Validity of the N\'{e}el-Arrhenius model for highly anisotropic Co_xFe_{3-x}O_4 nanoparticles

We report a systematic study on the structural and magnetic properties of Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between $5$ to $25$ nm, prepared by thermal decomposition of Fe(acac)_{3} and Co(acac)_{2}. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures ($42$ K \leqq $T_B$ $\leqq 345$ K for $5 \leqq$ d $\leqq 13$ nm ) and large coercive fields ($H_C \approxeq 1600$ kA/m for $T = 5$ K). The smallest particles ($=5$ nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the N\'{e}el-Arrhenius relaxation framework without the need of ad-hoc corrections, by including the thermal dependence of the magnetocrystalline anisotropy constant $K_1(T)$ through the empirical Br\"{u}khatov-Kirensky relation. This approach provided $K_1(0)$ values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times ($\tau_0 \simeq 10^{-10}$ s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener\'{}s relation between $K_1(T)$ and M(T)

GAS TURBINE PERFORMANCE ANALYSIS OPERATING WITH LOWHEATING VALUE FUELS

Usually, power plants work with gas turbine designed to fire natural gas; however, there are possibilities to use other types of gaseous fuels with different calorific values that may be available close to the power plant site. These fuels can be gases obtained from steel (from blast furnaces and coking plants), from gasification processes of coal or biomass, among others. In this work, a gas turbine performance was evaluated at different operational conditions in order to verify the technical feasibility of burning low calorific value fuels. A gas turbine designed to operate with natural gas was used as a reference, the model was built and the performance evaluated at design and off-design conditions using a commercial computer program, GasTurb 11®. A good agreement was obtained between the model operating with natural gas and the available data from open literature, at design and off-design conditions. The model was simulated using low heating value fuels under the same conditions established for natural gas. A reduction in compressor’s surge margin was identified when using low heating value fuels as well as an increase in power output. Therefore, for safe operation a strategy for recovering the surge margin was adopted. In this study the control strategy adopted was bleed air at the compressor discharge. This control strategy presents a technical viability and ensures that the gas turbine operates with the same surge margin level as when using natural gas

Quantum key distribution session with 16-dimensional photonic states

The secure transfer of information is an important problem in modern telecommunications. Quantum key distribution (QKD) provides a solution to this problem by using individual quantum systems to generate correlated bits between remote parties, that can be used to extract a secret key. QKD with D-dimensional quantum channels provides security advantages that grow with increasing D. However, the vast majority of QKD implementations has been restricted to two dimensions. Here we demonstrate the feasibility of using higher dimensions for real-world quantum cryptography by performing, for the first time, a fully automated QKD session based on the BB84 protocol with 16-dimensional quantum states. Information is encoded in the single-photon transverse momentum and the required states are dynamically generated with programmable spatial light modulators. Our setup paves the way for future developments in the field of experimental high-dimensional QKD.Comment: 8 pages, 3 figure

Eficiência no manejo reprodutivo: sucesso no rebanho de cria.

Aspectos sanitário na implementação da estação de monta. Nutrição e reprodução de bovinos. Manejo da estação de monta. Sincronizacao do cio em bovinos de corte. Aspectos fisiológicos da fecundação e estabelecimento da prenhez.bitstream/item/104815/1/Eficiencia-no-manejo-reprodutivo.pdfCNPGC

Dielectric lens antennas

Dielectric lens antennas are attracting a renewed interest for millimeter- and submillimeter-wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications. This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discussion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods, and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas

Wideband and high-selectivity dual-band filter for Ka-Band satellite antennas

A dual-band miniaturized Ka-band filter is presented, taking advantage of transmission in cut-off rectangular waveguides periodically loaded in the E-plane with Split-Ring Resonators (SRRs). High selectivity, wide bandwidth and high out-of-band rejection are achieved in a compact form factor. The use of SRRs in a waveguide configuration proves to be a valid and promising solution for the design of dual-band filters. The filter is specifically designed for Ka-band and a prototype was manufactured and its performance measured, providing a reasonably flat transmission at both 20 and 30 GHz sub-bands. For both bands the power roll-off rate is higher than 55 dB/decade, translating into a sharper than 10 dB drop per 0.2 GHz in a 38 × 6.6 × 4.5 mm3 device. The filter half-power bandwidth is B_20 = 1.1 GHz at 20 GHz (18.4 - 19.5 GHz) and B_30 = 1.2 GHz at 30 GHz (27.8 - 29.0 GHz).info:eu-repo/semantics/acceptedVersio