Strategies and protocols for highly parallel Linda servers

The tuple space abstraction is a powerful and general coordination model for parallel and distributed programming. However, this model is based on the abstraction of a global space, difficult to implement in distributed memory parallel systems with high-performance and scalability. The paper discusses the possible distribution strategies to implement a tuple space server and proposes a new replication policy suitable for massively parallel systems. The proposed strategy achieves scalability by organising the system in a hierarchical way and by integrating coherence protocols of limited overhead. Moreover, the chosen organisation encourages the presence of multiple tuple spaces each with a constrained scope. The paper describes and analyses a transputer-based implementation: the hierarchical organisation of the tuple space makes the access time proportional to the locality of the references and bounded by the logarithm of the system size. © 1998 John Wiley & Sons, Ltd.     

IMS-based presence service with enhanced scalability and guaranteed QoS for interdomain enterprise mobility

Enterprise mobility and IP multimedia system corporate services are becoming more relevant; in particular, the IMS-based presence service is starting to provide different kinds of seamlessly mobile services, with context awareness in a wide range of enterprise-deployment scenarios. However, the deployment of presence-based enterprise services in wide and heterogeneous wireless networks still faces several challenges. First of all, scalability and differentiated quality are considered crucial, especially under heavy traffic conditions and when dealing with inter-domain mobility scenarios. This article presents an overview of very recent research contributions about the standard IMS presence service and some novel proposals for scalability and quality optimization. In addition, we propose a novel presence service solution that presents three original extensions for scalability and quality: a federated model to optimize inter-domain distribution of notification messages through localitybased aggregation, a proposal for differentiated quality levels, and an extension of client-side buffering for reliable delivery of presence messages, even during user roaming. The prototype of the enhanced presence service has been deployed and validated by obtaining performance results of improved scalability in terms of CPU and memory usage in infrastructure nodes and message traffic. The prototype is openly available to the IMS community for possible refinement and extension.     

Mobeyes: smart mobs for urban monitoring with a vehicular sensor network

Vehicular sensor networks are emerging as a new network paradigm of primary relevance, especially for proactively gathering monitoring information in urban environments. Vehicles typically have no strict constraints on processing power and storage capabilities. They can sense events (e.g., imaging from streets), process sensed data (e.g., recognizing license plates), and route messages to other vehicles (e.g., diffusing relevant notification to drivers or police agents). In this novel and challenging mobile environment, sensors can generate a sheer amount of data, and traditional sensor network approaches for data reporting become unfeasible. This article proposes MobEyes, an efficient lightweight support for proactive urban monitoring based on the primary idea of exploiting vehicle mobility to opportunistically diffuse summaries about sensed data. The reported experimental/analytic results show that MobEyes can harvest summaries and build a low-cost distributed index with reasonable completeness, good scalability, and limited overhead     

Correlation between magnetic and electroacoustic parameters of audio magnetic tapes

Coercivity, squareness, remanent coercivity, coercivity factor, rotational hysteresis loss and its integral were measured on two sets of tapes (γ-Fe2O3and crO2) and related to their electroacoustic performances. The static magnetic measurements explain some of the properties of the particulate media: it was found that while CrO2rotates either coherently or incoherently depending on the direction of the applied field, γ-Fe2O3rotates incoherently, and the departure from the model of "fanning chain of spheres" can be related to the imperfections of the particles which are sources of demagnetizing fields. Good agreement with audio performance is found not only for parameters like coercivity and squareness, whose role is well known, but also with the other static parameters which were previously disregarded as ruling analogue recording.     

Computational experience with algorithms for separable nonlinear least squares problems

Nonlinear least squares problems frequently arise in which the fitting function can be written as a linear combination of functions involving further parameters in a nonlinear manner. This paper outlines an efficient implementation of an iterative procedure originally developed by Golub and Pereyra and successively modified by various authors, which takes advantage of the linear-nonlinear structure, and investigates its performances on various test problems as compared with the standard Gauss-Newton and Gauss-Newton-Marquardt schemes. A preliminary version of this note has been presented at the CNR-GNIM meeting held in Florence, september 1976.     

Shear behavior of masonry panels strengthened by high strength steel cords

The present experimental study was aimed to investigate the effectiveness of an alternative shear reinforcement technique, based on the use of high strength steel cords embedded in a cementitious matrix (SRG: Steel Reinforced Grout). Although FRPs are successfully used as shear reinforcement in masonry retrofitting, such a strengthening method represents a new opportunity to restoring ambit, with considerable development in unreinforced masonry (URM) strengthening. Particularly, the non application of epoxy resins may contribute to solve important problems in terms of high temperature and long term behavior, compatibility and reversibility of reinforcement. A series of eight URM panels and 23 strengthened panels manufactured using two different types of mortar have been subjected to diagonal compression tests. Different reinforcement configurations were evaluated. Experimental results pointed out a significant increase in shear strength and stiffness, with interesting implications for the practical utilization of the technique studied. Finally, experimental results are also used to calibrate existing analytical formulations for ultimate shear strength prediction.     

Mutagenic Analysis of the Putative ABCC6 Substrate-Binding Cavity Using a New Homology Model

Inactivating mutations in ABCC6 underlie the rare hereditary mineralization disorder pseudoxanthoma elasticum. ABCC6 is an ATP-binding cassette (ABC) integral membrane protein that mediates the release of ATP from hepatocytes into the bloodstream. The released ATP is extracellularly converted into pyrophosphate, a key mineralization inhibitor. Although ABCC6 is firmly linked to cellular ATP release, the molecular details of ABCC6-mediated ATP release remain elusive. Most of the currently available data support the hypothesis that ABCC6 is an ATP-dependent ATP efflux pump, an un-precedented function for an ABC transporter. This hypothesis implies the presence of an ATP-binding site in the substrate-binding cavity of ABCC6. We performed an extensive mutagenesis study using a new homology model based on recently published structures of its close homolog, bovine Abcc1, to characterize the substrate-binding cavity of ABCC6. Leukotriene C4 (LTC₄), is a high-affinity substrate of ABCC1. We mutagenized fourteen amino acid residues in the rat ortholog of ABCC6, rAbcc6, that corresponded to the residues in ABCC1 found in the LTC₄ binding cavity. Our functional characterization revealed that most of the amino acids in rAbcc6 corresponding to those found in the LTC₄ binding pocket in bovine Abcc1 are not critical for ATP efflux. We conclude that the putative ATP binding site in the substrate-binding cavity of ABCC6/rAbcc6 is distinct from the bovine Abcc1 LTC₄-binding site.     

A refined finite element model for the analysis of elastic–plastic frames

A finite element model for the elastic–plastic analysis of plane frames is proposed. The formulation is based on the independent modelling of the displacement and plastic strain fields; the latter is modelled both over the cross-section and along the element length as function of a finite number of parameters, which are considered as an extra set of independent variables, in addition to nodal displacements. Stress redistribution is allowed for over the cross-section, but not over the element length, where the distribution of stress resultants (axial forces and bending moments) is imposed consistently with the assumed displacement model; stress redistribution in terms of stress resultants becomes possible only because of the finite number of redundancies introduced when assembling. It is shown that the model can be formulated in such a way that not only compatibility and elasticity, but also equilibrium (in the sense of beam theory), are fully complied with and only the plastic portion of the constitutive relationship is approximately fulfilled, even if, in principle, to any desired level of accuracy. The model produces accurate results, including a detailed representation of the spreading of plastic zones, with a fairly limited number of elements.