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Quantitative Accuracy (quantitative + accuracy)
Selected AbstractsLarge eddy simulation of flow and scalar transport in a round jetHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2004Hitoshi Suto Abstract Large eddy simulation (LES) was performed for a spatially developing round jet and its scalar transport at four steps of Reynolds number set between 1200 and 1,000,000. A simulated domain, which extends 30 times the nozzle diameter, includes initial, transitional, and established stage of jet. A modified version of convection outflow condition was proposed in order to diminish the effect of a downstream boundary. Tested were two kinds of subgrid scale (SOS) models: a Smagorinsky model (SM) and a dynamic Smagorinsky model (DSM). In the former model, parameters are kept at empirically deduced constants, while in the latter, they are calculated using different levels of space filtering. Data analysis based on the decay law of jet clearly presented the performance of SGS models. Simulated results by SM and DSM compared favorably with existing measurements of jet and its scalar transport. However, the quantitative accuracy of DSM was better than that of SM at a transitional stage of flow field. Computed parameters by DSM, coefficient for SGS stresses, CR and SGS eddy diffusivity ratio, ,SGS, were not far from empirical constants of SM. Optimization of the model coefficient was suggested in DSM so that coefficient CR was nearly equal in the established stage of jet but it was reduced in low turbulence close to the jet nozzle. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 175,188, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20001 [source] A valence bond study of the dioxygen moleculeJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2007Peifeng Su Abstract The dioxygen molecule has been the subject of valence bond (VB) studies since 1930s, as it was considered as the first "failure" of VB theory. The object of this article is to provide an unambiguous VB interpretation for the nature of chemical bonding of the molecule by means of modern VB computational methods, VBSCF, BOVB, and VBCI. It is shown that though the VBSCF method can not provide quantitative accuracy for the strongly electronegative and electron-delocalized molecule because of the lack of dynamic correlation, it still gives a correct qualitative analysis for wave function of the molecule and provides intuitive insights into chemical bonding. An accurate quantitative description for the molecule requires higher levels of VB methods that incorporate dynamic correlation. The potential energy curves of the molecule are computed at the various VB levels. It is shown that there exists a small hump in the PECs of VBSCF for the ground state, as found in previous studies. However, higher levels of VB methods dissolve the hump. The BOVB and VBCI methods reproduce the dissociation energies and other physical properties of the ground state and the two lowest excited states in very good agreement with experiment and with sophisticated MO based methods, such as the MRCI method. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] CHARMM fluctuating charge force field for proteins: I parameterization and application to bulk organic liquid simulationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2004Sandeep Patel Abstract A first-generation fluctuating charge (FQ) force field to be ultimately applied for protein simulations is presented. The electrostatic model parameters, the atomic hardnesses, and electronegativities, are parameterized by fitting to DFT-based charge responses of small molecules perturbed by a dipolar probe mimicking a water dipole. The nonbonded parameters for atoms based on the CHARMM atom-typing scheme are determined via simultaneously optimizing vacuum water-solute geometries and energies (for a set of small organic molecules) and condensed phase properties (densities and vaporization enthalpies) for pure bulk liquids. Vacuum solute-water geometries, specifically hydrogen bond distances, are fit to 0.19 Å r.m.s. error, while dimerization energies are fit to 0.98 kcal/mol r.m.s. error. Properties of the liquids studied include bulk liquid structure and polarization. The FQ model does indeed show a condensed phase effect in the shifting of molecular dipole moments to higher values relative to the gas phase. The FQ liquids also appear to be more strongly associated, in the case of hydrogen bonding liquids, due to the enhanced dipolar interactions as evidenced by shifts toward lower energies in pair energy distributions. We present results from a short simulation of NMA in bulk TIP4P-FQ water as a step towards simulating solvated peptide/protein systems. As expected, there is a nontrivial dipole moment enhancement of the NMA (although the quantitative accuracy is difficult to assess). Furthermore, the distribution of dipole moments of water molecules in the vicinity of the solutes is shifted towards larger values by 0.1,0.2 Debye in keeping with previously reported work. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 1,15, 2004 [source] Gamma-SLAM: Visual SLAM in unstructured environments using variance grid mapsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2009Tim K. Marks This paper describes an online stereo visual simultaneous localization and mapping (SLAM) algorithm developed for the Learning Applied to Ground Robotics (LAGR) program. The Gamma-SLAM algorithm uses a Rao,Blackwellized particle filter to obtain a joint posterior over poses and maps: the pose distribution is estimated using a particle filter, and each particle has its own map that is obtained through exact filtering conditioned on the particle's pose. Visual odometry is used to provide good proposal distributions for the particle filter, and maps are represented using a Cartesian grid. Unlike previous grid-based SLAM algorithms, however, the Gamma-SLAM map maintains a posterior distribution over the elevation variance in each cell. This variance grid map can capture rocks, vegetation, and other objects that are typically found in unstructured environments but are not well modeled by traditional occupancy or elevation grid maps. The algorithm runs in real time on conventional processors and has been evaluated for both qualitative and quantitative accuracy in three outdoor environments over trajectories totaling 1,600 m in length. © 2008 Wiley Periodicals, Inc. [source] Is In Vivo Nuclear Magnetic Resonance Spectroscopy Currently a Quantitative Method for Whole-body Carbohydrate Metabolism?NUTRITION REVIEWS, Issue 10 2000Elizabeth Murphy M.D., Ph.D. In vivo nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for noninvasive metabolic research. NMR studies of tissue glycogen metabolism and glucose utilization have generated results with major implications for normal glucose homeostasis and the pathophysiology of type 2 diabetes mellitus. A key question for clinicians and physiologists reading these highly technical studies is: How accurate for whole-body carbohydrate metabolism is NMR spectroscopy? We review this topic and discuss technical, metabolic, and interpretive factors that may limit quantitative accuracy of this modality. We conclude that seeing is not yet believing regarding in vivo NMR spectroscopy; there are still important limitations to quantification of whole-body carbohydrate metabolism. [source] A MS data search method for improved 15N-labeled protein identificationPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 17 2009Yaoyang Zhang Abstract Quantitative proteomics using stable isotope labeling strategies combined with MS is an important tool for biomarker discovery. Methods involving stable isotope metabolic labeling result in optimal quantitative accuracy, since they allow the immediate combination of two or more samples. Unfortunately, stable isotope incorporation rates in metabolic labeling experiments using mammalian organisms usually do not reach 100%. As a consequence, protein identifications in 15N database searches have poor success rates. We report on a strategy that significantly improves the number of 15N-labeled protein identifications and results in a more comprehensive and accurate relative peptide quantification workflow. [source] | |||||||||||||