Structure and Reactivity of Al−O(H)−Al Moieties in Siloxide Frameworks: Solution and Gas-Phase Model Studies

2018 ◽  
Vol 58 (3) ◽  
pp. 902-906 ◽  
Author(s):  
Kapil Shyam Lokare ◽  
Beatrice Braun-Cula ◽  
Christian Limberg ◽  
Marcel Jorewitz ◽  
John T. Kelly ◽  
...  
Keyword(s):  
Gas Phase ◽  
Phase Model ◽  
Model Studies

Unifying the microscopic picture of His-containing turns: from gas phase model peptides to crystallized proteins

2017 ◽  
Vol 19 (26) ◽  
pp. 17128-17142 ◽  
Author(s):  
Woon Yong Sohn ◽  
Sana Habka ◽  
Eric Gloaguen ◽  
Michel Mons
Keyword(s):  
Gas Phase ◽  
Main Chain ◽  
Protein Structures ◽  
Phase Model ◽  
Side Chain ◽  
Central Position ◽  
Microscopic Picture ◽  
Model Peptides

The presence in crystallized proteins of a local anchoring between the side chain of a His residue, located in the central position of a γ- or β-turn, and its local main chain environment, is assessed by the comparison of protein structures with relevant isolated model peptides.

Unravelling the impact of hydrocarbon structure on the fumarate addition mechanism – a gas-phaseab initiostudy

2015 ◽  
Vol 17 (6) ◽  
pp. 4054-4066 ◽  
Author(s):  
Vivek S. Bharadwaj ◽  
Shubham Vyas ◽  
Stephanie M. Villano ◽  
C. Mark Maupin ◽  
Anthony M. Dean
Keyword(s):  
Gas Phase ◽  
Phase Model ◽  
Hydrocarbon Biodegradation ◽  
Fumarate Addition ◽  
The Impact

The fumarate addition mechanism for hydrocarbon biodegradation. Model aromatic and aliphatic fuel degradation is comparedviaa reduced gas-phase model.

Influence of in-cloud oxidation of organic compounds on tropospheric ozone

2021 ◽  
Author(s):  
Simon Rosanka ◽  
Rolf Sander ◽  
Bruno Franco ◽  
Catherine Wespes ◽  
Andreas Wahner ◽  
...  
Keyword(s):  
Gas Phase ◽  
Organic Compounds ◽  
Aqueous Phase ◽  
Phase Transfer ◽  
Sulfur Oxidation ◽  
Box Model ◽  
Atmospheric Models ◽  
Model Studies ◽  
Phase Chemistry ◽  
The Impact

<p>Large parts of the troposphere are affected by clouds, whose aqueous-phase chemistry differs significantly from gas-phase chemistry. Box-model studies have demonstrated that clouds influence the tropospheric oxidation capacity. However, most global atmospheric models do not represent this chemistry reasonably well and are largely limited to sulfur oxidation. Therefore, we have developed the Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC), making a detailed in-cloud oxidation model of oxygenated volatile organic compounds (OVOCs) readily available for box as well as for regional and global simulations that are affordable with modern supercomputers. JAMOC includes the phase transfer of species containing up to ten carbon atoms, and the aqueous-phase reactions of a selection of species containing up to four carbon atoms, e.g., ethanol, acetaldehyde, glyoxal. The impact of in-cloud chemistry on tropospheric composition is assessed on a regional and global scale by performing a combination of box-model studies using the Chemistry As A Boxmodel Application (CAABA) and the global atmospheric model ECHAM/MESSy (EMAC). These models are capable to represent the described processes explicitly and integrate the corresponding ODE system with a Rosenbrock solver. </p><p>Overall, the explicit in-cloud oxidation leads to a reduction of predicted OVOCs levels. By comparing EMAC's prediction of methanol abundance to spaceborne retrievals from the Infrared Atmospheric Sounding Interferometer (IASI), a reduction in EMAC's overestimation is observed in the tropics. Further, the in-cloud OVOC oxidation shifts the hydroperoxyl radicals (HO<sub>2</sub>) production from the gas- to the aqueous-phase. As a result, the in-cloud destruction (scavenging) of ozone (O<sub>3</sub>) by the superoxide anion (O<sub>2</sub><sup>-</sup>) is enhanced and accompanied by a reduction in both sources and sinks of tropospheric O<sub>3</sub> in the gas phase. By considering only the in-cloud sulfur oxidation by O<sub>3</sub>, about 13 Tg a<sup>-1</sup> of O<sub>3</sub> are scavenged, which increases to 336 Tg a<sup>-1</sup> when JAMOC is used. With the full oxidation scheme, the highest O<sub>3</sub> reduction of 12 % is predicted in the upper troposphere/lower stratosphere (UTLS). Based on the IASI O<sub>3</sub> retrievals, it is demonstrated that these changes in the free troposphere significantly reduce the modelled tropospheric O<sub>3</sub> columns, which are known to be generally overestimated by global atmospheric models. Finally, the relevance of aqueous-phase oxidation of organics for ozone in hazy polluted regions will be presented.  </p>

scholarly journals Comparative simulation study of gas-phase propylene polymerization in fluidized bed reactors using aspen polymers and two phase models

2013 ◽  
Vol 19 (1) ◽  
pp. 13-24 ◽  
Author(s):  
Ahmad Shamiria ◽  
M.A. Hussaina ◽  
Farouq Mjallic ◽  
Navid Mostoufid
Keyword(s):  
Molecular Weight ◽  
Gas Phase ◽  
Production Rate ◽  
Fluidized Bed ◽  
Average Molecular Weight ◽  
Phase Model ◽  
Propylene Polymerization ◽  
Flow Index ◽  
Fluidized Bed Reactors ◽  
Two Phase

A comparative study describing gas-phase propylene polymerization in fluidized-bed reactors using Ziegler-Natta catalyst is presented. The reactor behavior was explained using a two-phase model (which is based on principles of fluidization) as well as simulation using the Aspen Polymers process simulator. The two-phase reactor model accounts for the emulsion and bubble phases which contain different portions of catalysts with the polymerization occurring in both phases. Both models predict production rate, molecular weight, polydispersity index (PDI) and melt flow index (MFI) of the polymer. We used both models to investigate the effect of important polymerization parameters, namely catalyst feed rate and hydrogen concentration, on the product polypropylene properties, such as production rate, molecular weight, PDI and MFI. Both the two-phase model and Aspen Polymers simulator showed good agreement in terms of production rate. However, the models differed in their predictions for weight-average molecular weight, PDI and MFI. Based on these results, we propose incorporating the missing hydrodynamic effects into Aspen Polymers to provide a more realistic understanding of the phenomena encountered in fluidized bed reactors for polyolefin production.

scholarly journals Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies

2011 ◽  
Vol 11 (21) ◽  
pp. 11069-11102 ◽  
Author(s):  
B. Ervens ◽  
B. J. Turpin ◽  
R. J. Weber
Keyword(s):  
Relative Humidity ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Secondary Organic Aerosol ◽  
Current Knowledge ◽  
Laboratory Data ◽  
Organic Aerosol ◽  
Current Data ◽  
Aerosol Formation ◽  
Model Studies

Abstract. Progress has been made over the past decade in predicting secondary organic aerosol (SOA) mass in the atmosphere using vapor pressure-driven partitioning, which implies that SOA compounds are formed in the gas phase and then partition to an organic phase (gasSOA). However, discrepancies in predicting organic aerosol oxidation state, size and product (molecular mass) distribution, relative humidity (RH) dependence, color, and vertical profile suggest that additional SOA sources and aging processes may be important. The formation of SOA in cloud and aerosol water (aqSOA) is not considered in these models even though water is an abundant medium for atmospheric chemistry and such chemistry can form dicarboxylic acids and "humic-like substances" (oligomers, high-molecular-weight compounds), i.e. compounds that do not have any gas phase sources but comprise a significant fraction of the total SOA mass. There is direct evidence from field observations and laboratory studies that organic aerosol is formed in cloud and aerosol water, contributing substantial mass to the droplet mode. This review summarizes the current knowledge on aqueous phase organic reactions and combines evidence that points to a significant role of aqSOA formation in the atmosphere. Model studies are discussed that explore the importance of aqSOA formation and suggestions for model improvements are made based on the comprehensive set of laboratory data presented here. A first comparison is made between aqSOA and gasSOA yields and mass predictions for selected conditions. These simulations suggest that aqSOA might contribute almost as much mass as gasSOA to the SOA budget, with highest contributions from biogenic emissions of volatile organic compounds (VOC) in the presence of anthropogenic pollutants (i.e. NOx) at high relative humidity and cloudiness. Gaps in the current understanding of aqSOA processes are discussed and further studies (laboratory, field, model) are outlined to complement current data sets.

Gas Phase Model Systems for Catalysis

2019 ◽  
Vol 233 (6) ◽  
pp. 755-758
Author(s):  
Sandra M. Lang
Keyword(s):  
Gas Phase ◽  
Model Systems ◽  
Phase Model

Modified two-phase model with hybrid control for gas phase propylene copolymerization in fluidized bed reactors

2015 ◽  
Vol 264 ◽  
pp. 706-719 ◽  
Author(s):  
Ahmad Shamiri ◽  
Suk Wei Wong ◽  
Mohd Fauzi Zanil ◽  
Mohamed Azlan Hussain ◽  
Navid Mostoufi
Keyword(s):  
Gas Phase ◽  
Fluidized Bed ◽  
Hybrid Control ◽  
Phase Model ◽  
Fluidized Bed Reactors ◽  
Two Phase
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