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Characteristic Value (characteristic + value)
Selected AbstractsFluid flow and heat transfer in the transition process of natural convection over an inclined plateHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2001Katsuo Komori Abstract The present study deals with fluid flow and heat transfer in the transition process of natural convection over an inclined plate. In order to examine the mechanism of the transition process, experiments on the flow and heat transfer were performed for various plate inclination angles in the range of 20 to 75°. The wall temperature and fluid flow fields were visualized using a liquid crystal sheet and fluorescent paint, respectively. The visualization confirmed that separation of a boundary layer flow took place, and the onset point of streaks appeared over the plate wall when the modified Rayleigh number exceeded a characteristic value for each inclination angle. The local Nusselt number in the transition range was proportional to the one-third power of the local modified Rayleigh number. By introducing a nondimensional parameter, a new correlation between visualizations of the flow and temperature fields and heat transfer was proposed. © 2001 Scripta Technica, Heat Trans Asian Res, 30(8): 648,659, 2001 [source] Modeling of Diffusion Limitations in Bulk RAFT PolymerizationMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2006A. David Peklak Abstract Summary: The impact of diffusion limitations on RAFT polymerizations is investigated in this work. In particular, two models are compared: one accounting for diffusion limitations by using average chain lengths, the other accounting for the entire CLD. It is shown that such a description is necessary to correctly predict the kinetics of polymerization processes, as well as the evolution of average chain length and polydispersity. For properly selected study cases, differing conversion curves are obtained above 40% monomer conversion, if only average values of the CLD are considered. The same is valid for the calculation of the polydispersity, which starts differing above 80% conversion. Finally, for given conditions of diffusion limitations, it is found that an ideal polydispersity can be defined and it is shown that the polydispersity tends to this characteristic value during the entire evolution of the polymerization process. as a function of f for various values of . [source] Lifetime distribution of photoluminescence and radiative recombination rate of electron-hole pairs in a-Si:HPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Chisato Ogihara Abstract Temperature variations of radiative recombination rates of electron-hole pairs responsible for photoluminescence in a-Si:H films have been analysed from the intensity, I, and the characteristic value of the lifetime, ,, obtained from frequency resolved spectroscopy. In a defective a-Si:H film, the radiative recombinationrate increases with increasing temperature because of thermal excitation of the electrons and holes from the tail states to more ex-tended tail states. In the case of a high-quality a-Si:H film, the temperature variation of I,,1 is explained by contributions from regions in the vicinity of the defects and the regions not affected by the defects (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A comparison of three estimators of the Weibull parametersQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 4 2001Katina R. Skinner Abstract Using mean square error as the criterion, we compare two least squares estimates of the Weibull parameters based on non-parametric estimates of the unreliability with the maximum likelihood estimates (MLEs). The two non-parametric estimators are that of Herd,Johnson and one recently proposed by Zimmer. Data was generated using computer simulation with three small sample sizes (5, 10 and 15) with three multiply-censored patterns for each sample size. Our results indicate that the MLE is a better estimator of the Weibull characteristic value, ,, than the least squares estimators considered. No firm conclusions may be made regarding the best estimate of the Weibull shape parameter, although the use of maximum likelihood is not recommended for small sample sizes. Whenever least squares estimation of both Weibull parameters is appropriate, we recommend the use of the Zimmer estimator of reliability. Copyright © 2001 John Wiley & Sons, Ltd. [source] Agradient velocity, vortical motion and gravity waves in a rotating shallow-water modelTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 601 2004Georgi G. Sutyrin Abstract A new approach to modelling slow vortical motion and fast inertia-gravity waves is suggested within the rotating shallow-water primitive equations with arbitrary topography. The velocity is exactly expressed as a sum of the gradient wind, described by the Bernoulli function, B, and the remaining agradient part, proportional to the velocity tendency. Then the equation for inverse potential vorticity, Q, as well as momentum equations for agradient velocity include the same source of intrinsic flow evolution expressed as a single term J(B, Q), where J is the Jacobian operator (for any steady state J(B,Q)=0). Two components of agradient velocity are responsible for the fast inertia-gravity wave propagation similar to the traditionally used divergence and ageostrophic vorticity. This approach allows for the construction of balance relations for vortical dynamics and potential vorticity inversion schemes even for moderate Rossby and Froude numbers assuming the characteristic value of |J(B,Q)|=, to be small. The components of agradient velocity are used as the fast variables slaved to potential vorticity that allows for diagnostic estimates of the velocity tendency, the direct potential vorticity inversion with the accuracy of ,2 and the corresponding potential vorticity-conserving agradient velocity balance model (AVBM). The ultimate limitations of constructing the balance are revealed in the form of the ellipticity condition for balanced tendency of the Bernoulli function which incorporates both known criteria of the formal stability: the gradient wind modified by the characteristic vortical Rossby wave phase speed should be subcritical. The accuracy of the AVBM is illustrated by considering the linear normal modes and coastal Kelvin waves in the f -plane channel with topography. Copyright © 2004 Royal Meteorological Society [source] The estimation of sibling genetic risk parameters revisitedGENETIC EPIDEMIOLOGY, Issue 4 2004Guohua Zou Abstract This report points out that some sibling genetic risk parameters can be regarded as the ratios of the characteristic values in the ascertainment subpopulation. Based on this observation, we reconsider Olson and Cordell's ([2000] Genet. Epidemiol. 18:217,235) and Cordell and Olson's ([2000] Genet. Epidemiol. 18:307,321) estimators, and re-derive these estimators. Furthermore, we provide the closed-form variance estimators. Simulation results suggest that our proposed estimators perform very well, and single ascertainment may be better than complete ascertainment for estimating these genetic parameters. © 2004 Wiley-Liss, Inc. [source] The upper continental crust, an aquifer and its fluid: hydaulic and chemical data from 4 km depth in fractured crystalline basement rocks at the KTB test siteGEOFLUIDS (ELECTRONIC), Issue 1 2005I. STOBER Abstract Detailed information on the hydrogeologic and hydraulic properties of the deeper parts of the upper continental crust is scarce. The pilot hole of the deep research drillhole (KTB) in crystalline basement of central Germany provided access to the crust for an exceptional pumping experiment of 1-year duration. The hydraulic properties of fractured crystalline rocks at 4 km depth were derived from the well test and a total of 23100 m3 of saline fluid was pumped from the crustal reservoir. The experiment shows that the water-saturated fracture pore space of the brittle upper crust is highly connected, hence, the continental upper crust is an aquifer. The pressure,time data from the well tests showed three distinct flow periods: the first period relates to wellbore storage and skin effects, the second flow period shows the typical characteristics of the homogeneous isotropic basement rock aquifer and the third flow period relates to the influence of a distant hydraulic border, probably an effect of the Franconian lineament, a steep dipping major thrust fault known from surface geology. The data analysis provided a transmissivity of the pumped aquifer T = 6.1 × 10,6 m2 sec,1, the corresponding hydraulic conductivity (permeability) is K = 4.07 × 10,8 m sec,1 and the computed storage coefficient (storativity) of the aquifer of about S = 5 × 10,6. This unexpected high permeability of the continental upper crust is well within the conditions of possible advective flow. The average flow porosity of the fractured basement aquifer is 0.6,0.7% and this range can be taken as a representative and characteristic values for the continental upper crust in general. The chemical composition of the pumped fluid was nearly constant during the 1-year test. The total of dissolved solids amounts to 62 g l,1 and comprise mainly a mixture of CaCl2 and NaCl; all other dissolved components amount to about 2 g l,1. The cation proportions of the fluid (XCa approximately 0.6) reflects the mineralogical composition of the reservoir rock and the high salinity results from desiccation (H2O-loss) due to the formation of abundant hydrate minerals during water,rock interaction. The constant fluid composition suggests that the fluid has been pumped from a rather homogeneous reservoir lithology dominated by metagabbros and amphibolites containing abundant Ca-rich plagioclase. [source] Composite high resolution localized relaxation scheme based on upwinding for hyperbolic conservation lawsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2009Ritesh Kumar Dubey Abstract In this work we present an upwind-based high resolution scheme using flux limiters. Based on the direction of flow we choose the smoothness parameter in such a way that it leads to a truly upwind scheme without losing total variation diminishing (TVD) property for hyperbolic linear systems where characteristic values can be of either sign. Here we present and justify the choice of smoothness parameters. The numerical flux function of a high resolution scheme is constructed using wave speed splitting so that it results into a scheme that truly respects the physical hyperbolicity property. Bounds are given for limiter functions to satisfy TVD property. The proposed scheme is extended for non-linear problems by using the framework of relaxation system that converts a non-linear conservation law into a system of linear convection equations with a non-linear source term. The characteristic speed of relaxation system is chosen locally on three point stencil of grid. This obtained relaxation system is solved using composite scheme technique, i.e. using a combination of proposed scheme with the conservative non-standard finite difference scheme. Presented numerical results show higher resolution near discontinuity without introducing spurious oscillations. Copyright © 2008 John Wiley & Sons, Ltd. [source] Verhalten von hochduktilem Beton unter ImpaktbelastungBETON- UND STAHLBETONBAU, Issue 7 2010Oliver Millon Dipl.-Ing. Baustoffe; Versuche; Dynamische Einwirkungen/Erdbeben Abstract In diesem Aufsatz wird das Materialverhalten von Hochduktilem Beton (engl.: Strain Hardening Cementitious Composite , SHCC) bei Impaktbelastung beschrieben. Dazu werden Ergebnisse aus hochdynamischen Spallations-Experimenten an einem Hopkinson- Bar mit Dehnraten > 140 1/s den Resultaten aus quasi-statischen, zentrischen Zugversuchen mit Dehnraten von 0,001 1/s gegenübergestellt. Die Auswirkungen hoher Dehnraten auf das Materialverhalten erfolgt anhand eines Vergleiches der zentrischen Zugfestigkeit, des E-Moduls sowie der Bruchenergie. Die experimentellen Ergebnisse werden zudem mit den Kennwerten anderer Betone in Beziehung gesetzt. Unterschiede im Materialverhalten werden auf Grundlage von Phänomenen der Rissbildung und des Faserauszuges erklärt. Mechanical Behaviour of SHCC under Impact This paper describes the material behaviour of Strain Hardening Cementitious Composite (SHCC) at high strain rates. The results of high dynamic spall experiments using a Hopkinson Bar at strain rates > 140/sec were arrayed against the results of quasistatic, centric tensile tests at strain rates of 0,001/sec. This comparison is based on the parameters of tensile strength, elastic modulus, and fracture energy of the specimens. In addition, the experimental results of SHCC are related to the characteristic values of other concrete types. Differences in material behaviour are explained by the phenomena of crack formation and fibre pullout force. [source] | |||||||||||||