The automatic cab signal system shall be arranged so that cab signals will be continuously controlled in accordance with conditions described in Â§ 236.205 that obtain at least stopping distance in advance. Â§ 236.512 Cab signal indication when locomotive enters block where restrictive conditions obtain.
Dissolved oxygen (DO) is a measure of the quantity of free oxygen molecules in water. The concentration of DO is an important indicator of the health of an aquatic ecosystem because oxygen is essential for almost all forms of life. Oxygen is necessary for respiration and for some chemical reactions.
Oxygen makes up about 21% of the air we breathe and half of this oxygen is produced by phytoplankton in the ocean. All aerobic life requires oxygen to produce energy. In water, oxygen is found in a dissolved form and is much more limiting. For this reason, we measure dissolved oxygen in water not in % but in units of umol/kg. The highest concentrations of dissolved oxygen in the ocean are found within the surface mixed layer at concentrations of > 200 umol/kg.