Data Replication Effectiveness in Mobile Ad-Hoc Networks

In this paper the behavior of a MANET when, for several reasons, the node density varies in such a way to cause subnet disconnections, is considered. Data replication is usually employed to avoid data loss in case of unwanted disconnection of a node, increasing its availability. Considering a time-scale connectivity and node mobility, replicas can be distributed over the net, in order to make data available even during disconnection periods.A formula can be derived, which allows to evaluate the replica availability in different scenarios, using the probability density functions describing the partitioning of a network obtained by a simulator. Applying this formula to different kind of networks, it is possible to tune the degree of replication desired for different scenarios, looking for a trade-off between space occupancy and availability gain

Parallel Compression of 3D Meshes for Efficient Distributed Visualization

none3In a distributed visualization environment transmission time is dominant because of the amount of data to be moved and the limitations of available bandwidth. In this paper we address the problem to speed up the compression operation of large Triangulated Irregular Networks (TIN) using commodity clusters. In our case TINs represent isosurfaces extracted from volumetric data sets. The proposed parallel compression algorithm is based on Edgebreaker [ 1], one of the most powerful connectivity compression algorithm, and it exploits mesh partitioning produced during the parallel isosurface extraction operation. In this way a high speed-up of the compression module and a considerable improvement of the visualization system are obtained.A.CLEMATIS; V. GIANUZZI; D. D'AGOSTINOClematis, A.; Gianuzzi, Vittoria; D'Agostino, D

A Hierarchical Program Structure for Concurrent Fault Tolerant Software

A new approach to software fault tolerance in concurrent programs modeled as reactive systems is proposed. It is based on a hierarchical structure and on the combined use of different fault tolerant schemes (e.g. transaction to protect data and conversation like scheme to protect processes). Among the merits of this new approach there is the possibility of an effective use of different programming languages to implement diverse software versions also in concurrent programs

Using PVM to implement a Distributed Dependable Simulation System

In the past decade, the use of distributed algorithms to model simulations is considerably increased, in order to gain speedup over traditional sequential simulations. Also, there has been much interest in using inexpensive, powerful workstation nets, with high speed interconnection, instead of expensive parallel computers. In this paper, we briefly present the kernel of a distributed system (PV2M) implemented on top of PVM routines, where synchronization is based on the concept of Virtual Time. Special emphasis is given to the fault tolerant mechanisms provided in it. PV2M implements a checkpoint-restart mechanism, with respect to processes located on non master hosts, in such a way as to be 1-resilient with respect to failures occurring to these host

Experiencing a parallel mathematical library on a PC network

This paper presents an experience in use of a parallel mathematical library, ScaLAPACK, on a network composed by heterogeneous workstations. The good performance results have been obtained by means of a distributed programming environment which is able to dynamically evaluate available computing power at each workstation and to distribute accordingly the set of parallel processes

Art Images and Disabled Children: a software tool for therapists

We describe a browser which has been designed in order to allow severely disabled children to interact and express their "emotions" by means of art images and sequences of images. The browser is to be used under the supervision of art therapists

CPVM - Extending PVM for Consistent Checkpointing

This paper presents CPVM, a library that provides the user with a support to implement non blocking, blobal checkpoint- restart algorithms for applications written using PVM thereby achieving fault-tolerance. A salient feature of CPVM is the way in which, solely on the basis of a simple set of new PVM primitives, it provides several advanced facilities useful to solve different problems. CPVM can also be used as a platform on top of which to implement different algorithms to detect stable properties such as deadlocks and termination, and to support job-swapping and migration in an environment where there previously was none

ScanBrowser: un ausilio software per disabili gravi

Descriviamo uno strumento progettato per consentire l'interazione e l'espressione di emozioni anche a giovani affetti da disabilit\ue0 gravi. L'espressione delle emozioni avviene attraverso la selezione d'immagini artistiche e la loro composizione in sequenze, con l'aiuto di un apposito browser a scansione. Il browser, progettato per l'uso con la supervisione di un arte terapista, \ue8 stato realizzato facendo uso della tecnologia .Net di Microsoft