bluuebunny/crossref_metadata_2025_split huggingface dataset:
Untersuchungen zu struktur und eigenschaften der polyamide, 2. Einkristalle aus polyamid 6,6
Authors: Hinrichsen Georg 
Published: April 2003

AbstractPolyamid‐6,6‐Einkristalle wurden aus verdünnten Lösungen bei Temperaturen zwischen 20 und 150°C ausgefällt und mittels Röntgenweit‐ und Röntgenkleinwinkelstreuung, Elektronenmikroskopie, Differentialkalorimetrie und Dichtemessungen charakterisiert. Es stellt sich heraus, daß die morphologische Beschaffenheit, die Kristalldicke, die Dichte, die Schmelzwärme und das Schmelzverhalten der Einkristalle von deren Kristallisations‐temperatur stark beeinflußt werden. Die aus den Dichten und Schmelzwärmen der Einkristalle berechneten Kristallisationsgrade liegen im Bereich von 40 bis 60%, wobei der jeweilige Wert von der Kristallisationstemperatur bestimmt wird. Durch Tempern bei erhöhten Temperaturen wächst die röntgenografische Langperiode kontinuierlich mit der Tempertemperatur und ‐zeit an. Die Ergebnisse werden in Hinblick auf ein von KELLER et al. für Polyamid‐Einkristalle vorgeschlagenes Modell, das eine regelmäßige Faltungsstruktur vorsieht, ausführlich diskutiert.
Cationic polymerizations initiated by high energy radiation
Authors: Chapiro Adolphe 
Published: April 2003

AbstractIonizing radiations generate both free radicals and ions upon interaction with matter and under appropriate conditions either free radical or ionic polymerizations are observed. Cationic polymerizations are favored by the presence of halogenated solvents and by low reaction temperatures. Selective inhibitors and copolymerization studies make it possible to determine the relative proportions of the cationic and the free radical contributions to the overall process under a variety of experimental conditions (temperature, reaction medium, radiation dose‐rate). Pure, carefully dehydrated hydrocarbon monomers undergo cationic polymerization when irradiated at room temperature. This reaction proceeds at a very high rate and is believed to involve free propagating cations. Propagation rate constants are available for the following monomers: styrene (kp = 3,5·106 at 15°C), α‐methylstyrene (kp = 4.106 at 0°C), cyclopentadiene (kp = 6.108 at −78°C), isobutene (kp = 1,5·108 at 0°C), and isobutyl vinyl ether (kp = 3.105 at 30°C). The present views on the mechanism of radiation induced cationic chain initiation and chain propagation are briefly discussed.
Éthers‐oxydes polymères des composés azoïques. Hétéropolycondensation du azodiphénolate‐4,4′ de sodium avec des dérivés bis(chlorométhylés) du benzène
Authors: Iovu Mircea , Radu Stelian 
Published: April 2003

AbstractDans ce travail nous présentons les résultats de la hétéropolycondensation du azodiphénolate‐4,4′ de sodium (1) avec les dérivés bis(chlorométhylés) du benzène et du benzène substitué 2a, b et 4. Les composés résultants sont des polymères linéaires avec une couleur jaune, peu solubles dans les solvants organiques.De même nous présentons les résultats de l'analyse spectrophotométrique (UV, visible, IR) et de l'analyse thermogravimétrique pour les polymères synthétisés.
Alternating copolymerization of carbon dioxide and propylene oxide in the presence of organometallic catalysts
Authors: Kuran Witold , Pasynkiewicz Stanisław , Skupińska Jadwiga , Rokicki Andrzej 
Published: April 2003

AbstractCarbon dioxide and propylene oxide (PO) were copolymerized using diethylzinc in addition with benzenedi‐ and triols, aliphatic diols and triols, and aminophenols as catalyst systems. A large amount of CO2/PO alternating copolymer, {poly(propylene carbonate), poly(oxycarbonyloxypropylene), of high molecular weight was obtained using the homogeneous (C2H5)2Zn/pyrogallol (2:1 by mole) system (1). The (C2H5)2Zn/o‐aminophenol system (2) (also homogeneous) appeared to be much less active in the copolymerization of CO2 with PO than the former one. From the other studied systems, that appeared to be heterogeneous, (C2H5)2Zn/resorcinol (1:1 by mole) was the most active one, but less active than the system 1.Further, the copolymerization of CO2 and PO was studied in the presence of the (C2H5)2Zn/resorcinol (1:1 by mole) system at various temperatures and in reaction media of different basicity.On the basis of the obtained results of the copolymerization of CO2 with PO and of measurements of the quantity of ethane evolved in the reactions between the catalytic systems' components, structures of several catalysts, particularly homogeneous ones, are suggested and some aspects of the copolymerization mechanism are discussed.
Oligomerisierungsprodukte bei der olefin‐metathese von mehrfach ungesättigten aliphatischen carbonsäureestern
Authors: Ast Wolfgang , Rheinwald Günter , Kerber Robert 
Published: April 2003

AbstractDie Olefin‐Metathese von mehrfach ungesättigten Carbonsäureestern wie Linol‐ und Linolensäureester in Gegenwart eines WCl6/(CH3)4Sn‐Katalysators führt neben einem cyclischen Produkt zu linearen oligomeren Olefinen, Mono‐ und Diestern. Die Produkte werden durch Massenspektrometrie identifiziert. Die sich im Gleichgewicht einstellende Verteilung der Linearprodukte wird statistisch berechnet und mit der experimentellen Verteilung verglichen.
The effect of desorption in micellar particle nucleation in emulsion polymerization
Authors: Hansen Finn Knut , Ugelstad John 
Published: April 2003

AbstractThe effect of desorption of monomer radicals from particles on the particle number generated in interval I of an emulsion polymerization is calculated by means of a semi steady state model. It is shown that desorption leads to an increase in the particle number, and at the same time the orders of particle number with respect to emulsifier and initiator are changing. The general equation of Nomura N∝Sz0ϱ1−zi is found to apply, z increasing from 0,6 to 1,0 with increasing desorption. The values of z and N are dependent on the exact reaction mechanisms in the monomer/polymer system and on rate constants of chemical reactions and diffusion processes involved in the particle formation.
Branching in high molecular weight polyhydroxyethers based on bisphenol A
Authors: Burchard Walther , Bantle Siegfried , Zahir Sheik A. 
Published: April 2003

AbstractThe polyaddition reaction of bisphenol A with the diglycidyl ether of bisphenol A is treated statistically on the basis of cascade theory to describe the branching process. The chain lengthening step is based on the reaction of the epoxide functional group with the phenolic hydroxyl group and leads to the formation of a 1,3‐diphenoxy‐2‐propanol link. The peculiar feature of this polyaddition reaction is the possibility of further addition of an epoxide to a secondary hydroxyl group to form branched molecules. This branching reaction does not, however, lead to a loss of hydroxyl groups since a new secondary hydroxyl group is created when an epoxide functional group reacts with a secondary hydroxyl group. Closed analytic expressions are derived for the weight‐average (Mw) and number‐average (Mn) molecular weights in terms of the mole ratio R = mb/ma and the extents of reaction of the functional groups α(phenolic hydroxyl), β(epoxide), and p(branching), i.e. the probability p that an epoxide group has reacted with a secondary hydroxyl group, where mb and ma are the mole fractions of the diglycidyl ether of bisphenol A and of bisphenol A, respectively. Consideration of a simple kinetic mechanism shows that α,β and ρ are related to the ratio b = k2/k1, where k1 and k2 are the rate constants of the chain lengthening step and the chain branching step, respectively. The equations derived for Mw and Mn as a function of a α allow the determination of the branching probability p (or the kinetic rate constant ratio b). An equation for the gel point (Mw → ∞) is given which states a relationship between αc and pc where the subcript c refers to the critical point of gelation. Thus location of the gel point and measurement of αc, either directly or by extrapolation on samples taken prior to gelation, enables p to be measured.
Initiation processes in polymerizations of alkyl cyanoacrylates by tertiary amines: Inhibition by strong acids
Authors: Pepper David Charles , Ryan Bernard 
Published: April 2003

AbstractPolymerizations of butyl and ethyl cyanoacrylates, in the solvent THF, initiated by pyridine and other tertiary amines, are inhibited by strong acids, which cause well‐defined inhibition periods (ti) proportional to the concentration of acid added, but irrespective of its nature. The temperature and monomer concentration dependence of ti indicate that chain‐initiation is a composite sequence involving two or three successive additions of monomer. A detailed theory is proposed and used to evaluate the composite initiation rate constants over the temperature range 20°C to −80°C. The influence of steric factors on the initiation by pyridine, picolines and lutidine is exemplified and discussed.
Polymerisationsauslösung mit substituierten ethanen, 6. Polymerisation von methylmethacrylat mit verschiedenen tetraphenylethanen
Authors: Błedzki Andrezj , Braun Dietrich , Titzschkau Klaus 
Published: April 2003

AbstractThe polymerization of methyl methacrylate (MMA) was initiated with 1,1,2,2‐tetraphenyl‐1,2‐diphenoxyethane (TPPA), 1,1,2,2‐tetraphenyl‐1,2‐bis(trimethylsiloxy)ethane (TPSA), and 1,1,2,2‐tetraphenyl‐1,2‐dicyanoethane (TPCA). The polymerization with these initiators is characterised by three steps: in the first period oligomers from MMA and initiator radicals are formed by primary radical termination. These telechelics are effective initiators for the further free radical polymerization of MMA. After consumption of the initiator radicals with increasing conversion a normal polymerization occurs.
An isomorphism between moduli spaces of abelian varieties
Authors: Birkenhake Christina , Lange Herbert 
Published: April 2003

AbstractIn a previous paper we showed that for every polarization on an abelian variety there is a dual polarization on the dual abelian variety. In this note we extend this notion of duality to families of polarized abelian varieties. As a main consequence we obtain an involution on the set of moduli spaces of polarized abelian varieties of dimension g. In particular, the moduli spaces $ {\cal A}_{(d_{1}, \ldots, d_{g})} $ and $ {\cal A}_{\left( d_1, {{d_{1}d_{g} \over {d_{g-1}}}, \ldots, {d_{1}d_{g} \over {d_{2}}}}, d_{g}\right)} $ are canonically isomorphic.
Invariants for proper metric spaces and open Riemannian manifolds
Authors: Eichhorn Jürgen 
Published: April 2003

AbstractWe introduce uniform structures of proper metric spaces and open Riemannian manifolds, characterize their (arc) components, present new invariants like e.g. Lipschitz and Gromov–Hausdorff cohomology, specialize to uniform triangulations of manifolds and prove that the presence of a spectral gap above zero is a bounded homotopy invariant.
Infinitely many solutions for polyharmonic elliptic problems with broken symmetries
Authors: Lancelotti Sergio , Musesti Alessandro , Squassina Marco 
Published: April 2003

AbstractBy means of a perturbation argument devised by P. Bolle, we prove the existence of infinitely many solutions for perturbed symmetric polyharmonic problems with non–homogeneous Dirichlet boundary conditions. An extension to the higher order case of the estimate from below for the critical values due to K. Tanaka is obtained.
Generalized multivalued nonlinear quasivariational inclusions
Authors: Liu Zeqing , Kang Shin Min 
Published: April 2003

AbstractIn this paper, we introduce and study a few classes of generalized multivalued nonlinear quasivariational inclusions and generalized nonlinear quasivariational inequalities, which include many classes of variational inequalities, quasivariational inequalities and variational inclusions as special cases. Using the resolvent operator technique for maximal monotone mapping, we construct some new iterative algorithms for finding the approximate solutions of these classes of quasivariational inclusions and quasivariational inequalities. We establish the existence of solutions for this generalized nonlinear quasivariational inclusions involving both relaxed Lipschitz and strongly monotone and generalized pseudocontractive mappings and obtain the convergence of iterative sequences generated by the algorithms. Under certain conditions, we derive the existence of a unique solution for the generalized nonlinear quasivariational inequalities and obtain the convergence and stability results of the Noor type perturbed iterative algorithm. The results proved in this paper represent significant refinements and improvements of the previously known results in this area.
Duality of (1, 5)–polarized abelian surfaces
Authors: Melliez Franck 
Published: April 2003

AbstractThere is not many open questions about the moduli space of (1, 5)–polarized abelian surfaces and level structure, it has been carefully studied by Barth, Hulek and Moore in the 80's. The goal of this paper is to give a description of the moduli space of (1, 5)–polarized abelian surfaces (without level structure) up to duality. We prove that an open set of this moduli space is isomorphic to an open set of the moduli space of sextuplets of points on a complex projective line (up to homographies) and we study what happens on the boundary.
Bounded factorization property for Fréchet spaces
Authors: Terzioğlu Tosun , Zahariuta Vyacheslav 
Published: April 2003

AbstractAn operatorT∈L(E, F)factors over GifT=RSfor someS∈L(E, G) andR∈L(G, F); the set of such operators is denoted byLG(E, F). A triple (E, G, F) satisfiesbounded factorization property(shortly, (E, G, F) ∈ ℬ︁ℱ) ifLG(E, F) ⊂LB(E, F), whereLB(E, F) is the set of all bounded linear operators fromEtoF. The relationship (E, G, F) ∈ ℬ︁ℱ is characterized in the spirit of Vogt's characterisation of the relationshipL(E, F) =LB(E, F) [23]. For triples of K�othe spaces the property ℬ︁ℱ is characterized in terms of their K�othe matrices.As an application we prove that in certain cases the relationsL(E, G1) =LB(E, G1) andL(G2, F) =LB(G2, F) imply (E, G, F) ∈ ℬ︁ℱ whereGis a tensor product ofG1andG2.
High Temperature Construction Materials on the Basis of Nanodisperse Silicon Nitride
Authors: Zhilinska N. , Zalite I. , Grabis J. , Kladler G. 
Published: April 2003

AbstractSi3N4‐Al2O3‐Y2O3, Si3N4‐TiN and Si3N4‐AIN‐Al2O3‐Y2O3 (β‐sialon) nanopowders with the specific surface area of 60–70 m2/g and average particle size of 30–50 nm have been prepared by plasmachemical synthesis. By means of the hot pressing method at 1850°C compact materials with fine‐grained structure were prepared from this powders as well as from mixture of Si3N4‐Al2O3‐Y2O3 with the second phase (10 wt.% SiC‐Si3N4, ZrO2, TiN nanopowder). Addition of the second phase to silicon nitride improves material strength.
Investigation of C/Si3N4 Nanocomposites
Authors: Balázsi C. , Wéber F. , Arató P. 
Published: April 2003

AbstractNanocrystalline carbon black and graphite micrograins have been added to silicon nitride starting powder and sintering additives (Al2O3 and Y2O3). These mixtures were mechanochemically activated several hours in a planetary type alumina ball‐mill in order to achieve a homogenous mass. As an alternative to nano‐ and micrograins, carbon fibres have been added to carbon free silicon nitride batches. Sinter‐HIP has been applied to rectangular bars which were earlier dry pressed. Structural and morphological analysis were performed on as‐prepared samples. Bending strength and elastic modulus have been found to be influenced by amount of carbon black and graphite introduced in silicon nitride matrix.
Wear and Creep Characteristics of a Carbon‐Derived Si3N4/SiC Micro/Nanocomposite
Authors: Kašiarová M. , Rudnayová E. , Kovalčík J. , Dusza J. , Hnatko M. , Šajgalík P. , Merstallinger A. 
Published: April 2003

AbstractIn the presented work some properties of a recently developed Si3N4/SiC micro/nanocomposite have been investigated. The material was tested using a pin on disc configuration. Under unlubricated sliding conditions using Si3N4 pin at 50 % humidity, the friction coefficient was in the range of 0,6 ‐ 0,7. The reduction of humidity resulted in a lower coefficient of friction, in vacuum the coefficient of friction had a value of about 0,6. The wear resistance in vacuum was significantly lower then that in air. The wear patterns on the Si3N4+SiC disc revealed that mechanical fracture was the wear controlling mechanism.Creep tests were realized in four point bending configuration in the temperature interval 1200‐1400 °C at stresses 50,100 and 150 MPa and the minimal creep deformation rate was established for each stress level. The activation energy, established from the minimal creep deformation had a value of about 360 kJ/mol and the stress exponent values were in the range of 0.8‐1.28. From the achieved stress exponents it can be assumed that under the studied load/temperature conditions the diffusion creep was the most probable creep controlling mechanism.
Properties of new polyimide foams and polyimide foam filled honeycomb composites
Authors: Resewski C. , Buchgraber W. 
Published: April 2003

AbstractNew polyimide foams and polyimide foam filled honeycombs are currently being developed at NASA, its licensee Sordal Inc. (USA) and Newmet (UK) under the trade name Solrex®. These materials are foreseen for Space, Aerospace, Maritime & Medicine applications. In this paper selected properties of these new materials with different densities are described.The investigated key properties are compression strength, thermal conductivity and moisture gain. The dependence of these properties on density, temperature and thermal cycling is discussed. Limits of the used characterisation methods are discussed. Possible applications are defined.
Improving the properties of aluminium alloys by retrogression and reageing
Authors: Robinson J. S. 
Published: April 2003

AbstractRetrogression and reageing heat treatments offer the potential of improved tensile properties in combination with greatly increased resistance to stress corrosion cracking. The potential of this technique is reviewed with respect to the current application in the European and North American Aerospace Industry. To illustrate the performance increase associated with RRA treatments, the stress corrosion cracking performance of the established aerospace plate and forging alloy 7010 has been evaluated using an alternate immersion constant load tensile type test (ECSS‐Q‐70‐37A) Specimens were cut from a large aerospace rectilinear forging and tested in three different tempers, T652, T7452 and a retrogressed and reaged condition (RRA). In the T652 condition the material has been shown to be highly susceptible to intergranular corrosion and stress corrosion cracking. In the T7452 and RRA conditions 7010 showed much improved resistance to SCC but pitting corrosion resulted in failure of some specimens within the 30day requirement of the test standard.
Thermal Conductivity Measurement of Nanoparticle Based Solid Propellant Mixtures
Authors: Marmiroli B. , Manzoni G. , Frassine R. 
Published: April 2003

AbstractA Miniaturised Pyrotechnic Initiator (MPI) is a device used to ignite a charge. It is reduced in scale in order to be suitable for application in miniaturised satellites. Miniaturising the system presents challenges requiring careful consideration of propellant selection. Thermal conductivity tests have been conducted on different mixtures of composite solid propellant materials in order to determine the thermal conductivity of the propellant in the temperature range 0‐100 °C and to study the effect of the presence of porosity and bubbles on the thermal conductivity of the propellant. The applicability of semiempirical Ziebland Relation to predict the thermal conductivity of the composite propellant once the values of the single components are known has been assessed. Furthermore, mixtures of Al and Potassium Perchlorate powders with different compression factors have been examined in order to understand the influence of the processing conditions on thermal conductivity
A Study of Environmentally Friendly Titanium Pretreatments for Adhesive Bonding to a Thermoplastic Composite
Authors: Leahy W. , Young T. , Buggy M. , Barron V. 
Published: April 2003

AbstractThe increased use of fibre reinforced polymer composites for aircraft structures have highlighted the need for reliable methods of bonding these materials to metallic components such as titanium. There is also a need for a simple test to evaluate adhesive bonds with dissimilar substrates, while under load and in a variety of environments. In this study the Boeing wedge test has been adapted for use with metal to composite adhesive bonds. A flexural rigidity matching approach was used with the addition of a backing beam to the composite coupon. The titanium adherends were surface pre‐treated using novel environmental benign methods, namely argon gas plasma and silicon sputtering. Sodium hydroxide anodisation, which is currently used industrially and alumina grit blasting were used as benchmarks. The composite, glass fire reinforced polyphenylene sulphide was alumina grit blasted. An environmental cycle was used to mimic a typical aircraft service cycle; joints were subjected to 24‐hour cycles of ambient, 60 °C water immersion, 60 °C dry and –55 °C dry for 12 days. Crack propagation and locus of failure were monitored after each cycle.
Kerbspannungen sind Biegespannungen – was sind gute und böse Kerben?
Authors: Mattheck C. , Scherrer M. , Tesari I. 
Published: April 2003

AbstractDie Entstehung von Kerbspannungen in einem Bauteil kann durch die Vorstellung einer überlagerten Biegung anschaulich erklärt werden. Die gekrümmte Oberfläche der Kerbe kann als konkave Seite eines stark gekrümmten Biegeträgers angesehen werden. Die nichtlineare Biegespannungsverteilung des Biegeträgers überlagert sich mit der Nennspannung und erzeugt die Spannungskonzentration in der Kerbe. Zur Vermeidung solcher Kerbspannungen muss sich der Anstieg der Spannung in der Kerbe mit dem Abfall der Nennspannung kompensieren. Ein multilinearisiertes Modell der Kerbe veranschaulicht die Wechselwirkung zwischen Umlenkung des Kraftflusses und Querschnittsverbreiterung des Bauteils.
Fourier‐Motzkin elimination method in MOLP problems
Authors: Melachrinoudis Emanuel , Liu Songan 
Published: April 2003

AbstractThis paper introduces a method for finding the non‐dominated set in criterion space of an MOLP problem based on Fourier–Motzkin Elimination. The method incorporates a procedure that eliminates decision variables from constraints and transforms a feasible region from decision space to criterion space. While avoiding characterization of the efficient set in decision space, it finds the non‐dominated set in criterion space. After the decision maker's most preferred criterion vector has been identified, the corresponding efficient solutions can be found by backward substitution. The method was implemented in MATLAB using a tabular form and computational experiments were conducted. The results indicate that although the method performs well for relatively small problems, it can be computationally intensive for larger problems. Nonetheless, the method is intuitively appealing and it provides useful insights into the geometry and theory of MOLP. As such it makes it a valuable educational tool for students of multi‐criteria decision analysis. Copyright © 2003 John Wiley & Sons, Ltd.
A multicriteria assignment problem
Authors: Scarelli Antonino , Narula Subhash C. 
Published: April 2003

AbstractOur objective in this paper is to propose a procedure for solving a multicriteria assignment problem. Given qualitative and quantitative data, the proposed procedure makes assignments taking into consideration the multicriteria aspect of the problem. As an illustrative example, we consider the assignment of referees to the football matches in an Italian championship. Copyright © 2003 John Wiley & Sons, Ltd.