List of the 100 most densely populated cities in the United Kingdom, measured in people per square miles. 1  Portsmouth, Hampshire â 15,336. 2  London â 13,870. 3  Leicester, Leicestershire â 11,800. 4  Glasgow, Glasgow â 8,542. 5  Bristol, Bristol â 13,398. 6  Liverpool, Merseyside â 12,790. 7  Stoke-on-Trent, Staffordshire â 11,939.
In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty times before they cannot divide any further.
A short-term exposure limit is one that addresses the average exposure over a 15-30 minute period of maximum exposure during a single work shift.A ceiling limit is one that may not be exceeded for any period of time, and is applied to irritants and other materials that have immediate effects. TWA is the average exposure over a specified period of time, usually a nominal eight hours. This means that, for limited periods, a worker may be exposed to concentration excursions higher than the PEL, so long as the TWA is not exceeded and any applicable excursion limit is not exceeded.