Sharif Digital Repository

In this investigation, we have studied the elemental diffusion coefficients of the Cu/Ta and Ta/Si interfaces in the Cu/Ta/Si(1 1 1) structure. The diffusion parameters for Cu diffusion into the Ta barrier layer, Ta diffusion into the Si substrate and diffusion of Si atoms into the Ta layer have been calculated using conversion of RBS data to concentration-depth profile curves and the solution of Fick's equation based on a constant diffusing amount boundary conditions. Furthermore, by calculating grain boundary diffusion coefficients, we have estimated grain boundary slabs of the Ta layer at different temperatures. It was shown that, the width of grain boundary slabs in the Ta layer at 700°C... 

The equations of balance of a continuum under conditions of growth and mass diffusion are derived from a principle of invariance under general observer transformations. The resulting equations are invariant under inertial transformations. Apparent body forces stemming from the mass transport phenomenon are identified and shown to be associated with non-inertial observers. © The Author(s) 2018  

Diffused infrared transmission is one of thepreferred techniques used in indoor wirelesscommunications. Tolerance to shadowing and a lack ofalignment requirements are among the many advantagesoffered by this technique compared to the line-of-sighttechniques. However, it has its disadvantages, namelyhigh path loss and multipath dispersion. The limitationimposed by eye-safety requirements restricts the transmitted power. Therefore, efficient useof transmitted optical power is the key for practicalbroadband infrared systems. In this paper, we report onusing a holographic diffuser for shaping of infrared radiation pattern in an indoorinfrared transmission system. The holographic diffusershave... 

Isothermal solidification is a key feature of transient liquid phase bonding which prevents the formation of deleterious intermetallic phases in the joint centerline and results in bonds with improved mechanical performance. This paper discusses the metallurgical characteristics and mechanical properties of an as-cast IN718 superalloy bonded by diffusion-induced isothermal solidification of Ni-7Cr-4.5Si-3.2B-3Fe (wt%) filler metal. After transient liquid phase bonding of as-cast IN718 at 1000 C for 60 min, a bond exhibiting a solid solution microstructure with joint efficiency of 72% in terms of shear strength was obtained. The joining process was effectively able to prevent the formation of... 

Diffusion flame from electrospray of liquid ethanol and butanol was investigated experimentally. Stable flames were observed at two distinct modes recognized at different flow rates, applied voltages, and distances between the nozzle and counter electrode. The first mode occurred at minimum voltages in which individual larger droplets are dominantly generated. The second mode at higher voltages corresponds to multijets, which produce finer distribution of droplets. Using flame-imaging anal- ysis, flammability margins are introduced and flame lengths are measured versus nondimensional parameters for both fuels and modes of spraying. The fluctuation of the flames is characterized and the... 

In this research a mathematical model for controlled drug delivery of Ibuprofen has been developed which accounts for physical kinetics based upon variations of the drug concentration, size and release time for a spherical drug pill. Through this model, the drug release for three sizes of the active ingredient including; 213nm (representing existence of only diffusion limitations), 515nm (representing existence of only solubility limitations) and 367nm (representing both diffusion and solubility limitations) was calculated. Theoretical amounts of the drug after two hours of release are calculated to be 95.3, 99.5 and 95.5 percent, respectively. Comparison of theoretical and experimental data... 

The transient measurement of concentration profile within the liquid boundary layer close to the membrane interface and the flux of permeating species across the membrane coupled with transient model of membrane allows a more critical evaluation of membrane transport performance. The experimental procedure for transient measurement of pervaporation fluxes and data obtained for the {ethanol-water}/silicone rubber system and experimental set up for transient dialysis measurement by interferometry technique for the same system was described. A detailed analysis of optical effect accounting for the light deflection in a medium of varying refractive index profile was presented. A numerical... 

In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed  

Diffusion imaging with confinement tensor (DICT) is a new model that employs a tensorial representation of the geometry confining the movements of water molecules. The model differs substantially from the commonly employed diffusion tensor imaging (DTI) technique even at small diffusion weightings when the dependence of the signal on the timing parameters of the pulse sequence is concerned. In this work, we assess the accuracy of the two models on a data set acquired from an excised monkey brain. The publicly available data set features differing values for diffusion pulse duration and separation. Our results indicate that the normalized mean squared error is reduced in an overwhelming... 

The well known square root formula for the kinetics of adsorption by spherical particle U(t)=6/r0(Dt/π)1/2 is only valid in the early stage of adsorption (U(t) ≤ 0.3), where U(t) shows fractional attainment to the equilibrium. Present study shows that with a little manipulation of this formula, its application range can be extended to U (t) ≤ 0.95. The suggested formula U(t)=6/r0(Dt/π)1/2 -3Dt/r0 2 in addition of simplicity, has higher accuracy than both square root and Vermeulen's formulas  

We introduce the bivariate jump-diffusion process, consisting of two-dimensional diffusion and two-dimensional jumps, that can be coupled to one another. We present a data-driven, nonparametric estimation procedure of higher-order (up to 8) Kramers-Moyal coefficients that allows one to reconstruct relevant aspects of the underlying jump-diffusion processes and to recover the underlying parameters. The procedure is validated with numerically integrated data using synthetic bivariate time series from continuous and discontinuous processes. We further evaluate the possibility of estimating the parameters of the jump-diffusion model via data-driven analyses of the higher-order Kramers-Moyal... 

In this chapter we provide a generalization of jump-diffusion precesses (12.1) in two dimensions by considering a class of coupled systems that are described by a bivariate state vector x(t) contained in a two-dimensional state space {x}. The evolution of the state vector x(t) is assumed to be governed by a deterministic part to which diffusion parts and jump contributions are added. Generalization of the results to higher dimensions is straightforward. We note that for N multivariate time series, by assuming the presence of two-body type of interactions between time series, the analysis will reduce to analysing N(N − 1)/2 pairwise bivariate time series. © 2019, Springer Nature Switzerland... 

In this chapter we provide a generalization of jump-diffusion precesses (12.1) in two dimensions by considering a class of coupled systems that are described by a bivariate state vector x(t) contained in a two-dimensional state space {x}. The evolution of the state vector x(t) is assumed to be governed by a deterministic part to which diffusion parts and jump contributions are added. Generalization of the results to higher dimensions is straightforward. We note that for N multivariate time series, by assuming the presence of two-body type of interactions between time series, the analysis will reduce to analysing N(N − 1)/2 pairwise bivariate time series. © 2019, Springer Nature Switzerland... 

A molecule within the nonporous polymeric membrane moves in response to the local driving force and has no memory of how it entered the membrane or how the local gradients were generated. This means that a properly formulated model of transport within the membrane should be equally applicable to dialysis, pervaporation or vapour permeation. The phenomenological approach of irreversible thermodynamics was used to develop transient models of dialysis and pervaporation. The model developed in this study were validated against transient dialysis and pervaporation data for ethanol-water/silicone rubber system. A critical assessment was obtained by recovering the model parameters from the dialysis... 

Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5-17 wt pct graphite were isothermally oxidized at 1000-1350°C. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range... 

The diffusion phenomenon has a remarkable impact on Online Social Networks (OSNs). Gathering diffusion data over these large networks encounters many challenges which can be alleviated by adopting a suitable sampling approach. The contributions of this paper is twofold. First we study the sampling approaches over diffusion networks, and for the first time, classify these approaches into two categories, (1) Structure-based Sampling (SBS), and (2) Diffusion-based Sampling (DBS). The dependency of the former approach to topological features of the network, and unavailability of real diffusion paths in the latter, converts the problem of choosing an appropriate sampling approach to a trade-off.... 

Partially-observed data collected by sampling methods is often being studied to obtain the characteristics of information diffusion networks. However, these methods usually do not consider the behavior of diffusion process. In this paper, we propose a novel two-step (sampling/estimation) measurement framework by utilizing the diffusion process characteristics. To this end, we propose a link-tracing based sampling design which uses the infection times as local information without any knowledge about the latent structure of diffusion network. To correct the bias of sampled data, we introduce three estimators for different categories, link-based, node-based, and cascade-based. To the best of... 

Diffusion tensor magnetic resonance imaging (DTMRI) is a non-invasive method for investigating the brain white matter structure. It can be used to evaluate fiber bundles in the brain but in the regions with crossing fibers, it fails. To resolve this problem, high angular resolution diffusion imaging (HARDI) with a large number of diffusion encoding directions is used and for reconstruction, the Q-ball method is applied. In this method, orientation distribution function (ODF) of fibers can be calculated. Mathematical models play a crucial role in the field of ODF. For instance, in registering Q-ball images for applications like group analysis or atlas construction, one needs to interpolate... 

In this paper, we compare registration results obtained using different diffusion maps extracted from diffusion tensor imaging (DTI). Fractional Anisotropy (FA) and Ellipsoidal Area Ratio (EAR) are two diffusion maps (indices) that may be used for image registration. First, we use FA maps to find deformation matrix and register diffusion weighted images. Then, we use EAR maps and finally we use both of FA and EAR maps to register diffusion weighted images. The difference between FA values before deformation and after registration using the FA alone or EAR alone has a median of 0.57 and using both of them has a median of 0.29. Therefore, the results of registration using both of the FA and...