bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative analysis of cell adhesion on aligned micro‐ and nanofibers
Authors: Tian Furong , Hosseinkhani Hossein , Hosseinkhani Mohsen , Khademhosseini Ali , Yokoyama Yoshiro , Estrada Giovani Gomez , Kobayashi Hisatoshi
Published: July 2007

In this study, we quantitatively analyzed the affinity of cell adhesion to aligned nanofibers composed of composites of poly(glycolic acid) (PGA) and collagen. Electrospun composite fibers were fabricated at various PGA/collagen weight mixing ratio (7, 18, 40, 67, and 86%) to generate fibers that ranged in diameter from 10 μm to 500 nm. Scanning electron microscopy (SEM) observation revealed that the PGA/collagen fibers were long and uniformly aligned, irrespective of the PGA/collagen weight mixing ratio. In addition, it was observed that a significantly higher number of NIH3T3 fibroblasts adhered to nanofibers with smaller diameters in comparison to fibers with larger diameters. The highest affinity of cell adhesion was observed in the PGA/collagen fibers with diameter of 500 nm and PGA/collagen weight mixing ratio of 40%. Furthermore, the adherent cells were more elongated on fibers with smaller diameters. Thus, based on the results here, PGA/collagen composite fibers are suitable for tissue culture studies and provide an attractive material for tissue engineering applications. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
Tissue response around silicon nitride implants in rabbits
Authors: Guedes e Silva Cecilia C. , König Bruno , Carbonari Marcelo José , Yoshimoto Marcelo , Allegrini Sérgio , Bressiani José Carlos
Published: July 2007

The chemical and dimensional stability associated with suitable fracture toughness and propitious tribological characteristics make silicon nitride–based ceramics potential candidates for biomedical applications, mainly as orthopedic implants. Considering this combination of properties, silicon nitride components were investigated in relation to their biocompatibility. For this study, two cylindrical implants were installed in each tibia of five rabbits and were kept in the animals for 8 weeks. During the healing time, tissue tracers were administrated in the animals so as to evaluate the bone growth around the implants. Eight weeks after the surgery, the animals were euthanized and histological analyses were performed. No adverse reactions were observed close to the implant. The osteogenesis process occurred during the entire period defined by the tracers. However, this process occurred more intensely 4 weeks after the surgery. In addition, the histological analyses showed that bone growth occurred preferentially in the cortical areas. Different kinds of tissue were identified on the implant surface, characterized by lamellar bone tissue containing osteocytes and osteons, by a noncalcified matrix containing osteoblasts, or by the presence of collagen III, which may change to collagen I or remain as a fibrous tissue. The results demonstrated that silicon nitride obtained according to the procedure proposed in this research is a biocompatible material. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
The impact of sorption, buffering, and proteins on leaching of organic and inorganic substances from dental resin core material
Authors: Gregson Karen , Beiswanger A.J. , Platt Jeffrey
Published: July 2007

Dental core materials are resin‐based polymers that act as support for overlying dental restorations. Interaction with aqueous media, such as saliva in the oral cavity or serum in the pulp chamber, can cause leaching of substances from core materials. These substances can potentially have serious effects to tissues. The purpose of this study was to delineate the factors that cause leaching and to quantitate both organic and inorganic substances that leach from core materials. Two core materials and one control material were stored in distilled water, artificial saliva, buffered artificial saliva, or artificial serum for 30 days at 37°C. The materials were examined for changes in appearance and chemical composition, with a surface precipitate appearing on specimens stored in artificial saliva. The pH of the media was monitored and increased for all conditions. Organic eluants, triethyleneglycol dimethacrylate (TEGDMA), and camporquinone (CQ) were identified and measured in all media with high pressure liquid chromatography. Silicon, calcium, phosphate, and potassium were measured in the media using inductively coupled plasma optical emission spectroscopy. These results show that sorption, buffering, and the presence of proteins have an impact on the quantity of eluants that are leached from dental core materials. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
The efficient liquid‐phase oxidation of aromatic hydrocarbons by molecular oxygen in the presence of MnCO3
Authors: Gao Jin , Tong Xinli , Li Xiaoqiang , Miao Hong , Xu Jie
Published: July 2007

BACKGROUND: The liquid‐phase catalytic oxidation of aromatic hydrocarbons by molecular oxygen is a commercially important process. We consider the MnCO3‐promoted oxidation of toluene to produce benzaldehyde and benzoic acid. In this investigation, toluene was oxidized with 25.0% conversion and 80.8% selectivity with respect to benzoic acid in the presence of MnCO3 under 1.0 MPa of oxygen at 190 °C for 2 h.

RESULTS: Moreover, the oxidation of other aromatic hydrocarbons, such as ethylbenzene, p‐xylene, m‐xylene, o‐xylene, and p‐chlorotoluene, were also efficiently promoted by MnCO3.

CONCLUSION: It is concluded that an efficient oxidation of aromatic hydrocarbons can be achieved in the presence of MnCO3 under solvent‐free conditions. The catalytically active species are high‐valence Mn generated via the action of MnCO3 with oxygen. Copyright © 2007 Society of Chemical Industry
Optimization of chromium removal by the chromium resistant mutant of the cyanobacterium Anacystis nidulans in a continuous flow bioreactor
Authors: Khattar Jasvir IS , Sarma Tangirala A , Sharma Anuradha
Published: July 2007

BACKGROUND: Chromium removal potential of the cyanobacterium Anacystis nidulans and its chromium resistant strain CrrI8 has been optimized. Optimized parameters include biomass load, pH, temperature and dilution rate of the bioreactor.

RESULTS: Results show that chromium resistant strain has high EC50 dose for chromium compared to wild strain. Chromium removal potential of both strains is strongly influenced by various factors. Optimized conditions in batch system included pH 6.5, temperature 28 °C, biomass load 150 µg protein mL−1 for 30 µmol L−1 Cr6+ solution. In continuous flow bioreactor at optimum pH (6.5) and temperature (28 °C) at a fixed biomass of 10 mg protein and 30 µmol L−1 Cr6+, metal removal efficiency varied with dilution rate. For A. nidulans continuous flow bioreactor, optimum dilution rate was 0.076 h−1 (64.6 per cent metal removal) while for CrrI8 it was 0.152 h−1 (85.8 per cent metal removal). Operative time of the CrrI8 bioreactor was also more (85 h) compared to A. nidulans bioreactor (45 h).

CONCLUSION: Under optimized conditions resistant strain CrrI8 removed more Cr6+ compared to A. nidulans and thus has the potential to be exploited for Cr6+ removal from industrial effluents at large scale. Copyright © 2007 Society of Chemical Industry
Even‐electron ions: a systematic study of the neutral species lost in the dissociation of quasi‐molecular ions
Authors: Levsen Karsten , Schiebel Hans‐Martin , Terlouw Johan K. , Jobst Karl J. , Elend Manfred , Preiß Alfred , Thiele Herbert , Ingendoh Arnd
Published: July 2007

The collision‐induced dissociations of the even‐electron [M + H]+and/or [M − H]−ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH3, SO3H in the negative ion mode, or NO2in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH2in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H]+and [M − H]−ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even‐electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data andab initiocalculations at the CBS‐QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even‐electron [M + H]+and/or [M − H]−ions (generated by ESI or APCI) with that of the corresponding odd‐electron [M]+ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion. Copyright © 2007 John Wiley & Sons, Ltd.
Theoretical and experimental studies on the adsorption behavior of thiophenol on gold nanoparticles
Authors: Li Shujin , Wu Deyin , Xu Xiaoyan , Gu Renao
Published: July 2007

FT‐Raman spectra were obtained for thiophenol (TP) and TP on gold nanoparticles. All vibrational fundamentals for the TP molecule are assigned on the basis of the scaled quantum force field procedure. Three model systems are studied and compared for the interactions of TP with the Au atom: (1) TP with a Au atom, C6H5SHAu; (2) TP anion with a Au atom, C6H5S−Au; and (3) TP with a Au atom and subsequent formation of thiophenylate, C6H5SAu. The equilibrium structures and Raman spectra were calculated for the model systems using density functional theory (DFT) with the B3LYP functionals and the mixed basis set 6‐311 + G** (for C, S, H) and LANL2DZ (for Au), and theoretical Raman wavenumbers of C6H5SAu and C6H5S−Au were assigned according to potential energy distributions. The third model system is shown to be preferred over the other two. The calculated binding energies are also shown to support the third model system. It is suggested that a simple model, such as the one used in the present study, is reasonable to describe surface‐enhanced Raman spectroscopy of thiophenol adsorbed on gold nanoparticles. Copyright © 2007 John Wiley & Sons, Ltd.
Metabolism of phthalates in humans
Authors: Frederiksen Hanne , Skakkebaek Niels E. , Andersson Anna‐Maria
Published: July 2007

Phthalates are synthetic compounds widely used as plasticisers, solvents and additives in many consumer products. Several animal studies have shown that some phthalates possess endocrine disrupting effects. Some of the effects of phthalates seen in rats are due to testosterone lowering effects on the foetal testis and they are similar to those seen in humans with testicular dysgenesis syndrome. Therefore, exposure of the human foetus and infants to phthalates via maternal exposure is a matter of concern. The metabolic pathways of phthalate metabolites excreted in human urine are partly known for some phthalates, but our knowledge about metabolic distribution in the body and other biological fluids, including breast milk, is limited. Compared to urine, human breast milk contains relatively more of the hydrophobic phthalates, such as di‐n‐butyl phthalate and the longer‐branched, di(2‐ethylhexyl) phthalate (DEHP) and di‐iso‐nonyl phthalate (DiNP); and their monoester metabolites. Urine, however, contains relatively more of the secondary metabolites of DEHP and DiNP, as well as the monoester phthalates of the more short‐branched phthalates. This differential distribution is of special concern as, in particular, the hydrophobic phthalates and their metabolites are shown to have adverse effects following in utero and lactational exposures in animal studies.
What makes us so ignorant?
Authors: Gallup George E.
Published: July 2007

Dr. Gallup traces the voter's lack of information and interest to deadly dullness of our educational system.
New England pioneers again
Authors: Pelletier Lawrence
Published: July 2007

Manager plan spreads rapidly in Maine as operation in small towm wins approval and adoption is made easier.
The design of dynamic ship positioning control systems using stochastic optimal control theory
Authors: Grimble M. J. , Patton R. J. , Wise D. A.
Published: July 2007

The design of dynamic ship positioning control systems and their associated wave filters is considered. The control problems and the basic components in the system are discussed first. The model of the vessel is then described, since this plays an important role in the design of the Kalman filter which is used to estimate the low frequency motions of the vessel. The model involves both high and low frequency subsystems. The total linearized model for the vessel is represented by state equations, and simulation results are given to illustrate the performance of the Kalman filter. A comparison with a notch filter is also presented.

The design of the optimal control system using LQG stochastic control results is considered. The operation of the system under various operating conditions is illustrated. Schemes involving the extended Kalman filter are then described. These enable more realistic non‐linear models of the plant to be employed within the filter. This is shown to be unnecessary in the case of the low frequency ship model. However, the extended filter may be useful to track varying wave conditions (using parameter estimation) as represented in the high frequency model. Two extended filtering schemes are presented for this case.
A time‐optimal drug displacement problem
Authors: Bell D. J. , Katusiime F.
Published: July 2007

The interaction between the two drugs, warfarin and phenylbutazone, is considered through a previously derived model. A minimum time problem, which involves a state constraint is formulated. This problem is investigated both analytically and numerically. The numerical results are obtained by transforming the state constrained problem to one which is singular and then using a conjugate gradient algorithm to obtain approximations to the optimal control. Further approximations to the control, the rate of infusion of phenylbutazone, are made so that the time profile is feasible for practical implementation.
Primer vector theory applied to the linear relative‐motion equations
Authors: Jezewski Donald
Published: July 2007

Primer vector theory is used in analysing a set of linear relative‐motion equations—the Clohessy‐Wiltshire (C/W) equations—to determine the criteria and necessary conditions for an optimal N‐impulse trajectory. Since the state vector for these equations is defined in terms of a linear system of ordinary differential equations, all fundamental relations defining the solution of the state and costate equations and the necessary conditions for optimality can be expressed in terms of elementary functions. The analysis develops the analytical criteria for improving a solution by (1) moving any dependent or independent variable in the initial and/or final orbit, and (2) adding intermediate impulses. If these criteria are violated, the theory establishes a sufficient number of analytical equations. The subsequent satisfaction of these equations will result in the optimal position vectors and times of an N‐impulse trajectory.

The solution is examined for the specific boundary conditions of (1) fixed‐end conditions, two‐impulse, and time‐open transfer; (2) an orbit‐to‐orbit transfer; and (3) a generalized rendezvous problem. A sequence of rendezvous problems is solved to illustrate the analysis and the computational procedure.
Large finite horizon and infinite horizon lq‐optimal control problems
Authors: Willems J. L. , Callier F. M.
Published: July 2007

In this paper the relations between the finite horizon optimal control problem with receding horizon and the infinite horizon problem are discussed; the system is assumed to be linear, time‐invariant, and stabilizable. The cost function is quadratic but the output in the integral of the cost function may be undetectable. Control problems with terminal cost and problems with linear terminal state constraints are dealt with. The solution of the infinite horizon problem as well as the limiting behaviour of the solution of the finite horizon problem are derived. A necessary and sufficient condition for equivalence is developed; it is satisfied for the standard linear regulator problem.
Decentralized stochastic adaptive nash games
Authors: Chan Y. M. , Cruz J. B.
Published: July 2007

The optimization of stochastic systems with unknown parameters and multiple decision‐makers or controllers each having his own objective is considered. Two explicit self‐tuning type algorithms are proposed for decentralized stochastic adaptive Nash games under the ‘one‐step‐delay sharing pattern’. The first algorithm is an ad hoc constraint on the policy form, whereas the second one is based on an extension from static Nash game theory. Simulation results on a simplified economic system indicate that these algorithms are capable of stabilizing a system along targeted paths.
Deterministic and stochastic optimization of a dynamic advertising model
Authors: Sethi Suresh P.
Published: July 2007

This paper considers a variation of the Vidale‐Wolfe advertising model for which the maximum value of the objective function and the form of the optimal feedback advertising control are identical in both a deterministic and a stochastic environment. The stochastic environment is due to a white noise disturbance introduced in the deterministic sales‐advertising dynamics.
National welfare versus ‘economic independence’: The case of iran
Authors: Razavi Hossein
Published: July 2007

A linear‐quadratic welfare maximization model is formulated to study the trade‐offs between the political desirability and the economic cost of reducing foreign trade. The model is then applied to the case of Iran and a dynamic programming algorithm is employed to calculate the numerical values of the optimal trade policies. The effects of various political attitudes on the trade policies are discussed.
Output feedback pole assignment under system variation
Authors: Lee Gordon K. F. , Godbout Louis F.
Published: July 2007

The design of multivariable control systems using pole assignment has resulted in much research. Owing to system or parameter variation, the initial compensator design for constant conditions may lead to undesirable responses. Hence, it is important to design compensator structures which maintain desired pole locations under such changes.

This paper presents a design methodology for output feedback pole assignment when there is system variation. A performance measure is formulated which represents a squared‐error between desired pole locations and the actual pole locations generated via compensation under probabilistic variations. Optimization of this measure requires constructing gradient matrices necessary to obtain the compensator parameters.

Both constant output feedback and dynamic compensation are discussed for pole placement, and the unstable Boeing‐Vertol CH‐46 helicopter system is considered to illustrate the design algorithms.
A note on avoidance control
Authors: Leitmann G. , Skowronski J.
Published: July 2007

Earlier work has dealt with controls which guarantee that every trajectory of a given dynamical system remains outside (avoids) a prescribed set (anti‐target) for all time. In the present treatment, we permit the intersection of the anti‐target but consider two cases of avoidance: the anti‐target must be avoided during a prescribed time interval (finite‐time avoidance), or the anti‐target must be avoided for all time after some calculable or prescribed time interval (ultimate avoidance). Sufficient conditions are presented for these two kinds of avoidance. The use of these conditions is illustrated by two examples.
Minimum horizontal rotations
Authors: Marchal C.
Published: July 2007

The problem treated here is to rotate a rigid body from one arbitrary angular orientation to another using only rotations about horizontal axes. The total rotation angle is to be minimized. This problem is formulated and solved as an optimal control problem. The solution is both simple and elegant. Examples are provided to illustrate the results. The problem is motivated by the desire to use the Earth's magnetic field for satellite attitude control.
Globally optimal control of self‐adjoint distributed systems
Authors: Meirovitch L. , Silverberg L. M.
Published: July 2007

The partial differential equations of motion for an uncontrolled distributed structure can be transformed into a set of independent modal equations in terms of natural co‐ordinates. It is common practice to design control forces that recouple the modal equations so that the natural co‐ordinates for the open‐loop (uncontrolled) system cease to be natural co‐ordinates for the closed‐loop (controlled) system. This approach is referred to as coupled control. In contrast, the independent modal‐space control method is a natural control method, i.e. natural co‐ordinates for the open‐loop system remain natural co‐ordinates for the closed‐loop system. Moreover, natural control provides a unique and globally optimal closed‐form solution to the linear optimal control problem for the distributed structure. Indeed, discretization is not necessary. The optimal control forces are ideally distributed. The distributed control can be approximated by finite‐dimensional control, a process that does not require truncation of the plant. Two numerical examples are presented.
Quantized control with data compression constraints
Authors: Fischer Thomas R.
Published: July 2007

The linear‐quadratic‐Gaussian problem of quantized control subject to quantized measurements is considered with the measurement and control quantizers formulated as data compression systems. The optimum closed‐loop control is shown to be separable in control law, control quantizer and estimation. However, estimation and measurement quantization are non‐separable. The optimum measurement quantizer is of a differential structure but requires optimum state estimation at both encoder and decoder. A fixed total number of quantization levels should be equally allocated to the measurement and control quantizers, and the quantizer design depends on both the known control law and the solution to the matrix Riccati equation. A suboptimum control structure is developed, and the effect of quantization error on estimation error is shown to be stable.
On the compensation of optimal system asymptotic root‐loci
Authors: Owens D. H.
Published: July 2007

This paper describes a procedure for manipulating the free parameters of the asymptotes of the optimal closed‐loop poles of a time‐invariant linear regulator as the weight of the input in the performance criterion approaches zero by suitable choice of weighting matrices Q and R.
The determining set in the infinite horizon problem of optimal control
Authors: Stern Lynnell E.
Published: July 2007

This paper will study the adjoint vector in the infinite horizon optimal control problem. The approach used is to translate the adjoint vector, by means of the fundamental solution of the homogeneous variational equation, back to the initial time. Thus, the set of adjoint vectors ‘satisfying the maximum principle’ will be formed at the initial time. This set will be called the ‘determining set’ and will then be used to ascertain conditions of optimality. Properties, applications and an example of the determining set are given.
Gain optimization with non‐linear controls
Authors: Slater G. L. , Kandadai R. D.
Published: July 2007

An algorithm has been developed for the analysis and design of controls for non‐linear systems. The technical approach is to use statistical linearization to model the non‐linear dynamics of a system by a quasi‐Gaussian model. A covariance analysis is performed to determine the behaviour of the dynamical system and a quadratic cost function. Expressions for the cost function and its derivatives are determined so that numerical optimization techniques can be applied to determine optimal feedback laws.

The primary application for this paper is centred about the design of controls for nominally linear systems but where the controls are saturated or limited by fixed constraints. The analysis is general, however, and numerical computation requires only that the specific non‐linearity be considered in the analysis.
Design of optimal feedback controllers for minimum eigenvalue sensitivity
Authors: Qiu Haiming , Gourishankar V. G.
Published: July 2007

An iterative method for designing an optimal constant gain feedback controller for a linear system to achieve minimum eigenvalue sensitivity to parameter variations is presented. In addition to assigning eigenvalues to desired locations in the complex plane, one can also assign elements of eigenvectors by this method. This makes it possible to shape the response of the states. Examples to illustrate the effectiveness of this method are included.
The non‐co‐operative solution of a differential game: Advertising versus pricing
Authors: Gaugusch Julius
Published: July 2007

The purpose of this paper is to compare the effectiveness of advertising campaigns with a low‐price policy. A two‐person non‐zero‐sum differential game is considered in which two firms maximizing their profits are observed. One firm uses advertising expenditures as its control variable and keeps price fixed, whereas the other uses price as a control variable and does not advertise. A system of two differential equations for the Nash solution path is derived. Analysis of the phase diagram yields qualitative results on the structure of the optimal solutions.
An application of hierarchical optimization in calibration of large‐scale water networks
Authors: Coulbeck B.
Published: July 2007

The paper develops a new method for optimized calibration of large‐scale non‐linear water networks. Calibration requirements are first discussed with relevance to the limited monitored operating data, the ill‐defined network parameters and the potential benefits of more accurate network simulations for analysis and control purposes. A formulation is then made which incorporates simultaneous adjustment of network physical parameters and related operational data in order to force agreement between measured and simulated variables. The system non‐linear response is represented by a high‐dimensional set of linear‐equations relating controllable adjustment parameters to the observed discrepancies in operating conditions. Quadratic performance indices, with optional user‐defined weighting factors, are shown to be most appropriate for the control variables. Use of a hierarchical optimization technique permits a solution to be obtained to the problem of high dimensionality with constrained controls and variable performance factors. Application of the scheme to a test distribution system leads to optimal adjustment of all the permitted variables to give the best overall solution for the available measurements. An important practical feature is the ease with which engineering experience can be incorporated to yield alternative solutions.
A method of design against vibration resonance of beams and shafts
Authors: Bendsøe Martin P. , Olhoff Niels
Published: July 2007

We consider problems of designing vibrating beams or rotating shafts to obtain as large gaps as possible in the spectra of natural frequencies or critical speeds in order to avoid resonance or whirling instability for a wide range of external excitation frequencies or service speeds. Governing equations for such design problems are derived by variational analysis of a bound formulation, and a numerical solution to an example problem is discussed.
A homotopy algorithm for solving coupled riccati equations
Authors: Mariton M. , Bertrand P.
Published: July 2007

Many applications of optimization theory require the solution of a set of coupled Riccati equations. In multi‐person‐games problems, the players' decision for the Nash equilibrium depend on Riccati equations coupled through their quadratic terms. Another example is provided by linear‐quadratic control. When the system is subject to sudden and random changes in parameter values, the optimal feedback is computed from the solution of Riccati equations coupled through their weighting terms. After recalling the principle of homotopy methods, it is shown how it generates a new and efficient algorithm for this class of problem. An illustrative example is given.
A strategy for power system stabilization by control‐effort and response‐time minimization
Authors: Rahim A. H. M. A. , Gourishankar V. G.
Published: July 2007

A method is described for deriving a quasi‐optimal feedback control scheme for stabilizing power systems. This is achieved by minimizing a functional which is a linear combination of response time and control effort. The transient repsonse of a power system obtained using this control strategy is found to be superior to that achieved with a controller based on a linear regulator approach. This scheme, in a slightly modified form, is easily implemented in practice. The modification does not affect the effectiveness of the scheme to control transients. Simulation results are included.
A simple design method for single‐input optimum regulators
Authors: Flower J. O.
Published: July 2007

This paper considers the single‐input quadratic‐cost linear‐system‐design problem. It provides a simple design procedure for establishing the feedback‐gain terms by comparison of a determinant expansion (containing the unknown gain terms) with the optimal closed‐loop polynomial for the system. This leads to a set of linear simultaneous equations, the solution of which reveals the gain terms. The procedure closely parallels the method reported by Grimble. 1It is entirely straightforward, requiring no transformation of the state variables and is particularly attractive for dealing with systems of modest order or even large‐order sparse systems.
Skimming pricing for a class of diffusion models
Authors: Rao Ram C.
Published: July 2007

This paper examines the optimal dynamic pricing policy of a monopolist faced with demand that follows a first‐order adjustment process. This adjustment process is assumed to capture the diffusion of a new durable good. Under these conditions the optimal policy has the structure of skimming, i.e. high initial prices followed by monotonically declining prices. This corresponds to the usual notion of a price discriminating monopolist who travels down the demand curve in order to garner all consumer surplus, but with one difference. Specifically, it is seen that when cash flows are not discounted the policy is to travel down a line that is parallel to the demand curve if demand is linear in price. If demand is of the constant elasticity type, the policy is to travel down a curve that is steeper than the demand curve. Finally, when profits are discounted, initial prices are lower than in the undiscounted case, thus increasing the rate of product diffusion initially.
A method of on‐line optimal control via moving models
Authors: Wu Wen‐Teng , Tzeng Ren‐Yih
Published: July 2007

A method of on‐line optimal control is proposed. A control system with a quadratic performance index is investigated. The system is represented by a first‐order moving model. The difficulties involved in solving the two‐point boundary problems of the optimal control problem are avoided by the use of the proposed method. Illustrative examples are presented to show the promise that the method provides.
Insect pest eradication as a discrete non‐linear control problem
Authors: Plant Richard E.
Published: July 2007

The problem of eradication of an insect pest population can be viewed as a time optimal, discrete time, non‐linear control problem in which the objective is to achieve eradication as quickly as possible. We discuss the solution of a simple model problem in which eradication is carried out by means of the sterile insect technique. An algorithm for the resulting control problem is presented.
A discrete‐time optimal adaptive control law for a robot arm
Authors: Marchand Pauline A. , Lawrence Peter D. , Cherchas Dale B.
Published: July 2007

The equations of motion describing a robot's dynamics are coupled and non‐linear, making the design of an optimum controller difficult using classical techniques. In this work an explicit adaptive control law is proposed based on a discrete linear model for each link and on the minimization of a quadratic performance criterion for position error and total control effort. The system parameters are recursively estimated at each control step by use of least squares, with a typical sample time of 0.02 s. A computer simulation of the resulting scheme is performed to evaluate the controller. The simulation model, based on the first three links of an existing robot, includes detailed motor dynamics and treats the wrist assembly as a load mass. Simulated test paths requiring movement of the outer two links indicate that the controller adapts and that its behaviour is stable and convergent.
Robust control strategy for take‐off performance in a windshear
Authors: Chen Y. H. , Pandey S.
Published: July 2007

A robust control strategy has been designed for an aircraft during take‐off. The effects of different windshear intensities have been analysed for one‐ and two‐dimensional models. The robust control is designed to tolerate windshear regardless of its variations. The only information the control utilizes is the upper‐bound value of the allowable control magnitude.
Boundary feedback control of a vibrating beam subject to a displacement constraint
Authors: Sloss J. M. , Adali S. , Sadek I. S. , Bruch J. C.
Published: July 2007

The problem of controlling the dynamic response of a beam by means of boundary feedback is solved. The control is applied at one of the supports of the beam by means of a torque actuator in order to keep the maximum deflection within specified bounds. Since the location and time of the maximum deflection depend on the control itself, the feedback is determined by the solution of a min‐max problem. The theory is illustrated by a numerical example involving an impulsively loaded beam, and the effectiveness of the proposed control is studied numerically.
On the approximate identification of the leading coefficient of a linear elliptic equation by output error and equation error minimization
Authors: Crosta Giovanni
Published: July 2007

By definition, the approximate solution to the (finite‐dimensional) identification problem is a minimizing element of either cost function. The output error is minimized by two methods: finite difference‐discretized gradient (FD‐DZG) and finite element—discrete gradient (FE‐DG). The equation error is minimized by a DZG method. Two‐sided constraints are applied.

With reference to an example of polynomial type in a rectangular domain, some tests are carried out in which the role of several parameters, including data noise, is investigated. Most computational results pertaining to the output error are interpreted according to: (a) sensitivity analysis; (b) an error estimate, which compares FD‐DZG to FD‐DG; and (c) a dynamical system model of the algorithm.

An optimal uniform initial value of the unknown coefficient is found which yields a computed solution very close to the reference solution, regardless of domain discretization and output error minimization method. The superior noise immunity of FE‐DG over FD‐DZG is demonstrated. The results obtained from equation error minimization are less satisfactory.
Robust parameter estimation for fuel cost models in economic operation of electric power systems
Authors: Al Gobaisi Darwish M. K. , Bajpai A. C. , Singh P. N. P.
Published: July 2007

This paper is focused on optimal parameter estimation of fuel cost models intended for economic scheduling of electric power systems. The common approaches of least squares and conventional weighted least squares may not be appropriate for situations involving non‐normally distributed measurement errors. Techniques of robust parameter estimation, in particular the iteratively reweighted least‐squares estimator, offer an attractive option in these situations.

The paper discusses the theoretical aspects of this powerful technique and presents computational experience with a number of popular choices of weighting functions. A comparative evaluation of the parameter estimates obtained is carried out in terms of both accuracy of the estimates and their effects on economic scheduling strategies.
Time‐optimal control for robotic manipulators
Authors: Chernousko F. L. , Akulenko L. D. , Bolotnik N. N.
Published: July 2007

Optimal control methods present an efficient approach to construct controls of robotic manipulators. Much recent research has been devoted to different problems of optimal control for industrial robots. In this paper we give a brief survey of work done in this field and present some new results on optimization of robotic motions. Manipulation robots governed by electromechanical drives are considered. We obtain open‐loop and feedback time‐optimal controls for robotic motions using both analytical and numerical methods. The results show that optimal controls can lead to a considerable improvement in the time taken for transport operations performed by robots.
Minimum energy controllers with inequality constraints on output variances
Authors: Hsieh C. , Skelton R. E. , Damra F. M.
Published: July 2007

We consider the design of control systems to minimize the input energy subject to output variance inequality constraints. Necessary and sufficient conditions are developed for state feedback, measurement feedback and dynamic controllers. We find that all these problems are equivalent to LQ problems with a diagonal output weighting matrixQ, whereQhas some interesting properties which reflect the importance of each constraint. An algorithm which iteratively selects the weightQis given. Similar results are also derived for the dual problem where input variance inequality constraints are desired. All these results can be applied to the deterministic case with inequality constraints on theL∞,‐norm of the outputs.
Extended horizon self‐tuning control of a pulsed liquid‐liquid extraction column
Authors: Najim K. , Irving E.
Published: July 2007

This paper describes the application of an extended horizon self‐tuning control to a liquid‐liquid extraction column. The work forms part of an industrial collaborative project. The control law is derived from plant output prediction over several steps with the assumption that beyond a certain horizon the control increments become constant.

This technique is used to control the hydrodynamics of a liquid‐liquid extraction column. The purpose of control is to maintain the column in its optimal behaviour zone, which corresponds to a specific hydrodynamic operation defined as a limit between two operating regimes. The measure of the conductivity gives information on the hydrodynamic behaviour of the column and has been selected as a control variable. The pulse frequency was also selected as a control variable.

A single input‐output linear discrete model with time‐varying parameters was adopted to model the complex dynamics of the column. The model parameters are recursively estimated by a constant trace estimation algorithm. Some modifications have been introduced to improve the robustness of this estimation algorithm.

Experiments carried out show that the presented algorithm has excellent control properties.
Maximum principles applied to a model of consumer brand choice
Authors: Ferreira Josa A. Soeiro
Published: July 2007

This paper presents an application of the maximum principle and the generalized maximum principle (a recent extension of that principle) to a discrete‐time model of consumer choice behaviour. The model includes two brands in a market and uses a non‐stationary first‐order Markov chain. The optimization is carried out by algorithms based on the above mentioned principles. These algorithms are described, and their performances are discussed and compared both with and without fulfilment of the directional convexity property.
An optimal dynamic output feedback controller for a flexible spacecraft
Authors: Sreenatha A. G. , Bhat M. Seetharama , Shrivastava S. K.
Published: July 2007

The design of a low‐order dynamic output feedback controller for a flexible spacecraft is carried out using modified linear quadratic Gaussian (LQG) theory. The necessary conditions for optimization are given. The linear equations governing a flexible spacecraft with a central rigid body and two sun‐tracking solar panels are presented. The parameters of the Solar Electric Propulsion Spacecraft (SEPS) are selected for analysis and simulation. The optimal gains for the dynamic controller are estimated using an iterative algorithm. The sequential procedure which assures convergence is selected. The initial gains which stabilize the system are chosen on the basis of the principle of a PD controller. A third‐order controller for pitch, roll and yaw axes of the 18th‐order system, which includes sensor and actuator dynamics, is designed. Numerical simulations carried out to ascertain the performance of the controller show the performance to be satisfactory.
Sequential rank‐one/rank‐two updates for quasi‐newton differential dynamic programming
Authors: Rakshit A. , Sen S.
Published: July 2007

This communication presents computational results with a variant of differential dynamic programming. The class of methods is motivated by quasi‐Newton methods and constructs quadratic approximations by using stagewise gradients. We compare two methods of updating the approximations: the first is based on the symmetric Broyden update and the second is a sequential rank‐one/rank‐two update. Our computational results suggest that the latter is a practical and efficient algorithm for discrete‐time optimal control.
Optimal response in siso ripple‐free deadbeat systems
Authors: Sebakhy O. A. , Assiri J. A.
Published: July 2007

The ripple‐free deadbeat control problem for SISO plants subjected to arbitrary reference signals is considered. The trade‐off between the settling time and the integral square error between the system output and reference signal is investigated. Given a specific order of the controller, it is shown how to design an optimal ripple‐free deadbeat controller. An illustrative example is presented to show the feasibility of the proposed algorithm.
Optimal pole assignment into specified regions and its application to rotating mechanical systems
Authors: Kim Jong‐Sun , Lee Chong‐Won
Published: July 2007

This paper considers a pole assignment problem to cluster all poles of a closed‐loop system into some specified regions by introducing the complex state for systems having an isotropic property and by using the Riccati equation. The algebraic relations for the distribution of the eigenvalues of a complex matrix are used in order to cluster the poles into specified regions, which guarantees the relative stability margin, e.g. uniform damping or uniform damping ratio. The proposed scheme is essentially a combination of the pole assignment approach and linear quadratic design, taking the advantages of both. A block modal control method—an extension of recursive pole assignment—is also developed for the vibration control of rotating systems by clustering the forward and backward modes in order. Vibration control simulations with an isotropic rotor—bearing system, a magnetic bearing system and a rotating circular disc are treated in order to demonstrate the advantages of the proposed method.
Multivariable routh‐approximant model reduction method in the time domain
Authors: Ramakrishnan J. V. , Rao S. Vittal , Koval L. R.
Published: July 2007

The time‐domain Routh‐approximant method for model reduction of large‐scale systems is modified and enhanced in this paper. A new transformation matrix that overcomes a limitation of earlier work is proposed. This feature greatly enhances the multivariable method. Some interesting results on symmetry properties are developed in conjunction with a structure example. A sufficiency condition of stability of the reduced‐order model is identified. The response of the reduced‐order model traces the original system very well. Thus the Routh method offers promise for application in the suboptimal control of large space structures, given its inherent simplicity.
A dynamic net present value rule in a financial adjustment cost model
Authors: Kort Peter M.
Published: July 2007

A dynamic model of a self‐financing firm is presented in which a convex adjustment cost function is incorporated. The horizon date is assumed to be infinite. It turns out that the concept of ‘net present value of marginal investment’ is a useful tool to develop the firm's optimal investment policy. When this net present value is positive, negative or zero, it is optimal for the firm to fix the investment rate at its maximum level, minimum level or equilibrium level respectively.
A constrained H∞ smooth optimization technique
Authors: Fisher M. E. , Moore J. B. , Teo K. L.
Published: July 2007

In H∞ optimal control the cost function is the maximum singular value of a transfer function matrix over a frequency range. The optimization is over all stabilizing controllers. In constrained H∞ control the controllers typically have a fixed structure, perhaps conveniently parametrized in terms of a parameter vector. Also, there may be functional constraints involving singular values representing, for example, robustness requirements. Such problems are usually cast as non‐smooth optimization problems.

In this paper we consider a general class of constrained H∞ optimization problems and show that these problems can be approximated by a sequence of smooth optimization problems. Thus each of the approximate problems is readily solvable by standard optimization software packages such as those available in the NAG or IMSL library. The proposed approach via smooth optimization is simple in terms of mathematical content, easy to implement and computationally efficient.
The optimal control problem for the vidale‐wolfe advertising model revisited
Authors: Ferreyra Guillermo
Published: July 2007

The optimal control problem for the Vidale‐Wolfe advertising model with unbounded controls is reformulated rigorously. It is shown that even though the optimal control is a measure of bounded variation, there exist physically realizable approximations to it. These smoother controls converge to the optimal control together with the induced trajectories and costs. Also, closed‐form expressions are given for the optimal state trajectories and the induced costs.
Design of a field voltage controller for a synchronous generator using feedback linearization
Authors: Mielczarski Wladyslaw , Zajaczkowski Antoni M.
Published: July 2007

The problem of non‐linear field voltage controller synthesis for a synchronous generator is considered. The theory of feedback linearization of non‐linear systems is applied and the existence of a linearizing feedback controller for the improved reduced‐order three‐dimensional model of a generator is proved. Simulation results for the proposed non‐linear controller, which includes a non‐linear observer and two systems based on an automatic voltage regulator and a power system stabilizer, are presented.