676 research outputs found

    Isotopic composition of fragments in multifragmentation of very large nuclear systems: effects of the chemical equilibrium

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    Studies on the isospin of fragments resulting from the disassembly of highly excited large thermal-like nuclear emitting sources, formed in the ^{197}Au + ^{197}Au reaction at 35 MeV/nucleon beam energy, are presented. Two different decay systems (the quasiprojectile formed in midperipheral reactions and the unique source coming from the incomplete fusion of projectile and target in the most central collisions) were considered; these emitting sources have the same initial N/Z ratio and excitation energy (E^* ~= 5--6 MeV/nucleon), but different size. Their charge yields and isotopic content of the fragments show different distributions. It is observed that the neutron content of intermediate mass fragments increases with the size of the source. These evidences are consistent with chemical equilibrium reached in the systems. This fact is confirmed by the analysis with the statistical multifragmentation model.Comment: 9 pages, 4 ps figure

    Quantitative extensions of reaction systems based on SOS semantics

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    Reaction systems (RSs) are a successful natural computing framework inspired by chemical reaction networks. A RS consists of a set of entities and a set of reactions. Entities can enable or inhibit each reaction and are produced by reactions or provided by the environment. In this paper, we define two quantitative variants of RSs: the first one is along the time dimension, to specify delays for making available reactions products and durations to protract their permanency, while the second deals with the possibility to specify different concentration levels of a substance in order to enable or inhibit a reaction. Technically, both extensions are obtained by modifying in a modular way the Structural Operational Semantics (SOS) for RSs that was already defined in the literature. Our approach maintains several advantages of the original semantics definition that were: (1) providing a formal specification of the RS dynamics that enables the reuse of many formal analysis techniques and favours the implementation of tools, and (2) making the RS framework extensible, by adding or changing some of the SOS rules in a compositional way. We provide a prototype logic programming implementation and apply our tool to three different case studies: the tumour growth, the Th cell differentiation in the immune system and neural communication

    Morphology, rheological and mechanical properties of isotropic and anisotropic PP/rPET/GnP nanocomposite samples

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    The effect of graphene nanoplatelets (GnPs) on the morphology, rheological, and mechanical properties of isotropic and anisotropic polypropylene (PP)/recycled polyethylene terephthalate (rPET)-based nanocomposite are reported. All the samples were prepared by melt mixing. PP/rPET and PP/rPET/GnP isotropic sheets were prepared by compression molding, whereas the anisotropic fibers were spun using a drawing module of a capillary viscometer. The results obtained showed that the viscosity of the blend is reduced by the presence of GnP due to the lubricating effect of the graphene platelets. However, the Cox–Merz rule is not respected. Compared to the PP/rPET blend, the GnP led to a slight increase in the elastic modulus. However, it causes a slight decrease in elongation at break. Morphological analysis revealed a poor adhesion between the PP and PET phases. Moreover, GnPs distribute around the droplets of the PET phase with a honey-like appearance. Finally, the effect of the orientation on both systems gives rise not only to fibers with higher modulus values, but also with high deformability and a fibrillar morphology of the dispersed PET phase. A fragile-ductile transition driven by the orientation was observed in both systems

    Chemical and physical modifications of polyethylene containing nanostructures

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    The polyethylene is an interesting polymer with a good mechanical strength, ductility, biocompatibility and chemical inertia. It founds several applications in many fields, such as chemistry, engineering, bio-medicine and micro-electronics. The polyethylene chemical and physical properties can be modified embedding different nanostructures in its bulk. Carbon nanotubes, metallic oxides, coloured pigments and other species can be inserted at different concentrations in the polymer material during the preparation phase of thin films and sheets. Mechanical, optical, thermal and chemical properties can be modified significantly depending on the filler concentration. The absorption coefficient at different radiations can be controlled by the amount of doping structure. In the visible region, for example, the high transparency of pure polyethylene can be strongly reduced by low concentrations of carbon nanotubes. The colour, the mechanical resistance, the wet ability of the polyethylene and other parameters can be changed by the doping species in order to prepare special devices useful for many applications

    NWLEAR INSTRUMENTS a METwIas IN PHVUCS REsEARcH Sfxlm A A procedure to calibrate a multi-modular telescope

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    Abstract A procedure has been developed for the charge, mass and energy calibration of ions produced in nuclear heavy ion reactions. The charge and mass identification are based on a AE-E technique. A computer code determines the conversion from ADC channels into energy values, atomic number and mass of the detected fragments by comparing with energy loss calculations through a minimization routine. The procedure does not need prior measurements with beams of known energy and charge. An application of this technique to the calibration of the MULTlCS apparatus is described
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