Daily Archives: September 18, 2010

Popping the Kids' Balloons

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Minister for Home Affairs: I’d like to answer this question if I may in two ways. Firstly in my normal voice and then in a kind of silly high-pitched whine

Cocktail Party Physics: helium: a weighty question

One-fifth of the world’s helium supply is used in MRIs. The typical MRI requires superconducting magnets and, since we haven’t figured out room-temperature superconductivity yet, they require liquid nitrogen or liquid helium to keep them in the superconducting state. Most systems use a closed cycle – helium cools the magnet, warms up in the process, turns to a gas, and is re-liquefied. A typical MRI magnet, however, requires 1700-2000 liters of liquid helium. Older models have to be refilled on a timescale from months to years, while newer models advertise that they “never” need to be refilled. (I’m about to buy a system like that. We’ll see how long ‘never’ is.) MRI resolution gets better the larger the magnetic field. Larger magnetic fields require larger magnets and thus more liquid helium.

What's Cooking in the Pizza Lab?

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The Pizza Lab: Bringing Neapolitan Pizza Home (aka ‘The Skillet-Broiler Method’)

Real food science — bringing the physics along with the recipe.

It’s basic thermodynamics. Air at a given temperature has less energy than stone at a given temperature. Because of this, even if both my stone and the air in my oven are at 550 degrees, the part of the pizza in contact with the stone cooks much more rapidly than the top. By the time the bottom is crisp, the top has yet to take on any significant color.
The solution to this is quite simple, and happily makes for a much cooler kitchen as well: forget preheating the oven: just use the broiler. A broiler not only cooks via hot air like the oven, but more importantly, it adds a significant amount of radiant heat to the mix, cooking the top of the pizza directly with electro-magnetic waves—a much more efficient means of heat transfer.