Characteristics Of Diffusion Process Research Articles

Features of Diffusion Processes Occurring at Saturation with Atomic Elements and Formation of Surface Layer with Composite Structure

Features of Diffusion Processes Occurring at Saturation with Atomic Elements and Formation of Surface Layer with Composite Structure

Features of diffusion processes in the preparation of prepregs by the method of layered application of components

The modern production of products made of composite materials based on thermosetting binders is mainly based on the use of pre – impregnated reinforcing technical threads-prepregs. The binder used for such semi-finished products must meet two important technological requirements: have a low reactivity (high viability) when stored in the temperature range from -5 to +25 ° C and the ability to adjust the curing time at the molding temperatures of the product. To eliminate the disadvantages of the traditional method of obtaining polymer composite materials, to improve their strength characteristics and reduce the cost of the resulting reinforced composites, it is proposed to use the method of layered application of components. The essence of the method consists in layer-by-layer impregnation of the fibrous filler with a binder solution, and then a developed curing system consisting of an amine hardener that prevents the interaction of the hardener with the resin under storage conditions and protective polymer emulsions. The binder-filler system is activated only at an elevated temperature under curing conditions. It is established that the optimal parameters for processing by direct pressing of the pre-pegs components obtained by the method of layer deposition are a pressure of 15 MPa and a temperature of160-170 ?С with a pressure exposure of 15 minutes. If you get products by winding, then for such products, heat treatment for 6 hours at a temperature of 120 ?С is optimal. In the conditions of forming products, that is, at an elevated temperature and at an increased pressure, the mutual diffusion of components occurs due to the movement of oncoming flows. Oligomeric molecules from the resin volume diffuse from the inner layer to the outer one, and the components of the curing system meet them from the outer layer to the inner one. The method of layered application of components makes it possible to create a macroheterogenic system of interpenetrating polymer meshes in the contact area of sequentially applied layers. The result of the research is an increase in the shelf life, the viability of prepregs (up to 10 days) and an improvement in the complex of physical and mechanical properties of composites: the destructive stress during static bending increases to 60 %, during dynamic bending (impact) - up to 50 %. The use of carboxymethylcellulose as a protective polymer provides higher indicators of the studied properties than when using butadiene styrene latex as a protective polymer..

Modeling financial distress propagation on customer-supplier networks.

Financial networks have been the object of intense quantitative analysis during the last few decades. Their structure and the dynamical processes on top of them are of utmost importance to understand the emergent collective behavior behind economic and financial crises. In this paper, we propose a stylized model to understand the "domino effect" of distress in client-supplier networks. We provide a theoretical analysis of the model, and we apply it to several synthetic networks and a real customer-supplier network, supplied by one of the largest banks in Europe. Besides, the proposed model allows us to investigate possible scenarios for the functioning of the financial distress propagation and to assess the economic health of the full network. The main novelty of this model is the combination of two stochastic terms: an additive noise, accounting by the capability of trading and paying obligations, and a multiplicative noise representing the variations of the market. Both parameters are crucial to determining the maximum default probability and the diffusion process characteristics.

Estimation of the Diffusion Coefficient of Doxorubicin Molecules in a Water Solution in the Volume of a Porous Carrier Medium

An experimental investigation of the phenomenon of diffusion of the solution components in nanosized pores is extremely difficult and in certain cases impossible. An effective approach to obtaining qualitative and quantitative estimates of the diffusion process characteristics is computer simulation. Relying on the method of dissipative particle dynamics, a nanoscale numerical model is proposed for estimating the value of diffusion coefficient of the dissolved substance molecules in the pores of different sizes. An aqueous solution of doxorubicin, an antitumor antibiotic, in the pores of hydroxyapatite (a promising carrier medium for solving the problems of targeted administration of highly toxic drugs) is considered as a model system. Using the proposed model, the diffusion coefficient of doxorubicin in the pores of different linear sizes is evaluated at different volume concentrations of the antibiotic. In particular, it is found out that with an increase in the pore size the diffusion coefficient of doxorubicin increases by an order of magnitude and, starting from the pore size of 300 nm, it attains saturation. An increase in the antibiotic concentration from 0.1 to 5% gives rise to a decrease in the diffusion coefficient by more than a factor of 1.5. The developed model can be applied for solving the problems of predicting the release rate of the solution components (including drug molecules) from the pore volume of different solid-phase carrier media.

FRACTIONAL MODELS IN SPACE FOR DIFFUSIVE PROCESSES IN HETEROGENEOUS MEDIA WITH APPLICATIONS IN CELL MOTILITY AND ELECTRICAL SIGNAL PROPAGATION

This work addresses fundamental issues in the mathematical modelling of the diffusive motion of particles in biological and physiological settings. New mathematical results are proved and implemented in computer models for the colonisation of the embryonic gut by neural cells and the propagation of electrical waves in the heart, offering new insights into the relationships between structure and function. In particular, the thesis focuses on the use of non-local differential operators of non-integer order to capture the main features of diffusion processes occurring in complex spatial structures characterised by high levels of heterogeneity.

Features of diffusion processes during drop epitaxy of quantum rings

The drop epitaxy process in the GaAs/AlGaAs system is experimentally and theoretically studied. Epitaxial structure samples with arrays of single and double quantum rings are grown under various growth conditions. Diffusion processes of Ga and As adatoms are considered, steady-state diffusion equations are analytically solved, and the formation mechanisms of single and double quantum rings are revealed. The results obtained make it possible to model the quantum ring profile depending on growth conditions and, hence, to control the nanostructure profile during drop epitaxy.

The initial stage of mass transfer in porous material with two types of pores

The initial stage of substance penetration into a porous medium from a finite volume (capacity), after taking into account the relaxation of mass transfer, has been studied. It is suggested that a porous material is modeled by two continua with features of diffusion processes in each of them.

Growing Model of Interfacial Layer between Alloy Layer and Matrix in Diffusion Process of Hot Dip Aluminized Steel

Intermetallic compounds layer will be formed at the interfaces between alloy layer and matrix in the diffusion process of hot dip aluminized steel, which is beneficial to enhance the binding ability of alloy layer with matrix. However, when the thickness of intermetallic compounds exceeds the certain value, the vast extending force of interfacial void will cause the crack of intermetallic compounds and greatly weaken the spall resistance of aluminized layer. Therefore it is very important for the applications of hot dip aluminized steel to research and control the formation of intermetallic compounds at the interfaces. According to the characteristics of diffusion process of hot dip aluminized steel, the growing model of intermetallic compounds were established in the paper. The computed results were in accord with the experimental value. It can provide reference to the choice of the diffusion parameters of hot dip aluminized steel.

Diffusion phenomena and thermodynamics

The established theory of linear diffusion phenomena is reformulated in the framework of the non-Hamiltonian dynamical systems theory (Liouville's approach), through the introduction of a suitable characteristic velocity for the processes under consideration. The dissipative features of diffusion processes are studied in the Riemannian manifold which has flux densities and generalized forces as coordinates, and a tensor metrics defined by the phenomenological coefficients. Some relationships between diffusion phenomena and thermodynamics are explored. Finally, a preliminary extension of the proposed approach to the case of nonlinear constitutive equations is presented, and the effects of non-linearity on the processes dynamics are briefly discussed.

Multilevel modeling of volume changes in two-component powder bodies during sintering

Description of the multilevel behavior of powder mixtures as heterogeneous media during sintering is the only approach to understanding of regularities in volume changes in a two-component powder body as a result of high-temperature heating. In the framework of prevailing models, the role of heterodiffusion during the growth and densification of powder bodies as a result of sintering remains unclear. Consequently, it is very important to construct a physical model that, on the one hand, would reflect the actual structure of the body being sintered to the maximum possible extent and, on the other hand, would adequately describe the regularities of its behavior during sintering. A multiparticle model of a powder body consisting of a binary mixture is considered on a mesoscopic level; this model also takes into account the features of diffusion processes at the microscopic level. The model provides an adequate qualitative description for the observed concentration dependences of powder body densification during solid-phase sintering and both qualitative and quantitative description in the case of liquid-phase sintering.

High-temperature diffusion doping of porous silicon carbide

The results of experiments on high-temperature (2000–2200°C) diffusion doping of porous silicon carbide (PSC) by vanadium and erbium are reported. It is established that the specific features of diffusion processes in PSC at these temperatures are determined by modification of the porous structure due to the transport of vacancies. Based on a comparison of these results to available data on the low-temperature (900–1000°C) diffusion, it is concluded that the mechanisms of diffusion in PSC at low and high temperatures are different and that SiC with a porous structure is an effective medium particularly for low-temperature diffusion.

The mechanism of self-diffusion of ions in silicate systems

The special features of diffusion processes in noncrystalline models of SiO2, CaO · SiO2, and 2CaO · SiO2 with small admixtures of sodium oxide were studied by the method of molecular dynamics at 2000 and 3000 K. A purely ionic model with Born-Mayer potentials and parameters taken from the literature was used. In addition to the usual analysis of the mean-square displacements of particles, the maximum square displacements in each separate run 10000 time steps long were analyzed. Fairly long tunnels in the structure of silica were detected in the SiO2-Na2O system containing two sodium atoms only. Sodium ions can traverse these tunnels and execute a reciprocating motion in them at an approximately thermal velocity. The addition of calcium oxide gradually makes the silicate structure more compact, and long tunnels cease to exist in calcium meta-and orthosilicate models.

SCALING LAWS IN STOCHASTIC SYSTEMS WITH ANOMALOUS DIFFUSION

We consider the stochastic system with an anomalous diffusion. According to the obtained relations between characteristics of diffusion processes the special class of models which exhibit the anomalous behaviour is considered. It was shown that indexes of super- and subdiffusion are related to the Hürst exponent which defines the properties of the phase space inherent to the proposed model of stochastic system.

Nature of Superplastic Deformation

As known, there was made a number of hypotheses for the nature of superplastic (SP) deformation and many physical models of this phenomenon were suggested [1-2]. The majority of authors tried to explain the σ=σ(e) dependence on the basis of a mechanism of SP deformation. And though their concepts on diffusion creep or dislocation slip in combination with grain boundary sliding were absolutely different, the final constitutional equations were rather similar differing only by coefficients [1-2]. It is not wonder since the experimental dependence σ=σ(e) was studied rather thoroughly and its parameters are known. However, the theory of SP deformation should explain not only the phenomenology but also all structural features of material during SP flow. It is also very important to predict and explain new effects, such as low temperature and high strain rate superplasticity. The aim of the present work is to investigate the main mechanism and characteristics of diffusion processes during SP deformation, and to develop a physical model of this phenomenon. The review of experimental data on superplastic alloys and model materials [3-10] obtained recently in the Institute for Metals Superplasticity Problems (IMSP) of the Russian Academy of Sciences is presented in this paper.

Experimental observations on the relationship between diffusion characteristics and spectral coherence

The direct relationship of spectral coherence to space-time correlation is used to infer various characteristics of diffusion processes. Data gathered at three levels and at various downwind instrumental separations, along the mean wind direction are analyzed in terms of horizontal coherence of the longitudinal and lateral components of the wind. The analysis is within the framework of Davenport's ( Q. Jl R. met. Soc. 87, 194–211. 1961) empirical representation of coherence and a semi-empirical formulation of the decay parameter. The characteristics of the decay parameter are found to be consistent with its latest formulation which incorporates the relative importance of turbulent intensity and lateral diffusion. Atmospheric stability is seen to be the controlling factor in the results. The noted characteristics of the decay parameter are used to confirm its inverse relationship to Pasquill's β. This, in turn, confirms the usefulness of the determination of the latter from single point observations. Furthermore, Pasquill's nondimensional lateral dispersion function is shown to be stability dependent which must be borne in mind when calculating the lateral dispersion parameter of Gaussian models.

Characteristics of diffusion processes in commercial iron during ultrasonic welding

During ultrasonic spot welding of commerical iron there is intense diffusion of carbon, leading to the development of underheated areas. The results obtained can be explained either by the heating of local areas to 1100°C and higher or heating to lower temperatures as well as the acceleration of diffusion directly by ultrasonic vibrations.