23,032 research outputs found
The role of governance in agricultural expansion and intensification: a global study of arable agriculture
In this research we studied empirical relationships between agricultural production dynamics and six quantitative World Bank governance indicators for 173 countries between 1975 and 2007. It is hypothesized that in countries with lower quality of governance, agricultural production increases are more likely to be achieved by area expansions than by increases in yields. We distinguished four groups of countries: those with both area and yield increases; those with increasing yields but decreasing area; those with decreasing yields but a growing area; and those with both declines in yields and area. We analyzed differences between these four groups, and also analyzed governance-production relationships within these groups. On average, quality of governance is low in countries with both area and yield increases and high in countries with increasing yields but decreasing area. Countries with declining yields were too few in number to allow for quantitative analyses. The analysis of governance-production relationships within the four groups suggests that countries with a lower quality of governance are more inclined to achieve production increases by expanding agricultural area rather than increasing yields. Additional explanatory value of governance indicators to agricultural production dynamics is generally small, but nevertheless significant in most cases. Our results suggest that, in order for agricultural production to increase without excessive expansions of agricultural area, governance issues should be resolve
Strong coupling constant from bottomonium fine structure
From a fit to the experimental data on the fine structure, the
two-loop coupling constant is extracted. For the 1P state the fitted value is
at the scale GeV, which corresponds to the QCD constant MeV (n_f = 4) and \alpha_s(\mu_2) = 0.40 \pm 0.02(exp)\pm 0.02(th)\mu_2 = 1.02 \pm 0.2\alpha_s(1.0) \approx 0.40\alpha_s\alpha_s$ are found to be about 15%.Comment: 18 pages LaTe
The leptonic widths of high -resonances in unitary coupled-channel model
The leptonic widths of high -resonances are calculated in a
coupled-channel model with unitary inelasticity, where analytical expressions
for mixing angles between (n+1)\,^3S_1 and n\,^3D_1 states and
probabilities of the component are derived. Since these factors
depend on energy (mass), different values of mixing angles
and ,
, and are obtained. It gives
the leptonic widths ~keV,
~keV in good agreement with
experiment. For the leptonic width
~keV is calculated, while for the missing
resonance we predict ~MeV and
~keV.Comment: 10 pages, 6 references corrected, some new material adde
Higher excitations of the and mesons
The masses of higher and excitations are shown to decrease
due to the string contribution, originating from the rotation of the QCD string
itself: it lowers the masses by 45 MeV for and by 65 MeV for . An additional decrease MeV takes place if the current mass
of the light (strange) quark is used in a relativistic model. For
and the calculated masses agree with the
experimental values for and , and the masses of
, , , and are in
agreement with the new BaBar data. For the yet undiscovered resonances we
predict the masses MeV, MeV,
MeV, and MeV. We show that
for the states with and () are almost
completely unmixed (), which implies that the mixing
angles between the states with S=1 and S=0 () are for L=2 and for L=3.Comment: 22 pages, no figures, 4 tables Two references and corresponding
discussion adde
A rapid transition from ice covered CO2–rich waters to a biologically mediated CO2 sink in the eastern Weddell Gyre
Circumpolar Deep Water (CDW), locally called Warm Deep Water (WDW), enters the Weddell Gyre in the southeast, roughly at 25° E to 30° E. In December 2002 and January 2003 we studied the effect of entrainment of WDW on the fugacity of carbon dioxide (fCO2) and dissolved inorganic carbon (DIC) in Weddell Sea surface waters. Ultimately the fCO2 difference across the sea surface drives air-sea fluxes of CO2. Deep CTD sections and surface transects of fCO2 were made along the Prime Meridian, a northwest-southeast section, and along 17° E to 23° E during cruise ANT XX/2 on FS Polarstern. Upward movement and entrainment of WDW into the winter mixed layer had significantly increased DIC and fCO2 below the sea ice along 0° W and 17° E to 23° E, notably in the southern Weddell Gyre. Nonetheless, the ice cover largely prevented outgassing of CO2 to the atmosphere. During and upon melting of the ice, biological activity rapidly reduced surface water fCO2 by up to 100 µatm, thus creating a sink for atmospheric CO2. Despite the tendency of the surfacing WDW to cause CO2 supersaturation, the Weddell Gyre may well be a CO2 sink on an annual basis due to this effective mechanism involving ice cover and ensuing biological fCO2 reduction. Dissolution of calcium carbonate (CaCO3) in melting sea ice may play a minor role in this rapid reduction of surface water fCO2
Climate and Yield in a closed greenhouse
The so-called closed greenhouse (closed ventilation windows) is a recent innovation in Dutch greenhouse industry. The technical concept consists of a heat pump, underground (aquifer) seasonal energy storage as well as daytime storage, air treatment units with heat exchangers, and air distribution ducts. Savings of up to 30% in fossil fuel and production increases by up to 20%, mainly because of the continuously high CO2 concentration, have been reported. Economic feasibility of this innovative greenhouse highly depends on the yield increase that can be obtained. In this simulation study the effects of greenhouse climate on tomato yield in a closed greenhouse are presented. The explanatory model INTKAM was used, which has several submodels e.g. for light interception, leaf photosynthesis and biomass partitioning. The closed greenhouse offers possibilities for combinations of light, temperature, air humidity and CO2 concentration that are impossible in a conventional greenhouse. At high CO2 concentration and high light intensity, leaf photosynthesis shows a more narrow optimum for temperature than at high CO2 and moderate light intensity. However, the response of crop photosynthesis to temperature has a much broader optimum than that of leaf photosynthesis. Besides photosynthesis, temperature also influences aspects like partitioning, leaf area development and fruit development. Yield potential reduces at temperatures above 26°C, with fruit set being one of the first processes that is negatively influenced by supra-optimal temperatures. Based on actual climatic conditions in a conventional and a closed greenhouse (same crop management) measured during two years, INTKAM predicts an increase in yield by about 17%. Hence, in a closed greenhouse a higher stem density can be maintained for obtaining the same average fruit weight (size) as in a conventional greenhouse. In 2005 actual yield increase was similar to the simulated one (16%), but in 2004 only a 9% higher yield was realized, at least partly because of botrytis infection in the closed greenhouse
Numerical Results for the System Noise Temperature of an Aperture Array Tile and Comparison with Measurements
The purpose of this report is to document the noise performance of a complex
beamforming array antenna system and to characterize the recently developed
noise measurement facility called THACO, which was developed at ASTRON. The
receiver system includes the array antenna of strongly coupled 144 TSA
elements, 144 Low Noise Amplifiers (LNAs) (Tmin =35-40K) and the data
recording/storing facilities of the initial test station that allow for
off-line digital beamforming. The primary goal of this study is to compare the
measured receiver noise temperatures with the simulated values for several
practical beamformers, and to predict the associated receiver noise coupling
contribution, antenna thermal noise and ground noise pick-up (due to the back
radiation).Comment: ASTRON repor
Moving together towards participation:Insights into illness and care experiences of people with neuromuscular diseases
Late Quaternary Mammalian remains from Central and Eastern Sudan and their palaeoenvironment Significance
Comparison of relativistic bound-state calculations in Front-Form and Instant-Form Dynamics
Using the Wick-Cutkosky model and an extended version (massive exchange) of
it, we have calculated the bound states in a quantum field theoretical
approach. In the light-front formalism we have calculated the bound-state mass
spectrum and wave functions. Using the Terent'ev transformation we can write
down an approximation for the angular dependence of the wave function. After
calculating the bound-state spectra we characterized all states found.
Similarly, we have calculated the bound-state spectrum and wave functions in
the instant-form formalism. We compare the spectra found in both forms of
dynamics in the ladder approximation and show that in both forms of dynamics
the O(4) symmetry is broken.Comment: 22 pages Latex, 7 figures, style file amssymb use
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