Highly excited “nuclear molecules”: A way to explain the fluctuations in DBHIC excitation functions. Study of the28Si +28Si colliding system at 5.3 MeV ·A

The properties of the strong fluctuations observed in the excitation functions of Dissipative Binary Heavy Ion Collisions (DBHIC) have been studied for the system²⁸Si+²⁸Si in the energy range 150 MeV ≤E _lab ≤ 156 MeV with 150 keV step laboratory incident energy, by angular distributions and excitation functions measurements. Experimental results are compared to the the recently developed Partially Overlapping Molecular Level Model (POMLM). The parameters of the model have been determined with reasonable accuracy by describing all the quantities characterizing the fluctuations in the excitation functions i.e.: Average Angular Distributions, Energy Autocorrelation Functions, Variances, Angular Correlation Coefficients. The results of the analysis strongly support the idea of a process proceeding through the formation of an highly excited “nuclear molecule”. Experimental data collected at the most forward angles show the effects of strong excitation of a few final channels.     

Photoacoustic measurements of ion-implanted semiconductors

Summary We have measured photoacoustic-signal amplitude and phase of ion-implanted semiconductors. The main factors which determine the photoacoustic behaviour of implanted samples are the opticalabsorption coefficient and the thermal conductivity of the implanted layer. For the thermal conductivity of such a layer a value has been found like that for vitreous materials. Experimental results are in agreement with theoretical models which describe the photoacoustic response of a two-layer sample.

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Riassunto Sono state eseguite misure di segnale fotoacustico e di fase in semiconduttori impiantati. Le grandezze che caratterizzano il comportamento fotoacustico di tali sistemi sono il coefficiente di assorbimento ottico e la conducibilità termica dello strato impiantato. Si è trovato per lo strato impiantato una conducibilità termica simile a quella dei vetri. I risultati sperimentali sono in accordo con i modelli teorici che descrivono la risposta fotoacustica di campioni costituiti da due strati.

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Резюме Измеряются фотоакустические ситналы и фазы в ионно-имплантированных полупроводниках. Основные величины, которые характеризуют фотоакустическое поведение имплантированных образцов, представляют коэффициент оптического поглощения и теплопроводность имплантированного слоя. Для теплопроводности имплантированного слоя получена беличина аналогичная для стеклообразных материалов. Экспериментальные результаты согласуются с теоретнческими моделями, которые описывают фотоакустический отклик для двухслойного образца.

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To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Difference between standard and quasi-conformal BFKL kernels

As it was recently shown, the colour singlet BFKL kernel, taken in Möbius representation in the space of impact parameters, can be written in quasi-conformal shape, which is unbelievably simple compared with the conventional form of the BFKL kernel in momentum space. It was also proved that the total kernel is completely defined by its Möbius representation. In this paper we calculated the difference between standard and quasi-conformal BFKL kernels in momentum space and discovered that it is rather simple. Therefore we come to the conclusion that the simplicity of the quasi-conformal kernel is caused mainly by using the impact parameter space.     

An extension of proximal methods for quasiconvex minimization on the nonnegative orthant

In this paper we propose an extension of proximal methods to solve minimization problems with quasiconvex objective functions on the nonnegative orthant. Assuming that the function is bounded from below and lower semicontinuous and using a general proximal distance, it is proved that the iterations given by our algorithm are well defined and stay in the positive orthant. If the objective function is quasiconvex we obtain the convergence of the iterates to a certain set which contains the set of optimal solutions and convergence to a KKT point if the function is continuously differentiable and the proximal parameters are bounded. Furthermore, we introduce a sufficient condition on the proximal distance such that the sequence converges to an optimal solution of the problem.     

Pre-equilibrium γ ray emission in different reaction mechanisms at 8 MeV/nucleon

Recent experimental results on particles-γ coincidence measurements on the systems ¹²C +⁶⁴Ni and ³⁵Cl +⁶⁴Ni at about 8 MeV/nucleon are interpreted as due to the effect of a Dipole pre-equilibrium emission produced during the damping of the proton-neutron relative collective motion in very deformed intermediate systems formed in the first instants of the collision. The pre-equilibrium effects are evaluated through semiclassic kinetic theories and through modified statistical approach to include non-stationary effects in Fusion processes, Massive Transfer reactions (in the ¹²C +⁶⁴Ni system) and in Binary Dissipative reactions (in the ³⁵Cl +⁶⁴Ni system). In particular the study performed on the dipole molecular component allows to establish a link between the above phenomenon and the charge and mass transfer process in quasi-peripheral reactions. Received: 15 April 1998 / Revised version: 8 June 1998