Organic Soil Management: Impacts on Yields, Soil Quality and Economics

Understanding organic management practices is a key in developing sustainable organic farming systems. We report the results of four different organic fertilization strategies in a field trial on yields, soil quality and economic performance. We found highest yields and economic performance in two direct plant feeding strategies. One of these strategies, a newly developed strategy based on biowaste compost (GFT) and an additional fertilizer performed well in terms of yields but looks also very promising in terms of soil quality and biodiversity. The economic perspective of this strategy renders it promising in regions with little animal manures

Organic fertilisers of the mac trial and their impact on soil quality, environment and climate change

After 8 years, the MAC field trial in Lelystad, the Netherlands, shows the effects of different fertiliser strategies, ranging from animal manure to plant compost to mineral fertiliser. The impact on yield, soil quality, soil health, environment and climate change is discussed. The trial is unique in monitoring the effect of so many types of fertilisers over so many year

Electrocatalytic phenomena in gas phase reactions in solid electrolyte electrochemical cells

The recent literature on electrocatalysis and electrocatalytic phenomena occurring in gas phase reactions on solid, oxygen conducting electrolytes is reviewed. In this field there are a number of different subjects which are treated separately. These are: the use of electrochemical methods to study catalytic phenomena, electrocatalysis proper, the transfer of oxygen at the electrodes or electrolyte, and the (electro)catalytic properties of mixed, electronic and ionic, conducting materials

Statistics of mass substructure from strong gravitational lensing: quantifying the mass fraction and mass function

A Bayesian statistical formalism is developed to quantify the level at which the mass function slope (alpha) and the projected cumulative mass fraction (f) of (CDM) substructure in strong gravitational-lens galaxies, with arcs or Einstein rings, can be recovered as function of the lens-survey parameters and the detection threshold of the substructure mass. The method is applied to different sets of mock data to explore a range of observational limits: (i) the number of lens galaxies in the survey, (ii) the mass threshold, Mlow, for the detection of substructures and (iii) the uncertainty of the measured substructure masses. We explore two different priors on the mass function slope: a uniform prior and a Gaussian prior with alpha = 1.90+-0.1. With a substructure detection threshold Mlow=3x10^8 Msun, the number of lenses available now (n_l=30), a true dark-matter mass fraction in (CDM) substructure <=1.0% and a prior of alpha = 1.90+-0.1, we find that the upper limit of f can be constrained down to a level <=1.0% (95% CL). In the case of a Gaussian prior on alpha, it is always possible to set stringent constraints on both parameters. We also find that lowering the detection threshold has the largest impact on the ability to recover alpha, because of the (expected) steep mass-function slope. In the future, thanks to new surveys with telescopes, such as SKA, LSST and JDEM and follow-up telescopes with high-fidelity data, a significant increase in the number of known lenses will allow us to recover the satellite population in its completeness. For example, a sample of 200 lenses, equivalent in data-quality to the Sloan Lens ACS Survey and a detection threshold of 10^8 Msun, allows one to determine f=0.5+-0.1% (68% CL) and alpha=1.90+-0.2 (68% CL).Comment: MNRAS (in press

White Dwarfs: Contributors and Tracers of the Galactic Dark-Matter Halo

We examine the claim by Oppenheimer et al. (2001) that the local halo density of white dwarfs is an order of magnitude higher than previously thought. As it stands, the observational data support the presence of a kinematically distinct population of halo white dwarfs at the >99% confidence level. A maximum-likelihood analysis gives a radial velocity dispersion of sigma^h_U=150(+80/-40) km/s and an asymmetric drift of v_a^h=176(+102/-80) km/s, for a Schwarzschild velocity distribution function with sigma_U:sigma_V:sigma_W=1:2/3:1/2. Halo white dwarfs have a local number density of 1.1(+2.1/-0.7)x10^-4 pc-3, which amounts to 0.8(+1.6/-0.5) per cent of the nominal local dark-matter halo density and is 5.0(+9.5/-3.2) times higher and thus only marginally in agreement with previous estimates (all errors indicate the 90% C.L.). We discuss several direct consequences of this white-dwarf population (e.g. microlensing) and postulate a potential mechanism to eject young white dwarfs from the disc to the halo, through the orbital instabilities in triple or multiple stellar systems.Comment: 5 pages, to appear in the proceedings of the Yale Cosmology Workshop "The Shapes of Galaxies and their Halos" (ed. Priya Natarajan); revised numerical results, using a corrected likelihood function (thanks to David Graff and Andy Gould); general conclusions remain simila

The inner mass power spectrum of galaxies using strong gravitational lensing: beyond linear approximation

In the last decade the detection of individual massive dark matter sub-halos has been possible using potential correction formalism in strong gravitational lens imaging. Here we propose a statistical formalism to relate strong gravitational lens surface brightness anomalies to the lens potential fluctuations arising from dark matter distribution in the lens galaxy. We consider these fluctuations as a Gaussian random field in addition to the unperturbed smooth lens model. This is very similar to weak lensing formalism and we show that in this way we can measure the power spectrum of these perturbations to the potential. We test the method by applying it to simulated mock lenses of different geometries and by performing an MCMC analysis of the theoretical power spectra. This method can measure density fluctuations in early type galaxies on scales of 1-10 kpc at typical rms-levels of a percent, using a single lens system observed with the Hubble Space Telescope with typical signal-to-noise ratios obtained in a single orbit

Sub-milliarcsec-scale structure of the gravitational lens B1600+434

In the gravitational lens system B1600+434 the brighter image, A, is known to show rapid variability which is not detected in the weaker image, B (Koopmans & de Bruyn 2000). Since correlated variability is one of the fundamental properties of gravitational lensing, it has been proposed that image A is microlensed by stars in the halo of the lensing galaxy (Koopmans & de Bruyn 2000). We present VLBA observations of B1600+434 at 15 GHz with a resolution of 0.5 milliarcsec to determine the source structure at high spatial resolution. The surface brightness of the images are significantly different, with image A being more compact. This is in apparent contradiction with the required property of gravitational lensing that surface brightness be preserved. Our results suggest that both the lensed images may show two-sided elongation at this resolution, a morphology which does not necessarily favour superluminal motion. Instead these data may suggest that image B is scatter-broadened at the lens so that its size is larger than that of A, and hence scintillates less than image A.Comment: 4 pages, 2 figures, accepted in AA Letter

Quantifying Suppression of the Cosmological 21-cm Signal due to Direction Dependent Gain Calibration in Radio Interferometers

The 21-cm signal of neutral hydrogen - emitted during the Epoch of Reionization - promises to be an important source of information for the study of the infant universe. However, its detection is impossible without sufficient mitigation of other strong signals in the data, which requires an accurate knowledge of the instrument. Using the result of instrument calibration, a large part of the contaminating signals are removed and the resulting residual data is further analyzed in order to detect the 21-cm signal. Direction dependent calibration (DDC) can strongly affect the 21-cm signal, however, its effect has not been precisely quantified. In the analysis presented here we show how to exactly calculate what part of the 21-cm signal is removed as a result of the DDC. We also show how a-priori information about the frequency behavior of the instrument can be used to reduce signal suppression. The theoretical results are tested using a realistic simulation based on the LOFAR setup. Our results show that low-order smooth gain functions (e.g. polynomials) over a bandwidth of ~10\,MHz - over which the signal is expected to be stationary - is sufficient to allow for calibration with limited, quantifiable, signal suppression in its power spectrum. We also show mathematically and in simulations that more incomplete sky models lead to larger 21-cm signal suppression, even if the gain models are enforced to be fully smooth. This result has immediate consequences for current and future radio telescopes with non-identical station beams, where DDC might be necessary (e.g. SKA-low).Comment: Submitted to MNRAS on 10-Aug-201