Consider celery, often proposed as a negative-calorie food due to its low-calorie count, high water density, and impressive fibre content.

BBC: Who, Why, What: Can foods have negative calories?

Since then, Li-ion batteries have barely tripled their volumetric energy density, while processor transistor count has zoomed more than a thousand-fold.

FORBES: Battery Chemistry Is Getting In The Way Of Apple's Vision

China may count almost as many researchers as the USA but it has a density of researchers of 1.83 per 1000 labour force, compared to 9.40 in the USA. At 9.17, the Republic of Korea comes much closer to rivalling the USA for this indicator.

UNESCO: MEDIA SERVICES