Electrostatics of electron-hole interactions in van der Waals heterostructures

The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poissons equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.Comment: 10 pages, 8 figure

Introdução e avaliação de cultivares de sorgo sacarino no cerrado do Território Federal do Amapá.

A EMBRAPA buscando alternativas economicas, com vistas ao aproveitamento de cerca de 9.295 km2 de solos sob vegetação de campos cerrados do Território Federal do Amapá, introduziu em 1982, e colocou a competir variedades e hibridos de sorgo sacarino.bitstream/item/64995/1/AP-1982-introducao-avaliacao-cultivares-sorgo-sacarino.pd

Introdução e avaliação de cultivares de sorgo forrageiro no cerrado do Território Federal do Amapá.

Com o objetivo de indicar alternativas com vistas a ocupação racional dos solos sob vegetação de campos cerrados do Território Federal do Amapá, a EMBRAPA, através da Unidade de Execução de Pesquisa de Ambito Territorial - UEPAT - Macapá, conduziu em 1982, no Campo Experimental do Cerrado, o ensaio de Competição Nacional de Cultivares Sorgo Forrageiro.bitstream/item/64992/1/AP-1982-introducao-avaliacao-cultivares-sorgo-forrageiro.pd

Estresse por déficit hídrico em plantas forrageiras.

bitstream/CNPC-2010/23051/1/doc89.pd

Logarithmic periodicities in the bifurcations of type-I intermittent chaos

The critical relations for statistical properties on saddle-node bifurcations are shown to display undulating fine structure, in addition to their known smooth dependence on the control parameter. A piecewise linear map with the type-I intermittency is studied and a log-periodic dependence is numerically obtained for the average time between laminar events, the Lyapunov exponent and attractor moments. The origin of the oscillations is built in the natural probabilistic measure of the map and can be traced back to the existence of logarithmically distributed discrete values of the control parameter giving Markov partition. Reinjection and noise effect dependences are discussed and indications are given on how the oscillations are potentially applicable to complement predictions made with the usual critical exponents, taken from data in critical phenomena.Comment: 4 pages, 6 figures, accepted for publication in PRL (2004

Efeito do sistema de alimentação sobre o desempenho de cordeiros de três grupos genéticos.

O objetivo desse trabalho foi avaliar o efeito do sistema de alimentação e do grupo genético sobre o desempenho de cordeiros na fase de cria. O uso, tanto de pasto nativo como de cultivado para cria de cordeiros, possibilita a obtenção de animais em peso de desmame aos 90 dias.bitstream/CNPC/20240/1/cot64.pd