Klein tunneling of a quasirelativistic Bose-Einstein condensate in an optical lattice

A proof-of-principle experiment simulating effects predicted by relativistic wave equations with ultracold atoms in a bichromatic optical lattice that allows for a tailoring of the dispersion relation is reported. We observe the analog of Klein tunneling, the penetration of relativistic particles through a potential barrier without the exponential damping that is characteristic for nonrelativistic quantum tunneling. Both linear (relativistic) and quadratic (nonrelativistic) dispersion relations are investigated, and significant barrier transmission is observed only for the relativistic case.     

Mikrochemie

Ohne Zusammenfassung     

Impact of initiator characteristics on the thermal stability of vinylidene chloride copolymers

Two standard vinylidene chloride copolymers, the first containing approximately 9 mass% methyl acrylate and the second containing vinyl chloride at a nominal 15 mass% were prepared by radical suspension techniques using a series of peroxide and azo initiators (all of approximately the same half-life temperature for decomposition). The nature of the initiator could impact the stability of the resulting polymer in two ways. Instability could be introduced either via end-group effects or by attack of residual initiator fragments on the finished polymer during isolation and residual monomer stripping. In this case, the relative thermal stability of the resins produced was assessed by exposing samples to heat and shear in an air environment in a two-roll mill (Brabender Prep-Mill). The rate and extent of degradation was most readily apparent from color development during this treatment. The more thermally stable polymers were produced using initiator radicals that did not attack the polymer during isolation/stripping processes.