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 ${\cal N}=4$ 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$^3$ embedded in the S$^5$ of the AdS$_5\times$S$^5$ 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 $\tilde{t}=0$ 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 $t\rightarrow\infty$ 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