Least-squares integration of one-dimensional codistributions with application to approximate feedback linearization

We study the problem of approximating one-dimensional nonintegrable codistributions by integrable ones and apply the resulting approximations to approximate feedback linearization of single-input systems. The approach derived in this paper allows a linearizable nonlinear system to be found that is close to the given system in a least-squares (L ₂) sense. A linearly controllable single-input affine nonlinear system is feedback linearizable if and only if its characteristic distribution is involutive (hence integrable) or, equivalently, any characteristic one-form (a one-form that annihilates the characteristic distribution) is integrable. We study the problem of finding (least-squares approximate) integrating factors that make a fixed characteristic one-form close to being exact in anL ₂ sense. A given one-form can be decomposed into exact and inexact parts using the Hodge decomposition. We derive an upper bound on the size of the inexact part of a scaled characteristic one-form and show that a least-squares integrating factor provides the minimum value for this upper bound. We also consider higher-order approximate integrating factors that scale a nonintegrable one-form in a way that the scaled form is closer to being integrable inL ₂ together with some derivatives and derive similar bounds for the inexact part. This allows a linearizable nonlinear system that is close to the given system in a least-squares (L ₂) sense together with some derivatives to be found. The Sobolev embedding techniques allow us to obtain an upper bound on the uniform (L _∞) distance between the nonlinear system and its linearizable approximation. This research was supported in part by NSF under Grant PYI ECS-9396296, by AFOSR under Grant AFOSR F49620-94-1-0183, and by a grant from the Hughes Aircraft Company.     

Parents and procedures: a randomized controlled trial

INTRODUCTION: Previous work has shown that parents prefer to be present when their children undergo common invasive procedures, although physicians are ambivalent about parental presence. PURPOSE: To determine the effect of a parent-focused intervention on the pain and performance of the procedure, anxiety of parents and clinicians, and parental satisfaction with care. POPULATION: Children younger than 3 years old undergoing venipuncture, intravenous cannulation, or uretheral catheterization. SETTING: Pediatric emergency department of Boston City Hospital. DESIGN: Randomized controlled trial with three groups; parents present and given instructions on how to help their children; parents present, but no instructions given; and parents not present. INTERVENTION: The parents were instructed to touch, talk to, and maintain eye contact during the procedure. RESULTS: A total of 431 parents was randomized to the intervention (N = 153), present (N = 147), and not present (N = 131) groups. The groups were equivalent with respect to measured sociodemographic variables and parents' previous experience in the pediatric emergency department. No differences emerged with respect to pain (3-point scale measured by parent and clinician, and analysis of cry); performance of the procedure (number of attempts, completion of procedure by first clinician, time); clinician anxiety; or parental satisfaction with care. Parents who were present were more likely to rate the pain of the children as extreme/severe (52%) in comparison to clinicians (15%, kappa .07, poor agreement) and were significantly less anxious than parents who were not present. CONCLUSION: Overall, the intervention was not effective in reducing the pain of routine procedures. Parental presence did not negatively affect performance of the procedure or increase clinician anxiety. Parents who were present were less anxious than those who were not present. CLINICAL IMPLICATION: In general, parents have indicated that they want to be present when their children undergo procedures. The results of this study challenge the traditional belief that parental presence negatively affects our ability to successfully complete procedures. We should encourage parents who want to be present to stay during procedures.     

Interactions in the complement-mediated lysis of blood group AB erythrocytes sensitized simultaneously with anti-A and anti-B monoclonal antibodies

The lysis of group AB erythrocytes by human complement was studied by different anti-A and anti-B IgM monoclonal antibodies (mabs) in a 51Cr-release assay. The concentration of membrane-bound immunoglobulin was detected by ELISA, and the amount of C1q and C3 bound to sensitized red cells was measured by using purified, 125I-labelled molecules. We have demonstrated that there is an exponential relationship between the concentration of the sensitizing IgM mabs and C1q binding to the sensitized AB cell. The efficiency of binding was related to the number of antibodies bound; thus, anti-A sensitized cells bound 3-6 times more C1q than anti-B sensitized cells did. AB cells, on the other hand, bound similar amounts of C3 whether anti-A or anti-B was present. The lytic efficiencies of the various IgM mabs during short incubation times were different, suggesting that the complement activation rates vary widely with different antibodies on the AB cell membrane. The binding of C1q to an antibody-sensitized target activates a cascade, whose components may migrate away from the sensitizing antibody; interactions between the activation processes generated by the anti-A and anti-B antibodies may thus occur. Choosing appropriate pairs of anti-A and anti-B mabs for the simultaneous sensitization of AB cells has indeed resulted in stimulation in some and inhibition in other combinations of mabs. It is suggested that stimulation is observed when the activated intermediates are produced in excess, whereas inhibition occurs when a shortage of activated intermediates prevents mutual utilization.     

Scheduling in or-parallel Prolog systems: Survey and open problems

Implementation of or-parallel Prolog systems offers a number of interesting scheduling problems. The main issues are the interaction between memory models and scheduling, ordering of multiple solutions, and scheduling of speculative work. The problems occur partly because of the design choices (e.g. the choice of a memory model), and partly because of the desire to maintain observational equivalence between parallel and sequential implementations of Prolog, while achieving high efficiency. In the first part of this paper a common framework for discussing scheduling in or-parallel systems is introduced, and also a collection of issues that must be addressed in such systems is presented. In the second part of the paper we survey a number of solutions to these problems comparing their efficiency whenever possible. We close the survey with a short discussion of open problems.Current association: Carlstedt Elektronik AB     

Molecular orientation and stress in biaxially deformed polymers. II. Steady potential flow

The development of biaxial segmental orientation and stress in a flexible-chain polymer fluid subjected to steady biaxial extensional flow is analyzed. Closed-formula model based on the Padè approximation of the inverse Langevin function in the non-Gaussian distribution of the chain end-to-end vectors is considered. The approach is free from the limitations related to finite chain extensibility and slow convergence of the series expansion formulations at higher chain deformations.Segmental orientation is characterized by the average orientation tensor, related axial orientation factors and global orientation anisotropy. Orientational behavior and corresponding stresses in the biaxial elongational potential flow are discussed in a wide range of elongation rates. Orientation characteristics calculated for the biaxial flow deformation are much higher than those predicted for the affine biaxial stretch deformation in polymer solids.     

Inhibition of nitrification in the packed bed reactors by selected organic compounds

The effect of methanol, acetone, formalin and glucose on the nitrification process in the packed bed reactors has been investigated. For the utilized compounds the inhibition constant K_i was determined according to Dixon's method. The determined values were as follows: methanol K_i = 116.0 mg l^?1; acetone K_i = 804.2 mg l^?1; formalin K_i = 61.5 mg l^?1. The value of K_i for glucose has not been determined because glucose in applied concentration up to 11,325 mg l^?1 had no effect on the nitrification course.     

AlxGa−xAs/GaAs heterostructure characterization by wet chemical etching

Selective wet chemical etching of the Al_xGa_1−xAs/GaAs system has been applied to heterostructure characterization. Samples of LPE grown AlGaAs/GaAs laser double-heterostructures and separate confinement heterostructures as well as antiresonant reflecting optical waveguides heterostructures were treated with “I2 solution” (I₂:KI:H₂O) and hydrochloric acid. These compounds selectively etch the ternary Al_xGa_1−xAs layers, but with different “threshold composition” x_th values (the x value is that above which the etching rate of a given compound increases sharply). Selectively etched samples have been examined by SEM. The experimental dependence of etching rate on the x value for I2 solution has been derived. From this dependence, the x composition of any ternary layer can be estimated simply. Observations were made of the “microscopic” properties of the heterostructure, such as the smoothness of the interfaces and the uniformity of layers. All imperfections resulting from the growth process, such as interface perturbations or compositional nonuniformity of layers, are clearly seen. An additional advantage of this etching technique is its simplicity. It allows quick examination of grown heterostructure for the selection of wafers for further processing.     

Technical risk involved in long-term operation of steam turbines

The scope of the paper is the assessment of the technical risk involved in long-term operation of power units. Detailed analyses have been conducted for steam turbine components. The sources and consequences of risk have been identified and the probability of turbine components failure calculated. The quantitative assessment of the risk has been made and possibilities of its reduction discussed.