The ability to sleep in one chunk (整塊時(shí)間) overnight goes down as we age but the amount of sleep we need to function well does not change," Dr Drummond told the American Association for the Advancement of Science conference in San Diego.

A stated goal of the Obama administration is to restore a big chunk of this employment, along with the multitude of skills that many of the jobs required.

The city is the building block of civilisation and of almost everything people do; a guidebook to the city is really, therefore, a guidebook to how a large and ever-growing chunk of humanity chooses to live