Spin interactions and switching in vertically tunnel-coupled quantum dots

We determine the spin exchange coupling J between two electrons located in two vertically tunnel-coupled quantum dots, and its variation when magnetic (B) and electric (E) fields (both in-plane and perpendicular) are applied. We predict a strong decrease of J as the in-plane B field is increased, mainly due to orbital compression. Combined with the Zeeman splitting, this leads to a singlet-triplet crossing, which can be observed as a pronounced jump in the magnetization at in-plane fields of a few Tesla, and perpendicular fields of the order of 10 Tesla for typical self-assembled dots. We use harmonic potentials to model the confining of electrons, and calculate the exchange J using the Heitler-London and Hund-Mulliken technique, including the long-range Coulomb interaction. With our results we provide experimental criteria for the distinction of singlet and triplet states and therefore for microscopic spin measurements. In the case where dots of different sizes are coupled, we present a simple method to switch on and off the spin coupling with exponential sensitivity using an in-plane electric field. Switching the spin coupling is essential for quantum computation using electronic spins as qubits.Comment: 13 pages, 9 figure

7th Drug hypersensitivity meeting: part two

No abstract availabl

Efeitos alelopáticos de extratos vegetais na germinação, colonização micorrízica e crescimento inicial de milho, soja e feijão Allelopathic effects of plant aqueous extracts on germination, mycorrhization and Initial growth of corn, soybean and bean

Restos vegetais e liteira podem interferir no desenvolvimento de plantas. Este trabalho objetivou avaliar os efeitos alelopáticos de extratos aquosos de Pinus sp., milheto (Pennisetum americanum (L.) Leeke) e mucuna (Stizolobium aterrimum Piper & Tracy) sobre a germinação, colonização micorrízica e crescimento inicial de milho (Zea mays L.), soja (Glycine max L.) e feijão (Phaseolus vulgaris L.). Os extratos foram elaborados utilizando folhas trituradas. O experimento in vitro empregou papel Germitest umedecido com extratos ou água destilada por sete dias. O experimento em casa de vegetação teve esquema fatorial 3 x 3 x 4, com quatro repetições: três espécies vegetais (soja, milho e feijão), três extratos aquosos (Pinus, milheto e mucuna) e quatro doses de extrato (0,0; 0,5; 1,0; e 2,0 kg L-1). O substrato foi Latossolo Vermelho coletado no município de Selvíria-MS, no bioma Cerrado. Após a semeadura, os vasos receberam, a cada cinco dias, por 45 dias, 50 mL dos extratos. Para a soja, extratos de mucuna e milheto diminuíram o comprimento do hipocótilo e da radícula e os de Pinus aumentaram esses comprimentos. Em feijão, o extrato de Pinus diminuiu o comprimento do hipocótilo e da radícula, mas os extratos de mucuna e milheto aumentaram-no. O extrato do milheto reduziu a percentagem e a velocidade de germinação em feijão. Todos os extratos reduziram a colonização micorrízica e o número de esporos de fungos micorrízicos arbusculares em soja, milho e feijão.<br>Plant residues and litter may affect the plant growth. The objective of this study was to evaluate the allelopathic effects of aqueous extracts of pine (Pinus sp.), millet [Pennisetum americanum (L.) Leeke] and velvet bean (Stizolobium aterrimum Piper & Tracy) on germination, mycorrhizal colonization and initial growth of corn (Zea mays L.), soybean (Glycine max L.) and bean (Phaseolus vulgaris L.). Extracts of ground leaves were prepared. For the in vitro seven day- germination test, pH - neutral paper was previously wetted with the aqueous extracts or distilled water. The greenhouse experiment was arranged in a 3 x 3 x 4 factorial design, with four replications: three plant species (soybean, corn and bean), three aqueous extracts (Pinus, millet and velvet bean) and four extract doses (0.0; 0.5; 1.0 and 2.0 kg L-1). A Red Latossol (Oxisol) collected in Selvíria, state of Mato Grosso do Sul, in the Cerrado biome was used as substrate. After sowing in pots, 50 mL of the aqueous extracts was applied every 5 days, during 45 days. Opposite to pine, extracts of velvet bean and millet reduced the hypocotyl and root length in soybean. In common bean, pine extract reduced hypocotyl and root length, contrasting to velvet bean and millet. Millet extract decreased the germination percentage and germination rate of beans. All plant extracts reduced mycorrhization and the number of spores of arbuscular mycorrhizal fungi on soybean, maize and common bean

Palha de cana-de-açúcar associada ao herbicida trifloxysulfuron sodium + ametryn no controle de Rottboellia exaltata Sugarcane straw combined with trifloxysulfuron sodium + ametryn for Rottboellia exaltata control

O objetivo deste trabalho foi avaliar o potencial da palha da cana-de-açúcar e a associação entre ela e a mistura comercial de trifloxysulfuron sodium + ametryn no controle de Rottboellia exaltata L. O experimento foi desenvolvido na Unidade de Apoio à Pesquisa da UENF, no período de setembro a novembro de 2004. O delineamento experimental utilizado foi o de blocos casualizados com os tratamentos dispostos em esquema fatorial: cinco camadas de palha (0; 4; 8; 12 e 16 t ha-1) e cinco doses de trifloxysulfuron sodium + ametryn (0,0; 1,0; 1,5; 2,0 e 2,5 kg ha-1), em quatro repetições. Aplicaram-se os herbicidas em pós-emergência, quando as plântulas de R. exaltata estavam com altura entre 5 e 10 cm. Avaliou-se o número de plântulas aos 15, 30, 45 e 60 dias após a aplicação dos herbicidas. Determinou-se o ponto que corresponde à concentração do herbicida que inibe 50% da planta daninha (I50). Aos 60 dias, a parte aérea das plantas de R. exaltata foi coletada e transferida para estufa para avaliação da biomassa seca. A interação quantidade de palha e doses de trifloxysulfuron sodium + ametryn foi significativa. Observou-se que camadas de palha com 16 t ha-1 (sem aplicação de herbicida) e 2,5 kg ha-1 de trifloxysulfuron sodium + ametryn (isolado) foram eficientes no controle de R. exaltata. Níveis de palha entre 8 e 12 t ha-1 interceptaram o herbicida, o que elevou o valor de I50, ou seja, a concentração do herbicida para inibir 50% do crescimento da planta foi maior do que quando se utilizou 4 t de palha.<br>The objective of this work was to evaluate the sugarcane straw potential and the association between the straw and the commercial mix of the trifloxysulfuron sodium + ametryn to control itchgrass (Rottboellia exaltata L.). The experiment was developed in the Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF), Campos dos Goytacazes Rio de Janeiro State, Brazil, from September to November 2004. It was carried out in randomized blocks, with the treatments arranged in a factorial scheme: five layers of straw (0; 4; 8; 12 e 16 t ha-1) and five doses of trifloxysulfuron sodium + ametryn (0,0; 1,0; 1,5; 2,0 e 2,5 kg ha-1), with four replications. The herbicide was applied in post-emergence, when weeds (R. exaltata) height was between 5 and 10 cm. Number of weeds was evaluated at 15, 30, 45 and 60 days after herbicide application. The herbicide concentration that inhibits 50% of the weed emergency (I50) was determined. In the sixty day, the itchgrass plants were collected and dry biomass was determined. The interaction between straw quantity and doses of trifloxysulfuron sodium + ametryn was significant. Straw layer of 16 tha-1 without herbicide addition was efficient to control R. exaltata and the herbicide trifloxysulfuron sodium + ametryn at 2,5 kg ha-1 used alone was efficient to control this weed. Straw levels between 8 and 12 t ha-1 intercepted the herbicide and consequently, increased the I50 value. In other words, the concentration of the herbicide to inhibit 50% of the weeds growth was greater when there were 8 and 12 t ha-1 than when there was 4 t ha-1 of straw