The correlation of structure and electronic properties near the surface of transition metal oxides

The strong couplings between different degrees of freedom are believed to be responsible for novel and complex phenomena discovered in transition metal oxides (TMOs). The physical complexity is directly responsible for their tunability. Creating surfaces/interfaces add an additional ' man-made' twist, approaching the quantum phenomena of correlated materials. ^ The dissertation focused on the structural and electronic properties in proximity of surface of three prototype TMO compounds by using three complementary techniques: scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and low energy electron diffraction, particularly emphasized the effects of broken symmetry and imperfections like defects on the coupling between charge and lattice degrees of freedom. ^ Ca1.5Sr0.5RuO4 is a layered ruthenate with square lattice and at the boundary of magnetic/orbital instability in Ca2-xSrxRuO4. That the substitution of Sr 2+ with Ca2+ causing RuO6 rotation narrows the dxy band width and changes the Fermi surface topology. Particularly, the γ(dxy) Fermi surface sheet exhibited hole-like in Ca1.5Sr0.5RuO4 in contrast to electron-like in Sr2RuO4, showing a strong charge-lattice coupling. ^ Na0.75CoO2 is a layered cobaltite with triangular lattice exhibiting extraordinary thermoelectric properties. The well-ordered CoO2-terminated surface with random Na distribution was observed. However, lattice constants of the surface are smaller than that in bulk. The surface density of states (DOS) showed strong temperature dependence. Especially, an unusual shift of the minimum DOS occurs below 230 K, clearly indicating a local charging effect on the surface. ^ Cd2Re2O7 is the first known pyrochlore oxide superconductor (Tc ∼ 1K). It exhibited an unusual second-order phase transition occurring at TS1 = 200 K and a controversial first-order transition at TS2 = 120 K. While bulk properties display large anomalies at TS1 but rather subtle and sample-dependent changes at TS2, the surface DOS near the EF show no change at T s1 but a substantial increase below TS2---a complete reversal as the signature for the transitions. We argued that crystal imperfections, mainly defects, which were considerably enhanced at the surface, resulted in the transition at TS2. ^

A Conversation on the Economics of Transition in Cuba, Presentation by Jan švejnar, Columbia University with economists Jorge Salazar-Carrillo and Rolando Castaneda

This flyer promotes the event "A Conversation on the Economics of Transition in Cuba, Presentation by Jan švejnar, Columbia University with economists Jorge Salazar-Carrillo and Rolando Castaneda", sponsored by the Knight Foundation and co-sponsored by FlU's Cuban Research Institute.

Late adolescents in transition: The influence of support on post-transition adjustment

Points of transition, when major life roles undergo change, tend to be associated with an increased need for social support. The transition from adolescence to adulthood is ideal for the examination of the effect of normative stress on the development and functioning of social networks. A questionnaire was designed based on the convoy model to assess the influence of personal and situational characteristics on the utilization of support in the prediction of post-transition adjustment. Data were initially collected for a multi-ethnic sample of 741 sophomores and seniors in high school. Surveys were mailed to participants two years later, and one again the following year. The current study is based on data for 310 participants with complete data for all three time periods. A series of hierarchical regressions were conducted to compare three explanatory models of support: main effect, mediation, and moderation. A main effect model of support on post-transition adjustment was confirmed, a mediator model was not confirmed, and a moderator model was marginally confirmed. Family and friend support was related to significantly lower levels of loneliness, particularly for those with less adaptable temperaments. ^