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Selected AbstractsA dynamic mass budget for toxaphene in North AmericaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2002Matthew MacLeod Abstract A continental-scale dynamic mass budget for toxaphene in North America is presented, based on available information on physicochemical properties, usage patterns, and reported environmental concentrations and using the Berkeley-Trent North American mass balance contaminant fate model (BETR North America). The model describes contaminant fate in 24 ecological regions of North America, including advective transport between regions in the atmosphere, freshwater, and near-shore coastal water. The dynamic mass budget accounts for environmental partitioning, transport, and degradation of the estimated 534 million kg of toxaphene that were used in North America as an insecticide and piscicide between 1945 and 2000. Satisfactory agreement exists between model results and current and historically reported concentrations of toxaphene in air, water, soil, and sediments throughout North America. An estimated 15 million kg of toxaphene are believed to remain in active circulation in the North American environment in the year 2000, with the majority in soils in the southern United States and Mexico, where historic usage was highest. Approximately 70% of total toxaphene deposition from the atmosphere to the Great Lakes is attributed to sources outside the Great Lakes Basin, and an estimated total of 3.9 million kg of toxaphene have been transported to this region from other parts of the continent. The toxaphene mass budget presented here is believed to be the first reported continental-scalemultimedia mass budget for any contaminant. [source] Numerical model for the prediction of dilute, three-dimensional, turbulent fluid,particle flows, using a Lagrangian approach for particle tracking and a CVFEM for the carrier phaseINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2008L. A. Oliveira Abstract A numerical model for dilute, three-dimensional, turbulent, incompressible fluid,solid particle flows and its application to a demonstration problem are presented. An Eulerian description is used to model the flow of the fluid (carrier) phase, and the governing equations are solved using a control-volume finite element method (CVFEM). The motion of the solid (particulate) phase is simulated using a Lagrangian approach. An efficient algorithm is proposed for locating the particles in the finite element mesh. In the demonstration problem, which involves a particle-laden axisymmetric jet, a modified k,, turbulence model is used to characterize the velocity and length scales of the turbulent flow of the fluid phase. The effect of turbulence on the particle trajectories is accounted for through a stochastic model. The effect of the particles on the fluid time,mean velocity and turbulence (two-way coupling) is also addressed. Comparisons between predictions and available experimental data for the demonstration problem are presented. Satisfactory agreement is obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Free Radical Bulk Polymerization of Styrene: Simulation of Molecular Weight Distributions to High Conversion Using Experimentally Obtained Rate CoefficientsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 6 2003Per B. Zetterlund Abstract Previously obtained experimental conversion-dependences of the propagation rate coefficient (kp), the termination rate coefficient (kt) and the initiator efficiency (f) for the free-radical bulk polymerization of styrene at 70,°C have been used to simulate the full molecular weight distributions (MWD) to high conversion using the software package PREDICI, providing a robust test of the kinetic model adopted. Satisfactory agreement with the experimental MWD's (GPC) was obtained up to approximately 70% conversion. Beyond 70% conversion, the high MW shoulder that appears was correctly predicted, although the amount of such polymer was somewhat underestimated. This discrepancy is believed to probably have its origin in experimental error in the conversion-dependences of kp, kt and f, in particular kt, that were employed in the simulations, rather than indicate a more fundamental short-coming of the model employed. [source] Design of compact triple-band meander chip antenna using LTCC technology for mobile handsetsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2006Young Do Kim Abstract This paper presents the design simulation, implementation, and measurement of a miniaturized GPS/K-PCS/ISM (2.4-GHz) triple-band LTCC meander-chip antenna for mobile-communication handsets. The dimensions of the LTCC chip antenna is 8.6 × 15 × 1.5 mm. In this paper, the bottom meander radiating patch is tuned to the GPS-band, the middle meander antenna with via-hole connection contributes to the K-PCS-band operation and the top radiating patch is tuned to the ISM-band (2.4 GHz). With 2.0:1 VSWR impedance bandwidth definition, the lower, middle and upper bands have impedance-bandwidth values of 110, 140, and 60 MHz, covering the bandwidth of the GPS/K-PCS/ISM (2.4-GHz) bands. Satisfactory agreement between the simulated and measured results for the antenna patterns and impedance bandwidth are achieved. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 160,162, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21292 [source] Pressure evolution of the phonon modes and force constants of Tb3Al5O12 and Lu3Al5O12PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003K. Papagelis Abstract The pressure evolution of the Raman modes of Tb3Al5O12 and Lu3Al5O12 has been measured at room temperature and analyzed theoretically with the rigid ion model. Satisfactory agreement between experiment and theory has been found. The extracted pressure variation of the bond bending and bond stretching force constants shows that the compressibility of the various polyhedra types increases with increasing cation coordination, indicating that the dodecahedra play an important role in the compressibility of the garnet structure. Finally, an estimation of the pressure coefficients for the transverse optical infrared active mode frequencies is given. [source] Using ARX and NARX approaches for modeling and prediction of the process behavior: application to a reactor-exchangerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Yahya Chetouani Abstract Chemical industries are characterized often by nonlinear processes. Therefore, it is often difficult to obtain nonlinear models that accurately describe a plant in all regimes. The main contribution of this work is to establish a reliable model of a process behavior. The use of this model should reflect the normal behavior of the process and allow distinguishing it from an abnormal one. Consequently, the black-box identification based on the neural network (NN) approach by means of a nonlinear autoregressive with exogenous input (NARX) model has been chosen in this study. A comparison with an autoregressive with exogenous input (ARX) model based on the least squares criterion is carried out. This study also shows the choice and the performance of ARX and NARX models in the training and test phases. Statistical criteria are used for the validation of the experimental data of these approaches. The identified neural model is implemented by training a multilayer perceptron artificial neural network (MLP-ANN) with input,output experimental data. An analysis of the inputs number, hidden neurons and their influence on the behavior of the neural predictor is carried out. In order to illustrate the proposed ideas, a reactor-exchanger is used. Satisfactory agreement between identified and experimental data is found and results show that the neural model predicts the evolution of the process dynamics in a better way. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Theoretical framework for the distribution of trace metals among the operationally defined speciation phases of a sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2001René A. Nome Abstract The use of a model based on Langmuir's isotherm to evaluate the metal associated with separate geochemical phases of a sediment is proposed and its validity tested with sediments of certified composition. The model takes into account a standard procedure for a certified reference material (CRM601), which defines, experimentally, a set of sequential extractions that divide the sediment into four operational fractions. The derived equations allow the treatment of data from sediment of Flumendosa Lake, Italy, and certified material CRM601 and also allow the computation of corrected concentrations, i.e., the metal affinities for each fraction. Experimental values for Ni show its low sensitivity and an equal distribution among different phases, which suggests a similar adsorption mechanism in all cases. In the case of Cd, the corrected concentration in the Fe/Mn oxide phase is nine times higher than for the residual fraction. For sediment of the Bèsos River, Spain, results show the percentage distribution of Ni over different fractions. Affinity values for Ni on a Flumendosa Lake sediment have also been calculated. The present model is simple to apply and shows satisfactory agreement with experimental data. [source] Relationship between thermal conductivity and water content of soils using numerical modellingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003P. Cosenza Summary There is no simple and general relationship between the thermal conductivity of a soil, ,, and its volumetric water content, ,, because the porosity, n, and the thermal conductivity of the solid fraction, ,s, play a major part. Experimental data including measurements of all the variables are scarce. Using a numerical modelling approach, we have shown that the microscopic arrangement of water influences the relation between , and ,. Simulated values for n ranging from 0.4 to 0.6, ,s ranging from 2 to 5 W m,1 K,1 and , from 0.1 to 0.4 can be fitted by a simple linear formula that takes into account n, ,s and ,. The results given by this formula and by the quadratic parallel (QP) model widely used in physical property studies are in satisfactory agreement with published data both for saturated rocks and for unsaturated soils. Consequently, the linear formula and the QP model can be used as practical and efficient tools to investigate the effects of water content and porosity on the thermal conductivity of the soil and hence to optimize the design of thermal in situ techniques for monitoring water content. [source] Ionic-Liquid-Doped Polyaniline Inverse Opals: Preparation, Characterization, and Application for the Electrochemical Impedance Immunoassay of Hepatitis B Surface AntigenADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Xing-Hua Li Abstract A 3D ordered macroporous (3DOM) ionic-liquid-doped polyaniline (IL-PANI) inverse opaline film is fabricated with an electropolymerization method and gold nanoparticles (AuNPs) are assembled on the film by electrostatic adsorption, which offers a promising basis for biomolecular immobilization due to its satisfactory chemical stability, good electronic conductivity, and excellent biocompatibility. The AuNP/IL-PANI inverse opaline film could be used to fabricate an electrochemical impedance spectroscopy (EIS) immunosensor for the determination of Hepatitis B surface antigen (HBsAg). The concentration of HBsAg is measured using the EIS technique by monitoring the corresponding specific binding between HBsAg and HBsAb (surface antibody). The increased electron transfer resistance (Ret) values are proportional to the logarithmic value of the concentration of HBsAg. This novel immunoassay displays a linear response range between 0.032,pg mL,1 and 31.6,pg mL,1 with a detection limit of 0.001,pg mL,1. The detection of HBsAg levels in several sera showed satisfactory agreement with those using a commercial turbidimetric method. [source] An Approximation for the Rank Adjacency Statistic for Spatial Clustering with Sparse DataGEOGRAPHICAL ANALYSIS, Issue 1 2001John Paul Ekwaru The rank adjacency statistic D provides a simple method to assess regional clustering. It is defined as the weighted average absolute difference in ranks of the data, taken over all possible pairs of adjacent regions. In this paper the usual normal approximation to the D statistic is found to give inaccurate results if the data are sparse and some regions have tied ranks. Adjusted formulae for the moments of D that allow for the existence of ties are derived. An example of analyses of sparse mortality data (with many regions having no deaths, and hence tied ranks) showed satisfactory agreement between the adjusted formulae and the empirical distribution of the D statistic. We conclude that the D statistic, when used with adjusted moments, provides a valid approximate method to evaluate spatial clustering, even in sparse data situations. [source] Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysisHYDROLOGICAL PROCESSES, Issue 21 2010F. Rezanezhad Abstract In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air-filled pores control the unsaturated hydraulic conductivity of peat soils using high-resolution (45 µm) three-dimensional (3D) X-ray computed tomography (CT) and digital image processing of four peat sub-samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross-sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air-filled pore hydraulic radius, tortuosity, air-filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air-filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simulating soil-water movement under a hedgerow surrounding a bottomland reveals the importance of transpiration in water balanceHYDROLOGICAL PROCESSES, Issue 5 2008Z. Thomas Abstract The objective of this study was to quantify components of the water balance related to root-water uptake in the soil below a hedgerow. At this local scale, a two-dimensional (2D) flow domain in the x,z plane 6 m long and 1·55 m deep was considered. An attempt was made to estimate transpiration using a simulation model. The SWMS-2D model was modified and used to simulate temporally and spatially heterogeneous boundary conditions. A function with a variable spatial distribution of root-water uptake was considered, and model calibration was performed by adjusting this root-water uptake distribution. Observed data from a previous field study were compared against model predictions. During the validation step, satisfactory agreement was obtained, as the difference between observed and modelled pressure head values was less than 50 cm for 80% of the study data. Hedge transpiration capacity is a significant component of soil-water balance in the summer, when predicted transpiration reaches about 5·6 mm day,1. One of the most important findings is that hedge transpiration is nearly twice that of a forest canopy. In addition, soil-water content is significantly different whether downslope or upslope depending on the root-water uptake. The high transpiration rate was mainly due to the presence of a shallow water table below the hedgerow trees. Soil-water content was not a limiting factor for transpiration in this context, as it could be in one with a much deeper water table. Hedgerow tree transpiration exerts a strong impact not only on water content within the vadose zone but also on the water-table profile along the transect. Results obtained at the local scale reveal that the global impact of hedges at the catchment scale has been underestimated in the past. Transpiration rate exerts a major influence on water balance at both the seasonal and annual scales for watersheds with a dense network of hedgerows. Copyright © 2007 John Wiley & Sons, Ltd. [source] Implementation of the finite element method in the three-dimensional discontinuous deformation analysis (3D-DDA)INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2008Roozbeh Grayeli Abstract A modified three-dimensional discontinuous deformation analysis (3D-DDA) method is derived using four-noded tetrahedral elements to improve the accuracy of current 3D-DDA algorithm in practical applications. The analysis program for the modified 3D-DDA method is developed in a C++ environment and its accuracy is illustrated through comparisons with several analytical solutions that are available for selected problems. The predicted solutions for these problems using the modified 3D-DDA approach all show satisfactory agreement with the corresponding analytical results. Results presented in this paper demonstrate that the modified 3D-DDA method with discontinuous modeling capabilities offers a useful computational tool to determine stresses and deformations in practical problems involving fissured elastic media with reasonable accuracy. Copyright © 2008 John Wiley & Sons, Ltd. [source] Use of equivalent mass method for free vibration analyses of a beam carrying multiple two-dof spring,mass systems with inertia effect of the helical springs consideredINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2006Jia-Jang Wu Abstract This paper investigates the free vibration characteristics of a beam carrying multiple two-degree-of-freedom (two-dof) spring,mass systems (i.e. the loaded beam). Unlike the existing literature to neglect the inertia effect of the helical springs of each spring,mass system, this paper takes the last inertia effect into consideration. To this end, a technique to replace each two-dof spring,mass system by a set of rigidly attached equivalent masses is presented, so that the free vibration characteristics of a loaded beam can be predicted from those of the same beam carrying multiple rigidly attached equivalent masses. In which, the equation of motion of the loaded beam is derived analytically by means of the expansion theorem (or the mode superposition method) incorporated with the natural frequencies and the mode shapes of the bare beam (i.e. the beam carrying nothing). In addition, the mass and stiffness matrices including the inertia effect of the helical springs of a two-dof spring,mass system, required by the conventional finite element method (FEM), are also derived. All the numerical results obtained from the presented equivalent mass method (EMM) are compared with those obtained from FEM and satisfactory agreement is achieved. Because the equivalent masses of each two-dof spring,mass system are dependent on the magnitudes of its lumped mass, spring constant and spring mass, the presented EMM provides an effective technique for evaluating the overall inertia effect of the two-dof spring,mass systems attached to the beam. Furthermore, if the total number of two-dof spring,mass systems attached to the beam is large, then the order of the overall property matrices for the equation of motion of the loaded beam in EMM is much less than that in FEM and the computer storage memory required by the former is also much less than that required by the latter. Copyright © 2005 John Wiley & Sons, Ltd. [source] Experimental and modeling study of the autoignition of cyclopenteneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2008M. Yahyaoui Ignition delay times of cyclopentene,oxygen,argon mixtures were measured behind reflected shock waves. Mixtures contained 0.5% or 1% of hydrocarbons for equivalence ratios ranging from 0.5 to 1.5. Reflected shock wave conditions were as follows: temperatures from 1300 to 1700 K and pressures from 7 to 9 atm. When compared with the previous results obtained under similar conditions, it can be observed that the reactivity of cyclopentene is much lower than that of cyclohexene, but very close to that of cyclopentane. A kinetic mechanism recently proposed for the combustion of cyclopentene in a flame has been used to model these results, and a satisfactory agreement is obtained. The main reaction pathways have been derived from the flow rate, simulated temporal profiles of products, and sensitivity analyses. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 25,33, 2008 [source] The gas-phase oxidation of n -hexadecaneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2001R. Fournet Since n -hexadecane or cetane is a reference fuel for the estimation of cetane numbers in diesel engines, a detailed chemical model of its gas-phase oxidation and combustion will help to enhance diesel performance and reduce the emission of pollutants at their outlet. However, until recently the gas-phase reactions of n -hexadecane had not been experimentally studied, prohibiting a validation of oxidation models which could be written. This paper presents a modeling study of the oxidation of n -hexadecane based on experiments performed in a jet-stirred reactor, at temperatures ranging from 1000 to 1250 K, 1-atm pressure, a constant mean residence time of 0.07 s, and high degree of nitrogen dilution (0.03 mol% of fuel) for equivalence ratios equal to 0.5, 1, and 1.5. A detailed kinetic mechanism was automatically generated by using the computer package (EXGAS) developed in Nancy. The long linear chain of this alkane necessitates the use of a detailed secondary mechanism for the consumption of the alkenes formed as a result of primary parent fuel decomposition. This high-temperature mechanism includes 1787 reactions and 265 species, featuring satisfactory agreement for both the consumption of reactants and the formation of products. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 574,586, 2001 [source] Experiment and simulation investigations for effects of flow channel patterns on the PEMFC performanceINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2008Yuh-Ming Ferng Abstract Experiments and simulations are presented in this paper to investigate the effects of flow channel patterns on the performance of proton exchange membrane fuel cell (PEMFC). The experiments are conducted in the Fuel Cell Center of Yuan Ze University and the simulations are performed by way of a three-dimensional full-cell computational fluid dynamics model. The flow channel patterns adopted in this study include the parallel and serpentine flow channels with the single path of uniform depth and four paths of step-wise depth, respectively. Experimental measurements show that the performance (i.e. cell voltage) of PEMFC with the serpentine flow channel is superior to that with the parallel flow channel, which is precisely captured by the present simulation model. For the parallel flow channel, different depth patterns of flow channel have a strong influence on the PEMFC performance. However, this effect is insignificant for the serpentine flow channel. In addition, the calculated results obtained by the present model show satisfactory agreement with the experimental data for the PEMFC performance under different flow channel patterns. These validations reveal that this simulation model can supplement the useful and localized information for the PEMFC with confidence, which cannot be obtained from the experimental data. Copyright © 2007 John Wiley & Sons, Ltd. [source] Density functional study of the heme moiety of cytochrome c,,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Anil Kumar Abstract A model of cytochrome c (Cyt-c) including the porphyrin ring, a methionine residue (Met), and the imidazole ring of histidine (His), the latter two being situated above and below the iron (Fe) atom of the porphyrin ring, was studied using Density Functional Theory (DFT). The geometries of the model Cyt-c complex with the Fe atom in two different charge states were fully optimized, i.e., in singlet and triplet states for Fe and in doublet and quartet states for Fe3+. The B3LYP method of DFT along with the 3-21G* basis set for C, H, N, and O atoms and the Lanl2dz basis set for the Fe atom was used. We found that with Fe3+, the doublet spin state is the ground state and the quartet state lies slightly above it. The geometry of the singlet spin state is similar to that of the doublet and quartet states. However, methionine has different conformations when Fe has zero charge (singlet, triplet states) relative to the situation when Fe has +3 charges (doublet, quartet states). The Met chain is folded instead of remaining extended in going from the singlet or triplet spin state to the doublet or quartet state and the folding is stabilized by an intramolecular CH..O hydrogen bond. The optimized geometrical parameters of the model of Cyt-c are usually in satisfactory agreement with those observed experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] X-ray extinction changes due to dislocationsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2007M. Masimov A correct interpretation of the diffraction phenomenon in crystals with low dislocation content, for which the kinematical scattering theory does not yield any reasonable results, was carried out by X-ray extinction treatments. Different approaches to investigating the dislocation-induced X-ray extinction changes are reviewed and the applicability of the statistical dynamical theory to analysis of the substructure characteristics of crystals is discussed. A relationship between the scattering amplitudes and the dislocation density in crystals is established by using pair correlation functions. A procedure for determination of the substructure characteristics by means of measurements of the integrated intensities is proposed. The tests illustrate satisfactory agreement of the investigated approaches with experimental data. [source] Genome-scale modeling of Synechocystis sp.JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2009PCC 680, prediction of pathway insertion Abstract BACKGROUND: Cyanobacterium Synechocystis sp. PCC 6803 has been used widely as a model system for the study of photosynthetic organisms and higher plants. The aim of this work was to integrate the genomic information, biochemistry and physiological information available for Synechocystis sp. PCC 6803 to reconstruct a metabolic network for system biology investigations. RESULTS: A genome-scale Synechocystis sp. PCC 6803 metabolic network, including 633 genes, 704 metabolites and 831 metabolic reactions, was reconstructed for the study of optimal Synechocystis growth, network capacity and functions. Heterotrophic, photoautotrophic and mixotrophic growth conditions were simulated. The Synechocystis model was used for in silico predictions for the insertion of ethanol fermentation pathway, which is a novel approach for bioenergy and biofuels production developed in the authors' laboratory. Simulations of Synechocystis cell growth and ethanol production were compared with actual metabolic measurements which showed a satisfactory agreement. CONCLUSION: The Synechocystis metabolic network developed in this study is the first genome-scale mathematical model for photosynthetic organisms. The model may be used not only in global understanding of cellular metabolism and photosynthesis, but also in designing metabolic engineering strategies for desirable bio-products. Copyright © 2008 Society of Chemical Industry [source] Matrix formalism for site-specific binding of unstructured proteins to multicomponent lipid membranes,JOURNAL OF PEPTIDE SCIENCE, Issue 4 2008Vladimir B. Teif Abstract We describe a new approach to calculate the binding of flexible peptides and unfolded proteins to multicomponent lipid membranes. The method is based on the transfer matrix formalism of statistical mechanics recently described as a systematic tool to study DNA,protein,drug binding in gene regulation. Using the energies of interaction of the individual polymer segments with different membrane lipid species and the scaling corrections due to polymer looping, we calculate polymer adsorption characteristics and the degree of sequestration of specific membrane lipids. The method is applied to the effector domain of the MARCKS (myristoylated alanine rich C kinase substrate) protein known to be involved in signal transduction through membrane binding. The calculated binding constants of the MARCKS(151,175) peptide and a series of related peptides to mixed PC/PS/PIP2 membranes are in satisfactory agreement with in vitro experiments. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Enthalpies of formation and isomerization of cis - and trans -decalin, and their oxa-analogs by G3(MP2)//B3LYP calculationsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2009Esko Taskinen Abstract G3(MP2)//B3LYP calculations have been carried out on trans - and cis -decalin, and their mono-, di-, tri-, and tetraoxa-analogs. The main purpose of the work was to obtain enthalpies of formation for these compounds, and to study the relative stabilities of the cis,trans and positional isomers of the various (poly)oxadecalins. Comparison of the computational enthalpies of formation with the respective experimental ones, known only for the decalins and 1,3,5,7-tetraoxadecalins, shows that in both cases the computational values are more negative than the experimental ones, the deviations being ,5 to ,7,kJ,mol,1 for the decalins and ,12 to ,17,kJ,mol,1 for the 1,3,5,7-tetraoxadecalins. The respective computational enthalpies of cis,trans isomerization, however, are in excellent to satisfactory agreement with the experimental data. The cis,trans enthalpy differences vary from +11.0,kJ,mol,1 for decalin to ,15.4,kJ,mol,1 for 1,4,5,8-tetraoxadecalin. Low relative enthalpy values were also calculated for the cis isomers of 1,8-dioxadecalin (,3.7,kJ,mol,1), 1,3,6-trioxadecalin (,4.6,kJ,mol,1), 1,3,8-trioxadecalin (,9.7,kJ,mol,1), 1,4,5- trioxadecalin (,5.6,kJ,mol,1), 1,3,5,8-tetraoxadecalin (,7.3,kJ,mol,1), and 1,3,6,8-tetraoxadecalin (,14.5,kJ,mol,1). Copyright © 2009 John Wiley & Sons, Ltd. [source] The mechanism of alkaline hydrolysis of amides: a comparative computational and experimental study of the hydrolysis of N -methylacetamide, N -methylbenzamide, and acetanilideJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2009Diana Cheshmedzhieva Abstract Theoretical computations and experimental kinetic measurements were applied in studying the mechanistic pathways for the alkaline hydrolysis of three secondary amides: N -methylbenzamide, N -methylacetamide, and acetanilide. Electronic structure methods at the HF/6-31+G(d,p) and B3LYP/6-31+G(d,p) levels of theory are employed. The energies of the stationary points along the reaction coordinate were further refined via single point computations at the MP2/6-31+G(d,p) and MP2/6-311++G(2d,2p) levels of theory. The role of water in the reaction mechanisms is examined. The theoretical results show that in the cases of N -methylbenzamide and N -methylacetamide the process is catalyzed by an ancillary water molecule. The influence of water is further assessed by predicting its role as bulk solvent. The alkaline hydrolysis process in aqueous solution is characterized by two distinct free energy barriers: the formation of a tetrahedral adduct and its breaking to products. The results show that the rate-determining stage of the process is associated with the second transition state. The entropy terms evaluated from theoretical computations referring to gas-phase processes are significantly overestimated. The activation barriers for the alkaline hydrolysis of N -methylbenzamide and acetanilide were experimentally determined. Quite satisfactory agreement between experimental values and computed activation enthalpies was obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Studies of Adjacent Re-Entry Folds of Chains of Syndiotactic l,2-Poly(1,3-butadiene) by Molecular Mechanics CalculationsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Roberto Napolitano Abstract The mode of packing and the adjacent re-entry folds of chains of syndiotactic 1,2-poly(1,3-butadiene) have been studied by molecular mechanics calculations with the use of various sets of potential functions. The results of the packing analysis indicate that the crystal grows preferentially along the [100] and [110] directions. Models of fold have been built up on an infinite ab surface completely covered by adjacent re-entry folds in the (100) and (110) planes. The results of energy minimizations show that several almost isoenergetic folds, constituted by four monomeric units, can be realized in the (100) planes, while the fold in the (110) planes has higher energy. The calculated value of the work of fold is in satisfactory agreement with that derived by crystallization kinetics reported in literature. [source] Microimaging FTIR of head and neck tumors.MICROSCOPY RESEARCH AND TECHNIQUE, Issue 2 2009Abstract On continuing our studies on head and neck neoplasia, specimens from salivary gland tumors have been explored by using infrared microimaging spectroscopy to discern healthy from neoplastic tissues. Samples with Warthin tumor, epithelial displasia, marginal B-cell lymphoma, low-grade adenocarcinoma, and adenoid cystic carcinoma pathologies have been investigated by using conventional light sources. Changes were monitored at the molecular level, probing spectral markers such as Amide I and II, phosphate, nucleic acids, and carbohydrates vibrational modes. In all cases, supervised and unsupervised spectral analyses resulted in satisfactory agreement with histopathological findings. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc. [source] Prediction of oxygen transmission rate for thermoformed traysPACKAGING TECHNOLOGY AND SCIENCE, Issue 6 2004Marit KvalvÅg Pettersen Abstract There is a desire in the food industry to be able to estimate the oxygen transmission rate (OTR) of packages by knowing the permeability data of unconverted sheet/film, instead of measuring the OTR of packages. Due to thermoforming, the permeability of a material changes and therefore it is difficult to estimate the permeability (OTR) of converted trays from the OTR values of unconverted material. This paper evaluates the possibilities and limitations of predicting the OTR of thermoformed trays. Different methods for the calculation of OTR due to thickness measurements were compared. The use of theoretical thickness was satisfactory in the calculation of OTR of trays based on the OTR of unconverted sheet, area and thickness. Both linear and quadratic regression models were evaluated. Validation of the regression models was made by comparing the measured and calculated OTR of trays made of PS/EVOH/PE, A-PET/PE, PS/PE and PP/PE. These trays were manufactured on different thermoforming machines, different processing parameters and different sizes of mould. None of the models (linear and quadratic) were suitable for the calculation of OTR of trays made of PS/PE and PP/PE. Both linear and quadratic models gave satisfactory agreement with measured values for trays made of both PS/EVOH/PE and A-PET/PE. This case study indicates that a general equation for the calculation of OTR for different polymer combinations was not possible to generate. The equations presented in this paper are strictly applicable only for the polymer combinations used in this experiment, and can not be considered as general equations. Copyright © 2004 John Wiley & Sons, Ltd. [source] Study of prelocalized graphite/styrene acrylonitrile conducting composites for device applicationsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2006V. K. Sachdev Abstract Conductive polymer composites were prepared by compression molding of prelocalized graphite on to styrene acrylonitrile (SAN) particles. The electrical conductivity is found to be strongly dependent on the graphite content. Three different series were prepared for different processing and material parameters. A low percolation threshold has been noticed when only 1 wt% of graphite is incorporated. Resistivity as low as ,14 , cm has been achieved in a composite with SAN resin particles of 180,212 µm size and graphite 10,20 µm at 90 °C, 105 MPa and 15 min. An electrically conducting network of graphite channels has been observed using scanning electron microscopy. V,I characteristic reveals that at a lower percentage of graphite the increase in current with increase in electric field is due to the hopping/tunneling of electrons, while for higher percentages of graphite ohmic behavior similar to metals has been observed. The data has been analyzed using percolation model. The value of the exponent t that determines the increase in electrical conductivity above the percolation threshold is found to be close to the values given in the literature. The theoretically calculated values of conductivity are found to be in satisfactory agreement with the experimental ones. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Monte Carlo simulation of surface charge effects in T-branch nanojunctionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008T. González Abstract We analyze the influence of the surface charge on the operation of ballistic T-branch junctions based on InAlAs/InGaAs layers by means of a semi-classical 2-D Monte Carlo simulator. A new self-consistent model in which the local value of the surface charge is dynamically adjusted depending on the surrounding carrier density is used in the calculations. The rectifying behaviour exhibited by these devices (down-bending shape of the output voltage VC as a function of the applied voltage VR = -VL =V) is found to be much influenced by the surface charge. A satisfactory agreement is achieved between simulated results and experimental measurements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A validated spectrophotometric method for quantification of prenylated flavanones in pacific propolis from TaiwanPHYTOCHEMICAL ANALYSIS, Issue 2 2010Milena Popova Abstract Introduction , Because of its chemical diversity, the only way to standardise propolis is to specify multiple standards for different propolis types according to the corresponding chemical profile. So far, this has been done only for European propolis. Objective , To develop a rapid low-cost spectrophotometric procedure for quantification of bioactive prenylated flavanones in Taiwanese propolis. Methodology , The proposed method quantifies the total flavanones on the basis of their absorption as coloured phenylhydrazones formed by interaction with 2,4-dinitrophenylhydrazine. The procedure was validated through model mixture of compounds representing the composition of Taiwanese propolis according to previous studies. The major flavanones of the propolis samples (propolins C, D, F and G) were quantified by HPLC. Antiradical activity against DPPH was also measured. The DNP (dinitrophenylhydrazine) spectrophotometric method is applied for the first time for quantification of prenylated flavanones. Results , Spectophotometric procedure applicable to new type propolis (Macaranga type) was developed with recovery between 105 and 110% at the concentration range of 0.573,1.791,mg/mL. Six propolis samples were analysed by spectrophotometry using the procedure developed and validated, and by HPLC as the results demonstrated satisfactory agreement. Neither the spectrophotometric data nor the values measured by HPLC showed significant correlation with the antiradical activity against DPPH. Conclusion , The proposed spectrophotometric procedure is useful for routine analyses of Macaranga -type propolis, because of its simplicity, repeatability and acceptable accuracy. Its application to a number of commercial samples could be used as a basis for standardisation and quality control of Pacific propolis. Copyright © 2009 John Wiley & Sons, Ltd. [source] Evaluation of a second-generation portable blood lead analyzer in an occupational settingAMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 12 2007Noel V. Stanton MS Abstract Background A new blood lead testing instrument has qualities that make the instrument attractive for on-site testing of occupational lead exposures. This study evaluated the accuracy of the instrument when used in a manufacturing setting, and examined the impact of blood storage and shipment on results. Methods Venous blood specimens (n,=,121) were obtained and immediately analyzed on-site using the new instrument. They were then shipped to a reference laboratory and analyzed using electro-thermal atomization atomic absorption spectrometry (ETAAS), and retested using the new instrument. Results The cohort blood lead concentration averaged 40.1 µg/dl. Results obtained on the new analyzer with freshly collected blood averaged 38.7 µg/dl. The mean difference of 1.2 µg/dl on paired samples was not statistically significant. Following blood shipment and storage, results on the analyzer increased to an average of 42.4 µg/dl. The mean increase of 3.0 µg/dl on stored blood samples also failed to reach statistical significance. Under OSHA proficiency test acceptability requirements, 94% of the results had satisfactory agreement. Conclusions The new analyzer might be a useful tool for on-site monitoring of occupational lead exposures. The manufacturer's instructions should be adhered to with respect to specimen age and storage requirements. Am. J. Ind. Med. 50:1018,1024, 2007. © 2007 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||||||||||||||