Showing papers by "University of Piraeus published in 2001"

EMU and European Stock Market Integration

Abstract: The paper examines whether or not the convergence of European economies towards Economic and Monetary Union (EMU) and the launch of the single currency leads to an increase in stock market integration through a reduction in investment barriers. We estimate a conditional asset pricing model, which allows for a time-varying degree of integration that measures the importance of EU-wide risk relative to country-specific risk. The model accounts for intra-European currency risk, time-varying quantities and prices of risk. The results indicate that the degree of integration is closely related to forward interest differentials vis-a-vis Germany, i.e. to the probability of a country joining EMU. As the probability of the single currency materializing increases, restrictions on holding foreign assets become less binding, leading to higher market integration.

The dynamic berth allocation problem for a container port

Abstract: This paper addresses the problem of determining a dynamic berth assignment to ships in the public berth system. While the public berth system may not be suitable for most container ports in major countries, it is desired for higher cost-effectiveness in Japan's ports. The berth allocation to calling ships is a key factor for efficient public berthing. However, it is not calculated in polynomially-bounded time. To obtain a good solution with considerably small computational effort, we developed a heuristic procedure based on the Lagrangian relaxation of the original problem. We conducted a large amount of computational experiments which showed that the proposed algorithm is adaptable to real world applications.

Receipt-Freeness in Large-Scale Elections without Untappable Channels

Abstract: For an electronic election to be fully democratic there is a need for security mechanisms that will assure the privacy of the voters. With receipt-free electronic voting, a voter neither obtains nor is able to construct a receipt proving the content of her vote. In this paper we first consider the minimal requirements for receipt-free elections, without untappable communication channels between the voter and the voting authorities. We then propose a solution, which satisfies these requirements. This solution is based on an encryption blackbox, which uses its own randomness. Finally we present an implementation with smartcards, suitable for Internet voting.

Web search using a genetic algorithm

Abstract: Webnaut is an intelligent agent system that uses a genetic algorithm to collect and recommend Web pages. A feedback mechanism adapts to user interests as they evolve. The authors first describe intelligent assistant systems in general and then present the Webnaut architecture, its learning agent, and the genetic algorithm. They conclude with results from two preliminary experiments that tested the accuracy and adaptability of the learning agent.

On the use of EEG features towards person identification via neural networks

Abstract: Person identification based on spectral information extracted from the EEG is addressed in this work-a problem that has not yet been seen in a signal processing framework. Spectral features are extracted non-parametrically from real EEG data recorded from healthy individuals. Neural network classification is applied on these features using a Learning Vector Quantizer in an attempt to experimentally investigate the connection between a person's EEG and genetically specific information. The proposed method, compared with previously proposed methods, has yielded encouraging correct classification scores in the range of 80% to 100% (case-dependent). These results are in agreement with previous research showing evidence that the EEG carries genetic information.

On Modelling Speculative Prices: The Empirical Literature

Abstract: Traditionally, financial theory and in particular asset pricing models have assumed (implicitly or explicitly) a certain probabilistic structure for speculative prices. The probabilistic structure is usually defined in terms of specific statistical models and relates to the dependence, heterogeneity and the distribution of such prices. The primary objective of this paper is to trace the development of various statistical models proposed since Bachelier (1900), in an attempt to assess how well these models capture the empirical regularities exhibited by data on speculative prices.

Deterministic software-based self-testing of embedded processor cores

Abstract: A deterministic software-based self-testing methodology for processor cores is introduced that efficiently tests the processor datapath modules without any modification of the processor structure. It provides a guaranteed high fault coverage without repetitive fault simulation experiments which is necessary in pseudorandom software-based processor self-testing approaches. Test generation and output analysis are performed by utilizing the processor functional modules like accumulators (arithmetic part of ALU) and shifters (if they exist) through processor instructions. No extra hardware is required and there is no performance degradation.

SimHuman: A Platform for Real-Time Virtual Agents with Planning Capabilities

Abstract: In this paper, we present SimHuman, a platform for the generation of real-time 3D environments with virtual agents. SimHuman is highly dynamic and configurable, as it is not based on fixed scenes and models, and has an embedded physically based modelling engine. Its agents can use features such as path finding, inverse kinematics and planning to achieve their goals. The paper explains in detail design and implementation issues and presents the architecture of the system as well as an illustrative example.

Web Passive Voice Tutor: an intelligent computer assisted language learning system over the WWW

Abstract: We describe Web Passive Voice Tutor (Web PVT), an adaptive teaching Web-based intelligent computer assisted language learning (ICALL) program that is aimed at teaching non-native speakers the passive voice of the English language. The design of the system has been largely based on the results of an empirical study that was conducted at schools with the collaboration of human teachers. Web PVT incorporates techniques from intelligent tutoring systems (ITS) and adaptive hypermedia (AH) technologies to provide students with individualised instruction and feedback. The system uses a combination of stereotypes and the overlay technique for the initialisation of the student model, which is then refined by observing the student while working with the system. The resulting student model is used for the annotation of the links to topics presented to the student. In addition, it is also used in the process of error diagnosis and the adaptation of feedback and advice provided to the student.

Adding an Instructor Modelling Component to the Architecture of ITS Authoring Tools

Abstract: The role of instructors as users/authors of ITS authoring tools is very important for the effectiveness of the produced ITSs. In order for authoring tools to benefit the most from the involvement of instructors, they should provide individualised feedback to them throughout the ITS's life cycle. In most cases the addition of an instructor modelling component to the architecture of an authoring tool may be very beneficial both for the quality of the ITSs to be produced and for the instructor himself/herself. Such an instructor modelling component could acquire information about instructors' preferences, interests and usual activities concerning the courses they author. In addition, it could acquire information about the instructors' level of expertise in particular domains as well as in the authoring process itself. In return it may use this information to increase adaptivity and provision of help to the instructor's needs. The main aim of this paper is to show that an instructor modelling component would be beneficial to all ITS authoring tools. Therefore, we have reviewed the literature and discuss the role that an instructor modelling component could have played in existing authoring tools if it had been incorporated into them. In addition, this paper also describes how an instructor modelling component has been incorporated in an authoring tool that we have developed, which is called WEAR.

A study of the build-time estimation problem for Stereolithography systems

Abstract: In this paper the problem of build-time estimation for Stereolithography systems is examined. Experimental results from various case studies indicate that the accuracy of estimation greatly depends on the type of part geometry representation processed and the uncontrolled laser power fluctuations. It is shown that estimation based on sliced (CLI) representation can be extremely accurate, assuming that the average laser power during fabrication can be predicted. On the other hand, estimations based on tessellated (STL) representation, although not so accurate, satisfy the accuracy requirements imposed at early stages of the Stereolithography process, where no slice data are available. As part of this study, build-time itself is also analyzed and factors affecting it are identified and investigated experimentally. Results indicate that hatching time depends not only on the hatching distance and speed, as originally assumed, but also on the number of hatching vectors employed.

Distributions of numbers of success runs of fixed length in Markov dependent trials

Abstract: Let {Zn, n ≥ 1} be a time-homogeneous {0, 1}-valued Markov chain, and let Nn be a random variable denoting the number of runs of "1" of length k in the first n trials. In this article we conduct a systematic study of Nn by establishing formulae for the evaluation of its probability generating function, probability mass function and moments. This is done in three different enumeration schemes for counting runs of length k, the "non-overlapping", the "overlapping" and the "at least" scheme. In the special case of i.i.d. trials several new results are established.

The influence of enterprise type on the purchasing decision process

Abstract: This article reports on the influence of the enterprise type on the purchasing decision process within selected product types and phases by using analysis of variance on data from Greek manufacturing and utility enterprises Our study examined the influence of enterprise type on four parameters of the purchasing decision process, across two different product types and four phases of the purchasing process The results suggested that all but one parameter varied considerably among the different types of enterprises, and that companies adopt an appropriate structural configuration, which fits to the attributes of the purchased items and the mission of the enterprises

Multi-agent Systems as Intelligent Virtual Environments

Abstract: Intelligent agent systems have been the subject of intensive research over the past few years; they comprise one of the most promising computing approaches ever, able to address issues that require abstract modelling and higher level reasoning. Virtual environments, on the other hand, offer the ideal means to produce simulations of the real world for purposes of entertainment, education, and others. The merging of these two fields seems to have a lot to offer to both research and applications, if progress is made on a co-ordinated manner and towards standardization. This paper is a presentation of VITAL, an intelligent multi-agent system able to support general-purpose intelligent virtual environment applications.

Sea-going labour and greek owned fleet: a major aspect of fleet competitiveness.

Abstract: This analysis aims to examine the current picture of maritime manpower in the Greek registered and owned fleet, as it has been formed during the post-war years. This objective entails the analysis of the current supply and demand for seafarers, the estimation of any shortfalls and their confrontation. Moreover, this study further investigates the contributory factors of the present employment trends, which simultaneously constitute special problems of the sea manpower of the Greek owned fleet and attempt some recommendations. In the context of the above mentioned objective, this analysis emphasizes issues such as recruitment, marine education and wastage. Furthermore, special consideration is given to the significance of labour costs for the development of the Greek owned fleet, particularly to subjects such as the various ways of reducing manning costs and their repercussions on the employment of Greek seamen. Finally, this analysis examines the trends of the state shipping policy concerning labour issue...

The Asymmetric Relation Between Initial Margin Requirements and Stock Market Volatility Across Bull and Bear Markets

Abstract: Linear regressions as well as exponential GARCH-in-mean models reveal that in the post-1934 period higher initial margin requirements associate with lower subsequent stock market volatility during normal and bull periods, but show no relationship during bear periods. Higher initial margins are also negatively related to the conditional mean of stock returns, apparently because they reduce systemic risk. These empirical regularities are consistent with the pyramiding-depyramiding framework of stock prices that U.S. Congress had in mind when it instituted margin regulation in 1934 and suggest that a prudential rule for setting margins over time would be to lower them in bear markets in order to enhance liquidity and avoid a de-pyramiding effect, but subsequently raise them and keep them at the higher level in order to prevent a future pyramiding effect.

Design Principles for Closed Loop Supply Chains

Abstract: In this paper we study design principles for closed loop supply chains. Closed loop supply chains aim at closing material flows thereby limiting emission and residual waste, but also providing customer service at low cost. We study 'traditional' and 'new' design principles known in the literature. It appears that setting up closed loop supply chains requires some additional design principles because of sustainability requirements. At the same time however, we see that traditional principles also apply. Subsequently we look at a business situation at Honeywell. Here, only a subset of the relevant design principles is applied. The apparent low status of reverse logistics may provide an explanation for this. To some extent, the same mistakes are made again as were 20 years ago in, for instance, inbound logistics. Thus, obvious improvements can be made by applying traditional principles. Also new principles, which require a life cycle driven approach, need to be applied. This can be supported by advanced management tools such as LCA and LCC.

Student and Instructor Models: Two Kinds of User Model and Their Interaction in an ITS Authoring Tool

Abstract: WEAR is a Web-based authoring tool for Intelligent Tutoring Systems in Algebra related domains. Apart from modelling the student which is a common practice in almost all ITSs and ITS authoring tools, WEAR deals also with modelling the other class of its users: the instructors. Student and instructor models in WEAR interact with each other by exchanging information. This is in favour of both classes of WEAR's users, since they are affected by each other in a way similar to the one in a real educational setting. This paper describes the two kinds of user model and the type of information that they exchange. The issues raised in this research may be applied to other authoring t ools by the addition of an instructor modelling component.

Volatility in currency markets

Abstract: Restates the importance of asset volatility forecasts for option pricing and portfolio management and outlines previous research on forecasting models. Discusses the relative information content and predictive power of implied and historical volatility and the existence of overreaction in option markets. Analyses 1989‐1997 daily exchange rate data for six currencies to examine this. Presents the results, which suggest that implied volatility has more information than volatility based on past prices; and is better than GARCH‐based or historic volatility forecasts for horizons up to three months; but can be a biased predictor of future realized volatility. Finds limited evidence that long term volatilities in option prices overreact to short term volatilities.

Virtual Agent Societies with the mVITAL Intelligent Agent System

Abstract: Intelligent multi-agent systems are currently used for a variety of purposes, both in research and for real-world applications. One of their most interesting, yet not fully explored uses, is as frameworks to support computer-based simulations of virtual worlds inhabited by life-like entities, that is, intelligent virtual environments, for purposes of education, demonstration and entertainment. This paper is a presentation of mVITAL, an intelligent multi-agent system aiming to serve most of the fields such systems are today used in, while being fully capable of supporting intelligent virtual environment applications, where issues such as sophisticated virtual reality representation, advanced reasoning, as well as user embodiment, intervention and interaction, are crucial. To justify this, a fully operational example of such an application, namely, the Vital Playground, is also presented.

Macroeconomic factors and stock returns in a changing economic framework: the case of the Athens stock exchange

Abstract: Outlines previous research on the capital asset pricing model and its extensions; and fluctuations in the Greek economy and capital market between 1980 and 1992. Develops a mathematical, multi‐factor, risk‐return model and applies it to Greek data for this period, split into two sub‐periods: 1980‐1986 and 1986‐1992. Identifies and discusses the m ost important macrovariables influencing security returns for both periods. Concludes that the model does capture the features of a changing economic environment and links risk premia to macroeconomic factors, although it lacks intertemporal stability.

Maritime safety: facts and proposals for the European OPA

Abstract: Following the marine accident of Erika off the French coast in 1999 shipping administration (and especially the European Union) – in its familiar reactive way – is ready to legislate against tankers of more than 15 years of age, against negligent classification societies and against single‐hull tankers. The positive fact is the initiative of the European Parliament and the Council to set up a community framework for cooperation in the field of accidental or deliberate marine pollution. Moreover, the EU fears that all sub‐standard tankers will eventually be banned from the USA – due to the gradual enforcement of the Oil Pollution Act 1990 – and will come to European waters to continue their polluting habits. So, Europe is about to legislate its own Oil Pollution Act, on even stricter terms than the USA. Provides a survey of the issues involved by setting down the correct – in the author’s opinion – facts about marine accidents, the misunderstanding of which has negated the effectiveness of all measures taken so far against marine accidents.

Using Virtual Reality Techniques for the Simulation of Physics Experiments

Abstract: Educational software has known significant evolution over the past few years due to the introduction of technologies such as multimedia and the World Wide Web. These innovations have significantly offered in the field of computer-based instruction, by providing the means for remote, interactive and intuitive applications. There are, however, some categories of applications such as Virtual Laboratories, where these applications prove to be inadequate. In this paper we discuss some of the limitations of multimedia and the world wide web and present some of the advantages virtual reality technology has to offer in the field of education. We also propose an architecture and methodology for the development of Virtual Laboratory applications and present a case study on the development of a Virtual Physics Laboratory.

Authoring and delivering adaptive Web-based textbooks using WEAR

Abstract: The authors describe the adaptive courseware authoring capabilities of WEAR, an ITS authoring tool for algebra-related domains. The system allows the authoring of electronic textbooks and delivers them over the WWW. Then, learners are offered navigation support adapted to their individual needs and knowledge. The domain knowledge and the information kept in learner models are used in WEAR to provide adaptive navigation to students and also to support the instructional designers in the authoring process. An instructor model incorporated in WEAR's architecture contains additional information that is exploited by the system to achieve the goal of authoring support.

Emerging elements of a world view for sustainable quality

Abstract: The ongoing economic globalization is seen by many to inflict serious undesirable impacts. These are forcing governments, scientists and a number of businesses to question the validity of the assumptions of the way economic growth is created and its long-term effects on a sustainable quality of life. Increasing inequalities of wealth among and within developed and less developed societies, rising levels of discontent and international crime, increasing pollution of the natural environment and more intense and frequent climate-related natural disasters all combine to raise questions about how sustainable are our ways of improving our standards of living and the world view of aiming for a single global economy amidst violent conflicts related to control of natural resources, religious, ethnic and cultural differences that threaten our very existence on planet Earth. In this context, attempting to improve quality for specific products and services to make any single company more profitable might be a futile ...

Empowerment in Total Quality: Designing and Implementing Effective Employee Decision-Making Strategies

Abstract: The barrage of changes outside and inside contemporary business organizations adopting total quality management (TQM) principles has resulted in a trend toward the empowerment of their employees. T...

Study of composite patch repair by analytical and numerical methods

Abstract: A combined analytical and numerical study of an isotropic cracked plate that was repaired by using a bonded composite patch was conducted. The analytical work was based on Rose's equations, whereas for the numerical investigation a three-dimensional finite element analysis was implemented. A number of cracked plates with different crack lengths and overall dimensions of the composite repair were considered. The composite patch was made of unidirectional laminates with different stacking sequences. Both, one- and two-sided patches were analysed. Results are presented for the stress intensity factor in the patched crack and the maximum stress reinforcement stress and adhesive strain. It was found that for the case of a two-sided reinforcement the results obtained by both methods were in good agreement. However, for the case of a single reinforcement the accuracy of the analytical method decreased due to the tendency to out-of-plane bending as a result of bonding a reinforcing patch to only one face of a plate, which is ignored in the analysis.