Dipolar Bose-Einstein condensates at Finite temperature

We study a Bose-Einstein condensate (BEC) of a dilute gas with dipolar interactions, at finite temperature, using the Hartree-Fock-Bogoliubov (HFB) theory within the Popov approximation. An additional approximation involving the dipolar exchange interaction is made to facilitate the computation. We calculate the temperature dependence of the condensate fraction of a condensate confined in a cylindrically symmetric harmonic trap. We show that the bi-concave shaped condensates found in Ref. \cite{Ronen07} in certain pancake traps at zero temperature, are also stable at finite temperature. Surprisingly, the dip in the central density of these structured condensates is actually enhanced at low finite temperatures. We explain this effect.Comment: 9 figure

Electric field suppression of ultracold confined chemical rates

We consider ultracold collisions of polar molecules confined in a one dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking KRb molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased, but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes of KRb molecules of 1 s. We find a ratio of elastic to quenching collision rates of about 100, which may be sufficient to achieve efficient experimental evaporative cooling of polar KRb molecules.Comment: 4 pages, 3 figure

Automatic CAD-model Repair: Shell-Closure

Shell-closure is critical to the repair of CAD-models described in the .STL file-format, the de facto solid freeform fabrication industry-standard. Polyhedral CAD-models that do not exhibit shell-closure, i.e. have cracks, holes, or gaps, do not constitute valid solids and frequently cause problems during fabrication. This paper describes a solution for achieving shell-closure of polyhedral CAD-models. The solution accommodates nonmanifold conditions, and guarantees orientable shells. There are several topologically ambiguous situations that might arise during the shell-closure process, and the solution applies intuitively pleasing heuristics in these cases.Mechanical Engineerin