bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic optimization for hydro‐thermal power systems
Authors: Halliburton T. S. , Sirisena H. R.
Published: July 2007

A suboptimal stochastic optimization method for the long‐term scheduling of a hydroelectric reservoir is described. The objective of the optimization is to minimize thermal station fuel costs, in a mixed hydro‐thermal power system, over a one‐year horizon. Exact stochastic and deterministic solutions, obtained by dynamic programming (DP) for a simple one‐reservoir model, are compared. The two solutions differ significantly, indicating that deterministic solutions to the problem are inadequate. Stochastic DP is not computationally feasible for a multi‐reservoir system. A suboptimal linear feedback controller with non‐Gaussian reservoir water storages is then developed. It approximates the stochastic DP solution for one reservoir very well and is capable of extension to a multi‐reservoir version.
Optimal housing investment of a landlord
Authors: Saito Osami , Itaya Yuji , Morishima Takaharu
Published: July 2007

This paper presents the optimal behaviour of a landlord. A dynamical model is introduced for the deterioration of housing quality with periodic maintenance, and the optimal policy is investigated for maximizing the landlord's profit with respect to the construction time, the initial quality and the maintenance investment.
Numerical solution of the minimum‐time flight of a glider through a thermal by use of multiple shooting methods
Authors: Lorenz Jürgen
Published: July 2007

The problem of the time‐optimal flight of a glider through a given thermal is treated with the calculus of variations. The resulting two‐point boundary value problem is solved using the multiple shooting method. Solutions are obtained for various parameter values. For special values of these parameters, a branching of the solutions is observed. Additional solutions are obtained for which the control variable and the normal load factor are constrained by their maximum allowed values.
Decentralized structures for stream water quality control problems
Authors: Mahmoud Magdi S. , Hassan Mohamed F. , Saleh Saad J.
Published: July 2007

In this paper, the evolution of stream water quality components is described by a linear dynamic model of order seven. The model is controlled through two actions: one by changing the water discharge into the basin and another by manipulating the effluent flow rate. Computation of the decentralized gains is performed using two different multilevel structures. Results of simulating a reach of the River Nile are presented.
Digital implementation of strong variational algorithms
Authors: Virk G. S.
Published: July 2007

The paper presents numerical results for several optimal control problems. The results are derived using an algorithm based on strong variations in control (Mayne and Polak1, Virk2) and are, to the author's knowledge, the first such simulations. Delay as well as delay‐free examples are considered.
Phase lag and lead weighting in linear‐quadratic control
Authors: Anderson Brian D. O. , Gibson John A. , Sirisena Harsha R.
Published: July 2007

The effect of introducing a first order lag or lead weighting function into an otherwise conventional linear‐quadratic optimization problem is examined. Properties of the optimal compensator are derived, and the effect on robustness of the optimal system in different frequency ranges is examined.
Performance index sensitivity of optimal control systems with uncertain parameters
Authors: Ronge Peter
Published: July 2007

The solutions of optimal control problems are sensitive to the changes of parameters which can occur due to either their statistical nature or to an identification which is only approximate. To allow a reduction of this sensitivity two scalar sensitivity measures are proposed which can be incorporated into an augmented performance index. Different interpretations of the measures are given.

As a first application, the problem of an insensitive feedforward control is investigated. An efficient numerical method for its solution is given. An example demonstrates not only the feasibility of this new approach but also the possible improvement in comparison to the standard optimal control procedure for problems where knowledge about system uncertainties has to be included in the design.
Traffic regulation of an underground railway transportation system by state feedback
Authors: Campion G. , Van Breusegem V. , Pinson P. , Bastin G.
Published: July 2007

The commonly used state‐space models for the traffic description of urban underground railway lines are not suitable for practical on‐line control. On the other hand, the proposed orginal linear formulation is very convenient for optimal state feedback control implementation. Results of simulations relative to a theoretical line as well as to the Brussels Railway lines show the benefit to be expected using this new formulation for on‐line traffic control.
Auto‐weighted minimum‐variance self‐tuning controller
Authors: Zachariah K. J. , Warwick K.
Published: July 2007

A self‐tuning controller which automatically assigns weightings to control and set‐point following is introduced. This discrete‐time single‐input single‐output controller is based on a generalized minimum‐variance control strategy. The automatic on‐line selection of weightings is very convenient, especially when the system parameters are unknown or slowly varying with respect to time, which is generally considered to be the type of systems for which self‐tuning control is useful. This feature also enables the controller to overcome difficulties with non‐minimum phase systems.
Some remarks about open‐loop control in stochastic quasilinear systems
Authors: Socha Leslaw
Published: July 2007

A method of obtaining the optimal control in quasilinear systems which are influenced by disturbances is presented. The analysis is carried out for second‐order stationary and non‐stationary Gaussian processes. First, the stochastic problem is changed into an equivalent deterministic problem, and next the optimal control is constructed from the maximum principle. This method is applied to the optimal temperature profile in a chemical reactor. The results are illustrated by a numerical example.
An implicit pole‐assignment self‐tuning regulator
Authors: Karam K. Z. , Warwick K. , Farsi M.
Published: July 2007

A new self‐tuning implicit pole‐assignment algorithm is presented which, through the use of a pole compression factor and different RLS model and control structures, overcomes stability and convergence problems encountered in previously available algorithms. Computational requirements of the technique are much reduced when compared to explicit pole‐assignment schemes, whereas the inherent robustness of the strategy is retained.
Stochastic adaptive control of non‐minimum phase systems
Authors: Hersh M. A. , Zarrop M. B.
Published: July 2007

The explicit self‐tuning control of linear systems with constant but unknown parameters is analysed. The class of single‐input/single‐output, discrete‐time stochastic systems with coloured noise is considered without imposing a minimum‐phase condition. A stochastic approximation type of identification algorithm coupled with a general linear control law structure satisfying weak conditions is shown to lead to the required stability properties of the closed‐loop system. Similar approaches have been previously proposed for deterministic systems and for stochastic systems with uncorrelated disturbances. The specific example of a pole‐shifting algorithm is considered and it is shown that the required asymptotic behaviour is achieved under certain conditions.
Inadmissibility of siso singular observation lqg design
Authors: Halevi Y. , Palmor Z. J.
Published: July 2007

The widely known LQG design method for linear time invariant SISO plants may lead under certain circumstances to closed loop systems that have no stability margins; their sensitivity is infinite and the resulting system is non‐causal. We refer to such systems as inadmissible ones. This rather surprising phenomenon is analysed in the paper and is shown to be a generic property, depending on structural features of the plant, noises and criteria involved. Necessary and sufficient conditions guaranteeing admissibility of LQG design, in both the frequency and the time domains, are presented and proved. These conditions enable an a priori detection of such possible ‘traps’ in the LQG method. Although the paper focuses on LQG, some of the results are shown to be of wider applicability. It is shown that the common combination observer‐static state feedback is inadmissible if input derivatives are used by the observer. The conditions derived in the paper are used to identify suboptimal methods, developed for other purposes, by which the causality problem may be avoided. A new suboptimal method is suggested and the stability properties of suboptimal designs are discussed. In addition some apparent ambiguities regarding the stability properties of singular observation LQG designs are clarified by means of the results derived in the paper.
Non‐existence of solutions in optimal structural design
Authors: Stadler W.
Published: July 2007

Recently, much effort has been expended in establishing the well‐posedness of optimal structural design problems. Experience indicates, however, that awareness of the non‐existence of a solution may also be beneficial and can eliminate time wasted in searching for non‐existing numerical or analytical optima. Two standard approaches to non‐existence proofs are presented: the construction of suitable sequences and the use of necessary conditions — both within the context of contradiction proofs. The methods are illustrated with examples from optimal structural design ranging from the minimum weight design of an axially loaded rod to that of axisymmetrically loaded shells of revolution. It is shown that the causes of non‐existence can be the choice of function space, boundary conditions, and a discontinuous dependence on parameters, among others. Some possible guidelines for a successful formulation of well‐posedness in structural design are included.
An adaptive filter for dynamic positioning
Authors: Gourishankar V. G. , Trybus L. , Rink R. E.
Published: July 2007

An adaptive filter is developed to estimate the low frequency (LF) drift and high frequency (HF) wave‐induced oscillations of a floating vessel. The parameters of the HF model depend on the weather and must be updated. By applying a singular perturbation approximation, we decompose the filtering problem into two separate LF and HF designs. This results in an LF Kalman filter and an HF parameter estimator. The parameter estimator is implemented as an extended Kalman‐filter‐type robust algorithm. To some extent, our approach provides a bridge between existing dynamic positioning filter synthesis techniques. Simulation results are included.
Optimal hydrothermal load flow: Formulation and a successive approximation solution for fixed head systems
Authors: El‐Hawary M. E. , Rao R. S. , Christensen G. S.
Published: July 2007

This paper deals with the optimal load flow problem in a fixed‐head hydrothermal electric power system. Equality constraints on the volume of water available for active power generation at the hydro plants as well as inequality constraints on the reactive power generation at the voltage controlled buses are imposed. Conditions for optimal load flow are derived and a successive approximation algorithm for solving the optimal generation schedule is developed. Computer implementation of the algorithm is discussed, and the results obtained from the computer solution of test systems are presented.
Neighbouring extremals of dynamic optimization problems with parameter variations
Authors: Lee A. Y. , Bryson A. E.
Published: July 2007

Neighbouring extremals of dynamic optimization problems with a known parameter vector θ and an unknown parameter vector π are considered in this paper. The parameter vector π and the control are to be optimally determined to minimize a cost functional with a given θ. With some simplifications, the neighbouring extremal problem is reduced to one of solving a linear, time‐varying, two‐point boundary value problem with integral path equality constraints. A modified backward sweep method is used to solve this problem. Example problems are solved to illustrate the validity and usefulness of the solution technique.
Decentralized control for multimachine power systems
Authors: Lu Qiang , Lu Jin , Gao Jixang , Lee Gordon K. F.
Published: July 2007

A new approach to solve the problem of designing decentralized optimal controllers for large‐scale power systems is proposed. The control law that results from the design is a decentralized one; accordingly, each subsystem is controlled only by its own variables. In using the proposed scheme, the cost functional for each subsystem is minimized, and the interacting effects between the subsystems are not ignored in deriving the control strategy. As a result, the application of the control scheme proposed by this paper provides optimality even if the subsystems are very strongly coupled. Results of investigation into the decentralized optimal control of a 10‐machine system are satisfactory.
Optimal maintenance of a system of machines with weakest‐link‐dependent performance
Authors: Teo K. L. , Wong K. H. , Goh C. J.
Published: July 2007

This paper considers the maintenance policy of a system of machines whose deterioration is dependent on the machines' quality states and maintenance efforts. The return of the system of machines, however, is dependent only on the machine with the lowest quality state. This becomes a realistic feature when the machines are arranged in series as part of an assembly line production. This feature also gives rise to an unconventional optimization problem with an interesting theoretical challenge. The problem is subsequently formulated as a constrained optimal control problem. It is first shown that the problem admits an optimal control. Then, by using the control parametrization approach, an efficient computational scheme is devised for solving the problem.
Real‐time computation of feedback controls for constrained optimal control problems. part 1: Neighbouring extremals
Authors: Pesch Hans Josef
Published: July 2007

A numerical method is developed for the real‐time computation of neighbouring optimal feedback controls for constrained optimal control problems. The first part of this paper presents the theory of neighbouring extremals. Besides a survey of the theory of neighbouring extremals, special emphasis is laid on the inclusion of complex constraints, e.g. state and control variable inequality constraints and discontinuities of the system equations at interior points. The numerical treatment of these constraints is particularly emphasized. The linearization of all necessary conditions of optimal control theory leads to a linear, mulitpoint, boundary value problem with linear jump conditions that is especially well suited for numerical treatment.
On the design of active suspension incorporating human sensitivity to vibration
Authors: Lee Allan Y. , Salman Mutasim A.
Published: July 2007

The human sensitivity to vertical acceleration at various frequencies is incorporated in the design of active suspension by using the linear quadratic regulator (LQR) control method with a frequency‐shaped cost functional. With this method, a decrease in vertical acceleration of the sprung mass is achieved over the range of frequencies that causes maximum discomfort to the human passenger.
Numerical method for the solution of the singular riccati matrix
Authors: Subrahmanyam M. B.
Published: July 2007

A computational scheme is presented for the solution of the Riccati matrix associated with time‐varying quadratic regulation. It is shown that the local truncation error of the algorithm is at most O(Δt3) where Δt is the interval of computation. The main contribution of this short communication is to demonstrate that the scheme yields the solution even in the face of singularities. Higher‐order formulae are useful when the sensitivity of the Riccati matrix to error is large.
Servo controller design based on frequency‐dependent error
Authors: Furuta Katsuhisa , Suenaga Osamu
Published: July 2007

Variables to be controlled are usually taken from measured outputs. They may be filtered and the regulation of frequency‐dependent error has been considered in the design of robust controllers. Anderson considered the frequency‐dependent linear‐quadratic (LQ) problem. The frequency‐dependent weight he considered is restricted to the phase lag and lead type. This paper considers not only regulation of general frequency‐dependent errors but also a servo controller tracking to a given reference signal in the presence of disturbances. The control law is determined either on the basis of the quadratic criterion function or by pole assignment in a region. The control law to assign poles in a region is derived from one designed for the corresponding discrete‐time system obtained by bilinear transformation.
Stochastic adaptive control of a class of non‐minimum‐phase systems
Authors: Chan C. Y. , Sirisena H. R.
Published: July 2007

This paper presents a computationally efficient pole‐zero placement adaptive controller for linear discrete stochastic systems with coloured noise. The systems are assumed to be open‐loop stable, but not necessarily minimum phase. It is shown that the algorithm asymptotically achieves the required properties of the closed‐loop system.
Applications of the exterior penalty method in constrained optimal control problems
Authors: Xing An‐Qing , Wang Chung‐Lie
Published: July 2007

This paper gives a theoretical analysis of the applications of the exterior penalty method in continuous‐time non‐linear programs and constrained optimal control problems. As an example, the Cauchy Inequality in the continuous case is proved. Also, the exterior penalty method is used to treat constrained optimal control problems. It is proved, under suitable assumptions, that a constrained optimal control problem can be solved by performing a sequence of unconstrained optimal control problems, and the constrained solution to the constrained optimal control problem can be obtained as the limit of the solutions to the sequence of unconstrained optimal control problems. In using the exterior penalty method to solve constrained optimal control problems it is usually assumed that each of the modified unconstrained optimal control problems has at least one solution. An existence theorem for these problems is also given.
Finite‐dimensional approximation for optimal fixed‐order compensation of distributed parameter systems
Authors: Bernstein Dennis S. , Rosen I. Gary
Published: July 2007

In controlling distributed parameter systems it is often desirable to obtain low‐order, finite‐dimensional controllers in order to minimize real‐time computational requirements. Standard approaches to this problem employ model/controller reduction techniques in conjunction with LQG theory. In this paper we consider the finite‐dimensional approximation of the infinite‐dimensional Bernstein/Hyland optimal projection theory. Our approach yields fixed‐finite‐order controllers which are optimal with respect to high‐order, approximating, finite‐dimensional plant models. We illustrate the technique by computing a sequence of first‐order controllers for one‐dimensional, single‐input/single‐output parabolic (heat/diffusion) and hereditary systems using a spline‐based, Ritz‐Galerkin, finite element approximation. Our numerical studies indicate convergence of the feedback gains with less than 2% performance degradation over full‐order LQG controllers for the parabolic system and 10% degradation for the hereditary system.
Structural and robust optimality of discrete‐time optimal regulators
Authors: Mirza Kais Baker , Basha Akiel E.
Published: July 2007

The following problem is discussed: given an optimal control law for a linear, discrete‐time, single‐input system with respect to some quadratic cost, determine the necessary and sufficient condition whereby this control law remains optimal in the presence of small plant parameter variations. This condition is derived and expressed in terms of the loop transfer function of the optimal system, its Nyquist plot and the transfer function from the input to the controlled variables associated with the weighting matrix.
Optimal slidesmanship in conferences with unpredictable chairmen
Authors: Hartl Richard F. , Jørgensen Steffen
Published: July 2007

Conference attendance is an area of scientific endeavour that can be very rewarding to its skilled practitioners. However, the inexperienced conference attendee (speaker) may not be aware of the rules of the game and runs a risk of making disastrous mistakes.

In this paper we are concerned with slidesmanship and wish to design optimal policies for a slidesman who must decide on such questions as the number of slides to prepare, the timing of the slides and at what time to terminate the presentation. We suggest that the slidesman is facing a forgetful audience as well as an unpredicatable chairman.
On‐line optimal terrain‐tracking system
Authors: Lee Sung Mhan , Bien Zeungnam , Park Seung O.
Published: July 2007

The problem of on‐line optimal tracking control is considered for an aircraft terrain‐following system. An on‐line optimal control law which reflects the non‐linear airborne vehicle dynamics with bounded control input is obtained by using a pointwise optimization technique called optimal decision strategy. The stability of the resulting system is also discussed. To demonstrate the feasibility and effectiveness of the proposed scheme, simulations have been performed for a realistic terrain‐following system.
Design of a low‐sensitivity, minimum norm and structurally constrained control law using eigenstructure assignment
Authors: Burrows Simon P. , Patton Ron J.
Published: July 2007

The freedom for eigenvalue assignment in specified areas of the complex plane and of the scope for placing the corresponding eigenvectors is utilized to form an analytical gradient‐based optimization problem which may be used to determine a low‐sensitivity eigenvalue assignment with a structurally constrained and low‐norm linear gain matrix. Examples are used to compare the properties of such optimized controllers with those obtained using single‐objective design techniques.
On stable full‐order and reduced‐order LQG controllers
Authors: Halevi Yoram , Bernstein Dennis S. , Haddad Wassim M.
Published: July 2007

The problem of deriving a suboptimal LQG controller which is internally stable is considered. In the case where the controller is internally unstable a procedure is given for modifying the optimization parameters, i.e. the state weighting matrix and/or the process noise intensity. Sufficient conditions for controller stability of appropriately modified optimization problems are given for both the full‐order and reduced‐order cases. A final tuning procedure is then used to minimize the deviation from the original LQG problem.
Decision and forecast horizons for one‐dimensional optimal control problems: Existence results and applications
Authors: Rempala Ryszarda , Sethi Suresh
Published: July 2007

This paper obtains decision and forecast horizons for undiscounted, continuous‐time one‐dimensional control systems. Some general conditions for the existence of horizons arising from the constraints imposed on the system are derived by using the optimality principle. These conditions are applicable to a variety of problems, including those of production planning, machine maintenance and cash management. Also derived are existence results that depend on the interplay between various costs involved in the context of a generalized production‐inventory model. Horizons are obtained explicitly in some cases. The model includes as special cases a version of the wheat‐trading problem and some other inventory prblems that have appeared in the literature. The paper concludes with an application of the model to a continuous‐time concave production‐planning problem not yet treated in the horizon context.
Discrete‐time loop transfer recovery with multistep delays
Authors: Shen Jenny H. , Ray Asok
Published: July 2007

This paper focuses on delay compensation as an extension of the loop transfer recovery (LTR) procedure from one‐step prediction to the general case of p‐step prediction (p ≥ 1). The steady state minimum variance filter gain is shown to be the H2‐minimal solution of the relative error between the target sensitivity matrix and the actual sensitivity matrix for p‐step prediction (p ≥ 1). This result is useful for synthesis of robust delay compensators in multiple‐input/multiple‐output (MIMO) discrete‐time systems.
Computation of the digital lqg regulator and tracker for time‐varying systems
Authors: Van Willigenburg L. G.
Published: July 2007

Digital optimal control problems, i.e. problems where a continuous‐time system is controlled by a digital computer, are very often approximated by either discrete‐time or continuous‐time optimal control problems. A digital controller based on one of these approximations requires a small sampling time and constitutes only an approximate solution. The digital LQG regulator and tracker constitute solutions to real digital control problems which involve sampled‐data, piecewise constant controls and integral criteria. Until now only the numerical computation of the digital LQG regulator in the case of time‐invariant system and criterion matrices has been considered in the literature. The control of non‐linear stochastic systems about state trajectories is very often performed by an LQG regulator based on the linearized dynamics about the trajectory, which constitute a time‐varying system. We present a numerical procedure to compute the digital LQG regulator and tracker in the case where the system and criterion matrices are time‐varying. Finally we present a numerical example.
A state space self‐tuning controller with integral action
Authors: Desai Premal , Mahalanabis A. K.
Published: July 2007

The paper is concerned with the problem of designing a state space self‐tuning controller with integral action for a class of unknown linear stochastic systems. The observer form of the innovations model of the system is used along with a single‐stage quadratic‐in‐state‐and‐control performance index which includes a cross‐weighting between system states and inputs. This results in a proportional estimated state plus integral output (P + I) controller in an incremental form. While it is analogous to the LQG‐theory‐based optimal adaptive controller in structure, computational simplification is achieved by the choice of a single‐stage performance index and a direct estimation of the state estimator gain matrix. The new controller has the advantages of being applicable to both single‐input/single output (SISO) and multi‐input/multi‐output (MIMO) minimum phase and non‐minimum phase systems. The results are illustrated numerically through two simulation examples.
Feedback control of minimum‐time optimal control problems using neural networks
Authors: Goh C. J. , Edwards N. J. , Zomaya A. Y.
Published: July 2007

This paper presents an optimal feedback controller capable of driving a non‐linear control system from an arbitrary initial state to a fixed final state in minimum time. The controller is based on a feedforward multilayer neural network trained repeatedly using open‐loop optimal control data which densely span the field of extremals of the non‐linear system. The effectiveness of the controller is clearly demonstrated by a simulation on a two‐link robot manipulator. The effect of sensor/actuator noise and parameter variation is also included to confirm the robustness of the controller.
On the utopian approach to the multiobjective LQ problem
Authors: De Nicolao Giuseppe , Locatelli Arturo
Published: July 2007

The infinite horizon, multiobjective linear quadratic control problem for continuous time systems is considered. Following a utopian approach, the optimal solution is defined as the solution that minimizes the distance from the utopian point in the cost space. It is shown that under standard stabilizability and detectability assumptions the optimal solution always exists. The solution coincides with the solution of a scalar LQ problem in which the cost matrices are given by a suitably weighted sum of their counterparts in the individual criteria. By exploiting the characterization and properties of the optimal solution, it is shown that the problem can be efficiently solved by means of a Newton‐type algorithm.
Optimal production and maintenance decisions when a system experience age‐dependent deterioration
Authors: Cho Danny I. , Abad P. L. , Parlar Mahmut
Published: July 2007

Consider a production process whose performance deteriorates over time. It is assumed that the process performance can be measured in terms of the proportion of ‘good’ (non‐defective) units of end items produced. Preventive maintenance may be applied to the process to slow down the rate of decline of (or improve) the process performance. This paper incorporates a dynamic maintenance problem into a production control model and proposes a simultaneous determination of optimal production and maintenance policies. It focuses on the study of possible trade‐offs between the cost (level) of preventive maintenance applied to the process and the output of the production process.
On linear‐quadratic adaptive control for the design of missile autopilots
Authors: Bendotti P. , M'Saad M.
Published: July 2007

This paper presents an application of adaptive control techniques to the design of skid‐to‐turn (STT) missile autopilots. More specifically, a linear–quadratic robust adaptive controller is used to deal with the yaw channel control problem. The linear–quadratic control design is mainly motivated by its popular stability margins, while the robust parameter adaptation is expected to handle the missile model parameter uncertainties. The control design as well as the parameter estimation are derived in the discrete time domain using the delta operator formulation. The state variables as well as the stability margin are shown to demonstrate how the adaptive controller outperforms its underlying fixed parameter controller.
Multivariable non‐linear controller for a synchronous generator
Authors: Mielczarski Wladyslaw , Zajaczkowski Antoni M.
Published: July 2007

The problem of multivariable controller synthesis for a turbogenerator is considered. Using the feedback linearization approach for multi‐input non‐linear systems, the existence of a linearizing state feedback for the improved reduced‐order model of a turbogenerator is proved and the simplest form of this feedback is derived. Application of the obtained non‐linear controller to the multivariable control of a turbogenerator provides very good results not only for the reduced‐order model but also for the ‘exact’ (Park's) model of a turbogenerator. Simulations of fault and post‐fault conditions in the obtained nonlinear control system confirm its superiority over a system with a voltage regulator and power system stabilizer.
Discrete time optimal control of linear time‐delay systems
Authors: Lee Tsu‐Tian , Sheu Hsin‐Teng
Published: July 2007

A discrete time optimal control for linear time‐delay systems is developed to ensure that all closed‐loop eigenvalues will lie inside a circular region centred at (β;, 0) with radius α. It is shown that by suitable manipulations the problem can be reduced to a standard discrete time quadratic regulator problem. An illustrative example is included to demonstrate the applicability of the proposed method.
H∞ control for a singularly perturbed aircraft model
Authors: Vian John L. , Sawan M. Edwin
Published: July 2007

State space solutions for H∞ control are formulated for composite state feedback control of singularly perturbed systems. Scaled frequency domain realizations of dynamic systems are developed and used to generate H∞ solutions that approach the H2 solution as an H∞‐norm design parameter is allowed to approach infinity. The realizations also account for non‐orthogonal cost function terms that occur naturally in the slow subsystem design for singularly perturbed systems. Traditional H2 results are also provided. The formulation is applied to compute reduced, composite and full‐order controller gains for the longitudinal dynamics of an F‐8 aircraft.
Mechanism of fiber–matrix separation in ribbed compression molded parts
Authors: Londoño‐Hurtado Alejandro , Hernandez‐Ortiz Juan Pablo , Osswald T.A.
Published: July 2007

This paper presents a model that predicts fiber–matrix separation in ribbed sections of compression molded parts. The model combines a mechanical analysis of compression molding with some experimentally measured variables. It is shown that with a higher closing speed, the viscosity of the material will increase and fiber–matrix separation can be reduced. Specific applications for this method are compression molding of sheet molding compounds and glass mat‐reinforced thermoplastics. POLYM. COMPOS., 28:451–457, 2007. © 2007 Society of Plastics Engineers
Ethylene polymerization by chromium complexes with phosphorous‐bridged bisphenoxy ligand
Authors: Hanaoka Hidenori , Imamoto Yuka , Hino Takahiro , Kohno Tetsuya , Yanagi Kazunori , Oda Yoshiaki
Published: July 2007

Chromium catalysts combined with phosphorous‐bridged bisphenoxy ligands were found to be highly active for ethylene polymerization. The most efficient catalyst precursor among them, generated by combining bis[3‐tert‐butyl‐5‐methyl‐2‐hydroxyphenyl](phenyl)phosphine hydrochloride (1a) and CrCl3(THF)3, was characterized. X‐ray analysis of (3‐tert‐butyl‐5‐methyl‐2‐phenoxy)(3‐tert‐butyl‐5‐methyl‐ 2‐hydroxyphenyl)(phenyl)phosphine bis(tetrahydrofuran)chromium dichloride (6), obtained by the reaction of 1a and CrCl3(THF)3 in the presence of NaH, revealed a unique structure in which one phenol moiety of the bisphenol did not coordinate to the chromium center. Complex 6 showed higher activities than those observed in the in situ catalyst system. Polyethylene of various molecular weights was obtained with differing activators. The highest activity (113.5 kg mmol (cat)−1 h−1) was observed when TIBA/TB was used as a cocatalyst. A medium molecular weight polymer with narrow molecular weight distribution (Mw = 128,700, Mw/Mn = 1.8) was obtained using a 6‐TIBA/B(C6F5)3 system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3668–3676, 2007
Rheology and interdiffusion in miscible blends of a low molar mass liquid crystal and bisphenol A–polycarbonate
Authors: Motong N. , Clarke N. , Thompson R. L. , Collins S. A. , Thongyai S.
Published: July 2007

The melt rheology of blends of a low molar mass liquid crystal (LC) blended with bisphenol A–polycarbonate (PC), and the self‐diffusion of the polycarbonate in the blends are reported. Results of small angle light scattering indicate that the LC is miscible in the mixture for weight fraction of LC less than 6%. The rheological properties of the blended sample within the miscible regime of the blends vary significantly with LC content. Although at low shear rates, the viscosity is similar to that of the pure polycarbonate, at high shear rates the curves show three regions of behavior, as has been described previously for pure LCs. The diffusion coefficient was obtained from interdiffusion studies using nuclear reaction analysis of bilayer films. An addition of only 1 wt % LC to the polycarbonate significantly increased the diffusion coefficient, but at higher concentration the converse was found. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2187–2195, 2007
Steered molecular dynamics simulation of elastic behavior of adsorbed single polyethylene chains
Authors: Wang Yu , Zhang Linxi
Published: July 2007

We investigate the dynamics of the detachment of single polyethylene (PE) chains from a strongly adsorbing surface in vacuum using a united atom model. Various statistical properties, including the mean‐square end‐to‐end distance 〈R2〉, the mean‐square radii of gyration
$ \langle S^2\rangle_{xy} $, $ \langle S^2\rangle_z $, the shape factor $ \langle\delta \rangle $, the torsion angle distribution, the average surface adsorption energy $ \langle E_{\rm surface}\rangle $, the average total energy $ \langle U\rangle $, and the average force $ \langle f\rangle $, are analyzed. The relationship between the average force $ \langle f\rangle $
and the pulling velocity v shows two distinctive regions: a weakly dependence region at $ v\ <\ 10^{-2} $
Å/ps and a strongly dependence region at $ v\ >\ 10^{-2} $
Å/ps. Remarkably, the PE chain manifests force hysteresis under sequential stretching and releasing. These investigations may provide some insights into the elastic behavior of adsorbed polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2322–2332, 2007
Influence of sample preparation and processing on observed glass transition temperatures of polymer nanocomposites
Authors: Hub Christian , Harton Shane E. , Hunt Marcus A. , Fink Rainer , Ade Harald
Published: July 2007

Polymer composites composed of poly(methyl methacrylate) (PMMA) and silica (14 nm diameter) have been investigated. The influences of sample preparation and processing have been probed. Two types of sample preparation methods were investigated: (i) solution mixture of PMMA and silica in methyl ethyl ketone and (ii) in situ synthesis of PMMA in the presence of silica. After removing all solvent or monomer, as confirmed using thermogravimetric analysis, and after compression molding, drops in Tg of 5–15 °C were observed for all composites (2–12% w/w silica) and even pure polymer reference samples. However, after additional annealing for 72 h at 140 °C, all previously observed drops in Tg disappeared, and the intrinsic Tg of bulk, pure PMMA was again observed. This is indicative of nonequilibrium trapped voids being present in the as‐molded samples. Field‐emission scanning electron microscopy was used to show well‐dispersed particles, and dynamic mechanical analysis was used to probe the mechanical properties (i.e., storage modulus) of the fully equilibrated composites. Even though no equilibrium Tg changes were observed, the addition of silica to the PMMA matrices was observed to improve the mechanical properties of the glassy polymer host. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2270–2276, 2007
Distress among inflammatory bowel disease patients at high risk for colorectal cancer: a preliminary investigation of the effects of family history of cancer, disease duration, and perceived social support
Authors: Rini Christine , Jandorf Lina , Valdimarsdottir Heiddis , Brown Karen , Itzkowitz Steven H.
Published: July 2007

Patients with inflammatory bowel disease (IBD) are one of only three groups at high risk for colorectal cancer (CRC), a leading cause of cancer‐related mortality. Yet, no research has examined psychological effects of their high‐risk status. The present study offered an initial investigation of three potential predictors of patient distress: disease duration, family history of cancer, and perceived social support. Longer disease duration and stronger family history of cancer are associated with elevated CRC risk in this already high‐risk population. Perceived support was conceptualized as a resource that could decrease vulnerability to distress or buffer adverse psychological effects of disease duration and family history. Men and women (n = 223) with IBD participating in a colon disease family registry completed measures for this cross‐sectional study. Family history of CRC and non‐colorectal cancers among first‐degree relatives (FDRs) and more distant relatives (DRs) was examined separately. Hierarchical multiple regression analyses revealed that having greater perceived support predicted lower generalized distress (p<0.001). Having an FDR history of CRC predicted higher CRC‐specific distress (p = 0.02). Having a DR history of CRC also predicted higher CRC‐specific distress, but only among patients diagnosed more recently (p = 0.03). Clinical implications of these findings are discussed along with future research directions. Copyright © 2007 John Wiley & Sons, Ltd.
A review of studies of the biological effects of electromagnetic fields in the intermediate frequency range
Authors: Shigemitsu Tsukasa , Yamazaki Kenichi , Nakasono Satoshi , Kakikawa Makiko
Published: July 2007

Concerns have been raised regarding the relationship between electromagnetic fields and human health. Compared to the research on extremely low frequency (ELF) and radio frequency (RF) electromagnetic fields, very few studies have addressed the biological effects of the electromagnetic field with intermediate frequency (IF) from 300 Hz to 10 MHz. This paper reviews the biological effects of IF electromagnetic fields with around 20 kHz from in vivo and in vitro studies. In contrast to studies on the effects of ELF and RF electromagnetic fields, few studies on biological effects of IF elecromagnetic fields have been carried out. From a short review based on published articles, it is seen that the available research data is inadequate for health risk assessment of IF electromagnetic fields. In future, it will be very important to conduct biological effects studies and evaluate the effects on human health from exposure to IF electromagnetic fields. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Basic study of high‐frequency carrier‐type magnetic field sensor using shape anisotropy
Authors: Kato Tomoki , Ishiyama Kazushi , Arai Ken Ichi
Published: July 2007

We tried to control the magnetic anisotropy of a high‐frequency carrier‐type magnetic field sensor by the shape of the magnetic film instead of induced anisotropy. We confirmed that the impedance of the sensor could be changed by applying a magnetic field. In addition, we tried to control the magnetic anisotropy with magnetostatic energy. We show that the properties of the sensor can be controlled by designing the shape of the magnetic film. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Collaboration: Leveraging resources and expertise
Authors: Byrne Anne , Hansberry Jane
Published: July 2007

Successful collaboration is an art form but can be developed through several smart practices. The authors discuss the meaning of collaboration, stakeholder perceptions of collaborative partnerships, and the experience of Summer Scholars, a nonprofit community organization that successfully uses collaboration to accomplish its mission. Further, they offer strategies for successful collaborative efforts.
Laparoscopıc Fundoplicatıon with Prosthetic Hiatal Closure
Authors: Kepenekci İlknur
Published: July 2007

Background

Despite the good results reported after laparoscopic fundoplication, failure is still a major problem. Hiatal disruption is one of the common patterns of anatomical failure. The aim of this study was to compare the results of suture repair of diaphragmatic crura with routine polypropylene mesh reinforcement in addition to suture repair.

Methods

A total of 551 patients who underwent laparoscopic fundoplication for gastroesophageal reflux disease between March 1998 and July 2004 were included into the study. Crural closure had been performed with simple primary suture repair alone between March 1998 and July 2002 (n = 335, group I), and mesh reinforcement of the hiatal repair was performed routinely thereafter (n = 176, group II). These groups were evaluated prospectively.

Results

We observed a significantly lower rate of recurrence in group II than in group I. After a 2‐year follow‐up, the rate of anatomic morphologic recurrence was 6.0% in group I and 1.8% in group II. Considering the recurrence rate, there was significant statistical difference. The overall recurrence rate in our series was 4.6%. There was no correlation between the size of the hernia and recurrence. No significant difference was found between groups regarding the rate of postoperative dysphagia. We have not observed any complications related to the use of polypropylene mesh in group II.

Conclusion

The results of this study suggest that polypropylene mesh reinforcement increases the success rate for laparoscopic hiatal hernia repair without causing an additional complication burden. We propose routine use of mesh reinforcement in laparascopic antireflux surgery.
Bird assemblages in secondary forests developing after slash-and-burn agriculture in the Brazilian Amazon
Authors: Borges Sérgio Henrique
Published: July 2007

Although indigenous farmers and other traditional peoples have disturbed Amazonian forests for centuries, few studies investigate the effects of these disturbances on biodiversity. This short-term study investigates how bird assemblages are affected by agricultural practices adopted by the residents of a national park in the Brazilian Amazon. Twelve sites in secondary forest (four sites in three age categories) and 12 sites in primary forest were selected for bird sampling. Audio-visual censuses of birds were conducted in small plots (1 ha) of young secondary growth (4–5 y), middle-aged (7–15 y), and old (20–35 y) secondary forests. Each site in secondary forest had a corresponding control site in adjacent primary forest. Young secondary growth had fewer species than old secondary and primary forests. Bird species richness was similar in middle-aged, old secondary and primary forests. Bird communities of young secondary habitat were dominated by species normally found in open habitats, such as agricultural fields and igapó flooded forests. The bird species composition of young secondary growth was more similar to that of middle-aged forest, which in turn was more similar to that of old secondary forests. Bird species composition differed between young secondary growth and old secondary forests and primary forests and between middle-aged secondary and primary forests. Nectarivore/insectivores and frugivore/insectivores of monospecific flocks are significantly associated with secondary forests, especially in initial stages of forest regeneration. In contrast, specialized insectivorous birds that join mixed-flocks show a significant association with primary forest.
Use of a fragmented landscape by three species of opossum in south-eastern Brazil
Authors: Lira Paula Koeler , Fernandez Fernando Antonio dos Santos , Carlos Henrique Santiago Alberto , Curzio Patrícia de Lima
Published: July 2007

Spatial patterns presented by the opossums Caluromys philander, Philander frenata and Micoureus demerarae were studied, through radio-tracking, in a landscape composed of eight small (1.3–13.3 ha) forest fragments surrounded by a matrix of open vegetation in south-eastern Brazil. Sixteen individuals were fitted with radio-collar transmitters and monitored for 2–8 mo. Fixes were obtained by the ‘homing-in on the animal’ technique. Numbers of locations of each individual varied from 6 to 117. Home ranges sizes ranged from 2.5–7.0 ha for C. philander, 0.6–7.4 ha for P. frenata and 0.8–1.7 ha for M. demerarae. Fragments, both edges and interiors, were used more often than the matrix; they are the primary habitat for these marsupials in the landscape. The matrix was used for foraging by P. frenata and C. philander, and traversed in five movements between fragments by P. frenata. Ability to use fragment edges and the matrix is important in explaining how these marsupials are able to persist in the landscape.