6,828 research outputs found
Modeling impacts of management on carbon sequestration and trace gas emissions in forested wetland ecosystems, Environ
ABSTRACT / A process-based model, Wetland-DNDC, was modified to enhance its capacity to predict the impacts of management practices on carbon sequestration in and trace gas emissions from forested wetland ecosystems. The modifications included parameterization of management practices (e.g., forest harvest, chopping, burning, water management, fertilization, and tree planting), inclusion of detailed anaerobic biogeochemical processes for wetland soils, and utilization of hydrological models for quantifying water table variations. A 150-year management scenario consisting of three stages of wetland forest, deforestation/drainage, and wetland restoration was simulated with the Wetland-DNDC for two wetlands in Minnesota and Florida, USA. The impacts of the management scenario on carbon ecosystem exchange, methane emission, and nitrous oxide emission were quantified and assessed. The results suggested that: (1) the same management scenario produced very different consequences on global warming due to the contrast climate conditions; and (2) methane and nitrous oxide fluxes played nonnegligible roles in mitigation in comparison with carbon sequestration
Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample
The chemical compositions of seven Carbon-Enhanced Metal-Poor (CEMP) turn-off
stars are determined from high-resolution spectroscopy. Five of them are
selected from the SDSS/SEGUE sample of metal-poor stars. The effective
temperatures of these objects are all higher than 6000 K, while their
metallicities, parametrized by [Fe/H], are all below -2. Six of our program
objects exhibit high abundance ratios of barium ([Ba/H]> +1), suggesting large
contributions of the products of former AGB companions via mass transfer across
binary systems. Combining our results with previous studies provides a total of
20 CEMP main-sequence turn-off stars for which the abundances of carbon and at
least some neutron-capture elements are determined. Inspection of the [C/H]
ratios for this sample of CEMP turn-off stars show that they are generally
higher than those of CEMP giants; their dispersion in this ratio is also
smaller. We take these results to indicate that the carbon-enhanced material
provided from the companion AGB star is preserved at the surface of turn-off
stars with no significant dilution. In contrast, a large dispersion in the
observed [Ba/H] is found for the sample of CEMP turn-off stars, suggesting that
the efficiency of the s-process in very metal-poor AGB stars may differ greatly
from star to star. Four of the six stars from the SDSS/SEGUE sample exhibit
kinematics that are associated with membership in the outer-halo population, a
remarkably high fraction.Comment: 45 pages, 10 figures, 10 tables, Astrophysical Journal, in pres
Ultra-broadband Light Absorption by a Sawtooth Anisotropic Metamaterial Slab
We present an ultra broadband thin-film infrared absorber made of saw-toothed
anisotropic metamaterial. Absorbtivity of higher than 95% at normal incidence
is supported in a wide range of frequencies, where the full absorption width at
half maximum is about 86%. Such property is retained well at a very wide range
of incident angles too. Light of shorter wavelengths are harvested at upper
parts of the sawteeth of smaller widths, while light of longer wavelengths are
trapped at lower parts of larger tooth widths. This phenomenon is explained by
the slowlight modes in anisotropic metamaterial waveguide. Our study can be
applied in the field of designing photovoltaic devices and thermal emitters.Comment: 12 pages, 4 picture
Glueball spectrum based on a rigorous three-dimensional relativistic equation for two-gluon bound states II: calculation of the glueball spectrum
In the preceding paper, a rigorous three-dimensional relativistic equation
for two-gluon bound states was derived from the QCD with massive gluons and
represented in the angular momentum representation. In order to apply this
equation to calculate the glueball spectrum, in this paper, the equation is
recast in an equivalent three-dimensional relativistic equation satisfied by
the two-gluon positive energy state amplitude. The interaction Hamiltonian in
the equation is exactly derived and expressed as a perturbative series. The
first term in the series describes the one-gluon exchange interaction which
includes fully the retardation effect in it. This term plus the linear
confining potential are chosen to be the interaction Hamiltonian and employed
in the practical calculation. With the integrals containing three and four
spherical Bessel functions in the QCD vertices being analytically calculated,
the interaction Hamiltonian is given an explicit expression in the angular
momentum representation. Numerically solving the relativistic equation with
taking the contributions arising from the retardation effect and the
longitudinal mode of gluon fields into account, a set of masses for the
and glueball states are
obtained and are in fairly good agreement with the predictions given by the
lattice simulatio
The current system associated with the boundary of plasma bubbles
The current system associated with the boundary of plasma bubbles in the Earth's magnetotail has been studied by employing Cluster multipoint observations. We have investigated the currents in both the dipolarization front (DF, leading edge of the plasma bubble) and the trailing edge of the plasma bubble. The distribution of currents at the edge indicates that there is a current circuit in the boundary of a plasma bubble. The fieldâaligned currents in the trailing edge of the plasma bubble are flowing toward the ionosphere (downward) on the dawnside and away from the ionosphere (upward) on the duskside, in the same sense as regionâ1 current. Together with previous studies of the current distributions in the DF and magnetic dip region, we have obtained a more complete picture of the current system surrounding the boundary of plasma bubble. This current system is very similar to the substorm current wedge predicted by MHD simulation models but with much smaller scale.Key PointsWe have obtained a current circuit in the boundary of plasma bubbleThe FACs in the trailing edge of plasma bubble is also regionâ1âsenseThe current and FACs system is similar to SCW but with much smaller scalePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110641/1/grl52338.pd
Initial/boundary-value problems of tumor growth within a host tissue
This paper concerns multiphase models of tumor growth in interaction with a
surrounding tissue, taking into account also the interplay with diffusible
nutrients feeding the cells. Models specialize in nonlinear systems of possibly
degenerate parabolic equations, which include phenomenological terms related to
specific cell functions. The paper discusses general modeling guidelines for
such terms, as well as for initial and boundary conditions, aiming at both
biological consistency and mathematical robustness of the resulting problems.
Particularly, it addresses some qualitative properties such as a priori
nonnegativity, boundedness, and uniqueness of the solutions. Existence of the
solutions is studied in the one-dimensional time-independent case.Comment: 30 pages, 5 figure
Pressure effects on superconducting properties of single-crystalline Co doped NaFeAs
Resistivity and magnetic susceptibility measurements under external pressure
were performed on single-crystals NaFe1-xCoxAs (x=0, 0.01, 0.028, 0.075,
0.109). The maximum Tc enhanced by pressure in both underdoped and optimally
doped NaFe1-xCoxAs is the same, as high as 31 K. The overdoped sample with x =
0.075 also shows a positive pressure effect on Tc, and an enhancement of Tc by
13 K is achieved under pressure of 2.3 GPa. All the superconducting samples
show large positive pressure coefficient on superconductivity, being different
from Ba(Fe1-xCox)2As2. However, the superconductivity cannot be induced by
pressure in heavily overdoped non-superconducting NaFe0.891Co0.109As. These
results provide evidence for that the electronic structure is much different
between superconducting and heavily overdoped non-superconducting NaFe1-xCoxAs,
being consistent with the observation by angle-resolved photoemission
spectroscopy.Comment: 6 pages, 6 figure
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