bluuebunny/crossref_metadata_2025_split huggingface dataset:
Decision and forecast horizons for one‐dimensional optimal control problems: Existence results and applications
Authors: Rempala Ryszarda , Sethi Suresh 
Published: July 2007

AbstractThis 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

AbstractThis 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

AbstractDigital 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

AbstractThe 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

AbstractThis 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

AbstractThe 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

AbstractConsider 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

AbstractThis 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

AbstractThe 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

AbstractA 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

AbstractState 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

AbstractThis 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

AbstractChromium 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

AbstractThe 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

AbstractWe 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

AbstractPolymer 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

AbstractPatients 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

AbstractConcerns 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

AbstractWe 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.
Laparoscopıc Fundoplicatıon with Prosthetic Hiatal Closure
Authors: Kepenekci İlknur 
Published: July 2007

AbstractBackgroundDespite 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.MethodsA 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.ResultsWe 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.ConclusionThe 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.
The Reproducibility of Lists of Differentially Expressed Genes in Microarray Studies
Authors: Shi Leming , Jones Wendell , Jensen Roderick , Harris Stephen , Perkins Roger , Goodsaid Federico , Guo Lei , Croner Lisa , Boysen Cecilie , Fang Hong , Amur Shashi , Bao Wenjun , Barbacioru Catalin , Bertholet Vincent , Cao Xiaoxi Megan , Chu Tzu-Ming , Collins Patrick , Fan Xiao-hui , Frueh Felix , Fuscoe James , Guo Xu , Han Jing , Herman Damir , Hong Huixiao , Kawasaki Ernest , Li Quan-Zhen , Luo Yuling , Ma Yunqing , Mei Nan , Peterson Ron , Puri Raj , Qian Feng , Shippy Richard , Su Zhenqiang , Sun Yongming Andrew , Sun Hongmei , Thorn Brett , Turpaz Yaron , Wang Charles , Wang Sue-Jane , Warrington Janet , Willey James , Wu Jie , Xie Qian , Zhang Liang , Zhang Lu , Zhong Sheng , Chen James , Wolfinger Russell , Tong Weida 
Published: July 2007

AbstractReproducibility is a fundamental requirement in scientific experiments and clinical contexts. Recent publications raise concerns about the reliability of microarray technology because of the apparent lack of agreement between lists of differentially expressed genes (DEGs). In this study we demonstrate that (1) such discordance may stem from ranking and selecting DEGs solely by statistical significance (P) derived from widely used simple t-tests; (2) when fold change (FC) is used as the ranking criterion, the lists become much more reproducible, especially when fewer genes are selected; and (3) the instability of short DEG lists based on P cutoffs is an expected mathematical consequence of the high variability of the t-values. We recommend the use of FC ranking plus a non-stringent P cutoff as a baseline practice in order to generate more reproducible DEG lists. The FC criterion enhances reproducibility while the P criterion balances sensitivity and specificity.