A. Di Stefano

Stratigraphical and structural constraints in the Lucanian Apennines (southern Italy): tools for reconstructing the geological evolution

Abstract The southern Apennines are characterized by the presence of tectonic units of internal derivation (Liguridi/Sicilidi Units) that have suffered several phases of tectonic transport. For this reason relics of such units rest now on the extreme front of the chain and they are often confused with tectonic units of more external derivation. The attribution of the different units to their original paleodomains needs different geological aspects to be considered: geometries of the tectonic contacts, petrographical and stratigraphical characters; this in order to unequivocally distinguish apparently similar sequences which, on the contrary belong to different tectonic units. In three areas of the Southern Apennines (Lucanian sector) selected for the present study two tectonic wedges are distinguishible, both characterized by compressive deformation tied up to a thin-skinned tectonic context. The more ancient accretionary wedge (Late Oligocene-Early Miocene) is connected with the subduction of the Tethys oceanic crust (Liguride/Sicilide Units) which stopped at the collision between the European margin and the Maghrebide crust, a continental-type crust that separates the Tethys from the Ionian. The subduction of the Ionian oceanic crust took place since the Middle Miocene and continued in southern Apennines up to the Late Pliocene-Early Pleistocene. This tectonic phase resulted in the structuration of the accretionary wedge formed by the basinal Lagonegrese Units and by the External Flysch that overthrust upon the Pliocene foredeep deposits, as is clearly shown in well logs. The stratigraphic, petrographic and structural constraints lead us to the reconstruction of a geologic frame that takes into account the field evidence and provides a fruitful tool for understanding the geodynamic evolution of the Southern Apennines.

CALCAREOUS PLANKTON HIGH RESOLUTION BIO-MAGNETOSTRATIGRAPHY FOR THE LANGHIAN OF THE MEDITERRANEAN AREA

High-resolution quantitative and qualitative analyses of the planktonic foraminifer and calcareous nannofossil content have been carried out on three Middle Miocene sections, from the Mediterranean area. Such sections (Cretaccio section, Tremiti Islands, Southern Italy; Moria section, Marche Region, Central Italy; DSDP Site, 372 succession, Balearic Basin), all well known in the literature, have been chosen because of their high-quality biostratigraphic potential. Remarkable magnetostratigraphic data were provided by the Site 372 succession where all chrons and subchrons of the interval C5Br-C5AAn have been recognised. The investigated interval falls between the First Occurrence (FO) of Praeorbulina glomerosa sicana and the Last Occurrences (LO) of Sphenolithus heteromorphus and Globorotalia peripheroronda. The LO of S. heteromorphus was detected in the uppermost part of the investigated sequence of Site 372 at the same stratigraphic level as the G. peripheroronda LO. A drastic decrease in abundance of S. heteromorphus (Last Common Occurrence -LCO) was detected slightly below its last occurrence; this event is well correlatable with the same event astronomically calibrated at Ras-il Pellegrin section (Malta Island), which has been recently ratified as the Global Stratotype Section and Point (GSSP) for the base of the Serravallian by the International Union of Geological Sciences. The stratigraphic correlation of the studied sections is based on first and last occurrences, abundance fluctuations of selected taxa and additional biohorizons. In particular the peculiar distribution pattern of some taxa, e.g. Paragloborotalia siakensis and Helicosphaera waltrans, offered the opportunity to increase the biostratigraphic resolution of the Langhian interval. The resulting integrated calcareous plankton bio-magnetostratigraphic scheme represents the downward extension of that one previously established for the Serravallian - Tortonian interval. The biostratigraphic correlation of the studied sections with the Langhian historical Stratotype pointed out its low degree of reliability. On the other hand, none of the sections here studied is suitable to be proposed as candidate for defining the Langhian GSSP. Thus the problem of finding, in the Mediterranean area, a valid section which could yield a new GSSP for the Langhian Stage is still open.

Impact of fieldbus on communication in robotic systems

The aim of this paper is to discuss the problems relating to communication in distributed process control, highlighting the limits of traditional centralized communication systems based on point-to-point connections. The paper shows the real advantages that can be obtained by using a distributed common-bus communication system in time-critical process control applications, highlighting its impact on the architecture of control systems from the point of view of both hardware and software. Particular reference is made to the International Electrotechnical Commission/Instrument Society of America (IEC/ISA) communication system which is close to becoming an international standard. In particular, the solution based on the use of the distributed common-bus communication protocol is applied to the control of an orange-picking robot, which had previously been implemented in a traditional way using point-to-point communications. The choice of a case study referring to a robot control system seems an appropriate benchmark for the real potential of the fieldbus because the processes involved in a robot control system have highly critical time constraints which may stress the fieldbus communication system. The paper presents a qualitative analysis of the advantages that can be obtained by introducing the fieldbus into the orange picking robot control system. The analysis gives a detailed illustration of the hardware and software modification needed to replace the traditional point-to-point control systems of the orange picking robot with the fieldbus. Then an evaluation of the performance of fieldbus system is provided. The evaluation is made by modeling and simulating the distributed communication system with transition timed Petri nets (TTPNs). The results obtained in the study as a whole confirm the authors conviction that, by careful analysis, it is possible and advantageous even in difficult cases to replace classical centralized point-to-point control systems with distributed systems based on use of the fieldbus.

Optimization of acyclic bandwidth allocation exploiting the priority mechanism in the FieldBus data link layer

In process control applications, the bandwidth assigned to acyclic traffic is oversized in order to ensure that the time constraints of control traffic are met. In the FieldBus, a protocol designed to support the exchange of information between sensors/actuators and regulating elements in an automation environment, this means allocating an excessive portion of the macrocycle to acyclic traffic. The use of traffic management based on priority can allow more efficient management of the available bandwidth. The authors analyze the priority mechanism provided for in the FieldBus data link layer and assess various strategies for management of aperiodic traffic and different application scenarios. >

Pre-run-time scheduling to reduce schedule length in the FieldBus environment

The paper deals with the problem of scheduling the transmission of periodic processes in a distributed FieldBus system, defining the conditions guaranteeing correct transmission. The scheduling of periodic processes fixes the transmission times for each process in a table, whose length is equal to the Least Common Multiple (LCM) of all the periods. This involves great memorization problems when some periods are relatively prime. The authors identify the theoretical conditions which allow the length of the scheduling table to be drastically reduced, but still guarantee correct transmission. On the basis of the theoretical conditions given, the authors present a pre-run-time scheduling algorithm which determines a transmission sequence for each producing process within the desired scheduling interval. An online scheduling algorithm is also proposed to schedule new transmission requests which are made while the system is functioning. The reduction in the schedule length may increase the number of transmissions, thus reducing the effective bandwidth and increasing the communication overload. In order to make as complete an analysis as possible of the scheduling solution, the authors also present an analysis of both the computational complexity of the algorithms proposed and the communication overload introduced. >

Evaluating the field bus data link layer by a Petri net-based simulation

The performance of the data link layer of the field bus, an emerging LAN architecture for control systems presently under standardization, is discussed and evaluated. Some aspects of the communication mechanism are presented, referring to the use of the two kinds of tokens of the protocol and pointing out their main features and the advantages and disadvantages offered by each one. The protocol was specified by extended timed Petri-nets and was evaluated by a suitable simulation tool. The results provide some criteria according to which the designer can choose, among the various mechanisms made available by the standard proposal, those which provide the most efficient solution for the scenario being considered. >

Optimal path determination in a graph by Hopfield neural network

Abstract Recurrent stable neural networks seems to represent an interesting alternative to classical algorithms for the search for optimal paths in a graph. In this paper a Hopfield neural network is adopted to solve the problem of finding the shortest path between two nodes of a graph. The results obtained point out the validity of the solution proposed and its capability to adapt itself dynamically to the variations in the costs of the graph, acquiring an “awareness” of its structure.

Naming and locating mobile agents in an Internet environment

The problem of finding the position of a mobile agent in a wide distributed system still represents an open research area. In fact, although today several mobile agent platforms have been developed, each of them implements an ad hoc naming and location policy, suitably studied to address the specific requirements deriving from the design choices made. What is really needed is a naming and location scheme of general validity, able to effectively meet all the typical requirements of mobile agent environments and thus easy to integrate into different platforms. A first contribution of the paper is the identification of the main requirements which an agent naming scheme of general validity should meet. Then, some properties are suggested to be taken into account, in order to make a qualitative naming scheme classification. The second contribution of the paper is the proposal of a human readable agent naming scheme, based on the distributed environment outlined in MASIF, the standardization OMG proposal for mobile agent systems. In addition, two location protocols suitable for the proposed naming scheme are presented, which are particularly appropriate for Internet/intranet environments.

Seismic site effects observed on sediments and basaltic lavas outcropping in a test site of Catania, Italy

Ambient noise measurements and a set of 44 moderate magnitude earthquakes were used to study the role of local geology and morphology on the site response of a small hill in the northern part of Catania, on top of which the University Astronomical Observatory is located. The study area has a gentle topography with a flat surface at the top, and it is characterized by a complex sedimentary sequence lying between a clayey basement and an upper volcanic formation. The recorded data were processed through standard spectral ratio and horizontal-to-vertical spectral ratio techniques. Directional effects were also investigated by computing the spectral ratios after rotating the horizontal components of motion and performing polarization analysis. Results of noise and earthquakes analysis, although showing significant differences in amplitude, are comparable in frequency, especially in the sedimentary terrains. On the lava flows, spectral ratios show significant amplification of the vertical component, which appear related to a higher P velocity contrast with underlying soft sediments. Directional effects were identified in two frequency bands (0.2–0.4 and 1.0–10.0xa0Hz). The effects observed at the lower frequency interval are rather stable, and it spreads out in all the studied area. At higher frequencies, directional effects are variable and mostly observed on the slopes rather than at the hill top. Our findings appear linked to the complex wave field generated by the lithologic heterogeneities existing in the area which seem to be related to the alternation of sediments and basaltic lavas.

A distributed heterogeneous database system based on mobile agents

This paper proposes a new model of a distributed DBMS based on the mobile agent programming paradigm instead of the client/server one. The paper investigates the suitability of the mobile agents approach to the problem of integrating a collection of local DBMS into a single heterogeneous large-scale distributed DBMS and it presents a model of distributed transactions as a set of mobile agents, illustrating the relevant execution semantics. In addition, the mechanisms which are needed to guarantee the ACID properties in the considered environment are discussed.