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Chemical Species (chemical + species)
Selected AbstractsApplication of single-particle laser desorption/ionization time-of-flight mass spectrometry for detection of polycyclic aromatic hydrocarbons from soot particles originating from an industrial combustion processRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2003R. Zimmermann Combustion-related soot particles were sampled in situ from the stoker system of a 0.5,MW incineration pilot plant (feeding material was wood) at two different heights over the feed bed in the third air supply zone. The collected particles were re-aerosolized by a powder-dispersing unit and analyzed by a single-particle laser desorption/ionization (LDI) time-of-flight mass spectrometer (aerosol-time-of-flight mass spectrometry, ATOFMS). The ATOFMS instrument characterizes particles according to their aerodynamic size (laser velocimetry) and chemical composition (LDI mass spectrometry). Chemical species from the particles are laser desorbed/ionized by 266,nm Nd:YAG laser pulses. ATOFMS results on individual ,real world' particles in general give information on the bulk inorganic composition. Organic compounds, which are of much lower concentrations, commonly are not detectable. However, recent off-line laser microprobe mass spectrometric (LMMS) experiments on bulk soot aerosol samples have emphasized that organic compounds can be desorbed and ionized without fragmentation in LDI experiments from black carbonaceous matrices. This paper reports the successful transfer of the off-line results to on-line analysis of airborne soot particles by ATOFMS. The detection of polycyclic aromatic hydrocarbons from soot particles is addressed in detail. The results are interpreted in the context of the recent LMMS results. Furthermore, their relevance with respect to possible applications in on-line monitoring of combustion processes is discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Hydrogen peroxide-induced oxidative stress responses in Desulfovibrio vulgaris HildenboroughENVIRONMENTAL MICROBIOLOGY, Issue 10 2010Aifen Zhou Summary To understand how sulphate-reducing bacteria respond to oxidative stresses, the responses of Desulfovibrio vulgaris Hildenborough to H2O2 -induced stresses were investigated with transcriptomic, proteomic and genetic approaches. H2O2 and induced chemical species (e.g. polysulfide, ROS) and redox potential shift increased the expressions of the genes involved in detoxification, thioredoxin-dependent reduction system, protein and DNA repair, and decreased those involved in sulfate reduction, lactate oxidation and protein synthesis. A gene coexpression network analysis revealed complicated network interactions among differentially expressed genes, and suggested possible importance of several hypothetical genes in H2O2 stress. Also, most of the genes in PerR and Fur regulons were highly induced, and the abundance of a Fur regulon protein increased. Mutant analysis suggested that PerR and Fur are functionally overlapped in response to stresses induced by H2O2 and reaction products, and the upregulation of thioredoxin-dependent reduction genes was independent of PerR or Fur. It appears that induction of those stress response genes could contribute to the increased resistance of deletion mutants to H2O2 -induced stresses. In addition, a conceptual cellular model of D. vulgaris responses to H2O2 stress was constructed to illustrate that this bacterium may employ a complicated molecular mechanism to defend against the H2O2 -induced stresses. [source] Comment on general fugacity-based model for multiple chemical speciesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2003Kathrin Fenner [source] Clustering composition vectors using uncertainty informationENVIRONMETRICS, Issue 8 2007William F. Christensen Abstract In the biological and environmental sciences, interest often lies in using multivariate observations to discover natural clusters of objects. In this manuscript, the incorporation of measurement uncertainty information into a cluster analysis is discussed. This study is motivated by a problem involving the clustering of composition vectors associated with each of several chemical species. The observed abundance of each component is available along with its estimated uncertainty (measurement error standard deviation). An approach is proposed for converting the abundance vectors into composition (relative abundance) vectors, obtaining the covariance matrix associated with each composition vector, and defining a Mahalanobis distance between composition vectors that are suitable for cluster analysis. The approach is illustrated using particle size distributions obtained near Houston, Texas in 2000. Computer simulation is used to compare the performance of Mahalanobis-distance-based and Euclidean-distance-based clustering approaches. The use of a modified Mahalanobis distance along with Ward's method is recommended for use. Copyright © 2007 John Wiley & Sons, Ltd. [source] Surface-Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal NanocatalystsADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Qiao Zhang Abstract Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk,shell and core,satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability of the metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework. [source] Exploiting the genetic and biochemical capacities of bacteria for the remediation of heavy metal pollutionFEMS MICROBIOLOGY REVIEWS, Issue 4 2002Marc Valls Abstract The threat of heavy metal pollution to public health and wildlife has led to an increased interest in developing systems that can remove or neutralise its toxic effects in soil, sediments and wastewater. Unlike organic contaminants, which can be degraded to harmless chemical species, heavy metals cannot be destroyed. Remediating the pollution they cause can therefore only be envisioned as their immobilisation in a non-bioavailable form, or their re-speciation into less toxic forms. While these approaches do not solve the problem altogether, they do help to protect afflicted sites from noxious effects and isolate the contaminants as a contained and sometimes recyclable residue. This review outlines the most important bacterial phenotypes and properties that are (or could be) instrumental in heavy metal bioremediation, along with what is known of their genetic and biochemical background. A variety of instances are discussed in which valuable properties already present in certain strains can be combined or improved through state-of-the-art genetic engineering. In other cases, knowledge of metal-related reactions catalysed by some bacteria allows optimisation of the desired process by altering the physicochemical conditions of the contaminated area. The combination of genetic engineering of the bacterial catalysts with judicious eco-engineering of the polluted sites will be of paramount importance in future bioremediation strategies. [source] Nanolithography: Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-Objects (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Mater. On page 3696, Wang et al. report on the nanoscale chemical surface patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns by the iterative application of thermochemical nanolithography. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for the selective attachment of nanometer-sized objects, such as proteins or DNA, using standard chemical protocols. [source] Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-ObjectsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Debin Wang Abstract Nanoscale chemical patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns is achieved by the iterative application of thermochemical nanolithography (TCNL) to inscribe amine patterns followed by their chemical conversion to other functional groups. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for covalent and molecular-recognition-based attachment of nano-objects using standard chemical protocols. In particular, the ability of this method to attach proteins and DNA to the chemical nanopatterns and to create co-patterns of two distinctive bioactive proteins is demonstrated. [source] Photoluminescence-Based Sensing With Porous Silicon Films, Microparticles, and NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Michael J. Sailor Abstract Here, chemical sensors made from porous Si are reviewed, with an emphasis on systems that harness photoluminescence and related energy- and charge-transfer mechanisms available to porous Si-derived nanocrystallites. Quenching of luminescence by molecular adsorbates involves the harvesting of energy from a delocalized nanostructure that can be much larger than the molecule being sensed, providing a means to amplify the sensory event. The interaction of chemical species on the surface of porous Si can exert a pronounced influence on this process, and examples of some of the key chemical reactions that modify either the surface or the bulk properties of porous Si are presented. Sensors based on micron-scale and smaller porous Si particles are also discussed. Miniaturization to this size regime enables new applications, including imaging of cancerous tissues, indirect detection of reactive oxygen species (ROS), and controlled drug release. Examples of environmental and in vivo sensing systems enabled by porous Si are provided. [source] Bioinspired Electrochemically Tunable Block Copolymer Full Color PixelsADVANCED MATERIALS, Issue 30 2009Joseph J. Walish A variety of fish and cephalopods use tunable 1D photonic crystals to signal and display information. These animals control the color of the reflectors through chemical secretion by the sympathetic nervous system, which reduces the distance between platelets in reflective cells. This control can be mimicked by a bioinspired, 1D photonic block copolymer that is made tunable (see figure) by the production of chemical species through electrochemistry. [source] Investigation of a modified sequential iteration approach for solving coupled reactive transport problemsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2006David J. Z. Chen Abstract When contaminants enter the soil or groundwater, they may interact physically, geochemically and biochemically with the native water, microorganisms and solid matrix. A realistic description of a reactive transport regime that includes these processes requires joint consideration of multiple chemical species. Currently there are three common numerical approaches for coupling multispecies reaction and solute transport: the one-step approach, the sequential non-iterative approach (SNIA), and the sequential iterative approach (SIA). A modification of the SNIA method is the Strang-splitting method. In this study, a new modified sequential iteration approach (MSIA) for solving multicomponent reactive transport in steady state groundwater flow is presented. This coupling approach has been applied to two realistic reactive transport problems and its performance compared with the SIA and the Strang-splitting methods. The comparison shows that MSIA consistently converges faster than the other two coupling schemes. For the simulation of nitrogen and related species transport and reaction in a riparian aquifer, the total CPU time required by MSIA is only about 38% of the total CPU time required by the SIA, and only 50% of the CPU time required by the Strang-splitting method. The test problem results indicate that the SIA has superior accuracy, while the accuracy of MSIA is marginally better than that of the Strang-splitting method. The overall performance of MSIA is considered to be good, especially for simulations in which computational time is a critical factor. Copyright © 2005 John Wiley & Sons, Ltd. [source] Molecular dynamics and multiscale homogenization analysis of seepage/diffusion problem in bentonite clayINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2002Y. Ichikawa Abstract A scheme combining a molecular behaviour and macro-continuum phenomenon is presented for bentonite clay, which is a key component of a barrier system for disposal and containment of hazardous wastes. On designing a disposal facility we use a macro-phenomenological model. However the existing model is not sufficiently effective. Bentonite is a microinhomogeneous material. Properties of the saturated bentonite are characterized by montmorillonite and water, called montmorillonite hydrate. Since the crystalline structure of montmorillonite determines the fundamental properties of the montmorillonite hydrate, we analyse its molecular behaviour by applying a molecular dynamics simulation to enquire into the physicochemical properties of the montmorillonite hydrate such as diffusivity of chemical species. For extending the microscopic characteristics of constituent materials to a macroscopic diffusion behaviour of the microinhomogeneous material we apply a multiscale homogenization analysis, especially in order to treat micro-level of adsorption behaviour. Copyright © 2002 John Wiley & Sons, Ltd. [source] Flame structure and NO emissions in gas combustion of low calorific heating valueINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2003Jeong Park Abstract Numerical study on addition effects of CO and CO2 in fuel side (H2/Ar) on flame structure and NO emission behaviour in counterflow diffusion flame has been conducted with detailed chemistry to fundamentally understand gas combustion of low calorific heating value. A modified Miller,Bowman reaction scheme including a complementary C2 -reaction subset is adopted. The radiative heat loss term, which is based on an optically thin model and it especially important at low strain rates, is included to cover the importance of the temperature dependence on NO emission. Special interest is taken to estimate the roles of added CO and CO2 in fuel side on flame structure and NO emission characteristics. Increasing CO concentration in fuel side contributes to the enhancement of combustion due to the increase effect of the concentration of reactive species. The increase of added CO2 concentration in fuel side suppresses overall reaction rate due to the high heat capacity. It is seen that chemical effects due to the breakdown of added CO2 in fuel side make C2 -branch chemical species be remarkably formed and the prevailing contribution of prompt NO is a direct outcome of these effects. It is found that in the combined forms of H2/CO/CO2/Ar fuels the effects of added CO and CO2 concentrations in fuel side compete contrarily to each other in NO emission behaviour. Particularly the role of added CO is stressed in the side of restraining prompt NO. Copyright © 2003 John Wiley & Sons, Ltd. [source] Tailoring surface properties of cellulose acetate membranes by low-pressure plasma processingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Chun Huang Abstract The aim of this study was to tailor the surface properties of cellulose acetate membranes using low-pressure plasma processing. Argon (Ar) plasma and Difluoromethane (CH2F2) plasma were used to control the surface wettabilities of cellulose acetate membranes. Optical emission spectroscopy was used to examine the various chemical species of low-pressure plasma processing. In this investigation, the plasma-treated surfaces were analyzed by X-ray photoelectron spectroscopy, while changes in morphology and surface roughness were determined with confocal laser scanning microscopy. Ar plasma activation resulted in hydrophilic surface. CH2F2 plasma deposited hydrophobic layer onto the cellulose acetate membrane because of strong fluorination of the top layer. The results reveal low-pressure plasma processing is an effective method to control the surface properties of cellulose acetate membranes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Inhibition of human squalene monooxygenase by selenium compoundsJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 1 2002Nisha Gupta Abstract Selenosis in animals is characterized by a variety of neurological abnormalities, but the chemical species of selenium and the molecular targets that mediate this neurotoxicity are unknown. We have previously shown that selenite is a potent inhibitor of squalene monooxygenase, the second enzyme in the committed pathway for cholesterol biosynthesis; inhibition of this enzyme by dimethyltellurium leads to a peripheral demyelinating neuropathy similar to that seen in selenosis. To evaluate the role methylation plays in selenium toxicity, we examined the ability of three methylselenium compounds, methylselenol, dimethylselenide, and trimethylselenonium iodide, to inhibit purified recombinant human squalene monooxygenase. IC50 values for methylselenol (95 ,M) and dimethylselenide (680 ,M) were greater than that previously obtained for selenite (37 ,M), and inhibition by trimethylselenonium iodide was evident only at concentrations above 3 mM. Inhibition by methylselenol as well as by selenite was slow and irreversible, suggestive of covalent binding to the enzyme, and thiol-containing compounds could prevent and reverse this inhibition, indicating that these compounds were reacting with sulfhydryl groups on the protein. Monothiols such as glutathione and ,-mercaptoethanol provided better protection than did dithiols, suggesting that these selenium compounds bind to only one of the two proposed vicinal cysteines on squalene monooxygenase. Unexpectedly, the inhibition by selenite was significantly enhanced by dithiols, indicating that a more toxic species, possibly selenide, was formed in the presence of these dithiol reductants. © 2002 Wiley Periodicals, Inc. J Biochem Mol Toxicol 16:18,23, 2002; DOI 10.1002/jbt.10014 [source] Empirical preprocessing methods and their impact on NIR calibrations: a simulation studyJOURNAL OF CHEMOMETRICS, Issue 2 2005S. N. Thennadil Abstract The extraction of chemical information from dense particulate suspensions, such as industrial slurries and biological suspensions, using near-infrared (NIR) spectroscopic measurements is complicated by sample-to-sample path length variations due to light scattering. Empirical preprocessing techniques such as multiplicative scatter correction (MSC), extended MSC and derivatives have been applied to remove these effects and in some cases have shown promise. While the performance of these techniques and other related approaches is known to depend on the nature and extent of the variations and on the measurement configuration, detailed investigations into the efficacy of these approaches under various conditions have not been previously undertaken. The main obstacle to carrying out such investigations has been the lack of, and the difficulty in obtaining, an accurate and comprehensive experimental data set. In this work, simulations that generate ,actual' measurements were carried out to obtain ,experimental' spectroscopic data on particulate systems. This was achieved by solving the exact transport equation for light propagation. A model system comprising four chemical components with one consisting of spherical submicron particles was considered. Total diffuse transmittance and reflectance data generated through simulations for moderate particle concentrations were used as the basis for examining the effect of particle size variations and measurement configurations on the efficacy of a number of preprocessing techniques in enhancing the performance of partial least squares (PLS) models for predicting the concentration of one of the non-scattering chemical species. Additionally, a form of extended multiplicative signal correction based on considerations arising from fundamental light scattering theory is proposed and found to perform better than the other techniques for the cases considered in the study. Copyright © 2005 John Wiley & Sons, Ltd. [source] Flavonoids in Onion Cultivars (Allium cepa L.)JOURNAL OF FOOD SCIENCE, Issue 8 2008B. Rodríguez Galdón ABSTRACT:, Total phenol and flavonoid contents were analyzed by HPLC coupled with a diode array detector in 5 traditional onion cultivars from Tenerife (Guayonje, San Juan de la Rambla, Carrizal Alto, Carrizal Bajo, and Masca) and a commercial cultivar (Texas Early Grano 502). Five quercetin chemical species (isoquercetin, quercetin diglucoside, quercetin monoglucoside 1, quercetin monoglucoside 2, and free quercetin) and kaempferol were identified and quantified in the onion samples. Quercetin monoglucoside 1 and quercetin diglucoside were the major flavonoids accounting for 80% of the total quercetin content. The mean quercetin monoglucoside 1: quercetin diglucoside ratio (QMG/QDG) was 1: 2.2. There were differences between the onion cultivars in the cases of total phenol, quercetin diglucoside, isoquercetin, QMG/QDG ratio, and kaempferol. The Texas cultivar had a higher QMG/QDG ratio and a higher kaempferol content than the traditional cultivars. The correlation study showed significant correlations between the analyzed phenolic components. [source] Analysis of a pressure-driven folding flow microreactor with nearly plug-flow characteristicsAICHE JOURNAL, Issue 8 2010A. Vikhansky Abstract We discuss the possibility of designing a pressure-driven single-phase microreactor with characteristics similar to that in an ideal plug-flow reactor. We consider equations for the moments of the residence time distribution and investigate the behavior of the solution in long spatially-periodic channels. If the microreactor consists of a large number of folding flow elements, the chaotic advection plays a double role: it mixes the chemical species and suppresses the axial dispersion. It is shown using analytical estimates and numerical modeling that chemical reactions have different sensitivity to the axial dispersion and for some reactions the effect of dispersion can be successfully eliminated. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Peak width-mass correlation in CID MS/MS of isomeric oligosaccharides using traveling-wave ion mobility mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2009Tohru Yamagaki Abstract Isomeric oligosaccharides ,-cyclodextrin (,-CD), glucosyl-,CD (Glc1 -,CD) and maltosyl-,CD (Glc2 -,CD) were analyzed by traveling-wave ion mobility (twIM) mass spectrometry (MS). Their formation of multicharged multimers differed from each other. The ion mobility-mass spectrometry was useful in the self-assembling and complex formation analyses of CD isomers. The drift times of the isomers and their product ions with the same mass were almost the same in collision-induced dissociation (CID) MS/MS. In contrast, the ion mobility peak widths were sensitive to structural differences of the isomeric product ions. The twIM peak width (ms - µs) of the product ions [M , Glcn + H]+ (n = 0 , 6) of ,-CD correlated linearly with their masses (Da); the large and/or long chain product ions had wider peak widths, which were much wider than those from the general diffusion effect. This was a novel and useful ,trend line' to discriminate between the three isomers. Plots of [M , Glc2 , 6 + H]+ of Glc1 -,CD and [M , Glc3 , 6 + H]+ of Glc2 -,CD product ions' plots were on the same trend line as ,-CD. The plots of [M , Glc1 + H]+ of Glc1 -,CD and [M , Glc1, 2 + H]+ of Glc2 -,CD strayed from the ,-CD line; their peak widths were narrower than those of ,-CD. These results indicated that product ions from the chemical species of Glc1 -, CD and Glc2 -,CD retained their CD structure. Analyses of the IM peak widths enable us to elucidate the structures of the product ions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Determination of cubic equation of state parameters for pure fluids from first principle solvation calculationsAICHE JOURNAL, Issue 8 2008Chieh-Ming Hsieh Abstract A new method for estimation of parameters in cubic equations of state from ab initio solvation calculations is presented. In this method, the temperature-dependent interaction parameter a(T) is determined from the attractive component of solvation free energy, whereas the volume parameter b is assumed to be that of solvation cavity. This method requires only element-specific parameters, i.e., atomic radius and dispersion coefficient, and nine universal parameters for electrostatic and hydrogen-bonding interactions. The equations of state (EOS) parameters so determined allow the description of the complete fluid phase diagram, including the critical point. We have examined this method using the Peng,Robinson EOS for 392 compounds and achieved an accuracy of 43% in vapor pressure, 17% in liquid density, 5.4% in critical temperature, 11% in critical pressure, and 4% in critical volume. This method is, in principle, applicable to any chemical species and is especially useful for those whose experimental data are not available. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Design of reactive distillations for acetic acid esterificationAICHE JOURNAL, Issue 6 2005Yeong-Tarng Tang Abstract The reactive distillation provides an attractive alternative for reaction/separation processes with reversible reactions, especially for etherification and esterification. The discrete nature of chemical species and the complexity of phase equilibria seem to cloud the picture in understanding reactive distillation. The esterifications of acetic acid with five different alcohols, ranging from C1 to C5, are studied. First, qualitative relationships between macroscopic process flowsheet and microscopic phase equilibria are established, and the process flowsheets are classified into type I, II, and III for these five systems. Next, a systematic design procedure is devised to optimize the design, based on the total annual cost (TAC) and dominant design variables are identified for different flowsheets. Once quantitative design is available, process characteristic are analyzed and potential problems in process operation are identified. Finally, the economic potentials of these three different flowsheets are explored and explanations are given. The results clearly indicate that it is possible to systemize the design of reactive distillation by qualitatively generating flowsheet from phase equilibria and by quantitatively completing the process flow diagram from a sequential design procedure. Moreover, some of the flowsheets presented in this work cannot be found elsewhere in the open literature. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records,JOURNAL OF QUATERNARY SCIENCE, Issue 1 2009Mike Walker Abstract The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene,Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision. This climatic event is most clearly reflected in an abrupt shift in deuterium excess values, accompanied by more gradual changes in ,18O, dust concentration, a range of chemical species, and annual layer thickness. A timescale based on multi-parameter annual layer counting provides an age of 11 700 calendar yr b2,k (before AD 2000) for the base of the Holocene, with a maximum counting error of 99,yr. A proposal that an archived core from this unique sequence should constitute the Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) has been ratified by the International Union of Geological Sciences. Five auxiliary stratotypes for the Pleistocene,Holocene boundary have also been recognised. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification of chemical species of fluorescein isothiocyanate isomer,I (FITC) monolayers on platinum by doubly resonant sum-frequency generation spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2008Toshiki Maeda Abstract Doubly resonant sum-frequency generation (DR-SFG) spectroscopy of fluorescein-4-isothiocyanate isomer-I (FITC) monolayers on platinum was performed. Vibrational spectra of the monolayers for the IR wavenumber of 1750,1450 cm,1 were measured with visible probes ranging from 431 to 582 nm. Two vibrational bands at 1643 and 1610 cm,1 were observed, and their DR-SFG excitation profiles displayed different shapes. By rinsing the monolayers with an alkaline solution, the smaller wavenumber band disappeared and the larger wavenumber band gained intensity. On the basis of the spectral response to the rinsing, we concluded that the FITC molecules existed on platinum as deprotonated and protonated forms; the former corresponds to the 1643 cm,1 band and the latter to the 1610 cm,1 band. The deprotonated form was assigned to an anionic surface species, and the protonated form to a neutral surface species by comparing the DR-SFG excitation profiles with electronic absorption spectra of the protolytic forms of fluorescein in an aqueous solution (Sjöback R et al., Spectrochimica Acta A 1995; 51: L7,L21). The results demonstrate that the measurement of DR-SFG excitation profiles is a useful technique to identify chemical species of monolayers on metal surfaces. Copyright © 2008 John Wiley & Sons, Ltd. [source] Chloride-Ion Activities in Simplified Synthetic Concrete Pore Solutions: The Effect of the Accompanying IonsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Guillem de Vera Concrete pore solutions are concentrated electrolytes in which the activity of the chemical species must be calculated properly to determine the equilibrium state of such solutions. In this work, the chloride-ion activity coefficients in synthetic concrete pore solutions have been obtained potentiometrically, using different calibrated Cl, ion-selective electrodes (ISEs); also, a discussion about the performance of the different Cl, ISEs in alkaline media is presented. Experimental results are compared with the calculated results, using Pitzer's specific ionic-interaction model, and good agreement is observed between them. [source] The Watershed Deposition Tool: A Tool for Incorporating Atmospheric Deposition in Water-Quality Analyses,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2009Donna B. Schwede Abstract:, A tool for providing the linkage between air and water-quality modeling needed for determining the Total Maximum Daily Load (TMDL) and for analyzing related nonpoint-source impacts on watersheds has been developed. Using gridded output of atmospheric deposition from the Community Multiscale Air Quality (CMAQ) model, the Watershed Deposition Tool (WDT) calculates average per unit area and total deposition to selected watersheds and subwatersheds. CMAQ estimates the wet and dry deposition for all of its gaseous and particulate chemical species, including ozone, sulfur species, nitrogen species, secondary organic aerosols, and hazardous air pollutants at grid scale sizes ranging from 4 to 36 km. An overview of the CMAQ model is provided. The somewhat specialized format of the CMAQ files is not easily imported into standard spatial analysis tools. The WDT provides a graphical user interface that allows users to visualize CMAQ gridded data and perform further analyses on selected watersheds or simply convert CMAQ gridded data to a shapefile for use in other programs. Shapefiles for the 8-digit (cataloging unit) hydrologic unit code polygons for the United States are provided with the WDT; however, other user-supplied closed polygons may be used. An example application of the WDT for assessing the contributions of different source categories to deposition estimates, the contributions of wet and dry deposition to total deposition, and the potential reductions in total nitrogen deposition to the Albemarle-Pamlico basin stemming from future air emissions reductions is used to illustrate the WDT capabilities. [source] Matrix Representation of Polymer Chain Size Distributions, 2,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Fundamental Analysis of Linear Polymerization Mechanisms at Transient Conditions Abstract Analysis of the mass balance equations that describe a reaction system may be useful to provide information about its dynamics, such as the restricted set of compositions that can be achieved from a given set of initial compositions and the effect of feeding reactants to the reaction environment along the reaction course. Since these results may be important for the formulation of reaction policies, this work presents the properties of a matrix polymerization model previously developed and extended to describe transient conditions. This model is based on the definitions of two matrices: the consumption matrix (A,,,Kt), which contains information about chemical transformations among the many active polymer species in the system, and the propagation matrix Kp, which contains information about chain growth. It is shown that the set of mass balance equations that describes the dynamics of active chemical species in polymerization reactions has a stable and unique solution, which is bounded if feed rates are also bounded. It is also shown that the set of compositions that may be reached through manipulation of the feed rates is restricted and may not include all possible chemical compositions. Finally, it is shown that the obtained molecular weight distributions are special multiple time convolutions of the initiation rates. [source] Generalized k -space decomposition with chemical shift correction for non-cartesian water-fat imagingMAGNETIC RESONANCE IN MEDICINE, Issue 5 2008Ethan K. Brodsky Abstract Chemical-shift artifacts associated with non-Cartesian imaging are more complex to model and less clinically acceptable than the bulk fat shift that occurs with conventional spin-warp Cartesian imaging. A novel k -space based iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) approach is introduced that decomposes multiple species while simultaneously correcting distortion of off-resonant species. The new signal model accounts for the additional phase accumulated by off-resonant spins at each point in the k -space acquisition trajectory. This phase can then be corrected by adjusting the decomposition matrix for each k -space point during the final IDEAL processing step with little increase in reconstruction time. The technique is demonstrated with water-fat decomposition using projection reconstruction (PR)/radial, spiral, and Cartesian spin-warp imaging of phantoms and human subjects, in each case achieving substantial correction of chemical-shift artifacts. Simulations of the point-spread-function (PSF) for off-resonant spins are examined to show the nature of the chemical-shift distortion for each acquisition. Also introduced is an approach to improve the signal model for species which have multiple resonant peaks. Many chemical species, including fat, have multiple resonant peaks, although such species are often approximated as a single peak. The improved multipeak decomposition is demonstrated with water-fat imaging, showing a substantial improvement in water-fat separation. Magn Reson Med 59:1151,1164, 2008. © 2008 Wiley-Liss, Inc. [source] GSTM1 and GSTT1 null genotypes as possible heritable factors of rosaceaPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 4 2006Ayca Cordan Yazici Purpose: Rosacea might be related to an increased activity of reactive oxygen species (ROS) and deficient function of the antioxidant system. Glutathione S-transferases (GSTs) play a primer role in cellular defense against electrophilic chemical species and radical oxygen species. We hypothesized that increased ROS activity or decreased antioxidant potential, possibly induced by GST gene polymorphism, might have a pathogenic role in rosacea. Methods: The study group consisted of 45 patients with rosacea and 100 control subjects. DNA samples were isolated from blood samples using high pure polymerase chain reaction (PCR) Template preparation Kit. The GSTM1, GSTT1, and P1 polymorphisms were detected using a real-time PCR and fluorescence resonance energy transfer with a Light-Cycler Instrument. Associations between specific genotypes and the development of rosacea were examined using logistic regression analyses to calculate odds ratios (OR) and 95% confidence intervals (CI). Results: GSTM1 and GSTT1 null genotypes were found to be statistically different from control (P=0.005, P=0.009, respectively), and associated with an increased risk of rosacea (OR [95% CI]: 2.84 [1.37,5.89]; OR [95% CI]: 2.68 [1.27,5.67], respectively). There was a statistically significant relationship between both null combination of the GSTM1 and GSTT1 genotype polymorphisms and rosacea (P=0.003, OR [95% CI]: 4.18 [1.57,11.13]). There were no statistically significant differences between patient and control groups for the GSTP1 Ile/Ile, Ile/Val, and Val/Val genotypes (P>0.05). Conclusion: We demonstrated a significant association between the GSTT1 and/or GSTM1 null genotypes and rosacea. However, the potential role of GSTs as markers of susceptibility to rosacea needs further studies in larger patient groups. [source] Processing behavior of polycarbonate/functionalized-ethylene copolymer blendsPOLYMER ENGINEERING & SCIENCE, Issue 12 2000Marcos L. Dias The melt blending of polycarbonate (PC) and ethylene-methacrylic acid copolymers (EFC) either in the acid form (EFC-H) or partially neutralized with sodium (EFC-Na) or zinc (EFC-Zn) was investigated. Torque monitoring of the blending showed that the polymers are capable of reacting generating new chemical species that increase the melt viscosity. As general behavior, the torque curves pass by a maximum that takes place before 30 min, the final torque being higher than that of the individual polymers. SEC analyses reveal that PC degradation also occurs and is stronger in the case of blends with EFC-Na that acts to catalyze PC degradation, promoting CO2 formation. FTIR studies on chloroform insoluble fractions of the PC/EFC-Zn blends showed that in addition to a very small number of carbonate groups, feature absorption bands of aromatic ester and hydroxyl groups appear in the new chemical species formed during the reactive processing. [source] Improving feature detection and analysis of surface-enhanced laser desorption/ionization-time of flight mass spectraPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 11 2005Scott M. Carlson Abstract Discovering valid biological information from surface-enhanced laser desorption/ionization-time of flight mass spectrometry (SELDI-TOF MS) depends on clear experimental design, meticulous sample handling, and sophisticated data processing. Most published literature deals with the biological aspects of these experiments, or with computer-learning algorithms to locate sets of classifying biomarkers. The process of locating and measuring proteins across spectra has received less attention. This process should be tunable between sensitivity and false-discovery, and should guarantee that features are biologically meaningful in that they represent chemical species that can be identified and investigated. Existing feature detection in SELDI-TOF MS is not optimal for acquiring biologically relevant data. Most methods have so many user-defined settings that reproducibility and comparability among studies suffer considerably. To address these issues, we have developed an approach, called simultaneous spectrum analysis (SSA), which (i) locates proteins across spectra, (ii),measures their abundance, (iii),subtracts baseline, (iv),excludes irreproducible measurements, and (v),computes normalization factors for comparing spectra. SSA uses only two key parameters for feature detection and one parameter each for quality thresholds on spectra and peaks. The effectiveness of SSA is demonstrated by identifying proteins differentially expressed in SELDI-TOF spectra from plasma of wild-type and knockout mice for plasma glutathione peroxidase. Comparing analyses by SSA and CiphergenExpress Data Manager,2.1 finds similar results for large signal peaks, but SSA improves the number and quality of differences betweens groups among lower signal peaks. SSA is also less likely to introduce systematic bias when normalizing spectra. [source] | |||||||||||||||||||||||||||||||||||||