Randomized Controlled Studies: This is a study in which 1) There are two groups, one treatment group and one control group. The treatment group receives the treatment under investigation, and the control group receives either no treatment (placebo) or standard treatment. 2) Patients are randomly assigned to all groups.
winds that blow in a steady direction can move a dune. such wind will consistently pick up sand from one side and deposit it to a other side. this causes the entire dune to s â¦ lowly move in the direction if the wind.
Origin of Sand Dunes. The origin of sand dunes is very complex, but there are three essential prerequisites: An abundant supply of loose sand in a region generally devoid of vegetation (such as an ancient lake bed or river delta) A wind energy source sufficient to move the sand grains. A topography whereby the sand particles lose their momentum and settle out. Any number of objects, such as shrubs, rocks or fence posts can obstruct the wind force causing sand to pile up in drifts and ultimately, large dunes.