bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy models where the equations are defined on different domains
Authors: Glitzky Annegret 
Published: January 2007

AbstractWe investigate a stationary energy model for semiconductor devices and respect the more realistic assumption that the continuity equations for electrons and holes have to be investigated only in a subdomain Ω0 of the domain of definition Ω of the energy balance equation and of the Poisson equation. This nonlinear system of model equations is strongly coupled and has to be considered in heterostructures and with mixed boundary conditions. We obtain a local existence and uniqueness result for the two‐dimensional stationary energy model. For this purpose we derive a W1,p ‐regularity result for solutions of systems of elliptic equations with different regions of definition and use the Implicit Function Theorem. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A two‐scale reaction‐diffusion system with time‐dependent microstructure
Authors: Meier Sebastian A. , Böhm Michael 
Published: January 2007

AbstractWe present a two‐scale model for reactive transport in a unsaturated porous medium. Reaction and diffusion of a gas dissolved in the pore water is modelled at the pore‐scale, while the fast transport of the gas in the air phase is described by an averaged equation. The pore geometry is allowed to vary in time to account for temporal changes of the domain occupied by the pore water. The resulting semilinear parabolic system of PDEs is coupled in a non‐standard way. After a transformation to a fixed domain, the existence of a unique weak W1,p ‐solution is established by semigroup methods. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stochastic Modelling of Wind Speed Power Production Correlations
Authors: Gottschall Julia , Anahua Edgar , Barth Stephan , Peinke Joachim 
Published: January 2007

AbstractBased on measurements we investigate the velocity‐power characteristic of a 2 MW wind turbine. We apply a stochastic analysis where we describe the evolution of the power output with a Langevin equation, with special respect to short‐time fluctuations in wind speed.Standard procedures, such as the IEC 61400‐12 standard, are limited due to the fact that only mean values over several minutes of wind speed and power output are considered. According to this, short‐time dynamics of wind and power fluctuations are usually not taken into account. We introduce an improved method which enables us to extract these dynamics of the power characteristic from the measured data.In particular, we get the response dynamics of the power L (u (t)) via the estimation of Kramers‐Moyal coefficients, describing its evolution in time$ \dot L $(t) with a Langevin equation where we separate the power output into a relaxation and a noise part. A fixed‐point analysis provides the required power characteristic. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mixed Integer Models for Branched Sheet Metal Products
Authors: Günther Ute , Martin Alexander 
Published: January 2007

AbstractA new technique for forming sheet metal makes it possible to construct branched sheet metal products out of one piece of sheet metal. Since the number of potential ways to produce one and the same component increases exponentially with every additional branch, appropriate tools for handling the large number of possibilities are necessary. In this paper we give a Mixed Integer Program that models the different ways of producing branched profiles and show how to incorporate manufacturing constraints into the model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extra Precise Preconditioning for Non‐Hermitian Eigenvalue Problems
Authors: Drygalla Volker 
Published: January 2007

AbstractFor badly conditioned Non‐Hermite eigenvalue problems known iterative refinement procedures often fail. It is proposed to use extra precise iterative refinement in a precondition step. As preconditioners the matrix Q from the QR decomposition or at least the matrix of ‐ even not very accurate ‐ eigenvalues can be used. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On some numerical methods for an inverse potential problemin 2D semi infinite regions
Authors: Chapko R. , Vintonyak N. 
Published: January 2007

AbstractWe consider the inverse Dirichlet boundary value problem for the Laplace equation that consists in the reconstruction of the bounded inclusion in the 2D domain with infinite boundary from Cauchy data observed on it. In order to solve this problem we apply the Landweber [3] and hybrid [1] methods and investigate ‐ mostly numerically ‐ their goals and defects in the case of semi‐infinite regions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Dendritic Crystal Growth
Authors: Müller Rüdiger , Warnecke Gerald 
Published: January 2007

AbstractWe consider the modified Stefan‐Problem with Gibbs‐Thomson correction, but vanishing kinetic undercooling. In this case the interface velocity is not given by mean curvature flow, but has to be computed explicitly from the temperature gradients at the interface. A finite element method on adaptive refined multigrids is presented here. Dirichlet conditions have to be satisfied along the solid‐liquid interface that in general may intersect the elements. We use an implicit level‐set representation of the interface that preserves it as a sharp surface, in contrast to the phase‐field method. In numerical simulations we observe dendritic patterns that show good agreement with different features of physical experiments. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Level Set Methods in a Benchmark for Thermoacoustic Instabilities
Authors: Arens Kai , Klingshirn Hans‐Joachim , Rentrop Peter 
Published: January 2007

AbstractGas turbines can suffer from combustion instabilities and combustion driven oscillations. As a prestep a 3D benchmark tube geometry for the complicated interactions between acoustics and thermal heat release is investigated. For the representation of the flame surface a Level Set approach was chosen. The resulting model includes the impact of curvature on the laminar burning velocity as well as the potential flow field and underlying velocity fields due to vorticity and volume expansion across the flame front. The acoustic equations and the thermal heat release are coupled by the acoustic velocity which is also included in the flame model. A numerical simulation of this benchmark problem is presented as a first step toward optimizing or controlling the stability behavior of the system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of Linear System under Convex Endpoint Constraints
Authors: Balashevich Natalia 
Published: January 2007

AbstractAn algorithm of real‐time realization of optimal feedback for linear control system with convex endpoint constraints is suggested. It is based on solving linear approximative problems and correction of obtained solution by the Newton method. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling conditions for supply networks and resulting optimization problems
Authors: Göttlich Simone , Herty Michael 
Published: January 2007

AbstractWe discuss a continuous model for production lines based on ordinary and partial differential equations and recall coupling conditions for connecting different suppliers of the supply chain. Based on this model we state an optimization problem for distributing flows in supply chains and investigate this numerically. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Horizontal parametric resonant vibration of suspension footbridges
Authors: Grosel Jacek , Wójcicki Zbigniew 
Published: January 2007

AbstractThe possibility of exciting horizontal parametric resonance vibration in a cable stayed footbridge as a result of a premeditated action of a group of people, or of crowd movement, is analysed. Large horizontal transverse vibration are caused by the vertical periodic synchronised movement of people, which is analogical to the movements of a person on a swing. The problem studied is how large a group of people is able to excite dangerous parametric transversal vibration in the system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Method of Integro‐Differential Relations for Optimal Beam Control
Authors: Georgy Kostin , Vasily Saurin 
Published: January 2007

AbstractAn approach to modelling and optimization of controlled dynamical systems with distributed elastic and inertial parameters are considered. The general method of integro‐differential relations (IDR) for solving a wide class of boundary value problems is developed and criteria of solution quality are proposed [1]. A numerical algorithm for discrete approximation of controlled motions is worked out [2] and applied to design the optimal control low steering an elastic system to the terminal position and minimizing the given objective function [3]. The polynomial control of plane motions of a homogeneous cantilever beam is investigated. The optimal control problem of beam transportation from the initial rest position to given terminal states, in which the full mechanical energy of the system reaches its minimal value, is considered. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Trajectory planning and tracking control of lumped LTI systems
Authors: Lindert Sven‐Olaf , Reinschke Kurt 
Published: January 2007

AbstractMany plants can be modelled as lumped LTI‐systems and described by Differential‐Algebraic‐Equations (DAEs). Systems with m ≥ 1 control inputs are investigated in the frequency domain. It is proved that there exist m basis variables, whose trajectories may be chosen arbitrarily. Then, the trajectories of all system signals including the control signals are entirely determined. In case of unstable plants, trajectory tracking controllers must be added. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibration of a Complex Strings System under a Moving Force
Authors: Rusin J. , Śniady P. 
Published: January 2007

AbstractWe consider vibrations of an elastically connected double‐spring complex system subjected to moving concentrated forces. This system is treated as two strings connected by an elastic layer. The motion of the system is described by two partial differential equations. It is shown that some solutions of the system response can be obtained not only as series but also in closed forms. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical and experimental investigation of tyre dynamics
Authors: Takács Dénes , Stépán Gábor 
Published: January 2007

AbstractThe lateral vibration of towed wheels ‐ also called shimmy ‐ is related to the elasticity of the suspension system or to the elasticity of the wheel. The second case is studied here since the majority of the vehicles has pneumatic tyres. A one degree‐of‐freedom wheel model is considered with perfect rolling and elastic tyre. To verify the theoretical stability charts, an experimental rig is built and one of the stability boundaries is identified. Close to a double Hopf bifurcation point quasiperiodic vibrations are observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fuzzy supervised neurocontrol of electrohydraulic servos
Authors: Ursu Ioan , Ursu Felicia , Tecuceanu George , Cristea Radu 
Published: January 2007

AbstractThe work presents theoretical and experimental investigations concerning the neuro‐fuzzy control of electrohydraulic servos. The control algorithm is built around a neurocontroller designed to optimize a performance index. Whenever the neurocontrol saturates or a system performance parameter decreases, the control scheme switches to a feasible and reliable fuzzy logic control. In accordance with simulation studies developed in previous works of the authors, the neuro‐fuzzy controlled system proves often to be better than the corresponding classical PI or LQG systems. We emphasize that the entire control synthesis is thought as a model free approach, thus ensuring reduced design complexity and focusing on increased system robustness. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On positive descriptor systems
Authors: Virnik Elena 
Published: January 2007

AbstractWhen economical, biological or chemical systems are modelled by descriptor systems, in which the state x describes concentrations, populations of species, or numbers of cells, then the solution is a nonnegative vector function. Hence, the numerical methods for the control or simulation should respect this special structure. We define and characterise positivity for descriptor systems. Furthermore, for a special case, we show a Schur complement decoupling technique that reduces a descriptor system to the ODE case. We use this technique to present a characterisation of the existence of positive solutions to generalised Lyapunov equations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of biological studies of polyester composites filled carbon black and activated carbon from bamboo (Gigantochloa scortechinii)
Authors: Khalil H.P.S. Abdul , Noriman N.Z. , Ahmad M.N. , Fuaad N.A. Nik , Ratnam M.M. 
Published: January 2007

AbstractThe development of composites using various filler material increased significantly nowadays. Composite materials need to implement the biological and mechanicals impact in their life cycle. The carbon black (CB) and activated carbon (AC) from bamboo (Gigantochloa scortechinii) were used as filler in polyester composites. CB and AC were pyrolized to 700°C and activated with ZnCl2. The composites were prepared with 40% filler loading. The degradation of the composites CB and AC (mechanical properties) to the soil burial test was determined. Tensile, flexural, impact and mass changes of the buried samples were investigated. The deterioration of the samples affected by the biological attack was confirmed by SEM studies. The assessment was done after 0, 3, 6, and 12 months of the biological exposure and the results were compared with the composites filled CaCO3 (commercial filler) and cast polyester resin (as control). POLYM. COMPOS. 28:6–14, 2007. © 2007 Society of Plastics Engineers
Recycled milk pouch and virgin LDPE‐LLDPE‐based jute fiber composites
Authors: Choudhury Arup , Adhikari Basudam 
Published: January 2007

AbstractThe present investigation deals with the thermo‐mechanical recycling of post consumer milk pouches (LDPE‐LLDPE blend) and its use as jute fiber composite materials for engineering applications. The mechanical, thermal, morphological, and dynamic‐mechanical properties of recycled milk pouch‐based jute fiber composites with different fiber contents were evaluated and compared with those of the virgin LDPE‐LLDPE/jute fiber composites. Effect of artificial weathering on mechanical properties of different formulated composites was determined. The recycled polymer‐based jute fiber composites showed inferior mechanical properties as well as poor thermal stability compared to those observed for virgin polymer/jute fiber composites. However, the jute‐composites made with (50:50) recycled milk pouch‐virgin LDPE‐LLDPE blend as polymer matrix indicated significantly superior properties in comparison to the recycled milk pouch/jute composites. Overall mechanical performances of the recycled and virgin polymeric composites were correlated by scanning electron microscopy (SEM). The dynamic mechanical analysis showed that storage modulus values were lower for recycled LDPE‐LLDPE/jute composites compared to virgin LDPE‐LLDPE/jute composites throughout the entire temperature range, but an increase in the storage modulus was observed for recycled‐virgin LDPE‐LLDPE/jute composites. POLYM. COMPOS. 28:78–88, 2007. © 2007 Society of Plastics Engineers
Observation of boron enrichments in a heat‐treated quasi‐binary hypoeutectic NiAlHfB2 alloy by means of atom probe field‐ion microscopy (APFIM)
Authors: Deges J. , Rablbauer R. , Frommeyer G. , Schneider A. 
Published: January 2007

AbstractThe mechanical properties of the inter‐metallic phase NiAl with B2 superlattice structure can be improved by strengthening particles of the IV B transition‐metal diborides formed in situ. These compounds form with NiAl quasi‐binary eutectic systems. Among them, the quasi‐eutectic alloy with hafnium diboride exhibits favourable properties owing to its excellent oxidation resistance and high thermal stability up to 1400 °C. The eutectic composition of the quasi‐binary system NiAlHfB2 was determined to be 0.75 at.% Hf and 1.5 at.% B, and the eutectic temperature is Teut = 1640 °C.In the present study, the microstructure of the hypoeutectic NiAlHf0.6B1.2 alloy was characterised after heat treatment at 1400 °C for 100 h by means of SEM, TEM, and atom probe field‐ion microscopy (APFIM). The alloy consists of fine globular and fibrous eutectics HfB2 and primary NiAl, with high thermal stability. APFIM investigations on the heat‐treated alloy indicate a relatively high density of small boron clusters containing a few boron atoms (about 5–15 boron atoms) and line‐shaped enrichments of about 50–200 boron atoms. These are free from hafnium and other impurities of transition metals and exhibit a depletion of aluminium. For an exact determination of the composition even by using high‐resolution APFIM, their sizes seemed to be too small.The appearance of boron‐rich clusters is in contrast to the formation of HfB2 of high thermodynamic stability and the very low solubility of boron and hafnium in B2‐ordered NiAl. Copyright © 2007 John Wiley & Sons, Ltd.
Dietary carbohydrates with different rates of fermentation affect fermentation end-product profiles in different sites of gastro-intestinal tract of weaning piglet
Authors: Awati A. , Williams B. A. , Bosch M.W. , Verstegen M.W.A. 
Published: January 2007

AbstractAnin vivoexperiment was conducted to examine changes in fermentation end-products in the gastro-intestinal tract (GIT) of weaning piglets by the inclusion of fermentable carbohydrates in the diet. The experiment was repeated in three replicates of 36 piglets. Piglets were raised free of antibiotics and creep feeding prior to weaning at 4 weeks of age. Each replicate was conducted over a period of 10 days. The piglets were offered one of two dietary treatments: control diet (CON), and fermentable carbohydrate enriched diet (CHO); and were subjected to one of the two fasting treatments (i) fasting for 2 days in the beginning of the experimental period and (ii) non-fasting. Piglets were slaughtered on the 1st, 4th and 10th day of each period. Digesta samples were collected from: first half of small intestine, second half of small intestine, caecum, and colon. The dry matter, volatile fatty acid (VFA) profile, and ammonia concentrations were analysed. Food intake, growth and food conversion ratio were also recorded. There were no differences in production performances such as growth and food conversion ratio (FCR) between the treatment groups. Concentrations of VFA were significantly higher, while ammonia concentration was significantly lower in the CHO group compared to the CON group in different fermentation sites within the GIT (P<0·001), and on different slaughtering days (P<0·05). Fasting had no effect on fermentation end-products. This study concludes that the addition of fermentable carbohydrates of varying fermentabilities stimulated carbohydrate fermentation, with reduction in protein fermentation along the different parts of GIT studied, in weaning piglets.
Traceability of grass-feeding in young beef using carotenoid pigments in plasma and adipose tissue
Authors: Serrano E. , Prache S. , Chauveau-Duriot B. , Agabriel J. , Micol D. 
Published: January 2007

AbstractThe objective of the present study was to test the reliability of the analysis method of the reflectance spectrum of fat in the zone of light absorption by carotenoid pigments developed in lambs to trace grass feeding in calves. Six feeding treatments were compared in suckling calves: ad libitum cocksfoot hay plus ad libitum concentrate or half level of ad libitum concentrate (HH and HL), ad libitum cut grass plus ad libitum concentrate or half level of ad libitum concentrate (GH and GL), ad libitum highland grazed grass plus ad libitum concentrate (PH); ad libitum medium quality cocksfoot hay plus dam's milk (C0). Groups HH, HL, GH, GL and PH were slaughtered at approximately 10 months of age, after 150 days of experimental feeding diet. C0 calves were slaughtered at the beginning of the experiment at approximately 6 months of age. The concentration of carotenoids was analysed by HPLC on diets and calves' plasma at slaughter. The reflectance spectrum of perirenal and subcutaneous fat were measured at slaughter and expressed as AVI units. Plasma carotenoid content was higher (P<0·05) in PH and GL calves than in HH, HL and GH calves. There was an effect (P<0·05) of feeding treatment and measurement site on AVI. Values obtained for perirenal fat were higher (P<0·05) than those obtained for subcutaneous fat. For plasma carotenoid content and for AVI values in both fat tissues there was no overlapping between hay-fed calves on the one hand and GL or grazing calves on the other hand. However, there was some overlapping between hay-fed calves and GH calves. For plasma carotenoid content, values for C0 calves overlapped with values of GH and GL calves. For both fat tissues AVI values of C0 calves overlapped with values of HH, HL, GH and GL calves. AVI of cut grass fed calves (GH and GL groups) increased linearly (P<0·05) with average daily grass intake for both tissues considered. AVI in subcutaneous fat tissue decreased linearly (P<0·05) with average daily concentrate intake but this relation was not significant for AVI in perirenal fat (P>0·05). Plasma carotenoid concentration and the reflectance spectrum of the fat in the zone of light absorption by carotenoid pigments could be used to trace grass feeding in calves. Results obtained in this study suggest that different fatty tissues could differ in their reliability and interest for traceability of grass-feeding, depending on the animal age and production system.