1,207 research outputs found
Evidence of random magnetic anisotropy in ferrihydrite nanoparticles based on analysis of statistical distributions
We show that the magnetic anisotropy energy of antiferromagnetic ferrihydrite
depends on the square root of the nanoparticles volume, using a method based on
the analysis of statistical distributions. The size distribution was obtained
by transmission electron microscopy, and the anisotropy energy distributions
were obtained from ac magnetic susceptibility and magnetic relaxation. The
square root dependence corresponds to random local anisotropy, whose average is
given by its variance, and can be understood in terms of the recently proposed
single phase homogeneous structure of ferrihydrite.Comment: 6 pages, 2 figure
Spin torque resonant vortex core expulsion for an efficient radio-frequency detection scheme
Spin-polarised radio-frequency currents, whose frequency is equal to that of
the gyrotropic mode, will cause an excitation of the core of a magnetic vortex
confined in a magnetic tunnel junction. When the excitation radius of the
vortex core is greater than that of the junction radius, vortex core expulsion
is observed, leading to a large change in resistance, as the layer enters a
predominantly uniform magnetisation state. Unlike the conventional spin-torque
diode effect, this highly tunable resonant effect will generate a voltage which
does not decrease as a function of rf power, and has the potential to form the
basis of a new generation of tunable nanoscale radio-frequency detectors
Characteristics of nodule bacteria from Mimosa spp grown in soils of the Brazilian semiarid region.
The Brazilian Northeastern dry forest (Caatinga) is one of the diversification centers of Mimosa species. We determined the characteristics of native rhizobia isolates from nodules of Mimosa tenuiflora and Mimosa paraibana grown in pots with soils collected under Caatinga vegetation and compared the restriction ribosomal DNA profiles of the isolates with those of 16 reference strains. All plants formed abundant indeterminate nodules and all nodule isolates formed fast growing colonies. No colony altered the medium to an alkaline reaction and most of them produced low or medium amounts of extracellular polysaccharides. White and creamy colonies predominated among the isolates but orange and green colonies were present. Differences among the isolates from the Mimosa species tested are indicated by the greater phenotypic diversity of those obtained from M. tenuiflora. The analysis of the 16S rDNA gene suggests that the isolates from M. tenuiflora and M. paraibana are closely related and closer to B-rhizobia than to α-rhizobia. However, the similarity with all the tested B-rhizobia reference strains was relatively low suggesting that the isolates may belong to different bacteria species
Produção de biomassa de espécies utilizadas como adubação verde.
O objetivo do presente trabalho foi estimar a produção de fitomassa das espécies utilizadas nos coquetéis vegetais utilizados como adubação verde
BRS Novaera: cultivar de feijão-caupi de porte semi-ereto.
bitstream/item/27806/1/Com.Tec.215.pdfDisponível também on-line
Recomendação de híbridos de milho para o nordeste brasileiro: ensaios realizados no ano agrícola de 2002/2003.
bitstream/item/81108/1/CPATC-COM.-TEC.-23-04.pd
Comportamento produtivo de híbridos de milho no Nordeste Brasileiro. Ano agrícola 2000/2001.
bitstream/item/126435/1/boletim-45-Comportamento-produtivo-de-milho-2000-2001.pd
Estimativa de biomassa lenhosa da caatinga com uso de equações alométricas e índice de vegetação.
O presente trabalhou objetivou investigar a relação entre o índice de vegetação pela diferença normalizada (IVDN) e a biomassa estimada (t.ha-1) com uso de equações alométricas em uma área de caatinga hiperxerófila, com o intuito de ajustar um modelo de regressão linear que permita estimar a biomassa lenhosa em áreas de caatinga. Os valores de IVDN foram obtidos da cena 217/66 do sensor LANDSAT 5 TM. No campo, vinte parcelas com área de 10 x 20 m foram georeferenciadas e todas as plantas lenhosas vivas com diâmetro à altura do peito (DAP) igual ou maior que 3 cm foram identificadas, tiveram suas alturas e DAPs medidos e suas biomassas estimadas a partir de equações alométricas. A densidade média das plantas foi de 780 ind. ha-1 apresentando variação de 150 a 1900 ind.ha-1. A espécie Mimosa tenuiflora apresentou maior índice de valor de importância (IVI) e maior biomassa: 10,11 t.ha-1. Os valores de IVDN variaram entre 0,4161 e 0,7067, apresentando-se positivamente correlacionados com os valores de biomassa estimados, que variaram de 5,93 a 60,74 t.ha-1, com coeficiente de correlação de Pearson de 0,84 e p < 0,01. A regressão linear entre IVDN e a biomassa obteve coeficiente de determinação R2= 0,70 e desvio padrão de 8,43 t.h-1. O erro de predição na estimativa da biomassa, calculado por validação cruzada foi igual a 31%, considerado satisfatório para um método de estimativa não destrutivo
Hawking emission from quantum gravity black holes
We address the issue of modelling quantum gravity effects in the evaporation
of higher dimensional black holes in order to go beyond the usual
semi-classical approximation. After reviewing the existing six families of
quantum gravity corrected black hole geometries, we focus our work on
non-commutative geometry inspired black holes, which encode model independent
characteristics, are unaffected by the quantum back reaction and have an
analytical form compact enough for numerical simulations. We consider the
higher dimensional, spherically symmetric case and we proceed with a complete
analysis of the brane/bulk emission for scalar fields. The key feature which
makes the evaporation of non-commutative black holes so peculiar is the
possibility of having a maximum temperature. Contrary to what happens with
classical Schwarzschild black holes, the emission is dominated by low frequency
field modes on the brane. This is a distinctive and potentially testable
signature which might disclose further features about the nature of quantum
gravity.Comment: 36 pages, 18 figures, v2: updated reference list, minor corrections,
version matching that published on JHE
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