Calculated Diffusion Coefficients Research Articles

Increase of austenitic ductile iron type D5S durability by high temperature pre-treatment

In the present work, a performance of ASTM A439 Austenitic Ductile Iron type D5S at high temperature in the oxidizing environment was investigated. The obtained results revealed that exposure at temperatures 800?C, 850?C, and 900?C resulted in relatively high mass gain and an extensive oxide scale spallation from the samples? surfaces during cooling. However, the material exposed at 950?C revealed a better oxidation resistance and no oxide scale spallation. The material exposed at 1000?C showed the best oxidation resistance among the studied samples. The surfaces and cross-sectional investigation revealed that the material exposed at 950?C formed mostly Ni/Cr/Mn-mixed protective oxide scale and local formation of Fe-rich nodules. In comparison with the sample exposed at 1000?C, a smaller amount of Fe-rich nodules per area unit was observed and most of the surface was covered by Ni/Cr/Mn-mixed protective scale. The latter was explained by the change in the calculated diffusion coefficients in the alloy for Ni and Fe, namely up to 900?C the diffusion coefficient for Fe was much higher than for Ni, while above 900?C the diffusion coefficient for Ni becomes higher than for Fe. This phenomenon was correlated with a phase transformation from ?-Fe into ?-Fe resulting in the diffusion coefficient change.

Self-diffusion coefficient of fe, pb, ni and Cr by molecular dynamics simulation using the potential morse

The molecular dynamics simulation using the Morse potential has been applied to calculate the value of self-diffusion coefficients D(T) of some pure metals as Pb, Cr, Ni, and Fe. The simulation then was done using the MOLDY molecular dynamics program. The procedure to calculate these coefficients following several steps: first, determining the Morse potential parameters as , a and r 0; second, simulating the material under consideration using Moldy based on the appropriate ensemble; third, diffusion coefficient calculation using the Green-Kubo method for specific temperature; and fourth, the temperature-dependent diffusion coefficient D(T) based on the Arrhenius. The simulation work has obtained the best results as following: for Pb metal the Morse potential parameter (a = 1.4795 A−1, r 0 = 3.733 Å, and ) with ; for Cr metal the potential parameters (, a = 1.1005 A−1, and r 0 = 2.2032 Å), with ; for Ni metal the Morse potential parameter (, a = 1.0649 A−1, r 0 = 2.085 Å), with ; and for Fe metal the potential parameter (, a = 1.5974 A−1, r 0 = 2.840 Å) with . The calculated diffusion coefficients of the work have significant application as for the corrosion study of steels in nuclear reactor design.

Multi-parametric arterial spin labelling and diffusion-weighted magnetic resonance imaging in differentiation of grade II and grade III gliomas.

PurposeTo assess arterial spin labelling (ASL) perfusion and diffusion MR imaging (DWI) in the differentiation of grade II from grade III gliomas.Material and methodsA prospective cohort study was done on 36 patients (20 male and 16 female) with diffuse gliomas, who underwent ASL and DWI. Diffuse gliomas were classified into grade II and grade III. Calculation of tumoural blood flow (TBF) and apparent diffusion coefficient (ADC) of the tumoral and peritumoural regions was made. The ROC curve was drawn to differentiate grade II from grade III gliomas.ResultsThere was a significant difference in TBF of tumoural and peritumoural regions of grade II and III gliomas (p = 0.02 and p =0.001, respectively). Selection of 26.1 and 14.8 ml/100 g/min as the cut-off for TBF of tumoural and peritumoural regions differentiated between both groups with area under curve (AUC) of 0.69 and 0.957, and accuracy of 77.8% and 88.9%, respectively. There was small but significant difference in the ADC of tumoural and peritumoural regions between grade II and III gliomas (p = 0.02 for both). The selection of 1.06 and 1.36 × 10-3 mm2/s as the cut-off of ADC of tumoural and peritumoural regions was made, to differentiate grade II from III with AUC of 0.701 and 0.748, and accuracy of 80.6% and 80.6%, respectively. Combined TBF and ADC of tumoural regions revealed an AUC of 0.808 and accuracy of 72.7%. Combined TBF and ADC for peritumoural regions revealed an AUC of 0.96 and accuracy of 94.4%.ConclusionTBF and ADC of tumoural and peritumoural regions are accurate non-invasive methods of differentiation of grade II from grade III gliomas.

Electrochemical Properties of a Verdazyl Radical in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) have been widely investigated as alternative electrochemical solvents for a range of dissolved species over the past two decades. However, the behaviour of neutral radicals dissolved in RTILs is relatively unexplored. In this work, the electrochemistry of a stable verdazyl radical – 1,5-dimethyl-3-phenyl-6-oxoverdazyl (MPV) – has been studied on a platinum thin-film electrode using cyclic voltammetry and chronoamperometry in 10 different RTILs. The organic solvent propylene carbonate is also employed as a comparison. The nature of the solvent system was found to have a large effect on the electrochemical behaviour, particularly on the reduction reaction of the verdazyl radical. Chronoamperometry on a microdisk electrode was used to calculate diffusion coefficients (D), and plots of D versus the inverse of viscosity were linear, suggesting typical hydrodynamic diffusional characteristics of the radical, in line with the behaviour of dissolved neutral and charged compounds (e.g. ferrocene and cobaltocenium) in RTILs. Overall, this study demonstrates that different RTILs have a significant influence on the electrochemistry of MPV, and therefore careful selection of the solvent system for electrochemical applications is advised.

DWI and PRECISE criteria in men on active surveillance for prostate cancer: A multicentre preliminary experience of different ADC calculations

PurposeThe PRECISE score estimates the likelihood of radiological progression in patients on active surveillance (AS) for prostate cancer (PCa) with serial multiparametric magnetic resonance imaging (mpMRI). A PRECISE score of 1 or 2 denotes radiological regression, PRECISE 3 indicates stability and PRECISE 4 or 5 implies progression.We evaluated the inter-reader reproducibility of different apparent diffusion coefficient (ADC) calculations and their relationship to the PRECISE score. Material and methodsBaseline and follow-up scans (on the same MR systems) of 30 patients with visible lesions from two different institutions (University College London and Sapienza University of Rome) were analysed by two radiologists (one from each site). The PRECISE score was initially assessed in consensus. At least six weeks later, to reduce the likelihood of being influenced by the consensus PRECISE reading, each radiologist independently calculated ADC for the following: lesion, non-cancerous tissue and urine in the bladder. Normalised ADC ratios were calculated with respect to normal prostatic tissue (npADC) and urine. Spearman's correlation (ρ), intraclass correlation coefficients (ICC), differences in ADC and ROC curves were computed. ResultsInterobserver reproducibility was very good (ρ > 0.8; ICC > 0.90). Lesion ADC (0.91 vs 0.73 × 10−3 mm2/s; p=0.025) and npADC ratio (0.68 vs 0.53; p=0.012) at follow-up mpMRI were different between patients with radiological regression or stability vs progression. Cut-offs of 0.77 × 10−3 mm2/s (lesion ADC) and 0.59 (npADC ratio) could differentiate the two groups (area under the curve: 0.74 and 0.77, respectively). ConclusionThe ADC, npADC ratio and the PRECISE score should be recorded for MRI-based AS.

Approximation of Calcium Diffusion in Alzheimeric Cell

Alzheimer’s disease (AD) is the most common form of dementia prevailing worldwide. It has been found that the higher level of cytosolic calcium leads to the pathological symptoms of AD and the two cytoplasmic calcium binding buffers have their roles in sustaining this dementia. However, the area of their functioning and working is found to be different. Calmodulin is found in CA1-hippocampus neurons, whereas calbindin-D28k is found in basal forebrain cholinergic neurons. Based on this physiology, in this research paper an attempt has been made to delineate the physiological phenomenon of calcium diffusion at cytosolic level. Taking into consideration the physiology of the neuron, a two-dimensional mathematical model is used and is solved using finite element method (FEM). The appropriate initial and boundary conditions are assumed in presence of suitable diffusion coefficient of calcium and association rate of the buffer. The approximate geometries for both the neurons are taken into consideration to get a better insight about the pathology behind calcium diffusion taking place in AD. The desired results are shown graphically for Alzheimeric and non-Alzheimeric cells. Thus, the obtained results clearly show the significant impact of buffers on cytosolic calcium which affect the normal condition of the cell and maintain the cell calcium.

Sharply promoted CO2 diffusion in a mixed matrix membrane with hierarchical supra-nanostructured porous coordination polymer filler

Mixed matrix membranes incorporated with porous coordination polymers (PCP) fillers have been considered as the most promising platform to achieve highly efficient gas separation, where the gas diffusion channel can be facilely designed and engineered, as well as the resistance of general rule of trade-off between selectivity and permeability. In this study, a novel mixed matrix membrane that contains chemically robust CeBTB filler with hierarchical supra-nanostructure has been established via systematic optimization. The analysis of gas permeation experiment and calculated diffusion coefficient describes that rich micro- and meso-pore of the CeBTB fillers provide unique gas transmission channel, which enable faster CO2 permeability, as well as better CO2/CH4 selectivity. The wrapped CeBTB fillers by polymer segments demonstrated positive effect on the reduction of membrane plasticization at high pressure. More importantly, the membrane with 10 wt% CeBTB exhibited ultra-excellent CO2/CH4 separation not only in the dry state (PCO2 = 1150 barrer, S = 37.4), but also along with moisture (PCO2 = 892 barrer, S = 37.4). Importantly, these values far exceed the Robeson upper-bound which indicates the great potential for feasible application.

Statistical method for modeling Knudsen diffusion in nanopores.

This paper presents a statistical method for the calculation of gaseous flux and diffusion coefficients through a Knudsen-regime cylindrical nanopore. A general integral formula for the flux is derived in terms of collision frequency, molecular density, and a scattering path length probability distribution. Under appropriate steady-state assumptions, the general formula simplifies to Fick's first law, from which an expression for the diffusion coefficient is derived. The model is shown to be dimensionally consistent with the Einstein relation. The conditions for agreement with Fick's second law are investigated. Using a model probability distribution the model leads to an expression for the diffusion coefficient for a pore of finite length. This result is shown to compare favorably with a classic formula from the literature.

First-principle study of the solubility and diffusion of oxygen and boron in [formula omitted]-TiAl

Solubility and diffusion of boron and oxygen in the γ-TiAl intermetallic compound are herein investigated by first-principle calculations. On the basis of the space group of the γ phase, the accommodation of the light atoms in the various interstitial positions is studied by density functional theory. Diffusion coefficients are also obtained from ab initio calculations. Barrier energies for the boron and oxygen diffusion among the different stable interstitial sites are computed using the Nudged Elastic Band method and atomic jumping rates are obtained from the Transitional State Theory. Diffusion coefficients are obtained from the solution of the transport equation in the infinite time limit, using the analytical Multi-State Diffusion method. The methodology here applied is validated by the good agreement between the computed diffusion coefficient of boron and the experimental data available in the literature for this species.

A fast, low-memory, and stable algorithm for implementing multicomponent transport in direct numerical simulations

Implementing multicomponent diffusion models in reacting-flow simulations is computationally expensive due to the challenges involved in calculating diffusion coefficients. Instead, mixture-averaged diffusion treatments are typically used to avoid these costs. However, to our knowledge, the accuracy and appropriateness of the mixture-averaged diffusion models has not been verified for three-dimensional turbulent premixed flames. In this study we propose a fast, efficient, low-memory algorithm and use that to evaluate the role of multicomponent mass diffusion in reacting-flow simulations. Direct numerical simulation of these flames is performed by implementing the Stefan–Maxwell equations in NGA. A semi-implicit algorithm decreases the computational expense of inverting the full multicomponent ordinary diffusion array while maintaining accuracy and fidelity. We first verify the method by performing one-dimensional simulations of premixed hydrogen flames and compare with matching cases in Cantera. We demonstrate the algorithm to be stable, and its performance scales approximately with the number of species squared. Then, as an initial study of multicomponent diffusion, we simulate premixed, three-dimensional turbulent hydrogen flames, neglecting secondary Soret and Dufour effects. Simulation conditions are carefully selected to match previously published results and ensure valid comparison. Our results show that using the mixture-averaged diffusion assumption leads to a 15% under-prediction of the normalized turbulent flame speed for a premixed hydrogen-air flame. This difference in the turbulent flame speed motivates further study into using the mixture-averaged diffusion assumption for DNS of moderate-to-high Karlovitz number flames.

The Calculation of Turbulent Diffusion Coefficients in Aquatic Ecosystems

The paper deals with the issues related to the pollution of aquatic ecosystems. The influence of turbulence on the transport and dispersion of pollutants in the mentioned systems, as well as the calculation of the turbulent diffusion coefficients are studied. A case study on the determination of turbulent diffusion coefficients for some sectors of the Prut River is presented. A new method is proposed for the determination of the turbulent diffusion coefficients in the pollutant transport equation for specific sectors of a river, according to the associated number of Péclet, calculated for each specific area: the left bank, the right bank and the middle of the river.

The Calculation of Turbulent Diffusion Coefficients in Aquatic Ecosystems

The paper deals with the issues related to the pollution of aquatic ecosystems. The influence of turbulence on the transport and dispersion of pollutants in the mentioned systems, as well as the calculation of the turbulent diffusion coefficients are studied. A case study on the determination of turbulent diffusion coefficients for some sectors of the Prut River is presented. A new method is proposed for the determination of the turbulent diffusion coefficients in the pollutant transport equation for specific sectors of a river, according to the associated number of P�clet, calculated for each specific area: the left bank, the right bank and the middle of the river.

CALTPP: A general program to calculate thermophysical properties

A program CALTPP (CALculation of ThermoPhysical Properties) is developed in order to provide various thermophysical properties such as diffusion coefficient, interfacial energy, thermal conductivity, viscosity and molar volume mainly as function of temperature and composition. These thermophysical properties are very important inputs for microstructure simulations and mechanical property predictions. The general structure of CALTPP is briefly described, and the CALPHAD-type models for the description of these thermophysical properties are presented. The CALTPP program contains the input module, calculation and/or optimization modules and output module. A few case studies including (a) the calculation of diffusion coefficient and optimization of atomic mobility, (b) the calculation of solid/liquid, coherent solid/solid and liquid/liquid interfacial energies, (c) the calculation of thermal conductivity, (d) the calculation of viscosity, and (e) the establishment of molar volume database in binary and ternary alloys are demonstrated to show the features of CALTPP. It is expected that CALTPP will be an effective contribution in both scientific research and education.

Comparing the interobserver reproducibility of different regions of interest on multi-parametric renal magnetic resonance imaging in healthy volunteers, patients with heart failure and renal transplant recipients

ObjectiveTo assess interobserver reproducibility of different regions of interest (ROIs) on multi-parametric renal MRI using commercially available software.Materials and methodsHealthy volunteers (HV), patients with heart failure (HF) and renal transplant recipients (Tx) were recruited. Localiser scans, T1 mapping and pseudo-continuous arterial spin labelling (pCASL) were performed. HV and Tx also underwent diffusion-weighted imaging to allow calculation of apparent diffusion coefficient (ADC). For T1, pCASL and ADC, ROIs were drawn for whole kidney (WK), cortex (Cx), user-defined representative cortex (rep-Cx) and medulla. Intraclass correlation coefficient (ICC) and coefficient of variation (CoV) were assessed.ResultsForty participants were included (10 HV, 10 HF and 20 Tx). The ICC for renal volume was 0.97 and CoV 6.5%. For T1 and ADC, WK, Cx, and rep-Cx were highly reproducible with ICC ≥ 0.76 and CoV < 5%. However, cortical pCASL results were more variable (ICC > 0.86, but CoV up to 14.2%). While reproducible, WK values were derived from a wide spread of data (ROI standard deviation 17% to 55% of the mean value for ADC and pCASL, respectively). Renal volume differed between groups (p < 0.001), while mean cortical T1 values were greater in Tx compared to HV (p = 0.009) and HF (p = 0.02). Medullary T1 values were also higher in Tx than HV (p = 0.03), while medullary pCASL values were significantly lower in Tx compared to HV and HF (p = 0.03 for both).DiscussionKidney volume calculated by manually contouring a localiser scan was highly reproducible between observers and detected significant differences across patient groups. For T1, pCASL and ADC, Cx and rep-Cx ROIs are generally reproducible with advantages over WK values.

Exploring the role of the membrane bilayer in the recognition of candesartan by its GPCR AT1 receptor

Cardiovascular diseases and hypertension in particular are major health risks worldwide and the improvement on their treatment will be beneficial for the human health. AT1R antagonists belong to the sartans family that targets the renin-angiotensin aldosterone system (RAAS) through blocking the hormone angiotensin II to exert its detrimental effects in pathological states. As a consequence, they are beneficial to treat hypertension, diabetes related kidney failure and hyperaemic episodes. Long unbiased Molecular Dynamics (MD) simulations are performed in order to explore candesartan's possible 2D and 3D diffusion mechanisms towards AT1R receptor. 3D diffusion mechanism is referred to the direct binding of the AT1 antagonist candesartan to the AT1R 3D structure (PDB ID: 4YAY). 2D diffusion mechanism involves first, the incorporation of candesartan in the bilayer core and then its localization on the AT1R binding cavity, through a diffusion mechanism. The obtained results indicate that membranes interact significantly with the neutral form of candesartan, which is indeed approaching the receptors' active site through diffusion via the lipids. On the other hand, the deprotonated form of the drug is interacting with AT1R's extracellular loop and fails to enter the membrane, pointing out the importance of the pH microenvironment around the receptor. To validate the calculated diffusion coefficients of the drug in the lipid bilayers 2D DOSY NMR experiments were recorded and they were in good agreement. Information on the impact that has the interaction of candesartan with the membrane is very important for the rationally design and development of potent ARBs. Thus, its conformational features as well as its localization in the membrane core have to be thoroughly explored.

Diagnostic Value of Whole-Body DWI With Background Body Suppression Plus Calculation of Apparent Diffusion Coefficient at 3 T Versus 18F-FDG PET/CT for Detection of Bone Metastases.

OBJECTIVE. The purpose of this study is to evaluate the diagnostic performance of whole-body (WB) DWI with background body suppression (DWIBS) combined with calculation of the apparent diffusion coefficient (ADC) value at 3 T compared with the diagnostic performance of 18F-FDG PET/CT for detecting bone metastases in patients with malignant tumors. SUBJECTS AND METHODS. Thirty-nine consecutive patients with suspected bone metastases underwent both WB DWIBS and FDG PET/CT. Imaging findings were independently interpreted using qualitative and quantitative analyses. Pathologic findings or clinical or radiologic follow-up data were used as the diagnostic reference standard. The sensitivity, specificity, overall accuracy, positive predictive value, and negative predictive value of both modalities were calculated. The ADCs of benign lesions and metastases were compared. RESULTS. A total of 213 metastatic bone segments were confirmed among 39 patients. The sensitivity, specificity, overall accuracy, positive predictive value, and negative predictive value were 93.0%, 87.8%, 89.6%, 79.8%, and 96.0%, respectively, for WB DWIBS and 92.5%, 92.0%, 92.1%, 85.7% and 95.9%, respectively, for FDG PET/CT. The specificity of WB DWIBS in detecting bone metastases was significantly lower than that of FDG PET/CT (p < 0.05), whereas the sensitivity, overall accuracy, positive predictive value, and negative predictive value in detecting bone metastases were not significantly different between WB DWIBS and FDG PET/CT (p > 0.05). The ADCs for benign lesions were significantly higher than those for metastases (p < 0.001). In ROC curve analysis, the AUC value was 0.901. A cutoff ADC value of 920.5 × 10-6 mm2s-1 distinguished benign lesions from bone metastases with a sensitivity of 92.9% and a specificity of 73.4%. CONCLUSION. WB DWIBS coupled with ADC analysis at 3 T is effective for detecting bone metastases.

Synthesis of ternary electrocatalysts for exploration of methanol electro-oxidation in alkaline media

In the quest for alternate and efficient electrode materials, ternary metal electrocatalysts (TMEs), part of the perovskite family, were synthesized and tested for methanol electro-oxidation in alkaline media. La0.5Ca0.5MO3 (M = Ni, Co, or Mn) was synthesized via sol-gel method. X-ray diffraction analysis revealed that the perovskite crystal structure possesses characteristic sharp and crystalline peaks for all synthesized ternary electrocatalysts. The average particle size calculated using Debye–Scherrer equation was in the order of La0.5Ca0.5NiO3 (LCNO) > La0.5Ca0.5CoO3 (LCCO)> La0.5Ca0.5MnO3 (LCMO). The elemental composition of as prepared sample, LCCO was investigated via x-ray fluorescence spectroscopy. The qualitative and quantitative analysis revealed the presence of La, Ca and Co in parent crystal structure with percentage compositions of 9.0, 3.12 and 87.82% respectively. The particle size distribution was homogenous, as determined by scanning electron and transmission electron microscopes. The electrocatalytic activity of the synthesized ternary electrocatalysts was studied electrochemically by cyclic voltammetry. The calculated diffusion coefficient values showed that electrode surface of LCNO and LCCO have limited efficiency for diffusion related phenomenon. The heterogeneous rate constants inferred better electrode kinetics of LCCO and LCNO which exhibited good electrocatalytic behavior; sharp anodic peaks were observed in the potential range of +0.3 to 0.6 V and +0.6 to 0.8 V, respectively. Methanol electro-oxidation was found minimal in case of LCMO sample. We have observed that Co substitution at B-site of perovskite electrode materials attains better electrochemical properties, thus in relation with reported literature.

Atomic diffusion mediated by vacancy defects in L12-Zr3Al: A first-principles study

Systematic first-principles calculations based on density functional theory have been performed to determine the self-diffusion mechanism of Zr3Al. The formation energies of four intrinsic point defects were calculated and the relationship between concentration of different point defects and temperature was determined. Then, the effect of defect types on the stability of the system was explored after analyzing the electronic density of different supercells. In addition, the minimum energy pathways (MEPs) and the saddle point configurations during Zr or Al atom migration were calculated using the climbing image nudged elastic band method (CI-NEB). The energetic results show that the VZr-mediated nearest neighbor (NN) jump mechanism is the feasible migration mechanism for Zr atom and dominant Al atom diffusion mechanism is the antisite assisted (AS) mechanism because of the lowest diffusion activation energy barrier. The present study lays the foundation for further investigation, including solute-diffusion in Zr3Al and quantitative calculation of diffusion coefficients, and provides theoretical guideline for further design and improvement of the crucial diffusion-mediated properties of Zr3Al.

Experimental and mathematical study of the transdermal delivery of sumatriptan succinate from polyvinylpyrrolidone-based microneedles

A mechanistic model was developed and tested to predict the release of sumatriptan succinate from dissolving microneedles and its permeation across the epidermal skin layers. Material balance equations were written to describe molecular transport followed by absorption into the systemic circulation. The solid drug particles were encapsulated in pyramid-shaped, polyvinylpyrrolidone-based water-soluble microneedles. Plots, generated from literature values and designed to simulate concentration distributions in the epidermal layers, agreed with optical coherence tomography (OCT)images captured at early stages of the experiments. Simulations showed that an increase in the pitch width led to a faster release of the medication. By modifying the governing equations to include a microneedle baseplate, the model was able to estimate short- and long-term release behaviors from in vitro Franz cellexperiments. These studies were performed using three distinct dissolving microneedle formulations and minipig skin as the biological membrane. The calculated diffusion coefficients were one order of magnitude greater than the value estimated when the drug was directly applied to the skin surface. The dissolution rate constant was affected by the concentration of the polymer matrix.

Determining Diffusion Coefficients of Chemical Warfare Agents in Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) have shown potential for selective capture of chemical warfare agents (CWAs). To determine characteristic adsorption times, the kinetics of CWA uptake in MOFs must be known. Here, we calculate diffusion coefficients of the CWA sarin and simulants in prototypical MOFs using classical molecular simulations. Sarin can diffuse throughout a one micrometer crystal in less than a second in MIL-47 and Cu-BTC, but this process takes more than 3 h in ZIF-8 and UiO-66. A simple estimate based on Knudsen diffusion is able to describe diffusion of sarin in MIL-47 but fails to do so in other MOFs. This work has implications in designing devices to detect and capture CWAs.