Theodore K. Apostolopoulos

An open financial services architecture based on the use of intelligent mobile devices

The scope of this paper is to explore, analyze and develop a universal architecture that supports mobile payments and mobile banking, taking into consideration the third and the emerging fourth generation communication technologies. Interaction and cooperation between payment and banking systems, integration of existing technologies and exploitation of intelligent procedures provide the prospect to develop an open financial services architecture (OFSA), which satisfies requirements of all involved entities. A unified scenario is designed and a prototype is implemented to demonstrate the feasibility of the proposed architecture.

Information technology investment evaluation: Investments in telecommunication infrastructure

Evaluation of investments in information technology is quite a difficult task, difficulties being both conceptual and functional. The fact that the investments performance is very much dependent on the way a certain information technology project is implemented renders the evaluation procedure even more difficult. In this paper we propose a certain methodology for evaluating investments in information technology, placing special emphasis on investments in telecommunications infrastructure. In the first place, assessment of the alternative implementations/design solutions is conducted and selection of the one best satisfying user and system requirements is selected. At a second level, the selected alternative is compared with the present situation so that the expediency and feasibility of assuming the investment is determined. Evaluation is based on both economical and technical criteria.

Parallel computation for streamflow prediction with distributed hydrologic models

Abstract A parallel algorithm for solving streamflow prediction problems using distributed models is proposed and analyzed. The expanding utilization of distributed hydrologic models for the real-time prediction of floods and flash floods and for hydroclimatic studies provides the impetus for the study. The efficiency of the proposed algorithm, as compared to ordinary sequential algorithms, as well as the detailed parametric influence on the performance of the algorithm are investigated. First, theoretical results for the speedup of the parallel algorithm are obtained for a simple stream network of a typical flash flood prone basin, and then they are extended to include a larger, well developed network of streams. In the latter case, the results are given as functions of geomorphological characteristics of the stream network and of the cost of generic procedures for soil water accounting and for channel routing. It is shown that when the number of parallel processors is not limiting, parallel processing is much more cost effective than sequential processing for stream networks of a high order. It is also shown that the algorithm performs better for higher bifurcation ratios and lower average-length ratios. Performance improves as the ratio of the computational cost of channel routing to that of soil water accounting is reduced. The algorithm is tested experimentally for a flash-flood prone basin in Ohio using an ENCORE parallel computer, yielding satisfactory results. Guidelines are provided for partitioning the drainage basins in a particular application, as well as for developing parallel software.

Temporal network management model

Networks grow in scale and become more complex and heterogeneous as well. A lot of research effort is focused on the topic of network management. This is because nowadays a network management system is a vital component of any network installation. In this paper, we propose an extended network management information model that includes the time dimension. This view leads us to adopt a temporal data model as the underlying information model. Moreover, the services provided by this model, as well as the architecture supporting them, are presented. In addition to that, we have implemented a prototype incorporating the proposed network management view. The description of the prototype is also presented in this paper.

A model for SNMP based performance management services

This paper presents an SNMP-based management framework that can be used to monitor and control the performance of resources in a TCP/IP network. For the monitoring of diachronic network performance a set of indicators related to the host interfaces and to the TCP/IP implementation are defined. The layered architecture of the network management application and the performance services provided by each layer are also described. Moreover, an approach for collecting and efficiently storing the management information in a database, is proposed. The database schema reflects the MIB structure and includes time information as well. Finally, a brief description of the prototype that implements the proposed management concept is included in this paper.

The inverse scattering problem for a rigid ellipsoid in linear elasticity

The inverse scattering problem for the rigid ellipsoid in linear elasticity is examined. It has been proved that six measurements of the first-order imaginary coefficient of the radial scattering amplitude in the low-frequency region are necessary in order to evaluate the semi-axes of the ellipsoid and to fix the position of the principal axes of the ellipsoid. Numerical results and degenerate cases of the ellipsoidal geometry are also presented.

An e-learning service management architecture

We propose a configurable architecture for implementing e-learning service management, taking into account several diverse aspects concerning not only the educational process, but also network infrastructure, the QoS requirements, the types of educational content, etc. We present a flexible, parametrical and component-oriented management scheme, which dynamically creates a session profile for each request for e-learning service according to current context that depends on all diverse aspects that an e-learning service comprises. Continuously, we analyse the components comprising the management scheme and the management information bases that they maintain.

DHTbd: A Reliable Block-Based Storage System for High Performance Clusters

Large, reliable and efficient storage systems are becoming increasingly important in enterprise environments. Our research in storage system design is oriented towards the exploitation of commodity hardware for building a high performance, resilient and scalable storage system. We present the design and implementation of DHTbd, a general purpose decentralized storage system where storage nodes support a distributed hash table based interface and clients are implemented as in-kernel device drivers. DHTbd, unlike most storage systems proposed to date, is implemented at the block device level of the I/O stack, a simple yet efficient design. The experimental evaluation of the proposed system demonstrates its very good I/O performance, its ability to scale to large clusters, as well as its robustness, even when massive failures occur.

Managing the network state evolution over time using CORBA environment

This paper proposes a CORBA-based framework for managing the network state evolution over time. This framework is based on the concept of CORBA temporal agents, capable of managing the past and current behavior of network resources. Managed objects use specific time attributes for representing how their values are evolving in time. Moreover, specially designed operations (services) enable users to exploit the temporal dimension of management information in order to understand the past, control the present, and thus even predict the future of managed objects. The management environment is designed in order to provide coexistence and interoperability with existing management platforms.

Network management services using a temporal information model

In this paper we address the issue of time as an attribute of the network management information. More precisely, we incorporate the temporal dimension in the management information model proposed by the Internet Engineering Task Force (IETF), as it is described by SMI. The core of the proposed network management information model is the Temporal Management Information Base (TMIB), a conceptual representation of the diachronic behaviour of network resources. We define the architecture as well as the services supporting our view. Finally, we give the exact definition of one key service using ASN. 1 formulation.