1,531 research outputs found
Quantifying the role of fire in the Earth system – Part 2: Impact on the net carbon balance of global terrestrial ecosystems for the 20th century
Fire is the primary form of terrestrial ecosystem disturbance on a global
scale. It affects the net carbon balance of terrestrial ecosystems by
emitting carbon directly and immediately into the atmosphere from biomass
burning (the fire direct effect), and by changing net ecosystem productivity
and land-use carbon loss in post-fire regions due to biomass burning and
fire-induced vegetation mortality (the fire indirect effect). Here, we
provide the first quantitative assessment of the impact of fire on the net
carbon balance of global terrestrial ecosystems during the 20th century, and
investigate the roles of fire's direct and indirect effects. This is done by
quantifying the difference between the 20th century fire-on and fire-off
simulations with the NCAR Community Land Model CLM4.5 (prescribed vegetation
cover and uncoupled from the atmospheric model) as a model platform. Results
show that fire decreases the net carbon gain of global terrestrial ecosystems
by 1.0 Pg C yr<sup>−1</sup> averaged across the 20th century, as a result of the
fire direct effect (1.9 Pg C yr<sup>−1</sup>) partly offset by the indirect
effect (−0.9 Pg C yr<sup>−1</sup>). Post-fire regions generally experience
decreased carbon gains, which is significant over tropical savannas and some
North American and East Asian forests. This decrease is due to the direct
effect usually exceeding the indirect effect, while they have similar spatial
patterns and opposite sign. The effect of fire on the net carbon balance
significantly declines until ∼1970 with a trend of 8 Tg C yr<sup>−1</sup>
due to an increasing indirect effect, and increases subsequently with a trend
of 18 Tg C yr<sup>−1</sup> due to an increasing direct effect. These results help
constrain the global-scale dynamics of fire and the terrestrial carbon cycle
Phase Coexistence and Edge Currents in the Chiral Lennard-Jones Fluid
We study a model chiral fluid in two dimensions composed of Brownian disks
interacting via a Lennard-Jones potential and a non-conservative transverse
force, mimicking colloids spinning at a rate . The system exhibits a
phase separation between a chiral liquid and a dilute gas phase that can be
characterized using a thermodynamic framework. We compute the equations of
state and show that the surface tension controls interface corrections to the
coexisting pressure predicted from the equal-area construction. Transverse
forces increase surface tension and generate edge currents at the liquid-gas
interface. The analysis of these currents shows that the rotational viscosity
introduced in chiral hydrodynamics is consistent with microscopic bulk
mechanical measurements. Chirality can also break the solid phase, giving rise
to a dense fluid made of rotating hexatic patches. Our work paves the way for
the development of the statistical mechanics of chiral particles assemblies.Comment: 6 pages, 4 figures, Supplemental Materia
Meteorological factors in Earth-satellite propagation
Using the COMSTAR D/4 28.56 GHz beacon as a source, a differential gain experiment was performed by connecting a 5-meter paraboloidal antenna and a 0.6-meter paraboloidal antenna alternately to the same receiver. Substantial differential gain changes were observed during some, but not all, rain events. A site-diversity experiment was implemented which consists of two 28.56 GHz radiometers separated by 9 km. The look-angle corresponds to that of the D/4 beacon, and data were obtained with one radiometer during several weeks of concurrent beacon operation to verify the system calibration. A theoretical study of the effect of scattering from a nonuniform rain distribution along the path is under way to aid in interpreting the results of this experiment. An improved empirical site diversity-gain model was derived from data in the literature relating to 34 diversity experiments. Work on the experiment control and data acquisition system is continuing with a view toward future experiments
Cytotoxic Effects of Hexavalent and Trivalent Chromium on Mammalian Cells In Vitro
The cytotoxic effects of hexavalent (k2Cr2O7) and trivalent (CrCl3) chromium compounds have been studied in cultured hamster fibroblasts (BHK line) and human epithelial-like cells (HEp line)
Multi-View Polarimetric Scattering Cloud Tomography and Retrieval of Droplet Size
Tomography aims to recover a three-dimensional (3D) density map of a medium or an object. In medical imaging, it is extensively used for diagnostics via X-ray computed tomography (CT). We define and derive a tomography of cloud droplet distributions via passive remote sensing. We use multi-view polarimetric images to fit a 3D polarized radiative transfer (RT) forward model. Our motivation is 3D volumetric probing of vertically-developed convectively-driven clouds that are ill-served by current methods in operational passive remote sensing. Current techniques are based on strictly 1D RT modeling and applied to a single cloudy pixel, where cloud geometry defaults to that of a plane-parallel slab. Incident unpolarized sunlight, once scattered by cloud-droplets, changes its polarization state according to droplet size. Therefore, polarimetric measurements in the rainbow and glory angular regions can be used to infer the droplet size distribution. This work defines and derives a framework for a full 3D tomography of cloud droplets for both their mass concentration in space and their distribution across a range of sizes. This 3D retrieval of key microphysical properties is made tractable by our novel approach that involves a restructuring and differentiation of an open-source polarized 3D RT code to accommodate a special two-step optimization technique. Physically-realistic synthetic clouds are used to demonstrate the methodology with rigorous uncertainty quantification
One sided Star and Core orthogonality of matrices
We investigate two one-sided orthogonalities of matrices, the first of which
is left (right) -orthogonality for rectangular matrices and the other is
left (right) core-orthogonality of index matrices. We obtain some basic
results for these matrices, their canonical forms, and characterizations. Also,
relations between left (right) orthogonal matrices and parallel sums are
investigated. Finally under these one-sided orthogonalities we explore the
conditions of additivity of the Moore-Penrose inverse and the core inverse
The relationship of readiness factors to Jan. first grade reading achievement
Thesis (Ed.M.)--Boston Universit
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