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1
Prytula, A., V. Fedirko, Y. M. Pohreliuk, and Ya Matychak. "Surface Chemical Reactions in Processes of Diffusion Mass Transfer." Defect and Diffusion Forum 237-240 (April 2005): 1312–0. http://dx.doi.org/10.4028/www.scientific.net/ddf.237-240.1312.
Повний текст джерелаАнотація:
The phenomenological theory for describing high-temperature interaction between metal and diluted gaseous medium has been developed. The theory is based on the assumption of duplex contact layer existence in the vicinity of interface (with relative thickness 2 d), where chemical reactions and processes of gas component migration occur. The non-stationary conditions of mass transfer at the interface are described involving effective average parameters. These conditions allow considering a wide spectrum of boundary diffusion phenomena (in a short and prolonged time ranges), in order to describe the kinetics of accumulation of diffusing component close to the interface. The description of the kinetic of gaseous saturation of metal (nitriding and borating) in the diluted medium becomes a partial proof of the suggested models. In order to approach the diffusion phenomena, boundary conditions, which contain, besides the coordinate derivative of concentration function, also the time derivative, were suggested. The derived equations describe the time dependence of change of surface concentration of gaseous component, the kinetics of its accumulation owing to chemical reaction, the specimen mass change owing to both, the diffusive addition dissolution in metal and its chemical interaction. The role of temperature is also discussed.
2
Kostyk, K. O. "Features of Diffusion Processes Occurring at Saturation with Atomic Elements and Formation of Surface Layer with Composite Structure." METALLOFIZIKA I NOVEISHIE TEKHNOLOGII 44, no. 1 (April 4, 2022): 47–61. http://dx.doi.org/10.15407/mfint.44.01.0047.
Повний текст джерела
3
RAHAMATHUNISSA, G., and L. RAJENDRAN. "MODELING OF NONLINEAR REACTION–DIFFUSION PROCESSES OF AMPEROMETRIC POLYMER-MODIFIED ELECTRODES." Journal of Theoretical and Computational Chemistry 07, no. 01 (February 2008): 113–38. http://dx.doi.org/10.1142/s0219633608003642.
Повний текст джерелаАнотація:
A mathematical model of amperometric response for a polymer-modified electrode system has been developed. The model is based on nonstationary diffusion equations containing a nonlinear term related to Michaelis–Menten kinetics of the enzymatic reaction. In particular, the interplay between chemical reaction and substrate diffusion is specifically taken into account. The limiting situations of catalytic site unsaturation and site saturation are considered. The analytical solutions for substrate concentration and transient current for both steady and nonsteady-state are obtained using Danckwerts' relation and variable and separable method. An excellent agreement with the previous analytical results are noted. The combined analytical set of solution of steady-state current in all the nearest sites is also described in a case diagram. A general simple analytical approximate solution for steady-state current for all values of α is also given. A two-point Padé approximation is also derived for the nonsteady-state current for all values of saturation parameter α. Limiting case results (α ≪ 1 and α ≫ 1) are compared with Padé approximation results and are found to be in good agreement.
4
BELASHOVA, Irina S., Peter S. BIBIKOV, Alexander A. OREKHOV, and Eduard I. STAROVOITOV. "Controlled thermogasocyclic nitriding processes." INCAS BULLETIN 13, S (August 3, 2021): 13–20. http://dx.doi.org/10.13111/2066-8201.2021.13.s.2.
Повний текст джерелаАнотація:
The existing basic nitriding methods do not exploit many of the potential opportunities. To intensify it and increase its efficiency, this paper considers and proposes a new method of low-temperature nitriding, which makes it possible to optimise the classical process and reduce the consumption of ammonia from 2 to 10 times, reduce the nitriding time by 4-6.5 times with an increase in the thickness of the diffusion layer by 2-6 times without reducing the physical and mechanical properties. During the experiment, gas-cyclic and thermogasocyclic nitriding of armco iron was carried out on an experimental setup, which included a system for monitoring and maintaining the temperature in the working volume, a gas supply system, monitoring the flow rate and degree of ammonia dissociation, cleaning and drying gas, as well as two electromagnetic gas valves controlled from the control panel, allowing the processes to be carried out automatically. As a result, a new method of low-temperature nitriding has been developed – under the conditions of a thermo-gas cycle. This method consists in periodic alternation of saturation cycles during flow nitriding and resorption of the nitrided layer with the maximum possible decrease in the saturating capacity of the atmosphere. The proposed new method of thermogasocyclic nitriding is a new, effective hardening technology that allows to reduce the consumption of saturating gas and emissions into the atmosphere by up to 10 times, the nitriding time by 4-6.5 times, and also to increase the thickness of the diffusion layer by 2-6 times without reducing the physical and mechanical properties. A new technological parameter has been established – the duration of half-cycles, which allows simply and effectively regulating the phase composition and structure of the layer in order to obtain the required physical and mechanical properties.
5
MAINI, PHILIP K., LUISA MALAGUTI, CRISTINA MARCELLI, and SERENA MATUCCI. "AGGREGATIVE MOVEMENT AND FRONT PROPAGATION FOR BI-STABLE POPULATION MODELS." Mathematical Models and Methods in Applied Sciences 17, no. 09 (September 2007): 1351–68. http://dx.doi.org/10.1142/s0218202507002303.
Повний текст джерелаАнотація:
Front propagation for the aggregation-diffusion-reaction equation [Formula: see text] is investigated, where f is a bi-stable reaction-term and D(v) is a diffusion coefficient with changing sign, modeling aggregating-diffusing processes. We provide necessary and sufficient conditions for the existence of traveling wave solutions and classify them according to how or if they attain their equilibria at finite times. We also show that the dynamics can exhibit the phenomena of finite speed of propagation and/or finite speed of saturation.
6
Lanin, Vladimir Leonid. "Innovation Ultrasonic Assistant Soldering in Electronics." Journal of Electronic Research and Application 5, no. 3 (August 17, 2021): 18–27. http://dx.doi.org/10.26689/jera.v5i3.1662.
Повний текст джерелаАнотація:
Innovative approaches in ultrasonic assistant soldering consist consists of increasing the activity of cavitation and accelerating diffusion processes at the interface between the solder and the soldering material. Besides that, it improves the effectiveness of cavitation processes in melts by saturating gas cavities with diamete rs that are smaller than the resonant sizes of cavitation germs. Gas saturation of liquids and melts raises level of cavitation pressure by 20 25%25%, that intensifies US processing of cleaning, soldering and metallization. Modelling diffusion process showed that the US activation increased the concentration of diffusing elements of Zn and Al in the interface depth by 15 20% on average, and the combined activation by the US and electric field increased it by 30 45%. Furthermore, as the energy quantity adsorbed by melt increases, increased amplitude and frequency of US vibrations induces concentration rise. The heat energy was also boosted by combining the activation of the melt–soldered material system with US vibrations energy and high current pulses. This allows for a faster increase in soldering temperature, as well as improved solder wettability.
7
Eitelberger, Johannes, and Karin Hofstetter. "Modeling of Transient Moisture Diffusion in Wood below the Fiber Saturation Point." Defect and Diffusion Forum 312-315 (April 2011): 455–59. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.455.
Повний текст джерелаАнотація:
During the last two decades the macroscopic formulation of moisture transport in wood below the fiber saturation point has motivated many research efforts. From experiments the difference in steady-state and transient transport processes is well known, but could not be explained in a fully physically motivated manner. In the following article, first the microstructure of wood is depicted, followed by a description of the physical background of steady-state and transient transport processes in wood, and thereon based mathematical formulations. For a correct macroscopic description of transient transport processes, three coupled differential equations have to be solved in parallel, which is done using the finite element method. The validation of the whole model by comparison of model predictions with experimentally derived values is currently in progress and will be published in near future.
8
Gran, M., J. Carrera, S. Olivella, and M. W. Saaltink. "Modeling evaporation processes in a saline soil from saturation to oven dry conditions." Hydrology and Earth System Sciences Discussions 8, no. 1 (January 18, 2011): 529–54. http://dx.doi.org/10.5194/hessd-8-529-2011.
Повний текст джерелаАнотація:
Abstract. Thermal, suction and osmotic gradients interact during evaporation from a salty soil. Vapor fluxes become the main water flow mechanism under very dry conditions. A coupled nonisothermal multiphase flow and a reactive transport model of a salty sand soil was developed to study such an intricate system. The model was calibrated with data from an evaporation experiment (volumetric water content, temperature and concentration). The retention curve and relative permeability functions were modified to simulate oven dry conditions. Experimental observations were satisfactorily reproduced, which suggests that the model can be used to assess the underlying processes. Results show that evaporation is controlled by heat, and limited by salinity and liquid and vapor fluxes. Below evaporation front vapor flows downwards controlled by temperature gradient and thus generates a dilution. Vapor diffusion and dilution are strongly influenced by heat boundary conditions. Gas diffusion plays a major role in the magnitude of vapor fluxes.
9
Kaganovsky, Yuri S., A. A. Lipovskii, M. Rosenbluh, and V. Zhurikhina. "Spatially Periodic Formation of Nanoparticles in Metal-Doped Glasses." Defect and Diffusion Forum 263 (March 2007): 57–62. http://dx.doi.org/10.4028/www.scientific.net/ddf.263.57.
Повний текст джерелаАнотація:
In the course of reactive diffusion of hydrogen in metal-doped glasses, at some conditions, metallic nanoparticles grow forming quasi-periodic layered structure. We have developed a model defining conditions necessary for the formation of the layered structures. The model indicates relatively narrow range of parameters providing the quasi-periodic growth of the nanoparticles. The layered structure arises at relatively low over-saturation by neutral metal in the diffusion zone, due to the competition of two processes: enrichment of the glass by neutral metal atoms via reducing of metal ions by diffusing hydrogen and depletion of the glass by the metal atoms caused their diffusion to the nanoparticles. The model can be also applied to other situations where reactive diffusion inducing the formation and growth of nanoparticles occurs.
10
Zheplinska, Marija, Mikhailo Mushtruk, Tatiana Kos, Volodymyr Vasyliv, Yuliya Kryzhova, Roman Mukoid, Marina Bilko, Anatolii Kuts, Yuliia Kambulova, and Sergiy Gunko. "The influence of cavitation effects on the purification processes of beet sugar production juices." Potravinarstvo Slovak Journal of Food Sciences 14 (July 28, 2020): 451–57. http://dx.doi.org/10.5219/1284.
Повний текст джерелаАнотація:
The existing technology for the purification of diffusion juice and its hardware design has not fundamentally changed over the past four decades. The lack of the necessary theoretical developments and experimental data hinders the development of existing and the development of new technological processes. Therefore, the main direction of improving the purification efficiency of juices of sugar beet production is the disclosure of its unused reserves and their implementation in practice. The scientific problem of choosing the rational direction for improving the technology of juice purification, which ensures the production of consumer granulated sugar in the face of changes in a wide range of quality of raw materials, is relevant and has important economic importance, especially in the context of the transition of beet sugar factories to a market economy. One way to solve it is to make fuller use of the adsorption capacity of calcium carbonate particles while increasing the filtration properties of saturation sediments. Therefore, the study investigates the effect of cavitation effects – vapor condensation and hydrodynamic processing of diffusion juice on the processes of purification of diffusion juice, juices of preliminary defecation, first and second saturations. The analysis of the influence of various effects of cavitation processing of juices from the point of view of improving the purification efficiency, the optimal place of the purification process in the technological scheme of production is established.
11
Wang, Xiaoqin, and Yongli Cai. "Cross-Diffusion-Driven Instability in a Reaction-Diffusion Harrison Predator-Prey Model." Abstract and Applied Analysis 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/306467.
Повний текст джерелаАнотація:
We present a theoretical analysis of processes of pattern formation that involves organisms distribution and their interaction of spatially distributed population with cross-diffusion in a Harrison-type predator-prey model. We analyze the global behaviour of the model by establishing a Lyapunov function. We carry out the analytical study in detail and find out the certain conditions for Turing’s instability induced by cross-diffusion. And the numerical results reveal that, on increasing the value of the half capturing saturation constant, the sequences “spots → spot-stripe mixtures → stripes → hole-stripe mixtures → holes” are observed. The results show that the model dynamics exhibits complex pattern replication controlled by the cross-diffusion.
12
Fre´mont, H., J. Y. Dele´tage, A. Pintus, and Y. Danto. "Evaluation of the Moisture Sensitivity of Molding Compounds of IC’s Packages." Journal of Electronic Packaging 123, no. 1 (January 1, 2000): 16–18. http://dx.doi.org/10.1115/1.1326436.
Повний текст джерелаАнотація:
Plastic encapsulated devices are of great interest against their ceramic or metallic counterparts, as they permit significant cost reductions. However, they are more sensitive to moisture ingress, which can lead to reliability problems. Moisture can penetrate either through the polymer or along the interface between the leads and the encapsulant. Samples of 3 different polymers usually used for IC’s encapsulation, either pure or containing a lead frame with the lead terminations, were aged under different RH conditions. Results show that the penetration through the polymer is preponderant face to the progression along the leads. In a first approach, this penetration can be considered as a diffusion process, following the Fick’s law; the diffusion coefficient D and the saturation coefficient S can be deduced from the measurements as a function of the relative humidity. These values can be used in finite element simulations, in order to evaluate the moisture ingress as a function of time within an IC of a given geometry. Moisture diffusion within these new resins is a very long process. In fact, a first “saturation” occurs after a few hours of aging, but if samples are left longer in the oven, a new diffusion process occurs, not leading to a real saturation. Hence processes different than pure fickian diffusion occur in the polymers.
13
Chevalier, T., J. Labaume, A. Delbos, T. Clemens, V. M. Waeger, B. Bourbiaux, and M. Fleury. "A novel experimental approach for studying spontaneous imbibition processes with alkaline solutions." E3S Web of Conferences 89 (2019): 04004. http://dx.doi.org/10.1051/e3sconf/20198904004.
Повний текст джерелаАнотація:
Spontaneous imbibition processes can play an important role in oil production. It can be enhanced or influenced by wettability changes generated by properly designed chemicals or by the natural surfactants resulting from reactive crude oils in the presence of alkaline solutions. The reaction of basic salts with some components of oil can, indeed, lead to the formation of natural soaps that reduces the interfacial tension between oil and brine. The latter scenario is studied herein on samples and oil from the St Ulrich oil field in the Vienna basin. To that end, spontaneous imbibition experiments were performed with two brines differing by the absence or presence of alkali. We first present a general novel technique to monitor saturation changes on small rock samples for the purpose of assessing the efficiency of a given recovery process. Samples of only 15 mm in diameter and 20 mm in length and set at irreducible saturation were fully immersed in the solution of interest, and the evolution of the samples’ saturation with time was monitored thanks to a dedicated NMR technique involving the quantification of the sole oil phase present within the sample. A fully-3D imbibition configuration was adopted, involving counter-current flows through all faces of the sample. The experimental method is fast for two reasons: (i) the kinetics of capillary imbibition process is proportional to the square of sample size, i.e. very rapid if accurate measurements can be acquired on tiny samples, (ii) the present 3D situation also involves faster kinetics than the 1D configuration often used. The NMR technique was crucial to achieve such conditions that cannot be satisfied with conventional volumetric methods. The kinetics of oil desaturation during spontaneous imbibition is interpreted with the help of an analytical 3D diffusion model. For the alkaline solution, the diffusion coefficient is reduced by a factor of only two compared to the non-alkaline brine, although the interfacial tension between the oil and the imbibing solution is reduced by a factor of 10. Hence, a wettability change to a more water wet state has to be assumed when the alkaline solution replaces the non-alkaline solution in the imbibition process. However, no significant impact on the final saturation was observed.
14
TRUSH, V. S., І. М. POHRELIUK та V. M. FEDIRKO. "THERMODIFFUSION SATURATION OF THE SURFACE LAYERS OF α-TITANIUM BY OXYGEN, NITROGEN, CARBON". Physical Metallurgy and Heat Treatment of Metals, № 3 (28 вересня 2021): 65–72. http://dx.doi.org/10.30838/j.pmhtm.2413.010721.65.783.
Повний текст джерелаАнотація:
The purpose of the study is to analytically assess the depth of the gas-saturated zone in the case of a single-component diffusion saturation of alpha-titanium with nitrogen, oxygen and carbon from a rarefied controlled gas environment. Results. Based on the analysis of the literature data, the work schematically shows the interaction of alpha titanium with the elements of implementation and presents the processes with the corresponding parameters that characterize. It is shown that the surface impurity concentration is equal to the equilibrium concentration and is established instantly and does not depend on time. Consequently, with the proposed generalized nonstationary boundary condition in the absence of diffusion of impurities into the volume of the metal, the time dependence of its surface concentration is given, determined by the intensity of surface processes. The dependence of the relative change in the microhardness in the diffusion zone of titanium due to dissolved nitrogen (without taking into account the contribution of nitride inclusions) is presented. Analytically calculated concentration profiles of nitrogen generally correlate well with the distribution of the corresponding relative changes in microhardness in the surface layer. Analytical calculations of the concentration profiles of oxygen, nitrogen and carbon in titanium at a saturation temperature of 700 °C are presented. Practical value. The results obtained will make it possible to preliminarily estimate the size of the fortified near-surface layer depending on the parameters of chemical-thermal treatment and select the optimal parameters of thermal diffusion treatment to ensure the formation of reinforced layers on products made of alpha-titanium based on elements of interstitial in order to increase the functional properties.
15
Pastore, Nicola, Claudia Cherubini, and Concetta I. Giasi. "Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk." Journal of Hydrology and Hydromechanics 65, no. 3 (September 1, 2017): 287–96. http://dx.doi.org/10.1515/johh-2017-0033.
Повний текст джерелаАнотація:
AbstractWhen dealing with groundwater resources, a better knowledge of the hydrological processes governing flow in the unsaturated zone would improve the assessment of the natural aquifer recharge and its vulnerability to contamination. In North West Europe groundwater from unconfined chalk aquifers constitutes a major water resource, therefore the need for a good hydrological understanding of the chalk unsaturated zone is essential, as it is the main control for aquifer recharge. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a porous matrix with embedded fractures. The case study regards the role of the thick unsaturated zone of the Cretaceous chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In order to describe the flow rate that reaches the water table, the kinematic diffusion theory has been applied that treats the unsaturated water flow equation as a wave equation composed of diffusive and gravitational components. The kinematic diffusion model has proved to be a convenient method to study groundwater recharge processes in that it was able to provide a satisfactory fitting both for rising and falling periods of water table fluctuation. It has also proved to give an answer to the question whether unsaturated flow can be described using the theory of kinematic waves. The answer to the question depends principally on the status of soil moisture. For higher values of hydraulic Peclet number (increasing saturation), the pressure wave velocities dominate and the preferential flow paths is provided by the shallow fractures in the vadose zone. With decreasing values of hydraulic Peclet number (increasing water tension), rapid wave velocities are mostly due to the diffusion of the flow wave. Diffusive phenomena are provided by matrix and fracture-matrix interaction.The use of a kinematic wave in this context constitutes a good simplified approach especially in cases when there is a lack of information concerning the hydraulic properties of the fractures/macropores close to saturation.
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Sereda, Borys, Borys Khina, and Irina Kruglyak. "THERMODYNAMIC ANALYSIS OF THE GAS MEDIUM IN THE FORMATION OF DIFFUSION COATINGS USING COMPOSITE SATURATING CHARGES." Scientific Journal "Metallurgy", no. 1 (February 17, 2021): 43–49. http://dx.doi.org/10.26661/2071-3789-2020-1-06.
Повний текст джерелаАнотація:
Review of the main processes of formation of diffuse coatings doped with molybdenum,vanadium and tungsten. The basic features of the formation of diffusion layers during chemicalthermaltreatment are considered.: When the SHS is tested, the container is heated to temperaturesof 1173-1330 K. Within 1-2 hours, a diffusion coating is formed due to the saturation of thesurface of structural materials with atoms of saturating elements - Cr, Al, V, Ti, B, W, Mo. Assaturating elements, the defects of these elements and the chemical compounds of these elementswere used, and to determine the possibility of using specific substances, chemical reactionswere considered that can occur in the temperature range of diffusion saturation usingSOS. It should be noted that the metallothermal Reduced oxide, which is used in the synthesisof powder media for CHT, is very fast. When obtaining diffuse layers using the composition ofsaturating the medium, a gas phase is formed, containing spolo-I, I2, I3, H, H2, H3, Cl2, Cl3 withchemical elements. With an increase in temperature, an increase in the amount of halides isobserved. This confirms the possibility of transferring alloying elements for the formation of diffusioncoatings. Also, the amount of products in the gaseous phase increases and condensedproducts are released. It is characteristic that in the temperature range of 700-1500 K, the decompositionof reaction products occurs during CHT, which is confirmed by the production ofdecomposition substances and a sharp increase in the number of gas moles.
17
Zhou, Chongbo, Lingyi Guo, Li Chen, Xin Tian, Tiefeng He, and Qinghua Yang. "Pore-Scale Modeling of Air–Water Two Phase Flow and Oxygen Transport in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cell." Energies 14, no. 13 (June 24, 2021): 3812. http://dx.doi.org/10.3390/en14133812.
Повний текст джерелаАнотація:
Understanding multiphase flow and gas transport occurring in electrodes is crucial for improving the performance of proton exchange membrane fuel cells. In the present study, a pore-scale model using the lattice Boltzmann method (LBM) was proposed to study the coupled processes of air–water two-phase flow and oxygen reactive transport processes in porous structures of the gas diffusion layer (GDL) and in fractures of the microscopic porous layer (MPL). Three-dimensional pore-scale numerical results show that the liquid water generation rate is gradually reduced as the oxygen consumption reaction proceeds, and the liquid water saturation in the GDL increases, thus the constant velocity inlet or pressure inlet condition cannot be maintained while the results showed that at t = 1,200,000 iterations after 2900 h running time, the local saturation at the GDL/MPL was about 0.7, and the maximum value was about 0.83, while the total saturation was 0.35. The current density reduced from 2.39 to 0.46 A cm−2. Effects of fracture number were also investigated, and the results showed that for the fracture numbers of 8, 12, 16, and 24, the breakthrough point number was 4, 3, 3, and 2, respectively. As the fracture number increased, the number of the water breakthrough points at the GDL/GC interface decreased, the liquid water saturation inside the GDL increased, the GDL/MPL interface was more seriously covered, and the current density decreased. The pore-scale model for the coupled multiphase reactive transport processes is helpful for understanding the mechanisms inside the porous electrodes of PEMFC.
18
Bloch, Katarzyna. "The Influence of Isothermal Annealing and Structural Defects on Properties of Amorphous Fe78Si11B11 with High Magnetization Saturation." Revista de Chimie 68, no. 3 (April 15, 2017): 478–82. http://dx.doi.org/10.37358/rc.17.3.5482.
Повний текст джерелаАнотація:
This paper presents the results of numerical analysis of the primary magnetization curves, which were obtained under the assumptions of the theory of approach to ferromagnetic saturation described in by H. Kronm�ller. Test samples of the Fe78Si11B11 alloy were tape-shaped materials, which were subjected to isothermal annealing, not causing their crystallization. The investigated ribbons (tapes) were characterized by a very high saturation magnetization value of approximately 2T, which the thermal treatment has increased by about 10%. It was found that reason for the change of saturation magnetization of the investigated samples was the local rearrangement of atoms due to diffusion processes leading to the release of free volumes to the surface and combining of them into larger unstable defects called pseudodislocational dipoles.
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Gran, M., J. Carrera, S. Olivella, and M. W. Saaltink. "Modeling evaporation processes in a saline soil from saturation to oven dry conditions." Hydrology and Earth System Sciences 15, no. 7 (July 4, 2011): 2077–89. http://dx.doi.org/10.5194/hess-15-2077-2011.
Повний текст джерелаАнотація:
Abstract. Thermal, suction and osmotic gradients interact during evaporation from a salty soil. Vapor fluxes become the main water flow mechanism under very dry conditions. A coupled nonisothermal multiphase flow and reactive transport model was developed to study mass and energy transfer mechanisms during an evaporation experiment from a sand column. Very dry and hot conditions, including the formation of a salt crust, necessitate the modification of the retention curve to represent oven dry conditions. Experimental observations (volumetric water content, temperature and concentration profiles) were satisfactorily reproduced using mostly independently measured parameters, which suggests that the model can be used to assess the underlying processes. Results show that evaporation concentrates at a very narrow front and is controlled by heat flow, and limited by salinity and liquid and vapor fluxes. The front divides the soil into a dry and saline portion above and a moist and diluted portion below. Vapor diffusses not only upwards but also downwards from the evaporation front, as dictated by temperature gradients. Condensation of this downward flux causes dilution, so that salt concentration is minimum and lower than the initial one, just beneath the evaporation front. While this result is consistent with observations, it required adopting a vapor diffusion enhancement factor of 8.
20
De Prisco, Giuseppe, and Xiaowen Shan. "Mass Transport/Diffusion and Surface Reaction Process with Lattice Boltzmann." Communications in Computational Physics 9, no. 5 (May 2011): 1362–74. http://dx.doi.org/10.4208/cicp.021009.241210s.
Повний текст джерелаАнотація:
AbstractMulti-component flow with chemical reactions is a common problem in different industrial applications: the mixing chamber of a reaction injection molding (RIM) machine; the dynamics of diesel soot particles interacting with a porous-ceramic particulate filter; reactive transport in porous media; bio-chemical processes involving enzyme-catalyzed kinetics. In all these cases, mass diffusion/convection and wall or volume chemical interactions among components play an important role. In the present paper we underline the importance of diffusion/convection/reaction mechanisms in bio-chemical processes using the Lattice Boltzmann (LB) technique. The bio-application where we studied diffusion/convection/reaction mechanisms is the quorum-sensing pathway for the bio-synthesis of the AI-2, a molecule that allows the bacteria to launch a coordinated attack on a host immune system (see [9,10] for more details of the bio-application). The overall goal is to create a micro-device to screen potential drugs that inhibit AI-2 bio-synthesis. The Michaelis-Menten saturation kinetic model is implemented at the reactive surface and the results are shown in terms of two dimensionless numbers: Damkohler (Da) and Peclet (Pe) number. For high Pe number a small conversion of reactants into products is obtained at the reactive surface, but the overall flux of products is high; moreover, a fast saturation of the conversion of reactants to products is obtained for high Da numbers. The trade-off for setting the Pe and Da numbers depends on the specific application and the technologies used in the micro-device (e.g., sensitivity of the detector, cost of reactants).
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Egorov, M., R. Egorova, A. Atrohov, and V. Ekilik. "Influence of alloying components on diffusion and bonding processes in powder materials." Journal of Physics: Conference Series 2131, no. 4 (December 1, 2021): 042024. http://dx.doi.org/10.1088/1742-6596/2131/4/042024.
Повний текст джерелаАнотація:
Abstract At present, powder materials are used in practically all branches of industry, from medicine to aerospace technology. This is a wide range of materials ranging from constructional and instrumental materials and ending with special-purpose materials and medical implants. Powder metallurgy methods are most often used where the manufacture of products with desired properties is impossible using traditional methods: casting, stamping, etc. The production of all these materials is based on such basic operations as: obtaining starting materials, molding from these materials blanks of a given shape, size and strength, and sintering, intended for the final formation of the required properties and dimensions. The peculiarity of powder metallurgy technology allows creating a huge variety of developed technological schemes, which puts these technologies to a new level and allows for the rapid development of many industries. Alloying powder steels, in contrast to cast steels, has a number of characteristic features due to the specificity of their production. The structure of powder alloy steels and their properties depend on the methods of obtaining steels and technological features of their production. The following main methods of obtaining powder alloyed steels can be named: preparation of multicomponent mixtures of powders of iron and alloying elements and their subsequent processing; the use of alloyed iron powders, to which, if necessary, add carbon or other alloying elements; impregnation with liquid alloying metals or diffusion saturation of frameworks sintered from iron powders.
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Molnár, Gábor Y., Shenouda S. Shenouda, Gábor L. Katona, Gábor A. Langer, and Dezső L. Beke. "Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry." Beilstein Journal of Nanotechnology 7 (March 22, 2016): 474–83. http://dx.doi.org/10.3762/bjnano.7.41.
Повний текст джерелаАнотація:
Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself.
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Petrova, Larisa, Vladimir Alexandrov, and Alexandra Sergeeva. "Electric discharge as technological factor of intensification of chemical-thermal treatment of engineering products." Science intensive technologies in mechanical engineering 2019, no. 12 (December 16, 2019): 36–43. http://dx.doi.org/10.30987/2223-4608-2019-2019-12-36-43.
Повний текст джерелаАнотація:
The advantages of nitriding in an electrostatic and high-frequency field connected with the possibility of carrying out processes at normal pressure are shown. The acceleration of the process of diffusion saturation with nitrogen in an electric field with the formation of a spark discharge as compared with gas nitriding is confirmed experimentally. This method of steel nitriding allows forming layers of different structure and thickness with the specified gradient of hardness.
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Schlüter, Steffen, Jan Zawallich, Hans-Jörg Vogel, and Peter Dörsch. "Physical constraints for respiration in microbial hotspots in soil and their importance for denitrification." Biogeosciences 16, no. 18 (September 27, 2019): 3665–78. http://dx.doi.org/10.5194/bg-16-3665-2019.
Повний текст джерелаАнотація:
Abstract. Soil denitrification is the most important terrestrial process returning reactive nitrogen to the atmosphere, but remains poorly understood. In upland soils, denitrification occurs in hotspots of enhanced microbial activity, even under well-aerated conditions, and causes harmful emissions of nitric (NO) and nitrous oxide (N2O). The timing and magnitude of such emissions are difficult to predict due to the delicate balance of oxygen (O2) consumption and diffusion in soil. To study how spatial distribution of hotspots affects O2 exchange and denitrification, we embedded microbial hotspots composed of porous glass beads saturated with growing cultures of either Agrobacterium tumefaciens (a denitrifier lacking N2O reductase) or Paracoccus denitrificans (a “complete” denitrifier) in different architectures (random vs. layered) in sterile sand that was adjusted to different water saturations (30 %, 60 %, 90 %). Gas kinetics (O2, CO2, NO, N2O and N2) were measured at high temporal resolution in batch mode. Air connectivity, air distance and air tortuosity were determined by X-ray tomography after the experiment. The hotspot architecture exerted strong control on microbial growth and timing of denitrification at low and intermediate saturations, because the separation distance between the microbial hotspots governed local oxygen supply. Electron flow diverted to denitrification in anoxic hotspot centers was low (2 %–7 %) but increased markedly (17 %–27 %) at high water saturation. X-ray analysis revealed that the air phase around most of the hotspots remained connected to the headspace even at 90 % saturation, suggesting that the threshold response of denitrification to soil moisture could be ascribed to increasing tortuosity of air-filled pores and the distance from the saturated hotspots to these air-filled pores. Our findings suggest that denitrification and its gaseous product stoichiometry depend not only on the amount of microbial hotspots in aerated soil, but also on their spatial distribution. We demonstrate that combining measurements of microbial activity with quantitative analysis of diffusion lengths using X-ray tomography provides unprecedented insights into physical constraints regulating soil microbial respiration in general and denitrification in particular. This paves the way to using observable soil structural attributes to predict denitrification and to parameterize models. Further experiments with natural soil structure, carbon substrates and microbial communities are required to devise and parametrize denitrification models explicit for microbial hotspots.
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van Dorp, J. J. "Condensing Solvent Processes: In Search of the Production Function." SPE Reservoir Evaluation & Engineering 24, no. 02 (January 21, 2021): 409–28. http://dx.doi.org/10.2118/205009-pa.
Повний текст джерелаАнотація:
Summary The heavy-oil- and bitumen-recovery process by injection of a pure condensing solvent in a solvent vapor chamber provides an alternative to steam-based recovery techniques such as steam-assisted gravity drainage (SAGD). Because of the lower operating temperature between 40 and 80°C, the process uses a much lower energy budget than a steam process and thus results in significantly reduced greenhouse-gas emissions. This paper describes the route to a successful production function with the physical processes at play and using analytical tools. Physical relationships are derived for the solvent/bitumen (S/B) ratio, the bitumen drainage from the roof of the solvent vapor chamber, and for bitumen extraction from both sides of the solvent chamber by the draining condensed solvent. The fast diffusion of bitumen into this narrow liquid solvent zone is likely subtly enhanced by transverse dispersion. The speed of bitumen extraction from the roof of the solvent vapor chamber is constrained by the gas/oil capillary pressure. Extraction from the side of the chamber is approximately three times faster by the action of the thin gravity-draining liquid solvent film. Several equations are provided to enable creation of a heat balance for this condensing solvent process. Laboratory and field observations are matched, including the rates, the heat balance, and the S/B ratio. The model can explain constrained production performance by identifying the rate-limiting steps (e.g., when insufficient solvent condenses). The model predicts high solvent holdup during the rise of the solvent chamber. A method to estimate this solvent liquid saturation is provided. The S/B ratio depends on injector-wellbore heat losses, the (high) liquid saturation in the rising solvent chamber, and the process properties (operating temperature), reservoir properties (heat capacity, porosity, and oil saturation), and solvent properties (density and latent heat). In the existing body of literature, no satisfactory analytical model was available; this new approach helps to constrain production performance and to estimate solvent and heat requirements. The methods in this paper can be used in the future for subsurface project design and performance predictions.
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Golybin, V. A., V. A. Fedoruk, and N. A. Matvienko. "Problems of seasonality of sugar production from beets." Proceedings of the Voronezh State University of Engineering Technologies 82, no. 1 (May 15, 2020): 64–69. http://dx.doi.org/10.20914/2310-1202-2020-1-64-69.
Повний текст джерелаАнотація:
In recent years, the annual processing of sugar beet in Russia is 45 million tons or more, which allows to produce white sugar in the amount of 6.0 million tons or more. during the production season, the quality of beets does not remain constant – not only its sugar content changes, but also the content of harmful soluble non-sugars, as well as physical and chemical parameters - the mass of root crops decreases due to wilting, reducing turgor, respiration and germination, rotten mass appears as a result of microbiological and enzymatic processes and the formation of foci of mucous bacteriosis. One of the main tasks of improving the diffusion process is to increase the elasticity of beet tissue and reduce the intensity of the transition of pectin substances into the diffusion juice. This goal is achieved by using effective chemical reagents in the composition of the feed water introduced into the diffusion apparatus, as well as processing of beet chips immediately before the sucrose extraction process; reducing the temperature of desugarisation of beet pulp in the diffusion apparatus in the allowable interval. The method of intensification of sucrose extraction using the method of treatment of feed water in an electric field is proposed. Improvement of the dispersed composition of the resulting sediment particles is facilitated by the return to the preliming of the carbonate suspension of juice II saturation, carried out using an activated suspension of filter perlite. The homogeneity of calcium carbonate particles and correspondingly high filtration rates of saturation juice are formed due to the active circuit of the internal circulation of the juice. The use of the proposed recommendations during the implementation of technological processes in their implementation in modern equipment of the diffusion process and purification of the obtained juice allow to minimize the negative consequences of beet processing both at the initial stage of the production season when technically not ripe root crops are received, and during the end of the season when processing raw materials of reduced quality.
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Hania, P. R., A. Pugžlys, L. N. Lucas, J. J. D. de Jong, J. van Esch, B. Feringa, and K. Duppen. "Reaction Dynamics and Applications in Patterning of Bisthienylcyclopentene-Based Photochromic Switches." Solid State Phenomena 97-98 (April 2004): 207–14. http://dx.doi.org/10.4028/www.scientific.net/ssp.97-98.207.
Повний текст джерелаАнотація:
The structural and optical properties of the gel-forming photochromic switch 1,2-bis(2’-methyl-5’-{{((R) phenylethyl)amino}carbonyl}thienyl-3’-yl)cyclopentene are studied by means of the linear absorption and holographic grating techniques. The use of diffractive optics enables recording of holographic gratings with high long-term phase stability. The diffraction efficiency of the recorded holographic gratings approach values of 30% for low writing beam energies when diffusion is the rate determining factor. At higher writing pulse energies the competition between the diffusion and photodecomposition processes causes lower diffraction efficiencies. At irradiation doses above 10 mJ the spatial profile of the recorded gratings is strongly influenced by saturation effects. Because of the well-determined grating profile the holographic grating technique is potentially applicable for the quantitative characterisation of the diffusion process in photochromic gels.
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Jung, Jae Kap, Kyu Tae Kim, Un Bong Baek, and Seung Hoon Nahm. "Volume Dependence of Hydrogen Diffusion for Sorption and Desorption Processes in Cylindrical-Shaped Polymers." Polymers 14, no. 4 (February 15, 2022): 756. http://dx.doi.org/10.3390/polym14040756.
Повний текст джерелаАнотація:
In the actual application of gas transport properties under high pressure, the important factors are sample size dependence and permeation efficiency, related to gas sorption. With a modified volumetric analysis technique, we firstly measured the overall diffusion properties and equilibrium times for reaching the saturation of hydrogen content in both hydrogen sorption and desorption processes. The measured parameters of total uptake (C∞), total desorbed content (C0), diffusion coefficient in sorption (Ds), diffusion coefficient in desorption (Dd), sorption equilibrium time (ts) and desorption equilibrium time (td) of hydrogen in two polymers were determined relative to the diameter and thickness of the cylindrical-shaped polymers in the two processes. C∞ and C0 did not demonstrate an appreciable volume dependence for all polymers. The identical values of C∞ and C0 indicate the reversibility between sorption and desorption, which is interpreted by the occurrence of physisorption by sorbed hydrogen molecules. However, the measured diffusivity of the polymers was found to be increased with increasing thickness above 5 mm. Moreover, the larger Dd values measured in the desorption process compared to Ds may be attributed to an increased amorphous phase and volume swelling caused by increased hydrogen voids and polymer chain scission after decompression. The ts and td were found to be linearly proportional to the square of the thickness above an aspect ratio of 3.7, which was consistent with the numerical simulations based on the solution of Fick’s law. This finding could be used to predict the ts in a polymer without any measurement, depending on the sample size.
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Guzei, Dmitriy, Vladimir Zhigarev, Valery Rudyak, Sofia Ivanova, and Andrey Minakov. "Effect of Initial Water Saturation on Oil Displacement Efficiency by Nanosuspensions." Fluids 7, no. 2 (January 31, 2022): 59. http://dx.doi.org/10.3390/fluids7020059.
Повний текст джерелаАнотація:
This article deals with the study of the initial water saturation effect of a porous medium on the oil recovery factor using a water-based nanosuspension. The initial water saturation of the porous medium in the computations varied within the range from 0 to 90%. The nanoparticle SiO2 concentration varied from 0 to 1 wt%. The particle sizes were equal to 5, 18, 22, and 50 nm. Experimentally measured wetting angles and the interfacial tension coefficient depending on the concentration and size of nanoparticles were used in computations. A mathematical model was developed, describing the transfer and diffusion of nanoparticles within the aqueous phase during immiscible displacement of oil by nanosuspension from a porous medium. Using the developed model, a systematic computational study of the effect of the initial water saturation of the core micromodel on the oil recovery factor using nanosuspension was carried out. It was revealed that with an increase in the initial water saturation, the oil recovery factor monotonically decreased in the case of displacement both by water and nanosuspension. It was shown that with an increase in the concentration of nanoparticles and a decrease in their size, the oil recovery factor increased. At that, the relative increase in the recovery factor had a maximum at an initial water saturation equal to 60%.
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Seguí, Concepció. "Kinetics of Reordering in Quenched Ni2Mn0.8Cu0.2Ga Ferromagnetic Shape Memory Alloys." Metals 12, no. 5 (April 26, 2022): 738. http://dx.doi.org/10.3390/met12050738.
Повний текст джерелаАнотація:
Quenched Ni2Mn1−xCuxGa ferromagnetic shape memory alloys undergo two consecutive post-quench ordering processes. The kinetics of order recovery has been analysed in detail for Ni2Mn0.8Cu0.2Ga, based on the calorimetric curves obtained during post-quench heating at constant rates. Isoconversional methods have been used to determine the activation energy, the pre-exponential factor, and the reaction model that best fits the two reordering processes. The kinetic analysis has been extended to samples quenched from different temperatures. The kinetic study shows that order improvement processes in quenched Ni2Mn0.8Cu0.2Ga alloys can be described by a first order reaction model, consistent with site-saturation nucleation and homogeneous diffusion-controlled growth, with apparent activation energies around 1.1 eV. The pre-exponential factors, especially those obtained for samples quenched from different temperatures, highlight the crucial role of the vacancies retained by high temperature quenching on the atomic reordering underlying the observed processes.
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Jung, Jae-Kap, Kyu-Tae Kim, Nak-Kwan Chung, Un-Bong Baek, and Seung-Hoon Nahm. "Characterizing the Diffusion Property of Hydrogen Sorption and Desorption Processes in Several Spherical-Shaped Polymers." Polymers 14, no. 7 (April 4, 2022): 1468. http://dx.doi.org/10.3390/polym14071468.
Повний текст джерелаАнотація:
We developed a method for characterizing permeation parameters in hydrogen sorption and desorption processes in polymers using the volumetric measurement technique. The technique was utilized for three polymers: nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM). The total uptake (C∞), total desorbed content (C0), diffusivity in sorption (Ds), and diffusivity in desorption (Dd) of hydrogen in the polymers were determined versus the sample diameter used in both processes. For all the polymers, the diameter dependence was not detected for C∞ and C0. The average C∞ and C0 at 5.75 MPa were 316 wt∙ppm and 291 wt∙ppm for NBR, 270 wt∙ppm and 279 wt∙ppm for EPDM, and 102 wt∙ppm and 93 wt∙ppm for FKM. The coincidence of C∞ and C0 in the sorption and desorption process indicated physisorption upon introducing hydrogen molecules into the polymers. The larger Dd in the desorption process than Ds could be attributed to an increased amorphous phase and volume swelling after decompression. The equilibrium time to reach the saturation of the hydrogen content in both processes was experimentally confirmed as proportional to the squared radius and consistent with the COMSOL simulation. This method could be used to predict the equilibrium time of the sorption time, depending on the radius of the polymers without any measurement.
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Knyazev, S. A. "Features of structure formation of surface layers with high content of boron on steel 15Х11МФ in the conditions of furnace and induction heating". Кераміка: наука і життя, № 2(47) (12 липня 2020): 26–30. http://dx.doi.org/10.26909/csl.2.2020.4.
Повний текст джерелаАнотація:
The results of obtaining borated layers on 15H11MF high-alloy steel under equilibrium and non-equilibrium heating conditions are presented. Equilibrium conditions were achieved by slow furnace heating (with a heating rate of 0.1 oC/s), non-equilibrium – by induction heating (with a heating rate of 100 oC/s). The heating was controlled by measuring the thermoelectric power by a thermocouple welded to the surface of the sample by electric contact welding. The signal from the thermocouple was digitized by the ADC and transmitted to a computer where, at high speed, an array of data of temperature-time dependence of the process was formed. Furnace heating was carried out in a laboratory electric furnace at 1130 оС ± 5 оС, 1150 оС ± 5 оС and 1160 оС ± 5 оС. Induction heating was carried out to temperatures of 1180 oC ± 20oC, 1200 oC ± 20oC, 1220 oC ± 20oC. The possibility of significant reduction of the treatment process from 3 hours to 2 minutes due to the intensifying action in non-equilibrium conditions of structure formation is shown. Boron saturation came from the paste. Saturating paste consisted of 60% boron carbide, 30% NaF, 10% CaF2. The method of metallographic research shows not only the morphological differences of the obtained surface layers, but also established the predominant mechanism of boron diffusion into high-alloy martensitic steel. During furnace heating (1150оС), a solid boron with a thickness of up to 50 μm and a hardness of 15100 MPa is formed. At a depth of up to 150 μm, grain boundary diffusion is noticeable, which obviously dominates in the processes of boron saturation of high-alloy steels. At temperatures of 1160 oC and furnace heating under a solid layer of boride with a thickness of 110 μm, a two-phase zone is formed, which consists of boride and a solid solution with a thickness of 70 μm. This layer is more defective. Induction heating with boron saturation forms a thick (up to 200 μm) layer of coarse boride crystallites (18900 – 9270 MPa) with an eutectic structure (6440 MPa), which becomes coarser with increasing temperature from 1180 to 1220 оС. The ability to obtain solid hardened layers in a short treatment time makes boron saturation from pastes a more attractive alternative among other chemical-heat treatment technologies.
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Polyachenko, E. V., P. Berczik, A. Just, and I. G. Shukhman. "Simulation of the loss-cone instability in spherical systems – II. Dominating Keplerian potential." Monthly Notices of the Royal Astronomical Society 492, no. 4 (January 17, 2020): 4819–24. http://dx.doi.org/10.1093/mnras/staa141.
Повний текст джерелаАнотація:
ABSTRACT According to our previous theoretical findings, physical processes in centres of galaxies, star clusters, and the Oort comet cloud can be significantly altered by a new so-called ‘gravitational loss-cone instability’. Using N-body simulations of a spherical stellar model in the dominating Keplerian potential, we confirm the possibility of the instability and go beyond the linear theory. Unlike most other instabilities, the new one shows no notable change in spherical geometry of the cluster, but it significantly accelerates the speed of diffusion of particles in phase space leading to a repopulation of the loss cone and early instability saturation.
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Dorofeyev, V. Yu, D. N. Sviridova, and Kh S. Kochkarova. "On the question of the applicability of G.V. Samsonov’s activated sintering concept in studying the processes of powder material deformation." Izvestiya Vuzov. Poroshkovaya Metallurgiya i Funktsional’nye Pokrytiya (Universitiesʹ Proceedings. Powder Metallurgy аnd Functional Coatings), no. 4 (December 15, 2018): 6–14. http://dx.doi.org/10.17073/1997-308x-2018-4-6-14.
Повний текст джерелаАнотація:
Some Yu.G. Dorofeev’s memoirs about joint work and meetings with outstanding materials science expert G.V. Samsonov are given. Meetings in Yugoslavia were of particular importance where G.V. Samsonov and M.M. Ristićtogether with other worldfamous scientists created the International Institute for the Science of Sintering. In the last years of his life, G.V. Samsonov proposed the concept of sintering activation by additives that act as electron acceptors and additionally contribute to the ionic bond in the matrix material. The paper considers the possibility of using this concept in the development of activating additives that reduce the activation energy of the plastic deformation of iron-based powder materials. Sintering activation when forming stable electronic configurations can be accomplished by: 1) accelerating the grain-boundary heterodiffusion of the matrix material in the presence of phase segregations containing an activating microadditive (W–Ni system); 2) intensifying shrinkage durng the plastic flow of matrix material particles facilitated by diffusion porosity formed in the additive particles as a result of predominant additive atom diffusion into base metal particles (Fe–Ni, Fe–Co, Fe–Mn systems); 3) increasing the self-diffusion coefficient of base metal atoms due to the expanded area of a less close-packed crystal lattice (αphase) upon activating additive dissolution (Fe–Mo system). The article reviews the information available on the prospects for using manganese and chromium as compaction activating additives. The compaction activation energy of iron-based powder materials can be reduced by introducing manganese additives. At the same time, the use of diffusion saturation technology is promising. The question of using chromium as an activator does not have an unambiguous answer and suggests the need for further study.
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Yan, Ting-guo, and Li-juan Wang. "Adsorption of C.I. Reactive Red 228 and Congo Red dye from aqueous solution by amino-functionalized Fe3O4 particles: kinetics, equilibrium, and thermodynamics." Water Science and Technology 69, no. 3 (November 23, 2013): 612–21. http://dx.doi.org/10.2166/wst.2013.745.
Повний текст джерелаАнотація:
A magnetic adsorbent was synthesized by γ-aminopropyltriethoxysilane (APTES) modification of Fe3O4 particles using a two-step process. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and vibration sample magnetometry were used to characterize the obtained magnetic adsorbent. EDS and XPS showed that APTES polymer was successfully introduced onto the as-prepared Fe3O4/APTES particle surfaces. The saturation magnetization of the magnetic adsorbent was around 65 emu g−1, which indicated that the dye can be removed fast and efficiently from aqueous solution with an external magnetic field. The maximum adsorption capacities of Fe3O4/APTES for C.I. Reactive Red 228 (RR 228) and Congo Red (CR) were 51.4 and 118.8 mg g−1, respectively. The adsorption of C.I. Reactive Red 228 (RR 228) and Congo Red (CR) on Fe3O4/APTES particles corresponded well to the Langmuir model and the Freundlich model, respectively. The adsorption processes for RR 228 and CR followed the pseudo-second-order model. The Boyd's film-diffusion model showed that film diffusion also played a major role in the studied adsorption processes for both dyes. Thermodynamic study indicated that both of the adsorption processes of the two dyes are spontaneous exothermic.
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Jin, Sen, and Pengyu Chen. "Modelling drying processes of fuelbeds of Scots pine needles with initial moisture content above the fibre saturation point by two-phase models." International Journal of Wildland Fire 21, no. 4 (2012): 418. http://dx.doi.org/10.1071/wf10119.
Повний текст джерелаАнотація:
Modelling the drying process of fuel moisture with initial moisture content above the fibre saturation point can be used to determine when fuel will become sufficiently dry (after precipitation) to burn and provide a more accurate prediction of fire potential. Based on analysis of the mechanism by which the drying process occurs, we propose a model comprising two phases distinguished by a moisture threshold of 0.35 g g–1, the fibre saturation point; one phase is controlled by evaporation and the other by diffusion. Each phase has a distinct equation with a different timelag. We compared our two-phase model with a one-phase model (one-timelag model) and another two-phase model by estimating drying of 15 Scots pine (Pinus sylvestris var. mongolica) needle fuelbeds. The results indicate that the two-timelag model improves moisture modelling, thereby reducing mean absolute error by more than 30%, i.e. from 0.0047 g g–1 (one-phase model) to 0.0030 g g–1. The model yields consistent results, further suggesting its potential for improving fuel moisture prediction of fire danger rating systems. The first timelag of the model is affected by fuelbed properties. Equations based on variables that represent fuelbed properties were established, thus saving time when estimating parameters for stand-specific fuel moisture models.
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Touzeau, Alexandra, Amaëlle Landais, Samuel Morin, Laurent Arnaud, and Ghislain Picard. "Numerical experiments on vapor diffusion in polar snow and firn and its impact on isotopes using the multi-layer energy balance model Crocus in SURFEX v8.0." Geoscientific Model Development 11, no. 6 (June 20, 2018): 2393–418. http://dx.doi.org/10.5194/gmd-11-2393-2018.
Повний текст джерелаАнотація:
Abstract. To evaluate the impact of vapor diffusion on isotopic composition variations in snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. At each step and for each snow layer, (1) the initial isotopic composition of vapor is taken at equilibrium with the solid phase, (2) a kinetic fractionation is applied during transport, and (3) vapor is condensed or snow is sublimated to compensate for deviation to vapor pressure at saturation. We study the different effects of temperature gradient, compaction, wind compaction, and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor diffusion along isotopic gradients and of vapor diffusion driven by temperature gradients at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 7 to 12 % of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model attenuation due to diffusion is underestimated or that other processes, such as ventilation, influence attenuation. At Dome C, the attenuation is stronger (18 %), probably because of the lower accumulation and stronger δ18O gradients.
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Owejan, Jon P., Thomas A. Trabold, and Matthew M. Mench. "Oxygen transport resistance correlated to liquid water saturation in the gas diffusion layer of PEM fuel cells." International Journal of Heat and Mass Transfer 71 (April 2014): 585–92. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2013.12.059.
Повний текст джерела
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Polyachenko, E. V., P. Berczik, A. Just, and I. G. Shukhman. "Simulation of the loss-cone instability in spherical systems – I. Dominating harmonic potential." Monthly Notices of the Royal Astronomical Society 492, no. 1 (December 20, 2019): 645–50. http://dx.doi.org/10.1093/mnras/stz3544.
Повний текст джерелаАнотація:
ABSTRACT A new so-called ‘gravitational loss-cone instability’ in stellar systems has recently been investigated theoretically in the framework of linear perturbation theory and proved to be potentially important in understanding the physical processes in centres of galaxies, star clusters, and the Oort Cloud. Using N-body simulations of a toy model, we confirm previous findings for the dominating harmonic potential and go beyond the linear theory. Unlike the well-known instabilities, the new one shows no notable change in the spherical geometry of the cluster, but it significantly accelerates the speed of diffusion of particles in phase space leading to an early instability saturation.
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Jessen, Kristian, Margot G. Gerritsen, and Bradley T. Mallison. "High-Resolution Prediction of Enhanced Condensate Recovery Processes." SPE Journal 13, no. 02 (June 1, 2008): 257–66. http://dx.doi.org/10.2118/99619-pa.
Повний текст джерелаАнотація:
Summary This paper investigates the accuracy of first- and high-order numerical methods in simulating enhanced condensate processes in 1D, 2D, and 3D. We compare the predictions of a standard single point upwind (SPU) scheme with a third-order accurate finite difference (FD) simulator based on a third-order essentially nonoscillatory (ENO) flux reconstruction with matching temporal accuracy. We include physical dispersion in the mathematical model of these multiphase, multicomponent systems. The comparisons demonstrate that SPU schemes may fail to predict the formation of the mobile liquid bank at the leading edge of the displacement unless an impractical number of gridblocks is used in the simulations. In contrast, the high-order FD simulator is demonstrated to accurately predict the liquid bank at much lower grid resolution, providing for a more efficient simulation approach. In 2D displacement calculations with gravity included, the CPU requirement of the SPU scheme was found to be more than 50 times larger than for the ENO scheme for a given level of accuracy. In 2D vertical cross-sections, the predicted component recovery is demonstrated to vary upward of 8% depending on the selected numerical scheme for a given grid resolution and dispersivity. In these settings, the SPU solutions converge to the ENO results upon significant grid refinement. In 3D displacement calculations, the magnitude of the predicted condensate bank is also found to be very different depending on the selected numerical scheme. Relative to the 2D displacement calculations, condensate banking and gravity segregation is observed to have less impact on the process performance prediction because of the permeability configuration in the 3D model used here, but it could have a high impact in different settings. We include an explicit representation of longitudinal and transverse dispersion in the porous medium to demonstrate the grid resolution required to resolve physical dispersion at a given simulation length scale, and to show that condensate banks can also form in more realistic dispersive systems. Grid-refinement studies in 1D and 2D demonstrate, again, that the ENO scheme outperforms the SPU scheme for a given Peclet (Pe) number. Converged solutions are obtained with the ENO scheme using a relatively small number of grid cells. In addition, we show the behavior of the two schemes for varying Peclet numbers on a fixed simulation grid. For this grid, the ENO scheme is shown to be sensitive to the Peclet number, signifying that physical dispersion is not overwhelmed by numerical diffusion. For the SPU scheme, however, the solutions are almost independent of the Peclet number, which indicates that numerical diffusion dominates. Introduction Significant portions of the current hydrocarbon reserves are found in gas-condensate-carrying formations. Production of hydrocarbons from these reserves is expected to increase upward of 100% by 2015 (Cambridge Energy Research Associates 2005). Primary production of these reserves will result in significant loss of the heavy ends because of liquid dropout once the reservoir pressure reaches the dew point pressure. Enhanced condensate recovery by gas cycling/injection schemes are often applied to extend the lifetime of condensate reservoirs. These processes are inherently compositional, as the component transfer between an immobile liquid phase and a mobile gas phase is the key mechanism for enhancing recovery. Numerical simulation of such processes is very challenging because the prediction of the local displacement efficiency and the global sweep can be very sensitive to numerical diffusion. Various authors have shown that numerical artifacts can alter the displacement characteristics and lead to significant underprediction of the local displacement efficiency (Stalkup et al. 1990; Lim et al. 1997; Johns et al. 2002; Jessen et al. 2004). In their numerical studies of gas injection in depleted condensate reservoirs, Høier and Whitson (2001) demonstrated that near-miscible gas injection may, in some cases, lead to the formation of a condensate bank at the leading edge of the displacement. In addition, for some injection settings, the liquid bank was shown to exceed the critical liquid saturation and hence become mobile. Their analysis was based on 1D displacement calculations. The work of Jessen and Orr (2004) demonstrated that the prediction of condensate banks that exceed the critical condensate saturation by numerical calculations requires a firm control of numerical diffusion. They used analytical solutions based on the method of characteristics (MOC) (Johns et al. 1993) as well as a high-resolution FD simulator developed by Mallison et al. (2005) to investigate the complex interplay of flow and phase behavior in enhanced condensate recovery processes in 1D. In this work, we extend this investigation of enhanced condensate recovery processes to 2D and 3D. We include gravity to study the impact of a mobile liquid bank on the overall efficiency of the enhanced condensate recovery (ECR) process. We investigate the grid resolutions needed for both numerical schemes to resolve the condensate banks, and the impact of numerical errors on the predicted recovery in the presence of gravity. We also study the importance of physical dispersion in ECR processes. In particular, we are interested in understanding the grid resolution that is required to resolve the physical dispersion terms by controlling the level of numerical diffusion. We note that physical dispersion/diffusion is required to obtain a converged solution in 2D and 3D for this type of displacement problem. In the following section, we introduce the mathematical model for multicomponent multiphase flow in porous media, including an explicit representation of dispersive terms. We then describe the implementation in our compositional simulator. Next, we discuss the condensate system investigated in this work and present simulation results for enhanced condensate recovery in 1D, 2D, and 3D. Finally, we draw conclusions from the presented material.
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Lacorata, G., E. Aurell, and A. Vulpiani. "Drifter dispersion in the Adriatic Sea: Lagrangian data and chaotic model." Annales Geophysicae 19, no. 1 (January 31, 2001): 121–29. http://dx.doi.org/10.5194/angeo-19-121-2001.
Повний текст джерелаАнотація:
Abstract. We analyze characteristics of drifter trajectories from the Adriatic Sea with recently introduced nonlinear dynamics techniques. We discuss how in quasi-enclosed basins, relative dispersion as a function of time, a standard analysis tool in this context, may give a distorted picture of the dynamics. We further show that useful information may be obtained by using two related non-asymptotic indicators, the Finite-Scale Lyapunov Exponent (FSLE) and the Lagrangian Structure Function (LSF), which both describe intrinsic physical properties at a given scale. We introduce a simple chaotic model for drifter motion in this system, and show by comparison with the model that Lagrangian dispersion is mainly driven by advection at sub-basin scales until saturation sets in.Key words. Oceanography: General (marginal and semi-closed seas) – Oceanography: Physical (turbulence, diffusion, and mixing processes; upper ocean processes)
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Tapar, O. B., M. Steinbacher, J. Gibmeier, N. Schell, and J. Epp. "In situ Investigation during Low Pressure Carburizing by Means of Synchrotron X-ray Diffraction*." HTM Journal of Heat Treatment and Materials 76, no. 6 (December 1, 2021): 417–31. http://dx.doi.org/10.1515/htm-2021-0018.
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Abstract In situ X-ray diffraction investigations during low pressure carburizing (LPC) processes were performed with a specially developed process chamber at the German Electron Synchrotron Facility (DESY) in Hamburg, Germany. Carbon saturation in austenite was reached in less than 20 seconds for all processes with different parameters and carbides formed at the surface. Therefore, the direct contribution of carbon donor gas to the carbon profile after 20 seconds was reduced to very low levels. After that point, further supply of carbon donor gas increased the amount of carbides formed at the surface, which will contribute to the carbon profile indirectly by dissolution in the following diffusion steps. During quenching, martensite at higher temperatures had a lower c/a ratio than later formed ones. This difference is credited to self-tempering effects and reordering of carbon atoms within the martensite lattice.
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Bradshaw-Hajek, Bronwyn H., and Philip Broadbridge. "Analytic solutions for calcium ion fertilisation waves on the surface of eggs." Mathematical Medicine and Biology: A Journal of the IMA 36, no. 4 (February 15, 2019): 549–62. http://dx.doi.org/10.1093/imammb/dqz002.
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Abstract The evolution of calcium fertilisation waves on the cortex of amphibian eggs can be described by a nonlinear reaction-diffusion process on the surface of a sphere. Here, we use the nonclassical symmetry technique to find an exact analytic solution that describes the evolution of the calcium concentration. The solutions presented compare well with published experimental results. The analytic solution can be used to give insight into the processes governing the fertilisation wave, such as the flow of calcium ions from the sperm entry point. By finding a spiral solution to an approximate equation linearised near saturation, we also demonstrate how solutions with other properties may be constructed using this technique.
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Petrova, L. G., and Petr Demin. "Surface Modification Techniques for Steel Components Working in Wear and Corrosion Conditions." Key Engineering Materials 909 (February 4, 2022): 108–14. http://dx.doi.org/10.4028/p-4k0zjs.
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The process of electrolyte plasma nitriding is presented consisting in surface saturation of steels in low-temperature hydrostatic glow-discharged plasma generated in nitrogen containing liquid electrolyte. The method can be applied for strengthening of small machine parts made of carbon steels or of low-alloyed steels for increase wear and corrosion resistant of components working in corrosive and wear conditions (moisture, humidity, sand, etc.). Processes of steels surface strengthening by nitriding in low-temperature electrolyte plasma are combined with their surface alloying by a metal element (chromium, aluminum, vanadium, titanium, tungsten, molybdenum, and niobium) and also by combination of metals. Microstructure and phase composition of diffusion layers are examined; results of wear and corrosion tests are discussed.
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Zhou, J., B. Delille, F. Brabant, and J. L. Tison. "Insights into oxygen transport and net community production in sea ice from oxygen, nitrogen and argon concentrations." Biogeosciences Discussions 11, no. 2 (February 4, 2014): 2045–81. http://dx.doi.org/10.5194/bgd-11-2045-2014.
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Abstract. We present the evolution of O2 standing stocks, saturation levels and concentrations in landfast sea ice, collected in Barrow (Alaska), from February to June 2009. The comparison of the standing stocks and saturation levels of O2 against those of N2 and Ar suggests that the dynamic of O2 in sea ice strongly depends on physical processes (gas incorporation and subsequent transport). We then discuss on the use of O2 / Ar and O2 / N2 to correct for the physical contribution and to determine the biological contribution (NCP) to O2 supersaturations. We conclude that O2 / Ar suits better than O2 / N2, because O2 / N2 is more sensitive due to the relative abundance of O2, N2 and Ar, and less biased when gas bubble formation and gas diffusion are maximized. We further estimate the NCP in the impermeable layers during ice growth and in the permeable layers during ice decay. Our results indicate that NCP contributed to a~release of carbon to the atmosphere in the upper ice layers, but to an uptake of carbon at sea ice bottom. Overall, seawater (rather than the atmosphere) may be the main supplier of carbon for sea ice microorganisms.
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Sargsyan, Vruyr, and Emil Saratikyan. "Basics of Metals Theory of Extraction by Means of Chemical Water Solutions Filtration through Underground Ores." Advanced Materials Research 1020 (October 2014): 472–77. http://dx.doi.org/10.4028/www.scientific.net/amr.1020.472.
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Abstract. Geo-technological extraction methods recently are widely used in the mining industry. Removing the metals from underground ore deposits is carried out by injecting chemicals (solvents, oxidants, reducing agents) into wells drilled in them, and the subsequent extraction of metals from saturated solutions. Particularly, this method utilized for the extraction of uranium from flooded sediments and copper from poor (substandard) ores, as well as some non-ferrous and rare metals from waste dumps and tailings of substandard ore mines and processing enterprises. The paper discusses methods developed for prediction of moisture content (water saturation) in rocks under filtration of liquid with incomplete saturation of pores while changing the concentration of the metal in the liquid phase (in an ore body), as well as problems of dissolution and desorption of metal salts on the surface cracks or pores on ore body based on molecular diffusion equation of metal salts. The present work conducted for developing the methods for calculating the liquid filtration through underground deposits of minerals and forecasting of dissolving and washing out metals. It is shown that the processes which take place with the use of chemical reagents are different comparing to the similar processes with water injection. These data allow to predict the changes in the concentration of salts and metals in the liquid and solid phases depending on time.
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Ratnakar, Ram R., and Birol Dindoruk. "Measurement of Gas Diffusivity in Heavy Oils and Bitumens by Use of Pressure-Decay Test and Establishment of Minimum Time Criteria for Experiments." SPE Journal 20, no. 05 (October 20, 2015): 1167–80. http://dx.doi.org/10.2118/170931-pa.
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Summary Molecular diffusion plays a very important role in various reservoir processes, especially in the oil-recovery processes where convective forces are not dominant or when direct frontal contact and mixing are not possible. For example, in heavy-oil and bitumen recovery, injected light hydrocarbons can diffuse into the oil beyond the potential fronts and/or convective zones and promote the effectiveness of the displacement process, reducing in-situ viscosities and in turn enhancing the oil recovery. Similarly, diffusive mixing can also be a dominant mechanism in the gas-redissolution process, even in lighter-hydrocarbon systems. For example, it controls how much gas will be dissolved in oil and how long it will take to dissolve, in the absence of mechanical/convective mixing, as in the case of reservoir repressurization. The extent of dissolution of a gas into oil is governed by its solubility, but the rate is controlled by both molecular diffusivity and solubility. Thus, accurate determination of these parameters is essential to design and understand displacement processes. Despite the significance of diffusion in various aspects of oil recovery, there are very few experimental studies available in the literature addressing the diffusion of gas in heavy oils. Experimental work is most commonly based on the pressure-decay concept. However, the parameter inversion in these tests relies on an error-function solution that neglects the transient processes at the gas/oil interface and assumes constant-saturation concentration. This assumption is not appropriate when decay in pressure is large because pressure in the gas cap changes continuously as gas is dissolved in the oil, and hence the gas solubility varies with time. One of the major issues related to this experimental process is that it takes a long time (order of several days to several months) to achieve steady-state (converged) solution to determine diffusivity. In this work, we have Experimentally investigated the diffusion of methane in heavy oils as well as light oils by use of a pressure-decay test Captured properly the variation in gas concentration in oil at the gas/oil interface with time by expressing gas solubility in terms of Henry's constant in the mathematical model Developed the exact solution of the 1D pressure-decay (transient-diffusion) model with pressure-dependent gas/oil-interface concentration and shown that after a long time, pressure decays exponentially in time with an exponent that depends on diffusivity as well as solubility Presented the inversion technique to determine the diffusivity and other parameters from late-transient-pressure data, and shown the convergence in their estimates (Most importantly) developed a cutoff criterion permitting us to stop the experiments while still being able to extract the converged diffusivity values (this is important in situations when the experiment is stopped prematurely for technical or other reasons)
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Kulsartov, T. V., Zh A. Zaurbekova, Ye V. Chikhray, and M. T. Gabdullin. "Simulation of Hydrogen Isotopes Accumulation Processes in Materials in the Presence of Chemical Traps." Eurasian Chemico-Technological Journal, no. 1 (February 20, 2019): 25. http://dx.doi.org/10.18321/ectj783.
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The accumulation of hydrogen inside a solids occurs in traps of a different nature. The following things are known in addition to finding hydrogen in interstitial sites: dislocation mechanisms of hydrogen storage, micropores and microcracks, sorption on the free surface of microdefects, chemical traps with the formation of hydrides and other compounds, both with matrix material and with impurities or components of alloys. It is established that each type of trap has its own binding energy of hydrogen, which can vary from 0.2 eV for hydrogen gas in microdefects to several eV for hydrogen chemically bound in traps. Measurements of the distribution of hydrogen concentration dissolved in a solid body over binding energies provide a clue as to the understanding of hydrogen impact on mechanical properties and to the development of technologies for controlling the materials properties during their production and operation. The paper presents the results of simulation experiments on hydrogen saturation of materials in the presence of chemical traps. The proposed model, based on the numerical solution of the diffusion equation in the presence of irreversible capture, made it possible to describe the absorption process and determine the activation energies of hydrogen interaction with the material.
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Ren, Keguo, Xining Li, and Qimin Zhang. "Near-optimal control and threshold behavior of an avian influenza model with spatial diffusion on complex networks." Mathematical Biosciences and Engineering 18, no. 5 (2021): 6452–83. http://dx.doi.org/10.3934/mbe.2021321.
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<abstract><p>Near-optimization is as sensible and important as optimization for both theory and applications. This paper concerns the near-optimal control of an avian influenza model with saturation on heterogeneous complex networks. Firstly, the basic reproduction number $ \mathcal{R}_{0} $ is defined for the model, which can be used to govern the threshold dynamics of influenza disease. Secondly, the near-optimal control problem was formulated by slaughtering poultry and treating infected humans while keeping the loss and cost to a minimum. Thanks to the maximum condition of the Hamiltonian function and the Ekeland's variational principle, we establish both necessary and sufficient conditions for the near-optimality by several delicate estimates for the state and adjoint processes. Finally, a number of examples presented to illustrate our theoretical results.</p></abstract>
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Vorhauer-Huget, Nicole, Haashir Altaf, Robert Dürr, Evangelos Tsotsas, and Tanja Vidaković-Koch. "Computational Optimization of Porous Structures for Electrochemical Processes." Processes 8, no. 10 (September 23, 2020): 1205. http://dx.doi.org/10.3390/pr8101205.
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Porous structures are naturally involved in electrochemical processes. The specific architectures of the available porous materials, as well as their physical properties, crucially affect their applications, e.g., their use in fuel cells, batteries, or electrolysers. A key point is the correlation of transport properties (mass, heat, and charges) in the spatially—and in certain cases also temporally—distributed pore structure. In this paper, we use mathematical modeling to investigate the impact of the pore structure on the distribution of wetting and non-wetting phases in porous transport layers used in water electrolysis. We present and discuss the potential of pore network models and an upscaling strategy for the simulation of the saturation of the pore space with liquid and gas, as well as the computation of the relative permeabilities and oxygen dissolution and diffusion. It is studied how a change of structure, i.e., the spatial grading of the pore size distribution and porosity, change the transport properties. Several situations are investigated, including a vertical gradient ranging from small to large pore sizes and vice versa, as well as a dual-porosity network. The simulation results indicate that the specific porous structure has a significant impact on the spatial distribution of species and their respective relative permeabilities. In more detail, it is found that the continuous increase of pore sizes from the catalyst layer side towards the water inlet interface yields the best transport properties among the investigated pore networks. This outcome could be useful for the development of grading strategies, specifically for material optimization for improved transport kinetics in water electrolyser applications and for electrochemical processes in general.