Showing papers by "University of Patras published in 2006"

The genome of the sea urchin Strongylocentrotus purpuratus.

Abstract: We report the sequence and analysis of the 814-megabase genome of the sea urchin Strongylocentrotus purpuratus, a model for developmental and systems biology. The sequencing strategy combined whole-genome shotgun and bacterial artificial chromosome (BAC) sequences. This use of BAC clones, aided by a pooling strategy, overcame difficulties associated with high heterozygosity of the genome. The genome encodes about 23,300 genes, including many previously thought to be vertebrate innovations or known only outside the deuterostomes. This echinoderm genome provides an evolutionary outgroup for the chordates and yields insights into the evolution of deuterostomes.

Handling imbalanced datasets: A review

Abstract: Learning classifiers from imbalanced or skewed datasets is an impor- tant topic, arising very often in practice in classification problems. In such problems, almost all the instances are labelled as one class, while far fewer in- stances are labelled as the other class, usually the more important class. It is obvious that traditional classifiers seeking an accurate performance over a full range of instances are not suitable to deal with imbalanced learning tasks, since they tend to classify all the data into the majority class, which is usually the less important class. This paper describes various techniques for handling im- balance dataset problems. Of course, a single article cannot be a complete re- view of all the methods and algorithms, yet we hope that the references cited will cover the major theoretical issues, guiding the researcher in interesting re- search directions and suggesting possible bias combinations that have yet to be explored.

A survey of autonomic communications

Abstract: Autonomic communications seek to improve the ability of network and services to cope with unpredicted change, including changes in topology, load, task, the physical and logical characteristics of the networks that can be accessed, and so forth. Broad-ranging autonomic solutions require designers to account for a range of end-to-end issues affecting programming models, network and contextual modeling and reasoning, decentralised algorithms, trust acquisition and maintenance---issues whose solutions may draw on approaches and results from a surprisingly broad range of disciplines. We survey the current state of autonomic communications research and identify significant emerging trends and techniques.

Electronic structure and Slater–Pauling behaviour in half-metallic Heusler alloys calculated from first principles

Abstract: Intermetallic Heusler alloys are amongst the most attractive half-metallic systems due to their high Curie temperatures and their structural similarity to binary semiconductors. In this review we present an overview of the basic electronic and magnetic properties of both Heusler families: the so-called half-Heusler alloys like NiMnSb and the full-Heusler alloys like Co2MnGe. Ab initio results suggest that both the electronic and magnetic properties in these compounds are intrinsically related to the appearance of the minority-spin gap. The total spin magnetic moment Mt scales linearly with the number of the valence electrons Zt, such that Mt = Zt − 24 for the full-Heusler and Mt = Zt − 18 for the half-Heusler alloys, thus opening the way to engineer new half-metallic alloys with the desired magnetic properties.

Association Rules Mining: A Recent Overview

Abstract: In this paper, we provide the preliminaries of basic concepts about association rule mining and survey the list of existing association rule mining techniques. Of course, a single article cannot be a complete review of all the al- gorithms, yet we hope that the references cited will cover the major theoretical issues, guiding the researcher in interesting research directions that have yet to be explored.

Sol–gel preparation of mesoporous photocatalytic TiO2 films and TiO2/Al2O3 composite membranes for environmental applications

Abstract: This study describes the application of novel chemistry methods for the fabrication of robust nanostructured titanium oxide (TiO2) photocatalysts. Such materials can be applied in the development of efficient photocatalytic systems for the treatment of water. Mesoporous photocatalytic TiO2 films and membranes were synthesized via a simple synthesis method that involves dip-coating of appropriate substrates into an organic/inorganic sol composed of isopropanol, acetic acid, titanium tetraisopropoxide, and polyoxyethylenesorbitan monooleate surfactant (Tween 80) followed by calcination of the coating at 500 8C. Controlled hydrolysis and condensation reactions were achieved through in-taking of water molecules released from the esterification reaction of acetic acid with isopropanol. The subsequent stable incorporation of Ti–O–Ti network onto self-assembled surfactants resulted in TiO2 photocatalysts with enhanced structural and catalytic properties. The properties included high surface area (147 m 2 /g) and porosity (46%), narrow pore size distribution ranging from 2 to 8 nm, homogeneity without cracks and pinholes, active anatase crystal phase, and small crystallite size (9 nm). These TiO2 photocatalysts were highly efficient for the destruction of methylene blue and creatinine in water. High water permeability and sharp polyethylene glycol retention of the prepared photocatalytic TiO2/Al2O3 composite membranes evidenced the good structural properties of TiO2 films. In addition, the multi-coating procedure made it possible to effectively control the physical properties of TiO2 layer such as the coating thickness, amount of TiO2, photocatalytic activity, water permeability and organic retention. # 2005 Elsevier B.V. All rights reserved.

Discretization Techniques: A recent survey

Abstract: A discretization algorithm is needed in order to handle problems with real-valued attributes with Decision Trees (DTs), Bayesian Networks (BNs) and Rule-Learners (RLs), treating the resulting intervals as nominal val- ues. The performance of these systems is tied to the right election of these in- tervals. A good discretization algorithm has to balance the loss of information intrinsic to this kind of process and generating a reasonable number of cut points, that is, a reasonable search space. This paper presents the well known discretization techniques. Of course, a single article cannot be a complete re- view of all discretization algorithms. Despite this, we hope that the references cited cover the major theoretical issues and guide the researcher to interesting research directions and suggest possible combinations that have to be explored.

Two E3 ubiquitin ligases, SCF-Skp2 and DDB1-Cul4, target human Cdt1 for proteolysis.

Abstract: Replication licensing is carefully regulated to restrict replication to once in a cell cycle. In higher eukaryotes, regulation of the licensing factor Cdt1 by proteolysis and Geminin is essential to prevent re-replication. We show here that the N-terminal 100 amino acids of human Cdt1 are recognized for proteolysis by two distinct E3 ubiquitin ligases during S–G2 phases. Six highly conserved amino acids within the 10 first amino acids of Cdt1 are essential for DDB1-Cul4-mediated proteolysis. This region is also involved in proteolysis following DNA damage. The second E3 is SCF-Skp2, which recognizes the Cy-motif-mediated Cyclin E/A-cyclin-dependent kinase-phosphorylated region. Consistently, in HeLa cells cosilenced of Skp2 and Cul4, Cdt1 remained stable in S–G2 phases. The Cul4-containing E3 is active during ongoing replication, while SCF-Skp2 operates both in S and G2 phases. PCNA binds to Cdt1 through the six conserved N-terminal amino acids. PCNA is essential for Cul4- but not Skp2-directed degradation during DNA replication and following ultraviolet-irradiation. Our data unravel multiple distinct pathways regulating Cdt1 to block re-replication.

Bounds for multihop relayed communications in nakagami-m fading

Abstract: We present closed-form lower bounds for the performance of multihop transmissions with nonregenerative relays over not necessarily identically distributed Nakagami-m fading channels. The end-to-end signal-to-noise ratio is formulated and upper bounded by using an inequality between harmonic and geometric means of positive random variables (RVs). Novel closed-form expressions are derived for the moment generating function, the probability density function, and the cumulative distribution function of the product of rational powers of statistically independent Gamma RVs. These statistical results are then applied to studying the outage probability and the average bit-error probability for phase- and frequency-modulated signaling. Numerical examples compare analytical and simulation results, verifying the tightness of the proposed bounds.

Size-dependent band gap of colloidal quantum dots

Abstract: The size-dependent band gap of semiconductor quantum dots is a well-known and widely studied quantum confinement effect. In order to understand the size-dependent band gap, different theoretical approaches have been adopted, including the effective-mass approximation with infinite or finite confinement potentials, the tight-binding method, the linear combination of atomic orbitals method, and the empirical pseudopotential method. In the present work we calculate the size-dependent band gap of colloidal quantum dots using a recently developed method that predicts accurately the eigenstates and eigenenergies of nanostructures by utilizing the adiabatic theorem of quantum mechanics. We have studied various semiconductor (CdS, CdSe, CdTe, PbSe, InP, and InAs) quantum dots in different matrices. The theoretical predictions are, in most cases, in good agreement with the corresponding experimental data. In addition, our results indicate that the height of the finite-depth well confining potential is independent ...

Concrete Confinement with Textile-Reinforced Mortar Jackets

Abstract: The application of textile-reinforced mortars (TRMs) as a means of increasing the axial capacity of concrete through confinement is investigated experimentally in this study. TRM may be thought of as an alternative to fiber-reinforced polymers (FRPs), addressing many of the problems associated with application of the latter without compromising performance by a significant degree. Based on the response of confined cylinders and short rectangular columns, it is concluded that textile-mortar jacketing provides a substantial gain in compressive strength and deformability; this gain is higher as the number of confining layers increases and depends on the tensile strength of the mortar. Compared with their resin-impregnated counterparts, mortar-impregnated textiles may result in reduced effectiveness. This reduction was more pronounced in cylindrical specimens but rather insignificant in rectangular ones. Favorable confinement characteristics on rectangular columns were also obtained by using helically applied unbonded strips with end anchorages-an interesting concept that deserves further investigation. Modeling of concrete confined with jackets other than resin-impregnated ones is presented by the authors as a rather straightforward procedure through the proper introduction of experimentally derived jacket effectiveness coefficients. From the results obtained in this study, it is believed that TRM jacketing is an extremely promising solution for the confinement of reinforced concrete.

Optimization of the DRASTIC method for groundwater vulnerability assessment via the use of simple statistical methods and GIS

Abstract: The assessment of groundwater vulnerability to pollution has proved to be an effective tool for the delineation of protection zones in areas affected by groundwater contamination due to intensive fertilizer applications. By modifying and optimizing the well known and widely used DRASTIC model it was possible to predict the intrinsic vulnerability to pollution as well as the groundwater pollution risk more accurately. This method incorporated the use of simple statistical and geostatistical techniques for the revision of the factor ratings and weightings of all the DRASTIC parameters under a GIS environment. The criterion for these modifications was the correlation coefficient of each parameter with the nitrates concentration in groundwater. On the basis of their statistical significance, some parameters were subtracted from the DRASTIC equation, while land use was considered as an additional DRASTIC parameter. Following the above-mentioned modifications, the correlation coefficient between groundwater pollution risk and nitrates concentration was considerably improved and rose to 33% higher than the original method. The model was applied to a part of Trifilia province, Greece, which is considered to be a typical Mediterranean region with readily available hydrogeological and hydrochemical data.

The importance of being red when young: anthocyanins and the protection of young leaves of Quercus coccifera from insect herbivory and excess light.

Abstract: Young leaves of many plants are transiently red because of the accumulation of anthocyanins, with the redness disappearing as leaves mature. Among the many hypothetical functions of foliar anthocyanins, two are tested in this field study: the sunscreen photoprotective function against excess visible light and the handicap signal against herbivory. We took advantage of intraspecies variation in anthocyanin concentrations of young leaves of Quercus coccifera L. to compare in vivo chlorophyll fluorescence parameters, reflectance spectra, total phenolics and the extent of herbivory of leaves of red- and green-leaved phenotypes occupying the same habitat. Photosystem II (PSII) photochemical efficiencies obtained at various photon fluence rates of red light were similar in green and red leaves. In white light, PSII efficiencies were slightly higher in red leaves than in green leaves, indicating a slight photoprotective role of anthocyanins in the field. However, compared with red phenotypes, green phenotypes suffered greater herbivore damage, as judged by the number of leaves attacked and the area lost to herbivory. In addition, there was a positive correlation between the concentrations of anthocyanins and total phenolics. We suggest that the importance of a photoprotective anthocyanic screen is low in thin, young leaves with low chlorophyll concentrations because the green light attenuated by anthocyanins is less significant for chlorophyll excitation. However, the decreased reflectance in the green spectral band and the concomitant leveling of reflectance throughout the 400-570 nm spectral range may either make red leaves less discernible to some insect herbivores or make insect herbivores more discernible to predators, or both. Moreover, excessive herbivory may be additionally discouraged by the high phenolic concentrations in red leaves.

Effects of excitons in nonlinear optical rectification in semiparabolic quantum dots

Abstract: We study the effects of excitons in nonlinear optical rectification in one-dimensional semiparabolic quantum dots. We consider the cases that the electron and the hole are confined in semiparabolic potentials (i) with the same oscillator frequency and (ii) with the same width. In the first case we present approximate analytical results in the strong confinement regime and find a closed-form relation between the nonlinear optical rectification coefficient of an exciton and the nonlinear optical rectification coefficient when only one electron exists in the structure. In the second case we use the Hartree-Fock approximation and the potential morphing method and present results for the nonlinear optical rectification coefficient in all confinement regimes.

Hopping conductivity in polymer matrix–metal particles composites

Abstract: Charge transport properties, such as the temperature dependent dc conductivity and the frequency dependent conductance, of polymer matrix–metal particles composites, are investigated in the present study. Dc and ac conductivity is examined with varying parameters the filler content, temperature and the frequency in the case of ac field. The examined systems, though they are characterized as dielectrics, exhibit considerable conductivity, which alters by several orders of magnitude with temperature and frequency. The temperature and frequency dependence of conductivity gives evidence for the charge carriers transport mechanism via the occurred agreement of experimental results with the employed hopping models (variable range hopping model and random free-energy barrier model).

Reforming reactions of acetic acid on nickel catalysts over a wide temperature range

Abstract: Catalytic steam reforming of bio-oil, a liquid derived from pyrolysis of biomass, may be a viable process of renewable hydrogen production. Acetic acid is one of the major constituents of bio-oil, and for this reason, it is used as a model compound to study its reaction network under steam reforming conditions over Al2O3 and La2O3, and Ni catalyst supported on La2O3/Al2O3 carrier, employing transient and steady-state techniques. It is found that acetic acid interacts strongly with the Al2O3 carrier and less strongly with La2O3. Decomposition reactions as well as the ketonization reaction take place, especially at intermediate temperatures. In the presence of Ni, catalytic activity is shifted toward lower temperatures. Nickel promotes steam reforming reactions and retards the rate of carbon deposition onto the catalyst surface. It is also found that carbon formation is affected by reaction temperature, the HAc/H2O ratio and catalyst composition. Carbon deposition is favoured at low reaction temperatures and at high HAc/H2O ratio.

What is metamorphosis

Abstract: Metamorphosis (Gr. meta- "change" + morphe "form") as a biological process is generally attributed to a subset of animals: most famously insects and amphibians, but some fish and many marine invertebrates as well. We held a symposium at the 2006 Society for Integrative and Comparative Biology (SICB) annual meeting in Orlando, FL (USA) to discuss metamorphosis in a comparative context. Specifically, we considered the possibility that the term "metamorphosis" could be rightly applied to non-animals as well, including fungi, flowering plants, and some marine algae. Clearly, the answer depends upon how metamorphosis is defined. As we participants differed (sometimes quite substantially) in how we defined the term, we decided to present each of our conceptions of metamorphosis in 1 place, rather than attempting to agree on a single consensus definition. Herein we have gathered together our various definitions of metamorphosis, and offer an analysis that highlights some of the main similarities and differences among them. We present this article not only as an introduction to this symposium volume, but also as a reference tool that can be used by others interested in metamorphosis. Ultimately, we hope that this article-and the volume as a whole-will represent a springboard for further investigations into the surprisingly deep mechanistic similarities among independently evolved life cycle transitions across kingdoms.

Electrochemically synthesized CdS nanoparticle-modified TiO2 nanotube-array photoelectrodes : Preparation, characterization, and application to photoelectrochemical cells

Abstract: A novel electrodeposited CdS nanoparticle-modified highly-ordered TiO2 nanotube-array photoelectrode and its application to photoelectrochemical cells is reported. Results show formation of a thin, nanoparticulate CdS layer, comprised of sphere-like 10–20 nm diameter nanoparticles, on the anodic synthesized TiO2 nanotube-array (inner diameter of 70 nm, wall thickness 25 nm and ca. 400 nm length) electrode. The resulting CdS–TiO2 photoelectrode has an as-fabricated bandgap of 2.53, and 2.41 eV bandgap after sintering at 350 °C in N2 ambient. Photoelectrochemical properties are described in detail.

Closed-form statistics for the sum of squared Nakagami-m variates and its applications

Abstract: We present closed-form expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the sum of non-identical squared Nakagami-m random variables (RVs) with integer-order fading parameters. As it is shown, they can be written as a weighted sum of Erlang PDFs and CDFs, respectively, while the analysis includes both independent and correlated sums of RVs. The proposed formulation significantly improves previously published results, which are either in the form of infinite sums or higher order derivatives of the fading parameter m. The obtained formulas can be applied to the performance analysis of diversity combining receivers operating over Nakagami-m fading channels

Principles and applications of CVD powder technology

Abstract: Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique.