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相关概念视频

Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model01:09

Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model

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Various dissolution theories provide insight into the factors that influence the dissolution rate. Danckwerts' Model suggests that turbulence, rather than a stagnant layer, characterizes the dissolution medium at the solid-liquid interface. In this model, the agitated solvent contains macroscopic packets that move to the interface via eddy currents, facilitating the absorption and delivery of the drug to the bulk solution. The regular replenishment of solvent packets maintains the...
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Physiological Pharmacokinetic Models: Blood Flow-Limited Versus Diffusion-Limited Models00:57

Physiological Pharmacokinetic Models: Blood Flow-Limited Versus Diffusion-Limited Models

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Physiological pharmacokinetic models, often called flow-limited or perfusion models, typically assume a swift drug distribution between tissue and venous blood, creating a rapid drug equilibrium. This premise is based on the idea that drug diffusion is extremely fast, and the cell membrane presents no barrier to drug permeation. In this scenario, where no drug binding occurs, the drug concentration in the tissue equals that of the venous blood leaving the tissue. This greatly simplifies the...
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Theories of Dissolution: Diffusion Layer Model01:15

Theories of Dissolution: Diffusion Layer Model

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Dissolution, the process by which drug particles dissolve in a solvent, is explained by the diffusion layer model, a theoretical framework that simulates the absorption of oral drugs and allows us to analyze experimental data.
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
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Diffusion on Chromatography Columns01:07

Diffusion on Chromatography Columns

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In column chromatography, when an analyte is introduced as a narrow band at the top of the column, the solutes begin to separate and broaden, developing a Gaussian profile. This broadening occurs due to various factors, such as longitudinal diffusion.
Longitudinal diffusion occurs when the solute molecules in the mobile phase diffuse from the more concentrated center of the chromatographic band to the more dilute regions on either side, both towards and against the flow direction. This...
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Passive Diffusion: Overview and Kinetics01:17

Passive Diffusion: Overview and Kinetics

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Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
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Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
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相关实验视频

Updated: Jul 26, 2025

The Diffusion of Passive Tracers in Laminar Shear Flow
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非稳定状态的Fickian扩散模型降低了薄膜被动采样中的扩散梯度的估计凝层扩散系数不确定性.

Samuel D Hodges1, David G Wahman2, Levi M Haupert2

  • 1Department of Civil Engineering, University of Arkansas, Fayetteville, Arkansas 72701, United States.

Environmental science & technology
|June 21, 2023
PubMed
概括
此摘要是机器生成的。

一个新的有限差异模型 (FDM) 在被动样本中提高了凝扩散系数 (D_Gel) 的准确性. 这种先进的方法与标准分析相比,减少了不确定性的十倍,提高了大规模运输测量.

关键词:
扩散性边界层是一种扩散性边界层.环境采样环境采样实验方法 实验方法这种水凝是水凝.

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相关实验视频

Last Updated: Jul 26, 2025

The Diffusion of Passive Tracers in Laminar Shear Flow
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科学领域:

  • 环境科学 环境科学
  • 分析化学 分析化学
  • 化学工程是化学工程的重要组成部分.

背景情况:

  • 薄膜被动采样器中的质量传输依赖于通过凝层 (agarose或APA) 的扩散.
  • 凝层扩散系数 (D_Gel) 对采样器性能至关重要.
  • 使用Fick第一定律的标准分析 (SA) 通常假定伪稳定状态流量,限制准确性.

研究的目的:

  • 开发和验证一种更准确的方法来确定凝层扩散系数 (D_Gel).
  • 评估D细胞试验中标准分析 (SA) 的局限性.
  • 实施一个有限差异模型 (FDM),以计算非平稳状态 (N-SS) 流量.

主要方法:

  • 使用酸盐进行了72次双隔膜扩散细胞 (D细胞) 试验.
  • 基于Fick的第一定律和回归模型的应用标准分析 (SA).
  • 开发并使用基于Fick第二定律的有限差异模型 (FDM),结合N-SS流量.

主要成果:

  • SA确定了D_Gel具有显著的变异性 (例如,10.115.8 × 10−6 cm2·s−1对于阿加罗斯).
  • 使用SA的回归模型显示D_Gel的95%置信区间很宽 (例如,在500rpm时为agarose的1318 × 10−6cm2·s−1).
  • FDM将D_Gel的不确定性降低了十倍,产生了精确的值 (例如,14.5 ± 0.2 × 10−6 cm2·s−1对于500rpm的阿加罗斯).

结论:

  • 有限差异模型 (FDM) 在被动样本中显著提高了D_Gel测定的准确性.
  • 在FDM中,度和流量的动态变化,克服了SA的局限性.
  • 这种改进的方法为环境监测提供了更可靠的大众运输数据.