The gas must be far hotter than the dense matter at the centre of the sun for fusion to happen.

ECONOMIST: Nuclear fusion

While particulate matter emitted by vehicles make up a small part of overall particulate matter in China, in dense urban areas, it is almost certainly the highest contributor to human exposure of PM2.5, according to Vance Wagner, a senior researcher at the International Council on Clean Transportation.

WSJ: China's Pollution Fight Faces Resistance

It depends on a recent body of work which suggests that the brain's white matter (the wiring that connects the main bodies of the nerve cells, or grey matter, together) is less dense and less abundant in the brain of an autistic person than in that of a non-autist.

ECONOMIST: Autism

But even in this paradise, away from the city, with its dense population, disease and social ills, the villagers can relate to the same matter, and that residents of large cities ...

UNESCO: Communication and Information