145 research outputs found
Conversion of Cerrado into agricultural land in the south-western amazon: carbon stocks and soil fertility.
Mudanças de uso da terra e práticas de manejo modificam a dinâmica do C e a fertilidade do solo. Este estudo avaliou as implicações dos sistemas de cultivo (NT e CT) nos estoques de C e de nutrientes e identificou inter-relações entre estes estoques e outros atributos da fertilidade do solo em Latossolo após a mudança do uso da terra no cerrado amazônico. Os estoques de C e de nutrientes (P, K, Ca e Mg) ajustados pela massa equivalente do solo sob cerrado (CE), foram maiores principalmente sob NT. Após a adoção do NT, exceto em 2NT, os estoques de C foram maiores em relação às demais áreas avaliadas. Correlações entre estoques de C e de nutrientes revelaram algumas correlações positivas com Ca e Mg nas áreas sob NT, devido ao uso continuo de calcário, à maior quantidade de resíduos culturais e ao não revolvimento do solo, associado à correlações positivas com CTC, saturação por bases e pH. A correlação positiva (r = 0,91, p < 0,05) entre estoques de C e CTC em CE indica a importante contribuição da MOS na CT de solos tropicais, embora os sítios de troca estejam ocupados principalmente por H + Al. Estoques de P e K mostraram correlações positivas com estoques de C em CE (0,81 e 0,82; respectivamente), indicando a alta relação de P e K com a MOS em ecossistemas naturais. A alta variabilidade espacial associada à aplicação de fertilizantes (P e K) no sulco de plantio pode ter mascarado os resultados dos estoques. A principal fonte destes nutrientes para o solo foi o fertilizante aplicado e não a MOS
Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B
Aims. The aim of this paper is to study deuterated water in the solar-type
protostars NGC1333 IRAS4A and IRAS4B, to compare their HDO abundance
distribution with other star-forming regions, and to constrain their HDO/H2O
ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based
telescopes, we observed several HDO lines covering a large excitation range
(Eup/k=22-168 K) towards these protostars and an outflow position. Non-LTE
radiative transfer codes were then used to determine the HDO abundance profiles
in these sources. Results. The HDO fundamental line profiles show a very broad
component, tracing the molecular outflows, in addition to a narrower emission
component and a narrow absorbing component. In the protostellar envelope of
NGC1333 IRAS4A, the HDO inner (T>100 K) and outer (T<100 K) abundances with
respect to H2 are estimated at 7.5x10^{-9} and 1.2x10^{-11}, respectively,
whereas, in NGC1333 IRAS4B, they are 1.0x10^{-8} and 1.2x10^{-10},
respectively. Similarly to the low-mass protostar IRAS16293-2422, an absorbing
outer layer with an enhanced abundance of deuterated water is required to
reproduce the absorbing components seen in the fundamental lines at 465 and 894
GHz in both sources. This water-rich layer is probably extended enough to
encompass the two sources as well as parts of the outflows. In the outflows
emanating from NGC1333 IRAS4A, the HDO column density is estimated at about
(2-4)x10^{13} cm^{-2}, leading to an abundance of about (0.7-1.9)x10^{-9}. An
HDO/H2O ratio between 7x10^{-4} and 9x10^{-2} is derived in the outflows. In
the warm inner regions of these two sources, we estimate the HDO/H2O ratios at
about 1x10^{-4}-4x10^{-3}. This ratio seems higher (a few %) in the cold
envelope of IRAS4A, whose possible origin is discussed in relation to formation
processes of HDO and H2O.Comment: 16 pages, 13 figure
Master crossover behavior of parachor correlations for one-component fluids
The master asymptotic behavior of the usual parachor correlations, expressing
surface tension as a power law of the density difference
between coexisting liquid and vapor, is analyzed for a
series of pure compounds close to their liquid-vapor critical point, using only
four critical parameters , , and ,
for each fluid.
... The main consequences of these theoretical estimations are discussed in
the light of engineering applications and process simulations where parachor
correlations constitute one of the most practical method for estimating surface
tension from density and capillary rise measurements
Herschel-HIFI observations of high-J CO and isotopologues in star-forming regions:from low to high mass
Context. Our understanding of the star formation process has traditionally been confined to certain mass or luminosity boundaries because most studies focus only on low-, intermediate-, or high-mass star-forming regions. Therefore, the processes that regulate the formation of these different objects have not been effectively linked. As part of the "Water In Star-forming regions with Herschel" (WISH) key programme, water and other important molecules, such as CO and OH, have been observed in 51 embedded young stellar objects (YSOs). The studied sample covers a range of luminosities from 10(5) L-circle dot.Aims. We analyse the CO line emission towards a large sample of embedded protostars in terms of both line intensities and profiles. This analysis covers a wide luminosity range in order to achieve better understanding of star formation without imposing luminosity boundaries. In particular, this paper aims to constrain the dynamics of the environment in which YSOs form.Methods. Herschel-HIFI spectra of the (CO)-C-12 J = 10-9, (CO)-C-13 J = 10-9 and (CO)-O-18 J = 5-4, J = 9-8 and J = 10-9 lines were analysed for a sample of 51 embedded protostars. In addition, JCMT spectra of (CO)-C-12 J = 3-2 and (CO)-O-18 J = 3-2 extend this analysis to cooler gas components. We focussed on characterising the shape and intensity of the CO emission line profiles by fitting the lines with one or two Gaussian profiles. We compared the values and results of these fits across the entire luminosity range covered by WISH observations. The effects of different physical parameters as a function of luminosity and the dynamics of the envelope-outflow system were investigated.Results. All observed CO and isotopologue spectra show a strong linear correlation between the logarithms of the line and bolometric luminosities across six orders of magnitude on both axes. This suggests that the high-J CO lines primarily trace the amount of dense gas associated with YSOs and that this relation can be extended to larger (extragalactic) scales. The majority of the detected (CO)-C-12 line profiles can be decomposed into a broad and a narrow Gaussian component, while the (CO)-O-18 spectra are mainly fitted with a single Gaussian. For low-and intermediate-mass protostars, the width of the (CO)-O-18 J = 9-8 line is roughly twice that of the (CO)-O-18 J = 3-2 line, suggesting increased turbulence/infall in the warmer inner envelope. For high-mass protostars, the line widths are comparable for lower-and higher-J lines. A broadening of the line profile is also observed from pre-stellar cores to embedded protostars, which is due mostly to non-thermal motions (turbulence/infall). The widths of the broad (CO)-C-12 J = 3-2 and J = 10-9 velocity components correlate with those of the narrow (CO)-O-18 J = 9-8 profiles, suggesting that the entrained outflowing gas and envelope motions are related but independent of the mass of the protostar. These results indicate that physical processes in protostellar envelopes have similar characteristics across the studied luminosity range.</p
The abundance of C18O and HDO in the envelope and hot core of the intermediate mass protostar NGC 7129 FIRS 2
NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is
associated with two energetic bipolar outflows and displays clear signs of the
presence of a hot core. It has been extensively observed with ground based
telescopes and within the WISH Guaranteed Time Herschel Key Program. We present
new observations of the C18O 3-2 and the HDO 3_{12}-2_{21} lines towards NGC
7129 FIRS 2. Combining these observations with Herschel data and modeling their
emissions, we constrain the C18O and HDO abundance profiles across the
protostellar envelope. In particular, we derive the abundance of C18O and HDO
in the hot core. The intensities of the C18O lines are well reproduced assuming
that the C18O abundance decreases through the protostellar envelope from the
outer edge towards the centre until the point where the gas and dust reach the
CO evaporation temperature (~20-25 K) where the C18O is released back to the
gas phase. Once the C18O is released to the gas phase, the modelled C18O
abundance is found to be ~1.6x10^{-8}, which is a factor of 10 lower than the
reference abundance. This result is supported by the non-detection of C18O 9-8,
which proves that even in the hot core (T_k>100 K) the CO abundance must be 10
times lower than the reference value. Several scenarios are discussed to
explain this C18O deficiency. One possible explanation is that during the
pre-stellar and protostellar phase, the CO is removed from the grain mantles by
reactions to form more complex molecules. Our HDO modeling shows that the
emission of HDO 3_{12}-2_{21} line is maser and comes from the hot core
(T_k>100 K). Assuming the physical structure derived by Crimier et al. (2010),
we determine a HDO abundance of ~0.4 - 1x10^{-7} in the hot core of this IM
protostar, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS
16293-2422.Comment: 10 pages, 7 figure
Reconstruction of the birth of a male sex chromosome present in Atlantic herring
The mechanisms underlying sex determination are astonishingly plastic. Particularly the triggers for the molecular machinery, which recalls either the male or female developmental program, are highly variable and have evolved independently and repeatedly. Fish show a huge variety of sex determination systems, including both genetic and environmental triggers. The advent of sex chromosomes is assumed to stabilize genetic sex determination. However, because sex chromosomes are notoriously cluttered with repetitive DNA and pseudogenes, the study of their evolution is hampered. Here we reconstruct the birth of a Y chromosome present in the Atlantic herring. The region is tiny (230 kb) and contains only three intact genes. The candidate male-determining gene BMPR1BBY encodes a truncated form of a BMP1B receptor, which originated by gene duplication and translocation and underwent rapid protein evolution. BMPR1BBY phosphorylates SMADs in the absence of ligand and thus has the potential to induce testis formation. The Y region also contains two genes encoding subunits of the sperm-specific Ca2+ channel CatSper required for male fertility. The herring Y chromosome conforms with a characteristic feature of many sex chromosomes, namely, suppressed recombination between a sex-determining factor and genes that are beneficial for the given sex. However, the herring Y differs from other sex chromosomes in that suppression of recombination is restricted to an similar to 500-kb region harboring the male-specific and sex-associated regions. As a consequence, any degeneration on the herring Y chromosome is restricted to those genes located in the small region affected by suppressed recombination
Fluctuations of elastic interfaces in fluids: Theory and simulation
We study the dynamics of elastic interfaces-membranes-immersed in thermally
excited fluids. The work contains three components: the development of a
numerical method, a purely theoretical approach, and numerical simulation. In
developing a numerical method, we first discuss the dynamical coupling between
the interface and the surrounding fluids. An argument is then presented that
generalizes the single-relaxation time lattice-Boltzmann method for the
simulation of hydrodynamic interfaces to include the elastic properties of the
boundary. The implementation of the new method is outlined and it is tested by
simulating the static behavior of spherical bubbles and the dynamics of bending
waves. By means of the fluctuation-dissipation theorem we recover analytically
the equilibrium frequency power spectrum of thermally fluctuating membranes and
the correlation function of the excitations. Also, the non-equilibrium scaling
properties of the membrane roughening are deduced, leading us to formulate a
scaling law describing the interface growth, W^2(L,T)=L^3 g[t/L^(5/2)], where
W, L and T are the width of the interface, the linear size of the system and
the temperature respectively, and g is a scaling function. Finally, the
phenomenology of thermally fluctuating membranes is simulated and the frequency
power spectrum is recovered, confirming the decay of the correlation function
of the fluctuations. As a further numerical study of fluctuating elastic
interfaces, the non-equilibrium regime is reproduced by initializing the system
as an interface immersed in thermally pre-excited fluids.Comment: 15 pages, 11 figure
HERSCHEL-HIFI spectroscopy of the intermediate mass protostar NGC7129 FIRS 2
HERSCHEL-HIFI observations of water from the intermediate mass protostar
NGC7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this
star formation environment. Six spectral settings, covering four H216O and two
H218O lines, were observed and all but one H218O line were detected. The four
H2 16 O lines discussed here share a similar morphology: a narrower, \approx 6
km/s, component centered slightly redward of the systemic velocity of NGC7129
FIRS 2 and a much broader, \approx 25 km/s component centered blueward and
likely associated with powerful outflows. The narrower components are
consistent with emission from water arising in the envelope around the
intermediate mass protostar, and the abundance of H2O is constrained to \approx
10-7 for the outer envelope. Additionally, the presence of a narrow
self-absorption component for the lowest energy lines is likely due to
self-absorption from colder water in the outer envelope. The broader component,
where the H2O/CO relative abundance is found to be \approx 0.2, appears to be
tracing the same energetic region that produces strong CO emission at high J.Comment: 6 pages, 4 figures, accepted by A&
Sensitive limits on the abundance of cold water vapor in the DM Tau protoplanetary disk
We performed a sensitive search for the ground-state emission lines of ortho-
and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI
instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s
channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the
1_{11}--0_{00} line. We report a very tentative detection, however, of the
1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of
T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s.
The latter constitutes a 6sigma detection. Regardless of the reality of this
tentative detection, model calculations indicate that our sensitive limits on
the line strengths preclude efficient desorption of water in the UV illuminated
regions of the disk. We hypothesize that more than 95-99% of the water ice is
locked up in coagulated grains that have settled to the midplane.Comment: 5 pages, 3 figures. Accepted for publication in the Herschel HIFI
special issue of A&
Hydrides in Young Stellar Objects: Radiation tracers in a protostar-disk-outflow system
Context: Hydrides of the most abundant heavier elements are fundamental
molecules in cosmic chemistry. Some of them trace gas irradiated by UV or
X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a
prototypical region of high-mass star formation. Methods: W3 IRS5 was observed
by HIFI on the Herschel Space Observatory with deep integration (about 2500 s)
in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and
the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J=1-0 lines
are found mostly in absorption, but also appear to exhibit weak emission
(P-Cyg-like). Emission requires high density, thus originates most likely near
the protostar. This is corroborated by the absence of line shifts relative to
the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong
absorption components at a velocity shifted relative to W3 IRS5, which are
attributed to foreground clouds. Conclusions: The molecular column densities
derived from observations correlate well with the predictions of a model that
assumes the main emission region is in outflow walls, heated and irradiated by
protostellar UV radiation.Comment: Astronomy and Astrophysics Letters, in pres
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