Showing papers by "University of Crete published in 1989"
TL;DR: In this article, a general method for the explicit determination of all solutions of any Thue equation is presented, using a combination of Baker's theory of linear forms in logarithms and recent computational diophantine approximation techniques.
155 citations
TL;DR: In this article, the authors present evidence of family change due to mass tourism in a rural community on the island of Crete, Greece, and argue that such change is attributable to economic rather than ideological factors, introduced by outsiders.
145 citations
TL;DR: The results support the proposal that the D1-D2 complex binds the P-680+ and Pheo a species that are involved in the primary charge separation.
121 citations
TL;DR: It is suggested that the variable region A may be important in determining the specificity and affinity of integrin receptors for their ligands in the Drosophila PS2 α subunit.
113 citations
TL;DR: The Smith-Mclntyre grab from the offshore northern section of the North Sea was used to identify over one hundred and nine infaunal species from 76 selected macrofaunal stations as discussed by the authors.
Abstract: Between 1980 and 1985 ninety-seven stations were sampled by Smith-Mclntyre grab from the offshore northern section of the North Sea Four hundred and nine infaunal species were identified from the 76 selected macrofaunal stations The number of species per station varied from 25 to 80 with a maximum abundance of 9,600 individuals m−2 The biomass ranged from 013 to 1886 g dry weight m−2 At most stations, however, biomass varied between 1 and 4 g dry weight m−2 Diversity and abundance were highest in the 120–140 m zone, characterised by fine sand containing variable amounts of silt The highest biomasses were recorded in two areas; firstly where stronger currents predominate and the sediments are coarser (east of Shetland and west of the Norwegian Trough), and secondly in the fine sandy deposits of the centrally located area In the silty sediments (Fladen Ground and smaller depressions) there was a predominantly subsurface deposit-feeding community, whereas in the coarser area east of the Shetlands carnivores predominated Over the remaining area surface deposit feeders were dominant
107 citations
TL;DR: The exact static spherically symmetric solution of the coupled Einstein--massless-scalar-field equations for arbitrary spacetime dimensions is obtained.
Abstract: We obtain the exact static spherically symmetric solution of the coupled Einstein--massless-scalar-field equations for arbitrary spacetime dimensions. The general solution involves two parameters: it is asymptotically flat and the scalar field tends to zero at spacelike infinity. It exhibits a naked singularity unless the scalar field vanishes when it naturally reduces to the Schwarzschild solution in D spacetime dimensions.
94 citations
TL;DR: Genetic distances based on electrophoretic variation and multivariate analysis of several morpho-metric and meristic characters suggest that populations of sardine and anchovy from the Aegean and Ionian seas do not form one panmictic population, providing evidence for the dynamic population structure model.
Abstract: Genetic distances based on electrophoretic variation and multivariate analysis of several morpho-metric and meristic characters suggest that populations of sardine and anchovy from the Aegean and Ionian seas do not form one panmictic population. The distinction between these two classes of populations emerges only as a statistical property, and for some characters the within-sea variation is larger than the between-sea variation. Thus, the reproductive isolation between populations inhabiting the two seas appears to be only partial. Our findings do not support the‘ pure‘ or‘ discrete‘ stock concept. Instead, they provide evidence for the dynamic population structure model according to which physical (e.g., hydrographic) or biological (e.g., predation or behaviour) factors impose a population structure maintained in a semi-equilibrium state under the opposing influences of migration and selection. Such a dynamic state may not be stable in the long run, and it may not allow for the accumulation of genetic divergence necessary for the emergence of higher taxa. It must, nevertheless, be taken into account in the management of exploited natural populations.
90 citations
TL;DR: Using the augmented-plane-wave method, the location of gaps for positive energy and for various values of \ensuremath{\delta} and the sphere radius a are studied.
Abstract: We considered a muffin-tin periodic potential (-\ensuremath{\delta} inside the spheres and zero outside). Using the augmented-plane-wave method we studied systematically the location of gaps for positive energy and for various values of \ensuremath{\delta} and the sphere radius a. Our results are applicable to the problem of classical wave propagation in composite media and relevant to the problem of optical localization.
71 citations
TL;DR: In this paper, the authors investigated heterozygote deficiency and the correlation between single-and multiple-locus heterozygosity and phenotype in juveniles of the scallop Placopecten magellanicus (Gmelin).
Abstract: Heterozygosity and growth rate have been correlated in many molluscs, although the phenomenon is not universal. Enhanced growth of heterozygous molluscs has been attributed to lower energetic requirements for basal metabolism. We have investigated heterozygote deficiency, and the correlation between single-locus and multiple-locus heterozygosity and phenotype in juveniles of the scallop Placopecten magellanicus (Gmelin). Six samples were collected between 22 November 1984 and 11 December 1985 at Passamaquoddy Bay, New Brunswick, Canada. On average, heterozygote deficiency was small, although somewhat higher at the octopine dehydrogenase (Odh) locus, and decreased with age. No correlation was observed between genotype and growth rate. This result and published records indicate that allozyme heterozygosity of pectinids does not influence growth to the same degree as in other bivalves. However, we have observed in P. magellanicus a correlation between allozyme heterozygosity and octopine accumulation, a trait that relates to functional anaerobiosis, and may be related to the scallop's scope for movement. We combine these results and results from the literature into a model that relates the hypothesis of “associative overdominance” (at the population genetics level) with the hypothesis of “energetic efficiency” (at the physiological level). The model assumes that energy savings attributed to heterozygosity are used to maximize fitness. In freely moving molluscs this results in enhanced activity (such as searching for prey or swimming away from a predator), and in sessile molluscs either in enhanced somatic growth in juveniles or gonadal growth in adults.
55 citations
TL;DR: It is found that scalar waves do exhibit localization and a coherent potential approximation for x<0.2 is developed which can be easily generalized to electromagnetic fields as well.
Abstract: An exact mapping of the classical wave problem to that of electronic motion is utilized together with extensive numerical results to examine the question of the existence of genuine localization (i.e., one occurring when both components have real positive dielectric constants) of classical waves in random binary alloys A/sub 1-//sub x/B/sub x/. We find that scalar waves do exhibit localization. We have also developed a coherent potential approximation which for x<0.2 gives results not that much different from the numerical ones. This result can be easily generalized to electromagnetic fields as well.
51 citations
TL;DR: The disease affected both sexes equally and the peak incidence occurred between 21 and 30 years of age, while a second peak concerning only men was observed in the 6th decade of life.
Abstract: Epidemiologic and clinical observations were made in 217 cases of ulcerative colitis between 1977 and 1983 in Evangelismos Hospital, Athens, Greece. The disease affected both sexes equally. The peak incidence occurred between 21 and 30 years of age. A second peak concerning only men was observed in the 6th decade of life. Urban and highly educated sections of the population were more often affected. Severe attacks were seen in only 3.4% of the patients at onset of the disease. Surgical treatment (colectomy) was applied to one in every seven patients either for a severe attack or on suspicion of cancer or debilitating symptoms.
TL;DR: It is suggested that patients who receive IFS treatment should be monitored for the occurrence of cardiac abnormalities and readministration of the drug may be contraindicated in such patients.
Abstract: Ifosfamide (IFS) is a new alkylating oxazaphosphorine related to cyclophosphamide. Various side effects have been reported; however, cardiotoxicity is not known to occur in humans. We report for first time acute cardiac side effects upon IFS treatment in the form of supraventricular arrhythmias and ST-T wave changes. IFS dose ranged from 6.5 g/m2 to 10 g/m2 fractionated in 3 or 5 days and infused i.v. over 4 h daily together with 2-mercaptoethane sulphonate sodium (Mesna). Arrhythmias appeared to be reversible upon discontinuation of the drug. In one patient, readministration of IFS led to arrhythmia that was refractory to treatment. Factors predisposing to the development of cardiac side effects could not be determined in this study. We suggest that patients who receive IFS treatment should be monitored for the occurrence of cardiac abnormalities. Readministration of the drug may be contraindicated in such patients.
TL;DR: An interatomic potential for silicon is proposed, which is a significant improvement over the Stillinger-Weber model and introduced four-body interactions to the potential, which were essential to give good agreement with the melting point of the crystal and the geometries and the energies of the ground and low metastable states of silicon clusters.
Abstract: An interatomic potential for silicon is proposed, which is a significant improvement over the Stillinger-Weber model. This potential is valid for clusters with more than six atoms, where \ensuremath{\pi} bonding is not significant because of the large degree of coordination. Guided by ab initio electronic calculations, we introduced four-body interactions to the potential, which were essential to give good agreement with the melting point of the crystal and the geometries and the energies of the ground and low metastable states of silicon clusters.
02 Apr 1989
TL;DR: An interactive method that combines the advantageous features of both the paradigms of Satisfactory Goals and Multiattribute Utility Assesment is presented, a DSS oriented approach providing a ‘two level’ interaction.
Abstract: Most of practical linear programming problems involve multiple and conflicting objectives. The paper presents an interactive method to approach this kind of problems. The main original aspect of this method lies in the fact that it combines the advantageous features of both the paradigms of Satisfactory Goals and Multiattribute Utility Assesment. It is a DSS oriented approach providing a ‘two level’ interaction: 1. (1) interactive assessment of the decision maker's utility function using the UTA ordinal regression model; 2. (2) interactive modification of the satisfaction levels. Piecewise linear optimazation techniques are used to determine, at each iteration, a new compromise solution over the set of efficient solutions.
TL;DR: The reaction of singlet oxygen with cis olefins is regioselective and shows a general preference for hydrogen abstraction on the larger alkyl group of the double bond.
TL;DR: Twenty-two pairs of chorion genes belonging to the A and B multigene families have been characterized and mapped within two segments of a 320 kb chromosomal walk in the domesticated silkmoth Bombyx mori, and sequence comparisons of all these promoters identify short elements of possible regulatory significance.
TL;DR: The results show that depending on the anatomical localization of trophoblasts within the placenta, various regulatory elements control gene expression, so that the placental barrier provides fetal protection at different levels.
Abstract: Class II MHC antigen expression is required for recognition of an alloantigen and generation of immune response. In rodents as well as in humans primary trophoblasts do not express class II MHC antigens. In this study we focused our interest on the mechanism(s) of class II antigen suppression on murine trophoblasts. First, we examined the possibility of gene inactivation by methylation and second the possibility of lymphokine regulation of the class II genes. The first possibility was tested by treatment of placental cells with 5-azacytidine (5-AzaC), a cytidine analog which upon incorporation into the DNA inhibits further methylation, thus leading to gene activation. In order to test the second possibility we treated placental cells with interferon-gamma (IFN-gamma) or interleukin 4 (IL4) which are known to induce class II antigen expression in many systems. We showed that treatment with 5-AzaC or IFN-gamma but not IL4 significantly increased class II expression on cytokeratin-positive and vimentin-negative adherent placental cells. Following placental cell fractionation we distinguished three cell subsets with different responsiveness to 5-AzaC and IFN-gamma. The first, characterized as placental macrophages, were induced to express class II MHC antigens only after IFN-gamma treatment. The other two subsets, characterized as trophoblasts, were isolated from the labyrinthine- and spongio-trophoblast layer of the placenta and showed class II inducibility to 5-AzaC and IFN-gamma, respectively. The results show that depending on the anatomical localization of trophoblasts within the placenta, various regulatory elements control gene expression, so that the placental barrier provides fetal protection at different levels.
TL;DR: The anisotropic Tight-binding model, which is defined by a disordered tight-binding Hamiltonian with a transfer-energy-matrix element in the {ital z} direction, is studied using finite-size scaling methods and is found to be in satisfactory agreement with the predictions of the potential-well analogy, coupled with the coherent-potential approximation.
Abstract: The anisotropic tight-binding model, which is defined by a disordered tight-binding Hamiltonian with a transfer-energy-matrix element in the z direction, t, different than the one in the x-y plane is studied using finite-size scaling methods. The dependence of the mobility edge on the strength of anisotropy t (0\ensuremath{\le}t\ensuremath{\le}1) is obtained for the center of the band, E=0. Even for very low-t values an appreciable amount of disorder is needed to localize the E=0 state. These results are found to be in satisfactory agreement with the predictions of the potential-well analogy, coupled with the coherent-potential approximation.
TL;DR: In this paper, conditions for the existence of a saddle point for the time-invariant filtering problem were shown to be necessary and sufficient, whereas for all other cases only necessary conditions were shown.
Abstract: The problem of estimation and control for systems with multiplicative noise and unknown second-order statistics is considered. Conditions are found for the existence of a solution based on game theoretic ideas. The conditions for the existence of a saddle point for the time-invariant filtering problem are necessary and sufficient, whereas for all other cases only necessary. The central idea of the solution is to convert the stochastic problem to a deterministic optimal control problem whose minimax point is sought with respect to the control, filter, and unknown statistics parameters. The results that are derived show that the problem of estimation for systems with unknown covariances depends on the costate matrix, which in turn is a function of the performance measure. Thus, the filter loses one of its best known properties, that of independence of the performance functional. This property holds not only for the classical Kalman filter but also for multiplicative systems. >
TL;DR: A cDNA clone that encodes the Drosophila melanogaster elongation factor 2 (EF2), a protein involved in the elongation step of protein synthesis, is isolated based on the high degree of its amino acid sequence identity to that of hamster EF2.
Abstract: We have isolated a cDNA clone that encodes the Drosophila melanogaster elongation factor 2 (EF2), a protein involved in the elongation step of protein synthesis. This identification was based on the high degree of its amino acid sequence identity (greater than 80%) to that of hamster EF2. The gene encoding Drosophila EF2 is found at position 39E-F of the 2L chromosomal arm and maybe identical to the M(2)H locus, which produces a Minute phenotype when mutated. The genomic organization of the locus includes four exons. Conserved sequence segments shared with a variety of GTP binding proteins are found in the amino terminal third of the protein, and segments unique to EF2 and its prokaryotic functional homolog, EF-G, are in the carboxy terminal half; these two regions are segregated in two respective exons.
TL;DR: In this paper, the topological relationship between magnetic field lines and magnetic flux surfaces was considered and it was shown that magnetic helicity provides the most elementary description of the topology of magnetic fields lines.
Abstract: We consider the topological relationship between magnetic field lines and magnetic flux surfaces. Magnetic helicity provides the most elementary description of the topology of magnetic field lines ...
TL;DR: In this article, the polymerization in micellar and isotropic media of a head-tail pair of surfactants was investigated, i.e., of monomers bearing the methacrylate group either at the polar head or at the end of the lipophilic chain.
Abstract: The polymerization in micellar and isotropic media of a head-tail pair of surfactants, i.e. of monomers bearing the methacrylate group either at the polar head or at the end of the lipophilic chain is investigated in this study. Owing to the tailor-made structure of these monomers, any differentiations observed in their polymerization can be primarily attributed to topochemical effects resulting from the different location of the polymerizable group in the two monomers. Both monomers exhibited mesomorphic-like textures, which were examined by optical microscopy and DSC studies. Also, their respective polymers showed mesomorphic behaviour, which was found to be dependent on the position of the backbone relative to the polar head.
TL;DR: The densification and especially the expansion modes suggest considerable fluidity in the developing chorion, consistent with its proposed cholesteric liquid crystalline structure.
Abstract: The silkmoth chorion is a helicoidally layered, fibrous structure which is constructed in four sequential morphogenetic modes, beginning with the assembly of a thin, low density lamellar framework. Subsequently, the framework expands in height by the insertion of additional fiber sheets into the preexisting lamellae. This expansion mode begins farthest from the follicular secretory cells and progresses in reverse. Individual fibers then grow in thickness, presumably through accretion of newly synthesized proteins, and eventually fuse. This third mode, which also begins in the most distant lamellae and proceeds in reverse, is called densification, as it results in an approximately two fold increase in overall chorion density without further lamellar expansion. Finally, lamellogenesis is recapitulated in miniature in a region of the chorion's surface, where very-late-forming lamellae are molded into prominent surface structures, the aeropyle crowns. The densification and especially the expansion modes suggest considerable fluidity in the developing chorion, consistent with its proposed cholesteric liquid crystalline structure. Such a structure is also consistent with numerous deviations from the ideal helicoidal array. These distortions and defects are described and discussed in terms of their possible origin and function.
TL;DR: Results indicate that females grow faster than males after an estimated age of 3 years, and there was no significant difference in the length-weight relationship between males and females.
TL;DR: The ene reaction of triazolinedione with unsymmetrical cis-alkenes is regiospecific and shows a preferential abstraction of the allylic hydrogens on the larger alkyl group of the double bond as discussed by the authors.
TL;DR: In this article, nationalities and the state in Ethiopia are discussed and the authors present a survey of the state of Ethiopia in terms of ethnicity and ethnicity in the Third World Quarterly: Vol. 11, No. 4, pp. 118-130.
Abstract: (1989). Nationalities and the state in Ethiopia. Third World Quarterly: Vol. 11, No. 4, pp. 118-130.
TL;DR: Significant conservation of molecular interactions controlling transcription during choriogenesis is observed between the distantly related orders, Lepidoptera and Diptera, however, quantitative and fine temporal regulation in the Drosophila host does not fully parallel the in situ regulation in moths, indicating that some regulatory protein-DNA interactions have diversified in the approximately 250 million years since the last common ancestor of these insect groups.
Abstract: Bidirectional chorion gene promoter regions from three silkmoth species,Bombyx mori, Antheraea pernyi, orAntheraea polyphemus (members of two different moth families), were tested for their ability to transcriptionally activate a bacterial marker gene (chloramphenicol acetyltransferase) in transformantDrosophila. Relatively short 5′ flanking DNA fragments (272–367 bp) of chorion gene pairs are sufficient to confer a high degree of tissue and choriogenic stage specificity of expression to the marker gene. Thus, significant conservation of molecular interactions controlling transcription during choriogenesis is observed between the distantly related orders, Lepidoptera and Diptera. However, quantitative and fine temporal regulation in theDrosophila host does not fully parallel the in situ regulation in moths, indicating that some regulatory protein-DNA interactions have diversified in the approximately 250 million years since the last common ancestor of these insect groups. Limited in vitro mutagenesis of aB. mori promoter DNA has shown that a central 189-bp region includes elements sufficient for the qualitative specificity of chorion-specific expression. The same experiments have shown that a previously identified essential element, centered on the TCACGT hexamer, is not sufficient for chorion-specific expression: an additional essential element or elements are found farther upstream, within a 112-bp DNA region. Comparisons of silkmoth andDrosophila chorion gene promoter sequences have identified some candidates forcis-acting elements involved in the developmental regulation of chorion gene expression.
TL;DR: In this paper, a series of n-aldehydes (C20 to C32) with strong even-to-odd carbon preference was identified in aquatic sediments and waterborne particulates.
Abstract: Lipids in aquatic sediments and waterborne particulates are either of biogenic origin or derived from anthropogenic sources [1]. Among the well-studied natural products in lacustrine and marine sediments are lipids such as hydrocarbons, alcohols and fatty acids which are attributed to autochthonous bioproduction or to contribution of terrestrial organic materials. The latter are dominated by compounds which are contained in epicuticular waxes of vascular plants [2]. Fatty aldehydes have been identified in several plant waxes [2 -4] . The chain length distribution of aldehydes is usually very similar or identical to that of the alcohols, suggesting a close relationship. The strong even-to-odd carbon preference in the aldehydes excludes the possible involvement of an alpha-oxidation mechanism (of fatty acids) in their formation [3]. Investigations of the possible involvement of fatty acid reduction in lipid biosynthesis provided indirect evidence that fatty acids do undergo reduction to fatty alcohols possibly via aldehydes. Fatty aldehydes have been also tentatively identified in oil shales in Brazil [5], in the bound fraction of coastal lagoon sediments in Spain [6], in urban airborne particles [7, 8] and in rain water [9]. A series of n-aldehydes (C20 to C32) with strong
01 Nov 1989
TL;DR: This paper sketches a software development environment for data-intensive information systems based on the premise that software can be viewed as a multilayered description, which includes a requirements specification, a design and an implementation and that this description should be managed as a knowledge base.
Abstract: This paper sketches a software development environment for data-intensive information systems. It is based on the premise that software can be viewed as a multilayered description, which includes a requirements specification, a design and an implementation, and that this description should be managed as a knowledge base. The proposed environment uses the requirements modelling language CML, the design language Taxis, and the implementation language DBPL. The paper outlines the features of these languages and illustrates the proposed multilayered structure of software with an example. It also discusses the features that will have to be supported by an environment suitable for constructing, maintaining, and testing software knowledge bases.