bounded curve parameterized by time even if consist of straight line. In contrast with the majority of research in this field, the likelihood of actuators׳ saturation is considered and another adaptive controller is designed to overcome this problem, in which control signals are bounded using saturation functions. The nonlinear adaptive control scheme yields asymptotic convergence of the vehicle to the reference trajectory, in the presence of parametric uncertainties. The stability of the presented control laws is proved in the sense of Lyapunov theory and Barbalat׳s lemma. Efficiency of presented controller using saturation functions is verified through comparing numerical simulations of both controllers.

Development of pseudo-two-dimensional turbulent wakes

Pseudotwo-dimensional wakes are generated by introducing spanwise cellular structures into an otherwise plane turbulent wake by means of the castellated blunt trailing edges of different configurations. The transverse growths of these coflowing cellular wakes are found to be independent of each other without any noticeable spanwise interaction. This wake growth is examined in the light of the plane equilibrium wake analysis. Though these wakes are not found to be exactly self-similar, their growth shows a nonmonotonous approach toward the asymptotic state appropriate to that of a plane wake. The dye emission in the wakes illustrated a coherent vortical structure in the transverse plane, similar to that of the usual two-dimensional wake, in spite of the initial spanwise irregularities.

On a linear steady-state system of equations in microcontinuum fluid mechanics

Galerkin representations and integral representations are obtained for the linearized system of coupled differential equations governing steady incompressible flow of a micropolar fluid. The special case of 2-dimensional Stokes flows is then examined and further representation formulae as well as asymptotic expressions, are generated for both the microrotation and velocity vectors. With the aid of these formulae, the Stokes Paradox for micropolar fluids is established.