1,151 research outputs found
Quantificação do carbono das substâncias húmicas em diferentes sistemas de uso do solo e épocas de avaliação.
A quantificação do carbono nas diferentes frações da matéria orgânica do solo (MOS) torna-se necessária devido ao interesse de se conhecer o potencial de captura e armazenamento do carbono nos diferentes sistemas de uso do solo. O objetivo deste trabalho foi quantificar o carbono das substâncias húmicas em diferentes sistemas de uso do solo e épocas de avaliação e correlacioná-lo com algumas propriedades químicas e físicas do solo. Os sistemas selecionados foram: preparo convencional (PC-milho/feijão), plantio direto (PD-berinjela/milho), consórcio maracujá/Desmodium sp, cultivo com figo e sistema agroflorestal. As amostras de solo foram coletadas em duas profundidades (0-5 e 5-10 cm) e épocas (17/11/2005–verão e 23/6/2006-inverno). Foi determinado o carbono orgânico total (COT) e realizado o fracionamento químico da MOS, quantificando-se o carbono da fração humina (C-HUM), fração ácido húmico (C-FAH) e fração ácido fúlvico (C-FAF). O C-HUM constituiu a maior parte do COT, havendo correlação significativa com o COT em todos os sistemas avaliados e estações. Analisando o C-FAH foi possível identificar alterações no solo relacionadas aos sistemas de uso, na profundidade de 0-5 cm e no verão, destacando-se o PD com os maiores teores. Com o C-FAF ocorreu este mesmo comportamento, mas na profundidade de 5-10 cm e no inverno, destacando-se o PC com maiores valores. Foram verificadas correlações significativas entre Valor S, Valor T e DMP em todos os sistemas, com exceção da área de PC. O PD aumenta os teores de C-FAH, nas duas profundidades e nas duas estações, quando comparado ao PC do solo
Desempenho de sementes peletizadas de alface em função do material cimentante e da temperatura de secagem dos péletes
Theory of excited state absorptions in phenylene-based -conjugated polymers
Within a rigid-band correlated electron model for oligomers of
poly-(paraphenylene) (PPP) and poly-(paraphenylenevinylene) (PPV), we show that
there exist two fundamentally different classes of two-photon A states in
these systems to which photoinduced absorption (PA) can occur. At relatively
lower energies there occur A states which are superpositions of one
electron - one hole (1e--1h) and two electron -- two hole (2e--2h) excitations,
that are both comprised of the highest delocalized valence band and the lowest
delocalized conduction band states only. The dominant PA is to one specific
member of this class of states (the mA). In addition to the above class of
A states, PA can also occur to a higher energy kA state whose 2e--2h
component is {\em different} and has significant contributions from excitations
involving both delocalized and localized bands. Our calculated scaled energies
of the mA and the kA agree reasonably well to the experimentally
observed low and high energy PAs in PPV. The calculated relative intensities of
the two PAs are also in qualitative agreement with experiment. In the case of
ladder-type PPP and its oligomers, we predict from our theoretical work a new
intense PA at an energy considerably lower than the region where PA have been
observed currently. Based on earlier work that showed that efficient
charge--carrier generation occurs upon excitation to odd--parity states that
involve both delocalized and localized bands, we speculate that it is the
characteristic electronic nature of the kA that leads to charge generation
subsequent to excitation to this state, as found experimentally.Comment: Revtex4 style, 2 figures inserted in the text, three tables, 10 page
A estreita porta de entrada do Sistema Único de Saúde (SUS): uma avaliação do acesso na Estratégia de Saúde da Família
Fertilização com dejetos suínos: influência nas características bromatológicas da Brachiaria decumbens e alterações no solo
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
O itinerário de doadores de sangue: reflexões acerca da micropolítica no cuidado de enfermagem
Search for the standard model Higgs boson in tau final states
We present a search for the standard model Higgs boson using hadronically
decaying tau leptons, in 1 inverse femtobarn of data collected with the D0
detector at the Fermilab Tevatron ppbar collider. We select two final states:
tau plus missing transverse energy and b jets, and tau+ tau- plus jets. These
final states are sensitive to a combination of associated W/Z boson plus Higgs
boson, vector boson fusion and gluon-gluon fusion production processes. The
observed ratio of the combined limit on the Higgs production cross section at
the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of
115 GeV.Comment: publication versio
Search for a scalar or vector particle decaying into Zgamma in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for a narrow scalar or vector resonance decaying into
Zgamma with a subsequent Z decay into a pair of electrons or muons. The data
for this search were collected with the D0 detector at the Fermilab Tevatron
ppbar collider at a center of mass energy sqrt(s) = 1.96 TeV. Using 1.1 (1.0)
fb-1 of data, we observe 49 (50) candidate events in the electron (muon)
channel, in good agreement with the standard model prediction. From the
combination of both channels, we derive 95% C.L. upper limits on the cross
section times branching fraction (sigma x B) into Zgamma. These limits range
from 0.19 (0.20) pb for a scalar (vector) resonance mass of 600 GeV/c^2 to 2.5
(3.1) pb for a mass of 140 GeV/c^2.Comment: Published by Phys. Lett.
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