64,764 research outputs found
Frequency Modulation of Spin-Transfer Oscillators
Spin-polarized dc electric current flowing into a magnetic layer can induce
precession of the magnetization at a frequency that depends on current. We show
that addition of an ac current to this dc bias current results in a frequency
modulated (FM) spectral output, generating sidebands spaced at the modulation
frequency. The sideband amplitudes and shift of the center frequency with drive
amplitude are in good agreement with a nonlinear FM model that takes into
account the nonlinear frequency-current relation generally induced by spin
transfer. Single-domain simulations show that ac current modulates the cone
angle of the magnetization precession, in turn modulating the frequency via the
demagnetizing field. These results are promising for communications and signal
processing applications of spin-transfer oscillators.Comment: 13 pages, 3 Figure
Avaliação da qualidade do efluente gerado pelas ETE do Estado de Pernambuco em relação aos contaminantes emergentes.
Existem alguns compostos orgânicos presentes na água que ainda não são investigados pelas legislações ambientais brasileiras, mas que estão presentes mesmo em baixas concentrações (?g.L-1 ou ng.L-1) e causam efeitos adversos à saúde humana e dos animais, denominados contaminantes emergentes. Estes compostos são introduzidos no meio ambiente através de esgoto doméstico e efluentes de ETE. As classes de substâncias que são consideradas persistentes são: fármacos, produtos de cuidado pessoal e limpeza, interferentes endócrinos e subprodutos da desinfecção de água potável. O derramamento de esgoto sem tratamento é um grave problema ambiental, pois ocasiona poluição em rios, águas represadas, abastecimento de cidades e irrigação de plantações, e mesmo que as ETE disponham de diversas formas de tratamento, estas são insuficientes para garantir a ausência de poluição. Neste trabalho foi realizado um monitoramento em quatro estações de tratamento de esgoto (ETE) da Região Metropolitana do Recife, a saber: Caçote, Mangueira, Jardim Paulista e Cabanga. Foram quantificados cinco contaminantes classificados como interferentes endócrinos, foram selecionados para quantificação: progesterona e 17?-etinilestradiol (hormônios), dibutilftalato e dietilfitalato (plastificantes) e nonilfenol (surfactantes). Para a identificação e quantificação foi empregado LC/MS-MS de alta resolução e os dados tratados por análise por componentes principais e constatado a ineficiência da remoção dos micropoluentes do tratamento empregado pelas estações de tratamento de esgoto estudadas
The impact of inappropriate soil management on river water quality: a case study in the Kurundu Oya Sub-catchment of the Upper Mahaweli Catchment, Sri Lanka
The results of many studies have revealed that intensive farming on steep slopes, coupled with over application of fertilizers and accumulation of nutrients in downstream water bodies due to soil erosion, have contributed to environmental hazards in the Upper Mahaweli Catchment Area (UMCA) of Sri Lanka. The encroachment of riparian zones for exotic vegetable cultivation has aggravated this situation. In view of this, a study was conducted in the Kurundu Oya catchment, a micro-catchment of the UMCA, to investigate the soil management practices within the farming systems and their impacts on river water quality. Three villages were selected along the Kurundu Oya: Mahakudugala, Kumbalgamuwa and Batagolla. The study consisted of a survey of 150 households in 2007 and 2008, to gather information on the characteristics of householders and on soil management practices. A soil survey was carried out to analyze the soil fertility of farmlands. Water quality parameters were measured periodically in different sections of a selected stream. The results revealed that nearly 50 % of the riparian zones in the upper catchment of the Kurundu Oya stream are encroached to cultivate potato and other exotic vegetables. In addition, it was observed that over application of fertilizers on the vegetable plots was causing nutrient accumulation and the plots also recorded high levels of phosphorous (P) (above 75 ppm). Results of the water quality analysis showed that nitrate and available P levels were within the standard limits, but nitrate nitrogen (NO3-N) levels were close to the upper level of the standard limit. Therefore, in order to minimize water pollution, it is strongly recommended that fertilizer application is based on soil tests. In addition, encroachment of sensitive lands has to be addressed. Priority should be given to strengthening institutional capacity in order to facilitate the implementation of existing environmental legislation.Length: pp.49-60Soil managementSoil degradationCatchment areasErosionSedimentationWater pollutionFertilizer applicationNitrogenVegetable growing
Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz
We examine the possibility of using negative refraction stemming from the
phonon response in an anisotropic crystal to create a simple slab lens with
plane parallel sides, and show that imaging from such a lens should be possible
at room temperature despite the effects of absorption that are inevitably
present due to phonon damping. In particular, we consider the case of crystal
quartz, a system for which experimental measurements consistent with all-angle
negative refraction have already been demonstrated. Furthermore, we investigate
the possibility of subwavelength imaging from such materials, and show that it
should be possible for certain configurations.Comment: 12 pages, 10 figure
Limits on surface gravities of Kepler planet-candidate host stars from non-detection of solar-like oscillations
We present a novel method for estimating lower-limit surface gravities log g
of Kepler targets whose data do not allow the detection of solar-like
oscillations. The method is tested using an ensemble of solar-type stars
observed in the context of the Kepler Asteroseismic Science Consortium. We then
proceed to estimate lower-limit log g for a cohort of Kepler solar-type
planet-candidate host stars with no detected oscillations. Limits on
fundamental stellar properties, as provided by this work, are likely to be
useful in the characterization of the corresponding candidate planetary
systems. Furthermore, an important byproduct of the current work is the
confirmation that amplitudes of solar-like oscillations are suppressed in stars
with increased levels of surface magnetic activity.Comment: Accepted for publication in ApJ; 35 pages, 10 figures, 5 table
Limitações dos sistemas de produção dos assentamentos São Francisco (Eldorado dos Carajás, Pará) e agroextrativista Praialta/Piranheira (Nova Ipixuna, Pará).
Este trabalho, ao mesmo tempo em que fornece elementos essenciais à orientação técnico-científica ao uso e ocupação dos recursos naturais de uma região de fronteira da Amazônia Oriental, retoma a discussão sobre a questão agrária no país, particularizando os assentamentos rurais oficiais do Sudeste Paraense.bitstream/item/63437/1/Oriental-Doc138.pd
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