18 research outputs found
Estimating Carbon Dynamics in an Intact Lowland Mixed Dipterocarp Forest Using a Forest Carbon Model
Intact dipterocarp forests in Asia act as crucial carbon (C) reservoirs, and it is therefore important to investigate the C dynamics in these forests. We estimated C dynamics, together with net ecosystem production (NEP), in an intact tropical dipterocarp forest of Brunei Darussalam. Fifty-four simulation units (plots; 20 m Ă 20 m) were established and initial C stocks were determined via direct field measurement. The C dynamics were annually simulated with a regression model and the Forest Biomass and Dead organic matter Carbon (FBDC) model. The initial C stock (Mg CÎhaâ1) of biomass, litter, dead wood and mineral soil were 213.1 ± 104.8, 2.0 ± 0.8, 31.3 ± 38.8, and 80.7 ± 15.5, respectively. Their annual changes (Mg CÎhaâ1Îyearâ1) were 3.2 ± 1.1, 0.2 ± 0.2, â3.7 ± 6.1, and â0.3 ± 1.1, respectively. NEP was â0.6 ± 6.1 Mg CÎhaâ1Îyearâ1, showing large heterogeneity among the plots. The initial C stocks of biomass and dead wood, biomass turnover rates and dead wood decay rates were elucidated as dominant factors determining NEP in a sensitivity analysis. Accordingly, investigation on those input data can constrain an uncertainty in determining NEP in the intact tropical forests
Fabrication of CdS/CdTe-based thin film solar cells using an electrochemical technique
Thin film solar cells based on cadmium telluride (CdTe) are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i- and p-type CdTe can be grown easily by electroplating. These material layers consist of nano- and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n - p or p - n conversion upon heat treatment. The general trend of CdCl2 treatment is to gradually change the CdTe materialâs n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV) effect as well as making use of IR photons from the surroundings when fully optimised
Conformally flat spacetimes and Weyl frames
We discuss the concepts of Weyl and Riemann frames in the context of metric
theories of gravity and state the fact that they are completely equivalent as
far as geodesic motion is concerned. We apply this result to conformally flat
spacetimes and show that a new picture arises when a Riemannian spacetime is
taken by means of geometrical gauge transformations into a Minkowskian flat
spacetime. We find out that in the Weyl frame gravity is described by a scalar
field. We give some examples of how conformally flat spacetime configurations
look when viewed from the standpoint of a Weyl frame. We show that in the
non-relativistic and weak field regime the Weyl scalar field may be identified
with the Newtonian gravitational potential. We suggest an equation for the
scalar field by varying the Einstein-Hilbert action restricted to the class of
conformally-flat spacetimes. We revisit Einstein and Fokker's interpretation of
Nordstr\"om scalar gravity theory and draw an analogy between this approach and
the Weyl gauge formalism. We briefly take a look at two-dimensional gravity as
viewed in the Weyl frame and address the question of quantizing a conformally
flat spacetime by going to the Weyl frame.Comment: LATEX - 18 page
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
Genetic variation and demographic history of Sudan desert sheep reveal two diversified lineages
More than 400 million sheep are raised on the African continent, the majority of which are indigenous and are primarily reared for sustenance. They have effectively adapted to various climatic and production environments, surviving and flourishing. The genetic relationships among these sheep populations remain understudied. Herein, we sequenced the entire mitochondrial DNA control region of 120 animals from Hamary and Kabashi and their crossbreed (Hamary x Kabashi) of Sudan desert sheep (SDS) to understand their maternal-inherited genetic variation and demographic history profiles and relate those to the history of sheep pastoralism on the African continent. The results show a diversified and predominant D- loop haplogroup B (nâ=â102, 85%), with all other sequences belonging to haplogroup A. Most of the maternal genetic variation was partitioned between haplogroup (76.3%) while within haplogroup accounted for 23.7% of the variation. However, little genetic differentiation was observed among the two breeds and their crosses, with our results supporting a Hamari maternal origin for the crossbreed. Bayesian coalescent-based analysis reveals distinct demographic history between the two haplogroups, two breeds and their crosses. Comparison of the two haplogroup showed that haplogroup B experienced an earlier expansion than haplogroup A. Unlike the breed-based comparison, the expansion of the two breeds started roughly at the same time, around 6500 years ago, with Kabashi having a slightly greater effective population size. The maternal ancestors of SDS may have diverged before their introduction to the African continent. This study provides novel insights into the early history of these two main breeds of Sudan desert sheep and their crosses
Influence of Cu2+ substitution on the structural, optical, magnetic, and antibacterial behaviour of zinc ferrite nanoparticles
Ferrite nanoparticles are an emerging material for industrial and biomedical applications. Herein, a simple non-aqueous solâgel method is used to synthesize CuxZn(1-x)Fe2O4 (x = 0.0, 0.25, 0.5, and 0.75) nanoparticles. X-ray diffraction (XRD), scanning electron microscopy (SEM), UVâVis spectroscopy, and a vibrating-sample magnetometer (VSM) were utilized to investigate the structural formation and magnetic merits of the prepared ferrite nanoparticles. The Rietveld refinement of the X-ray diffraction pattern confirmed the formation of single-phase cubic structures with Fd3ÂŻm space groups for all samples. The increase in cu2+ concentration in zinc ferrite nanoparticles decreases the lattice parameters from 8.4418 to 8.4368. The energy gap of cu2+-doped zinc ferrite increases from 1.89 to 2.04 eV with a decrease in particle size. MH loop revealed an increase in Ms and Mr Parameters as Hc reduces with an increase in Cu2+ concentration in the zinc ferrite matrix. It was discovered that an increase in Cu2+ content improved the antibacterial activities of Cu2+-doped zinc ferrite against all bacterial species