bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the OCS2 Singlet potential energy surface
Authors: Carlsen Lars 
Published: December 2004

AbstractThe reaction between atomic oxygen and carbon disulfide is predicted to lead to at least two primary products, which are the dithiiranone (1) and the oxathiirane‐thione (2) and/or the carbon disulfide S‐oxide (4). The possible intramolecular equilibria 1 ⇄ 2, 1 ⇄ 3, 2 ⇄ 4, and 2 ⇄ 5 as well as the fragmentations of the possible intermediates 1–5 have been studied theoretically within the semiempirical CNDO/B framework as conceivable ground‐state reactions. On the basis of MO correlations and potential energy changes along the reaction paths, supplementary with previously reported experimental data, the single molecular transformations and the eventual product formations are discussed.
Approaches to charge calculations in molecular mechanics
Authors: Abraham Raymond J. , Griffiths Lee , Loftus Philip 
Published: December 2004

AbstractAlternative methods of estimating atomic charges in haloalkanes are presented, derived from quantum mechanical and classical treatments. A scheme based on a breakdown of the transmission of charge by polar atoms into one‐bond, two‐bond, and three‐bond additive contributions is given, in which the one‐bond effect is proportional to the difference in the electronegativities of the bonded atoms, and the two‐ and three‐bond effects functions of the atomic electronegativity and polarizability. Suitable developments of the basic scheme, including an iterative self‐consistent process, give calculated dipole moments for a variety of haloalkanes in good agreement with the observed values. The atomic charges obtained by this scheme are compared with other estimates of these charges. They are similar to those derived from a simple LCAO–MO scheme but differ from those obtained by population analysis of more refined quantum mechanical calculations.
Electronic structure of UH, UF, and their ions
Authors: Krauss M. , Stevens W. J. 
Published: December 2004

AbstractA relativistic effective core potential (REP) has been generated for the uranium atom and used in self‐consistent‐field calculations of the A states of UH, UF, and their ions. Energy curves were calculated at the base configuration level which ensures the dissociating atoms are described by Hartree–Fock wavefunctions. The electronic bonding of these molecules is found to be similar to that of comparable alkaline–earth hydrides and fluorides. The uranium 6p, 6d, and 5f orbitals retain their atomic character but the orbitals extend into the bonding region and are distorted by overlap repulsion and electrostatic effects. Nonetheless, the atomic energetic coupling determines that low energy states will have the maximum spin multiplicity and maximum orbital angular momentum projection consonant with the charge‐transfer bonding.
The use of CNDO/force and compliance constant methods in evaluating quadratic potential functions of carbonyl and formyl fluorides
Authors: Murthy A. S. N. , Ranganathan Shoba 
Published: December 2004

AbstractCNDO/Force and compliance constant methods were applied to define general quadratic potential functions for F2CO and HCOF. A satisfactory set of compliants was obtained by suitably scaling down the stretching and stretch–stretch elements of the initial force constant matrix, evaluated by the CNDO/force approach, followed by fitting the compliants to available experimental data.
A theoretical study of the interaction of monomethylammonium with double‐stranded oligonucleotides
Authors: Gresh Nohad 
Published: December 2004

AbstractTheoretical computations are performed of the interaction specificities of the monomethylammoniumion with double‐stranded oligonucleotides (dPu)n·(dPy)n in the B‐DNA conformation. The effects of base sequence and chain length are examined. In short oligomers (n = 2, 3), the interaction energies of the cation are larger in the major groove of (dG)n·(dC)n than in the minor groove of (dA)n·(dT)n. As a consequence of further shaping of the grooves and building up of the phosphates, a marked reversal in the affinities of the cation for the grooves occurs at the (dPu)5·(dPy)5 and the p(dPu)5p·p(dPy)5p levels: it is the binding in the minor groove of the adenine‐thymine oligomers that provides then the most favorable interaction energies.It is also shown, at the level of the double helices built from dinucleoside monophosphates, that the interaction of monomethylammonium in the minor groove occurs in specific configurations involving the three NH bonds of the cation, and two successive bases on one strand; this binding is sequence‐specific, the order of inherent preferences being (TpA) > (TpT) > (ApA) > (ApT).
Implementation of an electronic structure program system on the CYBER 205
Authors: Ahlrichs Reinhart , Böhm Hans‐Joachim , Ehrhardt Claus , Scharf Peter , Schiffer Heinz , Lischka Hans , Schindler Michael 
Published: December 2004

AbstractThe CGTO integral evaluation, SCF, SCF‐gradient, integral transformation, and MR‐CI (SD) steps of the COLUMBUS system of programs have been adapted for the CYBER 205. A description is given of our efforts and the partly heavy modifications necessary to exploit the potential of this supercomputer and to avoid its shortcomings. Typical timings are reported, vector and scalar performance are compared.
Cluster analysis of periodic distributions; application to conformational analysis
Authors: Nørskov‐Lauritsen L. , Bürgi H. B. 
Published: December 2004

AbstractA method is described to analyze observed conformations for molecular fragments with more than three torsional degrees of freedom. The method is an adaption of statistical cluster analysis to multidimensional, symmetric, periodic distributions of data points. Application to the molecular fragment M(PPh3)2 with eight torsional degrees of freedom reveals a model of conformational interconversion. The model implies gearing motion of the two PC3 fragments alternating with stepwise inversions of the helicities of the PPh3‐propellers.
Microscopic effect of an applied voltage on the solvated gramicidin a transmembrane channel in the presence of Na+and K+cations
Authors: Kim Kwang S. 
Published: December 2004

AbstractUsing the previously reportedab initiointeraction energies among K+, Na+, water, and Gramicidin A (GA), this report presents Monte Carlo simulations for the microscopic effect of an applied voltage (0.5 V/32 Å) on a solvated gramicidin. The reorientation of water molecules due to the applied voltage is found to be marginal for both cations. The energy contribution due to water dipoles was within 10% of the total energy contribution due to the applied voltage. Inside the channel the total energy contribution varied almost linearly along the channel axis; outside the channel the slope of the total energy contribution with respect to the channel axis decreased.
Ishtar: An interactive system for quantitative investigation on dipolar and quadrupolar spin‐lattice relaxation
Authors: Allouche A. , Pouzard G. 
Published: December 2004

AbstractWithin the model of anisotropic rotational diffusion, the quantitative treatment of dipolar and quadrupolar spin‐lattice relaxation provides valuable information about molecular structures and molecular associations. When quadrupolar relaxation is involved, the title program calculates: (1) the electric field gradient tensor (EFGT) which is diagonalized; (2) the assymetry parameter, the components of the principal axes of the EFGT in the molecular frame of reference and the quadrupole coupling constant; and (3) the rotational diffusion constants which are iteratively determined from the experimental quadrupolar relaxation times. Analogously, for dipolar relaxation ISHTAR calculates the tensor of inertia, the diagonalization of which leads to diffusion constants and free rotor correlation times and the rotational diffusion constants from the experimental spectral densities.
Characteristic polynomials of organic polymers and periodic structures
Authors: Balasubramanian K. 
Published: December 2004

AbstractIt is shown that the Frame's method (also, Le Verrier‐Faddeev's method) for characteristic polynomials of chemical graphs can be extended to periodic graphs and structures. The finite periodic structures are represented by cyclic structures in the Born‐von Kárman boundary condition which leads to complex matrices. In this article we demonstrate that our earlier computer program (based on Frame's method) can be extended to these periodic networks. The characteristic polynomials of several lattices such as polydiacetylenes, one‐dimensional triangular, square, and hexagonal lattices are obtained. These polynomials can be obtained with very little computer time using this method.
A fast algorithm for the interactive docking maneuver with flexible macromolecules and probes
Authors: Karfunkel H. R. 
Published: December 2004

AbstractA new algorithm for the interactive docking maneuver is presented. Full attention is given to the flexibility of both substrate and macromolecule, i.e., all the fragments are allowed to move. It is assumed that any numerical quantity which depends only on the isolated macromolecule at energy minimum is disposable when approximate expressions are derived. The central idea is the concept of relevant docking coordinates which reflect the essential features of the macromolecular deformations during the docking maneuver and which substantially diminish the number of considered degrees of freedom (DF). The conformational energy is divided into two parts. The first part, represented by condensed potential functions, needs no approximations. For the second part, termed Erest, a quadratic approximation in the subspace spanned by the relevant docking coordinates is used. All the pairwise interactions between the atoms of the macromolecule are eliminated. A simple computational example using the ECEPP force field is given. Atomic coordinate computations are simplified by the introduction of virtual rotation axes for the backbone. In connection with drug design the concept of pressure pattern is defined and related to quantities appearing in the energy gradient. Extensions to substrate induced allosteric transitions are discussed.
Sensitivity and uncertainty of reaction mechanisms for photochemical air pollution
Authors: Falls Andrew H. , McRae Gregory J. , Seinfeld John H. 
Published: December 2004

AbstractA sensitivity/uncertainty analysis is performed on a mechanism describing the chemistry of the polluted troposphere. General features of the photochemical reaction system are outlined together with an assessment of the uncertainties associated with the formulations of mechanistic details and rate data. The combined effects of sensitivity and uncertainty are determined using the Fourier amplitude sensitivity test (FAST) method. The results of this analysis identify the key parameters influencing the chemistry of NO2, O3, and PAN. Based on these findings, a series of recommendations are made for future experimental kinetic studies.
The kinetics of the addition of alkyl radicals to carbonyl groups. Part I. The addition of methyl radicals to hexafluoroacetone in the gas phase. The formation of the hexafluoro‐t‐butoxy radical
Authors: Drew Roger M. , Kerr J. Alistair 
Published: December 2004

AbstractBy pyrolyzing di‐t‐butyl peroxide over the temperature range of 405–450 K in the presence of hexafluoroacetone the kinetics of the addition reaction (1), CH3 + (CF3)2CO→; (CF3)2C(Ȯ)CH3, have been studied. Detailed analyses have shown that the principal product of the adduct radical, (CF3)2C(Ȯ)CH3, is CF3COCH3 from reaction (2), (CF3)2C(Ȯ)CH3 → CF3COCH3 + CF3. The rate constant of the addition reaction was determined to be k1(dm3/mol·s) = (1.1 ± 4.0) + 109 exp(‐(3680 ± 480)/T) over the temperature range 405–450 K, based on the value k3 = 2.2 × 1010 dm3/mol·s for reaction (3), 2CH3 → C2H6. The results are discussed in relation to existing data for radical additions to carbonyl groups.
Über den Angriff von heißem Imprägnieröl auf Stahlblech und seine Verhütung
Authors: Schikorr G. 
Published: December 2004

AbstractDie durchgeführte Untersuchung zeigte folgende Ergebnisse: Imprägnieröl kann Eisen in sehr erheblichem Ausmaß angreifen. Der Angriff nimmt mit steigender Temperatur zu und beträgt bei 240° etwa 200 g/m2.Tg. Er ist auf die sauren Bestandteile des Imprägnieröls zurückzuführen und kann durch Zugabe von etwa I % Calciumoxyd praktisch vollständig verhindert werden.
Wash‐Primer als Metall‐Vorbehandlung und universeller Haftgrund
Authors: Sarx H. F. 
Published: December 2004

AbstractAufgabe, Anwendungsmöglichkeit und Grenzen dieses Anstrichmittels, dem immer stärkere Bedeutung zukommt, sind in DIN E 55945 festgelegt.Wash‐Primer ist ein haftungsvermittelndes und passivierendes Mittel zur Metallvorbehandlung. Er wird in 2 Komponenten geliefert, deren wesentliche Bestandteile bei der einen aus Polyvinylbutyral und einem speziell entwickelten Zinkchromat, bei der anderen aus Phosphorsäure bestehen. Bei der Anwendung auf Metall wird neben einer ausgezeichneten Haftung eine Passivierung der Metalloberfläche, z. B. auf Eisen und Leichtmetall, erzielt.Auch auf nichtmetallischen Stoffen wie Glas, Hartfaserplatten, Bakelit‐Preßmassen und Beton ist das Problem der Anstrichhaftung durch Wash‐Primer in überzeugender Weise zu lösen.Mit dem sog. Eintopf‐Wash‐Primer wurde die universelle Wirkung des 2‐Komponenten‐Primers nicht erreicht.Da nach etwa 8 h die Umsetzung der Mischung soweit fortgeschritten ist, daß beim Auftragen die Haftung nicht mehr voll entwickelt werden kann, soll erst kurz vor der Verarbeitung gemischt werden. Die Konsistenz ist so zu wählen, daß ein Eindringen in tiefe Poren unter Ausbildung eines sehr dünnen Filmes gewährleistet ist.Eim Wash‐Primer‐Film gewährleistet keinen Korrosionsschutz über eine längere Zeit und erübrigt auch die eigentliche Grundierung nicht. Der Auftrag eines weiteren dem Untergrund angepaßten Anstriches sollte deshalb bei Anwendung im Freien nach einigen Tagen, bei Anwendung in hallen in einigen Wochen, vorgenommen werden.
Zum Zusammenhang zwischen Eigenschaften und Gefügestruktur mehrphasiger Werkstoffe Teil I: Zielsetzung, Kenntnisstand und stereologische Beschreibung der Gefügestruktur
Authors: Ondracek G. 
Published: December 2004

AbstractDie Eigenschaften mehrphasiger Werkstoffe hangen von den Eigenschaften ihrer Phasen und deren Geometrie und geometrischer Anordnung (Gefügestruktur) ab. Mikroskopische Gefügebilder mehrphasiger Werkstoffe sind vielfach auch dann verfügbar, wenn der Werkstoff extremen Zustandsbedingungen ausgesetzt ist (z. B. hohe Temperaturen, radioaktive Strahlung), unter denen Eigenschaftsmessungen unmöglich oder schwierig und daher aufwendig und/oder ungenau sind. Durch stereologische Gefügeanalyse kann aus solchen Gefügebildern die Gefügestruktur ermittelt werden. – Die Kenntnis des quantitativen Zusammenhangs zwischen Gefügestruktur und Eigenschaften würde dann die direkte Messung von Eigenschaftskenngrößen ersetzbar machen durch eine stereologische Gefügeanalyse. Da dies nicht nur für extreme Zustandsbedingungen gilt, würde die stereologische Gefügeanalyse in der konventionellen Qualitätskontrolle, ebenfalls ohne Eigenschaftsmessungen, Aussagen über Eigenschaftskenngrößen erlauben. Außerdem vertiefen solche Gefüge‐Eigenschafts‐Beziehungen das physikalische Verständnis des Verhaltens von Werkstoffen mit bestimmter Gefügestruktur und ermöglichen die Vorausberechnung von Eigenschaftsverbesserungen durch Gefügeoptimierung.Diese Arbeit handelt in 4 Teilen die Ableitung und experimentelle Prüfung quantitativer Beziehungen zwischen der Gefügestruktur und der Leitfähigkeit, dem Elastizitätsmodul sowie dem thermischen Ausdehnungskoeffizienten zweiphasiger Werkstoffe. Im vorliegenden 1. Teil wird die quantitative Beschreibung des räumlichen Aufbaus zweiphasiger Werkstoffe mit Einlagerungsgefüge durch drei Stereologiefaktoren erörtert: – den Konzentrationsfaktor – den Formfaktor – den Orientierungsfaktor Die Definition dieser Stereologiefaktoren und ihre Ermittlung aus stereologischen Gefügeanalysen erfolgt so, daß sie den Etnfluß der Gefügestruktur durch Konzentration, Form und Orientierung der Phasen in Gefüge‐Eigenschafts‐Gleichungen richtig wiedergeben.
Der Kunststoff im Apparate‐ und Anlagenbau
Authors: Gaube E. 
Published: December 2004

AbstractDie Arbeit soll in die Thematik „Konstruieren mit Kunststoffen im Apparate‐ und Anlagenbau”︁ einführen. Es wird ein Überblick über den Stand der Technik gegeben, wobei auch auf die Probleme hingewiesen wird, die nach Ansicht des Verfassers noch nicht oder noch nicht zufriedenstellend gelöst sind.
Qualitätskontrolle von Rohren aus HDPE
Authors: Diedrich G. , Müller W. , Gaube E. 
Published: December 2004

AbstractEs wird über Versuche berichtet, eine Korrelation zwischen Ergebnissen aus Zeitstand‐Innendruckversuchen an HDPE‐Rohren und Zeitstandversuchen an Längszugstäben aus diesen Rohren zu finden.
Fiber‐matrix interactions
Authors: Piggott M. R. 
Published: December 2004

AbstractThe mechanical properties of short, fiber‐reinforced polymers are governed as much by the interface as by the properties of fiber or polymer. Interface properties of importance include adhesion and radial and longitudinal (frictional) stresses. These directly govern strength, modulus, and toughness of the composite and indirectly affect the resistance of the composite to environmental influences, such as water. These interface properties and the resulting interactions under applied stresses are examined and their influence on mechanical properties is discussed.
Properties and economics of mica‐reinforced plastics related to processing conditions
Authors: Fenton Malcom , Hawley George 
Published: December 2004

AbstractUpgrading mica by increasing aspect ratio and coupling efficiency and combining mica with fibers has led to new uses as a reinforcement for thermoplastics and thermosets. The greatest growth in mica use has been in the thermoplastics, such as polypropylene and thermoplastic polyesters. Effects to be expected from using mica as a reinforcement include improved tensile and flexural strength, much‐increased dimensional stability and heat resistance, enhanced stiffness and electrical resistivity, and reduced permeability to gasses and liquids. Major parameters that influence the composite properties include the mica flake size, orientation, aspect ratio and volume fraction, coupling efficiency, and crystallinity of the polymer matrix. Mica composites are molded from direct blends or are precompounded in the manner used for fillers. Mica‐reinforced polypropylene (PP) is cost‐effective in replacing glass‐fiber‐reinforced PP and may even substitute for glass‐reinforced Nylon 66 in some applications. Markets for fillers for plastics are expected to grow faster than for the base polymers due to low cost, availability, and low energy utilization. Mica is expected to be one of the fillers with the highest market growth rate.
The effect of biaxial stress on the creep properties of polymethyl methacylate
Authors: Zaslawsky M. 
Published: December 2004

AbstractBiaxial creep tests have been performed on thin‐walled tubes of polymethyl methacrylate at 116°F and 50% R.H. The tubes were loaded radially up to a specified stress state, which was then maintained for a finite time. Additional tests involved a constant stress state for a period Δt1, after which the specimen was rapidly subjected to a second stress state which was maintained for a period Δt2. The experimental apparatus and procedure are described. The results for the range of stress, temperature, and time investigated show: 1) the creep behavior can be described by the form ϵ = ϵ0 + mtn, where ϵ is the strain, ϵ0 is the time‐independent portion of the strain, and m and n are constants; 2) n appears to be independent of stress state in the fourth quadrant (−σz axial stress, +σθ tangential stress), and m is a linear function (log‐log) of effective stress. In the first quadrant (+σz +σθ), the values of m and n are dependent on stress state, the constant m being also dependent on effective stress. Since two measurements are made for tangential strain ϵ0, a description of the deformation can be obtained. Some results of pre‐strain history and fracture are also presented.
The effect of aspect ratio on the fatigue life of short boron fiber reinforced composites
Authors: Lavengood R. E. , Gulbransen L. B. 
Published: December 2004

AbstractThe flexural fatigue characteristics of boron fiber reinforced epoxy were shown to be strongly dependent on the aspect ratio of the reinforcing fibers. These composites were evaluated in a stiffness limited, constant maximum stress mode. The failure mechanism was found to be a combination of interfacial failure and brittle rupture of the matrix at 45 deg to the axis of the fibers. These fatigue cracks result in debonding of the outer fibers, thereby reducing the effective moment of inertia of the specimen.
Derivative stress‐strain curves of polyacrylonitrile fibers
Authors: Egbers G. 
Published: December 2004

AbstractDerivative stress‐strain curves at constant strain rate for polyacrylonitrile copolymer fibers have been obtained by simple modification of conventional tensile testing apparatus. These derivative curves, considerably more complex and eventful than stress‐strain curves, have been interpreted as direct records of changes undergone by the apparent Young's modulus during experiments which extend from infinitesimal strain to failure. Analysis of the data shows that these changes in the apparent Young's modulus cannot be accounted for to any significant extent by viscoelastic time effects and must therefore be consequences of the deformation process itself. In the light of this analysis, it is concluded that polyacrylonitrile fibers “soften” considerably in the strain range 0.5–3% and that they exhibit moderate “hardening” in the strain range which extends from ca 3% to the breaking strain (10%).
Physical optics of iridescent multilayered plastic films
Authors: Alfrey T. , Gurnee E. F. , Schrenk W. J. 
Published: December 2004

AbstractThe physical optics of iridescent multilayered plastic films are analyzed theoretically relating the layer thickness, layer arrangement, and refractive index difference between layers to the reflection spectra for light at normal incidence. Very vivid iridescent and metallic‐appearing films may be made by proper control of layer distribution.
Microscopic observations of fracture in spherulitic films of polybutene‐1
Authors: Haas T. W. , Rae P. H. Mac 
Published: December 2004

AbstractSpherulitic films of polybutene‐1 have been stressed under biaxial tension. Direct microscopic observations indicate that the deformation is localized at the spherulite centers and at the intersections of boundaries in agreement with previous results obtained with linear polyethylene. The results demonstrate an increasing tendency for brittle failure with decreasing molecular weight. Effects of surfactants and solvents are also presented.
Glass‐Catalyzed hydrolysis of silane coupling agents
Authors: Daley L. R. , Rodriguez F. 
Published: December 2004

AbstractSilane coupling agents containing organo‐functional and alkoxy groups are applied to glass fiber reinforcements from an acid solution commercially. It is found that finely divided soda glass suspended in a methanol‐water solution of various silanes promotes hydrolysis without the presence of an acid catalyst. When acid is present in addition to the glass, as in commercial application baths, rate of hydrolysis is lower than with either acid or glass alone. There is evidence that basic glass components catalyze hydrolysis. Further work under commercial application conditions is indicated.