Showing papers by "University of Patras published in 1986"

Vibration isolation using open or filled trenches

Abstract: The problem of structural isolation from ground transmitted vibrations by open or infilled trenches under conditions of plane strain is numerically studied. The soil medium is assumed to be linear elastic or viscoelastic, homogeneous and isotropic. Horizontally propagating Rayleigh waves or waves generated by the motion of a rigid foundation or by surface blasting are considered in this work. The formulation and solution of the problem is accomplished by the boundary element method in the frequency domain for harmonic disturbances or in conjunction with Laplace transform for transient disturbances. The proposed method, which requires a discretisation of only the trench perimeter, the soil-foundation interface and some portion of the free soil surface on either side of the trench appears to be better than either finite element or finite difference techniques. Some parametric studies are also conducted to assess the importance of the various geometrical, material and dynamic input parameters and provide useful guidelines to the design engineer.

Network models for two-phase flow in porous media Part 1. Immiscible microdisplacement of non-wetting fluids

Abstract: A theoretical simulator of immiscible displacement of a non-wetting fluid by a wetting one in a random porous medium is developed. The porous medium is modelled as a network of randomly sized unit cells of the constricted-tube type. Under creeping-flow conditions the problem is reduced to a system of linear equations, the solution of which gives the instantaneous pressures at the nodes and the corresponding flowrates through the unit cells. The pattern and rate of the displacement are obtained by assuming quasi-static flow and taking small time increments. The porous medium adopted for the simulations is a sandpack with porosity 0.395 and grain sizes in the range from 74 to 148 μrn. The effects of the capillary number, Ca, and the viscosity ratio, κ = μo/μw, are studied. The results confirm the importance of the capillary number for displacement, but they also show that for moderate and high Ca values the role of κ is pivotal. When the viscosity ratio is favourable (κ 10−5, and becomes excellent as Ca → 10−3. On the other hand, when the viscosity ratio is unfavourable (κ > 1), the microdisplacement efficiency begins to improve only for Ca values larger than, say, 5 × 10−4, and is substantially inferior to that achieved with κ < 1 and the same Ca value. In addition to the residual saturation of the non-wetting fluid, the simulator predicts the time required for the displacement, the pattern of the transition zone, the size distribution of the entrapped ganglia, and the acceptance fraction as functions of Ca, κ, and the porous-medium geometry.

Dynamics of Hierarchical Systems: An Evolutionary Approach

Abstract: 1. Introduction.- 1.1 What This Book Is About.- 1.2 Statement of the Problem.- 1.3 Some Preliminary Definitions of Complexity and Organization.- 1.3.1 Complexity.- 1.3.2 Organization.- 2. Preliminaries from Nonlinear Dynamics and Statistical Physics.- 2.1 Symmetries and Conservation Principles.- 2.2 Instabilities at the Root of Broken Symmetries, Dissipation, and Irreversibility for Low-Dimensional (Not Statistical) Dynamical Systems.- 2.2.1 The Role of Gravitation.- 2.2.2 Comments on the Role of Coupling Among the Four Basic Interactions in Evolution.- 2.2.3 The Overdamped Nonlinear Oscillator: A Case of Spontaneously Breaking Symmetry.- 2.2.4 The Laser: A Case of Broken Symmetry.- 2.2.5 The Rotating Pendulum: A Case of Bifurcation Leading to Spontaneous Symmetry Breaking.- 2.2.6 Broken Symmetry Through a Hysteresis-Like Process.- 2.2.7 Essentials of Stability Theory.- a) General Criterion.- b) Specific Analyses.- 2.2.8 Behavior of a Two-Dimensional Dynamical System in the Vicinity of Singular Points (Steady States).- 2.2.9 First Encounter with Nontrivial Dissipative Systems: The Concept of the Attractor in Two Dimensions (Limit Cycle).- 2.3 Elements of Statistical Physics and Their Relevance to Evolutionary Phenomena.- 2.3.1 Some Characteristics of Stochastic Systems.- 2.3.2 Informational Entropy, Physical Entropy, Thermodynamic Entropy.- 2.3.3 Entropy of a Perfect Gas at Thermodynamic Equilibrium.- 2.3.4 Entropy of a Photon Gas at Thermodynamic Equilibrium.- 2.3.5 Elements of Newtonian Big Bang Cosmology.- 2.3.6 Expansion of a Mixture of Matter and Radiation. Differential Cooling and Entropy Production.- 2.3.7 The Concept of Complexity.- a) Structural Complexity and Its Relationship to the Stability of a System.- b) Algorithmic Complexity.- 2.4 Concluding Remarks.- 3. The Role of Spherical Electromagnetic Waves as Information Carriers.- 3.1 Radiation from Accelerated Charge in Vacuo. The Concept of "Self"-Force. Thermodynamics of Electromagnetic Radiation.- 3.1.1 Radiation in Vacuum.- 3.1.2 The Concept of Self-Force.- 3.1.3 Thermodynamics of Electromagnetic Radiation.- 3.2 Electromagnetic Wave Propagation in Dispersive Media and Lossy Media.- 3.3 Analysis of a Spherical Wave in Terms of Elemental "Rays". The Mode Theory of Wave Propagation. Excitable Modes (Degrees of Freedom) in a Closed Cavity.- 3.3.1 Spectral Decomposition of a Spherical Wave.- 3.3.2 The Wave-Guide Mode Theory of Wave Propagation.- 3.3.3 A Cavity Resonator.- 3.4 The Entropy of Electromagnetic Radiation. Information Received by an Electromagnetic Wave Impinging on a Finite Aperture. Ambiguity of Perception.- 4. Elements of Information and Coding Theory, with Applications.- 4.1 Information Transfer and the Concept of Channel Capacity for Discrete and Continuous Memoryless Signals.- 4.2 Some Ideas from Coding Theory Instrumental in Minimizing Reception Error.- 4.3 Some Efficient Coding Algorithms for Source-Channel Matching and Single-Error Detection and Correction.- 4.3.1 Coding for Source-Channel Matching.- 4.3.2 Coding for Error Detection and Correction.- 4.4 Information Sources with Memory. Markov Chains.- 4.5 Specific Examples of Some Useful Channels and Calculations of Their Capacities.- 4.5.1 Capacity of a Homogeneously Turbulent Channel.- 4.5.2 The Lossless Channel.- 4.5.3 The Deterministic Channel.- 4.5.4 The Uniform Channel.- 4.5.5 The Binary Symmetrical Channel.- 4.5.6 The Binary "Erasure" Channel.- 4.5.7 Capacity of an Optical Channel.- 4.5.8 Role of Quantum Noise in an Optical Channel.- 4.5.9 An Introduction to the "Genetic Channel" and the Genetic Code.- 4.5.10 The Phase-Locked Loop in the Absence and Presence of Noise.- 4.6 Modeling of Stochastic Time Series.- 4.7 Communication Between Two Hierarchical Systems Modeled by Controlled Markov Chains.- 4.7.1 Introduction: Elaboration of the Nature of Hierarchical Systems.- 4.7.2 Dynamics at the Base Levels Q, Q' and the Underlying Game.- 4.7.3 A Semi-Markov Chain Model for the Hierarchical Levels W and W'.- 4.7.4 The Control Problem.- a) Biological Rhythms Underlying the Games.- b) Description of the Communication and Control Processes.- c) Selection of Control Mechanisms.- 4.7.5 Computer Simulation.- 4.7.6 Biological Relevance of the Model.- 4.8 Emergence of New Hierarchical Levels in a Self-Organizing System.- 4.8.1 Formulation of the Problem.- 4.8.2 Creation of a New Hierarchical Level.- 4.8.3 A Comment on Typical Cases of "Psychosomatic Disturbances".- 5. Elements of Game Theory, with Applications.- 5.1 Constant-Sum Games.- 5.1.1 Both Players Have a Dominant Strategy.- 5.1.2 Only One Player Has a Dominant Strategy.- 5.1.3 Neither Player Has a Dominant Strategy.- 5.1.4 Mixed Strategies.- 5.2 Non-Constant-Sum Games.- 5.2.1 Non-Constant-Sum "Negotiable" Games.- 5.2.2 Non-Constant-Sum, Nonnegotiable "Paradoxical" Games.- 5.3 Competing Species.- 5.4 Survival and Extinction.- 5.5 Some Elementary Knowledge from Genetics: Selection and Fitness.- 5.6 Games Between Animals Adopting Specific Modes of Behavior (Roles). Concepts of Evolutionarily Stable Strategy.- 5.7 The Game of Competitive-Cooperative Production and Exchange. The Concept of "Parasite" at a Symbolic Level.- 5.8 Epidemiology of Rumors.- 6. Stochasticiky Due to Deterministic Dynamics in Three- or Higher-Dimensional Space: Chaos and Strange Attractors.- 6.1 A Reappraisal of Classical Statistical Mechanics. The Kolmogorov-Arnold-Moser Theorem.- 6.2 Dynamics in Three-Dimensional State Space (Three Degrees of Freedom). Steady States, Limit Cycles, Attracting Tori.- 6.3 Strange Attractors.- 6.3.1 One-Dimensional Maps on the Interval. The "Logistic" Model.- 6.3.2 Fractal Dimensionality. The Cantor Set.- 6.3.3 The Concept of the Lyapounov Exponents for the Period-Doubling and Chaotic Regimes.- 6.3.4 A Typical Three-Dimensional Strange Attractor. The Lorenz Model.- 6.3.5 The Rate of Information Production by the Lorenz Attractor.- 6.4 Parameters Characterizing the Average Behavior of Strange Attractors: Dimensions, Entropies, and Lyapounov Exponents.- 6.4.1 The Concept of Information Dimension.- 6.4.2 The Concept of Characteristic Lyapounov Exponents and Their Relation to Information Dimension.- 6.4.3 The Concept of Metric (Kolmogorov-Sinai) Entropy and Its Relation to Information Dimension.- 6.5 A Possible Role for Chaos in Reliable Information Processing.- 6.5.1 Theoretical Considerations and General Discussion.- 6.5.2 Application: The Electrical Activity of the Brain - Should It Be Chaotic?.- 6.5.3 Experimental Data from EEG Research.- 6.5.4 The Model.- 6.5.5 The Dual Role of Intermittency in Information Processing.- 6.5.6 The Origin of Conflict in Communicating Hierarchical Systems.- 6.6 Comments on the Effects of Internal Fluctuations and External Noise on the Stability Properties of Dynamical Systems.- 7. Epilogue: Relevance of Chaos to Biology and Related Fields.- 7.1 Computational Complexity.- 7.2 Towards a Dynamic Theory of Language.- 7.2.1 The Nature of the Problem.- 7.2.2 Structural and Functional Hierarchical Levels.- 7.2.3 An Evolutionary Linguistic Model: Digits and Patterns.- a) Total Entrainment.- b) Part Entrainment, Part "Jittery" Phase Locking.- c) Chaos.- 7.2.4 Unresolved Problems: Communication Between Two Hierarchical Systems.- 7.3 Concluding Remarks.- A. A View of the Role of External Noise at a Neuronal Hierarchical Level.- A.1 Introduction to the Problem.- A.2 Organization Through Weak Stationary-Amplitude Noise.- A.3 Relevance of the Model to Neuronal and Cognitive Organization.- B. On the Difficulty of Treating the Transaction Between Two Hierarchical Levels with Continuous Nonlinear Dynamics.- B.1 The Level Q of Partner I.- B.2 Homeostasis and Cross-Correlations.- B.3 The Level W of Partner I.- B.4 The Controller.- C. Noisy Entrainment of a Slightly Nonlinear Relaxation Oscillator by an External Harmonic Excitation.- C.1 General Description of the Model.- C.2 A Method for the Study of Entrainment.- C.2.1 Strict Entrainment.- C.2.2 Loose or "Jittery" Entrainment.- C.2.3 Pure "Free-Running" Oscillation.- C.2.4 Free-Running Oscillation.- C.3 Mathematical Treatment and Computer Simulation.- C.4 Behavior of the Oscillator Under an Applied Harmonic Excitation (Entrainment).- References.

Network models for two-phase flow in porous media Part 2. Motion of oil ganglia

Abstract: The behaviour of non-wetting ganglia undergoing immiscible displacement in a porous medium is studied with the help of a theoretical simulator. The porous medium is represented by a network of randomly sized unit cells of the constricted-tube type. The fluid of a non-wetting ganglion is in contact with the wetting fluid at menisci which are assumed to be spherical cups. The flow in every constricted unit cell occupied by a single fluid is modelled as flow in a sinusoidal tube. The flow in every unit cell that contains a meniscus and portions of both fluids is treated with a combination of a Washburn-type analysis and a lubrication-theory approximation. The flow problem is thus reduced to a system of linear equations the solution of which gives the instantaneous pressures on the nodes, the flowrates through the unit cells, and the velocities of the menisci. The motion of a ganglion is determined by assuming quasi-static flow, taking a small time increment, updating the positions of the menisci, and iterating. The behaviour of solitary ganglia is studied under conditions of quasi-static displacement (Ca slightly larger than critical), as well as dynamic displacement (Ca substantially larger than critical). Shape evolution, rate of flow, mode of break-up, and stranding are examined. The stranding and break-up coefficients are determined as functions of the capillary number and the ganglion size for a 100 × 200 sandpack. The dependence of the average ganglion velocity on ganglion size, capillary number, viscosity ratio and dynamic contact angle is examined for the simple case of motion between straight rows of spheres. It is found, among other things, that when μo < μw the velocity of ganglia can be substantially larger than that of the displacing fluid.

Dynamic response of 3-D embedded foundations by the boundary element method

Abstract: The dynamic response of three-dimensional rigid embedded foundations of arbitrary shape, resting on a linear elastic, homogeneous, and isotropic half-space is numerically obtained. The foundations are subjected either to externally applied forces or to obliquely incident seismic body or surface waves of arbitrary time variation. The time domain boundary element method (BEM) is utilized to simulate the soil medium with the aid of Stokes' fundamental solutions. The dynamic response of the foundation-soil system is obtained in a step-by-step time-marching solution. Use of this time domain BEM requires a minimum amount of surface discretization only and provides the basis for an extension to nonlinear soil-structure interaction (SSI) problems.

Compatible solutes and their effects on phosphoenolpyruvate carboxylase of C4-halophytes

Abstract: Phosphoenolpyruvate carboxylase (PEPCase), extracted from two Poaceae (Cynodon dactylon and Sporobolus pungens) grown on saline soil, was affected physiologically by betaine and proline. Its affinity for phosphoenolpyruvate (PEP) was increased and full protection against NaCl inhibition was observed; enzymic activity was also stabilized when assayed at low PEP levels. Betaine has the same effects on PEPCase extracted from a Chenopodiaceae (Salsola soda), whereas proline behaves as a competitive inhibitor, i.e. it does not protect the enzyme against NaCl and it accelerates inactivation at low PEP levels. Betaine was only compatible with PEPCase extracted from Saisola kali, without any effect on activity, protection or stabilization, but proline was again inhibitory. The levels of free proline in the two salt-stressed Poaceae were high, whereas in the Chenopodiaceae the free proline was low, as in non-stressed plants. The above data indicate that osmoregulators could not only be compatible with cytoplasmic enzymes, but they could either promote or inhibit enzyme activity, depending on the source of enzyme. Coevolution of PEPCase with the osmolyte selected for, could also be inferred.

On the generalized Cayley-Hamilton theorem

Abstract: The Cayley-Hamilton theorem is extended to the case where two A and B n \times n matrices are involved. Results similar to the regular case are presented. The results are useful for problems that concern the analysis as well as the synthesis of singular systems, for the definition of a function of two matrices f(A, B) and in various other problems in linear algebra.

A rapid generalized method of bisection for solving systems of non-linear equations

Abstract: A rapid Generalized Method of Bisection for solving Systems of Non-linear Equations is presented in this paper, based on the non-zero value of the topological degree. Further, while the method does not compute the topological degree, it takes care of keeping its non-zero value during the bisections and thus results in a fast bisection algorithm.

Kinetic studies on ribosomal peptidyltransferase. The behaviour of the inhibitor blasticidin S.

Abstract: In a cell-free system derived from Escherichia coli, the reaction between Ac[3H]Phe-tRNA and puromycin (S) is inhibited by blasticidin S (I). In this reaction Ac[3H]Phe-tRNA is part of the Ac[3H]Phe-tRNA—poly(U)—ribosome complex (C). After preincubating the complex C with I and then adding S, the degree of inhibition is greater than that observed when C reacts with a mixture of S and I. Without preincubation, the inhibition is competitive giving a Ki of 2 × 10−7 M. After preincubation the inhibition becomes of the mixed non-competitive type. A first-order kinetic analysis of the reaction between C and excess S, in the presence or in the absence of I, with or without preincubation, suggests that I acts as a modifier decreasing the catalytic rate constant of ribosomal peptidyltransferase (the putative enzyme that catalyzes the reaction between C and S). The effectiveness of I cannot be expressed by an equilibrium constant such as the above-mentioned Ki. A model is proposed which explains the results obtained. In this model, in the presence of I, C is converted to a modified species C*, which is still able to react with S but with a lower catalytic rate constant. This is a novel concept, in which the ribosome can be subjected to modulation of its activity by small ligands. It can be useful in studies on translational control of protein synthesis.

Cooperative Effects of Light and Temperature on the Activity of Phosphoenolpyruvate Carboxylase from Amaranthus paniculatus L.

Abstract: The phosphoenolpyruvate carboxylase of Amaranthus paniculatus shows in vitro optimum affinity (S0.5) to phosphoenolpyruvate at a relatively high temperature (about 35°C); even in the presence of activators, it functions efficiently only above 25 to 27°C. At lower temperatures, a steep increase of activity with temperature is observed, due to the high activation energy for the catalyzed reaction. The same behavior in vivo could amplify the photoactivation of the enzyme to a large extent, since the night/day transition is soon followed by a considerable rise in leaf temperature.

On Generalized Binomial and Multinomial Distributions and Their Relation to Generalized Poisson Distributions

Abstract: The binomial and multinomial distributions are, probably, the best known distributions because of their vast number of applications. The present paper examines some generalizations of these distributions with many practical applications. Properties of these generalizations are studied and models giving rise to them are developed. Finally, their relationship to generalized Poisson distributions is examined and limiting cases are given.

Suicide in southwestern Greece 1979―1984

Abstract: Study of suicide in a province of southwestern Greece (population 295,000) from 1979 through 1984 demonstrated: 1) mean suicide rate 0.48/10,000 population/year; 2) significant increase of the suicide rate in men after the age of 65, but not in women; 3) significantly higher suicide rate in men from rural than from urban areas; 4) significantly higher suicide rate in men than in women from rural areas, no difference in urban areas; 5) differences in suicide frequency or age at suicide were observed between subjects of different marital status; 6) violent methods of suicide were most frequently used; and 7) psychological disorders were the most frequent causes of suicide. Many of these findings are observed for the first time. Some may be related to the characteristics of the population studied, whereas others may also be present in other populations.

A cyclic multiaxial model for concrete

Abstract: A rate-independent plasticity constitutive model is proposed, for the stress-strain and strength behavior of plain concrete, under complex multiaxial stress-paths, including stress reversals. The only material parameters required by the model are the uniaxial cylinder strength f cand the strain at the peak of the monotonic stress-strain curve, e0 . The model is based on a bounding surface in stress space, which is the outermost surface that can be reached by the stress point. When the size of the bounding surface decreases with increasing maximum compressive principal strain emax on the material, strength degradation during cyclic loading as well as the falling “post-failure” branch of the stress-strain curves, can be modeled. The distance from the current stress point to the bounding surface, determines the values of the main parameters of the inelastic stress-strain relations, i.e. of the plastic shear modulus H P, and the shear-compaction/dilatancy factor β Strains are almost completely inelastic from the beginning of deformation. The inelastic portion of the incremental strain is computed by superposition of 1) the deviatoric strain increment, which occurs in the direction of the deviatoric stress and is proportional to the octahedral shear stress increment and inversely proportional to the plastic shear modulus 2) the volumetric strain increment, which consists of a portion which is proportional to the hydrostatic stress increment, and another which equals the product of the octahedral shear strain increment and the shear compaction/dilatancy factor β Stress reversals are defined separately for the hydrostatic and the deviatoric component of the stress tensor, and the parameters of the inelastic stress-strain relations are given as different functions of the stress and strain history, for virgin loading, unloading, reloading, or for the “post-failure” falling branch. The incremental stress-strain law is set in the form of incremental compliance and rigidity matrices, and implemented into a nonlinear dynamic finite element code.

Ethylene oxidation on silver catalysts: effect of ethylene oxide and of external transfer limitations

Abstract: Ethylene oxidation to ethylene oxide and to carbon dioxide over silver catalysts was studied in a CSTR. The effects of two factors on the catalyst performance were examined. The first was the presence of excess ethylene oxide in the feed. A kinetic model was introduced which assumed that ethylene and ethylene oxide compete for the same sites on the catalyst surface. This model provided reasonable quantitative agreement with kinetic and potentiometric measurements. The second factor that was studied was the presence of external heat and mass transfer limitations. It was found that such limitations cause a significant decrease of the selectivity to ethylene oxide. This decrease is a result of the temperature difference between the catalyst surface and the bulk of the gas phase and of the fact that the activation energy of ethylene combustion is greater than that of ethylene epoxidation. The contribution of other factors such as inhibition by CO2 or possible incomplete mixing in the reactor is shown to be in...

Raisin: A suitable rav material for ethanol production usingZymomonas mobilis

Abstract: A batch fermentation process for the production of ethanol from raisin usingZymomonas mobilis is described. This process shows significant advantages in ethanol production compared with yeasts, such as, faster fermentation time and higher ethanol productivity and yield. Moreover, fermentation of the raisin extracts byZ. mobilis gave three-fold higher ethanol productivity than of standard synthetic media of the same invert-sugar concentration.

Harmonic oscillator with complex frequency

Abstract: In the present paper we study the problem of the harmonic oscillator with complex frequency. A special case of this problem is the determination of the eigenvalues and eigenfunctions of the squeeze operator in quantum optics. The Hamilton operator of the complex harmonic oscillator is non-Hermitian and its study leads to the Lie-admissible theory. Because of the complex frequency the eigenvalues of the energy are complex numbers and the partition function of Boltzman and the free energy of Helmholtz are complex functions. Especially the imaginary part of the free energy describes the metastable states.

On the simultaneous determination of zeros of analytic or sectionally analytic functions

Abstract: It is shown how the total-step and single-step iterative methods, as well as their improvements, for the simultaneous determination of simple zeros of polynomials can be used (with one slight modification) for the determination of simple zeros of analytic functions (inside or outside a simple smooth closed contour in the complex plane) or sectionally analytic functions (outside their arcs of discontinuity). Numerical results, obtained by the single-step method, are also presented.