The most common shielding gases used for these main arc welding processes include argon (Ar), helium (He), carbon dioxide (CO2) and oxygen (O2). While Ar, He and CO2 may be used by themselves (i.e. 100%) for certain applications, in other cases the four gases are mixed together in different combinations to form shielding gas blends.
Cluster reduction in speech is when a consonant cluster, that is two or three consonants occurring in sequence in a word (like ândâ in friend), is reduced by a child into a single consonant through omission.
Font Size. A. A. A. The term cluster headache refers to a type of headache that recurs over a period of time. People who have cluster headaches experience an episode one to three times per day during a period of time (the cluster period), which may last from two weeks to three months.