Archivio della ricerca - Università degli studi di Napoli Federico II

    Thermal wave model for nonlinear longitudinal dynamics of a relativistic charged particle bunch in cold plasmas

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    We study the longitudinal dynamics of a relativistic charged particle bunch through a cold, unmagnetized plasma, within the framework of the recently proposed thermal wave model for relativistic charged particle beam propanation. We show that, under the action of both a purely electrostatic plasma wave potential well and the plasma wake potential (self-interaction), the longitudinal bunch dynamics is governed by a nonlinear Schrodinger equation for a complex wave function whose squared modulus is proportional to the longitudinal bunch density. This wave model, for which the diffraction parameter is represented here by the longitudinal emittance, allows us to study synchrotron-like oscillations in the plasma wave potential well as well as to obtain a longitudinal envelope equation which includes the self-interaction. Furthermore, we show that a soliton solution for the bunch density is possible and it results to be the natural asymptotic evolution of a modulational instability occurring when the bunch propagates in the plasma under the action of the self-force only

    Hydrogen sulfide is an endogenous inhibitor of phosphodiesterase activity

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    OBJECTIVE: Recent studies have demonstrated that hydrogen sulfide (H(2)S) is produced within the vessel wall from L-cysteine regulating several aspects of vascular homeostasis. H(2)S generated from cystathione γ-lyase (CSE) contributes to vascular tone; however, the molecular mechanisms underlying the vasorelaxing effects of H(2)S are still under investigation. METHODS AND RESULTS: Using isolated aortic rings, we observed that addition of L-cysteine led to a concentration-dependent relaxation that was prevented by the CSE inhibitors DL-propargylglyicine (PAG) and β-cyano-l-alanine (BCA). Moreover, incubation with PAG or BCA resulted in a rightward shift in sodium nitroprusside-and isoproterenol-induced relaxation. Aortic tissues exposed to PAG or BCA contained lower levels of cGMP, exposure of cells to exogenous H(2)S or overexpression of CSE raised cGMP concentration. RNA silencing of CSE expression reduced intracellular cGMP levels confirming a positive role for endogenous H(2)S on cGMP accumulation. The ability of H(2)S to enhance cGMP levels was greatly reduced by the nonselective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Finally, addition of H(2)S to a cell-free system inhibited both cGMP and cAMP breakdown. CONCLUSIONS: These findings provide direct evidence that H(2)S acts as an endogenous inhibitor of phosphodiesterase activity and reinforce the notion that this gasotransmitter could be therapeutically exploited

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    Studio dello zofenopril sulla reattività vascolare

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