464 research outputs found
Comment on the Adiabatic Condition
The experimental observation of effects due to Berry's phase in quantum
systems is certainly one of the most impressive demonstrations of the
correctness of the superposition principle in quantum mechanics. Since Berry's
original paper in 1984, the spin 1/2 coupled with rotating external magnetic
field has been one of the most studied models where those phases appear. We
also consider a special case of this soluble model. A detailed analysis of the
coupled differential equations and comparison with exact results teach us why
the usual procedure (of neglecting nondiagonal terms) is mathematically sound.Comment: 9 page
Análise de logs do sistema Agritempo por meio do log do PHPNuke e WebAlizer.
O foco deste trabalho é a análise dos logs do sistema Agritempo, um sistema de monitoramento agrometeorológico que disponibiliza informações meteorológicas e agrometeorológicas de diferentes regiões brasileiras gratuitamente na internet3. O Agritempo possui um amplo público-alvo: produtores, extensionistas, consultores, agentes do governo, estudantes e professores universitários, além da iniciativa privada
Berry's phase in the two-level model
We study the adiabatic evolution of a two-level model in the presence of an
external classical electric field. The coupling between the quantum model and
the classical field is taken in the electric dipole approximation. In this
regime, we show the absence of geometric phases in the interacting two-level
model in the presence of any periodic real time-dependent classical electric
field. We obtain a conservative scalar potential in the calculation of Berry's
phases of the instantaneous eigenstates of the model. For complex electric
fields, we recover the existence of geometric phases. In particular, the
geometric phases of the instantaneous eigenstates of the model in the presence
of a positive or of a negative frequency component of the monochromatic
electric field differ by an overall sign. As a check on our results, we map
this interacting two-level model onto a spin-1/2 model under the action of a
classical magnetic field. We confirm that the first one acquires Berry's phase
only in the rotating wave approximation [RWA].Comment: 11 pages, no figur
Efeito da adubação NPK em plantas jovens de paricá (Schizolobium amazonicum, Huber Ducke).
bitstream/item/27932/1/com.tec.193.pd
Poder calorífico da madeira e do carvão vegetal: lignina e carbono fixo como determinantes.
Resumo
Balanço energético da produção de Eucalyptus benthamii para uso em programas de bioenergia.
bitstream/item/16794/1/com_tec183.pd
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