Applications of Parallel-Element, Embedded Mesh-Cap Acoustic Liner Concepts

This study explores progress achieved with 2DOF, 3DOF, and MDOF acoustic liners constructed with mesh caps embedded within a honeycomb core. These liner configurations offer potential for broadband noise reduction, and are suitable for conventional aircraft implementation. Samples for each configuration are tested in the NASA normal incidence tube and grazing flow impedance tube, with and without a wire mesh facesheet. Impedances based on these measured data compare favorably with those predicted using a transmission line impedance prediction model. Predicted impedances are then used as input for an aeroacoustic propagation code to compute axial acoustic pressure distributions in the grazing flow tube. These predicted distributions compare favorably with the corresponding measured distributions at frequencies away from the frequency of peak attenuation, but suffer slight degradation for frequencies very near the peak attenuation frequency, where the predicted results are sensitive to input impedance changes. As expected, the noise reduction frequency range increases as more degrees of freedom are included. Although the specific results achieved herein may differ from those that would be achieved with other 2DOF, 3DOF, and MDOF liners, this comparison highlights some of the key features that can be exploited in the design of parallel-element, embedded mesh-cap liners

Scaling properties of the critical behavior in the dilute antiferromagnet Fe(0.93)Zn(0.07)F2

Critical scattering analyses for dilute antiferromagnets are made difficult by the lack of predicted theoretical line shapes beyond mean-field models. Nevertheless, with the use of some general scaling assumptions we have developed a procedure by which we can analyze the equilibrium critical scattering in these systems for H=0, the random-exchange Ising model, and, more importantly, for H>0, the random-field Ising model. Our new fitting approach, as opposed to the more conventional techniques, allows us to obtain the universal critical behavior exponents and amplitude ratios as well as the critical line shapes. We discuss the technique as applied to Fe(0.93)Zn(0.07)F2. The general technique, however, should be applicable to other problems where the scattering line shapes are not well understood but scaling is expected to hold.Comment: 17 pages, 5 figure

Transport, Growth Mechanisms, and Material Quality in GaN Epitaxial Lateral Overgrowth

Growth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1{micro}m nucleation zones. Although emission is comprised of both UV ({approximately}365nm) and yellow ({approximately}550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines

Zoneamento agroecológico do dendê para o estado de Pernambuco: alternativa para diversificação da região canavieira da Zona da Mata.

O objetivo geral do Zoneamento Agroecológico do Dendê para o Estado de Pernambuco foi fornecer subsídios técnicos para formulação de políticas públicas visando apoiar a introdução e produção sustentável de dendê no território pernambucano, como opção para a diversificação de cultivos, em especial para as terras atualmente cultivadas com da cana-de-açúcar. Foi feita uma avaliação do potencial das terras para a produção da cultura do dendê em regime de sequeiro (sem irrigação plena) tendo como base as características físicas, químicas e mineralógicas dos solos, expressos espacialmente em levantamentos de solos e em estudos sobre risco climático relacionados aos requerimentos da cultura (precipitação, temperatura, ocorrência de geadas e veranicos). Os principais indicadores considerados na elaboração do Zoneamento Agroecológico foram à vulnerabilidade das terras, o risco climático (deficiência hídrica máxima de 350 mm), o potencial de produção agrícola sustentável e a legislação ambiental vigente. Adicionalmente, foram excluídas as terras com declividade superior a 12%, as áreas com cobertura vegetal nativa, as áreas de proteção ambiental, terras indígenas, remanescentes florestais, dunas, mangues, escarpas e afloramentos de rocha, reflorestamentos, áreas urbanas e de mineração. As áreas indicadas para a expansão compreendem aquelas atualmente em produção agrícola intensiva, produção agrícola semi-intensiva, lavouras especiais (perenes, anuais) e pastagens. Os estudos foram realizados para todo o Estado de Pernambuco. Foram empregadas as melhores informações temáticas e cartográficas disponíveis com escala de abstração de 1:250.000. Os resultados estão apresentados em mapas nos formatos shape file e PDF e, em tabelas com estimativas de áreas aptas ao cultivo por município e tipo de uso da terra. Os resultados obtidos mostram que o Estado de Pernambuco dispõe de cerca de 252.703 ha de áreas aptas à expansão do cultivo com dendê, sendo que destas cerca de 40.258 de ha foram considerados com alta aptidão (déficit hídrico entre 0 e 150 mm), 99.784 de ha como média aptidão (déficit hídrico entre 150 e 250 mm) e 112.660 ha como de baixo potencial para o cultivo (déficit hídrico entre 250 e 350 mm)

The complex multiferroic phase diagram of Mn1−x_{1-x}Cox_xWO4_4

The complete magnetic and multiferroic phase diagram of Mn$_{1-x}$Co$_{x}$WO$_4$ single crystals is investigated by means of magnetic, heat capacity, and polarization experiments. We show that the ferroelectric polarization $\overrightarrow{P}$ in the multiferroic state abruptly changes its direction twice upon increasing Co content, x. At x$_{c1}$=0.075, $\overrightarrow{P}$ rotates from the $b-$axis into the $a-c$ plane and at x$_{c2}$=0.15 it flips back to the $b-$axis. The origin of the multiple polarization flops is identified as an effect of the Co anisotropy on the orientation and shape of the spin helix leading to thermodynamic instabilities caused by the decrease of the magnitude of the polarization in the corresponding phases. A qualitative description of the ferroelectric polarization is derived by taking into account the intrachain ($c-$axis) as well as the interchain ($a-$axis) exchange pathways connecting the magnetic ions. In a narrow Co concentration range (0.1$\leq$x$\leq$0.15), an intermediate phase, sandwiched between the collinear high-temperature and the helical low-temperature phases, is discovered. The new phase exhibits a collinear and commensurate spin modulation similar to the low-temperature magnetic structure of MnWO$_4$.Comment: 18 pages, 6 figure

Levantamento semidetalhado dos solos da microbacia dos Córregos Barroso/Barrozinho no Município de Camapuã, MS.

O objetivo principal é avaliar o desgaste físico causado pela erosão hídrica nesta microbacia sob as condições atuais de uso do solo, medindo-se a quantidade de solo arrastado pelas águas de chuvas anualmente, através do monitoramento e fornecer subsídios para atenuar as perdas ou impedir o desgaste dos solos na área.bitstream/CNPS/11832/1/doc49_2002_barroso_barrozinho.pd