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Sensitivity Coefficients (sensitivity + coefficient)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

OBSERVATION WELL NETWORK DESIGN FOR PUMPING TESTS IN UNCONFINED AQUIFERS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2003
Xunhong Chen
ABSTRACT: This paper presents a method for determining locations of observation wells to be used in conducting pumping tests in unconfined aquifers. Sensitivity coefficients, the distribution of relative errors, and the correlation coefficients between four aquifer parameters (horizontal and vertical hydraulic conductivities Kr and Kz, storage coefficient S, and specific yield Sy) are used as the criteria for the design of observation well networks and the interpretation of pumping tests. The contours of the relative errors over a vertical profile are very useful in selecting the "best" location of an observation well. Results from theoretical analyses suggest that a wide range of locations is suitable for the determination of Kr and that good locations for the determination of Kz and S may be poorly suited for the determination of Sy. Consideration must be given to the position and lengths of the pumping well screen in the selection of observation well locations. For a given location, the quality of test data can be improved by using high pumping rates and frequent sampling of drawdowns. We found that a minimum of two and preferably three observation locations are needed along a given transect. Results of the four parameters from a single well analysis may contain higher uncertainties. However, composite analyses of multiple observation wells can reduce the correlation between the four aquifer parameters, particularly between Kr and Sy, thus, improving the quality of parameter estimation. Results from two pumping tests conducted at sites located in Nebraska were examined with regard to the proposed methodology. [source]

Explicit calculation of smoothed sensitivity coefficients for linear problems

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2003
R. A. Bia, ecki
Abstract A technique of explicit calculation of sensitivity coefficients based on the approximation of the retrieved function by a linear combination of trial functions of compact support is presented. The method is applicable to steady state and transient linear inverse problems where unknown distributions of boundary fluxes, temperatures, initial conditions or source terms are retrieved. The sensitivity coefficients are obtained by solving a sequence of boundary value problems with boundary conditions and source term being homogeneous except for one term. This inhomogeneous term is taken as subsequent trial functions. Depending on the type of the retrieved function, it may appear on boundary conditions (Dirichlet or Neumann), initial conditions or the source term. Commercial software and analytic techniques can be used to solve this sequence of boundary value problems producing the required sensitivity coefficients. The choice of the approximating functions guarantees a filtration of the high frequency errors. Several numerical examples are included where the sensitivity coefficients are used to retrieve the unknown values of boundary fluxes in transient state and volumetric sources. Analytic, boundary-element and finite-element techniques are employed in the study. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Real-time accelerated interactive MRI with adaptive TSENSE and UNFOLD,

MAGNETIC RESONANCE IN MEDICINE, Issue 2 2003
Michael A. Guttman
Abstract Reduced field-of-view (FOV) acceleration using time-adaptive sensitivity encoding (TSENSE) or unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD) can improve the depiction of motion in real-time MRI. However, increased computational resources are required to maintain a high frame rate and low latency in image reconstruction and display. A high-performance software system has been implemented to perform TSENSE and UNFOLD reconstructions for real-time MRI with interactive, on-line display. Images were displayed in the scanner room to investigate image-guided procedures. Examples are shown for normal volunteers and cardiac interventional experiments in animals using a steady-state free precession (SSFP) sequence. In order to maintain adequate image quality for interventional procedures, the imaging rate was limited to seven frames per second after an acceleration factor of 2 with a voxel size of 1.8 × 3.5 × 8 mm. Initial experiences suggest that TSENSE and UNFOLD can each improve the compromise between spatial and temporal resolution in real-time imaging, and can function well in interactive imaging. UNFOLD places no additional constraints on receiver coils, and is therefore more flexible than SENSE methods; however, the temporal image filtering can blur motion and reduce the effective acceleration. Methods are proposed to overcome the challenges presented by the use of TSENSE in interactive imaging. TSENSE may be temporarily disabled after changing the imaging plane to avoid transient artifacts as the sensitivity coefficients adapt. For imaging with a combination of surface and interventional coils, a hybrid reconstruction approach is proposed whereby UNFOLD is used for the interventional coils, and TSENSE with or without UNFOLD is used for the surface coils. Magn Reson Med 50:315,321, 2003. Published 2003 Wiley-Liss, Inc. [source]

On the effect of pressure on the shear and elongational viscosities of polymer melts

POLYMER ENGINEERING & SCIENCE, Issue 7 2004
Tomas Sedlacek
The effect of pressure and temperature on the shear and elongational deformation rate,dependent viscosities has been experimentally investigated for several polymers (HDPE, LDPE, LLDPE, PP, PC, PMMA, and PS) on a capillary rheometer with a back-pressure device. Pressure, ,, and temperature, ,, coefficients have been determined through simultaneous fitting of the shear and extensional viscosity data by the modified White-Metzner model. The dependence of , and , on temperature and pressure, respectively, was investigated and it has been found that simple relationships exist between pressure and temperature sensitivity coefficients for individual polymers. Polym. Eng. Sci. 44:1328,1337, 2004. © 2004 Society of Plastics Engineers. [source]

THE FAMA-FRENCH MODEL, LEVERAGE, AND THE MODIGLIANI-MILLER PROPOSITIONS

THE JOURNAL OF FINANCIAL RESEARCH, Issue 3 2004
Martin Lally
Abstract For a cost-of-equity model to conform to the Modigliani-Miller cost-of-capital propositions, any sensitivity coefficients in the model must be related to the firm's leverage. In this paper I apply these principles to the Fama-French model for the cost of equity and develop the relation between its sensitivity coefficients and firm leverage. I then examine an empirical process developed by Fama and French (1997) to model the evolution through time of their sensitivity coefficients and show that this empirical process is inconsistent with the Modigliani-Miller propositions. Separable functions are proposed for these sensitivity coefficients that are consistent with the Modigliani-Miller propositions. [source]

Error propagation from prime variables into specific rates and metabolic fluxes for mammalian cells in perfusion culture

BIOTECHNOLOGY PROGRESS, Issue 4 2009
Chetan T. Goudar
Abstract Error propagation from prime variables into specific rates and metabolic fluxes was quantified for high-concentration CHO cell perfusion cultivation. Prime variable errors were first determined from repeated measurements and ranged from 4.8 to 12.2%. Errors in nutrient uptake and metabolite/product formation rates for 5,15% error in prime variables ranged from 8,22%. The specific growth rate, however, was characterized by higher uncertainty as 15% errors in the bioreactor and harvest cell concentration resulted in 37.8% error. Metabolic fluxes were estimated for 12 experimental conditions, each of 10 day duration, during 120-day perfusion cultivation and were used to determine error propagation from specific rates into metabolic fluxes. Errors of the greater metabolic fluxes (those related to glycolysis, lactate production, TCA cycle and oxidative phosphorylation) were similar in magnitude to those of the related greater specific rates (glucose, lactate, oxygen and CO2 rates) and were insensitive to errors of the lesser specific rates (amino acid catabolism and biosynthesis rates). Errors of the lesser metabolic fluxes (those related to amino acid metabolism), however, were extremely sensitive to errors of the greater specific rates to the extent that they were no longer representative of cellular metabolism and were much less affected by errors in the lesser specific rates. We show that the relationship between specific rate and metabolic flux error could be accurately described by normalized sensitivity coefficients, which were readily calculated once metabolic fluxes were estimated. Their ease of calculation, along with their ability to accurately describe the specific rate-metabolic flux error relationship, makes them a necessary component of metabolic flux analysis. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]