Ultrasonic nondestructive evaluation of impact-damaged graphite fiber composite

Unidirectional Hercules AS/3501-6 graphite fiber epoxy composites were subjected to repeated controlled low-velocity drop weight impacts in the laminate direction. The degradation was ultrasonically monitored using through-thickness attenuation and a modified stress wave factor (SWF). There appears to be strong correlations between the number of drop-weight impacts, the residual tensile strength, the through-thickness attenuation, and the SWF. The results are very encouraging with respect to the NDE potential of both of these ultrasonic parameters to provide strength characterizations in virgin as well as impact-damaged fiber composite structures

Effect of excited states and applied magnetic fields on the measured hole mobility in an organic semiconductor

Copyright 2010 by the American Physical Society. Article is available at

Negative capacitance in organic semiconductor devices: bipolar injection and charge recombination mechanism

We report negative capacitance at low frequencies in organic semiconductor based diodes and show that it appears only under bipolar injection conditions. We account quantitatively for this phenomenon by the recombination current due to electron-hole annihilation. Simple addition of the recombination current to the well established model of space charge limited current in the presence of traps, yields excellent fits to the experimentally measured admittance data. The dependence of the extracted characteristic recombination time on the bias voltage is indicative of a recombination process which is mediated by localized traps.Comment: 3 pages, 3 figures, accepted for publication in Applied Physics Letter

Performance indicators: a proposal for family-run livestock farming under the conceptual framework of the sustainable balanced scorecard.

Resumo Objetivo do estudo: Construir uma matriz de indicadores, conforme a ótica conceitual do BSC, adaptando às dimensões de sustentabilidade relacionadas à pecuária familiar. Metodologia/abordagem: Utilizou-se uma abordagem qualitativa, realizando um estudo bibliográfico e documental, além de entrevistas com produtores rurais e especialistas no tema. Originalidade/Relevância: Historicamente existe uma carência de ferramentas e metodologias de gestão para o contexto do trabalho, em especial frente as novas exigências ambientais e de sustentabilidade. Assim, o trabalho contribui para mitigar esta lacuna no contexto. Principais resultados: O trabalho gerou uma proposta/matriz com indicadores de sustentabilidade para a pecuária familiar. Matriz composta por 28 indicadores distribuídos nas quatro dimensões (ambiental, econômica, produtiva e social) de sustentabilidade. Contribuições teóricas/metodológicas: A principal contribuição metodológica foi descrever o processo de como propor uma matriz de indicadores, utilizando-se ferramentas de planejamento como a matriz SWOT e o BSC. Produtores e especialistas contribuíram para a construção da matriz SWOT, posteriormentetambém contribuíram para a construção da matriz de indicadores, de forma a tender a matriz SWOT. Contribuições sociais / para a gestão: Como contribuição social podemos citar a questão da matriz de indicadores estar apoiada nas quatro dimensões de sustentabilidade. Para a gestão, a própria matriz, além das especificações de cada indicador que pode viabilizar uma melhor gestão nas propriedades de pecuária familiar

Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution

A self-consistent, mean-field model of charge-carrier injection and unipolar transport in an organic semiconductor diode is developed utilizing the effective transport energy concept and taking into account a realistic density-of-states distribution as well as the presence of trap states in an organic material. The consequences resulting from the model are discussed exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic conductor structure. A comparison of the theory to experimental data of a unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic

Luttinger-liquid-like transport in long InSb nanowires

Long nanowires of degenerate semiconductor InSb in asbestos matrix (wire diameter is around 50 \AA, length 0.1 - 1 mm) were prepared. Electrical conduction of these nanowires is studied over a temperature range 1.5 - 350 K. It is found that a zero-field electrical conduction is a power function of the temperature $G\propto T^\alpha$ with the typical exponent $\alpha \approx 4$. Current-voltage characteristics of such nanowires are found to be nonlinear and at sufficiently low temperatures follows the power law $I\propto V^\beta$. It is shown that the electrical conduction of these nanowires cannot be accounted for in terms of ordinary single-electron theories and exhibits features expected for impure Luttinger liquid. For a simple approximation of impure LL as a pure one broken into drops by weak links, the estimated weak-link density is around $10^3-10^4$ per cm.Comment: 5 pages, 2 figure

Bipolar-Driven Large Magnetoresistance in Silicon

Large linear magnetoresistance (MR) in electron-injected p-type silicon at very low magnetic field is observed experimentally at room temperature. The large linear MR is induced in electron-dominated space-charge transport regime, where the magnetic field modulation of electron-to-hole density ratio controls the MR, as indicated by the magnetic field dependence of Hall coefficient in the silicon device. Contrary to the space-charge-induced MR effect in unipolar silicon device, where the large linear MR is inhomogeneity-induced, our results provide a different insight into the mechanism of large linear MR in non-magnetic semiconductors that is not based on the inhomogeneity model. This approach enables homogeneous semiconductors to exhibit large linear MR at low magnetic fields that until now has only been appearing in semiconductors with strong inhomogeneities.Comment: 23 pages, 4 figures (main text), 6 figures (supplemental material

Desdobramento da estratégia para avaliação de desempenho: implantação do Balanced Scorecard (BSC) no processo produtivo da pecuária de corte bovina.

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