WorldWideScience

Sample records for single-layer urban canopy

  1. The implementation of biofiltration systems, rainwater tanks and urban irrigation in a single-layer urban canopy model

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    Demuzere, Matthias; Coutts, Andrew; Goehler, Maren; Broadbent, Ashley; Wouters, Hendrik; van Lipzig, Nicole; Gebert, Luke

    2015-04-01

    Urban vegetation is generally considered as a key tool to modify the urban energy balance through enhanced evapotranspiration (ET). Given that vegetation is most effective when it is healthy, stormwater harvesting and retention strategies (such as water sensitive urban design) could be used to support vegetation and promote ET. This study presents the implementation of a vegetated lined bio-filtration system (BFS) combined with a rainwater tank (RWT) and urban irrigation system in the single-layer urban canopy model Community Land Model-Urban. Runoff from roof and impervious road surface fractions is harvested and used to support an adequate soil moisture level for vegetation in the BFS. In a first stage, modelled soil moisture dynamics are evaluated and found reliable compared to observed soil moisture levels from biofiltration pits in Smith Street, Melbourne (Australia). Secondly, the impact of BFS, RWT and urban irrigation on ET is illustrated for a two-month period in 2012 using varying characteristics for all components. Results indicate that (i) a large amount of stormwater is potentially available for indoor and outdoor water demands, including irrigation of urban vegetation, (ii) ET from the BFS is an order of magnitude larger compared to the contributions from the impervious surfaces, even though the former only covers 10% of the surface fraction and (iii) attention should be paid to the cover fraction and soil texture of the BFS, size of the RWT and the surface fractions contributing to the collection of water in the RWT. Overall, this study reveals that this model development can effectuate future research with state-of-the-art urban climate models to further explore the benefits of vegetated biofiltration systems as a water sensitive urban design tool optimised with an urban irrigation system to maintain healthy vegetation.

  2. A Study of the Oklahoma City Urban Heat Island Effect Using a WRF/Single-Layer Urban Canopy Model, a Joint Urban 2003 Field Campaign, and MODIS Satellite Observations

    Directory of Open Access Journals (Sweden)

    Hengyue Zhang

    2017-09-01

    Full Text Available The urban heat island effect (UHI for inner land regions was investigated using satellite data, ground observations, and simulations with an Single-Layer Urban Canopy Parameterization (SLUCP coupled into the regional Weather Research Forecasting model (WRF, http://wrf-model.org/index.php. Specifically, using the satellite-observed surface skin temperatures (Tskin, the intensity of the UHI was first compared for two inland cities (Xi’an City, China, and Oklahoma City (OKC, which have different city populations and building densities. The larger population density and larger building density in Xi’an lead to a stronger skin-level UHI by 2 °C. However, the ground observed 2 m surface air temperature (Tair observations showed an urban cooling island effect (UCI over the downtown region in OKC during the daytime of 19 July 2003, from a DOE field campaign (Joint Urban 2003. To understand this contrast between satellite-based Tskin and ground-based Tair, a sensitivity study using WRF/SLUCP was analyzed. The model reproduced a UCI in OKC. Furthermore, WRF/Noah/SLUCM simulations were also compared with the Joint Urban 2003 ground observations, including wind speeds, wind directions, and energy fluxes. Although the WRF/SLUCM model failed to simulate these variables accurately, it reproduced the diurnal variations of surface temperatures, wind speeds, wind directions, and energy fluxes reasonably well.

  3. Gainesville's urban forest canopy cover

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    Francisco Escobedo; Jennifer A. Seitz; Wayne Zipperer

    2009-01-01

    Ecosystem benefits from trees are linked directly to the amount of healthy urban forest canopy cover. Urban forest cover is dynamic and changes over time due to factors such as urban development, windstorms, tree removals, and growth. The amount of a city's canopy cover depends on its land use, climate, and people's preferences. This fact sheet examines how...

  4. An inter-model comparison of urban canopy effects on climate

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    Halenka, Tomas; Karlicky, Jan; Huszar, Peter; Belda, Michal; Bardachova, Tatsiana

    2017-04-01

    The role of cities is increasing and will continue to increase in future, as the population within the urban areas is growing faster, with the estimate for Europe of about 84% living in urban areas in about mid of 21st century. To assess the impact of cities and, in general, urban surfaces on climate, using of modeling approach is well appropriate. Moreover, with higher resolution, urban areas becomes to be better resolved in the regional models and their relatively significant impacts should not be neglected. Model descriptions of urban canopy related meteorological effects can, however, differ largely given the odds in the driving models, the underlying surface models and the urban canopy parameterizations, representing a certain uncertainty. In this study we try to contribute to the estimation of this uncertainty by performing numerous experiments to assess the urban canopy meteorological forcing over central Europe on climate for the decade 2001-2010, using two driving models (RegCM4 and WRF) in 10 km resolution driven by ERA-Interim reanalyses, three surface schemes (BATS and CLM4.5 for RegCM4 and Noah for WRF) and five urban canopy parameterizations available: one bulk urban scheme, three single layer and a multilayer urban scheme. Actually, in RegCM4 we used our implementation of the Single Layer Urban Canopy Model (SLUCM) in BATS scheme and CLM4.5 option with urban parameterization based on SLUCM concept as well, in WRF we used all the three options, i.e. bulk, SLUCM and more complex and sophisticated Building Environment Parameterization (BEP) connected with Building Energy Model (BEM). As a reference simulations, runs with no urban areas and with no urban parameterizations were performed. Effects of cities on urban and rural areas were evaluated. Effect of reducing diurnal temperature range in cities (around 2 °C in summer) is noticeable in all simulation, independent to urban parameterization type and model. Also well-known warmer summer city nights

  5. Urban Canopy Effects in Regional Climate Simulations - An Inter-Model Comparison

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    Halenka, T.; Huszar, P.; Belda, M.; Karlicky, J.

    2017-12-01

    To assess the impact of cities and urban surfaces on climate, the modeling approach is often used with inclusion of urban parameterization in land-surface interactions. This is especially important when going to higher resolution, which is common trend both in operational weather prediction and regional climate modelling. Model description of urban canopy related meteorological effects can, however, differ largely given especially the underlying surface models and the urban canopy parameterizations, representing a certain uncertainty. To assess this uncertainty is important for adaptation and mitigation measures often applied in the big cities, especially in connection to climate change perspective, which is one of the main task of the new project OP-PPR Proof of Concept UK. In this study we contribute to the estimation of this uncertainty by performing numerous experiments to assess the urban canopy meteorological forcing over central Europe on climate for the decade 2001-2010, using two regional climate models (RegCM4 and WRF) in 10 km resolution driven by ERA-Interim reanalyses, three surface schemes (BATS and CLM4.5 for RegCM4 and Noah for WRF) and five urban canopy parameterizations available: one bulk urban scheme, three single layer and a multilayer urban scheme. Effects of cities on urban and remote areas were evaluated. There are some differences in sensitivity of individual canopy model implementations to the UHI effects, depending on season and size of the city as well. Effect of reducing diurnal temperature range in cities (around 2 °C in summer mean) is noticeable in all simulations, independent to urban parameterization type and model, due to well-known warmer summer city nights. For the adaptation and mitigation purposes, rather than the average urban heat island intensity the distribution of it is more important providing the information on extreme UHI effects, e.g. during heat waves. We demonstrate that for big central European cities this effect

  6. Spatial variability of carbon dioxide in the urban canopy layer and implications for flux measurements

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    Crawford, B.; Christen, A.

    2014-12-01

    This contribution reports CO2 mixing ratios measured in the urban canopy layer (UCL) of a residential neighborhood in Vancouver, BC, Canada and discusses the relevance of UCL CO2 temporal and spatial variability to local-scale eddy covariance (EC) fluxes measured above the UCL. Measurements were conducted from a mobile vehicle-mounted platform over a continuous, 26-h period in the longterm turbulent flux source area of an urban EC tower. Daytime mixing ratios were highest along arterial roads and largely a function of proximity to vehicle traffic CO2 sources. At night, there was a distinct negative correlation between potential air temperature and CO2 mixing ratios. The spatial distribution of CO2 was controlled by topography and micro-scale advective processes (i.e. cold-air pooling). Mobile CO2 measurements were then used to calculate CO2 storage changes (FS) in the UCL volume and compared to single-layer FS estimates calculated from the EC system. In total, five variations of FS were calculated. On average, the choice of FS calculation method affected net measured hourly emissions (FC) by 5.2%. Analysis of FS using a four-year dataset measured at the EC tower show FS was 2.8% of hourly FC for this site on average. At this urban EC location, FS was relatively minor compared to FC and calculation of FS using a single-layer method was adequate, though FS still represents a potentially large uncertainty during individual hours.

  7. The impact of urban canopy meteorological forcing on summer photochemistry

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    Huszár, Peter; Karlický, Jan; Belda, Michal; Halenka, Tomáš; Pišoft, Petr

    2018-03-01

    The regional climate model RegCM4.4, including the surface model CLM4.5, was offline coupled to the chemistry transport model CAMx version 6.30 in order to investigate the impact of the urban canopy induced meteorological changes on the longterm summer photochemistry over central Europe for the 2001-2005 period. First, the urban canopy impact on the meteorological conditions was calculated performing a reference experiment without urban landsurface considered and an experiment with urban surfaces modeled with the urban parameterization within the CLM4.5 model. In accordance with expectations, strong increases of urban surface temperatures (up to 2-3 K), decreases of wind speed (up to -1 ms-1) and increases of vertical turbulent diffusion coefficient (up to 60-70 m2s-1) were found. For the impact on chemistry, these three components were considered. Additionally, we accounted for the effect of temperature enhanced biogenic emission increase. Several experiments were performed by adding these effects one-by-one to the total impact: i.e., first, only the urban temperature impact was considered driving the chemistry model; secondly, the wind impact was added and so on. We found that the impact on biogenic emission account for minor changes in the concentrations of ozone (O3), oxides of nitrogen NOx = NO + NO2 and nitric acid (HNO3). On the other hand, the dominating component acting is the increased vertical mixing, resulting in up to 5 ppbv increase of urban ozone concentrations while causing -2 to -3 ppbv decreases and around 1 ppbv increases of NOx and HNO3 surface concentrations, respectively. The temperature impact alone results in reduction of ozone, increase in NO, decrease in NO2 and increases of HNO3. The wind impact leads, over urban areas, to ozone decreases, increases of NOx and a slight increase in HNO3. The overall impact is similar to the impact of increased vertical mixing alone. The Process Analysis (PA) technique implemented in CAMx was adopted to

  8. Applications of urban tree canopy assessment and prioritization tools: supporting collaborative decision making to achieve urban sustainability goals

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    Dexter H. Locke; J. Morgan Grove; Michael Galvin; Jarlath P.M. ONeil-Dunne; Charles. Murphy

    2013-01-01

    Urban Tree Canopy (UTC) Prioritizations can be both a set of geographic analysis tools and a planning process for collaborative decision-making. In this paper, we describe how UTC Prioritizations can be used as a planning process to provide decision support to multiple government agencies, civic groups and private businesses to aid in reaching a canopy target. Linkages...

  9. Roles of Urban Tree Canopy and Buildings in Urban Heat Island Effects: Parameterization and Preliminary Results

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    Loughner, Christopher P.; Allen, Dale J.; Zhang, Da-Lin; Pickering, Kenneth E.; Dickerson, Russell R.; Landry, Laura

    2012-01-01

    Urban heat island (UHI) effects can strengthen heat waves and air pollution episodes. In this study, the dampening impact of urban trees on the UHI during an extreme heat wave in the Washington, D.C., and Baltimore, Maryland, metropolitan area is examined by incorporating trees, soil, and grass into the coupled Weather Research and Forecasting model and an urban canopy model (WRF-UCM). By parameterizing the effects of these natural surfaces alongside roadways and buildings, the modified WRF-UCM is used to investigate how urban trees, soil, and grass dampen the UHI. The modified model was run with 50% tree cover over urban roads and a 10% decrease in the width of urban streets to make space for soil and grass alongside the roads and buildings. Results show that, averaged over all urban areas, the added vegetation decreases surface air temperature in urban street canyons by 4.1 K and road-surface and building-wall temperatures by 15.4 and 8.9 K, respectively, as a result of tree shading and evapotranspiration. These temperature changes propagate downwind and alter the temperature gradient associated with the Chesapeake Bay breeze and, therefore, alter the strength of the bay breeze. The impact of building height on the UHI shows that decreasing commercial building heights by 8 m and residential building heights by 2.5 m results in up to 0.4-K higher daytime surface and near-surface air temperatures because of less building shading and up to 1.2-K lower nighttime temperatures because of less longwave radiative trapping in urban street canyons.

  10. Trees grow on money: Urban tree canopy cover and environmental justice

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    Kirsten Schwarz; Michail Fragkias; Christopher G. Boone; Weiqi Zhou; Melissa McHale; J. Morgan Grove; Jarlath O' Neil-Dunne; Joseph P. McFadden; Geoffrey L. Buckley; Dan Childers; Laura Ogden; Stephanie Pincetl; Diane Pataki; Ali Whitmer; Mary L. Cadenasso; Steven Arthur. Loiselle

    2015-01-01

    This study examines the distributional equity of urban tree canopy (UTC) cover for Baltimore, MD, Los Angeles, CA, New York, NY, Philadelphia, PA, Raleigh, NC, Sacramento, CA, and Washington, D.C. using high spatial resolution land cover data and census data. Data are analyzed at the Census Block Group levels using Spearman’s correlation, ordinary least squares...

  11. A comparison of two sampling approaches for assessing the urban forest canopy cover from aerial photography.

    Science.gov (United States)

    Ucar Zennure; Pete Bettinger; Krista Merry; Jacek Siry; J.M. Bowker

    2016-01-01

    Two different sampling approaches for estimating urban tree canopy cover were applied to two medium-sized cities in the United States, in conjunction with two freely available remotely sensed imagery products. A random point-based sampling approach, which involved 1000 sample points, was compared against a plot/grid sampling (cluster sampling) approach that involved a...

  12. Intra-Urban Variability in Elemental Carbon Deposition to Tree Canopies

    Science.gov (United States)

    Barrett, T. E.; Ponette-González, A.; Rindy, J. E.; Sheesley, R. J.

    2017-12-01

    Urban areas cover fog deposition) or they can settle directly onto receptor surfaces (dry deposition). Only limited measurements indicate that EC deposition is higher in urban than in rural and remote regions. However, EC deposition likely exhibits considerable intra-urban variability, with tree canopies serving as potentially important sinks for EC on the cityscape. The goal of this research is to quantify spatial variability in total (wet + dry) EC deposition to urban tree canopies in the Dallas-Fort Worth Metroplex. Using a stratified non-random sampling design, 41 oak trees (22 post oak (Quercus stellata) and 19 live oak (Quercus virginiana)) were selected near (100 m) for measurements of throughfall (water that falls from the canopy to the forest floor). Additionally, 16 bulk rainfall samplers were deployed in grassy areas with no canopy cover. Results from one rain event indicate a volume weighted mean concentration of 83 µg EC L-1 in post oak throughfall, 36 µg EC L-1 in live oak throughfall, and 4 µg EC L-1 in bulk rainfall. Total EC deposition to oak tree canopies was 2.0 ± 2.1 (SD) mg m-2 for post oak and 0.7 ± 0.3 mg m-2 for live oak. Bulk rainfall deposition was 0.08 ± 0.1 mg m-2. Our preliminary findings show that trees are effective urban air filters, removing 9-25 times more EC from the atmosphere than rainwater alone. Resolving surface controls on atmospheric EC removal is key to developing and assessing near-term climate and air quality mitigation strategies.

  13. Growing Canopy on a College Campus: Understanding Urban Forest Change through Archival Records and Aerial Photography.

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    Roman, Lara A; Fristensky, Jason P; Eisenman, Theodore S; Greenfield, Eric J; Lundgren, Robert E; Cerwinka, Chloe E; Hewitt, David A; Welsh, Caitlin C

    2017-12-01

    Many municipalities are setting ambitious tree canopy cover goals to increase the extent of their urban forests. A historical perspective on urban forest development can help cities strategize how to establish and achieve appropriate tree cover targets. To understand how long-term urban forest change occurs, we examined the history of trees on an urban college campus: the University of Pennsylvania in Philadelphia, PA. Using a mixed methods approach, including qualitative assessments of archival records (1870-2017), complemented by quantitative analysis of tree cover from aerial imagery (1970-2012), our analysis revealed drastic canopy cover increase in the late 20th and early 21st centuries along with the principle mechanisms of that change. We organized the historical narrative into periods reflecting campus planting actions and management approaches; these periods are also connected to broader urban greening and city planning movements, such as City Beautiful and urban sustainability. University faculty in botany, landscape architecture, and urban design contributed to the design of campus green spaces, developed comprehensive landscape plans, and advocated for campus trees. A 1977 Landscape Development Plan was particularly influential, setting forth design principles and planting recommendations that enabled the dramatic canopy cover gains we observed, and continue to guide landscape management today. Our results indicate that increasing urban tree cover requires generational time scales and systematic management coupled with a clear urban design vision and long-term commitments. With the campus as a microcosm of broader trends in urban forest development, we conclude with a discussion of implications for municipal tree cover planning.

  14. Growing Canopy on a College Campus: Understanding Urban Forest Change through Archival Records and Aerial Photography

    Science.gov (United States)

    Roman, Lara A.; Fristensky, Jason P.; Eisenman, Theodore S.; Greenfield, Eric J.; Lundgren, Robert E.; Cerwinka, Chloe E.; Hewitt, David A.; Welsh, Caitlin C.

    2017-12-01

    Many municipalities are setting ambitious tree canopy cover goals to increase the extent of their urban forests. A historical perspective on urban forest development can help cities strategize how to establish and achieve appropriate tree cover targets. To understand how long-term urban forest change occurs, we examined the history of trees on an urban college campus: the University of Pennsylvania in Philadelphia, PA. Using a mixed methods approach, including qualitative assessments of archival records (1870-2017), complemented by quantitative analysis of tree cover from aerial imagery (1970-2012), our analysis revealed drastic canopy cover increase in the late 20th and early 21st centuries along with the principle mechanisms of that change. We organized the historical narrative into periods reflecting campus planting actions and management approaches; these periods are also connected to broader urban greening and city planning movements, such as City Beautiful and urban sustainability. University faculty in botany, landscape architecture, and urban design contributed to the design of campus green spaces, developed comprehensive landscape plans, and advocated for campus trees. A 1977 Landscape Development Plan was particularly influential, setting forth design principles and planting recommendations that enabled the dramatic canopy cover gains we observed, and continue to guide landscape management today. Our results indicate that increasing urban tree cover requires generational time scales and systematic management coupled with a clear urban design vision and long-term commitments. With the campus as a microcosm of broader trends in urban forest development, we conclude with a discussion of implications for municipal tree cover planning.

  15. Mapping Urban Tree Canopy Cover Using Fused Airborne LIDAR and Satellite Imagery Data

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    Parmehr, Ebadat G.; Amati, Marco; Fraser, Clive S.

    2016-06-01

    Urban green spaces, particularly urban trees, play a key role in enhancing the liveability of cities. The availability of accurate and up-to-date maps of tree canopy cover is important for sustainable development of urban green spaces. LiDAR point clouds are widely used for the mapping of buildings and trees, and several LiDAR point cloud classification techniques have been proposed for automatic mapping. However, the effectiveness of point cloud classification techniques for automated tree extraction from LiDAR data can be impacted to the point of failure by the complexity of tree canopy shapes in urban areas. Multispectral imagery, which provides complementary information to LiDAR data, can improve point cloud classification quality. This paper proposes a reliable method for the extraction of tree canopy cover from fused LiDAR point cloud and multispectral satellite imagery data. The proposed method initially associates each LiDAR point with spectral information from the co-registered satellite imagery data. It calculates the normalised difference vegetation index (NDVI) value for each LiDAR point and corrects tree points which have been misclassified as buildings. Then, region growing of tree points, taking the NDVI value into account, is applied. Finally, the LiDAR points classified as tree points are utilised to generate a canopy cover map. The performance of the proposed tree canopy cover mapping method is experimentally evaluated on a data set of airborne LiDAR and WorldView 2 imagery covering a suburb in Melbourne, Australia.

  16. Characteristics and transport of organochlorine pesticides in urban environment: air, dust, rain, canopy throughfall, and runoff.

    Science.gov (United States)

    Zhang, Wei; Ye, Youbin; Hu, Dan; Ou, Langbo; Wang, Xuejun

    2010-11-01

    Characteristics and transport of organochlorine pesticides (OCPs) in urban multiple environments, including air, dust, rain, canopy throughfall, and runoff water, are explored in this study. Hexachlorocyclohexanes (HCHs) dominated in both air and rain water, and dichlorodiphenyltrichloroethane (DDT) related substances showed a higher affinity to dust. Relatively high concentrations of DDT and dichlorodiphenyldichloroethylene (DDE) in air, rain and dust imply that technical DDT in the environment has been degrading, and there may be unknown local or regional emission sources that contain DDTs in the study area. Source identification showed that DDTs in Beijing urban environments with a fresh signature may originate from the atmospheric transport from remote areas. The ratio of α-/γ-HCH in dust, rain, canopy throughfall and runoff were close to 1, indicating the possible use of lindane. OCPs in runoff were transported from various sources including rain, dust, and canopy throughfall. In runoff, DDTs and hexachlorobenzene (HCB) were mainly transported from dust, and HCHs were mainly from rain and canopy throughfall.

  17. Estimating the influence of different urban canopy cover types on atmospheric particulate matter (PM10) pollution abatement in London UK.

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    Tallis, Matthew; Freer-Smith, Peter; Sinnett, Danielle; Aylott, Matthew; Taylor, Gail

    2010-05-01

    In the urban environment atmospheric pollution by PM10 (particulate matter with a diameter less than 10 x 10-6 m) is a problem that can have adverse effects on human health, particularly increasing rates of respiratory disease. The main contributors to atmospheric PM10 in the urban environment are road traffic, industry and power production. The urban tree canopy is a receptor for removing PM10s from the atmosphere due to the large surface areas generated by leaves and air turbulence created by the structure of the urban forest. In this context urban greening has long been known as a mechanism to contribute towards PM10 removal from the air, furthermore, tree canopy cover has a role in contributing towards a more sustainable urban environment. The work reported here has been carried out within the BRIDGE project (SustainaBle uRban plannIng Decision support accountinG for urban mEtabolism). The aim of this project is to assess the fluxes of energy, water, carbon dioxide and particulates within the urban environment and develope a DSS (Decision Support System) to aid urban planners in sustainable development. A combination of published urban canopy cover data from ground, airborne and satellite based surveys was used. For each of the 33 London boroughs the urban canopy was classified to three groups, urban woodland, street trees and garden trees and each group quantified in terms of ground cover. The total [PM10] for each borough was taken from the LAEI (London Atmospheric Emissions Inventory 2006) and the contribution to reducing [PM10] was assessed for each canopy type. Deposition to the urban canopy was assessed using the UFORE (Urban Forest Effects Model) approach. Deposition to the canopy, boundary layer height and percentage reduction of the [PM10] in the atmosphere was assessed using both hourly meterological data and [PM10] and seasonal data derived from annual models. Results from hourly and annual data were compared with measured values. The model was then

  18. Quantifying the influence of geometrical details on urban canopy flow simulations

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    Hwang, Yunjae; Sousa, Jorge; Gorle, Catherine

    2017-11-01

    Computational Fluid Dynamics (CFD) methods are frequently used to investigate urban canopy flows. Since it is not possible to represent the full complexity of these flows in a single deterministic simulation, there is a need to quantify the uncertainty in the results. In previous work, we have investigated uncertainties related to the inflow boundary conditions and the turbulence model. The results indicated that additional uncertainties are likely non-negligible, and that uncertainty in the representation of the urban canopy geometry could be an important factor. The objective of this study is to explore methods to quantify geometrical uncertainties in urban canopy CFD simulations. We consider a model of Stanford University's Science and Engineering Quad, and investigate the effect of the geometry by gradually introducing features with smaller dimensions into the model, and by introducing momentum sinks to represent the presence of vegetation. The geometrical changes result in some considerable differences, such as higher wind amplification factors near the buildings around the quad. Since such differences can affect design decisions related to e.g. pedestrian wind comfort or wind loading, future work will focus on establishing a more formal framework to quantify these uncertainties.

  19. Atmospheric Inputs of Nitrogen, Carbon, and Phosphorus across an Urban Area: Unaccounted Fluxes and Canopy Influences

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    Decina, Stephen M.; Templer, Pamela H.; Hutyra, Lucy R.

    2018-02-01

    Rates of atmospheric deposition are declining across the United States, yet urban areas remain hotspots of atmospheric deposition. While past studies show elevated rates of inorganic nitrogen (N) deposition in cities, less is known about atmospheric inputs of organic N, organic carbon (C), and organic and inorganic phosphorus (P), all of which can affect ecosystem processes, water quality, and air quality. Further, the effect of the tree canopy on amounts and forms of nutrients reaching urban ground surfaces is not well-characterized. We measured growing season rates of total N, organic C, and total P in bulk atmospheric inputs, throughfall, and soil solution around the greater Boston area. We found that organic N constitutes a third of total N inputs, organic C inputs are comparable to rural inputs, and inorganic P inputs are 1.2 times higher than those in sewage effluent. Atmospheric inputs are enhanced two-to-eight times in late spring and are elevated beneath tree canopies, suggesting that trees augment atmospheric inputs to ground surfaces. Additionally, throughfall inputs may directly enter runoff when trees extend above impervious surfaces, as is the case with 26.1% of Boston's tree canopy. Our results indicate that the urban atmosphere is a significant source of elemental inputs that may impact urban ecosystems and efforts to improve water quality, particularly in terms of P. Further, as cities create policies encouraging tree planting to provide ecosystem services, locating trees above permeable surfaces to reduce runoff nutrient loads may be essential to managing urban biogeochemical cycling and water quality.

  20. Effects of Explicit Urban-Canopy Representation on Local Circulations Above a Tropical Mega-City

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    Flores Rojas, José L.; Pereira Filho, Augusto J.; Karam, Hugo A.; Vemado, Felipe; Masson, Valéry

    2018-01-01

    The Advanced Regional Prediction System (ARPS) is coupled with the tropical town energy budget (tTEB) scheme to analyze the effects of the urban canopy circulation over the metropolitan area of São Paulo and its interactions with the sea breeze and mountain-valley circulation in the eastern state of São Paulo, Brazil. Two experiments are carried out for the typical sea-breeze event occurring on 22 August 2014 under weak synoptic forcing and clear-sky conditions: (a) a control run with the default semi-desert surface parametrization and; (b) a tTEB run for the urban canopy of São Paulo. A realistic land-use database over the south-eastern domain of Brazil is used in the downscaling simulation to a horizontal grid resolution of 3 km. Our results indicate that ARPS effectively simulates features of the nighttime and early morning land-breeze circulation, which is affected by the surrounding hills and the nocturnal heat island of São Paulo. By early afternoon, the south-eastern sea-breeze circulation moves inland perpendicular to the upslope of the Serra do Mar scarp, which generates a line of moisture convergence and updrafts further inland. Later, the convergence line reaches São Paulo and interacts with the circulation arising from the urban heat island (UHI), which increases the moisture convergence and strength of updrafts. The surface energy balance indicates that the UHI is caused by large sensible heat storage within the urban canopy during the day, which is later released in the afternoon and at night. The simulations are verified with available radiosonde and surface weather station data, land-surface-temperature estimates from the moderate resolution imaging spectroradiometer, as well as the National Center for Atmospheric Research reanalysis databases. The three-dimensional geometry of the urban canyons within the tTEB scheme consistently improves the thermodynamically-induced circulation over São Paulo.

  1. The relationship between tree canopy and crime rates across an urban-rural gradient in the greater Baltimore region

    Science.gov (United States)

    Austin Troy; J. Morgan Grove; Jarlath. O' Neill-Dunne

    2012-01-01

    The extent to which urban tree cover influences crime is in debate in the literature. This research took advantage of geocoded crime point data and high resolution tree canopy data to address this question in Baltimore City and County, MD, an area that includes a significant urban-rural gradient. Using ordinary least squares and spatially adjusted regression and...

  2. Parameterizing Urban Canopy Layer transport in an Lagrangian Particle Dispersion Model

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    Stöckl, Stefan; Rotach, Mathias W.

    2016-04-01

    The percentage of people living in urban areas is rising worldwide, crossed 50% in 2007 and is even higher in developed countries. High population density and numerous sources of air pollution in close proximity can lead to health issues. Therefore it is important to understand the nature of urban pollutant dispersion. In the last decades this field has experienced considerable progress, however the influence of large roughness elements is complex and has as of yet not been completely described. Hence, this work studied urban particle dispersion close to source and ground. It used an existing, steady state, three-dimensional Lagrangian particle dispersion model, which includes Roughness Sublayer parameterizations of turbulence and flow. The model is valid for convective and neutral to stable conditions and uses the kernel method for concentration calculation. As most Lagrangian models, its lower boundary is the zero-plane displacement, which means that roughly the lower two-thirds of the mean building height are not included in the model. This missing layer roughly coincides with the Urban Canopy Layer. An earlier work "traps" particles hitting the lower model boundary for a recirculation period, which is calculated under the assumption of a vortex in skimming flow, before "releasing" them again. The authors hypothesize that improving the lower boundary condition by including Urban Canopy Layer transport could improve model predictions. This was tested herein by not only trapping the particles, but also advecting them with a mean, parameterized flow in the Urban Canopy Layer. Now the model calculates the trapping period based on either recirculation due to vortex motion in skimming flow regimes or vertical velocity if no vortex forms, depending on incidence angle of the wind on a randomly chosen street canyon. The influence of this modification, as well as the model's sensitivity to parameterization constants, was investigated. To reach this goal, the model was

  3. Edge-to-Stem Variability in Wet-Canopy Evaporation From an Urban Tree Row

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    Van Stan, John T.; Norman, Zachary; Meghoo, Adrian; Friesen, Jan; Hildebrandt, Anke; Côté, Jean-François; Underwood, S. Jeffrey; Maldonado, Gustavo

    2017-11-01

    Evaporation from wet-canopy (E_C) and stem (E_S) surfaces during rainfall represents a significant portion of municipal-to-global scale hydrologic cycles. For urban ecosystems, E_C and E_S dynamics play valuable roles in stormwater management. Despite this, canopy-interception loss studies typically ignore crown-scale variability in E_C and assume (with few indirect data) that E_S is generally {urban Pinus elliottii tree row to estimate E_C and E_S under the assumption that crown surfaces behave as "wet bulbs". From December 2015 through July 2016, 33 saturated crown periods (195 h of 5-min observations) were isolated from storms for determination of 5-min evaporation rates ranging from negligible to 0.67 mm h^{-1}. Mean E_S (0.10 mm h^{-1}) was significantly lower (p urban tree rows can be adequately estimated by simply assuming saturated tree surfaces behave as wet bulbs, avoiding problematic assumptions associated with other physically-based methods.

  4. Impact of an improved WRF urban canopy model on diurnal air temperature simulation over northern Taiwan

    Directory of Open Access Journals (Sweden)

    C.-Y. Lin

    2016-02-01

    Full Text Available This study evaluates the impact of urbanization over northern Taiwan using the Weather Research and Forecasting (WRF Model coupled with the Noah land-surface model and a modified urban canopy model (WRF–UCM2D. In the original UCM coupled to WRF (WRF–UCM, when the land use in the model grid is identified as "urban", the urban fraction value is fixed. Similarly, the UCM assumes the distribution of anthropogenic heat (AH to be constant. This may not only lead to over- or underestimation of urban fraction and AH in urban and non-urban areas, but spatial variation also affects the model-estimated temperature. To overcome the abovementioned limitations and to improve the performance of the original UCM model, WRF–UCM is modified to consider the 2-D urban fraction and AH (WRF–UCM2D.The two models were found to have comparable temperature simulation performance for urban areas, but large differences in simulated results were observed for non-urban areas, especially at nighttime. WRF–UCM2D yielded a higher correlation coefficient (R2 than WRF–UCM (0.72 vs. 0.48, respectively, while bias and RMSE achieved by WRF–UCM2D were both significantly smaller than those attained by WRF–UCM (0.27 and 1.27 vs. 1.12 and 1.89, respectively. In other words, the improved model not only enhanced correlation but also reduced bias and RMSE for the nighttime data of non-urban areas. WRF–UCM2D performed much better than WRF–UCM at non-urban stations with a low urban fraction during nighttime. The improved simulation performance of WRF–UCM2D in non-urban areas is attributed to the energy exchange which enables efficient turbulence mixing at a low urban fraction. The result of this study has a crucial implication for assessing the impacts of urbanization on air quality and regional climate.

  5. Investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using laser Doppler anemometry

    Science.gov (United States)

    Herpin, Sophie; Perret, Laurent; Mathis, Romain; Tanguy, Christian; Lasserre, Jean-Jacques

    2018-05-01

    Laser Doppler anemometry (LDA) is used to investigate the flow inside an idealized urban canopy consisting of a staggered array of cubes with a 25% density immersed into an atmospheric boundary layer with a Reynolds number of δ ^+=32{,}300. The boundary layer thickness to cube height ratio (δ /h=22.7) is large enough to be representative of atmospheric surface layer in neutral conditions. The LDA measurements give access to pointwise time-resolved data at several positions inside the canopy (z=h/4, h/2, and h). Synchronized hot-wire measurements above the canopy (inertial region and roughness sublayer) are also realized to get access to interactions between the different flow regions. The wall-normal mean velocity profile and Reynolds stresses show a good agreement with available data in the literature, although some differences are observed on the standard deviation of the spanwise component. A detailed spectral and integral time scale analysis inside the canopy is then carried out. No clear footprint of a periodic vortex shedding on the sides of the cubes could be identified on the power spectra, owing to the multiple cube-to-cube interactions occuring within a canopy with a building density in the wake interference regime. Results also suggest that interactions between the most energetics scales of the boundary layer and those related to the cube canopy take place, leading to a broadening of the energy peak in the spectra within the canopy. This is confirmed by the analysis of coherence results between the flow inside and above the canopy. It is shown that linear interactions mechanisms are significant, but reduced compared to smooth-wall boundary-layer flow. To our knowledge, this is the first time such results are shown on the dynamics of the flow inside an urban canopy.

  6. Experience with single-layer rectal anastomosis.

    OpenAIRE

    Khubchandani, M; Upson, J

    1981-01-01

    Anastomotic dehiscence following resection of the large intestine is a serious complication. Satisfactory results of single-layer anastomosis depend upon meticulous technique and a scrupulously clean colon. Out of 65 single-layer anastomoses involving the rectum, significant leakage occurred in 4 patients. The results are reported in order to draw attention to the safety and efficacy of one-layer anastomosis.

  7. A prediction model for wind speed ratios at pedestrian level with simplified urban canopies

    Science.gov (United States)

    Ikegaya, N.; Ikeda, Y.; Hagishima, A.; Razak, A. A.; Tanimoto, J.

    2017-02-01

    The purpose of this study is to review and improve prediction models for wind speed ratios at pedestrian level with simplified urban canopies. We adopted an extensive database of velocity fields under various conditions for arrays consisting of cubes, slender or flattened rectangles, and rectangles with varying roughness heights. Conclusions are summarized as follows: first, a new geometric parameter is introduced as a function of the plan area index and the aspect ratio so as to express the increase in virtual density that causes wind speed reduction. Second, the estimated wind speed ratios in the range 0.05 coefficients between the wind speeds averaged over the entire region, and the front or side region values are larger than 0.8. In contrast, in areas where the influence of roughness elements is significant, such as behind a building, the wind speeds are weakly correlated.

  8. Modeling Transport of Turbulent Fluxes in a Heterogeneous Urban Canopy Using a Spatially Explicit Energy Balance

    Science.gov (United States)

    Moody, M.; Bailey, B.; Stoll, R., II

    2017-12-01

    Understanding how changes in the microclimate near individual plants affects the surface energy budget is integral to modeling land-atmosphere interactions and a wide range of near surface atmospheric boundary layer phenomena. In urban areas, the complex geometry of the urban canopy layer results in large spatial deviations of turbulent fluxes further complicating the development of models. Accurately accounting for this heterogeneity in order to model urban energy and water use requires a sub-plant level understanding of microclimate variables. We present analysis of new experimental field data taken in and around two Blue Spruce (Picea pungens) trees at the University of Utah in 2015. The test sites were chosen in order study the effects of heterogeneity in an urban environment. An array of sensors were placed in and around the conifers to quantify transport in the soil-plant-atmosphere continuum: radiative fluxes, temperature, sap fluxes, etc. A spatial array of LEMS (Local Energy Measurement Systems) were deployed to obtain pressure, surrounding air temperature and relative humidity. These quantities are used to calculate the radiative and turbulent fluxes. Relying on measurements alone is insufficient to capture the complexity of microclimate distribution as one reaches sub-plant scales. A spatially-explicit radiation and energy balance model previously developed for deciduous trees was extended to include conifers. The model discretizes the tree into isothermal sub-volumes on which energy balances are performed and utilizes incoming radiation as the primary forcing input. The radiative transfer component of the model yields good agreement between measured and modeled upward longwave and shortwave radiative fluxes. Ultimately, the model was validated through an examination of the full energy budget including radiative and turbulent fluxes through isolated Picea pungens in an urban environment.

  9. Effects of urban tree canopy loss on land surface temperature magnitude and timing

    Science.gov (United States)

    Elmes, Arthur; Rogan, John; Williams, Christopher; Ratick, Samuel; Nowak, David; Martin, Deborah

    2017-06-01

    Urban Tree Canopy (UTC) plays an important role in moderating the Surface Urban Heat Island (SUHI) effect, which poses threats to human health due to substantially increased temperatures relative to rural areas. UTC coverage is associated with reduced urban temperatures, and therefore benefits both human health and reducing energy use in cities. Measurement of this relationship relies on accurate, fine spatial resolution UTC mapping, and on time series analysis of Land Surface Temperatures (LST). The City of Worcester, Massachusetts underwent extensive UTC loss and gain during the relatively brief period from 2008 to 2015, providing a natural experiment to measure the UTC/LST relationship. This paper consists of two elements to this end. First, it presents methods to map UTC in urban and suburban locations at fine spatial resolution (∼0.5 m) using image segmentation of a fused Lidar/WorldView-2 dataset, in order to show UTC change over time. Second, the areas of UTC change are used to explore changes in LST magnitude and seasonal variability using a time series of all available Landsat data for the study area over the eight-year period from 2007 to 2015. Fractional UTC change per unit area was determined using fine resolution UTC maps for 2008, 2010, and 2015, covering the period of large-scale tree loss and subsequent planting. LST changes were measured across a series of net UTC change bins, providing a relationship between UTC net change and LST trend. LST was analyzed for both monotonic trends over time and changes to seasonal magnitude and timing, using Theil-Sen slopes and Seasonal Trend Analysis (STA), respectively. The largest magnitudes of UTC loss occurred in residential neighborhoods, causing increased exposure of impervious (road) and pervious (grass) surfaces. Net UTC loss showed higher monotonic increases in LST than persistence and gain areas. STA indicated that net UTC loss was associated greater difference between 2008 and 2015 seasonal

  10. Mapping Changes in Urban Canopy Cover Following an Ice Storm Event: A Case Study of the December 2013 Ice Storm in Toronto and Mississauga

    Science.gov (United States)

    Robb, Angela

    Urban forests provide ecosystem services and functions, but are vulnerable to stressful environments and disruptive weather. One type of extreme weather, ice storms, can result in damage to trees. In December 2013, an ice storm hit southern Ontario with significant social and ecological impacts experienced in the Greater Toronto Area; where many cities are initiating management plans to increase canopy coverage. The objective of this project is to explore the changes in urban canopy cover before and after the ice storm through object-based image analysis. The results of this analysis successfully show broad level canopy distributions, patterns of canopy growth and loss, and 3-5% of canopy loss can be attributed to the ice storm on residential land uses. A better understanding of the impacts of the 2013 ice storm addresses a gap in our knowledge of how urban forests respond to extreme weather.

  11. Urban landscape genetics: canopy cover predicts gene flow between white-footed mouse (Peromyscus leucopus) populations in New York City.

    Science.gov (United States)

    Munshi-South, Jason

    2012-03-01

    In this study, I examine the influence of urban canopy cover on gene flow between 15 white-footed mouse (Peromyscus leucopus) populations in New York City parklands. Parks in the urban core are often highly fragmented, leading to rapid genetic differentiation of relatively nonvagile species. However, a diverse array of 'green' spaces may provide dispersal corridors through 'grey' urban infrastructure. I identify urban landscape features that promote genetic connectivity in an urban environment and compare the success of two different landscape connectivity approaches at explaining gene flow. Gene flow was associated with 'effective distances' between populations that were calculated based on per cent tree canopy cover using two different approaches: (i) isolation by effective distance (IED) that calculates the single best pathway to minimize passage through high-resistance (i.e. low canopy cover) areas, and (ii) isolation by resistance (IBR), an implementation of circuit theory that identifies all low-resistance paths through the landscape. IBR, but not IED, models were significantly associated with three measures of gene flow (Nm from F(ST) , BayesAss+ and Migrate-n) after factoring out the influence of isolation by distance using partial Mantel tests. Predicted corridors for gene flow between city parks were largely narrow, linear parklands or vegetated spaces that are not managed for wildlife, such as cemeteries and roadway medians. These results have implications for understanding the impacts of urbanization trends on native wildlife, as well as for urban reforestation efforts that aim to improve urban ecosystem processes. © 2012 Blackwell Publishing Ltd.

  12. Short-term gas dispersion in idealised urban canopy in street parallel with flow direction

    Directory of Open Access Journals (Sweden)

    Chaloupecká Hana

    2016-01-01

    Full Text Available Chemical attacks (e.g. Syria 2014-15 chlorine, 2013 sarine or Iraq 2006-7 chlorine as well as chemical plant disasters (e.g. Spain 2015 nitric oxide, ferric chloride; Texas 2014 methyl mercaptan threaten mankind. In these crisis situations, gas clouds are released. Dispersion of gas clouds is the issue of interest investigated in this paper. The paper describes wind tunnel experiments of dispersion from ground level point gas source. The source is situated in a model of an idealised urban canopy. The short duration releases of passive contaminant ethane are created by an electromagnetic valve. The gas cloud concentrations are measured in individual places at the height of the human breathing zone within a street parallel with flow direction by Fast-response Ionisation Detector. The simulations of the gas release for each measurement position are repeated many times under the same experimental set up to obtain representative datasets. These datasets are analysed to compute puff characteristics (arrival, leaving time and duration. The results indicate that the mean value of the dimensionless arrival time can be described as a growing linear function of the dimensionless coordinate in the street parallel with flow direction where the gas source is situated. The same might be stated about the dimensionless leaving time as well as the dimensionless duration, however these fits are worse. Utilising a linear function, we might also estimate some other statistical characteristics from datasets than the datasets means (medians, trimeans. The datasets of the dimensionless arrival time, the dimensionless leaving time and the dimensionless duration can be fitted by the generalized extreme value distribution (GEV in all sampling positions except one.

  13. The long-term changes in summer-time photochemistry due to urban canopy induced meteorological forcing

    Science.gov (United States)

    Huszar, Peter; Karlicky, Jan; Bardachova, Tatsiana; Belda, Michal; Halenka, Tomas

    2017-04-01

    Urban surfaces are clearly distinguished from rural ones and represent a specific forcing on meteorological conditions resulting in higher temperatures (urban heat island - UHI), reduced wind speed, enhanced turbulence, reduced humidity etc. It is straightforward to expect that these effects have further impact on the chemistry over these surfaces. This study intends to evaluate the summertime changes in ozone photo-chemistry due to urban canopy meteorological effects using the regional climate model RegCM4 coupled to the CAMx chemistry transport model. Experiments cover the 2001-2010 period focusing on central Europe. In all experiments, emission are kept the same and only the individual elements of meteorological forcing are varied. The most important ones are considered: changes of temperature, horizontal wind and turbulence. The surface ozone response to the inclusion of urban induced temperature increase is, over urban centers, is rather negative. Decreased wind speeds further contribute to ozone reduction due to suppressed transport of NOx to the surrounding rural areas, which in turn, increases the titration. The enhanced vertical mixing however have a leading impact on ozone levels: stronger vertical eddy transport removes NOx from urban environment and thus supports ozone formation. The combined effect of the individual ones is an increase of ozone. As each of the urban induced meteorological effects (changes of temperature, wind, turbulence) have a clear daily cycle, we examined the daily cycle of the impact on ozone and its precursors as well, and, it is shown that different mechanism become important throughout the day.

  14. Tunneling spin injection into single layer graphene.

    Science.gov (United States)

    Han, Wei; Pi, K; McCreary, K M; Li, Yan; Wong, Jared J I; Swartz, A G; Kawakami, R K

    2010-10-15

    We achieve tunneling spin injection from Co into single layer graphene (SLG) using TiO₂ seeded MgO barriers. A nonlocal magnetoresistance (ΔR(NL)) of 130  Ω is observed at room temperature, which is the largest value observed in any material. Investigating ΔR(NL) vs SLG conductivity from the transparent to the tunneling contact regimes demonstrates the contrasting behaviors predicted by the drift-diffusion theory of spin transport. Furthermore, tunnel barriers reduce the contact-induced spin relaxation and are therefore important for future investigations of spin relaxation in graphene.

  15. Simulations of Moscow megacity heat island with the COSMO-CLM model using two different urban canopy schemes and realistic building parameters, derived from OpenStreetMap data

    Science.gov (United States)

    Varentsov, Mikhail; Wouters, Hendrik; Trusilova, Kristina; Samsonov, Timofey; Konstantinov, Pavel

    2017-04-01

    In this study we present the application of the regional climate model COSMO-CLM to simulate urban heat island (UHI) phenomenon for Moscow megacity, which is the biggest agglomeration in Europe (with modern population of more than 17 million people). Significant differences of Moscow from the cities of Western Europe are related with much more continental climate with higher diurnal and annual temperature variations, and with specific building features such as its high density and almost total predominance of high-rise and low-rise blocks of flats on the private low-rise houses. Because of these building and climate features, the UHI of Moscow megacity is stronger than UHIs of many other cities of the similar size, with a mean intensity is about 2 °C and maximum intensity reaching up to 13 °C (Lokoschenko, 2014). Such a pronounced UHI together with the existence of an extensive observation network (more than 50 weather and air quality monitoring stations and few microwave temperature profilers) within the city and its surrounding make Moscow an especially interesting place for urban climate researches and good testbed for urban canopy models. In our numerical experiments, regional climate model firstly was adapted for investigated region with aim to improve quality of its simulations of rural areas. Then, to take into account urban canopy effects on thermal regime of the urbanized areas, we used two different versions of COSMO-CLM model. First is coupled with TEB (Town Energy Balance) single layer urban canopy model (Trusilova, 2013), and second is extended with bulk urban canopy scheme TERRA_URB using the Semi-empircal URban-canopY dependency parametriation SURY (Wouters et. al, 2016). Numerical experiments with these two versions of the model were run with spatial resolution about 1 km for several summer and winter months. To provide specific parameters, required for urban parameterizations, such as urban fraction, building height and street canyon aspect ratio

  16. Conviviality under the cosmopolitan canopy? Social mixing and friendships in an urban secondary school

    OpenAIRE

    Hollingworth, S; Mansaray, A

    2012-01-01

    This article is available open access through the publisher’s website at the link below. Copyright © Sociological Research Online 2012. Social mix and social mixing are topics of increasing significance to both the policy and academic communities in the UK, and have particular salience in urban multi-ethnic and socially diverse contexts. Enshrined in the comprehensive school ideal, and implicated in the now legal duty to promote 'community cohesion,' (urban) schools play a pivotal role in ...

  17. A Versatile, Production-Oriented Approach to High-Resolution Tree-Canopy Mapping in Urban and Suburban Landscapes Using GEOBIA and Data Fusion

    Directory of Open Access Journals (Sweden)

    Jarlath O'Neil-Dunne

    2014-12-01

    Full Text Available The benefits of tree canopy in urban and suburban landscapes are increasingly well known: stormwater runoff control, air-pollution mitigation, temperature regulation, carbon storage, wildlife habitat, neighborhood cohesion, and other social indicators of quality of life. However, many urban areas lack high-resolution tree canopy maps that document baseline conditions or inform tree-planting programs, limiting effective study and management. This paper describes a GEOBIA approach to tree-canopy mapping that relies on existing public investments in LiDAR, multispectral imagery, and thematic GIS layers, thus eliminating or reducing data acquisition costs. This versatile approach accommodates datasets of varying content and quality, first using LiDAR derivatives to identify aboveground features and then a combination of LiDAR and imagery to differentiate trees from buildings and other anthropogenic structures. Initial tree canopy objects are then refined through contextual analysis, morphological smoothing, and small-gap filling. Case studies from locations in the United States and Canada show how a GEOBIA approach incorporating data fusion and enterprise processing can be used for producing high-accuracy, high-resolution maps for large geographic extents. These maps are designed specifically for practical application by planning and regulatory end users who expect not only high accuracy but also high realism and visual coherence.

  18. A new Building Energy Model coupled with an Urban Canopy Parameterization for urban climate simulations—part II. Validation with one dimension off-line simulations

    Science.gov (United States)

    Salamanca, Francisco; Martilli, Alberto

    2010-01-01

    Recent studies show that the fluxes exchanged between buildings and the atmosphere play an important role in the urban climate. These fluxes are taken into account in mesoscale models considering new and more complex Urban Canopy Parameterizations (UCP). A standard methodology to test an UCP is to use one-dimensional (1D) off-line simulations. In this contribution, an UCP with and without a Building Energy Model (BEM) is run 1D off-line and the results are compared against the experimental data obtained in the BUBBLE measuring campaign over Basel (Switzerland) in 2002. The advantage of BEM is that it computes the evolution of the indoor building temperature as a function of energy production and consumption in the building, the radiation coming through the windows, and the fluxes of heat exchanged through the walls and roofs as well as the impact of the air conditioning system. This evaluation exercise is particularly significant since, for the period simulated, indoor temperatures were recorded. Different statistical parameters have been calculated over the entire simulated episode in order to compare the two versions of the UCP against measurements. In conclusion, with this work, we want to study the effect of BEM on the different turbulent fluxes and exploit the new possibilities that the UCP-BEM offers us, like the impact of the air conditioning systems and the evaluation of their energy consumption.

  19. LENA Conversion Foils Using Single-Layer Graphene, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Our key innovation will be the use of single-layer graphene as LENA conversion foils, with appropriate microgrids and nanogrids to support the foils. Phase I...

  20. Functionalization of Single Layer MoS$_2$ Honeycomb Structures

    OpenAIRE

    Ataca, C.; Ciraci, S.

    2010-01-01

    Based on the first-principles plane wave calculations, we studied the functionalization of the two-dimensional single layer MoS$_2$ structure via adatom adsorption and vacancy defect creation. Minimum energy adsorption sites are determined for sixteen different adatoms, each gives rise to diverse properties. Bare, single layer MoS$_2$, which is normally a nonmagnetic, direct band gap semiconductor, attains a net magnetic moment upon adsorption of specific transition metal atoms, as well as si...

  1. Land use and urban morphology parameters for Vienna required for initialisation of the urban canopy model TEB derived via the concept of "local climate zones"

    Science.gov (United States)

    Trimmel, Heidelinde; Weihs, Philipp; Oswald, Sandro M.; Masson, Valéry; Schoetter, Robert

    2017-04-01

    al. (2015) which is based on machine learning algorithms depending on satellite imagery and expert knowledge. The data on urban land use and morphology are used for initialisation of the town energy balance scheme TEB, but are also useful for other urban canopy models or studies related to urban planning or modelling of the urban system. The sensitivity of canyon air and surface temperatures, air specific humidity and horizontal wind simulated by the town energy balance scheme TEB (Masson, 2000) regarding the dominant parameters within the range determined for the present urban structure of Vienna and the expected changes (MA 18 (2011, 2014a+b), PGO (2011), Amtmann M and Altmann-Mavaddat N (2014)) was calculated for different land cover zones. While the buildings heights have a standard deviation of 3.2m which is 15% of the maximum average building height of one block the built and unsealed surface fraction vary stronger with around 30% standard deviation. The pre 1919 structure of Vienna is rather uniform and easier to describe, the later building structure is more diverse regarding morphological as well as physical building parameters. Therefore largest uncertainties are possible at the urban rims where also the highest development is expected. The analysis will be focused on these areas. Amtmann M and Altmann-Mavaddat N (2014) Eine Typology österreichischer Wohngebäude, Österreichische Energieargentur - Austrian Energy Agency, TABULA/EPISCOPE Bechtel B, Alexander P, Böhner J, et al (2015) Mapping Local Climate Zones for a Worldwide Database of the Form and Function of Cities. ISPRS Int J Geo-Inf 4:199-219. doi: 10.3390/ijgi4010199 Berger T, Formayer H, Smutny R, Neururer C, Passawa R (2012) Auswirkungen des Klimawandelsauf den thermischen Komfort in Bürogebäuden, Berichte aus Energie- und Umweltforschung Cordeau E / Les îlots morphologiques urbains (IMU) / IAU îdF / 2016 Magistratsabteilung 18 - Stadtentwicklung und Stadtplanung, Wien - MA 18 (2011

  2. Footprint Evaluation for Flux and Concentration Measurements for an Urban-Like Canopy with Coupled Lagrangian Stochastic and Large-Eddy Simulation Models

    Science.gov (United States)

    Hellsten, Antti; Luukkonen, Sofia-M.; Steinfeld, Gerald; Kanani-Sühring, Farah; Markkanen, Tiina; Järvi, Leena; Lento, Juha; Vesala, Timo; Raasch, Siegfried

    2015-11-01

    A footprint algorithm, based on a Lagrangian stochastic (LS) model embedded into a parallelized large-eddy simulation (LES) model, is used for the evaluation of flux and concentration footprints of passive scalars in flow in and above an urban-like canopy layer of a neutrally stratified 440 m deep boundary layer. The urban-like canopy layer is realized by an aligned array of cuboids whose height H is 40 m. The canopy flow involves strong small-scale inhomogeneities although it is homogeneous at the large scale. The source height is 1 m (0.025 H) above the ground in the street canyons, roughly mimicking traffic emissions. Footprints are evaluated for four heights from 0.25 H to 2.5 H, and for up to eight different horizontal sensor positions per measurement height, comprising sensor positions inside as well as outside of the street canyon that extend perpendicular to the mean wind direction. The LES-LS footprints are compared with footprints estimated by a conventional model (Kormann and Meixner, in Boundary-Layer Meteorol 99:207-224, 2001). It becomes evident that the local heterogeneity of the flow has a considerable impact on flux and concentration footprints. As expected, footprints for measurements within and right above the canopy layer show complex and completely different footprint shapes compared to the ellipsoidal shape obtained from conventional footprint models that assume horizontal homogeneity of the turbulent flow as well as the sources of passive scalars. Our results show the importance of street-canyon flow and turbulence for the vertical mixing of scalar concentration.

  3. Sensitivity of mesoscale model urban boundary layer meteorology to the scale of urban representation

    Directory of Open Access Journals (Sweden)

    D. D. Flagg

    2011-03-01

    Full Text Available Mesoscale modeling of the urban boundary layer requires careful parameterization of the surface due to its heterogeneous morphology. Model estimated meteorological quantities, including the surface energy budget and canopy layer variables, will respond accordingly to the scale of representation. This study examines the sensitivity of the surface energy balance, canopy layer and boundary layer meteorology to the scale of urban surface representation in a real urban area (Detroit-Windsor (USA-Canada during several dry, cloud-free summer periods. The model used is the Weather Research and Forecasting (WRF model with its coupled single-layer urban canopy model. Some model verification is presented using measurements from the Border Air Quality and Meteorology Study (BAQS-Met 2007 field campaign and additional sources. Case studies span from "neighborhood" (10 s ~308 m to very coarse (120 s ~3.7 km resolution. Small changes in scale can affect the classification of the surface, affecting both the local and grid-average meteorology. Results indicate high sensitivity in turbulent latent heat flux from the natural surface and sensible heat flux from the urban canopy. Small scale change is also shown to delay timing of a lake-breeze front passage and can affect the timing of local transition in static stability.

  4. Single-layer graphene on silicon nitride micromembrane resonators

    DEFF Research Database (Denmark)

    Schmid, Silvan; Bagci, Tolga; Zeuthen, Emil

    2014-01-01

    for exciting new devices, such as optoelectromechanical transducers. Here, we add a single-layer graphene on SiN micromembranes and compare electromechanical coupling and mechanical properties to bare dielectric membranes and to membranes metallized with an aluminium layer. The electrostatic coupling...

  5. Kernel Function Tuning for Single-Layer Neural Networks

    Czech Academy of Sciences Publication Activity Database

    Vidnerová, Petra; Neruda, Roman

    -, accepted 28.11. 2017 (2018) ISSN 2278-0149 R&D Projects: GA ČR GA15-18108S Institutional support: RVO:67985807 Keywords : single-layer neural networks * kernel methods * kernel function * optimisation Subject RIV: IN - Informatics, Computer Science http://www.ijmerr.com/

  6. Breakwater stability with damaged single layer armour units

    NARCIS (Netherlands)

    De Rover, R.; Verhagen, H.J.; Van den Berge, A.; Reedijk, B.

    2008-01-01

    The effect of single layer interlocking armour unit breakage on the hydraulic armour layer stability and potential damage progression is addressed in this paper. A 2-dimensional scale model of a rubble mound breakwater with an armour layer consisting of Xbloc armour units was tested. The residual

  7. Automatic settlement analysis of single-layer armour layers

    NARCIS (Netherlands)

    Hofland, B.; van gent, Marcel

    2016-01-01

    A method to quantify, analyse, and present the settlement of single-layer concrete armour layers of coastal structures is presented. The use of the image processing technique for settlement analysis is discussed based on various modelling
    studies performed over the years. The accuracy of the

  8. Assessment of Planetary-Boundary-Layer Schemes in the Weather Research and Forecasting Model Within and Above an Urban Canopy Layer

    Science.gov (United States)

    Ferrero, Enrico; Alessandrini, Stefano; Vandenberghe, Francois

    2018-03-01

    We tested several planetary-boundary-layer (PBL) schemes available in the Weather Research and Forecasting (WRF) model against measured wind speed and direction, temperature and turbulent kinetic energy (TKE) at three levels (5, 9, 25 m). The Urban Turbulence Project dataset, gathered from the outskirts of Turin, Italy and used for the comparison, provides measurements made by sonic anemometers for more than 1 year. In contrast to other similar studies, which have mainly focused on short-time periods, we considered 2 months of measurements (January and July) representing both the seasonal and the daily variabilities. To understand how the WRF-model PBL schemes perform in an urban environment, often characterized by low wind-speed conditions, we first compared six PBL schemes against observations taken by the highest anemometer located in the inertial sub-layer. The availability of the TKE measurements allows us to directly evaluate the performances of the model; results of the model evaluation are presented in terms of quantile versus quantile plots and statistical indices. Secondly, we considered WRF-model PBL schemes that can be coupled to the urban-surface exchange parametrizations and compared the simulation results with measurements from the two lower anemometers located inside the canopy layer. We find that the PBL schemes accounting for TKE are more accurate and the model representation of the roughness sub-layer improves when the urban model is coupled to each PBL scheme.

  9. Thermoelectric properties of single-layered SnSe sheet

    Science.gov (United States)

    Wang, Fancy Qian; Zhang, Shunhong; Yu, Jiabing; Wang, Qian

    2015-09-01

    Motivated by the recent study of inspiring thermoelectric properties in bulk SnSe [Zhao et al., Nature, 2014, 508, 373] and the experimental synthesis of SnSe sheets [Chen et al., J. Am. Chem. Soc., 2013, 135, 1213], we have carried out systematic calculations for a single-layered SnSe sheet focusing on its stability, electronic structure and thermoelectric properties by using density functional theory combined with Boltzmann transport theory. We have found that the sheet is dynamically and thermally stable with a band gap of 1.28 eV, and the figure of merit (ZT) reaches 3.27 (2.76) along the armchair (zigzag) direction with optimal n-type carrier concentration, which is enhanced nearly 7 times compared to its bulk counterpart at 700 K due to quantum confinement effect. Furthermore, we designed four types of thermoelectric couples by assembling single-layered SnSe sheets with different transport directions and doping types, and found that their efficiencies are all above 13%, which are higher than those of thermoelectric couples made of commercial bulk Bi2Te3 (7%-8%), suggesting the great potential of single-layered SnSe sheets for heat-electricity conversion.Motivated by the recent study of inspiring thermoelectric properties in bulk SnSe [Zhao et al., Nature, 2014, 508, 373] and the experimental synthesis of SnSe sheets [Chen et al., J. Am. Chem. Soc., 2013, 135, 1213], we have carried out systematic calculations for a single-layered SnSe sheet focusing on its stability, electronic structure and thermoelectric properties by using density functional theory combined with Boltzmann transport theory. We have found that the sheet is dynamically and thermally stable with a band gap of 1.28 eV, and the figure of merit (ZT) reaches 3.27 (2.76) along the armchair (zigzag) direction with optimal n-type carrier concentration, which is enhanced nearly 7 times compared to its bulk counterpart at 700 K due to quantum confinement effect. Furthermore, we designed four types of

  10. Building capacity for providing canopy cover and canopy height at FIA plot locations using high-resolution imagery and leaf-off LiDAR

    Science.gov (United States)

    Rachel Riemann; Jarlath O' Neil-Dunne; Greg C. Liknes

    2012-01-01

    Tree canopy cover and canopy height information are essential for estimating volume, biomass, and carbon; defining forest cover; and characterizing wildlife habitat. The amount of tree canopy cover also influences water quality and quantity in both rural and urban settings. Tree canopy cover and canopy height are currently collected at FIA plots either in the field or...

  11. Raman spectroscopy of boron-doped single-layer graphene.

    Science.gov (United States)

    Kim, Yoong Ahm; Fujisawa, Kazunori; Muramatsu, Hiroyuki; Hayashi, Takuya; Endo, Morinobu; Fujimori, Toshihiko; Kaneko, Katsumi; Terrones, Mauricio; Behrends, Jan; Eckmann, Axel; Casiraghi, Cinzia; Novoselov, Kostya S; Saito, Riichiro; Dresselhaus, Mildred S

    2012-07-24

    The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.

  12. Bandgap tunability at single-layer molybdenum disulphide grain boundaries

    KAUST Repository

    Huang, Yu Li

    2015-02-17

    Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40±0.05 eV for single-layer, 2.10±0.05 eV for bilayer and 1.75±0.05 eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85±0.05 eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.

  13. Persistence of long-distance, insect-mediated pollen movement for a tropical canopy tree species in remnant forest patches in an urban landscape.

    Science.gov (United States)

    Noreen, A M E; Niissalo, M A; Lum, S K Y; Webb, E L

    2016-12-01

    As deforestation and urbanization continue at rapid rates in tropical regions, urban forest patches are essential repositories of biodiversity. However, almost nothing is known about gene flow of forest-dependent tree species in urban landscapes. In this study, we investigated gene flow in the insect-pollinated, wind-dispersed tropical tree Koompassia malaccensis in and among three remnant forest patches in the urbanized landscape of Singapore. We genotyped the vast majority of adults (N=179) and a large number of recruits (N=2103) with 8 highly polymorphic microsatellite markers. Spatial genetic structure of the recruit and adult cohorts was significant, showing routine gene dispersal distances of ~100-400 m. Parentage analysis showed that 97% of recruits were within 100 m of their mother tree, and a high frequency of relatively short-distance pollen dispersal (median ~143-187 m). Despite routine seed and pollen dispersal distances of within a few hundred meters, interpatch gene flow occurred between all patches and was dominated by pollen movement: parentage analysis showed 76 pollen versus 2 seed interpatch dispersal events, and the seedling neighborhood model estimated ~1-6% seed immigration and ~21-46% pollen immigration rates, depending on patch. In addition, the smallest patch (containing five adult K. malaccensis trees) was entirely surrounded by >2.5 km of 'impervious' substrate, yet had the highest proportional pollen and seed immigration estimates of any patch. Hence, contrary to our hypothesis, insect-mediated gene flow persisted across an urban landscape, and several of our results also parallel key findings from insect-pollinated canopy trees sampled in mixed agricultural-forest landscapes.

  14. Impacts of Detailed Land-Use Types and Urban Heat in an Urban Canopy Model on Local Meteorology and Ozone Levels for Air Quality Modeling in a Coastal City, Korea

    Directory of Open Access Journals (Sweden)

    Yoon-Hee Kang

    2016-01-01

    Full Text Available An urban canopy model (UCM, with detailed urban land-use and anthropogenic heat information, is required to reproduce and understand the urbanization process and its impact on regional climate and urban air quality. This study investigates the UCM impact on simulated meteorology and surface ozone in the coastal city of Busan using the WRF-SMOKE-CMAQ model coupled with (UCM case, and without the UCM (NOUCM case. The UCM and NOUCM case results suggest that UCM case generally produces warmer temperatures and deeper planetary boundary layer (PBL heights, especially in the early morning and night time, than the NOUCM case. Owing to urban heating and enhanced turbulent mixing incorporation in the center of the city, the sea breeze in the UCM case tends to penetrate faster and more strongly than in the NOUCM case. After sea breeze arrival at the urban center, the urban heat island effect prevents its penetration further inland. In the UCM case in the late afternoon, local meteorological changes induce remarkable increases in simulated O3 concentrations over the downwind (up to 17.1 ppb and downtown (up to 10.6 ppb areas. This is probably due to an increase in temperature in the urban areas and the wind convergence zone movement due to the sea breeze interaction and offshore flows. The increase in O3 concentration in the late afternoon results in the model bias reduction under previously underestimated O3 conditions due to high NOx emissions. The simulated O3 concentrations in the UCM case are more similar to the observed O3 concentrations compared to those of the NOUCM case.

  15. Increased Spatial Variability and Intensification of Extreme Monsoon Rainfall due to Urbanization.

    Science.gov (United States)

    Paul, Supantha; Ghosh, Subimal; Mathew, Micky; Devanand, Anjana; Karmakar, Subhankar; Niyogi, Dev

    2018-03-02

    While satellite data provides a strong robust signature of urban feedback on extreme precipitation; urbanization signal is often not so prominent with station level data. To investigate this, we select the case study of Mumbai, India and perform a high resolution (1 km) numerical study with Weather Research and Forecasting (WRF) model for eight extreme rainfall days during 2014-2015. The WRF model is coupled with two different urban schemes, the Single Layer Urban Canopy Model (WRF-SUCM), Multi-Layer Urban Canopy Model (WRF-MUCM). The differences between the WRF-MUCM and WRF-SUCM indicate the importance of the structure and characteristics of urban canopy on modifications in precipitation. The WRF-MUCM simulations resemble the observed distributed rainfall. WRF-MUCM also produces intensified rainfall as compared to the WRF-SUCM and WRF-NoUCM (without UCM). The intensification in rainfall is however prominent at few pockets of urban regions, that is seen in increased spatial variability. We find that the correlation of precipitation across stations within the city falls below statistical significance at a distance greater than 10 km. Urban signature on extreme precipitation will be reflected on station rainfall only when the stations are located inside the urban pockets having intensified precipitation, which needs to be considered in future analysis.

  16. Determinations of Urban Political Ecology: The Distribution Pattern Canopy Cover of Tree and Spatial inequality in Tehran

    OpenAIRE

    T. Karami; M. Soleimani; H. Afrakhteh; H. Hataminejad

    2012-01-01

    Extended abstract1-IntroductionInequality of green space distribution is a type of social production which by creating uneven ecological conditions in a feedback cycle plays its role on the quality of environment and intensification of imbalances inside the urban living environment. Most of the studies conducted so far have focused on the development or distribution of public green space but the truth is that public green spaces have not been the only source of urban metabolism (from the view...

  17. Single-layer MoS2 transistors.

    Science.gov (United States)

    Radisavljevic, B; Radenovic, A; Brivio, J; Giacometti, V; Kis, A

    2011-03-01

    Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.

  18. Validation of Simplified Urban-Canopy Aerodynamic Parametrizations Using a Numerical Simulation of an Actual Downtown Area

    Science.gov (United States)

    Ramirez, N.; Afshari, Afshin; Norford, L.

    2018-02-01

    A steady-state Reynolds-averaged Navier-Stoke computational fluid dynamics (CFD) investigation of boundary-layer flow over a major portion of downtown Abu Dhabi is conducted. The results are used to derive the shear stress and characterize the logarithmic region for eight sub-domains, where the sub-domains overlap and are overlaid in the streamwise direction. They are characterized by a high frontal area index initially, which decreases significantly beyond the fifth sub-domain. The plan area index is relatively stable throughout the domain. For each sub-domain, the estimated local roughness length and displacement height derived from CFD results are compared to prevalent empirical formulations. We further validate and tune a mixing-length model proposed by Coceal and Belcher (Q J R Meteorol Soc 130:1349-1372, 2004). Finally, the in-canopy wind-speed attenuation is analysed as a function of fetch. It is shown that, while there is some room for improvement in Macdonald's empirical formulations (Boundary-Layer Meteorol 97:25-45, 2000), Coceal and Belcher's mixing model in combination with the resolution method of Di Sabatino et al. (Boundary-Layer Meteorol 127:131-151, 2008) can provide a robust estimation of the average wind speed in the logarithmic region. Within the roughness sublayer, a properly parametrized Cionco exponential model is shown to be quite accurate.

  19. Single-layer graphene on silicon nitride micromembrane resonators

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, Silvan; Guillermo Villanueva, Luis; Amato, Bartolo; Boisen, Anja [Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, 2800 Kongens Lyngby (Denmark); Bagci, Tolga; Zeuthen, Emil; Sørensen, Anders S.; Usami, Koji; Polzik, Eugene S. [QUANTOP, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen (Denmark); Taylor, Jacob M. [Joint Quantum Institute/NIST, College Park, Maryland 20899 (United States); Herring, Patrick K.; Cassidy, Maja C. [School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138 (United States); Marcus, Charles M. [Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen (Denmark); Cheol Shin, Yong; Kong, Jing [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2014-02-07

    Due to their low mass, high quality factor, and good optical properties, silicon nitride (SiN) micromembrane resonators are widely used in force and mass sensing applications, particularly in optomechanics. The metallization of such membranes would enable an electronic integration with the prospect for exciting new devices, such as optoelectromechanical transducers. Here, we add a single-layer graphene on SiN micromembranes and compare electromechanical coupling and mechanical properties to bare dielectric membranes and to membranes metallized with an aluminium layer. The electrostatic coupling of graphene covered membranes is found to be equal to a perfectly conductive membrane, without significantly adding mass, decreasing the superior mechanical quality factor or affecting the optical properties of pure SiN micromembranes. The concept of graphene-SiN resonators allows a broad range of new experiments both in applied physics and fundamental basic research, e.g., for the mechanical, electrical, or optical characterization of graphene.

  20. Single-layer and integrated YBCO gradiometer coupled SQUIDs

    Energy Technology Data Exchange (ETDEWEB)

    Baer, L.R.; Daalmans, G.M.; Barthel, K.H.; Ferchland, L.; Selent, M.; Kuehnl, M.; Uhl, D. [Siemens AG, Central Research and Development, Paul-Gossen-Strasse 100, D-91052 Erlangen (Germany)

    1996-04-01

    For many SQUID applications such as biomagnetism or non-destructive evaluation it is convenient or even necessary to work without the restrictions of a magnetically shielded room. This contribution deals with two sensors appropriate for this purpose. In the first concept we present a flip chip arrangement of a single-layer flux transformer and a single-layer SQUID, taking advantage of a simple technology. The SQUID was prepared on a 15x15 mm{sup 2} SrTiO{sub 3} 24 deg. bicrystal and located in the common line of two-parallel-loop arrangements. The flipped antenna was designed as a two-parallel-loop gradiometer with 26 mm baseline on a 10x40 mm{sup 2} LaAlO{sub 3} single-crystal substrate. A field gradient sensitivity of 1 nT cm{sup -1}{phi}{sub 0} was obtained. We could demonstrate a field gradient resolution of 20 fT cm{sup -1} Hz{sup 1/2} at 1 kHz in an unshielded environment. In the second concept we integrated both the flux antenna and the SQUID on a SrTiO{sub 3} bicrystal. The tighter coupling scheme results in smaller devices for similar field gradient sensitivities. The integrated SQUID is designed as a 3x8 mm{sup 2} device on a 10x10 mm{sup 2} bicrystal substrate. The remaining space is used for test structures and SQUIDs without antennae, in order to control the technology as well as the SQUID design. Parallel processed dummy substrates were used to monitor the quality of film growth by x-ray analysis. The quality of our SQUID design will be discussed on the basis of the measured field gradient sensitivity and noise. The reliability of the devices is demonstrated by an NDE type measurement. (author)

  1. Touch stimulated pulse generation in biomimetic single-layer graphene

    Science.gov (United States)

    Sul, Onejae; Chun, Hyunsuk; Choi, Eunseok; Choi, Jungbong; Cho, Kyeongwon; Jang, Dongpyo; Chun, Sungwoo; Park, Wanjun; Lee, Seung-Beck

    2016-02-01

    Detecting variation in contact pressure is a separate sensing mode in the human somatosensory system that differs from the detection of pressure magnitude. If pressure magnitude and variation sensing can be achieved simultaneously, an advanced biomimetic tactile system that better emulates human senses may be developed. We report on a novel single-layer graphene based artificial mechanoreceptor that generates a resistance pulse as the contact stimulus passes a specific threshold pressure, mimicking the generation of action potentials in a biological fast-adapting mechanoreceptor. The electric field from a flexible membrane gate electrode placed above a graphene channel raises the Fermi level from the valence band as pressure deflects the membrane. The threshold pressure is reached when the Fermi level crosses the Dirac point in the graphene energy band, which generates a sharp peak in the measured resistance. We found that by changing the gate potential it was possible to modulate the threshold pressure and using a series of graphene channels, a train of pulses were generated during a transient pressurizing stimulus demonstrating biomimetic behaviour.Detecting variation in contact pressure is a separate sensing mode in the human somatosensory system that differs from the detection of pressure magnitude. If pressure magnitude and variation sensing can be achieved simultaneously, an advanced biomimetic tactile system that better emulates human senses may be developed. We report on a novel single-layer graphene based artificial mechanoreceptor that generates a resistance pulse as the contact stimulus passes a specific threshold pressure, mimicking the generation of action potentials in a biological fast-adapting mechanoreceptor. The electric field from a flexible membrane gate electrode placed above a graphene channel raises the Fermi level from the valence band as pressure deflects the membrane. The threshold pressure is reached when the Fermi level crosses the Dirac

  2. Electrical and optical transport properties of single layer WSe2

    Science.gov (United States)

    Tahir, M.

    2018-03-01

    The electronic properties of single layer WSe2 are distinct from the famous graphene due to strong spin orbit coupling, a huge band gap and an anisotropic lifting of the degeneracy of the valley degree of freedom under Zeeman field. In this work, band structure of the monolayer WSe2 is evaluated in the presence of spin and valley Zeeman fields to study the electrical and optical transport properties. Using Kubo formalism, an explicit expression for the electrical Hall conductivity is examined at finite temperatures. The electrical longitudinal conductivity is also evaluated. Further, the longitudinal and Hall optical conductivities are analyzed. It is observed that the contributions of the spin-up and spin-down states to the power absorption spectrum depend on the valley index. The numerical results exhibit absorption peaks as a function of photon energy, ℏ ω, in the range ∼ 1.5 -2 eV. Also, the optical response lies in the visible frequency range in contrast to the conventional two-dimensional electron gas or graphene where the response is limited to terahertz regime. This ability to isolate carriers in spin-valley coupled structures may make WSe2 a promising candidate for future spintronics, valleytronics and optical devices.

  3. Plasmon enhanced terahertz emission from single layer graphene.

    Science.gov (United States)

    Bahk, Young-Mi; Ramakrishnan, Gopakumar; Choi, Jongho; Song, Hyelynn; Choi, Geunchang; Kim, Yong Hyup; Ahn, Kwang Jun; Kim, Dai-Sik; Planken, Paul C M

    2014-09-23

    We show that surface plasmons, excited with femtosecond laser pulses on continuous or discontinuous gold substrates, strongly enhance the generation and emission of ultrashort, broadband terahertz pulses from single layer graphene. Without surface plasmon excitation, for graphene on glass, 'nonresonant laser-pulse-induced photon drag currents' appear to be responsible for the relatively weak emission of both s- and p-polarized terahertz pulses. For graphene on a discontinuous layer of gold, only the emission of the p-polarized terahertz electric field is enhanced, whereas the s-polarized component remains largely unaffected, suggesting the presence of an additional terahertz generation mechanism. We argue that in the latter case, 'surface-plasmon-enhanced optical rectification', made possible by the lack of inversion symmetry at the graphene on gold surface, is responsible for the strongly enhanced emission. The enhancement occurs because the electric field of surface plasmons is localized and enhanced where the graphene is located: at the surface of the metal. We believe that our results point the way to small, thin, and more efficient terahertz photonic devices.

  4. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus.

    Science.gov (United States)

    Rudenko, A N; Brener, S; Katsnelson, M I

    2016-06-17

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n, two-phonon scattering in BP is less important and can be considered negligible at n≳10^{13}  cm^{-2}. At smaller n, however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μ_{xx}/μ_{yy}∼1.4 at n=10^{13} cm^{-2} and T=300  K), the electron mobility is found to be significantly more anisotropic (μ_{xx}/μ_{yy}∼6.2). Absolute values of μ_{xx} do not exceed 250 (700)  cm^{2} V^{-1} s^{-1} for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature.

  5. Synthesis of PbI(2) single-layered inorganic nanotubes encapsulated within carbon nanotubes.

    Science.gov (United States)

    Cabana, Laura; Ballesteros, Belén; Batista, Eudar; Magén, César; Arenal, Raúl; Oró-Solé, Judith; Rurali, Riccardo; Tobias, Gerard

    2014-04-02

    The template assisted growth of single-layered inorganic nanotubes is reported. Single-crystalline lead iodide single-layered nanotubes have been prepared using the inner cavities of carbon nanotubes as hosting templates. The diameter of the resulting inorganic nanotubes is merely dependent on the diameter of the host. This facile method is highly versatile opening up new horizons in the preparation of single-layered nanostructures. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Novel doping alternatives for single-layer transition metal dichalcogenides

    Science.gov (United States)

    Onofrio, Nicolas; Guzman, David; Strachan, Alejandro

    2017-11-01

    Successful doping of single-layer transition metal dichalcogenides (TMDs) remains a formidable barrier to their incorporation into a range of technologies. We use density functional theory to study doping of molybdenum and tungsten dichalcogenides with a large fraction of the periodic table. An automated analysis of the energetics, atomic and electronic structure of thousands of calculations results in insightful trends across the periodic table and points out promising dopants to be pursued experimentally. Beyond previously studied cases, our predictions suggest promising substitutional dopants that result in p-type transport and reveal interesting physics behind the substitution of the metal site. Doping with early transition metals (TMs) leads to tensile strain and a significant reduction in the bandgap. The bandgap increases and strain is reduced as the d-states are filled into the mid TMs; these trends reverse as we move into the late TMs. Additionally, the Fermi energy increases monotonously as the d-shell is filled from the early to mid TMs and we observe few to no gap states, indicating the possibility of both p- (early TMs) and n- (mid TMs) type doping. Quite surprisingly, the simulations indicate the possibility of interstitial doping of TMDs; the energetics reveal that a significant number of dopants, increasing in number from molybdenum disulfide to diselenide and to ditelluride, favor the interstitial sites over adsorbed ones. Furthermore, calculations of the activation energy associated with capturing the dopants into the interstitial site indicate that the process is kinetically possible. This suggests that interstitial impurities in TMDs are more common than thought to date and we propose a series of potential interstitial dopants for TMDs relevant for application in nanoelectronics based on a detailed analysis of the predicted electronic structures.

  7. Single-layer HDR video coding with SDR backward compatibility

    Science.gov (United States)

    Lasserre, S.; François, E.; Le Léannec, F.; Touzé, D.

    2016-09-01

    The migration from High Definition (HD) TV to Ultra High Definition (UHD) is already underway. In addition to an increase of picture spatial resolution, UHD will bring more color and higher contrast by introducing Wide Color Gamut (WCG) and High Dynamic Range (HDR) video. As both Standard Dynamic Range (SDR) and HDR devices will coexist in the ecosystem, the transition from Standard Dynamic Range (SDR) to HDR will require distribution solutions supporting some level of backward compatibility. This paper presents a new HDR content distribution scheme, named SL-HDR1, using a single layer codec design and providing SDR compatibility. The solution is based on a pre-encoding HDR-to-SDR conversion, generating a backward compatible SDR video, with side dynamic metadata. The resulting SDR video is then compressed, distributed and decoded using standard-compliant decoders (e.g. HEVC Main 10 compliant). The decoded SDR video can be directly rendered on SDR displays without adaptation. Dynamic metadata of limited size are generated by the pre-processing and used to reconstruct the HDR signal from the decoded SDR video, using a post-processing that is the functional inverse of the pre-processing. Both HDR quality and artistic intent are preserved. Pre- and post-processing are applied independently per picture, do not involve any inter-pixel dependency, and are codec agnostic. Compression performance, and SDR quality are shown to be solidly improved compared to the non-backward and backward-compatible approaches, respectively using the Perceptual Quantization (PQ) and Hybrid Log Gamma (HLG) Opto-Electronic Transfer Functions (OETF).

  8. Cooling and energy saving potentials of shade trees and urban lawns in a desert city

    International Nuclear Information System (INIS)

    Wang, Zhi-Hua; Zhao, Xiaoxi; Yang, Jiachuan; Song, Jiyun

    2016-01-01

    Highlights: • We developed a numerical framework incorporating trees in an urban canopy model. • Shade trees have more prominent energy saving potential than urban lawns. • The trade-off between water-energy is a key for urban landscape management. • Urban vegetation can significantly alleviate outdoor thermal stress. - Abstract: The use of urban vegetation in cities is a common landscape planning strategy to alleviate the heat island effect as well as to enhance building energy efficiency. The presence of trees in street canyons can effectively reduce environmental temperature via radiative shading. However, resolving shade trees in urban land surface models presents a major challenge in numerical models, especially in predicting the radiative heat exchange in canyons. In this paper, we develop a new numerical framework by incorporating shade trees into an advanced single-layer urban canopy model. This novel numerical framework is applied to Phoenix metropolitan area to investigate the cooling effect of different urban vegetation types and their potentials in saving building energy. It is found that the cooling effect by shading from trees is more significant than that by evapotranspiration from lawns, leading to a considerable saving of cooling load. In addition, analysis of human thermal comfort shows that urban vegetation plays a crucial role in creating a comfortable living environment, especially for cities located in arid or semi-arid region.

  9. High-resolution visibility and air quality forecasting using multi-layer urban canopy model for highly urbanized Hong Kong and the Pearl River Delta

    Science.gov (United States)

    Piu NG, Chak; HAO, Song; Fat LAM, Yun

    2015-04-01

    Visibility is a universally critical element which affects the public in many aspects, including economic activities, health of local citizens and safety of marine transportation and aviation. The Interagency Monitoring of Protected Visual Environments (IMPROVE) visibility equation, an empirical equation developed by USEPA, has been modified by various studies to fit into the application upon the Asian continent including Hong Kong and China. Often these studies focused on the improvement of the existing IMPROVE equation by modifying its particulate speciation using local observation data. In this study, we developed an Integrated Forecast System (IFS) to predict the next-day air quality and visibility using Weather Research and Forecasting model with Building Energy Parameterization and Building Energy Model (WRF-BEP+BEM) and Community Multi-scale Air Quality Model (CMAQ). Unlike the other studies, the core of this study is to include detailed urbanization impacts with calibrated "IMPROVE equation for PRD" into the modeling system for Hong Kong's environs. The ultra-high resolution land cover information (~1km x 1km) from Google images, was digitized into the Geographic Information System (GIS) for preparing the model-ready input for IFS. The NCEP FNL (Final) Operation Global Analysis (FNL) and the Global Forecasting System (GFS) datasets were tested for both hind-cast and forecast cases, in order to calibrate the input of urban parameters in the WRF-BEP+BEM model. The evaluation of model performance with sensitivity cases was performed on sea surface temperature (SST), surface temperature (T), wind speed/direction with the major pollutants (i.e., PM10, PM2.5, NOx, SO2 and O3) using local observation and will be presented/discussed in this paper. References: 1. Y. L. Lee, R. Sequeira, Visibility degradation across Hong Kong its components and their relative contribution. Atmospheric Environment 2001, 35, 5861-5872. doi:10.1016/S1352-2310(01)00395-8 2. R. Zhang, Q

  10. Experimental research on the stability of armour and secondary layer in a single layered Tetrapod breakwater

    NARCIS (Netherlands)

    De Jong, W.; Verhagen, H.J.; Olthof, J.

    2004-01-01

    Physical model tests were done on an armour of Tetrapods, placed in a single layer. The objective of the investigations was to study the stability of the secondary layer, and to see if the material of this secondary layer could be washed out through the single layer of Tetrapods. It was concluded

  11. A theoretical study of pump–probe experiment in single-layer ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 82; Issue 6. A theoretical study of pump–probe experiment in single-layer, bilayer and multilayer graphene ... Here we use it as a tool to study the phenomenon of anomalous Rabi oscillations in graphene that was predicted recently in single-layer graphene.

  12. Single-layer Ultralight, Flexible, Shielding Tension Shell System for Extreme Heat and Radiation

    Data.gov (United States)

    National Aeronautics and Space Administration — The objective of this project is to develop a flexible thermal protection system (FTPS) with a Boron Nitride Nanotube (BNNT)-based single-layer, lightweight,...

  13. Hydraulic Stability of Single-Layer Dolos and Accropode Armour Layers

    DEFF Research Database (Denmark)

    Christensen, M.; Burcharth, H. F.

    1995-01-01

    A new design for Dolos breakwater armour layers is presented: Dolos armour units are placed in a selected geometric pattern in a single layer. A series of model tests have been performed in order to determine the stability of such single-layer Dolos armour layers. The test results are presented...... and compared to the stability formula for the traditional double-layer, randomly placed Dolos armour layer design presented by Burcharth (1992). The results of a series of stability tests performed with Accropode® armour layers is presented and compared to the test results obtained with single-layer Dolos...... armour layers. Run-up and reflection are presented for both single-layer Dolos armour and Accropode armour....

  14. Evaluation of the WRF-Urban Modeling System Coupled to Noah and Noah-MP Land Surface Models Over a Semiarid Urban Environment

    Science.gov (United States)

    Salamanca, Francisco; Zhang, Yizhou; Barlage, Michael; Chen, Fei; Mahalov, Alex; Miao, Shiguang

    2018-03-01

    We have augmented the existing capabilities of the integrated Weather Research and Forecasting (WRF)-urban modeling system by coupling three urban canopy models (UCMs) available in the WRF model with the new community Noah with multiparameterization options (Noah-MP) land surface model (LSM). The WRF-urban modeling system's performance has been evaluated by conducting six numerical experiments at high spatial resolution (1 km horizontal grid spacing) during a 15 day clear-sky summertime period for a semiarid urban environment. To assess the relative importance of representing urban surfaces, three different urban parameterizations are used with the Noah and Noah-MP LSMs, respectively, over the two major cities of Arizona: Phoenix and Tucson metropolitan areas. Our results demonstrate that Noah-MP reproduces somewhat better than Noah the daily evolution of surface skin temperature and near-surface air temperature (especially nighttime temperature) and wind speed. Concerning the urban areas, bulk urban parameterization overestimates nighttime 2 m air temperature compared to the single-layer and multilayer UCMs that reproduce more accurately the daily evolution of near-surface air temperature. Regarding near-surface wind speed, only the multilayer UCM was able to reproduce realistically the daily evolution of wind speed, although maximum winds were slightly overestimated, while both the single-layer and bulk urban parameterizations overestimated wind speed considerably. Based on these results, this paper demonstrates that the new community Noah-MP LSM coupled to an UCM is a promising physics-based predictive modeling tool for urban applications.

  15. Inclusion of an ultraviolet radiation transfer component in an urban forest effects model for predicting tree influences on potential below-canopy exposure to UVB radiation

    Science.gov (United States)

    Gordon M. Heisler; Richard H. Grant; David J. Nowak; Wei Gao; Daniel E. Crane; Jeffery T. Walton

    2003-01-01

    Evaluating the impact of ultraviolet-B radiation (UVB) on urban populations would be enhanced by improved predictions of the UVB radiation at the level of human activity. This paper reports the status of plans for incorporating a UVB prediction module into an existing Urban Forest Effects (UFORE) model. UFORE currently has modules to quantify urban forest structure,...

  16. Plant canopy light absorption model with application to wheat

    Science.gov (United States)

    Chance, J. E.; Lemaster, E. W.

    1978-01-01

    A light absorption model (LAM) for vegetative plant canopies has been derived from the Suits reflectance model. From the LAM the absorption of light in the photosynthetically active region of the spectrum (400-700 nm) has been calculated for a Penjamo wheat crop for several situations including (a) the percent absorption of the incident radiation by a canopy of LAI 3.1 having a four-layer structure, (b) the percent absorption of light by the individual layers within a four-layer canopy and by the underlying soil, (c) the percent absorption of light by each vegetative canopy layer for variable sun angle, and (d) the cumulative solar energy absorbed by the developing wheat canopy as it progresses from a single layer through its growth stages to a three-layer canopy. This calculation is also presented as a function of the leaf area index and is shown to be in agreement with experimental data reported by Kanemasu on Plainsman V wheat.

  17. Diverse and tunable electronic structures of single-layer metal phosphorus trichalcogenides for photocatalytic water splitting

    International Nuclear Information System (INIS)

    Liu, Jian; Li, Xi-Bo; Wang, Da; Liu, Li-Min; Lau, Woon-Ming; Peng, Ping

    2014-01-01

    The family of bulk metal phosphorus trichalcogenides (APX 3 , A = M II , M 0.5 I M 0.5 III ; X = S, Se; M I , M II , and M III represent Group-I, Group-II, and Group-III metals, respectively) has attracted great attentions because such materials not only own magnetic and ferroelectric properties, but also exhibit excellent properties in hydrogen storage and lithium battery because of the layered structures. Many layered materials have been exfoliated into two-dimensional (2D) materials, and they show distinct electronic properties compared with their bulks. Here we present a systematical study of single-layer metal phosphorus trichalcogenides by density functional theory calculations. The results show that the single layer metal phosphorus trichalcogenides have very low formation energies, which indicates that the exfoliation of single layer APX 3 should not be difficult. The family of single layer metal phosphorus trichalcogenides exhibits a large range of band gaps from 1.77 to 3.94 eV, and the electronic structures are greatly affected by the metal or the chalcogenide atoms. The calculated band edges of metal phosphorus trichalcogenides further reveal that single-layer ZnPSe 3 , CdPSe 3 , Ag 0.5 Sc 0.5 PSe 3 , and Ag 0.5 In 0.5 PX 3 (X = S and Se) have both suitable band gaps for visible-light driving and sufficient over-potentials for water splitting. More fascinatingly, single-layer Ag 0.5 Sc 0.5 PSe 3 is a direct band gap semiconductor, and the calculated optical absorption further convinces that such materials own outstanding properties for light absorption. Such results demonstrate that the single layer metal phosphorus trichalcogenides own high stability, versatile electronic properties, and high optical absorption, thus such materials have great chances to be high efficient photocatalysts for water-splitting

  18. Morphology and atomic-scale structure of single-layer WS2 nanoclusters.

    Science.gov (United States)

    Füchtbauer, Henrik G; Tuxen, Anders K; Moses, Poul G; Topsøe, Henrik; Besenbacher, Flemming; Lauritsen, Jeppe V

    2013-10-14

    Two-dimensional sheets of transition metal (Mo and W) sulfides are attracting strong attention due to the unique electronic and optical properties associated with the material in its single-layer form. The single-layer MoS2 and WS2 are already in widespread commercial use in catalytic applications as both hydrotreating and hydrocracking catalysts. Consequently, characterization of the morphology and atomic structure of such particles is of utmost importance for the understanding of the catalytic active phase. However, in comparison with the related MoS2 system only little is known about the fundamental properties of single-layer WS2 (tungstenite). Here, we use an interplay of atom-resolved Scanning Tunneling Microscopy (STM) studies of Au(111)-supported WS2 nanoparticles and calculated edge structures using Density Functional Theory (DFT) to reveal the equilibrium morphology and prevalent edge structures of single-layer WS2. The STM results reveal that the single layer S-W-S sheets adopt a triangular equilibrium shape under the sulfiding conditions of the synthesis, with fully sulfided edges. The predominant edge structures are determined to be the (101[combining macron]0) W-edge, but for the smallest nanoclusters also the (1[combining macron]010) S-edges become important. DFT calculations are used to construct phase diagrams of the WS2 edges, and describe their sulfur and hydrogen coordination under different conditions, and in this way shed light on the catalytic role of WS2 edges.

  19. Canopy Chemistry (OTTER)

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: Canopy characteristics: leaf chemistry, specific leaf area, LAI, PAR, IPAR, NPP, standing biomass--see also: Meteorology (OTTER) for associated...

  20. Selective exfoliation of single-layer graphene from non-uniform graphene grown on Cu

    International Nuclear Information System (INIS)

    Lim, Jae-Young; Lee, Jae-Hyun; Jang, Hyeon-Sik; Whang, Dongmok; Joo, Won-Jae; Hwang, SungWoo

    2015-01-01

    Graphene growth on a copper surface via metal-catalyzed chemical vapor deposition has several advantages in terms of providing high-quality graphene with the potential for scale-up, but the product is usually inhomogeneous due to the inability to control the graphene layer growth. The non-uniform regions strongly affect the reliability of the graphene in practical electronic applications. Herein, we report a novel graphene transfer method that allows for the selective exfoliation of single-layer graphene from non-uniform graphene grown on a Cu foil. Differences in the interlayer bonding energy are exploited to mechanically separate only the top single-layer graphene and transfer this to an arbitrary substrate. The dry-transferred single-layer graphene showed electrical characteristics that were more uniform than those of graphene transferred using conventional wet-etching transfer steps. (paper)

  1. Fabrication of a single layer graphene by copper intercalation on a SiC(0001) surface

    International Nuclear Information System (INIS)

    Yagyu, Kazuma; Tochihara, Hiroshi; Tomokage, Hajime; Suzuki, Takayuki; Tajiri, Takayuki; Kohno, Atsushi; Takahashi, Kazutoshi

    2014-01-01

    Cu atoms deposited on a zero layer graphene grown on a SiC(0001) substrate, intercalate between the zero layer graphene and the SiC substrate after the thermal annealing above 600 °C, forming a Cu-intercalated single layer graphene. On the Cu-intercalated single layer graphene, a graphene lattice with superstructure due to moiré pattern is observed by scanning tunneling microscopy, and specific linear dispersion at the K ¯ point as well as a characteristic peak in a C 1s core level spectrum, which is originated from a free-standing graphene, is confirmed by photoemission spectroscopy. The Cu-intercalated single layer graphene is found to be n-doped

  2. Single layer of Ge quantum dots in HfO2for floating gate memory capacitors.

    Science.gov (United States)

    Lepadatu, A M; Palade, C; Slav, A; Maraloiu, A V; Lazanu, S; Stoica, T; Logofatu, C; Teodorescu, V S; Ciurea, M L

    2017-04-28

    High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO 2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO 2 /floating gate of single layer of Ge QDs in HfO 2 /tunnel HfO 2 /p-Si wafers. Both Ge and HfO 2 are nanostructured by RTA at moderate temperatures of 600-700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 × 10 15 m -2 is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO 2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO 2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO 2 NCs boundaries, while another part of the Ge atoms is present inside the HfO 2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 ± 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO 2 , distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

  3. Thermal vibration of a rectangular single-layered graphene sheet with quantum effects

    International Nuclear Information System (INIS)

    Wang, Lifeng; Hu, Haiyan

    2014-01-01

    The thermal vibration of a rectangular single-layered graphene sheet is investigated by using a rectangular nonlocal elastic plate model with quantum effects taken into account when the law of energy equipartition is unreliable. The relation between the temperature and the Root of Mean Squared (RMS) amplitude of vibration at any point of the rectangular single-layered graphene sheet in simply supported case is derived first from the rectangular nonlocal elastic plate model with the strain gradient of the second order taken into consideration so as to characterize the effect of microstructure of the graphene sheet. Then, the RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet simply supported on an elastic foundation is derived. The study shows that the RMS amplitude of the rectangular single-layered graphene sheet predicted from the quantum theory is lower than that predicted from the law of energy equipartition. The maximal relative difference of RMS amplitude of thermal vibration appears at the sheet corners. The microstructure of the graphene sheet has a little effect on the thermal vibrations of lower modes, but exhibits an obvious effect on the thermal vibrations of higher modes. The quantum effect is more important for the thermal vibration of higher modes in the case of smaller sides and lower temperature. The relative difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet decreases monotonically with an increase of temperature. The absolute difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet increases slowly with the rising of Winkler foundation modulus.

  4. Chemical etching of copper foils for single-layer graphene growth by chemical vapor deposition

    Science.gov (United States)

    Yoshihara, Naoki; Noda, Masaru

    2017-10-01

    Chemical etching on copper surface is essential as a pre-treatment for single-layer graphene growth by chemical vapor deposition (CVD). Here, we investigated the effect of chemical etching treatment on copper foils for single-layer graphene CVD growth. The chemical etching conditions, such as the type of chemical etchants and the treatment time, were found to strongly influence the graphene domain size. Moreover, a drastic change in the layer structure of graphene sheets, which was attributed to the surface morphology of the etched copper foil, was confirmed by graphene transmittance and Raman mapping measurements.

  5. A comprehensive approach for the simulation of the Urban Heat Island effect with the WRF/SLUCM modeling system: The case of Athens (Greece)

    Science.gov (United States)

    Giannaros, Christos; Nenes, Athanasios; Giannaros, Theodore M.; Kourtidis, Konstantinos; Melas, Dimitrios

    2018-03-01

    This study presents a comprehensive modeling approach for simulating the spatiotemporal distribution of urban air temperatures with a modeling system that includes the Weather Research and Forecasting (WRF) model and the Single-Layer Urban Canopy Model (SLUCM) with a modified treatment of the impervious surface temperature. The model was applied to simulate a 3-day summer heat wave event over the city of Athens, Greece. The simulation, using default SLUCM parameters, is capable of capturing the observed diurnal variation of urban temperatures and the Urban Heat Island (UHI) in the greater Athens Area (GAA), albeit with systematic biases that are prominent during nighttime hours. These biases are particularly evident over low-intensity residential areas, and they are associated with the surface and urban canopy properties representing the urban environment. A series of sensitivity simulations unravels the importance of the sub-grid urban fraction parameter, surface albedo, and street canyon geometry in the overall causation and development of the UHI effect. The sensitivities are then used to determine optimal values of the street canyon geometry, which reproduces the observed temperatures throughout the simulation domain. The optimal parameters, apart from considerably improving model performance (reductions in mean temperature bias from 0.30 °C to 1.58 °C), are also consistent with actual city building characteristics - which gives confidence that the model set-up is robust, and can be used to study the UHI in the GAA in the anticipated warmer conditions in the future.

  6. Modeling of 1-D nitrate transport in single layer soils | Dike | Journal ...

    African Journals Online (AJOL)

    The transport of nitrate in laboratory single soil columns of sand, laterite and clay were investigated after 21 days. The 1-D contaminant transport model by Notodarmojo et al (1991) for single layer soils were calibrated and verified using field data collected from a refuse dump site at avu, owerri, Imo state. The experimental ...

  7. Single-layer skull approximations perform well in transcranial direct current stimulation modeling

    NARCIS (Netherlands)

    Rampersad, S.M.; Stegeman, D.F.; Oostendorp, T.F.

    2013-01-01

    In modeling the effect of transcranial direct current stimulation, the representation of the skull is an important factor. In a spherical model, we compared a realistic skull modeling approach, in which the skull consisted of three isotropic layers, to anisotropic and isotropic single-layer

  8. Modelling and observing urban climate in the Netherlands

    International Nuclear Information System (INIS)

    Van Hove, B.; Steeneveld, G.J.; Heusinkveld, B.; Holtslag, B.; Jacobs, C.; Ter Maat, H.; Elbers, J.; Moors, E.

    2011-06-01

    impression of the model performance under Dutch climatic conditions is obtained from a number of online simulations with the non-calibrated versions of NSLUCM-WRF (NSLUCM stands for NOAH land surface model/Single-layer Urban Canopy model) and TEB-RAMS (Town Energy Balance - Regional Atmospheric Modeling System). These simulations have been carried out for the city of Rotterdam and their results are discussed in Chapter 4. Chapter 5 gives an inventory of the available datasets for model validation and parameterization. Also, the possibility to use data from hobby meteorologists will be discussed. Chapter 6 deals with the 'measuring strategy' that will be illustrated by the measurements carried out as part of the Hotspot Heat Stress Rotterdam project. Finally, in chapter 7, conclusions and recommendations are presented.

  9. Single Layered Versus Double Layered Intestinal Anastomosis: A Randomized Controlled Trial

    Science.gov (United States)

    Mohapatra, Vandana; Singh, Surendra; Rath, Pratap Kumar; Behera, Tapas Ranjan

    2017-01-01

    Introduction Gastrointestinal anastomosis is one of the most common procedures being performed in oesophagogastric, hepatobiliary, bariatric, small bowel and colorectal surgery; however, the safety and efficacy of single layer or double layer anastomotic technique is still unclear. Aim To assess and compare the efficacy, safety and cost effectiveness of single layered versus double layered intestinal anastomosis. Materials and Methods This prospective, double-blind, randomized controlled comparative study comprised of patients who underwent intestinal resection and anastomosis. They were randomly assigned to undergo either single layered extra-mucosal anastomosis (Group-A) or double layered intestinal anastomosis (Group-B). Primary outcome measures included average time taken for anastomosis, postoperative complications, mean duration of hospital stay and cost of suture material used; secondary outcome measures assessed the postoperative return of bowel function. Statistical analysis was done by Chi-square test and student t-test. Results A total of 97 participants were randomized. Fifty patients were allocated to single layered extramucosal continuous anastomosis (Group-A) and 47 patients to double layered anastomosis (Group-B). The patients in each group were well matched for age, sex and diagnosis. The mean time taken for anastomosis (15.12±2.27 minutes in Group-A versus 24.38±2.26 minutes in Group-B) and the length of hospital stay (5.90±1.43 days in Group-A versus 7.29±1.89 days in Group-B) was significantly shorter in Group-A {p-value anastomosis. However, there was no significant difference in the complication rates between the two groups. Conclusion It can be concluded that single layered extramucosal continuous intestinal anastomosis is equally safe and perhaps more cost effective than the conventional double layered method and may represent the optimal choice for routine surgical practice. PMID:28764239

  10. Diffusion of Supercritical Fluids through Single-Layer Nanoporous Solids: Theory and Molecular Simulations.

    Science.gov (United States)

    Oulebsir, Fouad; Vermorel, Romain; Galliero, Guillaume

    2018-01-16

    With the advent of graphene material, membranes based on single-layer nanoporous solids appear as promising devices for fluid separation, be it liquid or gaseous mixtures. The design of such architectured porous materials would greatly benefit from accurate models that can predict their transport and separation properties. More specifically, there is no universal understanding of how parameters such as temperature, fluid loading conditions, or the ratio of the pore size to the fluid molecular diameter influence the permeation process. In this study, we address the problem of pure supercritical fluids diffusing through simplified models of single-layer porous materials. Basically, we investigate a toy model that consists of a single-layer lattice of Lennard-Jones interaction sites with a slit gap of controllable width. We performed extensive equilibrium and biased molecular dynamics simulations to document the physical mechanisms involved at the molecular scale. We propose a general constitutive equation for the diffusional transport coefficient derived from classical statistical mechanics and kinetic theory, which can be further simplified in the ideal gas limit. This transport coefficient relates the molecular flux to the fluid density jump across the single-layer membrane. It is found to be proportional to the accessible surface porosity of the single-layer porous solid and to a thermodynamic factor accounting for the inhomogeneity of the fluid close to the pore entrance. Both quantities directly depend on the potential of mean force that results from molecular interactions between solid and fluid atoms. Comparisons with the simulations data show that the kinetic model captures how narrowing the pore size below the fluid molecular diameter lowers dramatically the value of the transport coefficient. Furthermore, we demonstrate that our general constitutive equation allows for a consistent interpretation of the intricate effects of temperature and fluid loading

  11. NLCD 2001 - Tree Canopy

    Data.gov (United States)

    Minnesota Department of Natural Resources — The National Land Cover Database 2001 tree canopy layer for Minnesota (mapping zones 39-42, 50-51) was produced through a cooperative project conducted by the...

  12. High Throughput Characterization of Epitaxially Grown Single-Layer MoS2

    Directory of Open Access Journals (Sweden)

    Foad Ghasemi

    2017-03-01

    Full Text Available The growth of single-layer MoS2 with chemical vapor deposition is an established method that can produce large-area and high quality samples. In this article, we investigate the geometrical and optical properties of hundreds of individual single-layer MoS2 crystallites grown on a highly-polished sapphire substrate. Most of the crystallites are oriented along the terraces of the sapphire substrate and have an area comprised between 10 µm2 and 60 µm2. Differential reflectance measurements performed on these crystallites show that the area of the MoS2 crystallites has an influence on the position and broadening of the B exciton while the orientation does not influence the A and B excitons of MoS2. These measurements demonstrate that differential reflectance measurements have the potential to be used to characterize the homogeneity of large-area chemical vapor deposition (CVD-grown samples.

  13. Edge structures and properties of triangular antidots in single-layer MoS2

    KAUST Repository

    Gan, Li Yong

    2016-08-30

    Density functional theory and experiments are employed to shed light on the edge structures of antidots in O etched single-layer MoS2. The equilibrium morphology is found to be the zigzag Mo edge with each Mo atom bonded to two O atoms, in a wide range of O chemical potentials. Scanning electron microscopy shows that the orientation of the created triangular antidots is opposite to the triangular shape of the single-layer MoS2 samples, in agreement with the theoretical predictions. Furthermore, edges induced by O etching turn out to be p-doped, suggesting an effective strategy to realize p-type MoS2 devices. Published by AIP Publishing.

  14. Quantum Hall states of atomic Bose gases: Density profiles in single-layer and multilayer geometries

    International Nuclear Information System (INIS)

    Cooper, N. R.; Lankvelt, F. J. M. van; Reijnders, J. W.; Schoutens, K.

    2005-01-01

    We describe the density profiles of confined atomic Bose gases in the high-rotation limit, in single-layer and multilayer geometries. We show that, in a local-density approximation, the density in a single layer shows a landscape of quantized steps due to the formation of incompressible liquids, which are analogous to fractional quantum Hall liquids for a two-dimensional electron gas in a strong magnetic field. In a multilayered setup we find different phases, depending on the strength of the interlayer tunneling t. We discuss the situation where a vortex lattice in the three-dimensional condensate (at large tunneling) undergoes quantum melting at a critical tunneling t c 1 . For tunneling well below t c 1 one expects weakly coupled or isolated layers, each exhibiting a landscape of quantum Hall liquids. After expansion, this gives a radial density distribution with characteristic features (cusps) that provide experimental signatures of the quantum Hall liquids

  15. White-light-emitting diode based on a single-layer polymer

    Science.gov (United States)

    Wang, B. Z.; Zhang, X. P.; Liu, H. M.

    2013-05-01

    A broad-band light-emitting diode was achieved in a single-layer device based on pure poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFB). Electromer emission was observed in the red with a center wavelength of about 620 nm in electroluminescence (EL) spectrum. This kind of emission exhibits strong dependence on the thickness of the PFB layer, so that the shape of the EL spectrum may be adjusted through changing the thickness of the active polymer layer to balance between the intrinsic PFB emission in the blue and the electromer emission in the red. Thus, white light emission may be achieved from such a single-layer single-material diode.

  16. Edge structures and properties of triangular antidots in single-layer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Gan, Li-Yong, E-mail: ganly@swjtu.edu.cn, E-mail: iamyccheng@njtech.edu.cn, E-mail: udo.schwingenschlogl@kaust.edu.sa [Key Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductivity and New Energy R& D Center, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Cheng, Yingchun, E-mail: ganly@swjtu.edu.cn, E-mail: iamyccheng@njtech.edu.cn, E-mail: udo.schwingenschlogl@kaust.edu.sa; Huang, Wei [Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials - SICAM, Nanjing Tech University - NanjingTech, 30 South Puzhu Road, Nanjing 211816 (China); Schwingenschlögl, Udo, E-mail: ganly@swjtu.edu.cn, E-mail: iamyccheng@njtech.edu.cn, E-mail: udo.schwingenschlogl@kaust.edu.sa [Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); Yao, Yingbang [Advanced Nanofabrication and Imaging Core Lab, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); School of Materials and Energy, Guangdong University of Technology, Guangdong 510006 (China); Zhao, Yong [Key Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductivity and New Energy R& D Center, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, 610031 Sichuan (China); Zhang, Xi-xiang [Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); Advanced Nanofabrication and Imaging Core Lab, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia)

    2016-08-29

    Density functional theory and experiments are employed to shed light on the edge structures of antidots in O etched single-layer MoS{sub 2}. The equilibrium morphology is found to be the zigzag Mo edge with each Mo atom bonded to two O atoms, in a wide range of O chemical potentials. Scanning electron microscopy shows that the orientation of the created triangular antidots is opposite to the triangular shape of the single-layer MoS{sub 2} samples, in agreement with the theoretical predictions. Furthermore, edges induced by O etching turn out to be p-doped, suggesting an effective strategy to realize p-type MoS{sub 2} devices.

  17. Persistent Charge-Density-Wave Order in Single-Layer TaSe2.

    Science.gov (United States)

    Ryu, Hyejin; Chen, Yi; Kim, Heejung; Tsai, Hsin-Zon; Tang, Shujie; Jiang, Juan; Liou, Franklin; Kahn, Salman; Jia, Caihong; Omrani, Arash A; Shim, Ji Hoon; Hussain, Zahid; Shen, Zhi-Xun; Kim, Kyoo; Min, Byung Il; Hwang, Choongyu; Crommie, Michael F; Mo, Sung-Kwan

    2018-02-14

    We present the electronic characterization of single-layer 1H-TaSe 2 grown by molecular beam epitaxy using a combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations. We demonstrate that 3 × 3 charge-density-wave (CDW) order persists despite distinct changes in the low energy electronic structure highlighted by the reduction in the number of bands crossing the Fermi energy and the corresponding modification of Fermi surface topology. Enhanced spin-orbit coupling and lattice distortion in the single-layer play a crucial role in the formation of CDW order. Our findings provide a deeper understanding of the nature of CDW order in the two-dimensional limit.

  18. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling.

    Science.gov (United States)

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2016-01-07

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.

  19. Identification of excitons, trions and biexcitons in single-layer WS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Plechinger, Gerd; Nagler, Philipp; Kraus, Julia; Paradiso, Nicola; Strunk, Christoph; Schueller, Christian; Korn, Tobias [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, 93040, Regensburg (Germany)

    2015-08-15

    Single-layer WS{sub 2} is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS{sub 2}, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Phonon-limited mobility in n-type single-layer MoS2 from first principles

    DEFF Research Database (Denmark)

    Kaasbjerg, Kristen; Thygesen, Kristian S.; Jacobsen, Karsten W.

    2012-01-01

    We study the phonon-limited mobility in intrinsic n-type single-layer MoS2 for temperatures T > 100 K. The materials properties including the electron-phonon interaction are calculated from first principles and the deformation potentials and Frohlich interaction in single-layer MoS2 are establish...

  1. Initial experience with application of single layer modified Kugel mesh for inguinal hernia repair: Case series of 72 consecutive patients

    Directory of Open Access Journals (Sweden)

    Pao-Hwa Chen

    2017-03-01

    Conclusion: The postoperative complication and recurrence rates of single-layer MK mesh herniorrhaphy was comparable with previously reported tension-free repair. Single-layer application is safe and feasible. A longer follow-up period and larger study group with a control group are needed to verify our method.

  2. Model for a collimated spin wave beam generated by a single layer, spin torque nanocontact

    OpenAIRE

    Hoefer, M. A.; Silva, T. J.; Stiles, M. D.

    2007-01-01

    A model of spin torque induced magnetization dynamics based upon semi-classical spin diffusion theory for a single layer nanocontact is presented. The model incorporates effects due to the current induced Oersted field and predicts the generation of a variety of spatially dependent, coherent, precessional magnetic wave structures. Directionally controllable collimated spin wave beams, vortex spiral waves, and localized standing waves are found to be excited by the interplay of the Oersted fie...

  3. Doping-controlled phase transitions in single-layer MoS2

    Science.gov (United States)

    Zhuang, Houlong L.; Johannes, Michelle D.; Singh, Arunima K.; Hennig, Richard G.

    2017-10-01

    The electronic properties of single-layer MoS2 make it an ideal two-dimensional (2D) material for application in electronic devices. Experiments show that MoS2 can undergo structural phase transitions. Applications of single-layer MoS2 will require firm laboratory control over the phase formation. Here we compare the stability and electronic structure of the three experimentally observed single-layer MoS2 phases, 2 H ,1 T , and 1 T' , and an in-plane metal/semiconductor heterostructure. We reveal by density-functional theory calculations that charge doping can induce the phase transition of single-layer MoS2 from the 2 H to the 1 T structure. Further, the 1 T structure undergoes a second phase transition due to the occurrence of a charge-density wave (CDW). By comparing the energies of several possible resulting CDW structures, we find that the 1 T' orthorhombic structure is the most stable one, consistent with experimental observations and previous theoretical studies. We show that the underlying CDW transition mechanism is not due to Fermi surface nesting, but nonetheless, can be controlled by charge doping. In addition, the stability landscape is highly sensitive to charge doping, which can be used as a practical phase selector. We also provide a prescription for obtaining the 1 T' structure via growth or deposition of MoS2 on a Hf substrate, which transfers electrons uniformly and with minimal structural distortion. Finally, we show that lateral heterostructures formed by the 2 H and 1 T' structures exhibit a low interfacial energy of 0.17 eV/Å, a small Schottky barrier of 0.3 eV for holes, and a large barrier of 1.6 eV for electrons.

  4. Growth of high-crystalline, single-layer hexagonal boron nitride on recyclable platinum foil.

    Science.gov (United States)

    Kim, Gwangwoo; Jang, A-Rang; Jeong, Hu Young; Lee, Zonghoon; Kang, Dae Joon; Shin, Hyeon Suk

    2013-04-10

    Hexagonal boron nitride (h-BN) is gaining significant attention as a two-dimensional dielectric material, along with graphene and other such materials. Herein, we demonstrate the growth of highly crystalline, single-layer h-BN on Pt foil through a low-pressure chemical vapor deposition method that allowed h-BN to be grown over a wide area (8 × 25 mm(2)). An electrochemical bubbling-based method was used to transfer the grown h-BN layer from the Pt foil onto an arbitrary substrate. This allowed the Pt foil, which was not consumed during the process, to be recycled repeatedly. The UV-visible absorption spectrum of the single-layer h-BN suggested an optical band gap of 6.06 eV, while a high-resolution transmission electron microscopy image of the same showed the presence of distinct hexagonal arrays of B and N atoms, which were indicative of the highly crystalline nature and single-atom thickness of the h-BN layer. This method of growing single-layer h-BN over large areas was also compatible with use of a sapphire substrate.

  5. Learning rate and attractor size of the single-layer perceptron

    International Nuclear Information System (INIS)

    Singleton, Martin S.; Huebler, Alfred W.

    2007-01-01

    We study the simplest possible order one single-layer perceptron with two inputs, using the delta rule with online learning, in order to derive closed form expressions for the mean convergence rates. We investigate the rate of convergence in weight space of the weight vectors corresponding to each of the 14 out of 16 linearly separable rules. These vectors follow zigzagging lines through the piecewise constant vector field to their respective attractors. Based on our studies, we conclude that a single-layer perceptron with N inputs will converge in an average number of steps given by an Nth order polynomial in (t/l), where t is the threshold, and l is the size of the initial weight distribution. Exact values for these averages are provided for the five linearly separable classes with N=2. We also demonstrate that the learning rate is determined by the attractor size, and that the attractors of a single-layer perceptron with N inputs partition R N +R N

  6. Laser-assisted fabrication of single-layer flexible touch sensor

    Science.gov (United States)

    Son, Seokwoo; Park, Jong Eun; Lee, Joohyung; Yang, Minyang; Kang, Bongchul

    2016-10-01

    Single-layer flexible touch sensor that is designed for the indium-tin-oxide (ITO)-free, bendable, durable, multi-sensible, and single layer transparent touch sensor was developed via a low-cost and one-step laser-induced fabrication technology. To this end, an entirely novel approach involving material, device structure, and even fabrication method was adopted. Conventional metal oxides based multilayer touch structure was substituted by the single layer structure composed of integrated silver wire networks of sensors and bezel interconnections. This structure is concurrently fabricated on a glass substitutive plastic film via the laser-induced fabrication method using the low-cost organometallic/nanoparticle hybrid complex. In addition, this study addresses practical solutions to heterochromia and interference problem with a color display unit. As a result, a practical touch sensor is successfully demonstrated through resolving the heterochromia and interference problems with color display unit. This study could provide the breakthrough for early realization of wearable device.

  7. Simulations of the Montréal urban heat island

    Science.gov (United States)

    Roberge, François; Sushama, Laxmi; Fanta, Gemechu

    2017-04-01

    The current population of Montreal is around 3.8 million and this number is projected to go up in the coming years to decades, which will lead to vast expansion of urban areas. It is well known that urban morphology impacts weather and climate, and therefore should be taken into consideration in urban planning. This is particularly important in the context of a changing climate, as the intensity and frequency of temperature extremes such as hot spells are projected to increase in future climate, and Urban Heat Island (UHI) can potentially raise already stressful temperatures during such events, which can have significant effects on human health and energy consumption. High-resolution regional climate model simulations can be utilized to understand better urban-weather/climate interactions in current and future climates, particularly the spatio-temporal characteristics of the Urban Heat Island and its impact on other weather/climate characteristics such as urban flows, precipitation etc. This paper will focus on two high-resolution (250 m) simulations performed with (1) the Canadian Land Surface Scheme (CLASS) and (2) CLASS and TEB (Town Energy Balance) model; TEB is a single layer urban canopy model and is used to model the urban fractions. The two simulations are performed over a domain covering Montreal for the 1960-2015 period, driven by atmospheric forcing data coming from a high-resolution Canadian Regional Climate Model (CRCM5) simulation, driven by ERA-Interim. The two simulations are compared to assess the impact of urban regions on selected surface fields and the simulation with both CLASS and TEB is then used to study the spatio-temporal characteristics of the UHI over the study domain. Some preliminary results from a coupled simulation, i.e. CRCM5+CLASS+TEB, for selected years, including extreme warm years, will also be presented.

  8. Future Urban Climate Projection in A Tropical Megacity Based on Global and Regional Scenarios

    Science.gov (United States)

    Darmanto, N. S.; Varquez, A. C. G.; Kanda, M.

    2017-12-01

    Cities in Asian developing countries experience rapid transformation in urban morphology and energy consumption, which correspondingly affects urban climate. Weather Research and Forecasting (WRF) Model coupled with improved single-layer urban canopy model incorporating realistic distribution of urban parameters and anthropogenic heat emission (AHE) in the tropic Jakarta Greater Area was conducted. Simulation was conducted during the dry months from 2006 to 2015 and agreed well with point and satellite observation. The same technology coupled with pseudo global warming (PGW) method based on representative concentration pathways (RCP) scenario 2.6 and 8.5 was conducted to produce futuristic climate condition in 2050. Projected urban morphology and AHE in 2050s were constructed using regional urban growing model with shared socioeconomic pathways (SSP) among its inputs. Compact future urban configuration, based on SSP1, was coupled to RCP2.6. Unrestrained future urban configuration, based on SSP3, was coupled to RCP8.5. Results show that background warming from RCP 2.6 and 8.5 will increase background temperature by 0.55°C and 1.2°C throughout the region, respectively. Future projection of urban sprawl results to an additional 0.3°C and 0.5°C increase on average, with maximum increase of 1.1°C and 1.3°C due to urban effect for RCP2.6/compact and RCP8.5/unrestrained, respectively. Higher moisture content in urban area is indicated in the future due to higher evaporation. Change in urban roughness is likely affect slower wind velocity in urban area and sea breeze front inland penetration the future compare with current condition. Acknowledgement: This research was supported by the Environment Research and Technology Development Fund (S-14) of the Ministry of the Environment, Japan.

  9. A photosynthesis-based two-leaf canopy stomatal conductance model for meteorology and air quality modeling with WRF/CMAQ PX LSM

    Science.gov (United States)

    A coupled photosynthesis-stomatal conductance model with single-layer sunlit and shaded leaf canopy scaling is implemented and evaluated in a diagnostic box model with the Pleim-Xiu land surface model (PX LSM) and ozone deposition model components taken directly from the meteorol...

  10. Single-layer centrifugation through colloid selects improved quality of epididymal cat sperm.

    Science.gov (United States)

    Chatdarong, K; Thuwanut, P; Morrell, J M

    2010-06-01

    The objectives were to determine the: 1) extent of epithelial and red blood cell contamination in epididymal cat sperm samples recovered by the cutting method; 2) efficacy of simple washing, single-layer centrifugation (SLC), and swim-up for selecting epididymal cat sperm; and 3) effects of freezing and thawing on cat sperm selected by various techniques. Ten unit samples were studied; each contained sperm from the cauda epididymides of four cats (total, approximately 200 x 10(6) sperm) and was equally allocated into four treatments: 1) simple washing, 2) single-layer centrifugation through colloid prior to cryopreservation (SLC-PC), 3) single-layer centrifugation through colloid after cryopreservation (SLC-AC), and 4) swim-up. Centrifugation (300 x g for 20 min) was done for all methods. The SLC-PC had a better recovery rate than the SLC-AC and swim-up methods (mean+/-SD of 16.4+/-8.7, 10.7+/-8.9, and 2.3+/-1.7%, respectively; Pblood cell contamination than simple washed samples (0.02+/-0.01, 0.02+/-0.04, 0.03+/-0.04, and 0.44+/-0.22 x 10(6) cells/mL, respectively; P0.05), SLC-PC yielded the highest percentage of sperm with normal midpieces and tails (P0.05). In conclusion, both SLC-PC and swim-up improved the quality of epididymal cat sperm, including better morphology, membrane and DNA integrity, and removal of cellular contamination. However, SLC had a better sperm recovery rate than swim-up. 2010 Elsevier Inc. All rights reserved.

  11. Spin effects in MoS{sub 2} and WS{sub 2} single layers

    Energy Technology Data Exchange (ETDEWEB)

    Kioseoglou, G. [Department of Materials Science and Technology, University of Crete, Heraklion (Greece); Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology Hellas (FORTH), Heraklion, Crete (Greece); Korkusinski, M. [Quantum Theory Group, Emerging Technologies Division, National Research Council, Ottawa, ON (Canada); Scrace, T. [University at Buffalo, SUNY, Buffalo, NY (United States); Hanbicki, A.T.; Currie, M.; Jonker, B.T.; Petrou, A. [Naval Research Laboratory, Washington, DC (United States); Hawrylak, P. [Quantum Theory Group, Emerging Technologies Division, National Research Council, Ottawa, ON (Canada); Department of Physics, University of Ottawa, ON (Canada)

    2016-01-15

    Replacing the two sublattices of carbon atoms in graphene with transition metal atoms and chalcogenide dimers results in single layers of transition metal dichalcogenides (TMDCs). TMDCs are promising new materials for light and energy harvesting, transistors, sensors and quantum information processing. One way to access the distinctive functionality of these materials is via their optical selection rules. In particular, light with positive or negative helicity is absorbed differently, therefore, understanding the interaction of circularly polarized light with various TMDCs should enable future applications. Using the examples of MoS{sub 2} and WS{sub 2} we summarize some recent results that illustrate the potential of these materials. First, when optically excited with circularly polarized light, single layers of MoS{sub 2} can emit light with an appreciable polarization. Depolarization mechanisms can be subsequently explored by monitoring the polarization of emitted photoluminescence as a function of the excess energy supplied to the system. As the energy of the pumping light increases further from the emission channel, the emission quickly becomes depolarized. The dominant relaxation mechanism is identified as phonon-assisted intervalley scattering. In single layers of WS{sub 2} containing electron gas, the main emission channel is from negatively charged excitons, or trions. In the presence of a two-dimensional electron gas this trion emission is circularly polarized at zero magnetic field, even when excited with linearly polarized light. This spontaneous circular polarization of the trion has a linear dependence on magnetic field and can be attributed to the existence of a valley polarized state of the two-dimensional electron gas. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Exploring single-layered SnSe honeycomb polymorphs for optoelectronic and photovoltaic applications

    Science.gov (United States)

    Ul Haq, Bakhtiar; AlFaify, S.; Ahmed, R.; Butt, Faheem K.; Laref, A.; Shkir, Mohd.

    2018-02-01

    Single-layered tin selenide that shares the same structure with phosphorene and possesses intriguing optoelectronic properties has received great interest as a two-dimensional material beyond graphene and phosphorene. Herein, we explore the optoelectronic response of the newly discovered stable honeycomb derivatives (such as α , β , γ , δ , and ɛ ) of single-layered SnSe in the framework of density functional theory. The α , β , γ , and δ derivatives of a SnSe monolayer have been found to exhibit an indirect band gap, however, the dispersion of their band-gap edges demonstrates multiple direct band gaps at a relatively high energy. The ɛ -SnSe, however, features an intrinsic direct band gap at the high-symmetry Γ point. Their energy band gaps (0.53, 2.32, 1.52, 1.56, and 1.76 eV for α -, β -, γ -, δ -, and ɛ -SnSe, respectively), calculated at the level of the Tran-Blaha modified Becke-Johnson approach, mostly fall right in the visible range of the electromagnetic spectrum and are in good agreement with the available literature. The optical spectra of these two-dimensional (2D) SnSe polymorphs (besides β -SnSe) are highly anisotropic and possess strictly different optical band gaps along independent diagonal components. They show high absorption in the visible and UV ranges. Similarly, the reflectivity, refraction, and optical conductivities inherit strong anisotropy from the dielectric functions as well and are highly visible-UV polarized along the cartesian coordinates, showing them to be suitable for optical filters, polarizers, and shields against UV radiation. Our investigations suggest these single-layered SnSe allotropes as a promising 2D material for next-generation nanoscale optoelectronic and photovoltaic applications beyond graphene and phosphorene.

  13. Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

    KAUST Repository

    Cheng, Yingchun

    2014-04-28

    We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we investigate Mn-doped MoS2 by first-principles calculations. We study how the valley polarization depends on the strength of the spin orbit coupling and the exchange interaction and discuss how it can be controlled by magnetic doping. Valley polarization by magnetic doping is also expected for other honeycomb materials with strong spin orbit coupling and the absence of inversion symmetry.

  14. Atomic-scale structure of single-layer MoS2 nanoclusters

    DEFF Research Database (Denmark)

    Helveg, S.; Lauritsen, J. V.; Lægsgaard, E.

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2 n...... nanoparticles synthesized on Au(lll), and establishes a new picture of the active edge sires of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in general....

  15. Single layer graphene electrodes for quantum dot-light emitting diodes

    Science.gov (United States)

    Yan, Long; Zhang, Yu; Zhang, Xiaoyu; Zhao, Jia; Wang, Yu; Zhang, Tieqiang; Jiang, Yongheng; Gao, Wenzhu; Yin, Jingzhi; Zhao, Jun; Yu, William W.

    2015-03-01

    Single layer graphene was employed as the electrode in quantum dot-light emitting diodes (QD-LEDs) to replace indium tin oxide (ITO). The graphene layer demonstrated low surface roughness, good hole injection ability, and proper work function matching with the poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) layer. Together with the hole transport layer and electron transport layer, the fabricated QD-LED showed good current efficiency and power efficiency, which were even higher than an ITO-based similar device under low current density. The result indicates that graphene can be used as anodes to replace ITO in QD-LEDs.

  16. Highly simplified small molecular phosphorescent organic light emitting devices with a solution-processed single layer

    Directory of Open Access Journals (Sweden)

    Zhaokui Wang

    2011-09-01

    Full Text Available A highly simplified single layer solution-processed phosphorescent organic light emitting device (PHOLED with the maximum ηP 11.5 lm/W corresponding to EQE 9.6% has been demonstrated. The solution-processed device is shown having comparable even exceeding device performance to vacuum-processed PHOLED. The simplified device design strategy represents a pathway toward large area, low cost and high efficiency OLEDs in the future. The charge injection and conduction mechanisms in two solution- and vacuum-processed devices are also investigated by evaluating the temperature dependence of current density – voltage characteristics.

  17. On the assessment of urban land-surface impacts on climate in regional climate model simulations over Central Europe

    Science.gov (United States)

    Huszar, Peter; Belda, Michal; Halenka, Tomas

    2016-04-01

    When aiming higher resolution in dynamical downscaling, which is common trend in CORDEX activities, the effects of land use and land use changes are playing increasing role. This is especially true for the urban areas, which in high resolution can occupy significant part of a single gridbox, if not being even bigger in case of big cities or megacities. Moreover, the role of cities will increase in future, as the population within the urban areas is growing faster, with the estimate for Europe of about 84% living in cities. For the purpose of qualifying and quantifying the impact of cities and in general the urban surfaces on climate, the surface parameterization in regional climate model RegCM4 has been coupled with the Single Layer Urban Canopy Model (SLUCM), which can be used both in dynamic scale within BATS scheme and in a more detailed SUBBATS scale to treat the surface on a higher resolution subgrid. A set of experiments was performed over the period of 2005-2009 over central Europe, either without considering urban surfaces and with the SLUCM treatment. Results show a statistically significant impact of urbanized surfaces on temperature (up to 1.5 K increase in summer), on the boundary layer height (ZPBL, increases up to 50 m). Additionally, the version of land-surface scheme using CLM is tested and effect of the urban environment, which is included in the CLM scheme, will be assessed. Both versions will be compared and validated using EOBS data.

  18. Strength Comparison of Flawed Single-Layer and Multilayer AISI 301 Stainless Steel Pressure Vessels at Cryogenic Temperatures

    National Research Council Canada - National Science Library

    Pierce, William

    1965-01-01

    An experimental investigation was conducted to determine the strengths of single-layer and multilayer scale model tanks of AISI 301 stainless steel containing sharp notches and having the same total wall thickness...

  19. Effect of Substrate Permittivity and Thickness on Performance of Single-Layer, Wideband, U-Slot Antennas on Microwave Substrates

    National Research Council Canada - National Science Library

    Natarajan, V; Chatterjee, D

    2004-01-01

    This paper presents effects of substrate permittivity and thickness on the performance characteristics like impedance bandwidth, radiation efficiency and gain of a single-layer, wideband, U-slot antenna...

  20. Electronic origin of high-temperature superconductivity in single-layer FeSe superconductor.

    Science.gov (United States)

    Liu, Defa; Zhang, Wenhao; Mou, Daixiang; He, Junfeng; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Zhao, Lin; He, Shaolong; Peng, Yingying; Liu, Xu; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Hu, Jiangping; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2012-07-03

    The recent discovery of high-temperature superconductivity in iron-based compounds has attracted much attention. How to further increase the superconducting transition temperature (T(c)) and how to understand the superconductivity mechanism are two prominent issues facing the current study of iron-based superconductors. The latest report of high-T(c) superconductivity in a single-layer FeSe is therefore both surprising and significant. Here we present investigations of the electronic structure and superconducting gap of the single-layer FeSe superconductor. Its Fermi surface is distinct from other iron-based superconductors, consisting only of electron-like pockets near the zone corner without indication of any Fermi surface around the zone centre. Nearly isotropic superconducting gap is observed in this strictly two-dimensional system. The temperature dependence of the superconducting gap gives a transition temperature T(c)~ 55 K. These results have established a clear case that such a simple electronic structure is compatible with high-T(c) superconductivity in iron-based superconductors.

  1. Single layer porous media with entrapped minerals for microscale studies of multiphase flow.

    Science.gov (United States)

    Liefferink, R W; Naillon, A; Bonn, D; Prat, M; Shahidzadeh, N

    2018-03-27

    The behaviour of minerals (i.e. salts) such as sodium chloride and calcite in porous media is very important in various applications such as weathering of artworks, oil recovery and CO2 sequestration. We report a novel method for manufacturing single layer porous media in which minerals can be entrapped in a controlled way in order to study their dissolution and recrystallization. In addition, our manufacturing method is a versatile tool for creating monomodal, bimodal or multimodal pore size microporous media with controlled porosity ranging from 25% to 50%. These micromodels allow multiphase flows to be quantitatively studied with different microscopy techniques and can serve to validate numerical models that can subsequently be extended to the 3D situation where visualization is experimentally difficult. As an example of their use, deliquescence (dissolution by moisture absorption) of entrapped NaCl crystals is studied; our results show that the invasion of the resulting salt solution is controlled by the capillary pressure within the porous network. For hydrophilic porous media, the liquid preferentially invades the small pores whereas in a hydrophobic network the large pores are filled. Consequently, after several deliquescence/drying cycles in the hydrophilic system, the salt is transported towards the outside of the porous network via small pores; in hydrophobic micromodels, no salt migration is observed. Numerical simulations based on the characteristics of our single layer pore network agree very well with the experimental results and give more insight into the dynamics of salt transport through porous media.

  2. Charge transferred doping of single layer graphene by mono-dispersed manganese-oxide nanoparticles adsorption

    Science.gov (United States)

    Phan, Thanh Luan; Kang, Myunggoo; Choi, Soo Ho; Kim, You Joong; Jung, Hyun; Yoon, Im Taek; Yang, Woochul

    2017-10-01

    We report an efficient and controllable method to introduce p-type doping in graphene by decoration with Mn3O4 nanoparticles (NPs) on mechanically exfoliated single layer graphene. A monolayer of Mn3O4 NPs, with a diameter in the range of 5-10 nm, was decorated on a graphene film using an ex-situ method, whereas by controlling the coverage of the NPs on the graphene surface, the carrier concentration could be continually adjusted. The p-type of the NP-decorated single layer graphene was confirmed by the Raman G-band. It was found that the carrier concentration could be gradually adjusted up to 26.09 × 1012 cm-2, with 90% coverage of Mn3O4 NPs. The Dirac point of the pristine graphene at the gate bias of 27 V shifted to 150 V for Mn3O4 NP decorated graphene. The p-type graphene doped with Mn3O4 NPs demonstrated significant high air-stability, even under an oxygen atmosphere for 60 days. This approach allows for the opportunity for simple, scalable, and highly stable doping of graphene for future high-performance electronic device applications.

  3. Strong piezoelectricity in single-layer graphene deposited on SiO2 grating substrates.

    Science.gov (United States)

    da Cunha Rodrigues, Gonçalo; Zelenovskiy, Pavel; Romanyuk, Konstantin; Luchkin, Sergey; Kopelevich, Yakov; Kholkin, Andrei

    2015-06-25

    Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V(-1), that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

  4. Epitaxial Single-Layer MoS2 on GaN with Enhanced Valley Helicity

    KAUST Repository

    Wan, Yi

    2017-12-19

    Engineering the substrate of 2D transition metal dichalcogenides can couple the quasiparticle interaction between the 2D material and substrate, providing an additional route to realize conceptual quantum phenomena and novel device functionalities, such as realization of a 12-time increased valley spitting in single-layer WSe2 through the interfacial magnetic exchange field from a ferromagnetic EuS substrate, and band-to-band tunnel field-effect transistors with a subthreshold swing below 60 mV dec−1 at room temperature based on bilayer n-MoS2 and heavily doped p-germanium, etc. Here, it is demonstrated that epitaxially grown single-layer MoS2 on a lattice-matched GaN substrate, possessing a type-I band alignment, exhibits strong substrate-induced interactions. The phonons in GaN quickly dissipate the energy of photogenerated carriers through electron–phonon interaction, resulting in a short exciton lifetime in the MoS2/GaN heterostructure. This interaction enables an enhanced valley helicity at room temperature (0.33 ± 0.05) observed in both steady-state and time-resolved circularly polarized photoluminescence measurements. The findings highlight the importance of substrate engineering for modulating the intrinsic valley carriers in ultrathin 2D materials and potentially open new paths for valleytronics and valley-optoelectronic device applications.

  5. Tuning the band structure and superconductivity in single-layer FeSe by interface engineering.

    Science.gov (United States)

    Peng, R; Xu, H C; Tan, S Y; Cao, H Y; Xia, M; Shen, X P; Huang, Z C; Wen, C H P; Song, Q; Zhang, T; Xie, B P; Gong, X G; Feng, D L

    2014-09-26

    The interface between transition metal compounds provides a rich playground for emergent phenomena. Recently, significantly enhanced superconductivity has been reported for single-layer FeSe on Nb-doped SrTiO3 substrate. Yet it remains mysterious how the interface affects the superconductivity. Here we use in situ angle-resolved photoemission spectroscopy to investigate various FeSe-based heterostructures grown by molecular beam epitaxy, and uncover that electronic correlations and superconducting gap-closing temperature (Tg) are tuned by interfacial effects. Tg up to 75 K is observed in extremely tensile-strained single-layer FeSe on Nb-doped BaTiO3, which sets a record high pairing temperature for both Fe-based superconductor and monolayer-thick films, providing a promising prospect on realizing more cost-effective superconducting device. Moreover, our results exclude the direct correlation between superconductivity and tensile strain or the energy of an interfacial phonon mode, and highlight the critical and non-trivial role of FeSe/oxide interface on the high Tg, which provides new clues for understanding its origin.

  6. Gold Dispersion and Activation on the Basal Plane of Single-Layer MoS2

    KAUST Repository

    Merida, Cindy S.

    2017-12-09

    Gold islands are typically associated with high binding affinity to adsorbates and catalytic activity. Here we present the growth of such dispersed nanoscale gold islands on single layer MoS2, prepared on an inert SiO2/Si support by chemical vapor deposition (CVD). This study offers a combination of growth process development, optical characterization, photoelectron spectroscopy at sub-micron spatial resolution, and advanced density functional theory modeling for detailed insight into the electronic interaction between gold and single-layer MoS2. In particular, we find the gold density of states in Au/MoS2/SiO2/Si to be far less well-defined than Au islands on other 2-dimensional materials such as graphene, for which we also provide data. We attribute this effect to the presence of heterogeneous Au adatom/MoS2-support interactions within the nanometer-scale gold cluster. As a consequence, theory predicts that CO will exhibit adsorption energies in excess of 1 eV at the Au cluster edges, where the local density of states is dominated by Au 5dz2 symmetry.

  7. Quality of bull spermatozoa after preparation by single-layer centrifugation.

    Science.gov (United States)

    Goodla, Lavanya; Morrell, Jane M; Yusnizar, Yulnawati; Stålhammar, Hans; Johannisson, Anders

    2014-01-01

    The present study aimed to evaluate the effect of single-layer centrifugation (SLC) through a species-specific colloid (Androcoll-B; patent pending, J. M. Morrell) on bull sperm quality. Computer-assisted sperm analysis of motility and flow cytometric analysis of sperm viability (SYBR-14/propidium iodide staining), chromatin integrity (acridine orange staining), reactive oxygen species production [Hoechst 33258-hydroethidine-2',7'-dichlorodihydrofluorescein diacetate (HO-HE-DCFDA) staining], mitochondrial membrane potential (staining with JC-1 probe), and protein tyrosine phosphorylation (specific antibody staining) were performed on unselected and SLC-selected sperm samples. Single-layer centrifugation of bull spermatozoa resulted in the selection of a sperm population that had high mitochondrial membrane potential, a higher content of phosphorylated protein, and more reactive oxygen species than control samples. Sperm chromatin damage was lower in the SLC samples although sperm viability and motility did not differ between SLC samples and controls. These observations suggest that SLC of bull semen in a soybean-containing extender improved some, but not all, parameters of sperm quality. Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

  8. Single Layer Nanomaterials: The Chemical Vapor Deposition Synthesis and Atomic Scale Characterization of Hexagonal Boron Nitride and Graphene

    OpenAIRE

    Gibb, Ashley L

    2015-01-01

    The design of novel nanomaterials with tunable geometries and properties has transformed chemistry and physics in recent years. In particular, recent advances in the isolation of two-dimensional films have inspired the exploration and development of stable, self-supporting single layer systems. Most notably graphene, a single layer of hexagonal sp2 carbon, has attracted interest due to intriguing electronic, optical, and mechanical properties. Hexagonal boron nitride (h-BN) is a closely relat...

  9. Magneto-transport in the zero-energy Landau level of single-layer and bilayer graphene

    International Nuclear Information System (INIS)

    Zeitler, U; Giesbers, A J M; Elferen, H J van; Kurganova, E V; McCollam, A; Maan, J C

    2011-01-01

    We present recent low-temperature magnetotransport experiments on single-layer and bilayer graphene in high magnetic field up to 33 T. In single layer graphene the fourfold degeneracy of the zero-energy Landau level is lifted by a gap opening at filling factor ν = 0. In bilayer graphene, we observe a partial lifting of the degeneracy of the eightfold degenerate zero-energy Landau level.

  10. Smartphone based hemispherical photography for canopy structure measurement

    Science.gov (United States)

    Wan, Xuefen; Cui, Jian; Jiang, Xueqin; Zhang, Jingwen; Yang, Yi; Zheng, Tao

    2018-01-01

    The canopy is the most direct and active interface layer of the interaction between plant and environment, and has important influence on energy exchange, biodiversity, ecosystem matter and climate change. The measurement about canopy structure of plant is an important foundation to analyze the pattern, process and operation mechanism of forest ecosystem. Through the study of canopy structure of plant, solar radiation, ambient wind speed, air temperature and humidity, soil evaporation, soil temperature and other forest environmental climate characteristics can be evaluated. Because of its accuracy and effectiveness, canopy structure measurement based on hemispherical photography has been widely studied. However, the traditional method of canopy structure hemispherical photogrammetry based on SLR camera and fisheye lens. This method is expensive and difficult to be used in some low-cost occasions. In recent years, smartphone technology has been developing rapidly. The smartphone not only has excellent image acquisition ability, but also has the considerable computational processing ability. In addition, the gyroscope and positioning function on the smartphone will also help to measure the structure of the canopy. In this paper, we present a smartphone based hemispherical photography system. The system consists of smart phones, low-cost fisheye lenses and PMMA adapters. We designed an Android based App to obtain the canopy hemisphere images through low-cost fisheye lenses and provide horizontal collimation information. In addition, the App will add the acquisition location tag obtained by GPS and auxiliary positioning method in hemisphere image information after the canopy structure hemisphere image acquisition. The system was tested in the urban forest after it was completed. The test results show that the smartphone based hemispherical photography system can effectively collect the high-resolution canopy structure image of the plant.

  11. Negative quantum capacitance induced by midgap states in single-layer graphene.

    Science.gov (United States)

    Wang, Lin; Wang, Yang; Chen, Xiaolong; Zhu, Wei; Zhu, Chao; Wu, Zefei; Han, Yu; Zhang, Mingwei; Li, Wei; He, Yuheng; Xiong, Wei; Law, Kam Tuen; Su, Dangsheng; Wang, Ning

    2013-01-01

    We demonstrate that single-layer graphene (SLG) decorated with a high density of Ag adatoms displays the unconventional phenomenon of negative quantum capacitance. The Ag adatoms act as resonant impurities and form nearly dispersionless resonant impurity bands near the charge neutrality point (CNP). Resonant impurities quench the kinetic energy and drive the electrons to the Coulomb energy dominated regime with negative compressibility. In the absence of a magnetic field, negative quantum capacitance is observed near the CNP. In the quantum Hall regime, negative quantum capacitance behavior at several Landau level positions is displayed, which is associated with the quenching of kinetic energy by the formation of Landau levels. The negative quantum capacitance effect near the CNP is further enhanced in the presence of Landau levels due to the magnetic-field-enhanced Coulomb interactions.

  12. Effect of humid-thermal environment on wave dispersion characteristics of single-layered graphene sheets

    Science.gov (United States)

    Ebrahimi, Farzad; Dabbagh, Ali

    2018-04-01

    In the present article, the hygro-thermal wave propagation properties of single-layered graphene sheets (SLGSs) are investigated for the first time employing a nonlocal strain gradient theory. A refined higher-order two-variable plate theory is utilized to derive the kinematic relations of graphene sheets. Here, nonlocal strain gradient theory is used to achieve a more precise analysis of small-scale plates. In the framework of the Hamilton's principle, the final governing equations are developed. Moreover, these obtained equations are deemed to be solved analytically and the wave frequency values are achieved. Some parametric studies are organized to investigate the influence of different variants such as nonlocal parameter, length scale parameter, wave number, temperature gradient and moisture concentration on the wave frequency of graphene sheets.

  13. Large theoretical thermoelectric power factor of suspended single-layer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Babaei, Hasan, E-mail: babaei@illinois.edu, E-mail: babaei@auburn.edu [Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-2906 (United States); Mechanical Engineering Department, Auburn University, Auburn, Alabama 36849-5341 (United States); Khodadadi, J. M. [Mechanical Engineering Department, Auburn University, Auburn, Alabama 36849-5341 (United States); Sinha, Sanjiv [Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-2906 (United States)

    2014-11-10

    We have calculated the semi-classical thermoelectric power factor of suspended single-layer (SL)- MoS{sub 2} utilizing electron relaxation times derived from ab initio calculations. Measurements of the thermoelectric power factor of SL-MoS{sub 2} on substrates reveal poor power factors. In contrast, we find the thermoelectric power factor of suspended SL-MoS{sub 2} to peak at ∼2.8 × 10{sup 4} μW/m K{sup 2} at 300 K, at an electron concentration of 10{sup 12} cm{sup −2}. This figure is higher than that in bulk Bi{sub 2}Te{sub 3}, for example. Given its relatively high thermal conductivity, suspended SL-MoS{sub 2} may hold promise for in-plane thin-film Peltier coolers, provided reasonable mobilities can be realized.

  14. Moisture barrier properties of single-layer graphene deposited on Cu films for Cu metallization

    Science.gov (United States)

    Gomasang, Ploybussara; Abe, Takumi; Kawahara, Kenji; Wasai, Yoko; Nabatova-Gabain, Nataliya; Thanh Cuong, Nguyen; Ago, Hiroki; Okada, Susumu; Ueno, Kazuyoshi

    2018-04-01

    The moisture barrier properties of large-grain single-layer graphene (SLG) deposited on a Cu(111)/sapphire substrate are demonstrated by comparing with the bare Cu(111) surface under an accelerated degradation test (ADT) at 85 °C and 85% relative humidity (RH) for various durations. The change in surface color and the formation of Cu oxide are investigated by optical microscopy (OM) and X-ray photoelectron spectroscopy (XPS), respectively. First-principle simulation is performed to understand the mechanisms underlying the barrier properties of SLG against O diffusion. The correlation between Cu oxide thickness and SLG quality are also analyzed by spectroscopic ellipsometry (SE) measured on a non-uniform SLG film. SLG with large grains shows high performance in preventing the Cu oxidation due to moisture during ADT.

  15. Single layered flexible photo-detector based on perylene/graphene composite through printed technology

    Science.gov (United States)

    Ali, Shawkat; Bae, Jinho; Lee, Chong Hyun

    2015-07-01

    In this paper, a single layered passive photo sensor based on perylene/graphene composite is proposed, which is deposited in comb type silver electrodes separated as 50 μm spacing. To increase an electrical conductivity of the proposed sensor, perylene and graphene are blended. Photo sensing layer (120nm thick) and Silver electrodes (50 μm width, 350 nm thick) are deposited on poly(ethylene terephthalate) (PET) substrate through electro-hydrodynamic (EHD) system. The proposed photo sensor detects a terminal resistance inversely varied by an incident light in the range between 78 GΩ in dark and 25 GΩ at light intensity of 400lux. The device response is maximum at 465 nm ~ 535 nm wavelength range at blue light. The device exhibited bendability up to 4mm diameter for 1000 endurance cycles. The surface morphology analysis is carried out with FE-SEM and microscope.

  16. A visualization method for probing grain boundaries of single layer graphene via molecular beam epitaxy

    Science.gov (United States)

    Zhan, Linjie; Wan, Wen; Zhu, Zhenwei; Zhao, Zhijuan; Zhang, Zhenhan; Shih, Tien-Mo; Cai, Weiwei

    2017-07-01

    Graphene, a member of layered two-dimensional (2D) materials, possesses high carrier mobility, mechanical flexibility, and optical transparency, as well as enjoying a wide range of promising applications in electronics. Adopting the chemical vaporization deposition method, the majority of investigators have ubiquitously grown single layer graphene (SLG), which inevitably involves polycrystalline properties. Here we demonstrate a simple method for the direct visualization of arbitrarily large-size SLG domains by synthesizing one-hundred-nm-scale MoS2 single crystals via a high-vacuum molecular beam epitaxy process. The present study based on epitaxial growth provides a guide for probing the grain boundaries of various 2D materials and implements higher potentials for the next-generation electronic devices.

  17. Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe 2

    KAUST Repository

    Zhang, Chendong

    2015-09-21

    By using a comprehensive form of scanning tunneling spectroscopy, we have revealed detailed quasi-particle electronic structures in transition metal dichalcogenides, including the quasi-particle gaps, critical point energy locations, and their origins in the Brillouin zones. We show that single layer WSe surprisingly has an indirect quasi-particle gap with the conduction band minimum located at the Q-point (instead of K), albeit the two states are nearly degenerate. We have further observed rich quasi-particle electronic structures of transition metal dichalcogenides as a function of atomic structures and spin-orbit couplings. Such a local probe for detailed electronic structures in conduction and valence bands will be ideal to investigate how electronic structures of transition metal dichalcogenides are influenced by variations of local environment.

  18. Polarized dependence of nonlinear susceptibility in a single layer graphene system in infrared region

    Energy Technology Data Exchange (ETDEWEB)

    Solookinejad, G., E-mail: ghsolooki@gmail.com

    2016-09-15

    In this study, the linear and nonlinear susceptibility of a single-layer graphene nanostructure driven by a weak probe light and an elliptical polarized coupling field is discussed theoretically. The Landau levels of graphene can be separated in infrared or terahertz regions under the strong magnetic field. Therefore, by using the density matrix formalism in quantum optic, the linear and nonlinear susceptibility of the medium can be derived. It is demonstrated that by adjusting the elliptical parameter, one can manipulate the linear and nonlinear absorption as well as Kerr nonlinearity of the medium. It is realized that the enhanced Kerr nonlinearity can be possible with zero linear absorption and nonlinear amplification at some values of elliptical parameter. Our results may be having potential applications in quantum information science based on Nano scales devices.

  19. Tensile loading induced phase transition and rippling in single-layer MoS2

    Science.gov (United States)

    Bao, Hongwei; Huang, Yuhong; Yang, Zhi; Miao, Yaping; Chu, Paul K.; Xu, Kewei; Ma, Fei

    2017-05-01

    Molecular dynamics (MD) simulation is performed to study the structural evolution of single-layer MoS2 nanosheets under tensile loading and a phase transition from hexagonal structure to quadrilateral one is observed at a large strain when loaded along the zigzag direction but not along the armchair direction. Density functional theory (DFT) calculation illustrates that the newly generated quadrilateral phase is metallic. Further loading along the zigzag direction promotes an inhomogeneous distribution of lateral and shear stress around the phase boundaries due to local mechanical mismatch. As a result, periodic rippling parallel to the loading direction emerges and the wavelength and wave height change with strain according to λ∼ε-1/4 and h∼ε1/4. Accordingly, a graded distribution of strain can be produced or modulated by a simple tensile loading and the strategy might be utilized to enhance the photoelectrical properties of 2D materials and design strain-tunable nanodevices.

  20. Effect of quenched disorder on charge-orbital-spin ordering in single-layer manganites

    International Nuclear Information System (INIS)

    Uchida, Masaya; Mathieu, Roland; He, Jinping; Kaneko, Yoshio; Tokura, Yoshinori; Asamitsu, Atsushi; Kumai, Reiji; Tomioka, Yasuhide; Matsui, Yoshio

    2006-01-01

    Structural and magnetic properties have been investigated for half-doped single-layer manganites RE 0.5 Sr 1.5 MnO 4 [RE=La, (La, Pr), Pr, Nd, Sm, and Eu]. Analyses of electron diffraction and ac susceptibility measurements have revealed that the long-range charge-orbital ordering (CO-OO) state as observed in La 0.5 Sr 1.5 MnO 4 is suppressed for the other materials: the CO-OO transition temperature, as well as the correlation length decreases with a decrease in the cation size of RE. Such a short-range CO-OO state shows a spin-glass behavior at low temperatures. A new electronic phase diagram is established with quenched disorder as the control parameter. (author)

  1. Biomimetic plasmonic color generated by the single-layer coaxial honeycomb nanostructure arrays

    Science.gov (United States)

    Zhao, Jiancun; Gao, Bo; Li, Haoyong; Yu, Xiaochang; Yang, Xiaoming; Yu, Yiting

    2017-07-01

    We proposed a periodic coaxial honeycomb nanostructure array patterned in a silver film to realize the plasmonic structural color, which was inspired from natural honeybee hives. The spectral characteristics of the structure with variant geometrical parameters are investigated by employing a finite-difference time-domain method, and the corresponding colors are thus derived by calculating XYZ tristimulus values corresponding with the transmission spectra. The study demonstrates that the suggested structure with only a single layer has high transmission, narrow full-width at half-maximum, and wide color tunability by changing geometrical parameters. Therefore, the plasmonic colors realized possess a high color brightness, saturation, as well as a wide color gamut. In addition, the strong polarization independence makes it more attractive for practical applications. These results indicate that the recommended color-generating plasmonic structure has various potential applications in highly integrated optoelectronic devices, such as color filters and high-definition displays.

  2. Thermal vibration of rectangular single-layered black phosphorus predicted by orthotropic plate model

    Science.gov (United States)

    Zhang, Yiqing; Wang, Lifeng; Jiang, Jingnong

    2018-03-01

    Vibrational behavior is very important for nanostructure-based resonators. In this work, an orthotropic plate model together with a molecular dynamics (MD) simulation is used to investigate the thermal vibration of rectangular single-layered black phosphorus (SLBP). Two bending stiffness, two Poisson's ratios, and one shear modulus of SLBP are calculated using the MD simulation. The natural frequency of the SLBP predicted by the orthotropic plate model agrees with the one obtained from the MD simulation very well. The root of mean squared (RMS) amplitude of the SLBP is obtained by MD simulation and the orthotropic plate model considering the law of energy equipartition. The RMS amplitude of the thermal vibration of the SLBP is predicted well by the orthotropic plate model compared to the MD results. Furthermore, the thermal vibration of the SLBP with an initial stress is also well-described by the orthotropic plate model.

  3. Water desalination with a single-layer MoS2 nanopore

    Science.gov (United States)

    Heiranian, Mohammad; Farimani, Amir Barati; Aluru, Narayana R.

    2015-01-01

    Efficient desalination of water continues to be a problem facing the society. Advances in nanotechnology have led to the development of a variety of nanoporous membranes for water purification. Here we show, by performing molecular dynamics simulations, that a nanopore in a single-layer molybdenum disulfide can effectively reject ions and allow transport of water at a high rate. More than 88% of ions are rejected by membranes having pore areas ranging from 20 to 60 Å2. Water flux is found to be two to five orders of magnitude greater than that of other known nanoporous membranes. Pore chemistry is shown to play a significant role in modulating the water flux. Pores with only molybdenum atoms on their edges lead to higher fluxes, which are ∼70% greater than that of graphene nanopores. These observations are explained by permeation coefficients, energy barriers, water density and velocity distributions in the pores. PMID:26465062

  4. Large theoretical thermoelectric power factor of suspended single-layer MoS2

    International Nuclear Information System (INIS)

    Babaei, Hasan; Khodadadi, J. M.; Sinha, Sanjiv

    2014-01-01

    We have calculated the semi-classical thermoelectric power factor of suspended single-layer (SL)- MoS 2 utilizing electron relaxation times derived from ab initio calculations. Measurements of the thermoelectric power factor of SL-MoS 2 on substrates reveal poor power factors. In contrast, we find the thermoelectric power factor of suspended SL-MoS 2 to peak at ∼2.8 × 10 4 μW/m K 2 at 300 K, at an electron concentration of 10 12 cm −2 . This figure is higher than that in bulk Bi 2 Te 3 , for example. Given its relatively high thermal conductivity, suspended SL-MoS 2 may hold promise for in-plane thin-film Peltier coolers, provided reasonable mobilities can be realized

  5. The strain rate effect on the buckling of single-layer MoS2.

    Science.gov (United States)

    Jiang, Jin-Wu

    2015-01-15

    The Euler buckling theory states that the buckling critical strain is an inverse quadratic function of the length for a thin plate in the static compression process. However, the suitability of this theory in the dynamical process is unclear, so we perform molecular dynamics simulations to examine the applicability of the Euler buckling theory for the fast compression of the single-layer MoS2. We find that the Euler buckling theory is not applicable in such dynamical process, as the buckling critical strain becomes a length-independent constant in the buckled system with many ripples. However, the Euler buckling theory can be resumed in the dynamical process after restricting the theory to an individual ripple in the buckled structure.

  6. Growth and electronic structure of single-layered transition metal dichalcogenides

    DEFF Research Database (Denmark)

    Dendzik, Maciej

    2016-01-01

    The discovery of graphene has opened a novel research direction focused on the properties of 2D materials. Transition metal dichalcogenides (TMDCs) were quickly identified as important materials due to the great variety of electronic properties that they manifest – properties that are markedly...... different from graphene’s. For example, semiconducting TMDCs undergo an indirectdirect band gap transition when thinned to a single layer (SL); this results in greatly enhanced photoluminescence, making those materials attractive for applications in optoelectronics. Furthermore, metallic TMDCs can host...... TMDCs is directly studied with angle-resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy (XPS) techniques. Experimental results are compared with density-functional theory calculations (DFT), both for a free-standing layer and for a layer adsorbed on a metallic substrate...

  7. Anomalous photoluminescence thermal quenching of sandwiched single layer MoS_2

    KAUST Repository

    Tangi, Malleswararao

    2017-09-22

    We report an unusual thermal quenching of the micro-photoluminescence (µ-PL) intensity for a sandwiched single-layer (SL) MoS2. For this study, MoS2 layers were chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N lattice matched templates. Later, to accomplish air-stable sandwiched SL-MoS2, a thin In0.15Al0.85N cap layer was deposited on the MoS2/In0.15Al0.85N heterostructure. We confirm that the sandwiched MoS2 is a single layer from optical and structural analyses using µ-Raman spectroscopy and scanning transmission electron microscopy, respectively. By using high-resolution X-ray photoelectron spectroscopy, no structural phase transition of MoS2 is noticed. The recombination processes of bound and free excitons were analyzed by the power-dependent µ-PL studies at 77 K and room temperature (RT). The temperature-dependent micro photoluminescence (TDPL) measurements were carried out in the temperature range of 77 – 400 K. As temperature increases, a significant red-shift is observed for the free-exciton PL peak, revealing the delocalization of carriers. Further, we observe unconventional negative thermal quenching behavior, the enhancement of the µ-PL intensity with increasing temperatures up to 300K, which is explained by carrier hopping transitions that take place between shallow localized states to the band-edges. Thus, this study renders a fundamental insight into understanding the anomalous thermal quenching of µ-PL intensity of sandwiched SL-MoS2.

  8. Single-Layer Plication for Repair of Diastasis Recti: The Most Rapid and Efficient Technique.

    Science.gov (United States)

    Gama, Luiz José Muaccad; Barbosa, Marcus Vinicius Jardini; Czapkowski, Adriano; Ajzen, Sergio; Ferreira, Lydia Masako; Nahas, Fábio Xerfan

    2017-06-01

    Plication of the anterior rectus sheath is the most commonly used technique for repair of diastasis recti, but is also a time-consuming procedure. The aim of this study was to compare the efficacy and time required to repair diastasis recti using different plication techniques. Thirty women with similar abdominal deformities, who had had at least one pregnancy, were randomized into three groups to undergo abdominoplasty. Plication of the anterior rectus sheath was performed in two layers with 2-0 monofilament nylon suture (control group) or in a single layer with either a continuous 2-0 monofilament nylon suture (group I) or using a continuous barbed suture (group II). Operative time was recorded. All patients underwent ultrasound examination preoperatively and at 3 weeks and 6 months postoperatively to monitor for diastasis recurrence. The force required to bring the anterior rectus sheath to the midline was measured at the supraumbilical and infraumbilical levels. Patient age ranged from 26 to 50 years and body mass index from 20.56 to 29.17 kg/m2. A significant difference in mean operative time was found between the control and study groups (control group, 35 min:22 s; group I, 14 min:22 s; group II, 15 min:23 s; P < 0.001). Three patients in group II had recurrence of diastasis. There were no significant within- and between-group differences in tensile force on the aponeurosis. Plication of the anterior rectus sheath in a single-layer with a continuous suture showed to be an efficient and rapid technique for repair of diastasis recti. © 2017 The American Society for Aesthetic Plastic Surgery, Inc. Reprints and permission: journals.permissions@oup.com

  9. Giant magnetoimpedance effect in sputtered single layered NiFe film and meander NiFe/Cu/NiFe film

    International Nuclear Information System (INIS)

    Chen, L.; Zhou, Y.; Lei, C.; Zhou, Z.M.; Ding, W.

    2010-01-01

    Giant magnetoimpedance (GMI) effect on NiFe thin film is very promising due to its application in developing the magnetic field sensors with highly sensitivity and low cost. In this paper, the single layered NiFe thin film and NiFe/Cu/NiFe thin film with a meander structure are prepared by the MEMS technology. The influences of sputtering parameters, film structure and conductor layer width on GMI effect in NiFe single layer and meander NiFe/Cu/NiFe film are investigated. Maximum of the GMI ratio in single layer and sandwich film is 5% and 64%, respectively. The results obtained are useful for developing the high-performance magnetic sensors based on NiFe thin film.

  10. Tuning Electronic Structure of Single Layer MoS2through Defect and Interface Engineering.

    Science.gov (United States)

    Chen, Yan; Huang, Shengxi; Ji, Xiang; Adepalli, Kiran; Yin, Kedi; Ling, Xi; Wang, Xinwei; Xue, Jianmin; Dresselhaus, Mildred; Kong, Jing; Yildiz, Bilge

    2018-03-27

    Transition-metal dichalcogenides (TMDs) have emerged in recent years as a special group of two-dimensional materials and have attracted tremendous attention. Among these TMD materials, molybdenum disulfide (MoS 2 ) has shown promising applications in electronics, photonics, energy, and electrochemistry. In particular, the defects in MoS 2 play an essential role in altering the electronic, magnetic, optical, and catalytic properties of MoS 2 , presenting a useful way to engineer the performance of MoS 2 . The mechanisms by which lattice defects affect the MoS 2 properties are unsettled. In this work, we reveal systematically how lattice defects and substrate interface affect MoS 2 electronic structure. We fabricated single-layer MoS 2 by chemical vapor deposition and then transferred onto Au, single-layer graphene, hexagonal boron nitride, and CeO 2 as substrates and created defects in MoS 2 by ion irradiation. We assessed how these defects and substrates affect the electronic structure of MoS 2 by performing X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, and scanning tunneling microscopy/spectroscopy measurements. Molecular dynamics and first-principles based simulations allowed us to conclude the predominant lattice defects upon ion irradiation and associate those with the experimentally obtained electronic structure. We found that the substrates can tune the electronic energy levels in MoS 2 due to charge transfer at the interface. Furthermore, the reduction state of CeO 2 as an oxide substrate affects the interface charge transfer with MoS 2 . The irradiated MoS 2 had a faster hydrogen evolution kinetics compared to the as-prepared MoS 2 , demonstrating the concept of defect controlled reactivity in this phase. Our findings provide effective probes for energy band and defects in MoS 2 and show the importance of defect engineering in tuning the functionalities of MoS 2 and other TMDs in electronics, optoelectronics, and

  11. Potential impacts of urban land expansion on Asian airborne pollutant outflows

    Science.gov (United States)

    Tao, Wei; Liu, Junfeng; Ban-Weiss, George A.; Zhang, Lin; Zhang, Jiachen; Yi, Kan; Tao, Shu

    2017-07-01

    Eastern part of China (EPC) has experienced rapid urbanization during the past few decades. Here we investigate the impacts of urban land expansion over EPC on the export of Asian pollutants to the western Pacific during January, April, July, and October of 2009 using the Weather Research and Forecasting model coupled to Chemistry (WRF/Chem) and a single-layer urban canopy scheme. Over urbanizing areas, increases in the urban land fraction result in a linearly enhanced uplift of surface primary pollutants to higher altitudes. We further examine how this local effect would change outflows of Asian pollutants to the western Pacific using the tagged black carbon (BC) and carbon monoxide (CO) tracers emitted from EPC (denoted by BCt and COt, respectively). Overall, a 0.1 increase in the fraction of land area that is urban over EPC would linearly (R2 = 0.70-0.96) increase the mean tropospheric eastward export of BCt and COt across meridional planes (i.e., 135°E and 150°E) by 4-40% and 1-6% in different months, respectively. The relative perturbation in exporting efficiency generally maximizes during July while minimizes during April. The urbanization-export relationship is largely driven by the elevation effect and is also impacted by urbanization-forced changes in zonal winds. The spatial pattern of the response of BCt over the downwind Pacific differs from that of COt mainly due to aerosol-cloud interactions. Our findings demonstrate that extensive urban land expansion could substantially impact climate and air quality from a local scale to a regional scale, especially for shorter-lived air pollutants such as BC and other aerosols.

  12. Regional climate model assessment of the urban land-surface forcing over central Europe

    Directory of Open Access Journals (Sweden)

    P. Huszar

    2014-11-01

    Full Text Available For the purpose of qualifying and quantifying the climate impact of cities and urban surfaces in general on climate of central Europe, the surface parameterization in regional climate model RegCM4 has been extended with the Single-layer Urban Canopy Model (SLUCM. A set of experiments was performed over the period of 2005–2009 for central Europe, either without considering urban surfaces or with the SLUCM treatment. Results show a statistically significant impact of urbanized surfaces on temperature (up to 1.5 K increase in summer as well as on the boundary layer height (increases up to 50 m. Urbanization further influences surface wind with a winter decrease up to −0.6 m s−1, though both increases and decreases were detected in summer depending on the location relative to the cities and daytime (changes up to 0.3 m s−1. Urban surfaces significantly reduce the humidity over the surface. This impacts the simulated summer precipitation rate, showing a decrease over cities of up to −2 mm day−1. Significant temperature increases are simulated over higher altitudes as well, not only within the urban canopy layer. With the urban parameterization, the climate model better describes the diurnal temperature variation, reducing the cold afternoon and evening bias of RegCM4. Sensitivity experiments were carried out to quantify the response of the meteorological conditions to changes in the parameters specific to the urban environment, such as street width, building height, albedo of the roofs and anthropogenic heat release. The results proved to be rather robust and the choice of the key SLUCM parameters impacts them only slightly (mainly temperature, boundary layer height and wind velocity. Statistically significant impacts are modelled not only over large urbanized areas, but the influence of the cities is also evident over rural areas without major urban surfaces. It is shown that this is the result of the combined effect of the distant

  13. The Impacts of Urbanization on Meteorology and Air Quality in the Los Angeles Basin

    Science.gov (United States)

    Li, Y.; Zhang, J.; Sailor, D.; Ban-Weiss, G. A.

    2017-12-01

    Urbanization has a profound influence on regional meteorology in mega cities like Los Angeles. This influence is driven by changes in land surface physical properties and urban processes, and their corresponding influence on surface-atmosphere coupling. Changes in meteorology from urbanization in turn influences air quality through weather-dependent chemical reaction, pollutant dispersion, etc. Hence, a real-world representation of the urban land surface properties and urban processes should be accurately resolved in regional climate-chemistry models for better understanding the role of urbanization on changing urban meteorology and associated pollutant dynamics. By incorporating high-resolution land surface data, previous research has improved model-observation comparisons of meteorology in urban areas including the Los Angeles basin, and indicated that historical urbanization has increased urban temperatures and altered wind flows significantly. However, the impact of urban expansion on air quality has been less studied. Thus, in this study, we aim to evaluate the effectiveness of resolving high-resolution heterogeneity in urban land surface properties and processes for regional weather and pollutant concentration predictions. We coupled the Weather Research and Forecasting model with Chemistry to the single-layer Urban Canopy Model to simulate a typical summer period in year 2012 for Southern California. Land cover type and urban fraction were determined from National Land Cover Data. MODIS observations were used to determine satellite-derived albedo, green vegetation fraction, and leaf area index. Urban morphology was determined from GIS datasets of 3D building geometries. An urban irrigation scheme was also implemented in the model. Our results show that the improved model captures the diurnal cycle of 2m air temperature (T2) and Ozone (O3) concentrations. However, it tends to overestimate wind speed and underestimate T2, which leads to an underestimation of O

  14. Monolithic-Structured Single-Layered Textile-Based Dye-Sensitized Solar Cells

    Science.gov (United States)

    Yun, Min Ju; Cha, Seung I.; Kim, Han Seong; Seo, Seon Hee; Lee, Dong Y.

    2016-10-01

    Textile-structured solar cells are frequently discussed in the literature due to their prospective applications in wearable devices and in building integrated solar cells that utilize their flexibility, mechanical robustness, and aesthetic appearance, but the current approaches for textile-based solar cells—including the preparation of fibre-type solar cells woven into textiles—face several difficulties from high friction and tension during the weaving process. This study proposes a new structural concept and fabrication process for monolithic-structured textile-based dye-sensitized solar cells that are fabricated by a process similar to the cloth-making process, including the preparation of wires and yarns that are woven for use in textiles, printed, dyed, and packaged. The fabricated single-layered textile-based dye-sensitized solar cells successfully act as solar cells in our study, even under bending conditions. By controlling the inter-weft spacing and the number of Ti wires for the photoelectrode conductor, we have found that the performance of this type of dye-sensitized solar cell was notably affected by the spacing between photoelectrodes and counter-electrodes, the exposed areas of Ti wires to photoelectrodes, and photoelectrodes’ surface morphology. We believe that this study provides a process and concept for improved textile-based solar cells that can form the basis for further research.

  15. Field electron emission characteristics and physical mechanism of individual single-layer graphene.

    Science.gov (United States)

    Xiao, Zhiming; She, Juncong; Deng, Shaozhi; Tang, Zikang; Li, Zhibing; Lu, Jianming; Xu, Ningsheng

    2010-11-23

    Due to its difficulty, experimental measurement of field emission from a single-layer graphene has not been reported, although field emission from a two-dimensional (2D) regime has been an attractive topic. The open surface and sharp edge of graphene are beneficial for field electron emission. A 2D geometrical effect, such as massless Dirac fermion, can lead to new mechanisms in field emission. Here, we report our findings from in situ field electron emission characterization on an individual singe-layer graphene and the understanding of the related mechanism. The measurement of field emission from the edges was done using a microanode probe equipped in a scanning electron microscope. We show that repeatable stable field emission current can be obtained after a careful conditioning process. This enables us to examine experimentally the typical features of the field emission from a 2D regime. We plot current versus applied field data, respectively, in ln(I/E(3/2)) ∼ 1/E and ln(I/E(3)) ∼ 1/E(2) coordinates, which have recently been proposed for field emission from graphene in high- and low-field regimes. It is observed that the plots all exhibit an upward bending feature, revealing that the field emission processes undergo from a low- to high-field transition. We discuss with theoretical analysis the physical mechanism responsible for the new phenomena.

  16. Pregnancy rates after artificial insemination with cooled stallion spermatozoa either with or without single layer centrifugation.

    Science.gov (United States)

    Morrell, J M; Richter, J; Martinsson, G; Stuhtmann, G; Hoogewijs, M; Roels, K; Dalin, A-M

    2014-11-01

    A successful outcome after artificial insemination with cooled semen is dependent on many factors, the sperm quality of the ejaculate being one. Previous studies have shown that spermatozoa with good motility, normal morphology, and good chromatin integrity can be selected by means of colloid centrifugation, particularly single layer centrifugation (SLC) using species-specific colloids. The purpose of the present study was to conduct an insemination trial with spermatozoa from "normal" ejaculates, i.e., from stallions with no known fertility problem, to determine whether the improvements in sperm quality seen in SLC-selected sperm samples compared with uncentrifuged controls in laboratory tests are reflected in an increased pregnancy rate after artificial insemination. In a multicentre study, SLC-selected sperm samples and uncentrifuged controls from eight stallions were inseminated into approximately 10 mares per treatment per stallion. Ultrasound examination was carried out approximately 16 days after insemination to detect an embryonic vesicle. The pregnancy rates per cycle were 45% for controls and 69% for SLC-selected sperm samples, which is statistically significant (P < 0.0018). Thus, the improvement in sperm quality reported previously for SLC-selected sperm samples is associated with an increase in pregnancy rate, even for ejaculates from stallions with no known fertility problem. Copyright © 2014 Elsevier Inc. All rights reserved.

  17. Monolithic-Structured Single-Layered Textile-Based Dye-Sensitized Solar Cells

    Science.gov (United States)

    Yun, Min Ju; Cha, Seung I.; Kim, Han Seong; Seo, Seon Hee; Lee, Dong Y.

    2016-01-01

    Textile-structured solar cells are frequently discussed in the literature due to their prospective applications in wearable devices and in building integrated solar cells that utilize their flexibility, mechanical robustness, and aesthetic appearance, but the current approaches for textile-based solar cells—including the preparation of fibre-type solar cells woven into textiles—face several difficulties from high friction and tension during the weaving process. This study proposes a new structural concept and fabrication process for monolithic-structured textile-based dye-sensitized solar cells that are fabricated by a process similar to the cloth-making process, including the preparation of wires and yarns that are woven for use in textiles, printed, dyed, and packaged. The fabricated single-layered textile-based dye-sensitized solar cells successfully act as solar cells in our study, even under bending conditions. By controlling the inter-weft spacing and the number of Ti wires for the photoelectrode conductor, we have found that the performance of this type of dye-sensitized solar cell was notably affected by the spacing between photoelectrodes and counter-electrodes, the exposed areas of Ti wires to photoelectrodes, and photoelectrodes’ surface morphology. We believe that this study provides a process and concept for improved textile-based solar cells that can form the basis for further research. PMID:27708359

  18. Investigating change of properties in gallium ion irradiation patterned single-layer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Quan, E-mail: wangq@mail.ujs.edu.cn [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (China); Dong, Jinyao; Bai, Bing [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); Xie, Guoxin [State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China)

    2016-10-14

    Besides its excellent physical properties, graphene promises to play a significant role in electronics with superior properties, which requires patterning of graphene for device integration. Here, we presented the changes in properties of single-layer graphene before and after patterning using gallium ion beam. Combined with Raman spectra of graphene, the scanning capacitance microscopy (SCM) image confirmed that a metal–insulator transition occurred after large doses of gallium ion irradiation. The changes in work function and Raman spectra of graphene indicated that the defect density increased as increasing the dose and a structural transition occurred during gallium ion irradiation. The patterning width of graphene presented an increasing trend due to the scattering influence of the impurities and the substrate. - Highlights: • The scanning capacitance microscopy image confirmed a metal–insulator transition occurred after large doses of gallium ion irradiation. • The changes indicated the defect density increased as increasing the dose and a structural transition occurred during gallium ion irradiation. • The patterning width of graphene presented a increasing trend due to the scattering influence of the impurities and the substrate.

  19. First-principles study of single-layer C-terminated BN quantum dots

    Science.gov (United States)

    Qu, Li-Hua; Zhang, Jian-Min; Xu, Ke-Wei

    2013-09-01

    We present a first-principles study of the structural, electronic and magnetic properties of single-layer C-terminated BN quantum dots (QDs) under different hydrotreating conditions. The morphologies of QDs with fully hydrogenated edges change slightly. For the fully bared cases, the edged C-C bonds become short and protrudent edged C atoms relax inwards therefore edged zigzag C chain tends to a straight line. The cases of the partially passivated by hydrogen atom at apex, the apex C atom is not relaxed inwards and a new C-C bond is formed. The fully hydrogenated QDs especially N-rich cases are energetically more favorable than those with bared or partially hydrogenated ones. The C-terminated BN-QDs have no magnetic moment when their protrudent edged C atoms are fully passivated by hydrogen atoms, while those with bared or partially hydrogenated edges possess magnetic moments and especially for N-rich cases their magnetic moments increase with increasing QD size n for either bared or partially hydrogenated edges. The band gap of the fully hydrogenated QDs decreases oscillatorily with increasing QD size n. Moreover, for the same size n, the energy gap is wider under N-rich condition than under B-rich condition.

  20. A single-layer, planar, optofluidic Mach–Zehnder interferometer for label-free detection†

    Science.gov (United States)

    Lapsley, Michael Ian; Chiang, I.-Kao; Zheng, Yue Bing; Ding, Xiaoyun; Mao, Xiaole

    2014-01-01

    We have developed a planar, optofluidic Mach–Zehnder interferometer for the label-free detection of liquid samples. In contrast to most on-chip interferometers which require complex fabrication, our design was realized via a simple, single-layer soft lithography fabrication process. In addition, a single-wavelength laser source and a silicon photodetector were the only optical equipment used for data collection. The device was calibrated using published data for the refractive index of calcium chloride (CaCl2) in solution, and the biosensing capabilities of the device were tested by detecting bovine serum albumin (BSA). Our design enables a refractometer with a low limit of detection (1.24 × 10−4 refractive index units (RIU)), low variability (1 × 10−4 RIU), and high sensitivity (927.88 oscillations per RIU). This performance is comparable to state-of-the-art optofluidic refractometers that involve complex fabrication processes and/or expensive, bulky optics. The advantages of our device (i.e. simple fabrication process, straightforward optical equipment, low cost, and high detection sensitivity) make it a promising candidate for future mass-producible, inexpensive, highly sensitive, label-free optical detection systems. PMID:21479332

  1. A single-layer, planar, optofluidic Mach-Zehnder interferometer for label-free detection.

    Science.gov (United States)

    Lapsley, Michael Ian; Chiang, I-Kao; Zheng, Yue Bing; Ding, Xiaoyun; Mao, Xiaole; Huang, Tony Jun

    2011-05-21

    We have developed a planar, optofluidic Mach-Zehnder interferometer for the label-free detection of liquid samples. In contrast to most on-chip interferometers which require complex fabrication, our design was realized via a simple, single-layer soft lithography fabrication process. In addition, a single-wavelength laser source and a silicon photodetector were the only optical equipment used for data collection. The device was calibrated using published data for the refractive index of calcium chloride (CaCl(2)) in solution, and the biosensing capabilities of the device were tested by detecting bovine serum albumin (BSA). Our design enables a refractometer with a low limit of detection (1.24 × 10(-4) refractive index units (RIU)), low variability (1 × 10(-4) RIU), and high sensitivity (927.88 oscillations per RIU). This performance is comparable to state-of-the-art optofluidic refractometers that involve complex fabrication processes and/or expensive, bulky optics. The advantages of our device (i.e. simple fabrication process, straightforward optical equipment, low cost, and high detection sensitivity) make it a promising candidate for future mass-producible, inexpensive, highly sensitive, label-free optical detection systems. © The Royal Society of Chemistry 2011

  2. Broadband photodetector based on carbon nanotube thin film/single layer graphene Schottky junction

    Science.gov (United States)

    Zhang, Teng-Fei; Li, Zhi-Peng; Wang, Jiu-Zhen; Kong, Wei-Yu; Wu, Guo-An; Zheng, Yu-Zhen; Zhao, Yuan-Wei; Yao, En-Xu; Zhuang, Nai-Xi; Luo, Lin-Bao

    2016-12-01

    In this study, we present a broadband nano-photodetector based on single-layer graphene (SLG)-carbon nanotube thin film (CNTF) Schottky junction. It was found that the as-fabricated device exhibited obvious sensitivity to a wide range of illumination, with peak sensitivity at 600 and 920 nm. In addition, the SLG-CNTF device had a fast response speed (τr = 68 μs, τf = 78 μs) and good reproducibility in a wide range of switching frequencies (50-5400 Hz). The on-off ratio, responsivity, and detectivity of the device were estimated to be 1 × 102, 209 mAW-1 and 4.87 × 1010 cm Hz1/2 W-1, respectively. What is more, other device parameters including linear performance θ and linear dynamic range (LDR) were calculated to be 0.99 and 58.8 dB, respectively, which were relatively better than other carbon nanotube based devices. The totality of the above study signifies that the present SLG-CNTF Schottky junction broadband nano-photodetector may have promising application in future nano-optoelectronic devices and systems.

  3. Adhesion and migration of CHO cells on micropatterned single layer graphene

    Science.gov (United States)

    Keshavan, S.; Oropesa-Nuñez, R.; Diaspro, A.; Canale, C.; Dante, S.

    2017-06-01

    Cell patterning technology on single layer graphene (SLG) is a fairly new field that can find applications in tissue engineering and biomaterial/biosensors development. Recently, we have developed a simple and effective approach for the fabrication of patterned SLG substrates by laser micromachining, and we have successfully applied it for the obtainment of geometrically ordered neural networks. Here, we exploit the same approach to investigate the generalization of the cell response to the surface cues of the fabricated substrates and, contextually, to quantify cell adhesion on the different areas of the patterns. To attain this goal, we tested Chinese hamster ovary (CHO) cells on PDL-coated micropatterned SLG substrates and quantified the adhesion by using single cell force spectroscopy (SCFS). Our results indicate higher cell adhesion on PDL-SLG, and, consequently, an initial CHO cell accumulation on the graphene areas, confirming the neuronal behaviour observed previously; interestingly, at later time point in culture, cell migration was observed towards the adjacent SLG ablated regions, which resulted more favourable for cell proliferation. Therefore, our findings indicate that the mechanism of interaction with the surface cues offered by the micropatterned substrates is strictly cell-type dependent.

  4. Compact Single-Layer Traveling-Wave Antenna DesignUsing Metamaterial Transmission Lines

    Science.gov (United States)

    Alibakhshikenari, Mohammad; Virdee, Bal Singh; Limiti, Ernesto

    2017-12-01

    This paper presents a single-layer traveling-wave antenna (TWA) that is based on composite right/left-handed (CRLH)-metamaterial (MTM) transmission line (TL) structure, which is implemented by using a combination of interdigital capacitors and dual-spiral inductive slots. By embedding dual-spiral inductive slots inside the CRLH MTM-TL results in a compact TWA. Dimensions of the proposed CRLH MTM-TL TWA is 21.5 × 30.0 mm2 or 0.372λ0 × 0.520λ0 at 5.2 GHz (center frequency). The fabricated TWA operates over 1.8-8.6 GHz with a fractional bandwidth greater than 120%, and it exhibits a peak gain and radiation efficiency of 4.2 dBi and 81%, respectively, at 5 GHz. By avoiding the use of lumped components, via-holes or defected ground structures, the proposed TWA design is economic for mass production as well as easy to integrate with wireless communication systems.

  5. Substitutional impurity in single-layer graphene: The Koster–Slater and Anderson models

    Energy Technology Data Exchange (ETDEWEB)

    Davydov, S. Yu., E-mail: sergei-davydov@mail.ru [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation)

    2016-06-15

    The Koster–Slater and Anderson models are used to consider substitutional impurities in free-standing single-layer graphene. The density of states of graphene is described using a model (the M model). For the nitrogen and boron impurities, the occupation numbers and the parameter η which defines the fraction of delocalized electrons of the impurity are determined. In this case, experimental data are used for both determination of the model parameters and comparison with the results of theoretical estimations. The general features of the Koster–Slater and Anderson models and the differences between the two models are discussed. Specifically, it is shown that the band contributions to the occupation numbers of a nitrogen atom in both models are comparable, whereas the local contributions are substantially different: the local contributions are decisive in the Koster–Slater model and negligible in the Anderson model. The asymptotic behavior of the wave functions of a defect is considered in the Koster–Slater model, and the electron states of impurity dimers are considered in the Anderson model.

  6. Determination of band offsets at GaN/single-layer MoS2 heterojunction

    KAUST Repository

    Tangi, Malleswararao

    2016-07-25

    We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E1 2g and A1 g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

  7. Single Layer Bismuth Iodide: Computational Exploration of Structural, Electrical, Mechanical and Optical Properties

    Science.gov (United States)

    Ma, Fengxian; Zhou, Mei; Jiao, Yalong; Gao, Guoping; Gu, Yuantong; Bilic, Ante; Chen, Zhongfang; Du, Aijun

    2015-12-01

    Layered graphitic materials exhibit new intriguing electronic structure and the search for new types of two-dimensional (2D) monolayer is of importance for the fabrication of next generation miniature electronic and optoelectronic devices. By means of density functional theory (DFT) computations, we investigated in detail the structural, electronic, mechanical and optical properties of the single-layer bismuth iodide (BiI3) nanosheet. Monolayer BiI3 is dynamically stable as confirmed by the computed phonon spectrum. The cleavage energy (Ecl) and interlayer coupling strength of bulk BiI3 are comparable to the experimental values of graphite, which indicates that the exfoliation of BiI3 is highly feasible. The obtained stress-strain curve shows that the BiI3 nanosheet is a brittle material with a breaking strain of 13%. The BiI3 monolayer has an indirect band gap of 1.57 eV with spin orbit coupling (SOC), indicating its potential application for solar cells. Furthermore, the band gap of BiI3 monolayer can be modulated by biaxial strain. Most interestingly, interfacing electrically active graphene with monolayer BiI3 nanosheet leads to enhanced light absorption compared to that in pure monolayer BiI3 nanosheet, highlighting its great potential applications in photonics and photovoltaic solar cells.

  8. Investigating change of properties in gallium ion irradiation patterned single-layer graphene

    International Nuclear Information System (INIS)

    Wang, Quan; Dong, Jinyao; Bai, Bing; Xie, Guoxin

    2016-01-01

    Besides its excellent physical properties, graphene promises to play a significant role in electronics with superior properties, which requires patterning of graphene for device integration. Here, we presented the changes in properties of single-layer graphene before and after patterning using gallium ion beam. Combined with Raman spectra of graphene, the scanning capacitance microscopy (SCM) image confirmed that a metal–insulator transition occurred after large doses of gallium ion irradiation. The changes in work function and Raman spectra of graphene indicated that the defect density increased as increasing the dose and a structural transition occurred during gallium ion irradiation. The patterning width of graphene presented an increasing trend due to the scattering influence of the impurities and the substrate. - Highlights: • The scanning capacitance microscopy image confirmed a metal–insulator transition occurred after large doses of gallium ion irradiation. • The changes indicated the defect density increased as increasing the dose and a structural transition occurred during gallium ion irradiation. • The patterning width of graphene presented a increasing trend due to the scattering influence of the impurities and the substrate.

  9. Two-band induced superconductivity in single-layer graphene and topological insulator bismuth selenide

    Science.gov (United States)

    Talantsev, E. F.; Crump, W. P.; Tallon, J. L.

    2018-01-01

    Proximity-induced superconductivity in single-layer graphene (SLG) and in topological insulators represent almost ideal examples of superconductivity in two dimensions. Fundamental mechanisms governing superconductivity in the 2D limit are of central interest for modern condensed-matter physics. To deduce fundamental parameters of superconductor/graphene/superconductor and superconductor/bismuth selenide/superconductor junctions we investigate the self-field critical currents in these devices using the formalism of the Ambegaokar–Baratoff model. Our central finding is that the induced superconducting state in SLG and bismuth selenide each exhibits gapping on two superconducting bands. Based on recent results obtained on ultra-thin films of natural superconductors, including single-atomic layer of iron selenide, double and triple atomic layers of gallium, and several atomic layer tantalum disulphide, we conclude that a two-band induced superconducting state in SLG and bismuth selenide is part of a wider, more general multiple-band phenomenology of currently unknown origin.

  10. Band Alignment at GaN/Single-Layer WSe2 Interface

    KAUST Repository

    Tangi, Malleswararao

    2017-02-21

    We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electronic and optoelectronic devices.

  11. A single-layer tilting actuator with multiple close-gap electrodes

    International Nuclear Information System (INIS)

    Shmilovich, T; Krylov, S

    2009-01-01

    We report on the design, fabrication and characterization of a novel tilting electrostatic actuator, fabricated by using a single layer of a silicon on insulator (SOI) wafer and investigate, both theoretically and experimentally, the electromechanical behavior of the device. The actuator incorporates high aspect ratio comb-like electrodes oriented in the direction parallel to the rotation axis of the tilting element. An increase in the tilting angle is accompanied by a decrease in the distance between the electrodes and by an increase of the actuating torque. Simultaneously, the overlap area between electrodes located farther apart the axis shrinks, resulting in a 'restoring' torque in the opposite direction. The electromechanical behavior and stability of the device were investigated using a simplified model of the actuator and verified by a coupled three-dimensional simulation. Model results suggest that by changing the design parameters, the actuator characteristic can be tailored in a large range. Devices of three different configurations incorporating elastic torsion axes or bending flexures were fabricated and characterized and both static and resonant responses, typical for parametrically excited nonlinear oscillators, were registered. Theoretical and experimental results indicate that the suggested architecture can be efficiently used for the static and dynamic operation of electrostatic tilting devices

  12. Single-layer tungsten oxide as intelligent photo-responsive nanoagents for permanent male sterilization.

    Science.gov (United States)

    Liu, Zhen; Liu, Xianjun; Ran, Xiang; Ju, Enguo; Ren, Jinsong; Qu, Xiaogang

    2015-11-01

    Permanent male sterilization has been recognized as useful tools for the development of neuter experimental animals and fattening livestock, as well as efficient control of pet overpopulation. Traditional routes such as surgical ways, chemical injections, and anti-fertility vaccines have addressed these crucial problems with idea outcomes. However, these routes usually bring out serious pain and infection towards animals, as well as induce long-term adverse reaction and immune suppression. Thus, a convenient, but non-surgical strategy for male sterilization under a mild manner is highly desirable. Here, for the first time, we demonstrate a novel platform for male sterilization by using single-layer WO2.72 nanosheets as smart photo-responsive sterilants. Upon a 980 nm irradiation, these nanoagents can possess intrinsic NIR-induced hyperthermia and sensitize the formation of singlet oxygen due to the cooperation of photothermal and photodynamic effects. Mechanism of cellular injury can be attributed to the denaturation of protein and apoptosis-related death. Moreover, long-term toxicity and possible metabolism route after testicular injection are discussed, indicating the neglectable systemic toxicity and high bio-compatibility of our nanoagents. Overall, our strategy can extremely overcome the shortcomings in various routine routes and suggest the new biological application of nanomaterials. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Unexpected strong magnetism of Cu doped single-layer MoS₂ and its origin.

    Science.gov (United States)

    Yun, Won Seok; Lee, J D

    2014-05-21

    The magnetism of the 3d transition-metal (TM) doped single-layer (1L) MoS2, where the Mo atom is partially replaced by the 3d TM atom, is investigated using the first-principles density functional calculations. In a series of 3d TM doped 1L-MoS2's, the induced spin polarizations are negligible for Sc, Ti, and Cr dopings, while the induced spin polarizations are confirmed for V, Mn, Fe, Co, Ni, Cu, and Zn dopings and the systems become magnetic. Especially, the Cu doped system shows unexpectedly strong magnetism although Cu is nonmagnetic in its bulk state. The driving force is found to be a strong hybridization between Cu 3d states and 3p states of neighboring S, which results in an extreme unbalanced spin-population in the spin-split impurity bands near the Fermi level. Finally, we also discuss further issues of the Cu induced magnetism of 1L-MoS2 such as investigation of additional charge states, the Cu doping at the S site instead of the Mo site, and the Cu adatom on the layer (i.e., 1L-MoS2).

  14. Engineering of electronic properties of single layer graphene by swift heavy ion irradiation

    Science.gov (United States)

    Kumar, Sunil; Kumar, Ashish; Tripathi, Ambuj; Tyagi, Chetna; Avasthi, D. K.

    2018-04-01

    In this work, swift heavy ion irradiation induced effects on the electrical properties of single layer graphene are reported. The modulation in minimum conductivity point in graphene with in-situ electrical measurement during ion irradiation was studied. It is found that the resistance of graphene layer decreases at lower fluences up to 3 × 1011 ions/cm2, which is accompanied by the five-fold increase in electron and hole mobilities. The ion irradiation induced increase in electron and hole mobilities at lower fluence up to 1 × 1011 ions/cm2 is verified by separate Hall measurements on another irradiated graphene sample at the selected fluence. In contrast to the adverse effects of irradiation on the electrical properties of materials, we have found improvement in electrical mobility after irradiation. The increment in mobility is explained by considering the defect annealing in graphene after irradiation at a lower fluence regime. The modification in carrier density after irradiation is also observed. Based on findings of the present work, we suggest ion beam irradiation as a useful tool for tuning of the electrical properties of graphene.

  15. Single track and single layer formation in selective laser melting of niobium solid solution alloy

    Directory of Open Access Journals (Sweden)

    Yueling GUO

    2018-04-01

    Full Text Available Selective laser melting (SLM was employed to fabricate Nb-37Ti-13Cr-2Al-1Si (at% alloy, using pre-alloyed powders prepared by plasma rotating electrode processing (PREP. A series of single tracks and single layers under different processing parameters was manufactured to evaluate the processing feasibility by SLM, including laser power, scanning speed, and hatch distance. Results showed that continuous single tracks could be fabricated using proper laser powers and scanning velocities. Both the width of a single track and its penetration depth into a substrate increased with an increase of the linear laser beam energy density (LED, i.e., an increase of the laser power and a decrease of the scanning speed. Nb, Ti, Si, Cr, and Al elements distributed heterogeneously over the melt pool in the form of swirl-like patterns. An excess of the hatch distance was not able to interconnect neighboring tracks. Under improper processing parameters, a balling phenomenon occurred, but could be eliminated with an increased LED. This work testified the SLM-processing feasibility of Nb-based alloy and promoted the application of SLM to the manufacture of niobium-based alloys. Keywords: Additive manufacturing, Melt pool, Niobium alloy, Powder metallurgy, Selective laser melting

  16. Abrupt change of luminescence spectrum in single-layer phosphorescent polymer light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, X.; Lee, D.-H.; Chae, H. [School of Chemical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Cho, S.M., E-mail: sungmcho@skku.edu [School of Chemical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Advanced Materials and Process Research Center for IT, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2012-01-15

    PVK-based single-layer phosphorescent polymer OLEDs (organic light emitting diodes) with different rubrene concentrations were fabricated and examined for the Foerster energy transfer from phosphorescent FIrpic dye to rubrene. We found out that at a certain rubrene concentration the energy transfer occurs abruptly and the transfer shows an abnormal evolution of electroluminescence (EL) spectrum due to the coincidence of peak wavelengths of bis[(4,6-difluorophenyl)-pyridinato-N,C{sup 2'}](picolinate) iridium(III) (FIrpic) emission and 5,6,11,12-tetraphenylnaphthacene (rubrene) absorption. With the calculation of Foerster radius and average distance between FIrpic molecules, we have related the calculated ratio between the number of FIrpic molecules within to that out of Foerster radius with the degree of Foerster energy transfer from EL spectra measured in the experiment. Experimental results were found to fit well with the predicted results especially at low rubrene concentrations. - Highlights: > Foerster energy transfer between FIrpic and rubrene. > Energy transfer shows an abnormal evolution of emission spectrum. > Calculated Foerster radius and degree of energy transfer by a simple model.

  17. A single-layer peptide nanofiber for enhancing the cytotoxicity of trastuzumab (anti-HER)

    Energy Technology Data Exchange (ETDEWEB)

    Malik, Ruchi; Wagh, Anil; Qian, Steven; Law, Benedict, E-mail: Shek.law@ndsu.edu [College of Pharmacy, Nursing, and Allied Sciences, North Dakota State University, Department of Pharmaceutical Sciences (United States)

    2013-06-15

    A multivalent system is often employed to enhance the effectiveness of a targeted therapy. In the present study, we report a single-layer peptide nanofiber (NFP) as a multivalent targeting platform to improve the cytotoxicity of trastuzumab (anti-HER), a monoclonal antibody targeting the human epidermal growth factor receptor 2 (HER-2) in approximately 20 % of breast cancer patients. The trastuzumab-conjugated nanofiber (anti-HER/NFP) was 100 Multiplication-Sign 4 nm in size and was assembled from multiple peptide units (mPEG-BK(FITC)SGASNRA-kldlkldlkldl-CONH{sub 2}). The optimized preparation was attached with approximately 10 antibodies at the surface. Because of an increase in the multivalency, anti-HER/NFP was able to truncate more cell surface HER-2 and, thus, showed an enhanced cytotoxicity toward HER-2 positive SKBr-3 human breast cancer as compared to the free anti-HER. Western blot analysis and fluorescence microscopic studies confirmed that there was a significant downregulation of the HER-2 level and also inhibition of the cell survival cell signaling pathways including the phosphatidylinositol 3-kinase (PI3K) and the mitogen activated protein kinase (MAPK) pathway. Our data suggested that NFP can be useful as a multivalent platform for immunotherapy, especially in combination with other chemotherapeutic agents in the future.

  18. The Stability of New Single-Layer Combined Lattice Shell Based on Aluminum Alloy Honeycomb Panels

    Directory of Open Access Journals (Sweden)

    Caiqi Zhao

    2017-11-01

    Full Text Available This article proposes a new type of single-layer combined lattice shell (NSCLS; which is based on aluminum alloy honeycomb panels. Six models with initial geometric defect were designed and precision made using numerical control equipment. The stability of these models was tested. The results showed that the stable bearing capacity of NSCLS was approximately 16% higher than that of a lattice shell with the same span without a reinforcing plate. At the same time; the properties of the NSCLS were sensitive to defects. When defects were present; its stable bearing capacity was decreased by 12.3% when compared with the defect-free model. The model with random defects following a truncated Gaussian distribution could be used to simulate the distribution of defects in the NSCLS. The average difference between the results of the nonlinear analysis and the experimental results was 5.7%. By calculating and analyzing nearly 20,000 NSCLS; the suggested values of initial geometric defect were presented. The results of this paper could provide a theoretical basis for making and revising the design codes for this new combined lattice shell structure.

  19. Effect of cushioned or single layer semen centrifugation before sex sorting on frozen stallion semen quality.

    Science.gov (United States)

    Mari, G; Bucci, D; Love, C C; Mislei, B; Rizzato, G; Giaretta, E; Merlo, B; Spinaci, M

    2015-04-01

    The aim of this study was to compare the effect of presorting centrifugation (cushioned [CC] or single-layer colloid [SLC]), with simple dilution (SD), on the quality of sex-sorted stallion semen before and after sorting and after freezing and thawing. Four ejaculates from each of two fertile stallions were collected 1 week apart and evaluated for percent total sperm motility (TM), percent viable acrosome-intact sperm (VAI), and DNA quality (percentage of DNA fragmentation index). Freezing caused, independently from CC and SLC treatments, a significant decrease of TM (P < 0.05) and VAI (P < 0.05) in both unsorted and sorted semen. On the other hand, sorting did not impair TM and VAI and, interestingly, improved DNA quality in all treatments only before freezing (28 vs 13, 28 vs 10, 22 vs 7 in SD, CC, and SLC for unsorted vs sorted groups, respectively; P < 0.05); this positive effect was lost in the same samples after freezing and thawing, suggesting that the freezing process reduces the DNA quality of sex-sorted sperm. Our results suggest that CC and SLC are not able to select those spermatozoa that possess a better ability to withstand sperm processing associated with sperm sorting and freezing. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Single layer centrifugation-selected boar spermatozoa are capable of fertilization in vitro

    Science.gov (United States)

    2013-01-01

    Background Good quality spermatozoa are important to achieve fertilization, viable embryos and offspring. Single Layer Centrifugation (SLC) through a colloid (Androcoll-P) selects good quality spermatozoa. However, it has not been established previously whether porcine spermatozoa selected by this method maintain their fertility. Methods The semen was prepared either by SLC or by standard centrifugation (control) and used for in vitro fertilization (IVF) at oocyte:spermatozoa ratios of 1:50; 1:100 and 1:300 (or 4 x 103, 8 x 103 and 24 x 103 spermatozoa/ml) to evaluate their subsequent ability to generate blastocysts. In addition, sperm motility was assessed by computer assisted sperm motility analysis. Results Total and progressive motility were significantly higher in sperm samples prepared by SLC compared to uncentrifuged samples. Sperm binding ability, polyspermy, cleavage and blastocyst rates were affected by the oocyte:sperm ratio, but not by sperm treatment. Conclusion The use of SLC does not adversely affect the in vitro fertilizing and embryo-generating ability of the selected spermatozoa compared to their unselected counterparts, but further modifications in the IVF conditions would be needed to improve the monospermy in IVF systems. Since SLC did not appear to have a negative effect on sperm fertilizing ability, and may in fact select for spermatozoa with a greater potential for fertilization, an in vivo trial to determine the usefulness of this sperm preparation technique prior to artificial insemination is warranted. PMID:23497680

  1. Local Electronic Structure of a Single-Layer Porphyrin-Containing Covalent Organic Framework

    KAUST Repository

    Chen, Chen

    2017-12-20

    We have characterized the local electronic structure of a porphyrin-containing single-layer covalent organic framework (COF) exhibiting a square lattice. The COF monolayer was obtained by the deposition of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMA) and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) onto a Au(111) surface in ultrahigh vacuum followed by annealing to facilitate Schiff-base condensations between monomers. Scanning tunneling spectroscopy (STS) experiments conducted on isolated TAPP precursor molecules and the covalently linked COF networks yield similar transport (HOMO-LUMO) gaps of 1.85 ± 0.05 eV and 1.98 ± 0.04 eV, respectively. The COF orbital energy alignment, however, undergoes a significant downward shift compared to isolated TAPP molecules due to the electron-withdrawing nature of the imine bond formed during COF synthesis. Direct imaging of the COF local density of states (LDOS) via dI/dV mapping reveals that the COF HOMO and LUMO states are localized mainly on the porphyrin cores and that the HOMO displays reduced symmetry. DFT calculations reproduce the imine-induced negative shift in orbital energies and reveal that the origin of the reduced COF wave function symmetry is a saddle-like structure adopted by the porphyrin macrocycle due to its interactions with the Au(111) substrate.

  2. Canopy for VERAView Installation Guide

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Ronald W. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-09-12

    With the addition of the 3D volume slicer widget, VERAView now relies on Mayavi and its dependents. Enthought's Canopy Python environment provides everything VERAView needs, and pre-built Canopy versions for Windows, Mac OSX, and Linux can be downloaded.

  3. Plasma process-induced latent damage on gate oxide - demonstrated by single-layer and multi-layer antenna structures

    NARCIS (Netherlands)

    Wang, Zhichun; Ackaert, Jan; Salm, Cora; Kuper, F.G.

    2001-01-01

    In this paper, by using both single-layer (SL) and multi-layer (ML) or stacked antenna structures, a simple experimental method is proposed to directly demonstrate the pure plasma process-induced latent damage on gate oxide without any impact of additional defects generated by normal constant

  4. Comparative study of hand sewn single layer anastomosis of dog's bowel Estudo comparativo das anastomoses manuais em plano único do intestino delgado de cães

    OpenAIRE

    João Luiz Moreira Coutinho Azevedo; Octávio Hypólito; Otávio Cansanção Azevedo; Otávio Monteiro Becker Jr.; Dalmer Faria Freire

    2008-01-01

    BACKGROUND: Two-layer intestinal anastomosis increases the inflammatory response while single-layer anastomosis results in a better wound healing. However the four main kinds of stitches which may be chosen in performing single layer intestinal sutures never before had been comparatively studied. AIM: To compare the four more commonly used types of single layer surgical anastomosis sutures of the digestive tract. METHODS: Six mongrel dogs were operated, each one receiving two anastomosis: one...

  5. [Single-layer colonic anastomoses using polyglyconate (Maxon) vs. two-layer anastomoses using chromic catgut and silk. Experimental study].

    Science.gov (United States)

    García-Osogobio, Sandra Minerva; Takahashi-Monroy, Takeshi; Velasco, Liliana; Gaxiola, Miguel; Sotres-Vega, Avelina; Santillán-Doherty, Patricio

    2006-01-01

    The safety of an intestinal anastomosis is usually measured by its complication rate, especially the incidence of anastomotic leakage. A wide variety of methods have been described to reestablish intestinal continuity including single-layer continuous or two-layer interrupted anastomosis. To evaluate if the single-layer continuous anastomosis using polygluconate is safer and reliable than two-layer interrupted anastomosis with chromic catgut and silk. A prospective, experimental, randomized and comparative analysis was conducted in 20 dogs. They were divided in two groups; group 1 underwent two-layer interrupted anastomosis and group 2 underwent sigle-layer continuous technique. Anastomoses were timed. Both groups were under observation. Anastomotic leakage, and other complications were evaluated. The animals were sacrified and the anastomosis was taken out together with 10 cm of colon on both sides of the anastomosis. Breaking strength, histologic evaluation and hydroxyproline determination were performed. Ten two-layer anastomosis and ten single-layer anastomosis were performed. A median of 25 minutes (range: 20-30 minutes) was required to construct the anastomoses in group 1 versus 20 minutes (range: 12-25 minutes) in group 2. All animals survived and no leakage was observed. Wound infection ocurred in four dogs (20%). Median breaking strength was 230 mm Hg in group 1 and 210 mm Hg in group 2. Hydroxyproline concentration was 8.94 mg/g in group 1 (range: 5.33-16.71) and 9.94 mg/g in group 2 (range: 2.96-21.87). There was no difference among groups about the inflammatory response evaluated by pathology. There was no statistical significance in any variable evaluated. CONCLUIONS: This study demonstrates that a single-layer continuous is similar in terms of safety to the two-layer technique, but because of its facility to perform, the single-layer technique could be superior.

  6. Seamless lamination of a concave-convex architecture with single-layer graphene

    Science.gov (United States)

    Park, Ji-Hoon; Lim, Taekyung; Baik, Jaeyoon; Seo, Keumyoung; Moon, Youngkwon; Park, Noejung; Shin, Hyun-Joon; Kyu Kwak, Sang; Ju, Sanghyun; Real Ahn, Joung

    2015-10-01

    Graphene has been used as an electrode and channel material in electronic devices because of its superior physical properties. Recently, electronic devices have changed from a planar to a complicated three-dimensional (3D) geometry to overcome the limitations of planar devices. The evolution of electronic devices requires that graphene be adaptable to a 3D substrate. Here, we demonstrate that chemical-vapor-deposited single-layer graphene can be transferred onto a silicon dioxide substrate with a 3D geometry, such as a concave-convex architecture. A variety of silicon dioxide concave-convex architectures were uniformly and seamlessly laminated with graphene using a thermal treatment. The planar graphene was stretched to cover the concave-convex architecture, and the resulting strain on the curved graphene was spatially resolved by confocal Raman spectroscopy; molecular dynamic simulations were also conducted and supported the observations. Changes in electrical resistivity caused by the spatially varying strain induced as the graphene-silicon dioxide laminate varies dimensionally from 2D to 3D were measured by using a four-point probe. The resistivity measurements suggest that the electrical resistivity can be systematically controlled by the 3D geometry of the graphene-silicon dioxide laminate. This 3D graphene-insulator laminate will broaden the range of graphene applications beyond planar structures to 3D materials.Graphene has been used as an electrode and channel material in electronic devices because of its superior physical properties. Recently, electronic devices have changed from a planar to a complicated three-dimensional (3D) geometry to overcome the limitations of planar devices. The evolution of electronic devices requires that graphene be adaptable to a 3D substrate. Here, we demonstrate that chemical-vapor-deposited single-layer graphene can be transferred onto a silicon dioxide substrate with a 3D geometry, such as a concave-convex architecture. A

  7. Performance assessment of a single-layer moisture store-and-release cover system at a mine waste rock pile in a seasonally humid region (Nova Scotia, Canada).

    Science.gov (United States)

    Power, Christopher; Ramasamy, Murugan; Mkandawire, Martin

    2018-03-03

    Cover systems are commonly applied to mine waste rock piles (WRPs) to control acid mine drainage (AMD). Single-layer covers utilize the moisture "store-and-release" concept to first store and then release moisture back to the atmosphere via evapotranspiration. Although more commonly used in semi-arid and arid climates, store-and-release covers remain an attractive option in humid climates due to the low cost and relative simplicity of installation. However, knowledge of their performance in these climates is limited. The objective of this study was to assess the performance of moisture store-and-release covers at full-scale WRPs located in humid climates. This cover type was installed at a WRP in Nova Scotia, Canada, alongside state-of-the-art monitoring instrumentation. Field monitoring was conducted over 5 years to assess key components such as meteorological conditions, cover material water dynamics, net percolation, surface runoff, pore-gas, environmental receptor water quality, landform stability and vegetation. Water balances indicate small reductions in water influx to the waste rock (i.e., 34 to 28% of precipitation) with the diminished AMD release also apparent by small improvements in groundwater quality (increase in pH, decrease in sulfate/metals). Surface water quality analysis and field observations of vegetative/aquatic life demonstrate significant improvements in the surface water receptor. The WRP landform is stable and the vegetative cover is thriving. This study has shown that while a simple store-and-release cover may not be a highly effective barrier to water infiltration in humid climates, it can be used to (i) eliminate contaminated surface water runoff, (ii) minimize AMD impacts to surface water receptor(s), (iii) maintain a stable landform, and (iv) provide a sustainable vegetative canopy.

  8. Design of a Single-Layer Microchannel for Continuous Sheathless Single-Stream Particle Inertial Focusing.

    Science.gov (United States)

    Zhang, Yan; Zhang, Jun; Tang, Fei; Li, Weihua; Wang, Xiaohao

    2018-02-06

    High-throughput, high-precision single-stream focusing of microparticles has a potentially wide range of applications in biochemical analysis and clinical diagnosis. In this work, we develop a sheathless three-dimensional (3D) particle-focusing method in a single-layer microchannel. This novel microchannel consists of periodic high-aspect-ratio curved channels and straight channels. The proposed method takes advantage of both the curved channels, which induce Dean flow to promote particle migration, and straight channels, which suppress the remaining stirring effects of Dean flow to stabilize the achieved particle focusing. The 3D particle focusing is demonstrated experimentally, and the mechanism is analyzed theoretically. The effects of flow rate, particle size, and cycle number on the focusing performance were also investigated. The experimental results demonstrate that polystyrene particles with diameters of 5-20 μm can be focused into a 3D single file within seven channel cycles, with the focusing accuracy up to 98.5% and focusing rate up to 98.97%. The focusing throughput could reach up to ∼10 5 counts/min. Furthermore, its applicability to biological cells is also demonstrated by 3D focusing of HeLa and melanoma cells and bovine blood cells in the proposed microchannel. The proposed sheathless passive focusing scheme, featuring a simple channel structure, small footprint (9 mm × 1.2 mm), compact layout, and uncomplicated fabrication procedure, holds great promise as an efficient 3D focusing unit for the development of next-generation on-chip flow cytometry.

  9. Determination of the optimized single-layer ionospheric height for electron content measurements over China

    Science.gov (United States)

    Li, Min; Yuan, Yunbin; Zhang, Baocheng; Wang, Ningbo; Li, Zishen; Liu, Xifeng; Zhang, Xiao

    2018-02-01

    The ionosphere effective height (IEH) is a very important parameter in total electron content (TEC) measurements under the widely used single-layer model assumption. To overcome the requirement of a large amount of simultaneous vertical and slant ionospheric observations or dense "coinciding" pierce points data, a new approach comparing the converted vertical TEC (VTEC) value using mapping function based on a given IEH with the "ground truth" VTEC value provided by the combined International GNSS Service Global Ionospheric Maps is proposed for the determination of the optimal IEH. The optimal IEH in the Chinese region is determined using three different methods based on GNSS data. Based on the ionosonde data from three different locations in China, the altitude variation of the peak electron density (hmF2) is found to have clear diurnal, seasonal and latitudinal dependences, and the diurnal variation of hmF2 varies from approximately 210 to 520 km in Hainan. The determination of the optimal IEH employing the inverse method suggested by Birch et al. (Radio Sci 37, 2002. doi: 10.1029/2000rs002601) did not yield a consistent altitude in the Chinese region. Tests of the method minimizing the mapping function errors suggested by Nava et al. (Adv Space Res 39:1292-1297, 2007) indicate that the optimal IEH ranges from 400 to 600 km, and the height of 450 km is the most frequent IEH at both high and low solar activities. It is also confirmed that the IEH of 450-550 km is preferred for the Chinese region instead of the commonly adopted 350-450 km using the determination method of the optimal IEH proposed in this paper.

  10. Electronic and optical properties of vacancy defects in single-layer transition metal dichalcogenides

    Science.gov (United States)

    Khan, M. A.; Erementchouk, Mikhail; Hendrickson, Joshua; Leuenberger, Michael N.

    2017-06-01

    A detailed first-principles study has been performed to evaluate the electronic and optical properties of single-layer (SL) transition metal dichalcogenides (TMDCs) (M X 2 ; M = transition metal such as Mo, W, and X = S, Se, Te), in the presence of vacancy defects (VDs). Defects usually play an important role in tailoring electronic, optical, and magnetic properties of semiconductors. We consider three types of VDs in SL TMDCs: (i) X vacancy, (ii) X2 vacancy, and (iii) M vacancy. We show that VDs lead to localized defect states (LDS) in the band structure, which in turn gives rise to sharp transitions in in-plane and out-of-plane optical susceptibilities, χ∥ and χ⊥. The effects of spin-orbit coupling (SOC) are also considered. We find that SOC splitting in LDS is directly related to the atomic number of the transition metal atoms. Apart from electronic and optical properties we also find magnetic signatures (local magnetic moment of ˜μB ) in MoSe2 in the presence of the Mo vacancy, which breaks the time-reversal symmetry and therefore lifts the Kramers degeneracy. We show that a simple qualitative tight-binding model (TBM), involving only the hopping between atoms surrounding the vacancy with an on-site SOC term, is sufficient to capture the essential features of LDS. In addition, the existence of the LDS can be understood from the solution of the two-dimensional Dirac Hamiltonian by employing infinite mass boundary conditions. In order to provide a clear description of the optical absorption spectra, we use group theory to derive the optical selection rules between LDS for both χ∥ and χ⊥.

  11. Numerical study of urbanization effect on a heavy storm event in Beijing

    Science.gov (United States)

    Liu, Z.

    2015-12-01

    In the past few decades, Great Beijing area has experienced rapid and widespread urbanization, which has substantially modified the land surface physical characteristics and affected urban regional weather and climate. A single layer urban canopy module has been developed based on the Community Land Surface Model Urban Module (CLMU) with several improvements: the energy balances on the five surface conditions (building roof, sun side and shaded side wall, pervious and impervious land surfaces) are considered separately. A method to calculate sky view factor is developed based on the physically process while most urban models simply provide an empirical value. This method improves the solar and long wave radiation simulation on each surface. The latent heat flux on both wall and impervious land is calculated; the anthropogenic heat is considered in terms of industrial production, domestic wastes, vehicles and air conditions. The urban effect on summer convective precipitation over Beijing was investigated by simulating a heavy storm event on July 21st 2012, when precipitation of averagely 164 mm was brought to Beijing within 6 hours, which is the heaviest during the past 60 years' record in the region. Numerical simulating experiment was set up by coupling Weather Research and Forecast (WRF)/SSiB3 model with the Modified CLMU (MCLMU). Several control cases without MCLMU were set up. The horizontal resolution in the inner domains was set to be 2 km. While all of the control results drastically underestimate the urban precipitation, the result of WRF/SSiB3/MCLMU is much closer to the observation. Sensitive experiments show that although large areas of impervious surfaces restrain the surface latent heat flux in urban, the anthropogenic heat and enhanced sensible heat flux warmed up the lower atmospheric layer then strengthen the vertical stratification instability, which is the key factor for heavy storm while moisture is sufficient.

  12. Numerical Study of Urbanization Effect on 2012 Heavy Storm Precipitation in Beijing

    Science.gov (United States)

    Liu, Z.; Liu, S.; Xue, Y.; Oleson, K. W.

    2014-12-01

    In the past few decades, Great Beijing area has experienced rapid and widespread urbanization, which has significantly modified the land surface physical characteristics and affects urban regional climate.A single layer urban canopy module has been developed based on the Community Land Surface Model Urban Module (CLMU) with improvements: the energy balances on the five surface conditions are considered separately: building roof, sun side and shaded side wall, pervious and impervious land surface. A method to calculate sky view factor is developed based on the physically process while most urban models simply provide an empirical value. This method improves the solar and long wave radiation simulation on each surface; a new scheme for calculating the latent heat flux is applied on both wall and impervious land; the anthropogenic heat is considered in terms of industrial production, domestic wastes, vehicles and air condition. The urban effect on summer convective precipitation under the unstable atmospheric condition over Beijing was investigated by simulating a heavy storm event in July 21st 2012. In this storm, precipitation of averagely 164 mm was brought to Beijing within 6 hours, which is the record of past 60 years in the region. Numerical simulating experiment was set up by coupling Weather Research and Forecast (WRF)/SSiB3 model with the Modified CLMU (MCLMU). Several control cases without MCLMU were set up. The horizontal resolution in the inner domains was set to be 2 km. While all of the control results drastically underestimate the urban precipitation, the result of WRF/SSiB3/MCLMU is much closer to the observation. Sensitive experiments show that the existence of large area of impervious surfaces restrain the surface evaporation and latent heat flux in urban while the anthropogenic heat and enhanced sensible heat flux warm up the lower atmospheric layer and strengthen the vertical stratification instability, which is the key factor for storm while

  13. Plant photomorphogenesis and canopy growth

    Energy Technology Data Exchange (ETDEWEB)

    Ballare, C.L.; Scopel, A.L. [Universidad de Buenos Aires (Argentina)

    1994-12-31

    An important motivation for studying photomorphogenesis is to understand the relationships among plant photophysiology in canopies, canopy productivity, and agronomic yield. This understanding is essential to optimize lighting systems used for plant farming in controlled environments (CE) and for the design of genetically engineered crop strains with altered photoresponses. This article provides an overview of some basic principles of plant photomorphogenesis in canopies and discusses their implications for (1) scaling up information on plant photophysiology from individual plants in CE to whole canopies in the field, and (2), designing lighting conditions to increase plant productivity in CE used for agronomic purposes [e.g. space farming in CE Life-Support-Systems]. We concentrate on the visible ({lambda} between 400 and 700 nm) and far red (FR; {lambda} > 700 nm) spectral regions, since the ultraviolet (UV; 280 to 400 nm) is covered by other authors in this volume.

  14. A learning rule for very simple universal approximators consisting of a single layer of perceptrons.

    Science.gov (United States)

    Auer, Peter; Burgsteiner, Harald; Maass, Wolfgang

    2008-06-01

    One may argue that the simplest type of neural networks beyond a single perceptron is an array of several perceptrons in parallel. In spite of their simplicity, such circuits can compute any Boolean function if one views the majority of the binary perceptron outputs as the binary output of the parallel perceptron, and they are universal approximators for arbitrary continuous functions with values in [0,1] if one views the fraction of perceptrons that output 1 as the analog output of the parallel perceptron. Note that in contrast to the familiar model of a "multi-layer perceptron" the parallel perceptron that we consider here has just binary values as outputs of gates on the hidden layer. For a long time one has thought that there exists no competitive learning algorithm for these extremely simple neural networks, which also came to be known as committee machines. It is commonly assumed that one has to replace the hard threshold gates on the hidden layer by sigmoidal gates (or RBF-gates) and that one has to tune the weights on at least two successive layers in order to achieve satisfactory learning results for any class of neural networks that yield universal approximators. We show that this assumption is not true, by exhibiting a simple learning algorithm for parallel perceptrons - the parallel delta rule (p-delta rule). In contrast to backprop for multi-layer perceptrons, the p-delta rule only has to tune a single layer of weights, and it does not require the computation and communication of analog values with high precision. Reduced communication also distinguishes our new learning rule from other learning rules for parallel perceptrons such as MADALINE. Obviously these features make the p-delta rule attractive as a biologically more realistic alternative to backprop in biological neural circuits, but also for implementations in special purpose hardware. We show that the p-delta rule also implements gradient descent-with regard to a suitable error measure

  15. Single layer and multilayer wear resistant coatings of (Ti,Al)N: a review

    International Nuclear Information System (INIS)

    PalDey, S.; Deevi, S.C.

    2003-01-01

    periodicity of 5-10 nm allow creation of coatings with different properties than PVD deposited single layered thick coatings with columnar grain structure. A range of (Ti,Al)N based multilayers containing layers of (Ti,Al)CN, (Ti,Nb)N, TiN, AlN/TiN, CrN, Mo and WC are also reviewed. It is now possible to design new wear resistant or functional coatings based on a multilayer or a multicomponent system to meet the demanding applications of advanced materials

  16. Urban

    Directory of Open Access Journals (Sweden)

    Paulo José Lisboa Nobre

    2007-12-01

    Full Text Available Natal is a city with environment singularities. The urban legislation tried to preserve the features of the local landscape delimiting “Areas for Controlling Building High”, destined to protect the scenic value of some parts of the city. In 1979 was created a “NonÆdificandi” area to protect the scenery of Ponta Negra beach, one of the most famous view of the city. Since this time, the real state market, the building constructers and the land owners of this area have exerted constant pressure in sense to abolish or to modify this legal instrument.Nowadays, the public administration presented a new project which try to answer public and private interests.This paper is the result of an inclusion of the University in this polemic issue. Architecture and Urban Planning and Statistic students of two universities of the city (UFRN and UNP, helped the process collecting data and producing information. The proposed of the investigation was to know the users of this area and their opinion about the subject. It was done together with the Public agency, Secretaria Especial de Meio Ambiente e Urbanismo. At the end, the students presented their particular solutions for the problem, inside the disciplines of Landscaping and Urban Planning.

  17. Magneto-electroluminescence effects in the single-layer organic light-emitting devices with macrocyclic aromatic hydrocarbons

    Directory of Open Access Journals (Sweden)

    S.-T. Pham

    2018-02-01

    Full Text Available Magneto-electroluminescence (MEL effects are observed in single-layer organic light-emitting devices (OLEDs comprising only macrocyclic aromatic hydrocarbons (MAHs. The fluorescence devices were prepared using synthesized MAHs, namely, [n]cyclo-meta-phenylene ([n]CMP, n = 5, 6. The MEL ratio of the resulting OLED is 1%–2% in the spectral wavelength range of 400-500 nm, whereas it becomes negative (−1.5% to −2% in the range from 650 to 700 nm. The possible physical origins of the sign change in the MEL are discussed. This wavelength-dependent sign change in the MEL ratio could be a unique function for future single-layer OLEDs capable of magnetic-field-induced color changes.

  18. Novel single-layer gas diffusion layer based on PTFE/carbon black composite for proton exchange membrane fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Chen-Yang, Y.W.; Hung, T.F.; Yang, F.L. [Department of Chemistry and Center for Nanotechnology, Chung Yuan Christian University, Chung-Li 32023 (China); Huang, J. [Yeu Ming Tai Chemical Industrial Co., Ltd, Taichung 40768 (China)

    2007-11-08

    A series of poly(tetrafluoroethylene)/carbon black composite-based single-layer gas diffusion layers (PTFE/CB-GDLs) for proton exchange membrane fuel cell (PEMFC) was successfully prepared from carbon black and un-sintered PTFE, which included powder resin and colloidal dispersion, by a simple inexpensive method. The scanning electron micrographs of PTFE/CB-GDLs indicated that the PTFE resins were homogeneously dispersed in the carbon black matrix and showed a microporous layer (MPL)-like structure. The as-prepared PTFE/CB-GDLs exhibited good mechanical property, high gas permeability, and sufficient water repellency. The best current density obtained from the PEMFC with the single-layer PTFE/CB-GDL was 1.27 and 0.42 A cm{sup -2} for H{sub 2}/O{sub 2} and H{sub 2}/air system, respectively. (author)

  19. Improving the light-emitting properties of single-layered polyfluorene light-emitting devices by simple ionic liquid blending

    Science.gov (United States)

    Horike, Shohei; Nagaki, Hiroto; Misaki, Masahiro; Koshiba, Yasuko; Morimoto, Masahiro; Fukushima, Tatsuya; Ishida, Kenji

    2018-03-01

    This paper describes an evaluation of ionic liquids (ILs) as potential electrolytes for single-layered light-emitting devices with good emission performance. As optoelectronic devices continue to grow in abundance, high-performance light-emitting devices with a single emission layer are becoming increasingly important for low-cost production. We show that a simple technique of osmosing IL into the polymer layer can result in high luminous efficiency and good response times of single-layered light-emitting polymers, even without the additional stacking of charge carrier injection and transport layers. The IL contributions to the light-emission of the polymer are discussed from the perspectives of energy diagrams and of the electric double layers on the electrodes. Our findings enable a faster, cheaper, and lower-in-waste production of light-emitting devices.

  20. Structure and Electronic Properties of In Situ Synthesized Single-Layer MoS2 on a Gold Surface

    DEFF Research Database (Denmark)

    Sørensen, Signe Grønborg; Füchtbauer, Henrik Gøbel; Tuxen, Anders Kyrme

    2014-01-01

    with scanning tunneling microscopy and X-ray photoelectron spectroscopy characterization of two-dimensional single-layer islands of MoS2 synthesized directly on a gold single crystal substrate. Thanks to a periodic modulation of the atom stacking induced by the lattice mismatch, we observe a structural buckling...... structure appears modified at the band gap edges. This electronic effect is further modulated by the moiré periodicity and leads to small substrate-induced electronic perturbations near the conduction band minimum in the band gap of MoS2. The results may be highly relevant in the context of nanopatterned......When transition metal sulfides such as MoS2 are present in the single-layer form, the electronic properties change in fundamental ways, enabling them to be used, e.g., in two-dimensional semiconductor electronics, optoelectronics, and light harvesting. The change is related to a subtle modification...

  1. A meta-analytic review of the effectiveness of single-layer clothing in preventing exposure from pesticide handling.

    Science.gov (United States)

    Miguelino, Eric S

    2014-01-01

    This review summarizes available information on the penetration of pesticides through single-layer clothing by pesticide handlers and introduces epidemiological and observational studies on pesticide exposure. The data for this report were taken from peer-reviewed articles, publicly available government reports, and publicly available government reviews of registrant-submitted data and information. The arithmetic mean of calculated clothing penetration was obtained for various parts of the body (upper arm, lower arm, chest/torso, back/torso, upper leg, and lower leg) that were exposed to pesticide. The range of pesticide penetration to the various parts of the body through single-layer clothing during mixing, loading, and application (MLA) activities was found to be 6.2% ± 5.7% to 21.4% ± 6.7%, which demonstrates a potential for increased and unintentional pesticide exposures. Based on this evaluation, some accepted default values for protection against pesticide exposure may be overestimated.

  2. Spin-dependent electron-phonon coupling in the valence band of single-layer WS2

    DEFF Research Database (Denmark)

    Hinsche, Nicki Frank; Ngankeu, Arlette S.; Guilloy, Kevin

    2017-01-01

    The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin....... Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of λK=0.0021 and 0.......40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results....

  3. Single-layer ZnS supported on Au(111): A combined XPS, LEED, STM and DFT study

    Science.gov (United States)

    Deng, Xingyi; Sorescu, Dan C.; Lee, Junseok

    2017-04-01

    Single-layer of ZnS, consisting of one atomic layer of ZnS(111) plane, has been grown on Au(111) and characterized using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the LEED measurement indicates a coincidence structure of ZnS-(3×3)/Au(111)-(4×4), high resolution STM images reveal hexagonal unit cells of 6.7×6.7 Å2 and 11.6×11.6 Å2, corresponding to √3 and 3 times the unit cell of the ideal zincblende ZnS-(1×1), respectively, depending on the tunneling conditions. Calculations based on density functional theory (DFT) indicate a significantly reconstructed non-planar structure of ZnS single-layer on Au(111) with 2/3 of the S anions being located nearly in the plane of the Zn cations and the rest 1/3 of the S anions protruding above the Zn plane. The calculated STM image shows similar characteristics to those of the experimental STM image. Additionally, the DFT calculations reveal the different bonding nature of the S anions in ZnS single-layer supported on Au(111).

  4. Comparing the urbanization and global warming impacts on extreme rainfall characteristics in Southern China Pearl River Delta megacity based on dynamical downscaling

    Science.gov (United States)

    Fung, K. Y.; Tam, C. Y.; Wang, Z.

    2017-12-01

    It is well known that urban land use can significantly influence the local temperature, precipitation and meteorology through altering land-atmosphere exchange of momentum, moisture and heat in urban areas. In recent decades, there has been a substantial increase ( 5-10%) on the intensity of extreme rainfall over Southeast China; it is projected to increase further according to the latest IPCC reports. In this study, we assess how urbanization and global warming together might impact on heavy precipitation characteristics over the highly urbanized Pearl River Delta (PRD) megacity, located in southern China. This is done by dynamically downscaling GFDL-ESM2M simulations for the present and future (RCP8.5) climate scenarios, using the Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model (UCM). Over the PRD area, the WRF model is integrated at a resolution of 2km x 2km. To focus on extreme events, episodes covering daily rainfall intensity above the 99th percentile in Southeast China in the GFDL-ESM2M daily precipitation datasets were first identified. These extreme episodes were then dynamically downscaled in two parallel experiments with the following model designs: one with anthropogenic heat flux (AH) = 0 Wm-2 and the other with peak AH = 300 Wm-2 in the AH diurnal cycle over the urban domain. Results show that, with AH in urban area, the urban 2m-temperature can rise by about 2oC. This in turn leads to an increase of the mean as well as the extreme rain rates by 10-15% in urban domain. The latter is comparable to the impact of global warming alone, according to downscaling experiments for the RCP8.5 scenario. Implications of our results on urban effects on extreme rainfall under a warming background climate will be discussed.

  5. Forests and Their Canopies: Achievements and Horizons in Canopy Science.

    Science.gov (United States)

    Nakamura, Akihiro; Kitching, Roger L; Cao, Min; Creedy, Thomas J; Fayle, Tom M; Freiberg, Martin; Hewitt, C N; Itioka, Takao; Koh, Lian Pin; Ma, Keping; Malhi, Yadvinder; Mitchell, Andrew; Novotny, Vojtech; Ozanne, Claire M P; Song, Liang; Wang, Han; Ashton, Louise A

    2017-06-01

    Forest canopies are dynamic interfaces between organisms and atmosphere, providing buffered microclimates and complex microhabitats. Canopies form vertically stratified ecosystems interconnected with other strata. Some forest biodiversity patterns and food webs have been documented and measurements of ecophysiology and biogeochemical cycling have allowed analyses of large-scale transfer of CO 2 , water, and trace gases between forests and the atmosphere. However, many knowledge gaps remain. With global research networks and databases, and new technologies and infrastructure, we envisage rapid advances in our understanding of the mechanisms that drive the spatial and temporal dynamics of forests and their canopies. Such understanding is vital for the successful management and conservation of global forests and the ecosystem services they provide to the world. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  6. Urbanization-induced urban heat island and aerosol effects on climate extremes in the Yangtze River Delta region of China

    Science.gov (United States)

    Zhong, Shi; Qian, Yun; Zhao, Chun; Leung, Ruby; Wang, Hailong; Yang, Ben; Fan, Jiwen; Yan, Huiping; Yang, Xiu-Qun; Liu, Dongqing

    2017-04-01

    The WRF-Chem model coupled with a single-layer urban canopy model (UCM) is integrated for 5 years at convection-permitting scale to investigate the individual and combined impacts of urbanization-induced changes in land cover and pollutant emissions on regional climate in the Yangtze River Delta (YRD) region in eastern China. Simulations with the urbanization effects reasonably reproduced the observed features of temperature and precipitation in the YRD region. Urbanization over the YRD induces an urban heat island (UHI) effect, which increases the surface temperature by 0.53 °C in summer and increases the annual heat wave days at a rate of 3.7 d yr-1 in the major megacities in the YRD, accompanied by intensified heat stress. In winter, the near-surface air temperature increases by approximately 0.7 °C over commercial areas in the cities but decreases in the surrounding areas. Radiative effects of aerosols tend to cool the surface air by reducing net shortwave radiation at the surface. Compared to the more localized UHI effect, aerosol effects on solar radiation and temperature influence a much larger area, especially downwind of the city cluster in the YRD. Results also show that the UHI increases the frequency of extreme summer precipitation by strengthening the convergence and updrafts over urbanized areas in the afternoon, which favor the development of deep convection. In contrast, the radiative forcing of aerosols results in a surface cooling and upper-atmospheric heating, which enhances atmospheric stability and suppresses convection. The combined effects of the UHI and aerosols on precipitation depend on synoptic conditions. Two rainfall events under two typical but different synoptic weather patterns are further analyzed. It is shown that the impact of urban land cover and aerosols on precipitation is not only determined by their influence on local convergence but also modulated by large-scale weather systems. For the case with a strong synoptic forcing

  7. Peculiarities of superconductivity in the single-layer FeSe /SrTi O3 interface

    Science.gov (United States)

    Gor'kov, Lev P.

    2016-02-01

    Observation of replica bands in the angle-resolved photoemission spectroscopy (ARPES) spectra of single-layer FeSe on a strontium titanate substrate revealed a phonon component contribution to mechanisms behind its high-Tc superconductivity. We study the interaction of the in-layer FeSe electrons with the electric potential of the longitudinal (LO) modes at the surface of bulk SrTi O3 . A two-dimensional system of charges at the FeSe /SrTi O3 interface includes both the itinerant and the immobile electrons. The latter significantly change the interface characteristics, increasing screening at the substrate surface and thereby reducing the strength of the electron-LO-phonon interaction. In what follows, the dielectric constant serves as a free parameter and is determined using the ARPES measurements of the replicas. Two-dimensional Coulomb screening is accounted for in the random-phase approximation. It is shown that the model is applicable over the entire range of the parameters typical for current experiments. The estimates from this model make possible the conclusion that the LO-phonon-mediated pairing alone cannot account for the temperatures of the superconducting transitions Tc in the single-layer FeSe /SrTi O3 reported in these experiments. This does not exclude that the LO-phonon mechanisms can become more significant in differently and better prepared single-layer FeSe films. Available experiments are briefly discussed. Thus far no measurements exist on the dependence of Tc on the concentration of electrons doped into the in-layer FeSe band.

  8. [Observation of single-layered inverted internal limiting membrane flap technique for macular hole with retinal detachment in high myopia].

    Science.gov (United States)

    Xu, C Z; Wu, J H; He, J W; Feng, C

    2017-05-11

    Objective: To compare the outcome of pars plana vitrectomy (PPV) with a single-layered inverted internal limiting membrane (ILM) flap versus PPV with ILM peeling for the treatment of macular hole associated retinal detachment (MHRD) in high myopia. Methods: In a retrospective cohort study, PPV with 2 kinds of adjuvant surgical procedures were used in 35 moderately high myopia eyes with MHRD. These eyes were divided into 2 groups: group 1 (17 eyes) receiving PPV and ILM peeling and group 2 (18 eyes) receiving PPV with a single-layered inverted ILM flap. Anatomical reattachment of the retina, macular hole closure, and best-corrected visual acuity (BCVA) were measured at 6 months after surgery. Results: The retina was successfully reattached in all cases. The difference of the retinal reattachment rate between the two groups was not statistically significant (Fisher's exact test, P= 1.000). The rate of macular hole closure was 47.1% in group 1 (8 eyes) and 88.9% in group 2 (16 eyes). The difference of the macular hole closure rate between the two groups was statistically significant (Fisher's exact test, P= 0.012). Significant improvement in logarithm of minimal angle of resolution (logMAR) BCVA was achieved in both groups. There was no difference in the initial, final, or improved logMAR BCVA in the 2 groups. Conclusion: Single-layered inverted ILM flap technique effectively helps close the macular hole in moderately high myopia with MHRD. This may prevent the possible redetachment from the macular hole. (Chin J Ophthalmol, 2017, 53: 338 - 343) .

  9. Canopy spectral invariants for remote sensing and model applications

    NARCIS (Netherlands)

    Huang, D.; Knyazikhin, Y.; Dickinson, R.E.; Rautiainen, M.; Stenberg, P.; Disney, M.; Lewis, P.; Cescatti, A.; Tian, Y.; Verhoef, W.; Martonchik, J.V.; Myneni, R.B.

    2007-01-01

    The concept of canopy spectral invariants expresses the observation that simple algebraic combinations of leaf and canopy spectral transmittance and reflectance become wavelength independent and determine a small set of canopy structure specific variables. This set includes the canopy interceptance,

  10. Self-assembly surface modified indium-tin oxide anodes for single-layer light-emitting diodes

    CERN Document Server

    Morgado, J; Charas, A; Matos, M; Alcacer, L; Cacialli, F

    2003-01-01

    We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.

  11. Effect of ethanethiolate spacer on morphology and optical responses of Ag nanoparticle array-single layer graphene hybrid systems

    Czech Academy of Sciences Publication Activity Database

    Sutrová, Veronika; Šloufová, I.; Melníková Komínková, Zuzana; Kalbáč, Martin; Pavlova, Ewa; Vlčková, B.

    2017-01-01

    Roč. 33, č. 50 (2017), s. 14414-14424 ISSN 0743-7463 R&D Projects: GA ČR(CZ) GA15-01953S; GA MŠk(CZ) LM2015073 Grant - others:GA MŠk(CZ) CZ.02.1.01/0.0/0.0/16_013/0001821 Institutional support: RVO:61389013 ; RVO:61388955 Keywords : Ag nanoparticle * single layer graphene * ethanethiol Subject RIV: JI - Composite Materials; CF - Physical ; Theoretical Chemistry (UFCH-W) OBOR OECD: Composites (including laminates, reinforced plastics, cermets, combined natural and synthetic fibre fabrics; Physical chemistry (UFCH-W) Impact factor: 3.833, year: 2016

  12. Self-assembly surface modified indium-tin oxide anodes for single-layer light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Morgado, Jorge [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Barbagallo, Nunzio [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Charas, Ana [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Matos, Manuel [Departamento de Engenharia Quimica, Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emidio Navarro-1, P-1949-001 Lisbon (Portugal); Alcacer, Luis [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Cacialli, Franco [Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT (United Kingdom)

    2003-03-07

    We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.

  13. Model for a collimated spin-wave beam generated by a single-layer spin torque nanocontact

    Science.gov (United States)

    Hoefer, M. A.; Silva, T. J.; Stiles, M. D.

    2008-04-01

    A model of spin-torque-induced magnetization dynamics based on semiclassical spin diffusion theory for a single-layer nanocontact is presented. The model incorporates effects due to the current-induced Oersted field and predicts the generation of a variety of spatially dependent, coherent, precessional magnetic wave structures. Directionally controllable collimated spin-wave beams, vortex spiral waves, and localized standing waves are found to be excited by the interplay of the Oersted field and the orientation of an applied field. These fields act as a spin-wave “corral” around the nanocontact that controls the propagation of spin waves in certain directions.

  14. Anisotropic Young's Modulus for Single-Layer Black Phosphorus: The Third Principle Direction Besides Armchair and Zigzag

    OpenAIRE

    Jiang, Jin-Wu

    2015-01-01

    We derive an analytic formula for the Young's modulus in single-layer black phosphorus using the valence force field model. By analyzing the directional dependence for the Young's modulus, we explore the third principle direction with direction angle phi_tp = 0.268pi besides armchair and zigzag directions. The maximum Young's modulus value is in the third principle direction. More specifically, the Young's modulus is 52.2 N/m, 85.4 N/m, and 111.4 N/m in the armchair direction, zigzag directio...

  15. Future Climate Prediction of Urban Atmosphere in A Tropical Megacity: Utilization of RCP/SSP Scenarios with an Urban Growth Model

    Science.gov (United States)

    Darmanto, N. S.; Varquez, A. C. G.; Kanda, M.; Takakuwa, S.

    2016-12-01

    Economic development in Southeast Asia megacities leads to rapid transformation into more complicated urban configurations. These configurations, including building geometry, enhance aerodynamic drag thus reducing near-surface wind speeds. Roughness parameters representing building geometry, along with anthropogenic heat emissions, contribute to the formation of urban heat islands (UHI). All these have been reproduced successfully in the Weather Research and Forecasting (WRF) Model coupled with an improved single-layer urban canopy model incorporating a realistic distribution of urban parameters and anthropogenic heat emission in the Jakarta Greater Area. We apply this technology to climate change studies by introducing future urbanization defined by urban sprawl, vertical rise in buildings, and increase anthropogenic heat emission (AHE) due to population changes, into futuristic climate modelling. To simulate 2050s future climate, pseudo-global warming method was used which relied on current and ensembles of 5 CMIP5 GCMs for 2 representative concentration pathways (RCP), 2.6 and 8.5. To determine future urbanization level, 2050 population growth and energy consumption were estimated from shared socioeconomic pathways (SSP). This allows the estimation of future urban sprawl, building geometry, and AHE using the SLEUTH urban growth model and spatial growth assumptions. Two cases representing combinations of RCP and SSP were simulated in WRF: RCP2.6-SSP1 and RCP8.5-SSP3. Each case corresponds to best and worst-case scenarios of implementing adaptation and mitigation strategies, respectively. It was found that 2-m temperature of Jakarta will increase by 0.62°C (RCP2.6) and 1.44°C (RCP8.5) solely from background climate change; almost on the same magnitude as the background temperature increase of RCP2.6 (0.5°C) and RCP8.5 (1.2°C). Compared with previous studies, the result indicates that the effect of climate change on UHI in tropical cities may be lesser than

  16. Growing vertical ZnO nanorod arrays within graphite: efficient isolation of large size and high quality single-layer graphene.

    Science.gov (United States)

    Ding, Ling; E, Yifeng; Fan, Louzhen; Yang, Shihe

    2013-07-18

    We report a unique strategy for efficiently exfoliating large size and high quality single-layer graphene directly from graphite into DMF dispersions by growing ZnO nanorod arrays between the graphene layers in graphite.

  17. Analytical and molecular dynamics studies on the impact loading of single-layered graphene sheet by fullerene

    Science.gov (United States)

    Hosseini-Hashemi, Shahrokh; Sepahi-Boroujeni, Amin; Sepahi-Boroujeni, Saeid

    2018-04-01

    Normal impact performance of a system including a fullerene molecule and a single-layered graphene sheet is studied in the present paper. Firstly, through a mathematical approach, a new contact law is derived to describe the overall non-bonding interaction forces of the "hollow indenter-target" system. Preliminary verifications show that the derived contact law gives a reliable picture of force field of the system which is in good agreements with the results of molecular dynamics (MD) simulations. Afterwards, equation of the transversal motion of graphene sheet is utilized on the basis of both the nonlocal theory of elasticity and the assumptions of classical plate theory. Then, to derive dynamic behavior of the system, a set including the proposed contact law and the equations of motion of both graphene sheet and fullerene molecule is solved numerically. In order to evaluate outcomes of this method, the problem is modeled by MD simulation. Despite intrinsic differences between analytical and MD methods as well as various errors arise due to transient nature of the problem, acceptable agreements are established between analytical and MD outcomes. As a result, the proposed analytical method can be reliably used to address similar impact problems. Furthermore, it is found that a single-layered graphene sheet is capable of trapping fullerenes approaching with low velocities. Otherwise, in case of rebound, the sheet effectively absorbs predominant portion of fullerene energy.

  18. First-principles study of thermal expansion and thermomechanics of single-layer black and blue phosphorus

    International Nuclear Information System (INIS)

    Sun, Hongyi; Liu, Gang; Li, Qingfang; Wan, X.G.

    2016-01-01

    The linear thermal expansion coefficients (LTEC) and thermomechanics of single-layer black and blue phosphorus are systematically studied using first-principles based on quasiharmonic approximation. We find the thermal expansion of black phosphorus is very anisotropic. The LTEC along zigzag direction has a turning from negative to positive at around 138 K, while the LTEC along armchair direction is positive (except below 8 K) and about 2.5 times larger than that along zigzag direction at 300 K. For blue phosphorus, the LTEC is negative in the temperature range from 0 to 350 K. In addition, we find that the Young's modulus and Poisson's ratio of black phosphorus along zigzag direction are 4 to 5 times larger than those along armchair direction within considered temperature range, showing a remarkable anisotropic in-plane thermomechanics property. The mechanisms of these peculiar thermal properties are also explored. This work provides a theoretical understanding of the thermal expansion and thermomechanics of this single layer phosphorus family, which will be useful in nanodevices. - Highlights: • The thermal properties of black and blue phosphorus are studied. • Black phosphorus shows remarkable anisotropic thermal expansion and thermomechanics properties. • Blue phosphorus shows novel negative thermal expansion. • The thermal expansion properties are well analyzed by grüneisen theory.

  19. A development of simulation and analytical program for through-diffusion experiments for a single layer of diffusion media

    International Nuclear Information System (INIS)

    Sato, Haruo

    2001-01-01

    A program (TDROCK1. FOR) for simulation and analysis of through-diffusion experiments for a single layer of diffusion media was developed. This program was made by Pro-Fortran language, which was suitable for scientific and technical calculations, and relatively easy explicit difference method was adopted for an analysis. In the analysis, solute concentration in the tracer cell as a function of time that we could not treat to date can be input and the decrease in the solute concentration as a function of time by diffusion from the tracer cell to the measurement cell, the solute concentration distribution in the porewater of diffusion media and the solute concentration in the measurement cell as a function of time can be calculated. In addition, solution volume in both cells and diameter and thickness of the diffusion media are also variable as an input condition. This simulation program could well explain measured result by simulating solute concentration in the measurement cell as a function of time for case which apparent and effective diffusion coefficients were already known. Based on this, the availability and applicability of this program to actual analysis and simulation were confirmed. This report describes the theoretical treatment for the through-diffusion experiments for a single layer of diffusion media, analytical model, an example of source program and the manual. (author)

  20. Alkali (Li, K and Na) and alkali-earth (Be, Ca and Mg) adatoms on SiC single layer

    Science.gov (United States)

    Baierle, Rogério J.; Rupp, Caroline J.; Anversa, Jonas

    2018-03-01

    First-principles calculations within the density functional theory (DFT) have been addressed to study the energetic stability, and electronic properties of alkali and alkali-earth atoms adsorbed on a silicon carbide (SiC) single layer. We observe that all atoms are most stable (higher binding energy) on the top of a Si atom, which moves out of the plane (in the opposite direction to the adsorbed atom). Alkali atoms adsorbed give raise to two spin unpaired electronic levels inside the band gap leading the SiC single layer to exhibit n-type semiconductor properties. For alkaline atoms adsorbed there is a deep occupied spin paired electronic level inside the band gap. These finding suggest that the adsorption of alkaline and alkali-earth atoms on SiC layer is a powerful feature to functionalize two dimensional SiC structures, which can be used to produce new electronic, magnetic and optical devices as well for hydrogen and oxygen evolution reaction (HER and OER, respectively). Furthermore, we observe that the adsorption of H2 is ruled by dispersive forces (van der Waals interactions) while the O2 molecule is strongly adsorbed on the functionalized system.

  1. Design of single-layer high-efficiency transmitting phase-gradient metasurface and high gain antenna

    Science.gov (United States)

    Zhang, Di; Yang, Xiaoqing; Su, Piqiang; Luo, Jiefang; Chen, Huijie; Yuan, Jianping; Li, Lixin

    2017-12-01

    In this paper, based on rotation phase-gradient principle, a single-layer, high-efficiency transmitting metasurface is designed and applied to high-gain antenna. In the case of circularly polarized incident wave, the PCR (polarization conversions ratio) of the metasurface element is greater than 90% in the band of 9.11–10.48 GHz. The transmitting wave emerges an anomalous refraction when left-handed circularly polarized wave are incident perpendicularly to the 1D phase-gradient metasurface, which is composed of cycle arrangement of 6 units with step value of 30°. The simulated anomalous refraction angle is 40.1°, coincided with the theoretical design value (40.6°). For further application, the 2D focused metasurface is designed to enhance the antenna performance while the left-handed circularly polarized antenna is placed at the focus. The simulated max gain is increased by 12 dB (182%) and the half-power beamwidth is reduced by 74.6°. The measured results are coincided with the simulations, which indicates the antenna has high directivity. The designed single-layer transmission metasurface has advantages of thin thickness (only 1.5 mm), high efficiency and light weight, and will have important application prospects in polarization conversion and beam control.

  2. Forests and their canopies: Archievements and horizons in canopy science

    Czech Academy of Sciences Publication Activity Database

    Nakamura, A.; Kitching, R. L.; Cao, M.; Creedy, T. J.; Fayle, Tom Maurice; Freiberg, M.; Hewitt, C. N.; Itioka, T.; Koh, L. P.; Ma, K.; Malhi, Y.; Mitchell, A.; Novotný, Vojtěch; Ozanne, C. M. P.; Song, L.; Wang, H.; Ashton, L. A.

    2017-01-01

    Roč. 32, č. 6 (2017), s. 438-451 ISSN 0169-5347 R&D Projects: GA ČR(CZ) GA16-09427S; GA ČR GB14-36098G EU Projects: European Commission(XE) 669609 - Diversity6continents Institutional support: RVO:60077344 Keywords : biodiversity * canopy * cranes Subject RIV: EH - Ecology, Behaviour OBOR OECD: Ecology Impact factor: 15.268, year: 2016 http://www.sciencedirect.com/science/article/pii/S0169534717300599

  3. A photosynthesis-based two-leaf canopy stomatal ...

    Science.gov (United States)

    A coupled photosynthesis-stomatal conductance model with single-layer sunlit and shaded leaf canopy scaling is implemented and evaluated in a diagnostic box model with the Pleim-Xiu land surface model (PX LSM) and ozone deposition model components taken directly from the meteorology and air quality modeling system—WRF/CMAQ (Weather Research and Forecast model and Community Multiscale Air Quality model). The photosynthesis-based model for PX LSM (PX PSN) is evaluated at a FLUXNET site for implementation against different parameterizations and the current PX LSM approach with a simple Jarvis function (PX Jarvis). Latent heat flux (LH) from PX PSN is further evaluated at five FLUXNET sites with different vegetation types and landscape characteristics. Simulated ozone deposition and flux from PX PSN are evaluated at one of the sites with ozone flux measurements. Overall, the PX PSN simulates LH as well as the PX Jarvis approach. The PX PSN, however, shows distinct advantages over the PX Jarvis approach for grassland that likely result from its treatment of C3 and C4 plants for CO2 assimilation. Simulations using Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) rather than LAI measured at each site assess how the model would perform with grid averaged data used in WRF/CMAQ. MODIS LAI estimates degrade model performance at all sites but one site having exceptionally old and tall trees. Ozone deposition velocity and ozone flux along with LH

  4. Phase manipulation of Goos–Hänchen shifts in a single-layer of graphene nanostructure under strong magnetic field

    Science.gov (United States)

    Solookinejad, Gh; Jabbari, M.; Panahi, M.; Ahmadi Sangachin, E.

    2017-11-01

    In this paper, we discuss the phase management of Goos–Hänchen (GH) shifts of a probe light through a cavity with a single-layer graphene nanostructure under a strong magnetic field. By using the quantum mechanical density matrix formalism we study the GH shifts of reflected and transmitted light beams. It is realized that negative or positive GH shifts can be achieved simultaneously by tuning some controllable parameters such as relative phase and the Rabi frequency of the applied fields. Moreover, the thickness effect of the cavity structure is considered as an effective parameter for adjusting the GH shifts of reflected and transmitted light beams. We find that by choosing suitable parameters, a maximum negative shift of 4.5 mm and positive shift of 5.4 mm are possible for GH shifts in reflected and transmitted light. Our proposed model may be useful for developing all-optical devices in the infrared region.

  5. p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor.

    Science.gov (United States)

    Di Bernardo, A; Millo, O; Barbone, M; Alpern, H; Kalcheim, Y; Sassi, U; Ott, A K; De Fazio, D; Yoon, D; Amado, M; Ferrari, A C; Linder, J; Robinson, J W A

    2017-01-19

    Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.

  6. Controlling the formation of wrinkles in a single layer graphene sheet subjected to in-plane shear

    KAUST Repository

    Duan, Wen Hui

    2011-08-01

    The initiation and development of wrinkles in a single layer graphene sheet subjected to in-plane shear displacements are investigated. The dependence of the wavelength and amplitude of wrinkles on the applied shear displacements is explicitly obtained with molecular mechanics simulations. A continuum model is developed for the characteristics of the wrinkles which show that the wrinkle wavelength decreases with an increase in shear loading, while the amplitude of the wrinkles is found to initially increase and then become stable. The propagation and growth process of the wrinkles in the sheet is elucidated. It is expected that the research could promote applications of graphenes in the transportation of biological systems, separation science, and the development of the fluidic electronics. © 2011 Elsevier Ltd. All rights reserved.

  7. Phase transitions and optical properties of the semiconducting and metallic phases of single-layer MoS₂.

    Science.gov (United States)

    Fair, K M; Ford, M J

    2015-10-30

    We report density functional theory calculations for single layer MoS2 in its 2H, semiconducting and 1T metallic phases in order to understand the relative stability of these two phases and transition between them in the presence of adsorbed lithium atoms and under compressive strain. We have determined the diffusion barriers between the two phases and demonstrate how the presence of Li adatoms or strain can significantly reduce these barriers. We show that the 2H and 1T structures have the same energy under 15% biaxial, compressive strain. This is the same strain value posited by Lin et al (2014 Nat. Nanotechnology 9 391-396) for their intermediate α phase. Calculations of the 1T and 2H permittivity and electron energy loss spectrum are also performed and characterized.

  8. 1617 nm emission control of an Er:YAG laser by a corrugated single-layer resonant grating mirror.

    Science.gov (United States)

    Aubourg, Adrien; Rumpel, Martin; Didierjean, Julien; Aubry, Nicolas; Graf, Thomas; Balembois, François; Georges, Patrick; Ahmed, Marwan Abdou

    2014-02-01

    A resonant grating mirror (RGM) that combines a single layer planar waveguide and a subwavelength grating is used to simultaneously control the beam quality, the spectral bandwidth, and the polarization state of an Er:YAG laser. This simple device is compared to classical methods using several intracavity components: an etalon for wavelength selection, a thin film polarizer for polarization selection, and an aperture for spatial filtering. It is demonstrated that the RGM provides the same polarization purity, an enhanced spectral filtering, and a significant improvement of the beam quality. In CW operation, the Er:YAG laser with a RGM emits an output power of 1.4 W at 1617 nm with a M2 of 1.4.

  9. Highly balanced single-layer high-temperature superconductor SQUID gradiometer freely movable within the Earth's magnetic field

    International Nuclear Information System (INIS)

    Schultze, Volkmar; IJsselsteijn, Rob; May, Torsten; Meyer, Hans-Georg

    2003-01-01

    We developed a gradiometer system based on a single-layer high-temperature superconductor dc superconducting quantum interference device (SQUID), which can be freely moved within the Earth's magnetic field during measurement. The problem of circumferential shielding currents in the parallel gradiometer pick-up loop is solved by the use of an appropriately designed magnetometer SQUID integrated on the gradiometer chip. The magnetometer's feedback coil of the flux-locked loop is laid out as a small Helmholtz coil pair, thus keeping the homogeneous magnetic field constant for both the magnetometer and the gradiometer. Therefore, the balance of the directly coupled gradiometer SQUID is enhanced from 100 up to 3800. The noise limited magnetic field gradient resolution of 45 pT m -1 Hz -1/2 is preserved down to frequencies of several Hz even after strong motion in the Earth's magnetic field

  10. Analysis of current-driven oscillatory dynamics of single-layer homoepitaxial islands on crystalline conducting substrates

    Science.gov (United States)

    Dasgupta, Dwaipayan; Kumar, Ashish; Maroudas, Dimitrios

    2018-03-01

    We report results of a systematic study on the complex oscillatory current-driven dynamics of single-layer homoepitaxial islands on crystalline substrate surfaces and the dependence of this driven dynamical behavior on important physical parameters, including island size, substrate surface orientation, and direction of externally applied electric field. The analysis is based on a nonlinear model of driven island edge morphological evolution that accounts for curvature-driven edge diffusion, edge electromigration, and edge diffusional anisotropy. Using a linear theory of island edge morphological stability, we calculate a critical island size at which the island's equilibrium edge shape becomes unstable, which sets a lower bound for the onset of time-periodic oscillatory dynamical response. Using direct dynamical simulations, we study the edge morphological dynamics of current-driven single-layer islands at larger-than-critical size, and determine the actual island size at which the migrating islands undergo a transition from steady to time-periodic asymptotic states through a subcritical Hopf bifurcation. At the highest symmetry of diffusional anisotropy examined, on {111} surfaces of face-centered cubic crystalline substrates, we find that more complex stable oscillatory states can be reached through period-doubling bifurcation at island sizes larger than those at the Hopf points. We characterize in detail the island morphology and dynamical response at the stable time-periodic asymptotic states, determine the range of stability of these oscillatory states terminated by island breakup, and explain the morphological features of the stable oscillating islands on the basis of linear stability theory.

  11. Global distribution of urban parameters derived from high-resolution global datasets for weather modelling

    Science.gov (United States)

    Kawano, N.; Varquez, A. C. G.; Dong, Y.; Kanda, M.

    2016-12-01

    Numerical model such as Weather Research and Forecasting model coupled with single-layer Urban Canopy Model (WRF-UCM) is one of the powerful tools to investigate urban heat island. Urban parameters such as average building height (Have), plain area index (λp) and frontal area index (λf), are necessary inputs for the model. In general, these parameters are uniformly assumed in WRF-UCM but this leads to unrealistic urban representation. Distributed urban parameters can also be incorporated into WRF-UCM to consider a detail urban effect. The problem is that distributed building information is not readily available for most megacities especially in developing countries. Furthermore, acquiring real building parameters often require huge amount of time and money. In this study, we investigated the potential of using globally available satellite-captured datasets for the estimation of the parameters, Have, λp, and λf. Global datasets comprised of high spatial resolution population dataset (LandScan by Oak Ridge National Laboratory), nighttime lights (NOAA), and vegetation fraction (NASA). True samples of Have, λp, and λf were acquired from actual building footprints from satellite images and 3D building database of Tokyo, New York, Paris, Melbourne, Istanbul, Jakarta and so on. Regression equations were then derived from the block-averaging of spatial pairs of real parameters and global datasets. Results show that two regression curves to estimate Have and λf from the combination of population and nightlight are necessary depending on the city's level of development. An index which can be used to decide which equation to use for a city is the Gross Domestic Product (GDP). On the other hand, λphas less dependence on GDP but indicated a negative relationship to vegetation fraction. Finally, a simplified but precise approximation of urban parameters through readily-available, high-resolution global datasets and our derived regressions can be utilized to estimate a

  12. Canopy Dynamics in Nanoscale Ionic Materials

    KAUST Repository

    Jespersen, Michael L.

    2010-07-27

    Nanoscale ionic materials (NIMS) are organic - inorganic hybrids in which a core nanostructure is functionalized with a covalently attached corona and an ionically tethered organic canopy. NIMS are engineered to be liquids under ambient conditions in the absence of solvent and are of interest for a variety of applications. We have used nuclear magnetic resonance (NMR) relaxation and pulse-field gradient (PFG) diffusion experiments to measure the canopy dynamics of NIMS prepared from 18-nm silica cores modified by an alkylsilane monolayer possessing terminal sulfonic acid functionality, paired with an amine-terminated ethylene oxide/propylene oxide block copolymer canopy. Carbon NMR studies show that the block copolymer canopy is mobile both in the bulk and in the NIMS and that the fast (ns) dynamics are insensitive to the presence of the silica nanoparticles. Canopy diffusion in the NIMS is slowed relative to the neat canopy, but not to the degree predicted from the diffusion of hard-sphere particles. Canopy diffusion is not restricted to the surface of the nanoparticles and shows unexpected behavior upon addition of excess canopy. Taken together, these data indicate that the liquid-like behavior in NIMS is due to rapid exchange of the block copolymer canopy between the ionically modified nanoparticles. © 2010 American Chemical Society.

  13. Estimating forest canopy fuel parameters using LIDAR data.

    Science.gov (United States)

    Hans-Erik Andersen; Robert J. McGaughey; Stephen E. Reutebuch

    2005-01-01

    Fire researchers and resource managers are dependent upon accurate, spatially-explicit forest structure information to support the application of forest fire behavior models. In particular, reliable estimates of several critical forest canopy structure metrics, including canopy bulk density, canopy height, canopy fuel weight, and canopy base height, are required to...

  14. VitiCanopy: A Free Computer App to Estimate Canopy Vigor and Porosity for Grapevine.

    Science.gov (United States)

    De Bei, Roberta; Fuentes, Sigfredo; Gilliham, Matthew; Tyerman, Steve; Edwards, Everard; Bianchini, Nicolò; Smith, Jason; Collins, Cassandra

    2016-04-23

    Leaf area index (LAI) and plant area index (PAI) are common and important biophysical parameters used to estimate agronomical variables such as canopy growth, light interception and water requirements of plants and trees. LAI can be either measured directly using destructive methods or indirectly using dedicated and expensive instrumentation, both of which require a high level of know-how to operate equipment, handle data and interpret results. Recently, a novel smartphone and tablet PC application, VitiCanopy, has been developed by a group of researchers from the University of Adelaide and the University of Melbourne, to estimate grapevine canopy size (LAI and PAI), canopy porosity, canopy cover and clumping index. VitiCanopy uses the front in-built camera and GPS capabilities of smartphones and tablet PCs to automatically implement image analysis algorithms on upward-looking digital images of canopies and calculates relevant canopy architecture parameters. Results from the use of VitiCanopy on grapevines correlated well with traditional methods to measure/estimate LAI and PAI. Like other indirect methods, VitiCanopy does not distinguish between leaf and non-leaf material but it was demonstrated that the non-leaf material could be extracted from the results, if needed, to increase accuracy. VitiCanopy is an accurate, user-friendly and free alternative to current techniques used by scientists and viticultural practitioners to assess the dynamics of LAI, PAI and canopy architecture in vineyards, and has the potential to be adapted for use on other plants.

  15. Single layers and multilayers of GaN and AlN in square-octagon structure: Stability, electronic properties, and functionalization

    Science.gov (United States)

    Gürbüz, E.; Cahangirov, S.; Durgun, E.; Ciraci, S.

    2017-11-01

    Further to planar single-layer hexagonal structures, GaN and AlN can also form free-standing, single-layer structures constructed from squares and octagons. We performed an extensive analysis of dynamical and thermal stability of these structures in terms of ab initio finite-temperature molecular dynamics and phonon calculations together with the analysis of Raman and infrared active modes. These single-layer square-octagon structures of GaN and AlN display directional mechanical properties and have wide, indirect fundamental band gaps, which are smaller than their hexagonal counterparts. These density functional theory band gaps, however, increase and become wider upon correction. Under uniaxial and biaxial tensile strain, the fundamental band gaps decrease and can be closed. The electronic and magnetic properties of these single-layer structures can be modified by adsorption of various adatoms, or by creating neutral cation-anion vacancies. The single-layer structures attain magnetic moment by selected adatoms and neutral vacancies. In particular, localized gap states are strongly dependent on the type of vacancy. The energetics, binding, and resulting electronic structure of bilayer, trilayer, and three-dimensional (3D) layered structures constructed by stacking the single layers are affected by vertical chemical bonds between adjacent layers. In addition to van der Waals interaction, these weak vertical bonds induce buckling in planar geometry and enhance their binding, leading to the formation of stable 3D layered structures. In this respect, these multilayers are intermediate between van der Waals solids and wurtzite crystals, offering a wide range of tunability.

  16. A framework for adapting urban forests to climate change

    Science.gov (United States)

    Leslie Brandt; Abigail Derby Lewis; Robert Fahey; Lydia Scott; Lindsay Darling; Chris Swanston

    2016-01-01

    Planting urban trees and expanding urban forest canopy cover are often considered key strategies for reducing climate change impacts in urban areas. However, urban trees and forests can also be vulnerable to climate change through shifts in tree habitat suitability, changes in pests and diseases, and changes in extreme weather events. We developed a three-step...

  17. Density functional theory study of chemical sensing on surfaces of single-layer MoS2 and graphene

    International Nuclear Information System (INIS)

    Mehmood, F.; Pachter, R.

    2014-01-01

    In this work, density functional theory (DFT) calculations have been used to investigate chemical sensing on surfaces of single-layer MoS 2 and graphene, considering the adsorption of the chemical compounds triethylamine, acetone, tetrahydrofuran, methanol, 2,4,6-trinitrotoluene, o-nitrotoluene, o-dichlorobenzene, and 1,5-dicholoropentane. Physisorption of the adsorbates on free-standing surfaces was analyzed in detail for optimized material structures, considering various possible adsorption sites. Similar adsorption characteristics for the two surface types were demonstrated, where inclusion of a correction to the DFT functional for London dispersion was shown to be important to capture interactions at the interface of molecular adsorbate and surface. Charge transfer analyses for adsorbed free-standing surfaces generally demonstrated very small effects. However, charge transfer upon inclusion of the underlying SiO 2 substrate rationalized experimental observations for some of the adsorbates considered. A larger intrinsic response for the electron-donor triethylamine adsorbed on MoS 2 as compared to graphene was demonstrated, which may assist in devising chemical sensors for improved sensitivity

  18. Electronic evidence of an insulator-superconductor crossover in single-layer FeSe/SrTiO3 films.

    Science.gov (United States)

    He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2014-12-30

    In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator-superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator-superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator-superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator-superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature.

  19. Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO3 films

    Science.gov (United States)

    He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X. J.

    2014-01-01

    In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator–superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator–superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator–superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator–superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature. PMID:25502774

  20. High performance of low band gap polymer-based ambipolar transistor using single-layer graphene electrodes.

    Science.gov (United States)

    Choi, Jong Yong; Kang, Woonggi; Kang, Boseok; Cha, Wonsuk; Son, Seon Kyoung; Yoon, Youngwoon; Kim, Hyunjung; Kang, Youngjong; Ko, Min Jae; Son, Hae Jung; Cho, Kilwon; Cho, Jeong Ho; Kim, BongSoo

    2015-03-18

    Bottom-contact bottom-gate organic field-effect transistors (OFETs) are fabricated using a low band gap pDTTDPP-DT polymer as a channel material and single-layer graphene (SLG) or Au source/drain electrodes. The SLG-based ambipolar OFETs significantly outperform the Au-based ambipolar OFETs, and thermal annealing effectively improves the carrier mobilities of the pDTTDPP-DT films. The difference is attributed to the following facts: (i) the thermally annealed pDTTDPP-DT chains on the SLG assume more crystalline features with an edge-on orientation as compared to the polymer chains on the Au, (ii) the morphological features of the thermally annealed pDTTDPP-DT films on the SLG electrodes are closer to the features of those on the gate dielectric layer, and (iii) the SLG electrode provides a flatter, more hydrophobic surface that is favorable for the polymer crystallization than the Au. In addition, the preferred carrier transport in each electrode-based OFET is associated with the HOMO/LUMO alignment relative to the Fermi level of the employed electrode. All of these experimental results consistently explain why the carrier mobilities of the SLG-based OFET are more than 10 times higher than those of the Au-based OTFT. This work demonstrates the strong dependence of ambipolar carrier transport on the source/drain electrode and annealing temperature.

  1. Single-layer 2nd-order high-T{sub c} SQUID gradiometer for use in unshielded environments

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Soon-Gul; Park, Seung Moon; Kang, Chan Seok [Korea University, Chungnam (Korea, Republic of); Kim, In-Seon [Korea Research Institute of Standards and Science, Daejon (Korea, Republic of); Kim, Sang-Jae [Cheju National University, Cheju (Korea, Republic of)

    2006-05-15

    We have studied the fabrication of second-order SQUID gradiometers from single-layer high-T{sub c} film and the feasibility of using those gradiometers in magnetocardiography. The gradiometer contains three parallel-connected pickup loops that are directly coupled to a step-edge junction SQUID with the coupling polarity of the center loop opposite to those of the two side loops. For a well-balanced gradiometer with a balancing factor of 10{sup 3}, we achieved an unshielded gradient noise of 0.84 pT/cm{sup 2}/Hz{sup 1/2} at 1 Hz, which corresponds to an equivalent field noise of 280 fT/Hz{sup 1/2}. A gradiometer with a 5.8-mm baseline successfully recorded the magnetocardic signals of a human subject, demonstrating the feasibility of using the device in biomagnetism. We have also studied the use of submicron YBCO bridges as Josephson elements of long-baseline gradiometers. The bridges were fabricated from 3-{mu}m-wide, 300-nm-thick YBCO lines with a thin layer of Au on top by using a focused-ion-beam (FIB) patterning method. The temperature-dependent critical currents, I{sub c}(T), and the normal state resistances, R{sub N}(T), showed SIS-type behaviors, which are believed to be due to naturally formed grain boundaries.

  2. Timing and Distribution of Single-Layered Ejecta Craters Imply Sporadic Preservation of Tropical Subsurface Ice on Mars

    Science.gov (United States)

    Kirchoff, Michelle R.; Grimm, Robert E.

    2018-01-01

    Determining the evolution of tropical subsurface ice is a key component to understanding Mars's climate and geologic history. Study of an intriguing crater type on Mars—layered ejecta craters, which likely form by tapping subsurface ice—may provide constraints on this evolution. Layered ejecta craters have a continuous ejecta deposit with a fluidized-flow appearance. Single-layered ejecta (SLE) craters are the most common and dominate at tropical latitudes and therefore offer the best opportunity to derive new constraints on the temporal evolution of low-latitude subsurface ice. We estimate model formation ages of 54 SLE craters with diameter (D) ≥ 5 km using the density of small, superposed craters with D D 1 km indicates that ice could be preserved as shallow as 100 m or less at those locations. Finally, there is a striking spatial mixing in an area of highlands near the equator of layered and radial (lunar-like ballistic) ejecta craters; the latter form where there are insufficient concentrations of subsurface ice. This implies strong spatial heterogeneity in the concentration of tropical subsurface ice.

  3. Dual functional porous anti-reflective coatings with a photocatalytic effect based on a single layer system

    Science.gov (United States)

    Jilavi, M. H.; Mousavi, S. H.; Müller, T. S.; de Oliveira, P. W.

    2018-05-01

    Anti-reflection and photocatalytic properties are desirable for improving the optical properties of electronic devices. We describe a method of fabrication a single-layer, anti-reflective (AR) thin film with an additional photocatalytic property. The layer is deposited on glass substrates by means of a low-cost dip-coating method using a SiO2-TiO2 solution. A comparative study was undertaken to investigate the effects of TiO2 concentrations on the photocatalytic properties of the film and to determine the optimal balance between transmittance and photocatalysis. The average transmittance increases from T = 90.51% to T = 95.46 ± 0.07% for the wavelengths between 380 and 1200 nm. The structural characterization indicated the formation of thin, porous SiO2-TiO2 films with a roughness of less than 7.5 nm. The quality of the samples was evaluated by a complete test program of the mechanical, chemical and accelerated weathering stability. This results open up new possibilities for cost-effective AR coatings for the glass and solar cell industries.

  4. Development and characterization of light-emitting diodes (LEDs) based on ruthenium complex single layer for transparent displays

    Energy Technology Data Exchange (ETDEWEB)

    Santos, G.; Fonseca, F.; Andrade, A.M. [Laboratorio de Microelectronica, Departamento de Engenharia de Sistemas Electronicos, Escola Politecnica da Universidade de Sao Paulo (Brazil); Patrocinio, A.O.T.; Mizoguchi, S.K.; Murakami Iha, N.Y. [Laboratorio de Fotoquimica Inorganica e Conversao de Energia, Instituto de Quimica da Universidade de Sao Paulo (Brazil); Peres, M.; Monteiro, T.; Pereira, L. [Departamento de Fisica e I3N, Universidade de Aveiro (Portugal)

    2008-08-15

    In this work, two ruthenium complexes,[Ru(bpy){sub 3}](PF{sub 6}){sub 2} and[Ru(ph2phen){sub 3}](PF{sub 6}){sub 2} in poly(methylmethacrylate) matrix were employed to build single-layer light-emitting electrochemical cells by spin coating on indium tin oxide substrate. In both cases the electroluminescence spectra exhibit a relatively broad band with maxima near to 625 nm and CIE (x,y) color coordinates of (0.64,0.36), which are comparable with the photoluminescence data in the same medium. The best result was obtained with the[Ru(bpy){sub 3}](PF{sub 6}){sub 2} device where the optical output power approaches 10{mu}W at the band maximum with a wall-plug efficiency higher than 0.03%. The lowest driving voltage is about 4 V for an electrical current of 20 mA. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Room-temperature superparamagnetism due to giant magnetic anisotropy in Mo S defected single-layer MoS2

    Science.gov (United States)

    Khan, M. A.; Leuenberger, Michael N.

    2018-04-01

    Room-temperature superparamagnetism due to a large magnetic anisotropy energy (MAE) of a single atom magnet has always been a prerequisite for nanoscale magnetic devices. Realization of two dimensional (2D) materials such as single-layer (SL) MoS2, has provided new platforms for exploring magnetic effects, which is important for both fundamental research and for industrial applications. Here, we use density functional theory (DFT) to show that the antisite defect (Mo S ) in SL MoS2 is magnetic in nature with a magnetic moment μ of  ∼2 μB and, remarkably, exhibits an exceptionally large atomic scale MAE =\\varepsilon\\parallel-\\varepsilon\\perp of  ∼500 meV. Our calculations reveal that this giant anisotropy is the joint effect of strong crystal field and significant spin–orbit coupling (SOC). In addition, the magnetic moment μ can be tuned between 1 μB and 3 μB by varying the Fermi energy \\varepsilonF , which can be achieved either by changing the gate voltage or by chemical doping. We also show that MAE can be raised to  ∼1 eV with n-type doping of the MoS2:Mo S sample. Our systematic investigations deepen our understanding of spin-related phenomena in SL MoS2 and could provide a route to nanoscale spintronic devices.

  6. Single-layer centrifugation separates spermatozoa from diploid cells in epididymal samples from gray wolves, Canis lupus (L.).

    Science.gov (United States)

    Muñoz-Fuentes, Violeta; Linde Forsberg, Catharina; Vilà, Carles; Morrell, Jane M

    2014-09-15

    Sperm samples may be used for assisted reproductive technologies (e.g., farmed or endangered species) or as a source of haploid DNA or sperm-specific RNA. When ejaculated spermatozoa are not available or are very difficult to obtain, as is the case for most wild endangered species, the epididymides of dead animals (e.g., animals that have been found dead, shot by hunters or poachers, or that that require euthanasia in zoological collections) can be used as a source of sperm. Such epididymal sperm samples are usually contaminated with cellular debris, erythrocytes, leukocytes, and sometimes also bacteria. These contaminants may be sources of reactive oxygen species that damage spermatozoa during freezing or contribute undesired genetic material from diploid cells. We used single-layer centrifugation through a colloid formulation, Androcoll-C, to successfully separate wolf epididymal spermatozoa from contaminating cells and cellular debris in epididymal samples harvested from carcasses. Such a procedure may potentially be applied to epididymal sperm samples from other species. Copyright © 2014 Elsevier Inc. All rights reserved.

  7. Planar heterostructures of single-layer transition metal dichalcogenides: Composite structures, Schottky junctions, tunneling barriers, and half metals

    Science.gov (United States)

    Aras, Mehmet; Kılıç, ćetin; Ciraci, S.

    2017-02-01

    Planar composite structures formed from the stripes of transition metal dichalcogenides joined commensurately along their zigzag or armchair edges can attain different states in a two-dimensional (2D), single-layer, such as a half metal, 2D or one-dimensional (1D) nonmagnetic metal and semiconductor. Widening of stripes induces metal-insulator transition through the confinements of electronic states to adjacent stripes, that results in the metal-semiconductor junction with a well-defined band lineup. Linear bending of the band edges of the semiconductor to form a Schottky barrier at the boundary between the metal and semiconductor is revealed. Unexpectedly, strictly 1D metallic states develop in a 2D system along the boundaries between stripes, which pins the Fermi level. Through the δ doping of a narrow metallic stripe one attains a nanowire in the 2D semiconducting sheet or narrow band semiconductor. A diverse combination of constituent stripes in either periodically repeating or finite-size heterostructures can acquire critical fundamental features and offer device capacities, such as Schottky junctions, nanocapacitors, resonant tunneling double barriers, and spin valves. These predictions are obtained from first-principles calculations performed in the framework of density functional theory.

  8. Single-layer ionic conduction on carboxyl-terminated silane monolayers patterned by constructive lithography.

    Science.gov (United States)

    Berson, Jonathan; Burshtain, Doron; Zeira, Assaf; Yoffe, Alexander; Maoz, Rivka; Sagiv, Jacob

    2015-06-01

    Ionic transport plays a central role in key technologies relevant to energy, and information processing and storage, as well as in the implementation of biological functions in living organisms. Here, we introduce a supramolecular strategy based on the non-destructive chemical patterning of a highly ordered self-assembled monolayer that allows the reproducible fabrication of ion-conducting surface patterns (ion-conducting channels) with top -COOH functional groups precisely definable over the full range of length scales from nanometre to centimetre. The transport of a single layer of selected metal ions and the electrochemical processes related to their motion may thus be confined to predefined surface paths. As a generic solid ionic conductor that can accommodate different mobile ions in the absence of any added electrolyte, these ion-conducting channels exhibit bias-induced competitive transport of different ionic species. This approach offers unprecedented opportunities for the realization of designed ion-conducting systems with nanoscale control, beyond the inherent limitations posed by available ionic materials.

  9. Efficient Nitrogen Doping of Single-Layer Graphene Accompanied by Negligible Defect Generation for Integration into Hybrid Semiconductor Heterostructures.

    Science.gov (United States)

    Sarau, George; Heilmann, Martin; Bashouti, Muhammad; Latzel, Michael; Tessarek, Christian; Christiansen, Silke

    2017-03-22

    While doping enables application-specific tailoring of graphene properties, it can also produce high defect densities that degrade the beneficial features. In this work, we report efficient nitrogen doping of ∼11 atom % without virtually inducing new structural defects in the initial, large-area, low defect, and transferred single-layer graphene. To shed light on this remarkable high-doping-low-disorder relationship, a unique experimental strategy consisting of analyzing the changes in doping, strain, and defect density after each important step during the doping procedure was employed. Complementary micro-Raman mapping, X-ray photoelectron spectroscopy, and optical microscopy revealed that effective cleaning of the graphene surface assists efficient nitrogen incorporation accompanied by mild compressive strain resulting in negligible defect formation in the doped graphene lattice. These original results are achieved by separating the growth of graphene from its doping. Moreover, the high doping level occurred simultaneously with the epitaxial growth of n-GaN micro- and nanorods on top of graphene, leading to the flow of higher currents through the graphene/n-GaN rod interface. Our approach can be extended toward integrating graphene into other technologically relevant hybrid semiconductor heterostructures and obtaining an ohmic contact at their interfaces by adjusting the doping level in graphene.

  10. Study of the mechanical properties of single- layer and multi-layer metallic coatings with protective-decorative applications

    Directory of Open Access Journals (Sweden)

    Cherneva Sabina

    2018-01-01

    Full Text Available Single thin coating of matt nickel (Nimat, a mirror bright copper (Cubright, a mirror bright nickel (Nibright and their combinations were electrochemically deposited on brass substrate with thickness 500 μm. The basic aim was electrodeposition of two-layer Cubright/Nimat and Nibright/Cubright systems, and three-layer Nibright Cubrigh/Nimat system, which are among the most widely applied protective and decorative systems in light and medium operating conditions of corrosion. The thicknesses of the obtained films varied from 1 μm to 3.25 μm. They were investigated via nanoindentation experiments, in order to characterize their basic physical and mechanical characteristics, related with their good adhesion and corrosion protective ability, as well as ensuring the integrity of the system “protective coating/substrate” to possible mechanical, dynamic and/or thermal stresses. As a result, load-displacement curves were obtained and indentation hardness and indentation modulus were calculated using the Oliver & Pharr approximation method. The dependence of the indentation modulus and the indentation hardness on the depth of the indentation, surface morphology and structure of the obtained coatings, their texture and surface roughness were investigated too. The obtained results showed that the three-layer Nibright/Cubright /Niimat/CuZn37 system has highest indentation modulus and indentation hardness, following by two-layer Nibright/Cubright system and single layer coatings.

  11. Junctionless Diode Enabled by Self-Bias Effect of Ion Gel in Single-Layer MoS2 Device.

    Science.gov (United States)

    Khan, Muhammad Atif; Rathi, Servin; Park, Jinwoo; Lim, Dongsuk; Lee, Yoontae; Yun, Sun Jin; Youn, Doo-Hyeb; Kim, Gil-Ho

    2017-08-16

    The self-biasing effects of ion gel from source and drain electrodes on electrical characteristics of single layer and few layer molybdenum disulfide (MoS 2 ) field-effect transistor (FET) have been studied. The self-biasing effect of ion gel is tested for two different configurations, covered and open, where ion gel is in contact with either one or both, source and drain electrodes, respectively. In open configuration, the linear output characteristics of the pristine device becomes nonlinear and on-off ratio drops by 3 orders of magnitude due to the increase in "off" current for both single and few layer MoS 2 FETs. However, the covered configuration results in a highly asymmetric output characteristics with a rectification of around 10 3 and an ideality factor of 1.9. This diode like behavior has been attributed to the reduction of Schottky barrier width by the electric field of self-biased ion gel, which enables an efficient injection of electrons by tunneling at metal-MoS 2 interface. Finally, finite element method based simulations are carried out and the simulated results matches well in principle with the experimental analysis. These self-biased diodes can perform a crucial role in the development of high-frequency optoelectronic and valleytronic devices.

  12. Single-layer 2nd-order high-Tc SQUID gradiometer for use in unshielded environments

    International Nuclear Information System (INIS)

    Lee, Soon-Gul; Park, Seung Moon; Kang, Chan Seok; Kim, In-Seon; Kim, Sang-Jae

    2006-01-01

    We have studied the fabrication of second-order SQUID gradiometers from single-layer high-T c film and the feasibility of using those gradiometers in magnetocardiography. The gradiometer contains three parallel-connected pickup loops that are directly coupled to a step-edge junction SQUID with the coupling polarity of the center loop opposite to those of the two side loops. For a well-balanced gradiometer with a balancing factor of 10 3 , we achieved an unshielded gradient noise of 0.84 pT/cm 2 /Hz 1/2 at 1 Hz, which corresponds to an equivalent field noise of 280 fT/Hz 1/2 . A gradiometer with a 5.8-mm baseline successfully recorded the magnetocardic signals of a human subject, demonstrating the feasibility of using the device in biomagnetism. We have also studied the use of submicron YBCO bridges as Josephson elements of long-baseline gradiometers. The bridges were fabricated from 3-μm-wide, 300-nm-thick YBCO lines with a thin layer of Au on top by using a focused-ion-beam (FIB) patterning method. The temperature-dependent critical currents, I c (T), and the normal state resistances, R N (T), showed SIS-type behaviors, which are believed to be due to naturally formed grain boundaries.

  13. Colloid single-layer centrifugation improves post-thaw donkey (Equus asinus) sperm quality and is related to ejaculate freezability.

    Science.gov (United States)

    Ortiz, I; Dorado, J; Acha, D; Gálvez, M J; Urbano, M; Hidalgo, M

    2015-01-01

    The aim of this study was to determine whether colloid single-layer centrifugation (SLC) improves post-thaw donkey sperm quality and if this potential enhancement is related to ejaculate freezability. Semen from Andalusian donkeys was frozen following a standard protocol. SLC was performed on frozen-thawed semen and post-thaw sperm parameters were compared with uncentrifuged samples. Sperm quality was estimated by integrating in a single value sperm motility (assessed by computer-assisted sperm analysis), morphology and viability (evaluated under brightfield or fluorescence microscopy). Sperm freezability was calculated as the relationship between sperm quality obtained before freezing and after thawing. Ejaculates were classified into low, medium and high freezability groups using the 25th and 75th percentiles as thresholds. All sperm parameters were significantly (P<0.01) higher in SLC-selected samples in comparison to uncentrifuged frozen-thawed semen and several kinematic parameters were even higher than those obtained in fresh semen. The increment of sperm parameters after SLC selection was correlated with ejaculate freezability, obtaining the highest values after SLC in semen samples with low freezability. We concluded that, based on the sperm-quality parameters evaluated, SLC can be a suitable procedure to improve post-thaw sperm quality of cryopreserved donkey semen, in particular for those ejaculates with low freezability.

  14. Nondestructive, stereological estimation of canopy surface area

    DEFF Research Database (Denmark)

    Wulfsohn, Dvora-Laio; Sciortino, Marco; Aaslyng, Jesper M.

    2010-01-01

    a canopy using the smooth fractionator, (ii) sampling of leaves from the selected plants using the fractionator, and (iii) area estimation of the sampled leaves using point counting. We apply this procedure to estimate the total area of a chrysanthemum (Chrysanthemum morifolium L.) canopy and evaluate both...

  15. Leaf Wetness within a Lily Canopy

    NARCIS (Netherlands)

    Jacobs, A.F.G.; Heusinkveld, B.G.; Klok, E.J.

    2005-01-01

    A wetness duration experiment was carried out within a lily field situated adjacent to coastal dunes in the Netherlands. A within-canopy model was applied to simulate leaf wetness in three layers, with equal leaf area indices, within the canopy. This simulation model is an extension of an existing

  16. Use of the forest canopy by bats.

    Science.gov (United States)

    L. Wunder; A.B. Carey

    1994-01-01

    Of the 15 species of bats in the Pacific Northwest, 11 are known to make regular use of the forest canopy for roosting, foraging, and reproduction. This paper reviews roosting requirements, foraging, and the importance of landscape-scale factors to canopy using species in the Northwest. Many northwest bats use several different types of tree roosts. Common roosting...

  17. The impact of modifying antenna size of photosystem II on canopy photosynthetic efficiency – development of a new canopy photosynthesis model scaling from metabolism to canopy level processes

    Science.gov (United States)

    Canopy photosynthesis describes photosynthesis of an entire crop field and positively correlates with biomass production. Much effort in crop breeding has focused on improving canopy architecture and hence light distribution inside the canopy. Here, we develop a new integrated canopy photosynthesis ...

  18. Microwave Propagation Through Cultural Vegetation Canopies

    Science.gov (United States)

    Tavakoli, Ahad

    The need to understand the interaction of microwaves with vegetation canopies has markedly increased in recent years. This is due to advances made in remote sensing science, microwave technology, and signal processing circuits. One class of the earth's vegetation cover is man-made canopies, such as agricultural fields, orchards, and artificial forests. Contrary to natural vegetation terrain, location, spacing, and density of plants in a man-made vegetation canopy are deterministic quantities. As a result, the semi-deterministic nature of cultural vegetation canopies violate the random assumption of the radiative transfer theory and leads to experimented results that are in variance with model calculations. Hence, an alternative approach is needed to model the interaction of microwaves with such canopies. This thesis examines the propagation behavior through a canopy of corn plants. The corn canopy was selected as a representative of cultural vegetation canopies that are planted in parallel rows with an approximately fixed spacing between adjacent plants. Several experimental measurements were conducted to determine the transmission properties of a corn canopy in the 1-10 GHz range. The measurements which included horizontal propagation through the canopy as well as propagation at oblique incidence, were performed for defoliated canopies and for canopies with leaves. Through experimental observations and model development, the propagation behavior was found to be strongly dependent on the wavelength and the path length. At a wavelength in the neighborhood of 20 cm, for example, it was found that scattering by the stalks was coherent in nature for waves propagating horizontally through the canopy, which necessitated the development of a coherent-field model that uses Bragg scattering to account for the observed interference pattern in the transmitted beam. As the wavelength is made shorter, the semi-random spacing between plants becomes significant relative to the

  19. Bone Canopies in Pediatric Renal Osteodystrophy

    DEFF Research Database (Denmark)

    Pereira, Renata C; Levin Andersen, Thomas; Friedman, Peter A

    2016-01-01

    Pediatric renal osteodystrophy (ROD) is characterized by changes in bone turnover, mineralization, and volume that are brought about by alterations in bone resorption and formation. The resorptive and formative surfaces on the cancellous bone are separated from the marrow cavity by canopies...... consisting of a layer of flat osteoblastic cells. These canopies have been suggested to play a key role in the recruitment of osteoprogenitors during the process of bone remodeling. This study was performed to address the characteristics of the canopies above bone formation and resorption sites...... and their association with biochemical and bone histomorphometric parameters in 106 pediatric chronic kidney disease (CKD) patients (stage 2-5) across the spectrum of ROD. Canopies in CKD patients often appeared as thickened multilayered canopies, similar to previous reports in patients with primary hyperparathyroidism...

  20. Holm Oak (Quercus ilex L.) canopy as interceptor of airborne trace elements and their accumulation in the litter and topsoil

    International Nuclear Information System (INIS)

    Fantozzi, Federica; Monaci, Fabrizio; Blanusa, Tijana; Bargagli, Roberto

    2013-01-01

    We investigated the role of urban Holm Oak (Quercus ilex L.) trees as an airborne metal accumulators and metals' environmental fate. Analyses confirmed Pb, Cd, Cu and Zn as a main contaminants in Siena's urban environment; only Pb concentrations decreased significantly compared to earlier surveys. Additionally, we determined chemical composition of tree leaves, litter and topsoil (underneath/outside tree crown) in urban and extra-urban oak stands. Most notably, litter in urban samples collected outside the canopy had significantly lower concentrations of organic matter and higher concentrations of Pb, Cu, Cd and Zn than litter collected underneath the canopy. There was a greater metals' accumulation in topsoil, in samples collected under the tree canopy and especially near the trunk (‘stemflow area’). Thus, in urban ecosystems the Holm Oak stands likely increase the soil capability to bind metals. -- Highlights: ► Of the main metal contaminants only leaf Pb concentrations decreased in the period 1994–2011. ► Leaf Cd, Cr, Cu, Pb and Zn concentrations were higher in urban than in extra urban park. ► In urban park litter, Cu, Cd, Pb and Zn concentrations were higher outside than underneath the tree crown. ► Conversely, in urban park soil, Cu, Cd, Pb and Zn concentrations were lower outside the crown. ► Soil therefore behaves as a sink for metal contaminants such as Cu, Pb and Cd. -- Quercus ilex leaves are efficient interceptors of airborne trace elements in urban environments and we found an increased accumulation of metals in topsoil under the tree canopy

  1. Single layers of WS2 nanoplates embedded in nitrogen-doped carbon nanofibers as anode materials for lithium-ion batteries

    Science.gov (United States)

    Yu, Sunmoon; Jung, Ji-Won; Kim, Il-Doo

    2015-07-01

    Single layers of WS2 nanoplates are uniformly embedded in nitrogen-doped carbon nanofibers (WS2@NCNFs) via a facile electrospinning method. Crystallization of the single-layered WS2 nanoplates and in situ nitrogen doping into the carbon nanofibers were simultaneously accomplished during a two-step heat treatment. The distinctive structure of the WS2@NCNFs enables outstanding electrochemical performances.Single layers of WS2 nanoplates are uniformly embedded in nitrogen-doped carbon nanofibers (WS2@NCNFs) via a facile electrospinning method. Crystallization of the single-layered WS2 nanoplates and in situ nitrogen doping into the carbon nanofibers were simultaneously accomplished during a two-step heat treatment. The distinctive structure of the WS2@NCNFs enables outstanding electrochemical performances. Electronic supplementary information (ESI) available: Experimental section, SEM images of WS2 powder and ground WS2 powder, TEM image and SAED pattern of the WS2 powder, Raman spectra of the WS2 powder, CV curves of the WS2 powder, voltage profiles of the WS2 powder, schematic diagram of WS2@NCNFs undergoing lithium storage reactions, electrochemical performance of NCNFs, morphologies and EDS mapping of WS2@NCNFs after cycling, and a table of contributions of NCNFs to the specific capacity. See DOI: 10.1039/c5nr02425k

  2. Effect of non-sperm cells removal with single-layer colloidal centrifugation on myeloperoxidase concentration in post-thaw equine semen.

    Science.gov (United States)

    Ponthier, Jérôme; Teague, Sheila R; Franck, Thierry Y; de la Rebière, Geoffroy; Serteyn, Didier D; Brinsko, Steven P; Love, Charles C; Blanchard, Terry L; Varner, Dickson D; Deleuze, Stéfan C

    2013-12-01

    Myeloperoxidase (MPO) is a pro-oxidant enzyme contained in and released by neutrophils during degranulation or after lysis. Post-thaw semen contains MPO and its concentration is associated with decreased sperm motility. Recently, MPO concentration in post-thaw semen was shown to be associated with the presence of non-sperm cells (NSC). The objective of this study was to evaluate the effect of a single-layer colloidal centrifugation before cryopreservation on NSC and MPO concentrations in equine semen. The experimental design consisted of freezing semen with or without previous centrifugation through two concentrations of single-layer colloid media. Non-sperm cells and MPO concentrations were assessed in pellet and upper layer at each step of the procedure and MPO was detected in cells by immunocytochemistry. Single-layer colloid centrifugation decreased NSC and MPO concentrations in post-thaw semen. The MPO concentration was correlated with concentration of NSC in the upper layer of the supernatant. In post-thaw semen, with or without previous single-layer colloid centrifugation, MPO concentration was correlated with concentration of NSC. Overall, neutrophils were rarely observed and NSC were mainly epithelial cells or cellular debris, as demonstrated by MPO immunocytochemistry. At all steps of the semen processing and cryopreservation, MPO immunostaining was clearly identified only on NSC. In conclusion, our study shows that NSC present in fresh semen release MPO during freezing. Copyright © 2013 Elsevier Inc. All rights reserved.

  3. Double-layer versus single-layer bone-patellar tendon-bone anterior cruciate ligament reconstruction: a prospective randomized study with 3-year follow-up.

    Science.gov (United States)

    Mei, Xiaoliang; Zhang, Zhenxiang; Yang, Jingwen

    2016-12-01

    To evaluate the clinical results of a randomized controlled trial of single-layer versus double-layer bone-patellar tendon-bone (BPTB) anterior cruciate ligament (ACL) reconstruction. Fifty-eight subjects who underwent primary ACL reconstruction with a BPTB allograft were prospectively randomized into two groups: single-layer reconstruction (n = 31) and double-layer reconstruction (n = 27). The following evaluation methods were used: clinical examination, KT-1000 arthrometer measurement, muscle strength, Tegner activity score, Lysholm score, subjective rating scale regarding patient satisfaction and sports performance level, graft retear, contralateral ACL tear, and additional meniscus surgery. Forty-eight subjects (24 in single-layer group and 24 in double-layer group) who were followed up for 3 years were evaluated. Preoperatively, there were no differences between the groups. At 3-year follow-up, the Lachman and pivot-shift test results were better in the double-layer group (P = 0.019 and P reconstruction, double-layer BPTB reconstruction was significantly better than single-layer reconstruction regarding anterior and rotational stability at 3-year follow-up. The results of KT measurements and the Lachman and pivot-shift tests were significantly better in the double-layer group, whereas there was no difference in the anterior drawer test results. The Tegner score was also better in the double-layer group; however, there were no differences in the other subjective findings.

  4. Aromatic structure degradation of single layer graphene on an amorphous silicon substrate in the presence of water, hydrogen and Extreme Ultraviolet light

    NARCIS (Netherlands)

    Mund, Baibhav Kumar; Sturm, J.M.; Lee, Christopher James; Bijkerk, Frederik

    2018-01-01

    In this paper we study the reaction of water and graphene under Extreme Ultraviolet (EUV) irradiation and in the presence of hydrogen. In this work, single layer graphene (SLG) on amorphous Si as an underlying substrate was dosed with water (0.75 ML) and exposed to EUV (λ = 13.5 nm, 92 eV) with

  5. Full-thickness skin wound healing using autologous keratinocytes and dermal fibroblasts with fibrin: bilayered versus single-layered substitute.

    Science.gov (United States)

    Idrus, Ruszymah Bt Hj; Rameli, Mohd Adha bin P; Low, Kiat Cheong; Law, Jia Xian; Chua, Kien Hui; Latiff, Mazlyzam Bin Abdul; Saim, Aminuddin Bin

    2014-04-01

    Split-skin grafting (SSG) is the gold standard treatment for full-thickness skin defects. For certain patients, however, an extensive skin lesion resulted in inadequacies of the donor site. Tissue engineering offers an alternative approach by using a very small portion of an individual's skin to harvest cells for propagation and biomaterials to support the cells for implantation. The objective of this study was to determine the effectiveness of autologous bilayered tissue-engineered skin (BTES) and single-layer tissue-engineered skin composed of only keratinocytes (SLTES-K) or fibroblasts (SLTES-F) as alternatives for full-thickness wound healing in a sheep model. Full-thickness skin biopsies were harvested from adult sheep. Isolated fibroblasts were cultured using medium Ham's F12: Dulbecco modified Eagle medium supplemented with 10% fetal bovine serum, whereas the keratinocytes were cultured using Define Keratinocytes Serum Free Medium. The BTES, SLTES-K, and SLTES-F were constructed using autologous fibrin as a biomaterial. Eight full-thickness wounds were created on the dorsum of the body of the sheep. On 4 wounds, polyvinyl chloride rings were used as chambers to prevent cell migration at the edge. The wounds were observed at days 7, 14, and 21. After 3 weeks of implantation, the sheep were euthanized and the skins were harvested. The excised tissues were fixed in formalin for histological examination via hematoxylin-eosin, Masson trichrome, and elastin van Gieson staining. The results showed that BTES, SLTES-K, and SLTES-F promote wound healing in nonchambered and chambered wounds, and BTES demonstrated the best healing potential. In conclusion, BTES proved to be an effective tissue-engineered construct that can promote the healing of full-thickness skin lesions. With the support of further clinical trials, this procedure could be an alternative to SSG for patients with partial- and full-thickness burns.

  6. Predicting Single-Layer Technetium Dichalcogenides (TcX₂, X = S, Se) with Promising Applications in Photovoltaics and Photocatalysis.

    Science.gov (United States)

    Jiao, Yalong; Zhou, Liujiang; Ma, Fengxian; Gao, Guoping; Kou, Liangzhi; Bell, John; Sanvito, Stefano; Du, Aijun

    2016-03-02

    One of the least known compounds among transition metal dichalcogenides (TMDCs) is the layered triclinic technetium dichalcogenides (TcX2, X = S, Se). In this work, we systematically study the structural, mechanical, electronic, and optical properties of TcS2 and TcSe2 monolayers based on density functional theory (DFT). We find that TcS2 and TcSe2 can be easily exfoliated in a monolayer form because their formation and cleavage energy are analogous to those of other experimentally realized TMDCs monolayer. By using a hybrid DFT functional, the TcS2 and TcSe2 monolayers are calculated to be indirect semiconductors with band gaps of 1.91 and 1.69 eV, respectively. However, bilayer TcS2 exhibits direct-bandgap character, and both TcS2 and TcSe2 monolayers can be tuned from semiconductor to metal under effective tensile/compressive strains. Calculations of visible light absorption indicate that 2D TcS2 and TcSe2 generally possess better capability of harvesting sunlight compared to single-layer MoS2 and ReSe2, implying their potential as excellent light-absorbers. Most interestingly, we have discovered that the TcSe2 monolayer is an excellent photocatalyst for splitting water into hydrogen due to the perfect fit of band edge positions with respect to the water reduction and oxidation potentials. Our predictions expand the two-dimensional (2D) family of TMDCs, and the remarkable electronic/optical properties of monolayer TcS2 and TcSe2 will place them among the most promising 2D TMDCs for renewable energy application in the future.

  7. Sperm yield after single layer centrifugation with Androcoll-E is related to the potential fertility of the original ejaculate.

    Science.gov (United States)

    Morrell, J M; Stuhtmann, G; Meurling, S; Lundgren, A; Winblad, C; Macias Garcia, B; Johannisson, A

    2014-05-01

    Many attempts have been made to identify laboratory tests that are predictive of sperm fertility, both to improve the quality of stallion semen doses for artificial insemination (AI) and to identify potential breeding sires if no fertility data are available. Sperm quality at the stud is mostly evaluated by assessing subjective motility, although this parameter can be poorly indicative of fertility. Sperm morphology and chromatin integrity in Swedish stallions are correlated to pregnancy rate after AI. Because single layer centrifugation (SLC) selects for spermatozoa with normal morphology and good chromatin, retrospective analysis was carried out to investigate whether sperm yield after SLC is linked to potential fertility. Commercial semen doses for AI from 24 stallions (five stallions with four ejaculates each, 19 stallions with three ejaculates each; n = 77) obtained during the breeding season were cooled, and sent overnight to the Swedish University of Agricultural Sciences in an insulated box for evaluation, with other doses being sent to studs for commercial AI. On arrival at Swedish University of Agricultural Sciences, the semen was used for SLC and also for evaluation of sperm motility, membrane integrity, chromatin integrity, and morphology. The seasonal pregnancy rates for each stallion were available. The yield of progressively motile spermatozoa after SLC (calculated as a proportion of the initial load) was found to be highly correlated with pregnancy rate (r = 0.75; P centrifugation is fast (30 minutes) and does not require expensive equipment, whereas other assays require a flow cytometer and/or specialist skills. An additional option could be to transport semen doses to a laboratory for SLC if the stud personnel do not want to perform the procedure themselves. Copyright © 2014 Elsevier Inc. All rights reserved.

  8. VitiCanopy: A Free Computer App to Estimate Canopy Vigor and Porosity for Grapevine

    Directory of Open Access Journals (Sweden)

    Roberta De Bei

    2016-04-01

    Full Text Available Leaf area index (LAI and plant area index (PAI are common and important biophysical parameters used to estimate agronomical variables such as canopy growth, light interception and water requirements of plants and trees. LAI can be either measured directly using destructive methods or indirectly using dedicated and expensive instrumentation, both of which require a high level of know-how to operate equipment, handle data and interpret results. Recently, a novel smartphone and tablet PC application, VitiCanopy, has been developed by a group of researchers from the University of Adelaide and the University of Melbourne, to estimate grapevine canopy size (LAI and PAI, canopy porosity, canopy cover and clumping index. VitiCanopy uses the front in-built camera and GPS capabilities of smartphones and tablet PCs to automatically implement image analysis algorithms on upward-looking digital images of canopies and calculates relevant canopy architecture parameters. Results from the use of VitiCanopy on grapevines correlated well with traditional methods to measure/estimate LAI and PAI. Like other indirect methods, VitiCanopy does not distinguish between leaf and non-leaf material but it was demonstrated that the non-leaf material could be extracted from the results, if needed, to increase accuracy. VitiCanopy is an accurate, user-friendly and free alternative to current techniques used by scientists and viticultural practitioners to assess the dynamics of LAI, PAI and canopy architecture in vineyards, and has the potential to be adapted for use on other plants.

  9. Testing a ground-based canopy model using the wind river canopy crane

    Science.gov (United States)

    Robert Van Pelt; Malcolm P. North

    1999-01-01

    A ground-based canopy model that estimates the volume of occupied space in forest canopies was tested using the Wind River Canopy Crane. A total of 126 trees in a 0.25 ha area were measured from the ground and directly from a gondola suspended from the crane. The trees were located in a low elevation, old-growth forest in the southern Washington Cascades. The ground-...

  10. BOREAS HYD-03 Canopy Density Data

    Data.gov (United States)

    National Aeronautics and Space Administration — The BOREAS HYD-03 team collected several data sets related to the hydrology of forested areas. This data set contains measurements of canopy density (closure) from a...

  11. BOREAS TE-18 Geosail Canopy Reflectance Model

    Data.gov (United States)

    National Aeronautics and Space Administration — The GEOSAIL model was created by combining the SAIL (Scattering from Arbitrarily Inclined Leaves) model with the Jasinski geometric model to simulate canopy spectral...

  12. Preparation and applications of mechanically exfoliated single-layer and multilayer MoS₂ and WSe₂ nanosheets.

    Science.gov (United States)

    Li, Hai; Wu, Jumiati; Yin, Zongyou; Zhang, Hua

    2014-04-15

    Although great progress has been achieved in the study of graphene, the small current ON/OFF ratio in graphene-based field-effect transistors (FETs) limits its application in the fields of conventional transistors or logic circuits for low-power electronic switching. Recently, layered transition metal dichalcogenide (TMD) materials, especially MoS2, have attracted increasing attention. In contrast to its bulk material with an indirect band gap, a single-layer (1L) MoS2 nanosheet is a semiconductor with a direct band gap of ~1.8 eV, which makes it a promising candidate for optoelectronic applications due to the enhancement of photoluminescence and high current ON/OFF ratio. Compared with TMD nanosheets prepared by chemical vapor deposition and liquid exfoliation, mechanically exfoliated ones possess pristine, clean, and high-quality structures, which are suitable for the fundamental study and potential applications based on their intrinsic thickness-dependent properties. In this Account, we summarize our recent research on the preparation, characterization, and applications of 1L and multilayer MoS2 and WSe2 nanosheets produced by mechanical exfoliation. During the preparation of nanosheets, we proposed a simple optical identification method to distinguish 1L and multilayer MoS2 and WSe2 nanosheets on a Si substrate coated with 90 and 300 nm SiO2. In addition, we used Raman spectroscopy to characterize mechanically exfoliated 1L and multilayer WSe2 nanosheets. For the first time, a new Raman peak at 308 cm(-1) was observed in the spectra of WSe2 nanosheets except for the 1L WSe2 nanosheet. Importantly, we found that the 1L WSe2 nanosheet is very sensitive to the laser power during characterization. The high power laser-induced local oxidation of WSe2 nanosheets and single crystals was monitored by Raman spectroscopy and atomic force microscopy (AFM). Hexagonal and monoclinic structured WO3 thin films were obtained from the local oxidization of single- to triple

  13. Uptake of small particles by tree canopies

    International Nuclear Information System (INIS)

    Belot, Y.; Camus, H.; Gauthier, D.; Caput, C.

    1992-01-01

    Most of the deposition data that are available to assess the radiological consequences of an accident have been acquired for low-growing vegetation and are inadapted to forest areas. Consequently, a programme was undertaken to study the deposition of particles on components of different trees and extrapolate the experimental data so obtained to large-scale canopies. The experiments were performed in a wind tunnel allowing canopy components to be exposed to a flow of suspended fluorescent particles of reasonably uniform size. Emphasis was put on particles in the 0.3-1.2 μm subrange, because most of the radioactive particles sampled at long distance from sources are comprised in this size interval. The uptake rates were determined for bare and leaf bearing twigs of several evergreen species (Picea abies, Pinus sylvestris and Quercus ilex), as a function of wind speed and particle size. The deposition rates obtained for the tree components were then used as input to a model that describes the uptake of particles by a large-scale canopy under specified conditions of weather and canopy structure. The model accounts for the diffusion of particles between different strata of the canopy, as well as deposition of particles on the canopy components. It calculates the rates of particle deposition to the horizontal surface of the canopy, and the repartition of the deposited particles within the canopy. Increases in wind speed cause increased deposition, but the effect is less important that it would have been for larger particles. The deposition is relatively insensitive to the size of particles within the subrange considered in this study. 13 refs., 2 figs., 1 tab

  14. Forest Canopy Height Estimation from Calipso Lidar Measurement

    Directory of Open Access Journals (Sweden)

    Lu Xiaomei

    2016-01-01

    Canopy penetration depths at two wavelengths indicate moderately strong relationships for estimating the canopy height. Results show that the CALIOP-derived canopy heights were highly correlated with the ICESat/GLAS-derived values with a mean RMSE of 3.4 m and correlation coefficient (R of 0.89. Our findings present a relationship between the penetration difference and canopy height, which can be used as another metrics for canopy height estimation, except the full waveforms.

  15. Assessing urban forest effects and values, Chicago's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E. III Hoehn; Daniel E. Crane; Jack C. Stevens; Cherie Leblanc Fisher

    2010-01-01

    An analysis of trees in Chicago, IL, reveals that this city has about 3,585,000 trees with canopies that cover 17.2 percent of the area. The most common tree species are white ash, mulberry species, green ash, and tree-of-heaven. Chicago's urban forest currently stores about 716,000 tons of carbon...

  16. Assessing urban forest effects and values: Morgantown's Urban Forest

    Science.gov (United States)

    David J. Nowak; Robert E. III Hoehn; Daniel E. Crane; Jack C. Stevens; Jonathan Cumming; Sandhya Mohen; Anne Buckelew. Cumming

    2012-01-01

    An analysis of the community forest in Morgantown, WV, was undertaken in 2004 to characterize the structural and functional attributes of this forest resource. The assessment revealed that this city has about 658,000 trees with canopies that cover 35.5 percent of the area. The most common tree species are sugar maple, black cherry, and hawthorn. The urban forest...

  17. Assessing urban forest effects and values, Scranton's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E. III Hoehn; Daniel E. Crane; Jack C. Stevens; Vincent. Cotrone

    2010-01-01

    An analysis of trees in the urbanized portion of Scranton, PA, reveals that this area has about 1.2 million trees with canopies that cover 22.0 percent of the area. The most common tree species are red maple, gray birch, black cherry, northern red oak, and quaking aspen. Scranton's urban forest currently store about 93,300 tons of carbon valued at $1.9 million. In...

  18. Self-Assembly of Single-Layer CoAl-Layered Double Hydroxide Nanosheets on 3D Graphene Network Used as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction.

    Science.gov (United States)

    Ping, Jianfeng; Wang, Yixian; Lu, Qipeng; Chen, Bo; Chen, Junze; Huang, Ying; Ma, Qinglang; Tan, Chaoliang; Yang, Jian; Cao, Xiehong; Wang, Zhijuan; Wu, Jian; Ying, Yibin; Zhang, Hua

    2016-09-01

    A non-noble metal based 3D porous electrocatalyst is prepared by self-assembly of the liquid-exfoliated single-layer CoAl-layered double hydroxide nanosheets (CoAl-NSs) onto 3D graphene network, which exhibits higher catalytic activity and better stability for electrochemical oxygen evolution reaction compared to the commercial IrO2 nanoparticle-based 3D porous electrocatalyst. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Raman excitation profiles of hybrid systems constituted by single-layer graphene and free base phthalocyanine: Manifestations of two mechanisms of graphene-enhanced Raman scattering

    Czech Academy of Sciences Publication Activity Database

    Uhlířová, T.; Mojzeš, P.; Melníková Komínková, Zuzana; Kalbáč, Martin; Sutrová, Veronika; Šloufová, I.; Vlčková, B.

    2017-01-01

    Roč. 48, č. 10 (2017), s. 1270-1281 ISSN 0377-0486 R&D Projects: GA ČR(CZ) GA15-01953S Institutional support: RVO:61388955 ; RVO:61389013 Keywords : graphene -enhanced Raman scattering * single-layer graphene * free base phthalocyanine * Raman excitation profiles * photoinduced charge transfer Subject RIV: CF - Physical ; Theoretical Chemistry; CD - Macromolecular Chemistry (UMCH-V) OBOR OECD: Physical chemistry; Polymer science (UMCH-V) Impact factor: 2.969, year: 2016

  20. Raman excitation profiles of hybrid systems constituted by single-layer graphene and free base phthalocyanine: Manifestations of two mechanisms of graphene-enhanced Raman scattering

    Czech Academy of Sciences Publication Activity Database

    Uhlířová, T.; Mojzeš, P.; Melníková Komínková, Zuzana; Kalbáč, Martin; Sutrová, Veronika; Šloufová, I.; Vlčková, B.

    2017-01-01

    Roč. 48, č. 10 (2017), s. 1270-1281 ISSN 0377-0486 R&D Projects: GA ČR(CZ) GA15-01953S Institutional support: RVO:61388955 ; RVO:61389013 Keywords : graphene-enhanced Raman scattering * single-layer graphene * free base phthalocyanine * Raman excitation profiles * photoinduced charge transfer Subject RIV: CF - Physical ; Theoretical Chemistry; CD - Macromolecular Chemistry (UMCH-V) OBOR OECD: Physical chemistry; Polymer science (UMCH-V) Impact factor: 2.969, year: 2016

  1. Homeowner interactions with residential trees in urban areas

    Science.gov (United States)

    Jana Dilley; Kathleen L. Wolf

    2013-01-01

    Urban forests are a critical element in sustainable urban areas because of the many environmental, economic, and social benefits that city trees provide. In order to increase canopy cover in urban areas, residential homeowners, who collectively own the majority of the land in most cities, need to engage in planting and retaining trees on their properties. This...

  2. Satellite air temperature estimation for monitoring the canopy layer heat island of Milan

    DEFF Research Database (Denmark)

    Pichierri, Manuele; Bonafoni, Stefania; Biondi, Riccardo

    2012-01-01

    across the city center from June to September confirming that, in Milan, urban heating is not an occasional phenomenon. Furthermore, this study shows the utility of space missions to monitor the metropolis heat islands if they are able to provide nighttime observations when CLHI peaks are generally......In this work, satellite maps of the urban heat island of Milan are produced using satellite-based infrared sensor data. For this aim, we developed suitable algorithms employing satellite brightness temperatures for the direct air temperature estimation 2 m above the surface (canopy layer), showing...... 2007 and 2010 were processed. Analysis of the canopy layer heat island (CLHI) maps during summer months reveals an average heat island effect of 3–4K during nighttime (with some peaks around 5K) and a weak CLHI intensity during daytime. In addition, the satellite maps reveal a well defined island shape...

  3. A retrospective study comparing the outcome of horses undergoing small intestinal resection and anastomosis with a single layer (Lembert) or double layer (simple continuous and Cushing) technique.

    Science.gov (United States)

    Close, Kristyn; Epstein, Kira L; Sherlock, Ceri E

    2014-05-01

    To (1) compare postoperative complications and survival in horses after small intestinal resection and anastomosis using 2 anastomosis techniques (single layer Lembert; double layer simple continuous oversewn with Cushing), and (2) to compare outcome by anastomosis type (jejunoileostomy; jejunojejunostomy). Retrospective case series. Horses (n = 53). Medical records (July 2006-July 2010) of all horses that had small intestinal resection and anastomosis. Horses were divided into groups based on technique and type of anastomosis. Comparisons of pre- and intraoperative findings (disease severity), postoperative complications, and survival rates were made between groups. There were no differences in disease severity, postoperative complications, or survival between single layer (n = 23) or double layer (n = 31) anastomoses. There were no differences in disease severity or survival between jejunoileostomy (n = 16) or jejunojejunostomy (n = 38). There was a higher incidence of postoperative colic in hospital after jejunoileostomy (13/16) compared with jejunojejunostomy (18/38) (P = .0127). Postoperative complications and survival are comparable between horses undergoing single layer and double layer small intestinal end-to-end anastomoses. With the exception of increased postoperative colic in the hospital, postoperative complications and survival after jejunoileostomy and jejunojejunostomy are also comparable. © Copyright 2014 by The American College of Veterinary Surgeons.

  4. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

    Science.gov (United States)

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2016-02-08

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

  5. Estimating canopy bulk density and canopy base height for interior western US conifer stands

    Science.gov (United States)

    Seth A. Ex; Frederick W. Smith; Tara L. Keyser; Stephanie A. Rebain

    2016-01-01

    Crown fire hazard is often quantified using effective canopy bulk density (CBD) and canopy base height (CBH). When CBD and CBH are estimated using nonlocal crown fuel biomass allometries and uniform crown fuel distribution assumptions, as is common practice, values may differ from estimates made using local allometries and nonuniform...

  6. Remote sensing of sagebrush canopy nitrogen

    Science.gov (United States)

    Mitchell, Jessica J.; Glenn, Nancy F.; Sankey, Temuulen T.; Derryberry, DeWayne R.; Germino, Matthew J.

    2012-01-01

    This paper presents a combination of techniques suitable for remotely sensing foliar Nitrogen (N) in semiarid shrublands – a capability that would significantly improve our limited understanding of vegetation functionality in dryland ecosystems. The ability to estimate foliar N distributions across arid and semi-arid environments could help answer process-driven questions related to topics such as controls on canopy photosynthesis, the influence of N on carbon cycling behavior, nutrient pulse dynamics, and post-fire recovery. Our study determined that further exploration into estimating sagebrush canopy N concentrations from an airborne platform is warranted, despite remote sensing challenges inherent to open canopy systems. Hyperspectral data transformed using standard derivative analysis were capable of quantifying sagebrush canopy N concentrations using partial least squares (PLS) regression with an R2 value of 0.72 and an R2 predicted value of 0.42 (n = 35). Subsetting the dataset to minimize the influence of bare ground (n = 19) increased R2 to 0.95 (R2 predicted = 0.56). Ground-based estimates of canopy N using leaf mass per unit area measurements (LMA) yielded consistently better model fits than ground-based estimates of canopy N using cover and height measurements. The LMA approach is likely a method that could be extended to other semiarid shrublands. Overall, the results of this study are encouraging for future landscape scale N estimates and represent an important step in addressing the confounding influence of bare ground, which we found to be a major influence on predictions of sagebrush canopy N from an airborne platform.

  7. Surface-atmosphere interactions with coupled within-canopy aerodynamic resistance and canopy reflection.

    Science.gov (United States)

    Timmermans, J.; van der Tol, C.; Verhoef, W.; Su, Z.

    2009-04-01

    Models that describe the exchange of CO2 and H2O between the surface and atmosphere use bulk-parametrization of the within-canopy aerodynamic resistance and leaf area density (eq. LAI). This bulk parametrization is based on the Monin-Obukhov Similarity (MOS) theory. The MOS theory however breaks down for sparse canopies and it cannot couple profiles in the leaf density to profiles in the within-canopy aerodynamic resistance. The objective of this research is to create a simple model that is able to couple the within-canopy aerodynamic resistance and canopy reflection for different levels in the canopy. This model should be able to represent the canopy using as fewer parameters as possible, in order to facilitate inversion of remote sensing imagery. A virtual canopy was simulated using an L-systems approach, Lindenmayer 1968. The L-system approach was chosen because it describes the canopy with fractals. It therefore needs very little inputs to simulate a virtual canopy. A vertical profile of leaf density was calculated for 60 levels from this virtual canopy. The within-canopy aerodynamic resistance was modeled from the vertical leaf density profile using foliage drag coefficient, Massman 1997. A modified version of the SCOPE (Soil Canopy Observations and Photosynthesis) model was used to calculate the H2O and CO2 fluxes using the vertical profiles of leaf density and within-canopy aerodynamic resistance. The simulated fluxes are compared with field measurements over a vineyard and a forested area. The field measurements in both areas are acquired using the same setup: a basic flux tower in addition with an eddy-covariance setup. We present in this article the methodology and the results, as a proof of concept. references Massman, W.J., An Analytical One-Dimensional Model of Momentum Transfer by vegetation of arbitrary structure, Boundary-Layer Meteorology, 1997, 83, 407-421 Lindenmayer, A., Mathematical Models for Cellular Interactions in Development, Journal of

  8. Elements of a dynamic systems model of canopy photosynthesis.

    Science.gov (United States)

    Zhu, Xin-Guang; Song, Qingfeng; Ort, Donald R

    2012-06-01

    Improving photosynthesis throughout the full canopy rather than photosynthesis of only the top leaves of the canopy is central to improving crop yields. Many canopy photosynthesis models have been developed from physiological and ecological perspectives, however most do not consider heterogeneities of microclimatic factors inside a canopy, canopy dynamics and associated energetics, or competition among different plants, and most models lack a direct linkage to molecular processes. Here we described the rationale, elements, and approaches necessary to build a dynamic systems model of canopy photosynthesis. A systems model should integrate metabolic processes including photosynthesis, respiration, nitrogen metabolism, resource re-mobilization and photosynthate partitioning with canopy level light, CO(2), water vapor distributions and heat exchange processes. In so doing a systems-based canopy photosynthesis model will enable studies of molecular ecology and dramatically improve our insight into engineering crops for improved canopy photosynthetic CO(2) uptake, resource use efficiencies and yields. Copyright © 2012 Elsevier Ltd. All rights reserved.

  9. INVISTIGATION ON CANOPY HEIGHT AND DENSITY DIFFERENTIATIONS IN THE MANAGED AND UNMANAGED FOREST STANDS USING LIDAR DATA (CASE STUDY: SHASTKALATEH FOREST, GORGAN

    Directory of Open Access Journals (Sweden)

    Sh. Shataee

    2015-12-01

    Full Text Available Forest management plans are interesting to keep the forest stand natural composite and structure after silvicultural and management treatments. In order to investigate on stand differences made by management treatments, comparing of these stands with unmanaged stands as natural forests is necessary. Aerial laser scanners are providing suitable 3D information to map the horizontal and vertical characteristics of forest structures. In this study, different of canopy height and canopy cover variances between managed and unmanaged forest stands as well as in two dominant forest types were investigated using Lidar data in Dr. Bahramnia forest, Northern Iran. The in-situ information was gathered from 308 circular plots by a random systematic sampling designs. The low lidar cloud point data were used to generate accurate DEM and DSM models and plot-based height statistics metrics and canopy cover characteristics. The significant analyses were done by independent T-test between two stands in same dominant forest types. Results showed that there are no significant differences between canopy cover mean in two stands as well as forest types. Result of statistically analysis on height characteristics showed that there are a decreasing the forest height and its variance in the managed forest compared to unmanaged stands. In addition, there is a significant difference between maximum, range, and mean heights of two stands in 99 percent confidence level. However, there is no significant difference between standard deviation and canopy height variance of managed and unmanged stands. These results showd that accomplished management treatments and cuttings could lead to reducing of height variances and converting multi-layers stands to two or single layers. Results are also showed that the canopy cover densities in the managed forest stands are changing from high dense cover to dense cover.

  10. Modeling Coherent Structures in Canopy Flows

    Science.gov (United States)

    Luhar, Mitul

    2017-11-01

    It is well known that flows over vegetation canopies are characterized by the presence of energetic coherent structures. Since the mean profile over dense canopies exhibits an inflection point, the emergence of such structures is often attributed to a Kelvin-Helmholtz instability. However, though stability analyses provide useful mechanistic insights into canopy flows, they are limited in their ability to generate predictions for spectra and coherent structure. The present effort seeks to address this limitation by extending the resolvent formulation (McKeon and Sharma, 2010, J. Fluid Mech.) to canopy flows. Under the resolvent formulation, the turbulent velocity field is expressed as a superposition of propagating modes, identified via a gain-based (singular value) decomposition of the Navier-Stokes equations. A key advantage of this approach is that it reconciles multiple mechanisms that lead to high amplification in turbulent flows, including modal instability, transient growth, and critical-layer phenomena. Further, individual high-gain modes can be combined to generate more complete models for coherent structure and velocity spectra. Preliminary resolvent-based model predictions for canopy flows agree well with existing experiments and simulations.

  11. Assessing the US Urban Forest Resources

    Science.gov (United States)

    David J. Nowak; Mary H. Noble; Susan M. Sisinni; John F. Dwyer

    2001-01-01

    Urban areas in the conterminous United States doubled in size between 1969 and 1994, and currently cover 3.5 percent of the total land area and contain more than 75 percent of the US population. Urban areas contain approximately 3.8 billion trees with an average tree canopy cover of 27 percent. The extent and variation of urban forests across the 48 states are explored...

  12. BOREAS TE-9 NSA Canopy Biochemistry

    Science.gov (United States)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Margolis, Hank; Charest, Martin; Sy, Mikailou

    2000-01-01

    The BOREAS TE-9 team collected several data sets related to chemical and photosynthetic properties of leaves. This data set contains canopy biochemistry data collected in 1994 in the NSA at the YJP, OJR, OBS, UBS, and OA sites, including biochemistry lignin, nitrogen, cellulose, starch, and fiber concentrations. These data were collected to study the spatial and temporal changes in the canopy biochemistry of boreal forest cover types and how a high-resolution radiative transfer model in the mid-infrared could be applied in an effort to obtain better estimates of canopy biochemical properties using remote sensing. The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  13. Mean and Turbulent Flow Statistics in a Trellised Agricultural Canopy

    Science.gov (United States)

    Miller, Nathan E.; Stoll, Rob; Mahaffee, Walter F.; Pardyjak, Eric R.

    2017-10-01

    Flow physics is investigated in a two-dimensional trellised agricultural canopy to examine that architecture's unique signature on turbulent transport. Analysis of meteorological data from an Oregon vineyard demonstrates that the canopy strongly influences the flow by channelling the mean flow into the vine-row direction regardless of the above-canopy wind direction. Additionally, other flow statistics in the canopy sub-layer show a dependance on the difference between the above-canopy wind direction and the vine-row direction. This includes an increase in the canopy displacement height and a decrease in the canopy-top shear length scale as the above-canopy flow rotates from row-parallel towards row-orthogonal. Distinct wind-direction-based variations are also observed in the components of the stress tensor, turbulent kinetic energy budget, and the energy spectra. Although spectral results suggest that sonic anemometry is insufficient for resolving all of the important scales of motion within the canopy, the energy spectra peaks still exhibit dependencies on the canopy and the wind direction. These variations demonstrate that the trellised-canopy's effect on the flow during periods when the flow is row-aligned is similar to that seen by sparse canopies, and during periods when the flow is row-orthogonal, the effect is similar to that seen by dense canopies.

  14. Alveolar ridge preservation with an open-healing approach using single-layer or double-layer coverage with collagen membranes.

    Science.gov (United States)

    Choi, Ho-Keun; Cho, Hag-Yeon; Lee, Sung-Jo; Cho, In-Woo; Shin, Hyun-Seung; Koo, Ki-Tae; Lim, Hyun-Chang; Park, Jung-Chul

    2017-12-01

    The aim of this prospective pilot study was to compare alveolar ridge preservation (ARP) procedures with open-healing approach using a single-layer and a double-layer coverage with collagen membranes using radiographic and clinical analyses. Eleven molars from 9 healthy patients requiring extraction of the maxillary or mandibular posterior teeth were included and allocated into 2 groups. After tooth extraction, deproteinized bovine bone mineral mixed with 10% collagen was grafted into the socket and covered either with a double-layer of resorbable non-cross-linked collagen membranes (DL group, n=6) or with a single-layer (SL group, n=5). Primary closure was not obtained. Cone-beam computed tomography images were taken immediately after the ARP procedure and after a healing period of 4 months before implant placement. Radiographic measurements were made of the width and height changes of the alveolar ridge. All sites healed without any complications, and dental implants were placed at all operated sites with acceptable initial stability. The measurements showed that the reductions in width at the level 1 mm apical from the alveolar crest (including the bone graft) were -1.7±0.5 mm in the SL group and -1.8±0.4 mm in the DL group, and the horizontal changes in the other areas were also similar in the DL and SL groups. The reductions in height were also comparable between groups. Within the limitations of this study, single-layer and double-layer coverage with collagen membranes after ARP failed to show substantial differences in the preservation of horizontal or vertical dimensions or in clinical healing. Thus, both approaches seem to be suitable for open-healing ridge preservation procedures.

  15. Comparison of light out-coupling enhancements in single-layer blue-phosphorescent organic light emitting diodes using small-molecule or polymer hosts

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Yung-Ting [Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Taiwan (China); Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan 10617, Taiwan (China); Liu, Shun-Wei [Department of Electronic Engineering, Mingchi University of Technology, New Taipei, Taiwan 24301, Taiwan (China); Yuan, Chih-Hsien; Lee, Chih-Chien [Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan 10607, Taiwan (China); Ho, Yu-Hsuan; Wei, Pei-Kuen [Research Center for Applied Science Academia Sinica, Taipei, Taiwan 11527, Taiwan (China); Chen, Kuan-Yu [Chilin Technology Co., LTD, Tainan City, Taiwan 71758, Taiwan (China); Lee, Yi-Ting; Wu, Min-Fei; Chen, Chin-Ti, E-mail: cchen@chem.sinica.edu.tw, E-mail: chihiwu@cc.ee.ntu.edu.tw [Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Taiwan (China); Wu, Chih-I, E-mail: cchen@chem.sinica.edu.tw, E-mail: chihiwu@cc.ee.ntu.edu.tw [Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan 10617, Taiwan (China)

    2013-11-07

    Single-layer blue phosphorescence organic light emitting diodes (OLEDs) with either small-molecule or polymer hosts are fabricated using solution process and the performances of devices with different hosts are investigated. The small-molecule device exhibits luminous efficiency of 14.7 cd/A and maximum power efficiency of 8.39 lm/W, which is the highest among blue phosphorescence OLEDs with single-layer solution process and small molecular hosts. Using the same solution process for all devices, comparison of light out-coupling enhancement, with brightness enhancement film (BEF), between small-molecule and polymer based OLEDs is realized. Due to different dipole orientation and anisotropic refractive index, polymer-based OLEDs would trap less light than small molecule-based OLEDs internally, about 37% better based simulation results. In spite of better electrical and spectroscopic characteristics, including ambipolar characteristics, higher carrier mobility, higher photoluminescence quantum yield, and larger triplet state energy, the overall light out-coupling efficiency of small molecule-based devices is worse than that of polymer-based devices without BEF. However, with BEF for light out-coupling enhancement, the improved ratio in luminous flux and luminous efficiency for small molecule based device is 1.64 and 1.57, respectively, which are significantly better than those of PVK (poly-9-vinylcarbazole) devices. In addition to the theoretical optical simulation, the experimental data also confirm the origins of differential light-outcoupling enhancement. The maximum luminous efficiency and power efficiency are enhanced from 14.7 cd/A and 8.39 lm/W to 23 cd/A and 13.2 lm/W, respectively, with laminated BEF, which are both the highest so far for single-layer solution-process blue phosphorescence OLEDs with small molecule hosts.

  16. Seedling Canopy Reflectance Spectra, 1992-1993 (ACCP)

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: The reflectance spectra of Douglas-fir and bigleaf maple seedling canopies were measured. Canopies varied in fertilizer treatment and leaf area density...

  17. West Coast Canopy-Forming Kelp, 1989-2014

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data include the general extents of canopy-forming kelp surveys from 1989 to 2014 and a compilation of existing data sets delineating canopy-forming kelp beds...

  18. Wireless sensor networks for canopy temperature sensing and irrigation management

    Science.gov (United States)

    For researchers, canopy temperature measurements have proven useful in characterizing crop water stress and developing protocols for irrigation management. Today, there is heightened interest in using remote canopy temperature measurements for real-time irrigation scheduling. However, without the us...

  19. ASSESSING THE CANOPY INTEGRITY USING CANOPY DIGITAL IMAGES IN SEMIDECIDUOUS FOREST FRAGMENT IN SÃO CARLOS - SP- BRAZIL1

    Directory of Open Access Journals (Sweden)

    Thiago Yamada

    2017-11-01

    Full Text Available ABSTRACT It is well-known that conducting experimental research aiming the characterization of canopy structure of forests can be a difficult and costly task and, generally, requires an expert to extract, in loco, relevant information. Aiming at easing studies related to canopy structures, several techniques have been proposed in the literature and, among them, various are based on canopy digital image analysis. The research work described in this paper empirically compares two techniques that measure the integrity of the canopy structure of a forest fragment; one of them is based on central parts of canopy cover images and, the other, on canopy closure images. For the experiments, 22 central parts of canopy cover images and 22 canopy closure images were used. The images were captured along two transects: T1 (located in the conserved area and T2 (located in the naturally disturbance area. The canopy digital images were computationally processed and analyzed using the MATLAB platform for the canopy cover images and the Gap Light Analyzer (GLA, for the canopy closure images. The results obtained using these two techniques showed that canopy cover images and, among the employed algorithms, the Jseg, characterize the canopy integrity best. It is worth mentioning that part of the analysis can be automatically conducted, as a quick and precise process, with low material costs involved.

  20. Deploying Fourier Coefficients to Unravel Soybean Canopy Diversity

    OpenAIRE

    Jubery, Talukder Z.; Shook, Johnathon; Parmley, Kyle; Zhang, Jiaoping; Naik, Hsiang S.; Higgins, Race; Sarkar, Soumik; Singh, Arti; Singh, Asheesh K.; Ganapathysubramanian, Baskar

    2017-01-01

    Soybean canopy outline is an important trait used to understand light interception ability, canopy closure rates, row spacing response, which in turn affects crop growth and yield, and directly impacts weed species germination and emergence. In this manuscript, we utilize a methodology that constructs geometric measures of the soybean canopy outline from digital images of canopies, allowing visualization of the genetic diversity as well as a rigorous quantification of shape parameters. Our ch...

  1. Scaling leaf measurements to estimate cotton canopy gas exchange

    Science.gov (United States)

    Diurnal leaf and canopy gas exchange of well watered field grown cotton were measured. Leaf measurements were made with a portable photosynthesis system and canopy measurements with open Canopy Evapo-Transpiration and Assimilation (CETA) systems. Leaf level measurements were arithmetically scaled to...

  2. Reaching state-of-the art requirements for MIM capacitors with a single-layer anodic Al2O3 dielectric and imprinted electrodes

    Science.gov (United States)

    Hourdakis, Emmanouel; Nassiopoulou, Androula G.

    2017-07-01

    Metal-Insulator-Metal (MIM) capacitors with a high capacitance density and low non-linearity coefficient using a single-layer dielectric of barrier-type anodic alumina (Al2O3) and an imprinted bottom Al electrode are presented. Imprinting of the bottom electrode aimed at increasing the capacitor effective surface area by creating a three-dimensional MIM capacitor architecture. The bottom Al electrode was only partly nanopatterned so as to ensure low series resistance of the MIM capacitor. With a 3 nm thick anodic Al2O3 dielectric, the capacitor with the imprinted electrode showed a 280% increase in capacitance density compared to the flat electrode capacitor, reaching a value of 20.5 fF/μm2. On the other hand, with a 30 nm thick anodic Al2O3 layer, the capacitance density was 7.9 fF/μm2 and the non-linearity coefficient was as low as 196 ppm/V2. These values are very close to reaching all requirements of the last International Technology Roadmap for Semiconductors for MIM capacitors [ITRS, http://www.itrs2.net/2013-itrs.html for ITRS Roadmap (2013)], and they are achieved by a single-layer dielectric instead of the complicated dielectric stacks of the literature. The obtained results constitute a real progress compared to previously reported results by our group for MIM capacitors using imprinted electrodes.

  3. Copper-vapor-assisted chemical vapor deposition for high-quality and metal-free single-layer graphene on amorphous SiO2 substrate.

    Science.gov (United States)

    Kim, Hyungki; Song, Intek; Park, Chibeom; Son, Minhyeok; Hong, Misun; Kim, Youngwook; Kim, Jun Sung; Shin, Hyun-Joon; Baik, Jaeyoon; Choi, Hee Cheul

    2013-08-27

    We report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer. The overall quality of graphene grown by Cu-vapor-assisted CVD is comparable to that of the graphene grown by regular metal-catalyzed CVD on a Cu foil. While Cu vapor induces the nucleation and growth of SLG on an amorphous substrate, the resulting SLG is confirmed to be Cu-free by synchrotron X-ray photoelectron spectroscopy. The SLG grown by Cu-vapor-assisted CVD is fabricated into field effect transistor devices without transfer steps that are generally required when SLG is grown by regular CVD process on metal catalyst substrates. This method has overcome two important hurdles previously present when the catalyst-free CVD process is used for the growth of SLG on fused quartz and hexagonal boron nitride substrates, that is, high degree of structural defects and limited size of resulting graphene, respectively.

  4. Phase diagram and electronic indication of high-temperature superconductivity at 65 K in single-layer FeSe films.

    Science.gov (United States)

    He, Shaolong; He, Junfeng; Zhang, Wenhao; Zhao, Lin; Liu, Defa; Liu, Xu; Mou, Daixiang; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2013-07-01

    The recent discovery of possible high-temperature superconductivity in single-layer FeSe films has generated significant experimental and theoretical interest. In both the cuprate and the iron-based high-temperature superconductors, superconductivity is induced by doping charge carriers into the parent compound to suppress the antiferromagnetic state. It is therefore important to establish whether the superconductivity observed in the single-layer sheets of FeSe--the essential building blocks of the Fe-based superconductors--is realized by undergoing a similar transition. Here we report the phase diagram for an FeSe monolayer grown on a SrTiO3 substrate, by tuning the charge carrier concentration over a wide range through an extensive annealing procedure. We identify two distinct phases that compete during the annealing process: the electronic structure of the phase at low doping (N phase) bears a clear resemblance to the antiferromagnetic parent compound of the Fe-based superconductors, whereas the superconducting phase (S phase) emerges with the increase in doping and the suppression of the N phase. By optimizing the carrier concentration, we observe strong indications of superconductivity with a transition temperature of 65±5 K. The wide tunability of the system across different phases makes the FeSe monolayer ideal for investigating not only the physics of superconductivity, but also for studying novel quantum phenomena more generally.

  5. Comparison of Single-Layer and Double-Layer Anti-Reflection Coatings Using Laser-Induced Damage Threshold and Photothermal Common-Path Interferometry

    Directory of Open Access Journals (Sweden)

    Caspar Clark

    2016-05-01

    Full Text Available The dielectric thin-film coating on high-power optical components is often the weakest region and will fail at elevated optical fluences. A comparison of single-layer coatings of ZrO2, LiF, Ta2O5, SiN, and SiO2 along with anti-reflection (AR coatings optimized at 1064 nm comprised of ZrO2 and Ta2O5 was made, and the results of photothermal common-path interferometry (PCI and a laser-induced damage threshold (LIDT are presented here. The coatings were grown by radio frequency (RF sputtering, pulsed direct-current (DC sputtering, ion-assisted electron beam evaporation (IAD, and thermal evaporation. Test regimes for LIDT used pulse durations of 9.6 ns at 100 Hz for 1000-on-1 and 1-on-1 regimes at 1064 nm for single-layer and AR coatings, and 20 ns at 20 Hz for a 200-on-1 regime to compare the //ZrO2/SiO2 AR coating.

  6. Investigation of the single layer model of GPS ionospheric data processing using IRI-90 and the attached diffusive equilibrium model of plasmaspheric electron density

    Directory of Open Access Journals (Sweden)

    L. Bànyai

    1997-06-01

    Full Text Available The single layer model of GPS ionospheric data processing is compared with the International Reference Ionosphere í 1990 and the attached Diffusive Equilibrium model of Plasmasphere (IRI-90+DEP which proved to be a good supplement to GPS data processing. These models can be used to estimate the single layer height and to improve the mapping function in day-time. The code delays estimated from IRI-90+DEP models are compared with GPS measurements carried out by TurboRogue receiver. These models can be used to estimate the preliminary receiver biases especially in the case of cross-correlation tracking mode. The practical drawback of the IRI-90 model is the sharp discontinuity of the ion components during sunset and sunrise at an elevation of 1000 km, because it also causes a sharp discontinuity in the TEC values computed from the DEP model. The GPS data may be a good source to improve the topside region of the IRI model estimating smooth TEC transition before and after sunrise in the plasmasphere.

  7. Canopy arthropod responses to experimental canopy opening and debris deposition in a tropical rainforest subject to hurricanes

    Science.gov (United States)

    Timothy D. Schowalter; Michael R. Willig; Steven J. Presley

    2014-01-01

    We analyzed responses of canopy arthropods on seven representative early and late successional overstory and understory tree species to a canopy trimming experiment designed to separate effects of canopy opening and debris pulse (resulting from hurricane disturbance) in a tropical rainforest ecosystem at the Luquillo Experimental Forest Long-Term Ecological Research (...

  8. Observing the Vertical Dimensions of Singapore's Urban Heat Island

    Science.gov (United States)

    Chow, W. T. L.; Ho, D. X. Q.

    2015-12-01

    In numerous cities, measurements of urban warmth in most urban heat island (UHI) studies are generally constrained towards surface or near-surface (quadcopter platforms to measure urban temperature and humidity profiles in Singapore, which is a rapidly urbanizing major tropical metropolis. These profiles were measured from the surface to ~100 m above ground level, a height which includes all of the urban canopy and parts of the urban boundary layer. Initial results indicate significant variations in stability measured over different land uses (e.g. urban park, high-rise residential, commercial); these profiles are also temporally dynamic, depending on the time of day and larger-scale weather conditions.

  9. Canopy conductance decrease in Florida as a result of anthropogenic CO2 increase

    Science.gov (United States)

    Lammertsma, E.; Wagner-Cremer, F.

    2009-04-01

    Precipitation is one of the main factors controlling vegetation cover, but in turn vegetation has a considerable effect on regional climate by modifying the atmospheric energy and water budget. In Florida approximately 20% of the annual precipitation originates from local evapotranspiration. Transpiration is in large parts controlled by the stomatal conductance of the vegetation. Stomatal conductance of trees in turn is influenced by the atmospheric CO2 concentration ([CO2]), which has increased by 100ppmv since the industrial revolution. The potential consequences of the anthropogenic [CO2] increase on stomatal conductance, however, are not well quantified yet, which hampers parameterization of this variable in models. In this study we assess the change in transpiration rates in Florida by calculating the canopy conductance over the [CO2] increase of the past century. Past and present stomatal conductance levels are calculated from stomatal density and dimensions measured on modern leaves and historical herbarium specimen for the in Florida most common canopy taxa. These values are consequently upscaled to canopy level by calculating the relative abundance of the taxa in the various vegetation units providing an indication of the general change in canopy conductance in each unit. A significant negative correlation of stomatal conductance and [CO2] over the past century is found in various Florida tree taxa leading to a decrease of up to 40% in canopy conductance for major forest types. For Florida, where extreme land-use changes and urbanization significantly alter the hydrological system, the vegetation adaptation to increasing [CO2] levels may amplify the disturbance of the water budget. Our results may help to improve model attempts to quantify the past, present and future hydrological conditions by providing more accurate assessments on the biosphere-atmosphere feedback. The description of the undisturbed, pre-industrial state will also provide more realistic

  10. Biophysical information in asymmetric and symmetric diurnal bidirectional canopy reflectance

    Science.gov (United States)

    Vanderbilt, Vern C.; Caldwell, William F.; Pettigrew, Rita E.; Ustin, Susan L.; Martens, Scott N.; Rousseau, Robert A.; Berger, Kevin M.; Ganapol, B. D.; Kasischke, Eric S.; Clark, Jenny A.

    1991-01-01

    The authors present a theory for partitioning the information content in diurnal bidirectional reflectance measurements in order to detect differences potentially related to biophysical variables. The theory, which divides the canopy reflectance into asymmetric and symmetric functions of solar azimuth angle, attributes asymmetric variation to diurnal changes in the canopy biphysical properties. The symmetric function is attributed to the effects of sunlight interacting with a hypothetical average canopy which would display the average diurnal properties of the actual canopy. The authors analyzed radiometer data collected diurnally in the Thematic Mapper wavelength bands from two walnut canopies that received differing irrigation treatments. The reflectance of the canopies varied with sun and view angles and across seven bands in the visible, near-infrared, and middle infrared wavelength regions. Although one of the canopies was permanently water stressed and the other was stressed in mid-afternoon each day, no water stress signature was unambiguously evident in the reflectance data.

  11. The roles of dimensionality, canopies and complexity in ecosystem monitoring.

    Directory of Open Access Journals (Sweden)

    Christopher H R Goatley

    Full Text Available Canopies are common among autotrophs, increasing their access to light and thereby increasing competitive abilities. If viewed from above canopies may conceal objects beneath them creating a 'canopy effect'. Due to complexities in collecting 3-dimensional data, most ecosystem monitoring programmes reduce dimensionality when sampling, resorting to planar views. The resultant 'canopy effects' may bias data interpretation, particularly following disturbances. Canopy effects are especially relevant on coral reefs where coral cover is often used to evaluate and communicate ecosystem health. We show that canopies hide benthic components including massive corals and algal turfs, and as planar views are almost ubiquitously used to monitor disturbances, the loss of vulnerable canopy-forming corals may bias findings by presenting pre-existing benthic components as an altered system. Our reliance on planar views in monitoring ecosystems, especially coral cover on reefs, needs to be reassessed if we are to better understand the ecological consequences of ever more frequent disturbances.

  12. A model-based comparison of organic matter dynamics between riparian-forested and open-canopy streams

    Directory of Open Access Journals (Sweden)

    Stenroth Karolina

    2014-06-01

    Full Text Available The food webs of forest streams are primarily based upon inputs of organic matter from adjacent terrestrial ecosystems. However, streams that run through open landscapes generally lack closed riparian canopies, and an increasing number of studies indicate that terrestrial organic matter may be an important resource in these systems as well. Combining key abiotically-controlled factors (stream discharge, water temperature, and litter input rate with relevant biotic processes (e.g. macroinvertebrate CPOM consumption, microbial processing, we constructed a model to predict and contrast organic matter dynamics (including temporal variation in CPOM standing crop, CPOM processing rate, FPOM production, and detritivore biomass in small riparian-forested and open-canopy streams. Our modeled results showed that the standing crop of CPOM was similar between riparian-forested and open-canopy streams, despite considerable differences in litter input rate. This unexpected result was partly due to linkages between CPOM supply and consumer abundance that produced higher detritivore biomass in the forest stream than the open-canopy stream. CPOM standing crop in the forest stream was mainly regulated by top-down consumer control, depressing it to a level similar to that of the open-canopy stream. In contrast, CPOM standing crop in the open-canopy stream was primarily controlled by physical factors (litter input rates and discharge, not consumption. This suggests that abiotic processes (e.g. discharge may play a greater role in limiting detrital resource availability and consumer biomass in open-canopy streams than in forest streams. These model results give insight on functional differences that exists among streams and they can be used to predict effects of anthropogenic influences such as forestry, agriculture, urbanization, and climate change on streams and how riparian management and conservation tools can be employed to mitigate undesirable effects.

  13. Modelling the canopy development of bambara groundnut

    DEFF Research Database (Denmark)

    Karunaratne, A.S.; Azam-Ali, S.N.; Al-Shareef, I.

    2010-01-01

    Canopy development of bambara groundnut (Vigna subterranea (L.) Verdc) is affected by temperature stress, drought stress and photoperiod. The quantification of these documented effects by means of a suitable crop model, BAMGRO is presented in this paper. Data on canopy development from five growth...... chamber, four glasshouse and three field experiments were analyzed to calibrate and validate the BAMGRO model to produce simulations for temperature stress, drought stress and photoperiodic effect on two contrasting landraces; Uniswa Red (Swaziland) and S19-3 (Namibia). The daily initiation rate of new...... leaves is calculated by means of a Gaussian function and is altered by temperature stress, drought stress, photoperiod and plant density. The rate in dead leaf number is dependent upon the maximum senescence fraction which can be explained by physiological maturity, mutual shading, temperature stress...

  14. Cockpit canopy shattering using exploding wire techniques

    International Nuclear Information System (INIS)

    Novac, B M; Smith, I R; Downs, P R; Marston, P; Fahey, D

    2007-01-01

    This paper presents the principal experimental results provided by a preliminary investigation into the possibility of using exploding wire (EW) techniques to shatter the plastic cockpit canopy of a modern jet aircraft. The data provided forms the basis for a qualitative understanding of the physics of interaction between the plasma produced by an EW and the surrounding elasto-plastic material in which the wire is embedded. To optimize the shock-wave 'clean cutting' effect, the significance of the material, the dimensions of the exploding wire and the amplitude of the current and voltage pulses are all considered. This leads to important conclusions concerning both the characteristics of the EW and the optimum arrangement of the electrical circuit, with the single most important optimization factor being the peak electrical power input to the EW, rather than the dissipated Joule energy. A full-scale system relevant to an actual cockpit canopy shattering is outlined and relevant results are presented and discussed

  15. Seagrass canopy photosynthetic response is a function of canopy density and light environment: a model for Amphibolis griffithii.

    Directory of Open Access Journals (Sweden)

    John D Hedley

    Full Text Available A three-dimensional computer model of canopies of the seagrass Amphibolis griffithii was used to investigate the consequences of variations in canopy structure and benthic light environment on leaf-level photosynthetic saturation state. The model was constructed using empirical data of plant morphometrics from a previously conducted shading experiment and validated well to in-situ data on light attenuation in canopies of different densities. Using published values of the leaf-level saturating irradiance for photosynthesis, results show that the interaction of canopy density and canopy-scale photosynthetic response is complex and non-linear, due to the combination of self-shading and the non-linearity of photosynthesis versus irradiance (P-I curves near saturating irradiance. Therefore studies of light limitation in seagrasses should consider variation in canopy structure and density. Based on empirical work, we propose a number of possible measures for canopy scale photosynthetic response that can be plotted to yield isoclines in the space of canopy density and light environment. These plots can be used to interpret the significance of canopy changes induced as a response to decreases in the benthic light environment: in some cases canopy thinning can lead to an equivalent leaf level light environment, in others physiological changes may also be required but these alone may be inadequate for canopy survival. By providing insight to these processes the methods developed here could be a valuable management tool for seagrass conservation during dredging or other coastal developments.

  16. The Canopy Horizontal Array Turbulence Study (CHATS): Influence of canopy density and atmospheric stability on turbulent exchange

    Science.gov (United States)

    Patton, E. G.

    2011-12-01

    Understanding the micrometeorology within and above forest canopies is of great interest for many environmental applications such as weather and climate forecasting as well as for vegetation-atmosphere scalar exchanges. Within a canopy, both the ground and the vegetation can act as scalar sources/sinks, where the distribution of canopy sources/sinks depends on the amount and state of the canopy foliage. For deciduous trees, the foliage evolves across a seasonal cycle from bare limbs in winter (no photosynthesis and an open canopy) to rapid growth in spring (increasing photosynthesis and canopy density), to maturity in summer (more constant photosynthesis and canopy density), to senescence and leaf-drop in fall (decreasing photosynthesis and canopy density). Thus a broad spectrum of different conditions occurs through the year, thereby imposing height and seasonal dependence on dynamical and scalar fluxes. The Canopy Horizontal Array Turbulence Study (CHATS) took place in 2007 focusing on a 10 m tall deciduous walnut orchard in Dixon, California (USA). High spatial resolution micrometeorological measurements were deployed aiming to establish the influence of seasonality (prior to, and follwing leaf-out) on canopy exchange. This talk will discuss the sensitivity of velocity, temperature and humidity fields within and above the deciduous walnut orchard at CHATS to the canopy evolution and atmospheric stability.

  17. Improved Windshield and Canopy Protection Development Program

    Science.gov (United States)

    1974-06-01

    canopy shots, i.e., 8" from the beam, 12" from the forward arch. The Impact resulted in a penetration with a football -shaped plug blown Inward...i7;«MpiWW.,i«iS,i»f.«.^^^ CVJ Cte / teä <%1 ^ u- o ro O in H UJ o to o L HH Hh o «^ o = —I ro O \\ N__ o a. CM X UJ

  18. Using Human Motion Intensity as Input for Urban Design

    DEFF Research Database (Denmark)

    Poulsen, Esben Skouboe; Andersen, Hans Jørgen; Gade, Rikke

    2012-01-01

    of a town square, human occupancy and motion intensities are used to generate situated or topologies presenting new adaptive methods for urban design. These methods incorporate local or as design drivers for canopy, pavement and furniture layout. The urban design solution may be congured due to various...... parameters such as security, comfort, navigation, eciency, or aesthetics....

  19. R&D for a single-layer $Nb_{3}Sn$ common coil dipole using the react-and-wind fabrication technique

    CERN Document Server

    Ambrosio, G; Barzi, E; Bauer, P; Chichili, D R; Ewald, K D; Fehér, S; Imbasciati, L; Kashikhin, V V; Limon, P J; Litvinenko, L; Novitski, I; Rey, J M; Scanlan, R M; Yadav, S; Yamada, R; Zlobin, A V

    2002-01-01

    A dipole magnet based on the common coil design, using prereacted Nb /sub 3/Sn superconductor, is under development at Fermilab, for a future Very Large Hadron Collider. This magnet has some innovative design and technological features such as single layer coils, a 22 mm wide 60-strand Rutherford type cable and stainless steel collars reinforced by horizontal bridges inserted between coil blocks. Both left and right coils are wound simultaneously into the collar structure and then impregnated with epoxy. In order to optimize the design and fabrication techniques an R&D program is underway. The production of cables with the required characteristics was shown possible. Collar laminations were produced, assembled and tested in order to check the effectiveness of the bridges and the validity of the mechanical design. A mechanical model consisting in a 165 mm long section of the magnet straight section was assembled and tested. This paper summarizes the status of the program, and reports the results of fabrica...

  20. NMR studies of Borrelia burgdorferi OspA, a 28 kDa protein containing a single-layer {beta}-sheet

    Energy Technology Data Exchange (ETDEWEB)

    Pham, Thuy-Nga; Koide, Shohei

    1998-05-15

    The crystal structure of outer surface protein A (OspA) from Borrelia burgdorferi contains a single-layer {beta}-sheet connecting the N- and C-terminal globular domains. The central {beta}-sheet consists largely of polar amino acids and it is solvent-exposed on both faces, which so far appears to be unique among known protein structures. We have accomplished nearly complete backbone H, C and N and C{sup ;}/H{sup {beta}} assignments of OspA (28 kDa) using standard triple resonance techniques without perdeuteration. This was made possible by recording spectra at a high temperature (45 {sup o}C ). The chemical shift index and {sup 15}N T{sub 1}/T{sub 2} ratios show that both the secondary structure and the global conformation of OspA in solution are similar to the crystal structure, suggesting that the unique central {beta}-sheet is fairly rigid.

  1. Remote N2 plasma treatment to deposit ultrathin high-k dielectric as tunneling contact layer for single-layer MoS2 MOSFET

    Science.gov (United States)

    Qian, Qingkai; Zhang, Zhaofu; Hua, Mengyuan; Wei, Jin; Lei, Jiacheng; Chen, Kevin J.

    2017-12-01

    Remote N2 plasma treatment is explored as a surface functionalization technique to deposit ultrathin high-k dielectric on single-layer MoS2. The ultrathin dielectric is used as a tunneling contact layer, which also serves as an interfacial layer below the gate region for fabricating top-gate MoS2 metal–oxide–semiconductor field-effect transistors (MOSFETs). The fabricated devices exhibited small hysteresis and mobility as high as 14 cm2·V‑1·s‑1. The contact resistance was significantly reduced, which resulted in the increase of drain current from 20 to 56 µA/µm. The contact resistance reduction can be attributed to the alleviated metal–MoS2 interface reaction and the preserved conductivity of MoS2 below the source/drain metal contact.

  2. The wave-driven current in coastal canopies

    Science.gov (United States)

    Abdolahpour, Maryam; Hambleton, Magnus; Ghisalberti, Marco

    2017-05-01

    Wave-driven flows over canopies of aquatic vegetation (such as seagrass) are characterized by the generation of a strong, shoreward mean current near the top of the canopy. This shoreward drift, which is observed to be up to 75% of the RMS above-canopy orbital velocity, can have a significant impact on residence times within coastal canopies. There have been limited observations of this current and an accurate formulation of its magnitude is still lacking. Accordingly, this study aims to develop a practical relationship to describe the strength of this current as a function of both wave and canopy characteristics. A simple model for the Lagrangian drift velocity indicates that the magnitude of the wave-driven current increases with the above-canopy oscillatory velocity, the vertical orbital excursion at the top of the canopy, and the canopy density. An extensive laboratory study, using both rigid and (dynamically scaled) flexible model vegetation, was carried out to evaluate the proposed model. Experimental results reveal a strong agreement between predicted and measured current velocities over a wide and realistic range of canopy and wave conditions. The validity of this model is also confirmed through available field measurements. Characterization of this wave-induced mean current will allow an enhanced capacity for predicting residence time, and thus key ecological processes, in coastal canopies.

  3. Assessing urban forest effects and values, Minneapolis' urban forest

    Science.gov (United States)

    David J. Nowak; Robert E. III Hoehn; Daniel E. Crane; Jack C. Stevens; Jeffrey T. Walton

    2006-01-01

    An analysis of trees in Minneapolis, MN, reveals that the city has about 979,000 trees with canopies that cover 26.4 percent of the area. The most common tree species are green ash, American elm, and boxelder. The urban forest currently stores about 250,000 tons of carbon valued at $4.6 million. In addition, these trees remove about 8,900 tons of carbon per year ($164,...

  4. Assessing urban forest effects and values, Philladelphia's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E., III Hoehn; Daniel E. Crane; Jack C. Stevens; Jeffrey T. Walton

    2007-01-01

    An analysis of trees in Philadelphia reveals that this city has about 2.1 million trees with canopies that cover 15.7 percent of the area. The most common tree species are black cherry, crabapple, and tree of heaven. The urban forest currently stores about 530,000 tons of carbon valued at $9.8 million. In addition, these trees remove about 16,100 tons of carbon per...

  5. Assessing urban forest effects and values, San Francisco's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E., III Hoehn; Daniel E. Crane; Jack C. Stevens; Jeffrey T. Walton

    2007-01-01

    An analysis of trees in San Francisco, CA reveals that this city has about 669,000 trees with canopies that cover 11.9 percent of the area. The most common tree species are blue gum eucalyptus, Monterey pine, and Monterey cypress. The urban forest currently stores about 196,000 tons of carbon valued at $3.6 million. In addition, these trees remove about 5,200 tons of...

  6. Assessing urban forest effects and values, Casper's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E., III Hoehn; Daniel E. Crane; Jack C. Stevens; Jeffrey T. Walton

    2006-01-01

    An analysis of trees in Casper, WY reveals that this city has about 123,000 trees with canopies that cover 8.9 percent of the area. The most common tree species are plains cottonwood, blue spruce, and American elm. The urban forest currently store about 37,000 tons of carbon valued at $689,000. In addition, these trees remove about 1,200 tons of carbon per year ($22,...

  7. Assessing urban forest effects and values: Toronto's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E. III Hoehn; Allison R. Bodine; Eric J. Greenfield; Alexis Ellis; Theodore A. Endreny; Yang Yang; Tian Zhou; Ruthanne. Henry

    2013-01-01

    An analysis of trees in Toronto, Ontario, reveals that this city has about 10.2 million trees with a tree and shrub canopy that covers approximately 26.6 percent of the city. The most common tree species are eastern white-cedar, sugar maple, and Norway maple. The urban forest currently stores an estimated 1.1 million metric tons of carbon valued at CAD$25.0 million. In...

  8. Canopy soil bacterial communities altered by severing host tree limbs

    Directory of Open Access Journals (Sweden)

    Cody R. Dangerfield

    2017-09-01

    Full Text Available Trees of temperate rainforests host a large biomass of epiphytic plants, which are associated with soils formed in the forest canopy. Falling of epiphytic material results in the transfer of carbon and nutrients from the canopy to the forest floor. This study provides the first characterization of bacterial communities in canopy soils enabled by high-depth environmental sequencing of 16S rRNA genes. Canopy soil included many of the same major taxonomic groups of Bacteria that are also found in ground soil, but canopy bacterial communities were lower in diversity and contained different operational taxonomic units. A field experiment was conducted with epiphytic material from six Acer macrophyllum trees in Olympic National Park, Washington, USA to document changes in the bacterial communities of soils associated with epiphytic material that falls to the forest floor. Bacterial diversity and composition of canopy soil was highly similar, but not identical, to adjacent ground soil two years after transfer to the forest floor, indicating that canopy bacteria are almost, but not completely, replaced by ground soil bacteria. Furthermore, soil associated with epiphytic material on branches that were severed from the host tree and suspended in the canopy contained altered bacterial communities that were distinct from those in canopy material moved to the forest floor. Therefore, the unique nature of canopy soil bacteria is determined in part by the host tree and not only by the physical environmental conditions associated with the canopy. Connection to the living tree appears to be a key feature of the canopy habitat. These results represent an initial survey of bacterial diversity of the canopy and provide a foundation upon which future studies can more fully investigate the ecological and evolutionary dynamics of these communities.

  9. Impact of Canopy Coupling on Canopy Average Stomatal Conductance Across Seven Tree Species in Northern Wisconsin

    Science.gov (United States)

    Ewers, B. E.; Mackay, D. S.; Samanta, S.; Ahl, D. E.; Burrows, S. S.; Gower, S. T.

    2001-12-01

    Land use changes over the last century in northern Wisconsin have resulted in a heterogeneous landscape composed of the following four main forest types: northern hardwoods, northern conifer, aspen/fir, and forested wetland. Based on sap flux measurements, aspen/fir has twice the canopy transpiration of northern hardwoods. In addition, daily transpiration was only explained by daily average vapor pressure deficit across the cover types. The objective of this study was to determine if canopy average stomatal conductance could be used to explain the species effects on tree transpiration. Our first hypothesis is that across all of the species, stomatal conductance will respond to vapor pressure deficit so as to maintain a minimum leaf water potential to prevent catostrophic cavitiation. The consequence of this hypothesis is that among species and individuals there is a proportionality between high stomatal conductance and the sensitivity of stomatal conductance to vapor pressure deficit. Our second hypothesis is that species that do not follow the proportionality deviate because the canopies are decoupled from the atmosphere. To test our two hypotheses we calculated canopy average stomatal conductance from sap flux measurements using an inversion of the Penman-Monteith equation. We estimated the canopy coupling using a leaf energy budget model that requires leaf transpiration and canopy aerodynamic conductance. We optimized the parameters of the aerodynamic conductance model using a Monte Carlo technique across six parameters. We determined the optimal model for each species by selecting parameter sets that resulted in the proportionality of our first hypothesis. We then tested the optimal energy budget models of each species by comparing leaf temperature and leaf width predicted by the models to measurements of each tree species. In red pine, sugar maple, and trembling aspen trees under high canopy coupling conditions, we found the hypothesized proportionality

  10. Radiation Distribution Within a Canopy Profile Calculated by a Multiple-Layer Canopy Scattering Model

    Science.gov (United States)

    Qualls, R. J.; Zhao, W.

    2004-05-01

    Remote sensing technology has tremendous potential for use in natural resource studies, agriculture, water and land use management because of the spatial information contained in remote sensing images and because of the ease and/or frequency of acquiring vast amounts of surface information. However, the quantitative application of remotely sensed data is restricted by several problems. One of them is that the entities a remote sensor views are not single targets. For example, measurement show that the skin temperature of many crops can exhibit more than a 10° C difference between the leaves at the bottom and those at the top of the canopy, in addition to the usually large difference between leaves and soil substrate. Directional radiometric surface temperatures measured from above a crop represent neither the skin temperature of the crop nor the surface temperature of the soil substrate but a complex aggregate of all elements viewed. When a remote sensing device views a vegetated surface from different view angles, different combinations of canopy and soil elements at different temperatures will be seen, producing different values of "remotely sensed surface temperature." As the first step in a series of models to be developed to simulate energy balance, sensible and latent heat fluxes, and temperature profiles within a vegetation canopy, a multiple-layer canopy scattering model to estimate short wave radiation distribution within a wheat canopy was developed. This model incorporates processes of radiation penetration through gaps between leaves, and radiation absorption, reflection and transmission in leaf layers. It is able to simulate the multiple scattering processes that occur among different canopy layers, and determine the vertical distributions of upwelling, downwelling, and reflected short wave radiation within the canopy, and at the soil surface. One of the primary advantages of this model, in contrast to other models, is that the multiple scattering

  11. Computing energy budget within a crop canopy from Penmann's ...

    Indian Academy of Sciences (India)

    R. Narasimhan, Krishtel eMaging Solutions

    iological profiles of the canopy are stated and will be used in simultaneity with the basic equations mentioned above. 3.1 Net radiation. The extinction of net radiation within the canopy can be described by Beer's law: Rn = Rn(h) exp. [. − αrLAI(z/h). ] ,. (10) where h is the height of canopy from the soil sur- face. The extinction ...

  12. Specular, diffuse and polarized imagery of an oat canopy

    Science.gov (United States)

    Vanderbilt, Vern C.; De Venecia, Kurt J.

    1988-01-01

    Light, polarized by specular reflection, has been found to be an important part of the light scattered by several measured plant canopies. The authors investigate for one canopy the relative importance of specularly reflected sunlight, specularly reflected light from other sources including skylight, and diffusely upwelling light. Polarization images are used to gain increased understanding of the radiation transfer process in a plant canopy. Analysis of the results suggests that properly analyzed polarized remotely sensed data, acquired under specific atmospheric conditions by a specially designed sensor, potentially provide measures of physiological and morphological states of plants in a canopy.

  13. Mechanistic study of aerosol dry deposition on vegetated canopies

    International Nuclear Information System (INIS)

    Petroff, A.

    2005-04-01

    The dry deposition of aerosols onto vegetated canopies is modelled through a mechanistic approach. The interaction between aerosols and vegetation is first formulated by using a set of parameters, which are defined at the local scale of one surface. The overall deposition is then deduced at the canopy scale through an up-scaling procedure based on the statistic distribution parameters. This model takes into account the canopy structural and morphological properties, and the main characteristics of the turbulent flow. Deposition mechanisms considered are Brownian diffusion, interception, initial and turbulent impaction, initially with coniferous branches and then with entire canopies of different roughness, such as grass, crop field and forest. (author)

  14. Modeling directional thermal radiance from a forest canopy

    International Nuclear Information System (INIS)

    McGuire, M.J.; Balick, L.K.; Smith, J.A.; Hutchison, B.A.

    1989-01-01

    Recent advances in remote sensing technology have increased interest in utilizing the thermal-infared region to gain additional information about surface features such as vegetation canopies. Studies have shown that sensor view angle, canopy structure, and percentage of canopy coverage can affect the response of a thermal sensor. These studies have been primarily of agricultural regions and there have been relatively few examples describing the thermal characteristics of forested regions. This paper describes an extension of an existing thermal vegetation canopy radiance model which has been modified to partially account for the geometrically rough structure of a forest canopy. Fourier series expansion of a canopy height profile is used to calculate improved view factors which partially account for the directional variations in canopy thermal radiance transfers. The original and updated radiance model predictions are compared with experimental data obtained over a deciduous (oak-hickory) forest site. The experimental observations are also used to document azimuthal and nadir directional radiance variations. Maximum angular variations in measured canopy temperatures were 4–6°C (azimuth) and 2.5°C (nadir). Maximum angular variations in simulated temperatures using the modified rough surface model was 4°C. The rough surface model appeared to be sensitive to large gaps in the canopy height profile, which influenced the resultant predicted temperature. (author)

  15. Radar return from a continuous vegetation canopy

    Science.gov (United States)

    Bush, T. F.; Ulaby, F. T.

    1975-01-01

    The radar backscatter coefficient, sigma deg, of alfalfa was investigated as a function of both radar parameters and the physical characteristics of the alfalfa canopy. Measurements were acquired with an 8-18 GHz FM-CW mobile radar over an angular range of 0 - 70 deg as measured from nadir. The experimental data indicates that the excursions of sigma deg at nadir cover a range of nearly 18 dB during one complete growing cycle. An empirical model for sigma deg was developed which accounts for its variability in terms of soil moisture, plant moisture and plant height.

  16. Evaporation from rain-wetted forest in relation to canopy wetness, canopy cover, and net radiation

    NARCIS (Netherlands)

    Klaassen, W.

    2001-01-01

    Evaporation from wet canopies is commonly calculated using E-PM, the Penman-Monteith equation with zero surface resistance. However, several observations show a lower evaporation from rain-wetted forest. Possible causes for the difference between E-PM and experiments are evaluated to provide rules

  17. Large-Eddy Simulation of Coherent Flow Structures within a Cubical Canopy

    Science.gov (United States)

    Inagaki, Atsushi; Castillo, Marieta Cristina L.; Yamashita, Yoshimi; Kanda, Manabu; Takimoto, Hiroshi

    2012-02-01

    Instantaneous flow structures "within" a cubical canopy are investigated via large-eddy simulation. The main topics of interest are, (1) large-scale coherent flow structures within a cubical canopy, (2) how the structures are coupled with the turbulent organized structures (TOS) above them, and (3) the classification and quantification of representative instantaneous flow patterns within a street canyon in relation to the coherent structures. We use a large numerical domain (2,560 m × 2,560 m × 1,710 m) with a fine spatial resolution (2.5 m), thereby simulating a complete daytime atmospheric boundary layer (ABL), as well as explicitly resolving a regular array of cubes (40 m in height) at the surface. A typical urban ABL is numerically modelled. In this situation, the constant heat supply from roof and floor surfaces sustains a convective mixed layer as a whole, but strong wind shear near the canopy top maintains the surface layer nearly neutral. The results reveal large coherent structures in both the velocity and temperature fields "within" the canopy layer. These structures are much larger than the cubes, and their shapes and locations are shown to be closely related to the TOS above them. We classify the instantaneous flow patterns in a cavity, specifically focusing on two characteristic flow patterns: flushing and cavity-eddy events. Flushing indicates a strong upward motion, while a cavity eddy is characterized by a dominant vortical motion within a single cavity. Flushing is clearly correlated with the TOS above, occurring frequently beneath low-momentum streaks. The instantaneous momentum and heat transport within and above a cavity due to flushing and cavity-eddy events are also quantified.

  18. Fluxes of trichloroacetic acid through a conifer forest canopy

    International Nuclear Information System (INIS)

    Stidson, R.T.; Heal, K.V.; Dickey, C.A.; Cape, J.N.; Heal, M.R.

    2004-01-01

    Controlled-dosing experiments with conifer seedlings have demonstrated an above-ground route of uptake for trichloroacetic acid (TCA) from aqueous solution into the canopy, in addition to uptake from the soil. The aim of this work was to investigate the loss of TCA to the canopy in a mature conifer forest exposed only to environmental concentrations of TCA by analysing above- and below-canopy fluxes of TCA and within-canopy instantaneous reservoir of TCA. Concentrations and fluxes of TCA were quantified for one year in dry deposition, rainwater, cloudwater, throughfall, stemflow and litterfall in a 37-year-old Sitka spruce and larch plantation in SW Scotland. Above-canopy TCA deposition was dominated by rainfall (86%), compared with cloudwater (13%) and dry deposition (1%). On average only 66% of the TCA deposition passed through the canopy in throughfall and stemflow (95% and 5%, respectively), compared with 47% of the wet precipitation depth. Consequently, throughfall concentration of TCA was, on average, ∼1.4 x rainwater concentration. There was no significant difference in below-canopy fluxes between Sitka spruce and larch, or at a forest-edge site. Annual TCA deposited from the canopy in litterfall was only ∼1-2% of above-canopy deposition. On average, ∼800 μg m -2 of deposited TCA was lost to the canopy per year, compared with estimates of above-ground TCA storage of ∼400 and ∼300 μg m -2 for Sitka spruce and larch, respectively. Taking into account likely uncertainties in these values (∼±50%), these data yield an estimate for the half-life of within-canopy elimination of TCA in the range 50-200 days, assuming steady-state conditions and that all TCA lost to the canopy is transferred into the canopy material, rather than degraded externally. The observations provide strong indication that an above-ground route is important for uptake of TCA specifically of atmospheric origin into mature forest canopies, as has been shown for seedlings (in

  19. Nonvolatile ferroelectric memory based on PbTiO3 gated single-layer MoS2 field-effect transistor

    Science.gov (United States)

    Shin, Hyun Wook; Son, Jong Yeog

    2018-01-01

    We fabricated ferroelectric non-volatile random access memory (FeRAM) based on a field effect transistor (FET) consisting of a monolayer MoS2 channel and a ferroelectric PbTiO3 (PTO) thin film of gate insulator. An epitaxial PTO thin film was deposited on a Nb-doped SrTiO3 (Nb:STO) substrate via pulsed laser deposition. A monolayer MoS2 sheet was exfoliated from a bulk crystal and transferred to the surface of the PTO/Nb:STO. Structural and surface properties of the PTO thin film were characterized by X-ray diffraction and atomic force microscopy, respectively. Raman spectroscopy analysis was performed to identify the single-layer MoS2 sheet on the PTO/Nb:STO. We obtained mobility value (327 cm2/V·s) of the MoS2 channel at room temperature. The MoS2-PTO FeRAM FET showed a wide memory window with 17 kΩ of resistance variation which was attributed to high remnant polarization of the epitaxially grown PTO thin film. According to the fatigue resistance test for the FeRAM FET, however, the resistance states gradually varied during the switching cycles of 109. [Figure not available: see fulltext.

  20. Current induced annealing and electrical characterization of single layer graphene grown by chemical vapor deposition for future interconnects in VLSI circuits

    Energy Technology Data Exchange (ETDEWEB)

    Prasad, Neetu, E-mail: neetu.prasad@south.du.ac.in, E-mail: neetu23686@gmail.com; Kumari, Anita; Bhatnagar, P. K.; Mathur, P. C. [Department of Electronic Science, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021 (India); Bhatia, C. S. [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore)

    2014-09-15

    Single layer graphene (SLG) grown by chemical vapor deposition (CVD) has been investigated for its prospective application as horizontal interconnects in very large scale integrated circuits. However, the major bottleneck for its successful application is its degraded electronic transport properties due to the resist residual trapped in the grain boundaries and on the surface of the polycrystalline CVD graphene during multi-step lithographic processes, leading to increase in its sheet resistance up to 5 MΩ/sq. To overcome this problem, current induced annealing has been employed, which helps to bring down the sheet resistance to 10 kΩ/sq (of the order of its initial value). Moreover, the maximum current density of ∼1.2 × 10{sup 7 }A/cm{sup 2} has been obtained for SLG (1 × 2.5 μm{sup 2}) on SiO{sub 2}/Si substrate, which is about an order higher than that of conventionally used copper interconnects.

  1. R and D for a single-layer Nb3Sn common coil dipole using the react-and-wind fabrication technique

    International Nuclear Information System (INIS)

    Ambrosio, Giorgio

    2002-01-01

    A dipole magnet based on the common coil design, using prereacted Nb 3 Sn superconductor, is under development at Fermilab, for a future Very Large Hadron Collider. This magnet has some innovative design and technological features such as single layer coils, a 22 mm wide 60-strand Rutherford type cable and stainless steel collars reinforced by horizontal bridges inserted between coil blocks. Both left and right coils are wound simultaneously into the collar structure and then impregnated with epoxy. In order to optimize the design and fabrication techniques an R and D program is underway. The production of cables with the required characteristics was shown possible. Collar laminations were produced, assembled and tested in order to check the effectiveness of the bridges and the validity of the mechanical design. A mechanical model consisting of a 165 mm long section of the magnet straight section was assembled and tested. This paper summarizes the status of the program, and reports the results of fabrication and test of cable, collars and the mechanical model

  2. Ultradispersed and Single-Layered MoS2 Nanoflakes Strongly Coupled with Graphene: An Optimized Structure with High Kinetics for the Hydrogen Evolution Reaction.

    Science.gov (United States)

    Huang, Haoliang; Huang, Junying; Liu, Weipeng; Fang, Yueping; Liu, Yingju

    2017-11-15

    As one of the most promising Pt alternatives for cost-effective hydrogen production, molybdenum disulfide (MoS 2 ), although has been studied extensively to improve its electrocatalytic activity, suffers from scarce active sites, low conductivity, and lack of interaction with substrates. To this end, we anchor ultradispersed and single-layered MoS 2 nanoflakes on graphene sheets via a hybrid intermediate (MoO x -cysteine-graphene oxide), which not only confines the subsequent growth of MoS 2 on the graphene surface but also ensures the intimate interaction between Mo species and graphene at the initial stage. Mo-O-C bond and a possible residual MoO 3-x layer are proposed to comprise the interface bridging the two inherent incompatible phases, MoS 2 and graphene. This strongly coupled structure together with the highly exposed MoS 2 morphology accelerates the electron injection from graphene to the active sites of MoS 2 , and thus the hydrogen evolution reaction (HER) can achieve an overpotential of ∼275 mV at ∼-740 mA cm -2 , and a Pt-like Tafel slope of ∼35 mV dec -1 . Our results shed light on the indispensable role of interfacial interaction within semiconducting material-nanocarbon composites and provide a new insight into the actual activity of MoS 2 toward the HER.

  3. Theoretical analysis of the combined effects of sulfur vacancies and analyte adsorption on the electronic properties of single-layer MoS2

    Science.gov (United States)

    Akdim, Brahim; Pachter, Ruth; Mou, Shin

    2016-05-01

    We report a first-principles theoretical investigation on the electronic structure and electron transport of defective single-layer (SL) MoS2, as well as of corresponding structures adsorbed with benzyl viologen (BV), which was shown to provide improved performance of a field effect transistor. O2 adsorption was included to gain an understanding of the response upon air-exposure. Following analysis of the structure and stability of sulfur single vacancy and line defects in SL MoS2, we investigated the local transport at the adsorbed sites via a transport model that mimics a scanning tunneling spectroscopy experiment. Distinct current-voltage characteristics were indicated for adsorbed oxygen species at a sulfur vacancy. The electronic structures of defective MoS2 indicated the emergence of impurity states in the bandgap due to sulfur defects and oxygen adsorption. Electron transport calculations for the MoS2 surface with an extended defect in a device setting demonstrated that physisorption of BV enhances the output current, while facile chemisorption by O2 upon air-exposure causes degradation of electron transport.

  4. Capacitance characteristics of metal-oxide-semiconductor capacitors with a single layer of embedded nickel nanoparticles for the application of nonvolatile memory

    International Nuclear Information System (INIS)

    Wei, Li; Ling, Xu; Wei-Ming, Zhao; Hong-Lin, Ding; Zhong-Yuan, Ma; Jun, Xu; Kun-Ji, Chen

    2010-01-01

    This paper reports that metal-oxide-semiconductor (MOS) capacitors with a single layer of Ni nanoparticles were successfully fabricated by using electron-beam evaporation and rapid thermal annealing for application to nonvolatile memory. Experimental scanning electron microscopy images showed that Ni nanoparticles of about 5 nm in diameter were clearly embedded in the SiO 2 layer on p-type Si (100). Capacitance–voltage measurements of the MOS capacitor show large flat-band voltage shifts of 1.8 V, which indicate the presence of charge storage in the nickel nanoparticles. In addition, the charge-retention characteristics of MOS capacitors with Ni nanoparticles were investigated by using capacitance–time measurements. The results showed that there was a decay of the capacitance embedded with Ni nanoparticles for an electron charge after 10 4 s. But only a slight decay of the capacitance originating from hole charging was observed. The present results indicate that this technique is promising for the efficient formation or insertion of metal nanoparticles inside MOS structures. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  5. Correlation between (in)commensurate domains of multilayer epitaxial graphene grown on SiC(0 0 0 1-bar ) and single layer electronic behavior

    International Nuclear Information System (INIS)

    Mendes-de-Sa, T G; Goncalves, A M B; Matos, M J S; Coelho, P M; Magalhaes-Paniago, R; Lacerda, R G

    2012-01-01

    A systematic study of the evolution of the electronic behavior and atomic structure of multilayer epitaxial graphene (MEG) as a function of growth time was performed. MEG was obtained by sublimation of a 4H-SiC(0 0 0 1-bar ) substrate in an argon atmosphere. Raman spectroscopy and x-ray diffraction were carried out in samples grown for different times. For 30 min of growth the sample Raman signal is similar to that of graphite, while for 60 min the spectrum becomes equivalent to that of exfoliated graphene. Conventional x-ray diffraction reveals that all the samples have two different (0001) lattice spacings. Grazing incidence x-ray diffraction shows that thin films are composed of rotated (commensurate) structures formed by adjacent graphene layers. Thick films are almost completely disordered. This result can be directly correlated to the single layer electronic behavior of the films as observed by Raman spectroscopy. Finally, to understand the change in lattice spacings as a result of layer rotation, we have carried out first principles calculations (using density functional theory) of the observed commensurate structures. (paper)

  6. A Complete Reporting of MCNP6 Validation Results for Electron Energy Deposition in Single-Layer Extended Media for Source Energies <= 1-MeV

    Energy Technology Data Exchange (ETDEWEB)

    Dixon, David A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hughes, Henry Grady [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-05-04

    In this paper, we expand on previous validation work by Dixon and Hughes. That is, we present a more complete suite of validation results with respect to to the well-known Lockwood energy deposition experiment. Lockwood et al. measured energy deposition in materials including beryllium, carbon, aluminum, iron, copper, molybdenum, tantalum, and uranium, for both single- and multi-layer 1-D geometries. Source configurations included mono-energetic, mono-directional electron beams with energies of 0.05-MeV, 0.1-MeV, 0.3- MeV, 0.5-MeV, and 1-MeV, in both normal and off-normal angles of incidence. These experiments are particularly valuable for validating electron transport codes, because they are closely represented by simulating pencil beams incident on 1-D semi-infinite slabs with and without material interfaces. Herein, we include total energy deposition and energy deposition profiles for the single-layer experiments reported by Lockwood et al. (a more complete multi-layer validation will follow in another report).

  7. Effect of single-layer centrifugation or washing on frozen-thawed donkey semen quality: Do they have the same effect regardless of the quality of the sample?

    Science.gov (United States)

    Ortiz, I; Dorado, J; Morrell, J M; Crespo, F; Gosálvez, J; Gálvez, M J; Acha, D; Hidalgo, M

    2015-07-15

    The aims of this study were to determine the sperm quality of frozen-thawed donkey sperm samples after single-layer centrifugation (SLC) using Androcoll-E in comparison to sperm washing or no centrifugation and to determine if the effect on the sperm quality after SLC or sperm washing depends on the quality of the sample. Frozen-thawed sperm samples from Andalusian donkeys were divided into three aliquots, and they were processed using three different techniques after thawing: uncentrifuged diluted control (UDC), sperm washing (SW), and SLC. Afterward, sperm quality index was estimated by integrating all parameters (total and progressive sperm motility, membrane integrity, and DNA fragmentation) in a single value. The relationship between the sperm quality of thawed UDC samples and the effect on sperm parameters in SW and SLC-selected samples was assessed. Sperm quality index was significantly higher (P < 0.001) in SLC (0.8 ± 0.0) samples than that in UDC (0.6 ± 0.0) and SW (0.6 ± 0.0) samples, regardless of the sperm quality index after thawing of the sperm sample. In conclusion, SLC of frozen-thawed donkey spermatozoa using Androcoll-E-Small can be a suitable procedure for selecting frozen-thawed donkey sperm with better quality, in particular in those samples where an improvement in motility is needed. Copyright © 2015 Elsevier Inc. All rights reserved.

  8. The effect of two pre-cryopreservation single layer colloidal centrifugation protocols in combination with different freezing extenders on the fragmentation dynamics of thawed equine sperm DNA.

    Science.gov (United States)

    Gutiérrez-Cepeda, Luna; Fernández, Alvaro; Crespo, Francisco; Ramírez, Miguel Ángel; Gosálvez, Jaime; Serres, Consuelo

    2012-12-05

    Variability among stallions in terms of semen cryopreservation quality renders it difficult to arrive at a standardized cryopreservation method. Different extenders and processing techniques (such us colloidal centrifugation) are used in order to optimize post-thaw sperm quality. Sperm chromatin integrity analysis is an effective tool for assessing such quality. The aim of the present study was to compare the effect of two single layer colloidal centrifugation protocols (prior to cryopreservation) in combination with three commercial freezing extenders on the post-thaw chromatin integrity of equine sperm samples at different post-thaw incubation (37°C) times (i.e., their DNA fragmentation dynamics). Post-thaw DNA fragmentation levels in semen samples subjected to either of the colloidal centrifugation protocols were significantly lower (pcentrifugation. The use of InraFreeze® extender was associated with significantly less DNA fragmentation than the use of Botu-Crio® extender at 6 h of incubation, and than the use of either Botu-Crio® or Gent® extender at 24 h of incubation (pcentrifugation performed with extended or raw semen prior to cryopreservation reduces DNA fragmentation during the first four hours after thawing. Further studies are needed to determine the influence of freezing extenders on equine sperm DNA fragmentation dynamics.

  9. The efficiency enhancement of single-layer solution-processed blue phosphorescent organic light emitting diodes by hole injection layer modification

    International Nuclear Information System (INIS)

    Yeoh, K H; Talik, N A; Whitcher, T J; Ng, C Y B; Woon, K L

    2014-01-01

    Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) PEDOT : PSS is extensively used as a hole injection layer (HIL) in solution-processed organic light emitting diodes (OLEDs). The high work function of a HIL is crucial in improving OLED efficiency. The work function of PEDOT : PSS is usually around 5.1–5.3 eV. By adding perfluorinated ionomer (PFI), the work function of PEDOT : PSS has been reported to reach as high as 5.95 eV. We investigated the effects of PFI-modified PEDOT : PSS in a single-layer solution-processed blue phosphorescent OLED (PHOLED). We observed that high concentrations of a PFI in PEDOT : PSS has detrimental effects on the device efficiency due to the low conductivity of the PFI. Using this approach, blue PHOLEDs with efficiencies of 9.4 lm W −1 (18.2 cd A −1 ) and 7.9 lm W −1 (20.4 cd A −1 ) at 100 cd m −2 and 1000 cd m −2 , respectively, were demonstrated. (paper)

  10. Changes in Urban Climate due to Future Land-Use Changes based on Population Changes in the Nagoya Region

    Science.gov (United States)

    Adachi, S. A.; Hara, M.; Takahashi, H. G.; Ma, X.; Yoshikane, T.; Kimura, F.

    2013-12-01

    Severe hot weather in summer season becomes a big social problem in metropolitan areas, including the Nagoya region in Japan. Surface air temperature warming is projected in the future. Therefore, the reduction of surface air temperature is an urgent issue in the urban area. Although there are several studies dealing with the effects of global climate change and urbanization to the local climate in the future, these studies tend to ignore the future population changes. This study estimates future land-use scenarios associated with the multi-projections of future population and investigates the impacts of these scenarios on the surface temperature change. The Weather Research and Forecast model ver. 3.3.1 (hereafter, WRF) was used in this study. The horizontal resolutions were 20km, 4km, and 2km, for outer, middle, and inner domains, respectively. The results from the inner domain, covering the Nagoya region, were used for the analysis. The Noah land surface model and the single-layer urban canopy model were applied to calculate the land surface processes and urban surface processes, respectively. The initial and boundary conditions were given from the NCEP/NCAR reanalysis data in August 2010. The urban area ratio used in the WRF model was calculated from the future land-use data provided by the S8 project. The land-use data was created as follows. (1) Three scenarios of population, namely, with high-fertility assumption and low-mortality assumption (POP-high), with medium-fertility assumption and medium-mortality assumption (POP-med), and with low-fertility assumption and high-mortality assumption (POP-low), are estimated using the method proposed by Ariga and Matsuhashi (2012). These scenarios are based on the future projections provided by the National Institute of Population and Social Security Research. (2) The future changes in urban area ratio were assumed to be proportional to the population change (Hanasaki et al., 2012). The averaged urban area ratio in

  11. Hierarchical Canopy Dynamics of Electrolyte-Doped Nanoscale Ionic Materials

    KAUST Repository

    Jespersen, Michael L.

    2013-12-23

    Nanoscale ionic materials (NIMs) are organic-inorganic hybrids prepared from ionically functionalized nanoparticles (NP) neutralized by oligomeric polymer counterions. NIMs are designed to behave as liquids under ambient conditions in the absence of solvent and have no volatile organic content, making them useful for a number of applications. We have used nuclear magnetic resonance relaxation and pulsed-field gradient NMR to probe local and collective canopy dynamics in NIMs based on 18-nm silica NPs with a covalently bound anionic corona, neutralized by amine-terminated ethylene oxide/propylene oxide block copolymers. The NMR relaxation studies show that the nanosecond-scale canopy dynamics depend on the degree of neutralization, the canopy radius of gyration, and crowding at the ionically modified NP surface. Two canopy populations are observed in the diffusion experiments, demonstrating that one fraction of the canopy is bound to the NP surface on the time scale (milliseconds) of the diffusion experiment and is surrounded by a more mobile layer of canopy that is unable to access the surface due to molecular crowding. The introduction of electrolyte ions (Na+ or Mg2+) screens the canopy-corona electrostatic interactions, resulting in a reduced bulk viscosity and faster canopy exchange. The magnitude of the screening effect depends upon ion concentration and valence, providing a simple route for tuning the macroscopic properties of NIMs. © 2013 American Chemical Society.

  12. Water stress effects on spatially referenced cotton crop canopy properties

    Science.gov (United States)

    rop canopy temperature is known to be affected by water stress. Canopy reflectance can also be impacted as leaf orientation and color respond to the stress. As sensor systems are investigated for real-time management of irrigation and nitrogen, it is essential to understand how the data from the sen...

  13. Biodiversity Meets the Atmosphere: A Global View of Forest Canopies

    Science.gov (United States)

    C. M. P. Ozanne; D. Anhuf; S. L. Boulter; M. Keller; R. L. Kitching; C. Korner; F. C. Meinzer; A. W. Mitchell; T. Nakashizuka; P. L. Silva Dias; N. E. Stork; S. J. Wright; M Yoshimura

    2003-01-01

    The forest canopy is the functional interface between 90% of Earth’s terrestrial biomass and the atmosphere. Multidisciplinary research in the canopy has expanded concepts of global species richness, physiological processes, and the provision of ecosystem services. Trees respond in a species-specific manner to elevated carbon dioxide levels, while climate change...

  14. Soil carbon estimation from eucalyptus grandis using canopy spectra

    African Journals Online (AJOL)

    Mapping soil fertility parameters, such as soil carbon (C), is fundamentally important for forest management and research related to forest growth and climate change. This study seeks to establish the link between Eucalyptus grandis canopy spectra and soil carbon using raw and continuum-removed spectra. Canopy-level ...

  15. Summertime canopy albedo is sensitive to forest thinning

    NARCIS (Netherlands)

    Otto, J.; Berveiller, D.; Bréon, F.M.; Delpierre, N.; Geppert, G.; Granier, A.; Jans, W.W.P.; Knohl, A.; Moors, E.J.

    2013-01-01

    Despite an emerging body of literature linking canopy albedo to forest management, understanding of the process is still fragmented. We combined a stand-level forest gap model with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning,

  16. The fauna and flora of a kelp bed canopy

    African Journals Online (AJOL)

    The fauna and flora of the canopy of a kelp bed off. Oudekraal, on the Cape Peninsula, is surveyed. Four species of epiphytic algae occur in the kelp canopy, three restricted to. Ecklonia maxima and the fourth to Laminaria pal/ida. Epiphyte biomass is equivalent to 4 - 9% of host standing crop amongst E. maxima, but less ...

  17. Forest canopy BRDF simulation using Monte Carlo method

    NARCIS (Netherlands)

    Huang, J.; Wu, B.; Zeng, Y.; Tian, Y.

    2006-01-01

    Monte Carlo method is a random statistic method, which has been widely used to simulate the Bidirectional Reflectance Distribution Function (BRDF) of vegetation canopy in the field of visible remote sensing. The random process between photons and forest canopy was designed using Monte Carlo method.

  18. Crop canopy BRDF simulation and analysis using Monte Carlo method

    NARCIS (Netherlands)

    Huang, J.; Wu, B.; Tian, Y.; Zeng, Y.

    2006-01-01

    This author designs the random process between photons and crop canopy. A Monte Carlo model has been developed to simulate the Bi-directional Reflectance Distribution Function (BRDF) of crop canopy. Comparing Monte Carlo model to MCRM model, this paper analyzes the variations of different LAD and

  19. Synthesis and Experiments of Inherently Balanced Umbrella Canopy Designs

    NARCIS (Netherlands)

    van der Wijk, V.; Kiper, G.; Yasir, A.

    2015-01-01

    This paper shows how umbrella canopies and umbrella canopy-like mechanisms can be designed inherently balanced. Inherently balanced means that the center of mass of the moving parts remains stationary at a single point for any position of the mechanism simply because of the specific design of the

  20. Thermal IR exitance model of a plant canopy

    Science.gov (United States)

    Kimes, D. S.; Smith, J. A.; Link, L. E.

    1981-01-01

    A thermal IR exitance model of a plant canopy based on a mathematical abstraction of three horizontal layers of vegetation was developed. Canopy geometry within each layer is quantitatively described by the foliage and branch orientation distributions and number density. Given this geometric information for each layer and the driving meteorological variables, a system of energy budget equations was determined and solved for average layer temperatures. These estimated layer temperatures, together with the angular distributions of radiating elements, were used to calculate the emitted thermal IR radiation as a function of view angle above the canopy. The model was applied to a lodgepole pine (Pinus contorta) canopy over a diurnal cycle. Simulated vs measured radiometric average temperatures of the midcanopy layer corresponded with 2 C. Simulation results suggested that canopy geometry can significantly influence the effective radiant temperature recorded at varying sensor view angles.

  1. Deploying Fourier Coefficients to Unravel Soybean Canopy Diversity.

    Science.gov (United States)

    Jubery, Talukder Z; Shook, Johnathon; Parmley, Kyle; Zhang, Jiaoping; Naik, Hsiang S; Higgins, Race; Sarkar, Soumik; Singh, Arti; Singh, Asheesh K; Ganapathysubramanian, Baskar

    2016-01-01

    Soybean canopy outline is an important trait used to understand light interception ability, canopy closure rates, row spacing response, which in turn affects crop growth and yield, and directly impacts weed species germination and emergence. In this manuscript, we utilize a methodology that constructs geometric measures of the soybean canopy outline from digital images of canopies, allowing visualization of the genetic diversity as well as a rigorous quantification of shape parameters. Our choice of data analysis approach is partially dictated by the need to efficiently store and analyze large datasets, especially in the context of planned high-throughput phenotyping experiments to capture time evolution of canopy outline which will produce very large datasets. Using the Elliptical Fourier Transformation (EFT) and Fourier Descriptors (EFD), canopy outlines of 446 soybean plant introduction (PI) lines from 25 different countries exhibiting a wide variety of maturity, seed weight, and stem termination were investigated in a field experiment planted as a randomized complete block design with up to four replications. Canopy outlines were extracted from digital images, and subsequently chain coded, and expanded into a shape spectrum by obtaining the Fourier coefficients/descriptors. These coefficients successfully reconstruct the canopy outline, and were used to measure traditional morphometric traits. Highest phenotypic diversity was observed for roundness, while solidity showed the lowest diversity across all countries. Some PI lines had extraordinary shape diversity in solidity. For interpretation and visualization of the complexity in shape, Principal Component Analysis (PCA) was performed on the EFD. PI lines were grouped in terms of origins, maturity index, seed weight, and stem termination index. No significant pattern or similarity was observed among the groups; although interestingly when genetic marker data was used for the PCA, patterns similar to canopy

  2. Deploying Fourier Coefficients to Unravel Soybean Canopy Diversity

    Science.gov (United States)

    Jubery, Talukder Z.; Shook, Johnathon; Parmley, Kyle; Zhang, Jiaoping; Naik, Hsiang S.; Higgins, Race; Sarkar, Soumik; Singh, Arti; Singh, Asheesh K.; Ganapathysubramanian, Baskar

    2017-01-01

    Soybean canopy outline is an important trait used to understand light interception ability, canopy closure rates, row spacing response, which in turn affects crop growth and yield, and directly impacts weed species germination and emergence. In this manuscript, we utilize a methodology that constructs geometric measures of the soybean canopy outline from digital images of canopies, allowing visualization of the genetic diversity as well as a rigorous quantification of shape parameters. Our choice of data analysis approach is partially dictated by the need to efficiently store and analyze large datasets, especially in the context of planned high-throughput phenotyping experiments to capture time evolution of canopy outline which will produce very large datasets. Using the Elliptical Fourier Transformation (EFT) and Fourier Descriptors (EFD), canopy outlines of 446 soybean plant introduction (PI) lines from 25 different countries exhibiting a wide variety of maturity, seed weight, and stem termination were investigated in a field experiment planted as a randomized complete block design with up to four replications. Canopy outlines were extracted from digital images, and subsequently chain coded, and expanded into a shape spectrum by obtaining the Fourier coefficients/descriptors. These coefficients successfully reconstruct the canopy outline, and were used to measure traditional morphometric traits. Highest phenotypic diversity was observed for roundness, while solidity showed the lowest diversity across all countries. Some PI lines had extraordinary shape diversity in solidity. For interpretation and visualization of the complexity in shape, Principal Component Analysis (PCA) was performed on the EFD. PI lines were grouped in terms of origins, maturity index, seed weight, and stem termination index. No significant pattern or similarity was observed among the groups; although interestingly when genetic marker data was used for the PCA, patterns similar to canopy

  3. Impacts of differing aerodynamic resistance formulae on modeled energy exchange at the above-canopy/within-canopy/soil interface

    Science.gov (United States)

    Application of the Two-Source Energy Balance (TSEB) Model using land surface temperature (LST) requires aerodynamic resistance parameterizations for the flux exchange above the canopy layer, within the canopy air space and at the soil/substrate surface. There are a number of aerodynamic resistance f...

  4. The impact of modifying photosystem antenna size on canopy photosynthetic efficiency-Development of a new canopy photosynthesis model scaling from metabolism to canopy level processes.

    Science.gov (United States)

    Song, Qingfeng; Wang, Yu; Qu, Mingnan; Ort, Donald R; Zhu, Xin-Guang

    2017-12-01

    Canopy photosynthesis (A c ) describes photosynthesis of an entire crop field and the daily and seasonal integrals of A c positively correlate with daily and seasonal biomass production. Much effort in crop breeding has focused on improving canopy architecture and hence light distribution inside the canopy. Here, we develop a new integrated canopy photosynthesis model including canopy architecture, a ray tracing algorithm, and C 3 photosynthetic metabolism to explore the option of manipulating leaf chlorophyll concentration ([Chl]) for greater A c and nitrogen use efficiency (NUE). Model simulation results show that (a) efficiency of photosystem II increased when [Chl] was decreased by decreasing antenna size and (b) the light received by leaves at the bottom layers increased when [Chl] throughout the canopy was decreased. Furthermore, the modelling revealed a modest ~3% increase in A c and an ~14% in NUE was accompanied when [Chl] reduced by 60%. However, if the leaf nitrogen conserved by this decrease in leaf [Chl] were to be optimally allocated to other components of photosynthesis, both A c and NUE can be increased by over 30%. Optimizing [Chl] coupled with strategic reinvestment of conserved nitrogen is shown to have the potential to support substantial increases in A c , biomass production, and crop yields. © 2017 The Authors Plant, Cell & Environment Published by John Wiley & Sons Ltd.

  5. Momentum and scalar transport within a vegetation canopy following atmospheric stability and seasonal canopy changes: the CHATS experiment

    Science.gov (United States)

    Dupont, S.; Patton, E. G.

    2012-07-01

    Momentum and scalar (heat and water vapor) transfer between a walnut canopy and the overlying atmosphere are investigated for two seasonal periods (before and after leaf-out), and for five thermal stability regimes (free and forced convection, near-neutral condition, transition to stable, and stable). Quadrant and octant analyses of momentum and scalar fluxes followed by space-time autocorrelations of observations from the Canopy Horizontal Array Turbulence Study's (CHATS) thirty meter tower help characterize the motions exchanging momentum, heat, and moisture between the canopy layers and aloft. During sufficiently windy conditions, i.e. in forced convection, near-neutral and transition to stable regimes, momentum and scalars are generally transported by sweep and ejection motions associated with the well-known canopy-top "shear-driven" coherent eddy structures. During extreme stability conditions (both unstable and stable), the role of these "shear-driven" structures in transporting scalars decreases, inducing notable dissimilarity between momentum and scalar transport. In unstable conditions, "shear-driven" coherent structures are progressively replaced by "buo-yantly-driven" structures, known as thermal plumes; which appear very efficient at transporting scalars, especially upward thermal plumes above the canopy. Within the canopy, downward thermal plumes become more efficient at transporting scalars than upward thermal plumes if scalar sources are located in the upper canopy. We explain these features by suggesting that: (i) downward plumes within the canopy correspond to large downward plumes coming from above, and (ii) upward plumes within the canopy are local small plumes induced by canopy heat sources where passive scalars are first injected if there sources are at the same location as heat sources. Above the canopy, these small upward thermal plumes aggregate to form larger scale upward thermal plumes. Furthermore, scalar quantities carried by downward

  6. Momentum and scalar transport within a vegetation canopy following atmospheric stability and seasonal canopy changes: the CHATS experiment

    Directory of Open Access Journals (Sweden)

    S. Dupont

    2012-07-01

    Full Text Available Momentum and scalar (heat and water vapor transfer between a walnut canopy and the overlying atmosphere are investigated for two seasonal periods (before and after leaf-out, and for five thermal stability regimes (free and forced convection, near-neutral condition, transition to stable, and stable. Quadrant and octant analyses of momentum and scalar fluxes followed by space-time autocorrelations of observations from the Canopy Horizontal Array Turbulence Study's (CHATS thirty meter tower help characterize the motions exchanging momentum, heat, and moisture between the canopy layers and aloft.

    During sufficiently windy conditions, i.e. in forced convection, near-neutral and transition to stable regimes, momentum and scalars are generally transported by sweep and ejection motions associated with the well-known canopy-top "shear-driven" coherent eddy structures. During extreme stability conditions (both unstable and stable, the role of these "shear-driven" structures in transporting scalars decreases, inducing notable dissimilarity between momentum and scalar transport.

    In unstable conditions, "shear-driven" coherent structures are progressively replaced by "buo-yantly-driven" structures, known as thermal plumes; which appear very efficient at transporting scalars, especially upward thermal plumes above the canopy. Within the canopy, downward thermal plumes become more efficient at transporting scalars than upward thermal plumes if scalar sources are located in the upper canopy. We explain these features by suggesting that: (i downward plumes within the canopy correspond to large downward plumes coming from above, and (ii upward plumes within the canopy are local small plumes induced by canopy heat sources where passive scalars are first injected if there sources are at the same location as heat sources. Above the canopy, these small upward thermal plumes aggregate to form larger scale upward thermal plumes. Furthermore, scalar

  7. Forest canopy temperatures: dynamics, controls, and relationships with ecosystem fluxes

    Science.gov (United States)

    Still, C. J.; Griffith, D.; Kim, Y.; Law, B. E.; Hanson, C. V.; Kwon, H.; Schulze, M.; Detto, M.; Pau, S.

    2017-12-01

    Temperature strongly affects enzymatic reactions, ecosystem biogeochemistry, and species distributions. Although most focus is on air temperature, the radiative or skin temperature of plants is more relevant. Canopy skin temperature dynamics reflect biophysical, physiological, and anatomical characteristics and interactions with the environment, and can be used to examine forest responses to stresses like droughts and heat waves. Thermal infrared (TIR) imaging allows for extensive temporal and spatial sampling of canopy temperatures, particularly compared to spot measurements using thermocouples. We present results of TIR imaging of forest canopies at eddy covariance flux tower sites in the US Pacific Northwest and in Panama. These forests range from an old-growth temperate rainforest to a second growth semi-arid pine forest to a semi-deciduous tropical forest. Canopy temperature regimes at these sites are highly variable. Canopy temperatures at all forest sites displayed frequent departures from air temperature, particularly during clear sky conditions, with elevated canopy temperatures during the day and depressed canopy temperatures at night compared to air temperature. Comparison of canopy temperatures to fluxes of carbon dioxide, water vapor, and energy reveals stronger relationships than those found with air temperature. Daytime growing season net ecosystem exchange at the pine forest site is better explained by canopy temperature (r2 = 0.61) than air temperature (r2 = 0.52). At the semi-deciduous tropical forest, canopy photosynthesis is highly correlated with canopy temperature (r2 = 0.51), with a distinct optimum temperature for photosynthesis ( 31 °C) that agrees with leaf-level measurements. During the peak of one heat wave at an old-growth temperate rainforest, hourly averaged air temperature exceeded 35 °C, 10 °C above average. Peak hourly canopy temperature approached 40 °C, and leaf-to-air vapor pressure deficit exceeded 6 kPa. These extreme

  8. What Does a Multilayer Canopy Model Tell Us About Our Current Understanding of Snow-Canopy Unloading?

    Science.gov (United States)

    McGowan, L. E.; Paw U, K. T.; Dahlke, H. E.

    2017-12-01

    In the Western U.S., future water resources depend on the forested mountain snowpack. The variations in and estimates of forest mountain snow volume are vital to projecting annual water availability; yet, snow forest processes are not fully known. Most snow models calculate snow-canopy unloading based on time, temperature, Leaf Area Index (LAI), and/or wind speed. While models crudely consider the canopy shape via LAI, current models typically do not consider the vertical canopy structure or varied energetics within multiple canopy layers. Vertical canopy structure influences the spatiotemporal distribution of snow, and therefore ultimately determines the degree and extent by which snow alters both the surface energy balance and water availability. Within the canopy both the snowpack and energetic exposures to the snowpack (wind, shortwave and longwave radiation, turbulent heat fluxes etc.) vary widely in the vertical. The water and energy balance in each layer is dependent on all other layers. For example, increased snow canopy content in the top of the canopy will reduce available shortwave radiation at the bottom and snow unloading in a mid-layer can cascade and remove snow from all the lower layers. We examined vertical interactions and structures of the forest canopy on the impact of unloading utilizing the Advanced Canopy-Atmosphere-Soil-Algorithm (ACASA), a multilayer soil-vegetation-atmosphere numerical model based on higher-order closure of turbulence equations. Our results demonstrate how a multilayer model can be used to elucidate the physical processes of snow unloading, and could help researchers better parameterize unloading in snow-hydrology models.

  9. First principles analysis of the CDW instability of single-layer 1T-TiSe2 and its evolution with charge carrier density

    Science.gov (United States)

    Guster, Bogdan; Canadell, Enric; Pruneda, Miguel; Ordejón, Pablo

    2018-04-01

    We present a density functional theory study of the electronic structure of single-layer TiSe2, and focus on the charge density wave (CDW) instability present on this 2D material. We explain the 2× 2 periodicity of the CDW from the phonon band structure of the undistorted crystal, which is unstable under one of the phonon modes at the M point. This can be understood in terms of a partial band gap opening at the Fermi level, which we describe on the basis of the symmetry of the involved crystal orbitals, leading to an energy gain upon the displacement of the atoms following the phonon mode in a 2  ×  1 structure. Furthermore, the combination of the corresponding phonons for the three inequivalent M points of the Brillouin zone leads to the 2  ×  2 distortion characteristic of the CDW state. This leads to a further opening of a full gap, which reduces the energy of the 2  ×  2 structure compared to the 2  ×  1 one of a single M point phonon, and makes the CDW structure the most stable one. We also analyze the effect of charge injection into the layer on the structural instability. We predict that the 2  ×  2 structure only survives for a certain range of doping levels, both for electrons and for holes, as doping reduces the energy gain due to the gap opening. We predict the transition from the commensurate 2  ×  2 distortion to an incommensurate one with increasing wavelength upon increasing the doping level, followed by the appearance of the undistorted 1  ×  1 structure for larger carrier concentrations.

  10. Radiative effect differences between multi-layered and single-layer clouds derived from CERES, CALIPSO, and CloudSat data

    International Nuclear Information System (INIS)

    Li Jiming; Yi Yuhong; Minnis, Patrick; Huang Jianping; Yan Hongru; Ma Yuejie; Wang Wencai; Kirk Ayers, J.

    2011-01-01

    Clouds alter general circulation through modification of the radiative heating profile within the atmosphere. Their effects are complex and depend on height, vertical structure, and phase. The instantaneous cloud radiative effect (CRE) induced by multi-layered (ML) and single-layer (SL) clouds is estimated by analyzing data collected by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, and Clouds and Earth's Radiation Energy Budget System (CERES) missions from March 2007 through February 2008. The CRE differences between ML and SL clouds at the top of the atmosphere (TOA) and at the surface were also examined. The zonal mean shortwave (SW) CRE differences between the ML and SL clouds at the TOA and surface were positive at most latitudes, peaking at 120 W m -2 in the tropics and dropping to -30 W m -2 at higher latitudes. This indicated that the ML clouds usually reflected less sunlight at the TOA and transmitted more to the surface than the SL clouds, due to their higher cloud top heights. The zonal mean longwave (LW) CRE differences between ML and SL clouds at the TOA and surface were relatively small, ranging from -30 to 30 W m -2 . This showed that the ML clouds only increased the amount of thermal radiation at the TOA relative to the SL clouds in the tropics, decreasing it elsewhere. In other words, ML clouds tended to cool the atmosphere in the tropics and warm it elsewhere when compared to SL clouds. The zonal mean net CRE differences were positive at most latitudes and dominated by the SW CRE differences.

  11. Adsorption of DNA/RNA nucleobases onto single-layer MoS2 and Li-Doped MoS2: A dispersion-corrected DFT study

    Science.gov (United States)

    Sadeghi, Meisam; Jahanshahi, Mohsen; Ghorbanzadeh, Morteza; Najafpour, Ghasem

    2018-03-01

    The kind of sensing platform in nano biosensor plays an important role in nucleic acid sequence detection. It has been demonstrated that graphene does not have an intrinsic band gap; therefore, transition metal dichalcogenides (TMDs) are desirable materials for electronic base detection. In the present work, a comparative study of the adsorption of the DNA/RNA nucleobases [Adenine (A), Cytosine (C) Guanine (G), Thymine (T) and Uracil (U)] onto the single-layer molybdenum disulfide (MoS2) and Li-doped MoS2 (Li-MoS2) as a sensing surfaces was investigated by using Dispersion-corrected Density Functional Theory (D-DFT) calculations and different measure of equilibrium distances, charge transfers and binding energies for the various nucleobases were calculated. The results revealed that the interactions between the nucleobases and the MoS2 can be strongly enhanced by introducing metal atom, due to significant charge transfer from the Li atom to the MoS2 when Lithium is placed on top of the MoS2. Furthermore, the binding energies of the five nucleobases were in the range of -0.734 to -0.816 eV for MoS2 and -1.47 to -1.80 eV for the Li-MoS2. Also, nucleobases were adsorbed onto MoS2 sheets via the van der Waals (vdW) force. This high affinity and the renewable properties of the biosensing platform demonstrated that Li-MoS2 nanosheet is biocompatible and suitable for nucleic acid analysis.

  12. Structural effects on charge order in single-layered manganites R{sub 1-x}A{sub 1+x}MnO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Engelmayer, Johannes; Ulbrich, Holger; Weber, Lisa; Braden, Markus; Lorenz, Thomas [II. Physikalisches Institut, Universitaet zu Koeln (Germany)

    2015-07-01

    Single-layered manganites show a complex interplay between charge, orbital, and magnetic degrees of freedom. For half-doped (x=1/2) R{sub 1-x}A{sub 1+x}MnO{sub 4} (R=Pr,La; A=Ca,Sr) the so-called Goodenough model is well established. This model proposes a site-centered charge order with a checkerboard pattern of Mn{sup 3+} and Mn{sup 4+} ions accompanied by an orbital order. Furthermore a magnetic order develops with ferromagnetic three-spin zig-zag chains and antiferromagnetic interchain coupling. For x=2/3 the charge order appears as stripe pattern with two adjacent stripes of Mn{sup 4+} ions alternating with a single stripe of Mn{sup 3+} ions, while in the magnetically ordered state four-spin zig-zag chains arise. For a deeper understanding of the emergence of charge order, it is appropriate to vary on the one hand the elements R and A while keeping the doping level x constant - involving structural changes at fixed charge carrier density - and on the other hand change the doping level with the same R and A. Therefore various single crystals of R{sub 1-x}A{sub 1+x}MnO{sub 4} with R=(Pr, Nd, Sm, Tb), A=(Ca, Sr) and 0.5 ≤ x ≤ 0.7 were grown and their structural parameters were determined by X-ray diffraction. Based on measurements of resistivity, magnetization, specific heat, and crystal structure we discuss the influence of structural variations on the ordering temperature.

  13. Medium term ecohydrological response of peatland bryophytes to canopy disturbance

    Science.gov (United States)

    Leonard, Rhoswen; Kettridge, Nick; Krause, Stefan; Devito, Kevin; Granath, Gustaf; Petrone, Richard; Mandoza, Carl; Waddington, James Micheal

    2016-04-01

    Canopy disturbance in northern forested peatlands is widespread. Canopy changes impact the ecohydrological function of moss and peat, which provide the principal carbon store within these carbon rich ecosystems. Different mosses have contrasting contributions to carbon and water fluxes (e.g. Sphagnum fuscum and Pleurozium schreberi) and are strongly influenced by canopy cover. As a result, changes in canopy cover lead to long-term shifts in species composition and associated ecohydrological function. Despite this, the medium-term response to such disturbance, the associated lag in this transition to a new ecohydrological and biogeochemical regime, is not understood. Here we investigate this medium term ecohydrological response to canopy removal using a randomised plot design within a north Albertan peatland. We show no significant ecohydrological change in treatment plots four years after canopy removal. Notably, Pleurozium schreberi and Sphagnum fuscum remained within respective plots post treatment and there was no significant difference in plot resistance to evapotranspiration or carbon exchange. Our results show that canopy removal alone has little impact on bryophyte ecohydrology in the short/medium term. This resistance to disturbance contrasts strongly with dramatic short-term changes observed within mineral soils suggesting that concurrent shifts in the large scale hydrology induced within such disturbances are necessary to cause rapid ecohydrological transitions. Understanding this lagged response is critical to determine the decadal response of carbon and water fluxes in response to disturbance and the rate at which important medium term ecohydrological feedbacks are invoked.

  14. Impacts of city-block-scale countermeasures against urban heat-island phenomena upon a building's energy-consumption for air-conditioning

    Energy Technology Data Exchange (ETDEWEB)

    Kikegawa, Yukihiro [Department of Environmental Systems, Meisei University, 2-1-1 Hodokubo, Hino-shi, Tokyo 191-8506 (Japan); Genchi, Yutaka [Research Center for Life Cycle Assessment, National Institute of Advanced Industrial Science and Technology, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569 (Japan); Kondo, Hiroaki [Institute for Environmental Management Technology, National Institute of Advanced Industrial Science and Technology, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569 (Japan); Hanaki, Keisuke [Department of Urban Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2006-06-15

    This study quantifies the possible impacts of urban heat-island countermeasures upon buildings' energy use during summer in Tokyo metropolis. Considering the dependency of the buildings air temperature upon the local urban canopy structure, Tokyo urban canopies were classified in the city-block-scale using the sky-view factor (svf). Then, a multi-scale model system describing the interaction between buildings' energy use and urban meteorological conditions was applied to each classified canopy. In terms of urban warming alleviation and cooling energy saving, simulations suggested that the reduction in the air-conditioning anthropogenic heat could be the most effective measure in office buildings' canopies, and that vegetative fraction increase on the side walls of buildings in residential canopies. Both measures indicated daily and spatially averaged decreases in near-ground summer air temperature of 0.2-1.2{sup o}C. The simulations also suggested these temperature decreases could result in the buildings' cooling energy-savings of 4-40%, indicating remarkable savings in residential canopies. These temperature drops and energy savings tended to increase with the decrease of the svf of urban canopies. (author)

  15. GEOMETRIC AND REFLECTANCE SIGNATURE CHARACTERIZATION OF COMPLEX CANOPIES USING HYPERSPECTRAL STEREOSCOPIC IMAGES FROM UAV AND TERRESTRIAL PLATFORMS

    Directory of Open Access Journals (Sweden)

    E. Honkavaara

    2016-06-01

    Full Text Available Light-weight hyperspectral frame cameras represent novel developments in remote sensing technology. With frame camera technology, when capturing images with stereoscopic overlaps, it is possible to derive 3D hyperspectral reflectance information and 3D geometric data of targets of interest, which enables detailed geometric and radiometric characterization of the object. These technologies are expected to provide efficient tools in various environmental remote sensing applications, such as canopy classification, canopy stress analysis, precision agriculture, and urban material classification. Furthermore, these data sets enable advanced quantitative, physical based retrieval of biophysical and biochemical parameters by model inversion technologies. Objective of this investigation was to study the aspects of capturing hyperspectral reflectance data from unmanned airborne vehicle (UAV and terrestrial platform with novel hyperspectral frame cameras in complex, forested environment.

  16. Effect of vegetation on urban climate and healthy urban colonies

    Energy Technology Data Exchange (ETDEWEB)

    Raza, S.H.; Murthy, M.S.R.; Bhagya Lakshmi, O.; Shylaja, G. (Ecology and Environmental Biology Lab., Dept. of Botany, Osmania Univ., Hyderabad (India))

    1991-01-01

    The role of plants in developing a healthy atmosphere is very desirable in the context of deteriorating environment resulting from increased urbanization, industrialization and improper environmental management. This investigation has attempted to screen plants for their ability to improve the design and development of healthy environments around buildings and urban centres of Hyderabad. Ability index values were computed on the basis of canopy area, physiological characters of trees growing in polluted environments, pollution stress and population load. Azadirachta indica, Pithecolobium dulce and Cassia fistula are suggested for plantations around buildings and urban centres for minimizing pollution. Certain susceptible trees like Pongamia glabra and Polyalthia longifolia have been suggested in the diagnosis and investigation of air quality through biological means. (orig.).

  17. Canopy openings and white-tailed deer influence the understory vegetation in mixed oak woodlots

    Science.gov (United States)

    Todd W. Bowersox; Gerald L. Storm; Walter M. Tzilkowski

    1995-01-01

    Effects of canopy opening and white-tailed deer on ground level vegetation are being assessed in south-central Pennsylvania. Herbaceous plants and woody seedlings are being monitored in three unevenaged, mixed oak woodlots at Gettysburg National Military Park. Canopy opening levels on 0.20 ha treatment units were closed (~100% canopy), small (50-60% canopy) and large (...

  18. SAFARI 2000 Canopy Structural Measurements, Kalahari Transect, Wet Season 2001

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: This data set contains leaf area index (LAI), leaf inclination angle, and canopy dimension data from study sites along the Kalahari Transect in southwest...

  19. SNF NS001-TMS Canopy Reflectance 1983-84

    Data.gov (United States)

    National Aeronautics and Space Administration — Canopy spectral reflectance data collected from the NASA C-130-mounted NS001 Thematic Mapper Simulator (TMS) over the Superior National Forest, MN on 13JUL1983,...

  20. An analytical solution for the estimation of the critical available soil water fraction for a single layer water balance model under growing crops

    Directory of Open Access Journals (Sweden)

    N. Brisson

    1998-01-01

    . The atmospheric demand together with the rooting depth appear as the most important factors. However, when assuming predictable climatic and crop evolution, compensation occurs between those two effects leading to a relative stability of F when the crop is fully developed. Though relying on well-known physical laws, the present approach remains in the framework of single layer models with the same limitations.

  1. Prototype pre-clinical PET scanner with depth-of-interaction measurements using single-layer crystal array and single-ended readout

    Science.gov (United States)

    Lee, Min Sun; Kim, Kyeong Yun; Ko, Guen Bae; Lee, Jae Sung

    2017-05-01

    In this study, we developed a proof-of-concept prototype PET system using a pair of depth-of-interaction (DOI) PET detectors based on the proposed DOI-encoding method and digital silicon photomultiplier (dSiPM). Our novel cost-effective DOI measurement method is based on a triangular-shaped reflector that requires only a single-layer pixelated crystal and single-ended signal readout. The DOI detector consisted of an 18  ×  18 array of unpolished LYSO crystal (1.47  ×  1.47  ×  15 mm3) wrapped with triangular-shaped reflectors. The DOI information was encoded by depth-dependent light distribution tailored by the reflector geometry and DOI correction was performed using four-step depth calibration data and maximum-likelihood (ML) estimation. The detector pair and the object were placed on two motorized rotation stages to demonstrate 12-block ring PET geometry with 11.15 cm diameter. Spatial resolution was measured and phantom and animal imaging studies were performed to investigate imaging performance. All images were reconstructed with and without the DOI correction to examine the impact of our DOI measurement. The pair of dSiPM-based DOI PET detectors showed good physical performances respectively: 2.82 and 3.09 peak-to-valley ratios, 14.30% and 18.95% energy resolution, and 4.28 and 4.24 mm DOI resolution averaged over all crystals and all depths. A sub-millimeter spatial resolution was achieved at the center of the field of view (FOV). After applying ML-based DOI correction, maximum 36.92% improvement was achieved in the radial spatial resolution and a uniform resolution was observed within 5 cm of transverse PET FOV. We successfully acquired phantom and animal images with improved spatial resolution and contrast by using the DOI measurement. The proposed DOI-encoding method was successfully demonstrated in the system level and exhibited good performance, showing its feasibility for animal PET applications with high spatial

  2. Corrosion Resistance Behavior of Single-Layer Cathodic Arc PVD Nitride-Base Coatings in 1M HCl and 3.5 pct NaCl Solutions

    Science.gov (United States)

    Adesina, Akeem Yusuf; Gasem, Zuhair M.; Madhan Kumar, Arumugam

    2017-04-01

    The electrochemical behavior of single-layer TiN, CrN, CrAlN, and TiAlN coatings on 304 stainless steel substrate, deposited using state-of-the-art and industrial size cathodic arc PVD machine, were evaluated in 1M HCl and 3.5 pct NaCl solutions. The corrosion behavior of the blank and coated substrates was analyzed by electrochemical impedance spectroscopy (EIS), linear polarization resistance, and potentiodynamic polarization. Bond-coat layers of pure-Ti, pure-Cr, alloyed-CrAl, and alloyed-TiAl for TiN, CrN, CrAlN, and TiAlN coatings were, respectively, first deposited for improved coating adhesion before the actual coating. The average coating thickness was about 1.80 µm. Results showed that the corrosion potentials ( E corr) of the coated substrates were shifted to more noble values which indicated improvement of the coated substrate resistance to corrosion susceptibility. The corrosion current densities were lower for all coated substrates as compared to the blank substrate. Similarly, EIS parameters showed that these coatings possessed improved resistance to defects and pores in similar solution compared to the same nitride coatings developed by magnetron sputtering. The charge transfer resistance ( R ct) can be ranked in the following order: TiAlN > CrN > TiN > CrAlN in both media except in NaCl solution where R ct of TiN is lowest. While the pore resistance ( R po) followed the order: CrAlN > CrN > TiAlN > TiN in HCl solution and TiAlN > CrN > CrAlN > TiN in NaCl solution. It is found that TiAlN coating has the highest protective efficiencies of 79 and 99 pct in 1M HCl and 3.5 pct NaCl, respectively. SEM analysis of the corroded substrates in both media was also presented.

  3. Strong visible and near infrared photoluminescence from ZnO nanorods/nanowires grown on single layer graphene studied using sub-band gap excitation

    Science.gov (United States)

    Biroju, Ravi K.; Giri, P. K.

    2017-07-01

    Fabrication and optoelectronic applications of graphene based hybrid 2D-1D semiconductor nanostructures have gained tremendous research interest in recent times. Herein, we present a systematic study on the origin and evolution of strong broad band visible and near infrared (NIR) photoluminescence (PL) from vertical ZnO nanorods (NRs) and nanowires (NWs) grown on single layer graphene using both above band gap and sub-band gap optical excitations. High resolution field emission scanning electron microscopy and X-ray diffraction studies are carried out to reveal the morphology and crystalline quality of as-grown and annealed ZnO NRs/NWs on graphene. Room temperature PL studies reveal that besides the UV and visible PL bands, a new near-infrared (NIR) PL emission band appears in the range between 815 nm and 886 nm (1.40-1.52 eV). X-ray photoelectron spectroscopy studies revealed excess oxygen content and unreacted metallic Zn in the as-grown ZnO nanostructures, owing to the low temperature growth by a physical vapor deposition method. Post-growth annealing at 700 °C in the Ar gas ambient results in the enhanced intensity of both visible and NIR PL bands. On the other hand, subsequent high vacuum annealing at 700 °C results in a drastic reduction in the visible PL band and complete suppression of the NIR PL band. PL decay dynamics of green emission in Ar annealed samples show tri-exponential decay on the nanosecond timescale including a very slow decay component (time constant ˜604.5 ns). Based on these results, the NIR PL band comprising two peaks centered at ˜820 nm and ˜860 nm is tentatively assigned to neutral and negatively charged oxygen interstitial (Oi) defects in ZnO, detected experimentally for the first time. The evidence for oxygen induced trap states on the ZnO NW surface is further substantiated by the slow photocurrent response of graphene-ZnO NRs/NWs. These results are important for tunable light emission, photodetection, and other cutting edge

  4. Leaf Aging of Amazonian Canopy Trees: Insights to Tropical Ecological Processes and Satellited Detected Canopy Dynamics

    Science.gov (United States)

    Chavana-Bryant, C.; Malhi, Y.; Gerard, F.

    2015-12-01

    Leaf aging is a fundamental driver of changes in leaf traits, thereby, regulating ecosystem processes and remotely-sensed canopy dynamics. Leaf age is particularly important for carbon-rich tropical evergreen forests, as leaf demography (leaf age distribution) has been proposed as a major driver of seasonal productivity in these forests. We explore leaf reflectance as a tool to monitor leaf age and develop a novel spectra-based (PLSR) model to predict age using data from a phenological study of 1,072 leaves from 12 lowland Amazonian canopy tree species in southern Peru. Our results demonstrate monotonic decreases in LWC and Pmass and increase in LMA with age across species; Nmass and Cmassshowed monotonic but species-specific age responses. Spectrally, we observed large age-related variation across species, with the most age-sensitive spectral domains found to be: green peak (550nm), red edge (680-750 nm), NIR (700-850 nm), and around the main water absorption features (~1450 and ~1940 nm). A spectra-based model was more accurate in predicting leaf age (R2= 0.86; %RMSE= 33) compared to trait-based models using single (R2=0.07 to 0.73; %RMSE=7 to 38) and multiple predictors (step-wise analysis; R2=0.76; %RMSE=28). Spectral and trait-based models established a physiochemical basis for the spectral age model. The relative importance of the traits modifying the leaf spectra of aging leaves was: LWC>LMA>Nmass>Pmass,&Cmass. Vegetation indices (VIs), including NDVI, EVI2, NDWI and PRI were all age-dependent. This study highlights the importance of leaf age as a mediator of leaf traits, provides evidence of age-related leaf reflectance changes that have important impacts on VIs used to monitor canopy dynamics and productivity, and proposes a new approach to predicting and monitoring leaf age with important implications for remote sensing.

  5. Isoprene emission from tropical forest canopy leaves

    Science.gov (United States)

    Keller, Michael; Lerdau, Manuel

    1999-03-01

    We screened 51 species of trees and vines for isoprene emission by using a tower crane to gain access to the top of the canopy in a semideciduous forest in the Republic of Panama. Of the species screened, 15 emitted isoprene at rates greater than 0.8 nmol m-2 s-1. We measured the influence of light and temperature on emissions. The species-dependent emission rates at 303 K and 1000 μmol m-2 s-1 of incident photosynthetically active radiation ranged from 9 to 43 nmol m-2 s-1 with coefficients of variation of about 20%. Isoprene emission showed a hyperbolic response to light intensity and an exponential response to temperature. We modified an existing algorithm developed for temperate plants to fit the temperature response of these tropical species. We suggest a new algorithm to fit the light response of isoprene emission. The new and modified algorithms are compared to the algorithms developed for temperate plants that are used in global models of isoprene emission. Both sets of algorithms also are compared to additional validation data collected in Panama and to published data on isoprene emission from a tropical dry forest in Puerto Rico. Our comparisons suggest that algorithms developed for temperate plants can significantly underestimate isoprene emissions from tropical forests at high-light and high-temperature levels.

  6. Convection regime between canopy and air in a greenhouse

    OpenAIRE

    Atarassi,Roberto Terumi; Folegatti,Marcos Vinicius; Brasil,René Porfírio Camponez do

    2006-01-01

    The use of covering materials in protected environments modifies the air movement close to the crop canopy compared to external environment, which changes the heat and mass transfer between canopy and air. Several researches have been made in greenhouses to estimate mass and heat flux using dimensionless numbers to characterize the type of convection (forced, free or mixed). The knowledge of which one is dominant allows simplifications and specific approaches. The dominant convection regime b...

  7. Study of momentum transfers within a vegetation canopy

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    reduces to the exponential canopy wind profile, exp {−n(1 − z/h)} and. • if Cd(z) is uniform throughout the canopy and if the effect of sheltering is ignored then ζ(h) reduces to CdLAI. Massman (1997) parameterized the surface drag coefficient Csurf = 2u2. ∗/u(h)2 from which the expo- nential power n can be expressed as n =.

  8. Subpixel urban land cover estimation: comparing cubist, random forests, and support vector regression

    Science.gov (United States)

    Jeffrey T. Walton

    2008-01-01

    Three machine learning subpixel estimation methods (Cubist, Random Forests, and support vector regression) were applied to estimate urban cover. Urban forest canopy cover and impervious surface cover were estimated from Landsat-7 ETM+ imagery using a higher resolution cover map resampled to 30 m as training and reference data. Three different band combinations (...

  9. Growing the urban forest: tree performance in response to biotic and abiotic land management

    Science.gov (United States)

    Emily E. Oldfield; Alexander J. Felson; D. S. Novem Auyeung; Thomas W. Crowther; Nancy F. Sonti; Yoshiki Harada; Daniel S. Maynard; Noah W. Sokol; Mark S. Ashton; Robert J. Warren; Richard A. Hallett; Mark A. Bradford

    2015-01-01

    Forests are vital components of the urban landscape because they provide ecosystem services such as carbon sequestration, storm-water mitigation, and air-quality improvement. To enhance these services, cities are investing in programs to create urban forests. A major unknown, however, is whether planted trees will grow into the mature, closed-canopied forest on which...

  10. A new approach to quantify and map carbon stored, sequestered and emissions avoided by urban forests

    Science.gov (United States)

    E. Gregory McPherson; Qingfu Xiao; Elena Aguaron

    2013-01-01

    This paper describes the use of field surveys, biometric information for urban tree species and remote sensing to quantify and map carbon (C) storage, sequestration and avoided emissions from energy savings. Its primary contribution is methodological; the derivation and application of urban tree canopy (UTC) based transfer functions (t C ha-1 UTC). Findings for Los...

  11. Characterizing tree canopy temperature heterogeneity using an unmanned aircraft-borne thermal imager

    Science.gov (United States)

    Messinger, M.; Powell, R.; Silman, M.; Wright, M.; Nicholson, W.

    2013-12-01

    Leaf temperature (Tleaf) is an important control on many physiological processes such as photosynthesis and respiration, is a key variable for characterizing canopy energy fluxes, and is a valuable metric for identifying plant water stress or disease. Traditional methods of Tleaf measurement involve either the use of thermocouples, a time and labor-intensive method that samples sparsely in space, or the use of air temperature (Tair) as a proxy measure, which can introduce inaccuracies due to near constant canopy-atmosphere energy flux. Thermal infrared (TIR) imagery provides an efficient means of collecting Tleaf for large areas. Existing satellite and aircraft-based TIR imagery is, however, limited by low spatial and/or temporal resolution, while crane-mounted camera systems have strictly limited spatial extents. Unmanned aerial systems (UAS) offer new opportunities to acquire high spatial and temporal resolution imagery on demand. Here, we demonstrate the feasibility of collecting tree canopy Tleaf data using a small multirotor UAS fitted with a high spatial resolution TIR imager. The goals of this pilot study were to a) characterize basic patterns of within crown Tleaf for 4 study species and b) identify trends in Tleaf between species with varying leaf morphologies and canopy structures. TIR imagery was acquired for individual tree crowns of 4 species common to the North Carolina Piedmont ecoregion (Quercus phellos, Pinus strobus, Liriodendron tulipifera, Magnolia grandiflora) in an urban park environment. Due to significantly above-average summer precipitation, we assumed that none of the sampled trees was limited by soil water availability. We flew the TIR imaging system over 3-4 individuals of each of the 4 target species on 3 separate days. Imagery of all individuals was collected within the same 2-hour period in the afternoon on all days. There was low wind and partly cloudy skies during imaging. Tair, relative humidity, and wind speed were recorded at

  12. Spatial variability of leaf wetness duration in different crop canopies

    Science.gov (United States)

    Sentelhas, Paulo C.; Gillespie, Terry J.; Batzer, Jean C.; Gleason, Mark L.; Monteiro, José Eduardo B. A.; Pezzopane, José Ricardo M.; Pedro, Mário J.

    2005-07-01

    The spatial variability of leaf wetness duration (LWD) was evaluated in four different height-structure crop canopies: apple, coffee, maize, and grape. LWD measurements were made using painted flat plate, printed-circuit wetness sensors deployed in different positions above and inside the crops, with inclination angles ranging from 30 to 45°. For apple trees, the sensors were installed in 12 east-west positions: 4 at each of the top (3.3 m), middle (2.1 m), and bottom (1.1 m) levels. For young coffee plants (80 cm tall), four sensors were installed close to the leaves at heights of 20, 40, 60, and 80 cm. For the maize and grape crops, LWD sensors were installed in two positions, one just below the canopy top and another inside the canopy. Adjacent to each experiment, LWD was measured above nearby mowed turfgrass with the same kind of flat plate sensor, deployed at 30 cm and between 30 and 45°. We found average LWD varied by canopy position for apple and maize (Pcoffee plants, average LWD did not differ between the top and inside the canopy. The comparison by geometric mean regression analysis between crop and turfgrass LWD measurements showed that sensors at 30 cm over turfgrass provided quite accurate estimates of LWD at the top of the crops, despite large differences in crop height and structure, but poorer estimates for wetness within leaf canopies.

  13. Forest canopy gap distributions in the southern Peruvian Amazon.

    Directory of Open Access Journals (Sweden)

    Gregory P Asner

    Full Text Available Canopy gaps express the time-integrated effects of tree failure and mortality as well as regrowth and succession in tropical forests. Quantifying the size and spatial distribution of canopy gaps is requisite to modeling forest functional processes ranging from carbon fluxes to species interactions and biological diversity. Using high-resolution airborne Light Detection and Ranging (LiDAR, we mapped and analyzed 5,877,937 static canopy gaps throughout 125,581 ha of lowland Amazonian forest in Peru. Our LiDAR sampling covered a wide range of forest physiognomies across contrasting geologic and topographic conditions, and on depositional floodplain and erosional terra firme substrates. We used the scaling exponent of the Zeta distribution (λ as a metric to quantify and compare the negative relationship between canopy gap frequency and size across sites. Despite variable canopy height and forest type, values of λ were highly conservative (λ mean  = 1.83, s  = 0.09, and little variation was observed regionally among geologic substrates and forest types, or at the landscape level comparing depositional-floodplain and erosional terra firme landscapes. λ-values less than 2.0 indicate that these forests are subjected to large gaps that reset carbon stocks when they occur. Consistency of λ-values strongly suggests similarity in the mechanisms of canopy failure across a diverse array of lowland forests in southwestern Amazonia.

  14. The canopy spiders (Araneae of the floodplain forest in Leipzig

    Directory of Open Access Journals (Sweden)

    Otto, Stefan

    2010-10-01

    Full Text Available The canopy spiders of the floodplain forest in Leipzig have become a focus of ecological studies in recent years. In 2006 we sampled 30 tree canopies in the ‘Burgaue’ nature reserve with pyrethrum knock-down fogging, recording 502 adult spiders belonging to 48 species and 11 families. Based on these data and the results of a previous fogging study, the studied spider community was dominated by forest and forest-edge species with a preference for the shrub and canopy strata as well as by spiders of the web spider feeding guild. The community structure was typical for arboreal spider communities from northern temperate forests but very different from communities in the tropics. Species richness and evenness were similar to the old growth near-primary Białowieża Forest in Poland. The checklist of 96 canopy spider species of the floodplain forest of Leipzig includes 54 additions to the spider fauna of Leipzig and vicinity by recent canopy studies and eight first canopy records for Leipzig from our field work. The theridiid Dipoena torva (Thorell, 1875 was recorded for the first time in Saxony. The floodplain forest of Leipzig sustains a large and species-rich arboreal spider community and is thus a valuable habitat for a large proportion of endangered species (12%.

  15. Estimating canopy fuel parameters for Atlantic Coastal Plain forest types.

    Energy Technology Data Exchange (ETDEWEB)

    Parresol, Bernard, R.

    2007-01-15

    Abstract It is necessary to quantify forest canopy characteristics to assess crown fire hazard, prioritize treatment areas, and design treatments to reduce crown fire potential. A number of fire behavior models such as FARSITE, FIRETEC, and NEXUS require as input four particular canopy fuel parameters: 1) canopy cover, 2) stand height, 3) crown base height, and 4) canopy bulk density. These canopy characteristics must be mapped across the landscape at high spatial resolution to accurately simulate crown fire. Currently no models exist to forecast these four canopy parameters for forests of the Atlantic Coastal Plain, a region that supports millions of acres of loblolly, longleaf, and slash pine forests as well as pine-broadleaf forests and mixed species broadleaf forests. Many forest cover types are recognized, too many to efficiently model. For expediency, forests of the Savannah River Site are categorized as belonging to 1 of 7 broad forest type groups, based on composition: 1) loblolly pine, 2) longleaf pine, 3) slash pine, 4) pine-hardwood, 5) hardwood-pine, 6) hardwoods, and 7) cypress-tupelo. These 7 broad forest types typify forests of the Atlantic Coastal Plain region, from Maryland to Florida.

  16. Predicting tropical plant physiology from leaf and canopy spectroscopy.

    Science.gov (United States)

    Doughty, Christopher E; Asner, Gregory P; Martin, Roberta E

    2011-02-01

    A broad regional understanding of tropical forest leaf photosynthesis has long been a goal for tropical forest ecologists, but it has remained elusive due to difficult canopy access and high species diversity. Here we develop an empirical model to predict sunlit, light-saturated, tropical leaf photosynthesis using leaf and simulated canopy spectra. To develop this model, we used partial least squares (PLS) analysis on three tropical forest datasets (159 species), two in Hawaii and one at the biosphere 2 laboratory (B2L). For each species, we measured light-saturated photosynthesis (A), light and CO(2) saturated photosynthesis (A(max)), respiration (R), leaf transmittance and reflectance spectra (400-2,500 nm), leaf nitrogen, chlorophyll a and b, carotenoids, and leaf mass per area (LMA). The model best predicted A [r(2) = 0.74, root mean square error (RMSE) = 2.9 μmol m(-2) s(-1))] followed by R (r(2) = 0.48), and A(max) (r(2) = 0.47). We combined leaf reflectance and transmittance with a canopy radiative transfer model to simulate top-of-canopy reflectance and found that canopy spectra are a better predictor of A (RMSE = 2.5 ± 0.07 μmol m(-2) s(-1)) than are leaf spectra. The results indicate the potential for this technique to be used with high-fidelity imaging spectrometers to remotely sense tropical forest canopy photosynthesis.

  17. CANOPY STRUCTURE AND DEPOSITION EFFICIENCY OF VINEYARD SPRAYERS

    Directory of Open Access Journals (Sweden)

    Gianfranco Pergher

    2007-06-01

    Full Text Available A field study was performed to analyse how deposition efficiency from an axial-fan sprayer was affected by the canopy structure of vines trained to the High Cordon, Low Cordon and Casarsa systems, at beginning of flowering and beginning of berry touch growth stages. An empirical calibration method, providing a dose rate adjustment roughly proportional to canopy height, was used. The canopy structure was assessed using the Point Quadrat method, and determining the leaf area index (LAI and the leaf layer index (LLI. Spray deposits were measured by colorimetry, using a water soluble dye (Tartrazine as a tracer. Correlation between deposits and canopy parameters were analysed and discussed. Foliar deposits per unit leaf area were relatively constant, suggesting that empirical calibration can reduce deposit variability associated with different training systems and growth stages. Total foliar deposition ranged from 33.6% and 82.3% of total spray volume, and increased proportionally with the LLI up to LLI<4. Deposits on bunches significantly decreased with the LLI in the grape zone. The results suggest that sprayer efficiency is improved by a regular, symmetrical canopy, with few leaf layers in the grape zone as in Low Cordon. However, a LLI<3 over the whole canopy and >40% gaps in the foliage both reduced total deposition, and may increase the risk for larger drift losses.

  18. Isotopic characteristics of canopies in simulated leaf assemblages

    Science.gov (United States)

    Graham, Heather V.; Patzkowsky, Mark E.; Wing, Scott L.; Parker, Geoffrey G.; Fogel, Marilyn L.; Freeman, Katherine H.

    2014-11-01

    The geologic history of closed-canopy forests is of great interest to paleoecologists and paleoclimatologists alike. Closed canopies have pronounced effects on local, continental and global rainfall and temperature patterns. Although evidence for canopy closure is difficult to reconstruct from the fossil record, the characteristic isotope gradients of the ;canopy effect; could be preserved in leaves and proxy biomarkers. To assess this, we employed new carbon isotopic data for leaves collected in diverse light environments within a deciduous, temperate forest (Maryland, USA) and for leaves from a perennially closed canopy, moist tropical forest (Bosque Protector San Lorenzo, Panamá). In the tropical forest, leaf carbon isotope values range 10‰, with higher δ13Cleaf values occurring both in upper reaches of the canopy, and with higher light exposure and lower humidity. Leaf fractionation (Δleaf) varied negatively with height and light and positively with humidity. Vertical 13C enrichment in leaves largely reflects changes in Δleaf, and does not trend with δ13C of CO2 within the canopy. At the site in Maryland, leaves express a more modest δ13C range (∼6‰), with a clear trend that follows both light and leaf height. Using a model we simulate leaf assemblage isotope patterns from canopy data binned by elevation. The re-sampling (bootstrap) model determined both the mean and range of carbon isotope values for simulated leaf assemblages ranging in size from 10 to over 1000 leaves. For the tropical forest data, the canopy's isotope range is captured with 50 or more randomly sampled leaves. Thus, with a sufficient number of fossil leaves it is possible to distinguish isotopic gradients in an ancient closed canopy forest from those in an open forest. For very large leaf assemblages, mean isotopic values approximate the δ13C of carbon contributed by leaves to soil and are similar to observed δ13Clitter values at forested sites within Panamá, including the

  19. Boreal forest BVOC exchange: emissions versus in-canopy sinks

    Science.gov (United States)

    Zhou, Putian; Ganzeveld, Laurens; Taipale, Ditte; Rannik, Üllar; Rantala, Pekka; Petteri Rissanen, Matti; Chen, Dean; Boy, Michael

    2017-12-01

    A multilayer gas dry deposition model has been developed and implemented into a one-dimensional chemical transport model SOSAA (model to Simulate the concentrations of Organic vapours, Sulphuric Acid and Aerosols) to calculate the dry deposition velocities for all the gas species included in the chemistry scheme. The new model was used to analyse in-canopy sources and sinks, including gas emissions, chemical production and loss, dry deposition, and turbulent transport of 12 featured biogenic volatile organic compounds (BVOCs) or groups of BVOCs (e.g. monoterpenes, isoprene+2-methyl-3-buten-2-ol (MBO), sesquiterpenes, and oxidation products of mono- and sesquiterpenes) in July 2010 at the boreal forest site SMEAR II (Station for Measuring Ecosystem-Atmosphere Relations). According to the significance of modelled monthly-averaged individual source and sink terms inside the canopy, the selected BVOCs were classified into five categories: 1. Most of emitted gases are transported out of the canopy (monoterpenes, isoprene + MBO). 2. Chemical reactions remove a significant portion of emitted gases (sesquiterpenes). 3. Bidirectional fluxes occur since both emission and dry deposition are crucial for the in-canopy concentration tendency (acetaldehyde, methanol, acetone, formaldehyde). 4. Gases removed by deposition inside the canopy are compensated for by the gases transported from above the canopy (acetol, pinic acid, β-caryophyllene's oxidation product BCSOZOH). 5. The chemical production is comparable to the sink by deposition (isoprene's oxidation products ISOP34OOH and ISOP34NO3). Most of the simulated sources and sinks were located above about 0.2 hc (canopy height) for oxidation products and above about 0.4 hc for emitted species except formaldehyde. In addition, soil deposition (including deposition onto understorey vegetation) contributed 11-61 % to the overall in-canopy deposition. The emission sources peaked at about 0.8-0.9 hc, which was higher than 0.6 hc

  20. Comparison of leaf beetle assemblages of deciduous trees canopies in Hungary (Coleoptera: Chrysomelidae).

    Science.gov (United States)

    Vig, K; Markó, V

    2005-01-01

    The species richness and species composition of Coleoptera assemblages were investigated in deciduous tree canopies in Hungary. Apple and pear orchards were investigated in Nagykovácsi, Kecskemét and Sárospatak in 1990-94, and limes and maples in Keszthely in 1999-2002. Faunistic results and conclusions of these investigations were published elsewhere. Examination of the fauna of parks, avenues and other planted urban plant stocks has only begun to occupy researchers in the last decade in Hungary. The proportion of leaf-beetle species in the material gathered on maples and limes ranged between 17.0 and 21.3 per cent. The commonest leaf-beetle specimens collected in the lime canopy were Aphthona euphorbiae, Chaetocnema tibialis, Longitarsus lycopi, L. pellucidus, L. pratensis and L. succineus. The commonest on maple were Aphthona euphorbiae, Chaetocnema concinna, C. tibialis, Longitarsus lycopi, L. pellucidus, L. succineus, Phyllotreta cruciferae and P. vittula. This study presents the details on the composition of the chrysomelid communities that was compared by metric ordination using the Syntax 5.1 program.

  1. Houston’s Urban Forest, 2015

    Science.gov (United States)

    David J. Nowak; Allison R. Bodine; Robert E. Hoehn; Christopher B. Edgar; Gretchen Riley; Dudley R. Hartel; Kerry J. Dooley; Sharon M. Stanton; Mark A. Hatfield; Thomas J. Brandeis; Tonya W. Lister

    2017-01-01

    An analysis of the urban forest in Houston, Texas, reveals that this area has an estimated 33.3 million live trees with tree canopy that covers 18.4 percent of the city. Roughly 19.2 million of the city’s trees are located on private lands. The most common tree species are yaupon, Chinese tallowtree, Chinese privet, Japanese privet, and sugarberry. Trees in Houston...

  2. Quantifying urban heat island effects and human comfort for cities of variable size and urban morphology in the Netherlands

    NARCIS (Netherlands)

    Steeneveld, G.J.; Koopmans, S.; Heusinkveld, B.G.; Hove, van B.; Holtslag, A.A.M.

    2011-01-01

    This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of small to large cities and villages in the Netherlands. So far, this subject has not been substantially studied in the Netherlands, since it has a relatively mild Cfb climate and impact was assumed to be

  3. How neighbor canopy architecture affects target plant performance

    Energy Technology Data Exchange (ETDEWEB)

    Tremmel, D.C.; Bazzaz, F.A. (Harvard Univ., Cambridge, MA (United States))

    1993-10-01

    Plant competition occurs through the negative effects that individual plants have on resource availability to neighboring individuals. Therefore competition experiments need to examine how different species change resource availability to their neighbors, and how different species respond to these changes-allocationally, architecturally, and physiologically-through time. In a greenhouse study we used a model system of annuals to examine how canopies of species having differing morphologies differed in their architectures and light-interception abilities, and how different species performed when grown in these canopies. Abutilon theophrasti, Datura stramonium, and Polygonum pensylvanicum were grown as [open quotes]targets[close quotes]. Plants were grown in pots, with one target plant and four neighbor plants. Detailed measurements of neighbor canopy structure and target plant canopy architecture were made at five harvests. Species with different morphologies showed large differences in canopy structure, particularly when grass and forb species were compared. Setaria, a grass, had a more open canopy than the other species (all forbs), and was a consistently weak competitor. Overall, however, the relative effects of different neighbors on target biomass varied with target species. Target biomass was poorly correlated with neighbor biomass and leaf area, but was highly correlated with a measure of target light-interception ability that took into account both target leaf deployment and neighbor light interception. Despite clear differences among neighbor species in canopy structure and effect on light penetration, the results suggest no broad generalizations about the effects of different species as neighbors. Knowledge of morphological, physiological, and life history characteristics of both the target and neighbor species may be necessary to explain the results of their competition. 53 refs., 4 figs., 4 tabs.

  4. A comparison between wet canopy evaporation estimated by stable isotope ratios of water and canopy interception measured by water balance

    Science.gov (United States)

    Murakami, Shigeki; Hattori, Shohei; Uemura, Ryu

    2017-04-01

    Some papers proved that canopy interception is proportional to rainfall not only on a rain event basis but also on an hourly basis (e.g. Murakami, 2006, J. Hydrol.; Saito et al., 2013, J. Hydrol.). However, theoretically, evaporation does not depend on rainfall amount. These results are enigmatic and we need to reevaluate wet canopy evaporation. We measured gross rainfall and net rainfall in a plastic Christmas tree stand with a height of 165 cm placed on a 180-cm square tray as described in Murakami and Toba (2013, Hydrol. Res. Lett.). The measurement was conducted outside under natural rainfall. We also estimated wet canopy evaporation using stable isotope ratios of water. During a rain event, we manually sampled gross and net rainwater on an hourly basis. Evaporation was calculated using the difference between the δ18O (or δ2H) values in gross and net rainfall using isotope fractionation factor. Total gross rainfall in a target rain event in October, 2014, was 28.0 mm and net rainfall (discharge from the tray) was 22.7 mm, i.e. canopy interception was 5.3 mm (18.9% of gross rainfall). The δ18O (or δ2H) value in net rainfall was higher than that in gross rainfall because of fractionation by evaporation on wet canopy surface. Hourly evaporation calculated by the values of δ18O varied from 2% to 24% of gross rainfall, and the weighted average by hourly gross rainfall was 5.2% of gross rainfall. Further, we estimated rainfall interception using a tank model (Yoshida et al., 1993) assuming constant evaporation rate, i.e. 20% of gross rainfall. Total net rainfall calculated by the model was 23.1 mm, i.e. calculated canopy interception was 4.9 mm (17.5% of gross rainfall). Then, keeping the parameters of the model, we simulated net rainfall using hourly surface evaporation obtained by the δ18O values. Calculated net rainfall was 25.6 mm, i.e. wet canopy evaporation was only 2.4 mm (8.6% of gross rainfall). So far, possible explanation of the discrepancy between

  5. Intra-Urban Microclimate Effects on Phenology

    Directory of Open Access Journals (Sweden)

    Tammy E. Parece

    2018-03-01

    Full Text Available The urban heat island effect is commonly defined as the thermal differences between cooler rural and warmer urban areas, but it also refers to microclimatic differences within an urban area that arises from varied combinations of land cover related to different land uses. Microclimatic variations should also produce intra-urban differences in vegetation phenophases, although few studies have investigated urban phenology. Most phenological studies are usually regional to continental in scale, predominantly tracking changes in start of season related to climate change. This study reports results of an exploratory analysis using TIMESAT (Lund University, Lund, Sweden software and MODIS NDVI 250-m resolution data (Goddard Space Flight Center, Greenbelt, MD, USA to identify intra-urban differences in start of season for the City of Roanoke, Virginia. We compare these results to our in-situ temperature collection campaign. Additionally, we completed an in-situ start of season data collection by observing select tree species. Our results demonstrate that MODIS, processed by TIMESAT software, identified intra-urban start of season variations, and these variations are consistent with differing intra-urban microclimates and our in-situ start of season observations. Furthermore, results from such analyses can aid plans for increasing the urban tree canopy or in cultivating locations for urban agriculture—i.e., warmer areas with a longer growing season could accommodate warmer weather trees and crops.

  6. Simulations of tropical rainforest albedo: is canopy wetness important?

    Directory of Open Access Journals (Sweden)

    Silvia N.M. Yanagi

    Full Text Available Accurate information on surface albedo is essential for climate modelling, especially for regions such as Amazonia, where the response of the regional atmospheric circulation to the changes on surface albedo is strong. Previous studies have indicated that models are still unable to correctly reproduce details of the seasonal variation of surface albedo. Therefore, it was investigated the role of canopy wetness on the simulated albedo of a tropical rainforest by modifying the IBIS canopy radiation transfer code to incorporate the effects of canopy wetness on the vegetation reflectance. In this study, simulations were run using three versions of the land surface/ecosystem model IBIS: the standard version, the same version recalibrated to fit the data of albedo on tropical rainforests and a modified version that incorporates the effects of canopy wetness on surface albedo, for three sites in the Amazon forest at hourly and monthly scales. The results demonstrated that, at the hourly time scale, the incorporation of canopy wetness on the calculations of radiative transfer substantially improves the simulations results, whereas at the monthly scale these changes do not substantially modify the simulated albedo.

  7. Eo-1 Hyperion Measures Canopy Drought Stress In Amazonia

    Science.gov (United States)

    Asner, Gregory P.; Nepstad, Daniel; Cardinot, Gina; Moutinho, Paulo; Harris, Thomas; Ray, David

    2004-01-01

    The central, south and southeast portions of the Amazon Basin experience a period of decreased cloud cover and precipitation from June through November. There are likely important effects of seasonal and interannual rainfall variation on forest leaf area index, canopy water stress, productivity and regional carbon cycling in the Amazon. While both ground and spaceborne studies of precipitation continue to improve, there has been almost no progress made in observing forest canopy responses to rainfall variability in the humid tropics. This shortfall stems from the large stature of the vegetation and great spatial extent of tropical forests, both of which strongly impede field studies of forest responses to water availability. Those few studies employing satellite measures of canopy responses to seasonal and interannual drought (e.g., Bohlman et al. 1998, Asner et al. 2000) have been limited by the spectral resolution and sampling available from Landsat and AVHRR sensors. We report on a study combining the first landscape-level, managed drought experiment in Amazon tropical forest with the first spaceborne imaging spectrometer observations of this experimental area. Using extensive field data on rainfall inputs, soil water content, and both leaf and canopy responses, we test the hypothesis that spectroscopic signatures unique to hyperspectral observations can be used to quantify relative differences in canopy stress resulting from water availability.

  8. Performance of an Ultrasonic Ranging Sensor in Apple Tree Canopies

    Science.gov (United States)

    Escolà, Alexandre; Planas, Santiago; Rosell, Joan Ramon; Pomar, Jesús; Camp, Ferran; Solanelles, Francesc; Gracia, Felip; Llorens, Jordi; Gil, Emilio

    2011-01-01

    Electronic canopy characterization is an important issue in tree crop management. Ultrasonic and optical sensors are the most used for this purpose. The objective of this work was to assess the performance of an ultrasonic sensor under laboratory and field conditions in order to provide reliable estimations of distance measurements to apple tree canopies. To this purpose, a methodology has been designed to analyze sensor performance in relation to foliage ranging and to interferences with adjacent sensors when working simultaneously. Results show that the average error in distance measurement using the ultrasonic sensor in laboratory conditions is ±0.53 cm. However, the increase of variability in field conditions reduces the accuracy of this kind of sensors when estimating distances to canopies. The average error in such situations is ±5.11 cm. When analyzing interferences of adjacent sensors 30 cm apart, the average error is ±17.46 cm. When sensors are separated 60 cm, the average error is ±9.29 cm. The ultrasonic sensor tested has been proven to be suitable to estimate distances to the canopy in field conditions when sensors are 60 cm apart or more and could, therefore, be used in a system to estimate structural canopy parameters in precision horticulture. PMID:22163749

  9. The MODIS Vegetation Canopy Water Content product

    Science.gov (United States)

    Ustin, S. L.; Riano, D.; Trombetti, M.

    2008-12-01

    Vegetation water stress drives wildfire behavior and risk, having important implications for biogeochemical cycling in natural ecosystems, agriculture, and forestry. Water stress limits plant transpiration and carbon gain. The regulation of photosynthesis creates close linkages between the carbon, water, and energy cycles and through metabolism to the nitrogen cycle. We generated systematic weekly CWC estimated for the USA from 2000-2006. MODIS measures the sunlit reflectance of the vegetation in the visible, near-infrared, and shortwave infrared. Radiative transfer models, such as PROSPECT-SAILH, determine how sunlight interacts with plant and soil materials. These models can be applied over a range of scales and ecosystem types. Artificial Neural Networks (ANN) were used to optimize the inversion of these models to determine vegetation water content. We carried out multi-scale validation of the product using field data, airborne and satellite cross-calibration. An Algorithm Theoretical Basis Document (ATBD) of the product is under evaluation by NASA. The CWC product inputs are 1) The MODIS Terra/Aqua surface reflectance product (MOD09A1/MYD09A1) 2) The MODIS land cover map product (MOD12Q1) reclassified to grassland, shrub-land and forest canopies; 3) An ANN trained with PROSPECT-SAILH; 4) A calibration file for each land cover type. The output is an ENVI file with the CWC values. The code is written in Matlab environment and is being adapted to read not only the 8 day MODIS composites, but also daily surface reflectance data. We plan to incorporate the cloud and snow mask and generate as output a geotiff file. Vegetation water content estimates will help predicting linkages between biogeochemical cycles, which will enable further understanding of feedbacks to atmospheric concentrations of greenhouse gases. It will also serve to estimate primary productivity of the biosphere; monitor/assess natural vegetation health related to drought, pollution or diseases

  10. Study of the effectiveness of several tree canopy types on roadside green belt in influencing the distribution of NO2 gas emitted from transportation

    Science.gov (United States)

    Desyana, R. D.; Sulistyantara, B.; Nasrullah, N.; Fatimah, I. S.

    2017-03-01

    Transportation is one significant factor which contributes to urban air pollution. One of the pollutants emitted from transportation which affect human’s health is NO2. Plants, especially trees, have high potential in reducing air pollutants from transportation through diffusion, absorbtion, adsorption and deposition. Purpose of this study was to analyze the effectiveness of several tree canopy types on roadside green belt in influencing distribution of NO2 gas emitted from transportation. The study conducted in three plots of tree canopy in Jagorawi Highway: Bungur (Lagerstroemia speciosa), Gmelina (Gmelina arborea) and Tanjung (Mimusops elengi). The tree canopy ability in absorbing pollutant is derived by comparing air quality on vegetated area with ambience air quality at control area (open field). Air sampling was conducted to measure NO2 concentration at elevation 1.5m, 5m and 10m at distance 0m, 10m and 30m, using Air Sampler Impinger. Concentration of NO2 was analyzed with Griess-Saltzman method. From this research, the result of ANOVA showed that tree plot (vegetated area) affected significantly to NO2 concentration. However the effect of distance from road and elevation was not significant. Among the plots, the highest NO2 concentration was found on Control plot (area without tree canopy), while the lowest NO2 concentration was found in Tanjung plot. Tanjung plot with round shape and high density canopy performed better in reducing NO2 than Bungur plot with round shape and medium density canopy, regardless the sampling elevation and distance. Gmelina plot performed the best in reducing horizontal distribution of NO2 concentration at elevation 1.5 and 5m, but the result at elevation 10m was not significant.

  11. Sunfleck dynamics and canopy structure in a Phaseolus vulgaris L. canopy

    Science.gov (United States)

    Barradas, Victor L.; Jones, Hamlyn G.; Clark, Jerry A.

    Photosynthetic photon flux density (PPFD) fluctuations were quantified in crops of beans (Phaseolus vulgaris L.) in the field as the canopy developed between July and October. Two different methods were used to select sunflecks and shadeflecks. Four ranges of zenith angles (60-70°, 50-60°, 40-50° and 30-40°) were selected for analysing PPFD fluctuations. At the base of the canopy, sunflecks contributed 18%, 53%, 10% and 4% during the 1st, 3rd, 5th and 7th week of growth, respectively. At a height of 20 cm above the soil surface, the respective contributions were 28% and 21% during the 6th and 7th weeks. Sunfleck lengths of 0-5 s were the most frequent, with the greatest number being found with smaller zenith angles. The proportion of short duration sunflecks increased as the growth period advanced. The number of long sunflecks decreased with time, with very few longer than 100 s by the 5th and 7th weeks. The distributions of sunfleck irradiance were similar to normal distributions and irradiance ranged in μmol m-2 s-1 from 600-900, 800-1500 and 1000-1600 respectively at zenith angles of 50-60°, 40-50° and 30-40°. A multiple regression showed that short sunflecks (100 s) depended on zenith angle and Ls. Shadefleck distributions were similar to those for sunflecks but there were fewer of the shortest examples and more of the longest. The best statistical distribution to describe sunflecks and shadeflecks was the gamma distribution, which could provide the basis for the future development of a good model for sunfleck and shadefleck distributions.

  12. Development of a 1D canopy module to couple mesoscale meteorogical model with building energy model

    Science.gov (United States)

    Mauree, Dasaraden; Kohler, Manon; Blond, Nadège; Clappier, Alain

    2013-04-01

    computational time. To simulate the processes at the micro-scale (building) as well as at the meso-scale (city and surroundings), it is necessary to connect these two types of models. It is proposed here to develop a canopy module able to act as an interface between these two scales. The meso-scale model provides the meteorological parameters to the micro-scale model via the canopy module. The micro-scale model then calculates the influence of the different type of surfaces on the variables and gives its back through the module to the meso-scale model. By simulating in a better way the interactions between the atmosphere and the urban surfaces, the model will enhance the estimation of the energy use by building. The tool produced by this research could be coupled in the future with an urban dynamics model to optimize urban planning in order to improve the sustainability of cities.

  13. The Atmospheric Chemistry and Canopy Exchange Simulation System (ACCESS: model description and application to a temperate deciduous forest canopy

    Directory of Open Access Journals (Sweden)

    R. D. Saylor

    2013-01-01

    Full Text Available Forest canopies are primary emission sources of biogenic volatile organic compounds (BVOCs and have the potential to significantly influence the formation and distribution of secondary organic aerosol (SOA mass. Biogenically-derived SOA formed as a result of emissions from the widespread forests across the globe may affect air quality in populated areas, degrade atmospheric visibility, and affect climate through direct and indirect forcings. In an effort to better understand the formation of SOA mass from forest emissions, a 1-D column model of the multiphase physical and chemical processes occurring within and just above a vegetative canopy is being developed. An initial, gas-phase-only version of this model, the Atmospheric Chemistry and Canopy Exchange Simulation System (ACCESS, includes processes accounting for the emission of BVOCs from the canopy, turbulent vertical transport within and above the canopy and throughout the height of the planetary boundary layer (PBL, near-explicit representation of chemical transformations, mixing with the background atmosphere and bi-directional exchange between the atmosphere and canopy and the atmosphere and forest floor. The model formulation of ACCESS is described in detail and results are presented for an initial application of the modeling system to Walker Branch Watershed, an isoprene-emission-dominated forest canopy in the southeastern United States which has been the focal point for previous chemical and micrometeorological studies. Model results of isoprene profiles and fluxes are found to be consistent with previous measurements made at the simulated site and with other measurements made in and above mixed deciduous forests in the southeastern United States. Sensitivity experiments are presented which explore how canopy concentrations and fluxes of gas-phase precursors of SOA are affected by background anthropogenic nitrogen oxides (NOx. Results from these experiments suggest that the

  14. Experimental relations between airborne and ground measured wheat canopy temperatures

    Science.gov (United States)

    Millard, J. P.; Reginato, R. J.; Idso, S. B.; Jackson, R. D.; Goettelman, R. C.; Leroy, M. J.

    1980-01-01

    Experiments using ground-based measurements of canopy temperatures have shown that plant temperatures are good indicators of plant water stress, and thus are useful for assessing water requirements and predicting yields. An intensive 23-day airborne- and ground-measurement program was conducted in Phoenix, Arizona in 1977 to compare airborne-acquired wheat canopy temperatures with simultaneous ground measurements. For canopies that covered at least 85 percent of the soil surface, airborne measurements differed from ground measurements of plant temperature by less than 2 C. Regardless of the amount of plant cover, the airborne measurements were virtually identical to ground-nadir measurements, and thus represent a combination of plant temperature and solid background temperature.

  15. THE PRE-PENUMBRAL MAGNETIC CANOPY IN THE SOLAR ATMOSPHERE

    Energy Technology Data Exchange (ETDEWEB)

    MacTaggart, David [School of Mathematics and Statistics University of Glasgow, Glasgow G12 8QW (United Kingdom); Guglielmino, Salvo L.; Zuccarello, Francesca [Dipartimento di Fisica e Astronomia—Sezione Astrofisica, Università di Catania, via S. Sofia 78, I-95123 Catania (Italy)

    2016-11-01

    Penumbrae are the manifestation of magnetoconvection in highly inclined (to the vertical direction) magnetic field. The penumbra of a sunspot tends to form, initially, along the arc of the umbra antipodal to the main region of flux emergence. The question of how highly inclined magnetic field can concentrate along the antipodal curves of umbrae, at least initially, remains to be answered. Previous observational studies have suggested the existence of some form of overlying magnetic canopy that acts as the progenitor for penumbrae. We propose that such overlying magnetic canopies are a consequence of how the magnetic field emerges into the atmosphere and are, therefore, part of the emerging region. We show, through simulations of twisted flux tube emergence, that canopies of highly inclined magnetic field form preferentially at the required locations above the photosphere.

  16. Experimental canopy removal enhances diversity of vernal pond amphibians.

    Science.gov (United States)

    Skelly, David K; Bolden, Susan R; Freidenburg, L Kealoha

    2014-03-01

    Vernal ponds are often treated as protected environments receiving special regulation and management. Within the landscapes where they are found, forest vegetation frequently dominates surrounding uplands and can grow to overtop and shade pond basins. Two bodies of research offer differing views of the role of forest canopy for vernal pond systems. Studies of landscape conversion suggest that removing forest overstory within uplands can cause local extinctions of amphibians by altering terrestrial habitat or hindering movement. Studies of canopy above pond basins imply an opposite relationship; encroachment of overstory vegetation can be associated with local extinctions potentially via changes in light, thermal, and food resource environments. Unresolved uncertainties about the role of forest canopy reveal significant gaps in our understanding of wetland species distributions and dynamics. Any misunderstanding of canopy influences is simultaneously important to managers because current practices emphasize promoting or conserving vegetation growth particularly within buffers immediately adjacent to ponds. We evaluated this apparent contradiction by conducting a landscape-scale, long-term experiment using 14 natural vernal ponds. Tree felling at six manipulated ponds was limited in spatial scope but was nevertheless effective in increasing water temperature. Compared with eight control ponds, manipulated ponds maintained more amphibian species during five years post-manipulation. There was little evidence that any species was negatively influenced, and the reproductive effort of species for which we estimated egg inputs maintained pretreatment population densities in manipulated compared with control ponds. Overall, our experiment shows that a carefully circumscribed reduction of overhead forest canopy can enhance the capacity of vernal ponds to support wildlife diversity and suggests a scale dependence of canopy influences on amphibians. These findings have

  17. Effect of canopy architectural variation on transpiration and thermoregulation

    Science.gov (United States)

    Linn, R.; Banerjee, T.

    2017-12-01

    One of the major scientific questions identified by the NGEE - Tropics campaign is the effect of disturbances such as forest fires, vegetation thinning and land use change on carbon, water and energy fluxes. Answers to such questions can help develop effective forest management strategies and shape policies to mitigate damages under natural and anthropogenic climate change. The absence of horizontal and vertical variation of forest canopy structure in current models is a major source of uncertainty in answering these questions. The current work addresses this issue through a bottom up process based modeling approach to systematically investigate the effect of forest canopy architectural variation on plant physiological response as well as canopy level fluxes. A plant biophysics formulation is used which is based on the following principles: (1) a model for the biochemical demand for CO2 as prescribed by photosynthesis models. This model can differentiate between photosynthesis under light-limited and nutrient-limited scenarios. (2) A Fickian mass transfer model including transfer through the laminar boundary layer on leaves that may be subjected to forced or free convection depending upon the mean velocity and the radiation load; (3) an optimal leaf water use strategy that maximizes net carbon gain for a given transpiration rate to describe the stomatal aperture variation; (4) a leaf-level energy balance to accommodate evaporative cooling. Such leaf level processes are coupled to solutions of atmospheric flow through vegetation canopies. In the first test case, different scenarios of top heavy and bottom heavy (vertical) foliage distributions are investigated within a one-dimensional framework where no horizontal heterogeneity of canopy structure is considered. In another test case, different spatial distributions (both horizontal and vertical) of canopy geometry (land use) are considered, where flow solutions using large eddy simulations (LES) are coupled to the

  18. Canopy effects on snow sublimation from a central Arizona Basin

    Science.gov (United States)

    Svoma, Bohumil M.

    2017-01-01

    Guided by 30 m terrain and forest cover data, snow sublimation from the Salt River basin in the Southwest U.S. is simulated for years 2008 (wet year) and 2007 (dry year). Downscaled meteorological input correlates well (r 0.80) with independent observations at AmeriFlux sites. Additionally, model correlation and bias with eddy-covariance vapor flux observations is comparable to previous localized modeling efforts. Upon a 30% reduction in effective leaf area index, canopy sublimation decreases by 1.29 mm (27.0%) and 1.05 mm (23.0%) at the basin scale for the 2008 and 2007 simulations, respectively. Ground sublimation decreases 0.72 mm (4.75%) in 2008 and only 0.17 mm (1.5%) in 2007. Canopy snow-holding capacity and frequent unloading events at lower elevations limit the variability in canopy sublimation from wet year to dry year at the basin scale. The greater decrease in snowpack sublimation in the wet year is partly due to decreased longwave radiation from the canopy reduction over a more extensive snowpack than the dry year. This decrease overcomes the increased solar radiation and wind speed during winter. A second factor is that a greater extent of the snowpack persisted into spring in 2008 than 2007, and the large increase in shortwave flux upon canopy reduction increases melt rates, reducing duration. Only in heavily forested high elevations (>2900 m above sea level) in 2008 does the snowpack persist long enough into spring to result in increased ground sublimation upon canopy reduction. As forest cover change can occur rapidly, these results are critical from water resource and ecosystem function perspectives.

  19. URBAN EFFICIENT ENERGY EVALUATION IN HIGH RESOLUTION URBAN AREAS BY USING ADAPTED WRF-UCM AND MICROSYS CFD MODELS

    Science.gov (United States)

    San Jose, R.; Perez, J. L.; Gonzalez, R. M.

    2009-12-01

    Urban metabolism modeling has advanced substantially during the last years due to the increased detail in mesoscale urban parameterization in meteorological mesoscale models and CFD numerical tools. Recently the implementation of the “urban canopy model” (UCM) into the WRF mesoscale meteorological model has produced a substantial advance on the understanding of the urban atmospheric heat flux exchanges in the urban canopy. The need to optimize the use of heat energy in urban environment has produced a substantial increase in the detailed investigation of the urban heat flux exchanges. In this contribution we will show the performance of using a tool called MICROSYS (MICRO scale CFD modelling SYStem) which is an adaptation of the classical urban canopy model but on a high resolution environment by using a classical CFD approach. The energy balance in the urban system can be determined in a micrometeorologicl sense by considering the energy flows in and out of a control volume. For such a control volume reaching from ground to a certain height above buildings, the energy balance equation includes the net radiation, the anthropogenic heat flux, the turbulent sensible heat flux, the turbulent latent heat flux, the net storage change within the control volume, the net advected flux and other sources and sinks. We have applied the MICROSYS model to an area of 5 km x 5 km with 200 m spatial resolution by using the WRF-UCM (adapted and the MICROSYS CFD model. The anthropogenic heat flux has been estimated by using the Flanner M.G. (2009) database and detailed GIS information (50 m resolution) of Madrid city. The Storage energy has been estimated by calculating the energy balance according to the UCM procedure and implementing it into the MICROSYS tool. Results show that MICROSYS can be used as an energy efficient tool to estimate the energy balance of different urban areas and buildings.

  20. Relationships Between Canopy Openness, Snow Cover and Ground Temperature.

    Science.gov (United States)

    Mattson, L.

    2004-05-01

    Red pine stands, which have undergone varying degrees of thinning and site preparation, are examined with a view to identifying the relationships which exist between canopy openness, snow cover and ground temperature. More specifically, eight red pine stands, which have been intentionally harvested at varying densities within the National Petawawa Research Forest, have been heavily instrumented for detailed measurements of canopy openness, snow cover characteristics, above and subsurface temperature profiles as well as micro-meteorological conditions. Results allow for the specification of relationships between the effect of thinning and site preparation on the soils thermal regime which, in turn, impacts upon the natural regeneration of the pine.

  1. Assessing urban forest effects and values, Washington, D.C.'s urban forest

    Science.gov (United States)

    David J. Nowak; Robert E. III Hoehn; Daniel E. Crane; Jack C. Stevens; Jeffrey T. Walton

    2006-01-01

    An analysis of trees in Washington, D.C. reveals that this city has about 1,928,000 trees with canopies that cover 28.6 percent of the area. The most common tree species are American beech, red maple, and boxelder. The urban forest currently store about 526,000 tons of carbon valued at $9.7 million. In addition, these trees remove about 16,200 tons of carbon per year...

  2. Assessing urban forest effects and values, New York City's urban forest

    Science.gov (United States)

    David J. Nowak; Robert E., III Hoehn; Daniel E. Crane; Jack C. Stevens; Jeffrey T. Walton

    2007-01-01

    An analysis of trees in New York City reveals that this city has about 5.2 million trees with canopies that cover 20.9 percent of the area. The most common tree species are tree of heaven, black cherry, and sweetgum. The urban forest currently stores about 1.35 million tons of carbon valued at $24.9 million. In addition, these trees remove about 42,300 tons of carbon...

  3. Modelling atmospheric deposition flux of Cadmium and Lead in urban areas

    International Nuclear Information System (INIS)

    Cherin, Nicolas

    2017-01-01

    According to WHO, air pollution is responsible for more than 3.7 million premature deaths each year (OMS, 2014). Moreover, among these deaths, more than 70 within urban areas. Consequently, the health and environmental impacts of pollutants within these urban areas are of great concern in air quality studies. The deposition fluxes of air pollutants, which can be significant near sources of pollution, have rarely been modeled within urban areas. Historically, atmospheric deposition studies have focused mostly on remote areas to assess the potential impacts on ecosystems of acid deposition and nitrogen loading. Therefore, current atmospheric deposition models may not be suitable to simulate deposition fluxes in urban areas, which include complex surface geometries and diverse land use types. Atmospheric dry deposition is typically modeled using an average roughness length, which depends on land use. This classical roughness-length approach cannot account for the spatial variability of dry deposition in complex settings such as urban areas. Urban canopy models have been developed to parameterize momentum and heat transfer. We extend this approach here to mass transfer, and a new dry deposition model based on the urban canyon concept is presented. It uses a local mixing-length parameterization of turbulence within the canopy, and a description of the urban canopy via key parameters to provide spatially distributed dry deposition fluxes. This approach provides spatially distributed dry deposition fluxes depending on surfaces (streets, walls, roofs) and flow regimes (recirculation and ventilation) within the urban area. (author) [fr

  4. Exploring Relationships between Canopy Architecture, Light Distribution, and Photosynthesis in Contrasting Rice Genotypes Using 3D Canopy Reconstruction

    Directory of Open Access Journals (Sweden)

    Alexandra J. Burgess

    2017-05-01

    Full Text Available The arrangement of leaf material is critical in determining the light environment, and subsequently the photosynthetic productivity of complex crop canopies. However, links between specific canopy architectural traits and photosynthetic productivity across a wide genetic background are poorly understood for field grown crops. The architecture of five genetically diverse rice varieties—four parental founders of a multi-parent advanced generation intercross (MAGIC population plus a high yielding Philippine variety (IR64—was captured at two different growth stages using a method for digital plant reconstruction based on stereocameras. Ray tracing was employed to explore the effects of canopy architecture on the resulting light environment in high-resolution, whilst gas exchange measurements were combined with an empirical model of photosynthesis to calculate an estimated carbon gain and total light interception. To further test the impact of different dynamic light patterns on photosynthetic properties, an empirical model of photosynthetic acclimation was employed to predict the optimal light-saturated photosynthesis rate (Pmax throughout canopy depth, hypothesizing that light is the sole determinant of productivity in these conditions. First, we show that a plant type with steeper leaf angles allows more efficient penetration of light into lower canopy layers and this, in turn, leads to a greater photosynthetic potential. Second the predicted optimal Pmax responds in a manner that is consistent with fractional interception and leaf area index across this germplasm. However, measured Pmax, especially in lower layers, was consistently higher than the optimal Pmax indicating factors other than light determine photosynthesis profiles. Lastly, varieties with more upright architecture exhibit higher maximum quantum yield of photosynthesis indicating a canopy-level impact on photosynthetic efficiency.

  5. Estimation of leaf area index for cotton canopies using the LI-COR LAI-2000 plant canopy analyzer

    International Nuclear Information System (INIS)

    Hicks, S.K.; Lascano, R.J.

    1995-01-01

    Measurement of leaf area index (LAI) is useful for understanding cotton (Gossypium hirsutum L.) growth, water use, and canopy light interception. Destructive measurement is time consuming and labor intensive. Our objective was to evaluate sampling procedures using the Li-Cor (Lincoln, NE) LAI 2000 plant canopy analyzer (PCA) for nondestructive estimation of cotton LAI on the southern High Plains of Texas. We evaluated shading as a way to allow PCA measurements in direct sunlight and the influence of solar direction when using this procedure. We also evaluated a test of canopy homogeneity (information required for setting PCA field of view), determined the number of below-canopy measurements required, examined the influence of leaf wilting on PCA LAI determinations, and tested an alternative method (masking the sensor's two outer rings) for calculating LAI from PCA measurements. The best agreement between PCA and destructively measured LAI values was obtained when PCA observations were made either during uniformly overcast conditions or around solar noon using the shading method. Heterogeneous canopies with large gaps between rows required both a restricted (45 degrees) azimuthal field of view and averaging the LAI values for two transects, made with the field of view parallel and then perpendicular to the row direction. This method agreed well (r2 = 0.84) with destructively measured LAI in the range of 0.5 to 3.5 and did not deviate from a 1:1 relationship. The PCA underestimated LAI by greater than or equal 20% when measurements were made on canopies wilted due to water stress. Masking the PCA sensor's outer rings did not improve the relationship between estimated and measured LAI in the range of LAI sampled

  6. LBA-ECO LC-15 Aerodynamic Roughness Maps of Vegetation Canopies, Amazon Basin: 2000

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, LBA-ECO LC-15 Aerodynamic Roughness Maps of Vegetation Canopies, Amazon Basin: 2000, provides physical roughness maps of vegetation canopies in the...

  7. Tree Canopy Cover for the Circumpolar Taiga-Tundra Ecotone: 2000-2005

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides a map of selected areas with defined tree canopy cover over the circumpolar taiga-tundra ecotone (TTE). Canopy cover was derived from the...

  8. The third RAdiation transfer Model Intercomparison (RAMI) exercise: Documenting progress in canopy reflectance models

    NARCIS (Netherlands)

    Widlowski, J.L.; Taberner, M.; Pinty, B.; Bruniquel-Pinel, V.; Disney, M.I.; Fernandes, R.; Gastellu-Etchegorry, J.P.; Gobron, N.; Kuusk, A.; Lavergne, T.; LeBlanc, S.; Lewis, P.E.; Martin, E.; Mõttus, M.; North, P.R.J.; Qin, W.; Robustelli, M.; Rochdi, N.; Ruiloba, R.; Thompson, R.; Verhoef, W.; Verstraete, M.M.; Xie, D.

    2007-01-01

    [1] The Radiation Transfer Model Intercomparison ( RAMI) initiative benchmarks canopy reflectance models under well-controlled experimental conditions. Launched for the first time in 1999, this triennial community exercise encourages the systematic evaluation of canopy reflectance models on a

  9. Tree Canopy Cover for the Circumpolar Taiga-Tundra Ecotone: 2000-2005

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: This data set provides a map of selected areas with defined tree canopy cover over the circumpolar taiga-tundra ecotone (TTE). Canopy cover was derived...

  10. Development of the multi-scale model for urban climate analysis and evaluation of urban greening effects on energy consumption

    Science.gov (United States)

    Hamano, H.; Nakayama, T.; Fujita, T.; Hori, H.; Tagami, H.

    2009-12-01

    It is necessary to reduce Greenhouse gases (GHG) emissions drastically to stabilize climate change, and Japan is also required to assess its long-term global warming policy. In achieving the low carbon society and sustainable cities, the numerical evaluation of environmental impacts of the application of different technologies and policies was preliminarily examined by utilizing integrative urban environmental model. This research aims to develop the multi-scale model for urban climate analysis and to evaluate the urban greening effects on energy consumption from household and business sectors. It developed the multi-scale model combined the process-based NIES integrated catchment-based eco-hydrology (NICE) model with the meso-scale meteorological model (Regional Atmospheric Modeling System : RAMS) and urban canopy model to estimate the urban climate mitigation effects by introduction of urban heat environmental mitigation technology and scenario. The numerical simulation conducted with the multi-scale level horizontally consisting regional scale (260×260km with 2km grid) and urban area scale (36×26km with 0.2km grid) against the objective area, Kawasaki city of Japan. The urban canopy model predicts the three dimensional atmospheric conditions including anthropogenic heat effect from household, business and factory sectors. Furthermore the tile method applied into the urban canopy model for the improvement of numerical accuracy and detailed land use information in each grid. The validation of this model was conducted by comparison with the observed air temperature of 29 points in entire Kawasaki area from 1st to 31th of August, 2006. From the quantitative validation of model performance, the coefficient of correlation was 0.72 and the root mean square error was 2.99C. The introduction of patch method into urban canopy model made it possible to calculate the each land use effect, and the accuracy of predicted results was improved against the land use area

  11. A comparison of ground-based methods for estimating canopy closure for use in phenology research

    OpenAIRE

    Smith, AM; Ramsay, PM

    2018-01-01

    Abstract Climate change is influencing tree phenology, causing earlier and more prolonged canopy closure in temperate forests. Canopy closure is closely associated with understorey light, so shifts in its timing have wide-reaching consequences for ecological processes in the understorey. Widespread monitoring of forest canopies through time is needed to understand changes in light availability during spring in particular. Canopy openness, derived from hemispherical photography, has frequently...

  12. Application of Lidar remote sensing to the estimation of forest canopy and stand structure

    Science.gov (United States)

    Lefsky, Michael Andrew

    A new remote sensing instrument, SLICER (Scanning Lidar Imager of Canopies by Echo Recovery), has been applied to the problem of remote sensing the canopy and stand structure of two groups of deciduous forests, Tulip Poplar-Oak stands in the vicinity of Annapolis, MD. and bottomland hardwood stands near Williamston, NC. The ability of the SLICER instrument to remotely sense the vertical distribution of canopy structure (Canopy Height Profile), bulk canopy transmittance, and several indices of canopy height has been successfully validated using twelve stands with coincident field and SLICER estimates of canopy structure. Principal components analysis has been applied to canopy height profiles from both field sites, and three significant factors were identified, each closely related to the amount of foliage in a recognizable layer of the forest, either understory, midstory, or overstory. The distribution of canopy structure to these layers is significantly correlated with the size and number of stems supporting them. The same layered structure was shown to apply to both field and SLICER remotely sensed canopy height profiles, and to apply to SLICER remotely sensed canopy profiles from both the bottomland hardwood stands in the coastal plain of North Carolina, and to mesic Tulip-Poplars stands in the upland coastal plain of Maryland. Linear regressions have demonstrated that canopy and stand structure are correlated to both a statistically significant and useful degree. Stand age and stem density is more highly correlated to stand height, while stand basal area and aboveground biomass are more closely related to a new measure of canopy structure, the quadratic mean canopy height. A geometric model of canopy structure has been shown to explain the differing relationships between canopy structure and stand basal area for stands of Eastern Deciduous Forest and Douglas Fir Forest.

  13. Floristic Composition, Tree Canopy Structure and Regeneration in a ...

    African Journals Online (AJOL)

    Floristic composition, plant species diversity, tree canopy structure and regeneration were assessed in a degraded tropical humid rainforest in Nigeria using a systematic line transect sampling technique for plot demarcation. All plants in a plot were identified and classified into families while the diameters and heights of ...

  14. A New Mechanism of Canopy Effect in Unsaturated Freezing Soils

    Directory of Open Access Journals (Sweden)

    Teng Jidong

    2016-01-01

    Full Text Available Canopy effect refers to the phenomenon where moisture accumulates underneath an impervious cover. Field observation reveals that canopy effect can take place in relatively dry soils where the groundwater table is deep and can lead to full saturation of the soil immediately underneath the impervious cover. On the other hand, numerical analysis based on existing theories of heat and mass transfer in unsaturated soils can only reproduce a minor amount of moisture accumulation due to an impervious cover, particularly when the groundwater table is relatively deep. In attempt to explain the observed canopy effect in field, this paper proposes a new mechanism of moisture accumulation in unsaturated freezing soils: vapour transfer in such a soil is accelerated by the process of vapour-ice desublimation. A new approach for modelling moisture and heat movements is proposed, in which the phase change of evaporation, condensation and de-sublimation of vapor flow are taken into account. The computed results show that the proposed model can indeed reproduce the unusual moisture accumulation observed in relatively dry soils. The results also demonstrate that soil freezing fed by vapour transfer can result in a water content close to full saturation. Since vapour transfer is seldom considered in geotechnical design, the canopy effect deserves more attention during construction and earth works in cold and arid regions.

  15. Canopy management, leaf fall and litter quality of dominant tree ...

    African Journals Online (AJOL)

    Small-scale farmers in the banana-coffee agro-zone of Central Uganda plant and maintain trees to provide a range of benefits. However, the impact of trees on soil fertility and crop yields is small. On many farms, trees exist in infinite numbers, compositions, with no proper spacing, sequencing and canopy management ...

  16. Tree canopies facilitate invasion of communal savanna rangelands ...

    African Journals Online (AJOL)

    canopy micro-sites is most likely explained by either seed dispersal patterns imposed by avian dispersal agents and/or micro-site variation. An assessment of population size class structure of Lantana in the communal lands suggested that the ...

  17. Estimates of forest canopy height and aboveground biomass using ICESat.

    Science.gov (United States)

    Michael A. Lefsky; David J. Harding; Michael Keller; Warren B. Cohen; Claudia C. Carabajal; Fernando Del Bom; Maria O. Hunter; Raimundo Jr. de Oliveira

    2005-01-01

    Exchange of carbon between forests and the atmosphere is a vital component of the global carbon cycle. Satellite laser altimetry has a unique capability for estimating forest canopy height, which has a direct and increasingly well understood relationship to aboveground carbon storage. While the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud and land...

  18. Incorporating Plant Phenology Dynamics in a Biophysical Canopy Model

    Science.gov (United States)

    Barata, Raquel A.; Drewry, Darren

    2012-01-01

    The Multi-Layer Canopy Model (MLCan) is a vegetation model created to capture plant responses to environmental change. Themodel vertically resolves carbon uptake, water vapor and energy exchange at each canopy level by coupling photosynthesis, stomatal conductance and leaf energy balance. The model is forced by incoming shortwave and longwave radiation, as well as near-surface meteorological conditions. The original formulation of MLCan utilized canopy structural traits derived from observations. This project aims to incorporate a plant phenology scheme within MLCan allowing these structural traits to vary dynamically. In the plant phenology scheme implemented here, plant growth is dependent on environmental conditions such as air temperature and soil moisture. The scheme includes functionality that models plant germination, growth, and senescence. These growth stages dictate the variation in six different vegetative carbon pools: storage, leaves, stem, coarse roots, fine roots, and reproductive. The magnitudes of these carbon pools determine land surface parameters such as leaf area index, canopy height, rooting depth and root water uptake capacity. Coupling this phenology scheme with MLCan allows for a more flexible representation of the structure and function of vegetation as it responds to changing environmental conditions.

  19. Amazonian functional diversity from forest canopy chemical assembly.

    Science.gov (United States)

    Asner, Gregory P; Martin, Roberta E; Tupayachi, Raul; Anderson, Christopher B; Sinca, Felipe; Carranza-Jiménez, Loreli; Martinez, Paola

    2014-04-15

    Patterns of tropical forest functional diversity express processes of ecological assembly at multiple geographic scales and aid in predicting ecological responses to environmental change. Tree canopy chemistry underpins forest functional diversity, but the interactive role of phylogeny and environment in determining the chemical traits of tropical trees is poorly known. Collecting and analyzing foliage in 2,420 canopy tree species across 19 forests in the western Amazon, we discovered (i) systematic, community-scale shifts in average canopy chemical traits along gradients of elevation and soil fertility; (ii) strong phylogenetic partitioning of structural and defense chemicals within communities independent of variation in environmental conditions; and (iii) strong environmental control on foliar phosphorus and calcium, the two rock-derived elements limiting CO2 uptake in tropical forests. These findings indicate that the chemical diversity of western Amazonian forests occurs in a regionally nested mosaic driven by long-term chemical trait adjustment of communities to large-scale environmental filters, particularly soils and climate, and is supported by phylogenetic divergence of traits essential to foliar survival under varying environmental conditions. Geographically nested patterns of forest canopy chemical traits will play a role in determining the response and functional rearrangement of western Amazonian ecosystems to changing land use and climate.

  20. Computing energy budget within a crop canopy from Penmann's ...

    Indian Academy of Sciences (India)

    R. Narasimhan, Krishtel eMaging Solutions

    Computing energy budget within a crop canopy from. Penmann's formulae. Mahendra Mohan∗ and K K Srivastava∗∗. ∗Radio and Atmospheric Science Division, National Physical Laboratory, New Delhi 110012, India. ∗∗Department of Chemical Engineering, Institute of Technology, Banaras Hindu University, Varanasi.

  1. Computing energy budget within a crop canopy from Penmann's ...

    Indian Academy of Sciences (India)

    layer model, is rede-fined as a function of micrometeorological and physiological profiles of crop canopy. The sources and sinks of sensible and latent heat uxes are assumed to lie on a fictitious plane called zero-displacement plane. Algorithms ...

  2. Amblyomma tapirellum (Dunn, 1933) collected from tropical forest canopy

    NARCIS (Netherlands)

    Loaiza, J.R.; Miller, M.J.; Bermingham, E.; Sanjur, O.I.; Jansen, P.A.; Rovira, J.R.; Alvarez, E.; Rodriguez, E.; Davis, P.; Dutari, L.C.; Pecor, J.; Foley, D.; Radtke, M.; Pongsiri, M.J.

    2013-01-01

    Free-ranging ticks are widely known to be restricted to the ground level of vegetation. Here, we document the capture of the tick species Amblyomma tapirellum in light traps placed in the forest canopy of Barro Colorado Island, central Panama. A total of forty eight adults and three nymphs were

  3. Tree diversity and canopy cover in cocoa systems in Ghana

    DEFF Research Database (Denmark)

    Asare, Richard; Ræbild, Anders

    2016-01-01

    Cocoa (Theobroma cacao L.) growing systems in Ghana and West Africa consist of diverse tree species and densities.This study was conducted to determine factors that influence tree species configurations and how tree characteristics affect canopy cover in cocoa farms. Eighty-six farmers...

  4. Mapping forest canopy disturbance in the Upper Great Lakes, USA

    Science.gov (United States)

    James D. Garner; Mark D. Nelson; Brian G. Tavernia; Charles H. (Hobie) Perry; Ian W. Housman

    2015-01-01

    A map of forest canopy disturbance was generated for Michigan, Wisconsin, and most of Minnesota using 42 Landsat time series stacks (LTSS) and a vegetation change tracker (VCTw) algorithm. Corresponding winter imagery was used to reduce commission errors of forest disturbance by identifying areas of persistent snow cover. The resulting disturbance age map was classed...

  5. Los Angeles 1-Million tree canopy cover assessment

    Science.gov (United States)

    Gregory E. McPherson; James R. Simpson; Qingfu Xiao; Wu Chunxia

    2008-01-01

    The Million Trees LA initiative intends to chart a course for sustainable growth through planting and stewardship of trees. The purpose of this study was to measure Los Angeles's existing tree canopy cover (TCC), determine if space exists for 1 million additional trees, and estimate future benefits from the planting. High resolution QuickBird remote sensing data,...

  6. A Soil Temperature Model for Closed Canopied Forest Stands

    Science.gov (United States)

    James M. Vose; Wayne T. Swank

    1991-01-01

    A microcomputer-based soil temperature model was developed to predict temperature at the litter-soil interface and soil temperatures at three depths (0.10 m, 0.20 m, and 1.25 m) under closed forest canopies. Comparisons of predicted and measured soil temperatures indicated good model performance under most conditions. When generalized parameters describing soil...

  7. Effect of forest canopy on GPS-based movement data

    Science.gov (United States)

    Nicholas J. DeCesare; John R. Squires; Jay A. Kolbe

    2005-01-01

    The advancing role of Global Positioning System (GPS) technology in ecology has made studies of animal movement possible for larger and more vagile species. A simple field test revealed that lengths of GPS-based movement data were strongly biased (Pof forest canopy. Global Positioning System error added an average of 27.5% additional...

  8. Improving canopy sensor algorithms with soil and weather information

    Science.gov (United States)

    Nitrogen (N) need to support corn (Zea mays L.) production can be highly variable within fields. Canopy reflectance sensing for assessing crop N health has been implemented on many farmers’ fields to side-dress or top-dress variable-rate N application, but at times farmers report the performance of ...

  9. Base Cation Leaching From the Canopy of a Rubber ( Hevea ...

    African Journals Online (AJOL)

    Base cations are essential to the sustainability of forest ecosystems. They are important for neutralizing the acidifying effects of atmospheric deposition. There is the need for in-depth understanding of base cation depletion and leaching from forest canopy. This is important particularly due to the increasing acidification and ...

  10. Blue Oak Canopy Effect on Seasonal Forage Production and Quality

    Science.gov (United States)

    William E. Frost; Neil K. McDougald; Montague W. Demment

    1991-01-01

    Forage production and forage quality were measured seasonally beneath the canopy of blue oak (Quercus douglasii) and in open grassland at the San Joaquin Experimental Range. At the March and peak standing crop sampling dates forage production was significantly greater (p=.05) beneath blue oak compared to open grassland. At most sampling dates, the...

  11. Estimation of in-canopy ammonia sources and sinks in a fertilized Zea mays field

    Science.gov (United States)

    An analytical model was developed that describes the in-canopy vertical distribution of NH3 source and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy concentration and wind speed profiles. This model was applied to quantify in-canopy air-s...

  12. Examining conifer canopy structural complexity across forest ages and elevations with LiDAR data

    Science.gov (United States)

    Van R. Kane; Jonathan D. Bakker; Robert J. McGaughey; James A. Lutz; Rolf F. Gersonde; Jerry F. Franklin

    2010-01-01

    LiDAR measurements of canopy structure can be used to classify forest stands into structural stages to study spatial patterns of canopy structure, identify habitat, or plan management actions. A key assumption in this process is that differences in canopy structure based on forest age and elevation are consistent with predictions from models of stand development. Three...

  13. Comparison of LiDAR- and photointerpretation-based estimates of canopy cover

    Science.gov (United States)

    Demetrios Gatziolis

    2012-01-01

    An evaluation of the agreement between photointerpretation- and LiDARbased estimates of canopy cover was performed using 397 90 x 90 m reference areas in Oregon. It was determined that at low canopy cover levels LiDAR estimates tend to exceed those from photointerpretation and that this tendency reverses at high canopy cover levels. Characteristics of the airborne...

  14. Evaporation and the sub-canopy energy environment in a flooded forest

    Science.gov (United States)

    The combination of canopy cover and a free water surface makes the sub-canopy environment of flooded forested wetlands unlike other aquatic or terrestrial systems. The sub-canopy vapor flux and energy budget are not well understood in wetlands, but they importantly control water level and understory...

  15. Simulation of Canopy Leaf Inclination Angle in Rice

    Directory of Open Access Journals (Sweden)

    Xiao-cui ZHANG

    2013-11-01

    Full Text Available A leaf inclination angle distribution model, which is applicable to simulate leaf inclination angle distribution in six heights of layered canopy at different growth stages, was established by component factors affecting plant type in rice. The accuracy of the simulation results was validated by measured values from a field experiment. The coefficient of determination (R2 and the root mean square error (RMSE between the simulated and measured values were 0.9472 and 3.93%, respectively. The simulation results showed that the distribution of leaf inclination angles differed among the three plant types. The leaf inclination angles were larger in the compact variety Liangyoupeijiu with erect leaves than in the loose variety Shanyou 63 with droopy leaves and the intermediate variety Liangyou Y06. The leaf inclination angles were distributed in the lower range in Shanyou 63, which matched up with field measurements. The distribution of leaf inclination angles in the same variety changed throughout the seven growth stages. The leaf inclination angles enlarged gradually from transplanting to booting. During the post-booting period, the leaf inclination angle increased in Shanyou 63 and Liangyou Y06, but changed little in Liangyoupeijiu. At every growth stage of each variety, canopy leaf inclination angle distribution on the six heights of canopy layers was variable. As canopy height increased, the layered leaf area index (LAI decreased in all the three plant types. However, while the leaf inclination angles showed little change in Liangyoupeijiu, they became larger in Shanyou 63 but smaller in Liangyou Y06. The simulation results used in the constructed model were very similar to the actual measurement values. The model provides a method for estimating canopy leaf inclination angle distribution in rice production.

  16. The influence of small urban parks characteristics on bird diversity

    DEFF Research Database (Denmark)

    Jasmani, Zanariah; Ravn, Hans Peter; van den Bosch, Cecil C.Konijnendijk

    2017-01-01

    of tree canopy cover, open grass/ground, native-exotic plants) are the important predictors of bird species richness and abundance. The percentage of canopy covers (negative relation) and park area (positive relation) are the best predictors of bird species richness in small urban parks. Meanwhile......, the best predictors for bird abundance are the percentage of canopy covers (negative relation) and native vegetation species (positive relation). Human activities and park surroundings have a marginal effect on the presence of bird species in small parks. Based on the findings, we provide two general...... using the combined field survey method of structured observation and field measurements. The measured variables were divided into three broad categories of physical characteristics, species richness and human factors. Bird species richness and abundance were used as the indicators for assessing...

  17. Comparative investigation on high-speed grinding of TiCp/Ti–6Al–4V particulate reinforced titanium matrix composites with single-layer electroplated and brazed CBN wheels

    Directory of Open Access Journals (Sweden)

    Li Zheng

    2016-10-01

    Full Text Available In order to develop the high-efficiency and precision machining technique of TiCp/Ti–6Al–4V particulate reinforced titanium matrix composites (PTMCs, high-speed grinding experiments were conducted using the single-layer electroplated cubic boron nitride (CBN wheel and brazed CBN wheel, respectively. The comparative grinding performance was studied in terms of grinding force, grinding temperature, grinding-induced surface features and defects. The results display that the grinding forces and grinding temperature obtained with the brazed CBN wheel are always lower than those with the electroplated CBN wheel. Though the voids and microcracks are the dominant grinding-induced surface defects, the brazed CBN wheel produces less surface defects compared to the electroplated wheel according to the statistical analysis results. The maximum materials removal rate with the brazed CBN wheel is much higher than that with the electroplated one. All above indicate that the single-layer brazed CBN super-abrasive wheel is more suitable for high-speed grinding of PTMCs than the electroplated counterpart.

  18. Estimating canopy bulk density and canopy base height for conifer stands in the interior Western United States using the Forest Vegetation Simulator Fire and Fuels Extension.

    Science.gov (United States)

    Seth Ex; Frederick Smith; Tara Keyser; Stephanie Rebain

    2017-01-01

    The Forest Vegetation Simulator Fire and Fuels Extension (FFE-FVS) is often used to estimate canopy bulk density (CBD) and canopy base height (CBH), which are key indicators of crown fire hazard for conifer stands in the Western United States. Estimated CBD from FFE-FVS is calculated as the maximum 4 m running mean bulk density of predefined 0.3 m thick canopy layers (...

  19. Neighbourhood-scale urban forest ecosystem classification.

    Science.gov (United States)

    Steenberg, James W N; Millward, Andrew A; Duinker, Peter N; Nowak, David J; Robinson, Pamela J

    2015-11-01

    Urban forests are now recognized as essential components of sustainable cities, but there remains uncertainty concerning how to stratify and classify urban landscapes into units of ecological significance at spatial scales appropriate for management. Ecosystem classification is an approach that entails quantifying the social and ecological processes that shape ecosystem conditions into logical and relatively homogeneous management units, making the potential for ecosystem-based decision support available to urban planners. The purpose of this study is to develop and propose a framework for urban forest ecosystem classification (UFEC). The multifactor framework integrates 12 ecosystem components that characterize the biophysical landscape, built environment, and human population. This framework is then applied at the neighbourhood scale in Toronto, Canada, using hierarchical cluster analysis. The analysis used 27 spatially-explicit variables to quantify the ecosystem components in Toronto. Twelve ecosystem classes were identified in this UFEC application. Across the ecosystem classes, tree canopy cover was positively related to economic wealth, especially income. However, education levels and homeownership were occasionally inconsistent with the expected positive relationship with canopy cover. Open green space and stocking had variable relationships with economic wealth and were more closely related to population density, building intensity, and land use. The UFEC can provide ecosystem-based information for greening initiatives, tree planting, and the maintenance of the existing canopy. Moreover, its use has the potential to inform the prioritization of limited municipal resources according to ecological conditions and to concerns of social equity in the access to nature and distribution of ecosystem service supply. Copyright © 2015 Elsevier Ltd. All rights reserved.

  20. Tersail - A numerical model for combined analysis of vegetation canopy bidirectional reflectance and thermal emissions

    Science.gov (United States)

    Hope, Allen S.; Coward, Samuel N.; Petzold, Donald E.

    1988-01-01

    A modification of the Tergra model (Soer, 1977) is presented, which incorporates the scattering from arbitrarily inclined leaves canopy reflectance model (Verhoef and Bunnik, 1981) for the calculation of albedo and canopy resistance. The combined model, known as Tersail, is capable of simulating the relationship between the bidirectional reflectance and the thermal response of a canopy. The accuracy of the model is tested using data over wheat canopies in Phoenix, Arizona, showing that the model is a good simulator of canopy temperatures under a variety of conditions.

  1. Urban Times

    DEFF Research Database (Denmark)

    Nielsen, Morten

    2017-01-01

    This is a proposed special issue with six thematic articles by different contributors on 'urban times' edited by me.......This is a proposed special issue with six thematic articles by different contributors on 'urban times' edited by me....

  2. Does urban vegetation mitigate air pollution in northern conditions?

    International Nuclear Information System (INIS)

    Setälä, Heikki; Viippola, Viljami; Rantalainen, Anna-Lea; Pennanen, Arto; Yli-Pelkonen, Vesa

    2013-01-01

    It is generally accepted that urban vegetation improves air quality and thereby enhances the well-being of citizens. However, empirical evidence on the potential of urban trees to mitigate air pollution is meager, particularly in northern climates with a short growing season. We studied the ability of urban park/forest vegetation to remove air pollutants (NO 2 , anthropogenic VOCs and particle deposition) using passive samplers in two Finnish cities. Concentrations of each pollutant in August (summer; leaf-period) and March (winter, leaf-free period) were slightly but often insignificantly lower under tree canopies than in adjacent open areas, suggesting that the role of foliage in removing air pollutants is insignificant. Furthermore, vegetation-related environmental variables (canopy closure, number and size of trees, density of understorey vegetation) did not explain the variation in pollution concentrations. Our results suggest that the ability of urban vegetation to remove air pollutants is minor in northern climates. -- Highlights: ► The ability of northern urban vegetation to remove air pollutants is minor. ► Vegetation-related environmental variables had no effect on air pollution levels. ► The ability of vegetation to clean air did not differ between summer and winter. ► Dry deposition passive samplers proved applicable in urban air pollution study. -- The ability of urban vegetation to remove air pollutants seems to be minor in northern climates

  3. Large eddy simulation of the atmospheric boundary layer above a forest canopy

    Science.gov (United States)

    Alam, Jahrul

    2017-11-01

    A goal of this talk is to discuss large eddy simulation (LES) of atmospheric turbulence within and above a canopy/roughness sublayer, where coherent turbulence resembles a turbulent mixing layer. The proposed LES does not resolve the near wall region. Instead, a near surface canopy stress model has been combined with a wall adapting local eddy viscosity model. The canopy stress is represented as a three-dimensional time dependent momentum sink, where the total kinematic drag of the canopy is adjusted based on the measurements in a forest canopy. This LES has been employed to analyze turbulence structures in the canopy/roughness sublayer. Results indicate that turbulence is more efficient at transporting momentum and scalars in the roughness sublayer. The LES result has been compared with the turbulence profile measured over a forest canopy to predict the turbulence statistics in the inertial sublayer above the canopy. Turbulence statistics between the inertial sublayer, the canopy sublayer, and the rough-wall boundary layer have been compared to characterize whether turbulence in the canopy sublayer resembles a turbulent mixing layer or a boundary layer. The canopy turbulence is found dominated by energetic eddies much larger in scale than the individual roughness elements. Financial support from the National Science and Research Council (NSERC), Canada is acknowledged.

  4. Chlorophyll Can Be Reduced in Crop Canopies with Little Penalty to Photosynthesis1[OPEN

    Science.gov (United States)

    Drewry, Darren T.; VanLoocke, Andy; Cho, Young B.

    2018-01-01

    The hypothesis that reducing chlorophyll content (Chl) can increase canopy photosynthesis in soybeans was tested using an advanced model of canopy photosynthesis. The relationship among leaf Chl, leaf optical properties, and photosynthetic biochemical capacity was measured in 67 soybean (Glycine max) accessions showing large variation in leaf Chl. These relationships were integrated into a biophysical model of canopy-scale photosynthesis to simulate the intercanopy light environment and carbon assimilation capacity of canopies with wild type, a Chl-deficient mutant (Y11y11), and 67 other mutants spanning the extremes of Chl to quantify the impact of variation in leaf-level Chl on canopy-scale photosynthetic assimilation and identify possible opportunities for improving canopy photosynthesis through Chl reduction. These simulations demonstrate that canopy photosynthesis should not increase with Chl reduction due to increases in leaf reflectance and nonoptimal distribution of canopy nitrogen. However, similar rates of canopy photosynthesis can be maintained with a 9% savings in leaf nitrogen resulting from decreased Chl. Additionally, analysis of these simulations indicate that the inability of Chl reductions to increase photosynthesis arises primarily from the connection between Chl and leaf reflectance and secondarily from the mismatch between the vertical distribution of leaf nitrogen and the light absorption profile. These simulations suggest that future work should explore the possibility of using reduced Chl to improve canopy performance by adapting the distribution of the “saved” nitrogen within the canopy to take greater advantage of the more deeply penetrating light. PMID:29061904

  5. Urban Pathology

    OpenAIRE

    Pitcher, Brian L.

    1997-01-01

    Urban theorists have long debated to what extend and how the social problems of the city have been brought about or exaggerated in some consistent way by the urban environments in which they occur. This presentation reviews theories of urbanism, and the features of cities which contribute to the augmentation and control of various types of social pathology. Special emphasis is given to some types and patterns of urban unrest, and the structural characteristics associated with deleterious urba...

  6. Application of two-stream model to solar radiation of rice canopy

    International Nuclear Information System (INIS)

    Kawakata, T.

    2005-01-01

    The amount of solar radiation absorbed by a crop canopy is correlated with crop production, and thus it is necessary to estimate both transmission and reflection around the canopy for crop growth models. The 'forward and backward streams' representation of radiation has been refined to account for both transmission and reflection in the crop canopy. However, this model has not been applied to a rice canopy through the growing period. The purpose of this study is to examine whether the two-stream model is applicable to the rice canopy, and to investigate the parameters of the model. The values for both transmittance below the rice canopy and reflectance above it that were derived from the two-stream model represent the observed values throughout the growing period. The inclination factor of leaves (F), which is used in the two-stream model, was almost equivalent to the extinction coefficient of transmittance in the case of the rice canopy

  7. Urban Jamification

    DEFF Research Database (Denmark)

    de Souza e Silva, Adriana; Froes, Isabel Cristina G.

    2013-01-01

    and the configuration of urban space influence the design and performance of location-based mobile games; and (2) how the urban and socio-economic context of developing countries, specifically Brazil, shape mobile technology appropriation and location-based mobile game design. We demonstrate that urban spaces can...

  8. Relationships between NDVI, canopy structure, and photosynthesis in three California vegetation types

    International Nuclear Information System (INIS)

    Gamon, J.A.; Field, C.B.; Goulden, M.L.; Griffin, K.L.; Hartley, A.E.; Joel, G.; Penuelas, J.; Valentini, R.

    1995-01-01

    In a range of plant species from three Californian vegetation types, we examined the widely used ''normalized difference vegetation index'' (NDVI) and ''simple ratio'' (SR) as indicators of canopy structure, light absorption, and photosynthetic activity. These indices, which are derived from canopy reflectance in the red and near-infrared wavebands, highlighted phenological differences between evergreen and deciduous canopies. They were poor indicators of total canopy biomass due to the varying abundance of non-green standing biomass in these vegetation types. However, in sparse canopies (leaf area index (LAI) apprxeq 0-2), NDVI was a sensitive indicator of canopy structure and chemical content (green biomass, green leaf area index, chlorophyll content, and foliar nitrogen content). At higher canopy green LAI values ( gt 2; typical of dense shrubs and trees), NDVI was relatively insensitive to changes in canopy structure. Compared to SR, NDVI was better correlated with indicators of canopy structure and chemical content, but was equivalent to the logarithm of SR. In agreement with theoretical expectations, both NDVI and SR exhibited near-linear correlations with fractional PAR intercepted by green leaves over a wide range of canopy densities. Maximum daily photosynthetic rates were positively correlated with NDVI and SR in annual grassland and semideciduous shrubs where canopy development and photosynthetic activity were in synchrony. The indices were also correlated with peak springtime canopy photosynthetic rates in evergreens. However, over most of the year, these indices were poor predictors of photosynthetic performance in evergreen species due to seasonal reductions in photosynthetic radiation-use efficiency that occurred without substantial declines in canopy greenness. Our results support the use of these vegetation indices as remote indicators of PAR absorption, and thus potential photosynthetic activity, even in

  9. Winter radiation extinction and reflection in a boreal pine canopy: measurements and modelling

    International Nuclear Information System (INIS)

    Pomeroy, J.W.; Dion, K.

    1996-01-01

    Predicting the rate of snow melt and intercepted snow sublimation in boreal forests requires an understanding of the effects of snow-covered conifers on the exchange of radiant energy. This study examined the amount of intercepted snow on a jack pine canopy in the boreal forest of central Saskatchewan and the shortwave and net radiation exchange with this canopy, to determine the effect of intercepted snow and canopy structure on shortwave radiation reflection and extinction and net radiation attenuation in a boreal forest. The study focused on clear sky conditions, which are common during winter in the continental boreal forest. Intercepted snow was found to have no influence on the clear-sky albedo of the canopy, the extinction of short wave radiation by the canopy or ratio of net radiation at the canopy top to that at the surface snow cover. Because of the low albedo of the snow-covered canopy, net radiation at the canopy top remains positive and a large potential source of energy for sublimation. The canopy albedo declines somewhat as the extinction efficiency of the underlying canopy increases. The extinction efficiency of short wave radiation in the canopy depends on solar angle because of the approximately horizontal orientation of pine branches. For low solar angles above the horizon, the extinction efficiency is quite low and short wave transmissivity through the canopy is relatively high. As the solar angle increases, extinction increases up to angles of about 50°, and then declines. Extinction of short wave radiation in the canopy strongly influences the attenuation of net radiation by the canopy. Short wave radiation that is extinguished by branches is radiated as long wave, partly downwards to the snow cover. The ratio of net radiation at the canopy top to that at the snow cover surface increases with the extinction of short wave radiation and is negative for low extinction efficiencies. For the pine canopy examined, the daily mean net radiation at

  10. Winter Radiation Extinction and Reflection in a Boreal Pine Canopy: Measurements and Modelling

    Science.gov (United States)

    Pomeroy, J. W.; Dion, K.

    1996-12-01

    Predicting the rate of snowmelt and intercepted snow sublimation in boreal forests requires an understanding of the effects of snow-covered conifers on the exchange of radiant energy. This study examined the amount of intercepted snow on a jack pine canopy in the boreal forest of central Saskatchewan and the shortwave and net radiation exchange with this canopy, to determine the effect of intercepted snow and canopy structure on shortwave radiation reflection and extinction and net radiation attenuation in a boreal forest. The study focused on clear sky conditions, which are common during winter in the continental boreal forest. Intercepted snow was found to have no influence on the clear-sky albedo of the canopy, the extinction of short wave radiation by the canopy or ratio of net radiation at the canopy top to that at the surface snow cover. Because of the low albedo of the snow-covered canopy, net radiation at the canopy top remains positive and a large potential source of energy for sublimation. The canopy albedo declines somewhat as the extinction efficiency of the underlying canopy increases. The extinction efficiency of short wave radiation in the canopy depends on solar angle because of the approximately horizontal orientation of pine branches. For low solar angles above the horizon, the extinction efficiency is quite low and short wave transmissivity through the canopy is relatively high. As the solar angle increases, extinction increases up to angles of about 50̂, and then declines. Extinction of short wave radiation in the canopy strongly influences the attenuation of net radiation by the canopy. Short wave radiation that is extinguished by branches is radiated as long wave, partly downwards to the snow cover. The ratio of net radiation at the canopy top to that at the snow cover surface increases with the extinction of short wave radiation and is negative for low extinction efficiencies. For the pine canopy examined, the daily mean net radiation at the

  11. Urban architecture in urban renewal

    DEFF Research Database (Denmark)

    Holmgren, Steen; Svensson, Ole

    2001-01-01

    In Denmark new issues in urban renewal are being introduced. Legislation on urban renewal now demands that residents be invited to take an active part in the development of their urban area. And urban renewal is increasingly taking place in inner suburbs which are recently built, complex...... and without obvious architectural value. These issues raise pertinent questions: what urban architectural problems and qualities exist in the complex, inner suburbs? What differences exist between professionals' and residents' perceptions and assessments of urban architecture? How can a shared language...... of urban architecture be developed? This research project attempts to answer these questions through a discourse on theories and methods and the development of "dialogue methods" by which professionals can learn about residents' perception of the urban architecture of their area, thus achieving a better...

  12. Urban lifestyle and urban biodiversity

    DEFF Research Database (Denmark)

    Petersen, L. K.; Lyytimäki, J.; Normander, B.

    2007-01-01

    This report is concerned with the relations between lifestyles of urban populations on one hand and protection of biodiversity in urban areas on the other. Urban areas are of importance for the general protection of biodiversity. In the surroundings of cities and within urban sprawls there can...... be important habitats and valuable corridors for both common and less common species. At the same time a comprehensive, functional and viable green structure is important for urban populations to whom it serves many functions and offers a whole range of benefits. Urban green structure should serve both...... biodiversity, recreational, educational and other needs. However, uncovered and unsealed space is constantly under pressure for building and infrastructure development in the urban landscape, and the design and usages of urban green structure is a matter of differing interests and expectations. Integrating...

  13. Canopy Measurements with a Small Unmanned Aerial System

    Science.gov (United States)

    Peschel, J.

    2015-12-01

    This work discusses the use of a small unmanned aerial system (UAS) for the remote placement of wireless environmental sensors in tree canopies. Remote presence applications occur when one or more humans use a robot to project themselves into an environment in order to complete an inaccessible or time-critical mission. The more difficult problem of physical object manipulation goes one step further by incorporating physical-based interaction, in additional to visualization. Forested environments present especially unique challenges for small UAS versus similar domains (e.g., disaster response, inspection of critical infrastructure) due to the navigation and interaction required with dense tree canopies. This work describes two field investigations that inform: i) the type of physical object manipulation and visualization necessary for sensor placement (ventral, frontal, dorsal), ii) the necessary display form (hybrid) for piloting and sensor placement, and iii) visual feedback mechanisms useful for handling human-robot team role conflicts.

  14. Strengthening the Ubuntu social canopy after the Afrophobic attacks

    Directory of Open Access Journals (Sweden)

    Zorodzai Dube

    2016-03-01

    Full Text Available In view of the aftermath of the Afrophobic attacks in South Africa, this study regards Paul�s emphasis concerning common humanity and morality as a possible lacuna towards strengthening Ubuntu. Paul taught that both the Jews and the Gentiles have their common ancestor � Adam, and that good morality is a better identity marker than ethnicity. In view of the aftermath of the Afrophobic attacks in South Africa, this study suggests that similar arguments can be used to amend the Ubuntu social canopy.Intradisciplinary and/or interdisciplinary implications: This study is interdisciplinary in nature in that it uses perspectives from social sciences to seek solutions towards a more inclusive communityKeywords: Afrophobia; Xenophobia; Ubuntu; Social Canopy; Christ-like Anthropology

  15. Spatial connectivity of urban clusters and regional climate effects

    Science.gov (United States)

    Jia, G.; Hu, Y.; Xu, R.

    2015-12-01

    Rapid urbanization in East Asia in past three decades is considered as a remarkable process that featured with expansion of urban clusters and tightened linkages within and among clusters. Such process could lead to much larger scale climate effects, and could even contribute to sub-regional and regional climate change. In large area of urban clusters with significant expansion of built-up in relatively short period, local urban heat islands could contribute to sub-regional climate forcing. Here we use visible/near infrared and thermal infrared satellite data to estimate multiple scale structure of urban clusters, and to assess effects of urban heat islands at local and regional scales in East Asia. Our estimates of urban extent were greater than previously reported in most global datasets. Strong spatial connection and internal expansion were found in major urban clusters in past 30 years, and was accelerated in past 10 years. Many city clusters were merging into each other, with gradual blurring boundaries and disappearing of gaps among member cities. Cities and towns were more connected with roads and commercial corridors, while wildland and urban greens became more isolated as patches among built-up areas. We would argue that in many cases in this region, urban clusters are no longer "islands", they are now "seas" in term of climate related urban canopy. Urban greens such as parks and plantation were long recognized for their cooling effects that buffer the urban heat island effect, however, such cooling effects tend to be weakened as their patches became smaller and isolated, and over dominated by urban surfaces. There were significant positive relations between urban fraction and urban heat island effects as demonstrated by VNIR and TIR data from multiple satellites. Those new estimates are expected to effectively improve climate simulation for better understanding the impacts of inter-connected urban clusters on air temperature, precipitation, wind speed

  16. Variation in crown light utilization characteristics among tropical canopy trees.

    Science.gov (United States)

    Kitajima, Kaoru; Mulkey, Stephen S; Wright, S Joseph

    2005-02-01

    Light extinction through crowns of canopy trees determines light availability at lower levels within forests. The goal of this paper is the exploration of foliage distribution and light extinction in crowns of five canopy tree species in relation to their shoot architecture, leaf traits (mean leaf angle, life span, photosynthetic characteristics) and successional status (from pioneers to persistent). Light extinction was examined at three hierarchical levels of foliage organization, the whole crown, the outermost canopy and the individual shoots, in a tropical moist forest with direct canopy access with a tower crane. Photon flux density and cumulative leaf area index (LAI) were measured at intervals of 0.25-1 m along multiple vertical transects through three to five mature tree crowns of each species to estimate light extinction coefficients (K). Cecropia longipes, a pioneer species with the shortest leaf life span, had crown LAI <0.5. Among the remaining four species, crown LAI ranged from 2 to 8, and species with orthotropic terminal shoots exhibited lower light extinction coefficients (0.35) than those with plagiotropic shoots (0.53-0.80). Within each type, later successional species exhibited greater maximum LAI and total light extinction. A dense layer of leaves at the outermost crown of a late successional species resulted in an average light extinction of 61% within 0.5 m from the surface. In late successional species, leaf position within individual shoots does not predict the light availability at the individual leaf surface, which may explain their slow decline of photosynthetic capacity with leaf age and weak differentiation of sun and shade leaves. Later-successional tree crowns, especially those with orthotropic branches, exhibit lower light extinction coefficients, but greater total LAI and total light extinction, which contribute to their efficient use of light and competitive dominance.

  17. Affective Urbanism

    DEFF Research Database (Denmark)

    Samson, Kristine

    Urban design and architecture are increasingly used as material and affective strategies for setting the scene, for manipulation and the production of urban life: The orchestration of atmospheres, the framing and staging of urban actions, the programming for contemplation, involvement, play......, experience and consumption are all strategic design tools applied by planners and architects. Whereas urban design in former modernist planning served merely functional or political means, urban design has increasingly become an aesthetical mediator of ideologies embedded in the urban field of life forces....... Under these circumstances affective aesthetics operate strategically within the urban field of interests, capital flows and desires of the social. This ‘affective urbanism’ (Anderson & Holden 2008) is linked to a society influenced by new kinds of information flows, where culture is mediated and enacted...

  18. Participatory urbanism

    DEFF Research Database (Denmark)

    Ejsing-Duun, Stine

    2016-01-01

    Urban areas are planned structures that cannot easily be changed. Urban areas do however still afford physical spaces for various types of leisure expression and participation, from street art to parkour and from urban gaming to artistic happenings. Thus, while citizens who inhabit the urban areas...... cannot directly influence their structures, they can influence their contours through such leisure practices. In this chapter focus will be on how citizens’ engagement in locative leisure activities may allow them to co-create urban space. This participatory urbanism is a form of everyday democracy......, which includes awareness of the structures in which we live as well as participation in the public sphere. Locative media projects shape events which seek to address everyday democracy. Specifically engaging in locative media projects can help create leisure experiences in the urban landscape that allow...

  19. Modelling bulk canopy resistance from climatic variables for evapotranspiration estimation

    Science.gov (United States)

    Perez, P. J.; Martinez-Cob, A.; Lecina, S.; Castellvi, F.; Villalobos, F. J.

    2003-04-01

    Evapotranspiration is a component of the hydrological cycle whose accurate computation is needed for an adequate management of water resources. In particular, a high level of accuracy in crop evapotranspiration estimation can represent an important saving of economical and water resources at planning and management of irrigated areas. In the evapotranspiration process, bulk canopy resistance (r_c) is a primary factor and its correct modelling remains an important problem in the Penman-Monteith (PM) method, not only for tall crops but also for medium height and short crops under water stress. In this work, an alternative approach for modelling canopy resistance is presented against th PM method with constant canopy resistance. Variable r_c values are computed as function of a climatic resistance and compared with other two models, Katerji and Perrier and Todorovic. Hourly evapotranspiration values (ET_o) over grass were obtained with a weighing lysimeter and an eddy covariance system at the Ebro and Guadalquivir valleys (Spain) respectively. The main objective is to evaluate whether the use of variable rather than fixed r_c values, would improve the ET_o estimates obtained by applying the PM equation under the semiarid conditions of the two sites, where evaporative demand is high particularly during summer.

  20. Thermal constraints on foraging of tropical canopy ants.

    Science.gov (United States)

    Spicer, Michelle Elise; Stark, Alyssa Y; Adams, Benjamin J; Kneale, Riley; Kaspari, Michael; Yanoviak, Stephen P

    2017-04-01

    Small cursorial ectotherms risk overheating when foraging in the tropical forest canopy, where the surfaces of unshaded tree branches commonly exceed 50 °C. We quantified the heating and subsequent cooling rates of 11 common canopy ant species from Panama and tested the hypothesis that ant workers stop foraging at temperatures consistent with the prevention of overheating. We created hot experimental "sunflecks" on existing foraging trails of four ant species from different clades and spanning a broad range of body size, heating rate, and critical thermal maxima (CT max ). Different ant species exhibited very different heating rates in the lab, and these differences did not follow trends predicted by body size alone. Experiments with ant models showed that heating rates are strongly affected by color in addition to body size. Foraging workers of all species showed strong responses to heating and consistently abandoned focal sites between 36 and 44 °C. Atta colombica and Azteca trigona workers resumed foraging shortly after heat was removed, but Cephalotes atratus and Dolichoderus bispinosus workers continued to avoid the heated patch even after >5 min of cooling. Large foraging ants (C. atratus) responded slowly to developing thermal extremes, whereas small ants (A. trigona) evacuated sunflecks relatively quickly, and at lower estimated body temperatures than when revisiting previously heated patches. The results of this study provide the first field-based insight into how foraging ants respond behaviorally to the heterogeneous thermal landscape of the tropical forest canopy.

  1. Assessing canopy performance using carbonyl sulfide (COS) measurements.

    Science.gov (United States)

    Yang, Fulin; Qubaja, Rafat; Tatarinov, Fyodor; Rotenberg, Eyal; Yakir, Dan

    2018-03-25

    Carbonyl sulfide (COS) is a tracer of ecosystem photosynthesis that can advance carbon cycle research from leaf to global scales; however, a range of newly reported caveats related to sink/source strength of various ecosystem components hinder its application. Using comprehensive eddy-covariance and chamber measurements, we systematically measure ecosystem contributions from leaf, stem, soil and litter and were able to close the ecosystem COS budget. The relative contributions of non-photosynthetic components to the overall canopy-scale flux are relatively small (~4% during peak activity season) and can be independently estimated based on their responses to temperature and humidity. Converting COS to photosynthetic CO 2 fluxes based on the leaf relative uptake of COS/CO 2 , faces challenges due to observed daily and seasonal changes. Yet, this ratio converges around a constant value (~1.6), and the variations, dominated by light intensity, were found unimportant on a flux-weighted daily time-scale, indicating a mean ratio of daytime gross-to-net primary productivity of ~2 in our ecosystem. The seasonal changes in the leaf relative uptake ratio may indicate a reduction in mesophyll conductance in winter, and COS-derived canopy conductance permitted canopy temperature estimate consistent with radiative skin temperature. These results support the feasibility of using COS as a powerful and much-needed means of assessing ecosystem function and its response to change. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

  2. Quantitative comparison of canopy conductance models using a Bayesian approach

    Science.gov (United States)

    Samanta, S.; Clayton, M. K.; Mackay, D. S.; Kruger, E. L.; Ewers, B. E.

    2008-09-01

    A quantitative model comparison methodology based on deviance information criterion, a Bayesian measure of the trade-off between model complexity and goodness of fit, is developed and demonstrated by comparing semiempirical transpiration models. This methodology accounts for parameter and prediction uncertainties associated with such models and facilitates objective selection of the simplest model, out of available alternatives, which does not significantly compromise the ability to accurately model observations. We use this methodology to compare various Jarvis canopy conductance model configurations, embedded within a larger transpiration model, against canopy transpiration measured by sap flux. The results indicate that descriptions of the dependence of stomatal conductance on vapor pressure deficit, photosynthetic radiation, and temperature, as well as the gradual variation in canopy conductance through the season are essential in the transpiration model. Use of soil moisture was moderately significant, but only when used with a hyperbolic vapor pressure deficit relationship. Subtle differences in model quality could be clearly associated with small structural changes through the use of this methodology. The results also indicate that increments in model complexity are not always accompanied by improvements in model quality and that such improvements are conditional on model structure. Possible application of this methodology to compare complex semiempirical models of natural systems in general is also discussed.

  3. Height increment of understorey Norway spruces under different tree canopies

    Directory of Open Access Journals (Sweden)

    Olavi Laiho

    2014-02-01

    Full Text Available Background Stands having advance regeneration of spruce are logical places to start continuous cover forestry (CCF in fertile and mesic boreal forests. However, the development of advance regeneration is poorly known. Methods This study used regression analysis to model the height increment of spruce understorey as a function of seedling height, site characteristics and canopy structure. Results An admixture of pine and birch in the main canopy improves the height increment of understorey. When the stand basal area is 20 m2ha-1 height increment is twice as fast under pine and birch canopies, as compared to spruce. Height increment of understorey spruce increases with increasing seedling height. Between-stand and within-stand residual variation in the height increment of understorey spruces is high. The increment of 1/6 fastest-growing seedlings is at least 50% greater than the average. Conclusions The results of this study help forest managers to regulate the density and species composition of the stand, so as to obtain a sufficient height development of the understorey. In pure and almost pure spruce stands, the stand basal area should be low for a good height increment of the understorey.

  4. A canopy trimming experiment in Puerto Rico: the response of litter invertebrate communities to canopy loss and debris deposition in a tropical forest subject to hurricanes

    Science.gov (United States)

    Barbara A. Richardson; Michael J. Richardson; Grizelle Gonzalez; Aaron B. Shiels; Diane S. Srivastava

    2010-01-01

    Hurricanes cause canopy removal and deposition of pulses of litter to the forest floor. A Canopy Trimming Experiment (CTE) was designed to decouple these two factors, and to investigate the separate abiotic and biotic consequences of hurricane-type damage and monitor recovery processes. As part of this experiment, effects on forest floor invertebrate communities were...

  5. Stallion spermatozoa selected by single layer centrifugation are capable of fertilization after storage for up to 96 h at 6°C prior to artificial insemination

    Science.gov (United States)

    2012-01-01

    Background One of the challenges faced by equine breeders is ensuring delivery of good quality semen doses for artificial insemination when the mare is due to ovulate. Single Layer Centrifugation (SLC) has been shown to select morphologically normal spermatozoa with intact chromatin and good progressive motility from the rest of the ejaculate, and to prolong the life of these selected spermatozoa in vitro. The objective of the present study was a proof of concept, to determine whether fertilizing ability was retained in SLC-selected spermatozoa during prolonged storage. Findings Sixteen mares were inseminated with SLC-selected sperm doses that had been cooled and stored at 6°C for 48 h, 72 h or 96 h. Embryos were identified in 11 mares by ultrasound examination 16–18 days after presumed ovulation. Conclusion SLC-selected stallion spermatozoa stored for up to 96 h are capable of fertilization. PMID:22788670

  6. Diurnal changes in urban boundary layer environment induced by urban greening

    Science.gov (United States)

    Song, Jiyun; Wang, Zhi-Hua

    2016-11-01

    Urban green infrastructure has been widely used for mitigating adverse environmental problems as well as enhancing urban sustainability of cities worldwide. Here we develop an integrated urban-land-atmosphere modeling framework with the land surface processes parameterized by an advanced urban canopy model and the atmospheric processes parameterized by a single column model. The model is then applied to simulate a variety of forms of green infrastructure, including urban lawns, shade trees, green and cool roofs, and their impact on environmental changes in the total urban boundary layer (UBL) for a stereotypical desert city, viz. Phoenix, Arizona. It was found that green roofs have a relatively uniform cooling effect proportional to their areal coverage. In particular, a reduction of UBL temperature of 0.3 °C and 0.2 °C per 10% increase of green roof coverage was observed at daytime and nighttime, respectively. In contrast, the effect of greening of street canyons is constrained by the overall abundance of green infrastructure and the energy available for evapotranspiration. In addition, the increase in urban greening causes boundary-layer height to decrease during daytime but increase at nighttime, leading to different trends of changes in urban air quality throughout a diurnal cycle.

  7. A LIDAR-Based Tree Canopy Characterization under Simulated Uneven Road Condition: Advance in Tree Orchard Canopy Profile Measurement

    Directory of Open Access Journals (Sweden)

    Yue Shen

    2017-01-01

    Full Text Available In real outdoor canopy profile detection, the accuracy of a LIDAR scanner to measure canopy structure is affected by a potentially uneven road condition. The level of error associated with attitude angles from undulations in the ground surface can be reduced by developing appropriate correction algorithm. This paper proposes an offline attitude angle offset correction algorithm based on a 3D affine coordinate transformation. The validity of the correction algorithm is verified by conducting an indoor experiment. The experiment was conducted on an especially designed canopy profile measurement platform. During the experiment, an artificial tree and a tree-shaped carved board were continuously scanned at constant laser scanner travel speed and detection distances under simulated bumpy road conditions. Acquired LIDAR laser scanner raw data was processed offline by exceptionally developed MATLAB program. The obtained results before and after correction method show that the single attitude angle offset correction method is able to correct the distorted data points in tree-shaped carved board profile measurement, with a relative error of 5%, while the compound attitude angle offset correction method is effective to reduce the error associated with compound attitude angle deviation from the ideal scanner pose, with relative error of 7%.

  8. Modeling canopy-induced turbulence in the Earth system: a unified parameterization of turbulent exchange within plant canopies and the roughness sublayer (CLM-ml v0)

    Science.gov (United States)

    Bonan, Gordon B.; Patton, Edward G.; Harman, Ian N.; Oleson, Keith W.; Finnigan, John J.; Lu, Yaqiong; Burakowski, Elizabeth A.

    2018-04-01

    Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multilayer canopy model (CLM-ml v0) to test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at seven forest, two grassland, and three cropland AmeriFlux sites over a range of canopy heights, leaf area indexes, and climates. CLM4.5 has pronounced biases during summer months at forest sites in midday latent heat flux, sensible heat flux, gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. Advances in modeling stomatal conductance and canopy physiology beyond what is in CLM4.5 substantially improve model performance at the forest sites. The signature of the roughness sublayer is most evident in nighttime friction velocity and the diurnal cycle of radiative temperature, but is also seen in sensible heat flux. Within-canopy temperature profiles are markedly different compared with profiles obtained using Monin-Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these canopies. The multilayer canopy with the roughness sublayer turbulence improves simulations compared with CLM4.5 while also advancing the theoretical basis for surface flux parameterizations.

  9. A note on estimating urban roof runoff with a forest evaporation model

    NARCIS (Netherlands)

    Gash, J.H.C.; Rosier, P.T.W.; Ragab, R.

    2008-01-01

    A model developed for estimating the evaporation of rainfall intercepted by forest canopies is applied to estimate measurements of the average runoff from the roofs of six houses made in a previous study of hydrological processes in an urban environment. The model is applied using values of the mean

  10. Urbane Projekter

    DEFF Research Database (Denmark)

    Andersen, Anne Juel

    2013-01-01

    This PhD thesis is about urban projects as part of strategic urban transformation. It is the result of a collaboration between Aalborg Municipality, Technical and Environmental Department, and Aalborg University, Department of Architecture, Design and Media Technology. The starting point has been...... a deep interest in the constant change and development of the city and a similar won- der towards the changing rationales and discourses present in the urban projects undertaken. The thesis focuses on the changing urban planning perspectives on the city and on urban projects as complex networks...... and answers questions about HOW? Finally, the discourse is said to express the rationality which govern the transformation and answer thus questions about WHY? The research questions are: 1.How can strategic urban projects be understood in a theoretical framework consisting of place, discourse and planning? 2...

  11. Urban interventions

    DEFF Research Database (Denmark)

    Pinder, David

    2008-01-01

    Challenging perspectives on the urban question have arisen in recent years from beyond academic realms through the work of artists and cultural practitioners. Often in dialogue with urban theory and political activism, and employing a range of tactical practices, they have engaged critically...... with cities and with the spatialities of everyday urban life. They are typically concerned less with representing political issues than with intervening in urban spaces so as to question, refunction and contest prevailing norms and ideologies, and to create new meanings, experiences, understandings......, relationships and situations. Such interventionist practices may rarely be seen as part of the traditional purview of urban studies. Yet in asserting their significance here, this essay argues that growing dialogues across and between urban and spatial theory, and artistic and cultural practice, have...

  12. Photosynthetic response of two seaweed species along an urban pollution gradient: evidence of selection of pollution-tolerant species.

    Science.gov (United States)

    Scherner, F; Bonomi Barufi, J; Horta, P A

    2012-11-01

    Urbanization leads to the expansion of ephemeral seaweed species and the decline of important perennial, canopy-forming seaweed species. Understanding the mechanisms that lead to these changes is a current challenge. In the present study, laboratory assays and field transplantations were performed with two seaweed species: the perennial, canopy-forming seaweed Sargassum stenophyllum and the ephemeral seaweed Ulva lactuca. Photosynthetic efficiency was assessed using modulated chlorophyll fluorometry. Brief exposure to urban waters does not appear to be a major stressor to the photosynthetic efficiency of either species. However, after 26 days of transplantation in urban waters, S. stenophyllum declined, whereas U. lactuca had enhanced photosynthetic efficiency. This difference reflects their divergent abilities to regulate the energy distribution at the PSII and shows that urban stressors alter these mechanisms. Our results provide evidence of the physiological causes for the decline of Sargassum species and the expansion of Ulva species in impacted urban areas. Copyright © 2012 Elsevier Ltd. All rights reserved.

  13. Microclimate in the vertical profile of wheat, rape and maize canopies

    Directory of Open Access Journals (Sweden)

    Zdeněk Krédl

    2012-01-01

    Full Text Available The differences of air temperature and relative air humidity in wheat, rape and maize canopies at three heights (ground level, effective canopy height and 2 meters above the soil surface, and their comparison with the temperature values of the nearest standard climatological station at the height of 2 meters were studied. The microclimatic data were obtained at the field trial station of the Mendel University in Brno in the Žabčice municipality (South Moravia in the canopies of winter wheat, winter rape and maize and from the standard climatological station located immediately next to the canopies. It was found, that wheat, rape and maize canopies microclimate differed significantly from those of their surrounding environments. The temperature was usually lower in the ground level and effective height in the wheat and rape stands, air humidity was usually higher in these crops. On the other hand, maize canopies had diverse air temperature values during the studied period.

  14. The theoretical relationship between foliage temperature and canopy resistance in sparse crops

    Science.gov (United States)

    Shuttleworth, W. James; Gurney, Robert J.

    1990-01-01

    One-dimensional, sparse-crop interaction theory is reformulated to allow calculation of the canopy resistance from measurements of foliage temperature. A submodel is introduced to describe eddy diffusion within the canopy which provides a simple, empirical simulation of the reported behavior obtained from a second-order closure model. The sensitivity of the calculated canopy resistance to the parameters and formulas assumed in the model is investigated. The calculation is shown to exhibit a significant but acceptable sensitivity to extreme changes in canopy aerodynamics, and to changes in the surface resistance of the substrate beneath the canopy at high and intermediate values of leaf area index. In very sparse crops changes in the surface resistance of the substrate are shown to contaminate the calculated canopy resistance, tending to amplify the apparent response to changes in water availability. The theory is developed to allow the use of a measurement of substrate temperature as an option to mitigate this contamination.

  15. Abundance of green tree frogs and insects in artificial canopy gaps in a bottomland hardwood forest.

    Energy Technology Data Exchange (ETDEWEB)

    Horn, Scott; Hanula, James L.; Ulyshen, Michael D.; Kilgo, John C.

    2005-01-01

    Horn, Scott, James L. Hanula, Michael D. Ulyshen, and John C. Kilgo. 2005. Abundance of green tree frogs and insects in artificial canopy gaps in a bottomland hardwood forest. Am. Midl. Nat. 153:321-326. Abstract: We found more green tree frogs (Hyla cinerea) in canopy gaps than in closed canopy forest. Of the 331 green tree frogs observed, 88% were in canopy gaps. Likewise, higher numbers and biomasses of insects were captured in the open gap habitat. Flies were the most commonly collected insect group accounting for 54% of the total capture. These data suggest that one reason green tree frogs were more abundant in canopy gaps was the increased availability of prey and that small canopy gaps provide early successional habitats that are beneficial to green tree frog populations.

  16. Impact of Vertical Canopy Position on Leaf Spectral Properties and Traits across Multiple Species

    Directory of Open Access Journals (Sweden)

    Tawanda W. Gara

    2018-02-01

    Full Text Available Understanding the vertical pattern of leaf traits across plant canopies provide critical information on plant physiology, ecosystem functioning and structure and vegetation response to climate change. However, the impact of vertical canopy position on leaf spectral properties and subsequently leaf traits across the entire spectrum for multiple species is poorly understood. In this study, we examined the ability of leaf optical properties to track variability in leaf traits across the vertical canopy profile using Partial Least Square Discriminatory Analysis (PLS-DA. Leaf spectral measurements together with leaf traits (nitrogen, carbon, chlorophyll, equivalent water thickness and specific leaf area were studied at three vertical canopy positions along the plant stem: lower, middle and upper. We observed that foliar nitrogen (N, chlorophyll (Cab, carbon (C, and equivalent water thickness (EWT were higher in the upper canopy leaves compared with lower shaded leaves, while specific leaf area (SLA increased from upper to lower canopy leaves. We found that leaf spectral reflectance significantly (P ≤ 0.05 shifted to longer wavelengths in the ‘red edge’ spectrum (685–701 nm in the order of lower > middle > upper for the pooled dataset. We report that spectral bands that are influential in the discrimination of leaf samples into the three groups of canopy position, based on the PLS-DA variable importance projection (VIP score, match with wavelength regions of foliar traits observed to vary across the canopy vertical profile. This observation demonstrated that both leaf traits and leaf reflectance co-vary across the vertical canopy profile in multiple species. We conclude that canopy vertical position has a significant impact on leaf spectral properties of an individual plant’s traits, and this finding holds for multiple species. These findings have important implications on field sampling protocols, upscaling leaf traits to canopy level

  17. Co-optimal distribution of leaf nitrogen and hydraulic conductance in plant canopies.

    Science.gov (United States)

    Peltoniemi, Mikko S; Duursma, Remko A; Medlyn, Belinda E

    2012-05-01

    Leaf properties vary significantly within plant canopies, due to the strong gradient in light availability through the canopy, and the need for plants to use resources efficiently. At high light, photosynthesis is maximized when leaves have a high nitrogen content and water supply, whereas at low light leaves have a lower requirement for both nitrogen and water. Studies of the distribution of leaf nitrogen (N) within canopies have shown that, if water supply is ignored, the optimal distribution is that where N is proportional to light, but that the gradient of N in real canopies is shallower than the optimal distribution. We extend this work by considering the optimal co-allocation of nitrogen and water supply within plant canopies. We developed a simple 'toy' two-leaf canopy model and optimized the distribution of N and hydraulic conductance (K) between the two leaves. We asked whether hydraulic constraints to water supply can explain shallow N gradients in canopies. We found that the optimal N distribution within plant canopies is proportional to the light distribution only if hydraulic conductance, K, is also optimally distributed. The optimal distribution of K is that where K and N are both proportional to incident light, such that optimal K is highest to the upper canopy. If the plant is constrained in its ability to construct higher K to sun-exposed leaves, the optimal N distribution does not follow the gradient in light within canopies, but instead follows a shallower gradient. We therefore hypothesize that measured deviations from the predicted optimal distribution of N could be explained by constraints on the distribution of K within canopies. Further empirical research is required on the extent to which plants can construct optimal K distributions, and whether shallow within-canopy N distributions can be explained by sub-optimal K distributions.

  18. The effect of urban growth on landscape-scale restoration for a fire-dependent songbird.

    Science.gov (United States)

    Pickens, Bradley A; Marcus, Jeffrey F; Carpenter, John P; Anderson, Scott; Taillie, Paul J; Collazo, Jaime A

    2017-04-15

    A landscape-scale perspective on restoration ecology has been advocated, but few studies have informed restoration with landscape metrics or addressed broad-scale threats. Threats such as urban growth may affect restoration effectiveness in a landscape context. Here, we studied longleaf pine savanna in the rapidly urbanizing southeastern United States where a habitat-specialist bird, Bachman's sparrow (Peucaea aestivalis), is closely associated with savanna vegetation structure and frequent fire. Our objectives were to construct a species distribution model for Bachman's sparrow, determine the relationship between fire and urbanization, quantify the urban growth effect (2010-2090), identify potential restoration areas, and determine the interaction between restoration potential and urban growth by 2050. Number of patches, patch size, and isolation metrics were used to evaluate scenarios. The species distribution model was 88% accurate and emphasized multiscale canopy cover characteristics, fire, and percent habitat. Fires were less common urban areas, and this fire suppression effect exacerbated urban growth effects. For restoration scenarios, canopy cover reduction by 30% resulted in nearly double the amount of habitat compared to the prescribed fire scenario; canopy cover reduction resulted in larger patch sizes and less patch isolation compared to current conditions. The effect of urban growth on restoration scenarios was unequal. Seventy-four percent of restoration areas from the prescribed fire scenario overlapped with projected urban growth, whereas the canopy cover reduction scenario only overlapped by 9%. We emphasize the benefits of simultaneously considering the effects of urban growth and landscape-scale restoration potential to promote a landscape with greater patch sizes and less isolation. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  19. Making direct use of canopy profiles in vegetation - atmosphere coupling

    Science.gov (United States)

    Ryder, James; Polcher, Jan; Peylin, Philippe; Ottlé, Catherine; Chen, Yiying; van Gorsel, Eva; Haverd, Vanessa; McGrath, Matthew; Naudts, Kim; Otto, Juliane; Valade, Aude; Luyssaert, Sebastiaan

    2015-04-01

    Most coupled land-surface regional models use the 'big-leaf' approach for simulating the sensible and latent heat fluxes of different vegetation types. However, there has been a progression in the types of questions being asked of these models, such as the consequences of land-use change or the behaviour of BVOCs and aerosol. In addition, recent years has seen growth in the availability of in-canopy datasets across a broaded range of species, with which to calibrate these simulations. Hence, there is now an argument for transferring some of the techniques and processes previously used in local, site-based land surface models to the land surface components of models which operate on a regional or even global scale. We describe here the development and evaluation of a vertical canopy energy budget model (Ryder, J et al., 2014) that can be coupled to an atmospheric model such as LMDz. Significantly, the model preserves the implicit coupling of the land-surface to atmosphere interface, which means that run-time efficiences are preserved. This is acheived by means of an interface based on the approach of Polcher et al. (1998) and Best et al. (2004), but newly developed for a canopy column. The model makes use of techniques from site-based models, such as the calculation of vertical turbulence statistics using a second-order closure model (Massman & Weil, 1999), and the distribution of long-wave and short-wave radiation over the profile, the latter using an innovate multilayer albedo scheme (McGrath et al., in prep.). Complete profiles of atmospheric temperature and specific humidity are now calculated, in order to simulate sensible and latent heat fluxes, as well as the leaf temperature at each level in the model. The model is shown to perform stably, and reproduces well flux measurements at an initial test site, across a time period of several days, or over the course of a year. Further applications of the model might be to simulate mixed canopies, the light

  20. Tree Death Not Resulting in Gap Creation: An Investigation of Canopy Dynamics of Northern Temperate Deciduous Forests

    Directory of Open Access Journals (Sweden)

    Jean-Francois Senécal

    2018-01-01

    Full Text Available Several decades of research have shown that canopy gaps drive tree renewal processes in the temperate deciduous forest biome. In the literature, canopy gaps are usually defined as canopy openings that are created by partial or total tree death of one or more canopy trees. In this study, we investigate linkages between tree damage mechanisms and the formation or not of new canopy gaps in northern temperate deciduous forests. We studied height loss processes in unmanaged and managed forests recovering from partial cutting with multi-temporal airborne Lidar data. The Lidar dataset was used to detect areas where canopy height reduction occurred, which were then field-studied to identify the tree damage mechanisms implicated. We also sampled the density of leaf material along transects to characterize canopy structure. We used the dataset of the canopy height reduction areas in a multi-model inference analysis to determine whether canopy structures or tree damage mechanisms most influenced the creation of new canopy gaps within canopy height reduction areas. According to our model, new canopy gaps are created mainly when canopy damage enlarges existing gaps or when height is reduced over areas without an already established dense sub-canopy tree layer.