Scavenging of radionuclides in multicomponent medium with first-order reaction kinetics: Lagrangian and Eulerian modeling

2021 ◽  
Author(s):  
Igor Brovchenko ◽  
Vladimir Maderich ◽  
Sergiy Kivva ◽  
Kyeong Ok Kim ◽  
Hanna Kim ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Reaction Kinetics ◽  
Convex Combination ◽  
Ocean Surface ◽  
Similarity Solutions ◽  
Diffusion Reaction ◽  
Observation Data ◽  
Time Step ◽  
Reactive Medium ◽  
First Order

<p>A process of the removal of dissolved elements in the ocean by adsorption onto sinking particulate matters (scavenging) is studied analytically and using Lagrangian and Eulerian numerical methods. The generalized model of scavenging in a multicomponent reactive medium with first-order kinetics consisting of water and multi-fraction suspended particular matter has developed. Two novel numerical schemes were used to solve advection-diffusion-reaction equations for advection-dominated flows. The particle tracking algorithm based on the method of moments was developed. It is free on time step limitation necessary for an application of a standard method to the equations with reaction kinetics. The modified flux-corrected transport method for the Eulerian equations is a flux-limiter method based on a convex combination of low-order and high-order schemes. The similarity solutions of the model equations for an idealized case of instantaneous release of reactive radionuclide on the ocean surface were obtained. It was found that the dispersion of reactive contamination caused by reversible phase transition can be much greater than caused by diffusion. The solutions using both numerical methods are consistent with the analytical similarity solution even at zero diffusivity. The scavenging of the <sup>239,240</sup>Pu that was introduced to the ocean surface due to the fallout from past nuclear weapon testing was simulated. The results of the simulation agreed with observation data in the north-western Pacific Ocean. The importance of the scavenging by both the large fast-sinking particles and small particles slowly sinking and dissolving with depth due to the biochemical processes was shown.</p>

Photocolouration of 2,4,4,6-Tetraaryl-4H-pyrans and Their Heteroanalogues: Importance of Hypervalent Photoisomers

1995 ◽  
Vol 60 (10) ◽  
pp. 1621-1633 ◽  
Author(s):  
Stanislav Böhm ◽  
Mojmír Adamec ◽  
Stanislav Nešpůrek ◽  
Josef Kuthan
Keyword(s):  
Reaction Kinetics ◽  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Theoretical Data ◽  
Order Reaction ◽  
Bleaching Process ◽  
First Order ◽  
Photodegradation Products ◽  
Hypervalent Molecules

Molecular geometries of 2,4,4,6-tetraphenyl-4H-pyran (Ia), 4,4-(biphenyl-2,2e-diyl)-2,6-diphenyl-4H-pyran (Ib) and their heterocyclic isomers II-V were optimized by the PM3 method and used for the calculation of electronic absorption spectra by the CNDO/S-CI procedure. Comparison of the theoretical data with experimental UV-VIS absorption spectra made possible to select hypervalent molecules IIIa, IIIb, IVa and IVb being responsible for the photocolouration of 4H-pyrans Ia, Ib, while compounds Va, Vb, VI and VII come into account as possible photodegradation products. The bleaching process of the UV illuminated compound Ia is analyzed in terms of dispersive first-order reaction kinetics.

scholarly journals A First-Order Explicit-Implicit Splitting Method for a Convection-Diffusion Problem

2020 ◽  
Vol 20 (4) ◽  
pp. 769-782
Author(s):  
Amiya K. Pani ◽  
Vidar Thomée ◽  
A. S. Vasudeva Murthy
Keyword(s):  
Splitting Method ◽  
Diffusion Problem ◽  
Euler Method ◽  
Second Order ◽  
Time Step ◽  
Convection Diffusion ◽  
First Order ◽  
Backward Euler ◽  
Strang Splitting ◽  
Spatially Periodic

AbstractWe analyze a second-order in space, first-order in time accurate finite difference method for a spatially periodic convection-diffusion problem. This method is a time stepping method based on the first-order Lie splitting of the spatially semidiscrete solution. In each time step, on an interval of length k, of this solution, the method uses the backward Euler method for the diffusion part, and then applies a stabilized explicit forward Euler approximation on {m\geq 1} intervals of length {\frac{k}{m}} for the convection part. With h the mesh width in space, this results in an error bound of the form {C_{0}h^{2}+C_{m}k} for appropriately smooth solutions, where {C_{m}\leq C^{\prime}+\frac{C^{\prime\prime}}{m}}. This work complements the earlier study [V. Thomée and A. S. Vasudeva Murthy, An explicit-implicit splitting method for a convection-diffusion problem, Comput. Methods Appl. Math. 19 2019, 2, 283–293] based on the second-order Strang splitting.

Complex network structure of flocks in the Vicsek Model with Vectorial Noise

2014 ◽  
Vol 25 (03) ◽  
pp. 1350095 ◽  
Author(s):  
Gabriel Baglietto ◽  
Ezequiel V. Albano ◽  
Julián Candia
Keyword(s):  
Phase Transition ◽  
Complex Network ◽  
Network Structure ◽  
Time Step ◽  
Vicsek Model ◽  
Disorder Phase Transition ◽  
First Order ◽  
Direction Of Movement ◽  
Long Range Ordering ◽  
Influence Of Noise

In the Vicsek Model (VM), self-driven individuals try to adopt the direction of movement of their neighbors under the influence of noise, thus leading to a noise-driven order–disorder phase transition. By implementing the so-called Vectorial Noise (VN) variant of the VM (i.e. the VM-VN model), this phase transition has been shown to be discontinuous (first-order). In this paper, we perform an extensive complex network study of VM-VN flocks and show that their topology can be described as highly clustered, assortative, and nonhierarchical. We also study the behavior of the VM-VN model in the case of "frozen flocks" in which, after the flocks are formed using the full dynamics, particle displacements are suppressed (i.e. only rotations are allowed). Under this kind of restricted dynamics, we show that VM-VN flocks are unable to support the ordered phase. Therefore, we conclude that the particle displacements at every time-step in the VM-VN dynamics are a key element needed to sustain long-range ordering throughout.

scholarly journals KINETIC INVESTIGATION OF PROPANE DISAPPEARANCE AND PROPENE FORMATION IN PROPANE OXIDATION ON DILUTED AND LEACHED MoVTeNb CATALYST

2010 ◽  
Vol 10 (2) ◽  
pp. 172-176
Author(s):  
Restu Kartiko Widi
Keyword(s):  
Reaction Kinetics ◽  
Partial Order ◽  
Reaction Order ◽  
Propane Oxidation ◽  
Kinetic Investigation ◽  
Formation Kinetic ◽  
Kinetic Reaction ◽  
First Order ◽  
Langmuir Hinshelwood Mechanism

Reaction kinetics for the oxidation of propane over diluted-leached MoVTeNb is described. This paper is focused on the study of products selectivity profile and determination of the orders of propane disappearance and propene formation. The result shows that selective oxidation of propane to propene over this catalyst follows the Langmuir-Hinshelwood mechanism. The disappearance of propane is first order with respect to hydrocarbon and partial order (0.21) with respect to oxygen. The propene formation is first order with respect to hydrocarbon and not depending on oxygen concentration.   Keywords: propane oxidation, propane disappearance, propene formation, kinetic, reaction order

Effect of Uni- and Bi-Directional Coupling of Ocean-Met Interaction on Significant Wave Height and Local Wind

2017 ◽  
Author(s):  
Adil Rasheed ◽  
Jakob Kristoffer Süld ◽  
Mandar Tabib
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Surface Wind ◽  
Wave Model ◽  
Ocean Surface ◽  
Observation Data ◽  
Local Wind ◽  
Near Surface ◽  
Significant Wave ◽  
Bidirectional Coupling

Accurate prediction of near surface wind and wave height are important for many offshore activities like fishing, boating, surfing, installation and maintenance of marine structures. The current work investigates the use of different methodologies to make accurate predictions of significant wave height and local wind. The methodology consists of coupling an atmospheric code HARMONIE and a wave model WAM. Two different kinds of coupling methodologies: unidirectional and bidirectional coupling are tested. While in Unidirectional coupling only the effects of atmosphere on ocean surface are taken into account, in bidirectional coupling the effects of ocean surface on the atmosphere are also accounted for. The predicted values of wave height and local wind at 10m above the ocean surface using both the methodologies are compared against observation data. The results show that during windy conditions, a bidirectional coupling methodology has better prediction capability.

Pre-Reduction of Chromite by Thermogravimetric (TG) Analysis

2013 ◽  
Vol 760 ◽  
pp. 23-32
Author(s):  
D.M.A. Khan
Keyword(s):  
Reaction Kinetics ◽  
Order Reaction ◽  
First Order Reaction ◽  
Reduction Mechanism ◽  
Muffle Furnace ◽  
Tg Analysis ◽  
First Order ◽  
Single Pellet ◽  
Reduction Smelting

Thermogravimetric experiments on prereduction of single pellet and multiple pellets were conducted in Muffle furnace at 1500oC. Reduction smelting of Chromite in Fe-C melt in TG setup indicates CR is reduced faster than CG and CB. The reduction mechanism takes the path of first order reaction kinetics. Only 50% Cr metallization could be obtained at 1550oC from the reduction smelting experiments.

Assimilation of inundation extent observations into a flood forecasting system:  a tempered particle filter for combatting degeneracy and sample impoverishment.

2021 ◽  
Author(s):  
Concetta Di Mauro ◽  
Renaud Hostache ◽  
Patrick Matgen ◽  
Peter Jan van Leeuwen ◽  
Nancy Nichols ◽  
...  
Keyword(s):  
Particle Filter ◽  
Main Idea ◽  
Water Levels ◽  
Smooth Transition ◽  
Observation Data ◽  
Flood Inundation ◽  
State Variables ◽  
Time Step ◽  
Radar Images ◽  
Forecasting System

<p>Data assimilation uses observation for updating model variables and improving model output accuracy. In this study, flood extent information derived from Earth Observation data (namely Synthetic Aperture Radar images) are assimilated into a loosely coupled flood inundation forecasting system via a Particle Filter (PF). A previous study based on a synthetic experiment has shown the validity and efficiency of a recently developed PF-based assimilation framework allowing to effectively integrate remote sensing-derived probabilistic flood inundation maps into a coupled hydrologic-hydraulic model. One of the main limitations of this recent framework based on sequential importance sampling is the sample degeneracy and impoverishment, as particles loose diversity and only few of them keep a substantial importance weight in the posterior distribution. In order to circumvent this limitation, a new methodology is adopted and evaluated: a tempered particle filter. The main idea is to update a set of state variables, namely through a smooth transition (iterative and adaptative process). To do so, the likelihood is factorized using small tempering factors. Each iteration includes subsequent resampling and mutation steps using a Monte Carlo Metropolis Hasting algorithm. The mutation step is required to regain diversity between the particles after the resampling. The new methodology is tested using synthetic twin experiments and the results are compared to the one obtained with the previous approach. The new proposed method enables to substantially improve the predictions of streamflow and water levels within the hydraulic domain at the assimilation time step. Moreover, the preliminary results show that these improvements are longer lasting. The proposed tempered particle filter also helps in keeping more diversity within the ensemble.</p>

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