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cath  
#1 Posted : Sunday, 14 September 2014 4:12:38 PM(UTC)
cath

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Why does dispersion occur?



Dispersion is due to refraction.

In optics, dispersion is a phenomenon that causes the separation of a wave into spectral components with different wavelengths, due to a dependence of the wave's speed on its wavelength. It is most often described in light waves, but it may happen to any kind of wave that interacts with a medium or can be confined to a waveguide, such as sound waves. Dispersion is sometimes called chromatic dispersion to emphasize its wavelength-dependent nature.

There are generally two sources of dispersion: material dispersion, which comes from a frequency-dependent response of a material to waves; and waveguide dispersion, which occurs when the speed of a wave in a waveguide depends on its frequency. The transverse modes for waves confined laterally within a finite waveguide generally have different speeds (and field patterns) depending upon the frequency (that is, on the relative size of the wave, the wavelength, compared the size of the waveguide).

Dispersion in a waveguide used for telecommunication results in signal degradation, because the varying delay in arrival time between different components of a signal "smears out" the signal in time. A similar phenomenon is modal dispersion, caused by a waveguide having multiple modes at a given frequency, each with a different speed. A special case of this is polarization mode dispersion (PMD), which comes from a superposition of two modes that travel at different speeds due to random imperfections that break the symmetry of the waveguide.
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Sheppie  
#2 Posted : Wednesday, 12 November 2014 3:23:05 AM(UTC)
Sheppie

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Dispersion refers to the distribution of a particular chemical constituent or element in a particular rock or soil, where the concentration of the element gradually reaches the average value (or background) from high concentrations with respect to space. Dispersion can be considered as primary or secondary, based on formational environment.

It occurs when a soil is sodic. When a sodic soil is wetted, the clay particles are forced apart. This is generally a major cause of erosion.

In geomorphology and geology, erosion is the action of exogenic processes (such as water flow or wind) which remove soil and rock from one location on the Earth's crust, then transport it to another location where it is deposited. Eroded sediment may be transported just a few millimetres, or for thousands of kilometres.

While erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. Excessive (or accelerated) erosion causes both 'on-site' and 'off-site' problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are now the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems world-wide.

Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils.

Resources:
http://en.wikipedia.org/wiki/Erosion
http://www.scienceclarif...Ga-He/Geologic-Time.html
http://www.unalmed.edu.c...z/geologia/mex/mex12.htm
jenni  
#3 Posted : Tuesday, 1 March 2016 1:33:14 PM(UTC)
jenni

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Hi Sheppie,

Non sodic aquifer units wont have dispersion, is that what you mean?

thanks for sharing!
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