The synthesis and characterization of copper indium sulfide and cadmium selenide nanocrystals and their applications in photodetectors

Semiconductor nanocrystals are a topic of much interest in electrical engineering. Their use has been explored for many applications. This paper investigates the synthesis and characterization of CuInS2 and CdSe nanocrystals. As the nanocrystals were left in reaction for increasing amounts of time, the bandgap of the material decreased as the nanocrystal size increased due to the quantum confinement effect. The CdSe nanocrystals were then investigated in a photodetector application which achieved a detectivity on the order of 10^9 cmHz^(1/2)W^(-1)

Spherical collapse model in agegraphic dark energy cosmologies

Under the commonly used spherical collapse model, we study how dark energy affects the growth of large scale structures of the Universe in the context of agegraphic dark energy models. The dynamics of the spherical collapse of dark matter halos in nonlinear regimes is determined by the properties of the dark energy model. We show that the main parameters of the spherical collapse model are directly affected by the evolution of dark energy in the agegraphic dark energy models. We compute the spherical collapse quantities for different values of agegraphic model parameter $\alpha$ in two different scenarios: first, when dark energy does not exhibit fluctuations on cluster scales, and second, when dark energy inside the overdense region collapses similar to dark matter. Using the Sheth-Tormen and Reed mass functions, we investigate the abundance of dark matter halos in the framework of agegraphic dark energy cosmologies. The model parameter $\alpha$ is a crucial parameter in order to count the abundance of dark matter halos. Specifically, the present analysis suggests that the agegraphic dark energy model with bigger (smaller) value of $\alpha$ predicts less (more) virialized halos with respect to that of $\Lambda$CDM cosmology. We also show that in agegraphic dark energy models, the number of halos strongly depends on clustered or uniformed distributions of dark energy.Comment: 14 pages, 7 figures. Accepted in Physical Review

Ecology of Floristic Quality Assessment: testing for correlations between coefficients of conservatism, species traits and mycorrhizal responsiveness

Many plant species are limited to habitats relatively unaffected by anthropogenic disturbance, so protecting these undisturbed habitats is essential for plant conservation. Coefficients of conservatism (C values) were developed as indicators of a species’ sensitivity to anthropogenic disturbance, and these values are used in Floristic Quality Assessment as a means of assessing natural areas and ecological restoration. However, assigning of these values is subjective and improved quantitative validation of C values is needed. We tested whether there are consistent differences in life histories between species with high and low C values. To do this, we grew 54 species of tallgrass prairie plants in a greenhouse and measured traits that are associated with trade-offs on the fast-slow continuum of life-history strategies. We also grew plants with and without mycorrhizal fungi as a test of these species’ reliance on this mutualism. We compared these traits and mycorrhizal responsiveness to C values. We found that six of the nine traits we measured were correlated with C values, and together, traits predicted up to 50 % of the variation in C values. Traits including fast growth rates and greater investment in reproduction were associated with lower C values, and slow growth rates, long-lived leaves and high root:shoot ratios were associated with higher C values. Additionally, plants with high C values and a slow life history were more responsive to mutualisms with mycorrhizal fungi. Overall, our results connect C values with life-history trade-offs, indicating that high C value species tend to share a suite of traits associated with a slow life history

Linguistics

Contains reports on seven research projects.National Science Foundation (Grant G-16526)National Institutes of Health (Grant MH-04737-02)United States Air Force, Electronic Systems Division (Contract AF19(628)-2487

Role of plant relatedness in plant–soil feedback dynamics of sympatric Asclepias species

Plants affect associated biotic and abiotic edaphic factors, with reciprocal feedbacks from soil characteristics affecting plants. These two-way interactions between plants and soils are collectively known as plant–soil feedbacks (PSFs). The role of phylogenetic relatedness and evolutionary histories have recently emerged as a potential driver of PSFs, although the strength and direction of feedbacks among sympatric congeners are not well-understood. We examined plant–soil feedback responses of Asclepias syriaca, a common clonal milkweed species, with several sympatric congeners across a gradient of increasing phylogenetic distances (A. tuberosa, A. viridis, A. sullivantii, and A. verticillata, respectively). Plant–soil feedbacks were measured through productivity and colonization by arbuscular mycorrhizal (AM) fungi. Asclepias syriaca produced less biomass in soils conditioned by the most phylogenetically distant species (A. verticillata), relative to conspecific-conditioned soils. Similarly, arbuscular mycorrhizal (AM) fungal colonization of A. syriaca roots was reduced when grown in soils conditioned by A. verticillata, compared with colonization in plants grown in soil conditioned by any of the other three Asclepias species, indicating mycorrhizal associations are a potential mechanism of observed positive PSFs. This display of differences between the most phylogenetically distant, but not close or intermediate, paring(s) suggests a potential phylogenetic threshold, although other exogenous factors cannot be ruled out. Overall, these results highlight the potential role of phylogenetic distance in influencing positive PSFs through mutualists. The role of phylogenetic relatedness and evolutionary histories have recently emerged as a potential driver of plant–soil feedbacks (PSFs), although the strength and direction of feedbacks among sympatric congeners are not well-understood. Congeneric, sympatric milkweeds typically generated positive PSFs in terms of productivity and AM fungal colonization, suggesting the low likelihood of coexistence among tested pairs, with a strength of feedback increasing as the phylogenetic distance increases

Hypoxia forecasts as a tool for Chesapeake Bay fisheries

The Estuarine Hypoxia component of the U.S. Integrated Ocean Observing System Coastal and Ocean Modeling Testbed (COMT) is evaluating existing hydrodynamic and water quality models used, or likely to be used, for operations in the Chesapeake Bay. As a proof-of-concept, an implementation of the Regional Ocean Modeling System in the Chesapeake Bay (ChesROMS) is linked to a simple respiration model for hypoxia (Hypoxia_SRM). The modeling system is presently being used to produce real-time nowcasts and short-term (3-day) hypoxia forecasts for the Chesapeake Bay, which are currently available on the Virginia Institute of Marine Science (VIMS) website. Workshops with citizen stakeholders have explored potential applications of the estuarine hypoxia nowcast/forecast products in support of recreational and commercial fishing. Interest in this product is high, particularly by recreational fishermen and charter boat captains, since reduced catch per unit effort in the Bay is clearly associated with regions where dissolved oxygen is low. This presentation reviews the insights gained at these stakeholder workshops, including how these stakeholders might apply these products to improve the efficiency and success of their fishing activities and what forecast presentation formats are most useful. Future work involves transporting the hypoxia forecast tool to the Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS), and eventually linking the product with NOAA’s Chesapeake Bay Operational Forecasting System (CBOFS)

Climate Affects Plant-Soil Feedback of Native and Invasive Grasses: Negative Feedbacks in Stable but Not in Variable Environments

This work is licensed under a Creative Commons Attribution 4.0 International License.The plant-soil feedback framework allows researchers to target the interaction of plants and root-associated microbes and to determine its interplay on plant-plant interactions. Plant-soil feedbacks in terrestrial ecology are well-documented, but the strength and direction of feedbacks as influenced by abiotic environmental factors, such as temperature and soil moisture, has not been fully explored. In our study, we examined plant-soil feedback responses of both cool- and warm-season native and non-native grasses to elevated temperatures (ambient and +5°C) and soil moisture (100 and 75% field capacity). In a previous experiment, grasses were grown under temperature and soil moisture conditions similar to our current study. The resultant trained soil communities served as the inoculum sources for our current experiment. We found that consistent training and experimental temperatures resulted in negative PSF, where plants produced greater biomass in soils conditioned by heterospecifics. However, the direction of PSF was reversed when training and experimental conditions were mismatched. That is, when training and experimental temperatures mirrored one another, negative PSF occurred, suggesting coexistence between the two species is likely under these conditions. However, when only training or testing temperatures were elevated, positive PSF were detected, favoring the non-native species. These alterations in plant-soil feedbacks were relatively consistent across pairings of warm- and cool-season grasses. Overall, our results indicate inconsistent year-to-year environmental conditions, such as extreme temperatures, may undermine the stabilizing forces of negative PSF and favor of non-native grasses