High-resolution mapping of forest carbon stocks in the Colombian Amazon

High-resolution mapping of tropical forest carbon stocks can assist forest management and improve implementation of large-scale carbon retention and enhancement programs. Previous high-resolution approaches have relied on field plot and/or light detection and ranging (LiDAR) samples of aboveground carbon density, which are typically upscaled to larger geographic areas using stratification maps. Such efforts often rely on detailed vegetation maps to stratify the region for sampling, but existing tropical forest maps are often too coarse and field plots too sparse for high-resolution carbon assessments. We developed a top-down approach for high-resolution carbon mapping in a 16.5 million ha region (> 40%) of the Colombian Amazon – a remote landscape seldom documented. We report on three advances for large-scale carbon mapping: (i) employing a universal approach to airborne LiDAR-calibration with limited field data; (ii) quantifying environmental controls over carbon densities; and (iii) developing stratification- and regression-based approaches for scaling up to regions outside of LiDAR coverage. We found that carbon stocks are predicted by a combination of satellite-derived elevation, fractional canopy cover and terrain ruggedness, allowing upscaling of the LiDAR samples to the full 16.5 million ha region. LiDAR-derived carbon maps have 14% uncertainty at 1 ha resolution, and the regional map based on stratification has 28% uncertainty in any given hectare. High-resolution approaches with quantifiable pixel-scale uncertainties will provide the most confidence for monitoring changes in tropical forest carbon stocks. Improved confidence will allow resource managers and decision makers to more rapidly and effectively implement actions that better conserve and utilize forests in tropical regions

Amazon tree dominance across forest strata

The forests of Amazonia are among the most biodiverse plant communities on Earth. Given the immediate threats posed by climate and land-use change, an improved understanding of how this extraordinary biodiversity is spatially organized is urgently required to develop effective conservation strategies. Most Amazonian tree species are extremely rare but a few are common across the region. Indeed, just 227 ‘hyperdominant’ species account for >50% of all individuals >10 cm diameter at 1.3 m in height. Yet, the degree to which the phenomenon of hyperdominance is sensitive to tree size, the extent to which the composition of dominant species changes with size class and how evolutionary history constrains tree hyperdominance, all remain unknown. Here, we use a large floristic dataset to show that, while hyperdominance is a universal phenomenon across forest strata, different species dominate the forest understory, midstory and canopy. We further find that, although species belonging to a range of phylogenetically dispersed lineages have become hyperdominant in small size classes, hyperdominants in large size classes are restricted to a few lineages. Our results demonstrate that it is essential to consider all forest strata to understand regional patterns of dominance and composition in Amazonia. More generally, through the lens of 654 hyperdominant species, we outline a tractable pathway for understanding the functioning of half of Amazonian forests across vertical strata and geographical locations

Temperature and hydrostatic pressure effects on the photonic band structure of a 2D honeycomb lattice

A standard plane-wave expansion method is used to investigate temperature and applied hydrostatic pressure dependence of the photonic band structure of a two-dimensional honeycomb lattice composed by cylindrical rods of GaAs, embedded in air. Present results suggest that for H-polarization an increment of hydrostatic pressure and temperature not only shifts the photonic band gaps, but diminish the energy width of the second and upper band gaps, while for E-polarization the first band gap is shifted to higher energies, without modifying the width of the other band-gaps, consequently modifying the tunability of this system.Departamento Administrativo de Ciencia, Tecnología e Innovación [CO] Colciencias1106-452-21296Control cuántico de las propiedades electrónicas y de espín en nanoestructuras inorgánicas, orgánicas y biológicasn

Theoretical study of the density of shallow-acceptor impurity states in quantum-size GaAs microcrystals

A theoretical study of the density of states of shallow-acceptor impurities in cylindrically shaped GaAs low-dimensional systems is presented. The acceptor states are described within a variational scheme in the effective-mass approximation and using an infinite confinement potential model. The density of impurity states is calculated for a homogeneous distribution of acceptor impurities within the low-dimensional heterostructure. For dimensions of the system in which the length is much larger than the radius we obtain two well-defined peaks, associated with accepters either at the on-centre position or at the edge position in the low-dimensional system. Ln addition, we have observed the appearance in the density of impurity states of an additional peak (with low relative intensity and binding energy) associated with impurities located near to the intersection between the cylindrical surface and the top or bottom end faces of the structure. The general behaviour we observed in the density of impurity states describes reasonably well the spectral features present in experimental and theoretical data about acceptor-related photoluminescence spectra in GaAs microcrystals, cylindrical GaAs quantum-well wires and cylindrically shaped finite-length GaAs heterostructures.14649650

Density of impurity states and donor-related optical absorption spectra of GaAs-(Ga,Al)As semiconductor heterostructures

A variational procedure in the effective-mass approximation was used in the study of both the density of donor states and the associated optical absorption spectra of GaAs-(Ga,Al)As semiconductor heterostructures. Calculations were performed for a finite, cylindrical-shaped quantum box of GaAs within the infinite-barrier approximation and considering an homogeneous distribution of impurities within the low-dimensional heterostructure. Theoretical results for the density of impurity states and donor-related optical absorption spectra were found to be in good agreement with previous studies in the Limiting cases of quantum wells and quantum-well wires.32243111311

Theoretical study of the effect of applied stress on the binding energy of a donor impurity in GaAs quantum well dot within an infinite potential barrier

908-911A theoretical study has been carried out on the effect of applied stress on the binding energy of a shallow monovalent donor impurity in a GaAs quantum well dot (QWD) of square cross-section. In our calculations, a variational technique [Csavinzky & Oyoko, Phys Rev B, 43 (1991) 9262.] within the effective mass approximation has been used. In our model the donor impurity is confined to the QWD by an infinite barrier potential unlike in a previous study [Oyoko et al. J Appl Phys, 90 (2001) 819.] where the barrier potential was finite. The donor impurity was located at various positions along the axis (Z-direction) of the QWD. The stress was applied along the same axis. The results show that for constant QWD dimensions Lx, Ly and Lz, for various donor positions, the binding energy increases with the applied stress as the donor position varies from on-edge to on-center locations. The binding energy is also found to increase as the QWD length decreases in both cases of on-edge and on-center donor locations for constant Lx and Ly as well as for decreasing QWD size. In all the cases considered, the binding energy is much larger for the on-center than for the on-edge positions for the same QWD dimensions and the same applied axial stress. The results obtained show that in experimental study of optical and electronic properties of such nanostructures as QWDs, the effect of stress on donor impurity binding energies should be taken into consideration

Theoretical modeling of the photoluminescence spectra associated with free-carrier to acceptor-impurity recombination in quantum-size GaAs wire crystals

A theoretical study of the photoluminescence spectra associated with free-carrier to acceptor-impurity recombination in quantum-size GaAs wire crystals is presented. We model the actual GaAs quantum wires via GaAs low-dimensional systems with finite cylindrical shape and hard-wall boundaries. The acceptor states are described within a variational scheme in the effective-mass approximation. The photoluminescence spectra associated with free carriers recombining with acceptor states are calculated for a homogeneous distribution of acceptor impurities within the low-dimensional heterostructure. We found that for a system whose length is comparable to the radius the photoluminescence line shape shows three structures associated with impurities located at special regions in the heterostructure, whereas for a system whose length is much larger than the radius we obtain two well-defined peaks, associated with accepters either at the center position or the edge position in the low-dimensional system. Both the peak positions and relative intensities are in good agreement with spectral features present in experimental data on GaAs quantum-wire microcrystals. (C) 1998 American Institute of Physics. [S0021-8979(98)09710-2]831116199620

Confined Magneto-excitons In Gaas-(ga, Al)as Quantum Wells

We have used the effective-mass approximation and a variational procedure in the study of internal transitions associated with 1s-, 2p-, 3p-, and 4p-like magneto-exciton confined states in GaAs-(Ga, Al)As quantum wells, under a magnetic field applied in the growth direction. Theoretical results were obtained as a function of the applied magnetic field and for several well widths. The calculated far-infrared intraexcitonic transition energies are found in good agreement with recent experimental measurements obtained via a highly sensitive optically detected resonance technique.2201137140Greene, R.L., Bajaj, K.K., Phelps, D.E., (1984) Phys. Rev. B, 29, p. 1807Greene, R.L., Bajaj, K.K., (1985) Phys. Rev. B, 31, p. 6498Bauer, G.E.W., Ando, T., (1988) Phys. Rev. B, 38, p. 6015Andreani, L.C., Pasquarello, S., (1990) Phys. Rev. B, 42, p. 8928Černe, J., Kono, J., Sherwin, M.S., Sundaram, M., Gossard, A.C., Bauer, G.E.W., (1996) Phys. Rev. Lett., 77, p. 1131Kono, J., Su, M.Y., Černe, J., Sherwin, M.S., Allen S.J., Jr., Inoshita, T., Noda, T., Sakaki, H., (1998) Physica, 249-251 B, p. 527Salib, M.S., Nickel, H.A., Herold, G.S., Petrou, A., McCombe, B.D., Chen, R., Bajaj, K.K., Schaff, W., (1996) Phys. Rev. Lett., 77, p. 1135Nickel, H.A., Herold, G.S., Salib, M.S., Kioseoglou, G., Petrou, A., McCombe, B.D., Broido, D., (1998) Physica, 249-251 B, p. 598Nickel, H.A., Herold, G.S., Yeo, T., Kioseoglou, G., Jiang, Z.X., McCombe, B.D., Petrou, A., Schaff, W., (1998) Phys. Stat. Sol. (B), 210, p. 341Luttinger, J.M., (1956) Phys. Rev., 102, p. 1030Duque, C.A., Beltrán, C.L., Montes, A., Porras-Montenegro, N., Oliveira, L.E., (2000) Phys. Rev. B, 61, p. 993

Detection of Giardia duodenalis antigen in human fecal eluates by enzyme-linked immunosorbent assay using polyclonal antibodies

The present study developed and standardized an enzime-linked immunosorbent assay (ELISA) to detect Giardia antigen in feces using rabbit polyclonal antibodies. Giardia cysts were purified from human fecal samples by sucrose and percoll gradients. Gerbils (Meriones unguiculatus) were infected to obtain trophozoites. Rabbits were inoculated with either cyst or trophozoite antigens of 14 Colombian Giardia isolates to develop antibodies against the respective stages. The IgG anti-Giardia were purified by sequential caprylic acid and ammonium sulfate precipitation. A portion of these polyclonal antibodies was linked to alkaline phosphatase (conjugate). One hundred and ninety six samples of human feces, from different patients, were tested by parasitologic diagnosis: 69 were positive for Giardia cysts, 56 had no Giardia parasites, and 71 revealed parasites other than Giardia. The optimal concentration of polyclonal antibodies for antigen capture was 40 µg/ml and the optimal conjugate dilution was 1:100. The absorbance cut-off value was 0.24. The parameters of the ELISA test for Giardia antigen detection were: sensitivity, 100% (95% CI: 93.4-100%); specificity, 95% (95% CI: 88.6-97.6%); positive predictive value, 91% (95% CI: 81.4-95.9%); and negative predictive value, 100% (95% CI: 96.1-100%). This ELISA will improve the diagnosis of Giardia infections in Colombia and will be useful in following patients after treatment