Showing papers by "University of Piraeus published in 2000"

Secure Transactions with Mobile Agents in Hostile Environments

Abstract: A major problem of mobile agents is their apparent inability to authenticate transactions in hostile environments. In this paper, we consider a framework for the prevention of agent tampering without compromising the mobility or autonomy of the agent. Our approach uses encrypted functions. We present an RSA implementation which answers affirmatively the open problem on undetachable signatures of Sander and Tschudin.

Low power/energy BIST scheme for datapaths

Abstract: Power in processing cores (microprocessors, DSPs) is primarily consumed in the functional modules of the datapath. Among these modules, multipliers consume the largest amount of power due to their size and complexity. We propose low power BIST schemes for datapath architectures built around multiplier-accumulator pairs, based on deterministic test patterns. Two alternatives are proposed depending on whether the target is low energy dissipation during a BIST session or low power dissipation (i.e. average energy dissipation between successive test vectors). The proposed BIST schemes are more efficient than pseudorandom BIST for the same high fault coverage target. Up to 78.33% energy saving is achieved by the proposed low energy BIST scheme and up to 82.22% power saving is achieved by the proposed low power BIST scheme, compared with pseudorandom BIST.

An explanatory study on electronic commerce for reverse logistics.

Abstract: E-commerce for reverse logistics is an area of web applications that has been active and progressing aggressively, especially in the US, though it has not been explicitly recognised until now. It has given reverse logistics in general and especially remanufacturing of parts and re-use of surplus goods an important stimulus. However, existing E-commerce models are rather restricted and represent simply the migration of conventionally practices over the Web.

Student Modelling in an Intelligent Tutoring System for the Passive Voice of English Language

Abstract: This paper describes an intelligent multimedia tutoring system for the passive voice of the English grammar. The system may be used to present theoretical issues about the passive voice and to provide exercises that the student may solve. The main focus of the tutor is on the student's error diagnosis process, which is performed by the student modelling component. When the student types the solution to an exercise, the system examines the correctness of the answer. If the student's answer has been erroneous it attempts to diagnose the underlying misconception of the mistake. In order to provide individualised help, the system holds a profile for every student, the long term student model. The student’s progress and his/her usual mistakes are recorded to this long term student model. This kind of information is used for the individualised error diagnosis of the student in subsequent sessions. In addition, the information stored about the student can also be used for the resolution of an arising ambiguity, as to what the underlying cause of a student error has been.

Valuation Effects of Greek Stock Dividend Distributions

Abstract: This study analyses the price reaction to stock dividend distributions by firms listed on the Athens Stock Exchange on both the announcement and the ex-dividend day. It also analyses earnings per share, dividends per share and trading volume in the pre- and post-announcement periods. The findings show statistically insignificant abnormal returns on both the announcement and the ex-dividend day. The analysis does not reveal any significant change in earnings per share and dividends per share, but it does reveal a significant decline in the market-adjusted trading volume in the post dividend period. The findings, based on a different institutional environment, expand the empirical evidence on the value effects of stock dividends.

Sequential fault modeling and test pattern generation for CMOS iterative logic arrays

Abstract: Iterative Logic Arrays (ILAs) are widely used in the datapath parts of digital circuits, like general purpose microprocessors, embedded processors, and digital signal processors. Testing strategies based on more comprehensive fault models than the traditional combinational fault models have become an imperative need in CMOS technology. In this paper, first, we introduce a comprehensive, cell-level, sequential fault model suitable for ILAs, termed Realistic Sequential Cell Fault Model (RS-CFM). RS-CFM drastically reduces test complexity compared to exhaustive two-pattern testing proposed so far in the literature for sequential ILA testing, without sacrificing test quality. In addition, it favors robustness of sequential test sets both at the cell and the array levels. Second, a new Automatic Test Pattern Generator (ILA-ATPG) based on RS-CFM for the case of one-dimensional ILAs is presented. ILA-ATPG can handle all classes of one-dimensional ILAs: unilateral or bilateral ILAs, with or without vertical inputs/outputs. Based on a graph model, ILA-ATPG explores the C-testability and linear-testability of the ILA under test and resolves the test invalidation problem constructing robust test sequences. The efficiency of ILA-ATPG is demonstrated through a comprehensive set of experimental results over all classes of one-dimensional ILAs, including all practical one-dimensional ILAs, as well as a number of more complex benchmarks.

Reliability Approximation for Markov Chain Imbeddable Systems

Abstract: In the present article, a simple method is developed for approximating the reliability of Markov chain imbeddable systems. The approximating formula reduces the problem to the reliability assessment of smaller systems with structure similar to the original systems. Two specific reliability structures which have attracted considerable research interest recently (r-within-consecutive-k-out-of-n system and two dimensional r-within-k1 × k2-out-of-n1 × n2 system) are studied by the new approach and numerical calculations are carried out, which reveal the high quality of our approximations. Several possible extensions and generalizations are also presented in brief.

The Emergence of Electronic Communications Networks in the U.S. Equity Markets

Abstract: Recent regulatory and technological changes have spurred the development of automated trading systems known as ECNs, or electronic communications networks. Proponents of the networks contend that ECNs can cut transaction costs, accelerate trade execution, and expand the price information available to investors. While some critics have questioned the effects of the ECNs on market integration, it is clear that the networks are poised to play an increasingly important role in the new electronic environment.

Involving Effectively Teachers and Students in the Life Cycle of an Intelligent Tutoring System

Abstract: This paper highlights the important role that teachers and students may play in the life cycle of an intelligent tutoring system. In this research, we have developed a system called “EasyMath”, a tutoring system for Algebra that incorporates intelligence. One of the primary aims of EasyMath is to make it useful in school classrooms. This is why, school teachers of mathematics and their students have been involved throughout the life cycle of EasyMath. The system was developed following the rational unified process, an object-oriented methodology for developing software through multiple iterations. The design of EasyMath has been based on the results of an empirical study that was conducted at schools and the resulting product was evaluated by school teachers as well as students.

Total involvement in quality management

Abstract: Involvement is a topic of long‐standing interest to management scholars and practitioners, as evidenced by the proliferation of concepts (job involvement, organisational involvement, employee involvement, total involvement) designed to operationalise the construct. Involvement is also of crucial importance to total quality management as a vital means to achieve customer satisfaction, delight and commitment through continuous quality improvement. Yet, involvement in total quality is different from traditional involvement – being a holistic, multi‐faceted construct; based on distinctive TQM principles; and aiming at different objectives. Furthermore, a number of team involvement mechanisms (i.e. quality circles, quality improvement teams and/or quality project teams) have been used interchangeably in the TQM literature, indicating that these concepts are theoretically redundant. The analysis undertaken in this paper reveals that, although closely related, these constructs are not identical since they fulfil differentiated functions. Suggestions for advancing the study of total involvement in quality management are rendered.

Reference values and prediction equations for FVC and FEV(1) in the Greek elderly.

Abstract: Spirometry prediction equations obtained from middle-age adults, when extrapolated for the elderly, may lead to inaccurate interpretations. The purpose of this study was to determine prediction equations for forced vital capacity (FVC) and forced expiratory volume (FEV1) in the Greek elderly population. Spirometry prediction equations for normal FVC and FEV1 have been derived from tests on 71 healthy persons (38 men, 33 women) aged older than 60 years (range, 65–85 years), nonsmokers, white race, urban population using techniques and equipment that meet American Thoracic Society recommendations. Regression analysis using age, height, and weight as independent variables was used to provide prediction equations and values for both sexes. The FVC age coefficient in this healthy group was about 47.19 mL/y for elderly men and 34.27 mL/y for elderly women, and the FEV1 age coefficient was about 52.8 mL/y for elderly men and 46.4 mL/y for elderly women . Values from this study predicted equations were compared with those from some of the most commonly used sources of spirometry predicted equations. The FVC and FEV1 predicted values were found to be of less mean square error than that of other compared studies. Higher correlation is between FVC and FEV1 predicted values by the present model and FVC and FEV1 observed values in both sexes. The higher correlation between FVC and FEV1 predicted and observed from this study allows the use of our model for predicting in a rather reliable way the FVC and FEV1 for elderly Greek individuals.

DIVA: Distributed Intelligent Virtual Agents

Abstract: In this paper we present DIVA, an architecture for Intelligent Virtual Environments. In DIVA, systems consist of three different modules. There is a World Server that represents the environment in an abstract way, an arb itrary number of Intelligent Agent Clients acting as the world’s inhabitants and a set of Visualisation Clients that generate the system’s visual output. All client modules are autonomous and can be dynamically connected and disconnected to the World Server.

Virtues and Problems of an Active Help System for UNIX

Abstract: An empirical study undertaken on a cross-section of UNIX users at an academic site reveals a role for an active form of help system, rather than the more usual passive kind. Sample scripts supporting this view are presented and the kind of aid required for these examples is discussed. It is then proposed that to provide such aid requires the construction and maintenance of an individual model of each user.

Modelling the Instructor in a Web-Based Authoring Tool for Algebra-Related ITSs

Abstract: This paper describes the development of a web-based authoring tool for Intelligent Tutoring Systems and focuses on its instructor modelling capabilities. The tool is called WEAR and aims to be useful to teachers and students of domains that make use of algebraic equations. Specifically, the tool provides assistance to human teachers while they are constructing exercises and it then monitors the students while they are solving the exercises and provides appropriate feedback. The instructor modelling mechanism renders the system adaptable to the specific needs and interests of each individual user (instructor), concerning the construction of new exercises and the retrieval of existing ones.

Tying, Investment, and the Dynamic Leverage Theory

Abstract: The idea that an incumbent supplier may tie two complementary products to fend off potential entrants is popular among practitioners yet is not fully understood in formal economic theory. We make sense of the argument by formally deriving a dynamic version of the old leverage doctrine. It is shown that when an incumbent monopolist faces the threat of entry in all complementary components, tying may make the prospects of successful entry less certain, discouraging rivals from investing and innovating. Tie-in sales may reduce consumer and total economic welfare.

Product liftings and densities with lifting invariant and density invariant sections

Abstract: Given two measure spaces equipped with liftings or densities (complete if liftings are considered) the existence of product liftings and densities with lifting invariant or density invariant sections is investigated. It is proved that if one of the marginal liftings is admissibly generated (a subclass of consistent liftings), then one can always find a product lifting which has the property that all sections determined by one of the marginal spaces are lifting invariant (Theorem 2.13). For a large class of measures Theorem 2.13 is the best possible (Theorem 4.3). When densities are considered, then one can always have a product density with measurable sections, but in the case of non-atomic complete marginal measures there exists no product density with all sections being density invariant. The results are then applied to stochastic processes. Introduction. It follows from a result of Talagrand [13] that given a complete finite measure space (Ω,Σ, μ) there exists a lifting (called consistent) ̺ on (Ω,Σ, μ) and a lifting π on the direct product (Ω,Σ, μ)⊗̂(Ω,Σ, μ) satisfying the equality π(E1 × E2) = ̺(E1) × ̺(E2) for arbitrary E1, E2 ∈ Σ. Macheras and Strauss [9] proved that given complete finite measure spaces (Ω,Σ, μ), (Θ,T, ν) and a fixed lifting ̺ on (Ω,Σ, μ), one can find liftings σ on (Θ,T, ν) and π on (Ω,Σ, μ) ⊗̂ (Θ,T, ν) such that π ∈ ̺⊗σ, i.e. (P) π(A×B) = ̺(A) × σ(B) for all A ∈ Σ,B ∈ T. There is now a question whether it is possible to get a lifting π that satisfies (P) and has all sections of π(E) lifting invariant for each E ∈ Σ ⊗̂ T . 2000 Mathematics Subject Classification: Primary 28A51; Secondary 60A10, 60G05. Research of N. D. Macheras partially supported by the Research Center of Piraeus University.

An Intelligent Learning Environment for Novice Users of a GUI

Abstract: This paper describes an intelligent learning environment for novice users of a GUI. The learning environment allows users to work in a protected way; it monitors their actions and reasons about them so that it can make hypotheses about what their real intentions have been and examine whether these have been met. In case the system believes that the user has made an error it informs him/her about the error and suggests alternative actions that would have met his/her real intentions. In this way, a novice user can learn from his/her mistakes. The system performs student modelling which is based on an adaptation and implementation of a cognitive theory called Human Plausible Reasoning. The theory is used to simulate a novice user's correct or incorrect thinking as long as this is plausible according to the theory.

The Dynamics of the S&P 500 Implied Volatility Surface

Abstract: This empirical study is motivated by the literature on "smile-consistent" arbitrage pricing with stochastic volatility. We investigate the number and shape of shocks that move implied volatility smiles and surfaces by applying Principal Components Analysis. Two components are identified under a variety of criteria. Subsequently, we develop a "Procrustes" type rotation in order to interpret the retained components. The results have implications for both option pricing and hedging and for the economics of option pricing.

Detection, analysis and rendering of audience reactions in distributed multimedia performance

Abstract: Recent advances in distributed multimedia technologies encourage the development of interactive performance systems. These systems allow multiple users to take part in a performance either as players or spectators and influence its development in real time. However, in order for these applications to become effective they have to provide meaningful interaction capabilities and adequate means of expression to all the participants. This research provide an interaction framework that seeks to address these requirements. In particular, the system allows players and spectators to exchange messages during the performance. These messages describe player actions and audience reactions. Furthermore, the framework monitors the development of the event and analyzes the behavior of the participants in order to: (i) detect and render shared audience reactions (ii) achieve a high degree of audience engagement. Finally, the system synchronizes the presentation of audience reactions with performance developments at each site. This method has been applied in MISSION, a multi-player game on the Web.