Class A (type D) CpG ODNs (CpG-A ODNs) contain a central palindromic phosphodiester (PO) CpG sequence and a PS-modified 3â poly-G tail. The poly G tails form intermolecular tetrads that result in high molecular weight ordered structures.
Why does a tornado form when cold and hot air meet? The collision of warm and cold air is not the direct cause of a tornado, nor is it absolutely necessary. When a cold air mass pushes into a warm air mass (this is called a câ¦old front) the warmer, less dense air is forced upwards.
Tornadoes tend to occur in the middle latitudes in both hemispheres, between 30Â° and 50Â°. These latitudes are regions where the warmer subtropical warm air meets the colder polar air, with different wind speeds and direction. These conditions can produce rotating air masses. Tornadoes most frequently occur in the United States, which sees about 1,000 per year. The tornadoes usually occur in the southeastern state of Florida or in Tornado Alley, the central part of the country (Midwest) where most of the violent tornadoes occur. Canada is a distant second with about 100 per year. Twenty to thirty tornadoes per year are reported in New Zealand. Most of Europe is susceptible to tornadoes, as are Argentina, South Africa, Australia, Bangladesh, Nepal, eastern China, Japan, and the Philippines.