Showing papers by "University of Patras published in 1989"
TL;DR: In this article, a review of results of the so-called Painleve singularity approach to the investigation of the integrability of dynamical systems with finite and infinite number of degrees of freedom is presented.
547 citations
TL;DR: In this article, the authors presented and modeled the physiochemical processes in the carbonation of concrete, which leads to the formation of a carbonation front and an analytical expression for the evolution in time of this front, in terms of the composition parameters of cement and concrete and of environmental conditions.
Abstract: Steel bars in reinforced concrete are protected from corrosion by the high pH environment of the surrounding concrete This alkaline environment is destroyed by the reaction of atmospheric CO2 with the Ca(OH)2 of the concrete mass When this process, called carbonation of concrete, reaches the reinforcing bars, corrosion of the latter may commence In this paper, the physiochemical processes in this phenomenon are presented and modeled mathematically The mathematical model is fairly complex, but certain simplifying assumptions are possible, which lead to the formation of a “carbonation front” and to a simple analytical expression for the evolution in time of this front, in terms of the composition parameters of cement and concrete and of the environmental conditions This simple expression is in very good agreement with experimental results obtained in this and in previous studies The effect of some parameters on the carbonation front propagation is also discussed
292 citations
TL;DR: The results indicate that progressive increases of Mn concentration in drinking water are associated with progressively higher prevalences of neurological signs of CMnP and Mn concentrations in hair of older persons.
Abstract: Three areas in the same region of northwest Peloponnesos, Greece, that had varying concentrations of manganese (Mn) in drinking water were selected for study. The Mn concentrations in areas A, B, and C were 3.6–14.6 μg/I, 81.6–252.6 μg/I, and 1 800–2 300 μg/I, respectively. A random sample (62 in area A, 49 in area B, and 77 in area C) of males and females who were at least 50 y of age were submitted to a thorough neurological examination and their whole-blood Mn and hair Mn concentrations were determined. Although all areas were similar with respect to social and dietary characteristics, significant differences were observed for prevalence of chronic manganese poisoning (CMnP) symptoms and hair Mn concentration. The means (both sexes) of neurological scores were 2.7, 3.9, and 5.2, respectively, for areas A, B, and C (Kruskal-Wallis, X 2 = 6.44, 2 df, p < .05 for males; X 2 = 7.78, 2 df, p < .05 for females). Hair Mn concentrations were also significantly different, the means for which were 3.51,...
289 citations
TL;DR: In this paper, it was shown that the catalytic activity of polycrystalline Pt for the oxidation of ethylene to CO 2 and H 2 O can be increased by up to a factor of 50 when oxygen anions O 2− are electrochemically pumped onto the Pt catalyst surface.
193 citations
TL;DR: The thermal desorption of carbon monoxide from alumina-supported platinum has been studied by monitoring of the infrared spectrum of adsorbed CO as the temperature is increased.
113 citations
TL;DR: In this article, the linear constrained regulation problem (LCRP) for continuous-time dynamical systems is studied, where linear state-feedback control laws that transfer asymptotically to the origin all initial states belonging to a given polyhedral subset of the state space, while respecting linear constraints on both state and control vectors are presented.
109 citations
TL;DR: Very fine cement grouts with a water-to-cement ratio as low as two can permeate several feet into well-compacted fine sands with D15 in the range of 0.15 mm.
Abstract: The use of very fine cement grouts for injection into fine to medium sands has been proposed recently to circumvent problems associated with the permanence and toxicity of chemical grouts and the inability of ordinary cement grouts to permeate soil formations finer than coarse sand. The results of a laboratory investigation conducted on a commercially available very fine cement grout indicate that this grout has better flow properties and bleed characteristics than ordinary portland cement grputs. Very fine cement grouts with a water‐to‐cement ratio as low as two can permeate several feet into well‐compacted fine sands with D15 in the range of 0.15 mm. The groutability ratio is not a universally applicable criterion, and experimental evidence suggests that the grain‐size distribution of the fine sand, and especially the amount of fines in the sand, may control the grouting operation. The granulometry of the fine sand influences the effectiveness of the grouting operation in terms of permeability and strength.
95 citations
TL;DR: A test section was established next to a 40-ft-deep, braced excavation made through soft to medium-stiff, saturated clays in Chicago as mentioned in this paper, where surface and subsurface 3D ground movements, pore water pressures, sheet pile deformations and strut loads were measured.
Abstract: A test section was established next to a 40-ft-deep, braced excavation made through soft to medium-stiff, saturated clays in Chicago. Surface and subsurface three-dimensional ground movements, pore water pressures, sheet pile deformations and strut loads were measured. Results of these observations were correlated with construction activities at the test section. Larger than expected ground-surface settlements adjacent to the excavation were observed. The large movements occurred as a result of overexcavation during construction. The largest incremental ground movements occurred when the excavation was approximately half completed. Base stability computations indicated that the factor of safety against basal heave at that point in construction was 1.1. Two distinct shear zones developed in the soil mass; their initiation corresponded to the times when the largest incremental movements occurred. Soil displacements were always directed towards the excavation with magnitudes, at later stages of construction, larger than those measured on the sheet pile. Pore water response was markedly influenced by sheet pile installation and strut preloading; as a result, little net change in pore pressures was observed at the end of construction. Magnitudes of measured strut loads were within the levels expected based on standard design procedures.
87 citations
TL;DR: In this paper, the Rayleigh principle is used to estimate the change in the natural frequencies and modes of vibation of the structure if the crack geometry is known, assuming that the eigenvalue problem for the uncracked structure has been solved in advance.
Abstract: Cracks that develop on machine members and structures influence their dynamic behavior. The Rayleigh principle is used for an estimation of the change in the natural frequencies and modes of vibation of the structure if the crack geometry is known, assuming that the eigenvalue problem for the uncracked structure has been solved in advance. The method reduces the computational effort needed for the full eigensolution of cracked structures and gives acceptable accuracy. It can be extended to higher modes and to decompose degenerate modes found in symmetric structures. To demonstrate the change in the dynamic behavior of linear structures with the crack depth, a cylindrical shaft and a plane frame consisting of prismatic bars were analyzed for dynamic sensitivity to surface cracks.
81 citations
TL;DR: In this paper, a system of boundary integral equations is derived for Biot's full equations of dynamic poroelasticity in the Laplace transformed domain starting from first principles, and the fundamental solutions for instantaneous point body forces acting in each of the two phases are found in closed form by exploiting the use of four scalar potentials that reduce the problem to two decoupled second-order systems.
Abstract: A system of boundary integral equations is derived for Biot's full equations of dynamic poroelasticity in the Laplace transformed domain starting from first principles. These equations give the displacement vector in both the solid and fluid phases in terms of surface tractions and displacements, as well as in terms of any non-zero initial conditions and body forces. The fundamental solutions for instantaneous point body forces acting in each of the two phases are found in closed form by exploiting the use of four scalar potentials that reduce the problem to two decoupled second-order systems in the Laplace transformed domain. Finally, a parallel is drawn between dynamic poroelasticity and dynamic thermoelasticity by discovering analogies between the variables and material constants of each case.
80 citations
TL;DR: In this article, a three-dimensional porous medium model that pertains to consolidated permeable porous rocks and similar structures is proposed, where the porous medium is considered as a network of chambers connected through long narrow throats and it is approximated as network of unit cells of the constricted tube type.
Abstract: A three-dimensional porous medium model that pertains to consolidated permeable porous rocks and similar structures is proposed. The porous medium is considered as a network of chambers connected through long narrow throats and it is approximated as a network of unit cells of the constricted tube type. The skeleton of the network can be either regular or randomized, and the throat-to-chamber coordination number can be varied by randomly removing a number of throats. The sizes of contiguous chambers and throats can be cither independent random variables, or they can be correlated. This correlation can be positive (large chambers preferring large throats), or negative (large chambers preferring small throats). The permeability of the network is found to be minimal when the chambers and throats are completely uncorrected. The degree of correlation also affects the throat-to-chamber size ratio, a parameter which is very important in two-phase flows through porous media. A substantial correlation betw...
TL;DR: In this paper, it was shown that the catalytic activity and selectivity of polycrystalline Ag for the dehydrogenation and decomposition of CH 3 OH can be markedly affected by electrochemically pumping oxygen anions from the catalyst surface via stabilized zirconia solid electrolyte cells.
TL;DR: The data demonstrate that in the human epileptogenic neocortex a purinergic mechanism can control Mg2+-free epileptiform activity and that endogenous adenosine can by itself influence epileptogenicity.
TL;DR: In this article, the Mel'nikoV function for general perturbations of two-dimensional maps possessing a saddle connection was calculated explicitly for integrable planar maps.
Abstract: This paper calculates explicitly the Mel’nikoV function for general perturbations of two-dimensional maps possessing a saddle connection. This result may be considered as the discrete analogue of Ziglin’s calculation of the Mel’nikoV function for time-periodic perturbations of two-dimensional continuous flows.Key words. integrable planar maps, perturbations, homoclinic orbits, Mel'nikoV's function, Poisson summation formula
TL;DR: In this article, the formation of low-valence crystalline vanadium compounds was studied in the V2O5M2S2O7 (M = Na, K, Cs) unsupported melt systems in the temperature range 350-480 °C during SO2 oxidation with unconverted 10% SO2, 11% O2, and 79% N2 as the feed gas.
TL;DR: The catalytic activity and selectivity of metal catalysts used as electrodes in high temperature solid electrolyte cells can be altered dramatically and in a reversible manner by electrochemically supplying oxygen anions onto catalytic surfaces via polarized metal-solid electrolyte interfaces.
Abstract: The catalytic activity and selectivity of metal catalysts used as electrodes in high temperature solid electrolyte cells can be altered dramatically and in a reversible manner. This is accomplished by electrochemically supplying oxygen anions onto catalytic surfaces via polarized metal-solid electrolyte interfaces. Oxygen anions, forced electrochemically to adsorb on the metal catalyst surface, alter the catalyst work function in a predictable way and lead to reaction rate increases as high as 4000%. Changes in catalytic rates typically exceed the rate of O2− transport to or from the catalyst surface by 102-3 · 105. Significant changes in product selectivity have been also observed. The case of several catalytic reactions in which this new phenomenon has been observed is presented and the origin of the phenomenon is discussed.
TL;DR: In this article, a chaotic dynamics model creating Markovian strings of symbols as well as sequences of words is presented, and its possible relevance to Zipf's law is discussed, and it is shown that the model can be used to solve the problem.
Abstract: A chaotic dynamics model creating Markovian strings of symbols as well as sequences of “words” is presented, and its possible relevance to Zipf's law is discussed.
01 Jan 1989
TL;DR: In this paper, it was shown that cholesterol can nucleate vaterite on its surface following well-defined induction periods, and the apparent rate order was found to be 2, suggesting a surface-controlled mechanism.
Abstract: In gallstones the occurrence of stones of cholesterol with calcite and vaterite has been observed. Cholesterol is a crystalline, water-insoluble matrix, with favorable lattice matching with both calcite and vaterite. In the present work it was shown that cholesterol can nucleate vaterite on its surface following well-defined induction periods. Kinetics analysis of the initial rates showed that they were proportional with the relative supersaturation with respect to vaterite. The apparent rate order was found to be 2, suggesting a surface-controlled mechanism. Analysis of the dependence of the induction periods on the initial solution conditions showed that the number of ions forming the critical nucleus was 4. From the kinetics data the surface energy of the overgrowing vaterite was found to be 11 mJ m−2, a value too low for sparingly soluble salts. The low value may be attributed to the heterogeneous character of vaterite nucleation.
Journal Article•
TL;DR: Monitoring the rate of collagenous protein biosynthesis in the chick chorioallantoic membrane system can be used as a quantitative method for evaluating angiogenesis inhibitors.
Abstract: In the chick chorioallantoic membrane system heparin plus cortisone caused a marked depression in the rate of collagenous protein biosynthesis in vivo during inhibition of angiogenesis. This suggests that monitoring the rate of collagenous protein biosynthesis in the chick chorioallantoic membrane system can be used as a quantitative method for evaluating angiogenesis inhibitors.
TL;DR: No reduction in ethanol productivity and yield was observed for up to 29 repeated batch fermentations in the attachment of Saccharomyces cerevisiae cells on the cheap and abundant ore Kissiris.
TL;DR: In this paper, a crossover is observed in the variation of the reduced viscosity, η sp c, as a function of the concentration, c, for the systems poly(methyl methyacrylate)/nitromethane and poly(vinyl-2 pyridine)/benzene.
TL;DR: The formation of calcium sulfate dihydrate is important in a number of environmental geological, industrial and energy production processes as mentioned in this paper, and the kinetics of precipitation were found to be independent of pH, and an apparent order of reaction of n = 4.
TL;DR: The results suggest that dynamometry is a useful, rapid, and inexpensive test that can identify cancer patients at a high risk of developing major postoperative complications, and predict the postoperative morbidity and mortality.
Abstract: We studied 95 patients with cancer of the gastrointestinal tract in various sites. The aim of the study was to compare the forearm dynamometry vs the prognostic nutritional index which was reported by Busby et al, 1890. We used these methods as preoperative prognostic indicators for postoperative mortality and morbidity. The forearm muscle dynamometry has greater positive predictive value (58.33 vs 32.4%), higher sensitivity (77.78 vs 66.6%), and specificity (86.11 vs 65.28%) than the prognostic nutritional index. The forearm muscle dynamometry predicted the patients mortality with a high rate of sensitivity (100%). The results suggest that dynamometry is a useful, rapid, and inexpensive test. It is more accurate than the nutritional index, and can indentify cancer patients at a high risk of developing major postoperative complications, and predict the postoperative morbidity and mortality. (Journal of Parenteral and Enteral Nutrition 13:34-36, 1989)
TL;DR: These abnormalities were observed in patients with both forms of β thalassemia, major and intermedia, and there was no correlation between the abnormalities observed and the serum ferritin level, the mean hematocrit value, and the dose of deferoxamine given to the patients.
TL;DR: In this paper, the sessile drop technique has been used to measure the contact angle of liquid metals Sn, Bi and Pb in contact with polycrystalline calcia-stabilized zirconia.
TL;DR: Studies on nests of pine processionary caterpillars were carried out in different parts of Greece in the years 1985 to 1988 as discussed by the authors, where most of the nests could be found at the southeast, south and southwest of pine trees.
Abstract: Studies on nests of the pine processionary caterpillar were carried out in different parts of Greece in the years 1985 to 1988. Most of the nests could be found at the southeast, south and southwest of pine trees. Deviations in the distribution could be due to the slope of forests and a high population pressure. Registering of temperature data verified that the inner temperature of the caterpillar nests could rise quite high. Such a warming is clearly dependent on the intensity of the insolation and the thickness of the nest webs. The biogenic heat production has not a significant role.
Zusammenfassung
Untersuchungen zur Exposition und Temperatur von Raupennestern von Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Thaumetopoeidae) in Griechenland
In den Jahren 1985 bis 1988 erfolgten in verschiedenen Regionen Griechenlands Untersuchungen an Gespinstnestern des Pinienprozessionsspinners. Die meisten Nester konnten auf der Sudost-, Sud- und Sudwestseite der Kiefern festgestellt werden. In diesem Zusammenhang wurde auf die klimatischen Verhaltnisse in den Wintermonaten in dieser Region hingewiesen. Abweichungen von der Verteilung an den Kiefern wurden mit der Hanglage des Waldes und eines hohen Populationsdruckes in Verbindung gebracht. Messungen ergaben, das im Inneren der Raupennester recht hohe Temperaturen erreicht werden konnen. Diese Aufheizung war deutlich von der Intensitat der Sonneneinstrahlung und der Dichte der die Nester umgebenden Gespinste abhangig. Die biogene Warmeproduktion spielte nur eine untergeordnete Rolle.
TL;DR: In this article, a direct boundary element method is developed for the dynamic analysis of thin elastic flexural plates of arbitrary planform and boundary conditions, which employs the static fundamental solution of the problem and creates not only boundary integrals but surface integrals as well owing to the presence of the inertia force.
Abstract: A direct boundary element method is developed for the dynamic analysis of thin elastic flexural plates of arbitrary planform and boundary conditions. The formulation employs the static fundamental solution of the problem and this creates not only boundary integrals but surface integrals as well owing to the presence of the inertia force. Thus the discretization consists of boundary as well as interior elements. Quadratic isoparametric elements and quadratic isoparametric or constant elements are employed for the boundary and interior discretization, respectively. Both free and forced vibrations are considered. The free vibration problem is reduced to a matrix eigenvalue problem with matrix coefficients independent of frequency. The forced vibration problem is solved with the aid of the Laplace transform with respect to time and this requires a numerical inversion of the transformed solution to obtain the plate dynamic response to arbitrary transient loading. The effect of external viscous or internal viscoelastic damping on the response is also studied. The proposed method is compared against the direct boundary element method in conjunction with the dynamic fundamental solution as well as the finite element method primarily by means of a number of numerical examples. These examples also serve to illustrate the use of the proposed method.
TL;DR: The premenopausal period is characterized by increased FSH and LH and decreased progesterone/estradiol ratio resulting in irregular bleeding, endometrial hyperplasia, polyps, fibromas, mamary distrophies, disturbance of mood, appetite and thermoregulation.
Abstract: Oocyte depletion and ovarian aging results in profound alterations at the biological level. The reduction in numbers of follicles leads to reduction of circulating inhibin and increased serum FSH, characteristic marker of ovarian failure. The remaining follicles are overstimulated and premature ovulation may ensue. This, leads to luteal deficiency and reduction in progesterone production and relative hyperestrogenemia. The above changes characterize the premenopausal period. In a second phase, anovulatory cycles interchange with premature and occasionally normal ovulatory cycles. This phase is characterized by increased FSH and LH and decreased progesterone/estradiol ratio resulting in irregular bleeding, endometrial hyperplasia, polyps, fibromas, mamary distrophies, disturbance of mood, appetite and thermoregulation. Lastly, the sensitivity of ovarian follicles to FSH and LH is lost with a decline of E2. below 20pg/ml produced almost exclusively from peripheral conversion from circulating androgens. The beneficial effects of E2 are lost resulting in atrophy of the sensitive tissues, decreased calcium absorption, increased bone resorption, accelerated bone loss and osteoporosis, rise in serum triglycerides, increased VLDL and LDL lipoproteins, increased LDL/HDL cholesterol, a profile which favors atherosclerosis.
TL;DR: The immobilization of Saccharomyces cerevisiae cells on γ-alumina pellets was examined by electron microscope and by measurement of the electrokinetic charge of the cells and the γ’s of the pellets.
TL;DR: For example, this paper found that lime treatment at an optimum pH level near 11 requiring a dose less than 10g/l effected COD removals from 15 to 22% for classic and from 33 to 46% for centrifugal mill waste.
Abstract: Classic and centrifugal olive oil mill wastewater volumes of 1.18 and 1.68m3/Mg olives and corresponding polluting loads of 37 and 53 Kg BOD5 and 82 and 121 Kg COD/Mg olives were established in a systematic study of 15 mills. Lime treatment at an optimum pH level near 11 requiring a dose less than 10g/l effected COD removals from 15 to 22% for classic and from 33 to 46% for centrifugal mill waste. The volume of resulting sludge was large and could not be adequately handled by sedimentation; the sludge had good dewatering characteristics and was amenable to simple straining. Excess lime treatment using up to 50 g/l lime offered little additional benefit.