The one-orbital model for manganites with cooperative phonons and superexchange coupling JAF is investigated via large-scale Monte Carlo simulations. The results for two orbitals are also briefly discussed. Focusing on the electron density n=0.75, a regime of competition between ferromagnetic metallic and charge-ordered (CO) insulating states is identified. In the vicinity of the associated bicritical point, colossal magnetoresistance (CMR) effects are observed. The CMR is associated with the development of short-distance correlations among polarons, above the spin ordering temperatures, resembling the charge arrangement of the low-temperature CO state.

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ABSTRACT:The influence of cooling rates on the thermal behavior and solid-state morphologies of polyhydroxyalkanoates have been investigated. The thermal behavior was studied by differential scanning calorimetry (DSC). The crystal structures ($ Å ), lamellar (tens of nanometers), fibrillar (several hundred nanometers), and spherulitic ($ lm) morphologies of poly (3-hydroxybutyrate) (PHB) and the copolymers of poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) and poly (3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) (PHBHx) crystallized under different cooling rates were studied using simultaneous small angle X-ray scattering (SAXS) and wide angle X-ray scattering, simultaneous ultra small angle X-ray scattering (USAXS) and SAXS, and polarized optical microscopy, respectively. The experimental results showed that the lamellar and spherulitic morphologies depended strongly on cooling rates. However, there was little influence of cooling rates on the crystal structures.

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