We study the energy dependence of the fusion cross-section with the goal of understanding the evolution of the underlying reaction mechanism as a function of input channel parameters and the causes ...of its (non-)disappearance. The heart of this work is a systematic and as wide as possible overview of measured cross-sections. Normalized by the reaction cross-section and plotted as a function of the available energy per ucleon corrected for the Coulomb barrier, fusion crosssection show a rather universal behavior leading to a disappearance of the fusion around 10A MeV, except in the case of very asymmetric systems for which incomplete fusion persists and tends towards a constant value that can be explained in the frame of a simple geometrical approach. These trends are confirmed by the semiclassical Landau-Vlasov transport calculations.
An extensive study of maximal values that the main forms of energy take during the compact dynamical phase of heavy-ion reactions has been carried out within the framework of a semiclassical ...transport approach. Several systems having different total mass and asymmetry have been studied over a full range of impact parameter and a wide range of incident energies below 100 MeV/u. It has been found that maxima of compression and thermal energy as a function of impact parameter closely follow the reaction geometry in the spirit of the participant–spectator picture and in head-on collisions are proportional to the available center-of-mass energy. Indication of a smooth transition between the low-energy reaction mechanism (deep inelastic model) and the higher-energy reaction mechanism (participant–spectator-like geometrical picture) is identified around the Fermi energy.
Induction of tolerance to transplantation antigens is believed to be a promising way to achieve long-term allograft survival without a deleterious immunosuppressive regimen. T-cell activation, which ...is an essential feature of graft rejection, requires a first signal provided by T-cell receptor (TCR) ligation and a second signal provided by engagement of co-stimulatory molecules with their respective ligands on antigen-presenting cells. The coordinated triggering of these two independent signalling systems ensures the full T-cell activation, including proliferation and acquisition of effector function. TCR occupancy in the absence of co-stimulatory signals leads to a sustained loss of antigen responsiveness called clonal anergy, which could be of major importance in transplantation. In vivo, co-stimulation blockade was indeed shown to allow for long-term allograft survival in several transplantation models. However, the current continuous identification of new co-stimulatory molecules suggests that a functional redundancy of the system exists and that tolerance to transplantation antigens might be achieved more easily through the combined blockade of two or several co-stimulatory signals. In this review, we analyse the biological effects of the disruption of some co-stimulation pathways in vitro and in vivo and discuss their potential interest for tolerance induction.
Neutron-induced reactions around the Fermi energy are investigated in the framework of the microscopic DYWAN model. Comparisons with experimental data in particle spectra are performed. Special ...attention has been devoted to pre-equilibrium emissions. The theoretical results show that the emission processes are sensitive to the nucleon–nucleon cross-section and to the characteristics of the self-consistent nuclear mean field, as the isospin dependence and the equation of state. Accordingly, nucleon-induced reactions provide a precious probe of the nuclear interaction in the concerned energy domain.
The direct pathway of allorecognition is involved in acute allograft rejection and is characterised by TCR-mediated recognition of the MHC framework; this is thought to occur in a peptide-dependent ...but not peptide-specific manner. In contrast, the indirect pathway is restricted to the recipient's own MHC molecules and prevails in chronic rejection. In this pathway, the peptide has a major influence on the TCR recognition and selects alloreactive T cells with altered TCR Vβ usage. However, qualitative analysis of Vβ usage alone might limit our understanding of alloreactivity. The advantages of a combined quantitative assessment of Vβ mRNA usage are discussed.
Despite the fact that valuable experimental measures are still lacking, available nuclear data on nucleon-induced reactions open new opportunities to address either reaction mechanisms or nuclear ...interaction characteristics. In this work single and double differential cross sections of emitted particles are analyzed and compared with the experiment. It will be evidenced that these cross sections follow a precise hierarchy. The preequilibrium components of the spectra are built up by the dynamics of the reaction as well as by the properties of the nuclear interaction.
We report on a systematics of fusion cross section data at energies above the reaction threshold to those of disappearance of fusion process. By an appropriate scaling of both cross sections and ...energy, a fusion excitation function common to all the data points is established. A universal description of the fusion excitation function relying on basic nuclear concepts is proposed and its dependence on the reaction cross section used for the cross section normalization is discussed.
Fusion excitation function revisited Eudes, Ph; Basrak, Z; Sébille, F ...
Journal of physics. Conference series,
01/2013, Letnik:
420, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
We report on a comprehensive systematics of fusion-evaporation and/or fusion-fission cross sections for a very large variety of systems over an energy range 4A-155A MeV. Scaled by the reaction cross ...sections, fusion cross sections do not show a universal behavior valid for all systems although a high degree of correlation is present when data are ordered by the system mass asymmetry. For the rather light and close to mass-symmetric systems the main characteristics of the complete and incomplete fusion excitation functions can be precisely determined. Despite an evident lack of data above 15A MeV for all heavy systems the available data suggests that geometrical effects could explain the persistence of incomplete fusion at incident energies as high as 155A MeV.
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