Showing papers by "University of Patras published in 1988"
TL;DR: In this paper, a simplified model of several adjacent buildings in a block is used to study the pounding of such buildings due to strong earthquakes, and a parametric investigation of this problem shows that the end structures experience almost always substantial increases in their response while for interior structures the opposite often happens.
Abstract: A simplified model of several adjacent buildings in a block is used to study the pounding of such buildings due to strong earthquakes. Considerable structural damage and even some collapses have sometimes been attributed to this effect. Each structure is modelled as a S.D.O.F. system and pounding is simulated using impact elements. A parametric investigation of this problem shows that the end structures experience almost always substantial increases in their response while for ‘interior’ structures the opposite often happens. This may explain why high percentages of corner buildings have collapsed in some earthquakes.
443 citations
TL;DR: In this article, a finite element for the cracked prismatic beam is developed to evaluate the dynamic response of a cracked cantilever beam to harmonic point force excitation, which can be used in any appropriate matrix analysis of structures program.
228 citations
TL;DR: In this article, the problem of stabilizing linear discrete-time systems under state and control linear constraints is studied, and existence conditions of linear state feedback control laws respecting both the constraints are established.
Abstract: In this paper the problem of stabilizing linear discrete-time systems under state and control linear constraints is studied. Based on the concept of positive invariance, existence conditions of linear state feedback control laws respecting both the constraints are established. These conditions are then translated into an algorithm of linear programming.
196 citations
TL;DR: The problem of the existence of positively invariant polyhedral sets for linear discrete-time dynamical systems is studied in this paper, where necessary and sufficient conditions for a polyhedral polyhedral set are given.
Abstract: The problem of the existence of positively invariant polyhedral sets for linear discrete-time dynamical systems is studied. In the first part of the paper, necessary and sufficient conditions for a...
193 citations
TL;DR: In this paper, necessary and sufficient conditions for a polyhedral set to be positively invariant set of a linear discrete-time system are established, where the polyhedral sets are defined as polytopes.
181 citations
TL;DR: In this article, the authors studied sediment transport processes on the escarpment of a listric fault in the tectonically active and terrigenous sediment-dominated Corinth graben in Greece using 3.5 kHz and airgun profiles and sidescan sonar images.
105 citations
TL;DR: In this paper, the effect of electrochemically pumping 02- to or from a porous polycrystalline Pt catalyst film used for CO oxidation at atmospheric pressure and temperatures 250-600°C was studied.
103 citations
TL;DR: In this paper, the coupling of bending and longitudinal vibration of a stationary cracked shaft with an open crack is modeled by way of a 2×2 local flexibility matrix with coupling terms.
Abstract: This paper describes the coupling of bending and longitudinal vibration of a stationary cracked shaft with an open crack. The crack is modeled by way of a 2×2 local flexibility matrix with coupling terms. The elements of this matrix are obtained analytically. One of the elements compares well with experimental data of other investigators. The free vibration of the shaft, and the influence of the crack on the vibrational behavior of the shaft is studied. The relation of the eigenvalues of the system and the crack depth as functions of the slenderness ratio are presented. The forced vibration of the shaft is also studied and the coupling of the vibration modes is verified analytically and experimentally. The applicability of the method as a crack identification tool is demonstrated.
99 citations
TL;DR: Results indicate that most of the collagenous protein synthesized by CAM was BM collagen and this can be used as a biochemical index of angiogenesis.
Abstract: A method was developed for assessing collagenous protein biosynthesis from [U-14C]proline in relation to angiogenesis in the chick chorioallantoic membrane (CAM). The rate of collagenous protein biosynthesis both in vitro and in vivo was maximum between days 8 and 11 of chick embryo development. This was the stage of maximum angiogenesis as shown by morphological evaluation of the vascular density. At day 10 the rate of collagenous protein biosynthesis was 11-fold higher than that of day 15, when angiogenesis had reached a plateau. The collagenous protein formed by CAM co-elutes on SDS-agarose chromatography with the collagenous component of [3H]-acetylated-basement membrane (BM) from bovine lens capsule. 8,9-dihydroxy-7-methyl-benzo[b]quinolizinium bromide (GPA1734), which was shown previously to be a specific inhibitor of BM collagen biosynthesis, caused about 80% reduction in collagenous protein synthesis by CAM. These results indicate that most of the collagenous protein synthesized by CAM was BM collagen and this can be used as a biochemical index of angiogenesis.
76 citations
TL;DR: The reduction of uronic acids in glycosaminoglycans prior to depolymerization reactions is one way in which the uronic acid content of polysaccharides can be studied without major losses.
73 citations
Journal Article•
TL;DR: Results suggest that inhibitors of BM collagen biosynthesis prevent angiogenesis by interfering with the formation of an essential component of the vessel wall, and the search for such inhibitors may be a new approach in the development of antiangiogenic agents.
Abstract: GPA1734, an inhibitor of BM collagen biosynthesis, was investigated in the CAM model system for its effect on angiogenesis. Evaluation of angiogenesis was performed by placing a thin plastic coverslip inscribed with concentric circles on the CAM and counting the number of vessels intercepting the circles. The rate of BM collagen biosynthesis was monitored using [U-14C] proline incorporation into CAM proteins and determining the collagenase-digestible protein fraction. A marked depression in the vascular density was observed in the CAM area under a plastic disc containing GPA1734 as compared to control discs placed on the CAM about 1 cm apart from days 9 to 12 of incubation. A concomitant decrease in collagenous protein biosynthesis was observed in the area under the discs containing GPA1734 and [U-14C]proline as compared to control discs containing only the radiolabeled proline. The forementioned effects of GPA1734 on CAM were specific because no similar effects were observed with a closely related compound, 9,10-dihydroxy-7-methyl-benzo[b]quinolizinium bromide or with GPA1734 plus Fe++, which did not affect the rate of BM collagen biosynthesis. These results suggest that inhibitors of BM collagen biosynthesis prevent angiogenesis by interfering with the formation of an essential component of the vessel wall. The search for such inhibitors may be a new approach in the development of antiangiogenic agents.
TL;DR: In this article, the mechanism of CO oxidation on polycrystalline Pt at atmospheric pressure was investigated by combining kinetic and simultaneous potentiometric studies in a gradientless reactor containing one or two polycrystaline Pt films supported on stabilized zirconia, and the oscillatory behavior of the system was studied in detail by simultaneous mass spectroscopic monitoring of the concentrations of O2 and CO2.
TL;DR: In this article, a series of FNiMo/γ-Al2O3 catalysts containing constant MoO3 and NiO loadings were characterized using X-ray photoelectron spectroscopy (XPS).
TL;DR: In this paper, chemical analyses for As and Sb in Santorini sediments, and As in waters, from the vicinity of active hydrothermal vents indicated that these elements were scavenged into the sediments by freshly precipitating Fe-oxides and that the conditions for this become increasingly favorable away from the vents.
TL;DR: In this paper, exact coherent states for a damped harmonic oscillator with time-dependent mass and frequency were constructed, and the new coherent states result exactly as partial cases of the coherent states of Yuen which are equivalent to the well-known squeezed states.
TL;DR: In this paper, theoreme de regle rapide is introduced, which permet un calcul immediat du processus d'evolution, i.e., un comportement soliton.
Abstract: On etudie des automates cellulaires qui presentent un comportement soliton. On introduit le theoreme de regle rapide qui permet un calcul immediat du processus d'evolution
TL;DR: Compared hippocampal slices from epileptic and phenotypically healthy mice revealed no significant difference between tg/tg and tg/+ mice, and results were qualitatively similar to those previously described in rats and guinea pigs.
Abstract: The petit-mal seizures of the "tottering" mutant mouse (tg) have been attributed to an exaggerated noradrenergic projection from locus coeruleus to the telencephalon (Noebels 1984). In order to investigate the possible epileptogenic mechanisms involved, we have compared hippocampal slices from epileptic (tg/tg) and phenotypically healthy (tg/+) mice. Resting potentials, action potentials and afterpotentials, membrane impedances and time constants were not significantly different in 11 neurons from each group. Bath application of noradrenaline, isoproterenol and histamine or a transient exposure to Mg++-free medium caused a long lasting increase in extracellularly recorded population spikes induced in CA1 by electrical stimulation of stratum radiatum. Isoproterenol blocked the calcium dependent afterhyperpolarization and accommodation of firing. Tetanization of afferent fibres evoked post-tetanic potentiation and long-term potentiation. All these results are qualitatively similar to those previously described in rats and guinea pigs and have revealed no significant difference between tg/tg and tg/+ mice.
TL;DR: The results suggest that, in MS, a general immune dysregulation exists which leads to a local expansion of B lymphocytes producing autoantibodies with reactivities similar to those of serum natural autoantsibodies.
Abstract: Using a panel of antigens (actin, myosin, tubulin, albumin, transferrin, peroxidase, thyroglobulin, DNA, prolactin, TNP and myelin basic protein (MBP)), we have tested the antibody activity of serum and cerebrospinal fluid (CSF) from healthy individuals, patients with multiple sclerosis (MS) and individuals with other neurological diseases. No differences in the concentrations and specificities of the serum antibodies were observed among the 3 groups. In contrast, we found that MS patients often had elevated CSF antibody levels against many antigens of the panel. The MS patients with local immunoglobulin production in the central nervous system (CNS) had the highest antibody levels. Restricted antibody activity against a given antigen of the panel was not observed. Compared to the two other groups, the MS group had equivalent titres of anti-MBP antibodies in the CSF. These results suggest that, in MS, a general immune dysregulation exists which leads to a local expansion of B lymphocytes producing autoantibodies with reactivities similar to those of serum natural autoantibodies.
TL;DR: In this article, a wet-only precipitation study was conducted in Patras, Greece from October 1985 to April 1986, where very high pH variations were recorded ranging from pH = 4.12 to pH = 8.76, indicating high variability in the acid sources and neutralization.
TL;DR: In this paper, the regions of stability for the out-of-plane equilibrium points of the photogravitational restricted three-body problem are given and the corresponding families are computed.
Abstract: The regions of stability for the ‘out of plane’ equilibrium points of the photogravitational restricted three-body problem are given. Second order expansions of periodic solutions around these points are constructed and the corresponding families are computed. It is found that two such families exist. One of them originates and terminates on the same equilibrium point while the other terminates by flattening on the orbital plane.
TL;DR: The data emphasize the stringent and discriminating structural requirements in the N-terminal domain of sarmesin that endow this analogue with its antagonist properties and suggest the presence of defined steric constraints in this region of the molecule during receptor blockade.
Abstract: Analogues of the competitive angiotensin antagonist [Sar1,Tyr(ME)4]angiotensin II (sarmesin) with modifications at the N-terminus have been prepared by the solid-phase method and purified by reversed-phase HPLC. Substitution of the Sar1 residue of sarmesin with N,N-dimethyl-Gly, N-ethyl-Gly, aminoisobutyric, (methylamino)isobutyric, aminocaproic, and oxamic acids gave analogues that had the following respective antagonist activities (pA2) in the rat isolated uterus assay: less than 6, 6.9, 5.5, 6.0, less than 6, and 5.3. The additional substitution of Ile for Phe at the C-terminus of the latter four peptides gave pA2 values of 7.1, 5.1, less than 5, and 5. Substitution of the Arg2 residue of sarmesin with Nle or Sar abolished antagonist activity. These data emphasize the stringent and discriminating structural requirements in the N-terminal domain of sarmesin that endow this analogue with its antagonist properties and suggest the presence of defined steric constraints in this region of the molecule during receptor blockade.
TL;DR: In this paper, the mutual miscibility of poly(ethylene oxide)/poly(vinyl acetate) (PEO/PVAC) blends is investigated using DSC and polarized microscopy.
TL;DR: This method uses monthly average meteorological data and easily acquirable system parameters in order to determine possible photovoltaic system sizes, capable of supplying any given monthly average hourly load profile.
TL;DR: In this paper, the point of zero charge (ZPC), the surface dissociation constants and the concentration of the charged surface groups, SiOH+2 and SiO−, of silica over a wide pH range were determined by potentiometric titrations for pure silica at various temperatures between 25 and 5 °C and for a series of very low-Na+-doped silicas at 25 °C.
TL;DR: In this article, a negative binomial distribution of order k is obtained by compounding the extended (or multiparameter) Poisson distribution by the gamma distribution, as the zero truncated limit of the first distribution.
Abstract: A multiparameter negative binomial distribution of order k is obtained by compounding the extended (or multiparameter) Poisson distribution of order k by the gamma distribution. A multiparameter logarithmic series distribution of order k is derived next, as the zero truncated limit of the first distribution. Finally a few genesis schemes and interrelationships are established for these three multiparameter distributions of order k. The present work extends several properties of distributions of order k.
TL;DR: In this paper, generic formulas for obtaining optimal estimates of the reflection coefficient sequence are derived, which can utilize any estimation/smoothing scheme and yield optimal fixed-point, fixed-lag and fixed-interval estimates.
TL;DR: In this paper, the authors investigated the role of low collisional cooling rates combined with strong thermal conduction along geomagnetic field lines played a key role in elevating F region temperatures and spreading the electron temperature enhancements far outside the region where radio wave energy is deposited.
Abstract: Under current solar minimum conditions at Arecibo, Puerto Rico, large (∼1000–2000 K) enhancements in electron temperature are observed in the winter, nighttime ionosphere when high-power 3-MHz radio waves reflect near the F region peak. Computational modeling has been performed to determine the cause of the unusually large temperature enhancements. The results indicate that low collisional cooling rates combined with strong thermal conduction along geomagnetic field lines play a key role in elevating F region temperatures and spreading the electron temperature enhancements far outside of the region where radio wave energy is deposited. Thus, the dramatically large temperature enhancements are attributable primarily to expected low cooling rates of the electron gas, rather than unexpectedly high heating rates.
01 Sep 1988
TL;DR: In this article, current measurements collected across the Otranto Straits, from mid-September to mid-October 1979, are discussed, showing that there is a two-layer circulation: a northerly flowing current, restricted to the surface and mid-water depths over the Greek continental slope; and a southerly flow, which occupies the whole of the water column over the Italian continental shelf and slope and extends as far as the mid-channel.
Abstract: Current measurements collected across the Otranto Straits, from mid-September to mid-October 1979, are discussed. Data analyses show there to be two-layer circulation: a northerly flowing current, which is restricted to the surface and mid-water depths over the Greek continental slope; and a southerly flowing current, which occupies the whole of the water column over the Italian continental shelf and slope and extends as far as the mid-channel. The northerly flow was found to be continuous over the period of measurement, whilst the southerly flow was interrupted by short period reversals, often followed by rotatory currents with an inertial period. Flow in the shear zone, between the northerly and southerly flow was variable and the result of inertially drifting parcels of water and northwards propagating cyclonic eddies; these were formed probably through baroclinic instability processes within the shear zone.
TL;DR: In this article, the number of overlapping appearances of a given pattern of letters is studied and it is shown that under quite general conditions, the number is approximately distributed according to a Polya-Aeppli distribution.
Abstract: A sequence of independent experiments is performed, each one producing a letter from a given alphabet. We study the number of overlapping appearances of a given pattern of letters and we prove that, under quite general conditions, the number of overlapping appearances of long patterns is approximately distributed according to a Polya-Aeppli distribution.
TL;DR: In this article, 2,6-di(4-hydroxystyryl)pyridine (DHSP) with terephthaloyl or adipoyl chloride was used to synthesize new polyesters.