Showing papers by "University of Patras published in 1997"
509 citations
TL;DR: In this article, the authors investigated the catalytic combustion of volatile organic compounds (VOCs) in industrial effluent streams, present in low concentrations (10-1000 ppm) of VOCs, using group VII metal catalysts supported on alumina carriers.
Abstract: Catalytic combustion of volatile organic compounds (VOCs), present in low concentrations (10–1000 ppm) in industrial effluent streams, is a promising air abatement technology. The oxidation of benzene, butanol and ethyl acetate over group VII metal catalysts supported on alumina carriers has been investigated. Pt, Pd and Co were found to be the most active among group VIII metals, while ethyl acetate was found to be the most-difficult-to-oxidize compound. Benzene and ethyl acetate oxidations over Pt/Al2O3 were found to be structure sensitive reactions with the turnover frequency (TOF) increasing with increasing mean metal particle size. The presence of chloride on the catalyst surface, originating from chloride-containing metal precursor compounds was found to exert an inhibiting effect on the activity of Pt. Apparent activation energies of the reactions over Pt and Pd catalysts were found to be in the 70–120 kJ/mol range while the reaction order with respect to the VOC was positive in all cases. During oxidation of benzene-butanol mixtures, benzene oxidation was completely suppressed as long as butanol was present in the reaction mixture.
261 citations
TL;DR: A novel speech enhancement technique is presented based on the definition of the psychoacoustically derived quantity of audible noise spectrum and its subsequent suppression using optimal nonlinear filtering of the short-time spectral amplitude (STSA) envelope.
Abstract: A novel speech enhancement technique is presented based on the definition of the psychoacoustically derived quantity of audible noise spectrum and its subsequent suppression using optimal nonlinear filtering of the short-time spectral amplitude (STSA) envelope. The filter operates with sparse spectral estimates obtained from the STSA, and, when these parameters are accurately known, significant intelligibility gains, up to 40%, result in the processed speech signal. These parameters can be also estimated from noisy data, resulting into smaller but significant intelligibility gains.
205 citations
TL;DR: Backpropagation training is based on a modified steepest descent method which allows variable stepsize and is computationally efficient and posseses interesting convergence properties utilizing estimates of the Lipschitz constant without any additional computational cost.
188 citations
TL;DR: In this paper, the effects of masonry infills on the global seismic response of reinforced concrete structures through numerical analyses were studied, and it was shown that, despite their apparent stiffening effect on the system, infills reduce spectral displacements and forces mainly through their high damping in the first large post-cracking excursion.
Abstract: The effects of masonry infills on the global seismic response of reinforced concrete structures is studied through numerical analyses. Response spectra of elastic SDOF frames with nonlinear infills show that, despite their apparent stiffening effect on the system, infills reduce spectral displacements and forces mainly through their high damping in the first large post-cracking excursion. Parametric analyses on a large variety of multi-storey infilled reinforced concrete structures show that, due to the hysteretic energy dissipation in the infills, if the infilling is uniform in all storeys, drifts and structural damage are dramatically reduced, without an increase in the seismic force demands. Soft-storey effects due to the absence of infills in the bottom storey are not so important for seismic motions at the design intensity, but may be very large at higher motion intensities, if the ultimate strength of the infills amounts to a large percentage of the building weight. The Eurocode 8 provisions for des...
174 citations
TL;DR: In this article, the reforming of methane by carbon dioxide is studied over a Ni/La2O3 catalyst which presents an unusual catalytic stability compared to other nickel-based catalysts.
172 citations
TL;DR: In this article, the optimum thickness of each dielectric layer required to maximise the film luminous transmittance for a given metal layer thickness was established, and optical properties of the films designed were also predicted and the most suitable materials were identified.
149 citations
TL;DR: Evidence is provided for the angiogenesis-promoting effect of thrombin in vivo and the induction byThrombin of the ang iogenic phenotype of endothelial cells in vitro in the absence of other cell types such as smooth muscle cells, pericytes, and inflammatory cells.
Abstract: We have tested the effect of thrombin on endothelial cell tube formation in vitro and angiogenesis in vivo. Thrombin induces the differentiation of endothelial cells into capillary structures in a ...
147 citations
TL;DR: Ozone pretreatment studies of wastewater containing a specific azo dye - Orange II - were conducted in order to assess the kinetics of ozone oxidation and to evaluate the effect of ozonation on the biodegradability of the wastewater.
147 citations
TL;DR: In this article, the authors give an overview of recent developments and research trends in laser assisted machining. But there are still unresolved problems regarding the limitations of the techniques, optimum machining conditions, etc.
Abstract: Since laser technology has considerable synergy with machining technologies, Laser Machining (LM) and Laser Assisted Machining (LAM) are relevant research topics. This paper attempts to give an overview of recent developments and research trends. Although scientific work on this area has contributed to the understanding of the process, there are still unresolved problems regarding the limitations of the techniques, optimum machining conditions, etc. The outcome of experimental investigations on LAM shows potential applications for this process but there are several issues to be resolved.
139 citations
TL;DR: Low birth weight and maternal smoking are both associated with decreased leptin concentrations, and these effects are more pronounced in premature newborns.
Abstract: Prematurity, maternal smoking, and low birth weight each result in neuroendocrine dysfunction and increased perinatal morbidity and mortality. Leptin, an adipocyte-secreted protein, has provided the first physiological link to the regulatory system controlling starvation-induced neuroendocrine changes in rodents. This study investigated whether leptin concentrations were detectable in cord blood of newborns, and assessed the effect of birth weight, prematurity, and maternal smoking on cord blood leptin concentrations. Fifty consecutively enrolled full-term and 12 preterm newborns born to mothers who smoked during pregnancy were compared to 50 full-term and 12 preterm newborns born to parents who were nonsmokers. RIA for leptin was performed using cord blood samples collected immediately after birth. Leptin concentrations were detectable in newborns and correlated positively with obesity (full-term, r = 0.30, P < 0.01; preterm, r = 0.47, P < 0.05). Maternal smoking during pregnancy was associated with decr...
TL;DR: Chitin, a nitrogen-containing polysaccharide which is a major component of the exoskeletons of arthropods, was found to be a substrate favouring the deposition of calcite crystals from stable supersaturated solutions at pH 8.50 and at 25°C.
01 Jan 1997
TL;DR: In this article, a multipurpose computational optics tool based on the characteristic matrix formulation has been developed for the design and optimisation of the D/M/D films: the optimum thickness of each dielectric layer required to maximise the film luminous transmittance for a given metal layer thickness was established.
Abstract: Copyright (c) 1997 Elsevier Science S.A. All rights reserved. Dielectric/Metal/Dielectric (D/M/D) thin films deposited on glass offer the possibility of significant energy savings in buildings and can find other applications as components of advanced materials design. In an effort to reduce the complexity and cost of production of D/M/D films, physical vapour deposition was used for the laboratory manufacture of ZnS/Ag/ZnS films on glass. ZnS was used because of its high refractive index, ease of deposition and low cost; Ag was used because of its low absorption in the visible spectrum. The films produced were of good quality, with luminous transmittance as high as 83.9%, IR reflectance above 90% and total hemispherical emittance equal to 6%. The ZnS layers were found not only to antireflect the Ag layer, but also to stabilise the ZnS/Ag/ZnS film, improve its adherence on glass and increase the film thermal resistance up to 240°C. A multipurpose computational optics tool based on the characteristic matrix formulation has been developed for the design and optimisation of the D/M/D films: The optimum thickness of each dielectric layer required to maximise the film luminous transmittance for a given metal layer thickness was established. The optical properties of the films designed were also predicted and the most suitable materials were identified. The optical properties of the films produced were measured and were found to compare favourably with the theoretical predictions. © 1997 Elsevier Science S.A.
29 Oct 1997
TL;DR: It is proved that the models commonly used for generating random CSP instances do not have an asymptotic threshold and, in the spirit of random k-SAT, a new model is presented and lower and upper bounds for its parameters are derived so that instances are "almost surely" underconstrained and over Constraint Satisfaction Problems.
Abstract: Recently there has been a great amount of interest in Random Constraint Satisfaction Problems, both from an experimental and a theoretical point of view. Rather intriguingly, experimental results with various models for generating random CSP instances suggest a "threshold-like" behavior and some theoretical work has been done in analyzing these models when the number of variables becomes large (asymptotic). In this paper we prove that the models commonly used for generating random CSP instances do not have an asymptotic threshold. In particular, we prove that as the number of variables becomes large, almost add instances they generate are trivially overconstrained. We then present a new model for random CSP and, in the spirit of random k-SAT, we derive lower and upper bounds for its parameters so that instances are "almost surely" underconstrained and overconstrained, respectively. Finally, for the case of one of the popular models in Artificial Intelligence we derive sharper estimates for the probability of being overconstrained, as a function of the number of variables. Canada PGS B Scholarship. E-mail: optas@cs.toronto.edu
Partially supported by the EU ESPRIT Long-term Research Project ALCOM-IT (Project Nr. 20244).
Supported in part by an NSERC grant.
Partially supported by the EU ESPRIT Long-term Research Project ALCOM-IT (Project Nr. 20244).
TL;DR: This paper introduces a class of fugitive-search games where the searchers do not see the fugitive and the fugitive can only move just before a searcher is placed on the vertex it occupies, and gives an equivalent characterization of the search number for any given fugitive speed in terms of an elimination ordering of the vertices of the graph.
TL;DR: The authors compared the development of orthographic representations in children learning to read English and Greek, and found that the level of phonology that is represented in the orthographic recognition units being developed by children who are learned to read more and less transparent orthographies.
Abstract: Two experiments were conducted to compare the development of orthographic representations in children learning to read English and Greek. Nonsense words that either shared both orthography and phonology at the level of the rhyme with real words (comic-bomic), phonology only (comic-bommick), or neither (dilotaff) were created for each orthography. Experiment 1 compared children’s reading of bisyllabic and trisyllabic nonsense words likebomic vs.bommick, taffodil vs.tafoddyl, and found a significant facilitatory effect of orthographic rhyme familiarity for English only. Experiment 2 compared children’s reading of trisyllabic nonsense words that either shared rhyme phonology with real words (tafoddyl) or did not (dilotaff). Significant facilitation in reading accuracy was found for shared rhyme phonology in English, with a significant speed advantage in Greek. These results are interpreted in terms of the level of phonology that is represented in the orthographic recognition units being developed by children who are learning to read more and less transparent orthographies.
TL;DR: This method is superior to others since it can separate and determine twelve different non- and variously sulphated delta-disaccharides derived from heparan sulphate, heparin and Fragmin containing either N-sulphated, N-acetylated or unsubstituted glucosamine in a single HPLC run.
TL;DR: In this article, the application of unidirectional fiber-reinforced polymer tendons for the reversible strengthening of masonry monuments is discussed. And the effect of temperature changes on the tendons and the masonry are shown to be negligible.
Abstract: This paper deals with the applications of unidirectional fibre-reinforced polymer tendons for the reversible strengthening of masonry monuments. The tendons, anchored to the masonry only at the ends, are circumferentially applied on the external face of the structure and posttensioned to provide horizontal confinement. The relevant properties of fibre-reinforced polymer materials and prestressing systems are summarised; in addition, the concepts for their application, including anchorage, to masonry structures are developed, and a general design procedure is presented. The effectiveness of the strengthening technique is established both analytically, for structures with simple geometries, and numerically, for a real three-dimensional structure with openings, based on the finite element method. The effects of temperature changes on the tendons and the masonry are shown to be negligible. It is concluded that the effectiveness of the proposed method in the consolidation of historic masonry structures is quite satisfactory, especially when the strengthening elements are made of carbon fibre-reinforced polymer.
TL;DR: In this paper, a magnetohydrodynamic laminar boundary-layer flow over a wedge, the flow being subjected to a velocity caused by suction or injection, is studied.
Abstract: Magnetohydrodynamic laminar boundary-layer flow over a wedge, the flow being subjected to a velocity caused by suction or injection, is studied. The fluid is assumed to be viscous, incompressible, and electrically conducting with a magnetic field applied transversally to the direction of the flow. The governing partial differential equations of this problem, subjected to their boundary conditions, are solved numerically by applying an efficient solution scheme for local nonsimilarity boundary-layer analysis. Numerical calculations, up to the third level of truncation, are carried out for the different values of the dimensionless parameters in the problem and an analysis of the results obtained show that the flow field is influenced appreciably by the applied magnetic field. Resume : Nous etudions 1’ecoulement magnetohydrodynamique de couche limite laminaire autour d’un fil (wedge) quand il est soumis a une injection ou succion de vitesse. Le fluide est suppose etre visqueux, incompressible et conducteur electrique et le champ magnetique est applique perpendiculairement e la direction de 1’ecoulement. Les equations differentielles du probleme considere avec les conditions aux limites associees vent resolues en appliquant un schema numerique efficace pour 1’etude locale non-similaire de couche limite. Des calculs numeriques jusqu’ au troisieme niveau de tronquation vent effectues pour differentes valeurs des parametres sans-dimension du probleme et 1’analyse des resultats obtenus montre que le champ d’ ecoulement est considerablement infuence par le champ magnetique applique. [Traduit par la redaction]
TL;DR: Evidence is suggested that although the negative responses to the treatments were small, damage may be increasing with time in some long-lived woody perennials, and the necessity for long-term field investigations to predict the likely ecological consequences of increasing UV-B radiation.
Abstract: The effects of enhanced UV-B radiation on three examples of European shrub-dominated vegetation were studied in situ The experiments were in High Arctic Greenland, northern Sweden and Greece, and at all sites investigated the interaction of enhanced UV-B radiation (simulating a 15% reduction in the ozone layer) with artificially increased precipitation The Swedish experiment also involved a study of the interaction between enhanced UV-B radiation and elevated CO2 (600 ppm) These field studies were supported by an outdoor controlled environment study in the United Kingdom involving modulated enhancement of UV-B radiation in combination with elevated CO2 (700 ppm) Effects of the treatments on plant growth, morphology, phenology and physiology were measured The effects observed were species specific, and included both positive and negative responses to the treatments In general the negative responses to UV-B treatments of up to three growing seasons were small, but included reductions in shoot growth and premature leaf senescence Positive responses included a marked increase in flowering in some species and a stimulation of some photosynthetic processes UV-B treatment enhanced the drought tolerance of Pinus pinea and Pinus halepensis by increasing leaf cuticle thickness In general, there were few interactions between the elevated CO2 and enhanced UV-B treatments There was evidence to suggest that although the negative responses to the treatments were small, damage may be increasing with time in some long-lived woody perennials There was also evidence in the third year of treatments for effects of UV-B on insect herbivory in Vaccinium species The experiments point to the necessity for long-term field investigations to predict the likely ecological consequences of increasing UV-B radiation
TL;DR: In this paper, the problem of crack depth and position identification in frame structures is examined, using eigenfrequency measurements, and it has been established that a crack has an important effect on the dynamic behavior of a structure.
TL;DR: The results support the postulate of a function of leaf hairs as a UV-B radiation screen and suggest that trichome density and/or itsUV-B absorbing capacity may depend on irradiance during leaf development.
TL;DR: ZnSCdS:Ag is an efficient phosphor well suited to radiography and displayed the highest x-ray to light conversion efficiency and had optical properties close to those of and , and its emission spectrum was well matched to optical detectors.
Abstract: ZnSCdS:Ag was evaluated as a radiographic image receptor and was compared with Gd2O2S:Tb and Y2O2S:Tb phosphors often used in radiography. The evaluation of a radiographic receptor was modelled as a three-step process: (i) determination of light output intensity as related to the input radiation dose, (ii) determination of visible light characteristics with respect to radiographic optical detectors, and (iii) determination of image information transfer efficiency. The light intensity emitted per unit of x-ray exposure rate was measured and theoretically calculated for laboratory prepared screens with coating thicknesses from 20 to 220 mg cm-2 and tube voltages from 50 to 250 kVp. ZnSCdS:Ag light intensity was higher than that of Gd2O2S:Tb or Y2O2S:Tb for tube voltages less than 70 and 80 kVp respectively. ZnSCdS:Ag displayed the highest x-ray to light conversion efficiency (0.207) and had optical properties close to those of Gd2O2S:Tb and Y2O2S:Tb, and its emission spectrum was well matched to optical detectors. The image information transfer properties described by the modulation transfer function, the quantum noise transfer function, and the detective quantum efficiency were calculated for both general radiographic and mammographic conditions and were found to be intermediate between those of Gd2O2S:Tb and Y2O2S:Tb screens. Conclusively, ZnSCdS:Ag is an efficient phosphor well suited to radiography.
TL;DR: In this article, the authors present and discuss two important transient techniques, namely the Steady State Trace (SSITKA) and the Transient Isothermal Hydrogenation (THH) of adsorbed surface reaction intermediate species.
Abstract: Experimental features of the transient method using concentration forcing functions to study the surface dynamics of a heterogeneous catalytic reaction at 1 atm and with on line mass spectroscopy are discussed. Emphasis is given in the presentation and discussion of two important transient techniques, namely the ‘steady state tracing’ or ‘steady state isotopic transient kinetic analysis (SSITKA)’ and the ‘transient isothermal hydrogenation’ of adsorbed surface reaction intermediate species. The SSITKA technique allows to measure the concentration of the active reaction intermediate species, the intrinsic reactivity of the site associated with a given adsorbed reaction intermediate species and elementary step, and also velocities of elementary steps in the reaction network. The ‘transient isothermal hydrogenation’ technique, when applied in an appropriate reaction system and coupled with the SSITKA technique, allows for the measurement of concentration of inactive (spectator) reaction intermediate species. In addition, important intrinsic kinetic parameters and other mechanistic information related to the hydrogenation process can be obtained. The bulk of this paper concerns the application of transient methods (various kinds of transient experiments) in order to elucidate mechanistic aspects of: (a) the oxidative coupling of methane (OCM) reaction to C2-hydrocarbons over mixed metal oxide catalysts, where a synergy phenomenon between the two components of the mixed metal oxide catalyst occurs, (b) the ammonia oxidation reaction over V2O5/TiO2 catalysts, and (c) the NO decomposition reaction over Rh supported on TiO2 and W6+-doped TiO2 carriers.
TL;DR: In this article, a trickling filter for iron removal from potable water has been constructed and tested, and the possible duration of the filter operating cycles was studied as a function of the inlet iron concentration and the volumetric flow-rate.
TL;DR: Petropoulou et al. as mentioned in this paper investigated the effect of supplemental UV-B radiation on Mediterranean pinea seedlings during the summer of 1994 and concluded that the effect depends on the amount of summer precipitation.
Abstract: The possible mechanism(s) by which supplemental UV-B radiation alleviates the adverse effects of summer drought in Mediterranean pines (Petropoulou et al. 1995) were investigated with seedlings of Pinus pinea. Plants received ambient or ambient plus supplemental UV-B radiation (biologically equivalent to a 15% ozone depletion over Patras, 38.3° N, 29.1° E) and natural precipitation or additional irrigation. Treatments started on 1 February, 1994 and lasted up to the end of the dry period (29 September). In well-watered plants, UV-B radiation had no influence on photosystem II photochemical efficiency and biomass accumulation. Water stressed plants suffered from needle loss and reduced photosystem II photochemical efficiency during the summer. These symptoms, however, were less pronounced in plants receiving supplemental UV-B radiation, resulting in higher total biomass at plant harvest. Laboratory tests showed that enhanced UV-B radiation did not improve the tolerance of photosystem II against drought, high light, high temperature and oxidative stress. Enhanced UV-B radiation, however, improved the water economy of water stressed plants, as judged by measurements of needle relative water content. In addition, it caused an almost two-fold increase of cuticle thickness. No such UV-B radiation effects were observed in well-watered pines. The results indicate that the combination of water stress and UV-B radiation may trigger specific responses, enabling the plants to avoid excessive water loss and, thereby, maintain a more efficient photosynthetic apparatus during the summer. The extent of this apparently positive UV-B radiation effect would depend on the amount of summer precipitation.
TL;DR: In this article, the authors investigated the catalytic activity of catalysts comprising of combinations of one of three metals, Pt, Pd or Rh supported on five different supports, that is, SiO 2, γ-Al 2 O 3, ZrO 2 (8% Y 2 O3 ), TiO 2 or TiO 6+, and found that up to 100-fold increase in catalytic activation was observed by supplying O 2− ions to the catalyst surface via positive potential application to the catalysts.
Abstract: The kinetics of oxidation of a light hydrocarbon (C 2 H 4 ) were studied on catalysts comprising of combinations of one of three metals, Pt, Pd or Rh supported on five different supports, that is, SiO 2 , γ-Al 2 O 3 , ZrO 2 (8% Y 2 O 3 ), TiO 2 or TiO 2 (W 6+ ). Significant variation of turnover frequency with the carrier was observed, which cannot be explained by structure sensitivity considerations and is attributed to interactions between the metal crystallites and the carrier. The catalytic activity of these metal-support combinations was investigated over a wide range of partial pressures of ethylene and oxygen. In a separate set of experiments, the kinetics of C 2 H 4 oxidation were also investigated on polycrystalline Rh films interfaced with ZrO 2 (8 mol% Y 2 O 3 ) solid electrolyte in a galvanic cell of the type: C 2 H 4 , O 2 , Rh/YSZ/Pt, air, during regular open-circuit conditions as well as under Non-Faradic Electrochemical Modification of Catalytic Activity (NEMCA), that is, closed-circuit conditions. Up to 100-fold increase in catalytic activity was observed by supplying O 2− ions to the catalyst surface via positive potential application to the catalyst. The observed kinetic behavior upon increasing catalyst potential parallels qualitatively the observed alteration of turnover frequency with variation of the support of the Rh crystallites.
TL;DR: In this paper, an offshore survey using 3.5 kHz subbottom profiling system and a remote operated vehicle (ROV) has shown that the earthquake caused small sized subaerial to submarine sediment failure in at least four sites, in three fan delta deposits: the Rododafni, the Eliki and the Tolofonas.
TL;DR: Implantation of a metal self-expandable or balloon expanding stent is safe and effective for the palliative treatment of malignant ureteral obstruction in late stage cancer patients.