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We perform a statistical clustering analysis of upper main-sequence stars in the Large Magellanic Cloud (LMC) using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds. We map over 2500 young stellar structures at 15 significance levels across ~120 square degrees centred on the LMC. The structures have sizes ranging from a few parsecs to over 1 kpc. We find that the young structures follow power-law size and mass distributions. From the perimeter-area relation, we derive a perimeter-area dimension of 1.44+-0.20. From the mass-size relation and the size distribution, we derive two-dimensional fractal dimensions of 1.50+-0.10 and 1.61+-0.20, respectively. We find that the surface density distribution is well-represented by a lognormal distribution. We apply the Larson relation to estimate the velocity dispersions and crossing times of these structures. Our results indicate that the fractal nature of the young stellar structures has been inherited from the gas clouds from which they form and that this architecture is generated by supersonic turbulence. Our results also suggest that star formation in the LMC is scale-free from 10 pc to 700 pc., Comment: 20 pages, 17 figures, accepted for publication in MNRAS

P. maculata is a freshwater snail native to a wide geographical area in South America from the Rio de la Plata in Argentina and Uruguay to the Amazon in Brazil. It is commonly confused with any number of similar large apple snails, including the well-known invasive golden apple snail Pomacea canaliculata (listed among '100 of the world's worst invasive species'). Both species have been introduced to South-East and East Asia, although for many years they were not distinguished and the Asian introductions were widely identified as "golden apple snails" and the name P. canaliculata was applied to them. Due to the confusion in species identification, the history of introduction of P. maculata remains somewhat uncertain as does its invasiveness and pest potential. Much of the literature is confounded, for example, the snails illustrated by Cowie (2002) as P. canaliculata are in fact P. maculata. The majority of invasive populations in Asia appear to be P. canaliculata, often not mixed with P. maculata (Hayes et al., 2008; Tran et al., 2008) and the pest potential of P. canaliculata in such cases is clear. However, much less has been written about the invasiveness and pest potential of 'P. maculata'.

We have derived high-spatial-resolution metallicity maps covering $\sim$105~deg$^2$ across the Large Magellanic Cloud (LMC) using near-infrared passbands from the VISTA Survey of the Magellanic Clouds. We attempt to understand the metallicity distribution and gradients of the LMC up to a radius of $\sim$ 6~kpc. We identify red giant branch (RGB) stars in spatially distinct $Y, (Y-K_{\rm s})$ colour-magnitude diagrams. In any of our selected subregions, the RGB slope is used as an indicator of the average metallicity, based on calibration to metallicity using spectroscopic data. The mean LMC metallicity is [Fe/H] = $-$0.42~dex ($\sigma$[Fe/H] = 0.04~dex). We find the bar to be mildly metal-rich compared with the outer disc, showing evidence of a shallow gradient in metallicity ($-0.008 \pm 0.001$ dex kpc$^{-1}$) from the galaxy's centre to a radius of 6~kpc. Our results suggest that the LMC's stellar bar is chemically similar to the bars found in large spiral galaxies. The LMC's radial metallicity gradient is asymmetric. It is metal-poor and flatter towards the southwest, in the direction of the Bridge. This hints at mixing and/or distortion of the spatial metallicity distribution, presumably caused by tidal interactions between the Magellanic Clouds., Comment: 13 pages, 15 figures, accepted for publication in the MNRAS

Full list of authors: Nidever, David L.; Olsen, Knut; Choi, Yumi; Ruiz-Lara, Tomas; Miller, Amy E.; Johnson, L. Clifton; Bell, Cameron P. M.; Blum, Robert D.; Cioni, Maria-Rosa L.; Gallart, Carme; Majewski, Steven R.; Martin, Nicolas F.; Massana, Pol; Monachesi, Antonela; Noël, Noelia E. D.; Sakowska, Joanna D.; van der Marel, Roeland P.; Walker, Alistair R.; Zaritsky, Dennis; Bell, Eric F. Conn, Blair C.; de Boer, Thomas J. L.; Gruendl, Robert A.; Monelli, Matteo; Muñoz, Ricardo R.; Saha, Abhijit; Vivas, A. Katherina; Bernard, Edouard; Besla, Gurtina; Carballo-Bello, Julio A.; Dorta, Antonio; Martinez-Delgado, David; Goater, Alex; Rusakov, Vadim; Stringfellow, Guy S., We present an analysis of the ionosphere and thermosphere response to Solar Proton Events (SPE) and magnetospheric proton precipitation in January 2005, which was carried out using the model of the entire atmosphere EAGLE. The ionization rates for the considered period were acquired from the AIMOS (Atmospheric Ionization Module Osnabrück) dataset. For numerical experiments, we applied only the proton-induced ionization rates of that period, while all the other model input parameters, including the electron precipitations, corresponded to the quiet conditions. In January 2005, two major solar proton events with different energy spectra and proton fluxes occurred on January 17 and January 20. Since two geomagnetic storms and several sub-storms took place during the considered period, not only solar protons but also less energetic magnetospheric protons contributed to the calculated ionization rates. Despite the relative transparency of the thermosphere for high-energy protons, an ionospheric response to the SPE and proton precipitation from the magnetotail was obtained in numerical experiments. In the ionospheric E layer, the maximum increase in the electron concentration is localized at high latitudes, and at heights of the ionospheric F2 layer, the positive perturbations were formed in the near-equatorial region. An analysis of the model-derived results showed that changes in the ionospheric F2 layer were caused by a change in the neutral composition of the thermosphere. We found that in the recovery phase after both solar proton events and the enhancement of magnetospheric proton precipitations associated with geomagnetic disturbances, the TEC and electron density in the F region and in topside ionosphere/plasmasphere increase at low- and mid-latitudes due to an enhancement of atomic oxygen concentration. Our results demonstrate an important role of magnetospheric protons in the formation of negative F-region ionospheric storms. According to our results, the topside ionosphere/plasmasphere and bottom-side ionosphere can react to solar and magnetospheric protons both with the same sign of disturbances or in different way. The same statement is true for TEC and foF2 disturbances. Different disturbances of foF2 and TEC at high and low latitudes can be explained by topside electron temperature disturbances. © 2021. The American Astronomical Society. All rights reserved, Y.C., E.F.B., and A.M. acknowledge support from NSF grant AST 1655677. A.D., C.G., T.R.L., and M.M. acknowledge support by the Spanish Ministry of Economy and Competitiveness (MINECO) under the grants AYA2014-56795-P and AYA2017-89076-P as well as AYA2016-77237-C3-1-P. T.R.L. has support from a Spinoza grant (NWO) awarded to A. Helmi and acknowledges support by an MCIU Juan de la CiervaFormacion grant (FJCI-2016-30342). C.P.M.B. and M.-R.L.C. acknowledge support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 682115). A.M. acknowledges support from FONDECYT Regular 1181797. R. R.M. acknowledges partial support from project BASAL AFB170002 as well as FONDECYT project No. 1170364. D.M.D. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709). Image processing: Travis Rector (University of Alaska Anchorage), Mahdi Zamani, and Davide de Martin. Based on observations at Cerro Tololo Inter-American Observatory, NSF's National Optical-Infrared Astronomy Research Laboratory (NOAO Prop. ID: 2013A-0411 and 2013B-0440; PI: D. L. Nidever), which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. IRAF is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and Astro-Particle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico and the Ministerio da Ciencia, Tecnologia e Inovacao, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the Dark Energy Survey. The Collaborating Institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, the Eidgenossische Technische Hochschule (ETH) Zurich, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Institut de Ciencies de l'Espai (IEEC/CSIC), the Institut de Fisica d'Altes Energies, Lawrence Berkeley National Laboratory, the Ludwig-Maximilians Universitat Munchen and the associated Excellence Cluster Universe, the University of Michigan, the National Optical Astronomy Observatory, the University of Nottingham, the Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A&M University. This work has made use of data from the European Space Agency (ESA) mission Gai a (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC,.https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Regional warming has led to increased productivity near the boreal forest margin in Alaska. To date, the effects of warming on seedling recruitment have received little attention, in spite of forecasted forest expansion. Here, we used stand structure and environmental data from ninety-five white spruce (Picea glauca) plots sampled across a longitudinal gradient in southwest Alaska to explore factors influencing spruce establishment and recruitment near western treeline. We used total counts of live seedlings, saplings, and trees, representing five life stages, to evaluate whether geospatial, climate, and measured plot covariates predicted abundance, using current abundance distributions as a surrogate for climate conditions in the past. We used generalized linear models to test the null hypothesis that conditions favorable for recruitment were similar along the environmental gradient represented by longitude, by exploring relationships between per-plot counts of each life stage and the covariates hypothesized to affect abundance. We also examined the relationship between growing degree days (GDD) and seedling establishment over a period of three decades using tree-ring chronologies obtained from cores taken at a subset of our sites (n=30). Our results indicated that seedling, sapling and tree abundance were positively correlated with temperature across the study area. The response to longitude was mixed, with earlier life stages (seedlings, saplings) most abundant at the western end of the gradient, and later life stages (trees) most abundant to the east. The differential relationship between longitude and life stage abundance suggests a moving front of white spruce establishment through time, driven by changes in environmental conditions near the species’ western range limit. Likewise, we found a positive relationship between periods of seedling establishment and GDD, suggesting that longer summers and/or greater heat accumulation might enhance establishment, consistent with the positive relationship we found between life stage abundance and temperature. This article is protected by copyright. All rights reserved.

Increasing temperatures have resulted in reduced growth and increased tree mortality across large areas of western North American forests. We use tree-ring isotope chronologies (δ13 C and δ18 O) from live and dead trees from four locations in south-central Alaska, USA, to test whether white spruce trees killed by recent spruce beetle (Dendroctonus rufipennis Kirby) outbreaks showed evidence of drought stress prior to death. Trees that were killed were more sensitive to spring/summer temperature and/or precipitation than trees that survived. At two of our sites, we found greater correlations between the δ13 C and δ18 O chronologies and spring/summer temperatures in dead trees than in live trees, suggesting that trees that are more sensitive to temperature-induced drought stress are more likely to be killed. At one site, the difference between δ13 C in live and dead trees was related to winter/spring precipitation, with dead trees showing stronger correlations between δ13 C and precipitation, again suggesting increased water stress in dead trees. At all sites where δ18 O was measured, δ18 O chronologies showed the greatest difference in climate response between live and dead groups, with δ18 O in live trees correlating more strongly with late winter precipitation than dead trees. Our results indicate that sites where trees are already sensitive to warm or dry early growing-season conditions experienced the most beetle-kill, which has important implications for forecasting future mortality events in Alaska.

Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow cover products provide an opportunity for determining snow onset and melt dates across broad geographic regions; however, cloud cover and polar darkness are limiting factors at higher latitudes. This study presents snow onset and melt dates for Alaska, portions of western Canada and the Russian Far East derived from Terra MODIS snow cover daily 500 m grid data (MOD10A1) and evaluates our method for filling data gaps caused by clouds or polar darkness. Pixels classified as cloud or no data were reclassified by: spatial filtering using neighboring pixel values; temporal filtering using pixel values for days before/after cloud cover; and snow-cycle filtering based on a time series assessment of a pixel’s position within snow accumulation, cover or melt periods. During the 2012 snow year, these gap-filling methods reduced cloud pixels from 27.7% to 3.1%. A total of 12 metrics (e.g., date of first and last snow, date of persistent snow cover and periods of intermittence) for each pixel were calculated by snow year. A comparison of MODIS-derived snow onset and melt dates with in situ observations from 244 weather stations generally showed an early bias in MODIS-derived dates and an effect of increasing cloudiness exacerbating bias. Our results show that mean regional duration of seasonal snow cover is 179–311 days/year and that snow cover is often intermittent, with 41% of the area experiencing ≥2 snow-covered periods during a snow season. Other regional-scale patterns in the timing of snow onset and melt are evident in the yearly 500 m gridded products publically available at http://static.gina.alaska.edu/NPS_products/MODIS_snow/.

The association of tree species with particular soil types contributes to high β diversity in forests, but the mechanisms producing such distributions are still debated. Soil nitrogen (N) often limits growth and occurs in differentially available chemical forms. In a Bornean forest where tree species composition changes dramatically along a soil gradient varying in supplies of different N-forms, we investigated whether tree species’ N-uptake and soil specialization strategies covaried. We analyzed foliar 15N natural abundance for a total of 216 tree species on clay or sandy loam (the soils at the gradient’s extremes) and conducted a 15N-tracer experiment with nine specialist and generalist species to test whether species displayed flexible or differential uptake of ammonium and nitrate. Despite variation in ammonium and nitrate supplies and nearly 4 ‰ difference in foliar δ15N between most soil specialists and populations of generalists on these soils, our 15N tracer experiment showed little support for the hypothesis that soil specialists vary in N-form use or the ratios in which they use these forms. Instead, our results indicate that these species possess flexible capacities to take up different inorganic N forms. Variation between soil specialists in uptake of different N forms is thus unlikely to cause the soil associations of tree species and high β diversity characteristic of this Bornean rain forest. Flexible uptake strategies would facilitate N-acquisition when supply rates of N-forms exhibit spatiotemporal variation and suggest that these species may be functionally redundant in their responses to N gradients and influences on ecosystem N-cycles.

We conducted a vascular plant inventory of six National Park Service units in southwestern and south-central Alaska to establish baseline floristic information and identify species of conservation concern. Between 1998 and 2005, we collected 815 taxa, the majority of which were new records for one or more park units. We present descriptions of the rare taxa (Alaska Natural Heritage Program S1–S3 ranks) collected as part of the National Park Service inventories, as well as new collections that represent significant range extensions. Of the 45 taxa reported here, all but one are considered globally rare or rare within Alaska. Collections of six taxa, including the common species, represent range extensions of greater than 450 km, and collections of an additional 16 taxa were minor range extensions (> 150 km, < 450 km). We include brief synopses of the vouchers, including general notes on the biogeography and rarity of these taxa. These and previous collections support the demarcation of southwester...

Monitoring natural resources in Alaskan national parks is challenging because of their remoteness, limited accessibility, and high sampling costs. We describe an iterative, three-phased process for developing sampling designs based on our efforts to establish a vegetation monitoring program in southwest Alaska. In the first phase, we defined a sampling frame based on land ownership and specific vegetated habitats within the park boundaries and used Path Distance analysis tools to create a GIS layer that delineated portions of each park that could be feasibly accessed for ground sampling. In the second phase, we used simulations based on landcover maps to identify size and configuration of the ground sampling units (single plots or grids of plots) and to refine areas to be potentially sampled. In the third phase, we used a second set of simulations to estimate sample size and sampling frequency required to have a reasonable chance of detecting a minimum trend in vegetation cover for a specified time period and level of statistical confidence. Results of the first set of simulations indicated that a spatially balanced random sample of single plots from the most common landcover types yielded the most efficient sampling scheme. Results of the second set of simulations were compared with field data and indicated that we should be able to detect at least a 25% change in vegetation attributes over 31 years by sampling 8 or more plots per year every five years in focal landcover types. This approach would be especially useful in situations where ground sampling is restricted by access.

The rewetting of a dry soil causes a pulse in decomposition of soil organic matter (SOM). This mechanism may dominate carbon (C) and nitrogen (N) cycles in arid, semi-arid and Mediterranean ecosystems. Existing biogeochemical models perform poorly for systems characterized by pulsed events. In this study, we added a rewetting factor into the DAYCENT soil biogeochemical model to better represent the drying-rewetting pulses. Based on a 4-month laboratory incubation from a parallel study, we developed a simple rewetting factor for representing the enhanced mineralization pulse by rewetting stimulation. The rewetting factor was then incorporated into DAYCENT by modifying the soil moisture factor. The DAYCENT modification significantly improved model performance in predicting soil C respiration rates in drying-rewetting treatments through the capture of rewetting pulses. The modification also improved prediction performance for net N mineralization in treatments with shorter rewetting intervals, but did not improve predictions in treatments with longer rewetting intervals. The model modifications were validated by using a laboratory incubation data set from a different field site. The modified DAYCENT predictions showed that active and slow SOM pools were major contributors to mineralization pulses while the contribution from the passive pool was minimal. The modifications we made improved model performance and should be considered in future field representations of biogeochemical processes. (C) 2010 Elsevier B.V. All rights reserved.

High-elevation periglacial soils are among the most extreme soil systems on Earth and may be good analogs for the polar regions of Mars where oligotrophic mineral soils abut with polar ice caps. Here we report on preliminary studies carried out during an expedition to an area where recent glacial retreat has exposed porous mineral soils to extreme, daily freeze-thaw cycles and high UV fluxes. We used in situ methods to show that inorganic nitrogen (NO(3) (-) and NH(4) (+)) was being actively cycled even during a period when diurnal soil temperatures (5 cm depth) ranged from -12 to 27 degrees C and when sub-zero, soil cooling rates reached 1.8 degrees C h(-1) (the most rapid soil cooling rates recorded to date). Furthermore, phylogenetic analyses of microbial phylotypes present at our highest sites (5410 m above sea level) showed the presence of nitrifying bacteria of the genus Nitrospira and newly discovered nitrite-oxidizing Betaproteobacteria. These soils were overwhelmingly dominated (>70% of phylotypes) by photosynthetic bacteria that were related to novel cyanobacteria previously found almost exclusively in other plant-free, high-elevation soils. We also demonstrated that soils from our highest sites had higher potential for mineralizing glutamate and higher microbial biomass than lower elevation soils that had been more recently covered by ice. Overall, our findings indicate that a diverse and robustly functioning microbial ecosystem is present in these previously unstudied high-elevation soils.

Impacts of global climate change are expected to result in greater variation in the seasonality of snowpack, lake ice, and vegetation dynamics in southwest Alaska. All have wide-reaching physical and biological ecosystem effects in the region. We used Moderate Resolution Imaging Spectroradiometer (MODIS) calibrated radiance, snow cover extent, and vegetation index products for interpreting interannual variation in the duration and extent of snowpack, lake ice, and vegetation dynamics for southwest Alaska. The approach integrates multiple seasonal metrics across large ecological regions. Throughout the observation period (2001–2007), snow cover duration was stable within ecoregions, with variable start and end dates. The start of the lake ice season lagged the snow season by 2 to 3 months. Within a given lake, freeze-up dates varied in timing and duration, while break-up dates were more consistent. Vegetation phenology varied less than snow and ice metrics, with start-of-season dates comparatively consistent across years. The start of growing season and snow melt were related to one another as they are both temperature dependent. Higher than average temperatures during the El Nino winter of 2002–2003 were expressed in anomalous ice and snow season patterns. We are developing a consistent, MODIS-based dataset that will be used to monitor temporal trends of each of these seasonal metrics and to map areas of change for the study area.

In arctic and alpine ecosystems, soil nitrogen (N) dynamics can differ markedly between winter and summer months, and nitrogen losses can be measurable during the spring and fall transitions. To explore the effect of seasonality on biogeochemical processes in a temperate alpine environment, we used a combination of field incubations (year-round) and 15N tracer additions (late fall, early spring, summer) to characterize soil N dynamics in a wet and dry meadow in the Sierra Nevada, California. The snowmelt to early summer season marked a period of high 15N uptake and turnover in the two soils, coincident with the increase in microbial N pools at the start of snowmelt (wet and dry meadow); an increase in net N mineralization and net nitrification as snowmelt progressed (wet meadow only); and measureable net production of 15N-NH4 + in mid-summer (wet and dry meadow). Whereas fluctuations in microbial biomass were generally synchronous between the wet and dry meadow soils, only wet meadow soils appeared to mineralize N in response to declines in the microbial N pool. Net N mineralization and net nitrification rates in the dry meadow soil were negligible on all but one sampling date, in spite of periodic decreases in biomass of up to 60%. Across both sites, high 15N recoveries in microbial biomass N, rapid 15N-NH4 + turnover, and low or negative net 15N-NH4 + fluxes suggested tight cycling of N, particularly in the late fall and early spring.

Long-term studies in Alaska have demonstrated that bears may capture and carry to the riparian forest a large number of salmon that return to spawn in small freshwater streams. Most of the carcasses are partially consumed, resulting in a large amount of salmon nutrients in the form of biomass deposited on the forest floor. Using an experimental approach, we examined how these carcasses may influence the spatial and temporal dynamics of soil C and N in a riparian forest in southeastern Alaska. At their peak, ammonium (NH4+-N) concentrations in soil 10 cm from carcasses were as much as several orders of magnitude greater than soils in adjacent control plots without carcasses and remained elevated until the onset of winter. Nitrate (NO3–-N) and δ15N concentrations also increased coincident with maximum NH4+-N concentrations. However, soil N concentrations were only moderately elevated 20 cm from carcasses and closely resembled background concentrations at 30 cm. These results suggest that salmon carcasses, via bear foraging activities, can dramatically influence soil N pools, although the impacts appear to be highly localized and largely dependent on the spatial distribution of carcasses in the riparian forest.

Cold-season processes are known to contribute substantially to annual carbon (C) and nitrogen (N) budgets in continental high elevation and high-latitude soils, but their role in more temperate alpine ecosystems has seldom been characterized. We used a 4-month lab incubation to describe temperature (−2, 0, 5°C) and moisture [50, 90% water-holding capacity (WHC)] effects on soil C and N dynamics in two wet and one dry meadow soil from the Sierra Nevada, California. The soils varied in their capacity to process N at and below 0°C. Only the dry meadow soil mineralized N at −2°C, but the wet meadow soils switched from net N consumption at −2°C to net N mineralization at temperatures ≥0°C. When the latter soils were incubated at −2°C at either moisture level (50 or 90% WHC), net NO3 − production decreased even as NH4 + continued to accumulate. The same pattern occurred in saturated (90% WHC) soils at warmer temperatures (≥0°C), suggesting that dissimilatory processes could control N cycling in these soils when they are frozen.

Primary succession is a fundamental process in macroecosystems; however, if and how soil development influences microbial community structure is poorly understood. Thus, we investigated changes in the bacterial community along a chronosequence of three unvegetated, early successional soils ( approximately 20-year age gradient) from a receding glacier in southeastern Peru using molecular phylogenetic techniques. We found that evenness, phylogenetic diversity, and the number of phylotypes were lowest in the youngest soils, increased in the intermediate aged soils, and plateaued in the oldest soils. This increase in diversity was commensurate with an increase in the number of sequences related to common soil bacteria in the older soils, including members of the divisions Acidobacteria, Bacteroidetes, and Verrucomicrobia. Sequences related to the Comamonadaceae clade of the Betaproteobacteria were dominant in the youngest soil, decreased in abundance in the intermediate age soil, and were not detected in the oldest soil. These sequences are closely related to culturable heterotrophs from rock and ice environments, suggesting that they originated from organisms living within or below the glacier. Sequences related to a variety of nitrogen (N)-fixing clades within the Cyanobacteria were abundant along the chronosequence, comprising 6-40% of phylotypes along the age gradient. Although there was no obvious change in the overall abundance of cyanobacterial sequences along the chronosequence, there was a dramatic shift in the abundance of specific cyanobacterial phylotypes, with the intermediate aged soils containing the greatest diversity of these sequences. Most soil biogeochemical characteristics showed little change along this approximately 20-year soil age gradient; however, soil N pools significantly increased with soil age, perhaps as a result of the activity of the N-fixing Cyanobacteria. Our results suggest that, like macrobial communities, soil microbial communities are structured by substrate age, and that they, too, undergo predictable changes through time.

The Mediterranean climate, with its characteristic of dry summers and wet winters, influences the hydrologic and microbial processes that control carbon (C) and nitrogen (N) biogeochemical processes in chaparral ecosystems. These biogeochemical processes in turn determine N cycling under chronic N deposition. In order to examine connections between climate and N dynamics, we quantified decadal-scale water, C and N states and fluxes at annual, monthly and daily time steps for a California chaparral ecosystem in the Sierra Nevada using the DAYCENT model. The daily output simulations of net mineralization, stream flow and stream nitrate (NO3−) export were developed for DAYCENT in order to simulate the N dynamics most appropriate for the abrupt rewetting events characteristic of Mediterranean chaparral ecosystems. Overall, the magnitude of annual modeled net N mineralization, soil and plant biomass C and N, nitrate export and gaseous N emission agreed with those of observations. Gaseous N emission was a major N loss pathway in chaparral ecosystems, in which nitric oxide (NO) is the dominant species. The modeled C and N fluxes of net primary production (NPP), N uptake and N mineralization, NO3− export and gaseous N emission showed both high inter-annual and intra-annual variability. Our simulations also showed dramatic fire effects on NPP, N uptake, N mineralization and gaseous N emission for three years of postfire. The decease in simulated soil organic C and N storages was not dramatic, but lasted a longer time. For the seasonal pattern, the predicted C and N fluxes were greatest during December to March, and lowest in the summer. The model predictions suggested that an increase in the N deposition rate would increase N losses through gaseous N emission and stream N export in the chaparral ecosystems of the Sierra Nevada due to changes in N saturation status. The model predictions could not capture stream NO3− export during most rewetting events suggesting that a dry-rewetting mechanism representing the increase in N mineralization following soil wetting needs to be incorporated into biogeochemical models of semi-arid ecosystems.

The short-term pulse of carbon (C) and nitrogen (N) mineralization that accompanies the wetting of dry soils may dominate annual C and N production in many arid and semi-arid environments characterized by seasonal transitions. We used a laboratory incubation to evaluate the impact of short-term fluctuations in soil moisture on long-term carbon and nitrogen dynamics, and the degree to which rewetting enhances C and N release. Following repeated drying and rewetting of chaparral soils, cumulative CO2 release in rewet soils was 2.2–3.7 times greater than from soils maintained at equivalent mean soil moisture and represented 12–18% of the total soil C pool. Rewetting frequency did not affect cumulative CO2 release but did enhance N turnover, and net N mineralization and nitrification increased with rewetting in spite of significant reductions in nitrification potential. Litter addition decreased inorganic N release but enhanced dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) from dry soils, indicating the potential importance of a litter-derived pulse to short-term nutrient dynamics.

Compound eyes of insects are attractive biological systems for engineered biomimicry as artificial sources of light, given their characteristic wide angular field of view. A blowfly eye was coated with a thin conformal fluorescent film, with the aim of achieving wide field-of-view emission. Experimental results showed that the coated eye emitted visible light and that the intensity showed a weaker angular dependence than a fluorescent thin film deposited on a flat surface.

In the N-limited alpine tundra, plants may utilize a diversity of N sources (organic and inorganic N) in order to meet their nutritional requirements. To characterize species-level differences in traits related to N acquisition, we analyzed foliar δ15N, nitrate reductase activity (NRA) and mycorrhizal infection in co-occurring alpine species during the first half of the growing season and compared these traits to patterns of N uptake using a 15N (15N-NH4+, 15N-NO3–) or 13C,15N ([1]-13C-15N-glycine) tracer addition in the greenhouse. 13C enrichment in belowground tissue indicated that all species were capable of taking up labeled glycine, although only one species showed uptake of glycine potentially exceeding that of inorganic N. Species showing the most depleted foliar δ15N and elevated NRA in the field also tended to show relatively high rates of NO3– uptake in the greenhouse. Likewise, species showing the most enriched foliar δ15N also showed high rates of NH4+ uptake. The ratio of NO3–:NH4+ uptake rates and growth rate explained 64% and 72% of the variance in foliar δ15N, respectively, suggesting that species differ in the ability to take up NO3– and NH4+ in the field and that such differences may enable species to partition soil N on the basis of N form.

In this paper we consider modern methods of optical process monitoring and control in the context of atomic layer epitaxy. One specific method, p-polarized reflectance spectroscopy (PRS), is chosen to assess details of layer-by-layer growth. We show that PRS monitoring under conditions of steady-state growth by pulsed chemical beam epitaxy (PCBE) can achieve the deposition of molecular layers of GaP on silicon (100) deposited with a precision of 5%, which can be improved by reducing the growth rate and increasing the period of time averaging of the reflectance data. Since in the nucleation period prior to formation of a contiguous heteroepitaxial film inhomogeneous surface chemistry and roughening complicates the modeling of the overgrowth process, advances in both experimental methods and theory are required for extending the control to non-steady-state growth conditions. Results of simultaneous single-wavelength PR monitoring and laser light scattering measurements in conjunction with atomic force microscopy studies of short period heteroepitaxial overgrowth processes are presented. The extension of PRS to the monitoring of organometallic chemical vapor deposition at higher pressures is also discussed.

The heteroepitaxial overgrowth of silicon by nearly lattice‐matched compound semiconductors is reviewed in the context of the separation of the chemical problems associated with the initial sealing of the silicon surface by a contiguous epitaxial compound film from the problems associated with the generation of strain during heteroepitaxial growth. Of the mixed compound systems available dilute solid solutions of composition AlxGa1−xNyP1−y and ZnSySe1−y as well as ZnSixGe1−xP are suitable candidates for the exactly lattice‐matched epitaxial overgrowth of silicon. Real‐time process monitoring by nonintrusive methods is important for gaining an understanding of the epitaxial overgrowth mechanism and for controlling the film properties. A new method, p‐polarized reflectance spectroscopy is introduced that provides detailed information about the growth rate per cycle, the bulk optical properties of the film and its topography. Submonolayer resolution is accomplished for thousands of A of film growth by pulsed...

In this paper, we present results on the heteroepitaxial growth of GaP on Si by migration enhanced pulsed chemical beam epitaxy (PCBE) using additional hydrogen and filament assisted techniques. For the real-time monitoring we applied a new technique, p-polarized reflectance spectroscopy (PRS) which provides information on the bulk, interface and surface properties of the grown GaP/Si heterostructures. The monitoring is initiated close to the Brewster angle for the substrate material, achieving high sensitivity in the initial phase of heteroepitaxial overgrowth. The bulk properties and growth rate are monitored using the quarter wave periodic structure in the reflectance based on interference in the film. The surface vicinity properties are monitored by the periodic fine structures in the intensity of the reflected light, which are correlated with the switching cycles of the metalorganic precursor pulses and are amplitude-modulated in accord with the repeat cycle of the heteroepitaxial growth process. Additional information regarding the surface roughness was revealed by scattered light measurements during the growth of the film. The results of real-time monitoring of nucleation and growth are combined with results of the ex-situ characterization of the GaP/Si heterostructure by cross-sectional transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies to gain an understanding of the critical phase, in which the silicon surface becomes sealed by a contiguous epitaxial film of GaP. The defects formed in the GaP film during this phase determine the quality of the epilayers obtained upon prolonged growth.

The low temperature epitaxial growth of Si-GaP heterostructures by chemical beam epitaxy (CBE) and interrupted cycle chemical beam epitaxy (ICCBE) on patterned partially SiO2 masked silicon substrates is investigated to achieve dielectric isolation layers for Si circuits as well as for optical interconnections. Excellent selectivity of the growth on exposed Si windows versus SiO2 covered surface areas is observed and verified by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). Low temperature processing is essential to minimize interdiffusion and strain due to substantial mismatch of the thermal expansion coefficients of GaP and Si. We describe the deposition of GaP by CBE and ICCBE using sources of tertiarybutylphosphine (TBP) and triethylgallium (TEG) on (100) silicon at 310°C and the influence of photon assistance on the growth temperature and surface morphology. Secondary ion mass spectroscopy (SIMS) studies reveal that no measurable interdiffusion occurs under these conditions, including subsequent processing steps that require rapid thermal annealing for 30 s at 900°C. The GaP/Si interface is examined by high resolution cross-sectional transmission electron microscopy (HRTEM) before and after the 900°C anneal.

We used tree ring data (AD 1601-2007) to examine the occurrence of and climatic influences on spruce beetle (Dendroctonus rufipennis) outbreaks in south-central and southwest Alaska and found evidence of regional-scale outbreaks dating from the mid-1700s, related to climate variability at multiple temporal scales. Over interannual time scales (approximately 1-3 years), El Nino years, combined with severe late-summer drought, appeared to contribute significantly to spruce beetle outbreaks in the study area. Over multidecadal time scales (up to approximately 40 years), cool-phase Pacific Decadal Oscillation (PDO) conditions tended to precede beetle outbreaks, regardless of the phase of El Nino-Southern Oscillation (ENSO). All sites showed low-severity disturbances attributed to spruce beetle damage, most notably during the 1810s. During other major periods of disturbance (i.e., 1870s, 1910s, 1970s), the effects of spruce beetle outbreaks were of moderate or higher severity. The highly synchronized timing of spruce beetle outbreaks at interannual to multidecadal scales, and particularly the association between cool-phase PDO conditions and beetle disturbance, suggests that climate (i.e., temperature, precipitation) is a primary driver of outbreaks in the study area. Our disturbance chronologies (mid-1700s to present) suggest that recent irruptions (1990s to present) in south-central and southwest Alaska are within the historical geographic range, but that outbreaks since the 1990s show greater spatiotemporal synchrony (i.e., more sites record high-severity infestations) than at any other time in the past approximatly 250 years.

Niche complementarity, in which coexisting species use different forms of a resource, has been widely invoked to explain some of the most debated patterns in ecology, including maintenance of diversity and relationships between diversity and ecosystem function. However, classical models assume resource specialization in the form of distinct niches, which does not obviously apply to the broadly overlapping resource use in plant communities. Here we utilize an experimental framework based on competition theory to test whether plants partition resources via classical niche differentiation or via plasticity in resource use. We explore two alternatives: niche preemption, in which individuals respond to a superior competitor by switching to an alternative, less-used resource, and dominant plasticity, in which superior competitors exhibit high resource use plasticity and shift resource use depending on the competitive environment. We determined competitive ability by measuring growth responses with and without neighbors over a growing season and then used 15N tracer techniques to measure uptake of different nitrogen (N) forms in a field setting. We show that four alpine plant species of differing competitive abilities have statistically indistinguishable uptake patterns (nitrate > ammonium > glycine) in their fundamental niche (without competitors) but differ in whether they shift these uptake patterns in their realized niche (with competitors). Competitively superior species increased their uptake of the most available N form, ammonium, when in competition with the rarer, competitively inferior species. In contrast, the competitively inferior species did not alter its N uptake pattern in competition. The existence of plasticity in resource use among the dominant species provides a mechanism that helps to explain the manner by which plant species with broadly overlapping resource use might coexist.

Study Objective. To evaluate the effectiveness of switching statin therapy using a therapeutic conversion program versus usual care conversion among patients enrolled in the Colorado Indigent Care Program when atorvastatin was removed from the formulary. Design. Prospective cohort study. Setting. Family medicine center and other ambulatory care clinics of a university-based health care system. Patients. One hundred seventeen ambulatory care patients with dyslipidemia who were treated with atorvastatin. Intervention. Clinical pharmacists in the family medicine center implemented a therapeutic conversion program (30 patients), switching atorvastatin to a new formulary regimen of simvastatin, rosuvastatin, or ezetimibe-simvastatin, using an algorithm designed to achieve patient-specific goals for low-density lipoprotein cholesterol (LDL). Usual care occurred in the other ambulatory care clinics without clinical pharmacists (87 patients), where medical providers switched atorvastatin to a formulary regimen based on a suggested (but optional) equipotency conversion algorithm. Measurements and Main Results. Primary end points were LDL concentration and LDL goal attainment before and after conversion. Before and after conversion, respectively, mean LDL concentrations were 86.7 and 82.3 mg/dl in the therapeutic conversion group (p=0.44) versus 78.3 and 85.2 mg/dl in the usual care group (p=0.01). Percentages of patients attaining LDL goal were 80% before and 97% after conversion in the therapeutic conversion group (p=0.04) compared with 90% before and 75% after conversion in the usual care group (p=0.01). Conclusion. Use of a prospective, therapeutic statin conversion program was associated with increased control of dyslipidemia, whereas usual care statin conversion was associated with decreased control. These data suggest that proactive involvement of clinical pharmacists in converting lipid-lowering drugs results in superior patient care outcomes compared with a less aggressive approach.

The importance of interspecific competition as a cause of resource partitioning among species has been widely assumed but rarely tested. Using neighbor removals in combination with 15N tracer additions in the field, we examined variation among three alpine species in the uptake of 15N-NH4+, 15N-NO3-, and 15N-13C-[2]-glycine in intact neighborhoods, when paired with a specific neighbor, and when all neighbors were removed. Species varied in the capacity to take up 15N-labeled NH4+, NO3-, and glycine in intact neighborhoods and in interspecific pairs. When interspecific neighbor pairs were compared with no neighbor controls, neighbors reduced 15N uptake in target species by as much as 50%, indicating competition for N. Furthermore, neighbor identity influenced the capacity of species to take up different forms of N. Thus, competition within interspecific neighbor pairs often caused reduced uptake of a particular form of N, as well as shifts to uptake of an alternative form of N. Such shifts in resource use as a result of competition are an implicit assumption in studies of resource partitioning but have rarely been documented. Our study suggests that plasticity in the uptake of different forms of N may be a mechanism by which cooccurring plants reduce competition for N.

Parents often focus on independence in activities of daily living and social participation when setting goals for their children with autism spectrum disorders. Occupational therapy practitioners use clinical reasoning to translate these goals to define occupation-based outcomes. This article describes an exploratory analysis of 160 parent-identified goals for children with autism. We identified sensory integrative factors hypothesized to influence each goal and then categorized the goals using the Occupational Therapy Practice Framework: Domain and Process and the International Classification of Functioning, Disability and Health (ICF). Most goals were at the ICF participation and activity levels. Activities of daily living were the most common area of occupation identified, followed by social participation and play. Sensory reactivity and somatopraxis were the most frequently occurring sensory integrative factors. The value of addressing parent goals using a systematic reasoning process to identify factors affecting participation and the importance of measuring participation outcomes are discussed.

Plant resource partitioning of chemical forms of nitrogen (N) may be an important factor promoting species coexistence in N-limited ecosystems. Since the microbial community regulates N-form transformations, plant partitioning of N may be related to plant-soil feedbacks. We conducted a (15)N tracer addition experiment to study the ability of two alpine plant species, Acomastylis rossii and Deschampsia caespitosa, to partition organic and inorganic forms of N. The species are codominant and associated with strong plant-soil feedbacks that affect N cycling. We manipulated interspecific interactions by removing Acomastylis or Deschampsia from areas where the species were codominant to test if N uptake patterns varied in the presence of the other species. We found that Deschampsia acquired organic and inorganic N more rapidly than Acomastylis, regardless of neighbor treatment. Plant N uptake-specifically ammonium uptake-increased with plant density and the presence of an interspecific neighbor. Interestingly, this change in N uptake was not in the expected direction to reduce niche overlap and instead suggested facilitation of ammonium use. To test if N acquisition patterns were consistent with plant-soil feedbacks, we also compared microbial rhizosphere extracellular enzyme activity in patches dominated by one or the other species and in areas where they grew together. The presence of both species was generally associated with increased rhizosphere extracellular enzyme activity (five of ten enzymes) and a trend towards increased foliar N concentrations. Taken together, these results suggest that feedbacks through the microbial community, either in response to increased plant density or specific plant neighbors, could facilitate coexistence. However, coexistence is promoted via enhanced resource uptake rather than reduced niche overlap. The importance of resource partitioning to reduce the intensity of competitive interactions might vary across systems, particularly as a function of plant-soil feedbacks.

Repercussions of species loss on ecosystem processes depend on the effects of the lost species as well as the compensatory responses of the remaining species in the community. We experimentally removed two co-dominant plant species and added a 15N tracer in alpine tundra to compare how species’ functional differences influence community structure and N cycling. For both of the species, production compensated for the biomass removed by the second year. However, the responses of the remaining species depended on which species was removed. These differences in compensation influenced how species loss impacted ecosystem processes. After the removal of one of the co-dominant species, Acomastylis rossii, there were few changes in the relative abundance of the remaining species, and differences in functioning could be predicted based on effects associated with the removed species. In contrast, the removal of the other co-dominant, Deschampsia caespitosa, was associated with subsequent changes in community structure (species relative abundances and diversity) and impacts on ecosystem properties (microbial biomass N, dissolved organic N, and N uptake of subordinate species). Variation in compensation may contribute to the resulting effects on ecosystem functioning, with the potential to buffer or accelerate the effects of species loss.

In this communication we describe a simple, inexpensive technique for the real‐time monitoring of epitaxial processes based on the reflection of a parallel‐polarized light that impinges onto the surface of the substrate close to the Brewster angle for the substrate material. In the case of heteroepitaxy, a quarter‐wavelength modulation of the intensity of the reflected light is observed, which contains information concerning the evolution of the optical properties as well as a record of the growth rate for the entire duration of film deposition. Changes in the amplitude of this signal provides information about deviations in bulk dielectric properties of the growing film caused by absorption and inhomogeneities in the refractive index of the film as well as changes in the surface roughness. Furthermore, under the conditions of pulsed chemical beam epitaxy (PCBE), the reflected intensity contains a periodic oscillation that is superimposed on the polarized reflectance spectroscopy (PRS) signal with an A sc...

Purpose:To objectively assess swallowing function after an intensive chemoradiation regimen for locally advanced head-and-neck cancer and to assess the clinical implications of swallowing dysfunction. Patients and Methods:Twenty-nine patients with nonresectable Stage IV head-and-neck cancer participated in a Phase I study of radiation, 70 Gy/7 weeks, concurrent with weekly gemcitabine. Because of a high rate of mucosal toxicity, reduced drug doses were delivered to subsequent patient groups: 300, 150, 50, and 10 mg/m 2 /week. Twenty-six of these patients underwent prospective evaluation of swallowing function with videofluoroscopy and esophagogram. Studies were performed pretherapy, early post-therapy (1–3 months), and late post-therapy (6–12 months). Results:Complete tests were performed pretherapy in 22 patients, early post-therapy in 20, and late post-therapy in 13. Twenty-five patients had at least one post-therapy study. Post-therapy dysfunction was characterized by reduced inversion of the epiglottis, delayed swallow initiation and uncoordinated timing of the propulsion of the bolus, opening of the cricopharyngeal muscle, and closure of the larynx, all of which promoted aspiration during and after the swallow. In addition, reduced base-of-tongue retraction with reduced contact to the posterior pharyngeal wall and incomplete cricopharyngeal relaxation resulted in pooling in the pyriform sinuses and vallecula of residue, which was frequently aspirated after the swallow. Post-therapy aspirations were typically "silent," eliciting no cough reflex, or the cough was delayed and noneffective in expelling the residue. Aspiration was observed in 3 patients (14%) in the pretherapy studies, in 13 (65%) in the early post-therapy studies, and in 8 (62%) in the late post-therapy studies (aspiration rates post-therapy vs. pretherapy: p = 0.0002). Six patients had pneumonia requiring hospitalization 1–14 months after therapy (median: 2.5 months), being the likely cause of death in 2 patients. Five cases of pneumonia occurred among 17 patients who had demonstrated aspiration in the post-therapy studies, compared with no cases of pneumonia among 8 patients who had not demonstrated aspiration ( p = 0.1). Of the 4 patients who had not undergone any post-therapy study, 1 developed pneumonia. Mucositis scores, prolonged tube feeding, presence of tracheostomy tube, and gemcitabine doses were not found to be related to aspiration or pneumonia risk. Conclusions:After intensive chemoradiotherapy, significant objective swallowing dysfunction is prevalent. It promotes aspiration, which may not elicit a cough reflex and may be associated with pneumonia. Aspiration pneumonia may be an underdocumented complication of chemoradiotherapy for head-and-neck cancer. Future studies should examine whether routine post-therapy videofluoroscopy and training aspirating patients in safe swallowing strategies can reduce this risk.

The complex morphology of the apposition compound eyes of insects of many species provides them a wide angular field of view. This characteristic makes these eyes attractive for bioreplication as artificial sources of light. The cornea of a blowfly eye was conformally coated with a fluorescent thin film with the aim of achieving wide field-of-view emission. On illumination by shortwave-ultraviolet light, the conformally coated eye emitted visible light whose intensity showed a weaker angular dependence than a fluorescent thin film deposited on a flat surface.

Epitaxial GaP films grown on silicon by chemical beam epitaxy contain planar defects that are related to three dimensional island formation of GaP nucleating on the silicon substrate. Attention in the surface preconditioning and to the surface chemistry during the initial stages of nucleation and growth allow the control from pronounced three-dimensional growth behavior toward almost two-dimensional growth. New results on defect structure and surface morphology obtained by a combination of atomic force microscope (AFM) and a new method p-polarized reflectance spectroscopy (PRS) are presented and related to growth conditions during the initial stages of heteroepitaxy.