Chemical mechanism of the radical feedback loop in the classical BZ reaction. Malonyl bromite and oxalic acid as flow-through intermediates

2000 ◽  
Vol 2 (18) ◽  
pp. 4023-4028 ◽  
Author(s):  
László Hegedüs ◽  
Horst-Dieter Försterling ◽  
Enikö Kókai ◽  
Krisztina Pelle ◽  
Gabriella Taba ◽  
...  
Keyword(s):  
Oxalic Acid ◽  
Feedback Loop ◽  
Chemical Mechanism ◽  
Bz Reaction ◽  
Flow Through

Influence of substrate on modified oscillation reactions of the Belousov-Zhabotinskii type

1983 ◽  
Vol 48 (11) ◽  
pp. 3223-3228 ◽  
Author(s):  
Peter Ševčík ◽  
Ľubica Adamčíková
Keyword(s):  
Oxalic Acid ◽  
Kinetic Parameters ◽  
Tartaric Acid ◽  
Bz Reaction ◽  
Oscillation Cycle ◽  
Influence Of Substrate

The kinetic parameters of the reaction steps of the oscillation cycle and the parameters of modified oscillation reactions of the Belousov-Zhabotinskii (BZ) type with oxalic acid, tartaric acid, and hypophosphite ions were compared with predictions of Edelson's analysis based on the mechanism of the classical BZ reaction.

scholarly journals Multiphase MCM–CAPRAM modeling of the formation and processing of secondary aerosol constituents observed during the Mt. Tai summer campaign in 2014

2020 ◽  
Vol 20 (11) ◽  
pp. 6725-6747 ◽  
Author(s):  
Yanhong Zhu ◽  
Andreas Tilgner ◽  
Erik Hans Hoffmann ◽  
Hartmut Herrmann ◽  
Kimitaka Kawamura ◽  
...  
Keyword(s):  
Oxalic Acid ◽  
Aqueous Phase ◽  
Glyoxylic Acid ◽  
Northern China ◽  
Chemical Mechanism ◽  
Radical Mechanism ◽  
Formation Mechanisms ◽  
Major Pathway ◽  
Voc Emissions ◽  
Secondary Aerosol

Abstract. Despite the high abundance of secondary aerosols in the atmosphere, their formation mechanisms remain poorly understood. In this study, the Master Chemical Mechanism (MCM) and the Chemical Aqueous-Phase Radical Mechanism (CAPRAM) are used to investigate the multiphase formation and processing of secondary aerosol constituents during the advection of air masses towards the measurement site of Mt. Tai in northern China. Trajectories with and without chemical–cloud interaction are modeled. Modeled radical and non-radical concentrations demonstrate that the summit of Mt. Tai, with an altitude of ∼1.5 km a.m.s.l., is characterized by a suburban oxidants budget. The modeled maximum gas-phase concentrations of the OH radical are 3.2×106 and 3.5×106 molec. cm−3 in simulations with and without cloud passages in the air parcel, respectively. In contrast with previous studies at Mt. Tai, this study has modeled chemical formation processes of secondary aerosol constituents under day vs. night and cloud vs. non-cloud cases along the trajectories towards Mt. Tai in detail. The model studies show that sulfate is mainly produced in simulations where the air parcel is influenced by cloud chemistry. Under the simulated conditions, the aqueous reaction of HSO3- with H2O2 is the major contributor to sulfate formation, contributing 67 % and 60 % in the simulations with cloud and non-cloud passages, respectively. The modeled nitrate formation is higher at nighttime than during daytime. The major pathway is aqueous-phase N2O5 hydrolysis, with a contribution of 72 % when cloud passages are considered and 70 % when they are not. Secondary organic aerosol (SOA) compounds, e.g., glyoxylic, oxalic, pyruvic and malonic acid, are found to be mostly produced from the aqueous oxidations of hydrated glyoxal, hydrated glyoxylic acid, nitro-2-oxopropanoate and hydrated 3-oxopropanoic acid, respectively. Sensitivity studies reveal that gaseous volatile organic compound (VOC) emissions have a huge impact on the concentrations of modeled secondary aerosol compounds. Increasing the VOC emissions by a factor of 2 leads to linearly increased concentrations of the corresponding SOA compounds. Studies using the relative incremental reactivity (RIR) method have identified isoprene, 1,3-butadiene and toluene as the key precursors for glyoxylic and oxalic acid, but only isoprene is found to be a key precursor for pyruvic acid. Additionally, the model investigations demonstrate that an increased aerosol partitioning of glyoxal can play an important role in the aqueous-phase formation of glyoxylic and oxalic acid. Overall, the present study is the first that provides more detailed insights in the formation pathways of secondary aerosol constituents at Mt. Tai and clearly emphasizes the importance of aqueous-phase chemical processes on the production of multifunctional carboxylic acids.

Automating the quantification of heme in feces.

1988 ◽  
Vol 34 (10) ◽  
pp. 2125-2126 ◽  
Author(s):  
J W van den Berg ◽  
R Koole-Lesuis ◽  
A Edixhoven-Bosdijk ◽  
N Brouwers
Keyword(s):  
Acetic Acid ◽  
Oxalic Acid ◽  
Screening Test ◽  
Analytical Procedure ◽  
Extraction Procedure ◽  
Occult Blood ◽  
Original Method ◽  
Significant Difference ◽  
Flow Through ◽  
Initial Sampling

Abstract We present a modification of the HemoQuant assay, a good but lengthy and tedious method for determining heme in feces by means of its transformation to porphyrins. The laborious extraction procedure was replaced by a simple centrifugation procedure. The nonhomogeneous hot oxalic acid suspension was replaced by acetic acid. We observed no significant difference in results between samples analyzed by the older method vs the present modification (r = 0.996, n = 52). Mean (and SD) analytical recoveries of added hemoglobin and protoporphyrin were 99% (7%) and 93% (6%), respectively. The analytical procedure can now be automated by using discrete samplers and a flow-through fluorometer. Initial sampling and dilution of feces are still done manually, however. The excellent specificity, sensitivity, and overall analytical performance of the original method are retained, while circumventing the practical inconveniences of this reliable screening test for occult blood in feces.

Dynamic Response of Automotive Catalytic Converters to Variations in Air-Fuel Ratio

2003 ◽  
Vol 125 (2) ◽  
pp. 547-554 ◽  
Author(s):  
T. Shamim ◽  
V. C. Medisetty
Keyword(s):  
Dynamic Response ◽  
Coupling Effect ◽  
Chemical Mechanism ◽  
Catalytic Converters ◽  
Engine Exhaust ◽  
Fuel Ratio ◽  
Flow Through ◽  
Automotive Catalytic Converters ◽  
Conversion Efficiencies ◽  
The Mathematical Model

The automotive catalytic converters, which are employed to reduce engine exhaust emissions, operate in transient conditions under all modes of operation. The fluctuation in air-fuel ratio is a major contributor to these transients. The consideration of these transients is essential in accurate modeling of catalyst operation during actual driving conditions. In this work, a numerical investigation is carried out to comprehend the dynamic response of three-way catalytic converters subjected to changes in air-fuel ratio. The mathematical model considers the coupling effect of heat and mass transfer with the catalyst reactions as exhaust gases flow through the catalyst. The converter dynamic response is studied by considering a converter operating under steady conditions, which is suddenly subjected to air-fuel ratio variations. Two types of imposed fluctuations (sinusoidal and step changes) are considered. The catalyst response is predicted by using a detailed chemical mechanism. The paper elucidates the effect of air-fuel modulations on the catalyst HC, CO, and NO conversion efficiencies.

Digital Hunters

2020 ◽  
Vol 9 (1) ◽  
pp. 42-52
Author(s):  
Juan Pablo Pacheco Bejarano
Keyword(s):  
Social Media ◽  
Information Technologies ◽  
Feedback Loop ◽  
The Internet ◽  
Surveillance Systems ◽  
New Agents ◽  
Discursive Analysis ◽  
The Us ◽  
Mexico Border ◽  
Flow Through

As the infrastructure of the internet continues to expand, networked computational surveillance becomes an essential practice of territorial and biopolitical control. The feedback loop between information technologies and global structures of power creates new territorial and biopolitical regimes that sanction the mobility of people and information across Earth. These new ‘techno-territories’ lead to the emergence of new agents of power, who weave virtual and material worlds together in order to exercise control over these new spaces and the bodies that flow through them. This article discusses the emergence of ‘digital hunters’ as both subjects and objects of power through a discursive analysis of AZ: move and get shot (2011-2014) and The Virtual Watchers (2016), two artworks by Joana Moll based on research into crowdsourced surveillance systems at the US/Mexico border. Through a discussion of these projects I trace the emergence of digital hunting as a new practice of territorial control through networked images, as citizens are militarized through participatory architectures of surveillance and social media.

Modelling the non-ideal multiphase chemical processing in aqueous aerosol particles with SPACCIM-SpactMod

2020 ◽  
Author(s):  
Ralf Wolke ◽  
Andreas Tilgner ◽  
Ahmad Jhony Rusumdar ◽  
Hartmut Herrmann
Keyword(s):  
Oxalic Acid ◽  
Organic Compounds ◽  
Glyoxylic Acid ◽  
Transition Metal Ions ◽  
Chemical Mechanism ◽  
Base Case ◽  
Chemical Processing ◽  
Ideal Solutions ◽  
The Impact ◽  
Concentration Levels

<p>Tropospheric deliquesced particles including haze particles are a complex multiphase and multi-component environment with simultaneously occurring multiphase chemical transformations. Such chemical processes are able to alter the chemical composition and the deduced physical aerosol properties. Deliquesced particles are characterized by concentrated non-ideal solutions (‘aerosol liquid water’ or ALW) that can affect the occurring multiphase chemical processing. The effects of such non-ideal solutions have generally not been adequately investigated by present complex multiphase chemistry models. Thus, the present study is aimed at investigating the impact of non-ideality on multiphase chemical processing. Therefore, simulations with a multiphase chemistry model (SPACCIM-SpactMod) including the CAPRAM chemical mechanism are performed for polluted and less polluted environmental conditions and different ALW conditions.</p><p>The present study shows that activity coefficients of inorganic ions are often below unity under deliquesced aerosol conditions, and that most uncharged organic compounds exhibit activity coefficient values around or even above unity. The model studies demonstrated that the inclusion of non-ideality considerably affects the multiphase chemical processing of transition metal ions (TMIs), key oxidants, and related chemical subsystems, e.g. organic chemistry. In detail, both the chemical formation and oxidation fluxes of Fe(II) are substantially lowered by a factor of 2.8 under polluted haze conditions compared to a case study without non-ideality treatment. The reduced Fe(II) processing in the polluted base case, including lowered chemical fluxes of the Fenton reaction (-70 %), results in a reduced processing of HO<sub>x</sub>/HO<sub>y.</sub> under deliquesced aerosol conditions. Therefore, higher multiphase H<sub>2</sub>O<sub>2</sub> concentrations (by a factor of 3.1 larger) and lower aqueous-phase OH concentrations (by a factor of ≈ 4 lower) were modelled during aerosol conditions. For H<sub>2</sub>O<sub>2</sub>, the consideration of non-ideality increases S(VI) oxidation fluxes under aqueous aerosol conditions by 40 %. Moreover, the chemical fluxes of the OH radical are about 50 % lower in the non-ideal haze case. Accordingly, the consideration of non-ideality affects the chemical processing and the concentrations of organic compounds under deliquesced particle conditions in a compound-specific manner. For important organic carboxylic acids, e.g. glyoxylic acid and oxalic acid, the reduced radical oxidation budget under aqueous particle conditions leads to increased concentration levels. For oxalic acid, the present study demonstrates that the non-ideality treatment enables more realistic predictions of high oxalate concentrations observed under ambient highly polluted conditions. Furthermore, the simulations show that lower humidity conditions, i.e. more concentrated solutions, might promote higher oxalic acid concentration levels in aqueous aerosols due to differently affected formation and degradation processes. Overall, the performed studies demonstrate the crucial role of a detailed non-ideality treatment in multiphase models dealing with aqueous aerosol chemistry and the needs to further improve current model implementations.</p>

Dynamic Response of Automotive Catalytic Converters to Variations in Air-Fuel Ratio

2001 ◽  
Author(s):  
Tariq Shamim ◽  
Vishnu C. Medisetty
Keyword(s):  
Dynamic Response ◽  
Coupling Effect ◽  
Chemical Mechanism ◽  
Catalytic Converters ◽  
Engine Exhaust ◽  
Fuel Ratio ◽  
Flow Through ◽  
Automotive Catalytic Converters ◽  
Conversion Efficiencies ◽  
The Mathematical Model

Abstract The automotive catalytic converters, which are employed to reduce engine exhaust emissions, operate in transient conditions under all modes of operation. The fluctuation in air-fuel ratio is a major contributor to these transients. The consideration of these transients is essential in accurate modeling of catalyst operation during actual driving conditions. In this work, a numerical investigation is carried out to comprehend the dynamic response of three-way catalytic converters subjected to changes in air-fuel ratio. The mathematical model considers the coupling effect of heat and mass transfer with the catalyst reactions as exhaust gases flow through the catalyst. The converter dynamic response is studied by considering a converter operating under steady conditions, which is suddenly subjected to air-fuel ratio variations. Two types of imposed fluctuations (sinusoidal and step changes) are considered. The catalyst response is predicted by using a detailed chemical mechanism. The paper elucidates the effect of air-fuel modulations on the catalyst HC, CO, and NO conversion efficiencies.

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