bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hyphenated techniques of thermal analysis for characterisation of soil humic substances
Authors: Dell'Abate Maria Teresa , Benedetti Anna , Brookes Phil C. 
Published: April 2003

AbstractOur aim was to investigate the thermal behaviour of humic substances extracted from temperate and tropical soils by means of hyphenated techniques of thermal analysis (e. g. simultaneous thermal analysis DSC/TG coupled with mass spectrometry, MS, for the analysis of evolved gas, EGA) in order (i) to verify whether the chemical composition of isolated humic substances also reflected the differences in microbial parameters previously measured in related soil samples and (ii) to identify suitable indices of thermal stability. Our results show that the investigation of humic substances by thermal methods can provide information on soil organic matter dynamics. Differences in thermal behaviour between the two groups of soils were found. The indices of thermal stability here proposed, IR (index of thermal recalcitrance), and ID (index of thermal decomposability) clearly showed that in humic substances from tropical soils the thermally recalcitrant organic fraction dominated, whilst in temperate humic substances the opposite held. This agrees with previous results on the microbial dynamics and organic matter turnover of the respective soils and indicates that these indices of thermal stability could represent a useful tool in soil environmental quality investigations.
Study of Self‐Assembly of the Lignin Model Compound on Cellulose Model Substrate
Authors: Micic Miodrag , Radotic Ksenija , Jeremic Milorad , Leblanc Roger M. 
Published: April 2003

AbstractHerein we report a topographical study of the supramolecular organization of enzymatically polymerized lignin model compound – dehydrogenative polymer (DHP) of coniferyl alcohol – on cellulose substrate, using the Environmental Scanning Electron Microscopic (ESEM) technique. A comparison of deposits obtained by bulk polymerization in solution and direct polymerization in the presence of cellulose substrate shows distinct differences in supramolecular organization. DHP polymerized in solution expresses a 3‐D structure with short‐range ordered motifs, while the polymer formed in the presence of cellulose substrate arranges in a single layer compact structure consisting of several domains. Such structures could be described as a two‐dimensional hexagonal close packed lattice(HCPL), with the dimension of unit cell in 1 μm range. The domains have a quite regular structure with few lattice defects, forming a good example of two‐dimensional colloidal crystal. The growth of DHP globules and their assembly into supramolecular structures are interpreted in terms of cooperative electrostatic interaction of polymer precursors, with a framework of cellulose OH groups and interfacial interactions (hydrophilic/hydrophobic) in the course of the structure growth. The results strongly suggest that the carbohydrate matrix in plant cells can serve as a template for lignin structure formation in the plant cell wall.
Self‐assembled lignin model compound on cellulose substrate.magnified imageSelf‐assembled lignin model compound on cellulose substrate.
Application of the Weyl–Hörmander calculus to generators of Feller semigroups
Authors: Baldus Frank 
Published: April 2003

AbstractIn this article we apply the S(M, g)–calculus of L. Hörmander and, in particular, results concerning the spectral invariance of the algebra of operators of order zero in ℒ︁(L2(ℝn)) to study generators of Feller semigroups. The core of the article is the proof of the invertibility of λ Id + P for a strongly elliptic operator P in Ψ(M, g) and suitable weight functions M and metrics g. The proof depends highly on precise estimates of the remainder term in asymptotic expansions of the product symbol in Weyl and Kohn–Nirenberg quantization. Due to the Hille–Yosida–Ray theorem and a theorem of Courrège, the result concerning the invertibility of λ Id + P is applicable to obtain sufficient conditions for an operator to extend to a generator of a Feller semigroup. Moreover, we discuss Sobolev spaces adapted to our weight functions and apply our results to study the generator of a subordinate Feller semigroup. As for the Feller semigroups and the subordination in the sense of Bochner, we build on results of N. Jacob and R. L. Schilling.
Organosilicon‐Assisted Transformation of Living Anionic into Living Cationic Polymerization
Authors: Sanji Takanobu , Sunaga Daisuke , Muto Yasuhiro , Sakurai Hideki 
Published: April 2003

AbstractA novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The SiO linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.magnified image
Subharmonic motion of floating cranes
Authors: Ellermann K. , Kreuzer E. 
Published: April 2003

AbstractAs an example of the nonlinear phenomena in offshore engineering the subharmonic motion of a floating crane is investigated. This nonlinear behavior was observed in experiments [1] as well as simulations [3] for a periodically forced floating crane. The range of operation, in which initial conditions and disturbances influence the type of motion significantly, are of special interest – as well as bifurcation points, where the dynamics change qualitatively due to a small change of one of the parameters.Two different mathematical tools for the investigation of these critical ranges are described: The multiple scales method allows for the analysis of the oscillating system in frequency domain. Path following algorithms are applied in the numerical bifurcation analysis. The results of both tools are in good agreement and can assist in the evaluation of operating conditions.
Stability Analysis of A Floating Caliper Disc Brake
Authors: Jearsiripongkul T. , Chakraborty G. , Hagedorn P. 
Published: April 2003

AbstractIn this paper, the onset of the dynamic instability in a .oating caliper disc brake system is studied. The disc is modelled as a .exible rotating plate, the pad is taken as a small mass and a distributed sti.ness, and the motion of the caliper is also taken into consideration. The linearized equations of motion about the equilibrium position are derived assuming a constant braking force. The equations are subsequently discretized with the help of appropriate shape functions. The eigenvalue problem is then solved to detect the onset of instability. The effects of damping on the stability of motion are investigated as well.
Collapse of Keldysh chains and stability boundaries of non‐conservative systems
Authors: Kirillov Oleg 
Published: April 2003

AbstractEigenvalue problems for non‐selfadjoint linear differential operators smoothly dependent on a vector of real parameters are considered. Bifurcation of eigenvalues along smooth curves in the parameter space is studied. The case of a multiple eigenvalue with the Keldysh chain of arbitrary length is investigated. Explicit expressions describing bifurcation of eigenvalues are found. The obtained formulae use eigenfunctions and associated functions of the adjoint eigenvalue problems as well as the derivatives of the differential operator taken at the initial point of the parameter space. These results are important for the stability theory and sensitivity analysis of non‐conservative systems. Mechanical examples are considered and discussed in detail.
Internal stabilization of standard sampled‐data systems
Authors: Lampe B. P. , Rosenwasser E. N. 
Published: April 2003

AbstractThe paper presents necessary and sufficient conditions under which for a standard sampled‐data system there exists a digital controller, that ensures the internal stability of the system. For the case of stabilizability a general expression for the set of all stabilizing controllers is given. The stabilizability conditions are formulated as divisibility of certain polynomials, controllability and observability concepts are not used.
On the Optimal Stabilisation for a set of Programmed Motions of the Bilinear Control System
Authors: Smirnov N. V. , Smirnov T. E. 
Published: April 2003

AbstractDuring recent years there has been considerable interest in using bilinear systems [1, 2] as mathematical models to represent the dynamic behavior of a wide class of engineering, biological and economic systems. Moreover, there are some methods [3] which may approximate nonlinear control systems by bilinear systems. For the first time Zubov has proposed a method of stabilization control synthesis for a set of programmed motions in linear systems [4]. In papers [5, 6] this method has been developed and used to solve the same problem for bilinear systems.In the present paper the following problems are considered. First, synthesis of nonlinear control as feedback under which the bilinear control system has a given set of programmed and asymptotic stable motions. Because this control is not unique, the second problem concerns optimal stabilization. In this paper a method for the design of nonlinear optimal control is suggested. This control is constructed in the form of a convergent series. The theorem on the sufficient conditions to solve this problem is represented.
Model Based Trajectory Control of an Overhead Travelling Crane
Authors: Aschemann H. , Sawodny O. , Hofer E.P. 
Published: April 2003

AbstractUntil now, most papers concerning control of overhead travelling cranes have only focussed on position control of the translational degrees of freedom, see for example [1], [3], [4], and [5]. With more advanced robotic applications envisaged, however, there is a demand for both trajectory control in six degrees of freedom and active damping of the weakly damped load oscillations due to the rope suspension [2]. Hence, a model based trajectory control is presented for an overhead travelling crane that has been upgraded with an orientation unit providing three additional axes. Starting from a central multibody model, decentralised design models are derived for each crane axis. By this, couplings between the axes are identified and appear as disturbance inputs in these decentralised design models. Each decentralised axis controller consists of linear state feedback, feedforward control, and observer based disturbance compensation and is derived in symbolic form. This allows for an adaptation of the complete control structure employing the gain scheduling technique with respect to varying system parameters like rope length and load mass. Couplings between the crane axes are compensated by feedforward control, whereas the e.ects of nonlinear friction forces are counteracted by combination of feedforward control and disturbance estimation. Experimental results, taken at a 5 t ‐ bridge crane, show the bene.ts of the proposed control scheme as regards control performance and steady‐state accuracy.
An Elastic Model of a Metal V‐Belt CVT
Authors: Bullinger M. , Pfeiffer F. 
Published: April 2003

AbstractA simulation model has been developed to determine the behaviour of power transmission of a metal pushing V‐belt CVT at steady states. This allows to calculate the characteristics of forces and permits to evaluate the necessary pulley thrust, the maximum transmittable torque and the efficiency. Therefor the pulley and shaft deflection and the unilateral constraints of contacts must be modelled properly. The dynamics of the belt is specified by separate longitudinal and transversal approaches. The transversal dynamics is modelled continuously applying a Ritz‐approach based on B‐Splines. The longitudinal dynamics is described with Lagrange coordinates. So discontinuous effects as separation of elements can be modelled by continuous shape functions. Concluding, the obtained results of the presented simulation model are compared with measurements published by Doshisha University [2].
Coupled Multibody‐Aerodynamic Simulation of High‐Speed Trains Manoeuvres
Authors: Carrarini A. 
Published: April 2003

AbstractA co‐simulation MBS/CFD was implemented to investigate the effects of unsteady aerodynamic loads on the driving dynamics of high speed trains during common manoeuvres in absence of cross wind. A linear aerodynamic model, the panel method, was applied to the computation of the flow around the driving trailers and the multibody simulation program SIMPACK simulated the dynamic response of the vehicles to the resulting aerodynamic loads.
Rekursive Lösung der Bewegungsgleichung von Mehrkörperketten mit Microcontrollerketten
Authors: Ferrara P. , Bremer H. 
Published: April 2003

AbstractBei der Erstellung von Bewegungsgleichungen für Mehrkörpersysteme wird man mit einer grundlegenden Schwierigkeit konfrontiert: die dabei entstehenden Matrizen wachsen schnell zu unhandlicher und unübersichtlicher und damit fehleranfälliger Größe an. Eine numerische Lösung ist durch die Inversion der Massenmatrix zwar auf den aktuellen PC's, aber nicht auf kleineren Microcontrollern möglich. Genau diese werden in der mobilen Robotik (Serviceroboter, Krabbeltiere, intelligente Prothesen,…) zunehmend häufiger eingesetzt. In dieser Arbeit wird ein modulares Konzept für die Lösung der Bewegungsgleichung auf solchen kleinen Rechnern vorgestellt.
Model Based Control of a Parallel Robot – A Comparison of Control Algorithms
Authors: Hahn Hubert 
Published: April 2003

AbstractIn this contribution the control behavior of a special construction of a parallel robot, called multi‐axes test facility, is investigated. After a brief discussion of the different tasks of the robot the construction of the robot is briefly presented. To solve the tasks, different control algorithms are derived based on model equations of different complexity of the robot. Depending on the task to be performed by the robot, the controllers compensate the kinematic and/or kinetic coupling of the degrees of freedom of the robot, stabilize the system and achieve the desired spatial motion of each degree of freedom as well as sufficient robustness with respect to parameter uncertainties and load variations. A few results obtained in computer simulations and laboratory experiments are presented and judged with respect to the quality of control, the closeness to reality of the computer simulations, and the amount of costs and work needed to realize the different solutions.
Development of a Toolbox for Model‐Based Real‐Time Simulation and Analysis of Legged Robots
Authors: Alexander Helm , Hardt Michael , von Stryk Oskar , Höpler Robert 
Published: April 2003

AbstractMultibody systems such as legged robots require sophisticated and efficient methods for their modeling, control and simulation. This paper discusses the development of a software library based on modern tools such as C++, OpenGL and XML for highly efficient dynamics modeling. A primary focus lies on modularity permitting its easy extensibility in connection with different actuation and contact models, optimization algorithms, localized and centralized on‐line control schemes as well as animation and simulation environments.
Simulation of Multibody Systems with Nonholonomic Constraints
Authors: Kielau G. , Maißer P. 
Published: April 2003

AbstractThe paper deals with the nonholonomic multibody system dynamics from a point of view resulting from some present applications in high‐tec areas like high‐speed train technology or biomechanics of some disciplines in high‐performance sports. A formulation of nonholonomic constraints which are linear related to generalized velocities is based on a derivative‐free approach for generating Lagrangian motion equations of multibody systems with kinematical tree structure as well as for constrained multibody systems. This has been done by using di.erential‐geometric concepts in a Riemannian space. The ideas are illustrated by the classical edge condition on double‐curved surfaces. The surfaces are described by C2‐vector functions, for example by NURBS‐approximation. As an example a bobsleigh is regarded moving on a double‐curved surface.
Verallgemeinerung der kinematischen Modelle integrierter Navigationssysteme
Authors: Wagner J.F. 
Published: April 2003

AbstractBei integrierten Navigationssystemen spielt die Modellvorstellung über die Kinematik des jeweils betreffenden Fahrzeugs eine zentrale Rolle. Eingang finden die kinematischen Modelle in die Gleichungen eines erweiterten Kalman‐Filters, das die Zustandsgrößen des betrachteten Fahrzeugs z. B. für Regelungszwecke schätz und Messsignale von Inertialsensoren sowie von Struktursensoren und äußeren Vermessungseinrichtungen zusammenführt.
A Nonlinear Sandwich Shell Theory Accounting for Transverse Core Compressibility
Authors: Hohe J. , Librescu L. 
Published: April 2003

AbstractThe present study is concerned with an advanced theory of sandwich shells with transversely compressible core. The model is based on the standard Kirchhoff‐Love hypothesis for the face sheets and a third‐order displacement expansion for the core. Consistent equations of motion and boundary conditions are derived by means of Hamilton's variational principle. The model is applied to a postbuckling analysis of cylindrical shells under axial compression.
Analyse von Spannungslokalisierungen in Mehrschichtverbunden mittels der Rand‐Finite‐Elemente‐Methode
Authors: Lindemann J. , Becker W. 
Published: April 2003

AbstractDie Rand‐Finite‐Elemente‐Methode wird als Randdiskretisierungsverfahren vorgestellt, das vorteilhaft zur Analyse von Spannungskonzentrationen in Mehrschichtverbunden eingesetzt werden kann. Wie auch in anderen Situationen ergibt sich für den Fall eines transversalen Matrixrisses eine gute übereinstimmung mit vergleichenden Finite‐Elemente‐Analysen.
Rate‐type Model for electro‐rheological Material Behaviour consistent with Extended Thermodynamics: Application to a steady viscometric flow
Authors: Sadiki A. , Balan C. 
Published: April 2003

AbstractBased on extended thermodynamics, a class of rate‐type constitutive equations for electrorheological materials is presented. It is shown unlike many recent works using standard methods of continuum mechanics, that this approach, which consists in postulating expressions which relate the time derivative of the Cauchy stress to the motion, takes well account of the viscoelastic‐plastic effects as well as the coupling between the motion and the electric field. By considering special cases it turns out that the derived nonlinear algebraic model embeds a variety of existing differential models in the literature. The accuracy of the model is illustrated by considering a steady shear flow in which the electric field is applied perpendicularly to the flow direction. Analytical solutions with various parameter variations are obtained and discussed. The model predicts well the behaviour associated with material instabilities observed in viscometric flows for which the existence of the yield stress is required as confirmed by many experiments.
An Elasto‐Plastic Formulation of a Soil‐Foundation Interface
Authors: Ehlers Wolfgang , Blome Peter 
Published: April 2003

AbstractIn this paper, a special interface formulation for the continuum mechanical description of the contact zone between soil and geotechnical foundation is presented. The proposed model is based on the Theory of Porous Media (TPM), a consistent approach to describe geomaterials in a macroscopic frame [1]. Assuming quasi‐static conditions, strains in the porous soil body are due to an elasto‐plastic work‐hardening model, whereas the constitutive properties of the interface are based on the continuous elasto‐plastic behaviour of the soil body and on the failure kinematics of the contact zone. Using the FE method, a 3‐d initial‐boundary‐value problem of a soil‐foundation interaction is discussed with a close look on the occurring localization phenomenon.
On the formulation and finite element implementation of anisotropic multiplicative finite strain elastoplasticity
Authors: Eidel B. , Gruttmann F. 
Published: April 2003

AbstractA constitutive model for orthotropic elastoplasticity at finite plastic strains is presented and aspects of its numerical implementation are addressed. The constitutive equations are related to the plastic intermediate configuration, which is introduced by F = Fe Fp. Isotropic tensor functions are used for the description of orthotropic material response in the elasticity law and the yield function. The latter is formulated in terms of the Mandel stress tensor.
Parameter Identification for Inelastic Constitutive Models
Authors: Harth Tobias 
Published: April 2003

AbstractThe identification of material parameters of constitutive models is based on identification experiments. Since even specimens from the same lot show high deviations in the experimental data, the identification of the material parameters leads to different results for one and the same material. The number of identification experiments is usually not large enough for a statistical analysis of the deviations in the identified parameters. In order to overcome this problem we present a method of stochastic simulation which is based on time series analysis for generating artificial data with the same stochastic behaviour as the experimental data. The stochastic simulations allow an investigation of the confidence in the fits of the material parameters. We validate the stochastic simulations by comparing the results of the parameter identification from experimental data with the results from artificial data. The presented simulation method applied here turns out to be a suitable tool for generating artificial data for various kinds of analysis purposes. However, it is very important to take into account that the machines which perform the experiments do not maintain constant strain rates in the loading history of the tension and cyclic experiments.
Parameteridentifikation inelastischer Lotwerkstoffmodelle mittels experimenteller und numerischer Analyse
Authors: Nguyen v.S. , Herrmann K.P. , Müller W.H. 
Published: April 2003

AbstractDie Bestimmung der Materialparameter des Lotwerkstoffmodells spielt eine wichtige Rolle für die Modellierung des Materialverhaltens. Dabei enthalten die Lotwerkstoffmodelle sowohl elastisch‐plastische als auch viskoplastische Materialparameter. Die Identifikation der Modellparameter anhand der Versuchsergebnisse stellt eine inverse Problemstellung dar. Zur Lösung des inversen Problems werden nichtlineare Optimierungsverfahren verwendet. Es handelt sich um die Fehlerminimierung zwischen experimentell bestimmten Meßkurven und simulierten Kurven. Anhand von Small‐Punch‐Testversuchen wird die Parameteridentifikation an Zinn‐Blei‐Lot SnPb37 unter Benutzung der Finiten Elemente Methode und des nichtlinearen Optimierungsverfahrens vorgenommen.
On the role of energy in chip formation
Authors: Nachname Martin Bäker 
Published: April 2003

AbstractThe implicit code ABAQUS/Standard is used to simulate the formation of continuous and segmented chips. Using the described model, the idealized process of friction‐less machining of an elastic ideally‐plastic material is studied. It is shown that Merchant's classical shear angle relation does not hold, as chip formation does not minimize the energy as assumed by Merchant. The model is also used to study segmented chip formation using a realistic material law for the Titanium alloy Ti6Al4V at high cutting speeds.
A Domain Decomposition Method for Frictional Contact Problem
Authors: Lotfi A. , Kiss B. 
Published: April 2003

AbstractThe bilateral or unilateral contact problem with Coulomb friction between two elastic bodies is considered [1]. An algorithm is introduced to solve the resulting finite element system by a non‐overlapping domain decomposition method. The global problem is transformed to a smaller problem on the contact surface. The solution is obtained by using a successive approximation method, in each step of this algorithm we solve two intermediate problems the first with prescribed tangential pressure and the second with prescribed normal pressure.