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| Registros recuperados: 83 | |
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| Sierra Rayne; Kaya Forest. |
| Gas to aqueous phase standard state (1 atm to 1 mol/L; 298.15 K) free energies of solvation ([DELTA]G^o^~solv~) were calculated for a range of neutral and ionic inorganic and organic compounds using various levels and combinations of Hartree-Fock and density functional theory (DFT) and composite methods (CBS-Q//B3, G4MP2, and G4) with the IEFPCM-UFF, CPCM, and SMD solvation models in Gaussian 09 (G09). For a subset of highly polar and generally polyfunctional neutral organic compounds previously identified as problematic for prior solvation models, we find significantly reduced [DELTA]G^o^~solv~ errors using the revised solvent models in G09. The use of composite methods for these compounds also substantially reduces their apparent [DELTA]G^o^~solv~... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/4864/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Vertical, well-to-well, and adiabatic ionization energies (IEs) and electron affinities (EAs) were calculated for the n=1-10 [n]acenes using a wide range of semiempirical, Hartree-Fock, density functional, and second order Moller-Plesset perturbation theory model chemistries. None of the model chemistries examined were able to accurately predict the IEs or EAs for both short- through mid-length [n]acenes, as well as for extrapolations to the polymeric limit, when compared to available experimental and benchmark theoretical data. Provided a minimal basis set size is employed, basis set effects on predicted IEs and EAs are not significant relative to the choice of model chemistry. The poor IE/EA prediction performance for the parent [n]acenes likely extends... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6578/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Theoretical investigations were conducted on the gas phase all-anti zigzag geometries of C~3~ through C~7~ perfluoro-n-alkanes and the perfluoro-n-octanoate anion using various semiempirical, density functional theory, and composite method approaches. The major theoretical methods are in agreement that the gas phase zigzag geometry of >=C~3~ perfluoro-n-alkyl chains is a transition state between the left and right handed helical/twisted global minima. For the C~3~ perfluoropropyl group, a slightly twisted (about 1 to 2 degree central F-C-C-F dihedral angle) near zigzag conformation exists as a global minimum, whereas helical global minima are obtained for C~4~ and longer perfluoroalkyl chains. The left to right handed helix inversion activation... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5061/version/1 |
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| Sierra Rayne. |
| Increasing concentrations of carbon dioxide (CO2) in the atmosphere have stimulated significant global research and development efforts regarding the reduction in CO2 emissions from all point and non-point sources. In addition to technologies that do not use carbon feedstocks or which capture and "permanently" store CO2 (i.e., sequestration), there is considerable worldwide interest among the academic, industrial, and government communities regarding methods for dissociating waste stream carbon dioxide molecules into their constituent carbon and oxygen ("CO2 splitting") atoms as a final "end-of-pipe" treatment option. The splitting of carbon dioxide has also been actively discussed and researched in the... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2008 |
URL: http://precedings.nature.com/documents/1741/version/1 |
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| Sierra Rayne; Kaya Forest; Ken J. Friesen. |
| A statistical analysis was conducted on long-term climate records in the Okanagan Valley wine grape growing region of British Columbia, Canada. No observable trends for average annual temperatures were found in the region. Analyses of monthly mean and extreme temperatures show wide spatial and temporal heterogeneity, indicating that future studies using downscaling of global climate models for this region will require resolutions on the order of several kilometers. Mean winter temperatures are increasing throughout the valley, and extreme minimum temperatures are also increasing during the winter at the central and northern sites which have historically presented the most risk of winter damage to grapevines. Only the most southern and northern sub-regions... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3162/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase standard state (298.15 K, 1 atm) structures, enthalpies of formation, and ionization energies (IEs) were calculated at the G4MP2 composite method level of theory for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives. Increasing nitrogen content increases the enthalpies of formation for the carbon-nitrogen, nitrogen-phosphorus, and silicon-nitrogen binary cubanes, with the opposite enthalpies of formation trend for increasing phosphorus content within the carbon-phosphorus, nitrogen-phosphorus, and silicon-phosphorus derivatives. Varying carbon/silicon content in the carbon-silicon cubanes results in no general trends for enthalpies of formation. Isomerization enthalpies within the homolog groups having more... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5154/version/1 |
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| Sierra Rayne; Kaya Forest. |
| A hydrometric analysis over the available historical record (1973-2010) was conducted for the Moose Jaw River station near Burdick in south-central Saskatchewan, Canada. Frequency analyses on mean monthly, average annual, monthly minimum/maximum, and annual minimum flows generally yielded poor fits, and problems with negative flow predictions for mid- to long-term return periods regardless of distribution type. The annual maximum streamflow time series is reasonably well-described by linear and log Pearson Type III distributions, although both distribution types underestimate extreme maximum flows. Mann-Kendall linear time series analysis on mean monthly and annual streamflows reveals no trend in annual water yields, nor in mean monthly flows between March... |
| Tipo: Poster |
Palavras-chave: Earth & Environment. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6697/version/1 |
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| Sierra Rayne. |
| Dr. Sierra Rayne will be speaking on the interplay of sustainability and environmental chemistry in semi-arid and arid regions worldwide. Drawing on his previous, current, and proposed research on organic and inorganic contaminants in aquatic systems, Dr. Rayne will illustrate the importance of multidisciplinary and interdisciplinary approaches towards tackling environmental problems. A key element of his work is looking at chemical dynamics in environmental matrices, and in particular, photochemically generated reactive intermediates and their impact on biological systems and net ecosystem functions. Semi-arid/arid regions also offer unique opportunities to focus on the role of photochemistry in the biogeochemical cycling of oxyanion-forming heavy metals... |
| Tipo: Presentation |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2007 |
URL: http://precedings.nature.com/documents/689/version/1 |
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| Sierra Rayne; Ken J. Friesen. |
| It appears likely that the installation of many large dams on major rivers worldwide over the past century has led to large and complex contaminant loadings becoming trapped in the sediments behind these dams. Future planned large dam removal efforts or unintentional breaches may result in substantial contaminant releases downstream. We review the current state of the art regarding knowledge of contaminant loadings behind large dams and potential downstream impacts following dam breaches. |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/2965/version/1 |
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| Sierra Rayne; Kaya Forest. |
| A time trend study of groundwater monitoring well levels was conducted in British Columbia, Canada. Trend data was available for a total of 210 groundwater monitoring well stations throughout the province with end-of-month water levels over the period of record. Significant temporal trends in groundwater levels were found at 67 stations (40.4% of all stations amenable to statistical examination, and 31.9% of all available stations). Of these 67 stations, 10 had increasing groundwater level trends and the remaining 57 had declining groundwater level trends. Thus, 34.3% of stations with a sufficiently long time series for analysis displayed declining groundwater level trends, while 6.0% have increasing trends, and 59.6% of these stations appear to have no... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2012 |
URL: http://precedings.nature.com/documents/6844/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Historical trends in streamflow and climate were investigated for the Coldwater River watershed in south-central British Columbia, Canada. Temporal increases in rainfall and total precipitation during the spring, summer, and autumn periods, as well as on an annual basis, at the city of Merritt near the mouth of the watershed, and year-round temperature increases at this site, compare with declining summertime and annual streamflows at the nearby Merritt hydrometric station on the Coldwater River. Declining summer flows at this site could reflect the dominance of temporally increasing evaporation that is offsetting increased precipitation over the same periods of the hydrologic year. Alternatively, increased water abstractions, altered regulation regimes,... |
| Tipo: Manuscript |
Palavras-chave: Earth & Environment. |
| Ano: 2012 |
URL: http://precedings.nature.com/documents/6785/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Gas phase standard state (298.15 K, 1 atmosphere) relative enthalpies and free energies of formation were calculated for all mono- through hepta-halogenated (X=F, Cl, Br) anthraquinone congeners using the B3LYP, BHandHLYP, M062X, PBE0, and B97D density functionals with the 6-311++G(d,p) basis set. All levels of theory yielded similar results with strong intra- and inter-method correlations for both the relative enthalpy and free energy values and the corresponding thermodynamic stability rank. Within each homolog group, the most thermodynamically stable isomers are those which maximize substitution at the lateral positions (2, 3, 7, and 8) versus the less stabilizing peri positions (1, 4, 6, and 9), while also minimizing destabilizing adjacent substitution... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5153/version/1 |
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| Sierra Rayne. |
| Increasing concentrations of carbon dioxide (CO~2~) in the atmosphere have stimulated significant global research and development efforts regarding the reduction in CO~2~ emissions from all point and non-point sources. In addition to technologies that do not use carbon feedstocks or which capture and "permanently" store CO~2~ (i.e., sequestration), there is considerable worldwide interest among the academic, industrial, and government communities regarding methods for dissociating waste stream carbon dioxide molecules into their constituent carbon and oxygen ("CO~2~ splitting") atoms as a final "end-of-pipe" treatment option. The splitting of carbon dioxide has also been actively discussed and... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2008 |
URL: http://precedings.nature.com/documents/1741/version/2 |
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| Sierra Rayne; Kaya Forest. |
| A molecular mechanics force field method (MMFF94) systematic rotor conformational search was conducted on the well known environmental contaminant n-perfluorooctanoic acid (n-PFOA). The MMFF94 conformational search yielded 2915 separate low- through high-energy conformers of n-PFOA. Ranking of these structures gave the 94 lowest MMFF94 energy conformations that were subjected to subsequent density functional theory (DFT) computational investigations at the B3LYP/6-311++G(d,p) level of theory. Application of a thermodynamic cycle approach, coupled with aqueous and gas phase DFT calculations on the molecular and anionic forms for each of the 94 lowest energy n-PFOA conformers, gave estimated acidity constants (pK~a~ values) for a final converged set of... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3837/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Aroma compounds in the Flavornet database were screened for potentially hydrolyzable carboxylic acid ester functionalities. Of the 738 aroma compounds listed in this database, 140 molecules contain carboxylic acid ester groups that may be amenable to hydrolysis in various food and beverage products. Acid- (k~A~) and base- (k~B~) catalyzed and neutral (k~N~) hydrolysis rate constants in pure water at 25°C were estimated for these aroma compounds. Where available, good agreement between theoretical and experimental hydrolytic half-lives was obtained at various pH values. Wide ranges and broad frequency distributions for k~A~, k~B~, and k~N~ are expected among the various hydrolyzable aroma compounds, with estimated k~A~ ranging from... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Plant Biology. |
| Ano: 2011 |
URL: http://precedings.nature.com/documents/6471/version/1 |
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| Sierra Rayne; Kaya Forest. |
| Semiempirical, ab initio, and density functional theory (DFT) studies were conducted on a homologous series of straight chain perfluoroalkyl carboxylic acids (PFCAs) ranging in chain length from C~1~ (trifluoroacetic acid; TFA) to C~9~ (perfluorodecanoic acid). Regardless of perfluoroalkyl chain length and computational method and level employed, no significant change in the electrostatic or steric characteristics of the carboxylate head group was found between C~2~ and C~9~. Application of a thermodynamic cycle to calculations at the B3LYP/6-311++G(3df,2p) level provided an accurate prediction of the experimental monomeric pK~a~ for TFA. At this – and similar – levels of theory, monomeric pK~a~ values of longer straight chain PFCAs... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2009 |
URL: http://precedings.nature.com/documents/3829/version/1 |
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| Sierra Rayne; Kaya Forest. |
| The octanol/water distribution coefficients (log D~ow~) of the C~1~ through C~7~ perfluoro-n-alkyl sulfonates (PFSAs) were calculated using the M062X/6-311++G(d,p) and MP2/6-311++G(d,p)//M062X/6-311++G(d,p) levels of theory and the IEFPCM-UFF, CPCM, and SMD solvation models. At both levels of theory with all solvation models, absolute log D~ow~ calculated for the straight chain C~1~ through C~7~ PFSAs display a substantial negative bias against available experimental data and expected trends by several log units. However, the SMD solvation model achieves accurate relative log D~ow~ accuracy, yielding fragmental contributions of a -CF~2~- group towards the log D~ow~ of 0.51+/-0.02 to 0.54+/-0.01 units (-3.0+/-0.1 to -3.1+/-0.1 kJ/mol), in good agreement... |
| Tipo: Manuscript |
Palavras-chave: Chemistry. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5103/version/1 |
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| Sierra Rayne; Kaya Forest. |
| The KOWWIN and ALOGPS octanol-water partition coefficient (K~ow~) estimation software programs were compared for their capacity to accurately predict log K~ow~ values of 1545 organic compounds on the publicly available Domestic Substances List (DSL) from Environment Canada for which experimental data is available. Approximately equivalent log K~ow~ error statistics were observed between KOWWIN and ALOGPS against available experimental data. Substantial predictive differences were observed between the two programs for 6529 compounds not having experimental K~ow~ data on the Canadian DSL. Predictive differences of up to 40 log K~ow~ units were found between KOWWIN and ALOGPS, and in some cases, the discrepancies were sufficiently large that strongly opposing... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Pharmacology; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/3882/version/2 |
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| Sierra Rayne. |
| Increasing concentrations of carbon dioxide in the atmosphere have stimulated significant global research and development efforts regarding the reduction in emissions from all point and non-point sources. In addition to technologies that do not use carbon feedstocks or which capture and "permanently" store carbon dioxide (i.e., sequestration), there is considerable worldwide interest for dissociating waste stream carbon dioxide molecules into their constituent carbon and oxygen atoms ("CO2 splitting") as a final "end-of-pipe" treatment option. This document presents a review of on-point issued and applied for patents in the field of carbon dioxide splitting. The findings suggest patents in this area... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2008 |
URL: http://precedings.nature.com/documents/1739/version/1 |
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| Sierra Rayne; Kaya Forest. |
| CBS-Q//B3, G4MP2, and G4 composite method calculations were used to estimate gas phase standard state (298.15 K, 1 atm) free energies of hydration (Δ~hydr~G°~(g)~), hydration equilibrium constants (log K~hydr,(g)~), bond dissociation enthalpies (BDEs), and enthalpies (Δ~d~H°~(g)~) and free energies (Δ~d~G°~(g)~) of aldehydic proton acid dissociation for various substituted aldehydes with electron withdrawing and electron releasing groups. Good quality log K~hydr,(g)~ correlations with the Swain-Lupton resonance effect parameters R and R^+^ were found, allowing extension of the model to predict log K~hydr,(g)~ values for 487 substituted aldehydes having available R-values and 108 substituted aldehydes... |
| Tipo: Manuscript |
Palavras-chave: Chemistry; Earth & Environment. |
| Ano: 2010 |
URL: http://precedings.nature.com/documents/5084/version/1 |
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| Registros recuperados: 83 | |
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