12,596 research outputs found
Assessing nutrient flux control in agroforestry.
Studies on the strategies for the assessment of relevant factors for the determination of the nutrient output in order to control unporductive nutrient losses and off-site effects of land use by agroforestry, in the Central Amazonia, Brasil
Using ultra-thin parylene films as an organic gate insulator in nanowire field-effect transistors
We report the development of nanowire field-effect transistors featuring an
ultra-thin parylene film as a polymer gate insulator. The room temperature,
gas-phase deposition of parylene is an attractive alternative to oxide
insulators prepared at high temperatures using atomic layer deposition. We
discuss our custom-built parylene deposition system, which is designed for
reliable and controlled deposition of <100 nm thick parylene films on III-V
nanowires standing vertically on a growth substrate or horizontally on a device
substrate. The former case gives conformally-coated nanowires, which we used to
produce functional -gate and gate-all-around structures. These give
sub-threshold swings as low as 140 mV/dec and on/off ratios exceeding at
room temperature. For the gate-all-around structure, we developed a novel
fabrication strategy that overcomes some of the limitations with previous
lateral wrap-gate nanowire transistors. Finally, we show that parylene can be
deposited over chemically-treated nanowire surfaces; a feature generally not
possible with oxides produced by atomic layer deposition due to the surface
`self-cleaning' effect. Our results highlight the potential for parylene as an
alternative ultra-thin insulator in nanoscale electronic devices more broadly,
with potential applications extending into nanobioelectronics due to parylene's
well-established biocompatible properties
Biaxial order parameter in the homologous series of orthogonal bent-core smectic liquid crystals
The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter (S) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: S for the long axes and C for the ordering of the short axes of molecules. The temperature dependencies of S and C are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-APA) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both S and C, particularly the temperature dependency of the latter, are being experimentally determined. Results show that S in the orthogonal smectic phase composed of bent cores is higher than in Sm-A calamatic LCs and C is also significantly large
Water and nutrient fluxes as indicators for the sustainability of different land-use systems on the terra firme near Manaus - a project overview.
Comparision of the water and nutrient fluxes in different perennial land-se systems, either monocultures or mixed cropping systems, in order to determine the resource efficiency of perennial land-se systems. They were comparision of the monocultue systems with Theobroma grandiflorum (cupuacu) or Bactris gasipaes (pupunha), polyculture systems with cupuacu, pupunh, Bixa orellana (urucum) and Bertholletia excelsa (castanha-do-Para) and primary and secondary forest sites. In the first experimental year, the equipment was installed to measure raianfall, throughfall, stemflow and soil water fluxes. These data combined with measurements of nutrient concentrations inform about the element fluxes. for this purpose, laboratory facilities were implemented to analyze anions and cations in the different land-se systems. Additionally, the nutrient and organic matter content of the soils were studied. Firt results showed that the investigated tree species differ in their effect on the water distribution and nutrient accumulation within the different cropping systems
Nutrient and water dynamics in a multi-strata agroforestry system.
In the presentel project, the nutriente and water fluxes are studied ann used as indicators for the stability of the agroforestry systems. The effects of the trees on soil properties, water and nutrient dynamics highly differed between species. To evaluate the sustaninability on an agroforestry system it is important to stress the consideration of spatial variability in the studied parameters. This variability creates the possibility to develop agroforestry with a complementary use of water and nutriente resources. The cropping sysytem with the current management is not seen as viable solution for land use in Amazonia at the moment. However, the discovered features of single trees and the effects on crop production and sustainability so far described encourage futher efforts to improve multi-strata agroforestry as a land use system for the Amazon region
Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal.
Inspired by the sustained fertility of anthropogenic Terra Preta soils in the central Amazon Basin, we studied the effect of charcoal as soil amendment
Corte e carbonização como uma alternativa ao corte e queima: estudos na Amazônia.
Neste capítulo são apresentados vários estudos realizados em Manaus cujo principal objetivo foi verificar o efeito da aplicação de carvão vegetal no manejo do Latossolo Amarelo (xanthic Ferralsol) na terra firme em Manaus - Brasil. Os estudos foram conduzidos na Estação Experimental da Embrapa Amazônia Ocidental no km 30 da Rodovia AM-010. Também é descrito uma forma de manejo indígena da fertilidade do solo pela queima e uso de fontes orgânica
Fast soil solution nutrient and water dynamics in top- and subsoil.
Study for find out the short-term dynamics of applied fertilizer. In a soil pit a data logger system connected to tensiometers and TDR was installed up to a depth of 3.5m under pueraria in an agroforestry system (cupuacu, peach palm, Brazil nut, urucum). After a rainfall event, the soil water suction at 0.1m depth increased immediately, and fast responses were seen even up to a depth of 0.9m. This result may indicate that nutrients may be leached very fast even in these soil with high clay contents. The N concentrations in the soil solution relevantly increased at 0.1m depth during the same time period, as shown for peach palm. First, the ammonium concentrations increased, but nitrate contents followed rapidly indicanting a fast nitrification in the studied soils.bitstream/item/210595/1/Water-and-nutrient-p54.pd
CMB Temperature Polarization Correlation and Primordial Gravitational Waves
We examine the use of the CMB's TE cross correlation power spectrum as a
complementary test to detect primordial gravitational waves (PGWs). The first
method used is based on the determination of the lowest multipole, ,
where the TE power spectrum, , first changes sign. The second
method uses Wiener filtering on the CMB TE data to remove the density
perturbations contribution to the TE power spectrum. In principle this leaves
only the contribution of PGWs. We examine two toy experiments (one ideal and
another more realistic) to see their ability to constrain PGWs using the TE
power spectrum alone. We found that an ideal experiment, one limited only by
cosmic variance, can detect PGWs with a ratio of tensor to scalar metric
perturbation power spectra at 99.9% confidence level using only the TE
correlation. This value is comparable with current constraints obtained by WMAP
based on the upper limits to the B-mode amplitude. We demonstrate
that to measure PGWs by their contribution to the TE cross correlation power
spectrum in a realistic ground based experiment when real instrumental noise is
taken into account, the tensor-to-scalar ratio, , should be approximately
three times larger.Comment: 13 pages, 13 figures, version matches published version. Combined
with 0710.365
Extremely Metal-Poor Stars. VII. The Most Metal-Poor Dwarf, CS 22876-032
We report high-resolution, high-signal-to-noise, observations of the
extremely metal-poor double-lined spectroscopic binary CS 22876-032. The system
has a long period : P = 424.7 0.6 days. It comprises two main sequence
stars having effective temperatures 6300 K and 5600 K, with a ratio of
secondary to primary mass of 0.89 0.04. The metallicity of the system is
[Fe/H] = -3.71 0.11 0.12 (random and systematic errors) -- somewhat
higher than previous estimates. We find [Mg/Fe] = 0.50, typical of values of
less extreme halo material. [Si/Fe], [Ca/Fe], and [Ti/Fe], however, all have
significantly lower values, ~ 0.0-0.1, suggesting that the heavier elements
might have been underproduced relative to Mg in the material from which this
object formed. In the context of the hypothesis that the abundance patterns of
extremely metal-poor stars are driven by individual enrichment events and the
models of Woosley and Weaver (1995), the data for CS 22876-032 are consistent
with its having been enriched by a zero-metallicity supernova of mass 30
M. As the most metal-poor near-main-sequence-turnoff star currently
known, the primary of the system has the potential to strongly constrain the
primordial lithium abundance. We find A(Li) (= log(N(Li)/N(H)) + 12.00) = 2.03
0.07, which is consistent with the finding of Ryan et al. (1999) that for
stars of extremely low metallicity A(Li) is a function of [Fe/H].Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical
Journal, Sept. 1, 2000 issu
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