bluuebunny/crossref_metadata_2025_split huggingface dataset:
Asymmetric ABC‐Triblock Copolymer Membranes Induce a Directed Insertion of Membrane Proteins
Authors: Stoenescu Roxana , Graff Alexandra , Meier Wolfgang 
Published: October 2004

AbstractSummary: Asymmetric molecules and materials provide an important basis for the organization and function of biological systems. It is well known that, for example, the inner and outer leaflets of biological membranes are strictly asymmetric with respect to lipid composition and distribution. This plays a crucial role for many membrane‐related processes like carrier‐mediated transport or insertion and orientation of integral membrane proteins. Most artificial membrane systems are, however, symmetric with respect to their midplane and membrane proteins are incorporated with random orientation. Here we describe a new approach to induce a directed insertion of membrane proteins into asymmetric membranes formed by amphiphilic ABC triblock copolymers with two chemically different water‐soluble blocks A and C. In a comparative study we have reconstituted His‐tag labeled Aquaporin 0 in lipid, ABA block copolymer, and ABC block copolymer vesicles. Immunolabeling, colorimetric, and fluorescence studies clearly show that a preferential orientation of the protein is only observed in the asymmetric ABC triblock copolymer membranes.
magnified image
Spectrophotometric Determination of Deacetylation Degree of Chitinous Materials Dissolved in Phosphoric Acid
Authors: Hsiao Hsien‐Yi , Tsai Chih‐Cheng , Chen Suming , Hsieh Bo‐Chuan , Chen Richie L.C. 
Published: October 2004

AbstractSummary: A simple spectrophotometric method is proposed for determining deacetylation degrees (DD) of chitinous materials using phosphoric acid as the UV‐transparent solvent system. Calibrating by the extinction coefficients (A210) of D‐glucosamine and N‐acetyl‐D‐glucosamine, DD values (24–88%) were computed numerically. The results correlated well (R2 = 0.9805, n = 50) with those obtained by solid‐state 13C NMR.Comparison of the results obtained by the proposed UV method and solid‐state 13C NMR.magnified imageComparison of the results obtained by the proposed UV method and solid‐state 13C NMR.
Modeling of the Phase Separation Behavior of Polydisperse Semi‐Flexible Diblock Copolymers
Authors: John Andreas , Friedel Peter , Pospiech Doris , Jehnichen Dieter , Kunert Christoph 
Published: October 2004

AbstractSummary: A modified random phase approximation method with a cumulant expansion for the semi‐flexible structure factor of diblock copolymers was exercised to describe the phase separation behavior of semi‐flexible and polydisperse diblock copolymers. Scattering curves and spinodal diagrams were calculated applying monomer specific input parameters. The influence of polydispersity was included applying basic concepts of mathematical statistics utilizing several probability density distributions in the case of the two single blocks. In contrast to semi‐flexibility, the main effect of polydispersity was found to shift the spinodal up, thus to enlarge the range of existence of the homogeneous phase.Twofold Schultz‐Zimm distribution of diblock copolymers.magnified imageTwofold Schultz‐Zimm distribution of diblock copolymers.
Adsorption Behavior of Asymmetrical Triblock Copolymers at the Solid‐Liquid Interface by Monte Carlo Simulation
Authors: Peng Changjun , Li Jiankang , Liu Honglai , Hu Ying 
Published: October 2004

AbstractSummary: Monte Carlo simulation on a simple lattice model has been used to study the adsorption of asymmetrical triblock copolymers from a non‐selective solvent at the solid‐liquid interface. The size distributions of train, loop and tail configurations for those copolymers are obtained as well as other details of the adsorption layer microstructure. Also the influence of adsorption energy and the role of molecular symmetry are investigated. A segment‐density profile, the adsorption amount, the surface coverage, and the adsorption layer thickness have been determined. Finally, it is shown that the adsorption behavior of an asymmetrical copolymer can be predicted from the symmetrical copolymer.Size distributions of the tail configuration for A8−kB20Ak.magnified imageSize distributions of the tail configuration for A8−kB20Ak.
Mean‐Square Radius of Gyration and Degree of Branching of Highly Branched Copolymers Resulting from the Copolymerization of AB2 With AB Monomers
Authors: Zhou Zhiping , Yu Minqiang , Yan Deyue , Li Zeshen 
Published: October 2004

AbstractSummary: The evolution of the various structural units incorporated into hyperbranched polymers formed from the copolymerization of AB2 and AB monomers has been derived by the kinetic scheme. The degree of branching was calculated with a new definition given in this work. The degree of branching monotonously increased with increasing A group conversion (x) and the maximum value could reach 2r/(1 + r)2, where r is the initial fraction of AB2 monomers in the total. Like the average degree of polymerization, the mean‐square radius of gyration of the hyperbranched polymers increased moderately with A group conversion in the range x < 0.9 and displayed an abrupt rise when the copolymerization neared completion. The characteristic ratio of the mean‐square radius of gyration remained constant for the linear polymers. However, the hyperbranched polymers did not possess this character. In comparison with the linear polymerization, the weight average and z‐average degree of polymerization increased due to the addition of the branched monomer units AB2 and the mean‐square radius of gyration decreased quickly for the products of copolymerization.
magnified image
Online‐Messung des Schmierungszustandes mit Hilfe des Übergangswiderstandes
Authors: Deters L. , Bosse H. 
Published: October 2004

AbstractHeute findet die Begutachtung von aufgetretenen Schmierungszuständen in der Regel erst nach einem Testlauf oder nach einem Schaden statt. Das ist zu spät und liefert keine Hinweise darüber, ob und bis wann der Schmierungszustand gut war oder wann er sich verschlechtert hat. Deshalb ist ein kontinuierlich arbeitendes Online‐Messverfahren wichtig. Vor allem bei Misch‐ und Grenzreibung wird ein kritischer Zustand erst angezeigt, wenn der Schaden bereits eingetreten ist. Das an der Universität Magdeburg entwickelte und in mehreren Forschungsvorhaben eingesetzte Messverfahren auf der Basis der Übergangswiderstandsmessung ermöglicht die Online‐Messung und Identifizierung des Schmierungszustandes im Misch‐ und Grenzreibungsgebiet. Dies wird an Versuchsergebnissen gezeigt, die mit oszillierenden Gleit‐ und Wälzlagern gewonnen wurden.
Wear Aspects During Green Machining of Warm Compacted PM Steels
Authors: Benner A. , Beiss P. 
Published: October 2004

AbstractThe automobile industry is by far the most important end user for structural PM steel parts. Structural PM parts are most frequently used in engines and transmissions. Usually, the PM components are produced by die pressing. The demand for cost reduction and constantly rising quality requirements in this field of application led to the development of new variants of die pressing in the recent past which facilitate the pressing of higher densities and, consequently, higher strengths. One of these new techniques is the warm compaction technology. Apart from improving the materials properties after sintering, this technique offers the advantage that the green compact shows a significantly higher green strength already after the pressing step so that machining can be executed before sintering. Particularly for high‐strength PM steels, which usually show very uncomfortable machining properties in the as‐sintered condition, a clear cost advantage is attributed to green machining. Initially, it was expected that wear aspects were completely unimportant during green machining and could be neglected to a great extent. However, more detailed investigations prove that in contrast to that assumption a certain wear resistance of the tools is necessary, as well. Taking the example of drilling, this study deals with the wear mechanisms relevant for green machining and with the different wear behaviour of current tool substrates during green machining.
Struktur‐, Härte‐ und Spannungsmessung von ölgeschmierten Metall‐Metall Tribokontakten
Authors: Shakhvorostov D. , Pinto H. , Pyzalla A. , Enders S. , Pöhlmann K. , Scherge M. 
Published: October 2004

AbstractMit einem Stift‐Scheibe Tribometer, bei dem eine Graugussscheibe gegen einen verchromten Stahlstift rotiert, wurde kontinuierlich und mit hoher Auflösung Reibung und Verschleiß gemessen. Durch Variation von Normalkraft und Gleitgeschwindigkeit wurden Proben generiert, die sich deutlich in der Höhe der dissipierten Energie unterschieden. Diese Proben wurden vor und nach der tribologischen Belastung strukturell durch eine Feinfokus‐Ionenstrahlanlage (Focused Ion Beam ‐ FIB) untersucht. Es stellte sich heraus, dass im oberflächennahen Bereich durch tribologische Wechselwirkung der Korndurchmesser drastisch abnimmt. Parallel dazu kommt es zum Eintrag von Fremdatomen aus dem Schmierstoff und Umgebung, was durch Augerelektronenspektroskopie nachgewiesen wurde. Mittels Röntgenbeugungsverfahren wurde der mechanische Spannungszustand analysiert, und durch Nanoindentation konnten die mechanischen Eigenschaften im oberflächennahen Bereich bestimmt werden. Tribologisch optimal eingelaufenes Material zeigte im oberflächennahen Bereich nanokristalline Struktur, die erheblich verringerten Reibungswiderstand besaß.
A parallel Galerkin boundary element method for surface radiation and mixed heat transfer calculations in complex 3‐D geometries
Authors: Cui X. , Li B. Q. 
Published: October 2004

AbstractThis paper presents a parallel Galerkin boundary element method for the solution of surface radiation exchange problems and its coupling with the finite element method for mixed mode heat transfer computations in general 3‐D geometries. The computational algorithm for surface radiation calculations is enhanced with the implementation of ideas used for 3‐D computer graphics applications and with data structure management involving creating and updating various element lists optimized for numerical performance. The algorithm for detecting the internal third party blockages of thermal rays is presented, which involves a four‐step procedure, i.e. the primary clip, secondary clip and adaptive integration with checking. Case studies of surface radiation and mixed heat transfer in both simple and complex 3‐D geometric configurations are presented. It is found that a majority of computational time is spent on the detection of foreign element blockages and parallel computing is ideally suited for surface radiation calculations. Results show that the decrease of the CPU time approaches asymptotically to an inverse rule for parallel computing of surface radiation exchanges. For large‐scale computations involving complex 3‐D geometries, an iterative procedure is a preferred approach for the coupling of the Galerkin boundary and finite elements for mixed mode heat transfer calculations. Copyright © 2004 John Wiley & Sons, Ltd.
Volume determination for bulk materials in bunkers
Authors: Ahmed S. A. , Buckingham R. , Gremaud P. A. , Hauck C. D. , Kuster C. M. , Prodanovic M. , Royal T. A. , Silantyev V. 
Published: October 2004

AbstractA simple model for the determination of the shape of large granular piles in complicated geometries is discussed. An eikonal formulation of the problem is proposed. Two distinct cases arise. In cylindrical geometries, i.e., if both container and possible obstacles have vertical walls, the problem is equivalent to a two‐dimensional travel time problem with obstacles, while in general geometries, this analogy breaks down. In the first case, classical one‐sided discretizations are generalized to handle obstacles without loss in accuracy. In the second case, a fast and efficient numerical method is proposed, implemented and tested. The discrete problems are solved through fast marching. Copyright © 2004 John Wiley & Sons, Ltd.
Common‐refinement‐based data transfer between non‐matching meshes in multiphysics simulations
Authors: Jiao Xiangmin , Heath Michael T. 
Published: October 2004

AbstractIn multiphysics simulations using a partitioned approach, each physics component solves on its own mesh, and the interfaces between these meshes are in general non‐matching. Simulation data (e.g. jump conditions) must be exchanged across the interface meshes between physics components. It is highly desirable for such data transfers to be both numerically accurate and physically conservative. This paper presents accurate, conservative, and efficient data transfer algorithms utilizing a common refinement of two non‐matching surface meshes. Our methods minimize errors in a certain norm while achieving strict conservation. Some traditional methods for data transfer and related problems are also reviewed and compared with our methods. Numerical results demonstrate significant advantages of common‐refinement based methods, especially for repeated transfers. While the comparisons are performed with matching geometries, this paper also addresses additional complexities associated with non‐matching surface meshes and presents some experimental results from 3‐D simulations using our methods. Copyright © 2004 John Wiley & Sons, Ltd.
Parallel global optimization with the particle swarm algorithm
Authors: Schutte J. F. , Reinbolt J. A. , Fregly B. J. , Haftka R. T. , George A. D. 
Published: October 2004

AbstractPresent day engineering optimization problems often impose large computational demands, resulting in long solution times even on a modern high‐end processor. To obtain enhanced computational throughput and global search capability, we detail the coarse‐grained parallelization of an increasingly popular global search method, the particle swarm optimization (PSO) algorithm. Parallel PSO performance was evaluated using two categories of optimization problems possessing multiple local minima—large‐scale analytical test problems with computationally cheap function evaluations and medium‐scale biomechanical system identification problems with computationally expensive function evaluations. For load‐balanced analytical test problems formulated using 128 design variables, speedup was close to ideal and parallel efficiency above 95% for up to 32 nodes on a Beowulf cluster. In contrast, for load‐imbalanced biomechanical system identification problems with 12 design variables, speedup plateaued and parallel efficiency decreased almost linearly with increasing number of nodes. The primary factor affecting parallel performance was the synchronization requirement of the parallel algorithm, which dictated that each iteration must wait for completion of the slowest fitness evaluation. When the analytical problems were solved using a fixed number of swarm iterations, a single population of 128 particles produced a better convergence rate than did multiple independent runs performed using sub‐populations (8 runs with 16 particles, 4 runs with 32 particles, or 2 runs with 64 particles). These results suggest that (1) parallel PSO exhibits excellent parallel performance under load‐balanced conditions, (2) an asynchronous implementation would be valuable for real‐life problems subject to load imbalance, and (3) larger population sizes should be considered when multiple processors are available. Copyright © 2004 John Wiley & Sons, Ltd.
Thermal analysis of 1,4‐di[n′‐(quinolyl)]buta‐1,3‐diynes, structure, and topo‐oligomerization: Polymerization of 3‐ethynylquinoline with the triethyl aluminum/vanadium 2,4‐pentanedionate catalyst system
Authors: Rodríguez J. G. , Lafuente A. , De Los Ríos C. 
Published: October 2004

AbstractConjugated 1,4‐bis(n′‐quinolyl)‐1,3‐butadiynes were obtained through the oxidative dimerization of the corresponding n′‐ethynylquinolines catalyzed by cuprous chloride. Differential scanning calorimetry analysis of the 1,4‐bis[n′‐(quinolyl)]buta‐1,3‐diyne molecules produced evidence of a syn–anti rotational equilibrium around the 1,3‐diyne axis and an irreversible transformation into a thermopolymer. The topo‐oligomerization of 1,4‐bis[3′‐(quinolyl)]buta‐1,3‐diyne, which took place by irradiation with sunlight, was investigated with matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. Accurate X‐ray molecular structure and refinement analysis of 1,4‐bis[3′‐(quinolyl)]buta‐1,3‐diyne was conducted. The molecular crystalline packing consisted of parallel arrays of two groups of centrosymmetric molecules (antirotamer) in a herringbone assemblage in the solid state. The polymerization of 3‐ethynylquinoline was carried out with the AlEt3/V(acac)3 system to produce a mixture of 1,2,4‐ and 1,3,5‐tris(3′‐quinolyl)benzene cyclotrimers and a trans–cisoid polyene structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6031–6040, 2004
New results on the influence of the nature of the nucleophile in the stereospecific modification of poly(vinyl chloride)
Authors: Martínez Gerardo , Millán José Luis 
Published: October 2004

AbstractThe nucleophilic substitution reactions on poly(vinyl chloride) (PVC) with potassium 4‐acetamidothiophenolate, potassium 2‐naphthalenethiolate, and sodium 2‐mercaptobenzothiazolate have been undertaken in a cyclohexanone solution. The aim was to study, from a comparative point of view, the influence of nucleophile characteristics, in particular bulkiness, reactivity, and nucleophile polarity, on the reaction mechanisms by following the microstructural evolution with the degree of substitution of the same PVC sample with three types of nucleophile under the same experimental conditions. The quantitative microstructural analysis as a function of conversion has been followed by 13C NMR spectroscopy. Because of the steric hindrance and moderate reactivity of 2‐mercaptobenzothiazolate, the stereoselective nature of the reaction is enhanced, occurring via the meso‐racemic (mr) triad of mmr tetrad, inoperative in practice, unlike the other nucleophiles. This circumstance and the fact that the bulkiness of the nucleophile and interacting effects provide an enhancement of the molecular microstructure‐based mechanisms, such that glass‐transition temperature (Tg) varies with the degree of substitution, in all cases, along with the ratio between the extent to which mmr and rrmr structure intervene in the substitution reaction, thereby providing new and valuable information regarding the Tg–microstructure relationship. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6052–6060, 2004
Molecular mixing of incompatible polymers through formation of and coalescence from their common crystalline cyclodextrin inclusion compounds
Authors: Rusa C. C. , Wei M. , Shuai X. , Bullions T. A. , Wang X. , Rusa M. , Uyar T. , Tonelli A. E. 
Published: October 2004

AbstractWe describe the successful mixing of polymer pairs and triplets that are normally incompatible to form blends that possess molecular‐level homogeneity. This is achieved by the simultaneous formation of crystalline inclusion compounds (ICs) between host cyclodextrins (CDs) and two or more guest polymers, followed by coalescing the included guest polymers from their common CD–ICs to form blends. Several such CD–IC fabricated blends, including both polymer1/polymer2 binary and polymer1/ polymer2/polymer3 ternary blends, are described and examined by means of X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and solid‐state NMR to probe their levels of mixing. It is generally observed that homogeneous blends with a molecular‐level mixing of blend components is achieved, even when the blend components are normally immiscible by the usual solution and melt blending techniques. In addition, when block copolymers composed of inherently immiscible blocks are coalesced from their CD–ICs, significant suppression of their normal phase‐segregated morphologies generally occurs. Preliminary observations of the thermal and temporal stabilities of the CD–IC coalesced blends and block copolymers are reported, and CD–IC fabrication of polymer blends and reorganization of block copolymers are suggested as a potentially novel means to achieve a significant expansion of the range of useful polymer materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4207–4224, 2004
Molecular characterization of an improved vector for evaluation of the tumor suppressor versus oncogene abilities of the androgen receptor
Authors: Litvinov Ivan V. , Antony Lizamma , Isaacs John T. 
Published: October 2004

AbstractBackgroundThere is a growing body of evidence demonstrating that the function of the ligand‐occupied androgen receptor (AR) within the nuclei of normal prostatic epithelial cells acts as a tumor suppressor gene. This is in contrast to the well‐documented ability of the AR within prostate cancer cells to function as an oncogene. Thus, many groups are attempting to understand the biochemistry and signaling cascade differences involved in the switching of AR from a tumor suppressor to an oncogene.MethodsTo do this, of plasmid vectors for transgenic expression of AR are very useful. AR negative PC‐3 human prostate cancer cells were transfected with a plasmid containing the full length coding sequence of AR without its 5′‐ or 3′‐untranslated regions (UTRs) (i.e., pSG5‐AR).ResultsTransgenic expression of the AR protein results in profound growth inhibition which is not relieved by the addition of ligand. A new expression vector for the AR, pAR‐IRES‐EGFP, has been constructed that contains full‐length 5′‐UTR which includes the identified translation regulatory regions, the full length coding sequence and the partial 3′‐UTR, which includes the identified post‐transcriptional regulatory regions. When PC‐3 cells were transfected with the pAR‐IRES‐EGFP vector, it was found that transgenic AR protein expression was not growth inhibitory until ligand was added.ConclusionsThese pSG5‐AR versus pSAR‐IRES‐EGFP clones are being studied to determine the molecular pathways explaining their different response to AR and ligand. © 2004 Wiley‐Liss, Inc.
Enhanced specificity of bacterial spore identification by oxidation and mass spectrometry
Authors: Demirev Plamen A. 
Published: October 2004

AbstractAddition of an oxidizing agent (e.g., hydrogen peroxide) to intact spores selectively and completely oxidizes Met‐containing biomarker proteins by formation of Met sulfoxides. This reaction increases the masses of the biomarker proteins observed in matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) of Bacillus spores by Δm = (16 × n) Da, where n is the number of Met residues in the sequence of each individual protein. The procedure is very rapid, and can be performed in situ (i.e., on the MALDI target). It confirms the identity of individual biomarkers by comparing the number of Met amino acids from the experimentally determined mass shifts with predictions for n from the tentative amino acid sequence for each protein. In turn, accurate determination of n for several biomarkers allows rapid validation of the initial spore identification by MALDI‐MS. Copyright © 2004 John Wiley & Sons, Ltd.