170,287 research outputs found
Measuring the composition-curvature coupling in binary lipid membranes by computer simulations
No full textThe coupling between local composition fluctuations in binary lipid membranes and curvatureaffects the lateral membrane structure. We propose an efficient method to compute the composition-curvature coupling in molecular simulations and apply it to two coarse-grained membrane models—aminimal, implicit-solvent model and the MARTINI model. Both the weak-curvature behavior that istypical for thermal fluctuations of planar bilayer membranes as well as the strong-curvature regimecorresponding to narrow cylindrical membrane tubes are studied by molecular dynamics simulation.The simulation results are analyzed by using a phenomenological model of the thermodynamics ofcurved, mixed bilayer membranes that accounts for the change of the monolayer area upon bending.Additionally the role of thermodynamic characteristics such as the incompatibility between thetwo lipid species and asymmetry of composition are investigated.Fil: Barragán Vidal, I. A.. Georg August Universität, Gottingen; AlemaniaFil: Rosetti, Carla Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Pastorino, Claudio. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Müller, M.. Georg August Universität, Gottingen; Alemani
The 93Zr(n,γ) reaction up to 8 keV neutron energy
No full textThe (n,γ) reaction of the radioactive isotope 93Zr has been measured at the n-TOF high-resolution time-of-flight facility at CERN. Resonance parameters have been extracted in the neutron energy range up to 8 keV, yielding capture widths smaller (14%) than reported in an earlier experiment. These results are important for detailed nucleosynthesis calculations and for refined studies of waste transmutation concepts. © 2013 American Physical Society
Comparison between the Monte Carlo codes mcnpx and fluka within the framework of calculations for the trade experiment
No full textThe TRADE experiment, to be performed at the TRIGA nuclear reactor of the ENEA Casaccia Centre (Rome, Italy) consists in the coupling of an external proton accelerator to a spallation target to be installed in the central channel of the reactor kept in a sub-critical configuration. TRADE is meant to represent a major demonstration step of the Accelerator-Driven-Systems concept. Monte Carlo calculations are needed for the radiation transport analysis of various aspects of the experiment. The Monte Carlo general purpose codes MCNPX and FLUKA have been applied, among other issues, to the analysis of the shielding configuration of the beam transport line and to the assessment of the radioactivity induced by the impact of the 140 MeV proton beam with the target. In the shielding analysis the dose rates due to the proton beam leakage along the transport line have been calculated for points beyond the barytic concrete shields. Various leakage angles with respect to the beam axis have been considered. The analysis of the induced radioactivity has involved the calculation of the type and amount of the residual nuclei produced by the spallation process within the tantalum target and of the evolution of such nuclei. The results obtained with MCNPX and FLUKA are compared and discussed
197 - Au(n, gamma) cross section in the resonance region
No full textThe (n, gamma) cross section of 197 - Au has been measured at n_TOF in the resolved resonance region, up to 5 keV, with the aim of improving the accuracy in an energy range where it is not yet considered standard. The measurements were performed with two different experimental setup and detection techniques, the total energy method based on C6D6 detectors, and the total absorption calorimetry based on a 4 BaF2 array. By comparing the data collected with the two techniques, two accurate sets of neutron-capture yields have been obtained, which could be the basis for a new evaluation leading to an extended cross-section standard. Overall good agreement is found between the n_TOF results and evaluated cross sections, with some significant exceptions for small resonances. A few resonances not included in the existing databases have also been observed
Intake manifold primary trumpet tuning options for fuel flow limited high Performance I.C.E
No full textThe 2014 change in Formula One regulations, from naturally aspirated to highly-downsized and heavily-boosted hybridized power units, led to a relevant increase of the internal combustion engine brake specific power output in comparison with former V-8 units. The newly designed “downsized” engines are characterized by a fuel flow limitation and a relevant increase in the thermal loads acting on the engine components, in particular on those facing the combustion chamber. Furthermore, efficiency becomes an equivalent paradigm as performance. In the power unit layout, the air path is defined by the compressor, the intercooler and the piping from the intake plenum to the cylinder. Intake duct length is defined from intake plenum to valve seat and it is a key parameter for engine performance. In order to find the optimum length different design criteria can be applied: the so called “tuning”, the “un-tuning” or the “anti-tuning” are all valid possibilities, showing pros and cons. The scope of the paper is to study and present the possible different tuning options for the internal combustion engine (ICE) part of a hybrid F1 powertrain. From 2015, variable trumpet can be used: the continuous variable length may be used to optimize volumetric efficiency and furthermore to reduce knocking and improve combustion accordingly. The scope of the paper is to show and qualitatively compare all the different options for a hybrid powertrain with fuel flow limited combustion unit
New Measurement of Neutron Capture Resonances in 209Bi
No full textThe neutron capture cross section of 209Bi has been measured at the CERN n_TOF facility by employing the pulse-height-weighting technique. Improvements over previous measurements are mainly because of an optimized detection system, which led to a practically negligible neutron sensitivity. Additional experimental sources of systematic error, such as the electronic threshold in the detectors, summing of gamma-rays, internal electron conversion, and the isomeric state in bismuth, have been taken into account. Gamma-Ray absorption effects inside the sample have been corrected by employing a nonpolynomial weighting function. Because 209Bi is the last stable isotope in the reaction path of the stellar s-process, the Maxwellian averaged capture cross section is important far the recycling of the reaction flow by alfa -decays. In the relevant stellar range of thermal energies between kT = 5 and 8 keV our new capture rate is about 16 percent higher than the presently accepted value used for nucleosynthesis calculations. At this low temperature an important part of the heavy Pb-Bi isotopes are supposed to be synthesized by the s-process in the He shells of low mass, thermally pulsing asymptotic giant branch stars. With the improved set of cross sections we obtain an s-process fraction of 19 plus or minus 3 per cent of the solar bismuth abundance, resulting in an r-process residual of 81 plus or minus 3 per cent. The present (n, gamma) cross-section measurement is also of relevance for the design of accelerator driven systems based on a liquid metal Pb/Bi spallation target
- …
