Science Physics Geometric optics Reflection and refraction. Specular and diffuse reflection.
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Specular and diffuse reflection 2. Refraction and Snell's law. Snell's law example 1. Snell's law example 2. Total internal reflection.
Next lesson. Current timeTotal duration Video transcript Voiceover: Check out this ray of light. When it enters a new medium, like water, its path will bend, and the larger the index of refraction of the new medium, the more the light will bend from its initial direction that it had in the air. Higher-order moments about the mean — such as skewness and kurtosis — can be used in their own right to help describe a distribution, or as the means to an end: detecting departures from normality.
Distler, in Encyclopedia of Materials: Science and Technology , Polymer dispersions or lattices are liquid two-phase systems, wherein polymer particles are dispersed in a continuous liquid phase. Because of the high interior surface area of the polymer particles, these dispersions are not stable over time, but agglomerate to form larger particles and finally coagulate. This macroscopic phase separation is prevented by adding surface-active agents of amphiphilic character. These molecules adsorb at the particle surface and extend into both the liquid and particle phases, stabilizing the dispersion by electrostatic or steric means.
Amorphous solid dispersions are one way to improve the properties of an API and they are typically used to help improve the solubility of poorly soluble compounds. They also have disadvantages, such as poor physical stability, which can result in crystallization, and poor chemical stability, which can lead to degradation. The screening and selection process needs to include knowledge of required dispersion properties as well as downstream processing to produce the formulated product.
Since they are metastable forms, development of amorphous dispersions involves a greater understanding of the handling, storage, and processing conditions needed to prevent crystallization and to maintain a miscible dispersion.
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A number of marketed products containing amorphous solid dispersions show that this technology has been successful in developing poorly soluble compounds. Brian L. As previously noted, flow in groundwater is laminar.
However, that does not mean that dispersion is due to molecular diffusion alone. Fluid moving through the center of a pore space moves faster than fluid near the solid surfaces, which is more retarded by drag. In traveling around solid-particles, flow paths spread transversely to the hydraulic gradient or main flow direction. Homogeneities in the soil and pore structure also contribute to dispersion. Hydrodynamic dispersion includes both molecular diffusion and mechanical dispersion. At sufficiently low velocities, molecular diffusion dominates.
It is customary to write the hydrodynamic dispersion coefficients as:. Walter F. Solid dispersions are first generation crystalline solid dispersions. The first description of solid dispersions for pharmaceutical application was made by Sekiguchi and Obi , using urea as a carrier to form a eutectic mixture with sulfathiazole.
They found that formulating eutectic mixtures improves the drug release rate, and consequently the bioavailability of poorly water-soluble drugs.
These solid dispersions produced faster release, and improved the bioavailability of the drug, as compared with conventional formulations of these drugs. The small particle size and a better drug wettability were the main reasons for the observed improvements in bioavailability.
Such carriers, especially sugars, have a high melting point that is not favorable for the preparation of solid dispersions by the melt method. Urea exhibits a high solubility in water, and many common organic solvents, while the sugars have a low solubility in most organic solvents. Improvement was attributed to more rapid dissolution of the carrier, releasing the drug microcrystals or particles. Isabel B. QRS dispersion represents regional inhomogeneity of depolarization, as a consequence of ventricular conduction defects.
There was no significant correlation between QRS dispersion and fibro-fatty infiltration of the myocardium.
Pragasam Viswanathan, Gokulakannan Ragavan, in Nanostructures for Oral Medicine , Drug dispersion employs dispersion of one or more active ingredients in amorphous particles or crystalline particles by melting, solvent, or fusion-solvent methods. Further, the dissolution characteristics of the dispersed drug depend on the selection of the carrier. A water soluble carrier promotes faster release of drug from matrix, and a poorly soluble or insoluble carrier causes slower release of drug from matrix.
Solid dispersions enhance the dissolution rate by reducing particle size, improving wettability, and increasing particle porosity. However, these characteristics are achieved when the parameters, such as carrier molecular weight and composition, drug crystallinity, and particle porosity and wettability are successfully controlled. Besides, solid dispersions also possess certain disadvantages, including conversion of amorphous state to crystalline state, phase separation due to moisture absorption, crystal growth, or conversion from a metastable crystalline form to a more stable structure during storage.
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Sign In Help. Dispersion Dispersion is defined as the wavelength-dependent refractive index of the material, which causes rays of light of various wavelengths to be bent refracted to a different degree when entering the lens. Download as PDF. Set alert. About this page. Learn more about Dispersion. Epilepsy Maria Thom, Edward H. Creep of Oxide-dispersion Strengthened Alloys E.
Arzt, in Encyclopedia of Materials: Science and Technology , Dispersion strengthening is a particularly efficient means of raising the high-temperature creep strength of metallic materials. Environmental Biochemodynamic Processes Daniel A. Vallero PhD, in Environmental Biotechnology , Dispersion Numerous dispersion processes are at work in environmental biochemodynamic systems. Huber US Environmental Protection Agency. Dynamic dispersion is expressed as: 3. Thus, the path each particle takes during this time is an ensemble mean field that relates to the probabilities for particle displacement: 3.
Measures of Dispersion, Skewness and Kurtosis D. Shiyko, in International Encyclopedia of Education Third Edition , Conclusion Dispersion is the most basic concept in statistics; in fact, the field of statistics is often defined as the study of variation in data. Polymer Dispersions D. Distler, in Encyclopedia of Materials: Science and Technology , Polymer dispersions or lattices are liquid two-phase systems, wherein polymer particles are dispersed in a continuous liquid phase.
It is customary to write the hydrodynamic dispersion coefficients as: 7.