3,166 research outputs found
Quantum Interference of Force
We show that a quantum particle subjected to a positive force in one path of
a Mach-Zehnder interferometer and a null force in the other path may receive a
negative average momentum transfer when it leaves the interferometer by a
particular exit. In this scenario, an ensemble of particles may receive an
average momentum in the opposite direction of the applied force due to quantum
interference, a behavior with no classical analogue. We discuss some
experimental schemes that could verify the effect with current technology, with
electrons or neutrons in Mach-Zehnder interferometers in free space and with
atoms from a Bose-Einstein condensate.Comment: 5 figures. Accepted in Quantum on 2018-12-0
Finite-size, magnetic and chemical-potential effects on first-order phase transitions
We perform a study about effects of an applied magnetic field and a finite
chemical potential on the size-dependent phase structure of a first-order
transition. These effects are introduced by using methods of quantum fields
defined on toroidal spaces, and we study in particular the case of two
compactified dimensions, imaginary time and a spatial one (a heated film). It
is found that for any value of the applied field, there is a minimal size of
the system, independent of the chemical potential, below which the transition
disappears.Comment: 19 pages, 3 figures, version accepted for publication in Phys. Lett.
Suscetibilidade da soja a percevejos na fase anterior ao desenvolvimento das vagens.
O objetivo deste trabalho foi avaliar os efeitos das populaçÔes de percevejos Euschistus heros (F.) e Piezodorus guildinii (West.) nas lavouras de soja nos meses de novembro/dezembro, antes do aparecimento das vagens nas plantas. Foram realizados experimentos em casa de vegetação e no campo, comparando-se infestaçÔes no perĂodo vegetativo e reprodutivo da cultura. As plantas de soja, mesmo sob o ataque de pesadas infestaçÔes de percevejos (atĂ© 8 por planta), no perĂodo vegetativo e no florescimento, nĂŁo sofreram reduçÔes significativas no rendimento. A qualidade das sementes foi semelhante entre os tratamentos e entre as espĂ©cies. No estĂĄdio R4, o nĂșmero mĂ©dio de vagens chochas foi diretamente proporcional ao aumento do nĂșmero de percevejos por planta. No campo, as plantas com atĂ© quatro percevejos por metro, no final do perĂodo vegetativo-floração, tiveram rendimentos mĂ©dios e qualidade de sementes semelhantes aos das plantas livres de insetos. No perĂodo R5-R6, para as duas espĂ©cies de percevejos, o nĂșmero de grĂŁos picados e inviabilizados cresceram, e os rendimentos mĂ©dios decresceram com o aumento da população, tendo-se obtido, para a qualidade da soja, um dano duas vezes maior para a espĂ©cie P. guildinii em relação a E. heros. InfestaçÔes desses percevejos, na fase vegetativa-floração, nĂŁo causam reduçÔes no rendimento e na qualidade das sementes de soja
Investigations on the tolerance of several trees to submergence in blackwater (igapĂł) and whitewater (vĂĄrzea) inundation forests near Manaus, Central Amazonia
Physiological, cytological, and anatomical studies were carried out on the tolerance of trees to submergence in blackwater and whitewater inundation forests, locally called IgapĂł and VĂĄrzea, respectively. For this purpose, the leaves of several abundant tree species were investigated to determine their functional capability after submersion during the inundation phase. Their performance was compared with that of genetically identical leaves on the same branch that had sprouted after the flood water had receded. The studies showed that, in spite of submersion for up to several months and sometimes even in spite of the fact that they were still partially under water, these leaves had full functional capability at the beginning of the terrestrial phase, as determined by examination under the light and scanning electron microscope, the water potential, and the CO2 exchange
Controle biolĂłgico da podridĂŁo de raĂzes causada por Pythium spp. em cultivos hidropĂŽnicos.
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