Artur Vicente Pfeifer Coelho

Roadkills of vertebrate species on two highways through the Atlantic Forest Biosphere Reserve, southern Brazil

We assessed the magnitude, composition, and spatial and temporal patterns of road mortality of native vertebrates on two highways in southern Brazil from 18 January 2003 to 26 January 2004. The highways cross remnants of the Atlantic Rainforest, a global biodiversity hotspot, and differ in vehicle traffic and surrounding landscape. We compared the road-kill magnitude and composition of birds, mammals, and reptiles between roads and seasons. We used a modified K statistic to depict the spatial patterns of roadkills of these groups and tested the association between vehicle traffic and road mortality through linear regression. We recorded 869 kills of 92 species. The two roads differed regarding the abundance and composition of roadkills. Reptile road mortality was higher in summer than winter, but all other groups did not show significant difference in the magnitude of mortality between seasons. The composition of killed assemblages differed significantly for some of the taxonomic groups among seasons. We found only one positive association between roadkills and vehicle traffic (reptiles on one of the roads), suggesting that vehicle flow does not explain the road-kill temporal variation on these roads. Total vertebrate, bird, and mammal roadkills showed significant spatial aggregations possibly due to variation in vehicle traffic, highway design, and local landscape condition and arrangement. With expected expansion of the road network, mitigation measures for multi-species assemblages should include habitat protection, soil use regulation, road crossing structures, speed reducers, and campaigns to raise people’s awareness about road impacts on wildlife.

Anuran road-kills neighboring a peri-urban reserve in the Atlantic Forest, Brazil

Mortality from road-kills may figure among the important causes of decline in amphibian populations and species extinctions worldwide. Evaluation of the magnitude, composition, and temporal and spatial distributions of amphibian road-kills is a key step for mitigation planning, especially in peri-urban reserves. Once a month for 16 months, we surveyed, on foot, a 4.4 km section of state road ERS-389 bordering the Itapeva reserve in the southern Atlantic Forest. We recorded 1433 anuran road-kills and estimated a mortality rate of 9002 road-kills/km/year. The species most often recorded were the largest ones: Leptodactylus latrans, Rhinella icterica, Leptodactylus gracilis and Hypsiboas faber; 54.5% of the carcasses could not be identified. Anuran mortality was concentrated in summer, and was associated with temperature, rainfall and photoperiod. Leptodactylus road-kills were strongly influenced by vehicle traffic, probably because of its high abundance during the entire study period. Road-kill hotspots differed for anurans as a group and for single species, and we found an association among spatial patterns of mortality and types of land cover, distance from the nearest waterbody, roadside ditches, and artificial light. Traffic should be banned temporarily during periods of high mortality, which can be forecasted based on meteorological data. A comprehensive mitigation approach should take into account hotspots of all anuran records, and also of target species for selecting locations for amphibian passages and fencing. Roadside ditches, artificial waterbodies, and conventional street lights should be reduced as much as possible, since they may represent ecological traps for anuran populations.

Characterization of deep level traps responsible for isolation of proton implanted GaAs

Deep level transient spectroscopy was employed to determine the electrical properties of defects induced in metalorganic chemical-vapor deposition grown n-type and p-type GaAs during proton bombardment. Thermal stability of these defects was investigated and correlation with defects responsible for isolation of GaAs by ion bombardment was discussed. The annealing temperature region (220–250 °C) is similar to proton isolated GaAs below the threshold dose for complete isolation. At least four of the five traps observed in n-type GaAs are not simple interstitial-vacancy pairs. For p-type GaAs we have observed an unknown level with apparent energy of ∼0.64 eV.

Distinguishing bulk traps and interface states in deep-level transient spectroscopy

A new method for the distinction of discrete bulk deep levels and interface states related peaks in deep-level transient spectroscopy spectra is proposed. The measurement of two spectra using different reverse voltages while keeping pulse voltage fixed causes different peak maximum shifts in each case: for a reverse voltage modulus increase, a bulk deep-level related peak maximum will remain unchanged or shift towards lower temperatures while only interface states related peak maximum will be able to shift towards higher temperatures. This method has the advantage of being non-destructive and also works in the case of bulk traps with strong emission rate dependence on the electric field. Silicon MOS capacitors and proton implanted GaAs Schottky diodes were employed to experimentally test the method.

Electrical isolation of p-type GaAs layers by ion irradiation

The electrical isolation of p-type GaAs layers doped with acceptor impurities incorporated in the Ga sublattice (Mg) or As sublattice (C) was studied using proton bombardment. It was found that practically the same proton dose is required to reach complete isolation (isolation threshold dose, Dth) in layers doped with either Mg or C of comparable original sheet hole concentration (ps). This result is evidence that the sublattice where the acceptor dopant atoms are incorporated does not play any significant role for the isolation formation process in GaAs. The behavior of the recovery of the conductivity during subsequent thermal annealing was found very similar in Mg and C doped samples irradiated to equal proton doses. In samples irradiated to doses 100 °C, reaches a maximum at ≅200 °C, and then decreases progressively toward the original value. For proton doses ranging from Dth to 5Dth, the isolation is preserved up to the tempe...

Deep levels fine structure in proton implanted p-type GaAs

Proton irradiation related deep levels in p-type GaAs were measured by deep level transient spectroscopy (DLTS) at T < 70 K and Laplace DLTS at 42 K ≤ T ≤ 48 K. Besides level H0 (apparent energy Epa = 0.06 eV and apparent hole capture cross section σpa = 1.6 × 10−16 cm2), also present in electron irradiated GaAs, three other levels were identified (Epa = 0.1 eV, σpa = 2.5 × 10−15 cm2; Epa = 0.085 eV, σpa = 1 × 10−14 cm2 and Epa = 0.065 eV, σpa = 3 × 10−16 cm2). Another level (Epa = 0.095 eV and σpa = 2 × 10−15 cm2) became evident after annealing steps at the temperature range 150 °C ≤ T ≤ 200 °C. All levels suffered a strong concentration reduction after annealing steps at 250 °C ≤ T ≤ 300 °C.

Electrical isolation of p-type GaAs layers by proton bombardment

The electrical isolation of p-type GaAs was investigated using proton ion bombardment at room temperature. Carbon and magnesium doped samples were used to compare the isolation and thermal stability for different acceptor atoms. As the C is manifested like a p-type impurity in the As sublattice site and the Mg in the Ga sublattice site, it was possible to study the influence of the dopant sublattice position. The acceptor concentration for C and Mg doped samples was similar. The evolution of the sheet resistance (R/sub s/) with dose during 400 keV H/sup +/ ion irradiation was studied. Three regions of R/sub s/ versus dose curve are distinguished: (1) R/sub s/ enhancement up to /spl ap/2/spl times/10/sup 9/ /spl Omega///spl notin/; (2) a plateau starting at a dose of 1/spl times/10/sup 14/ cm/sup -2/ (named threshold dose of isolation D/sub th/); and (3) decreasing of R/sub s/ for doses above 1/spl times/10/sup 15/ cm/sup -2/ as a result of hopping conduction. The thermal stability of isolation was found to increase with the irradiation dose. In the samples, irradiated to doses/spl les/D/sub th/, R/sub s/ starts to recover at annealing temperatures /spl ap/ 250/spl deg/C. When the dose is increased to 100D/sub th/, R/sub s/ increases with the annealing temperature up to 500/spl deg/C. For this dose the isolation is maintained up to 650/spl deg/C and a fast recovery of R/sub s/ by 3-4 orders of magnitude occurs at 650-700/spl deg/C.