On the energy conversion efficiency in magnetic hyperthermia applications: A new perspective to analyze the departure from the linear regime

The success of magnetic hyperthermia cancer treatments rely strongly on the magnetic properties of the nanoparticles and their intricate dependence on the externally applied field. This is particularly more so as the response departs from the low field linear regime. In this paper we introduce a new parameter, referred to as the efficiency in converting electromagnetic energy into thermal energy, which is shown to be remarkably useful in the analysis of the system response, especially when the power loss is investigated as a function of the applied field amplitude. Using numerical simulations of dynamic hysteresis, through the stochastic Landau-Lifshitz model, we map in detail the efficiency as a function of all relevant parameters of the system and compare the results with simple-yet powerful-predictions based on heuristic arguments about the relaxation time. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4705392]

Study of the Influence of Localized Vibrational Modes in Charge Transport Properties at Nanoscale Systems.

In molecular and atomic devices the interaction between electrons and ionic vibrations has an important role in electronic transport. The electron-phonon coupling can cause the loss of the electron's phase coherence, the opening of new conductance channels and the suppression of purely elastic ones. From the technological viewpoint phonons might restrict the efficiency of electronic devices by energy dissipation, causing heating, power loss and instability. The state of the art in electron transport calculations consists in combining ab initio calculations via Density Functional Theory (DFT) with Non-Equilibrium Green's Function formalism (NEGF). In order to include electron-phonon interactions, one needs in principle to include a self-energy scattering term in the open system Hamiltonian which takes into account the effect of the phonons over the electrons and vice versa. Nevertheless this term could be obtained approximately by perturbative methods. In the First Born Approximation one considers only the first order terms of the electronic Green's function expansion. In the Self-Consistent Born Approximation, the interaction self-energy is calculated with the perturbed electronic Green's function in a self-consistent way. In this work we describe how to incorporate the electron-phonon interaction to the SMEAGOL program (Spin and Molecular Electronics in Atomically Generated Orbital Landscapes), an ab initio code for electronic transport based on the combination of DFT + NEGF. This provides a tool for calculating the transport properties of materials' specific system, particularly in molecular electronics. Preliminary results will be presented, showing the effects produced by considering the electron-phonon interaction in nanoscale devices.

Nonoriented Electrical Steels

The physical origins of the magnetic properties of nonoriented electrical steels; its relations to microstructural features like grain size, nonmetallic inclusions, dislocation density distribution, crystallographic texture, and residual stresses; and its processing by cold rolling and annealing are overviewed, using quantitative relations whenever available.

Experimental study of the He stopping power into Al2O3 films

In the present work, we report experimental results of He stopping power into Al2O3 films by using both transmission and Rutherford backscattering techniques. We have performed measurements along a wide energy range, from 60 to 3000 key, covering the maximum stopping range. The results of this work are compared with previously published dap-, showing a good agreement for the high-energy range, but evidencing discrepancies in the low-energy region. The existing theories follow the same tendency: good theoretical-experimental agreement for higher energies, but they failed to reproduce previous and present results in the low energy regime. On the other hand it is interesting to note that the semi-empirical SRIM code reproduces quite well the present data. (C) 2012 Elsevier B.V. All rights reserved.

Algebraic-graph method for identification of islanding in power system grids

In this paper, a new algebraic-graph method for identification of islanding in power system grids is proposed. The proposed method identifies all the possible cases of islanding, due to the loss of a equipment, by means of a factorization of the bus-branch incidence matrix. The main features of this new method include: (i) simple implementation, (ii) high speed, (iii) real-time adaptability, (iv) identification of all islanding cases and (v) identification of the buses that compose each island in case of island formation. The method was successfully tested on large-scale systems such as the reduced south Brazilian system (45 buses/72 branches) and the south-southeast Brazilian system (810 buses/1340 branches). (C) 2011 Elsevier Ltd. All rights reserved.

Stopping power and depth dose profile of H+ and He+ ion beams in hydroxyapatite thin films.

Hadron therapy is a promising technique to treat deep-seated tumors. For an accurate treatment planning, the energy deposition in the soft and hard human tissue must be well known. Water has been usually employed as a phantom of soft tissues, but other biomaterials, such as hydroxyapatite (HAp), used as bone substitute, are also relevant as a phantom for hard tissues. The stopping power of HAp for H+ and He+ beams has been studied experimentally and theoretically. The measurements have been done using the Rutherford backscattering technique in an energy range of 450-2000 keV for H+ and of 400-5000 keV for He+ projectiles. The theoretical calculations are based in the dielectric formulation together with the MELF-GOS (Mermin Energy-Loss Function – Generalized Oscillator Strengths) method [1] to describe the target excitation spectrum. A quite good agreement between the experimental data and the theoretical results has been found. The depth dose profile of H+ and He+ ion beams in HAp has been simulated by the SEICS (Simulation of Energetic Ions and Clusters through Solids) code [2], which incorporates the electronic stopping force due to the energy loss by collisions with the target electrons, including fluctuations due to the energy-loss straggling, the multiple elastic scattering with the target nuclei, with their corresponding nuclear energy loss, and the dynamical charge-exchange processes in the projectile charge state. The energy deposition by H+ and He+ as a function of the depth are compared, at several projectile energies, for HAp and liquid water, showing important differences.