Magnetic-field effects in defect-controlled ferromagnetic Ga_{1-x}Mn_xAs semiconductors

We have studied the magnetic-field and concentration dependences of the magnetizations of the hole and Mn subsystems in diluted ferromagnetic semiconductor Ga_{1-x}Mn_xAs. A mean-field approximation to the hole-mediated interaction is used, in which the hole concentration p(x) is parametrized in terms of a fitting (of the hole effective mass and hole/local moment coupling) to experimental data on the Tc critical temperature. The dependence of the magnetizations with x, for a given temperature, presents a sharply peaked structure, with maxima increasing with applied magnetic field, which indicates that application to diluted-magnetic-semiconductor devices would require quality-control of the Mn-doping composition. We also compare various experimental data for Tc(x) and p(x) on different Ga_{1-x}Mn_xAs samples and stress the need of further detailed experimental work to assure that the experimental measurements are reproducible.Comment: RevTeX 4, 3 two-column pages, 4 colour figures; to appear in J Appl Phy

Exponential behavior of the interlayer exchange coupling across non-magnetic metallic superlattices

It is shown that the coupling between magnetic layers separated by non-magnetic metallic superlattices can decay exponentially as a function of the spacer thickness $N$, as opposed to the usual $N^{-2}$ decay. This effect is due to the lack of constructive contributions to the coupling from extended states across the spacer. The exponential behavior is obtained by properly choosing the distinct metals and the superlattice unit cell composition.Comment: To appear in Phys. Rev.

Scaling relations for magnetic nanoparticles

A detailed investigation of the scaling relations recently proposed by [J. d'Albuquerque e Castro, D. Altbir, J. C. Retamal, and P. Vargas, Phys. Rev. Lett. 88, 237202 (2002)] to study the magnetic properties of nanoparticles is presented. Analytical expressions for the total energy of three characteristic internal configurations of the particles are obtained, in terms of which the behavior of the magnetic phase diagram for those particles upon scaling of the exchange interaction is discussed. The exponent $\eta$ in scaling relations is shown to be dependent on the geometry of the vortex core, and results for specific cases are presented.Comment: 6 pages, 4 figure

Static and dynamical properties of elliptic quantum corrals

Due to their focalizing properties, elliptic quantum corrals present very interesting physical behaviors. In this work, we analyze static and dynamical properties of these systems. Results are presented for realistic values of the parameters, which might be useful for comparison with experiments. We study noninteracting corrals and their response to several kinds of external perturbations, observing that, for realistic values of the Fermi level, the dynamics involves only a few number of excited states, making the system quite robust with respect to possible sources of decoherence. We also study the system in the presence of two S=1/2 impurities located at its foci, which interact with the electrons of the ellipse via a superexchange interaction J. This system is diagonalized numerically and properties such as the spin gap and spin-spin static and dynamical correlations are studied. We find that, for small J, both spins are locked in a singlet or triplet state, for even or odd filling, respectively, and its spin dynamics consists mainly of a single peak above the spin gap. In this limit, we can define an effective Heisenberg Hamiltonian to describe the low-energy properties. For larger J, more states are involved and the localized spins decorrelate in a manner similar to the Ruderman-Kittel-Kasuya-Yosida-Kondo transition for the two-impurity problem.Comment: 6 pages, 10 Encapsulated Postscript figure

Prophylactic application of laser light restores L-FABP expression in the livers of rats submitted to partial ischemia

OBJECTIVES: The objective of the present study was to evaluate the protective effect of pre-conditioning treatment with laser light on hepatic injury in rats submitted to partial ischemia using mitochondrial function and liver fatty acid binding protein as markers. METHODS: Rats were divided into four groups (n=5): 1) Control, 2) Control + Laser, 3) Partial Ischemia and 4) Partial Ischemia + Laser. Ischemia was induced by clamping the hepatic pedicle of the left and middle lobes of the liver for 60 minutes. Laser light at 660 nm was applied to the liver immediately prior to the induction of ischemia at 22.5 J/cm2 , with 30 seconds of illumination at five individual points. The animals were sacrificed after 30 minutes of reperfusion. Blood and liver tissues were collected for analysis of mitochondrial function, determination of malondialdehyde and analysis of fatty acid binding protein expression by Western blot. RESULTS: Mitochondrial function decreased in the Partial Ischemia group, especially during adenosine diphosphate-activated respiration (state 3), and the expression of fatty acid binding protein was also reduced. The application of laser light prevented bioenergetic changes and restored the expression of fatty acid binding protein. CONCLUSION: Prophylactic application of laser light to the livers of rats submitted to partial ischemia was found to have a protective effect in the liver, with normalization of both mitochondrial function and fatty acid binding protein tissue expression

An exploration of how the profile of crowdfunding project owners is related to their results

The aim of this dissertation is to understand how the profile of crowdfunding project owners is related to their results. Crowdfunding is a phenomenon that has developed over the last decade, and thereby there is already extent literature about this interesting topic, on which the literature review relies. A survey was administered to crowdfunding project owners to analyze how their profile, in terms of risk and communication, would impact their results. The findings are that creators with recent experience working for someone else reach better results than entrepreneurs who have been self-employed before engaging in a crowdfunding campaign. Social Media were confirmed as being used by the large majority of founders, and although it was not possible to prove, nor disprove, their effectiveness, dynamism and direct communication were confirmed to be prevalent in all campaigns. O objetivo desta dissertação é compreender o perfil dos criadores de projectos em plataformas de crowdfunding. O crowdfunding é um fenómeno que se tem desenvolvido ao longo da última década, e consequentemente existe já alguma literatura sobre este tema, na qual se baseia a literature review. Foi enviado um questionário dirigido a criadores de projectos de crowdfunding de modo a analisar como é que o seu perfil, quer em termos de tolerância ao risco quer de capacidade de comunicação, afeta os seus resultados. As conclusões que se tiram são as de que os criadores de projectos que tiveram experiências recentes de trabalho por contra de outrem alcançam melhores resultados do que aqueles que trabalhavam por conta própria antes de iniciar o projecto. Quanto ao uso de social media foi confirmado pela larga maioria dos criadores de projectos, e apesar de não ter sido possível provar a sua eficiência, o dinamismo e um estilo de comunicação mais direto mostraram ter efeitos positivos nas campanhas de angariação