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Experimental Uncertainty (experimental + uncertainty)
Selected AbstractsRate constants for the gas-phase reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals at 250,430 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2004L. Chen The rate constants k1 for the reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250,430 K using the flash photolysis,laser-induced fluorescence (FP-LIF) technique and the laser photolysis,laser-induced fluorescence (LP-LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253,328 K in an 11.5-dm3 reaction chamber with either CHF2Cl or CH2FCF3 as a reference compound. OH radicals were produced by UV photolysis of an O3,H2O,He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k1 (298 K) values determined by the absolute method were (1.69 ± 0.07) × 10,15 cm3 molecule,1 s,1 (FP-LIF method) and (1.72 ± 0.07) × 10,15 cm3 molecule,1 s,1 (LP-LIF method), whereas the K1 (298 K) values determined by the relative method were (1.87 ± 0.11) × 10,15 cm3 molecule,1 s,1 (CHF2Cl reference) and (2.12 ± 0.11) × 10,15 cm3 molecule,1 s,1 (CH2FCF3 reference). These data are in agreement with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was K1 = (4.71 ± 0.94) × 10,13 exp[,(1630 ± 80)/T] cm3 molecule,1 s,1. Using kinetic data for the reaction of tropospheric CH3CCl3 with OH radicals [k1 (272 K) = 6.0 × 10,15 cm3 molecule,1 s,1, tropospheric lifetime of CH3CCl3 = 6.0 years], we estimated the tropospheric lifetime of CF3CF2CF2CF2CF2CHF2 through reaction with OH radicals to be 31 years. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 26,33, 2004 [source] Determination of rank by median absolute deviation (DRMAD): a simple method for determining the number of principal factors responsible for a data matrix,JOURNAL OF CHEMOMETRICS, Issue 1 2009Edmund R. Malinowski Abstract Median absolute deviation (MAD) is a well-established statistical method for determining outliers. This simple statistic can be used to determine the number of principal factors responsible for a data matrix by direct application to the residual standard deviation (RSD) obtained from principal component analysis (PCA). Unlike many other popular methods the proposed method, called determination of rank by MAD (DRMAD), does not involve the use of pseudo degrees of freedom, pseudo F -tests, extensive calibration tables, time-consuming iterations, nor empirical procedures. The method does not require strict adherence to normal distributions of experimental uncertainties. The computations are direct, simple to use and extremely fast, ideally suitable for online data processing. The results obtained using various sets of chemical data previously reported in the chemical literature agree with the early work. Limitations of the method, determined from model data, are discussed. An algorithm, written in MATLAB format, is presented in the Appendix. Copyright © 2008 John Wiley & Sons, Ltd. [source] Proper Assessment of the JFK Assassination Bullet Lead Evidence from Metallurgical and Statistical PerspectivesJOURNAL OF FORENSIC SCIENCES, Issue 4 2006Erik Randich Ph.D. ABSTRACT: The bullet evidence in the JFK assassination investigation was reexamined from metallurgical and statistical standpoints. The questioned specimens are comprised of soft lead, possibly from full-metal-jacketed Mannlicher-Carcano (MC), 6.5-mm ammunition. During lead refining, contaminant elements are removed to specified levels for a desired alloy or composition. Microsegregation of trace and minor elements during lead casting and processing can account for the experimental variabilities measured in various evidentiary and comparison samples by laboratory analysts. Thus, elevated concentrations of antimony and copper at crystallographic grain boundaries, the widely varying sizes of grains in MC bullet lead, and the 5,60 mg bullet samples analyzed for assassination intelligence effectively resulted in operational sampling error for the analyses. This deficiency was not considered in the original data interpretation and resulted in an invalid conclusion in favor of the single-bullet theory of the assassination. Alternate statistical calculations, based on the historic analytical data, incorporating weighted averaging and propagation of experimental uncertainties also considerably weaken support for the single-bullet theory. In effect, this assessment of the material composition of the lead specimens from the assassination concludes that the extant evidence is consistent with any number between two and five rounds fired in Dealey Plaza during the shooting. [source] Bound and unextractable pesticidal plant residues: chemical characterization and consumer exposurePEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 7 2004Heinrich Sandermann Jr Abstract Plants are well known to incorporate pesticides into bound and unextractable residues that resist solubilization in common laboratory solvents and are therefore not accessible to standard residue analysis. A characterization of such residues has been proposed for incorporation rates above trigger values of 0.05 mg kg,1 parent pesticide equivalents, or percentage values of 10% (United States Environmental Protection Agency, 1995) or 25% (Commission of the European Communities, 1997) of the total radioactive residue. These trigger values are often exceeded. The present review describes the current status of the chemical characterization and animal bioavailability of bound and unextractable residues that may be xenobiotic in nature or result from natural recycling of simple degradation products. The latter case represents a mechanism of detoxification. Bound residues have been shown to be covalent or non-covalent in nature. With regard to the plant matrix molecules involved, incorporation into proteins, lignins, pectins, hemicelluloses and cutins has been demonstrated, and four covalent linkage types are known. Animal feeding experiments have revealed cases of low as well as high bioavailability. Many of the studies are limited by experimental uncertainties and by results only being reported as relative percentage values rather than absolute exposure. A preliminary value of absolute exposure from bound and unextractable residues is derived here for the first time from eight case studies. The mean exposure (ca 1.5 mg kg,1 pesticidal equivalents) exceeds some of the existing maximum residue levels (MRLs) of residual free pesticides that are typically in the range of 0.05,1 mg kg,1. A mathematical framework for the correction of current maximum residue levels is presented for cases of highly bioavailable bound residues. As bound pesticidal residues in food plants could represent a source of significant consumer exposure, an experimental test scheme is proposed here. It consists of basic chemical characterization, model digestibility tests and, in exceptional cases, animal bioavailability and additional toxicological studies. Copyright © 2004 Society of Chemical Industry [source] Identification of plastic material parameters with error estimationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Jaan Unger In recent years, inverse analysis has become a common approach to typical engineering problems such as model identification. In this contribution, the inverse problem is discussed in light of taking experimental uncertainties into account. This involves in particular the propagation of experimental errors and the analysis of the sensitivity of the model response to variations in the model parameters to be determined. The method is applied to an elasto-viscoplastic material model which is used in the context of electromagnetic high-speed forming. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure-factor extrapolation using the scalar approximation: theory, applications and limitationsACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2007Ulrich K. Genick For many experiments in macromolecular crystallography, the overall structure of the protein/nucleic acid is already known and the aim of the experiment is to determine the effect a chemical or physical perturbation/activation has on the structure of the molecule. In a typical experiment, an experimenter will collect a data set from a crystal in the unperturbed state, perform the perturbation (i.e. soaking a ligand into the crystal or activating the sample with light) and finally collect a data set from the perturbed crystal. In many cases the perturbation fails to activate all molecules, so that the crystal contains a mix of molecules in the activated and native states. In these cases, it has become common practice to calculate a data set corresponding to a hypothetical fully activated crystal by linear extrapolation of structure-factor amplitudes. These extrapolated data sets often aid greatly in the interpretation of electron-density maps. However, the extrapolation of structure-factor amplitudes is based on a mathematical shortcut that treats structure factors as scalars, not vectors. Here, a full derivation is provided of the error introduced by this approximation and it is determined how this error scales with key experimental parameters. The perhaps surprising result of this analysis is that for most structural changes encountered in protein crystals, the error introduced by the scalar approximation is very small. As a result, the extrapolation procedure is largely limited by the propagation of experimental uncertainties of individual structure-factor amplitudes. Ultimately, propagation of these uncertainties leads to a reduction in the effective resolution of the extrapolated data set. The program XTRA, which implements SASFE (scalar approximation to structure-factor extrapolation), performs error-propagation calculations and determines the effective resolution of the extrapolated data set, is further introduced. [source] Toward accurate relative energy predictions of the bioactive conformation of drugsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2009Keith T. Butler Abstract Quantifying the relative energy of a ligand in its target-bound state (i.e. the bioactive conformation) is essential to understand the process of molecular recognition, to optimize the potency of bioactive molecules and to increase the accuracy of structure-based drug design methods. This is, nevertheless, seriously hampered by two interrelated issues, namely the difficulty in carrying out an exhaustive sampling of the conformational space and the shortcomings of the energy functions, usually based on parametric methods of limited accuracy. Matters are further complicated by the experimental uncertainty on the atomic coordinates, which precludes a univocal definition of the bioactive conformation. In this article we investigate the relative energy of bioactive conformations introducing two major improvements over previous studies: the use sophisticated QM-based methods to take into account both the internal energy of the ligand and the solvation effect, and the application of physically meaningful constraints to refine the bioactive conformation. On a set of 99 drug-like molecules, we find that, contrary to previous observations, two thirds of bioactive conformations lie within 0.5 kcal mol,1 of a local minimum, with penalties above 2.0kcal mol,1 being generally attributable to structural determination inaccuracies. The methodology herein described opens the door to obtain quantitative estimates of the energy of bioactive conformations and can be used both as an aid in refining crystallographic structures and as a tool in drug discovery. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Mathematical modeling of 13C label incorporation of the TCA cycle: The concept of composite precursor functionJOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2007Kai Uffmann Abstract A novel approach for the mathematical modeling of 13C label incorporation into amino acids via the TCA cycle that eliminates the explicit calculation of the labeling of the TCA cycle intermediates is described, resulting in one differential equation per measurable time course of labeled amino acid. The equations demonstrate that both glutamate C4 and C3 labeling depend in a predictible manner on both transmitochondrial exchange rate, VX, and TCA cycle rate, VTCA. For example, glutamate C4 labeling alone does not provide any information on either VX or VTCA but rather a composite "flux". Interestingly, glutamate C3 simultaneously receives label not only from pyruvate C3 but also from glutamate C4, described by composite precursor functions that depend in a probabilistic way on the ratio of VX to VTCA: An initial rate of labeling of glutamate C3 (or C2) being close to zero is indicative of a high VX/VTCA. The derived analytical solution of these equations shows that, when the labeling of the precursor pool pyruvate reaches steady state quickly compared with the turnover rate of the measured amino acids, instantaneous labeling can be assumed for pyruvate. The derived analytical solution has acceptable errors compared with experimental uncertainty, thus obviating precise knowledge on the labeling kinetics of the precursor. In conclusion, a substantial reformulation of the modeling of label flow via the TCA cycle turnover into the amino acids is presented in the current study. This approach allows one to determine metabolic rates by fitting explicit mathematical functions to measured time courses. © 2007 Wiley-Liss, Inc. [source] The effective hard particle model provides a simple, robust, and broadly applicable description of nonideal behavior in concentrated solutions of bovine serum albumin and other nonassociating proteinsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2007Allen P. Minton Abstract Published data on the concentration dependence of osmotic pressure of solutions of bovine serum albumin in 0.15 M NaCl at concentrations up to greater than 400 g/L are shown to be described to within experimental uncertainty by a simple one-parameter model in which protein molecules are represented by effective hard spherical particles. The volume of the effective hard particle reflects both steric and electrostatic repulsion and thus varies with pH and ionic strength. The pH dependence of the effective volume is shown to agree well with that previously obtained from analysis of the concentration dependence of sedimentation equilibrium and static light scattering. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 3466,3469, 2007 [source] Strain-induced correlations between the phonon frequencies of indium nitridePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2004O. Briot Abstract Using measurements of phonons frequencies in large size InN quantum dots deposited by Metal-organic vapor phase epitaxy, we found these frequencies to experience a blue shift with increasing compression. Next we show that all the phonon frequencies reported in the literature are correlated to the strain state of InN and are, within the experimental uncertainty, consistent with each other. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Building native protein conformation from NMR backbone chemical shifts using Monte Carlo fragment assemblyPROTEIN SCIENCE, Issue 8 2007Haipeng Gong Abstract We have been analyzing the extent to which protein secondary structure determines protein tertiary structure in simple protein folds. An earlier paper demonstrated that three-dimensional structure can be obtained successfully using only highly approximate backbone torsion angles for every residue. Here, the initial information is further diluted by introducing a realistic degree of experimental uncertainty into this process. In particular, we tackle the practical problem of determining three-dimensional structure solely from backbone chemical shifts, which can be measured directly by NMR and are known to be correlated with a protein's backbone torsion angles. Extending our previous algorithm to incorporate these experimentally determined data, clusters of structures compatible with the experimentally determined chemical shifts were generated by fragment assembly Monte Carlo. The cluster that corresponds to the native conformation was then identified based on four energy terms: steric clash, solvent-squeezing, hydrogen-bonding, and hydrophobic contact. Currently, the method has been applied successfully to five small proteins with simple topology. Although still under development, this approach offers promise for high-throughput NMR structure determination. [source] Tris(4-bromophenyl)aminium hexachloridoantimonate (`Magic Blue'): a strong oxidant with low inner-sphere reorganizationACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Mauricio Quiroz-Guzman Both the radical cation tris(4-bromophenyl)aminium hexachloridoantimonate (`Magic Blue'), (C18H12Br3N)[SbCl6], (I), and neutral tris(4-bromophenyl)amine, C18H12Br3N, (II), show extremely similar three-bladed propeller structures with planar N atoms. Key geometric features, such as the C,N bond distances and the angles between the planes of the aryl groups and the central NC3 plane, are identical within experimental uncertainty in the two structures. This contrasts with the significant structural changes observed on oxidation of more electron-rich triarylamines, where resonance contributes to the stabilization of the radical cation, and suggests that, in general, more strongly oxidizing triarylaminium cations will have lower inner-sphere reorganization energies than their lower-potential analogues. [source] Orthorhombic aluminium oxyfluoride, AlOFACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Alexander D. Vasiliev Crystals of the title compound were extracted from the bulk of grown SrAlF5 crystals as unexpected inclusions that were identified as the long sought after aluminium oxyfluoride. The structure of AlOF is built up from tetrahedral and octahedral polyhedra. Each tetrahedron is bisected by a mirror plane, with the Al atom and two vertex anions in the plane. All tetrahedral vertices are positions of competing oxide and fluoride ions and are shared with octahedra. These shared vertices belong to two octahedral edges which join the octahedra to form infinite zigzag chains. The chains are strung along twofold screw axes that run parallel to the unit-cell b axis. The remaining two octahedral vertices are occupied only by fluoride ions. A small deficiency in the occupation of the octahedral Al position was suggested by the refinement. However, the stoichiometry of the compound is AlOF within experimental uncertainty. The Al,F(O) distances are separated into three groups with average values of 1.652,(3) (tetrahedra), 1.800,(2) (octahedra) and 1.894,(2),Å (octahedra). This structure differs widely from the reported tetragonal phase Al1,xO1,3xF1+3x (x = 0.0886) [Kutoglu (1992). Z. Kristallogr.199, 197,201], which consists solely of octahedral structural units. [source] Dichloro[1,1,-(5,9-dithia-2,12-diazoniatrideca-1,12-diene-1,13-diyl)dinaphthalen-2-olato-,2O,O,]dimethyltin(IV) acetonitrile solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2003Stanley A. Bajue Reaction of the potentially hexadentate ligand 1,9-bis(2-hydroxy-1-naphthalenemethylimino)-3,7-dithianonane with dimethyltin chloride gave the title 1:1 adduct, in which the long ligand wraps around the SnCl2Me2 unit and in which the stereochemistry is fully trans. This compound crystallizes from acetonitrile as the 1:1 solvate [Sn(CH3)2(C29H30N2O2S2)Cl2]·C2H3N. During the reaction, the hydroxyl protons move to the N atoms. Most of the chemically equivalent bond lengths agree to within experimental uncertainty, but the Sn,Cl bond that is inside the ligand pocket is substantially longer than the Sn,Cl bond that points away from the long ligand [2.668,(1) versus 2.528,(1),Å]. The O,Sn,O angle is 166.0,(1)°. Comparison of the Sn,O, C,O and aryl C,C bond lengths with those of related compounds shows that the most important resonance forms for the Schiff base aryloxide ligand are double zwitterions, but that the uncharged resonance forms having carbonyl groups also contribute significantly. [source] METHODOLOGICAL DEVELOPMENTS IN THE LUMINESCENCE DATING OF BRICK FROM ENGLISH LATE-MEDIEVAL AND POST-MEDIEVAL BUILDINGS,ARCHAEOMETRY, Issue 4 2007I. K. BAILIFF Fired clay brick samples, obtained from a group of seven high-status late-medieval and post-medieval buildings in England ranging in age from c. ad 1390 to 1740, were dated by the luminescence method using an optically stimulated luminescence (OSL) technique. The results obtained indicate that, when applied to quartz extracted from brick, the technique is capable of producing dates that are in consistently good agreement with independent dating evidence for the buildings. For six samples taken from a group of four dating ,control' buildings the mean difference between the central values of luminescence and assigned ages was 5 ± 10 years (SD, n = 6). The methodology used is appropriate for application to other standing buildings in other temporal and geographic regions, and may be used with confidence where conventional dating methods are less certain. The study also examines the luminescence characteristics of quartz and the characteristics of the lithogenic radionuclides in brick samples and identifies various aspects related to the assessment of experimental uncertainty in testing the reliability of the method. [source] Combinatorial Initiated CVD for Polymeric Thin Films,CHEMICAL VAPOR DEPOSITION, Issue 11 2006P. Martin Abstract A new combinatorial initiated (i)CVD system is fabricated and used to efficiently determine the deposition kinetics for two new polymeric thin films, poly(diethylaminoethylacrylate) (PDEAEA) and poly(dimethylaminomethylstyrene) (PDMAMS). The results of combinatorial depositions are compared to blanket iCVD under identical conditions using the appropriate vinyl monomer with tert -amylperoxide as the initiator. Fourier transform infrared spectroscopy (FTIR) reveals similar chemical structure in blanket and combinatorial films. FTIR also shows that functional groups are retained in iCVD of PDMAMS, whereas essentially all fine chemical structure of the material is destroyed in plasma-enhanced (PE)CVD. The maximum observed growth rates of PDEAEA and PDMAMS were 43 and 11,nm,min,1, respectively. The activation energy of growth with respect to filament temperature (Ea,filament) was 88.4±1.6 kJ,mol,1 for PDEAEA and 42.0±1.7 kJ,mol,1 for PDMAMS. Activation energies for growth with respect to substrate temperature (Ea,substrate) are ,59.5±2.7 kJ,mol,1 for PDEADA and ,82.7±2.6 kJ,mol,1 for PDMAMS, with the negative values consistent with adsorption-limited kinetics. The molecular weight of PDEAEA films ranges from 1 to 182 kDa as a function of substrate temperature. It is found that in all cases the combinatorial system agreed (within experimental uncertainty) with results of blanket iCVD, thus validating the use of the combinatorial system for future iCVD studies. [source] | ||||||||||