9,090 research outputs found
Magnetism and Electronic Correlations in Quasi-One-Dimensional Compounds
In this contribution on the celebration of the 80th birthday anniversary of
Prof. Ricardo Ferreira, we present a brief survey on the magnetism of
quasi-one-dimensional compounds. This has been a research area of intense
activity particularly since the first experimental announcements of magnetism
in organic and organometallic polymers in the mid 80s. We review experimental
and theoretical achievements on the field, featuring chain systems of
correlated electrons in a special AB2 unit cell structure present in inorganic
and organic compounds
Effect of dairy effluents pre-treatment on N2O emissions and N-organic degradation after soil application
Nitrous oxide (N2O) is a potent greenhouse gas that plays a key role in climatic forcing
contributing to the greenhouse effect by about 4 %, and also contributes to stratospheric
ozone depletion. Cattle slurries are commonly applied to agricultural soils, inducing an
increase of soil nitrous oxide emissions. Therefore, many procedures were developed for
slurry pre-treatment in order to improve soil slurry application and reduce nitrogen
losses, namely N2O emissions.
The aim of this work was to compare N2O emissions and the kinetic of N organic
degradation from treated and untreated cattle-slurry after its incorporation in agricultural
soils
Separação de sólidos e nutrientes com PAM e bentonite em chorumes bovinos
A separação de sólidos do chorume e a aplicação de agentes floculantes à fracção lÃquida
obtida constituem processos de tratamento deste efluente pecuário que permitem a obtenção de
materiais com caracterÃsticas distintas que ampliam as opções de utilização e de gestão do chorume.
A redução do teor de sólidos e nutrientes na fracção sobrenadante apresenta vantagens em termos
de odores, armazenamento, tratamento, aplicação aos solos e irrigação. Este trabalho teve como
objectivo avaliar a utilização dos agentes floculantes poliacrilamida (PAM) e bentonite na remoção de
sólidos e nutrientes da fracção lÃquida do chorume de explorações de bovinicultura leiteira.
O trabalho experimental decorreu em Vila do Conde durante 2004, numa exploração de
bovinicultura leiteira intensiva. O chorume bruto foi sujeito a separação mecânica de sólidos.
Posteriormente a fracção lÃquida obtida foi bombeada para recipientes, e definiram-se 3 tratamentos
com 2 repetições: controlo, adição de 200 mg L
-1
de PAM e adição de 2 g L
-1
de bentonite. Após a
aplicação dos floculantes foram recolhidas amostras às fracções sobrenadante e sedimentada nos
tempos 0, 2, 4, 20 e 30 horas. Essas amostras foram analisadas relativamente à concentração de N
Kjeldahl, P e K totais, N-NH4
+
, P solúvel em água, C orgânico solúvel em água, valor de pH e %MS.
A separação mecânica do chorume bruto conduziu a uma eficiência de remoção pela fracção
sólida obtida de 22, 25, 44 e 21%, respectivamente, dos teores de N Kjeldahl, P total, P solúvel em
água e MS. Quanto à capacidade de remoção dos floculantes, a aplicação de PAM conduziu Ã
eficiência de remoção da fracção sobrenadante de 46, 40, 65, 57 e 40%, respectivamente para o N
Kjeldahl, P e K totais, P solúvel em água e MS; e a aplicação de bentonite a remoções de 19, 21, 11,
16 e 12%
Conservation of Orbital Angular Momentum in Stimulated Down-Conversion
We report on an experiment demonstrating the conservation of orbital angular
momentum in stimulated down-conversion. The orbital angular momentum is not
transferred to the individual beams of the spontaneous down-conversion, but it
is conserved when twin photons are taken individually. We observe the
conservation law for an individual beam of the down-conversion through
cavity-free stimulated emission.Comment: Submitted for publication in Phys. Rev. Let
Influence of two nitrification inhibitors (DCD and DMPP) on annual ryegrass yield and soil mineral N dynamics after incorporation with cattle slurry
Nitrogen (N) losses through nitrate leaching, occurring after slurry
spreading, can be reduced by the use of nitrification inhibitors (NIs) such as
dicyandiamide (DCD) and 3,4-dimethyl pyrazole phosphate (DMPP). In the
present work, the effects of DCD and DMPP, applied at two rates with cattle
slurry, on soil mineral N profiles, annual ryegrass yield, and N uptake were
compared under similar pedoclimatic conditions. Both NIs delayed the nitrate
formation in soil; however, DMPP ensured that the soil mineral N was
predominantly in the ammonium form rather than in the nitrate form for about
100 days, whereas with DCD such effect was observed only during the first 40
days after sowing. Furthermore, the use of NIs led to an increase of the drymatter
(DM) yields in a range of 32–54% and of the forage N removal in a range
of 34–68% relative to the slurry-only (SO) treatment (without NIs). A DM yield
of 8698 kg ha21 was obtained with the DMPP applied at the greater rate against
only 7444 kg ha21 obtained with the greater rate of DCD (4767 kg ha21 in the SO
treatment). Therefore, it can be concluded that DMPP is more efficient as an NI
than DCD when combined with cattle slurr
3-3-1 exotic quark search at CERN LEPII-LHC
The 3-3-1 electroweak model is the simplest chiral extension of the standard
model which predicts single and double charged bileptons and exotic quarks
carrying -4/3 and 5/3 units of the positron charge. In this paper we study the
possibilities of the production and decay of one of these exotic quarks at CERN
LEPII-LHC collider. For typical vector bilepton, exotic quark masses and mixing
angles we obtained between 20 and 750 events per year. Angular distributions
are also presented.Comment: 5 pages, RevTex 3.1, 9 eps figures, to appear in Phys. Rev.
Manejo de campos de produção de sementes de Brachiaria humidicola "comum?": I - efeito de doses de nitrogênio1.
As baixas produtividades obtidas em áreas de produção de sementes de Brachiaria humidicola ?comum?, uma gramÃnea tropical usada como pastagem cultivada, são causadas por associação do curto perÃodo de retenção das sementes nas inflorescências e do marcante sincronismo da emergência das inflorescências. Em conseqüência, o perÃodo de disponibilidade das sementes puras à colheita é pequeno. O escalonamento da produção de sementes entre e dentro de campos permitiria estender os perÃodos de colheita e de uso de equipamentos em sistemas comerciais de produção dessas sementes. Neste trabalho foram avaliados os efeitos de doses de N para estender o perÃodo de colheita. Foram avaliadas cinco doses de N (0, 25, 50, 75 e 100 kg ha-1de N) aplicadas em cobertura na forma de uréia, no inÃcio da estação chuvosa do ano 2.000. Amostras de sementes foram colhidas após 66, 69 e 72 dias da aplicação do N. Os efeitos dos tratamentos foram estimados em termos de produtividade potencial de sementes puras e germináveis e de vários componentes da produção de sementes. A época de maior disponibilidade de sementes puras à colheita e o perÃodo da disponibilidade variaram em função da dose de N. A maior produtividade potencial (295 kg ha-1) foi obtida com 75 kg ha-1de N. A máxima produtividade resultante da aplicação de 50 kg ha-1de N foi 16% menor e foi alcançada quatro dias mais tarde. Apesar dos efeitos sobre a disponibilização à colheita haverem ocorrido à custa de redução da produtividade, o uso de diferentes doses de N pode contribuir à redução de riscos e de custos na produção de sementes dessa espécie
Controlling a resonant transmission across the -potential: the inverse problem
Recently, the non-zero transmission of a quantum particle through the
one-dimensional singular potential given in the form of the derivative of
Dirac's delta function, , with , being a
potential strength constant, has been discussed by several authors. The
transmission occurs at certain discrete values of forming a resonance
set . For
this potential has been shown to be a perfectly reflecting wall. However, this
resonant transmission takes place only in the case when the regularization of
the distribution is constructed in a specific way. Otherwise, the
-potential is fully non-transparent. Moreover, when the transmission
is non-zero, the structure of a resonant set depends on a regularizing sequence
that tends to in the sense of
distributions as . Therefore, from a practical point of
view, it would be interesting to have an inverse solution, i.e. for a given
to construct such a regularizing sequence
that the -potential at this value is
transparent. If such a procedure is possible, then this value
has to belong to a corresponding resonance set. The present paper is devoted to
solving this problem and, as a result, the family of regularizing sequences is
constructed by tuning adjustable parameters in the equations that provide a
resonance transmission across the -potential.Comment: 21 pages, 4 figures. Corrections to the published version added;
http://iopscience.iop.org/1751-8121/44/37/37530
Fluorescence and diffuse reflectance spectroscopy for early cancer detection using a new strategy towards the development of a miniaturized system
This paper describes the design of a miniature, cost-effective spectroscopy system for assessing tissue biochemical and morphological information using a few wavelengths. This instrument will integrate thin-film optical filters and silicon photodiodes, avoiding the use of a spectrograph and optical fibers. The components in the set-up design are described. The feasibility of using only 16 wavelengths to accurately extract tissue properties is confirmed on physical tissue models. Also, the suitable spectral performance of several optical filters for the selection of these wavelengths is demonstrated. The small size of this device will enable implementation in an endoscopic capsule.This research was supported by the Portuguese Foundation of Science and Technology and the MIT|Portugal Program (SFRH/BD/38978/2007
- …