Colossal dielectric constants in transition-metal oxides

Many transition-metal oxides show very large ("colossal") magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices. In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation. In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu3Ti4O12 and related systems, which is today's most investigated material with colossal dielectric constant. Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La2-xSrxNiO4 where electronic phase separation may play a role in the generation of a colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

Incorporating different proportions of exotic maize germplasm into two adapted populations

Maize breeders frequently wish to use exotic germplasm in their breeding programs without losing specific characteristics of their adapted material. The objective of this study was to determine the optimal proportions of exotic germplasm to incorporate into adapted populations (F2 = 50% exotic, BC1 = 25% exotic, BC2 = 12.5% exotic and BC3 = 6.25% exotic) to form the initial foundation population and to determine the heterosis between adapted x exotics. We used six exotic populations of different origins and two adapted populations representing a Brazilian heterotic pattern. In 1993-94 and 1994-95, the parents, F1, F2, BC1, BC2, BC3 and four checks were evaluated in six environments in central Brazil using an 8 x 9 simple rectangular lattice design. Higher mean values for yield were obtained as the proportion of exotic germplasm decreased. Some backcrosses produced more than the adapted populations BR 105 (7.59 ton/ha) and BR 106 (8.43 ton/ha). The best results were obtained when incorporating 6.25 or 12.5% of exotic genes. This trend was true for root lodging, stalk lodging and ear diseases but not for plant and ear height. The midparent heterosis for yield varied from -16.1 to 40.3%. Midparent heterosis with positive and negative values were also found for the other traits. The results indicate the potential of exotic germplasm for developing good hybrids. After choosing the best exotic source, some recurrent selection might be appropriate in order to adapt and improve the exotic populations.<br>Os melhoristas de milho que utilizam germoplasmas exóticos nos programas de melhoramento têm a preocupação de não perder as características desejáveis dos materiais adaptados. Buscando atender esta demanda, o presente trabalho teve por objetivo determinar a proporção ideal de germoplasma exótico que deve ser incorporado em populações melhoradas (F2 = 50% exótico; RC1 = 25% exótico; RC2 = 12,5% exótico; RC3 = 6,25% exótico), para formar as populações base para seleção e determinar a heterose entre os germoplasmas exóticos e adaptados. Em 1993/94 e 1994/95, os parentais, F1, F2, RC1, RC2, RC3 e quatro testemunhas foram avaliados em seis ambientes da região central do Brasil, utilizando-se o delineamento em látice simples 8 x 9. De um modo geral, à medida que a proporção de germoplasma exótico decresceu, valores médios mais altos foram obtidos para o caráter peso de espigas. Alguns retrocruzamentos produziram mais que as populações melhoradas BR 105 (7.500 kg/ha) e BR 106 (8.430 kg/ha). Os melhores resultados foram obtidos quando houve a incorporação de 6,25 ou 12,5% de genes exóticos. Esta tendência foi observada para acamamento, quebramento e espigas doentes, mas não para altura de planta e de espiga. A heterose média para peso de espiga variou de -16,1 a 40,3%. Heteroses médias com valores positivos e negativos também foram encontradas para outros caracteres. Os resultados obtidos mostraram o potencial em se utilizar germoplasmas exóticos para a obtenção de híbridos. Sugere-se, após a escolha dos germoplasma, algum esquema de seleção recorrente para adaptar e melhorar as populações exóticas

A microeconometric study of theatre demand

We develop a model of theatre demand with learning by consuming, and test some of its implications on a large random sample of theatregoers and non-theatregoers. This seems to be the most comprehensive econometric study of demand for the theatre from individual data. We hypothesize that each time the consumer watches a play, he experiences a degree of pleasant or unpleasant surprise on the basis of which he will revise his future expectations of his own taste. The learning phase is likely to be unusually long for highly differentiated cultural goods. Our set of data contains unique information about the full price and the fixed cost of theatre, the objective quality of the outing, past experience of and taste for the theatre, and consumption of substitute leisure activities such as reading, television and cinema. Our methodology and data enable us to infer price elasticity on survey data from knowledge of theatregoing experience and taste. After controlling for many variables, we conclude that demand for the theatre is price-elastic, which contradicts previous estimates on aggregate time-series data. Moreover, we estimate demand conditional on past attendance after controlling for selectivity bias. Satisfaction reported by consumers after the last play is also estimated and interpreted as an ordinal conditional choice. Copyright Kluwer Academic Publishers 1996theatre demand, learning by consuming, individual data, conditional choice and satisfaction (JEL: Z1, L82),