Showing papers by "University of Patras published in 1982"

Application of finite-part integrals to the singular integral equations of crack problems in plane and three-dimensional elasticity

Abstract: A modification of the form of the singular integral equation for the problem of a plane crack of arbitrary shape in a three-dimensional isotropic elastic medium is proposed. This modification consists in the incorporation of the Laplace operator δ into the integrand. The integral must now be interpreted as a finite-part integral. The new singular integral equation is equivalent to the original one, but simpler in form. Moreovet, its form suggests a new approach for its numerical solution, based on quadrature rules for one-dimensional finite part integrals with a singularity of order two. A very simple application to the problem of a penny-shaped crack under constant pressure is also made. Moreover, the case of straight crack problems in plane isotropic elasticity is also considered in detail and the corresponding results for this special case are also derived.

Heat transfer in flow through a porous medium bounded by an infinite vertical plate under the action of a magnetic field

Abstract: An analysis of steady two-dimensional flow, of an electrically conducting fluid through a porous medium, occupying a semi-infinite region of the space bounded by an infinite, vertical and porous limiting surface under the action of a transverse magnetic field is considered. Approximate solutions have been derived for the velocity and temperature fields and the rate of heat transfer (Nusselt number). The variations of the velocity and Nusselt number are shown on graphs.

Sedimentation Field-Flow Fractionation of Colloidal Particles in River Water

Abstract: Sedimentation field-flow fractionation (sedimentation FFF) is a new technique that has been used to separate and characterize a variety of submicron particles. With the aid of a newly developed on-channel concentration procedure, sedimentation FFF was used to study the colloidal particles contained in samples collected from the Colorado, Green, and Price Rivers in eastern Utah during the spring run-off season. Samples from the different rivers displayed distinctly different fractograms, which could serve to “fingerprint” and characterize the colloidal content. The fractions obtained, when analyzed, displayed distinct differences in chemical composition. Each fraction re-emerged at its original elution volume when re-injected into the apparatus, indicating that the sedimentation FFF procedure had successfully concentrated then fractionated the colloidal particles in the river water.

Adaptation of Drosophila to temperature: Heat‐shock proteins and survival in Drosophila melanogaster

Abstract: Two stocks of Drosophila melanogaster, one sensitive (6.5% survival) and one resistant (76.24%) to heat shock (40"C/25 min) were derived through indirect selection [I]. Genetic analysis of heat-sensitive and heat-resistant lines we had selected revealed that the survival rate is chiefly determined by cytoplasmic inheritance but also depends to some extent on the nucleus [I]. The ability of the fly to survive thermal stress was found to have an excellent correlation with the kinetics of protein synthesis in ovaries or glands subjected to heat treatment. The incorporation rate of 35S-methionine into proteins was found to be higher for strains exhibiting higher survival (RI, RIS~) than for strains with a lesser ability (Sl, S1 RI) to survive heat shock. Moreover, the intensity of labeling of the proteins synthesized and especially of the hsps (heat-shock proteins) after the heat shock is higher in the RI and RISl stocks than in the SI and SIRl stocks. This convergence between survival and the cellular level of hsps (both manipulated by selection) bears on the physiological significance of these proteins which seems to participate in the control of the survival as an additive component.

The Introduction of Non-Recursive Methods into Mathematics*

Abstract: The authors summarize the use of recursive function theory as a tool to understand the transition from constructive to non-constructive mathematics in the 19th century. Certain classical theorems of algebra and analysis are analyzed for recursive content.

Compatibility of poly(ethylene oxide)–poly(vinyl acetate) blends

Abstract: The compatibility of poly(ethylene oxide)–poly(vinyl acetate) (PEO-PVA) blends was examined at five compositions covering the complete range. Samples were prepared by coprecipitation and solution casting. Dynamic mechanical properties were studied at 110 Hz between −120 and 65°C for dry, quenched, and annealed samples. The study also included tensile testing at 25°C, examination of blend morphology, and DSC measurements at elevated temperatures. Optical microscopy revealed that crystallization of PEO proceeds essentially unhindered at up to 25% poly(vinyl acetate) content by weight. Higher levels of this component drastically reduce spherulite size, and at the highest PVA compositions there was no evidence of crystallization. Thermomechanical spectra of quenched and annealed samples indicate limited mixing of the two components except for the higher (>75%) PVA compositions. Tensile properties show a mutual reinforcement at 10-25% PVA content due to possible polymer segment association. The melting-point depression of PEO is significant above 25% PVA and has been attributed to morphological changes of the PEO crystalline phase.

Adaptation of Drosophila enzymes to temperature IV. Natural selection at the alcohol-dehydrogenase locus

Abstract: Studies were carried out on the temperature-dependent kinetic properties (Km, Q10, Ea, thermostability) of alcohol-dehydrogenase allozymes from D. melanogaster. It was shown that there is a parallelism between the biochemical properties of the enzymes and the behaviour of the genes in natural and cage populations. Furthermore, the relationship between the temperature-dependent kinetic properties of alcohol dehydrogenase and assay temperature was examined in three tropical and two temperate Drosophila species. Km patterns were similar among species from the same habitat and different between habitats. No such parallelism was seen with respect to thermal inactivation. The Q10 values in general reflected temperature-dependent changes in Km. It is discussed that the mechanistic connection observed between the biochemical and population levels (intra-and interspecifically) strongly suggests that temperature acts as a selective factor on the structural Adh locus in the genus Drosophila.

Exact model-matching control of three-dimensional systems using state and output feedback

Abstract: For a general state space model of three-dimensional (3-D) systems, the exact model-matching control problem via state and output feedback ia considered. A frequency domain approach is employed in which the 3-D prototype system (model) is given in transfer function matrix of the form G m(p, w, z). The approach is based on equating the closed-loop transfer matrix function G c(p, w, z) to G m(p, w, z) and solving for the required feedback matrix gains through an application of Kronecker matrix product concept. We start with the static feedback case, and then treat the dynamic feedback problem for the important case of proportional plus integral plus derivative (PID) control. The approach leads to a set of linear algebraic equations, which involve the necessary and sufficient conditions for the exact model matching problem to have a solution. Two simple, but non-trivial examples, are computed.

Recombinogenic and mutagenic effects of the antitumour antibiotic bleomycin in Aspergillus nidulans

Abstract: Bleomycin, an antibiotic and antineoplastic drug that inhibits DNA synthesis and causes several types of chromosomal aberration, was found to increase mitotic recombination in Aspergillus nidulans. Heterozygous prototrophic diploid strains grown on media containing bleomycin produced significant increases of yellow and white sectors compared with controls. Further, the increased colour segregants were due to mitotic crossing-over, whereas the non-disjunctional segregants remained at the control level. Bleomycin also induced point mutations in the methionine-suppressor system of the methG1 biA1 strain of Aspergillus nidulans. Conidia treated in suspension with various concentrations of Neomycin increased the methionine-independent mutants 30-fold and more.

Temperature adaptation of Drosophila populations. The heat shock proteins system

Abstract: 1. 1. The heat shock proteins (hsps) system has been studied in two replicate cage populations (1D, 1C) of Drosophila melanogaster , which were maintained under different environmental conditions (temperature and relative humidity) for approximately 7 yr and exhibited different survival when they were subjected to temperature shock. 2. 2. The kinetics of protein synthesis in ovaries from D and C flies (and their reciprocal hybrids DC and CD) were subjected to heat stress, and the electrophoretic patterns of heat shock proteins (especially of the hsp 70 K), are correlated with the survival of the fly. 3. 3. These results confirm already obtained results using different stocks which were subjected to different type of selection (indirect selection; Stephanou et al. , 1982), which represents good evidence for the biological significance of the hsps. 4. 4. The capacity of protein synthesis (and especially of hsp 70 K) following temperature shock is higher in ovaries from D (25°C) or DC flies as compared with those from C (14°C) or CD ones. 5. 5. It is proposed that the regulation of hsps synthesis can be considered as a major target of temperature-induced selection, and an effective molecular mechanism for temperature compensation.

Storm graded sand at 200 m water depth, Scotian Shelf, Eastern Canada

Abstract: Graded sand-to-mud beds are a common shelf facies in the rock record. Similar beds were studied in nine cores from the sandmud transition at the edge of Emerald Basin to determine their frequency and mode of origin. Graded sand-to-mud beds 5 to 20 cm thick can be correlated between cores and thicken basinwards, with average sand content decreasing from 60% to 5% over 7 km. European weed pollen distribution indicates only the top bed is less than 200 years old. The graded beds were deposited from suspension during storms with a several hundred year recurrence interval.

Thermotropic liquid crystalline polymers. II. Further examples on their synthesis by the interaction of poly(acryloyl chloride) with mesogenic compounds

Abstract: A recently reported method for the synthesis of thermotropic liquid crystalline polymers by the interaction of reactive polymers with mesogenic compounds is further illustrated by the preparation of two mesomorphic polymers. Specifically, poly(acryloyl chloride) is esterified with p-hydroxybiphenyl and p-hydroxyazobenzene for the synthesis of poly(p-biphenyl acrylate) and poly(p-acryloyloxyazobenzene), respectively. The liquid crystalline character of both polymers was established by optical microscopy, x-ray diffraction analysis, and differential scanning calorimetry.

Kinetic study of the drying step of supported catalysts by reversed-flow gas chromatography

Abstract: Application of reversed-flow gas chromatography to study the drying step in the preparation of supported catalysts is proposed. It is demonstrated that this technique can be applied to investigate the kinetic law followed, as well as to obtain kinetic parameters of drying (rate constants, activation energies and frequency factors). Amaterial illustrating this application is γ-Al2O3 impregnated with usual organic solvents (n-C5H12,n-C6H14,n-C7H16, CH3COCH3 and CH3CH2OH). It was found that in all cases above a simple first-order law based onone kind of active site is followed. Moreover, it was observed that the activation energyEa of the drying process increases almost linearly with the relative molecular mass of the solvent, whereas for the same solventEa increases with the amount used. The operation of a kinetic compensation effect suggests “similar” activated complexes of the various solvents used.

Catalytic deactivation of Co-Mo hydrodesulphurization catalysts supported on γ-Al2O3 doped with Li+ ions

Abstract: A series of hydrodesulphurization (HDS) catalysts containing 12% MoO3 and 2.8% Co3O4 were prepared using γ-Al2O3 modified with various amounts of Li+. The effect of the Li+ cations on the catalytic activity with respect to the HDS of thiophene was studied. A marked decrease in the catalytic activity with increasing Li+ content was found. An explanation based on the Co-Mo bilayer model proposed recently is suggested. This work provides more information about the well-known synergistic effect. Diffuse reflectance spectroscopy and X-ray spectroscopy were used to characterize the specimens.

Molybdena catalysts prepared on modified carriers: Regulation of the symmetry and valence of the molybdenum species formed on γ-Al2O3 modified with alkali cations

Abstract: Five series of modified carriers were prepared by the dry impregnation of γ-Al 2 O 3 with various amounts of MNO 3 (M + ≡ Li + , Na + , K + , Rb + and Cs + ). Each modified carrier was used as a support in the preparation of three MoO 3 (6%, 12% and 18%) supported catalysts. The combined use of X-ray powder spectroscopy, diffuse reflectance spectroscopy and the classical analysis of NO 3 − and NO 2 − allows the structure of the modified supports to be investigated as well as the effects of the type of modifier and the modifier concentration on the molybdenum species formed on the carrier surface and on their valence and symmetry. It was found that a large quantity of MNO 3 remained on the carrier surface at temperatures below 400 °C. An increase in the calcination temperature from 400 to 500 °C produced a partial dissociation of MNO 3 to MNO 2 . A further increase in the temperature from 500 to 600°C resulted in the formation of Li 2 Al 2 O 4 and/or LiAl 5 O 8 and the complete disappearance of LiNO 3 and LiNO 2 . At this temperature some of the other alkali cations were still present on the γ-Al 2 O 3 surface in the form MNO 3 and MNO 2 . A critical alkali concentration must be present before surface crystallization of MNO 3 and MNO 2 commences. The symmetry and valence of the molybdenum species can be regulated by changing the doping parameters. At 300 °C all the modifiers inhibited the reduction of molybdenum(VI) to molybdenum(V) and this effect increased with the size of the dopant cation and with the dopant concentration. At 300 and 600 °C, all the alkali cations except Li + produced a transition from octahedral to tetrahedral coordination symmetry in the molybdenum(VI) species. The magnitude of this effect increased with increasing alkali content. These effects were independent of the MoO 3 concentration. A mechanism explaining the doping effects is developed.

Changes in properties of phosphoenolpyruvate carboxylase from the CAM plant Sedum praealtum D.C. upon dark/light transition and their stabilization by glycerol.

Abstract: A prenounced decrease in phosphoenolpyruvate earboxylase (PEPC) activity is observed upon dark/light transition in Sedum praealtum D.C., only when glycerol is included in the extraction medium. If glycerol is omitted, the activity extracted in light is initially low, but soon reaches night levels. The stabilization of the light-induced form of the enzyme by glycerol, in crude or desalted extracts, made it possible to study its kinetic properties in comparison to those of the dark form. The behaviour towards substrate (PEP) changes from hyperbolic (dark) to sigmoid (light), S0.5 is increased and the enzymic activity becomes more sensitive to malate inhibition. Quite different activity/pH profiles are also obtained for the two forms of PEPC. It is inferred that the in vivo regulation of PEPC in CAM is effected by a concerted action of light, malate and pH shifting.

Should a reliable information processor be chaotic

Abstract: Brain‐like structures have evolved by performing signal processing initially by minimizing “tracking errors” on a competitive basis. Such systems are highly complex and at the same time notoriously “disordered”. The functional trace of the cerebral cortex of the (human) brain is a good example. The Electroencephalogram (E.E.G) appears particularly fragmented during the execution of mental tasks, as well as during the recurrent episodes of R.E.M. sleep. A stochastically regular or a highly synchronized E.E.G on the other hand, characterises a drowsy (relaxing) or epileptic subject respectively and indicates—in both cases—a very incompetent information processor. We suggest that such behavioral changeovers are produced via bifurcations which trigger the thalamocortical non‐linear pacemaking oscillator to switch from an unstable limit cycle to a strange attractor regime (i.e. to chaos), or vice versa. Our analysis aims to show that the E.E.G's characteristics are not accidental but inevitable and even necessary and, therefore, functionally significant.

Fatigue damage of turbine-generator shafts due to fast reclosing

Abstract: Breaking in a large electric power system causes torsional vibrations on the turbogenerator shafts. Damping of such vibrations is very low compared with the damping of the electrical system. Therefore, during a strong electric transient, the shafts connecting the turbine and the generator rotors may undergo heavy loading and considerable deformations, both elastic and plastic, for prolonged periods of time. As a result, the fatigue life of the shafts may be substantially reduced. The paper introduces an improved mechanical dynamic model of the system for torsional response, which can account for the plastic material model, to yield the cumulative damage during the transients due to high and low cycle fatigue. Moreover, a procedure for the calculation of fatigue life expenditure is developed based on the `equivalent strain range? derived from a known twist angle history of the shaft. A detailed discrete model for both the mechanical and the electrical system was used in conjunction with modelling of the fast reclosing mechanism. In this manner, fatigue life reduction due to a certain fast reclosing strategy was evaluated. The system thus developed can lead to a better understanding of the mechanism of fatigue life reduction due to the electrical transients.