342 research outputs found
Allometric Equations to Estimate Aboveground Biomass in Spotted Gum (Corymbia citriodora Subspecies variegata) Plantations in Queensland
Accurate equations are critical for estimating biomass and carbon accumulation for forest carbon projects, bioenergy, and other inventories. Allometric equations can provide a reliable and accurate method for estimating and predicting biomass and carbon sequestration. Cross-validatory assessments are also essential to evaluate the prediction ability of the selected model with satisfactory accuracy. We destructively sampled and weighed 52 sample trees, ranging from 11.8 to 42.0 cm in diameter at breast height from three plantations in Queensland to determine biomass. Weighted nonlinear models were used to explore the influence of different variables using two datasets: the first dataset (52 trees) included diameter at breast height (D), height (H) and wood density (ρ); and the second dataset (40 trees) also included crown diameter (CD) and crown volume (CV). Cross validation of independent data showed that using D alone proved to be the best performing model, with the lowest values of AIC = 434.4, bias = −2.2% and MAPE = 7.2%. Adding H and ρ improved the adjusted. R2 (Δ adj. R2 from 0.099 to 0.135) but did not improve AIC, bias and MAPE. Using the single variable of CV to estimate aboveground biomass (AGB) was better than CD, with smaller AIC and MAPE less than 2.3%. We demonstrated that the allometric equations developed and validated during this study provide reasonable estimates of Corymbia citriodora subspecies variegata (spotted gum) biomass. This equation could be used to estimate AGB and carbon in similar spotted gum plantations. In the context of global forest AGB estimations and monitoring, the CV variable could allow prediction of aboveground biomass using remote sensing datasets
Prospects for Determining the Mass Distributions of Galaxy Clusters on Large Scales Using Weak Gravitational Lensing
For more than two decades, the Navarro, Frenk, and White (NFW) model has stood the test of time; it has been used to describe the distribution of mass in galaxy clusters out to their outskirts. Stacked weak lensing measurements of clusters are now revealing the distribution of mass out to and beyond their virial radii, where the NFW model is no longer applicable. In this study we assess how well the parameterised Diemer & Kravstov (DK) density profile describes the characteristic mass distribution of galaxy clusters extracted from cosmological simulations. This is determined from stacked synthetic lensing measurements of the 50 most massive clusters extracted from the Cosmo-OWLS simulations, using the Dark Matter Only run and also the run that most closely matches observations. The characteristics of the data reflect the Weighing the Giants survey and data from the future Large Synoptic Survey Telescope (LSST). In comparison with the NFW model, the DK model favored by the stacked data, in particular for the future LSST data, where the number density of background galaxies is higher. The DK profile depends on the accretion history of clusters which is specified in the current study. Eventually however subsamples of galaxy clusters with qualities indicative of disparate accretion histories could be studied
Species-Specific Allometric Equations for Predicting Belowground Root Biomass in Plantations: Case Study of Spotted Gums (Corymbia citriodora subspecies variegata) in Queensland
Spotted gum (Corymbia citriodora spp. variegata; CCV) has been widely planted, has a wide natural distribution, and is the most important commercially harvested hardwood species in Queensland, Australia. It has a great capacity to sequester carbon, thus reducing the impact of CO2 emissions on climate. Belowground root biomass (BGB) plays an important role as a carbon sink in terrestrial ecosystems. To explore the potential of biomass and carbon accumulation belowground, we developed and validated models for CCV plantations in Queensland. The roots of twenty-three individual trees (size range 11.8–42.0 cm diameter at breast height) from three sites were excavated to a 1-m depth and were weighed to obtain BGB. Weighted nonlinear regression models were most reliable for estimating BGB. To evaluate the candidate models, the data set was cross-validated with 70% of the data used for training and 30% of the data used for testing. The cross-validation process was repeated 23 times and the validation of the models were averaged over 23 iterations. The best model for predicting spotted gum BGB was based on a single parameter, with the diameter at breast height (D) as an independent variable. The best equation BGB = 0.02933 × D2.5805 had an adjusted R2 of 0.854 and a mean absolute percentage error of 0.090%. This equation was tested against published BGB equations; the findings from this are discussed. Our equation is recommended to allow improved estimates of BGB for this species
Species-Specific Allometric Equations for Predicting Belowground Root Biomass in Plantations: Case Study of Spotted Gums (Corymbia citriodora subspecies variegata) in Queensland
Spotted gum (Corymbia citriodora spp. variegata; CCV) has been widely planted, has a wide natural distribution, and is the most important commercially harvested hardwood species in Queensland, Australia. It has a great capacity to sequester carbon, thus reducing the impact of CO2 emissions on climate. Belowground root biomass (BGB) plays an important role as a carbon sink in terrestrial ecosystems. To explore the potential of biomass and carbon accumulation belowground, we developed and validated models for CCV plantations in Queensland. The roots of twenty-three individual trees (size range 11.8–42.0 cm diameter at breast height) from three sites were excavated to a 1-m depth and were weighed to obtain BGB. Weighted nonlinear regression models were most reliable for estimating BGB. To evaluate the candidate models, the data set was cross-validated with 70% of the data used for training and 30% of the data used for testing. The cross-validation process was repeated 23 times and the validation of the models were averaged over 23 iterations. The best model for predicting spotted gum BGB was based on a single parameter, with the diameter at breast height (D) as an independent variable. The best equation BGB = 0.02933 × D2.5805 had an adjusted R2 of 0.854 and a mean absolute percentage error of 0.090%. This equation was tested against published BGB equations; the findings from this are discussed. Our equation is recommended to allow improved estimates of BGB for this species
Relics of cosmological quark-hadron phase transition
We propose that the amplified density fluctuations by the vanishing sound
velocity effect during the cosmological quark-hadron phase transition lead to
quark-gluon plasma lumps decoupled from the expansion of the universe, which
may evolve to quark nuggets (QNs). Assuming power-law spectrum of density
fluctuations, we investigate the parameter ranges for the QNs to play the role
of baryonic dark matter and give inhomogeneities which could affect big-bang
nucleosynthesis within the observational bounds of CMBR anisotropy. The QNs can
give the strongest constraint ever found on the spectral index.Comment: REVTEX, 4 pages, 2 eps figure
Wound healing gene-family expression differences between fetal and foreskin cells used for bioengineered skin substitutes
For tissue engineering, several cell types and tissues have been proposed as starting material. Allogenic skin products available for therapeutic usage are mostly developed with cell culture and with foreskin tissue of young individuals. Fetal skin cells offer a valuable solution for effective and safe tissue engineering for wounds due to their rapid growth and simple cell culture. By selecting families of genes that have been reported to be impli- cated in wound repair and particularly for scarless fetal wound healing including transforming growth factor-beta (TGF-b) superfamily, extracellular matrix, and nerve/angiogenesis growth factors, we have analyzed differences in their expression between fetal skin and foreskin cells, and the same passages. Of the five TGF-b superfamily genes analyzed by real-time reverse transcription–polymerase chain reaction, three were found to be signifi- cantly different with sixfold up-regulated for TGF-b2, and 3.8-fold for BMP- 6 in fetal cells, whereas GDF-10 was 11.8-fold down-regulated. For nerve growth factors, midkine was 36-fold down-regulated in fetal cells, and pleiotrophin was 4.76-fold up-regulated. We propose that fetal cells present technical and therapeutic advantages compared to foreskin cells for effective cell-based therapy for wound management, and overall differences in gene expression could contribute to the degree of efficiency seen in clinical use with these cells
The giant planet orbiting the cataclysmic binary DP Leonis
Planets orbiting post-common envelope binaries provide fundamental
information on planet formation and evolution, especially for the yet nearly
unexplored class of circumbinary planets. We searched for such planets in \odp,
an eclipsing short-period binary, which shows long-term eclipse-time
variations. Using published, reanalysed, and new mid-eclipse times of the white
dwarf in DP\,Leo, obtained between 1979 and 2010, we find agreement with the
light-travel-time effect produced by a third body in an elliptical orbit. In
particular, the measured binary period in 2009/2010 and the implied radial
velocity coincide with the values predicted for the motion of the binary and
the third body around the common center of mass. The orbital period, semi-major
axis, and eccentricity of the third body are P_c = 28.0 +/- 2.0 yrs, a_c = 8.2
+/- 0.4 AU, and e_c = 0.39 +/- 0.13. Its mass of M_c sin(i_c) = 6.1 +/- 0.5 M_J
qualifies it as a giant planet. It formed either as a first generation object
in a protoplanetary disk around the original binary or as a second generation
object in a disk formed in the common envelope shed by the progenitor of the
white dwarf. Even a third generation origin in matter lost from the present
accreting binary can not be entirely excluded. We searched for, but found no
evidence for a fourth body.Comment: Accepted by A&
Dynamical evolution of the Universe in the quark-hadron phase transition and possible nugget formation
We study the dynamics of first-order phase transition in the early Universe
when it was old with quarks and gluons condensing into hadrons.
We look at how the Universe evolved through the phase transition in small as
well as large super cooling scenario, specifically exploring the formation of
quark nuggets and their possible survival. The nucleation of the hadron phase
introduces new distance scales in the Universe, which we estimate along with
the hadron fraction, temperature, nucleation time etc. It is of interest to
explore whether there is a relic signature of this transition in the form of
quark nuggets which might be identified with the recently observed dark objects
in our galactic halo and account for the Dark Matter in the Universe at
present.Comment: LaTeX file with four postscript figure
The quest for companions to post-common envelope binaries. II. NSVS14256825 and HS0705+6700
We report new mid-eclipse times of the two close binaries NSVS14256825 and
HS0705+6700, harboring an sdB primary and a low-mass main-sequence secondary.
Both objects display clear variations in the measured orbital period, which can
be explained by the action of a third object orbiting the binary. If this
interpretation is correct, the third object in NSVS14256825 is a giant planet
with a mass of roughly 12 M_Jup. For HS0705+6700, we provide evidence that
strengthens the case for the suggested periodic nature of the eclipse time
variation and reduces the uncertainties in the parameters of the brown dwarf
implied by that model. The derived period is 8.4 yr and the mass is 31 M_Jup,
if the orbit is coplanar with the binary. This research is part of the
PlanetFinders project, an ongoing collaboration between professional
astronomers and student groups at high schools.Comment: Accepted by Astron. and Astrophy
The quest for companions to post-common envelope binaries: I. Searching a sample of stars from the CSS and SDSS
As part of an ongoing collaboration between student groups at high schools
and professional astronomers, we have searched for the presence of
circum-binary planets in a bona-fide unbiased sample of twelve post-common
envelope binaries (PCEBs) from the Catalina Sky Survey (CSS) and the Sloan
Digital Sky Survey (SDSS). Although the present ephemerides are significantly
more accurate than previous ones, we find no clear evidence for orbital period
variations between 2005 and 2011 or during the 2011 observing season. The
sparse long-term coverage still permits O-C variations with a period of years
and an amplitude of tens of seconds, as found in other systems. Our
observations provide the basis for future inferences about the frequency with
which planet-sized or brown-dwarf companions have either formed in these
evolved systems or survived the common envelope (CE) phase.Comment: accepted by A&
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