bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impurity levels in layered semiconductor n‐InSe doped with Ge
Authors: Shigetomi S. , Ikari T. 
Published: February 2003

AbstractThe impurity levels in Ge‐doped n‐InSe have been investigated by using photoluminescence (PL), photocurrent (PC), and Hall effect measurements. Two emission bands related with impurity level are observed at about 1.28 and 1.25 eV in PL spectra at 77 K. In addition to the results of temperature dependence of PC spectra and electron concentration, it is found that the 1.28 and 1.25 eV emission bands are associated with the donor levels at about 0.09 and 0.06 eV below the conduction band, respectively. The effect of excitation intensity of peak energy for the 1.25 eV emission band is characterized by the donor–acceptor recombination. The temperature dependence of mobility is influenced by adding an amount of Ge atom. The scattering mechanism of the 0.05 at.% Ge‐doped sample can be well explained by the combined mechanism of the optical phonon, ionized impurity and neutral impurity scatterings.
Evidence for pseudo‐gap behavior in defect‐doped infinite layer (Ca, Sr)CuO2 thin films
Authors: Norton David P. , Chakoumakos Bryan C. , Budai John D. , Lowndes Douglas H. 
Published: February 2003

AbstractA distinct crossover between the high temperature and low temperature normal state dc transport properties of epitaxial (Ca, Sr)CuO2 single crystal thin films has been observed. Defect‐doped (Ca, Sr)CuO2 films with dc conductivity behavior ranging from insulating to metallic‐like were obtained by growing stoichiometric and cation‐deficient material under various film growth conditions. The results indicate that 2D variable‐range hopping is the dominant transport mechanism at low temperatures. The high temperature behavior depends on the magnitude of the conductivity, resulting in either activated conduction or a ln ρ ∼ 1/T1/2 dependence that is reminiscent of thermally‐activated tunneling in a granular metal/insulator matrix. The distinct crossover in behavior suggests the possibility of gap formation in the temperature range 150–200 K.
Far infrared magneto‐optical transitions in quantum disks: New results
Authors: Comas F. , Gondar J. L. 
Published: February 2003

AbstractWe have reconsidered the problem of far infrared magneto‐optical transitions in a Quantum‐Disk (QD). For this spectral region we are essentially concerned with intraband electronic transitions and excitonic effects do not contribute. The system is modelled by a cylindrical geometry with a uniform magnetic field B acting along the cylinder axis. The confinement in the radial direction is given by a parabolic potential, while along the cylinder axis we assume two interfaces located at z = ± d/2. We have calculated the transition probabilities for the electron interaction with an electromagnetic radiation field using the dipole approximation. Inaccuracies found in some previous fundamental works on the subject are analyzed and amended. New possible magneto‐optical transitions are predicted and a detailed discussion of their oscillator‐strength is made.
Tight‐binding parameters from the full‐potential linear muffin‐tin orbital method: A feasibility study on NiAl
Authors: Djajaputra David , Cooper Bernard R. 
Published: February 2003

AbstractWe have examined a method of direct extraction of accurate tight‐binding parameters from anab‐initioband‐structure calculation. The linear muffin‐tin potential method, in its full‐potential implementation, has been used to provide the hamiltonian and overlap matrix elements in the momentum space. These matrix elements are Fourier transformed to real space to produce the tight‐binding parameters. The feasibility of this method has been tested on the intermetallic alloy NiAl, usingspdorbitals for each atom. The parameters generated for this alloy have been used as input to a real‐space calculation of the local density of states using the recursion method.
Temperature dependence of the quantum dot lateral size in the Ge/Si(100) system
Authors: Tonkikh A. A. , Dubrovskii V. G. , Cirlin G. E. , Egorov V. A. , Ustinov V. M. , Werner P. 
Published: February 2003

AbstractThe temperature dependence of morphological characteristics of Ge/Si(100) quantum dots grown by molecular beam epitaxy with constant growth rate at different substrate temperatures is investigated. The mean lateral size of quantum dots at 6.2 ML is shown to increase at rising substrate temperature. Comparison of experimental and theoretical results obtained in the frame of kinetic model is performed.
Structural modulation of spinel ZnCr2Se4 in the vicinity of antiferromagnetic phase transition induced by an applied magnetic field
Authors: Hidaka M. , Yoshimura N. , Takahasi S. , Watanabe S. , Akimitsu J. 
Published: February 2003

AbstractThe cover picture of physica status solidi (b) shows a structure model of ZnCr2Se4, a spinel compound which exhibits remarkable structural and magnetic modulations near its antiferromagnetic phase transi‐tion around 20 K as well as under an applied magnetic field. Results of extensive neutron diffraction investigations of these phenomena are reported in this issue's Editor's Choice [1].The first author, Masanori Hidaka, is at the Department of Fundamental Physics of the Graduate School of Sciences at Kyushu University, and is working on the correlation between functional physical properties and the structure of condensed matter such as high‐TC superconductors, ferro‐antiferromagnetic and ‐electric compounds by neutron or X‐ray diffraction and XANES experiments.
Discontinuous feedbacks, discontinuous optimal controls, and continuous‐time model predictive control
Authors: A. C. C. Fontes Fernando 
Published: February 2003

AbstractIt is known that there is a class of nonlinear systems that cannot be stabilized by a continuous time‐invariant feedback. This class includes systems with interest in practice, such as nonholonomic systems, frequently appearing in robotics and other areas. Yet, most continuous‐time model predictive control (MPC) frameworks had to assume continuity of the resulting feedback law, being unable to address an important class of nonlinear systems. It is also known that the open‐loop optimal control problems that are solved in MPC algorithms may not have, in general, a continuous solution. Again, most continuous‐time MPC frameworks had to artificially assume continuity of the optimal controls or, alternatively, impose some demanding assumptions on the data of the optimal control problem to achieve the desired continuity. In this work we analyse the reasons why traditional MPC approaches had to impose the continuity assumptions, the difficulties in relaxing these assumptions, and how the concept of ‘sampling feedbacks’ combines naturally with MPC to overcome these difficulties. A continuous‐time MPC framework using a strictly positive inter‐sampling time is argued to be appropriate to use with discontinuous optimal controls and discontinuous feedbacks. The essential features for the stability of such MPC framework are reviewed. Copyright © 2003 John Wiley & Sons, Ltd.
Output feedback stabilization of constrained systems with nonlinear predictive control
Authors: Findeisen Rolf , Imsland Lars , Allgöwer Frank , Foss Bjarne A. 
Published: February 2003

AbstractWe present an output feedback stabilization scheme for uniformly completely observable nonlinear MIMO systems combining nonlinear model predictive control (NMPC) and high‐gain observers. The control signal is recalculated at discrete sampling instants by an NMPC controller using a system model for the predictions. The state information necessary for the prediction is provided by a continuous time high‐gain observer. The resulting ‘optimal’ control signal is open‐loop implemented until the next sampling instant. With the proposed scheme semi‐global practical stability is achieved. That is, for initial conditions in any compact set contained in the region of attraction of the NMPC state feedback controller, the system states will enter any small set containing the origin, if the high‐gain observers is sufficiently fast and the sampling time is small enough. In principle the proposed approach can be used for a variety of state feedback NMPC schemes. Copyright © 2003 John Wiley & Sons, Ltd.
Robust model predictive control for nonlinear discrete‐time systems
Authors: Magni L. , De Nicolao G. , Scattolini R. , Allgöwer F. 
Published: February 2003

AbstractThis paper describes a model predictive control (MPC) algorithm for the solution of a state‐feedback robust control problem for discrete‐time nonlinear systems. The control law is obtained through the solution of a finite‐horizon dynamic game and guarantees robust stability in the face of a class of bounded disturbances and/or parameter uncertainties. A simulation example is reported to show the applicability of the method. Copyright © 2003 John Wiley & Sons, Ltd.
Suboptimal control of constrained nonlinear systems via receding horizon constrained control Lyapunov functions
Authors: Sznaier Mario , Suárez Rodolfo , Cloutier James 
Published: February 2003

AbstractIn this paper we propose a new controller design method, based on the combination of receding horizon and control Lyapunov functions, for nonlinear systems subject to input constraints. The main result shows that this control law renders the origin an asymptotically stable equilibrium point in the entire region where stabilization with constrained controls is feasible, while, at the same time, achieving near‐optimal performance. Contrary to other approaches, the proposed controller does not require forcing the trajectory at the end of the prediction horizon to lie in a region where the constraints are not binding, allowing for the use of (potentially substantially) smaller horizons in the optimization. Copyright © 2003 John Wiley & Sons, Ltd.
Model predictive control of constrained piecewise affine discrete‐time systems
Authors: Mayne D. Q. , Raković S. 
Published: February 2003

AbstractThe paper deals with model predictive control of a class of non‐smooth nonlinear systems, namely piecewise affine systems. A novel procedure for solving the associated optimal control problem is presented and its convergence established. Stability properties of the closed‐loop system using model predictive control with the new algorithm are derived. Examples illustrate the proposed algorithm for determining optimal control of constrained piecewise affine systems and the performance of the closed‐loop system. Copyright © 2003 John Wiley & Sons, Ltd.
Predictive control of constrained nonlinear systems via LPV linear embeddings
Authors: Casavola Alessandro , Famularo Domenico , Franzè Giuseppe 
Published: February 2003

AbstractThis paper analyzes the applicability of convex MPC schemes, synthesized for LPV polytopic systems, to nonlinear plants. The nonlinear systems under consideration are those whose trajectories can be embedded within those of a polytopic LPV discrete‐time system. It is postulated that the latter belongs to a polytopic family of linear systems, each member of which is parameterized by the value that a parameter vector assumes in the unit simplex. Such a parameter can be measured on‐line and exploited for feedback while a bound on its rate of change is known and exploited for predictions. Different customizations and improvements of a recently introduced MPC scheme for LPV systems are presented and contrasted in terms of their numerical burdens and control performance. The proposed predictive controllers are proved to quadratically stabilize LPV polytopic systems, as well as any other embedded non‐linear system, in the presence of input and state constraints. Copyright © 2003 John Wiley & Sons, Ltd.
Gain‐scheduling MPC of nonlinear systems
Authors: Chisci Luigi , Falugi Paola , Zappa Giovanni 
Published: February 2003

AbstractPredictive control of nonlinear systems is addressed by embedding the dynamics into an LPV system and by computing robust invariant sets. This mitigates the on‐line computational burden by transferring most of the computations off‐line. Benefits and conservatism of this approach are discussed in relation with the control of a critical mechanical system. Copyright © 2003 John Wiley & Sons, Ltd.
Efficient optimization approaches to nonlinear model predictive control
Authors: Mahadevan R. , J. Doyle III F. 
Published: February 2003

AbstractEfficient optimization approaches for nonlinear model predictive control (NMPC) are described in this paper. The first approach is based on the differential flatness property of a system of ordinary differential equations. The nonlinear process model is represented in terms of the flat outputs and their derivatives, and the nonlinear dynamic optimization problem is transformed into a nonlinear programming problem, with exact representation of the system dynamics. The approach is illustrated through the control of substrate concentration of a fed‐batch bioreactor. The second approach is motivated by the idea of differential flatness, but is applicable to broader class of nonlinear systems. Here, the nonlinear process model is recast through the elimination of a subset of the system variables. This results in a nonlinear dynamic optimization with a reduced number of system variables that have to be solved for, as well as the dynamic equations. Applications of this approach to the optimization of a recombinant product in a fed‐batch bioreactor and the control of a chemical reactor are presented. Both the approaches discussed in this paper provide up to a five fold improvement in the solution time for the optimization problem as compared to the traditional formulation. Copyright © 2003 John Wiley & Sons, Ltd.
Efficient scheduled stabilizing model predictive control for constrained nonlinear systems
Authors: Wan Zhaoyang , Kothare Mayuresh V. 
Published: February 2003

AbstractWe present a computationally efficient scheduled model predictive control (MPC) algorithm for constrained nonlinear systems with large operating regions. We design a set of local predictive controllers with estimates of their regions of stability covering the desired operating region, and implement them as a single scheduled MPC which on‐line switches between the set of local controllers and achieves nonlinear transitions with guaranteed stability. This algorithm is computationally efficient and provides a general framework for the scheduled MPC design. The algorithm is illustrated with two examples. Copyright © 2003 John Wiley & Sons, Ltd.
Simulation based strategy for nonlinear optimal control: application to a microbial cell reactor
Authors: Kaisare Niket S. , Lee Jong Min , Lee Jay H. 
Published: February 2003

AbstractOptimal control of systems with complex nonlinear behaviour such as steady state multiplicity results in a nonlinear optimization problem that needs to be solved online at each sample time. We present an approach based on simulation, function approximation and evolutionary improvement aimed towards simplifying online optimization. Closed loop data from a suboptimal control law, such as MPC based on successive linearization, are used to obtain an approximation of the ‘cost‐to‐go’ function, which is subsequently improved through iterations of the Bellman equation. Using this offline‐computed cost approximation, an infinite horizon problem is converted to an equivalent single stage problem—substantially reducing the computational burden. This approach is tested on continuous culture of microbes growing on a nutrient medium containing two substrates that exhibits steady state multiplicity. Extrapolation of the cost‐to‐go function approximator can lead to deterioration of online performance. Some remedies to prevent such problems caused by extrapolation are proposed. Copyright © 2003 John Wiley & Sons, Ltd.
Nonlinear predictive control of hot strip rolling mill
Authors: Cannon M. , Kouvaritakis B. , Grimble M. , Bulut B. 
Published: February 2003

AbstractLinear Model Predictive Control (MPC) has been applied successfully to numerous industrial problems, but its various extensions to the nonlinear case have not enjoyed the same measure of success. One of the major obstacles in this development is the prohibitive online computation required to execute receding horizon minimization of the predicted cost. This paper combines recent linear techniques, which allow for significant reductions in online computational load, with Linear Difference Inclusion in order to apply MPC to a rolling mill problem described by a set of algebraic and differential/integral nonlinear equations, discretized to give a suitable time‐varying uncertain linear model. Through successive optimization of an approximate cost derived by linearization about predicted trajectories, we obtain MPC laws with guaranteed stability and convergence to a (possibly local) minimum of the performance index predicted on the basis of the full nonlinear model dynamics. The efficacy of the approach is illustrated by means of simulation results presented at the end of the paper. Copyright © 2003 John Wiley & Sons, Ltd.
Nonlinear receding horizon control of an underactuated hovercraft
Authors: Seguchi Hiroaki , Ohtsuka Toshiyuki 
Published: February 2003

AbstractThis paper describes nonlinear receding horizon control of an underactuated hovercraft with discrete‐valued inputs and its hardware implementation. The hovercraft has two fixed thrusters, and the thrusters generate thrusts of only three discrete values, that is, forward, backward and zero thrusts. Nonlinear receding horizon control is applied to position control of the hovercraft with the discrete‐valued inputs approximated by constrained continuous‐valued inputs. Although nonlinear receding horizon control requires real‐time constrained optimization, a fast algorithm is successfully implemented for the hardware experiment. Copyright © 2003 John Wiley & Sons, Ltd.
The effects of axial deformation and axial force on vibration characteristics of tall buildings
Authors: Swaddiwudhipong S. , Sidji S. Soelarno , Lee S.‐L. 
Published: February 2003

AbstractA tall building comprising frames and shear walls coupled together is idealized as a shear–flexure cantilever through the continuum approach. The effects of axial deformation as well as axial force in the frames are considered and incorporated in the formulation of the governing equations. Numerical examples are solved through the Galerkin method and the results compared with finite element solutions. The study indicates that the effect of axial deformation in the frame should be considered for tall and/or slender buildings while the effect of axial force in the column should be included for buildings with soft‐storeys resulting from the termination of core walls in the lower portion of the building. Copyright © 2002 John Wiley & Sons, Ltd.
Overstrength and force reduction factors of multistorey reinforced‐concrete buildings
Authors: Elnashai A. S. , Mwafy A. M. 
Published: February 2003

AbstractThis paper addresses the issue of horizontal overstrength in modern code‐designed reinforced‐concrete (RC) buildings. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. The lateral capacity and the overstrength factor are estimated by means of inelastic static pushover as well as time‐history collapse analysis for 12 buildings of various characteristics representing a wide range of contemporary RC buildings. The importance of employing the elongated periods of structures to obtain the design forces is emphasized. Predicting this period from free vibration analysis by employing ‘effective’ flexural stiffnesses is investigated. A direct relationship between the force reduction factor used in design and the lateral capacity of structures is confirmed in this study. Moreover, conservative overstrength of medium and low period RC buildings designed according to Eurocode 8 is proposed. Finally, the implication of the force reduction factor on the commonly utilized overstrength definition is highlighted. Advantages of using an additional measure of response alongside the overstrength factor are emphasized. This is the ratio between the overstrength factor and the force reduction factor and is termed the inherent overstrength (Ω
i). The suggested measure provides more meaningful results of reserve strength and structural response than overstrength and force reduction factors. Copyright © 2002 John Wiley & Sons, Ltd.
Seismic analysis of Tehran Telecommunication Tower using complex fractional modulus
Authors: Horr A. M. , Safi M. , Asadpour N. 
Published: February 2003

AbstractSeismic response of large concrete tower structures with passive or active damping is important in terms of performance under earthquake loads. The conventional finite element method has been used successfully in linear and nonlinear analyses in large concrete structures. The method can be performed by subdividing the large structure into small uniform elements having approximate shape functions. Although this replaces a single complicated structural system with a number of simple uniform elements, in cases of tall concrete tower structures with cracking and crushing behaviour in the concrete material and yielding in the reinforcement, the computer time and memory can be large. Hence, it is desirable to search for a procedure requiring fewer elements and also less computer time and effort to model the structure. In this respect, attention is paid to the advanced complex damped spectral element method, which benefits from the more accurate and also mathematically complicated shape functions. Use of the advanced spectral element method can help engineers to design a complex structure, such as a tall concrete tower, with lower cost and lower weight. Using a computer program, the proposed formulation has been used to derive the nonlinear dynamic response of the 435‐m Tehran Telecommunication Tower. Copyright © 2002 John Wiley & Sons, Ltd.
Exact method of analysis of shear lag in framed tube structures
Authors: Haji‐Kazemi H. , Company M. 
Published: February 2003

AbstractFramed tube structures are particularly suitable for tall buildings. Owing to flexural and shear flexibilities of the frame members, the overall bending of the frame is complicated by the occurance of shear lag. The shear lag phenomenon in framed‐tube structures under lateral loads is explained in the literature, but explanation of its origin and comprehensive studies of it is lacking. In this paper an analogy between the shear lag behaviour of a cantilever box representing a uniform framed‐tube building is used for exact analysis of stress and displacement components of perimeter columns. The coefficients of the power series used for the governing equilibrium and compatibility equations are functions of the height and width of the frame panels. Numerical examples are given to demonstrate the accuracy of the proposed method. Copyright © 2002 John Wiley & Sons, Ltd.