Showing papers by "University of Crete published in 2001"
TL;DR: In this paper, a buck-type DC/DC converter is used to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics.
Abstract: Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.
1,309 citations
TL;DR: The Cluster Ion Spectrometry (CIS) experiment as discussed by the authors measured the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e.
Abstract: . On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)
1,209 citations
TL;DR: Evidence for the existence of an ionic lock that constrains the relative mobility of the cytoplasmic ends of TM3 and TM6 in the inactive state of the β2-adrenergic receptor is provided and ionic interactions between Asp/Glu3.49, Arg3.50, and Glu6.30 may constitute a common switch governing the activation of many rhodopsin-like G-protein-coupled receptors.
626 citations
TL;DR: Parameters besides residual corneal bed thickness (eg, age, attempted correction) may have to be considered to avoid post‐LASIK ectasia, and there was a statistically significant positive correlation betweenCorneal residual bed thickness and increasing patient age.
Abstract: Purpose: To identify factors that can lead to corneal ectasia after laser in situ keratomileusis (LASIK). Setting: University refractive surgery center. Methods: In this retrospective study, the charts of all patients (2873 eyes) who had LASIK between May 1995 and November 1999 were reviewed. Fourteen patients (19 eyes, 0.66%) developed post-LASIK ectasia. The mean follow-up was 16.32 months (range 6 to 42 months). Results: No patient with an attempted correction less than 8.00 diopters or a residual corneal bed thickness greater than 325 μm experienced post-LASIK ectasia. There was a statistically significant positive correlation between corneal residual bed thickness and increasing patient age. Conclusion: Despite the limitations of the small sample size, the study's results suggest that parameters besides residual corneal bed thickness (eg, age, attempted correction) may have to be considered to avoid post-LASIK ectasia.
380 citations
TL;DR: Both drug combinations had comparable activity in patients with advanced cancer who had not previously had chemotherapy; however, gemcitabine and docetaxel had the most favourable toxicity profile.
354 citations
TL;DR: In this paper, the authors discuss the morphology, photometry and kinematics of the bars which have formed in three N-body simulations, and show that the disc dominates over the halo in the inner parts, even for model MH, for which the contribution were initially comparable in that region.
Abstract: We discuss the morphology, photometry and kinematics of the bars which have formed in three N-body simulations. These have initially the same disc and the same halo-to-disc mass ratio, but their haloes have very different central concentrations. The third model includes a bulge. The bar in the model with the centrally concentrated halo (model MH) is much stronger, longer and thinner than the bar in the model with the less centrally concentrated halo (model MD). Its shape, when viewed side-on, evolves from boxy to peanut and then to X-shaped, as opposed to that of model MD, which stays boxy. The projected density profiles obtained from cuts along the bar major axis, both for the face-on and the edge-on views, show a flat part, as opposed to those of model MD which are falling rapidly. A Fourier analysis of the face-on density distribution of model MH shows very large m = 2, 4, 6 and 8 components. Contrary to this for model MD the components m = 6 and 8 are negligible. The velocity field of model MH shows strong deviations from axial symmetry, and in particular has wavy isovelocities near the end of the bar when viewed along the bar minor axis. When viewed edge-on, it shows cylindrical rotation, which the MD model does not. The properties of the bar of the model with a bulge and a non-centrally concentrated halo (MDB) are intermediate between those of the bar of the other two models. All three models exhibit a lot of inflow of the disc material during their evolution, so that by the end of the simulations the disc dominates over the halo in the inner parts, even for model MH, for which the halo and disc contributions were initially comparable in that region.
309 citations
TL;DR: A diagnostic polymerase chain reaction (PCR) assay is set up to distinguish mosquitoes belonging to the three chromosomal forms, facilitating studies on the distribution and the ecology of these incipient taxa.
Abstract: The sequence of a 2.3 kb long DNA segment derived from the 5′-most end of the ribosomal intergenic spacer was determined in three chromosomal forms of Anopheles gambiae s.s. The analysis revealed that the sequence of the Mopti form differed from that of the Bamako and Savanna forms by a total of ten nucleotide substitutions. Using these sequence variations we set up a diagnostic polymerase chain reaction (PCR) assay to distinguish mosquitoes belonging to the three chromosomal forms, facilitating studies on the distribution and the ecology of these incipient taxa. The assay also allows to distinguish whether a given specimen could represent a heterozygote between Mopti and Savanna or Bamako.
278 citations
TL;DR: It is found that Dl endocytosis and N signaling are greatly stimulated by expression of neuralized (neur) and the potent modulatory effect of Neur on Dl activity makes Neur a candidate for establishing signaling asymmetries within cellular equivalence groups.
265 citations
TL;DR: It is shown that different synthetic dsRNA cassettes, consisting of two 5'-phosphorylated RNA strands of 22 nt each, can initiate RNAi in Drosophila embryos, indicating that the silencing machinery does not require perfect sequence identity.
260 citations
TL;DR: In this article, the relationship between human capital accumulation and economic growth using various measures of human capital frequently employed by researchers was studied and the authors used semiparametric estimation techniques to uncover any nonlinearities that may exist.
Abstract: In this paper we study the relationship between human capital accumulation and economic growth using various measures of human capital frequently employed by researchers. We use semiparametric estimation techniques to uncover any nonlinearities that may exist. Using mean years of schooling measures of human capital we find a nonlinear effect on economic growth. There seem to be important differences in the growth effect of educational attainment by gender and level of education. Enrollment rates do not yield a nonlinear effect.
248 citations
TL;DR: It is suggested that animal mtDNA molecules may recombine regularly and that the extent to which this generates new haplotypes may depend only on the frequency of biparental inheritance of the mitochondrial genome.
Abstract: The assumption that animal mitochondrial DNA (mtDNA) does not undergo homologous recombination is based on indirect evidence, yet it has had an important influence on our understanding of mtDNA repair and mutation accumulation (and thus mitochondrial disease and aging) and on biohistorical inferences made from population data. Recently, several studies have suggested recombination in primate mtDNA on the basis of patterns of frequency distribution and linkage associations of mtDNA mutations in human populations, but others have failed to produce similar evidence. Here, we provide direct evidence for homologous mtDNA recombination in mussels, where heteroplasmy is the rule in males. Our results indicate a high rate of mtDNA recombination. Coupled with the observation that mammalian mitochondria contain the enzymes needed for the catalysis of homologous recombination, these findings suggest that animal mtDNA molecules may recombine regularly and that the extent to which this generates new haplotypes may depend only on the frequency of biparental inheritance of the mitochondrial genome. This generalization must, however, await evidence from animal species with typical maternal mtDNA inheritance.
TL;DR: It is suggested that locally produced CRH promotes implantation and maintenance of early pregnancy primarily by killing activated T cells.
Abstract: The semi-allograft embryo in the blastocyst stage implants itself in the endometrium, yet no immune rejection processes are activated. Embryonic trophoblast and maternal decidua produce corticotropin-releasing hormone (CRH) and express Fas ligand (FasL), a proapoptotic cytokine. We found that antalarmin, a CRH receptor type 1 antagonist, decreased FasL expression and promoted apoptosis of activated T lymphocytes, an effect which was potentiated by CRH and inhibited by antalarmin. Female rats treated with antalarmin showed a marked decrease in implantation sites and live embryos and diminished endometrial FasL expression. Embryos from mothers that lacked T cells or from syngeneic matings were not rejected when the mothers were given antalarmin. These findings suggested that locally produced CRH promotes implantation and maintenance of early pregnancy primarily by killing activated T cells.
TL;DR: A new technique for off-line signature recognition and verification based on global, grid and texture features and implemented in a special two stage Perceptron OCON (one-class-one-network) classification structure.
TL;DR: In this article, the technical efficiency of organic and conventional olive-growing farms using a stochastic production frontier methodology and a translog functional specification is analyzed. But, both input-and output-oriented technical efficiency scores are still relatively low for both types of olive-farming.
TL;DR: It was found that amphiphilic PVP incorporated into negatively chargedliposomes effectively prevents polycation(poly-ethylpyridinium-4-vinylchloride)-induced liposome aggregation, completely abolishing it at ca.
TL;DR: In SB immune-mediated diseases, there is repartitioning of CCR9(+) lymphocytes between SB and blood and an altered pattern of TECK expression in SB Crohn's, and the TECK/CCR9 ligand/receptor pair may play an important role in the pathogenesis of SBCrohn's disease.
TL;DR: In this paper, a mixed quantum mechanics/molecular mechanics (QM/MM) model is used for investigating the nature of molecular hydrogen adsorption in pure and alkali-metal-doped single-walled carbon nanotubes (SWNTs).
Abstract: A mixed quantum mechanics/molecular mechanics (QM/MM) model is used for investigating the nature of molecular hydrogen adsorption in pure and alkali-metal-doped single-walled carbon nanotubes (SWNTs). Our results demonstrate that the charge transfer from the alkali metal to the tube polarizes the H2 molecule and this charge-induced dipole interaction is responsible for the higher hydrogen uptake of the doped tubes.
TL;DR: Observations reveal a mechanism by which the adhesion molecule TAG-1, known to be involved in axonal pathfinding, also takes part in neuronal migration.
Abstract: Cortical nonpyramidal cells, the GABA-containing interneurons, originate mostly in the medial ganglionic eminence of the ventral telencephalon and follow tangential migratory routes to reach the dorsal telencephalon. Although several genes that play a role in this migration have been identified, the underlying cellular and molecular cues are not fully understood. We provide evidence that the neural cell adhesion molecule TAG-1 mediates the migration of cortical interneurons. We show that the migration of these neurons occurs along the TAG-1-expressing axons of the developing corticofugal system. The spatial and temporal pattern of expression of TAG-1 on corticofugal fibers coincides with the order of appearance of GABAergic cells in the developing cortex. Blocking the function of TAG-1, but not of L1, another adhesion molecule and binding partner of TAG-1, results in a marked reduction of GABAergic neurons in the cortex. These observations reveal a mechanism by which the adhesion molecule TAG-1, known to be involved in axonal pathfinding, also takes part in neuronal migration.
TL;DR: The authors argue that argument externalization is related to Case and that it is forced because movement of both arguments to a single head T0 that contains two active Case features in the covert component is banned.
Abstract: The article establishes a novel generalization concerning the placement of arguments by Spell-Out. It centers on the principles that force arguments to leave the VP across languages. The empirical domain consists of constructions where subject movement is not required for reasons that have to do with the Extended Projection Principle. In these environments and whenever a sentence contains both a subject and a direct object, one of the arguments must vacate the VP. We argue that argument externalization is related to Case. It is forced because movement of both arguments to a single head T0 that contains two active Case features in the covert component is banned.
TL;DR: It is demonstrated that HP1 forms a quaternary complex with the inner nuclear membrane protein LBR and a sub‐set of core histones that mediate binding of LBR to HP1 and cross‐link these two proteins that do not interact directly with each other.
Abstract: We have recently shown that heterochromatin protein 1 (HP1) interacts with the nuclear envelope in an acetylation-dependent manner. Using purified components and in vitro assays, we now demonstrate that HP1 forms a quaternary complex with the inner nuclear membrane protein LBR and a sub-set of core histones. This complex involves histone H3/H4 oligomers, which mediate binding of LBR to HP1 and cross-link these two proteins that do not interact directly with each other. Consistent with previous observations, HP1 and LBR binding to core histones is strongly inhibited when H3/H4 are modified by recombinant CREB-binding protein, revealing a new mechanism for anchoring domains of under-acetylated chromatin to the inner nuclear membrane.
TL;DR: Sp1 must play a critical role in regulating important biological processes controlled by p53 via p21 gene activation such as DNA repair, cell growth, differentiation, and apoptosis through its physical interaction with p53.
TL;DR: A simple, novel mechanism for inducing highly selective and efficient energy transfer and focusing in certain discrete nonlinear systems is proposed and could be relevant for energy transfer in bioenergetics and electron transfer in chemical reactions.
Abstract: We propose a simple, novel mechanism for inducing highly selective and efficient energy transfer and focusing in certain discrete nonlinear systems. Under a precise condition of nonlinear resonance, when a specific amount of energy is injected as a discrete breather at a donor system, it can be transferred as a discrete breather to another weakly coupled acceptor system. This general mechanism could be relevant for energy transfer in bioenergetics and electron transfer in chemical reactions and could be used for engineering functional materials and devices.
TL;DR: Radiation risk from RF cardiac ablation is moderate compared with other complications, but it may highly exceed radiation risk from common radiological procedures, so efforts should be made toward minimization of patient radiation risk.
Abstract: Background—Radiofrequency (RF) cardiac catheter ablation procedures may require extended fluoroscopic exposure resulting in elevated radiation risk. The aim of the present study was to accurately establish RF ablation radiation risk levels and to provide means for accurate patient risk estimation from studies performed in any electrophysiology laboratory. Methods and Results—Fluoroscopy required during cardiac ablation was classified into 4 types identified by beam orientation and irradiated tissue: (1) posteroanterior exposure during catheter advancing from the groin to the heart, (2) posteroanterior heart exposure, (3) left anterior oblique heart exposure, and (4) right anterior oblique heart exposure. The duration of each exposure was monitored in 24 patients undergoing RF cardiac ablation. Dose per minute of fluoroscopy was measured at 15 organs/tissues for each projection with the use of anthropomorphic phantom and thermoluminescence dosimetry. The effective dose rate was 219, 144, 136, and 112 μGy/m...
TL;DR: In this paper, the P840 reaction center complex (RC) of green sulfur bacteria is compared to the PsaAB/PsaC-core of the P700 reaction center in Photosystem I.
01 Aug 2001
TL;DR: An electrostatic potential field (EPF) path planner is combined with a two-layered fuzzy logic inference engine and implemented for real-time mobile robot navigation in a 2-D dynamic environment.
Abstract: An electrostatic potential field (EPF) path planner is combined with a two-layered fuzzy logic inference engine and implemented for real-time mobile robot navigation in a 2-D dynamic environment. The environment is first mapped into a resistor network; an electrostatic potential field is then created through current injection into the network. The path of maximum current through the network corresponds to the approximately optimum path in the environment. The first layer of the fuzzy logic inference engine performs sensor fusion from sensor readings into a fuzzy variable, collision, providing information about possible collisions in four directions, front, back, left and right. The second layer guarantees collision avoidance with dynamic obstacles while following the trajectory generated by the electrostatic potential field. The proposed approach is experimentally tested using the Nomad 200 mobile robot.
01 Jan 2001
TL;DR: Microsatellite markers have recently become the favourite type of DNA marker for identification of grapevine cultivars, and their properties enable a wide range of applications from cultivar identification based on various parts of the grapevine plant to pedigree reconstruction and genome mapping.
Abstract: Microsatellite markers have recently become the favourite type of DNA marker for identification of grapevine cultivars, and their properties enable a wide range of applications from cultivar identification based on various parts of the grapevine plant to pedigree reconstruction and genome mapping. Before such highly informative markers were made available, numerous methods were tested with the goal to provide a reliable method of genotype identification for the management of germplasm collections. Such a desired method, could then be potentially used as an accurate certification system for global international trade of grapevine and rootstock plant material.
TL;DR: The saddleback syndrome and severe caudal fin deformities were anatomically and ontogenetically related to each other, originating at the early larval stage as a result of abnormalities of the primordial marginal finfold and of the posterior tip of the notochord.
27 May 2001
TL;DR: The proposed approach combines FCM and ES concepts and sets the basis for the establishment and deployment of structural evolution, which broadens the applicability of FCMs.
Abstract: Fuzzy cognitive maps (FCMs) are recognized as a flexible and powerful modeling and simulating technique. However, it is a relatively new methodology, which exhibits weaknesses mainly in the algorithmic background. Such weaknesses become evident during heuristic evaluations of the cause-effect relationships describing FCM-based systems. External intervention (typically from experts) for the determination and fine-tuning of the FCM parameters cannot be regarded as an accurate and efficient way to design and manage FCMs, especially in the case of highly complicated structures, where even experts meet difficulties in their attempts at a holistic interpretation. The introduction and implementation of a training procedure based on a robust and flexible optimization tool constitutes a promising alternative. This study focuses on evolutionary computation, since this domain encompasses optimization techniques possessing the needed features for this type of problems. Evolution strategies (ESs) appear to be the most appropriate methodology and, as such, they are tested in this work for a potential implementation in FCM-based systems. The proposed approach combines FCM and ES concepts and sets the basis for the establishment and deployment of structural evolution, which broadens the applicability of FCMs.
TL;DR: In this article, the ambient air concentrations of many saturated and aromatic hydrocarbons were measured in several sites around an oil refinery, near the city of Corinth in Greece, during 1997.
TL;DR: Two DEAD family motifs in IRA2 are essential for IRA2–NBD1 binding, optimal nucleotide turnover and polypeptide translocation, and it is proposed that translocation ligands alleviate C‐terminal domain suppression, allowing IRA2 to stimulateucleotide turnover at NBD1.
Abstract: SecA, the motor subunit of bacterial polypeptide translocase, is an RNA helicase. SecA comprises a dimerization C‐terminal domain fused to an ATPase N‐terminal domain containing conserved DEAD helicase motifs. We show that the N‐terminal domain is organized like the motor core of DEAD proteins, encompassing two subdomains, NBD1 and IRA2. NBD1, a rigid nucleotide‐binding domain, contains the minimal ATPase catalytic machinery. IRA2 binds to NBD1 and acts as an intramolecular regulator of ATP hydrolysis by controling ADP release and optimal ATP catalysis at NBD1. IRA2 is flexible and can undergo changes in its α‐helical content. The C‐terminal domain associates with NBD1 and IRA2 and restricts IRA2 activator function. Thus, cytoplasmic SecA is maintained in the thermally stabilized ADP‐bound state and unnecessary ATP hydrolysis cycles are prevented. Two DEAD family motifs in IRA2 are essential for IRA2–NBD1 binding, optimal nucleotide turnover and polypeptide translocation. We propose that translocation ligands alleviate C‐terminal domain suppression, allowing IRA2 to stimulate nucleotide turnover at NBD1. DEAD motors may employ similar mechanisms to translocate different enzymes along chemically unrelated biopolymers.