Showing papers by "University of the Aegean published in 1996"

Quasimonotone variational inequalities in Banach spaces

Abstract: Various existence results for variational inequalities in Banach spaces are derived, extending some recent results by Cottle and Yao. Generalized monotonicity as well as continuity assumptions on the operatorf are weakened and, in some results, the regularity assumptions on the domain off are relaxed significantly. The concept of inner point for subsets of Banach spaces proves to be useful.

Electric Polarizability and Hyperpolarizability of Carbon Monoxide

Abstract: We report an extensive ab initio study of the electric dipole polarizability and hyperpolarizability of carbon monoxide. The bond length dependence of the molecular properties has been determined f...

Existence theorems for vector variational inequalities

Abstract: ane Y =d wa Rssubsequently studied by many other authors [2, 3, 4, 14, 17] in connection with vectoroptimisation. Theorems asserting the existence of solutions of the VVIP are contained in[3, Theorem 2.1] for single-valued, monotone operators T, where Y has a constant coneC (that is, not depending on x), in [2, Theorem 2.1] for T a single-valued, monotoneoperator, where Y is equipped with a non-constant C(x) and in [14, Theorem 2.1] formultivalued, pseudomonotone operators T, with C(x) constant. However, the proofsof all these theorems contain a mistake: a certain set defined in these papers in assertedto be weakly compact, while this is not the case (see Remark 2 at the end of the presentpaper for details).In the following paragraph we prove the existence of a solution of the VVIP for amulti-valued, monotone operator [9] with constant cone C (Theore 3). Wme also prove

Theoretical and experimental determination of the polarizabilities of the zinc 1S0 state.

Abstract: A combined experimental and theoretical study of the polarizabilities of the ground-state zinc atom is presented In our interferometric measurements we have obtained the frequency dependence of the linear dipole polarizability \ensuremath{\alpha}(\ensuremath{\omega}) between \ensuremath{\omega}=005${\mathit{E}}_{\mathit{H}}$${\mathrm{\ensuremath{\Elzxh}}}^{\mathrm{\ensuremath{-}}1}$ and 014${\mathit{E}}_{\mathit{H}}$${\mathrm{\ensuremath{\Elzxh}}}^{\mathrm{\ensuremath{-}}1}$ (here ${\mathit{E}}_{\mathit{H}}$ is the Hartree energy) A detailed theoretical CCSD(T) study (coupled-cluster with single and double excitations and perturbational treatment of triple excitations) gives the static (zero-frequency) values of the linear dipole polarizability \ensuremath{\alpha}, the second dipole hyperpolarizability \ensuremath{\gamma}, the quadrupole-quadrupole polarizability ${\mathrm{\ensuremath{\alpha}}}_{2}$, and the dipole-dipole-quadrupole polarizability B From these studies we conclude with the static values of \ensuremath{\alpha}=388(8)${\mathit{e}}^{2}$${\mathit{a}}_{0}^{2}$${\mathit{E}}_{\mathit{H}}^{\mathrm{\ensuremath{-}}1}$ (from experiment), \ensuremath{\alpha}=392(8)${\mathit{e}}^{2}$${\mathit{a}}_{0}^{2}$${\mathit{E}}_{\mathit{H}}^{\mathrm{\ensuremath{-}}1}$ (from theory), \ensuremath{\gamma}=31(6)\ifmmode\times\else\texttimes\fi{}${10}^{3}$${\mathit{e}}^{4}$${\mathit{a}}_{0}^{4}$${\mathit{E}}_{\mathit{H}}^{\mathrm{\ensuremath{-}}3}$, ${\mathrm{\ensuremath{\alpha}}}_{2}$=3248(162)${\mathit{e}}^{2}$${\mathit{a}}_{0}^{4}$${\mathit{E}}_{\mathit{H}}^{\mathrm{\ensuremath{-}}1}$, and B=-237(24)\ifmmode\times\else\texttimes\fi{}${10}^{3}$${\mathit{e}}^{3}$${\mathit{a}}_{0}^{4}$${\mathit{E}}_{\mathit{H}}^{\mathrm{\ensuremath{-}}2}$ \textcopyright{} 1996 The American Physical Society

Ferry traffic in the aegean islands: a simulation study.

Abstract: A simulation of ferry traffic in the Aegean islands, which is being used as a decision aiding system for regional development, is presented The model has been developed using SIMSCRIPT II5 and its major variables and parameters, for which data are available, consist of types of vessels, harbour layouts, weather conditions, passenger and vehicle demand, types of vehicles, and loading and unloading times The model has inbuilt flexibility to consider additional variables and parameters depending on data availability and scenarios to be examined The graphics interface is based on a chart of the Aegean Islands and the various types of vessels appear as dynamic entities on the screen either moving or queuing outside busy ports Itineraries are defined through the graphics editor on the basis of coordinates on the chart It has been used for studying the scenarios to compare many combinations of various types of vessels, various types of harbour layout, differing routes, passenger and vehicle demands, and even the establishing of new ports It can also be used to aid decision making about non-profit making itineraries which could then qualify for government subsidies

ARCH effects and cointegration: Is the foreign exchange market efficient?

Abstract: Extensive empirical work has produced mixed evidence regarding the validity of the unbiased efficient expectations hypothesis in the foreign exchange market. Empirical analysis in this paper, via cointegration techniques, produces the same inconclusive results for three currency markets, namely, the FFR/$US, the DM/$US and the Yen/$US foreign exchange market. However, when modeling conditional heteroskedasticity of exchange rates, through autoregressive conditional heteroskedasticity (ARCH) models, the results are fairly conclusive; the presence of the efficient foreign exchange market hypothesis is found in all these three currency markets.

Quantitative assessment of eutrophication: A scoring system for characterising water quality in coastal marine ecosystems

Abstract: A scoring system based on nutrient concentrations was developed to assess coastal water quality according to the trophic level Three nutrient data sets from eutrophic, mesotrophic and oligotrophic waters were used as the reference information for setting up a semi quantitative water quality scale (from 0 to 5) to express different nutrient loadings The validity and sensitivity of the method was applied to a number of stations spaced out along the coastal area of Rhodes (Greece) A score for each nutrient/sampling site was calculated and the scorecard formed, was the data matrix used for numerical classification of the stations The results showed (a) good discrimination between cutrophic, mesotrophic and oligotrophic waters (b) nitrate among the nutrients showed the maximum sensitivity in characterising pollution levels The reference data sets used for assessing eutrophication levels ensured the objectivity of the method The proposed method is described step-by-step and it is suggested that the method can be further adapted to describe other forms of pollution becoming a useful quantitative technique in coastal management practices

A field service support system using a queueing network model and the priority MVA algorithm

Abstract: In many companies, the field service (FS) department plays an important role, contributing up to 40% to the company's total revenue FS managers have to cope with conflicting objectives: (a) to maintain a high level of customer service and (b) to keep the spares inventory level as low as possible Therefore, they need tools to analyse the impact of their decisions on customer service and inventory cost Such a tool is presented in this paper We have developed a closed queueing network model, similar to one due to Waller, incorporating priority classes of customers via the application of the priority mean value analysis (PMVA) algorithm, developed by Shalev-Oren et al This model has been applied to the FS organization of the Greek subsidiary of a multinational computer company, and it has proved to be very efficient from the computational point of view, thus constituting a powerful tool for the FS managers

Intention modelling: approximating computer user intentions for detection and prediction of intrusions

Abstract: This paper introduces and describes an innovative modelling approach which utilises models that are synthesised through approximate calculations of user actions and extensive representation of knowledge about how to perform these actions. The Intention modelling approach is based on theories of cognitive and task modelling as well as on theories of intention, rational action and plan recognition. Intention Models (IMs) have been used in the detection of malicious attacks which usually do not consist of illegal actions, but of a set of actions individually acceptable to the system which at a higher level may form non acceptable task(s). A first effort at implementing these models for a real application was for the creation of the UII system, a research prototype for the detection of anomalous behaviour of network users obtained by reasoning about the characterisation of their intentions. It was developed as an autonomous module within SECURENET, a European funded programme that aims at defending open computer systems, employing advanced techniques and methodologies.

THM Formation in the high‐bromide water supply of Athens

Abstract: For many years the water supply systems in Greece have been disinfected mainly by chlorination. A consequence of chlorination is the formation of trihalomethanes (THM). The aim of this investigation was to determine their levels in the Athens water supply system over a period of time. The sources for this system are the lakes Marathon and Iliki and a number of boreholes. Because of the high bromide concentration, bromoform is the dominant THM formed. Samples from different points of the Galatsi Treatment Plant (GTP) and the distribution network of Athens were taken and analysed for THMs. It was shown that the THM concentrations were lower in the spring and winter than in the summer and autumn. All THM levels measured were lower than the EPA standard. It was also shown that when the water supply from the boreholes was stopped, the concentration of the brominated halomethanes decreased. Bearing in mind that the boreholes were the main source of bromide ions, this behavior was expected.

Seasonal fluctuations of nutrients and pesticides in the basin of Evrotas river, Greece

Abstract: Water and sediment samples from several stations along the Evrotas river, were collected for one year period, from August 1991 to August 1992, and were analysed for nutrients (Total N, NO3‐N and Total P) and pesticides. Higher nutrient concentrations were detected in the part of the river which is flowing through the plain of Sparta and is receiving industrial and domestic effluents, as well as the runoff from the agricultural land of the area. The industrial effluents (orange juice plants) and the agricultural land runoff, seem to play the major role during winter and spring, while the discharge of domestic septage (cesspools contents) in the reduced water flow, appears to be an important source of nutrient pollution during summer. In the water and sediments of the river were detected the herbicides alachlor, atrazine, amitrol and simazine, the insecticides azinphos ethyl, carbofuran, diazinon, dicofol, endosulfan, fenlhion, methyl parathion, as well as the fungicide captan. In the river water, ...

Compact operators and the geometric structure of *-algebras

Abstract: Given a C∗-algebra A and an element A ∈ A, we give necessary and sufficient geometric conditions equivalent to the existence of a representation (φ,H) of A so that φ(A) is a compact or a finite-rank operator. The implications of these criteria on the geometric structure of C∗-algebras are also discussed. Given a C∗-algebra A and an element A of A, we give necessary and sufficient geometric conditions equivalent to the existence of a representation (φ,H) of A so that φ(A) is a compact operator. Our work goes into further detail; as we shall see, we can characterize when A can be represented as a finite-rank or a rank-one operator. In order to implement these characterizations we introduce a new Banach space-geometric notion, the geometric rank. Roughly speaking, elements of finite geometric rank lie at the opposite pole of extreme points in the intuitive sense that they are located on the “flat” parts of the boundary of the unit ball. It turns out that the finiteness of the geometric rank for a particular element A ∈ A guarantees that A can be represented as a finite-rank operator and vice versa. There are many ways one can interpret the results of the present work. One can actually view them as necessary conditions for a Banach space (X , ‖ ‖) to be isometrically isomorphic to a C∗-algebra. Indeed, the spatial structure of the compact operators translates into a purely geometric structure (Theorem 3.2). We consider this as one of the main accomplishments of our work. There is some work which relates to the one in the present paper. Indeed, the problem of characterizing which elements of a C∗-algebra can be represented as rank-one operators has already attracted some attention (see [3]). However, the existing criteria are of algebraic (and not of geometric) nature. 1. Notation and preliminaries If (X , ‖ ‖) is a Banach space, then Xa denotes the closed ball with center 0 and radius a. If S is any subset of X1, then the contractive perturbations of S is the set cp(S) = {x ∈ X | ‖x± s‖ ≤ 1, ∀s ∈ S}. The n-th contractive perturbations of S are defined as cp(S) = cp(cp(n−1)(S)), n = 2, 3, . . . . It is clear that cp(S) is a norm-closed convex subset of X1. One can also verify that S ⊆ cp(S); from this it follows that cp(S) = cp(S). Thus, Received by the editors September 12, 1994 and, in revised form, January 30, 1995. 1991 Mathematics Subject Classification. Primary 47C15, 46B20; Secondary 47D25. c ©1996 American Mathematical Society

Pesticide residues and heavy metals in the evros river delta, n.e. greece

Abstract: Water and sediment samples from six stations of Evros river delta, were collected during different seasons, from August 1992 to July 1993, and were analysed for herbicides, insecticides and heavy metals (sediments). The highest concentrations of herbicides, atrazine, simazine and alachlor, in the water samples from all stations, were detected in August 1992. The same herbicides and organochlorine insecticides, as well as β‐BHC and 4,4'‐DDT, were found in significant amounts in sediments of the river delta. The highest concentrations of the human‐related metals, Cr, Cu and Zn were found in the river sediments during summer, but in the other wetland stations no significant differences were found between seasons. Also, the natural occurring metals (Fe and Mn) did not present important differences between the various areas of the delta, or seasons.

Inflation volatility and stock prices: Evidence from ARCH effects

Abstract: This paper examines the impact of inflation uncertainty on stock prices in developed as well as in emerging capital markets over the period 1980:1–93:12 via an Autoregressive Conditional Heteroskedasticity (ARCH) model for inflation. The results seem to support the presence of a negative association between inflation uncertainty and stock prices.

A non-selfadjoint Russo-Dye Theorem

Abstract: One of the well-known results in the theory of C* algebras is the Russo-Dye Theorem [19]: given a C* algebra .~r the closed convex hull of the unitary elements in ~r equals the closed unit ball of ~r This result was later refined by Gardner and reached its final form by Kadison and Pedersen; today it is known that every operator in a C* algebra ~r whose norm is less than 1, is the average of unitaries from A. The Russo-Dye Theorem initiated the theory of unitary rank in selfadjoint operator algebras. If ~r is an operator algebra, the unitary rank of an element A E ~r is defined as the smallest number for which there is a convex combination of unitaries from ~r of length u(A) and equaling A. If no such decomposition exists (in particular if liAII > 1) we define u(A) = oo. The literature on unitary rank is vast. The earliest result is due to Murray and yon Neumann who proved that any selfadjoint operator of norm I or less is the mean of two unitary operators ([12] p. 239, 1937). The first systematic study was given by R. Kadison and G. Pedersen [8] in 1984 (previous work in the field included contributions by Popa [15], Robertson [17], Gardner [6] and others). In 1986, C. Olsen and G. Pedersen [14] characterized all elements in a factor von Neumarm algebra with finite unitary rank. In the general case of a C*-algebra, a characterization was obtained by Rordam in his important paper [18]. For more details and further information on the theory of unitary rank we refer to the excellent articles of U. Haagerup [7] and M. Rordam [ 18]. In the first section of the present paper, we prove a Russo-Dye type Theorem for infinite multiplicity nest algebras. The techniques employed in the proof of our result are different from that of Gardner and Kadison-Pedersen. To our knowledge, this is the first result of this type, for non-selfadjoint operator algebras and clearly initiates the unitary rank theory for such algebras.

Bases for vector spaces over the two-element field and the axiom of choice

Abstract: It is shown that the axiom of choice follows in a weaker form than the Zermelo Fraenkel set theory from the assertion: every set of generators G of a vector space V over the two element field includes a basis L for V. It is also shown that: for every family A = {Ai : i E k} of non empty sets there exists a family Y ={F i: i E k}of odd sized sets such that, for every i E k, Fi C A iff in every vector space B over the two-element field every subspace V C B has a complementary subspace S iff every quotient group of an abelian group each of whose elements has order 2 has a set of representatives. Blass [1] proved, in ZF, that the axiom of choice, AC (if A is a pairwise disjoint family of non empty sets, then there exists a set C which consists of one and only one element from each element of A), is deducible from the assertion (1) Every vector space has a basis. It is an open question (see [1], p. 33]) whether (1) can be replaced by the weaker statement (2) Every vector space over a specific field has a basis. Halpern [3], working in a weaker theory than ZF (called WZF in [1] and being ZF with the axiom of regularity omitted and the axiom of extensionality weakened so as to admit atoms), deduced AC from the following assertion: (3) In every vector space every generating set contains a basis. Thus, in analogy with (2), one may ask whether (3) can be replaced by the weaker statement In every vector space over the two-element field every generating set contains a basis. It is also an open question (see [2], Theorem 1) whether AC follows, in WZF, from the statement: (5) In every vector space B over the two-element field, every (5) subspace V C B has a complementary subspace S. The research in this paper is motivated by the above mentioned questions. We show in Theorem 1 that, in WZF, AC follows from (4), and we show in Theorem 2 that, also in WZF, the odd axiom of choice, OAC, i.e., the statement: Received by the editors June 21, 1993 and, in revised form, February 16, 1995. 1991 Mathematics Subject Classification. Primary 03E25. (?1996 American Mathematical Society 2527 This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:30:01 UTC All use subject to http://about.jstor.org/terms 2528 KYRIAKOS KEREMEDIS For every family A = {Ai : i E k} of non empty sets there exists a family F ={Fi: i E k} of odd sized sets such that for every i E k Fi C A is equivalent to (5). (OAC is actually equivalent to the statement MC 4(2) from [5], p. 83, and it is due to M. N. Bleicher [2].) In Theorem 3, we show, in WZF, that AC is equivalent to the combination of the statements OAC and EAC, where EAC is the statement given by: For every family A = {Ai: i E k} of non empty sets with IAAi > 1 there exists a family F ={Fi : i E k} of non empty even sized sets such that, for every i E k, Fi C Ai. Finally, in Theorem 4 we show, in ZF, that AC is equivalent to the statement: Every quotient group of an abelian group each of whose elements has order 2 has a set of representatives. Since AC is expressed in terms of sets, it is only natural to work with vector spaces whose elements as well as scalars are sets, and, as expected, addition, ED, and scalar multiplication, * , are symmetric difference and set-theoretic intersection, respectively. Since the set of scalars has to be a field under the above mentioned operations, we see that it must be the two-element field. We are obliged to Professor Andreas Blass for several very useful and intriguing remarks concerning Theorems 1 and 3. Theorem 1. In WZF, AC is deducible from the assertion that in every vector space B over the two-element field, every generating set contains a basis. Proof. Fix A = {Ai : i E k}, a family of non empty sets. Without loss of generality we may assume that Ai n Aj= 0 and Ai is infinite for all i :A j, i, j E k. For every i E k, define (6) Ai = {a C Ai : a or Ai\a is finite}. It is straightforward to see that (Ai, (D), where (D denotes the operation of symmetric difference, is an abelian group in which all elements satisfy xEDx = 0. As is well known, a vector space over the two-element field is the same thing as an abelian group each of whose elements satisfies the equation (7) x+x = 0. Thus, (Ai, (D) is a vector space over the two-element field. From now on, we shall treat vector spaces over the two-element field as abelian groups satisfying (7). Let A denote the direct sum of the family {Ai: i E k}. Then (A,ff), where D: A x A -* A is given by (aED b) (i) = -a(i) ED b (i), is an abelian group satisfying (7). Let G = U{Dja : j E k, a E Aj}, where Dja = {a E A: a(i) = 0 if i # j and a(i) E {{a}, Ai\{a}} otherwise}. It is straightforward to see that G is a set of generators for A. By the assertion of the theorem, there exists a basis L C G for A. This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:30:01 UTC All use subject to http://about.jstor.org/terms BASES FOR VECTOR SPACES AND THE AXIOM OF CHOICE 2529 For every i E k, let ai E A be the element given by: ai (j)Ai if i = j and ai(j) = 0 otherwise. LI Claim 1. For every i E k there is a unique Yi E Ai such that {jy}* E L and ({yi}C)* E L, where {jy}* and ({yi}C)* denote the elements of A which equal {Yi} and {yi}c (= the complement of {y2} with respect to Ai) at i and 0 elsewhere, respectively. Proof of Claim 1. Fix i E k. Let (8) ai = be the unique expression of ai as a finite linear combination of elements from L. Let J ={v < m: ief(i)l is infinite}. Note that KI' cannot be an even number because the symmetric difference of {&v (i) v E J} will be a finite set, and consequently Ai = di(i) will be finite since the remaining vectors will only contribute a finite set. If 1J1 is odd, then the symmetric difference of {e()v E ,} will have a finite complement, say c. Thus, for every element c E c there must be a u < m and a w E J with fu(i) = {c} and f,,(i) = Ai\{c}. (If c E ?v(i) for all v E J, then c E V EJ ?v(i) because 1871 is odd, but this contradicts c E c.) Thus, ai = fu ED ?, This means that in (8) m must be equal to 1, and the conclusion of the claim now follows from the fact that L C G and L is a basis (needed for the uniqueness part). On the basis of the claim we define C={yi :iEk}. Then C is a choice set for A, finishing the proof of Theorem 1. O Theorem 2. OAC iff (5). Proof. (+-) Fix A = {Ai: i E k}, a family of non empty sets. Let A be as in Theorem 1 and (9) V = {a E A: la(i)I = even natural number for every i E k}. It is straightforward to see that V is a subspace of A. Let S be its complementary subspace. Claim 2. For every i E k there is a unique element si E S such that (10) Isi(i)l = odd natural number and Isi(j)I = even natural number for all j E k, j :A i. This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:30:01 UTC All use subject to http://about.jstor.org/terms 2530 KYRIAKOS KEREMEDIS Proof of Claim 2. Fix y E A such that: Iy(i)I = odd natural number and y(j) = 0 for all j E k, j 7& i. Since S and V are complementary subspaces, there exist elements s E S and v E V such that

The Economic Determinants of Greek Return Migration to the Islands of the East Aegean

Abstract: The purpose of this article is to investigate the economic determinants of Greek return migration to the islands of the East Aegean a region comprising hundreds of islands of different size in four administrative departments....[It] examines the sensitivity of return migration flows to changes in economic variables which influence decisions to return....The purpose...is to investigate the effect on return migration not only of economic development in the host country (push factors) but also of economic development in the islands of the East Aegean (pull factors) given their isolation from the mainland and their different economic structures. (SUMMARY IN SPA AND FRE) (EXCERPT)

Second-Language Help for Windows Applications

Abstract: This paper describes an approach to the second-language problem for user-support in the context of existing MS-Windows applications. We outline a methodology for deriving foci for support, and present guidelines for the addition of second-language enhancements. Finally, we detail our procedure for implementing such help facilities with examples of enhanced Chinese and Greek second-language support.

Evaluating the direct costs of controlling NOx emissions in Europe

Abstract: This study summarises the available information on the costs of those nitrogen oxides abatement technologies in operation at present or coming into operation in the near future. Relying on disaggregated source data and using engineering cost functions and various technical and economic assumptions, the least cost curves of nitrogen oxides abatement for all the European countries have been derived and some examples are presented.