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.
Spring and summer often see the collisions between air masses with very different temperatures. This can create strong thunderstorms that can in turn create tornadoes. Further information:   Tornadoes need a combination of factors to form, and these factors are often associated with thunderstorms, which are most likely to occur in the warmer months.