User-centric mobility management for multimedia content access

Current mobility protocols and architectures are mainly targeted to devices or applications and they usually lack the ability to support user-centric paradigms; moreover, they usually face a single aspect of the problem, i.e., terminal handover or session mobility. Full mobility support is only available to specific applications or protocols (e.g., SIP) but these approaches do not exploit all facilities for movement detection at the network/link layers and do not allow to use the same framework for different applications. This paper proposes a generic mobility framework for terminal handover and session migration. It pursues the user-centric paradigm and builds a cross-layer architecture, yielding to a high level of generality, applicability and flexibility. Unlike other approaches, it does not require any modification in correspondent peers and works with a minimal network infrastructure. Software implementations are described for two representative real-time multimedia applications, i.e., media streaming and interactive conference. The effectiveness of the framework was analyzed by means of both performance measurements in local and Internet testbeds and user evaluation during a live demo conducted at a national science exhibition.     

A Clustering Algorithm for Planning the Integration Process of a Large Number of Conceptual Schemas

When tens and even hundreds of schemas are involved in the integration process, criteria are needed for choosing clusters of schemas to be integrated, so as to deal with the integration problem through...     

Comparing meteorological spaceborne and ground-based radars: optimal satellite overpass distance from a ground-based radar site

Spaceborne and ground-based radars (GRs) provide a complementary view of the complex precipitation field. As there are significant differences between the two instruments, it is possible to use the peculiarities of one sensor to check the consistency of the results of the other. For instance, the radar measurement is affected by changes in the spatial resolution, which ‘worsens’ with the square of the range. Unfortunately, the GR has to measure rain from small to large distances. In contrast, changes in size of the Tropical Rainfall Measuring Mission (TRMM) radar sampling volume are almost negligible, since its measurements originate from similar distances of 400–420 km. However, the TRMM precipitation radar (TPR) vertical resolution becomes poorer when the angle of incidence increases (i.e. when the distance of the TPR samples from the nadir increases). This article shows that part of this problem, which affects the reference radar (namely the TPR), can be transferred to the radar under investigation (namely the GR), depending on the satellite overpass distance from the GR site. Given the present swath of the TPR (～240 km), the worst cases occur when the satellite passes close or at the maximum range of the GR. A small influence is found when the satellite passes at approximately half of the GR range. These results, which have been derived for the first-ever spaceborne radar (the TRMM radar), can be easily adapted to future missions (e.g. the global precipitation measuring dual-wavelength radar).     

A New Training Method for Large Self Organizing Maps

Self Organizing Maps (SOMs) are widely used neural networks for classification or visualization of large datasets. Like many neural network simulations, implementations of the SOM algorithm need a scan of all the neural units in order to simulate the work of a parallel machine. This paper reports a new learning algorithm that speeds up the training of a SOM with a little loss of the performance on many quality tests. The very low computation time, means that this algorithm can be used as a fast visualization tool for large multidimensional datasets.     

Hyper Media News: a fully automated platform for large scale analysis, production and distribution of multimodal news content

This paper describes Hyper Media News (HMNews), a system for the automated aggregation and consumption of information streams from digital television and the Internet. TV newscasts are automatically segmented, annotated and indexed. Such information is then integrated with those available from Internet blogs, newspapers and press agencies. The end result is a set of innovative information services that supplies retrieval, recommendation and browsing of multi-modal news items across different production paradigms, ranging from traditional professional media, e.g. television and press, to new user-centric media platforms such as social networking sites, internet forums and blogs.     

An incremental clustering scheme for data de-duplication

We propose an incremental technique for discovering duplicates in large databases of textual sequences, i.e., syntactically different tuples, that refer to the same real-world entity. The problem is approached from a clustering perspective: given a set of tuples, the objective is to partition them into groups of duplicate tuples. Each newly arrived tuple is assigned to an appropriate cluster via nearest-neighbor classification. This is achieved by means of a suitable hash-based index, that maps any tuple to a set of indexing keys and assigns tuples with high syntactic similarity to the same buckets. Hence, the neighbors of a query tuple can be efficiently identified by simply retrieving those tuples that appear in the same buckets associated to the query tuple itself, without completely scanning the original database. Two alternative schemes for computing indexing keys are discussed and compared. An extensive experimental evaluation on both synthetic and real data shows the effectiveness of our approach.     

Analytical study of intradomain handover in multiple-mobile-routers-based multihomed NEMO networks

The need to stay connected to the Internet “anytime” and “anywhere” is becoming more and more required in the recent years with the development of wireless networks. The NEMO basic support protocol was developed to grant the Internet connection for an entire mobile network, like vehicle or aircraft network. In NEMO a Mobile Router manages the mobility of the entire network on behalf of the other nodes in order to reduce the overhead of signaling messages. The critical part of mobility support is to reduce the handover latency, particularly when a Mobile Router is not reachable. This handover period degrades the performance of most delay sensitive applications. Referring to our proposition for NEMO handover improvement which is conceived for multiple-mobile-routers-based multihomed NEMO network, we find out a mathematical model to study the intradomain handover performance. We derive the mathematical model to analyze interruption interval (the time interval during which none of mobile routers can transport packets) during the intradomain handover. We study the impact of varying critical parameters, like vehicle speed, overlapping coverage distance, distance between mobile routers, and scanning frequency. The obtained results reveal that the seamless handover can be achieved if network configuration parameters are correctly chosen.     

Validating scheduling approaches against executional uncertainty

This paper introduces a general methodology to perform a comparative evaluation of different approaches to the problem of scheduling with uncertainty. Different proactive (off-line) and reactive (on-line) scheduling policies are evaluated by simulating the execution of a number of baseline schedules under uncertain environmental conditions, and observing the solution behaviors as such schedules get stressed by exogenous events. The analysis aims at assessing the impact of both proactive and reactive scheduling efforts on the robustness of the baseline solutions, against measurable disrupting factors, through reproducible experiments. As the results show, this dynamic approach reveals extremely useful to unveil some subtle aspects, which would have remained undetected through static metric evaluations.     

A conservative and monotone mixed-hybridized finite element approximation of transport problems in heterogeneous domains

In this article, we discuss the numerical approximation of transport phenomena occurring at material interfaces between physical subdomains with heterogenous properties. The model in each subdomain consists of a partial differential equation with diffusive, convective and reactive terms, the coupling between each subdomain being realized through an interface transmission condition of Robin type. The numerical approximation of the problem in the two-dimensional case is carried out through a dual mixed-hybridized finite element method with numerical quadrature of the mass flux matrix. The resulting method is a conservative finite volume scheme over triangular grids, for which a discrete maximum principle is proved under the assumption that the mesh is of Delaunay type in the interior of the domain and of weakly acute type along the domain external boundary and internal interface. The stability, accuracy and robustness of the proposed method are validated on several numerical examples motivated by applications in biology, electrophysiology and neuroelectronics.     

Optimal Control of Production Processes with Variable Execution Times

The paper deals with the optimal control of production processes characterized by the possibility of performing operations (relevant to the processing of a set of jobs) with variable execution times. A production process relevant to a single machine is addressed first. An optimization problem with a quite general cost function is considered, and some properties of optimal solutions are derived. Then, a particular version of the problem is analyzed, in which the cost function is the weighted sum of the quadratic earliness and tardiness of jobs and of quadratic deviations between pre-defined nominal unitary processing times and the actual ones. The decision variables of the problem are the possible idle times inserted before job executions and the processing times of jobs. This single machine problem is stated as an optimal control problem and a closed-loop solution is derived. Then, a second production process is considered, in which multiple machines serve jobs in parallel, again with variable processing times and with different processing costs. With reference to this second production scheme, a significant decision problem refers to the splitting of jobs over the different machines. Then, on the basis of a sensitivity analysis of the single machine problem solution, some conditions to verify the optimality of a pre-defined splitting are derived. An on-line splitting scheme using such conditions is finally presented.