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The novelty of this study is to model and investigate the free and forced thermal vibration and buckling behaviors of a porous functionally graded magneto-electro-elastic (MEE) nanoplate made of barium-titanate and cobalt-ferrite and subjected to moving loads. In the modeling, the strains are assumed to originate from classical mechanics, thermal expansion, electroelastic, and magnetostrictive properties, nonlocal elasticity, and strain gradient elasticity, and the motion equations of MEE nanoplate are obtained by Hamilton's principle Considering various cases, the effects of thermal stresses, magneto-electro-elastic coupling, externally applied electric and magnetic field potential, nonlocal properties (nonlocal and material size parameters), porosity volume fraction on the free vibration and buckling behavior have been studied. Additionally, the forced response to the moving load for various cases of the velocity of the load is also investigated. It is observed that the free-response and buckling of the nanoplate vary with the material composition, externally applied electrical and magnetic fields, temperature rise, and porosity volume fraction. Furthermore, it is also noticed that the velocity of the load is the most influential factor in the forced response of the MEE nanoplate. Moreover, the material composition of the nanoplate characterizes the magneto-electro-elastic response depending on the amounts of barium-titanate (electro-elastic) and cobalt-ferrite (magnetostrictive). The stiffness of the MEE nanoplate can be controlled by regulating the intensities of electric and magnetic fields. This property can keep the bending and buckling stability of the nanoplate exposed to severe thermal and high-speed moving loads. [ABSTRACT FROM AUTHOR]

Topology optimization with classical mechanics has already made tremendous advances for macroscopic structure in the last few decades. However, size effects are detected from small-scale structures when the structure's feature size is reduced to the micro or nano level. To tackle this problem, the Solid Isotropic Material with Penalization method (SIMP) is merged with the modified couple stress theory to explore the size effect on the topology optimization. Furthermore, temperature effect and buckling requirement are taken into consideration in this framework. Finally, several examples are provided to illustrate the size effects on the topology optimization and mechanical behavior. [ABSTRACT FROM AUTHOR]

Owing to the excellent performance of microstructures or nanomaterials with well-designed topological configuration, the characteristic scale of structural design is gradually shifting from macroscopic to nanoscale or microscale structural design. However, the size effect that emerges from the small-scale structures may not be explained effectively with the hypothesis of classical mechanics owing to the lack of microscopic parameters in the classical constitutive model. In addition, slender beams within such small-scale structures are prone to buckling failure, which puts forward additional requirements for the stability design of the structure except for the overall compliance of the structure. Therefore, a topology optimization framework combining the modified couple stress theory with the solid isotropic material penalization (SIMP) model is constructed to illustrate the size effect on topology optimization. Numerical results show that the size effect affects the compliance, buckling performance, and topological configurations of the evolutionary structures. [ABSTRACT FROM AUTHOR]

The perforated stiffened panel is generally found as a sub-component of sophisticated structures. The fundamental purpose of this panel is to withstand against buckling under complicated loading and environmental conditions. Hence, an accurate knowledge of critical buckling behaviour of stiffened panels is very much essential for a reliable and lightweight structural design. In this paper, the focus is on quasi-laminated panels with different cutout shapes of various sizes and their responses to hygrothermal environments under nonlinearly varying edge loads and is compared with the locally stiffened panels. Towards this, the modelling of the panel and stiffener is done by adopting nine-noded heterosis plate elements and three noded beam elements respectively. The stiffener formulation is suitably modified in order to take the torsional effect also into consideration along with the effect of shear deformation. Initially, the plate and the stiffener elements are treated separately, and then the displacement compatibility is maintained between them by using the transformation matrix. For a given loading and geometric discontinuity, the stress distribution within the perforated panel is highly non-uniform in nature and hence a dynamic approach has been used to calculate buckling loads by adopting two sets of boundary conditions, one set for pre-buckling stress analysis and the second set for buckling analysis. Four different quasi-isotropic stacking sequences are deliberated in this work by varying different plyorientation in each scheme. The study also addresses the effect of various parameters such as nonlinear loads, hygro-thermal loads, cutout size and shapes, position of cutout, stiffener parameters, stacking sequences, thickness of plate and boundary conditions. [ABSTRACT FROM AUTHOR]

• The compressive buckling analysis of cracked nanosheets is performed by XFEM, considering small-scale effect. • The contribution of this work is the study of buckling of nanosheets in the presence of a crack. • The studied variables include small-scaling parameter, crack length, nanosheet dimensions, and boundary supports. • The results show that the cracking phenomenon and the increase of its length intensify the nonlocal effect. The process used to produce nanosheets may cause damage such as cracks in them. These cracks can adversely affect the buckling capacity of nanosheets. The main contribution of this research endeavor is to extend the previous studies on undamaged nanosheets to the cracked ones concerning the size-dependent effect. On the nanoscale, the assumption of material continuity, which is the fundamental assumption in classical continuum mechanics, is not valid. In this case, nonlocal non-classical theories are employed to analyze nanosheets. The present paper examines the nonlocal buckling of cracked graphene sheets under uniaxial and biaxial loads. To this end, the governing equations are developed based on the first-order shear deformation theory and using Eringen's nonlocal elasticity theory. Moreover, cracked nanosheets with various boundary conditions are analyzed via the extended finite element method. The variables under study are the small scaling parameter, crack length, nanosheet dimensional parameters, and support conditions. The results indicate that while the small scaling parameter reduces the critical buckling capacity of nanosheets, the presence of a crack in the nanosheet and the increase in its length intensify the nonlocal effect. In addition, as the aspect ratio of the nanosheet increases from one, the nonlocal effect decreases gradually. The small-scale effect increases by constraining the edges of the cracked nanosheets. [ABSTRACT FROM AUTHOR]

In this paper, we investigate stability and optimization of an axially loaded nonlocal beam that is simply supported at one end and elastically restrained against rotation on the other. Nonlocal continuum mechanics is a theoretical framework that extends classical continuum mechanics to account for the influence of small length scales, especially in nanostructures. We analyze elastically buckling nanobeam based on Eringen's nonlocal elasticity theory. The Euler method of adjacent equilibrium configuration is used to derive the nonlinear governing equations. The critical axial force and postbuckling shape are obtained for the beam with the unit cross-sectional area. The shape of the nonlocal beam stable against buckling that has minimal volume is determined by using Pontryagin's maximum principle. The optimality conditions are derived. The cross-sectional area for optimally designed beam is found from the solution of a nonlinear boundary value problem. New numerical results are obtained. The first integral (Hamiltonian) is used to monitor the accuracy of the integration. The numerical analysis includes the influence of the characteristic parameter of the small length scale on the critical load, the postbuckling shape and the optimal shape of the analyzed beams. It is shown that there are the saving materials for optimally designed nanobeam in all numerical examples. [ABSTRACT FROM AUTHOR]

This paper assesses thermoelastic damping (TED) in circular nanoplates by incorporation of the small-scale effect into structural and thermal domains. The nonlocal elasticity theory and dual-phase-lag (DPL) heat conduction model are exploited for achieving the size-dependent coupled thermoelastic equations. By choosing time-harmonic and asymmetric form for deflection and temperature change, and solving the size-dependent thermoelastic eigenvalue problem, the damped natural frequency of circular nanoplate is extracted. On the basis of the complex frequency approach, an analytical relation, for the description of TED in circular nanoplates, is derived. For different boundary conditions and vibration modes, a comparison study is performed between the size-dependent results and those provided by classical continuum mechanics and heat conduction theories. Outcomes show a discrepancy between results acquired by the size effect on the structure and heat conduction. It is elucidated that how nonlocal and DPL characteristic parameters can represent the size-dependent phenomenon and can affect the magnitude of TED. A comprehensive parametric study is conducted to specify the influence of boundary constraints, vibration mode and the type of material on the amount of energy loss from TED. [ABSTRACT FROM AUTHOR]

Wrinkling instabilities occur when a stiff thin film bonded to an elastic substrate undergoes compression. Regardless of the nature of compression, this phenomenon has been extensively studied through local models based on classical continuum mechanics. However, the experimental behavior is not yet fully understood and the influence of nonlocal effects remains largely unexplored. The objective of this paper is to fill this gap from a computational perspective by investigating nonlocal wrinkling instabilities in a bilayered system. Peridynamics (PD), a nonlocal continuum formulation, serves as a tool to model nonlocal material behavior. This manuscript presents a methodology to precisely predict the critical conditions by employing an eigenvalue analysis. Our results approach the local solution when the nonlocality parameter, the horizon size, approaches zero. An experimentally observed influence of the boundaries on the wave pattern is reproduced with PD simulations which suggests nonlocal material behavior as a physical origin. The results suggest that the level of nonlocality of a material model has quantitative influence on the main wrinkling characteristics, while most trends qualitatively coincide with predictions from the local analytical solution. However, a relation between the film thickness and the critical compression is revealed that is not existent in the local theory. Moreover, an approach to determine the peridynamic material parameters across a material interface is established by introducing an interface weighting factor. This paper, for the first time, shows that adding a nonlocal perspective to the analysis of bilayer wrinkling by using PD can significantly advance our understanding of the phenomenon. [ABSTRACT FROM AUTHOR]

The present article pertains to the assessment of thermoelastic damping (TED) in rectangular nanoplates by incorporation of size effect within the constitutive and heat conduction relations. With the purpose of establishing size-dependent coupled thermoelastic equations, nonlocal elasticity theory and dual-phase-lag heat conduction model are utilized. By considering time-harmonic vibrations, nonclassical frequency equation affected by thermoelastic coupling is derived. By solving this equation and extracting the real and imaginary parts of damped natural frequency via some mathematical operations, an explicit expression for description of TED in circular nanoplates is obtained. With the goal of better understanding the small-scale effect on TED, a comparison is made between the results predicted by the size-dependent formulation and those determined according to classical continuum mechanics and heat conduction theories for two kinds of boundary constraints. Considerable difference between classical and nonclassical results, especially at smaller sizes, implies the necessity of incorporating small-scale effect into both structural and thermal areas. [ABSTRACT FROM AUTHOR]

Carbon nanotubes are one of the most influential constituents of advanced engineering systems. The classical continuum mechanics, however, ceases to hold in accurate description of the structural response of nanobars. The mixture unified gradient theory of elasticity is invoked for the nanoscopic study of the structural characteristics of nanobars. The associated boundary-value problem of equilibrium is established within a consistent stationary variational framework. The differential condition of equilibrium is properly equipped with extra non-standard boundary conditions. To examine the more realistic response of nano-sized bars, deformable boundary conditions are prescribed where the elastic deformation of the support is modeled by a translational restraint at the boundary. The idealized free and fixed end conditions are, accordingly, retrieved for ad hoc values of the translational elastic spring stiffness. The mechanics of the mixture unified gradient bar is analytically addressed and a closed-form solution of the axial deformation of the nanobar is detected. The axial structural features of the nanobar with elastic boundary conditions are numerically studied and the asymptotic structural behavior of the mixture unified gradient bar is analytically examined. A new benchmark is detected that can be efficaciously applied in the analysis and design of pioneering nano-systems. [ABSTRACT FROM AUTHOR]

Purpose: Considering the size-dependent influence ignored by classical continuum mechanics, a new non-classical Euler–Bernoulli beam model is proposed in this paper. The new fractional viscoelastic nanobeam model is set up using the fractional Kelvin–Voigt viscoelastic model and Hamilton's principle. And the new model studies the total effects of nonlocal elasticity, modified couple stress, and surface energy. Methods: The model represented the fractional integral-partial differential governing equation is solved by Galerkin's and predictor–corrector methods. First, the effects of nonlocal elasticity, modified couple stress, surface energy, and their coupling impact on the nonlinear time response of free vibration of fractional viscoelastic nanobeam are analyzed. Then, in the frame of nonlocal couple-stress elasticity and surface energy theory, the effects of different parameters on the nonlinear time responses of free and forced vibration of fractional viscoelastic nanobeam are discussed. Results and Conclusion: The numerical results show that the fractional order must be considered in the modeling of viscoelastic nanobeam, and the system's damping enhances by the increase of fractional order. Moreover, owing to the correlation between fractional order and excitation frequency, the nonlinear time responses of fractional order to free and forced vibration are different. [ABSTRACT FROM AUTHOR]

The generalized Reissner-type operator of three-dimensional micropolar mechanics of solids is presented, on the basis of which the generalized Reissner-type operator of three-dimensional micropolar mechanics of thin solids with one small size is obtained under the new parameterization of the domains of these bodies. From the last Reissner-type operator, in turn, the generalized Reissner-type variational principle of three-dimensional micropolar mechanics of thin solids with one small size is derived under the new parametrization of the domains of these bodies. It should be noted that the advantage of the new parameterization is that it is experimentally more accessible than other parameterizations (Nikabadze in Development of the method of orthogonal polynomials in the classical and micropolar mechanics of elastic thin bodies, MSU Publishing House, 2014; Contemp Math. Fundam Dir 55:3–194, 2015; J Math Sci 225:1, 2017). Further, applying the method of orthogonal polynomials (expansion of unknown quantities in series in terms of a system of orthogonal polynomials), from the generalized Reissner-type variational principle of three-dimensional micropolar mechanics of thin solids with one small size under the new parameterization of the domains of these bodies, the Reissner variational principle of micropolar mechanics of thin solids with one small size in the moments with respect to the system of Legendre polynomials is derived. In addition, the method is described for obtaining the variational principles of Lagrange and Castigliano of micropolar mechanics of thin solid with one small size under the new parametrization of the domains of these bodies in moments with respect to systems of the first and second kind Chebyshev polynomials. The paper is a continuation of the work "Nikabadze, Ulukhanyan, On some variational principles in the three-dimensional micropolar theories of solid"; therefore, before reading this paper, the authors invite the interested reader to familiarize themselves with the work (Nikabadze and Ulukhanyan in On some variational principles in the three-dimensional micropolar theories of solids, submitted). [ABSTRACT FROM AUTHOR]

The vigorous development of additive manufacturing technology promotes the tendency of lattice infill design to be miniaturized. The representative scale of the deformation field becomes equivalent to the length scale of the microstructures when the characteristics size of the lattice infill design is down to micron or nanoscale, and strain gradient effects or size effects arise in the structure. Due to the lack of microscopic material properties, the typical topology optimization framework based on classical mechanics for lattice infill structure cannot represent the performance difference induced by the size effect. Therefore, single-scale lattice infill structure design and couple stress theory are combined to explore the size effect on topology optimization. Numerical examples show that when the size ratio of the macroscopic feature size to the material characteristic length is reduced to a comparable range, the topological configurations and the target compliance values exhibit a significant size effect. [ABSTRACT FROM AUTHOR]

This work is devoted to modeling the dynamics of large molecules. The key issue in modeling the dynamics of real molecular systems is to correctly represent the temperature of the system using the available theoretical tools. In most works on molecular dynamics, vibrations of atoms inside a molecule are modeled with enviable persistence, which has nothing to do with physical temperature. These vibrations represent the energy internal to the molecule. Therefore, it should not be present in problems in the dynamics of inert molecular systems. In this work, by means of classical mechanics, it is shown that the simplest system containing only three molecular bodies, due to multiple acts of pair interactions of these bodies, reproduces the temperature even in an extremely complex unstable motion of the system. However, at the same time, it is necessary to separate the stochastic part of the movement from the deterministic one. Calculations also show that translational fluctuations in the motion of molecules make the greatest contribution to temperature. The contribution of rotational energy to the total energy of fluctuation motions is small. It follows from these results that the thermal state of the system is determined only by the translational temperature. The latter, in turn, opens up possibilities for a simplified description of many complex systems composed of carbon molecules such as fullerenes and nanotori. [ABSTRACT FROM AUTHOR]

This work studies the size-dependent free vibration response of functionally graded (FG) nanoplates using a layerwise theory. The proposed model supposes not only a higher-order displacement field for the core but also the first-order displacement field for the two face sheets, thereby maintaining an interlaminar displacement continuity among layers. Unlike the conventional layerwise models, the number of variables is kept fixed and does not increase for an increased number of layers. This is a very important feature compared to conventional layerwise models and facilitates significantly the engineering analyses. The material properties of the FG nanoplate are graded continuously through the thickness direction in accordance with a power-law function. The Eringen's nonlocal elasticity theory is here adopted to relax the continuum axiom required in classical continuum mechanics and hence hopeful to capture the small size effects of naturally discrete nanoplates. The equations of motion of the problem are obtained via a classical Hamilton's principle. The present layerwise model is implemented with a computationally efficient C0- continuous isoparametric serendipity elements and applied to solve a large-scale discrete numerical problem. The robustness and reliability of the developed finite element model are demonstrated by a comparative evaluation of results against predictions from literature. The comparative studies show that the proposed finite element model is: (a) free of shear locking, (b) accurate with a fast rate convergence for both thin and thick FG nanoplates, and (c) excellent in terms of numerical stability. Moreover, a detailed parametric analysis checks for the sensitivity of the vibration response of FG nanoplates to the aspect ratio, length-to-thickness ratio, nonlocal parameter, boundary conditions, power-law index, and modes shapes. Referential results are also reported, for the first time, for natural frequencies of FGM nanoplates which will serve as benchmarks for further computational investigations. [ABSTRACT FROM AUTHOR]

For nano/micro-scale structures, the classical continuum mechanics can't properly depict the size-dependent effect arising in them anymore. In addition, Fourier's law is limited in describing the heat transfer process in nano/microstructures due to its nature of predicting infinite heat speed. To amend such defects, the non-classical continuum mechanics based on the nonlocal elasticity theory and the modified couple stress theory incorporating the non-Fourier heat transfer model with memory-dependent effect is formulated to characterize the thermoelastic behaviors in micro/nano-scale system in the present work. Then, the model is used to study the dynamic response of an Euler-Bernoulli nanobeam subjected to a ramp-type heating. The corresponding governing equations are derived and then solved by Laplace transform method and its numerical inversion. The distributions of the non-dimensional transverse deflection, temperature and displacement are obtained and illustrated graphically. In calculation, the influences of the ramp heating time parameter, the material length parameter, the nonlocal parameter, the time-delay factor and the kernel functions on the considered physical quantities are examined and discussed in detail. [ABSTRACT FROM AUTHOR]

With the development and applications of nano-electro-mechanical systems, academic interest in the mechanical behavior of piezoelectric structures at nanoscale is increasing. Interesting unconventional phenomena have been observed either experimentally or through molecular dynamics simulation. The most common and also important one is the size-dependent characteristics. Classical continuum mechanics with necessary modifications has been proven to be very powerful in explaining these particular characteristics in a relatively simple theoretical framework. This article reviews the recent advances in understanding the size-dependent dynamic responses of piezoelectric nanostructures from the viewpoint of modified continuum mechanics. Particular attentions are paid to three advanced theories of piezoelectricity (e.g. gradient piezoelectricity, surface piezoelectricity, and nonlocal piezoelectricity) and their abilities to predict unconventional vibration and wave characteristics in piezoelectric structures and devices at the nanoscale. The article could serve as a useful reference for the future research on or design of nanostructures with multifield couplings. [ABSTRACT FROM AUTHOR]

This paper presents a new conceptualization of complex nonlinear mechanical systems and develops new and novel computational methods for determining their response to given applied forces and torques. The new conceptualization uses the idea of including particles of zero mass to describe the dynamics of such systems. This leads to simplifications in the development of their equations of motion and engenders a straightforward new computational approach to simulate their behavior. The purpose of the paper is to develop a new analytical and computational methodology to handle complex systems and to illustrate it through the study of an old unsolved problem in classical mechanics, that of a non-uniform rigid spherical shell rolling, without slipping, under gravity on an arbitrary dimpled bowl-shaped rigid surface. The new conceptualization provides the explicit equations of motion for the system, the analytical determination of the reaction forces supplied by the surface, and a straightforward computational approach to simulate the dynamics. Detailed analytical and numerical results are provided. The computations illustrate the complexity of the dynamical behavior of the system and its high sensitivity to the initial orientation of the shell and to the presence of any initial angular velocity normal to the surface. [ABSTRACT FROM AUTHOR]

The vertical and horizontal bending of micro-beams subjected to axial compressive and transverse concentrated loadings is a common lateral deformation in micro-/nano-engineering that plays a significant role in the design and optimization of micro-/nano-devices. The present study aims to investigate it using the nonlocal theory. For this purpose, the simplified mathematical model is developed, and the nonlocal differential constitutive equation is applied. Since the mechanical properties of micro-beams are different from those of macro-beams, the non-classical nonlocal bending moment is introduced to improve the classical bending formulation in order to adapt to the vertical and horizontal bending of micro-beams. The effects of the external load, external size, structural stiffness, and internal characteristic scale on the vertical and horizontal bending deformation including the midpoint deflection and critical compression are presented. The present analytical model and results are validated by the finite element method. It is shown that the critical compression decreases with increasing the internal characteristic scale. Moreover, the midpoint deflection varies remarkably with respect to the axial and transverse loadings, structural stiffness, internal characteristic scale, and external size. An obvious nonlocal scale effect is found, in which the internal characteristic scale cannot be neglected compared with the external size. Besides, a threshold value of the structural stiffness is determined, and the connotation of the nonlocal interaction requires that the structural stiffness shall not be lower than that threshold. A mutual restriction between structural stiffness and external loadings is observed in the vertical and horizontal bending. In particular, it is further proved that the classical continuum mechanics can not be used in micro-/nano-scaled mechanics through a strange phenomenon that is contrary to mechanical common sense in the calculation example. The study is expected to be beneficial to the design and application of micro-beams subjected to the vertical and horizontal bending. [ABSTRACT FROM AUTHOR]

A novel non-classical continuum model for pull-in analysis of multilayer graphene sheets (MLGSs) is developed to consider the effect of shear interaction between layers based on the nonlocal elasticity theory. The equation governing the motion and corresponding boundary conditions of electrostatically actuated MLGSs are obtained based on the nonlocal shear multiplate theory. The Galerkin method along with the first mode shapes for clamped and cantilever MLGSs together with the method of parameter expansion is used to obtain closed-form expressions of the normalized frequency and time history response. In addition, molecular dynamics (MD) simulations are carried out to validate the pull-in voltages predicted by the developed model for both cantilever and clamped MLGSs. According to the presented results, the nonlocal interlayer shear model can significantly reduce the differences between the results of the classical continuum mechanics and molecular dynamics. Finally, parametric studies are implemented to show the effects of number of layers, initial gap, nonlocal parameter, bending- interlayer shear rigidities, and coefficients of the elastic medium. The results indicate that the pull-in voltage of MLGSs changes remarkably with the interlayer shear modulus and the nonlocal parameter. For cantilever MLGSs (contrary to clamped cases), the nonlocal model predicts larger pull-in voltages than the classical continuum theory. Therefore, it can be concluded that the classical continuum model is inadequate for pull-in analysis of electrostatically actuated MLGSs. [ABSTRACT FROM AUTHOR]

This work investigates quasi‐static crack propagation in specimens made of brittle materials by combining local and non‐local elasticity models. The portion of the domain where the failure initiates and then propagates is modeled via three‐dimensional bond‐based peridynamics (PD). On the other hand, the remaining regions of the structure are analyzed with high order one‐dimensional finite elements based on the Carrera unified formulation (CUF). The coupling between the two zones is realized by using Lagrange multipliers. Static solutions of different fracture problems are provided by a sequential linear analysis. The proposed approach is demonstrated to combine the advantages of the CUF‐based classical continuum mechanics models and PD by providing, in an efficient manner, both the failure load and the shape of the crack pattern, even for three‐dimensional problems. [ABSTRACT FROM AUTHOR]

This work presents an efficient online system identification approach by integrating a reduced sigma points–based filter with a high-fidelity mechanics-based state-space hysteretic finite-element modeling framework. The efficacy and computational efficiency of any sampling/sigma points–based nonlinear filtering process are conditional on the number of sigma/sample points required by the filter at each time step to quantify statistical properties of the involved quantities, as well as on the accuracy and computational cost of the underlying system model. A scaled spherical simplex filter (S3F) with a significantly decreased n+2 sigma points set size is thus presented that is able to achieve similar robustness and accuracy as the state-of-the-art 2n+1 sigma points unscented Kalman filter (UKF) for an n -dimensional state-space, yet with approximately 50% less computational requirements. The filtering framework is integrated with a recently developed fully parametrized damage plasticity–consistent hysteretic finite-element modeling approach that is able to account for distributed plasticity, axial-moment–shear interactions, and degradations in one unified formulation by employing the concepts of continuum damage mechanics and classical multiaxial plasticity. In the presented hysteretic model, the system matrices are constant and do not require updating throughout the analysis, whereas the degradations and inelasticity are updated through element-level hysteretic evolution equations in the form of resultant stress–strain laws. Overall, the system can be presented in a state-space form and can be solved with any first-order ordinary differential equation solver, without any linearization or gradient requirements, rendering the high-fidelity formulation robust and computationally efficient and enabling ideal compatibility in terms of computational implementation with the filtering methodology for online joint state-parameter identification. [ABSTRACT FROM AUTHOR]