SENSITIVITY Analysis | Academic Articles

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Posts Tagged ‘SENSITIVITY analysis’

Sensitivity analysis of the magflow cellular automaton model for lava flow simulation

Abstract: MAGFLOW is a physics-based numerical model for lava flow simulations based on the Cellular Automaton approach that has been successfully used to predict the lava flow paths during the recent eruptions on Mt Etna. We carried out an extensive sensitivity analysis of the physical and rheological parameters that control the evolution function of the automaton and which are measured during eruptive events, in an effort to verify the reliability of the model and improve its applicability to scenario forecasting. The results obtained, which include Sobol” sensitivity indices computed using polynomial chaos expansion, confirm the consistency of MAGFLOW with the underlying physical model and identify water content and solidus temperature as critical parameters for the automaton. Additional tests also indicate that flux rates can have a strong influence on the emplacement of lava flows, and that to obtain more accurate simulations it is better to have continuous monitoring of the effusion rates, even if with moderate errors, rather than sparse accurate measurements. [Copyright &y& Elsevier]

July 6, 2012 Tags: CELLULAR automata, CHAOTIC behavior in systems, COMPUTER simulation, LAVA flows, MATHEMATICAL models, PARAMETER estimation, SENSITIVITY analysis, TEMPERATURE effect
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Reanalysis of a global soil database for crop and environmental modeling

Abstract: There is an increased need for detailed soil information that can be used for applications of crop and environmental modeling. The goal of this project was to conduct a reanalysis of the ISRIC-WISE 1.1 Soil Profile Dataset. As part of the procedures, the soil reanalysis database was fitted to the standard formats of the International Consortium for Agricultural Systems Application (ICASA). Thus, the soil reanalysis database tailors dynamic crop models such as the Cropping System Model (CSM) of the Decision Support System for Agrotechnology Transfer (DSSAT). During the reanalysis, the physical and chemical parameters of the soil profiles were revised and estimated, where necessary and possible, using pre-established ranges given by the literature and correlations among other more stable variable. To evaluate each of the 3404 reanalyzed soil profiles, the CSM-CERES-Maize model was run for a standard crop management scenario using both the original and the new improved soil databases. Nine hundred seventy-eight soil profiles were considered to be not useful during the reanalysis due to missing values for one or more critical variables and were, therefore, not considered for quality control procedures. A pre-diagnostic for only nitrogen and soil organic carbon in the original dataset showed 70% and 5% of missing values respectively. A sensitivity analysis based on crop simulations comparing the original and the reanalyzed soil databases, showed that 1294 soil profiles yielded different results due to improvement of either the original data or improved conversion procedures. The details and considerations for detecting missing and erroneous values and for estimating soil variable values are presented in this paper for further use. The final soil reanalysis global database contains 3404 soil profiles and is available at https://harvestchoice.wufoo.com/forms/download-wisol. [Copyright &y& Elsevier]

July 5, 2012 Tags: COMPUTER simulation, CORRELATION (Statistics), CROP management, CROPS -- Effect of soil acidity on, DATABASES, DECISION support systems, ENVIRONMENTAL impact analysis, SENSITIVITY analysis, SOIL profiles, SOILS -- Carbon content
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How to compute variance-based sensitivity indicators with your spreadsheet software

Abstract: The use of sensitivity indicators is explicitly recommended by authorities like the EC, the US EPA and others in model valuation and audit. In this note, we want to draw the attention to a numerically efficient algorithm that computes first order global sensitivity effects from given data using a discrete cosine transformation. [Copyright &y& Elsevier]

June 22, 2012 Tags: ALGORITHMS, ANALYSIS of variance, COMPUTER software, DATA analysis, DISCRETE cosine transforms, ELECTRONIC spreadsheets, MATHEMATICAL models, SENSITIVITY analysis
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Applying high-power lasers in perforating oil and gas wells: sensitivity analysis of laser-related parameters during laser perforation in sandstone

Laser perforation is one of the newest techniques recommended as an alternative for the conventional explosive shaped charge perforating methods in oil and gas wells. Considerable permeability increase and no need to have costly post-perforation operations to reduce the effect of formation damage caused by current perforation methods are the most important priorities of laser perforation over the conventional explosive shaped charges. In this paper a neural network approach has been applied for backward elimination sensitivity analysis of laser-related parameters during laser perforation in sandstone. For this purpose a feed-forward with back-propagation neural network was developed that predicted the volume removed due to laser power, lasing time and pulsation. The data is related to around 110 laser perforation laboratory tests on sandstone core samples. Finally, sensitivity analysis was done and the effectiveness of each laser-related parameter was determined. [ABSTRACT FROM AUTHOR]

May 19, 2012 Tags: GAS wells, HOLES, NEURAL networks (Computer science), OIL wells, PULSATION (Electronics), SANDSTONE, SENSITIVITY analysis
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Automatic segmentation of dermoscopy images using histogram thresholding on optimal color channels

Automatic segmentation of skin lesions is the first step towards development of a computer-aided diagnosis of melanoma. Although numerous segmentation methods have been developed, few studies have focused on determining the most discriminative and effective color space for melanoma application. This paper proposes a novel automatic segmentation algorithm using color space analysis and clustering-based histogram thresholding, which is able to determine the optimal color channel for segmentation of skin lesions. To demonstrate the validity of the algorithm, it is tested on a set of 30 high resolution dermoscopy images and a comprehensive evaluation of the results is provided, where borders manually drawn by four dermatologists, are compared to automated borders detected by the proposed algorithm. The evaluation is carried out by applying three previously used metrics of accuracy, sensitivity, and specificity and a new metric of similarity. Through ROC analysis and ranking the metrics, it is shown that the best results are obtained with the X and XoYoR color channels which results in an accuracy of approximately 97%. The proposed method is also compared with two state-of the- art skin lesion segmentation methods, which demonstrates the effectiveness and superiority of the proposed segmentation method. [ABSTRACT FROM AUTHOR]

May 1, 2012 Tags: COMPUTER-aided design, DIAGNOSIS, IMMUNOSPECIFICITY, MELANOMA, SENSITIVITY analysis, SKIN -- Wounds & injuries
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Examining interior grid nudging techniques using two-way nesting in the wrf model for regional climate modeling

This study evaluates interior nudging techniques using the Weather Research and Forecasting (WRF) model for regional climate modeling over the conterminous United States (CONUS) using a two-way nested configuration. NCEP-Department of Energy Atmospheric Model Intercomparison Project (AMIP-II) Reanalysis (R-2) data are downscaled to 36 km × 36 km by nudging only at the lateral boundaries, using gridpoint (i.e., analysis) nudging and using spectral nudging. Seven annual simulations are conducted and evaluated for 1988 by comparing 2-m temperature, precipitation, 500-hPa geopotential height, and 850-hPa meridional wind to the 32-km North American Regional Reanalysis (NARR). Using interior nudging reduces the mean biases for those fields throughout the CONUS compared to the simulation without interior nudging. The predictions of 2-m temperature and fields aloft behave similarly when either analysis or spectral nudging is used. For precipitation, however, analysis nudging generates monthly precipitation totals, and intensity and frequency of precipitation that are closer to observed fields than spectral nudging. The spectrum of 250-hPa zonal winds simulated by the WRF model is also compared to that of the R-2 and NARR. The spatial variability in the WRF model is reduced by using either form of interior nudging, and analysis nudging suppresses that variability more strongly than spectral nudging. Reducing the nudging strengths on the inner domain increases the variability but generates larger biases. The results support the use of interior nudging on both domains of a two-way nest to reduce error when the inner nest is not otherwise dominated by the lateral boundary forcing. Nevertheless, additional research is required to optimize the balance between accuracy and variability in choosing a nudging strategy. [ABSTRACT FROM AUTHOR]

April 1, 2012 Tags: CLIMATIC changes, METEOROLOGY, PRECIPITATION (Meteorology), SENSITIVITY analysis, WEATHER forecasting
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Multi heart-cutting two-dimensional liquid chromatography–atmospheric pressure photoionization-tandem mass spectrometry method for the determination of endocrine disrupting compounds in water

Abstract: The multi-heart-cutting two-dimensional liquid chromatography–tandem mass spectrometry method using atmospheric pressure photoionization has been developed and successfully validated for the determination of nine endocrine disrupting compounds in river water. The method is based on the use of two different reverse-phase columns connected through a six-port two-position switching valve equipped with a 200μl loop. An orthogonal separation was achieved by proper selection of stationary phases, mobile phases, and the use of a gradient elution in both dimensions. The method shows excellent performance in terms of accuracy (86.2–111.1%), precision (intra-batch: 6.7–11.2%, inter-batch: 7.2–13.5%), and sensitivity (1.2–7.1ngl−1). Twenty real samples collected from the Loučka and the Svratka rivers were analyzed, the studied compounds were found in all Svratka samples (9.7–11.2ngl−1 for β-estradiol, 7.6–9.3ngl−1 for estrone, and 24.6–38.7ngl−1 for bisphenol A). [Copyright &y& Elsevier]

March 1, 2012 Tags: ATMOSPHERIC pressure, ENDOCRINE disruptors, LIQUID chromatography, PHOTOIONIZATION, SENSITIVITY analysis, SEPARATION (Technology), TANDEM mass spectrometry, WATER -- Analysis
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Superplastic behavior of ti–6al–4v–0.1b alloy

Abstract: The superplastic behavior of Ti–6Al–4V–0.1B sheet was evaluated. The strain rate sensitivity (m) is ≥0.47 in the temperature range 775–900°C and at strain rate, The material exhibits tensile elongations>200% in the temperature range 725–950°C at The optimum superplastic forming temperature is 900°C, which is similar to conventional Ti–6Al–4V. However, a lower flow stress is needed in the case of Ti–6Al–4V–0.1B. The superplastic deformation mechanism is suggested from estimates of activation energy to be grain boundary sliding (GBS) accommodated by dislocation motion along grain boundaries at and is diffusion-controlled dislocation climb at Microstructural observations also confirm that GBS is the operating deformation mechanism at 900°C and [Copyright &y& Elsevier]

March 1, 2012 Tags: DEFORMATIONS (Mechanics), DISLOCATIONS in crystals, GRAIN boundaries, SENSITIVITY analysis, STRAINS & stresses, SUPERPLASTICITY, TEMPERATURE effect, TITANIUM alloys
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Constitutive formation of an rxfp1-signalosome: a novel paradigm in gpcr function and regulation

The classical second messenger cAMP is important in diverse physiological processes, where its spatial and temporal compartmentalization allows precise control over multiple cellular events. Within this context, G-protein-coupled receptors (GPCRs) govern specialized pools of cAMP, which are functionally specific for the unique cellular effects attributed to a particular system. The relaxin receptor, RXFP1, is a GPCR that exerts pleiotropic physiological effects including a potent anti-fibrotic response, increased cancer metastases, and has efficacy as a vasodilator in heart failure. On a cellular level, relaxin stimulation of RXFP1 results in the activation of multiple G-protein pathways affecting cAMP accumulation. Specificity and diversity in the cAMP signal generated by RXFP1 is controlled by differential G-protein coupling dependent upon the background of cellular expression, and cAMP compartmentalization. Further complexity in cAMP signalling results from the constitutive assembly of an RXFP1-signalosome, which specifically responds to low concentrations of relaxin, and activates a distinct cAMP pathway. The RXFP1-signalosome is a higher-order protein complex that facilitates receptor sensitivity to attomolar concentration of peptide, exhibits constitutive activity and dual coupling to G-proteins and β-arrestins and reveals a concentration-biased agonism mediated by relaxin. The specific and directed formation of GPCR-centered signalosomes allows an even greater spatial and temporal control of cAMP, thus rationalizing the considerable physiological scope of this ubiquitous second messenger. LINKED ARTICLES This article is part of a themed section on the Molecular Pharmacology of G Protein-Coupled Receptors (GPCRs). To view the other articles in this section visit . To view the 2010 themed section on the same topic visit [ABSTRACT FROM AUTHOR]

March 1, 2012 Tags: CELLULAR signal transduction, GENETIC regulation, MOLECULAR pharmacologyG protein coupled receptors, SECOND messengers (Biochemistry), SENSITIVITY analysis, VASODILATORS
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Discrete surprises in the computation of sensitivities from boundary integrals in the continuous adjoint approach to inviscid aerodynamic shape optimization

Abstract: The computation of flow sensitivities for shape optimization in flow problems using continuous adjoint-based boundary integrals reduces the computational costs and makes the scheme independent of the numerical solvers. However, certain analytic manipulations involved in the boundary formulation of the gradients do not hold valid at the discrete level near geometric singularities and lead to inconsistencies in the sensitivities, which add to already known mesh sensitivity issues at the same locations. Both questions appear to be relevant for inviscid flow problems only. These matters are examined and detailed numerical testing is performed on several conventional flow configurations. [Copyright &y& Elsevier]

March 1, 2012 Tags: AERODYNAMICS, BOUNDARY layer, INVISCID flow, NUMERICAL analysis, SENSITIVITY analysis, SINGULARITIES (Mathematics), STRUCTURAL optimization
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