bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron ionization mass spectra of ephedrines in a doping confirmatory procedure: a curious migration of the trimethylsilyl group in the N‐acetyl‐O‐trimethylsilyl derivatives
Authors: de Oca Porto Rodny Montes , Pérez Arístides Rosado , Correa Vidal Margarita Teresa
Published: May 2007

Ephedrines have central nervous system stimulating properties and, for this reason, some of them are forbidden in sport by the World Antidoping Agency (WADA). They are screened and quantitated in urine by several published techniques and confirmed by gas chromatography/mass spectrometry (GC/MS). In this paper, a simple confirmation procedure for norpseudoephedrine, norephedrine, ephedrine and pseudoephedrine in human urine by GC/electron ionization (EI)‐MS is described. After the addition of levallorphane as internal standard, a liquid‐liquid extraction procedure under alkaline conditions with tert‐butyl methyl ether was applied to the samples. The analytes were derivatized with acetic acid anhydride and N‐methyl‐N‐trimethylsilyltrifluoroacetamide to form N‐acetyl‐O‐trimethylsilyl derivatives. The EI mass spectra of all the studied substances have many diagnostic ions with relative abundance in accordance with WADA requirements and show great structural information content. A curious migration of the trimethylsilyl group is proposed. Copyright © 2007 John Wiley & Sons, Ltd.
Blood glucose regulation using higher‐order sliding mode control
Authors: Kaveh Parisa , Shtessel Yuri B.
Published: May 2007

Diabetes is discussed as a serious condition in which the body's production and use of insulin are impaired, causing glucose concentration level to increase in the bloodstream. In this paper, higher‐order sliding mode control techniques, in specific prescribed convergence law, quasi‐continuous and super‐twisting control algorithms, are used to robustly stabilize the glucose concentration level of a diabetic patient in presence of the parameter variations and meal disturbance. The structure of the proposed higher‐order sliding mode controllers is appropriate for making the insulin delivery pumps in closed‐loop control of diabetes. A computer simulation is performed to manifest the theoretical analysis. The super‐twisting algorithm is employed to attenuate the effect of chattering and obtain continuous control in the simulations. The efficiency of the proposed controller, i.e. robustness and high accuracy, in presence of physical disturbances like food intake and parametric uncertainties is verifiedviasimulations. Copyright © 2007 John Wiley & Sons, Ltd.
High‐order sliding‐mode observer for a quadrotor UAV
Authors: Benallegue A. , Mokhtari A. , Fridman L.
Published: May 2007

In this paper, a feedback linearization‐based controller with a high‐order sliding mode observer running parallel is applied to a quadrotor unmanned aerial vehicle. The high‐order sliding mode observer works as an observer and estimator of the effect of the external disturbances such as wind and noise. The whole observer–estimator–control law constitutes an original approach to the vehicle regulation with minimal number of sensors. Performance issues of the controller–observer are illustrated in a simulation study that takes into account parameter uncertainties and external disturbances. Copyright © 2007 John Wiley & Sons, Ltd.
On the number of sparse connected graphs
Authors: Łuczak Tomasz
Published: May 2007

We present a short way of estimating the number of connected graphs with k vertices k + l edges, when k→∞, l = l(k)→∞ but l = o(k).
Sparse pseudorandom distributions
Authors: Goldreich Oded , Krawczyk Hugo
Published: May 2007

The existence of sparse pseudorandom distributions is proved. These are probability distributions concentrated in a very small set of strings, yet it is infeasible for any polynomial‐time algorithm to distinguish between truly random coins and coins selected according to these distributions. It is shown that such distributions can be generated by (nonpolynomial) probabilistic algorithms, while probabilistic polynomial‐time algorithms cannot even approximate all the pseudorandom distributions. Moreover, we show the existence of evasive pseudorandom distributions which are not only sparse, but also have the property that no polynomial‐time algorithm may find an element in their support, except for a negligible probability. All these results are proved independently of any intractability assumption.
A note on the probabilistic analysis of patricia trees
Authors: Devroye Luc
Published: May 2007

We consider random PATRICIA trees constructed from n i.i.d. sequences of independent equiprobable bits. We study the height Hn (the maximal distance between the root and a leaf), and the minimal fill‐up level Fn (the minimum distance between the root and a leaf). We give probabilistic proofs of .
Can eco‐footprinting analysis be used successfully to encourage more sustainable behaviour at the household level?
Authors: Sutcliffe Marcus , Hooper Paul , Howell Ros
Published: May 2007

The human family is currently on an unsustainable development path, which is likely to lead to a full blown environmental crisis. Humanity is overshooting nature's carrying capacity by over 20%. In the absence of politically applied environmental limits to growth, some authors believe the solution to environmental sustainability has to include a bottom‐up approach, whereby individuals are encouraged to take action to reduce their own environmental impact. One factor that has limited the potential to develop this approach to date has been the inability to measurably personalize the link between global unsustainable consumption and individual lifestyles.

Ecological footprinting analysis (EFA) has the potential to bridge this gap. EFA aggregates a range of individual consumption and waste components and converts them into the bioproductive land area required to support this activity. This empirical pilot study tests whether there is scope to utilize EFA at the household level to see whether it can be used to encourage changes in behaviour towards less resource intensive lifestyles. The results support this hypothesis in that all participating households took some action to reduce their ecological footprints. Copyright © 2007 John Wiley & Sons, Ltd and ERP Environment.
Dendrimer‐Entrapped Gold Nanoparticles as a Platform for Cancer‐Cell Targeting and Imaging
Authors: Shi Xiangyang , Wang Suhe , Meshinchi Sasha , Van Antwerp Mary E. , Bi Xiangdong , Lee Inhan , Baker James R.
Published: May 2007

We present a general approach for the targeting and imaging of cancer cells using dendrimer‐entrapped gold nanoparticles (Au DENPs). Au DENPs were found to be able to covalently link with targeting and imaging ligands for subsequent cancer‐cell targeting and imaging. The Au DENPs linked with defined numbers of folic acid (FA) and fluorescein isothiocyanate (FI) molecules are water soluble, stable, and biocompatible. In vitro studies show that the FA‐ and FI‐modified Au DENPs can specifically bind to KB cells (a human epithelial carcinoma cell line) that overexpress high‐affinity folate receptors and they are internalized dominantly into lysosomes of target cells within 2 h. These findings demonstrate that Au DENPs may serve as a general platform for cancer imaging and therapeutics.
Improving process decisions in COTS‐based development via risk‐based prioritization
Authors: Yang Ye , Boehm Barry
Published: May 2007

Good project planning requires the use of appropriate process models as well as effective decision support techniques. However, current software process models provide very little Commercial Off‐the‐Shelf (COTS)‐specific insight and guidance on helping COTS‐based application developers to make better decisions with respect to their particular project situations. This article presents a risk‐based prioritization approach that is used in the context of a COTS Process Decision Framework. This method is particularly useful in supporting many dominant decisions during a COTS‐based development (CBD) process, such as establishing COTS assessment criteria, scoping and sequencing development activities, prioritizing features to be implemented in incremental development, etc. In this way, the method not only provides a basis for optimal COTS selection but also helps focus limited development resources on more critical tasks that represent greater risks. The article also shows the evaluation results of applying this approach on the COTS Process Decision Framework through an experiment. Copyright © 2007 John Wiley & Sons, Ltd.
Using simulation to evaluate global software development task allocation strategies
Authors: Setamanit Siri‐on , Wakeland Wayne , Raffo David
Published: May 2007

We describe a hybrid computer simulation model of the software development process that is specifically architected to study alternative ways to configure global software development (GSD) projects, including phase‐based, module‐based, and follow‐the‐sun allocation strategies. The model is a hybrid system dynamics and discrete‐event model. In this paper, test cases have been developed for each allocation strategy, and project duration is computed for each configuration under a range of plausible assumptions for key parameters. The primary finding is that although under ideal assumptions follow‐the‐sun is able to produce impressive reductions in time‐to‐market, under more realistic assumptions the reverse is true, thus corroborating findings by other researchers. We also conducted a factorial design to examine the impact of GSD factors including distance, culture, language, trust, and time zone on project duration under different task allocation strategies. The analysis reveals that different factors affected the performance of the selected allocation strategies in unique ways. These findings show how the unique ability of our GSD model to represent detailed development processes and work artifact transfer allows researchers to address challenging questions that are critical to GSD project success. Copyright © 2007 John Wiley & Sons, Ltd.
Managing process change in software organizations: Experience and reflection
Authors: Qin Shaowen
Published: May 2007

Managing process change in software organizations involves many challenges. It requires an array of skills beyond the technical expertise associated with the process change. Based on the author's recent industrial working experience at Motorola's Global Software Group (GSG) as an organizational technology deployment champion, this article identifies challenges of change management through real world case studies and provides a summary of good practices and lessons learned in implementing process change in today's software organizations. Upon further reflection of the process change management experience and other relevant learning and observations, the author proposes the notion of creating a perception of freedom as a more fundamental success strategy and suggests that the strategy together with the change be built into software tools to facilitate seamless process change deployment. Copyright © 2007 John Wiley & Sons, Ltd.
Effects of antipsychotic treatments and D‐serine supplementation on the electrophysiological activation of midbrain dopamine neurons induced by the noncompetitive NMDA antagonist MK 801
Authors: Bennett Stephen , Gronier Benjamin
Published: May 2007

The acute administration of the noncompetitive glutamate N‐methyl‐D‐aspartate (NMDA) receptor antagonist dizocilpine (MK 801) is known to increase central dopaminergic activity in rats and to elicit schizophreniform behavior in human. The current study was undertaken to compare the effects of different acute or chronic neuroleptic treatments, on the response of ventral tegmental area dopamine (DA) neurons to MK 801, using the in vivo electrophysiological paradigm in anesthetized preparations. Sprague Dawley male rats were treated, acutely or chronically during 3 weeks, with saline, olanzapine (10 mg/kg), haloperidol (1 mg/kg) or the combination of haloperidol with D‐serine (1 mg/kg/300 mg/kg), a gliotransmitter coagonist of the NMDA receptor that has been shown to improve the efficacy of typical neuroleptics. In control animals, the acute administration of MK 801 (0.5 mg/kg, i.v.) increased significantly both the firing and burst activity of DA neurons by 20 and 26%, respectively, the latter effect being partially reversed by the selective 5‐HT2A antagonist M 100,907 (0.4 mg/kg, i.v.). The acute preadministration of haloperidol (1 mg/kg, i.p.) and olanzapine (10 mg/kg, i.p.) failed to prevent or reverse the activatory effect of MK 801 on firing activity. On the other hand, MK 801‐induced burst activity, was partially prevented by olanzapine, but not by haloperidol pretreatment. All antipsychotic treatments, when administered chronically, prevent the activatory effect of MK 801 on both firing and burst activity, and occasionally convert the response to MK 801 on burst activity to an inhibitory response, the latter occurring more predominantly in rats treated with the combination haloperidol/D‐serine. These results suggest that a chronic antipsychotic regime alters the function of the NMDA receptors that tonically control the firing activity of midbrain dopaminergic neurons. Synapse 61:679–688, 2007. © 2007 Wiley‐Liss, Inc.
Contribution of prenatal imaging to the anatomical assessment of fetal hydrocolpos
Authors: Dhombres F. , Jouannic J.‐M. , Brodaty G. , Bessiere B. , Daffos F. , Bénifla J.‐L.
Published: May 2007

Hydrocolpos may be associated with a lower urinary tract obstruction in a spectrum of urorectal malformations ranging from persistent urogenital sinus to cloacal dysgenesis. As cloacal dysgenesis carries the worst postnatal prognosis, detailed prenatal ultrasound should focus on the fetal pelvic anatomy to provide the parents with appropriate prenatal counseling. We report three cases of fetal hydrocolpos associated with low urinary tract obstructions, including two with a normal appearance of the anal canal and rectum on prenatal ultrasound and one with a complex cloacal malformation which contributed to the precise prenatal assignment of the malformation in each case within the spectrum of urogenital sequence malformations. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.
More or less CHAOS: case report and literature review suggesting the existence of a distinct subtype of congenital high airway obstruction syndrome
Authors: Vidaeff A. C. , Szmuk P. , Mastrobattista J. M. , Rowe T. F. , Ghelber O.
Published: May 2007

Congenital obstruction of the upper airway (CHAOS) is a rare, usually lethal abnormality. A literature review of 36 prenatally diagnosed cases of CHAOS and the analysis of our own case suggest the existence of a distinct subtype of CHAOS, raising important implications for diagnosis and management. Serial fetal ultrasound examinations at 17–23 weeks' gestation showed hyperechoic and enlarged lungs, mediastinal shift, flattened diaphragm, polyhydramnios and apparently fluid‐filled esophagus, findings interpreted as bilateral cystic adenomatoid malformation Type III. Ultrasound findings normalized around 32 weeks. The diagnosis of CHAOS was made after birth at term by direct laryngoscopy prompted by ventilatory difficulties and failed attempts at intubation. A pinhole opening posterior to the cricoid cartilage allowed the passage of an endotracheal tube. Based on observations in our case and those of five similar cases in the literature, we describe for the first time a subtype of CHAOS that is characterized by minor pharyngotracheal or laryngotracheal communications and associated with a less severe natural history and even resolution of ultrasound findings. In spite of this, a high index of awareness should be maintained because resolution of ultrasound findings does not necessarily indicate resolution of underlying pathology. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.
Abnormal first‐trimester ductus venosus blood flow: a risk factor for adverse outcome in fetuses with normal nuchal translucency
Authors: Oh C. , Harman C. , Baschat A. A.
Published: May 2007

Objectives

First‐trimester nuchal translucency thickness (NT) is a potent tool for assessment of fetal risks of aneuploidy and other adverse outcomes. When NT is increased, Doppler assessment of the ductus venosus (DV) enhances the prediction specificity for Down syndrome. This study assessed abnormal Doppler DV waveform as a predictor of adverse outcome when the NT is normal.

Methods

This was a case–control study of 2505 consecutive patients undergoing NT screening in our certified first‐trimester screening program. First‐trimester Doppler assessment of DV was performed and atrial systolic velocity was rated as antegrade (normal) or absent/reversed (DV‐RAV; abnormal). Each case with normal NT (< 95th percentile) and DV‐RAV was matched with two controls with respect to maternal age within 1 year, NT within 0.2 mm, crown–rump length within 3 mm, and closest calculated aneuploidy risk. Outcomes for paired variables were compared using t‐test and Chi‐square test.

Results

Forty‐seven (1.9%) patients had normal NT and DV‐RAV. After exclusion of three cases with obvious first‐trimester anomalies and two with incomplete outcome data, 42 remained for analysis. Adverse outcome included cardiovascular defects (n = 6), fetal growth restriction (n = 3), renal anomaly (n = 2), aneuploidy (n = 3) and multiple defects (n = 3), in a total of 11/42 cases (26.2%). Cardiac abnormalities, renal abnormalities and perinatal death were all significantly more common in the study group (all P < 0.05).

Conclusions

Abnormal first‐trimester DV Doppler findings appear to predict adverse outcome independently of a normal NT. These patients need detailed mid‐trimester assessment of fetal anatomy with formal echocardiography, and subsequent follow‐up. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.
Non‐parametric probabilistic forecasts of wind power: required properties and evaluation
Authors: Pinson Pierre , Nielsen Henrik Aa. , Møller Jan K. , Madsen Henrik , Kariniotakis George N.
Published: May 2007

Predictions of wind power production for horizons up to 48–72 h ahead comprise a highly valuable input to the methods for the daily management or trading of wind generation. Today, users of wind power predictions are not only provided with point predictions, which are estimates of the conditional expectation of the wind generation for each look‐ahead time, but also with uncertainty estimates given by probabilistic forecasts. In order to avoid assumptions on the shape of predictive distributions, these probabilistic predictions are produced from non‐parametric methods, and then take the form of a single or a set of quantile forecasts. The required and desirable properties of such probabilistic forecasts are defined and a framework for their evaluation is proposed. This framework is applied for evaluating the quality of two statistical methods producing full predictive distributions from point predictions of wind power. These distributions are defined by a number of quantile forecasts with nominal proportions spanning the unit interval. The relevance and interest of the introduced evaluation framework are discussed. Copyright © 2007 John Wiley & Sons, Ltd.
Strenge Lösung für den durch zwei Einzelkräfte belasteten Kreisring
Authors: Kappus Robert
Published: May 2007

Es werden der am Außenrand und der am Innenrand durch 2 Druckkräfte belastete Kreisring auf Grund der komplexen Lösungsmethode von Muskhelishvili allgemein behandelt. Dabei wird die komplexe Fourier analyse in geschlossener Form in Funktion des Radienverhältnisses δ ≡ R2/R1 durchgeführt. Numerische Ergebnisse für Spannungen und Verschiebungen werden mitgeteilt für δ = 2.
Differenzenverfahren für die 2. und 3. Randwertaufgabe mit krummlinigen Rändern bei Δu(x, y) = r(x, y<, u)
Authors: Uhlmann W.
Published: May 2007

Für die Differentialgleichung Δu(x,y) = r(x, y, u) werden finite Gleichungen aufgestellt, die es gestatten, die Randbedingungen der 2. und 3. Randwertaufgabe bei krummlinigen Rändern zu erfassen. Die finiten Gleichungen — alle für quadratische Gitter — weisen einen Taylor‐Abgleich bis h2 einschl. und für die 2. Randwertaufgabe sogar bis h3 einschließlich auf. Am Schluß finden sich numerische Erprobungen.
Effect of Transverse Shear on the Behaviour of a Beam Under Dynamic Loading
Authors: Mittal R. K.
Published: May 2007

In this paper the response of a beam subjected to an arbitrary time‐dependent concentrated load has been considered without neglecting the effect of transverse shear and closed form solutions to determine deflection and bending moment under the point of loading have been obtained. It is shown that the effect of transverse shear on the solutions, when compared with classical solutions, can be represented by a single parameter which depends upon the radius of gyration of the beam cross‐section and the ratio of the Young's modulus E in axial direction to the shear modulus G in transverse direction. The correction for bending moment due to transverse shear can be very significant when dealing with beams of a particular class of materials, viz. aligned fibre reinforced composites.
On the Morphology of Multi‐Valued Solutions of a Simple Shallow Arch Problem
Authors: Labisch F. K.
Published: May 2007

The exact, global, strong and complete solution of a shallow arch problem is constructed equivalently by means of the boundary value problem, by means of a variational problem in terms of displacements, or by means of a variational problem in terms of dual static field quantities, respectively. It is shown that in contrast to all known results, duality and equivalence of the variational problems are preserved on the degeneracy set, too. The paradox appearing in the so‐called complementary variational approach, where the same solution point should be stable in a displacement approach and simultaneously unstable in a genuinely dual static approach is resolved.
Perturbation of Domains for Some Non‐Classical BVP in Elasticity
Authors: Maul J.
Published: May 2007

The paper deals with two non‐classical boundary value problems of plane elastostatics, which have mechanical significance. The first problem A is studied for epitrochoids, but the second one for domains, upon which the unit circle can be mapped conformally by a rational function. The behaviour of the defect (dimension of the kernel) of these problems is investigated for small perturbations of the domain. In the case of problem B the following result is obtained: For a given simply connected bounded domain D of the class Cm, m ≧ 2, there exists a sequence of domains {Dp} such that lim p→∞ n = ∞ (n – defect of problem B in Dp). Simultaneously, the defect nD is finite, and the boundaries δDp converge to δD in the sense of Cm.
On Approximate Computation of the Heat Flux of a Body from the Known Surface Temperature
Authors: Gerlach W. , Unger F. , Von Wolfersdorf L.
Published: May 2007

In the present paper the application of a recently proposed (cf. [1]) regularization method to the problem mentioned in the title of the paper is discussed by means of approximately given inverse operators.
Zur Laminarströmung in einem Rohr mit der Querschnittsform eines Kreisbogendreieckes
Authors: Klotz K.
Published: May 2007

Für den Fall der laminaren Strömung in einem Rohr mit der Querschnittsform eines Kreisbogendreieckes wird ein analytischer Ausdruck in Integralform för das Geschwindigkeitsfeld abgeleitet. Die dabei entwickelte Methode zur Lösung des Dirichletschen Problems kann sowohl bei anderen zwei‐ als auch bei dreidimensionalen Gebieten mit stückweise sphärischer Berandung benutzt werden. Ausgehend von notwendigen Bedingungen wird für die Stromstärke im Rohr ein analytischer Näherungsausdruck bestimmt.
Über Monotonie und Fehlerkontrolle bei den Gregoryschen Quadraturverfahren
Authors: Fuml;rster K.‐J.
Published: May 2007

In dieser Arbeit werden die Quadraturverfahren von Gregory auf Monotonie untersucht. Es werden Ergebnisse sowohl für den Fall gleichbleibender Stufe und Erhöhung der Stützstellenanzahl als auch für den Fall gleichbleibender Stützstellenanzahl und Erhöhung der Stufe erzielt. Hierbei ergibt sich insbesondere der Nachweis eines praxisnahen Abbruchkriteriums. Grundlage der Ausführungen ist ein Vergleich zwischen Gregory‐Formeln und zusammengesetzten Newton‐Cotes‐Formeln.
Die Auftriebsverteilung von flexiblen Segeln längs der Spannweite
Authors: Wohlfahrt M.
Published: May 2007

Die aerodynamischen und elastischen Eigenschaften eines Segels werden untersucht. Dabei wird die Prandtlsche Integrodifferentialgleichung mit der eindimensionalen Laplacegleichung kombiniert. Die entstehende Integrodifferentialgleichung des Segels kann unter dem Gesichtspunkt der ersten und zweiten Grundaufgabe Prandtls betrachtet werden. Diese Gleichung wird äquivalent umgeformt auf eine Fredholmsche Integralgleichung zweiter Art. Unter bestimmten Voraussetzungen an die Segelgestalt werden Eindeutigkeit, Existenz und stetige Abhängigkeit der Lösung von den Daten bewiesen. Zur Bestimmung von Näherungen wird ein Kollokationsverfahren angegeben.
Zum Staudammproblem mit Drainage
Authors: Oestreich D.
Published: May 2007

Es wird das zweidimensionale Staudammproblem mit Drainage bei gekrümmter Dammkurve mittels konformer Abbildung auf ein nichtlineares Riemann‐Hilbert‐Problem bzw. eine singuläre Integralgleichung vom Cauchy‐Typ geführt. Die Lösbarkeit wird mit Hilfe des Schauderschen Fixpunktsatzes gezeigt und der freie Parameter (Durchflußrate) aus einer Integralgleichung bestimmt. Die Sickerlinie kann explizit angegeben werden.
Intensification of Wave Energy on the Lee Side of a Wavy Plateau
Authors: Chow C.‐Y. , Olorunsola O. , Huang M.‐K.
Published: May 2007

A stably stratified channel flow over a wavy plateau is analyzed to examine the effect of topographic wavelength on wave energy in the flow downstream. A resonance phenomenon is found to occur at wavelengths that are determined by the Richardson number and channel geometry. Results show that in a resonant state, the unbounded wave drag of the plateau is caused by the sinusoidal pressure distribution when it becomes out of phase with the topographic deformation.
Concerning Cusps and Vertices on the Yield Surface of Annealed Mild Steel
Authors: Findley W. N. , Michno M. J.
Published: May 2007

In the present paper the authors review the findings in [2, 3] and discuss possible causes of the observation of cusps and pointed vertices reported in the paper of N. K. Gupta and H. A. Lauert, ZAMM 63 (1983), 497–504.
Die elastisch‐plastische Scheibe mit nichtlinearer Verfestigung unter der Einwirkung einer ringförmigen Wärmequelle
Authors: Gamer U. , Mack W.
Published: May 2007

Gegenstand der Untersuchung sind die Spannungen in einer elastisch‐plastischen Kreisscheibe mit nichtlinearer Verfestigung, welche durch eine kreisringförmige Wärmequelle hervorgerufen werden. Der Rechnung zugrundegelegt ist die Trescasche Fließbedingung und die ihr zugeordnete Fließregel. Wenn im plastischen Bereich Radial‐ und Umfangsspannung verschiedene Vorzeichen haben, dann sind die Grenzen des plastischen Bereichs und die Spannungen in der elastischen Randzone unabhängig vom Verfestigungsverhalten.
Stability of the Linearized Transient Semiconductor Device Equations
Authors: Markowich P. A. , Ringhofer Ch. A.
Published: May 2007

We present a stability analysis of the linearized transient semiconductor device equations by means of semigroup theory. Central to the developed theory is an estimate for the real parts of the eigenvalues of the linearized device problem with an upper bound which only depends on the biasing situation of the device. Under realistic assumptions we show that the device problem and its implicit Euler time discretisation are uniformly (with respect to an intrinsic singular perturbation parameter) stable ‘in the linearized sense’.
Initial Boundary Value Problems from Semiconductor Device Theory
Authors: Gröger K.
Published: May 2007

This paper is concerned with the basic equations for carrier transport in semiconductors in case of boundary conditions allowing the electrostatic potential at a contact to depend on the total current through this contact. An existence‐uniqueness result is proved and, under additional assumptions, the global boundedness and the asymptotic behaviour of solutions are investigated.
Aussagen über die Stabilität quasiperiodischer Lösungen durch Einbettung in höherdimensionale Räume
Authors: Baumgarte J.
Published: May 2007

Zur Untersuchung der Stabilität quasiperiodischer Lösungen wird ein neues Verfahren vorgestellt. Der wesentliche Gedanke hierzu ist, das Ausgangsdifferentialgleichungssystem approximativ in einen beliebig höherdimensionalen Raum einzubetten. Das so gewonnene neue Differentialgleichungssystem läßt sich mit den klassischen Mitteln der Stabilitätsuntersuchung bearbeiten. Numerische Experimente zeigen, daß das Stabilitätsverhalten des Ausgangssystems und das des höherdimensionalen Näherungssystems miteinander korrespondieren.
Neue Runge‐Kutta‐Nyström Formelpaare 3(4)‐ter und 4(5)‐ter Ordnung für ẍ = f(t, x, ẋ)
Authors: Fehlberg E.
Published: May 2007

Für Differentialgleichungen der Form ẍ = ƒ(t, x, ẋ) werden RKN‐Formeln 3(4)‐ter und 4(5)‐ter Ordnung mit Schrittweiten‐Kontrolle in ẋ hergeleitet. Die Formel 4(5)‐ter Ordnung erfordert erheblich weniger Aufwand als eine ältere RKN4(5)‐Formel von E. J. Nyström. Es werden verschiedene Beispiele mitgeteilt, für die diese neuen RKN‐Formeln bei gleicher Genauigkeit weniger oder höchstens gleichviel Aufwand erfordern als unsere früheren RK‐Formeln 3(4)‐ter bzw. 4(5)‐ter Ordnung. Dies rechtfertigt die Aufstellung solcher RKN‐Formeln für ẍ = ƒ(t, x, ẋ).
Weight Minimization of an Elastic Beam with Classical and Non‐Classical Boundary Conditions
Authors: Hlaváček I.
Published: May 2007

A minimum weight optimal design problem for an elastic homogeneous beam is studied. The existence of an optimal solution – i.e. of an optimal variable height of the rectangular cross‐section of the beam – is proven. To this end, a dual variational formulation in terms of the bending moments (generalized principle of minimum complementary energy) is employed. We propose piecewise linear approximations and present a convergence analysis.
Ein Beitrag zum dynamischen Verhalten eines rotierenden Stabes
Authors: Gürgöze M.
Published: May 2007

In dieser Mitteilung wird das dynamische Verhalten eines mit seinem unteren Ende auf einer mit konstanter Drehzahl rotierenden Basis eingespannten Stabes untersucht, wobei die Schwerkraft mitberücksichtigt wird. Aufgrund der Euler‐Bernoulli‐Theorie wird mit Hilfe der Störungsrechnung für die Eigenfrequenzen eine Näherungsformel hergeleitet, die sogar für höhere Eigenfrequenzen ganz gute Näherungswerte liefert. Anschließend wird die stationäre Biegelinie des Stabes mit dem Galerkinschen Verfahren näherungsweise ermittelt.
Inelastische Rotationsschalen in konjugierten Variablen
Authors: Bergander H.
Published: May 2007

Es werden Rotationsschalen aus beliebigem inelastischem Material in der konvektiven Metrik betrachtet. Die kinematischen Grundgleichungen und die Gleichgewichtsbedingungen werden in der Geschwindigkeitsform angegeben. Für das Material wird die Existenz eines lokalen Potentials in den Geschwindigkeiten vorausgesetzt. Das globale Potential für die Formänderung in den Geschwindigkeiten und die kanonischen Gleichungen des Randwertproblems werden hergeleitet. Dabei erweist sich die Verwendung von konjugierten Geschwindigkeiten der dynamischen Variablen als wesentlich.
Coupled Thermal and Electromagnetic Evolution in a Ferromagnetic Body
Authors: Visintin A.
Published: May 2007

The coupled electric and thermal evolution of a ferromagnetic body leads to a free boundary problem. A model based on the theory of “non‐equilibrium thermodynamics” is proposed. A variational inequality is obtained by transforming the unknown functions by time integration. Existence and uniqueness results are proved.
Variational Principles for Nonlinear Buckling of Elastic Columns (A Revival of Euler's Theory)
Authors: Komkov V.
Published: May 2007

Following a historical introduction, a known finite element model of a column is suggested, which can be generalized to plate and shell theory. A loss of stability and certain paradoxical results in computing the corresponding deflection are discussed. It is shown that static equilibrium is impossible to attain for large loads, thus contradicting “the usual” spectral theory for the linear beam or plate operators. The static and dynamic models are compared. A computational algorithm is offered for the nonlinear model of buckling.
Modelling a One‐Dimensional Fracture Process in Thin Coatings
Authors: Stoyan D.
Published: May 2007

Patterns of parallel fractures are studied by means of methods of the theory of point processes. It is shown that two hardcore models do not fit sufficiently well data which result from four‐point bending experiments of coatings on steel substrates. A new soft‐core model turns out to be more appropriate. It can be used to estimate physical parameters.
On the Galerkin Approximation for Small Solutions of Noncoercive Quasilinear Boundary Value Problems
Authors: Kosler R.
Published: May 2007

Small solutions of noncoercive quasilinear boundary value problems of order 2m in n dimensions are approximated by Galerkin's method, Some uniqueness results and abstract error estimates are shown. Quasioptimal Wm, 2‐error estimates for the finite element method can be obtained from this.
Adaptive Approximation
Authors: Lippold G.
Published: May 2007

The adaptivity of transitions on the mesh sequence ℋ in some mesh refinement structure is defined as a selection strategy which is performed by means of a monotone local indicator on the set of cells in that structure. Adaptivity then turns out to be a local optimality property relative to some maximum or sum indicator on ℋ. – Adaptive transitions generate optimal mesh sequences. The notion of δ‐adaptivity is introduced to catch problems where only perturbed error indicators are available. δ‐adaptive transitions generate quasi‐optimal mesh sequences. – For the solution of one‐dimensional elliptic boundary value problems by linear finite elements δ‐adaptive transitions are defined by means of the local defects in the differential equation which are caused by the finite element solutions.
Analysis of Smoothing Matrices for the Preconditioning of Elliptic Difference Equations
Authors: van der Houwen P. J. , Boon C. , Wubs F. W.
Published: May 2007

Smoothing techniques have been used for stabilizing explicit time integration of parabolic and hyperbolic initial‐boundary value problems. Similar techniques can be used for the preconditioning of elliptic difference equations. Such techniques are analysed in this paper. It is shown that the spectral radius of the Jacobian matrix associated with the system of equations can be reduced considerably by this type of preconditioners, without much computational effort. Theoretically, this results in a much more rapid convergence of function iteration methods like the Jacobi type methods. The use of smoothing techniques is illustrated for a few one‐dimensional and two‐dimensional problems, both of linear and nonlinear type. The numerical results show that the use of rather simple smoothing matrices reduces the number of iterations by at least a factor 10.
Potential Flow Past a Circular Cylinder with Permeable Surface
Authors: Wolfersdorf L. V.
Published: May 2007

A new mathematical model for the plane potential flow of an inviscid incompressible fluid past a cylinder with porous surface is presented. In the case of a circular cylinder with a general linear filtration law formulae for the velocity and pressure distributions on the cylinder are derived.
Stability of Boundary Layers along a Rotating Disk with Uniform Suction
Authors: Watanabe T.
Published: May 2007

A theory is developed for the linear stability analysis on the effect of uniform suction through the disk due to three‐dimensional rotating disk flow, in which the effect of Coriolis forces and streamline curvature are included. The characteristics of the laminar boundary layer with uniform suction along a rotating disk are calculated, and then the perturbation equation describing the spatial evolution of disturbances is solved numerically according to the Adams‐Bashforth method for the velocity profiles obtained above. Variation of neutral stability curves and also of the critical Reynolds number are given for the values of the suction parameter. The results show that the boundary layer flow with uniform suction along a rotating disk becomes stable.
Analytische Mechanik polarer Systeme
Authors: Heinz C.
Published: May 2007

Die Motorrechnung wird angewendet, um die Bewegung polarer Systeme von Massenpunkten zu beschreiben, Hierbei wird angenommen, daß jeder Massenpunkt nicht nur eine Masse, sondern auch ein Trägheitsmoment besitzt. Es zeigt sich, daß die Motorrechnung ein für die Beschreibung solcher Systeme adäquater Kalkül ist.
Particular Integrable Cases in Rigid Body Dynamics
Authors: Yehia H. M.
Published: May 2007

The problem of motion of a rigid body about a fixed point under the action of axisymmetric potential and gyroscopic forces is considered. Particular solvable cases are found, which generalize the results due to Hess, Kharlamov and others.
Aggregate isotroper Tensoren zur Darstellung hyperelastischer anisotroper Stoffe
Authors: Silber G.
Published: May 2007

Mit Hilfe von isotropen Tensoren und einfachen tensoriellen Rechenoperationen wird eine Systematik für Materialgesetze hyperelastischer anisotroper Stoffe in einfacher und neuartiger Weise hergeleitet. Der bekannte Elastizitätstensor vierter Stufe läßt sich beispielsweise als vierstufige Tensorfunktion zweistufiger Richtungstensoren identifizieren. Gleichzeitig fallen die jeweiligen Invarianten des Verzerrungsmaßes einschließlich der Richtungstensoren in der zugeordneten spezifischen Formänderungsenergie automatisch an, wie die Beispiele orthotropen und transversal‐isotropen Materials zeigen.
Zum elastisch‐plastischen Hohlzylinder unter Innendruck
Authors: Gamer U.
Published: May 2007

Im folgenden wird eine Modifikation von Blands Behandlung des drehsymmetrisch belasteten elastisch‐plastischen Hohlzylinders mit nichtlinearer Verfestigung angegeben.
Ähnlichkeitslösungen der Grenzschichtgleichungen nicht‐newtonscher Flüssigkeiten, die das Potenzgesetz erfüllen
Authors: Rott W.
Published: May 2007

Die ebenen, stationären Grenzschichtgleichungen nicht‐newtonscher Flüssigkeiten, die das Potenzgesetz (das sogenannte Ostwald‐de Waele‐Modell) erfüllen, werden mit Hilfe der gruppentheoretischen Methode auf eine gewöhnliche Differentialgleichung transformiert. Diese stellt eine Erweiterung der Falkner‐Skan‐Gleichung für derartige Flüssigkeiten dar, es handelt sich dabei also um Grenzschichtströmungen an Keilen. Dieses Randwertproblem mit einer Randbedingung im Unendlichen wird mit dem Runge‐Kutta‐Verfahren numerisch gelöst, wobei die Anfangssteigung des Geschwindigkeitsprofils iterativ korrigiert werden muß. Der erste Wert dieser Anfangssteigung wird dabei aus dem auf das Ostwald‐de Waele‐Modell angewendeten Näherungsverfahren von Kármán‐Pohlhausen ermittelt.
Über die Lösung von eindimensionalen Modellgleichungen des Ladungsträgertransportes in Halbleitern mit einer Quadraturformelmethode
Authors: Micke A. , Wendt W.
Published: May 2007

Gegenstand der Untersuchung ist eine Klasse linearer Integrodifferentialgleichungen, die als eindimensionale Modellgleichungen für den Ladungsträgertransport in Halbleitern unter dem Einfluß konstanter elektrischer Felder dienen kann. Es werden Quadraturverfahren zur Lösung dieser Gleichung in Integralgleichungsformulierung (Fredholmsche Integralgleichung zweiter Art mit unstetigem Kern) betrachtet. Vorgestellt wird ein vollständiger Lösungsalgorithmus, der auf einer Quadratur vom Mehrfachinterpolationstyp basiert und an numerischen Beispielen demonstriert wird.
Stability of Numerical Methods for Volterra Integro‐Differential Equations of Convolution Type
Authors: Bakke V. L. , Jackiewicz Z.
Published: May 2007

Stability properties of numerical methods for Volterra integro differential equations based on the convolution test equation

are investigated. Stability regions of reducible linear multistep methods and modified multilag methods are given and compared.
Monotonicity of Brown's Method
Authors: Frommer A.
Published: May 2007

Sufficient conditions are given in order that the iterates of Brown's method converge monotonically to a solution of a system of (nonlinear) equations. It is shown that in many cases it is possible to construct a second sequence of iterates such that each iteration step yields an inclusion for a solution of the system. Similar results hold for the analytic and the multistage modifications of Brown's method. The monotonicity results apply in particular to discrete analogs of certain ordinary and elliptic boundary value problems and integral equations. A numerical example is included.
Representation of Joints in Multibody Systems
Authors: Schwertassek R. , Senger K.‐H.
Published: May 2007

A description of the interconnections between the bodies of a multibody system is given in terms of mode vectors representing constrained relative motion and generalized applied and constraint interaction across joints. The representation can be applied to develop joint libraries for general purpose multibody programs thus releasing the user from formulating constraint equations and force laws describing the joints. An example provides the physical interpretation of the concepts introduced here.
Application of a Mixed Variational Principle to Buckling Analysis of Circular Cylinders
Authors: Dost S. , Tabarrok B.
Published: May 2007

A mixed variational formulation for large deformation analysis of circular cylinders is introduced. In this formulation the equilibrium and compatibility equations are satisfied identically by means of stress functions and by the use of displacement components, respectively, and the constitutive equations are satisfied in a least squares sense. The variational functional is linearized in the neighborhood of an initial equilibrium for the stability analysis of cylinders. Two classical examples are solved to illustrate the theory.
Exact Plane Stress Solution for Some Simple Cases in Anisotropic Elasticity
Authors: Nishioka K. , Arimitsu Y.
Published: May 2007

Exact plane stress solutions in stretching deformation are investigated for plates of cubic, tetragonal and hexagonal crystals with a crystallographic axis perpendicular to their faces. For cubic and tetragonal crystals, requirement to satisfy all the three‐dimensional compatibility conditions limits the existence of the solution to cases where stress or strain varies as polynomials of degree three in the middle plane of a plate. Whereas, for hexagonal crystals with the c‐axis perpendicular to the faces, any biharmonic stress function in the middle plane can provide the solution as in the isotropic system.
Internal Stresses and Relations between Effective Thermoelastic Properties of Stochastic Solids – Some Exact Solutions
Authors: Kreher W.
Published: May 2007

We consider composites made of two phases and polycrystalline aggregates composed of hexagonal, tetragonal, or trigonal crystals. Within linear elasticity exact relations between effective elastic constants, effective thermal expansion, stored elastic energy, and internal stresses are derived. Two sources of internal stresses are taken into account: external loading and differential or anisotropic thermal expansion. If the fluctuation of elastic constants can be neglected, we obtain solutions for internal stresses and stored energy which are valid for any phase topology.
Micropolar Flow past a Slightly Deformed Fluid Sphere
Authors: Ramkissoon H. , Majumdar S. R.
Published: May 2007

The Stokes flow of a micropolar fluid past a Newtonian fluid spheriod whose shape deviates slightly from that of a sphere is investigated. To the first‐order in the small parameter characterizing the deformation, an exact solution is obtained. As an application, the case of a fluid oblate spheroid is considered and the drag experienced by it is evaluated. Special known cases are deduced.
Zur Integration über Unstetigkeiten in gewöhnlichen Differentialgleichungen
Authors: Model R.
Published: May 2007

Für Differentialgleichungen mit Unstetigkeiten liegt der Aufwand bei Anwendung eines numerischen Standardverfahrens sehr hoch, wobei keine gültigen Aussagen zur Genauigkeit beim Übergang existieren. Für das Verfahren mit rückwärtigen Differenzen wird eine Schätzung des lokalen Fehlers im kritischen Schritt über die Unstetigkeit gegeben. Die Einbettung dieses Ergebnisses in eine Steuerungsstrategie zur Integration über Unstetigkeiten führt zu einem effektiven Integrationsalgorithmus, dessen Wirksamkeit an einigen Beispielen demonstriert wird.
Singularly Perturbed Spline Difference Schemes on a Non‐Equidistant Grid
Authors: Surla K. , Stojanović M.
Published: May 2007

An exponentially fitted spline difference scheme on a non‐equidistant grid is formed for solving the singularly perturbed two point boundary value problem: ϵy″ + p(x) y′ = f(x), 0 < x < 1,0 < ϵ ≪1, y(0) = α0, y(1) = α1, p(x) ≧ p > 0. Uniform convergence of first order is proved under the condition on the grid: 0 ≦ hi − hi−1 ≦ M ihi−1 max(xi, ϵ), hi=xi+1 − xi, 0 = x0 < x1 <… < xn+1 = 1, 0 ≦ Mi ≦ M, M is a constant independent of hi and ϵ. Numerical examples are given, too.
Berechenbare Fehlerschranken für ein Eigenpaar beim verallgemeinerten Eigenwertproblem
Authors: Alefeld G.
Published: May 2007

Für eine Näherung eines Eigenpaares des verallgemeinerten Eigenwertproblems Ax = λBx werden Schranken berechnet. Davon ausgehend wird ein Iterationsverfahren betrachtet, mit dessen Hilfe die Schranken verbessert werden können. Numerische Beispiele erläutern das Vorgehen. Alle Rundungsfehler werden dabei miterfaßt.
Heat Transfer from a stretching Sheet in Viscous Flow with Suction of Blowing
Authors: Dutta B. K.
Published: May 2007

Analytical solutions have been developed for the conjugate problem of cooling of a stretching sheet in viscous flow. The velocity of the sheet is proportional to the distance from the slit from which it issues and it is subjected to uniform suction or blowing. Solutions are presented in the form of alternating series which converge reasonably rapidly. The sufficient conditions for convergence have been established. It has been found that the rate of colling of the sheet increases with stretching speed, Prandtl number and the suction or blowing parameter.
Axisymmetric Stagnation Flow of a Micropolar Fluid on a Cylinder
Authors: Guram G. S. , Kamal M. Anwar
Published: May 2007

Axisymmetric stagnation flow of a micropolar fluid, in contact with an infinite circular cylinder, and tending to potential flow at infinity, with a stagnation line on the cylinder, is considered. The equations of motion ae reduced to dimensionless forms and solved numerically using the Gauss‐Seidel iterative procedure and Simpson's rule, for three different combinations of the three parameters involved and for the range 0.2 to 100 of the fourth parameter
equation image
. Results are given in the tabular form and compared with the known results for a Newtonian fluid. The accuracy o the numerical solutions is checked using different grid sizes. This type of stagnation flow has applications in certain cooling processes.
Über eine Zentralgleichung in der Dynamik
Authors: Bremer H.
Published: May 2007

Für die mathematische Behandlung mechanischer Systeme steht eine Vielzahl von Methoden zur Verfügung, von denen, entsprechend einer Forderung von Hertz, die einfachste ausgewählt werden sollte. Für eine Methodenwahl, die diesem Kriterium gerecht wird, ist die Diskussion einer Zentralgleichung, die eine Reihe von Ergebnissen der theoretischen Mechanik zusammenfaßt, hilfreich. Dabei kommt neben der problemangepaßten Wahl von Minimalkoordinaten (verallgemeinerten Koordinaten) der Einführung von Minimalgeschwindigkeiten besondere Bedeutung zu.