5,003 research outputs found
Confinement of two-dimensional excitons in a non-homogeneous magnetic field
The effective Hamiltonian describing the motion of an exciton in an external
non-homogeneous magnetic field is derived. The magnetic field plays the role of
an effective potential for the exciton motion, results into an increment of the
exciton mass and modifies the exciton kinetic energy operator. In contrast to
the homogeneous field case, the exciton in a non-homogeneous magnetic field can
also be trapped in the low field region and the field gradient increases the
exciton confinement. The trapping energy and wave function of the exciton in a
GaAs two-dimensional electron gas for specific circular magnetic field
configurations are calculated. The results show than excitons can be trapped by
non-homogeneous magnetic fields, and that the trapping energy is strongly
correlated with the shape and strength of the non-homogeneous magnetic field
profile.Comment: 9 pages, 12 figure
Exciton trapping in magnetic wire structures
The lateral magnetic confinement of quasi two-dimensional excitons into wire
like structures is studied. Spin effects are take into account and two
different magnetic field profiles are considered, which experimentally can be
created by the deposition of a ferromagnetic stripe on a semiconductor quantum
well with magnetization parallel or perpendicular to the grown direction of the
well. We find that it is possible to confine excitons into one-dimensional (1D)
traps. We show that the dependence of the confinement energy on the exciton
wave vector, which is related to its free direction of motion along the wire
direction, is very small. Through the application of a background magnetic
field it is possible to move the position of the trapping region towards the
edge of the ferromagnetic stripe or even underneath the stripe. The exact
position of this 1D exciton channel depends on the strength of the background
magnetic field and on the magnetic polarisation direction of the ferromagnetic
film.Comment: 10 pages, 7 figures, to be published in J. Phys: Condens. Matte
The Eccentric Binary Millisecond Pulsar in NGC 1851
PSR J0514-4002A is a 5-ms pulsar is located in the globular cluster NGC 1851;
it belongs to a highly eccentric (e = 0.888) binary system. It is one of the
earliest known examples of a numerous and fast-growing class of eccentric
binary MSPs recently discovered in globular clusters. Using the GBT, we have
obtained a phase-coherent timing solution for the pulsar, which includes a
measurement of the rate of advance of periastron: 0.01289(4) degrees per year,
which if due completely to general relativity, implies a total system mass of
2.453(14) solar masses. We also derive m_p 0.96
solar masses. The companion is likely to be a massive white dwarf star.Comment: 3 pages, including 2 figures. To appear in the proceedings of "40
Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17,
2007, McGill University, Montreal, Canad
Production, breeding and potential of cowpea crop in Brazil.
About 50 years ago cowpea was reported as a relatively minor tropical legume. However, in the last years, it has been emerging as one of the most important food legume of the 21st century (SINGH, 2010). Brazil is not out of this panorama. Brazilian agriculture is undergoing major technological changes and, in addition, globalization in agribusiness has caused impacts on the production chain of several crops, particularly those heavily dependent on the use of a large volume of agricultural inputs, mainly fertilizers and pesticides. Such crops have had a higher production cost each year. On the other hand, this situation has brought new opportunities. Business farmers have sought new alternatives for their production arrangements. In this context cowpea constitutes one of the best options.bitstream/item/85620/1/Doc-216-Production.pd
Ocorrência de ferrugem em folhas de ata e atemóia no Estado do Ceará.
bitstream/item/33792/1/RT10009.pd
Doenças emergentes da ata ou pinha (Annona squamosa L.) no estado do Ceará.
bitstream/item/48115/1/COT11006.pd
Organic cheese market (Río Cuarto, Argentina). Consumer attitudes
The consumer attitudes and buying behaviour to ecological cheese, in Río Cuarto city were studied. This research was carried out as a semi -structured survey, based on personal interviews and taste panels. Forty-four percent of the consumers showed willingness to pay up to a 25 to 35 percent premium price for organic foods. Flavour and ecological nature of the product were the chief motivations for buying behaviour.Se estudió mediante encuestas semiestructuradas, la actitud de los consumidores respecto a un queso ecológico y su valoración, en la ciudad de Río Cuarto. El 44 p.100 de los consumidores manifestó intención de pagar desde un 25 a 35 p.100 de sobreprecio por el producto ecológico. Entre las principales motivaciones para la compra están el sabor (91 p.100) y la naturaleza ecológica del producto (81 p.100)
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