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Excess Concentrations (excess + concentration)
Selected AbstractsHydrogen Peroxide in Plants: a Versatile Molecule of the Reactive Oxygen Species NetworkJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 1 2008Li-Juan Quan Abstract Plants often face the challenge of severe environmental conditions, which include various biotic and abiotic stresses that exert adverse effects on plant growth and development. During evolution, plants have evolved complex regulatory mechanisms to adapt to various environmental stressors. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species (ROS), which are subsequently converted to hydrogen peroxide (H2O2). Even under normal conditions, higher plants produce ROS during metabolic processes. Excess concentrations of ROS result in oxidative damage to or the apoptotic death of cells. Development of an antioxidant defense system in plants protects them against oxidative stress damage. These ROS and, more particularly, H2O2, play versatile roles in normal plant physiological processes and in resistance to stresses. Recently, H2O2 has been regarded as a signaling molecule and regulator of the expression of some genes in cells. This review describes various aspects of H2O2 function, generation and scavenging, gene regulation and cross-links with other physiological molecules during plant growth, development and resistance responses. [source] Synthesis of new cationic surfactants based on recycled poly(ethylene terephthalate) for deinking of solvent-based ink from low-density polyethylene surfaceJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2010Samya I. El-Sherbiny Abstract Water-soluble oligomers based on poly-(ethylene terephthalate) waste, PET, were prepared from transesterification of PET with diethanolamine and triethanolamine in the presence of manganese acetate as a catalyst at temperature of 200°C for 8 h. New cationic surfactants were prepared by reaction of the produced recycled oligomers with bromoacetic acid followed by quaternization with pyridine. The chemical structure of the prepared surfactants was confirmed by 1H-NMR analysis. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (,max max), the area per molecule at interface (Amin), and the effectiveness of surface tension reduction (,CMC) were determined from the adsorption isotherms of the prepared surfactants. The prepared surfactants were tested as ink removal for printed low-density polyethylene surface. The effect of surfactants concentrations, pH, soaking time, and shaking time were investigated for deinking process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Orientation Control in Sol,Gel-Derived BiScO3,PbTiO3 Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2007Hai Wen BiScO3,PbTiO3 (BSPT) thin films were fabricated via a sol,gel method on Pt(111)/Ti/SiO2/Si(111) substrates. The effects of different factors on the orientation of the sol,gel-derived BSPT thin films were investigated. The results showed that a higher lead excess concentration, longer drying time, higher pyrolysis temperature, longer pyrolysis time, higher crystallization temperature, and longer crystallization time could enhance the (100) orientation of the BSPT thin films. Based on the experimental results, a mechanism for the orientation evolution in the sol,gel-derived BSPT thin films was proposed. The production of the (100) orientation was attributed to the (100)-oriented PbO nanocrystals forming during the pyrolysis process due to the lattice match. [source] Microstructural Evolution of Calcium-Doped ,-AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Arzu Altay Effect of different calcium doping levels on the microstructure of high-purity ,-alumina was studied as a function of sintering time and temperature using scanning electron microscopy (SEM). Microstructural evolution was related to hypothetical calcium excess at the grain boundaries (,Ca) that was calculated assuming zero solubility of calcium in bulk ,-alumina. Under all sintering conditions, grains were uniform in size and equiaxed for low calcium concentrations (<3 Ca atoms/nm2). The grain morphology became elongated when the calcium concentration at the grain boundaries reached calcium excess of ,Ca= 3,3.5 Ca atoms/nm2 in all samples. The average grain sizes of undoped samples were ,10% larger than the average grain sizes of low-calcium-doped samples. This decrease is believed to be due to solute drag effect of segregated Ca impurities on the grain boundary mobility. For the samples that were sintered at 1500° and 1600°C, slablike abnormally grown grains appeared for critical calcium excess concentrations of ,Ca= 4.5,8 Ca atoms/nm2. With abnormally grown grains a dramatic increase in average grain size was observed. However, when the calcium concentration was increased further, above certain calcium excess concentration depending on sintering temperature, a significant decrease in grain size was observed. In contrast to samples sintered at 1500° and 1600°C, when the samples sintered at 1400°C, although the hypothetical calcium coverage exceeded ,Ca= 11 Ca atoms/nm2, only few grains grew abnormally without significantly affecting the average grain size. Observations clearly indicated that calcium impurities caused elongated (slablike) grain morphology when their excess concentrations reached a critical level at the grain boundaries. [source] Hydrothermal Synthesis of Tetragonal Barium Titanate from Barium Chloride and Titanium Tetrachloride under Moderate ConditionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Huarui Xu Tetragonal BaTiO3powders were prepared hydrothermally at 240°C, in only 12 h, using BaCl2·2H2O and TiCl4, which are rather easy to manipulate. Characterization via X-ray diffractometry, scanning electron microscopy, Brunauer,Emmett,Teller analysis, and differential scanning calorimetry confirmed that increasing the NaOH excess concentration (from 0.5M to 2.0M) and decreasing the initial TiCl4concentration (from 0.625M to 0.15M) promotes the formation of tetragonal BaTiO3powders. After reaction, the powders were proved to be phase-pure BaTiO3, with no impurities, such as Cl, and CO32,. [source] Uncatalyzed and ruthenium(III)-catalyzed reaction of acidic chlorite with methylene violetINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2003S. B. Jonnalagadda The kinetics and mechanism of the uncatalyzed and Ru(III)-catalyzed oxidation of methylene violet (3-amino-7-diethylamino-5-phenyl phenazinium chloride) (MV+) by acidic chlorite is reported. With excess concentrations of other reactants, both uncatalyzed and catalyzed reactions had pseudo-first-order kinetics with respect to MV+. The uncatalyzed reaction had first-order dependence on chlorite and H+ concentrations, but the catalyzed reaction had first-order dependence on both chlorite and catalyst, and a fractional order with respect to [H+]. The rate coefficient of the uncatalyzed reaction is (5.72 ± 0.19) M,2 s,1, while the catalytic constant for the catalyzed reaction is (22.4 ± 0.3) × 103 M,1 s,1. The basic stoichiometric equation is as follows: 2MV+ + 7ClO2, + 2H+ = 2P + CH3COOH + 4ClO2 + 3Cl,, where P+ = 3-amino-7-ethylamino-5-phenyl phenazinium-10-N-oxide. Stoichiometry is dependent on the initial concentration of chlorite present. Consistent with the experimental results, pertinent mechanisms are proposed. The proposed 15-step mechanism is simulated using literature; experimental and estimated rate coefficients and the simulated plots agreed well with the experimental curves. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 294,303, 2003 [source] Kinetics and simulations of reaction between safranine- O and acidic bromate and role of bromide thereinINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2002S. B. Jonnalagadda Safranine- O, a dye of the phenazinium class, was found to exhibit intricate kinetics during its reaction with bromate at low pH conditions. Under conditions of excess concentrations of acid and bromate, safranine- O (SA+) initially depleted very slowly (k = (3.9 ± 0.3) × 10,4 M,3 s,1) but after an induction time, the reaction occurred swiftly. Bromide exhibited a dual role in the reaction mechanism, both as an autocatalyst and as an inhibitor. The added bromide increased the initial rate of depletion of SA+, but delayed the transition to rapid reaction. The overall stiochiometric reaction was found to be 6SA+ + 4 BrO3, = 6SP + 3N2O + 3H2O + 6H+ + 4Br,, where SP is 3-amino-7-oxo-2,8-dimethyl-5-phenylphenazine. The fast kinetics of the reaction between aqueous bromine and safranine- O (k = (2.2 ± 0.1) × 103 M,1 s,1) are also reported in this paper A 17-step mechanism, consistent with the overall reaction dynamics and supported by simulations, is proposed and the role of various bromo and oxybromo species is also discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 542,549, 2002 [source] Increased gas solubility in nanoliquids: Improved performance in interfacial catalytic membrane contactorsAICHE JOURNAL, Issue 2 2009Marc Pera-Titus Abstract The kinetics of gas-liquid catalytic reactions can be strongly promoted when these are performed in interfacial catalytic membrane reactors instead of other three-phase reactors such as slurry stirrers or trickle beds. The well-defined gas-liquid-catalyst contact in this system avoiding diffusional limitations is usually argued as the main reason for such enhancement. In this work, using nitrobenzene hydrogenation as a model reaction, we propose that this increased catalytic performance might also be attributed, at least partially, to increased gas solubilities in mesoconfined solvents (or simply "nanoliquids") in interfacial contactors overcoming the values predicted by Henry's Law. To support this hypothesis, we provide experimental evidence of a dramatic increase of H2 solubility in confined ethanol using mesoporous ,-Al2O3 as confining solid. Gas-liquid solubilities can be enhanced up to five times over the corresponding bulk values for nanoliquid sizes lower than 15 nm as long as the gas-liquid interface is confined in a mesoporous array. In such a situation, the volume of the gas-liquid interface is no longer negligible compared to the total volume of the confined liquid, and the high surface excess concentrations of the gas adsorbed on the liquid surface make solubility grow up dramatically. According to these measurements, we discuss how nanoliquids might form in catalytic membrane contactors, which gas-liquid configuration in the reactor appears to be more appropriate, and how the structure of the mesoporous catalytic layer contributes to their increased gas solubilization performance. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Microstructural Evolution of Calcium-Doped ,-AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Arzu Altay Effect of different calcium doping levels on the microstructure of high-purity ,-alumina was studied as a function of sintering time and temperature using scanning electron microscopy (SEM). Microstructural evolution was related to hypothetical calcium excess at the grain boundaries (,Ca) that was calculated assuming zero solubility of calcium in bulk ,-alumina. Under all sintering conditions, grains were uniform in size and equiaxed for low calcium concentrations (<3 Ca atoms/nm2). The grain morphology became elongated when the calcium concentration at the grain boundaries reached calcium excess of ,Ca= 3,3.5 Ca atoms/nm2 in all samples. The average grain sizes of undoped samples were ,10% larger than the average grain sizes of low-calcium-doped samples. This decrease is believed to be due to solute drag effect of segregated Ca impurities on the grain boundary mobility. For the samples that were sintered at 1500° and 1600°C, slablike abnormally grown grains appeared for critical calcium excess concentrations of ,Ca= 4.5,8 Ca atoms/nm2. With abnormally grown grains a dramatic increase in average grain size was observed. However, when the calcium concentration was increased further, above certain calcium excess concentration depending on sintering temperature, a significant decrease in grain size was observed. In contrast to samples sintered at 1500° and 1600°C, when the samples sintered at 1400°C, although the hypothetical calcium coverage exceeded ,Ca= 11 Ca atoms/nm2, only few grains grew abnormally without significantly affecting the average grain size. Observations clearly indicated that calcium impurities caused elongated (slablike) grain morphology when their excess concentrations reached a critical level at the grain boundaries. [source] Direct Volumetric Measurement of Gas Oversolubility in Nanoliquids: Beyond Henry's LawCHEMPHYSCHEM, Issue 12 2009Marc Pera-Titus Dr. Abstract The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H2 in a series of solvents (CHCl3, CCl4, n -hexane, ethanol, and water) when confined in the cavities of mesoporous solids (,-alumina, silica, and MCM-41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry's law constant apparently no longer applies under these confinement, the concentration of dissolved H2 still increases linearly with increasing pressure in the range 1,5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility. [source] | |||||||||||||