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  • Articles  (182)
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  • 1
    Publication Date: 2011-05-01
    Print ISSN: 0304-3894
    Electronic ISSN: 1873-3336
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Technology
    Published by Elsevier
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  • 2
    Electronic Resource
    Electronic Resource
    Bingley : Emerald
    Journal of quality in maintenance engineering 6 (2000), S. 287-295 
    ISSN: 1355-2511
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Technology , Economics
    Notes: This paper reports on the reliability data analysis and modelling of offshore oil platform plant. We first analysed the effectiveness of preventive maintenance to the plant concerned, and then identified the key sub-units and major preventive maintenance activities to be modelled. A modelling technique called the delay time is then used to determine the optimal periodic inspection intervals. The analysis showed that preventive maintenance is generally effective, but a slight decrease of the periodic inspection intervals is favourable.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Advances in science and technology Vol. 46 (Oct. 2006), p. 73-78 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Deep-level defects related with 5d transition metal, osmium (Os) have been studied in ntypeGaAs. Os has been incorporated in epitaxial n-GaAs layers in situ, during growth by lowpressuremetal-organic chemical vapour phase epitaxy (MOVPE) technique. Mesa p+nn+ junctiondiodes are fabricated for investigations by deep level transient spectroscopy (DLTS). Two deeplevelpeaks, observed in majority carrier (electron) emission spectra, Os1 and Os2, show asignificant shift in peak positions to lower temperatures with the applied junction reverse bias,demonstrating enhancement of the thermal emission rate by the junction electric field. DoublecorrelationDLTS (DDLTS) measurements have been employed for accurate quantitativeinvestigations of the observed field dependence. However, in view of the relatively smallconcentration of the deep level Os1, this technique is found to yield reliable data only for the deeplevel corresponding to the dominant peak, Os2. Detailed data have been obtained on the field effectfor Os2, extending over junction electric field values 3 x 106 V/m - 1.2 x 107 V/m. The measuredemission rate signatures show a reduction of the thermal activation energy from 0.48 eV to 0.21 eVfor Os2 over this electric field range. Analysis of the data in terms of the recent theoretical work onfield dependence indicates that Os2 is associated with a substitutional Os donor
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 23 (1996), S. 107-124 
    ISSN: 1573-1634
    Keywords: solute transport ; Fick's law ; dispersion ; dispersivity ; equation of motion ; non-Fickian dispersion equation ; scale effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The Fickian dispersion equation is the basic relationship used to describe the nonconvective mass flux of a solute in a porous medium. This equation prescribes a linear relationship between the dispersive mass flux and the concentration gradient. An important characteristic of the Fickian relationship is that it is independent of the history of dispersion (e.g. the time rate of change of the dispersion flux). Also, the dispersivities are supposed to be medium constants and invariant with temporal and spatial scales of observation. It is believed that in general these restrictions do not hold. A number of authors have proposed various alternative relationships. For example, differential equations have been employed that prescribe a relationship between the dispersion flux and its time and space derivatives. Also, stochastic theories result in integro-differential equations in which dispersion tensor grow asymptotically with time or distance. In this work, three different approaches, which lead to three different non-Fickian equations with a transient character, are discussed and their primary features and differences are highlighted. It is shown that an effective dispersion tensor defined in the framework of the transient non-Fickian theory, grows asymptotically with time and distance; a result which also follows from stochastic theories. Next, principles of continuum mechanics are employed to provide a solid theoretical basis for the non-Fickian transient dispersion theory. The equation of motion of a solute in a porous medium is used to provide a rigorous derivation of various dispersion relationships valid under different conditions. Under various simplifying assumptions, the generalized theory is found to agree with the conventional Fickian theory as well as several other non-Fickian relationships found in the literature. Moreover, it is shown that for nonconservative solutes, the traditional dispersion tensor is affected by the rate of mass exchange of the solute.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 3 (1988), S. 319-321 
    ISSN: 1573-1634
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 3 (1988), S. 299-318 
    ISSN: 1573-1634
    Keywords: Brine transport ; species transport ; radionuclides ; aggregated porous media ; micropores ; macropores ; structured porous media ; Darcy's law ; Fick's law
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Basic equations governing the transport of species by concentrated brine flowing through an aggregated porous medium are developed. Some simple examples are solved numerically. The medium is considered to be composed of porous rock aggregates separated by ‘macropores’ through which the brine flows and transport of salt and low-concentration species takes place. The aggregates contain dead-end pores, cracks, and stationary pockets collectively called ‘micropores’. The micropore space does not contribute to the flow, but it serves as a storage for salt and species. Adsorption of fluid species takes place at internal surface of aggregates where it is assumed that a linear equilibrium isotherm describes the process. The effects of high salt concentrations are accounted for in the brine density relation, the viscosity relation, Darcy's and Fick's laws, and the rate of mass transfer between macropores and micropores. Mass balance equations, supplemented by extended forms of Darcy's and Fick's laws, are employed to arrive at two sets of equations. One set consists of seven coupled equations for the salt mass fraction and fluid density in macropores, salt mass fraction in micropores, fluid velocity vector, and the fluid pressure. The other set consists of two coupled equations to be solved for the mass fractions of low-concentration species in micropores and macropores. Based on these equations, a mathematical model called TORISM is developed. Using this model, the potential significance of modifications to Darcy's Law are demonstrated.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 2 (1987), S. 521-531 
    ISSN: 1573-1634
    Keywords: Porous media ; high velocity flow ; non-Darcy flow ; Forchheimer equation ; inertial effects ; constitutive equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Experimental observations have established that the proportionality between pressure head gradient and fluid velocity does not hold for high rates of fluid flow in porous media. Empirical relations such as Forchheimer equation have been proposed to account for nonlinear effects. The purpose of this work is to derive such nonlinear relationships based on fundamental laws of continuum mechanics and to identify the source of nonlinearity in equations. Adopting the continuum approach to the description of thermodynamic processes in porous media, a general equation of motion of fluid at the macroscopic level is proposed. Using a standard order-of-magnitude argument, it is shown that at the onset of nonlinearities (which happens at Reynolds numbers around 10), macroscopic viscous and inertial forces are negligible compared to microscopic viscous forces. Therefore, it is concluded that growth of microscopic viscous forces (drag forces) at high flow velocities give rise to nonlinear effects. Then, employing the constitutive theory, a nonlinear relationship is developed for drag forces and finally a generalized form of Forchheimer equation is derived.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 4 (1972), S. 561-578 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The task of optimum design of structures is one that involves non-linear Programming. This is particularly the case when deflection as well as stress limitation are imposed as design criteria. In this paper a Fundamental approach is presented for the minimum weight design of statically indeterminate elastic structure subject to non-linear deflection and stress constrains.The matrix force method is adopted to formulate the problem. The constraints thus derived prove to have separable variables and therefore can be linearized in a piecewise manner. The computation aspects concerning the restricted entry in to the simplex tableau are briefly discussed and illustrative examples are given to verify the validity of the proposed method.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 671-681 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The theorems of structural variation for rigidly jointed frames are extended to cover the nonlinear elastic-plastic analysis of frames to collapse. Strain hardening and other material changes are included in the analysis. It is shown that the entire load-deflection history of a frame, following the successive formation of plastic hinges up to and including collapse, is obtained from a single initial elastic analysis.The manner in which these theorems are used to insert real (or plastic) hinges to a frame is presented and details of the manual calculations involved in the elastic-plastic analysis of a portal is given to demonstrate the simplicity of the method. This is followed by a comparison of the results with those obtained experimentaly by Baker and Charlton. The versatility of the method is then demonstrated by altering the shape of a frame before its elastic-plastic analysis.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2020-06-13
    Print ISSN: 0948-4280
    Electronic ISSN: 1437-8213
    Topics: Geosciences , Technology
    Published by Springer
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