Showing papers by "University of the Aegean published in 1997"

The Economics of Tourism

Abstract: 1. The scope and limitations of economic analysis 2. The microfoundations of tourism demand 3. Empirical studies of tourism demand 4. The theory of tourism supply and its market structure 5. The structure, performance and strategies of tourism firms 6. Tourism in an international context 7. Tourism and environmental issues 8. Environmental valuation and sustainability 9. Conclusions

Lightweight languages as software engineering tools

Abstract: Software subsystems can often be designed and implemented in a clear, succinct, and aesthetically pleasing way using specialized linguistic formalisms In cases where such a formalism is incompatible with the principal language of implementation, we have devised specialized lightweight languages Such cases include the use of repeated program code or data, the specification of complex constants, the support of a complicated development process, the implementation of systems not directly supported by the development environment, multiparadigm programming, the encapsulation of system level design, and other complex programming situations We describe applications and subsystems that were implemented using this approach in the areas of user interface specification, software development process support, text processing, and language implementation Finally, we analyze a number of implementation techniques for lightweight languages based on the merciless exploitation of existing language processors and tools, and the careful choice of their syntax and semantics

Connectedness of the efficient set for three-objective quasiconcave maximization problems

Abstract: For three-objective maximization problems involving continuous, semistrictly quasiconcave functions over a compact convex set, it is shown that the set of efficient solutions is connected. With that, an open problem stated by Choo, Schaible, and Chew in 1985 is solved.

Aspects of heterogeneity in the distribution of diversity of the European herpetofauna

Abstract: In the western Palearctic, species richness decreases with increasing latitude for amphibians and reptiles. Hotspots are found in the southermost parts of the area for reptiles, while for amphibians they are in western middle latitude parts. Rapoport's rule predicts that species range increases with latitude and that hotspots contain many species of small range. Both prediction are upheld in the case of reptiles, but the hotspots for amphibians contain mostly widespread species. Most amphibian species of small range are found in southern areas. The seasonal climatic variation hypothesis that has been proposed as an explanation for Rapoport's rule is not verified for the Palearctic herpetofauna.

Assessment of Metal Contamination in Shallow Coastal Sediments Around Mytilene Greece

Abstract: Different normalisation procedures were applied on a data set of metal concentrations of sediments from 28 stations in the harbour and coastal area of Mytilene, Lesvos island, Greece Due to the great granulometric variability of the sediments the normalisation for grain-size was not applicable Also, the normalisation to a carbonate-free basis did not provide additional information On the other hand the normalisation to Al and the calculation of enrichment factors of metals enabled to distinguish between contaminated and non-contaminated areas The harbour sediments were highly enriched in Cd, Cu and Zn and also slightly enriched in Pb No enrichment was found in the sediments of the coastal area outside the harbour, indicating that the metal rich deposits of that confined area are not affecting the quality of the neighbouring coastal environment

Students, Natives, Colleagues: Encounters in Academia and in the Field

Abstract: institutions. In general, U.S. anthropologists have paid more attention than Europeans to issues concerning the situation of "native" or "indigenous" anthropologists. In the 1970s, discussions about native anthropologists focused primarily on their relative capacity to achieve a neutral or objective perspective and on their relative ease of access to "inside" information. Moreover, there have been many assertions that native anthropologists, and especially scholars "of color," infuse the discipline with politically relevant questions and perspectives, which derive from their own positionality and experience. In fact, many of the arguments sustaining this view have been central to critiques addressing the politics of anthropological knowledge that have been put forth by academics engaged in ethnic or cultural studies in the United States as well as by anthropologists.' However, nowadays it is reasonable to doubt that native anthropologists constitute a distinct category, on several grounds. The "insider"-"native" versus "outsider"-"foreigner" dichotomy has been relativized or deconstructed, as have many other categories (e.g., periphery versus center, private versus public) that were central to anthropological theorizing. From the perspective of the current theoretical emphasis on the multiplicity and negotiability of identity in general, the meaning of native seems far from given. Also, on a practical level, the proliferation of channels for international communication has facilitated the integration of non-Euro-Americans into the international community of anthropologists. Nevertheless, I doubt that these developments have fundamentally altered the ways in which anthropologists think and practice. Many of the ideas associated with now obsolete conceptual dichotomies are not exhausted, but are rephrased in more fashionable terms, like the "local" versus "global" contrast, which seems quite central in current anthropological discourse. The understanding

Variational and conformal structure of nonlinear metric-connection gravitational lagrangians

Abstract: We examine the variational and conformal structures of higher order theories of gravity which are derived from a metric-connection Lagrangian that is an arbitrary function of the curvature invariants. We show that the constrained first order formalism when applied to these theories may lead consistently to a new method of reduction of order of the associated field equations. We show that the similarity of the field equations which are derived from appropriate actions via this formalism to those produced by Hilbert varying purely metric Lagrangians is not merely formal but is implied by the diffeomorphism covariant property of the associated Lagrangians. We prove that the conformal equivalence theorem of these theories with general relativity plus a scalar field, holds in the extended framework of Weyl geometry with the same forms of field and self-interacting potential but, in addition, there is a new `source term' which plays the role of a stress. We point out how these results may be further exploited and address a number of new issues that arise from this analysis.

Pupils’ Ideas on Conservation during Changes in the State of Water

Abstract: The aim of this paper is to explore both the qualitative and quantitative dimensions of pupils’ ideas relevant to conservation during the changes occurring in the physical state of water. For the study of these ideas a questionnaire was developed and applied to a large sample of primary and secondary students. The items of the questionnaire concern the phenomena of evaporation, boiling and condensation. The analysis of the data showed that qualitative understanding precedes quantitative. The latter is achieved by pupils of 14‐15 years old. Furthermore, our analysis showed that pupils acquire the school science view at an earlier age than that suggested in previous literature.

How the Others Plan: Exploring the Shape and Forms of Informal Planning:

Abstract: Informal planning, although non-institutionalized, leads to planned outcomes that serve particular interests. The informal planning path runs parallel to or mixes with formal planning, shaping the ...

The Rationality of Distinctions and the Emergence of Power: A Critical Systems Perspective of Power in Organizations

Abstract: Power in organizations is usually regarded as a phenomenon generated by their structural features, or by existing social relationships. By sharing the ideas of Habermas and Foucault, critical systems thinking endeavours to offer an understanding of power based on its dialectical nature. Power is thus conceived as a coercive yet positive force, able to trigger resistance and emancipation. This paper proposes that critical systems thinking ought to link power with action in an analytical framework based on a systems perspective of organizations. By adopting a second-order cybernetics perspective of organizations, the paper deals with power as a phenomenon which emerges in the operational and observational distinctions during interactions mediated by language. A generic linguistic force, namely a command, concealed in any speech act, is considered responsible for the detachment (distinction) of a part from the whole, and thus, alternatively, from its reduction to the role of subject or object. According to this view, more attention should be paid to the fears felt by human beings when confronting their subjectivity, than to the fears felt in response to the repression of their subjectivity, as established theories of power suggest. © 1997 by John Wiley & Sons, Ltd.

A survey of recursive algorithms for the solution of the discrete time Riccati Equation

Abstract: The Riccati Equation plays a fundamental role in many fields of mathematics, science and engineering. Its solution constitutes an integral prerequisite to the solution of important problems in the above fields. Due to the importance of the Riccati Equation, there exists considerable literature on its algebraic as well as algorithmic solution. A very large number of those studies are devoted to the continuous time Riccati Equation. In this paper we present a survey of classical as well as more recent recursive algorithms that solve the discrete time Riccati Equatbn emanating from the Kaiman Filter as well as from the Lainiotis Filter equations either using per step calculations or the doubling principle. It is established that these algorithms converge fast and are numerically stable.

Proof of the Cosmic No-Hair Conjecture for Quadratic Homogeneous Cosmologies

Abstract: We prove the cosmic no-hair conjecture for all orthogonal Bianchi cosmologies with matter in the $R+\beta R^2$ theory using the conformally equivalent Einstein field equations, with the scalar field having the full self-interacting potential, in the presence of the conformally related matter fields. We show, in particular, that the Bianchi IX universe asymptotically approaches de Sitter space provided that initially the scalar three-curvature does not exceed the potential of the scalar field associated with the conformal transformation. Our proof relies on rigorous estimates of the possible bounds of the so-called Moss-Sahni function which obeys certain differential inequalities and a non-trivial argument which connects the behaviour of that function to evolution of the spatial part of the scalar curvature.

Addressing Threats and Security Issues in World Wide Web Technology

Abstract: We outline the Web technologies and the related threats within the framework of a Web threat environment. We also examine the issue surrounding dowloadable executable content and present a number of security services that can be used for Web transactions categorised according to the Internet layering model.

Cryptographic Protocols over Open Distributed Systems: A Taxonomy of Flaws and related Protocol Analysis Tools

Abstract: When designing and implementing cryptographic protocols one must avoid a number of possible flaws. In this paper we divide possible flaws based on the flaw pathology and the corresponding attack method, into elementary protocol flaws, password/key guessing flaws, stale message flaws, parallel session flaws, internal protocol flaws, and cryptosystem flaws. We then outline and comment on different attack construction and inference-based formal methods, protocol analysis tools, and process integration techniques and their effectiveness in aiding the cryptographic protocol design process by discovering protocol flaws with regard to the aforementioned proposed taxonomy of them.

Aquatic microcosms: a methodological approach for the quantification of eutrophication processes

Abstract: Aquatic microcosm systems were evaluated as a tool for thequantitative description of phytoplankton, bacteria andnutrient relationshipsand the study of nutrient cycling and eutrophication. Thecriteria for the self-developing microcosms were their relative complexity compared to the naturalsystem and the replicability of similar treatments. Theobjective of the work wasto establish standardized procedures for their design,initiation, methodologyand modeling. Glass aquaria were used, each containing 30liters of seawater anda number of inorganic nutrient enrichments was attempted,based on medium ’f‘.The ’f/40‘ dilution treatment was found to be the mostsuccessful on the basisof system complexity and the replication between treatments.The quantitativedescription of the flow of energy through the microbialfood-web was performedusing a simulation model. The relatively high ecosystemcomplexity, thesatisfactory reproducibility and the goodness-of-fit of thedata to the simulation model indicated that the naturally derived aquatic microcosms enriched with medium ’f/40‘ can be used for the study of eutrophication processesconcerning nutrient enrichment and phytoplankton –; bacteriacycling in the coastal marine environment.

A model management system (MMS) for the design and operation of production lines

Abstract: This work presents a prototype model management system (MMS) for the design and operation of manufacturing systems. The model management system classifies different models according to the type of the manufacturing system to which they apply and according to the particular technique employed. In its present state, the system comprises three different techniques, namely, analytical, simulation and artificial intelligence (AI) based techniques for production lines. The first two are evaluative methods, whereas the last one is a generative (optimization) method that solves the well-known buffer allocation problem in a production line. The contribution of this work is twofold. First, the development of an architecture of a MMS which provides a simple and intelligible framework for classifying different modelling techniques, enables the interaction among these models and does not restrict developers to follow a particular model development task. Second, the development of a knowledge based system, called ASBA,...

Attack modelling in open network environments

Abstract: In this paper, the beginnings of a formal generic model describing the process of a malicious attack against a computer network, has been proposed, leading to a Markov chain description. This model can be used for better understanding the nature of malicious attacks against open networks, for defining a simulator to analyse the impact of malicious attacks against computer networks, or for analytically and quantitatively studying the power of several attacks versus the effectiveness of protection mechanisms. A worked out example of the description of a virus attack against a computer network is also given.

An attack detection system for secure computer systems—outline of the solution

Abstract: The spread of distributed information technology has increased the number of opportunities for crime and fraud in computer systems. Despite the fact that computer systems are typically protected by a number of security mechanisms, attacks continue to occur. In addition, it seems infeasible to close all the known security loopholes of today’s systems. No combination of technologies can prevent legitimate users from abusing their authority in a system. Thus, new lines of defence are required to ensure safe operation of computer systems as well as data protection. Attack Detection Systems are an approach to enhancing the security of a computer system. The Attack Detection System (ADS) which is the subject of this paper, is a real-time attack detection system which allocates points to users who are attempting to attack the target system, detects attacks by examining the number of points each user has been given, and takes countermeasures according to this number of points. The outline of the solution that implements the ADS is described in detail in this paper.

The radiographic investigation of the visibility of secondary caries adjacent to the gingiva in Class II amalgam restorations.

Abstract: The aim of this study was to investigate the visibility of secondary caries in the gingivobuccal and gingivolingual corners of teeth restored with amalgam restorations. Standard Class II cavities were created in 15 orthodontically extracted mandibular premolar teeth, and the teeth were randomly divided into five groups of three teeth each. In four of the groups, a 1.0- or 1.5-mm cavity was prepared in the gingivolingual or gingivobuccal corner of the restoration. No lesions were created in group 5, the control group. The teeth were restored with amalgam. The teeth were adapted in the actual tooth space of 15 volunteers with one mandibular premolar missing. Radiographs of each patient were taken with the bisecting-angle technique and the bite wing technique. The radiographs were sorted at random and given to 15 members of the professoriate who were often involved in detecting caries and to 17 members who were not normally involved in detecting caries. The bitewing technique was found to be more reliable than the bisecting-angle technique in detecting secondary caries in gingivobuccal approximal corners (P < .05). It was also found that, in group 1, the bisecting-angle technique was more reliable than the bitewing technique in detecting caries in gingivolingual corners (P < .05). No significant differences were found in the correct evaluation of radiographs between the faculty who were normally involved in the detection of caries and those who were not.

Mathematical problems in higher order gravity and cosmology

Abstract: We discuss the issue of motivating the analysis of higher order gravity theories and their cosmologies and introduce a rule which states that these theories may be considered as a vehicle for testing whether certain properties may be of relevance to quantum theory. We discuss the physicality issue arising as a consequence of the conformal transformation theorem, the question of formulating a consistent first order formalism of such theories and also the isotropization problem for a class of generalized cosmologies. We point out that this field may have an important role to play in clarifying issues arising also in general relativity.

Factorisation in nest algebras

Abstract: We give a necessary and sufficient condition on an operator A for the existence of an operator B in the nest algebra AlgN of a continuous nest N satisfying AA∗ = BB∗ (resp. A∗A = B∗B). We also characterise the operators A in B(H) which have the following property: For every continuous nest N there exists an operator BN in AlgN satisfying AA ∗ = BNB∗ N (resp. A∗A = B∗ NBN ).