Mean Values Of Diffusion Coefficient Research Articles

Simulation of Boriding Kinetics of AISI D2 Steel using Two Different Approaches

Diffusion of boron in FeB and Fe2B layers under solid boriding of steel AISI D2 (the Russian counterpart is Kh12MF) is simulated. Two approaches are used to assess the diffusion coefficients in solid-phase boriding, i.e., the concept of the mean value of diffusion coefficient in the FeB – Fe2B system and consideration of the growth kinetics of each of the two boride layers with the use of a system of conventional differential equations describing the partial chemical reactions by a parabolic law (the Dybkov method). The activation energies of boron diffusion in the FeB and Fe2B layers of steel AISI D2 are computed. The condition of extreme boriding is used to verify the two approaches experimentally. Comparative analysis of the computed and published data shows their good agreement.

DIFFUSION-WEIGHTED MAGNETIC RESONANCE IMAGING IN THE DIAGNOSIS OF INTERVERTEBRAL DISC DEGENERATION IN THE LUMBOSACRAL SPINE

Objective: to quantify the degree of degeneration of intervertebral discs (IVDs), by constructing functional diffusion-weighted imaging (DWI) maps, and to determine a correlation between the measured diffusion coefficient (DC) values and IVD changes on T1- and T2-weighted images. Material and methods. 545 IVDs were examined in 109 patients with no history of back pain syndrome and surgical spinal interventions. All the patients underwent magnetic resonance imaging of the lumbar spine; DWI maps were constructed and DC values estimated. Results. Statistically significant differences in the mean values of DC were determined for each of five IVDs. Multiple regression analysis showed that age and degree of degeneration were the most significant factors. The degree of IVD degeneration was negatively correlated with the values of DC at all levels (p<0.001). Also, there was a negative correlation between age and the value of DC at all levels (p<0.001). However, gender did not affect the value of DC (p>0.05), with the exception of L3-4. Conclusion. Age and the degree of degenerative changes in IVDs affect the value of DC. The value of DC is negatively correlated with the IVD degeneration graded by Pfirrmann and with the age of the examined patients. DW MRI can be used as a promising noninvasive method to diagnose the early stages of IVD degeneration.

Influence of uncertainty in diffusion coefficients on moisture field during wood drying

The paper presents an experimental measurement of diffusion coefficients of wood and theoretical analysis (stochastic analysis) based on influence of uncertainty in these coefficients on moisture field during wood drying simulations. Experimental measurement was used to verify of analytic equations for calculation of diffusion coefficients, which were implemented in the numerical simulations. Histograms show on normal distribution, but stochastic analysis was used for uniform distribution as well. Mean value of diffusion coefficient in tangential direction was calculated as 1.016·10−10m2s−1 and standard deviation as 0.153·10−10m2s−1. Stochastic analysis is based on the Monte Carlo method. The analysis proves that final moisture field has a same probability distribution as the diffusion coefficient (normal or uniform distribution) and also depicts a character of course and distribution of uncertainty in lumber during drying.