Each car starts with a certain position and speed, and the road thus has a particular density of cars that changes as they move along, and as new cars are injected from a junction slip-road.

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It's an airtight pod that changes air pressure, temperature and density.

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Double your vegetable intake and reduce fat -- Both of these changes will significantly decrease the calorie density of your diet without decreasing the volume of food that you consume.

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Children also showed improvement in hearing, skeletal rigidity or cardiovascular changes such as decreased arterial stiffness and improved vessel-wall density.

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Japanese researchers will now study how the bone density of the Medaka fish has changed over time, helping them understand similar changes that occur in human astronauts.

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