6,614 research outputs found

    The Pueblo Crisis and Public Opinion

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    The capture of the U.S.S. Pueblo by a third-rate power provoked an internal conflict between the forces of domestic public opinion and the U.S. Navy

    Microscopic Enhancement of Heavy-Element Production

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    Realistic fusion barriers are calculated in a macroscopic-microscopic model for several soft-fusion heavy-ion reactions leading to heavy and superheavy elements. The results obtained in such a realistic picture are very different from those obtained in a purely macroscopic model. For reactions on 208:Pb targets, shell effects in the entrance channel result in fusion-barrier energies at the touching point that are only a few MeV higher than the ground state for compound systems near Z = 110. The entrance-channel fragment-shell effects remain far inside the touching point, almost to configurations only slightly more elongated than the ground-state configuration, where the fusion barrier has risen to about 10 MeV above the ground-state energy. Calculated single-particle level diagrams show that few level crossings occur until the peak in the fusion barrier very close to the ground-state shape is reached, which indicates that dissipation is negligible until very late in the fusion process. Whereas the fission valley in a macroscopic picture is several tens of MeV lower in energy than is the fusion valley, we find in the macroscopic-microscopic picture that the fission valley is only about 5 MeV lower than the fusion valley for soft-fusion reactions leading to compound systems near Z = 110. These results show that no significant ``extra-extra-push'' energy is needed to bring the system inside the fission saddle point and that the typical reaction energies for maximum cross section in heavy-element synthesis correspond to only a few MeV above the maximum in the fusion barrier.Comment: 7 pages. LaTeX. Submitted to Zeitschrift fur Physik A. 5 figures not included here. Complete preprint, including device-independent (dvi), PostScript, and LaTeX versions of the text, plus PostScript files of the figures, available at http://t2.lanl.gov/publications/publications.html or at ftp://t2.lanl.gov/pub/publications/mehe

    A Self Triggered Amplifier/Digitizer Chip for CBM

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    The development of front-end electronics for the planned CBM experiment at FAIR/GSI is in full progress. For charge readout of the various sub-detectors a new self-triggered amplification and digitization chip is being designed and tested. The mixed signal readout chip will have 32-64 channels each containing a low-power/low-noise preamplifier/shaper front-end, an 8-9 bit ADC and a digital post-processing based on a FIR/IIR-filter. The ADC has a pipeline architecture that uses a novel current-mode storage cell as a basic building block. The current prototype provides 26 different parametrized preamplifier/shaper/discriminator channels, 8 pipeline ADCs, a readout shift register matrix and a synthesized redundant signed binary (RSD) decoder

    Modelling sulphate stream concentrations in the Black Forest catchments Schluchsee and Villingen

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    International audienceThe sulphate (SO4) released by mineralisation and desorption from soil can play an important role in determining concentrations of SO4 in streams. The MAGIC model was calibrated for two catchments in the Black Forest, Germany (Schluchsee and Villingen) and SO4 concentrations in the streams for the years 2016 and 2030 were predicted. Special emphasis was placed on the dynamics of soil sulphur (S) pools. At Schluchsee, 90% of soil S is stored in the organic S (Sorg) pool, whereas at Villingen, 54% is in the inorganic (Sinorg) pool. The Villingen stream chemistry was modelled successfully by measured Langmuir isotherm parameters (LIPs) for Sinorg. Schluchsee data could not be modelled satisfactorily using measured or freely adapted LIPs only, as the Sinorg pool would have to be more than five times larger than what was measured. With 60.5 mmolc SO4 m-2 yr-1 as internal soil source by mineralisation and the measured LIPs, stream data was modelled successfully. The modelling shows that in these two catchments pre-industrial concentrations of SO4 in runoff can be reached in the next two decades if S deposition decreases as intended under currently agreed national and international legislation. Sorg is the most likely dominant source of SO4 released at Schluchsee. Mineralization from the Sorg pool must be included when modelling SO4 concentrations in the stream. As the dynamics and the controlling factors of S release by mineralisation are not yet clear, this process remains a source of uncertainty for predictions of SO4 concentrations in streams. Future research should concentrate on dynamics of S mineralisation in the field, such that mathematical descriptions of long-term S-mineralisation can be incorporated into biogeochemical models. Keywords: sulphate release, organic S, mineralisation, acidification, recovery, modelling, MAGIC, catchments, predictions, Germany, fores

    Mesure de durées de vie au moyen de champs hyperfréquences

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    Des champs électriques synchrones pulsent le faisceau, puis modulent en énergie des électrons K, ou bien modulent les deux électrons K d'une cascade
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