The Kelvin-Helmholtz instability looks like a series of overturning ocean waves and occurs between layers of fluids undergoing shear. This video has a great lab demo of the phenomenon, including the set-up prior to execution. When the tank is tilted, the denser dyed salt water flows left while the fresh water flows to the right. These opposing flow directions shear the interface between the two fluids, which, once a certain velocity is surpassed, generates an instability in the interface. Initially, this disturbance is much too small to be seen, but it grows at an exponential rate. This is why nothing appears to happen for many seconds after the tilt before the interface suddenly deforms, overturns, and mixes. In actuality, the unstable perturbation is present almost immediately after the tilt, but it takes time for the tiny disturbance to grow. The Kelvin-Helmholtz instability is often seen in clouds, both on Earth and on other planets, and it is also responsible for the shape of ocean waves. (Video credit: M. Hallworth and G. Worster)
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Building a better cup of coffee
The brave new world of coffee? Think genetics.
UC Davis geneticist Juan Medrano is known for his research on the genetics of milk (and the effect it has on humans), but recently has turned his research efforts towards coffee.
The goal is to understand the variability of coffee genes at the DNA level. This would allow Medrano and others to accurately identify genetic forces that contribute to certain flavors as well as the crucial factor of disease resistance.
The key is to identify the gene regulators that are related to flavor and other qualities, such as how coffee feels in the mouth. Gene regulators are involved in controlling the expression of other genes.
Other variables, like altitude can be crucial in coffee growing. Coffee flavor and aromas change significantly with changes in altitude, as temperature and microclimates vary greatly. The higher-altitude coffees are generally of better cupping quality, Medrano explains.