A measurement of direct photon production in {sup 208}Pb+ {sup 208}Pb collisions at 158A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central ...collisions is extracted as a function of transverse momentum in the interval 0.5<p{sub T}<4 GeV/c . A significant direct photon signal, compared to statistical and systematical errors, is seen at p{sub T}>1.5 GeV/c . The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. It could be significant for diagnosis of quark-gluon-plasma formation.
Neutral pion production in central 158A GeV sup 208Pb+ sup 208 Pb collisions has been studied in the WA98 experiment at the CERN Super Proton Synchrotron. The pisup 0 transverse mass spectrum has ...been analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement allow one to limit previously noted ambiguities in the extracted freeze-out parameters. The results are shown to be sensitive to the shape of the velocity distribution at freeze-out. copyright ital 1999 ital The American Physical Society
The production of neutral pions in 158AGeV Pb+Pb collisions has been studied in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied for the range 0.3 GeV/c mT-m0 4.0 GeV/c. ...The results for central collisions are compared to various models. The centrality dependence of the neutral pion spectral shape and yield is investigated. An invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons is observed for centralities with greater than about 30 participating nucleons which is most naturally explained by assuming an equilibrated system.
Northern hemisphere peatlands are substantial carbon stores. However, recent climate change and human impacts (e.g., drainage and atmospheric nutrient deposition) may trigger the emission of their ...stored carbon to the atmosphere. Biodiversity losses are also an important consequence of those changes. Therefore, there is a need to recognise these processes in space and time. Global change experiments are often conducted to improve our understanding of the potential responses of various ecosystems to global warming and drought. Most of the experiments carried out in peatlands are focused on carbon balance and nitrogen deposition. Nevertheless, it is still unclear how fast peatlands respond to temperature changes and water-table lowering in the continental climate setting. This is important because continental regions account for a significant proportion of all northern hemisphere peatlands. A combination of short-term and long-term approaches in a single research project is especially helpful because it facilitates the correct interpretation of experimental data. Here we describe the CLIMPEAT project-a manipulative field experiment in a Sphagnum-dominated peatland supported by a high-resolution multi-proxy palaeoecological study. The design of the field experiment (e.g., treatments), methodology and biogeographical setting are presented. We suggest it is beneficial to support field experiments with an investigation of past environmental changes in the studied ecosystem, as human impacts during the past 300 years have already caused substantial changes in ecosystem functioning which may condition the response in experimental studies.
The thermal effect on the phase evolution and crystallinity of raw and cobalt-modified Brazilian bentonites was investigated. The modified bentonites were prepared dispersing the bentonite particles ...in Co2+ hydroxide gels. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermal analyses and energy dispersive X-ray spectroscopy. An endothermic peak around 900°C indicated the formation of olivine. A test with benzyl alcohol confirmed the catalytic activity as acidic catalyst for alcohol oxidation.
► A modification of Brazilian bentonites through the addition of a cobalt gel, was proposed. ► Modified-bentonites are thermal stables until 600°C. ► Cobalt-bentonites presented catalytic activity as acid catalyst in alcohol oxidation reactions.
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