Search

SUMMARY In this study, we investigate the correlation between the residuals of a neGMM (non-ergodic Ground Motion Model) and the physics-based parameters obtained using a non-parametric GIT approach (Generalized Inversion Technique) to lay the groundwork for the implementation of an ad-hoc FAS (Fourier Amplitude Spectra) neGMM for the Central Italy region. This region is particularly suitable for data-driven methodologies as those applied in this work because of the large amount of available data due to the recent multiple main shock–aftershock sequences occurred in this area. Both neGMM and GIT models are developed for Fourier spectra in the frequency range between 0.5 and 25 Hz and using the same reference sites. The comparison of the non-ergodic terms with the source, path and site spectral parameters provides interesting results. First, we find a strong correlation between the source parameters, stress drop Δσ and decay ${k}_{\mathrm{ source}}$ and the source neGMM corrective terms (the combination of the between-event δBe and the location-to-location terms δL2L). This correlation is frequency dependent and, at high frequency, is remarkably positive for Δσ and negative for ${k}_{\mathrm{ source}}$. Concerning the attenuation terms, the path-to-path residuals (δP2P) are clearly associated with the deviations from the regional Q estimates obtained from GIT analysis. This indicates that the neGMM properly captures the properties of the anelastic attenuation and that the corrective terms δP2P can be used to account for differences in travel paths across different crustal domains. Finally, adopting the same reference sites for neGMM and non-parametric GIT, we observe that the systematic site terms (δS2Ss) and the GIT-derived amplification functions are in good agreement. The next step for an appropriate modelling is to identify the physical parameters (e.g. VS,30 and ${k}_0$) describing the empirical amplification curves to be introduced as explanatory variables in the ground motion model.

Breast reconstruction is fundamental and urgent for patients in order to avoid future psychological and physical issues. That’s why immediate breast reconstruction has been requested increasingly in the last years. In this study two prosthesis with different structures and properties were compared according the aesthetic appearance (BREAST-Q© was employed) and five complications (seroma, hematoma, infections, dehiscence and red breast syndrome). The overall population was composed by 56 patients: 24 received a Tutomesh prosthesis and 32 received a Surgimend prosthesis. The DMAIC (define, measure, analyse, improve and control) cycle was implemented as a problem-solving strategy of the Six Sigma to compare the prostheses. While statistically significant difference between the two groups wasn’t found according to the overall BREAST-Q© (p-value = 0.674), the number of complications of the two groups resulted statistically different (p-value of chi-square test less than 0.001). Although it is not possible to understand from this study the reasons of the differences between the complications, this research proved that Surgimend and Tutomesh prostheses can be both implanted safely for immediate breast reconstruction since the higher costs of Surgimend could be neutralized with its lower hospitalization compared to Tutomesh. © 2021, Springer Nature Switzerland AG.

The first mainshock (Mw 6.0) of the 2016 Central Italy seismic sequence, severely struck the Amatrice village and the surrounding localities. After few days, some Italian Institutions, coordinated by the "Center for Seismic Microzonation and its applications", carried out several preparatory activities for seismic microzonation of the area. A temporary seismic network was installed that monitored about 50 sites in epicentral area. The network produced a huge amount of records in a wide range of magnitude up to Mw 6.5. For about half of the recording stations, detailed site characterization was undertaken, encompassing singlestation noise measurements and S-wave velocity profiles. The geological and geophysical data together with the collected dataset of seismic signals were exploited to investigate the site response of selected stations. Significant amplifications are found in correspondence of several sites that experienced high level of damage (Imcs >IX), mainly at short and intermediate periods.

In the framework of the project for the update of the national seismic hazard model (MPS19), a task was devoted to selecting and weighing the predictive equations for the ground motion parameters and the macroseismic in- tensity to be used in the different seismotectonic contexts in Italy. To this purpose, from many available recent Ground Motion Prediction Equations (GMPEs) at global, European and regional/local scale, we pre-selected six- teen models for shallow active crustal regions, three for subduction zones to be applied to the Calabrian arc, and two for volcanic areas to be applied to Mount Etna, Aeolian islands and Neapolitan volcanoes. Each pre-selected GMPE was scored according to a specific metric using the strong-motion recordings available at the Italian ac- celerometric archive (itaca.mi.ingv.it) and the Engineering strong-motion database (esm.mi.ingv.it). In particular, three proper metrics were used, i.e. the log-likelihood, the parimutuel gambling score, and the quantile score, which give emphasis on different aspects of the forecasting performance. For shallow active crustal regions, we finally selected only three GMPEs, which show the best forecasting skill and also use different metrics for the distance and cover different spatial domains of the calibration dataset (national, European, and global). A weight was then assigned to each selected GMPE by combining two different evaluations: a weight based on the scoring using the observed accelerometric data and a weight derived by experts' judgment. Since the MPS19 model will also produce seismic hazard estimates in terms of macroseismic intensity, a similar procedure is being applied to select and weight the most recent Intensity Prediction Equations (IPEs) using the Italian macroseismic dataset (emidius.mi.ingv.it/CPTI15-DBMI15/).

During the Mw 6.0 Amatrice earthquake, which struck Central Italy on the 24th August 2016, the accelerometric station IT.AMT, located at about 10km from the epicentre recorded the highest values of the ground motion (Peak Ground Acceleration of the east component reached 0.87 g). Was IT.AMT station affected also by local soil conditions? To understand the role played by the site effects in the ground motion observed at AMT, we performed a detailed geological - geotechnical characterization of the site. Then, numerical analyses of seismic site response were carried out using 2D approaches. In parallel, several analysis were also performed on seismic records, to infer empirical amplification functions, used to compare the results of the numerical simulations. This study was partially supported by the Italian Department of Civil Protection (DPC) of the Presidency of Council of Ministers. The INGV-CNR IGAG collaboration made possible the realization of this multidisciplinary study, which includes detailed seismological, geological and geophysical analyses.

The MPS16 project, started in 2015, aims at updating the existing reference seismic hazard model for Italy, released in 2004-2006 (Stucchi et al., 2011). As known, ground-motion prediction equations (GMPEs) play a basic role in probabilistic seismic hazard assessment and, thus, special care should be taken to select and rank them in a proper way. GMPEs predict an IM at a given location as a function of earthquake magnitude, style of faulting, distance from the earthquake source, site characteristics and other variables, depending on the complexity of the model. In PSHA calculations GMPEs are combined in a logic tree framework, in order to take into account epistemic uncertainties, therefore ranking/scoring procedures have become very popular, although the selection of branch models and weights is still treated rather informally. We briefly describe the preliminary selection and ranking of the ground motion models for the new Italian hazard map. We describe the procedure for the following IMs: PGA, PGV and acceleration spectral ordinates (SA).

After the first mainshock of the 2016 Central Italy seismic sequence, several Italian Institutions (under the umbrella of the Italian Center for Seismic Microzonation; http://www.centromicrozonazionesismica.it) conducted a preparatory survey to seismic microzonation of the Amatrice municipality, badly affected by the Mw 6.0 Amatrice earthquake of August 24. Despite the difficulties due to the heavily damaged investigated area and the winter weather condition, a large amount of different data were gathered in a very short time: (i) geological and geomorphological surveys (field trip and photo-geological interpretation), (ii) geophysical measurements (noise single-station and arrays, geoelectric, seismic refraction, MASW), and (iii) continuous seismic recordings from temporary network. In particular, 35 seismic stations were installed from half-September to early-December in an area of 170 km2, equipped with both velocimeter and accelerometer. They recorded thousands of earthquakes, including the Mw 6.5 of October 30, 2016; the continuous data will be organized in the EIDA repository (http://www.orfeuseu.org/data/eida) through the INGV EIDA-node. The sites selection was performed according to the following criteria: representativeness of the geological conditions of 26 hamlets that experienced a damage level greater than VII MCS degree, optimization of the network geometry for array analysis, redundancy of bedrock reference sites, safety and accessibility. The photo-geology and the field investigations allowed the realization of a detailed geological-technical map of the area, characterized by peculiar features, namely the distinction between bedrock and Quaternary deposits (alluvial deposits and terraces, alluvial fans, landslides) and morpho-structural features (faults, folds, bedding attitude). Preliminary results allowed also the evaluation of the velocity models that show surface shear wave velocities (Vs) ranging from 200 m/s to 600 m/s. Data analysis of seismic recordings (earthquakes and noise) indicate peculiar amplification effect in several hamlets and in the village of Amatrice itself, even though the correlation with geology is not always straightforward.

International audience; The nuclear reaction (40)Ca+(12)C at 25 MeV per nucleon incident energy was used to produce excited alpha-conjugate fragments from projectile fragmentation mechanism. From a careful selection provided by a complete detection and from comparisons with models of sequential and simultaneous decays, evidence in favor of α-particle clustering from excited light alpha-conjugate nuclei is reported.

The use of NE102A-BaF2 phoswich detector drastically improves the particle identification with respect to BaF2 crystals. To better exploit the possibility of light ion discrimination we have applied digital signal processing to the signals, on-beam collected with NE102A-BaF2 phoswich. We present the results obtained for the heavy ion charge identification (up to Z=50) and light particle mass identification, using digital pulse shape acquisition and a 12-bit, 2 GSample/s sampling analog to digital converter. The results concerning the response of BaF2-plastic phoswich to the reaction products issued at forward angles in the collision of 35.1 MeV/u 124Sn beam on 64Ni target have been obtained at the Superconducting Cyclotron of the Laboratori Nazionali del Sud in Catania.

The MPS16 project, started in 2015, aims at updating the existing reference seismic hazard model for Italy, released in 2004-2006. As known, ground-motion prediction equations (GMPE) play a basic role in probabilistic seismic hazard assessment and, thus, special care should be taken to select and rank them in a proper way. The increasing amount of strong-motion records that are now available at the Italian accelerometric archive (itaca.mi.ingv.it) and the Engineering strong-motion database (esm.mi.ingv.it) allow us to rank a set of GMPEs developed at global and regional scales for different tectonic environments in the Italian peninsula. The performance of all selected GMPEs is tested against several intensity measures, such as PGA, PGV and acceleration spectral ordinates in the range 0.05 - 4 s. In particular, from many available models at global, European and regional/local scale, we select: i) 13 GMPEs for shallow active crustal regions; ii) 4 for subduction zones to be applied to the Calabrian arc, and iii) 2 for volcanic areas, specifically for Mount Etna. Several scoring techniques have been applied, included the renowned method based on the log-likelihood value (Scherbaum et al., 2009), the Euclidean Distance-Based Ranking (EDR) method (Kale and Akkar, 2013) and two novel methods commonly used for evaluating general probabilistic forecasts, such as the gambling score (Zechar and Zuang, 2014) and the scoring rule for quantiles (Gneiting and Raftery, 2005). Besides presenting the selection and scoring of a set of GMPEs, we also aim at investigating if regional GMPEs are consistently better than global models, and assessing the overall fit of the selected GMPEs for the whole country and some specific tectonic environments such as, for example, volcanic areas and subduction zones.

Storage rings as the ESR and the future NESR in the FAIR project are unique tools to study the dynamics of electron-ion and ion-atom collisions in the realm of strong perturbations and short interaction times. A telling sign of the character of such collisions are the electrons emitted into the continuum. For high Z projectiles and low Z targets the projectile centred continuum is dominating. Precision studies of these electrons emitted in relativistic collisions thus are of paramount importance for an understanding of the ionization mechanisms active in transferring electrons into the continua. Forward electron spectroscopy thus appears to be the tool of choice. For high precision studies in collision spectroscopy of high Z projectiles we have implemented an imaging forward electron spectrometer into the ESR supersonic jet target zone. In combination with a reaction microscope to be implemented next this enables investigations of several fundamental processes ranging from kinematically complete studies of multiple ionization and (e, 2e) on ions to radiative and non-radiative electron transfer processes to the projectile continuum and for the first time kinematically complete measurements of the short-wavelength limit of the electron nucleus Bremsstrahlung. We report first results.

Swift heavy-ion induced effects in condensed matter have important applications in, for example, materials science (materials under irradiation as in present or future nuclear power plants, nano-structuring of materials and their surfaces), radiation chemistry (radiolysis), and radiation medicine (tumor therapy with ions human exposure to cosmic rays). We refer the readers to Ref. [1] for a recent book on the fundamentals and applications of ion beams. At high projectile energies, collisions between the ions and the target electrons are the dominant processes of energy loss of the projectiles. The primary electrons and their subsequent secondary interactions lead to the deposition of energy around the ion trajectory.

A rather complete experimental study of forward and backward electron velocity spectra from thin foils bombarded with ions at constant velocity of 30 atomic units (23MeV u^-1) was performed. Three different beams ( 12C3+ , 58Ni14+ and 197Au36+ and six different targets ( 12C , 27Al , natNi , natAg , 197Au and 209Bi of approximately 90μg cm^-2 thickness were used. This procedure allowed to study the evolution of electron emission (velocity and angular distributions) for the [projectile; target] matrix [ C , Ni , Au ; C , Al , Ni , Ag , Au , Bi ] in a wide angular range. The projectile and target dependence of absolute cross-sections for binary encounter-, Auger- and backward-emitted electrons are analyzed.

Insulating (MYLAR), semi-insulating (MYLAR-Au) and conducting foils have been bombarded by very energetic 64 MeV u−1 78Kr32+ ions. The velocity spectra of fast electrons emitted in the backward and forward directions have been measured and analyzed as a function of the elapsed time in the run. A shift of binary encounter and convoy electrons emitted in the forward direction toward lower velocities has been observed with insulating targets. No such shift occurs with metallic targets. The surface potential evolves with time (i.e. ion fluence) both at forward and backward emission angle. It is shown that strong bulk charging of insulating targets leads to a positive potential as high as 9 kV before charge breakdown.

Highly energetic projectiles (20 MeV/u E beam v beam (the ion beam velocity) and 2 v beam . Results obtained both at the Catania LNS superconducting cyclotron CS with 58 Ni 14+,19+ (23 and 45 MeV/u) and at Ganil with 78 Kr 32+,34+ (64 MeV/u) are presented. Absolute emission cross-sections and kinematic properties are discussed.

Collisions of a very heavy 197 Au + 197 Au system have been studied at an energy of 15 MeV/nucleon with the aim to investigate a possible change of the energy dissipation mechanism from one-body dissipation (presumably dominating at low excitation energies) to two-body dissipation. The experiment was carried out in 4π geometry using the CHIMERA multidetector array. A class of ternary events satisfying nearly complete balance of mass numbers was selected. Preliminary results suggest that the selected ternary events represent mostly prompt ternary partitions of the colliding system, in which the lightest fragment is quite massive. In the light of theoretical predictions of Cârjan, Sierk and Nix this result may imply that the observed ternary reactions are driven by the two-body dissipation mechanism already at 15 MeV/nucleon.

Two-particle correlation functions, involving protons, deuterons, tritons, and α -particles, have been measured at very forward angles ( 0.7 ° ⩽ θ lab ⩽ 7 ° ), in order to study projectile-like fragment (PLF) emission in E / A = 44 and 77 MeV 40 Ar + 27 Al collisions. The observed correlations are similar for the two reactions at E / A = 44 and 77 MeV, except for peaks originating from resonance decays, which are larger at the lower bombarding energy. Particle-velocity gated correlation functions are presented, and possible implications on the time sequence of the light charged particles, emitted from the PLF, are discussed.

In nuclear and atomic experiments at high incident ion energies, 20 MeV/ u E u , the impact of swift heavy ions on thin solid targets is a source of fast electrons. The knowledge of their spatial and kinematical distributions is very useful for experimental nuclear and radiobiological applications as well as testing atomic ionization theories. An overview on the main mechanisms underlying the production of the electrons is given. Some recent results obtained at the Catania LNS superconducting cyclotron, mainly with a 45 MeV/ u 58 Ni 19+ beam are shown. In particular, the production and the properties of binary encounter-, convoy-, in-flight Auger- and backward emitted electrons are discussed.

The “Fermi shuttle” acceleration of electrons in ion–atom collisions, i.e. multiple collision sequences of electrons bouncing off the projectile and target nuclei, can lead to the emission of very energetic electrons (i.e. with velocities higher than the binary encounter electrons). We performed measurements of the evolution of the Fermi shuttle electron yield with the induced perturbation and the target atomic number. The yield increases with the perturbation parameter (ratio of projectile charge and projectile velocity q/vP), which was varied from q/vP ≈ 0.2 (weak perturbation) to q/vP ≈ 2 (strong perturbation). We also introduce a more realistic scaling parameter, which accounts for the re-bouncing of the electrons on target and projectile, and show that the yields increase as a function of this parameter. For a given projectile, the Fermi shuttle electron yield increases with the target atomic number. Furthermore, we show that the velocity distribution of the high-energy electrons is exponentially decreasing N(v) ∼ exp(−nv) and exhibits the same evolution of the slope n with projectile velocity as in the case of Fermi accelerated deuterons.

Nel presente lavoro è illustrata una metodologia di livello II di zonazione della suscettibilità all'innesco di frane sismoindotte sviluppata in ambiente GIS. L'area di studio prescelta è rappresentata dal territorio provinciale di Campobasso (Molise), in quanto caratterizzato da un'elevata franosità e una pericolosità sismica medio-alta per la vicinanza di due importanti aree sismogenetiche, la catena Appenninica ed il Gargano. La metodologia è basata su relazioni derivate dal modello di Newmark (1965), che richiedono la stima dell'accelerazione critica (ac), ottenibile considerando il principio dell'equilibrio limite applicato al pendio indefinito. L'analisi ha consentito di rappresentare la variabilità territoriale di questo parametro, assunta come indice della suscettibilità all'innesco di frane in condizioni sismiche. Le aree caratterizzate dalla soglia di accelerazione (ac) più bassa, in concomitanza con la presenza di importanti strutture e/o infrastrutture, saranno oggetto di analisi di stabilità maggiormente affinate e complesse.

A 100 Msamples/s 14-bit sampling analog-to-digital converter has been used to perform digital pulse-shape acquisition of signals collected from CHIMERA telescopes. Two different kinds of tests have been carried out to check the performances. The signals from a typical CHIMERA detection cell have been collected using both a standard CHIMERA electronic chain up to the amplifier, and a very simple analog front end, basically reduced to the preamplifier. The obtained on-beam and on-line results are presented.

Doubly differential electron velocity spectra induced by 36Ar18 + (95 MeV/u) from thin target foils (C, Ni, Ag, Au) were measured at GANIL (Caen, France) by means of the ARGOS multidetector and the time-of-flight technique. The main features observed in the forward spectra are convoy electrons, binary-encounter electrons, and (for the Au target only) a high-velocity tail which we attribute to a “Fermi shuttle” acceleration mechanism. Backward spectra do not show distinct structures. The spectra allow us to determine absolute singly differential cross-sections as a function of the target material and the emission angle. The convoy electron yield increases with the target atomic number, but for C their yield is so small that our experiment is not able to detect them. Absolute doubly differential cross-sections for binary-encounter electron ejection from C targets are well described by a transport theory which is based on the relativistic electron impact approximation (EIA) for electron production and which accounts for angular deflection, energy loss and energy straggling of the transmitted electrons.

In order to study the emission of energetic electrons induced by the impact of swift heavy ions on thin solid targets, we carried out a series of experiments at the superconducting cyclotron of the Catania Laboratori Nazionali del Sud. We report results on a recent experiment where electron–electron coincidences were measured in a forward ring by bombarding a thin carbon target of 7.4 μg/cm2 with 19+ 45 A MeV 58Ni beam. The velocity1–velocity2 bidimensional plot is dominated by events in which the two detected electrons have a velocity close to the beam velocity 9.03 cm/ns (convoy electrons). The remaining small fraction of coincidences has still a convoy electron and a second electron having either a velocity almost twice the beam velocity 16.5 cm/ns (binary encounter, BE electrons) or a velocity of about 12.7 cm/ns intermediate between BE and convoy velocities (IV electrons). We interprete this last intermediate component as due to in-flight de-excitation of highly excited n+58Ni ions by Auger electrons. Although less distinct, we observe also an intense peak close to the convoy velocity peak, centered at ≈9.7 cm/ns, corresponding to electrons emitted with an energy of only about ≈170 eV in the projectile rest frame of reference.

Background: In heavy-ion collisions at intermediate energies the production of light charged particles and intermediate mass fragments (IMFs) is due to different reaction mechanisms and different time scales, ranging from fast dynamical processes to statistical emission from the equilibrated system.Purpose: We compare the IMF statistical and dynamical emission probabilities in collisions of a neutron-rich $^{124}\mathrm{Sn}+^{64}\mathrm{Ni}$ system and a neutron-poor $^{112}\mathrm{Sn}+^{58}\mathrm{Ni}$ system at the laboratory energy of 35 $A$ MeV.Method: The IMFs production mechanism in semiperipheral reactions has been investigated in our previous works. In this paper, the analysis is expanded for the same set of data and production cross sections have been evaluated for dynamical and statistical emission in a coherent way for light and heavy fragments.Results: The data analysis has evidenced a strong competition between dynamical and statistical emission mechanisms. Probability of the dynamical emission of IMFs is strongly influenced by the ($N/Z$) ratio of the colliding system.Conclusions: It is demonstrated that the statistical emission is equally probable for the two systems, while the dynamical emission is enhanced for the neutron-rich system, especially for heavy fragments ($Z\ensuremath{\ge}6$). The observed effect points at a high sensitivity of the prompt-dynamical emission to the ($N/Z$) ratio of a given system.

The CHIMERA 4/spl pi/ detector trigger system is described. The trigger decisions are based on a combination of geometrical multiplicity of detected particles and other logic signals. The trigger can manage the buffer memory of the used analog to digital converters. This allows performance of parallel data conversion and readout and substantial improvement of the acquisition system dead-time performances. The trigger module generates all the necessary gate signals for the converters and the control signals necessary to synchronize the readout. It also allows the remote control of the whole system.

We have built and tested a computational unit for on-line processing of special algorithms to be embedded in the central processing unit VERSAmodule Eurocard (CPU VME)-crate of the CHIMERA data acquisition system. The computational unit consists of a number of VME digital signal processor (DSP)-based commercial boards delivering 720 MFlops/board.

Biological vision processes are at the basis of many studies in the image-processing field. In this context, neural networks developed by S. Grossberg constitute an interesting approach. The paper presents a novel method for the automatic analysis of scatter plots from CHIMERA experimental data based on Grossberg's pre-attentive neural systems. The design and implementation of a system developed for this purpose are illustrated. The proposed method yields satisfactory results also in very noisy cases.

Measurements of the momentum distribution of high-energy electrons emitted in weakly relativistic ion-solid collisions are compared with a transport theory which is based on the relativistic electron impact approximation for electron production and which accounts for angular deflection and energy loss but also energy straggling of the transmitted electrons. The measurements on electron ejection by 45 MeV u-1 Ni28+ projectiles colliding with carbon foils of thickness 10-8300 µg cm-2 were made on an absolute scale, providing a sensitive test of the transport theory. The theory gives a satisfactory description of earlier (relative) data from 13.6 MeV u-1 Ar18+ impact on carbon. Absolute singly differential cross sections for Ni28+ agree within 10% in the case of thin targets, but the width of the binary encounter peak is underestimated by theory. For the thickest targets the measured doubly differential cross sections are overpredicted by up to one order of magnitude, particularly at forward emission angles, but peak shapes are well reproduced.

In nuclear physics at intermediate energies, the use of multidetector arrays consisting of thousands of detectors is customary. This paper presents a novel approach to the automatic classification of data collected by the 4/spl pi/ detector CHIMERA, constituted by 1192 telescopes of a thin silicon transparent detector coupled to a thick CsI(Tl) scintillator. The method is based on spatial density data processing and produces frequency distributions of the most significant physical parameters. These one-dimensional spectra can be more easily analyzed than the standard two-dimensional scatter plots. With respect to manual or semiautomatic procedures, presently used for data analysis, our method offers the advantages of drastic time reduction and unbiased criteria for cluster identification. The proposed method can be successfully used in both off-line data analysis and multidetector stability control.

We present a three source analysis of velocity spectra of light charged particles (LCP) and neutrons emitted in the reaction 40 Ar+ 27 Al at 44 A MeV . The light particle (LP) velocity spectra are studied as a function of the detection angle (1.5° θ 3 He, 4 He, d , t ratios and the PLF proton temperature parameter. The characteristics of the PLF sources are derived. Present results are discussed with regards to the degree of thermalization which could be achieved in the PLF and TLF sources.

CHIMERA is a second generation 4/spl pi/ detector for high resolution light particle and fragment measurements in the field of intermediate energy nuclear reactions. An enhanced data acquisition, control and trigger system has been developed to manage the almost 5000 electronic channels of the detector. The data acquisition system is based on a Fast Data Link (FDL) connection between 9U VME crates. The FDL is a highly programmable VME device. It performs data readout and transfer to a destination VME CPU, the FIC8243, running the real time OS9 operating system. Data read and transfer is performed by a fast protocol (Sparse Data Scan) whose performances have been improved introducing the Chained Block Transfer mode (CBLT) technique. Data collected by the CPU are broadcast to analysis work-stations for on-line data analysis and storage. All commands from and to the VME CPU are sent by socket-based network protocols. Complete remote control of the electronic front-end is obtained by a system of client-server applications. A first level event selection and control during readout is made by a trigger system based on a new VME 9U board (MUSE), fully integrated with the FDL readout system.

A commercial two-DSP-based board is the basic unit of the on-line computational and control system under development for the multidetector array CHIMERA. The system design includes a small scale parallel and distributed architecture of PCs and DSP boards. The PCs are used both as host computer and interface between user and network. Each PC can host up to three DSP boards. The system is able to accomplish the on-beam control of CHIMERA, by means of the on-line computation of special algorithms, instead of using the usual techniques of special pulses to be sent off-beam. The physical data, collected and organized in UDP packets by the data acquisition system, are read through a 10 Mbit/s Ethernet network. The PC software, running under Windows NT 4.0, is based on threads and assures the communication and program managing as well as the result presentation. The DSP-software is written in C++ and takes care of the communication with the PC and of the computation of algorithms. The preliminary on beam results for the first three wheels (about 100 telescopes), obtained by employing two biprocessor boards located in the PCI bus of a Pentium MMX PC, are also presented.

International audience; Multi-breakup processes for the $^{124}$Sn+$^{64}$Ni system at 35 MeV/nucleon have been studied with the forward part of the CHIMERA detector. An extensive comparison between experimental data corresponding to almost complete ternary events and constrained molecular dynamics (CoMD-II) calculations suggests different characteristic times in the selected processes. This is in agreement with previous studies of the same reaction already published concerning the prompt intermediate-mass-fragment emission. Stimulated by CoMD-II calculations, we investigate the existence of more complex dynamical multi-breakup processes occurring on the same time scale. A detailed study of the rotational dynamics leading to slower dynamical fission processes is also presented.

Matière Nucléaire NIM; Semiperipheral collisions in the $^{124}$Sn+${64}Ni reaction at 35 MeV/nucleon were studied using the forward part of the Charged Heavy Ion Mass and Energy Resolving Array. Nearly completely determined ternary events involving projectilelike fragments (PLF), targetlike fragments (TLF), and intermediate mass fragments (IMF) were selected. A new method of studying the reaction mechanism, focusing on the analysis of the correlations between relative velocities in the IMF+PLF and IMF+TLF subsystems, is proposed. The relative velocity correlations provide information on the time sequence and time scale of the neck fragmentation processes leading to production of IMFs. It is shown that the majority of light IMFs are produced within 40–80 fm/c after the system starts to reseparate. Heavy IMFs are formed at times of about 120 fm/c or later and can be viewed as resulting from two-step (sequential) neck rupture processes.

Fast electron velocity spectra have been measured by means of the multidetector ARGOS (actually located at Laboratorio Nazionale del Sud, Catania) in a large angular range for atomic collisions induced by a $77A\ensuremath{-}\mathrm{MeV}$ ${}^{40}\mathrm{Ar}$ beam on an Al target. The results are in a fair agreement with a recently proposed relativistic billiard ball model and quasielastic scattering approximation calculations. However, the experimental binary-encounter peak velocities are found to be significantly lower than theoretically predicted. The data also show evidence for an excess of fast electrons in the backward direction.

CHIMERA (Charged Heavy Ions Mass and Energy Resolving Array), a new 4/spl pi/ detector for charged particles is under development at various sites of the Istituto Nazionale di Fisica Nucleare. This paper describes the new data acquisition system built to handle the signals coming out from the detector with a rate up to 1 kHz on almost 5000 electronic channels. The required average throughput for the system is in the order of the 1 MB/s. The used converters allow double-range conversion on 15 bits, in less than 50 /spl mu/s for all the 64 channels. The FDL link connects the different VME 9U crates performing a programmable hardware readout with a rate up to 100 MB/s. It uses a fast hardware protocol (Sparse Data Scan) to read the data buffers and send them to a FIC 8243 CPU board. A FIC 8243 dual-processor board forwards data (through Ethernet) to the analysis station (266 MHz Digital AlphaStation or Sun Sparcstation). A DLT (Digital Linear Tape) unit connected to analysis station is used to store data. The new data acquisition system has been tested under beam conditions at the Laboratorio Nazionale del Sud (Catania, Italy) and at GANIL (Caen, France).

The on-line computation of special algorithms, such as those required for controlling multidetectors in heavy-ion nuclear physics experiments, is a fundamental problem. It requires real-time computational resources capable of satisfying the associated time constraints. The work presented describes general considerations on real-time architectures, and tests performed employing, as a benchmark, the computation of a power law, used for particle identification in nuclear physics experiments.