Home About us Contact
|
Home About us Contact | ||
|
|
||
Layer Model (layer + model)
Selected AbstractsOn the importance of the reaction between OH and RO2 radicalsATMOSPHERIC SCIENCE LETTERS, Issue 2 2009A. T. Archibald Abstract A new model, BAMBO (Bristol's Atmospheric Marine Boundary layer mOdel), was developed in order to investigate the reaction between peroxy radicals (RO2) and the hydroxyl radical (OH) under typical marine boundary layer (MBL) conditions. The results of this work have shown that the inclusion of the title reaction has negligible effects on inorganic species and ozone but can have significant effects on predicted atmospheric mixing ratios of oxygenated volatile organic compounds (OVOCs), which are generally poorly represented in atmospheric models. This work highlights that the title reaction may be important to modelling trace gas composition in the MBL. However, thorough experimental and theoretical studies are needed to clarify many of the assumptions made. Copyright © 2009 Royal Meteorological Society [source] Hydrogen Balmer Spectrum from a High-Pressure Arc Discharge: RevisitedCONTRIBUTIONS TO PLASMA PHYSICS, Issue 4-5 2007B. Omar Abstract The interpretation of hydrogen Balmer spectra emitted from a high-pressure arc discharge (Radtke and Günther, Contrib. Plasma Phys. 26, 143 (1986)) is re-examined. Assuming local thermodynamic equilibrium, synthetic Balmer spectra are calculated for given temperature and density conditions. Radiation transport is accounted for using a one-dimensional plasma layer model. The lineshape of bound-bound transitions is determined using a microscopic quantum-statistical approach. Free-free and free-bound contributions are added by taking expressions from literature. Comparing the synthetic spectra with experimental ones, plasma temperature and density conditions are inferred. The plasma parameters are confronted with theoretical results for the compositions of dense plasma. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Experimental and analytical study on falling film absorption in smooth and chute low-ribbed tubesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2005Wang Meixia Abstract A mathematical model was applied to falling film absorption outside the smooth and chute low-ribbed tubes to analyze the heat and mass transfer in the absorber. The liquid film outside tubes was assumed to consist of two layers, i.e., internal and external layers. A numerical calculation method was used to solve for the outer layer model of smooth tubes and the chute low-ribbed tubes. An analytical method was employed to solve for the velocity, temperature, and concentration in the internal layer of the tubes mentioned above. A second-order coupling method was adopted to couple the results of the two layers. It was shown that the agreement between the calculation results and the experimental data is high, with all errors assessed at less than 10%. The causes leading to the errors were analyzed. It was concluded that the chute low-ribbed tubes could serve as intensification tubes suitable for use in the absorber of lithium bromide absorption. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(1): 29,39, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20039 [source] Use of neural networks for the prediction of frictional drag and transmission of axial load in horizontal wellboresINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2003Tanvir Sadiq Abstract The use of mud motors and other tools to accomplish forward motion of the bit in extended reach and horizontal wells allows avoiding large amounts of torque caused by rotation of the whole drill string. The forward motion of the drill string, however, is resisted by excessive amount of friction. In the presence of large compressive axial loads, the drill pipe or coiled tubing tends to buckle into a helix in horizontal boreholes. This causes additional frictional drag resisting the transmission of axial load (resulting from surface slack-off force) to the bit. As the magnitude of the frictional drag increases, a buckled pipe may become ,locked-up' making it almost impossible to drill further. In case of packers, the frictional drag may inhibit the transmission of set-up load to the packer. A prior knowledge of the magnitude of frictional drag for a given axial load and radial clearance can help avoid lock-up conditions and costly failure of the tubular. In this study a neural network model, for the prediction of frictional drag and axial load transmission in horizontal wellbores, is presented. Several neural network architectures were designed and tested to obtain the most accurate prediction. After cross-validation of the Back Propagation Neural Network (BPNN) algorithm, a two-hidden layer model was chosen for simultaneous prediction of frictional drag and axial load transmission. A comparison of results obtained from BPNN and General Regression Neural Network (GRNN) algorithms is also presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Perfectly matched layers for transient elastodynamics of unbounded domainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2004Ushnish Basu Abstract One approach to the numerical solution of a wave equation on an unbounded domain uses a bounded domain surrounded by an absorbing boundary or layer that absorbs waves propagating outward from the bounded domain. A perfectly matched layer (PML) is an unphysical absorbing layer model for linear wave equations that absorbs, almost perfectly, outgoing waves of all non-tangential angles-of-incidence and of all non-zero frequencies. In a recent work [Computer Methods in Applied Mechanics and Engineering 2003; 192: 1337,1375], the authors presented, inter alia, time-harmonic governing equations of PMLs for anti-plane and for plane-strain motion of (visco-) elastic media. This paper presents (a) corresponding time-domain, displacement-based governing equations of these PMLs and (b) displacement-based finite element implementations of these equations, suitable for direct transient analysis. The finite element implementation of the anti-plane PML is found to be symmetric, whereas that of the plane-strain PML is not. Numerical results are presented for the anti-plane motion of a semi-infinite layer on a rigid base, and for the classical soil,structure interaction problems of a rigid strip-footing on (i) a half-plane, (ii) a layer on a half-plane, and (iii) a layer on a rigid base. These results demonstrate the high accuracy achievable by PML models even with small bounded domains. Copyright © 2004 John Wiley & Sons, Ltd. [source] Simplified solution of developing laminar forced flow between parallel platesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2002Esmail M. A. Mokheimer Abstract A simplified simulation for developing laminar forced flow in the entrance region between two parallel plates is presented. This simulation is based on an implicit finite difference numerical representation of a boundary layer model describing the flow in the entry region. This boundary layer model comprises the two conservation equations of mass and momentum. A non-iterative implicit numerical scheme is developed to convert the partial differential form of these governing equations into algebraic equations. The resultant algebraic equations have been solved simultaneously via a simplified simulation using spreadsheet programs as well as a Fortran code for the sake of comparison. The numerically obtained developing axial velocity profile at large distance downstream of the entrance shows excellent agreement with the available fully developed analytical profile. Comparison between the abilities of the spreadsheet simulation with other high-level programming languages is outlined. Copyright © 2002 John Wiley & Sons, Ltd. [source] The influence of pH and digestion with commercial enzymes on calcium adsorption in casabeINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2006Petra Beatriz Navas Summary The Ca2+ binding capacity of a sample of casabe made from cassava (Manihot esculenta) was evaluated by using adsorption isotherms after a digestion process with commercial enzymes. It was found that enzymatic treatment increased the ability of vegetable material to retain calcium and to release endogenous mineral ions as a consequence of possible modifications to the carbohydrate matrix. Untreated casabe did not release mineral ions. pH also influenced the retention of Ca2+: at pH 4.5 release was the main process but adsorption increases with alkalinity up to pH 8.5. The Ca concentrations at which neither adsorption nor release occurred [Ca2+]e were as follows: 5.2 mm (pH 4.5), 3.5 mm (pH 7.1), and 0.63 mm (pH 8.5). The pH effect was explained by an increase in the density of negatively charged functional groups produced by ionization reactions at pH below the point of zero net charge (pHo) which was evaluated by using the Gouy,Chapman double layer model. Values of pHo were 6.4 for raw material and 4.1 after digestion with enzymes. In both cases, the density of positively charged sites below pHo was much higher that the density of negatively charged sites above pHo. [source] Cation Ordering and Domain Boundaries in Ca[(Mg1/3Ta2/3)1,xTix]O3 Microwave Dielectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Mao Sen Fu Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1,xTix]O3 (x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111)c plane with a projected displacement vector in the ,001,c direction and ferroelastic domain boundaries parallel to the ,100,c direction. [source] Effect of Surface-Active Substances on the Rheological Properties of Silicon Carbide Suspensions in ParaffinJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Reinhard Lenk In this paper, the possibility of stabilization of SiC suspensions in paraffin (hot-molding slips) was investigated from the colloid science point of view. By considering the surface properties of finely dispersed silicon carbide, surface-active agents (fatty amine and alkylsuccinimide) which are suitable for surface modification by chemical adsorption on SiC were selected. Adsorption of fatty amines and alkylsuccinimide was carried out in model experiments in chloroform. Increasing the length of the carbon,hydrogen chain caused the adsorption to decrease, and the adsorption area of one molecule in the saturated adsorption layer to increase. The stabilizing effect of surface-active agents resulted in improved flow behavior of hot-molding slips. The efficiency of surface-active agents increased with increased adsorption layer thickness. In highly concentrated SiC hot-molding slips, a combination of alkylsuccinimide and fatty amine proved to be very efficient. This synergistic effect of long- and short-chained surface-active agents is discussed in terms of an adsorption layer model. [source] Heat transfer at high energy devices with prescribed cooling flowMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 4 2007Jens Breuer Abstract We study the heat transfer from a high-energy electric device into a surrounding cooling flow. We analyse several simplifications of the model to allow an easier numerical treatment. First, the flow variables velocity and pressure are assumed to be independent from the temperature which allows a reduction to Prandtl's boundary layer model and leads to a coupled nonlinear transmission problem for the temperature distribution. Second, a further simplification using a Kirchhoff transform leads to a coupled Laplace equation with nonlinear boundary conditions. We analyse existence and uniqueness of both the continuous and discrete systems. Finally, we provide some numerical results for a simple two-dimensional model problem. Copyright © 2006 John Wiley & Sons, Ltd. [source] Transmission Fluctuation Spectrometry in Concentrated Suspensions Part Two: Particle OverlappingPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2004Ulrich Riebel Abstract Transmission fluctuations measured on a flowing suspension of particles with a high spatial and temporal resolution can be used to measure the particle size distribution and particle concentration. The theory of transmission fluctuation spectrometry (TFS) was recently developed, whereby the statistical behavior of the entire suspension is described on the basis of a single monolayer, in combination with a layer model describing the suspension as a series of independent monolayers. As the monolayers are assumed to be statistically independent from each other, the transmission through the 3-dimensional suspension is modeled as the product of transmissions through the monolayers. [source] Structure, genesis and scale selection of the tropical quasi-biweekly modeTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 599 2004Piyali Chatterjee Abstract The quasi-biweekly mode (QBM) and the 30,60 day mode are two major intraseasonal oscillations (ISOs) in the tropics. The QBM is known to have a major influence in determining the active and break conditions of the Indian monsoon during the northern summer. A westward-propagating equatorial Rossby wave with quasi-biweekly period influences the Australian monsoon during the northern winter. Universality between the summer and winter QBM is established through analysis of daily circulation and convection data for 10 years. It is shown that the mean spatial structure of the QBM in circulation and convection resembles that of a gravest meridional mode equatorial Rossby wave with wavelength of about 6000 km and westward phase speed of approximately 4.5 m s,1. However, the maximum zonal wind occurs at around 5°N (5°S) during the northern summer (winter). The wave structure appears to be translated northward (southward) by about 5° during the northern summer (winter). The relationship between outgoing long-wave radiation and circulation data indicates that the mode is driven unstable by coupling with moist convection. Similarity in temporal and spatial characteristics of the mode during the two seasons leads us to propose that the same mechanism governs the genesis and scale selection of the mode in both the seasons. An acceptable mechanism for genesis and scale selection of the QBM has been lacking. In the present study, a mechanism for genesis and scale selection of the observed QBM is proposed. A simple 2½-layer model that includes a steady Ekman boundary layer (BL) formulation incorporating effect of entrainment mixing is constructed for the convectively coupled equatorial waves. Without influence of the background mean flow, moist feedback in the presence of frictional BL convergence drives the gravest meridional mode equatorial Rossby wave unstable with observed wavelength and period but with zonal winds symmetric about the equator. Potential temperature perturbation associated with the Rossby wave is in phase with relative vorticity perturbation at low level. The BL drives moisture convergence in phase with the relative vorticity at the top of the BL. Release of latent heat associated with the BL convergence enhances the potential temperature leading to a positive feedback. The mean flow over the Indian Ocean and western Pacific at low levels is such that the zero ambient absolute vorticity or the ,dynamic equator' shifts to around 5°N (5°S) during summer (winter) and results in a shift of the unstable Rossby waves towards the north (south) by about 5°. The resulting structure of the unstable Rossby mode resembles the observed structure of the biweekly mode. It is shown that neither evaporation,wind feedback nor vertical shear of the mean flow is crucial for the existence of the mode. However these processes marginally modify the growth rate and make the structure of the unstable wave more realistic. Copyright © 2004 Royal Meteorological Society [source] Evaluation of Intrinsic Ionization and Complexation Constants of TiO2 and Mg-Fe Hydrotalcite-like CompoundsCHINESE JOURNAL OF CHEMISTRY, Issue 10 2006Wan-Guo Hou Abstract The intrinsic surface reaction constants, pKinta1, pKinta2, p*KintC and p*KintA, were evaluated by a modified double extrapolation (MDE) for TiO2 without structural charge and Mg-Fe hydrotalcite-like compounds (HTlc) with structural charge, respectively. The results of intrinsic surface reaction constants for TiO2 were compared with those obtained by class double extrapolation (CDE) in literature. Furthermore, the values of intrinsic surface reaction constants obtained by MDE were used to simulate the charging behaviors of the materials. The following conclusions were obtained. For TiO2 without structural charge, the pKinta1 and pKinta2 evaluated by MDE are equal to those by CDE, however the p*KintC and p*KintA evaluated by MDE are much different from those by CDE. In principle, the results of the p*KintC and p*KintA evaluated by MDE are more accurate than those by CDE. The values of intrinsic surface reaction constants obtained by MDE can excellently simulate the charging curves for TiO2 with the triple layer model (TLM). For HTlc with positive structural charge, the results of *KintC=0 and *KintA,, were obtained by MDE, which means the inert electrolyte chemical binding does not exist; the point of zero net charge (PZNC) of c -independence also exist as the same as solid without structural charge, and the pHPZNC obtained by the acid-base titration can excellently be simulated and the surface charging tendency can be simulated to a great extent using the pKinta1 and pKinta2 evaluated by MDE and the diffuse layer model (DLM). [source] | |||||||||||||||||||