35 research outputs found
Near Threshold K+K- Meson-Pair Production in Proton-Proton Collisions
The near threshold total cross section and angular distributions of K+K- pair
production via the reaction pp --> ppK+K- have been studied at an excess energy
of Q = 17 MeV using the COSY-11 facility at the cooler synchrotron COSY. The
obtained cross section as well as an upper limit at an excess energy of Q = 3
MeV represent the first measurements on the K+K- production in the region of
small excess energies where production via the channel pp --> pp Phi --> ppK+K-
is energetically forbidden. The possible influence of a resonant production via
intermediate scalar states f0(980) and a0(980) is discussed.Comment: 8 pages, 6 figures, replaced with revised version, accepted for
publication in Phys. Lett.
S-wave eta'-proton FSI; phenomenological analysis of near-threshold production of pi0, eta, and eta' mesons in proton-proton collisions
We describe a novel technique for comparing total cross sections for the
reactions pp --> pp pi(0), pp --> pp eta, and pp --> pp eta' close to
threshold. The initial and final state proton-proton interactions are factored
out of the total cross section, and the dependence of this reduced cross
section on the volume of phase space is discussed. Different models of the
proton-proton interaction are compared. We argue that the scattering length of
the S-wave eta'-proton interaction is of the order of 0.1 fm.Comment: 10 pages, 5 figure
Kaon pair production close to threshold
The total cross section of the reaction pp->ppK+K- has been measured at
excess energies Q=10 MeV and 28 MeV with the magnetic spectrometer COSY-11. The
new data show a significant enhancement of the total cross section compared to
pure phase space expectations or calculations within a one boson exchange
model. In addition, we present invariant mass spectra of two particle
subsystems. While the K+K- system is rather constant for different invariant
masses, there is an enhancement in the pK- system towards lower masses which
could at least be partially connected to the influence of the Lambda(1405)
resonance.Comment: accepted for publication in Phys. Lett.
Energy Dependence of the Near-Threshold Total Cross-Section for the pp --> pp eta' Reaction
Total cross sections for the pp --> pp eta' reaction have been measured in
the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has
been performed at the internal installation COSY-11 using a stochastically
cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster
target. The determined energy dependence of the total cross section weakens the
hypothesis of the S-wave repulsive interaction between the eta' meson and the
proton. New data agree well with predictions based on the phase-space
distribution modified by the proton-proton final-state-interaction (FSI) only.Comment: 12 pages, 1 table, 4 figure
Soil erosion processes in european vineyards: a qualitative comparison of rainfall simulation measurements in Germany, Spain and France
Small portable rainfall simulators are considered a useful tool to analyze soil erosion processes in cultivated lands. European research groups in Spain (Valencia, Málaga, Lleida, Madrid and La Rioja), France (Reims) and Germany (Trier) have used different rainfall simulators (varying in drop size distribution and fall velocities, kinetic energy, plot forms and sizes, and field of application) to study soil loss, surface flow, runoff and infiltration coefficients in different experimental plots (Valencia, Montes de Málaga, Penedès, Campo Real and La Rioja in Spain, Champagne in France and Mosel-Ruwer valley in Germany). The measurements and experiments developed by these research teams give an overview of the variety of methodologies used in rainfall simulations to study the problem of soil erosion and describe the erosion features in different climatic environments, management practices and soil types. The aims of this study are: (i) to investigate where, how and why researchers from different wine-growing regions applied rainfall simulations with successful results as a tool to measure soil erosion processes; (ii) to make a qualitative comparison about the general soil erosion processes in European terroirs; (iii) to demonstrate the importance of the development of standard method for measurement of soil erosion processes in vineyards, using rainfall simulators; and (iv) and to analyze the key factors that should be taken into account to carry out rainfall simulations. The rainfall simulations in all cases allowed infiltration capacity, susceptibility of the soil to detachment and generation of sediment loads to runoff to be determined. Despite using small plots, the experiments were useful to analyze the influence of soil cover to reduce soil erosion, to make comparisons between different locations, and to evaluate the influence of different soil characteristics. The comparative analysis of the studies performed in different study areas points out the need to define an operational methodology to carry out rainfall simulations, which allows us to obtain representative and comparable results and to avoid errors in the interpretation in order to achieve comparable information about runoff and soil los
Analysis of physical pore space characteristics of two pyrolytic biochars and potential as microhabitat
Background and Aims
Biochar amendment to soil is a promising practice of enhancing productivity of agricultural systems. The positive effects on crop are often attributed to a promotion of beneficial soil microorganisms while suppressing pathogens e.g. This study aims to determine the influence of biochar feedstock on (i) spontaneous and fungi inoculated microbial colonisation of biochar particles and (ii) physical pore space characteristics of native and fungi colonised biochar particles which impact microbial habitat quality.
Methods
Pyrolytic biochars from mixed woods and Miscanthus were investigated towards spontaneous colonisation by classical microbiological isolation, phylogenetic identification of bacterial and fungal strains, and microbial respiration analysis. Physical pore space characteristics of biochar particles were determined by X-ray μ-CT. Subsequent 3D image analysis included porosity, surface area, connectivities, and pore size distribution.
Results
Microorganisms isolated from Wood biochar were more abundant and proliferated faster than those from the Miscanthus biochar. All isolated bacteria belonged to gram-positive bacteria and were feedstock specific. Respiration analysis revealed higher microbial activity for Wood biochar after water and substrate amendment while basal respiration was on the same low level for both biochars. Differences in porosity and physical surface area were detected only in interaction with biochar-specific colonisation. Miscanthus biochar was shown to have higher connectivity values in surface, volume and transmission than Wood biochars as well as larger pores as observed by pore size distribution. Differences in physical properties between colonised and non-colonised particles were larger in Miscanthus biochar than in Wood biochar.
Conclusions
Vigorous colonisation was found on Wood biochar compared to Miscanthus biochar. This is contrasted by our findings from physical pore space analysis which suggests better habitat quality in Miscanthus biochar than in Wood biochar. We conclude that (i) the selected feedstocks display large differences in microbial habitat quality as well as physical pore space characteristics and (ii) physical description of biochars alone does not suffice for the reliable prediction of microbial habitat quality and recommend that physical and surface chemical data should be linked for this purpose
Effect of ground-cover type on surface runoff and subsequent soil erosion in Champagne vineyards in France
This study was conducted in Champagne vineyards in France, and the objectives were to compare the main cultivation practices in Champagne vineyards and to specify the conditions required for the optimum effect of inter-row grass cover on runoff and erosion in experimental plots of 0.25 m(2) under simulated rainfall. Three types of ground cover were studied. In the bark-and-vine-prunings plots, the runoff coefficient (RC) ranged from 1.3 to 4.0% and soil losses were <1 g/m(2) /h. In the bare soil (BS) plot, the highest RC of the study was found (80.0%) and soil losses reached 7.4 g/m(2)/h. In the grass cover plots, the RC and amount of eroded soil were highly variable: the RCs ranged from 0.4 to 77.0%, and soil losses were between less than 1 and 13.4 g/m(2)/h. Soil type, soil moisture, slope and agricultural practices did not account for the variability. In fact, the density of grass cover in the wheel tracks explained a portion of this variability. The lack of grass in the centre of the inter-row allowed for a preferential flow and created an erosion line in the wheel tracks where the soil was compacted. This study showed that grass cover in a vineyard was not necessarily sufficient to reduce surface runoff and prevent soil erosion. To be effective, the grass cover must be dense enough in the wheel tracks of agricultural machinery to avoid RCs close to the RC achieved with BS
Can biochar and hydrochar stability be assessed with chemical methods?
Field application of biochar is intended to increase soil carbon (C) storage. The assessment of C storage potential of biochars lacks methods and standard materials. The reactivity of biochars and hydrochars may be one possible means of evaluating their environmental stability. The aim of this study was to evaluate the reactivity of biochar produced by gasification (GS) and hydrochar produced by hydrothermal carbonisation (HTC). The approach included analysis of the two different char types produced from the same three feedstocks. Moreover, we analysed the reactivity of Holocene charcoal (150 and 2000 yr old) to evaluate whether or not their use as standard materials to represent stable biochar is meaningful. We assessed carbon loss following oxidation with acid dichromate as well as hydrolysis with HCl. Our results showed that chemical reactivity is not a straightforward approach for characterising the stability of biochar and hydrochar. Acid hydrolysis showed little difference between HTCs and GSs, despite the contrasting elemental composition. Using acid dichromate oxidation, we determined that GSs contained ca. 70% of oxidation resistant C while the proportion for HTCs was 2000 yr old charcoal > HTCs > feedstock and was related to elemental composition. This shows that acid dichromate oxidation may allow differentiation of the reactivity of modern biochars but that there is not necessarily a relationship between reactivity and age of Holocene charcoals. As the chemical reactivity of biochars may change with exposure time in soil, it is poorly suited for assessing their environmental residence tim