Some simple flows of a Johnson-Segalman fluid

Summary Unlike most other fluid models, the Johnson-Segalman fluid allows for a non-monotonic relationship between the shear stress and rate of shear in a simple shear flow for certain values of the material parameter. This has been used for explaining a phenomenon such as spurt. Here, we study three simple flows of a Johnson-Segalman fluid with a view towards understanding its response characteristics. We find that boundary conditions can have a very interesting effect on the regularity of the solution; changing them continuously leads to solutions that change their regularity. First, we consider the flow through a circular pipe and find solutions that have discontinuous velocity profiles which have been used to explain the phenomenon of spurt (cf. [10], [11]). Second, we consider the flow past an infinite porous plate and show that it will not admit solutions which have discontinuous velocity gradients, the solutions being necessarity smooth. Lastly, we study Poiseuille flow in a concentric annulus with porous boundaries. While spurt could be explained alternatively by allowing for stick-slip at the wall, the Johnson-Segalman model seems particularly suited in describing the appearance of shear-layers (cf. [13]).     

On the “scientometric decline” of British science. One additional graph in reply to Ben Martin

With respect to the issue of whether the scientometric measurement of the decline of British science is an artifact of the specific database and underlying assumptions in methods, I argue that there are fewer analytical objections against measurement by usingSciSearch Online than against other methods (based on the fixed journal set and fractional counting). The measurement of international co-authorship, i.e. a network indicator, should not be confounded with measurement of performance of a single nation. The time series for the different subsets of UK-publications, which have been proposed, are given. None of the indicators can be shown to exhibit a trend (in contrast to a drift). The hypothesis of a decline has therefore to be rejected.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

The stacked lamellar texture on the fracture surfaces of fibre composites

A fracture surface texture, which has been variously termed as lacerations, hackles or serrations, is often observed on the matrix surface of fibre composites, most often in resin-rich regions. This texture, referred to here as a stacked lamellar texture to emphasize its plate-like nature, was studied in an E-glass/epoxy composite. Scanning electron fractographs of these materials suggest that the stacked lamellar texture arises from crack fingers due to a meniscus instability mechanism interacting with a reorienting stress field.     

Relationship between superconductivity and band structures of electrons and phonons

The relationship between superconductivity and band structures of electrons and phonons is established on the basis of a generalized Bardeen-Cooper-Schrieffer model in which the interaction strengths (V ₁₁,V ₁₂,V ₁₂) among and between electron (1) and hole (2) Cooper pairs are differentiated. Elemental superconductors must have local hyperboloidal Fermi surfaces called necks or inverted double caps.     

Novel poly(etheraroyl-co-terephthal) hydrazides with liquid crystalline behaviour

Novel poly(etheraroyl-co-terephthal)hydrazides with liquid crystalline (LC) behaviour, synthesized by solution polycondensation followed by non-solvent coagulation in water, have been characterized by means of Fourier Transform infrared (FT-i.r.), differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS) techniques. DSC thermograms and WAXS intensity profiles of as polymerized and coagulated homo- and copolymers are strongly dependent upon the molecular structure and constitution of the polymers: the poly(etheraroyl-hydrazide) homopolymer shows an LC behaviour and such a characteristic is maintained in copolymers with low content of terephthaloyldichloride comonomer, while a further increase in comonomer content attenuates this LC attitude. Annealing treatments on as polymerized and coagulated copolymers are able to transform the LC phase metastable at room temperature into crystalline and/or amorphous phases.     

Evidence for collective excitations in superconducting tin whiskers

Based on the assumption that a phase-slip center in a clean quasi-one-dimensional superconductor excites a collective oscillation, the time-averaged value of the electrochemical potential of quasiparticles is calculated. At larger distances from the phase-slip center, swings below (or above) the electrochemical potential _p of the Cooper pairs. This makes it possible to understand the unexpected results of previous measurements.     

Checking contact angles of radial-thrust bearings

Summary On the basis of the above method of measurement, using expression (4), highly productive semiautomatic devices were made for sorting out bearings by their contact angles into three groups: small, good and large.The adoption by our industry of these measuring devices for checking the contact angles will raise considerably the quality and life of radial-thrust bearings.     

Parametrische Kerbspannungsuntersuchung am elastischen Kern

Zusammenfassung Für die zugbeanspruchte Scheibe mit elastischem Rechteck-bzw. Rhombuskern wird der Einfluß der Kernstifigkeit und der geometrischen Parameter auf die Kerbspannungen nach Finit-Element-Verfahren bestimmt. Die errechneten Formzahlen werden im Grenzfall Öffnung und starrer Kern mit einer funktionentheoretischen Lösung verglichen. Die Kernsteifigkeit bestimmt die Höhe der Kerbspannungen, deren Verteilung von der Form des Kerns und der Belastung der Scheibe vorgegeben wird.

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Parametrical investigation of notch stresses at an elastic core

Summary The influence of the geometrical parameters on the stress concentration is determined with finite element methods for the disc under tension with an elastic rectangular or rhombic core. The calculated stress concentration factors are compared with the function analysis stress concentration factors in the limiting cases cut-out and rigid core. The core stiffness is essential for the value of the notch stresses, the distribution of which is given by the shape of the core and the loading of the disc.

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Mit 9 Abbildungen     

Interfacial and mechanical properties of environment-friendly “green” composites made from pineapple fibers and poly(hydroxybutyrate-co-valerate) resin

Physical and tensile properties of pineapple fibers were characterized. Tensile properties of pineapple fibers, like most natural fibers, showed a large variation. The average interfacial shear strength between the pineapple fiber and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa as measured by the microbond technique. Scanning electron microscopy (SEM) photomicrographs of the microbond specimens revealed an adhesive failure of the interface. Fully degradable and environment-friendly green composites were prepared by combining pineapple fibers and PHBV with 20 and 30% weight content of fibers placed in a 0°/90°/0° fiber arrangement. Tensile and flexural properties of these green composites were compared with different types of wood specimens. Even though tensile and flexural strength and moduli of these green composites were lower than those of some wood specimens tested in grain direction, they were significantly higher than those of wood specimens tested in perpendicular to grain direction. Compared to PHBV virgin resin, both tensile and flexural strength and moduli of these green composites were significantly higher. SEM photomicrographs of the fracture surface of the green composites, in tensile mode, showed partial fiber pull-out indicating weak bonding between the fiber and the matrix.     

Where Are We in HTCS?

Address given at the closing of the conference on Major Trends in Superconductivity in the New Millennium, MTSC 2000 and the opening of the Symposium on Itinerant and Localized States in HTCS SILS in HTCS.     

Theoretical estimation of the effect of interfacial energy on the mechanical strength of spinodally decomposed alloys

New interfaces are produced on the slip plane when a crystal with continuous composition fluctuation arising from spinodal decomposition is deformed by slip. In this work, the energy of such interfaces is evaluated for both modulated and mottled structures, and their effects on slip behaviour are discussed. It is concluded that the contribution of this interfacial energy is large enough to account for the age-hardening concomitant with spinodal decomposition.     

Microstructure of laser melted/rapidly solidified γ/Cr3Si metal silicide “in situ” composites

In order to improve the ductility of Cr₃Si metal silicide alloys, rapidly solidified /Cr₃Si metal silicide in situ composites were fabricated by laser melting/rapid solidification technology using Cr-Si-Ni alloy powders. Microstructure of the /Cr₃Si in situ composites was characterized by OM, SEM, XRD and EDS. The effect of Ni content in the alloy powder on microstructure and hardness of the /Cr₃Si composites was investigated. The /Cr₃Si metal silicide in situ composites have high hardness and rapidly solidified fine microstructure consisting of primary Cr₃Si dendrites and the interdendritic /Cr₃Si eutectics. The volume fraction of the Cr₃Si primary dendrites in the laser melted/rapidly solidified /Cr₃Si metal silicide in situ composites decreases with the increasing nickel content. Because of the presence of the ductile nickel-base solid solution and the rapidly solidified fine microstructure, the /Cr₃Si metal silicide in situ composites are expected to have adequate combination of strength and toughness. The results demonstrate that laser melting/rapid solidification for /Cr₃Si metal silicide in situ composites is a promising toughening method for improving the ductility of Cr₃Si metal silicide alloys.     

A scientometric assessment of agricultural research in South Africa

This article reports the results of a scientometric assessment of agricultural research in South Africa over the period 1974–1984. The Science Literature Indicators Database of CHI is used and South Africa is compared with 7 other countries spread in America, Asia, Oceania, and Africa. The criteria used for the assessment are the contribution of each country to international agricultural literature (in terms of publications) and their impact in the Schubert-Glänzel-Braun Impact Scale. It was found that, although the South African contribution has improved in that period, it is comparable to that of Brazil and Argentina; that Nigeria and Israel produce 3 times more, and: that Australia and Canada contribute more than one order of magnitude of publications more than South Africa. As far as research impact is concerned Plant Science research in South Africa is rated fair in the Schubert-Glänzel-Braun scale, whilst Dairy and Animal Science and Veterinary research are rated poor.     

An induced interaction model for arbitrarily polarized Fermi systems

A model for calculating the interactions in arbitrarily spin-polarized Fermi systems is presented. Starting from the four-point vertex functions, the induced part of the interactions is deduced by explicitly treating the one-particle, one-hole irreducible diagrams and using some general crossing symmetry relations. Extrapolation away from the Fermi surface is carried out by replacing the particle-hole phase space by Lindhard functions in the crossed channel; consequently, calculation of the necessary - phase space function is presented. The longitudinal spin-density and density responses for polarized systems are obtained by diagrammatic means. A possible way of treating the direct part of the interactions using Born approximation is also discussed. Finally, the limits of the model for zero and full polarization are given.     

Mathematical simulation of the process of combustion of slightly gaseous porous compositions

A one-dimensional model of combustion of slightly gaseous porous compositions is considered. Using this model an analysis of the dependence of the combustion characteristics on the basic parameters such as the mass ratio of the gas-free and volatile components in the starting composition, initial porosity, position of the gas liberation source relative to the reaction front of the gas-free component, and degree of sample hermetic sealing is performed for different exothermicity and endothermicity levels of the chemical processes taking place.Deceased.Institute of Structural Macrokinetics of the Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 4, pp. 461–465, October, 1993.     

Study of the zero-field magnetic ordering, charge fluctuation and trapping in the oxo-bridged heterometallic acetylacetonate complex Fe3YO6R3[Y11(C5O2H7)33]; (R = C5H7)

The Mössbauer, magnetic susceptibility and EXAFS data for the oxo-bridged heterometallic acetylacetonate Fe₃YO₆R₃[Y₁₁(C₅O₂H₇)₃₃] (R = C₅H₇) are analyzed in terms of a bound-to-free model describing the transition from the state of delocalized valence, denoted Fe_deloc ^(3–)+, in the magnetically disordered paramagnetic complex at 300 K to the states of localized valence, denoted Fe_loc ²⁺ and Fe_loc ³⁺, in the magnetically ordered complex at 4.2 and 77 K.     

Apparent screening breakdown mechanism in ultrasonic attenuation

Robinson and Levy have suggested that the mechanism of apparent screening breakdown may be responsible for an anomalous peak observed in the attenuation of transverse ultrasonic waves in metals. We show that this mechanism is consistent with Pippard's real metal theory despite a recent claim of Almond and Rayne to the contrary. Numerical calculations within a two-band model suggest that apparent screening breakdown effects may be important in compensated metals. This is in agreement with experimental data.Research sponsored by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant No. AFOSR-76-3082. The United States Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation hereon.     

Die GuV-synchrone Abschöpfung der Konditionsbeiträge

Zusammenfassung Alle geistigen Väter der neuenMarktzinsmethode sind sich bis auf beliebig viele Stellen hinter dem Komma einig über die Höhe desBarwerts der Konditionsbeiträge; die Unterschiede beginnen erst bei derVerrentung dieses Gegenwartswertes einer zukünftigen Zahlungsreihe (= Abschöpfung der Konditionsbeiträge), d. h. bei der Frage nach der richtigen Entnahmevorschrift für die Konditionsbeiträge bzw. der richtigen Bezugsbasis (= Kapital-Basis) für die Errechnung einerMarge.

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Summary All the founders of the new opportunity costs concept agree unanimously on the cash value of the net interest incomes irrespective of the number of positions to the right of the decimal point. Disagreement first becomes apparent by their approach to the distribution of the current value of this future payment sequence over the periods (= skimming off net interest incomes), i.e. in the question of the correct capital base for the calculation of an interest profit margin.

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Bereichsleiter Betriebswirtschaft/Controlling     

On chaos in bibliometric terminology

On behalf of a case study of articles on bibliometric selection and ranking the variance in terminology of the properties of journals is shown: the same properties are called in various manners, while one and the same terms have different meanings. Similar inconsistencies are found in the terms denoting readers' activities which are studied in bibliometrics for the assessment of the use of periodicals. The author concludes that there are actually only two properties of periodicals that are quantitatively assessed, viz. productivity, and value. Their definitions are suggested for terminology standardization of general properties of journals and of readers' activities.