Low Mole Fractions Research Articles

Analysis of patterns in the concentrations of atmospheric greenhouse gases measured in two typical urban clusters in China

China is the largest emitter of greenhouse gases, and urban clusters play an essential role in China's carbon emissions because of the country's unbalanced economic development. In this paper, the discrete air sample measurements of atmospheric CO2, CH4, and CO during the period between 2007 and 2013 from Shangdianzi (SDZ) station in Jing-Jin-Ji (JJJ) region and Linan (LAN) station in Yangtze River Delta (YRD) region, respectively, are presented and characterized. By backward trajectory cluster analysis, the low background CO2 mole fraction and similar long-term trends with Waliguan global station (WLG) were observed at SDZ because most of the air masses originate mostly from remote clean terrestrial areas in the north with limited information of anthropogenic emissions. But the background CH4 and CO are influenced mainly by ruminants and rice field emission from the surrounding regions and urban cluster emission in the JJJ region, which lead to the higher CH4 and CO in summer at SDZ. Whereas, the CO2, CH4 and CO background values observed at LAN are higher by the combined effects of long-distance atmospheric transportation from Northern and Central China and urban clusters emission from the YRD region. The observed polluted data at SDZ and LAN are all strongly affected by regional and local anthropogenic emissions, which lead to the higher GHGs concentrations compared to the background data. However, because the air mass transportation from the north is weak in winter and no winter heating is required and vegetation photosynthesis is still stronger in the south of China, the CO2 concentration at LAN is lower than that at SDZ in autumn and winter. The polluted CO value at SDZ is found considerably higher than that at LAN, especially in spring and winter. By analyzing the correlations of observed regional enhanced values of CO2, CH4 and CO at the two stations, we find the significant correlation between them, which means they may share the common-source of anthropogenic emissions from the regional fossil fuel and biomass burning in cold season. Moreover, the high coal-consumption proportion with the low CO2 emissions factors, and much biomass burning with low combustion efficiency in JJJ region lead to the higher slope values of △CO2 and △CO in spring and winter at SDZ and considerably higher than that at LAN. The results can provide a further understanding of regional/local features of atmospheric GHGs under the influence of human activities in the urban clusters in China.

Aggregation Number in Water/n-Hexanol Molecular Clusters Formed in Cyclohexane at Different Water/n-Hexanol/Cyclohexane Compositions Calculated by Titration 1H NMR.

Upon titration of n-hexanol/cyclohexane mixtures of different molar compositions with water, water/n-hexanol clusters are formed in cyclohexane. Here, we develop a new method to estimate the water and n-hexanol aggregation numbers in the clusters that combines integration analysis in one-dimensional 1H NMR spectra, diffusion coefficients calculated by diffusion-ordered NMR spectroscopy, and further application of the Stokes-Einstein equation to calculate the hydrodynamic volume of the clusters. Aggregation numbers of 5-15 molecules of n-hexanol per cluster in the absence of water were observed in the whole range of n-hexanol/cyclohexane molar fractions studied. After saturation with water, aggregation numbers of 6-13 n-hexanol and 0.5-5 water molecules per cluster were found. O-H and O-O atom distances related to hydrogen bonds between donor/acceptor molecules were theoretically calculated using density functional theory. The results show that at low n-hexanol molar fractions, where a robust hydrogen-bond network is held between n-hexanol molecules, addition of water makes the intermolecular O-O atom distance shorter, reinforcing molecular association in the clusters, whereas at high n-hexanol molar fractions, where dipole-dipole interactions dominate, addition of water makes the intermolecular O-O atom distance longer, weakening the cluster structure. This correlates with experimental NMR results, which show an increase in the size and aggregation number in the clusters upon addition of water at low n-hexanol molar fractions, and a decrease of these magnitudes at high n-hexanol molar fractions. In addition, water produces an increase in the proton exchange rate between donor/acceptor molecules at all n-hexanol molar fractions.

Combustion Characteristics of Single Particles from Bituminous Coal and Pine Sawdust in O2/N2, O2/CO2, and O2/H2O Atmospheres

Burning fuels in an O2/H2O atmosphere is regarded as the next generation of oxy-fuel combustion for CO2 capture and storage (CCS). By combining oxy-fuel combustion and biomass utilization technology, CO2 emissions could be further reduced. Therefore, this work focuses on investigating the combustion characteristics of single particles from bituminous coal (BC) and pine sawdust (PS) in O2/N2, O2/CO2 and O2/H2O atmospheres at different O2 mole fractions (21%, 30%, and 40%). The experiments were carried out in a drop tube furnace (DTF), and a high-speed camera was used to record the combustion processes of fuel particles. The combustion temperatures were measured by a two-color method. The results reveal that the particles from BC and PS all ignite homogeneously. Replacing N2 by CO2 results in a longer ignition delay time and lower combustion temperatures. After substituting H2O for N2, the ignition delay time is shortened, which is mainly caused by the steam gasification reaction (C + H2O → CO + H2) and steam shift reaction (CO + H2O → CO2 + H2). In addition, the combustion temperatures are first decreased at low O2 mole fractions, and then increased at high O2 mole fractions because the oxidation effect of H2O performs a more important role than its volumetric heat capacity and thermal radiation capacity. At the same condition, particles from PS ignite earlier because of their higher reactivity, but the combustion temperatures are lower than those of BC, which is owing to their lower calorific values.

Measurement of the electron attachment properties of SF5CF3 and comparison to SF6

The electron attachment properties of are experimentally investigated using a pulsed Townsend setup. Different / and / mixtures, with mole fractions ranging from to 1, are characterized. The effective ionization rate coefficient, electron drift velocity and reduced longitudinal electron diffusion coefficient in these mixtures are obtained. For low mole fractions of , the effective ionization rate coefficient is compared to calculations from available electron scattering cross sections, and is also used for estimating the electron attachment cross section of . For pure , the present data is compared to early data from a steady-state Townsend experiment. The presentation of the measurement results is followed by a discussion on the properties of and and their significance for gaseous electrical insulation.

Synthesis of palygorskite-supported Mn1−xCexO2 clusters and their performance in catalytic oxidation of formaldehyde

Abstract Nano-scale Mn 1 − x Ce x O 2 catalysts supported on palygorskite (PG) with different dopant fractions were prepared by the co-precipitation method and applied in the catalytic oxidation of formaldehyde (HCHO). The obtained samples were characterized using BET, XRD, Raman spectroscopy, TEM, EDS, and H 2 -TPR to illustrate the physicochemical properties of the catalysts. After the introduction of cerium, the growth of manganese oxide was inhibited. However, an increase of the Ce/(Ce + Mn) ratio from 0.1 to 0.5 increased the particle size from 2.87 to 6.86 nm. A remarkable interface (grain boundaries) between MnO 2 and CeO 2 was observed, especially for low cerium molar fractions (0.1–0.4). The doping of cerium significantly enhanced the activity of manganese oxide for HCHO oxidation at 100–180 °C. The Mn 0.9 Ce 0.1 /PG catalyst exhibited the best activity, and HCHO was completely converted to CO 2 and H 2 O at 160 °C. The characterization results indicated that smaller particle size, surface-adsorbed oxygen species and abundant oxygen vacancies accounted for the high catalytic activity of the Mn 0.9 Ce 0.1 /PG catalyst for HCHO conversion. In addition, the Mn 0.9 Ce 0.1 /PG catalyst also displayed high stability in lifetime testing and excellent water-resistant performance. The experimental results suggest that palygorskite-supported Mn 0.9 Ce 0.1 is a promising catalyst for the catalytic oxidation of formaldehyde at low temperatures.

SL2B aptamer and folic acid dual-targeted DNA nanostructures for synergic biological and chemotherapy to combat colorectal cancer

The influence of chemical structure on NAPL mixture nonideality evolution, rate-limited dissolution, and contaminant mass flux was examined. The variability of measured and UNIFAC modeled NAPL activity coefficients as a function of mole fraction was compared for two NAPL mixtures containing structurally-different contaminants of concern including toluene (TOL) or trichloroethene (TCE) within a hexadecane (HEXDEC) matrix. The results showed that dissolution from the NAPL mixtures transitioned from ideality for mole fractions > 0.05 to nonideality as mole fractions decreased. In particular, the TCE generally exhibited more ideal dissolution behavior except at lower mole fractions, and may indicate greater structural/polarity similarity between the two compounds. Raoult's Law and UNIFAC generally under-predicted the batch experiment results for TOL:HEXDEC mixtures especially for mole fractions ≤ 0.05. The dissolution rate coefficients were similar for both TOL and TCE over all mole fractions tested. Mass flux reduction (MFR) analysis showed that more efficient removal behavior occurred for TOL and TCE with larger mole fractions compared to the lower initial mole fraction mixtures (i.e. < 0.2). However, compared to TOL, TCE generally exhibited more efficient removal behavior over all mole fractions tested and may have been the result of structural and molecular property differences between the compounds. Activity coefficient variability as a function of mole fraction was quantified through regression analysis and incorporated into dissolution modeling analyses for the dynamic flushing experiments. TOL elution concentrations were modeled (predicted) reasonable well using ideal and equilibrium assumptions, but the TCE elution concentrations could not be predicted using the ideal model. Rather, the dissolution modeling demonstrated that TCE elution was better described by the nonideal model whereby NAPL-phase activity coefficient varied as a function of COC mole fraction. For dynamic column flushing experiments, dissolution rate kinetics can vary significantly with changes in NAPL volume and surface area. However, under conditions whereby NAPL volume and area are not significantly altered during dissolution, mixture nonideality effects may have a greater relative control on dissolution (elution) and MFR behavior compared to kinetic rate limitations.

Concentration-Dependent Hydrogen Bond Behavior of Ethylammonium Nitrate Protic Ionic Liquid–Water Mixtures Explored by Molecular Dynamics Simulations

The detailed hydrogen bond (HB) behavior of ethylammonium nitrate (EAN) ionic liquid (IL)–water mixtures with different water concentrations has been investigated at a molecular level by using classical molecular dynamics simulations. The simulation results demonstrate that the increasing water concentration can weaken considerably all cation–anion, cation–water, anion–water, and water–water HBs in EAN–water mixtures, and the corresponding HB networks around cations, anions, and water molecules also change significantly with the addition of water. Meanwhile, both the translational and the rotational motions of anions, cations, and water molecules are found to be much faster as the water concentration increases. On the other hand, the order of their HB strength is found to be cation–anion > anion–water > cation–water > water–water at low water mole fractions ( cation–water > anion–water > water–water at high water mole fractions (>38%). The opposite ord...

Mixed micellization study of ibuprofen (sodium salt) and cationic surfactant (conventional as well as gemini)

AbstractHerein, we have studied the interaction between cationic surfactant (conventional [myristyltrimethylammonium bromide, MTAB] as well as gemini surfactant 1, 4‐butanediyl‐α, ω‐bis(dimethyltetradecylammonium bromide) (14‐4‐14)) and anti‐inflammatory sodium salt of ibuprofen (IBU) drug in aqueous solutions by using tensiometry method at 298.15 K. The means of the interaction of drugs by added foreign materials is of paramount importance in the drug delivery. Ibuprofen is used for the relief of pain, fever, and swelling. From this study we have evaluated different parameters, for example, critical micelle concentration (cmc), micellar mole fraction of mixed micelles/mixed interface (X1m/X1σ), micellar/surface interaction parameter (βm/βσ), activity coefficients (f1m/f1σ and f2m/f2σ) of the mixed micelles/mixed interface, excess Gibbs free energy of mixed monolayer/mixed micelle formation ( / ), surface excess concentration (Γmax) etc. and discussed in detail. The micellar interaction parameter (βm) was determined from the critical micelle concentration values of the pure surfactant (MTAB/14‐4‐14) and IBU (cmc1 and cmc2) and the mixed system (cmc) using the Rubingh's model. In addition to this, various other parameters such as packing parameters of amphiphiles in the micelles (P), volume contribution of the hydrophobic chain (V0), and its effective length (lc), have also been calculated. The value of micellar mole fraction ( ) is found to be more for IBU + 14‐4‐14 mixtures as compared to IBU + MTAB mixtures at lower mole fraction and vice versa at a higher mole fraction of surfactant. The ΔGom and ΔGoads values for all studied systems were found out to be negative, ie, micellization, as well as adsorption processes, are found to be energetically favorable.

Transport properties of mixtures composed of acetone, water, and supercritical carbon dioxide by molecular dynamics simulation

Transport properties of various mixtures of supercritical carbon dioxide, acetone, and water at different concentrations are evaluated at temperatures 313.15K and pressure 150bar by molecular dynamics simulations. The results show that the self-diffusion (viscosity) coefficient is increased (decreased) for all various mixtures studied when the concentration of the acetone is increased. In addition, the densities of the mixtures will rise (lower), when the supercritical carbon dioxide (acetone) concentrations is increased. We have observed that the first peak heights of the radial distribution functions will rise at very low mole fraction of water (xw=0.016) when the acetone and carbon dioxide concentrations are increasing, and hence the self-diffusion coefficients will decrease while its density and viscosity will increase.

Interaction and binding efficiency of cationic drug chlorpheniramine maleate – anionic amino acid gemini surfactants mixture as media for the synthesis of silver nanoparticles

The advantages of drug–surfactant interactions as drug delivery vehicles are valuable for developing pharmaceutical formulations. The interaction of a drug, chlorpheniramine maleate (CPM), and (N,N′-dialkyl-N,N′-diacetate ethylenediamine, Ace(m)-2-Ace(n)), amino acid gemini surfactants (GSs) was investigated for various micellar, interfacial, and thermodynamic parameters at different mole fractions of CPM and GS mixtures using surface tension techniques. The values of the interaction parameter (β) suggested that CPM (cationic drug) exhibited low synergistic interactions with anionic GSs. Using UV measurement to evaluate the binding of CPM with GS, we determined the binding constant of drugs in the presence of GS and CPM+GS mixtures. Anionic GSs bound preferentially with CPM, because of the presence of cationic ions on the head group of the drug, and as an important drug-carrier, GSs showed higher binding constant (Kb) than that of ionic surfactant even at very low mole fractions. The values of different binding constant (Kb) indicated the binding mechanism of the CPM+GS mixed system. Mixed compositions of drug–surfactants were used to stabilize silver nanoparticles in aqueous media. The UV spectroscopy, dynamic light scattering, and transmission electron microscopy indicated a strong hydrophobic and the electrostatic interaction between CPM and GS. Specific morphologies were formed by adopting different supramolecular assemblies in aqueous media, depending on the internal packing arrangements and on the numbers of methylene units [–(CH2) n–].

Local structure of dilute aqueous DMSO solutions, as seen from molecular dynamics simulations.

The information about the structure of dimethyl sulfoxide (DMSO)-water mixtures at relatively low DMSO mole fractions is an important step in order to understand their cryoprotective properties as well as the solvation process of proteins and amino acids. Classical MD simulations, using the potential model combination that best reproduces the free energy of mixing of these compounds, are used to analyze the local structure of DMSO-water mixtures at DMSO mole fractions below 0.2. Significant changes in the local structure of DMSO are observed around the DMSO mole fraction of 0.1. The array of evidence, based on the cluster and the metric and topological parameters of the Voronoi polyhedra distributions, indicates that these changes are associated with the simultaneous increase of the number of DMSO-water and decrease of water-water hydrogen bonds with increasing DMSO concentration. The inversion between the dominance of these two types of H-bonds occurs around XDMSO = 0.1, above which the DMSO-DMSO interactions also start playing an important role. In other words, below the DMSO mole fraction of 0.1, DMSO molecules are mainly solvated by water molecules, while above it, their solvation shell consists of a mixture of water and DMSO. The trigonal, tetrahedral, and trigonal bipyramidal distributions of water shift to lower corresponding order parameter values indicating the loosening of these orientations. Adding DMSO does not affect the hydrogen bonding between a reference water molecule and its first neighbor hydrogen bonded water molecules, while it increases the bent hydrogen bond geometry involving the second ones. The close-packed local structure of the third, fourth, and fifth water neighbors also is reinforced. In accordance with previous theoretical and experimental data, the hydrogen bonding between water and the first, the second, and the third DMSO neighbors is stronger than that with its corresponding water neighbors. At a given DMSO mole fraction, the behavior of the intensity of the high orientational order parameter values indicates that water molecules are more ordered in the vicinity of the hydrophilic group while their structure is close-packed near the hydrophobic group of DMSO.

Molecular dynamics analysis of the friction between a water-methanol liquid mixture and a non-polar solid crystal surface.

We performed molecular dynamics analysis of the momentum transfer at the solid-liquid interface for a water-methanol liquid mixture between parallel non-polar solid walls in order to understand the strong decrease of the friction coefficient (FC) induced by the methanol adsorption at the surface observed in our previous work [S. Nakaoka et al., Phys. Rev. E 92, 022402 (2015)]. In particular, we extracted the individual contributions of water and methanol molecules to the total FC and found that the molecular FC for methanol was larger than that for water. We further showed that the reduction of the total solid-liquid FC upon the increase of the methanol molar fraction in the first adsorption layer occurred as a result of a decrease in the molecular number density as well as a decrease in the molecular FCs of both molecules. Analysis of the molecular orientation revealed that the decrease of the molecular FC of methanol resulted from changes of the contact feature onto the solid surface. Specifically, methanol molecules near the solid surface had their C-O bond parallel to the surface with both CH3 and O sites contacting the solid at low methanol molar fraction, while they had their C-O bond outward from the surface with only the CH3 site contacting the solid at higher methanol molar fraction. The mechanisms discussed in this work could be used to search for alternative water additives to further reduce the solid-liquid friction.

Nanosegregation and Structuring in the Bulk and at the Surface of Ionic-Liquid Mixtures

Ionic-liquid (IL) mixtures hold great promise, as they allow liquids with a wide range of properties to be formed by mixing two common components rather than by synthesizing a large array of pure ILs with different chemical structures. In addition, these mixtures can exhibit a range of properties and structural organization that depend on their composition, which opens up new possibilities for the composition-dependent control of IL properties for particular applications. However, the fundamental properties, structure, and dynamics of IL mixtures are currently poorly understood, which limits their more widespread application. This article presents the first comprehensive investigation into the bulk and surface properties of IL mixtures formed from two commonly encountered ILs: 1-ethyl-3-methylimidazolium and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][Tf2N] and [C12mim][Tf2N]). Physical property measurements (viscosity, conductivity, and density) reveal that these IL mixtures are not well described by simple mixing laws, implying that their structure and dynamics are strongly composition dependent. Small-angle X-ray and neutron scattering measurements, alongside molecular dynamics (MD) simulations, show that at low mole fractions of [C12mim][Tf2N], the bulk of the IL is composed of small aggregates of [C12mim]+ ions in a [C2mim][Tf2N] matrix, which is driven by nanosegregation of the long alkyl chains and the polar parts of the IL. As the proportion of [C12mim][Tf2N] in the mixtures increases, the size and number of aggregates increases until the C12 alkyl chains percolate through the system and a bicontinuous network of polar and nonpolar domains is formed. Reactive atom scattering-laser-induced fluorescence experiments, also supported by MD simulations, have been used to probe the surface structure of these mixtures. It is found that the vacuum-IL interface is enriched significantly in C12 alkyl chains, even in mixtures low in the long-chain component. These data show, in contrast to previous suggestions, that the [C12mim]+ ion is surface active in this binary IL mixture. However, the surface does not become saturated in C12 chains as its proportion in the mixtures increases and remains unsaturated in pure [C12mim][Tf2N].

Extraction of bismuth with mixing systems of sec-octylphenoxy acetic acid and 1,10-phenanthroline

ABSTRACTsec-Octylphenoxy acetic acid and 1,10-phenanthroline were employed for the extraction of bismuth from chloride medium, showing evident synergistic effects on bismuth extraction. Stoichiometry of the synergistic extraction was determined, giving a logarithm value of equilibrium constant of 6.75, which was much higher than those obtained by single sec-octylphenoxy acetic acid or 1,10-phenanthroline. Thermodynamic studies indicated that the synergistic extraction was an endothermic and spontaneous process. Moreover, antagonistic effects were found when the mixture was employed for lead extraction, demonstrating its potential to be applied to the separation of bismuth and lead at low mole fractions of sec-octylphenoxy acetic acid.

Combining molecular and bioprocess techniques to produce poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with controlled monomer composition by Burkholderia sacchari

Biopolymers as polyhydroxyalkanoates (PHA) composed by different co-monomers 3-hydroxybutyrate and 3-hydroxyhexanoate [P(3HB-co-3HHx)] has attracted interest since its properties are similar to low density polyethylene. Burkholderia sacchari produces this copolymer with a very low 3HHx molar fraction, about 2 mol%. B. sacchari mutant (unable to produce polymer) was engineered to host PHA biosynthesis genes (phaPCJ) from Aeromonas sp. In addition, a two-step bioprocess to increase biopolymer production was developed. The combination of these techniques resulted in the production of P(3HB-co-3HHx) with 3HHx content up to 20 mol%. The PHA content was about 78% of dry biomass, resulting in PHA volumetric productivities around 0.45gl−1h−1. The P(3HB-co-3HHx) containing 20 mol% of 3HHx presented an elongation at brake of 945%, higher than reported before for this PHA composition. Here we have described an approach to increase 3HHx content into the copolymer, allowing the precise control of the 3HHx molar fractions.

Chemical structure influence on NAPL mixture nonideality evolution, rate-limited dissolution, and contaminant mass flux

The influence of chemical structure on NAPL mixture nonideality evolution, rate-limited dissolution, and contaminant mass flux was examined. The variability of measured and UNIFAC modeled NAPL activity coefficients as a function of mole fraction was compared for two NAPL mixtures containing structurally-different contaminants of concern including toluene (TOL) or trichloroethene (TCE) within a hexadecane (HEXDEC) matrix. The results showed that dissolution from the NAPL mixtures transitioned from ideality for mole fractions >0.05 to nonideality as mole fractions decreased. In particular, the TCE generally exhibited more ideal dissolution behavior except at lower mole fractions, and may indicate greater structural/polarity similarity between the two compounds. Raoult's Law and UNIFAC generally under-predicted the batch experiment results for TOL:HEXDEC mixtures especially for mole fractions ≤0.05. The dissolution rate coefficients were similar for both TOL and TCE over all mole fractions tested. Mass flux reduction (MFR) analysis showed that more efficient removal behavior occurred for TOL and TCE with larger mole fractions compared to the lower initial mole fraction mixtures (i.e. <0.2). However, compared to TOL, TCE generally exhibited more efficient removal behavior over all mole fractions tested and may have been the result of structural and molecular property differences between the compounds. Activity coefficient variability as a function of mole fraction was quantified through regression analysis and incorporated into dissolution modeling analyses for the dynamic flushing experiments. TOL elution concentrations were modeled (predicted) reasonable well using ideal and equilibrium assumptions, but the TCE elution concentrations could not be predicted using the ideal model. Rather, the dissolution modeling demonstrated that TCE elution was better described by the nonideal model whereby NAPL-phase activity coefficient varied as a function of COC mole fraction. For dynamic column flushing experiments, dissolution rate kinetics can vary significantly with changes in NAPL volume and surface area. However, under conditions whereby NAPL volume and area are not significantly altered during dissolution, mixture nonideality effects may have a greater relative control on dissolution (elution) and MFR behavior compared to kinetic rate limitations.

Metabolomics analysis of postphotosynthetic effects of gaseous O2 on primary metabolism in illuminated leaves.

The response of underground plant tissues to O2 limitation is currently an important topic in crop plants since adverse environmental conditions (e.g. waterlogging) may cause root hypoxia and thus compromise plant growth. However, little is known on the effect of low O2 conditions in leaves, probably because O2 limitation is improbable in these tissues under natural conditions, unless under complete submersion. Nevertheless, an O2-depleted atmosphere is commonly used in gas exchange experiments to suppress photorespiration and estimate gross photosynthesis. However, the nonphotosynthetic effects of gaseous O2 depletion, particularly on respiratory metabolism, are not well documented. Here, we used metabolomics obtained under contrasting O2 and CO2 conditions to examine the specific effect of a changing O2 mole fraction from ambient (21%) to 0%, 2% or 100%. In addition to the typical decrease in photorespiratory intermediates (glycolate, glycine and serine) and a build-up in photosynthates (sucrose), low O2 (0% or 2%) was found to trigger an accumulation of alanine and change succinate metabolism. In 100% O2, the synthesis of threonine and methionine from aspartate appeared to be stimulated. These responses were observed in two species, sunflower (Helianthus annuus L.) and Arabidopsis thaliana (L.) Heynh. Our results show that O2 causes a change in the oxygenation : carboxylation ratio and also alters postphotosynthetic metabolism: (i) a hypoxic response at low O2 mole fractions and (ii) a stimulation of S metabolism at high O2 mole fractions. The latter effect is an important piece of information to better understand how photorespiration may control S assimilation.

The 15N NMR chemical shift in the characterization of weak halogen bonding in solution.

We have studied the applicability of 15N NMR spectroscopy in the characterization of the very weak halogen bonds of nonfluorinated halogen bond donors with a nitrogenous Lewis base in solution. The ability of the technique to detect the relative strength of iodine-, bromine- and chlorine-centered halogen bonds, as well as solvent and substituent effects was evaluated. Whereas computations on the DFT level indicate that 15N NMR chemical shifts reflect the diamagnetic deshielding associated with the formation of a weak halogen bond, the experimentally observed chemical shift differences were on the edge of detectability due to the low molar fraction of halogen-bonded complexes in solution. The formation of the analogous yet stronger hydrogen bond of phenols have induced approximately ten times larger chemical shift changes, and could be detected and correlated to the electronic properties of substituents of the hydrogen bond donors. Overall, 15N NMR is shown to be a suitable tool for the characterization of comparably strong secondary interactions in solution, but not sufficiently accurate for the detection of the formation of thermodynamically labile, weak halogen bonded complexes.

Some issues of industrial scale boron isotopes separation by the laser assisted retarded condensation (SILARC) method

Abstract More cheap production of boron isotopes is needed to provide further progress in nuclear engineering, microelectronics, and nuclear medicine. In this paper feasibility of boron isotopes separation scheme by laser assisted retarded condensation (SILARC) on industrial scale is investigated. Proposed industrial scale facility has a modular structure. Each module corresponds to irradiation cell with nozzle and skimmer installed on the opposite sides. BCl 3 was chosen as a target gas mixed at low molar fraction with argon carrier gas. Photo-absorption line, corresponding to 11 B 35 Cl 2 35 ; 37 Cl , can be excited by CO 2 laser emission line 10P(4), but corresponding to boron-10, has no overlap with CO 2 laser emission spectrum. Therefore, core gas flow will be enriched by boron-10. It is shown that continuous gas flow irradiation is preferable. In this case excitation time (gas flow length) is desirable to make as long as possible (its upper limit is constrained by optimal pressure and temperature range and condensation rate) in order to increase excitation probability. Saving of expensive laser photons is implemented by fabrication of irradiation cell as resonator. Increasing of isotope separation rate at smaller energy expenses can be provided by appropriate choice of gas flow expansion conditions, which include concentration of target gas, carrier gas choice, gas flow and ambient gas pressure and temperature. Related optimization criterion was introduced. It was found, that even at optimal conditions isotopes separation rate is rather small, which suggests, that isotope separation should be extracted iteratively. It was considered one of possible schemes for iterative isotope recovery on industrial scale. Corresponding final equilibrium isotopic concentration in product gas is rather small. Nevertheless, this method remains attractive, because energy spent per separated isotope is still significantly smaller than other prospective methods (about three times smaller than in Molecular Obliteration Laser induced Isotope Separation (MOLIS)).

Effect of different fuel NO models on the prediction of NO formation/reduction characteristics in a pulverized coal combustion field

To investigate the effects of fuel NO formation models on the prediction of NO concentrations in a coal combustion field, numerical simulations for a coal combustion field in a 760 kW test furnace were performed. Three models, those proposed by De Soete, Chen et al. and Mitchell et al. were employed to calculate fuel NO formation originating from volatile matter. The results show that the model proposed by Mitchell et al. reproduces the tendency of the experimental data better than the other two models. In addition, the difference between the NO conversion ratios of bituminous coal and sub-bituminous coal that contains a high level of moisture was examined in detail using simulation results from the model of Mitchell et al. It was found that the formation of a region with a low oxygen mole fraction immediately downstream of a region with a high NO production rate is essential to realize a low NO conversion ratio.