$\latex

instead of

$latex

A common mistake. I’ll fix it.

]]>/A

]]>Analysis of the diffraction data shows that in the ice crystals the stacking of the atomic layers is disordered. “The crystals that form have randomly stacked layers of cubic and hexagonal sequences,” Murray says. “As each new layer is added, there is a 50% probability of it being either hexagonal or cubic.” The result is a novel, metastable form of ice with a stacking-disordered structure.

Rahul Siddarthan wrote:

But this estimate is ‘naive’ because it assumes the 6 out of 16 hydrogen configurations for oxygen atoms in the second set can be independently chosen, which is false. More complex methods can be employed to better approximate the exact number of possible configurations, and achieve results closer to measured values.

Did they do time series also at constant temperature ?

If one assumes that no heat energy would be transferred to a block of ice (I don’t know wether this could be seen as applying to the experiment, i.e. if this is an adiabatic process) and moreover if the block could be seen as isolated (pressure, volume) (again I don’t know to which extend this would apply here) then within a certain time there should on average be more disorder and this may refer not only to the hydrogen atoms but also to the oxygen atoms, moreover the disorder change should go together with different pressure, temperature and volume change of the block, i.e. dS = 1/T p dV

There’s also an uncountable infinity of other patterns that all give you equally dense packings. For example:

-a-b-a-c-b-a-c-b-c-b-a-c-

But then since the volume stays the same, where would the work come from? By sucking heat from the oil bath?

]]>John Baez’s article on the many (at least sixteen) known crystal phases of water ice, on the blog for the Azimuth Project, described as “an international collaboration to create a focal point for scientists and engineers interested in saving the planet. Our goal is to make clearly presented, accurate information on the relevant issues easy to find, and to help people work together on our common problems.” ]]>