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.
Coalescence is preferred to reduction, but only in utterance-final position, not elsewhere. Example (22e) shows that coalescence of /t/ or /d/ with /s/ or /z/ is a general pattern which is not restricted to words with stem-final clusters or to utterance-final forms.