A pulmonary nodule is a discrete opacity in the lung which may be caused by: 1  Neoplasm: benign or malignant. 2  Granuloma: tuberculosis. 3  Infection: roundish pneumonia. 4  Vascular: infarct, varix, granulomatosis with polyangiitis, rheumatoid arthritis.
1 Helium is also commonly used to pressurize and purge systems of unwanted gases. 2  It is also used in controlled atmospheres when the levels of different gases have to be kept constant. 3  It is used as a protective gas when growing silicon and germanium crystals and when producing titanium and zirconium.
Although neon is the fourth most abundant element in the universe, only 0.0018% of the earth's atmosphere is neon. The largest use for neon gas is in advertising signs. Neon is also used to make high voltage indicators and is combined with helium to make helium-neon lasers. Liquid neon is used as a cryogenic refrigerant.