8,928 research outputs found

    Unravelling collembolan life belowground: Stoichiometry, metabolism and release of carbon and nitrogen

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    This thesis investigated carbon and nitrogen dynamics of soil dwelling Collembola by using direct measurements and stable isotope additions. In an isotope change experiment, collembolans exchanged between 6 and 10% of carbon and nitrogen in their body tissue per day to metabolism and between 0.5 and 2% to reproduction. When collembolans on low and high protein diets were compared, animals on the low protein quality depleted their tissue 15N values relative to those on high quality diet indicating that the nitrogen turnover decreased on the low protein quality diet. In a wheat microcosm investigating source contributions from soil, roots and isotope labelled green manure the mixing model analysis indicated that photosynthate (root derived C) was the main carbon source for collembolans (54–79% of total C) indicating that the rhizosphere channel is very important for collembolans in addition to the detritus based channel

    Compressed Sensing Based Direct Conversion Receiver With Interference Reducing Sampling

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    This paper describes a direct conversion receiver applying compressed sensing with the objective to relax the analog filtering requirements seen in the traditional architecture. The analog filter is cumbersome in an \gls{IC} design and relaxing its requirements is an advantage in terms of die area, performance and robustness of the receiver. The objective is met by a selection of sampling pattern matched to the prior knowledge of the frequency placement of the desired and interfering signals. A simple numerical example demonstrates the principle. The work is part of an ongoing research effort and the different project phases are explained.Comment: 3 pages, 5 figures, submitted to IEEE International Conference On Sensing Communication and Networking 2014 (poster

    Charting the Midwest: An Inventory and Analysis of Greenhouse Gas Emissions in America's Heartland

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    Presents a comprehensive overview of the Midwest's role in global climate change as a major emitter of greenhouse gases in both national and international terms. Analyzes emissions data, trends, and drivers by region, state, economic sector, and gas

    Contracts in the Salmon Aquaculture Industry: An Analysis of Norwegian Salmon Exports

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    Sales and distribution innovations have increased productivity in the salmon aquaculture industry. In this article, we investigate the use of fixed price contracts for Norwegian salmon exports to France based on all export transactions between the two countries. Our analysis shows that almost 25% of these exports were traded using fixed price contracts and contract prices were renegotiated at different intervals, including as infrequently as once a year. Some contracts allow the contracting parties to adjust contract prices when the export price moves significantly. Benchmark analysis, which shows a marginal 0.5% difference between average unit revenue for the year from spot sales relative to contract sales, indicates that contracts primarily change revenue time profiles. The use of contracts creates a wedge between salmon export prices and spot prices in periods of price volatility, which in turn reduces price transmission.Contracts, salmon aquaculture, International Relations/Trade, Productivity Analysis, Research Methods/ Statistical Methods, L14, Q22,

    Model-Based Calibration of Filter Imperfections in the Random Demodulator for Compressive Sensing

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    The random demodulator is a recent compressive sensing architecture providing efficient sub-Nyquist sampling of sparse band-limited signals. The compressive sensing paradigm requires an accurate model of the analog front-end to enable correct signal reconstruction in the digital domain. In practice, hardware devices such as filters deviate from their desired design behavior due to component variations. Existing reconstruction algorithms are sensitive to such deviations, which fall into the more general category of measurement matrix perturbations. This paper proposes a model-based technique that aims to calibrate filter model mismatches to facilitate improved signal reconstruction quality. The mismatch is considered to be an additive error in the discretized impulse response. We identify the error by sampling a known calibrating signal, enabling least-squares estimation of the impulse response error. The error estimate and the known system model are used to calibrate the measurement matrix. Numerical analysis demonstrates the effectiveness of the calibration method even for highly deviating low-pass filter responses. The proposed method performance is also compared to a state of the art method based on discrete Fourier transform trigonometric interpolation.Comment: 10 pages, 8 figures, submitted to IEEE Transactions on Signal Processin

    Old Metal-rich Globular Cluster Populations: Peak Color and Peak Metallicity Trends with Mass of Host Spheroids

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    We address the problem of the factors contributing to a peak color trend of old metal-rich globular cluster (MRGC) populations with mass of their hosts, early-type galaxies and spheroidal subsystems of spiral ones (spheroids). The color-mass trend is often converted to a metallicity-mass trend under the assumption that age effects are small or negligible. While direct estimates of the ages of MRGC populations neither can rule out nor reliably support the populations' age trend, key data on timing of the formation of spheroids and other indirect evidence imply it in the sense: the more massive spheroid the older on average its MRGC population. We show that the contribution of an allowable age trend of the MRGC populations to their peak color trend can achieve up to ~50 % or so. In this event the comparable value of the color trend, ~30 %, is due to alpha-element ratio systematic variations of the order of Delta[alpha/Fe] ~ 0.1 to 0.2 dex because of a correlation between the [alpha/Fe] ratios and age. Hence a systematic variation of exactly [Fe/H] ratios may turn out to be less significant among the contributors, and its range many times lower, i.e. of the order of Delta[Fe/H] ~ 0.1 or even none, than the corresponding range deduced by assuming no age trend.Comment: 5 pages, 1 figure, accepted for publication in Astronomische Nachrichte

    Exploratory modeling: Extracting causality from complexity

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    On 22 May 2011 a massive tornado tore through Joplin, Mo., killing 158 people. With winds blowing faster than 200 miles per hour, the tornado was the most deadly in the United States since modern record keeping began in the 1950s. ©2014. American Geophysical Union. All Rights Reserved

    Dual-labelled (13C/15N) green manure to differentiate between plant uptake of organic and inorganic N

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    Experimental data is still lacking for determining whether plant uptake of organic nitrogen in agricultural soils contributes substantially to the total N uptake. Pulseinjection studies with dual-labelled amino acids have confirmed that non-mycorrhizal crops possess the capacity to take up organic N but failed to quantify the uptake relative to total N uptake

    Federal Regulation of Strip Mining

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