Showing papers by "University of the Aegean published in 2004"

Interaction strengths in food webs: issues and opportunities

Abstract: Summary 1. Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory. 2. Much confusion stems from lack of clarity about whether the questions posed relate to community-level patterns or to species dynamics, and to what authors actually mean by the term ‘interaction strength’. Here, we describe the various ways in which this term has been applied and discuss the implications of loose terminology and definition for the development of this field. 3. Of particular concern is the clear gap between theoretical and empirical investigations of interaction strengths and food web dynamics. The ecological community urgently needs to explore new ways to estimate biologically reasonable model coefficients from empirical data, such as foraging rates, body size, metabolic rate, biomass distribution and other species traits. 4. Combining numerical and analytical modelling approaches should allow exploration of the conditions under which different interaction strengths metrics are interchangeable with regard to relative magnitude, system responses, and species identity. 5. Finally, the prime focus on predator‐prey links in much of the research to date on interaction strengths in food webs has meant that the potential significance of nontrophic interactions, such as competition, facilitation and biotic disturbance, has been largely ignored by the food web community. Such interactions may be important dynamically and should be routinely included in future food web research programmes.

The role of emotional intelligence and personality variables on attitudes toward organisational change

Abstract: Although the role of organisational characteristics in the change process has been extensively analysed and discussed in the literature, individual characteristics, which are equally crucial for the success of change, have been neglected. Therefore, the purpose of the present study is to add a different way of looking and working with organisational change by focusing on individuals’ emotions and personality traits. This paper explores how emotional intelligence and the “big five” dimensions of personality can facilitate organisational change at an individual level by exploring the relationship between these attributes and attitudes toward organisational change. The sample consisted of 137 professionals who completed self‐report inventories assessing emotional intelligence, personality traits and attitudes towards organisational change. The results confirmed that there is a relationship between personality traits and employees’ attitudes toward change. Similarly, the contribution of emotional intelligence to the attitudes to change was found to be significant, indicating the added value of using an emotional intelligence measure above and beyond the effect of personality. The practical implications of these findings are discussed in relation to the phases of a change project.

Patterns and Universals of Adult Romantic Attachment Across 62 Cultural Regions Are Models of Self and of Other Pancultural Constructs

Abstract: As part of the International Sexuality Description Project, a total of 17,804 participants from 62 cultural regions completedthe RelationshipQuestionnaire(RQ), a self-reportmeasure of adult romanticattachment. Correlational analyses within each culture suggested that the Model of Self and the Model of Other scales of the RQ were psychometrically valid within most cultures. Contrary to expectations, the Model of Self and Model of Other dimensions of the RQ did not underlie the four-category model of attachment in the same way across all cultures. Analyses of specific attachment styles revealed that secure romantic attachment was normative in 79% of cultures and that preoccupied romantic attachment was particularly prevalent in East Asian cultures. Finally, the romantic attachment profiles of individual nations were correlated with sociocultural indicators in ways that supported evolutionary theories of romantic attachment and basic human mating strategies.

Trend analysis of precipitation time series in Greece and their relationship with circulation using surface and satellite data: 1955–2001

Abstract: In this study, the trends of annual and seasonal precipitation time series were examined on the basis of measurements of 22 surface stations in Greece for the period 1955–2001, and satellite data during the period 1980–2001. For this purpose, two statistical tests based on the least square method and one based on the Mann-Kendall test, which is also capable of detecting the starting year of possible climatic discontinuities or changes, are applied. Greece, in general, presents a clear significant downward trend in annual precipitation for the period 1955–2001, which is determined by the respective decreasing trend in winter precipitation. Both winter and annual series exhibit a downward trend with a starting year being 1984. Satellite-derived precipitation time series could be an alternative means for diagnosing the variability of precipitation in Greece and detecting trends provided that they have been adjusted by surface measurements in the wider area of interest. The relationship between precipitation variability in Greece and atmospheric circulation was also examined using correlation analysis with three circulation indices: the well-known North Atlantic Oscillation Index (NAOI), a Mediterranean Oscillation Index (MOI) and a new Mediterranean Circulation Index (MCI). NAOI is the index that presented the most interesting correlation with winter, summer and annual precipitation in Greece, whereas the MOI and MCI were found to explain a significant proportion of annual and summer precipitation variability, respectively. The observed downward trend in winter and annual precipitation in Greece is linked mainly to a rising trend in the hemispheric circulation modes of the NAO, which are connected with the Mediterranean Oscillation Index.

Minimizing logistics risk through real‐time vehicle routing and mobile technologies: Research to date and future trends

Abstract: Vehicle routing (VR) is critical in successful logistics execution The emergence of technologies and information systems allowing for seamless mobile and wireless connectivity between delivery vehicles and distribution facilities is paving the way for innovative approaches to real‐time VR and distribution management This paper investigates avenues for building upon recent trends in VR‐related research towards an integrated approach to real‐time distribution management A review of the advances to‐date in both fields, ie the relevant research in the VR problem and the advances in mobile technologies, forms the basis of this investigation Further to setting requirements, we propose a system architecture for urban distribution and real‐time event‐driven vehicle management

Questioning the effectiveness of the Natura 2000 Special Areas of Conservation strategy: the case of Crete

Abstract: Aim This study examines the effectiveness of the selected 'network' of Natura 2000 Special Areas of Conservation (SACs) at a regional scale in Greece, in terms of its representativeness of plant biodiversity. Location The island of Crete is used as a case study because it is considered to be one of the 10 hotspots for biodiversity in the Mediterranean Basin. Methods Hotspot analysis and complementarity algorithms are used to define priority areas for conservation and calculate their spatial overlap with the Natura 2000 SACs in Crete. Results The various categories of hotspots contain subsamples of plant categories, used for their definition. Spatial overlap among different categories of hotspots, areas of complementary diversity and Natura 2000 SCAs is low. Main conclusions The results show that the Natura 2000 SACS 'network' in Crete seems insufficient to ensure satisfactory representation of the regional plant biodiversity elements.

Using Data Envelopment Analysis for Measuring and Benchmarking Productivity in the Hotel Sector

Abstract: SUMMARY Low productivity within the hospitality industry has been a major concern, but this situation is unlikely to improve without a general change in the way productivityis measured and managed. This paper aims to illustrate the value of stepwise Data Envelopment Analysis (DEA) for measuring and benchmarking hotel productivity. The issues regarding productivity measurement as well as the advantages of using DEA for measuring productivity are analysed. However, the paper extends current DEA applications by developing a stepwise approach to DEA. The latter technique combines correlation and DEA analysis for developing robust DEA models and its advantages are illustrated by applying it in a dataset of three star hotels in the UK.

Fuzzy cognitive maps in business analysis and performance-driven change

Abstract: Business process reengineering (BPR) has made a significant impact on managers and academics. Despite the rhetoric surrounding BPR, articulated mechanisms, which support reasoning on the effect of the redesign activities to the performance of the business model, are still emerging. This paper describes an attempt to build and operate such a reasoning mechanism as a novel supplement to performance-driven change (PDC) exercises. This new approach proposes the utilization of the fuzzy causal characteristics of fuzzy cognitive maps (FCMs) as the underlying methodology in order to generate a hierarchical and dynamic network of interconnected performance indicators. By using FCMs, the proposed mechanism aims at simulating the operational efficiency of complex process models with imprecise relationships to quantify the impact of performance-driven reengineering activities. This research also establishes generic maps that supplement the strategic planning and business analysis phases of typical redesign projects in order to implement the integration of hierarchical FCMs into PDC activities. Finally, this paper discusses experiments with the proposed mechanism and comments on its usability.

ICT Paradox Lost? A Stepwise DEA Methodology to Evaluate Technology Investments in Tourism Settings

Abstract: Despite the continuous increase of investment in information and communication technologies (ICT) in the tourism industry, empirical studies have not persuasively established corresponding increases in productivity. Indeed several shortcomings have been identified in past studies. This study proposes a new way of assessing ICT productivity. The methodology is tested in a data set from the three-star hotel sector in the United Kingdom using a nonparametric technique called data envelopment analysis (DEA). Empirical findings reveal that productivity gains accrue not from investments per se, but from the full exploitation of the ICT networking and informationalization capabilities. A model for managing ICT applications and benefits is proposed.

Vector evaluated differential evolution for multiobjective optimization

Abstract: A parallel, multi-population differential evolution algorithm for multiobjective optimization is introduced. The algorithm is equipped with a domination selection operator to enhance its performance by favouring non-dominated individuals in the populations. Preliminary experimental results on widely used test problems are promising. Comparisons with the VEGA approach are provided and discussed.

A fuzzy cognitive map approach to support urban design

Abstract: This paper is concerned with proposing a fuzzy cognitive map (FCM) driven approach for implementing expert decision support in the area of urban design. Previous research activities modeled a knowledge-based system using first order predicate calculus. The current approach utilizes the inherent analogies between SLD resolution trees and FCMs and proposes the generation of multi-branch map hierarchies in order to model the disjointed conjuncts of the logic-based rules. This research proposes specific algorithms for interpreting the logic-based rules to FCMs as well as specific algorithms and formulas for calculating the values of multi-branch map hierarchies. Finally, this paper presents preliminary experiments and comments on the usefulness of the proposed methodology tool.

On the response of the Aegean Sea to climatic variability: a review

Abstract: The Aegean Sea is a region of special interest for the Mediterranean oceanographic community, as one of the densewater formation sites of the Mediterranean, driving its thermohaline circulation. Early oceanographic literature exhibits significantly varying opinions regarding the role of the Aegean as a contributor to the water masses of the eastern Mediterranean. The higher temporal and spatial resolution studies that followed the introduction of ConductivityTemperature-Depth (CTD) profilers in the 1980s, revealed that the various scenarios were within the interannual variability of dense water formation in the region. A peak in this variability was the appearance of the Eastern Mediterranean Transient event in the early 1990s. This phenomenon showed that the Aegean Sea has the potential to function as a source of dense water for the eastern Mediterranean; however, it takes over this role only sporadically, depending on the meteorological conditions over the eastern Mediterranean and, possibly, central/eastern Europe. The North Atlantic oscillation appears to be a contributor to this bimodal behaviour. Palaeoceanographic information has confirmed the large sensitivity of the Aegean Sea to climatic variability. Based on the available information, possible scenarios are examined for the response of the Aegean to the current climatic trends. Copyright  2004 Royal Meteorological Society.

DBP levels in chlorinated drinking water: effect of humic substances.

Abstract: Chlorination is the most widely used technique for disinfection of drinking water A consequence of chlorination is the formation of Disinfection By-Products (DBPs) The formation of DBPs in drinking water results from the reaction of chlorine with naturally occurring organic materials, principally humic and fulvic acids This paper focuses on the effect of humic substances on the formation of twenty-four compounds belonging to different categories of DBPs This investigation was conducted in two water treatment plants in Greece, Menidi and Galatsi, from July 1999 to April 2000 Humic substances were determined by the diethylaminoethyl (DEAE) method with subsequent UV measurement The techniques used for the determination of DBPs were liquid-liquid extraction, gas chromatography and mass spectrometry The concentrations of DBPs were generally low Total trihalomethanes (TTHMs) ranged from 51 to 246 microg L(-1), and total haloacetic acids (HAAs) concentration ranged from 86 to 284 microg L(-1), while haloaketones (HKs) and chloral hydrate (CH) occurred below 1 microg L(-1) The content of humic substances was found to influence the formation of DBPs and especially TTHMs, trichloroacetic acid (TCA), dibromoacetic acid (DBA), CH, 1,1-dichloropropanone (11-DCP) and 1,1,1-trichloropropanone (1,1,1-TCP) Seasonal variation of TTHMs and HAAs generally followed that of humic substances content with peaks occurring in autumn and spring The trends of 1,1-DCP, 1,1,1-TCP and CH formation seemed to be in contrast to TTHMs and HAAs Trends of formation of individual compounds varied in some cases, probably due to influence of parameters other than humic substances content Statistical analysis of the results showed that the concentrations of TTHMs, CH, 1,1-DCP, 1,1,1-TCP, TCA and DBA are strongly affected from humic substances content (at 001 confidence level) The opposite is true for dichloroacetic acid (DCA) concentration Humic substances also vary to a statistically significant degree during different months, as well as the concentrations of TTHMs, CH, 1,1-DCP, 1,1,1-TCP, TCA and DCA The variance of DBA was not statistically significant Regarding the effect of sampling station, humic substances content showed no statistically significant difference between the two raw water sources studied

A decision tree – based method for the differential diagnosis of Aortic Stenosis from Mitral Regurgitation using heart sounds

Abstract: New technologies like echocardiography, color Doppler, CT, and MRI provide more direct and accurate evidence of heart disease than heart auscultation. However, these modalities are costly, large in size and operationally complex and therefore are not suitable for use in rural areas, in homecare and generally in primary healthcare set-ups. Furthermore the majority of internal medicine and cardiology training programs underestimate the value of cardiac auscultation and junior clinicians are not adequately trained in this field. Therefore efficient decision support systems would be very useful for supporting clinicians to make better heart sound diagnosis. In this study a rule-based method, based on decision trees, has been developed for differential diagnosis between "clear" Aortic Stenosis (AS) and "clear" Mitral Regurgitation (MR) using heart sounds. For the purposes of our experiment we used a collection of 84 heart sound signals including 41 heart sound signals with "clear" AS systolic murmur and 43 with "clear" MR systolic murmur. Signals were initially preprocessed to detect 1st and 2nd heart sounds. Next a total of 100 features were determined for every heart sound signal and relevance to the differentiation between AS and MR was estimated. The performance of fully expanded decision tree classifiers and Pruned decision tree classifiers were studied based on various training and test datasets. Similarly, pruned decision tree classifiers were used to examine their differentiation capabilities. In order to build a generalized decision support system for heart sound diagnosis, we have divided the problem into sub problems, dealing with either one morphological characteristic of the heart-sound waveform or with difficult to distinguish cases. Relevance analysis on the different heart sound features demonstrated that the most relevant features are the frequency features and the morphological features that describe S1, S2 and the systolic murmur. The results are compatible with the physical understanding of the problem since AS and MR systolic murmurs have different frequency contents and different waveform shapes. On the contrary, in the diastolic phase there is no murmur in both diseases which results in the fact that the diastolic phase signals cannot contribute to the differentiation between AS and MR. We used a fully expanded decision tree classifier with a training set of 34 records and a test set of 50 records which resulted in a classification accuracy (total corrects/total tested) of 90% (45 correct/50 total records). Furthermore, the method proved to correctly classify both AS and MR cases since the partial AS and MR accuracies were 91.6% and 88.5% respectively. Similar accuracy was achieved using decision trees with a fraction of the 100 features (the most relevant). Pruned Differentiation decision trees did not significantly change the classification accuracy of the decision trees both in terms of partial classification and overall classification as well. Present work has indicated that decision tree algorithms decision tree algorithms can be successfully used as a basis for a decision support system to assist young and inexperienced clinicians to make better heart sound diagnosis. Furthermore, Relevance Analysis can be used to determine a small critical subset, from the initial set of features, which contains most of the information required for the differentiation. Decision tree structures, if properly trained can increase their classification accuracy in new test data sets. The classification accuracy and the generalization capabilities of the Fully Expanded decision tree structures and the Pruned decision tree structures have not significant difference for this examined sub-problem. However, the generalization capabilities of the decision tree based methods were found to be satisfactory. Decision tree structures were tested on various training and test data set and the classification accuracy was found to be consistently high.

Functional analysis : an introduction

Abstract: Hilbert spaces and basic operator theory: Linear spaces normed spaces first examples Hilbert spaces The dual space Bounded linear operators Spectrum. Fredholm theory of compact operators Self-adjoint operators Functions of operators spectral decomposition Basics of functional analysis: Spectral theory of unitary operators The fundamental theorems and the basic methods Banach algebras Unbounded self-adjoint and symmetric operators in $H$ Solutions to exercises Bibliography Symbols index Subject index.

Quantifying the spatial properties of forest canopy gaps using LiDAR imagery and GIS

Abstract: The spatial properties of gaps have an important influence upon the regeneration dynamics and species composition of forests. However, such properties can be difficult to quantify over large spatial areas using field measurements. This research considers how we conceptualize and define forest canopy gaps from a remote sensing point of view and highlights the inadequacies of passive optical remotely sensed data for delineating gaps. The study employs the analytical functions of a geographical information system to extract gap spatial characteristics from imagery acquired by an active remote sensing device, an airborne light detection and ranging instrument (LiDAR). These techniques were applied to an area of semi-natural broadleaved deciduous forest, in order to map gap size, shape complexity, vegetation height diversity and gap connectivity. A vegetation cover map derived from imagery from an airborne multispectral scanner was used in combination with the LiDAR data to characterize the dominant vegetation...

Constructing social representations of science and technology: the role of metaphors in the press and the popular scientific magazines

Abstract: This paper aims to reveal the social representations about the nature and the evolution of Space-Science & Astronomy, Genetics & Biotechnology, Natural Sciences and Engineering & Informatics, throu...

On Quasimonotone Variational Inequalities

Abstract: The purpose of this paper is to prove the existence of solutions of the Stampacchia variational inequality for a quasimonotone multivalued operator without any assumption on the existence of inner points. Moreover, the operator is not supposed to be bounded valued. The result strengthens a variety of other results in the literature.

Enhancing Web privacy and anonymity in the digital era

Abstract: This paper presents a state‐of‐the‐art review of the Web privacy and anonymity enhancing security mechanisms, tools, applications and services, with respect to their architecture, operational principles and vulnerabilities. Furthermore, to facilitate a detailed comparative analysis, the appropriate parameters have been selected and grouped in classes of comparison criteria, in the form of an integrated comparison framework. The main concern during the design of this framework was to cover the confronted security threats, applied technological issues and users' demands satisfaction. GNUnet's Anonymity Protocol (GAP), Freedom, Hordes, Crowds, Onion Routing, Platform for Privacy Preferences (P3P), TRUSTe, Lucent Personalized Web Assistant (LPWA), and Anonymizer have been reviewed and compared. The comparative review has clearly highlighted that the pros and cons of each system do not coincide, mainly due to the fact that each one exhibits different design goals and thus adopts dissimilar techniques for protecting privacy and anonymity.

The ASP‐Qual model: measuring ASP service quality in Greece

Abstract: Service quality is argued to be a crucial success factor for application service providers (ASPs), but yet an empirically validated instrument for measuring the service quality of ASP vendors needs to be developed. This paper aimed to fill in this gap. After synthesising previous literature on the service quality construct within the context of IS, e‐commerce, ICT outsourcing and ASP effectiveness, the paper proposes a set of dimensions and model for measuring ASP service quality. The model is tested by surveying and analysing data from Greek companies using ASP for developing and maintaining their Web stores. Directions for future research, as well as suggestions for improving the practices of ASP suppliers and users’ are also provided.

The HCONE approach to ontology merging

Abstract: Existing efforts on ontology mapping, alignment and merging vary from methodological and theoretical frameworks, to methods and tools that support the semi-automatic coordination of ontologies. However, only latest research efforts ”touch” on the mapping/merging of ontologies using the whole breadth of available knowledge. This paper aims to thoroughly describe the HCONE approach on ontology merging. The approach described is based on (a) capturing the intended informal interpretations of concepts by mapping them to WordNet senses using lexical semantic indexing, and (b) exploiting the formal semantics of concepts’ definitions by means of description logics’ reasoning services.

E‐volution of a supply chain: cases and best practices

Abstract: Supply chain management (SCM) is an integrating philosophy to manage the total flow of materials, information and finance from supplier to ultimate customer. The goal of SCM is to meet the needs of the final consumer by supplying the right product at the right place, time and price. Companies use SCM as a way to meet the competitive challenges of today's business environment. The focus of SCM has shifted from engineering efficient functional processes to the co‐ordination of activities in a supply chain network. The aim of this paper is to examine the stages in the evolution of the supply chain to an electronic supply chain. To illustrate and support the types of evolutionary progress involved, best practices and case studies are provided and analysed.