671 research outputs found
Hole spin injection from a GaMnAs layer into GaAs-AlAs-InGaAs resonant tunneling diodes
We have investigated the polarization-resolved electroluminescence (EL) of a p–i–n GaAs/AlAs/InGaAs resonant tunneling diode (RTD) containing a GaMnAs (x = 5%) spin injector under high magnetic fields. We demonstrate that under hole resonant tunneling condition, the GaMnAs contact acts as an efficient spin-polarized source for holes tunneling through the device. Polarization degrees up to 80% were observed in the device around the hole resonance at 2 K under 15 T. Our results could be valuable for improving the hole-spin injection in GaMnAs-based spintronic devices
Giant Gravitons - with Strings Attached (III)
We develop techniques to compute the one-loop anomalous dimensions of
operators in the super Yang-Mills theory that are dual to open
strings ending on boundstates of sphere giant gravitons. Our results, which are
applicable to excitations involving an arbitrary number of open strings,
generalize the single string results of hep-th/0701067. The open strings we
consider carry angular momentum on an S embedded in the S of the
AdSS background. The problem of computing the one loop anomalous
dimensions is replaced with the problem of diagonalizing an interacting Cuntz
oscillator Hamiltonian. Our Cuntz oscillator dynamics illustrates how the
Chan-Paton factors for open strings propagating on multiple branes can arise
dynamically.Comment: 66 pages; v2: improved presentatio
A review of the applications of SAR polarimetry and polarimetric interferometry - an ESA funded study
International audienc
Soil organisms in organic and conventional cropping systems.
Apesar do crescente interesse pela agricultura orgânica, são poucas as informações de pesquisa disponíveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrófico foram comparados os efeitos de sistemas de cultivo orgânico e convencional, para as culturas do tomate (Lycopersicum esculentum) e do milho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populações de fungos,bactérias e actinomicetos, determinadas pela contagem de colônias em meio de cultura, foram semelhantes para os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO2, manteve-se superior no sistema orgânico, sendo que em determinadas avaliações foi o dobro da evolução verificada no sistema convencional. O número de espécimes de minhoca foi praticamente dez vezes maior no sistema orgânico. Não foi observada diferença na taxa de decomposição de matéria orgânica entre os dois sistemas. De modo geral, o número de indivíduos de microartrópodos foi superior no sistema orgânico do que no sistema convencional, refletindo no maior índice de diversidade de Shannon. As maiores populações de insetos foram as da ordem Collembola, enquanto para os ácaros a maior população foi a da superfamília Oribatuloidea. Indivíduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foram ocasionalmente coletados e de forma similar entre os sistemas
Non-vacuum Solutions of Bianchi Type VI_0 Universe in f(R) Gravity
In this paper, we solve the field equations in metric f(R) gravity for
Bianchi type VI_0 spacetime and discuss evolution of the expanding universe. We
find two types of non-vacuum solutions by taking isotropic and anisotropic
fluids as the source of matter and dark energy. The physical behavior of these
solutions is analyzed and compared in the future evolution with the help of
some physical and geometrical parameters. It is concluded that in the presence
of isotropic fluid, the model has singularity at and represents
continuously expanding shearing universe currently entering into phantom phase.
In anisotropic fluid, the model has no initial singularity and exhibits the
uniform accelerating expansion. However, the spacetime does not achieve
isotropy as in both of these solutions.Comment: 20 pages, 5 figures, accepted for publication in Astrophys. Space Sc
The INTERFRUTA II project and the study of phytossanitary problems that affect Azorean fruit orchards and vineyards
The INTERFRUTA project is financed by the
European Commission Interreg III-B Programme and was developed for the islands of
“Madeira”, “Tenerife” and “Terceira”, for the improvement of fruit and vineyard
production in these three Atlantic regions. The project goal is a better knowledge of the
phytossanitary problems that affect apples, bananas, chestnut and vineyards, applying
methods that will contribute to solutions based on the survey of key pests, diseases and
beneficial organisms. In the three fruit crops and vineyards analyzed, the methodology
used was mainly direct observation of predefined parts of each plant (such as leaves and
flowers) on which pests might be expected to occur. The key pest C. capitata was
monitored as adults using sexual lures in a net of traps around the island of “Terceira”
up to 200 meters altitude. The beneficial insect survey was conducted using the beating
technique. For diseases, a direct sampling was carried out by the observation of 10 %
of the plants in each orchard or vineyard plot looking for visible symptoms. In apples
and vineyards, flowers and branches were collected and tested for microorganisms using
serologic and molecular techniques (Elisa and PCR). In banana plantations, the most
damaging pests were banana weevil, thrips and a fungi complex that causes symptoms
similar to Fusarium wilt. In chestnut, the pest that causes the most severe damage,
affecting around 40 % of the nuts produced, is the Chestnut tortrix, but there were some
difficulties in identifying which of the three known species was present in the Azores
islands. In vineyards, diseases that are most frequent and important include grapevine
downy mildew, powdery mildew and Botrytis. Invertebrate pests included grape
leafhoppers, thrips and eriophyid mites. The European vine moth was also surveyed but
none were found and is still not present. In apple orchards the most important problems
were thrips, mites, oriental fruit moth and codling moth. Anarsia lineatella Zeller, the
peach twig borer, was not detected and new Eriophyid species have been recorded for
the first time in the Azores as a result of the surveys. With the information collected it
was possible to create a phytossanitary diagnostic database for the Macaronesian islands
(PROFITOMAC) on the project internet pages (www.interfruta.uac.pt), to help users to
identify problems that affect the studied cultures
The First Magnetic Fields
We review current ideas on the origin of galactic and extragalactic magnetic
fields. We begin by summarizing observations of magnetic fields at cosmological
redshifts and on cosmological scales. These observations translate into
constraints on the strength and scale magnetic fields must have during the
early stages of galaxy formation in order to seed the galactic dynamo. We
examine mechanisms for the generation of magnetic fields that operate prior
during inflation and during subsequent phase transitions such as electroweak
symmetry breaking and the quark-hadron phase transition. The implications of
strong primordial magnetic fields for the reionization epoch as well as the
first generation of stars is discussed in detail. The exotic, early-Universe
mechanisms are contrasted with astrophysical processes that generate fields
after recombination. For example, a Biermann-type battery can operate in a
proto-galaxy during the early stages of structure formation. Moreover, magnetic
fields in either an early generation of stars or active galactic nuclei can be
dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also
downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd
Golden flaxseed and its byproducts in beef patties: physico-chemical evaluation and fatty acid profile
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