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In this paper, spherical core@shell (multi-Fe3O4@C) magnetic beads ( D\textrm {MB}\sim 100 nm), composed of several single cores of magnetite nanoparticles (MNPs) ( D\textrm {single-core}\sim 15 nm) surrounded by a wide carbon shell ( $\delta \sim 20$ nm), have been synthesized by a solvothermal procedure in organic solvent that provides good control over size, shape, and crystallinity of the iron oxide nanostructures. Large colloidal stability and good biocompatibility are ensured by the carbon shell, whose thickness can be tuned by the synthesis conditions, and endow the NP with robust stability under extreme physicochemical conditions (acid and base media, or high temperatures and pressures). In vitro testing with rat mesenchymal cells shows high stability and high labeling capacities combined with poly-L-lysine for further cell tracking applications. The so-obtained multi-core MNPs, present: 1) superparamagnetic behavior with a saturation magnetization around 70 emu/g Fe3O4 at 25 kOe and room temperature and 2) negligible heating by magnetic hyperthermia procedure and an enhanced magnetic resonance imaging (MRI) response. The simultaneous fulfillment of all the previously listed properties makes these multi- Fe3O4@C NPs ideal candidates for MRI brain multifunctional applications, where deleterious heating of tissues is a major restriction that ends up in the rejection of, otherwise, magnetically and chemically well-engineered NPs. [ABSTRACT FROM PUBLISHER]

Magnetic hyperthermia (MH) applications based on superparamagnetic nanoparticles are behind many theragnostic developments, some of which are entering into a stage of commercial maturity (see Magforce). Theoretical frames, such as the well-established Rosensweig formulation, rely on studies performed on ideal ferrofluids in which viscosity, concentration, or pH are homogeneous throughout the sample. However, biological environments are deeply complex, dynamic, and heterogeneous, making the nanobiointeraction the leading variable controlling the MH performance. Biological MH applications depend on a larger set of parameters than those currently studied: agglomeration, type of coating, viscosity, and local concentration are marginally studied and produce intricate and nonlinear responses in biological MH applications. [ABSTRACT FROM PUBLISHER]

In this work, we report the effectiveness of magnetic hyperthermia as a potential disinfection method against food spoilage microorganisms. High structural-magnetic quality magnetite nanoparticles have been found to be effective against bacterial microorganisms in solution under an oscillating magnetic field. Samples containing both magnetite nanoparticles and Pseudomonas fluorescens cells in aqueous solution have been subjected to an alternating magnetic field of chosen amplitude 100 Oe with frequency of 873 kHz for different times, achieving different maximum temperatures ranging from 35 ^\circC to 55 ^\circC. The subsequent colony forming units count evidenced an important decreasing of the cell survival with temperature in comparison to a conventional direct heating, ending in the total eradication of the microorganisms in relatively short times (\sim8 min). This ability of magnetic hyperthermia to control bacteria cells constitutes a novel contribution to the finding of new useful applications of hyperthermia different from biomedicine. [ABSTRACT FROM AUTHOR]

In this work we report an irreversible behavior in the magnetization of oleic acid (OA)-coated magnetite nanoparticles (NPs) at high temperature. On one hand, when the sample is heated-up, an irreversible magnetization drop is observed at 550 K, while the Curie temperature (Tc\approx 840\ K) remains close to that of bulk magnetite. On the other hand, a significant reduction of the magnetic moment has been found after heating and cooling the sample above and below its Curie temperature, respectively. Both magnetic features have been also observed in other surface modified magnetite nanoparticles [e.g., polyvynil pyrrolidone (PVP)-coated]. However, no reduction of the magnetic moment upon a heating-cooling cycle has been found in ligand-free magnetite nanoparticles. This fact suggests that surface effects derived from the OA-coating could be the origin of such reduction of the magnetic moment, as a consequence of thermal decomposition of the organic layer surrounding the nanoparticle and the subsequent loss of the magnetic surface order. This feature could be an important factor for those applications requiring high temperatures. [ABSTRACT FROM AUTHOR]

This paper presents a resonant single-ended-primary-inductor-converter (SEPIC) converter and control method suitable for high frequency (HF) and very high frequency (VHF) dc-dc power conversion. The proposed design provides high efficiency over a wide input and output voltage range, up-and-down voltage conversion, small size, and excellent transient performance. In addition, a resonant gate drive scheme is presented that provides rapid startup and low-loss at HF and VHF frequencies. The converter regulates the output using an ON-OFF control scheme modulating at a fixed frequency (170 kHz). This control method enables fast transient response and efficient light-load operation while providing controlled spectral characteristics of the input and output waveforms. A hysteretic override technique is also introduced which enables the converter to reject load disturbances with a bandwidth much greater than the modulation frequency, limiting output voltage disturbances to within a fixed value. An experimental prototype has been built and evaluated. The prototype converter, built with two commercial vertical MOSFETs, operates at a fixed switching frequency of 20 MHz, with an input voltage range of 3.6-7.2 V, an output voltage range of 3-9 V, and an output power rating of up to 3 W. The converter achieves higher than 80% efficiency across the entire input voltage range at nominal output voltage and maintains good efficiency across the whole operating range. [ABSTRACT FROM AUTHOR]

This paper describes the development of an analytical method for predicting the steady-state response of an integrated “pump-motor-containment.” These pumps employ a canned line-start permanent-magnet motor providing synchronous operation and high load efficiencies. The steady-state performance of the pump motor is assessed under different operating conditions. A laboratory prototype machine is used to validate the model. [ABSTRACT FROM AUTHOR]

The application of Optical Wireless Links to intra-Spacecraft communications (OWLS) is presented here. This work summarizes ten years of developments, ranging from basic optoelectronic parts and front-end electronics, to different in-orbit demonstrations. Several wireless applications were carried out in representative environments at ground level, and on in-flight experiments. A completely wireless satellite will be launched at the beginning of 2010. The benefits of replacing standard data wires and connectors with wireless systems are: mass reduction, flexibility, and simplification of the Assembly, Integration and Tests phases (AIT). However, the Aerospace and Defense fields need high reliability solutions. The use of COTS (Commercial-Off-The-Shelf) parts in these fields require extensive analyses in order to attain full product assurance. The current commercial optical wireless technology needs a deep transformation in order to be fully applicable in the aforementioned fields. Finally, major breakthroughs for the implementation of optical wireless links in Space will not be possible until dedicated circuits such as mixed analog/digital ASICs are developed. Once these products become available, it will also be possible to extend optical wireless links to other applications, such as Unmanned Air and Underwater Vehicles (UAV and UUV). The steps taken by INTA to introduce Optical Wireless Links in the Space environment are presented in this paper. [ABSTRACT FROM AUTHOR]

The nature of the magnetic phase transition of the itinerant ferromagnet CoS2 has been studied. We have measured high-pressure X-ray diffraction and magnetization, at different temperatures and fields. Our results are discussed on the basis of a thermodynamic model applicable to itinerant ferromagnets with strong spin fluctuations. [ABSTRACT FROM AUTHOR]

Studies the structural and magnetic properties of colloids consisting of different concentrations of magnetite particles dispersed in kerosene. Preparation of samples and experimental techniques; Experimental results; Discussion.