Modeling of Microwave Semiconductor Diodes

The paper deals with the multi-physical mode-ling of microwave diodes. The electrostatic, drift-diffusion and thermal phenomena are considered in the physical model of the components. The basic semiconductor equati-ons are summarized, and modeling issues are discussed. The simulations of the Gunn Effect in transferred electron devices and the carrier injection effect in PIN diodes are investigated and discussed. The analysis was performed in COMSOL Multiphysics using the finite element method

Transmission Line on Semiconductor Substrate with Distributed Amplification

In order to compensate losses in metal strips, an active microstrip line on a semiconductor substrate is proposed, and its finite element model is presented. The active medium is provided by A3B5 semiconductor in highintensity electric field. The simple model of the active media is developed and used for calculation of the propagation properties of the fundamental mode and for the thermal analysis of the device. The problem of system self-oscillation is discussed and empirical stability criteria are introduced. A proper heat-sink is proposed to provide the operation in a continuous regime

Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) marker efficacy for maize hybrid identification

Knowledge as to genetic diversity and relationships among maize hybrids is important for breeding strategies. The main aims of this study were to (1) estimate molecular genetic diversity among 30 maize hybrids by random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers; and (2) compare the genetic relatedness values obtained from these marker types. A set of 30 maize hybrids was assessed. To compare these two methods, genetic parameters were computed such as the number of polymorphic bands, average number of alleles per locus, effective number of alleles per locus, expected heterozygosity, effectiveness index of analysis and polymorphism information content (PIC). Better results were provided by SSR. The discrimination ability of individual markers was also determined. The SSR system provided an average PIC of 0.71 (ranging from 0.47 to 0.91) and RAPD provided an average value of 0.61 (ranging from 0.44 to 0.82). Genetic similarities (GS) were estimated using Nei and Li’s coefficients for SSR and Jaccard’s coefficient for RAPD. For SSR, GS ranged from 26.3 to 88.5% (with average of 58.8%); for RAPD, GS ranged from 6.7 to 86.7% (with average of 49.5%). Hybrids were clustered using unweighted pair group method with arithmetic mean (UPGMA). The correlation between similarity matrices for RAPD and SSR was 0.11.Key words: Random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), genetic similarity, molecular marker, Zea mays L. var. indurata, Zea mays L. var. indentata

Enhancement of the Dynamic Performance of Single Phase Active Power Filters Using Virtual Two Axis Strategy Publication

In this paper the orthogonal transformation technique or virtual two axis strategy which was instigated by Akagi et al in 1984 for three phase power systems has been extended by Dobrucky and Pokorny in 1999 for the determination of instantaneous power in single phase power systems. This technique is described in detail in two of the authors’ previous publications,[2] and [3], by adopting this technique, an expression for the reference current used in an active power filter for the compensation of harmonic distortion and reactive power is derived. This expression is implemented by a digital signal processor and results in providing an excellent transient response of the filter which is demonstrated experimentally. This excellent response is realized due to the fast evaluation of the filter reference current when the two axis strategy described in this paper is used

Study of polycaprolactone wet electrospinning process

Wet electrospinning is a useful method for 3-dimensional structure control of nanofibrous materials. This innovative technology uses a liquid collector instead of the metal one commonly used for standard electrospinning. The article compares the internal structural features of polycaprolactone (PCL) nanofibrous materials prepared by both technologies. We analyze the influence of different water/ethanol compositions used as a liquid collector on the morphology of the resultant polycaprolactone nanofibrous materials. Scanning electron micro-photographs have revealed a bimodal structure in the wet electrospun materials composed of micro and nanofibers uniformly distributed across the sample bulk. We have shown that the full-faced, twofold fiber distribution is due to the solvent composition and is induced and enhanced by increasing the ethanol weight ratio. Moreover, the comparison of fibrous layers morphology obtained by wet and dry spinning have revealed that beads that frequently appeared in dry spun materials are created by Plateau-Rayleigh instability of the fraction of thicker fibers. Theoretical conditions for spontaneous and complete immersion of cylindrical fibers into a liquid collector are also derived here

Custos de operações florestais: noções e conceitos.

A base conceitual; Os fatores de produção; Objetivos das empresas florestais; Os diferentes níveis financeiros; Os custos; Tipos de custos; Custos fixos e custos variáveis; O comportamento dos custos; Os momentos de custos empresariais; As categorias de análise financeira; Análise econômica versus análise financeira Análise financeira dos diferentes níveis; Limitações da análise financeira; Análise de investimentos; Cálculo de investimento; Avaliação de risco; Consideração de outros aspectos; Proposta de controle de custos; O sistema de registros; Inventário patrimonial; Os custos comuns; Os mecanismos de análise.bitstream/item/51985/1/DOC-373.pdfVersão eletrônica

Equilibrum Composition of Thermal Plasma with Copper and Chromium Vapours Admixtures

Thermal plasma of electric arc is widely used in various technological applications: welding, cutting, lamps, spraying, protection of electrical installations, etc. Process efficiency is defined by different parameters that determine arc operation and influence the energy transfer within the medium. All energy exchanges depend on the medium, which is modified by the presence of the arc and more particularly by the appearance of new species from contact erosion. Sintered Cu-Cr composites are widely used as electrical contacts for vacuum circuit breakers. These materials take advantage of the high thermal and electrical conductivity of Cu and of the refractory and oxygen getter properties of reinforcing Cr particles. The aim of this paper is to give results of the calculation of the equilibrium composition of argon and air plasma with various admixtures of Cu and Cr

Modelling of Radiative Transfer in Air Arc Plasma

The objective of this work is to compare the accuracy of several approximate models of radiative properties for the prediction of radiative transfer in air arc plasma at the temperatures in the range of 300 - 25 000 K and the pressure of 0.1 MPa. Calculated absorption coefficients are used to generate the parameters of different models. The radiative transfer inside the cylindrically symmetrical air plasma with prescribed temperature profile was studied. The equation of radiative transfer was solved using the P1 and SP3 approximations, calculated radiative source term in the energy equation (net emission) was compared with results obtained by spectral integration