Identifying invasive species threats, pathways, and impacts to improve biosecurity

Managing invasive species with prevention and early-detection strategies can avert severe ecological and economic impacts. Horizon scanning, an evidence-based process combining risk screening and consensus building to identify threats, has become a valuable tool for prioritizing invasive species management and prevention. We assembled a working group of experts from academic, government, and nonprofit agencies and organizations, and conducted a multi-taxa horizon scan for Florida, USA, the first of its kind in North America. Our primary objectives were to identify high-risk species and their introduction pathways, to detail the magnitude and mechanism of potential impacts, and, more broadly, to demonstrate the utility of horizon scanning. As a means to facilitate future horizon scans, we document the process used to generate the list of taxa for screening. We evaluated 460 taxa for their potential to arrive, establish, and cause negative ecological and socioeconomic impacts, and identified 40 potential invaders, including alewife, zebra mussel, crab-eating macaque, and red swamp crayfish. Vertebrates and aquatic invertebrates posed the greatest invasion threat, over half of the high-risk taxa were omnivores, and there was high confidence in the scoring of high-risk taxa. Common arrival pathways were ballast water, biofouling of vessels, and escape from the pet/aquarium/horticulture trade. Competition, predation, and damage to agriculture/forestry/aquaculture were common impact mechanisms. We recommend full risk analysis for the high-risk taxa; increased surveillance at Florida's ports, state borders, and high-risk pathways; and periodic review and revision of the list. Few horizon scans detail the comprehensive methodology (including list-building), certainty estimates for all scoring categories and the final score, detailed pathways, and the magnitude and mechanism of impact. Providing this information can further inform prevention efforts and can be efficiently replicated in other regions. Moreover, harmonizing methodology can facilitate data sharing and enhance interpretation of results for stakeholders and the general public.</p

Temperature dependence of excitonic photoluminescence and residual shallow donors in high-purity GaN/Al2O3

The temperature dependence of free and bound exciton lines in high-purity, undoped wurtzite GaN layers has been studied by photoluminescence (PL) between 2 and 300 K. Below 30 K the neutral donor bound exciton D deg X produces the strongest near band gap PL signal whereas free A and B excitons dominate the spectrum at room temperature. A deconvolution of the asymmetric D deg X line shape provides strong evidence for two residual shallow donors differing in ionisation energies by a factor of 1.5. The origin of a PL line occurring at Eg = 116 meV is discussed in two alternative models

Origin of defect-related photoluminescence bands in doped and nominally undoped GaN

The efficient room-temperature photoluminescence bands of wurtzite GaN, which are peaked in the red (1.8 eV), the yellow (2.2 eV), and the blue (2.8 eV) spectral range, have been studied as a function of doping (species and concentration) and excitation power density (PD). It is shown that the yellow and the blue band are induced by Si and Mg doping, respectively, while codoping with Si and Mg generates the red band. At high-doping levels, the yellow and the blue band reveal strong peak shifts to higher energy with increasing PD providing very strong evidence for their distant donor-acceptor (DA) pair recombination character. The deep centers involved in DA recombination having electrical activity opposite to that of the shallow level of the dopant, are suggested to arise from self-compensation and to be vacancy-dopant associates. Self-compensation is found to be weak in the case of Si doping, but significant for Mg doping. A recombination model is presented, which accounts for the ess ential properties of all three bands in deliberately doped GaN. These results also suggest that the yellow and the blue bands in nominally undoped GaN arise from distant DA pairs involving residual Si and Mg impurities, respectively, as well as their respective vacancy associates

NEW AND NOTEWORTHY PLANTS FROM FLORIDA

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(AlGaIn)N UV LEDs for integrated metal-oxide based ozone sensors

There is high demand for compact low-cost ozone (O3) sensors. It has been shown that indium oxide (In2O3) thin films grown by metal-organic vapor-phase epitaxy (MOVPE) act as an O3 sensitive material, which can be activated at room-temperature by ultraviolet (UV) light. In the present work we integrated the In2O3 sensing thin film and an (AlGaIn)N based near-UV LED back-to-back on a single sensor chip. The integrated in2O3 film-LED sensor was exposed to varying ozone concentrations ranging from 38 ppb to 726 ppb and found to be sensitive to even the lowest O3 concentration