Search results for " diffusion"

Numerical simulations of air pollutant dispersion in a stratified planetary boundary layer

1978

Abstract A numerical model is described for computing pollutant concentration distributions downwind from a source. It is based on the three-dimensional dispersion equation governing the time-dependent advective and diffusive transport of air pollutants and is solved numerically by a mixed Lagrangian-Eulerian finite-difference scheme. The model includes the vertical wind shear, the turning of the actual wind, and vertical variations of the vertical eddy diffusivity. In this paper the model is used to simulate the pollutant dispersion process in a stratified planetary boundary layer. The vertical profiles of horizontal mean wind and vertical eddy diffusivities are calculated numerically from…

Validation of a Microscale Pollution Dispersal Model

1996

The three-dimensional numerical model MISCAM (Micro Scale Air Pollution Model) has been developed to study wind flow and pollutant dispersal in densely built-up urban areas (Eichhorn, 1989). The model has been successfully applied for planning purposes by a variety of institutions in Germany. MISCAM consists of the non-hydrostatic Eulerian equations of motion and a transport equation for pollutants. Turbulence closure is carried out by means of a k-e-model. To reduce numerical diffusion errors, Smolarkiewicz and Grabowski’s (1989) scheme may be used for the calculation of advective transport. Additionally, sedimentation and dry deposition of pollutants may be taken into account.

Novel poly (ionic liquid)-based anion exchange membranes for efficient and rapid acid recovery from industrial waste

2020

Abstract Owing to the less energy consumption, positive impact on the environment, and prospect of providing clean water resources, anion exchange membranes (AEMs) are promising materials for acid recovery from various industrial wastewater/effluent. Based on the diffusion dialysis process, AEMs selectively allow rapid proton permeation while efficiently retaining metal ions. To enhance the efficiency of the acid recovery process, precise control of macromolecular architecture and chemical composition that enables high hydrophilicity, proton conductivity through the membrane, and ion exchange capacity is required. In this direction, we report on the one-step fabrication of novel poly (ionic…

Relaxation of self-entangled many-arm star polymers

1989

We present a description of the relaxation of star polymers based on the conformational scaling properties predicted by Daoud and Cotton and confirmed in our recent simulations. We identify three typical relaxation mechanisms. The first describes elastic deformation of the overall shape. Its relaxation time is nearly independent off. A second type of relaxation occurs via rotational diffusion. We predict that the relaxation time should scale with Nwlfz-v where Y is the correlation length exponent. A third relaxation process is the disentanglement of two or more arms. Here the longest relaxation time should increase exponentially with f llz. We measure various relaxation processes by molecul…

Determination of the oxygen transmissibility and permeability of hydrogel contact lenses

1999

To test the validity of the method of stacked hydrogel contact lenses to obtain the oxygen permeability and transmissibility coefficients of the lenses, the coefficients of one low hydration (38% water) and two high hydration (55 and 58% water) hydrogel contact lenses stacked one to five on an oxygen electrode were deter- mined. From the oxygen diffusion through the lenses, the current intensity in the stationary state was determined, and from this the "instrument" the oxygen transmis- sibility was obtained. The permeability coefficients of the lenses, corrected for edge effects, were obtained from the slope of the plot of the reciprocal of the transmissibility coefficients versus the lens …

Review of gas diffusion cathodes for alkaline fuel cells

2009

Abstract This paper gives a technical background to alkaline fuel cells (AFCs), introducing the advantages and drawbacks of the technology. AFCs offer the potential for low cost, mass producible fuel cells, without the dependency on platinum based catalysts and (currently) expensive membrane electrolytes. The AFC uses relatively low cost electrolytes based on aqueous bases such as potassium hydroxide. The inherent CO 2 sensitivity of the electrolyte can be addressed by filtering out the CO 2 from the air intake using a simple scrubber and periodically replacing the liquid electrolyte. A review of the state-of-the-art in gas diffusion cathode development is given. The overall cell performanc…

Linear instability of the vertical throughflow in a horizontal porous layer saturated by a power-law fluid

2016

Abstract The effects of the vertical throughflow of a non-Newtonian power-law fluid on the onset of convective instability in a horizontal porous layer are investigated. The extended Darcy’s model of momentum diffusion is employed together with the Oberbeck–Boussinesq approximation. A stationary basic solution for the vertical throughflow is determined analytically. The basic velocity and temperature fields turn out to be independent of the non-Newtonian rheology. A linear stability analysis is carried out, leading to a fourth-order eigenvalue problem. A numerical solution of the eigenvalue problem is employed to obtain the neutral stability curves and the critical Rayleigh number for the o…

Application of White Mustard Bran and Flour on Bread as Natural Preservative Agents.

2021

In this study, the antifungal activity of white mustard bran (MB), a by-product of mustard (Sinapis alba) milling, and white mustard seed flour (MF) was tested against mycotoxigenic fungi in the agar diffusion method. The results obtained were posteriorly confirmed in a quantitative test, determining the minimum concentration of extract that inhibits the fungal growth (MIC) and the minimum concentration with fungicidal activity (MFC). Since MF demonstrated no antifungal activity, the MB was stored under different temperature conditions and storage time to determine its antifungal stability. Finally, an in situ assay was carried out, applying the MB as a natural ingredient into the dough to …

PERFORMANCE OF DIFFUSION KURTOSIS IMAGING FOR CHARACTERIZATION OF PROSTATE LESIONS USING 1.5T MAGNETIC RESONANCE IMAGING SCANNER

2020

The aim of the study is to evaluate the diagnostic performance of apparent diffusion coefficient (ADC) and apparent kurtosis coefficient (Kapp) for the characterization of prostate lesions on 1.5T MRI. This retrospective study included 34 patients with at least one lesion with PI-RADS score≥ 3. Performances of ADC and Kapp were evaluated using the Mann-Whitney U test and receiver operating characteristics curve (AUROC). Lesions with Gleason score≥6 had significantly lower Kapp compared to benign lesions (p=0.025). The ADC-ratio was the only significantly different parameter between GS≥7 and GS=6 lesions (p=0.039). Kapp showed the largest AUROC for the diagnosis of GS≥6 prostate cancers (AUR…

Role of the Apparent Diffusion Coefficient (ADC) values analysis in Diffusion Weighted Imaging (DWI-MR) in the characterization of prostatic disease …

Purpose To evaluate if apparent diffusion coefficient analysis on magnetic resonance imaging can differentiate between normal and pathological prostate tissue, including prostate cancer and precancerous conditions (ASAP and PIN). Materials and Methods Prostate MRI with endorectal coil was performed in 93 patients (mean age 65.4). Regions of interest were placed over suspicious areas, detected on MRI, and over areas with normal appearance, and ADC values were recorded. Statistical differences between ADC values of suspicious and normal areas were evaluated. Histopathological diagnosis, obtained from targeted biopsy in 51 patients and from prostatectomy in 42 patients, were correlated to ADC …