bluuebunny/crossref_metadata_2025_split huggingface dataset:
Teilautomatisiertes preforming zur Qualitätssicherung und Verkürzung von Fertigungszeiten bei der Herstellung von Rotorblättern von Windenergieanlagen
Authors: Dörsch C. , Ohlendorf J. H. , Gebauer I. , Müller D. H. , Weigel L. 
Published: November 2007

AbstractRotorblätter von Windenergieanlagen werden aufgrund des guten Verhältnisses von Steifigkeit und Gewicht zu großen Teilen aus Faserverbundwerkstoffen gefertigt. Dabei kommen hauptsächlich Glasfasern (GF) als verstärkendes Material sowie duroplastische Harze als Matrix zur Anwendung.Um die wachsenden Herausforderungen des Offshore‐Einsatzes von Windenergieanlagen, insbesondere die steigende Rotorblattgröße, technisch und wirtschaftlich erfolgreich bewältigen zu können, wird die Verkürzung der Fertigungszeit sowie der zunehmende Qualitätsanspruch an die Rotorblätter eine immer stärkere Rolle einnehmen.Um diese Ansprüche erfüllen zu können, beschäftigen sich das Bremer Institut für Konstruktionstechnik und das Unternehmen Abeking & Rasmussen Rotec GmbH & Co KG unter anderem mit der Handhabung und Erstellung von sogenannten Preforms, dies sind trockene, textile Halbzeuglagen, die als vorgeformter Lagenstapel in den Fertigungsprozess des Rotorblattes eingebracht werden. Mit Hilfe der Technologie des Preformings ist es möglich, Bereiche der Fertigung zu parallelisieren. Dies ist ein großer Vorteil bei der Produktion, da aufgrund der notwendigen Temperzeiten, alle anderen Fertigungsschritte möglichst zeitoptimiert gestaltet werden müssen, um kurze Zykluszeiten zu realisieren.Betrachtet werden soll die Handhabung von textilen Halbzeugen, insbesondere das preforming und dessen Auswirkungen auf die Wirtschaftlichkeit der Faserverbundfertigung. Ebenfalls sollen die Aspekte der Qualitätssicherung in Verbindung mit dem preforming aufgezeigt werden und mögliche Ansätze zu einer Teilautomatisierung gegeben werden.
Entwicklung der Konnektivität der Phasen in einer kurzfaserverstärkten Aluminium‐Kolbenlegierung unter Kriechbelastung
Authors: Requena G.C. , Degischer H.P. , Marks E.D. , Boller E. 
Published: November 2007

AbstractDas drei‐dimensionale Gefüge einer AlSi12CuMgNi‐Kolbenlegierung verstärkt mit 15 vol% Al2O3‐Kurzfasern wird mittels Synchrotron Mikro‐Tomographie dargestellt. Der lösungsgeglühte Ausgangszustand enthält ein zusammenhängendes Netzwerk aus Kurzfasern und Fe‐ und Ni‐reichen Primärausscheidungen, das darüber hinaus durch eine Vielzahl von Si‐Brücken des Eutektikums verbunden wird. Die Konnektivität nimmt mit der Dauer der Kriechbelastung bei 300 °C zu, besonders durch die Reifung der Si‐Teilchen, die zu einer in sich zusammenhängenden Struktur zusammenwachsen, die mit dem bereits vorhandenen Netzwerk mit den Fasern verbunden ist. Nach 6400 h Belastungsdauer ist die Konnektivität der steifen Phasen nahezu vollständig. Die Orientierung der Fasern wird mit drei‐dimensionalen Fast Fourier Transformationen analysiert, was auf keine Umorientierung der Fasern in die Lastrichtung schließen lässt. Die früher beobachtete Verfestigung des Materials während der Kriechbelastung wird mit der zunehmenden Steifigkeit der hybriden Verstärkungsstruktur erklärt.Die Proben enthalten im Ausgangszustand bereits Poren an den Grenzflächen der Verstärkungsphasen. Die Porenanzahl ändert sich während der Kriechbelastung im sekundären Kriechstadium nicht, jedoch wachsen die Poren, sodass der Porenvolumenanteil verdoppelt wird. In der α‐Aluminiummatrix wurden keine Kriechporen gefunden.
Verbundwerkstoffe mit Aluminiumschaum – Anwendungen im Schienenfahrzeugbau
Authors: Baumeister J. , Rausch G. , Stöbener K. , Lehmhus D. , Busse M. 
Published: November 2007

AbstractNach ihrer Wiederentdeckung Anfang der 90er Jahre werden geschäumte Metalle inzwischen im industriellen Maßstab hergestellt. In den meisten Fällen handelt es sich dabei um Anwendungen, bei denen der Metallschaum im Verbund mit anderen Werkstoffen eingesetzt wird.Die Verbundkörper können in ebene oder komplex geformte Sandwichstrukturen und 3‐dimensionale Formkörper eingeteilt werden. Die erforderlichen Prozessschritte und realisierbaren Geometrien werden beschrieben. Die Eigenschaften der Werkstoffe werden beleuchtet und die industriellen Anwendungen anhand von Beispielen erläutert.Im Rahmen eines öffentlich geförderten Projekts wurde die Verwendung von Sandwichverbunden mit einer Kernlage aus Aluminiumschaum für Anwendungen im Schienenfahrzeugbau evaluiert. Insbesondere stand die Herstellung eines Frontmodulsegments im Mittelpunkt der Untersuchungen. Die Ergebnisse dieses Projekts werden vorgestellt.
Joining of cemented carbides to steel by laser beam welding
Authors: Barbatti C. , Garcia J. , Liedl G. , Pyzalla A. 
Published: November 2007

AbstractWelding of dissimilar materials such as steel and cemented carbides (hardmetals, cermets) is particularly challenging e.g. because mismatches in their thermal expansion coefficients and thermal conductivities result in residual stress formation and because of the formation of brittle intermetallic phases. Laser beam welding of cemented carbides to steel appears as an attractive complementary technique to conventional brazing processes due to its high precision, high process speed, low heat input and the option of welding without filler.Here a laser welding process including pre‐heat treatment and post‐heat treatment was applied successfully to joining as‐sintered and nitrided hardmetals and cermets to low alloyed steel. The microstructure and mechanical properties of the welds are investigated by microscopy, X‐ray diffraction, microhardness measurements, and bending tests. The results reveal that the three‐step laser beam welding process produced crack‐free and non‐porous joints. Nitridation of the cemented carbides results in a significant reduction of the amount of brittle intermetallic phases. The mechanical properties of the joints are competitive to those of the conventional brazed steel‐cemented carbide joints.
Thermische Ausdehnung, innere Spannungen und Porenverteilung in AlSiCp Metallmatrix‐ verbundwerkstoffen
Authors: Schöbel M. , Requena G. , Degischer H. P , Kaminski H. , Buslaps T. , di Michiel M. 
Published: November 2007

AbstractAlSi7Mg/SiC/70p (AlSiC) eignet sich als Kühlkörper wegen seiner guten Leitfähigkeit bei gleichzeitig niedrigem thermischen Ausdehnungskoeffizienten (CTE) für Applikationen in der Hochleistungselektronik. Ein niedriger CTE ermöglicht dauerhaft einen guten thermischen Kontakt zwischen der Kühlplatte und dem Elektronikbauteil. Materialien mit hohem Ausdehnungskoeffizienten würden durch thermische induzierte makroskopische Spannungen in der Grenzfläche zu Delaminationen in der Kontaktfläche führen. Aus diesem Grund ersetzt AlSiC Kupfer als Kühlkörpermaterial in der Leistungselektronik.Das Problem der unterschiedlichen Ausdehnungskoeffizienten ist in den Verbundwerkstoff transferiert und wirkt sich durch innere Mikrospannungen zwischen der Aluminiummatrix und den SiC‐Partikeln aus. Insitu Messungen während thermischer Aufheizzyklen bis 400 °C an AlSi7Mg/SiC/70p Proben wurden vorgenommen, um den Porenanteil und die inneren Spannungen zu bestimmen. Der Porenanteil wird aus Synchrotron Tomografie und die inneren Spannungen mittels Synchrotron Diffraktion (ESFR/ID15A) gemessen. Messungen während des Heizens, Kühlens und nach mehrfachem Zyklieren zeigen einen Zusammenhang zwischen den inneren Spannungen und dem Porenvolumenanteil und der Temperatur.AlSiC verhält sich von Raumtemperatur bis etwa 200 °C thermo‐elastisch, wobei sich die dominanten Zugspannungen in der Matrix in Druckspannungen umkehren. Mit zunehmender Temperatur verformt sich die Matrix plastisch und vermindert dabei den Porenvolumenanteil. Beim Kühlen von 500 °C wird nach einer elastischen Spannungsumkehr in die Zugrichtung wieder eine Erhöhung des Porenvolumenanteils beobachtet. Unter 200 °C verhält sich AlSiC bis Raumtemperatur wieder thermo‐elastisch. Nach mehreren, extremen Temperaturzyklen von –100 °C bis 400 °C wird die Haftung der SiC‐Partikel an die Al‐Matrix des MMCs lokal gelöst und Porenwachstum beobachtet.
Danon disease due to a novel splice mutation in the LAMP2 gene
Authors: Nadeau Amelie , Therrien Christian , Karpati George , Sinnreich Michael 
Published: November 2007

AbstractDanon disease is a rare X‐linked dominant disorder caused by lysosomal‐associated membrane protein 2 (LAMP2) deficiency and is characterized by hypertrophic cardiomyopathy, cardiac conduction abnormalities, skeletal vacuolar myopathy, variable degree of mental retardation, and peripheral pigmentary retinopathy. We describe a novel splice mutation in the LAMP2 gene in a French Canadian family. By identifying this novel mutation we were able to offer genetic screening and counseling to all family members. Presymptomatic diagnosis is important as cardiac surveillance can be life‐saving. Muscle Nerve, 2007
A basis function for approximation and the solutions of partial differential equations
Authors: Tian H. Y. , Reutskiy S. , Chen C. S. 
Published: November 2007

AbstractIn this article, we introduce a type of basis functions to approximate a set of scattered data. Each of the basis functions is in the form of a truncated series over some orthogonal system of eigenfunctions. In particular, the trigonometric eigenfunctions are used. We test our basis functions on recovering the well‐known Franke's and Peaks functions given by scattered data, and on the extension of a singular function from an irregular domain onto a square. These basis functions are further used in Kansa's method for solving Helmholtz‐type equations on arbitrary domains. Proper one level and two level approximation techniques are discussed. A comparison of numerical with analytic solutions is given. The numerical results show that our approach is accurate and efficient. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008
Numerical solution of the free‐surface viscous flow on a horizontal rotating elliptical cylinder
Authors: Hunt Roland 
Published: November 2007

AbstractThe numerical solution of the free‐surface fluid flow on a rotating elliptical cylinder is presented. Up to the present, research has concentrated on the circular cylinder for which steady solutions are the main interest. However, for noncircular cylinders, such as the ellipse, steady solutions are no longer possible, but there will be periodic solutions in which the solution is repeated after one full revolution of the cylinder. It is this new aspect that makes the investigation of noncircular cylinders novel. Here we consider both the time‐dependent and periodic solutions for zero Reynolds number fluid flow. The numerical solution is expedited by first mapping the fluid film domain onto a rectangle such that the position of the free‐surface is determined as part of the solution. For the time‐dependent case a simple time‐marching method of lines approach is adopted. For the periodic solution the discretised nonlinear equations have to be solved simultaneously over a time period. The resulting large system of equations is solved using Newton's method in which the form of the Jacobian enables a straightforward decomposition to be implemented, which makes matrix inversion manageable. In the periodic case all derivatives have been approximated pseudospectrally with the time derivative approximated by a differentiation matrix which has been specially derived so that the weight of fluid is algebraically conserved. Of interest is the solution for which the weight of fluid is at its maximum possible value, and this has been obtained by increasing the weight until a consistency break‐down occurs. Time‐dependent solutions do not produce the periodic solution after a long time‐scale but have protuberances which are constantly appearing and disappearing. Periodic solutions exhibit spectral accuracy solutions and maximum supportable weight solutions have been obtained for ranges of eccentricity and angular velocity. The maximum weights are less than and approximately proportional to those obtained for the circular case. The shapes of maximum weight solutions is distinctly different from sub‐maximum weight solutions. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008
The blind search for the closed states of hinge‐bending proteins
Authors: Yesylevskyy Semen O. , Kharkyanen Valery N. , Demchenko Alexander P. 
Published: November 2007

AbstractThe hinge‐bending proteins provide the most pronounced example of the large‐amplitude slow motions in a number of proteins, which are critical for their functioning. They are often used as the test ground for developing novel approaches to the simulation of slow protein dynamics. In the present study, we present the algorithm, which allows physically‐consistent simulations of slow protein dynamics in globular proteins. Our algorithm is based on the hierarchical clustering of the correlation patterns (HCCP) technique of domain identification, which allows subdividing the protein into the hierarchy of the rigid‐body‐like clusters. The clusters are allowed to rotate relative to one another on the automatically identified hinges. The clusters are found in the course of automated, objective and well‐tested procedure. In the present communication, our technique is applied to 10 hinge‐bending proteins. For each of the proteins, we performed the blind search for the closed conformation, staring from the open one. Resulting closed conformations are compared with the closed states observed in crystallographic structures. It is shown that our technique produces realistic closed conformations for 8 out of 10 studied proteins. This demonstrates that HCCP technique can be used for finding alternative protein conformations and for sampling the slow motions in proteins. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Human uroporphyrinogen III synthase: NMR‐based mapping of the active site
Authors: Cunha Luis , Kuti Miklos , Bishop David F. , Mezei Mihaly , Zeng Lei , Zhou Ming‐Ming , Desnick Robert J. 
Published: November 2007

AbstractUroporphyrinogen III synthase (URO‐synthase) catalyzes the cyclization and D‐ring isomerization of hydroxymethylbilane (HMB) to uroporphyrinogen (URO'gen) III, the cyclic tetrapyrrole and physiologic precursor of heme, chlorophyl, and corrin. The deficient activity of human URO‐synthase results in the autosomal recessive cutaneous disorder, congenital erythropoietic porphyria. Mapping of the structural determinants that specify catalysis and, potentially, protein‐protein interactions is lacking. To map the active site and assess the enzyme's possible interaction in a complex with hydroxymethylbilane‐synthase (HMB‐synthase) and/or uroporphyrinogen‐decarboxylase (URO‐decarboxylase) by NMR, an efficient expression and purification procedure was developed for these cytosolic enzymes of heme biosynthesis that enabled preparation of special isotopically‐labeled protein samples for NMR characterization. Using an 800 MHz instrument, assignment of the URO‐synthase backbone 13Cα (100%), 1Hα (99.6%), and nonproline 1HN and 15N resonances (94%) was achieved as well as 85% of the side‐chain 13C and 1H resonances. NMR analyses of URO‐synthase titrated with competitive inhibitors ND‐methyl‐1‐formylbilane (NMF‐bilane) or URO'gen III, revealed resonance perturbations of specific residues lining the cleft between the two major domains of URO synthase that mapped the enzyme's active site. In silico docking of the URO‐synthase crystal structure with NMF‐bilane and URO'gen III was consistent with the perturbation results and provided a 3D model of the enzyme‐inhibitor complex. The absence of chemical shift changes in the 15N spectrum of URO‐synthase mixed with the homogeneous HMB‐synthase holoenzyme or URO‐decarboxylase precluded occurrence of a stable cytosolic enzyme complex. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Molecular dynamics simulations of ethanol binding to the transmembrane domain of the glycine receptor: Implications for the channel potentiation mechanism
Authors: Cheng Mary Hongying , Coalson Rob D. , Cascio Michael 
Published: November 2007

AbstractThe glycine receptor (GlyR) is potentiated by ethanol and other anesthetics. The potentiation mechanism at the molecular level is unknown and remains elusive, but mutagenic studies have shown that ethanol and other volatile anesthetics bind to a pocket between TM1, TM2, and TM3. The present study extends previous studies (Cheng et al., Proteins 2007;68:581–593) wherein we conducted homology modeling and molecular dynamics (MD) simulations to construct models of the homopentameric α1 subunits of the GlyR transmembrane domain in open and closed states. To understand the potentiation of GlyR by ethanol we compare the binding of ethanol molecules to the channel in these different states. We observe that ethanol stably resides inside solvent‐accessible cavities found in the open state of GlyR that are formed by I229 (of TM1) in one subunit and S267 and A288 (of TM2 and TM3, respectively) in the adjacent subunit. The volume of these putative binding pockets is state‐dependent. Selective binding to the open states of receptors has been proposed to explain the potentiating actions of this class of anesthetics. In accordance with this model, our MD simulations suggest that the potentiation of ethanol on GlyR may be effected through preferential binding of ethanol molecules to an inter‐subunit binding pocket in the open state. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Combining the polymerase incomplete primer extension method for cloning and mutagenesis with microscreening to accelerate structural genomics efforts
Authors: Klock Heath E. , Koesema Eric J. , Knuth Mark W. , Lesley Scott A. 
Published: November 2007

AbstractSuccessful protein expression, purification, and crystallization for challenging targets typically requires evaluation of a multitude of expression constructs. Often many iterations of truncations and point mutations are required to identify a suitable derivative for recombinant expression. Making and characterizing these variants is a significant barrier to success. We have developed a rapid and efficient cloning process and combined it with a protein microscreening approach to characterize protein suitability for structural studies. The Polymerase Incomplete Primer Extension (PIPE) cloning method was used to rapidly clone 448 protein targets and then to generate 2143 truncations from 96 targets with minimal effort. Proteins were expressed, purified, and characterized via a microscreening protocol, which incorporates protein quantification, liquid chromatography mass spectrometry and analytical size exclusion chromatography (AnSEC) to evaluate suitability of the protein products for X‐ray crystallography. The results suggest that selecting expression constructs for crystal trials based primarily on expression solubility is insufficient. Instead, AnSEC scoring as a measure of protein polydispersity was found to be predictive of ultimate structure determination success and essential for identifying appropriate boundaries for truncation series. Overall structure determination success was increased by at least 38% by applying this combined PIPE cloning and microscreening approach to recalcitrant targets. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Evaluating the potency of HIV‐1 protease drugs to combat resistance
Authors: Hou Tingjun , McLaughlin William A. , Wang Wei 
Published: November 2007

AbstractHIV‐1 protease has been an important drug target for the antiretroviral treatment of HIV infection. The efficacy of protease drugs is impaired by the rapid emergence of resistant virus strains. Understanding the molecular basis and evaluating the potency of an inhibitor to combat resistance are no doubt important in AIDS therapy. In this study, we first identified residues that have significant contributions to binding with six substrates using molecular dynamics simulations and Molecular Mechanics Generalized Born Surface Area calculations. Among the critical residues, Asp25, Gly27, Ala28, Asp29, and Gly49 are well conserved, with which the potent drugs should form strong interactions. We then calculated the contribution of each residue to binding with eight FDA approved drugs. We analyzed the conservation of each protease residue and also compared the interaction between the HIV protease and individual residues of the drugs and substrates. Our analyses showed that resistant mutations usually occur at less conserved residues forming more favorable interactions with drugs than with substrates. To quantitatively integrate the binding free energy and conservation information, we defined an empirical parameter called free energy/variability (FV) value, which is the product of the contribution of a single residue to the binding free energy and the sequence variability at that position. As a validation, the FV value was shown to identify single resistant mutations with an accuracy of 88%. Finally, we evaluated the potency of a newly approved drug, darunavir, to combat resistance and predicted that darunavir is more potent than amprenavir but may be susceptible to mutations on Val32 and Ile84. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Ion pairs and their role in modulating stability of cold‐ and warm‐active uracil DNA glycosylase
Authors: Olufsen Magne , Papaleo Elena , Smalås Arne Oskar , Brandsdal Bjørn Olav 
Published: November 2007

AbstractMD simulations and continuum electrostatics calculations have been used to study the observed differences in thermostability of cold‐ and warm‐active uracil DNA glycosylase (UDG). The present study focuses on the role of ion pairs and how they affect the thermal stability of the two enzymes. Analysis of the MD generated structural ensembles show that cod UDG (cUDG) and human UDG (hUDG) have 11 and 12 ion pairs which are present in at least 30% of the conformations. The electrostatic contribution of the ion pairs, computed using continuum electrostatics, is slightly more favorable in cUDG at 298 K. This is primarily attributed to more optimized interactions between the ion pairs and nearby dipoles/charges in cUDG. More global salt bridges are found in hUDG and are more stabilizing when compared to cUDG, possibly playing a role in maintaining overall stability and reducing conformational entropy. Both enzymes contain one three‐member ionic network, but the one found in hUDG is far more stabilizing. Our results also suggest that care should be taken when performing statistical analysis of crystal structures with respect to ion pairs, and that crystallization conditions must be carefully examined when performing such analysis. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Coherence and spatial resolution of transport in quantum cascade lasers
Authors: Wacker Andreas 
Published: November 2007

AbstractThe method of nonequilibrium Greens functions allows for a spatial and energetical resolution of the electron current in Quantum Cascade Lasers. While scattering does not change the spatial position of carriers, the entire spatial evolution of charge can be attributed to coherent transport by complex wave functions.We discuss the hierarchy of transportmodels and derive the density matrix equations as well as the hopping model starting from the nonequilibrium Greens functions approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)