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Variable Values (variable + value)
Selected AbstractsModelling for an expert system and a parameter validation methodEXPERT SYSTEMS, Issue 5 2002A. Chatzinikolaou A model,based engineering diagnostic method is typically based on the evaluation of the residuals generated from a comparison of important variable values from a simulated system and the corresponding measured values from the system's performance. Consequently, a model should describe the dynamic behaviour of the system as accurately as possible using suitably selected parameter values. This implies the need for validation of the performance of the model by comparison with the measurements of the actual system. This process is especially important when the detection of faults is performed in real,time conditions. In this paper, the modelling process for hydraulic systems as well as a new parameter validation method that has been developed using the DASYLab data acquisition and control software for the estimation of the uncertain parameter values of the model is presented. This model validation process led to the establishment of a model,based expert system that is able to diagnose real,time faults working in parallel with actual dynamic industrial automated processes. [source] Topographic parameterization in continental hydrology: a study in scaleHYDROLOGICAL PROCESSES, Issue 18 2003Robert N. Armstrong Abstract Digital elevation models (DEMs) are useful and popular tools from which topographic parameters can be quickly and efficiently extracted for various hydrologic applications. DEMs coupled with automated methods for extracting topographic information provide a powerful means of parameterizing hydrologic models over a wide range of scales. However, choosing appropriate DEM scales for particular hydrologic modelling applications is limited by a lack of understanding of the effects of scale and grid resolution on land-surface representation. The scale effects of aggregation on square-grid DEMs of two continental-scale basins are examined. Base DEMs of the Mackenzie and Missouri River basins are extracted from the HYDRO1k DEM of North America. Successively coarser grids of 2, 4, 8, , 64 km were generated from the ,base' DEMs using simple linear averaging. TOPAZ (Topographic Parameterization) was applied to the base and aggregated DEMs using constant critical source area and minimum source channel length values to extract topographic variables at varying scales or resolutions. The effects of changing DEM resolution are examined by considering changes in the spatial distribution and statistical properties of selected topographic variables of hydrological importance. The effects of increasing grid size on basin and drainage network delineation, and derived topographic variables, tends to be non-linear. In particular, changes in overall basin extent and drainage network configuration make it impractical to apply a simple scaling function to estimate variable values for fine-resolution DEMs from those derived from coarse-resolution DEMs. Results also suggest the resolution to which a DEM can be reduced by aggregation and still provide useful topographic information for continental-scale hydrologic modelling is that at which the mean hydraulic slope falls to approximately 1%. In this study, that generally occurred at a resolution of about 10 km. Copyright © 2003 John Wiley & Sons, Ltd. [source] A hybrid immersed boundary and material point method for simulating 3D fluid,structure interaction problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008Anvar Gilmanov Abstract A numerical method is developed for solving the 3D, unsteady, incompressible Navier,Stokes equations in curvilinear coordinates containing immersed boundaries (IBs) of arbitrary geometrical complexity moving and deforming under forces acting on the body. Since simulations of flow in complex geometries with deformable surfaces require special treatment, the present approach combines a hybrid immersed boundary method (HIBM) for handling complex moving boundaries and a material point method (MPM) for resolving structural stresses and movement. This combined HIBM & MPM approach is presented as an effective approach for solving fluid,structure interaction (FSI) problems. In the HIBM, a curvilinear grid is defined and the variable values at grid points adjacent to a boundary are forced or interpolated to satisfy the boundary conditions. The MPM is used for solving the equations of solid structure and communicates with the fluid through appropriate interface-boundary conditions. The governing flow equations are discretized on a non-staggered grid layout using second-order accurate finite-difference formulas. The discrete equations are integrated in time via a second-order accurate dual time stepping, artificial compressibility scheme. Unstructured, triangular meshes are employed to discretize the complex surface of the IBs. The nodes of the surface mesh constitute a set of Lagrangian control points used for tracking the motion of the flexible body. The equations of the solid body are integrated in time via the MPM. At every instant in time, the influence of the body on the flow is accounted for by applying boundary conditions at stationary curvilinear grid nodes located in the exterior but in the immediate vicinity of the body by reconstructing the solution along the local normal to the body surface. The influence of the fluid on the body is defined through pressure and shear stresses acting on the surface of the body. The HIBM & MPM approach is validated for FSI problems by solving for a falling rigid and flexible sphere in a fluid-filled channel. The behavior of a capsule in a shear flow was also examined. Agreement with the published results is excellent. Copyright © 2007 John Wiley & Sons, Ltd. [source] Design techniques of two-layer architectures for WDM optical networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2001Andrea Borella Abstract A general method for designing multilayered WDM optical networks, based on the combined use of single-and multi-hop connection modes, is presented. It takes into account variable values for the number of users and wavelengths in each cluster. Closed form expressions are derived for the transmission capacity and the optimum number of channels for intra-cluster communications, either in the case of uniform or non-uniform traffic distribution. The analytical approach is particularly useful in the presence of constraints on the number of wavelengths, due to technological limits or non-linear phenomena, when sub-optimal solutions must be necessarily addressed. The proposed method is integrated with the adoption of well-known selection procedures, like simulated annealing or genetic algorithms, to reduce the computational effort. Copyright © 2001 John Wiley & Sons, Ltd. [source] ELECTRONEUROGRAPHY IN GUILLAIN-BARRE, SYNDROME (GBS): SENSITIVITY AND SPECIFICITYJOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 1 2000G. Iuliano We assessed clinical sensitivity and specificity of different electroneurographic (ENG) parameters versus clinical diagnosis of GBS. Clinical data of 24 patients affected by upper and lower limb neuropathy were revised. In all the patients the neurophysiologic examination was performed according to the AAEM guidelines for GBS diagnosis. Fourteen patients (10 males, mean age 47.9, range 13-70, and 4 females 71.5, 69,76) received a diagnosis of GBS. The non-GBS group included nine males (59.11, 35,78) and one female (41 years) with different neuropathies (3 diabetic, 2 alcoholic, 5 unknown ethiology). Sensitivity and specificity of various neurophysiologic parameters were calculated. The single classical neurophysiological paremeters gave variable values of sensitivity and specificity. The new variables we introduced, Polineuropathy (diffusion of abnormal findings and F - Wave latency) and Demyelination (distal motor evoked potential amplitude and/or motor conduction blocks) gave the highest value of sensitivity and specificity, when associated. [source] Colloids decrease clot propagation and strength: role of factor XIII-fibrin polymer and thrombin,fibrinogen interactionsACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 8 2005V. G. Nielsen Colloid-mediated hypocoagulability is clinically important, but the mechanisms responsible for coagulopathy have been incompletely defined. Thus, my goal was to elucidate how colloids decrease plasma coagulation function. Plasma was diluted 0% or 40% with 0.9% NaCl, three different hydroxyethyl starches (HES, mean molecular weight 450, 220 or 130 kDa), or 5% human albumin. Samples (n = 6 per condition) were activated with celite, and diluted samples had either no additions or addition of fibrinogen (FI), thrombin (FIIa) or activated Factor XIII (FXIIIa) to restore protein function to prediluted values. Thrombelastographic variables measured included clot propagation (angle, ,), and clot strength (amplitude, A; or shear elastic modulus, G). Dilution with 0.9% NaCl significantly decreased ,, A and G -values compared to undiluted samples. Supplementation with FI, but not FIIa or FXIIIa, resulted in 0.9% NaCl-diluted thrombelastographic variable values not different from those of undiluted samples. FI supplementation of HES 450, HES 220, HES 130 and albumin-diluted samples only partially restored ,, A and G -values compared to undiluted samples. FIIa addition only improved clot propagation and strength in albumin-diluted samples. FXIIIa supplementation improved propagation in samples diluted with HES 450, HES 220 and albumin, and clot strength improved in HES 450 and albumin-diluted plasma. Considered as a whole, these data support compromise of FIIa-FI and FXIIIa , fibrin polymer interactions as the mechanisms by which colloids compromise plasma coagulation. Investigation to determine if clinical enhancement of FXIII activity and/or FI concentration (e.g. fresh-frozen plasma, cryoprecipitate) can attenuate colloid-mediated decreases in hemostasis is warranted. [source] Exploring the possibility of enhancing the bandwidth of ,-negative metamaterials by employing tunable varactorsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2007Andrea Alù Abstract We analyze here the performance of ,-negative metamaterials in different configurations at microwave and optical frequencies that employ variable values of capacitances or tunable varactors, with the purpose of increasing their bandwidth of operation. The proposed method shows moderately good results both in resonant-like and in transmission-line configurations. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 55,59, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22036 [source] | |||||||||||||