Myelosuppression - a decrease in the production of blood cells, which may lead to low blood count. Pancytopenia - a lowering of all three types of blood cells; red blood cells, platelets, and white blood cells, which may lead to low red blood cell count, low blood platlet count, and/or low white blood cell count.
Helium is used as a cooling medium for the Large Hadron Collider (LHC), and the superconducting magnets in MRI scanners and NMR spectrometers. It is also used to keep satellite instruments cool and was used to cool the liquid oxygen and hydrogen that powered the Apollo space vehicles.
Using Density. One of the most common uses of density is in how different materials interact when mixed together. Wood floats in water because it has a lower density, while an anchor sinks because the metal has a higher density. Helium balloons float because the density of the helium is lower than the density of the air.