bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geostatistical analysis of ground‐survey elevation data to elucidate spatial and temporal river channel change
Authors: Chappell Adrian , Heritage George L. , Fuller Ian C. , Large Andrew R. G. , Milan David J. 
Published: April 2003

AbstractA digital elevation model (DEM) of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time. Elevation was measured above an arbitrary datum using a ground‐based three‐dimensional tacheometric survey in two reaches of the River Nent, UK, in July 1998, October 1998 (after flood conditions) and June 1999. A detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce DEMs in each reach and for each survey period. Maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period. The parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales.The analysis of channel change on the River Nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers. A flood modified the channel features, but low magnitude and high frequency flows rationalized the morphology. In spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material. The blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel. Such small changes suggested that the distributary system was sensitive to variation in sediment regime.Plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy (ranging between −11 per cent and +93 per cent). These curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime. Variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness. Copyright © 2003 John Wiley & Sons, Ltd.
The importance of plant root characteristics in controlling concentrated flow erosion rates
Authors: Gyssels G. , Poesen J. 
Published: April 2003

AbstractWhile it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross‐sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley & Sons, Ltd.
Flow hydraulics and geomorphic effects of glacial‐lake outburst floods in the Mount Everest region, Nepal
Authors: Cenderelli Daniel A. , Wohl Ellen E. 
Published: April 2003

AbstractGlacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m−2 in wide, low‐gradient valley segments to as high as 51 700 W m−2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd.
Identification of halocarbons in the Tiber and Marta rivers by static headspace and liquid–liquid extraction analysis
Authors: Russo Mario V. , Campanella Luigi , Avino Pasquale 
Published: April 2003

AbstractVolatile organochlorine compounds in the Tiber and Marta rivers have been analyzed by liquid–liquid extraction and headspace gas chromatography. Several different halogenated compounds were identified, in particular chloroform, bromoform, trichloroethane, trichloroethene, and tetrachloroethene. The concentrations of the halocarbons varied between 0.05 and 4.5 μg L–1 with a relative standard deviation ≤4.0%. The highest concentrations were observed for chloroform, bromoform, and tetrachloroethene in the Marta and Tiber rivers. The results obtained by use of the two analytical methods were similar.
CO/Alkene Copolymers as a Promising Class of Biocompatible Materials, 1. Examination of the In Vitro Toxicity
Authors: Reuter P. , Fuhrmann R. , Mücke A. , Voegele J. , Rieger B. , Franke R.‐P. 
Published: April 2003

AbstractNovel 1,4‐polyketones were synthesized by a PdII catalyzed copolymerization reaction from cheap technical monomers. The spectrum of mechanical properties ranges from highly crystalline, hard materials to thermoplastic, soft elastomers. The hydrophilicity of the surface is adjustable from nonpolar to highly polar by a proper choice of the α‐olefin component. This control of polymer properties is a basis for the development of new biocompatible materials. The results of standardized as well as more specific in vitro tests clearly demonstrate the nontoxicity of the investigated copolymers.Polyketone synthesis.magnified imagePolyketone synthesis.
A Note on Analysis and Numerics for Radiative MHD in 3D
Authors: Dedner Andreas , Rohde Christian , Wesenberg Matthias 
Published: April 2003

AbstractThe equations of radiative magnetohydrodynamics describe the dynamics of an electrically conducting fluid interacting with magnetic fields and radiation. In particular they provide a widely accepted mathematical model for the physics in the solar photosphere and convection zone. In the spatially three‐dimensional case we present several notions of solutions for the Cauchy problem and discuss existence and uniqueness issues. Furthermore we report on numerical experiments in the context of solar physics.
Construction and complexity of hierarchical matrices
Authors: Grasedyck Lars , Hackbusch Wolfgang 
Published: April 2003

AbstractIn previous papers a class of ℋ︁‐matrices was introduced which are data‐sparse and allow an approximate matrix arithmetic of nearly optimal complexity. The complexity analysis for the (approximate) matrix arithmetics in the class of ℋ︁‐matrices is based on two criteria, the sparsity and the idempotency. We describe a general strategy for the construction of the ℋ︁‐matrices where the two criteria are fulfilled.
Stability Analysis of Full Annular Rub in Rotor‐to‐Stator Systems
Authors: Jiang Jun , Ulbrich Heinz 
Published: April 2003

AbstractThis paper outlines the analytical study of the stability of a more realistic rotor‐to‐stator contact model, which considers the stator as an elastic body having finite mass and being elastically supported. For this model, no report on the stability analysis is available in the literature by our knowledge. In this study, the analytical solution, corresponding to the synchronous full annular rub motion, is first solved, then the stability condition of it is derived. Based on the systematic parametric studies, one gains a deeper insight into the nature of the dynamical behavior of the rotor‐to‐stator contact system. Since the previously investigated simpler rotor‐to‐stator contact models are only the special cases of the present model, the limitation of the simpler models and the influence of the system parameters, which were omitted or assigned to specific values in the simpler models, have been revealed through the present investigation.
Nonlinear Controller Design for PWM–Controlled Converters
Authors: Kugi A. , Schlacher K. 
Published: April 2003

AbstractThis contribution is concerned with the nonlinear controller design for a certain class of PWM (pulse width modulation) – controlled converter systems. It will be shown that under certain assumptions the SSA (state space averaging) – model of the PWM–controlled converter with the duty ratio as the plant input has a very special mathematical structure. Based on this mathematical model a modified version of the nonlinear H2–design where an integral term is systematically included in the nonlinear controller will be presented.
Modelling and identification of rigid‐body dynamics of parallel kinematic structures
Authors: Grotjahn Martin 
Published: April 2003

AbstractA new approach for modelling the dynamics of parallel kinematic (PKM) structures is presented in this paper. It leads to a formulation of the dynamic equations which is linear with respect to a dynamic parameter vector of minimal dimension. Thus, the equations can be directly used for parameter identi.cation by linear estimation techniques. The algorithm utilisesJourdain's principle of virtual power which leads to very efficient resulting code. The parameter reduction is based on opening the kinematic loops so that analytic rules known from serial robots can be implemented. Additionally, a new approach for dynamic parameter identification is suggested. The application to modelling the PKM PaLiDa and identifying its gravitational parameters proves the capacity of the presented approaches.
Asymptotic evaluation of effective complex moduli of fibre‐reinforced viscoelastic composite materials
Authors: Andrianov I. , Danishevs'kyy V. , Weichert D. 
Published: April 2003

AbstractWe propose an asymptotic approach for the evaluation of effective complex moduli of viscoelastic fibre‐reinforced composite materials. Our method is based on the homogenization technique. We start with a non‐trivial expansion of the input plane‐strain boundary value problem by ratios of visco‐elastic constants. This allows to simplify the governing equations to forms analogous to the complex transport problem. Then we apply the asymptotic homogenization method, coming from the original problem on multi‐connected domain to the cell problem, defined on a unit cell of the periodic structure. For the analytical solution of the cell problem we apply the boundary perturbation technique, the asymptotic expansion by a distance between two neighbouring fibres and the method of two‐point Padé approximants. As results we derive uniform analytical representations for effective complex moduli, valid for all values of the components volume fractions and properties.
On the construction of conservation laws with the Neutral Action Method
Authors: Nordbrock Uwe , Kienzler Reinhold 
Published: April 2003

AbstractIn constructing conservation laws, Noether's classical theorem can only be applied, if a Lagrangian function is available for the system of interest. A recently developed procedure, the so called Neutral‐Action Method, allows a systematic construction, even if no Lagrangian function exists.
Thermo–mechanical behaviour of steel including phase transitions and transformation–induced plasticity
Authors: Wolff Michael , Böhm Michael , Schmidt Alfred 
Published: April 2003

AbstractIn the framework of Rational Mechanics, we formulate a continuum‐mechanical model for the thermo‐mechanical behaviour of steel. Our plasticity model is based on the assumption of intermediate configurations. We include phase transitions, plasticity as well as transformation‐induced plasticity (TRIP) and allow for general material laws. Some consequences will be derived from the Clausius‐Duhem inequality. The resulting model is a system of strongly coupled PDE's for displacement, temperature and phase distributions. A quenching test is numerically simulated. This work has been partially supported by the DFG via the SFB 570 “Distortion Engineering”, University of Bremen.
Modelling of 3‐D Linear Viscoelastic Swelling of Charged Tissues and Gels
Authors: Ehlers Wolfgang , Acartürk Ayhan , Markert Bernd 
Published: April 2003

AbstractThe skeleton of hydrated tissues or gels exhibits flow‐independent viscoelastic properties [2] which are strongly coupled with the dissipative phenomena resulting from the interstitial fluid flow and the electrochemical swelling mechanisms [4]. Following this, it is the goal of this contribution to combine a linear viscoelasticity formulation with an electrochemical swelling theory in the framework of a well‐founded multiphasic concept. Proceeding from a macroscopic mixture approach, the governing equations can be expressed in terms of three primary variables, namely the solid displacement uS, the effective pore‐fluid pressure p and the molar salt concentration cm of the interstitial fluid.
A Time Finite Element Method Based on the Generalized Variational Calculus
Authors: Ehlers Wolfgang , Ammann Martin 
Published: April 2003

AbstractIn this contribution, a new finite element method in the temporal domain is presented, in which the time step size is introduced as an additional variable. Thus, the variation of the time integral of the Lagrangean resulting from Hamilton's principle has to be carried out with respect to the rules of the generalized variational calculus. Apart from the usual time integral of the Euler‐Lagrange differential equations, the so‐called transversality condition is obtained as an additional result representing a time‐boundary term, which is used to obtain an optimal step size in the time domain.
Kontaktformulierung für lineare und quadratische ‘Solid‐Shell’ Elemente
Authors: Harnau M. , Schweizerhof K. 
Published: April 2003

AbstractMit ‘Solid‐Shell’ Elementen können auch direkt Deformationen in Dickenrichtung abgebildet werden [4], was insbesondere für Metallumformprobleme mit kleinen Radien wichtig ist. Zur Beschreibung des Kontaktes der Werkstücke zu den Werkzeugen, die als analytisch zu definierende starre Flächen betrachtet werden können, werden entsprechend der Ansatzordnung der ‘Solid‐Shell’ Elemente vier‐ bzw. neun‐Knoten Kontaktelemente entwickelt. Die verwendete Penaltyformulierung wird durch Integration der Kontaktkraftverteilung über die Elementfläche [5] ausgewertet. Die Überprüfung der Kontaktbedingung erfolgt somit an den Gausspunkten, wie dies wohl auch in [7] vorgeschlagen wird. Probleme bei ausschließlicher Knotenbetrachtung, wie die erforderliche unterschiedliche Gewichtung der Kontaktknoten bei ‘Solid‐Shell’ Elementen mit Ansätzen höherer Ordnung, werden umgangen.
An Explanation of the Non‐unique Behaviour of a Textile Probe in the Drape Experiment ‐ Numerical Stability Analysis
Authors: Jański Ł. , Ulbricht V. 
Published: April 2003

AbstractThe paper proves, that the ambiguous behaviour of a textile probe in the drape experiment is connected with many possible equilibrium states. This experiment is usually used for the evaluation of the drapeability of textiles. We treat a textile surface in our mathematical model as a two‐dimensional Cosserat continuum, which equilibrium equations can be easily formulated. To solve the boundary value problem, which assures equilibrium, we use the finite element method in connection with the arc‐length method. This strategy allows us to trace the highly non‐linear behaviour of the system. This nonlinearity is responsible for the non‐unique behaviour of a textile probe in drape. In our investigation we calculate some of the possible final configurations of a round textile probe supported on the round table. Such configurations can be observed in the drape experiment.
Anwendung der Materialpunktmethode für die numerische Simulation von Kaschierprozessen
Authors: Schilling Olaf , Reese Stefanie 
Published: April 2003

AbstractBei Kaschierprozessen werden Einzelmaterialien (Bleche und Folien) einer Anlage kontinuierlich zugeführt und unter Wärmezufuhr und Druck zu einem Schichtverbundmaterial vereinigt. Da sich die auftretenden Randbedingungen am einfachsten unter Eulerscher Betrachtungsweise angeben lassen, wohingegen die Berechnung der Materialverformungen eine Lagrangesche Betrachtungsweise erfordert, bietet sich der Einsatz der aus den “Particle‐in‐cell methods” [1] hervorgegangene Materialpunktmethode [2] an. Damit sich länger andauernde Prozesse mit dieser Methode simulieren lassen, wird das explizite Zeitintegrationsverfahren durch ein implizites ersetzt. Die Diskretisierung dünner Schichten mit wenigen Materialpunkten und wenigen Elementen erfordert eine Änderung der Datenübertragung zwischen Materialpunkten und Elementknoten.
Optimal placement of distributed actuators for a controlled smart elastic plate
Authors: Seeger F. , Gabbert U. 
Published: April 2003

AbstractThe performance and the efficiency of smart structures controlled by piezoelectric wafers decisively depend on the locations of the actuators and sensors. For the evaluation and testing of time consuming numerical optimisation techniques, which are currently a part of our research, benchmark examples are required. As such a benchmark example a simply supported plate structure is inverstigated, where the active controlled behaviour can still be described analytically. In the paper the optimisation algorithm is briefly described and the results of a typical example are presented.
Parameteridentifikation des mechano‐sorptiven Kriechens von Rotbuche
Authors: Entenmann V. , Hardtke H.‐J. 
Published: April 2003

AbstractBedingt durch die Simulation des Trocknungsvorganges von Schnittholz in den letzten Jahren wurden Möglichkeiten zur Modellierung des sogenannten mechano‐sorptiven Kriechens benötigt. Die mechano‐sorptiven Parameter wurden durch Messungen, die in einer Trocknungskammer stattfanden, bestimmt. Dabei wurden geeignete Zugprüfkörperproben verwendet, die in den drei Bezugsrichtungen radial, tangential und longitudinal zur Jahrringrichtung jeweils belastet wurden. Anschließend wurden die ermittelten Meßwerte an die Lösungen der zur Modellierung verwendeten Differentialgleichungen adaptiert. So konnten die gesuchten Werkstoffparameter für das mechano‐sorptive Kriechen bestimmt werden. Alternativ zu dem Wege der Bestimmung der Parameter mittels Adaption an die Lösungen der Differentialgleichungen soll die Methode der nichtlinearen Optimierung angewandt werden. Dabei soll versucht werden, globale Minima für das gestellte nichtlineare Optimierungsproblem aufzufinden.
Modelling of Shape Memory Alloys and Experimental Verification
Authors: Schleich M. , Pfeiffer F. 
Published: April 2003

AbstractPrestrained shape memory alloys change their length when heated above their transformation temperature. This effect can be used to generate high forces in a small workspace, which has particular advantages in actuator design.The optimization and control of the shape memory actuator requires a comprehensive simulation of the material behavior. However, many of the existing models are limited to specific load cases or offer rough approximations only. A material model for shape memory alloys from Seelecke [1] is examined in this paper. This model describes the behavior of a shape memory wire, which is heated by electric current. It is implemented in a simulation program to investigate the actuator output and to improve the performance. Finally, the parameters of the simulation are adapted to experimental results.
Application of a posteriori error estimates for Navier‐Stokes equations to fluid flow in a channel with corners
Authors: Burda P. , Novotný J. , Sousedík B. 
Published: April 2003

AbstractWe investigate a posteriori error estimates for the Stokes and Navier‐Stokes equations for incompressible fluid problem on 2D polygonal domains. We have determined accurately the constant that appears in the estimates. We apply these results to the technique of adaptive mesh refinement ‐ we solve an incompressible flow problem in a domain with corners that cause singularities in the solution.
Damping Behavior of the Free Liquid Interface Oscillation upon Step Reduction in Gravity
Authors: Michaelis M. , Gerstmann J. , Dreyer M. E. , Rath H.J. 
Published: April 2003

AbstractExperiments were carried out to investigate the damping behavior of the reorientation of a free liquid interface in a right circular cylinder, partly filled with a liquid and suddenly exposed to a step reduction in gravity. The damping behavior basically depends on the Ohnesorge number and the static contact angle. This study shows the strong influence of the contact point for low static contact angles.
Oblique Shock‐Vortex Interaction
Authors: Thomer O. , Klaas M. , Schröder W. 
Published: April 2003

AbstractBreakdown of a slender vortex caused by an oblique (OSVI) shock is studied using numerical solutions of the Euler equations for unsteady three‐dimensional flow. A Burgers vortex with a given circulation and axial velocity distribution is prescribed at the inflow boundary. The calculations show that like in incompressible flows supersonic breakdown is primarily controlled by pressure forces. The shock is deformed into an ‘s’‐shaped part near the vortex core where the shock becomes normal. The results indicate that initiation of breakdown is more sensitive to variations in the axial velocity than in the circulation, and that the .ow structure is clearly time‐dependent.