Understanding the underlying processes and extracting detailed characteristics of rivers is criti... more Understanding the underlying processes and extracting detailed characteristics of rivers is critical and has not yet been fully developed. The purpose of this study was to examine the performance of non-linear time series methods on environmental data. Specifically, we performed an analysis of water level measurements, extracted from sensors, located on specified stations along the Nestos River (Greece), with Recurrence Plots (RP) and Recurrence Quantification Analysis (RQA) methods. A more detailed inspection with the sliding windows (epoqs) method was applied on the Recurrence Rate, Average Diagonal Line and Trapping Time parameters, with results showing phase transitions providing useful information about the dynamics of the system. The suggested method seems to be promising for the detection of the dynamical transitions that can characterize distinct time windows of the time series and reveals information about the changes in state within the whole time series. The results will ...
International Journal of Bifurcation and Chaos, 2012
In the present work, we extend the results of the study of the structural stability of the Julia ... more In the present work, we extend the results of the study of the structural stability of the Julia sets of noise-perturbed complex quadratic maps in the presence of dynamic and output noise both for the additive and the multiplicative cases. The critical values of the strength of the noise for which the Julia set of a family of noise-perturbed complex quadratic maps completely loses its original Julia structure were also calculated. Using graphical tools we demonstrate how one can localize the regions of the Julia sets that are affected by the presence of noise in each case. Finally, two numerical invariants for the Julia set of noise-perturbed complex quadratic maps are proposed for the study of the noise effect.
ABSTRACT In the present work we investigate the effect of wall protrusions on flows in microchann... more ABSTRACT In the present work we investigate the effect of wall protrusions on flows in microchannels using Dissipative Particle Dynamics (DPD). Protrusions are introduced by periodically placing rectangular protruding elements on the upper channel wall. The protrusion length and height are varied and their effect on the flow is examined. Periodic boundary conditions are imposed in the streamwise and spanwise directions. Bounce-back reflecting boundary conditions are enforced at the fluid–solid wall interface. Simulations are performed for a range of values of the external driving force.Analysis of fluid particle trajectories and average residence time reveals temporary trapping of fluid inside the upper wall cavities for a considerable amount of time. This trapping affects macroscopic quantities such as density, velocity, pressure and temperature distribution inside and close to the cavities as well as the functional relations between the flow friction factor and the flow Reynolds number. When compared to the channel with flat walls, lower flow velocities are observed in the core region of the channel. The reduction of velocities as the protrusion size varies is quantified. Density, pressure and temperature remain almost constant in the core of the channel and their distribution near and inside the cavities depend on the protrusion size. For all channel cases, the friction factor/Reynolds number relationship, follows a power law relation of the form, f Re = A = const, i.e. the Poiseuille number of the flow is constant. The value of constant A increases as the protrusion length decreases and the protrusion height increases, and represents the dependence of the flow resistance on the protrusion size.
In the present work we expand our previous work in [1] by introducing the Julia Deviation Distanc... more In the present work we expand our previous work in [1] by introducing the Julia Deviation Distance and the Julia Deviation Plot in order to study the stability of the Julia sets of noiseperturbed Mandelbrot maps. We observe a power-law behaviour of the Julia Deviation Distance of the Julia sets of a family of additive dynamic noise Mandelbrot maps from the Julia set of the Mandelbrot map as a function of the noise level. Additionally, using the above tools, we support the invariance of the Julia set of a noise-perturbed Mandelbrot map under different noise realizations.
In this work, we propose new applications of analytic and non-analytic perturbations of the Mande... more In this work, we propose new applications of analytic and non-analytic perturbations of the Mandelbrot map as expressed in a two-parameter deformation family of it. The influence of alternative applications of noise for specific choices of a Mandelbrot set is also provided. Hence, we are in a position of examining the stability of this set under stochastic perturbations.
Journal of Water Supply: Research and Technology-Aqua
The ability of heavy metals to accumulate in living organisms, combined with the fact that they a... more The ability of heavy metals to accumulate in living organisms, combined with the fact that they are not biodegradable, necessitates an expansion and improvement of the existing water purification methods. An effective mixing of contaminated water with heavy metals and magnetic nanoparticles is crucial for water treatment applications. In the present work, electromagnetic and shear mixing are combined to explore optimization mixing strategies. Mixing is studied through simulations under various initial conditions for two streams that are loaded with nanoparticles and one contaminated water stream that lies between the nanoparticle streams. In the present work, magnetic mixing is superimposed with a time-modulated gradient external magnetic field. The results show that as the radius ratio between the nanoparticles and the heavy metals increases, the external magnetic field is more effective insofar as the mixing of the nanoparticles is concerned. Moreover, for simulations where the ra...
Smoothed Particle Hydrodynamics (SPH) is a promising simulation technique in the family of Lagran... more Smoothed Particle Hydrodynamics (SPH) is a promising simulation technique in the family of Lagrangian mesh-free methods, especially for flows that undergo large deformations. Particle methods do not require a mesh (grid) for their implementation, in contrast to conventional Computational Fluid Dynamics (CFD) methods. Conventional CFD algorithms have reached a very good level of maturity and the limits of their applicability are now fairly well understood. In this paper we investigate the application of the SPH method in Poiseuille and transient Couette flow along with a free surface flow example. Algorithmically, the method is viewed within the framework of an atomic-scale method, Molecular Dynamics (MD). In this way, we make use of MD codes and computational tools for macroscale systems.
We present molecular dynamics simulation results on fluid and transport properties for nanochanne... more We present molecular dynamics simulation results on fluid and transport properties for nanochannel flows. The upper channel wall is constructed from periodic roughness elements and flows are simulated both in longitudinal (ribs) and transverse (grooves) direction and are compared to respective flat-wall channel flows. Various wall/fluid interaction strength ratios are considered for the simulations, covering typical hydrophilic and hydrophobic channels. We show that groove orientation (ribs and grooves) has a primitive effect on flow mainly due to slip length increase in a ribbed-wall channel. The transport properties of the fluid are significantly affected by wall wettability, as, in flows past an hydrophobic wall, the diffusion coefficient presents anisotropy, shear viscosity attains a minimum value and thermal conductivity increases.
Abstract: The study of genetic sequences is of great importance in biology and medicine. Sequence... more Abstract: The study of genetic sequences is of great importance in biology and medicine. Sequence analysis and taxonomy are two major fields of application of bioinformatics. In this survey, we present results concerning genetic sequences and Chou's pseudo amino acid composition as well as methodologies developed based on this concept along with elements of fuzzy set theory, and emphasize on fuzzy clustering and its application in analysis of genetic sequences.
Physica A: Statistical Mechanics and its Applications, 2019
• Recurrence Plots (RPs) of velocity data in a turbulent MHD channel flow are analyzed. • Differe... more • Recurrence Plots (RPs) of velocity data in a turbulent MHD channel flow are analyzed. • Different time scale and location underlying mechanisms are identified. • The RPs analysis identifies the spatial effect of the magnetic field on the flow. • The methodology has potential applications in spatiotemporal phenomena.
We present non-equilibrium molecular dynamics simulations of liquid argon flow through nano-chann... more We present non-equilibrium molecular dynamics simulations of liquid argon flow through nano-channels formed by two infinite krypton plates. Density, velocity and temperature distributions across the channel are studied for channels widths in the range 2.65sigma-18.58sigma (sigma is the argon atom diameter). For small channels (2.65sigma-7.9sigma) the fluid is ordered in layers and this ordering persists close to the walls even
Journal of Environmental Science and Health, Part A, 2001
An advanced statistical analysis technique using the fuzzy clustering method was employed in this... more An advanced statistical analysis technique using the fuzzy clustering method was employed in this work, for the evaluation of PCDD/F emissions during solid waste combustion. In addition, this technique was applied for the assessment of the effect of an inhibitor (urea) on the toxic compound releases and on the various isomer distributions. Municipal solid wastes were combusted in a lab-scale reactor and the toxic gas emissions were measured at the unit outlet. Combustion tests of urea-fuel mixtures were classified in the same group, indicating that urea affected the formation mechanisms of toxic gases. Combustion tests of single fuel were not included in the same group. Furthermore, urea ability to modify the gas emissions pathways was not affected by the method of its addition to the fuel.
The main parameters influencing the mechanical performance of glass-ceramic materials are the sha... more The main parameters influencing the mechanical performance of glass-ceramic materials are the shape and mean size of the ceramic phase, i.e. the crystalline inclusions. The aim of the present work is twofold: first, to study the effect of the above parameters on the modes of fracture in two kinds of glass-ceramic materials by the use of the static microindentation technique; second, to interpret the experimental results by the application of a simple physical model. It was found that reduction in the size of granularly shaped crystallite inclusions or reduction of the width of needle-like crystalline inclusions results in an increase of the extent of crack propagation, while the fracture mode shifts from intergranular to transgranular. These observations were successfully interpreted in terms of energetic arguments related to the size of the crystalline inclusions with respect to the width of a disordered zone acting as an interface between them and the amorphous matrix.
International Journal of Decision Support System Technology
The sensor-era has brought rapid changes in transportation; the abundance of data has started cha... more The sensor-era has brought rapid changes in transportation; the abundance of data has started changing the traditional way in which planners and engineers approach mobility. Nowadays, traffic monitoring and information provision systems heavily rely on floating car data usually of special vehicles (e.g., trucks, taxi), and the question that arises is whether such sources can provide reliable data for the whole traffic in a complex urban environment. The current paper, through Thessaloniki's (GR) case study, seeks to evaluate the reliability of taxi data compared to the overall traffic. The analysis reveals that for the examined critical urban road paths, there is a strong relation among floating taxi data with the overall traffic that is additionally influenced by other significant factors (e.g., number of lanes, day, time period). Furthermore, a modelling approach with a generalized linear model (gamma with log link) seems appropriate when dealing with skewed and heteroscedasti...
Understanding the underlying processes and extracting detailed characteristics of rivers is criti... more Understanding the underlying processes and extracting detailed characteristics of rivers is critical and has not yet been fully developed. The purpose of this study was to examine the performance of non-linear time series methods on environmental data. Specifically, we performed an analysis of water level measurements, extracted from sensors, located on specified stations along the Nestos River (Greece), with Recurrence Plots (RP) and Recurrence Quantification Analysis (RQA) methods. A more detailed inspection with the sliding windows (epoqs) method was applied on the Recurrence Rate, Average Diagonal Line and Trapping Time parameters, with results showing phase transitions providing useful information about the dynamics of the system. The suggested method seems to be promising for the detection of the dynamical transitions that can characterize distinct time windows of the time series and reveals information about the changes in state within the whole time series. The results will ...
International Journal of Bifurcation and Chaos, 2012
In the present work, we extend the results of the study of the structural stability of the Julia ... more In the present work, we extend the results of the study of the structural stability of the Julia sets of noise-perturbed complex quadratic maps in the presence of dynamic and output noise both for the additive and the multiplicative cases. The critical values of the strength of the noise for which the Julia set of a family of noise-perturbed complex quadratic maps completely loses its original Julia structure were also calculated. Using graphical tools we demonstrate how one can localize the regions of the Julia sets that are affected by the presence of noise in each case. Finally, two numerical invariants for the Julia set of noise-perturbed complex quadratic maps are proposed for the study of the noise effect.
ABSTRACT In the present work we investigate the effect of wall protrusions on flows in microchann... more ABSTRACT In the present work we investigate the effect of wall protrusions on flows in microchannels using Dissipative Particle Dynamics (DPD). Protrusions are introduced by periodically placing rectangular protruding elements on the upper channel wall. The protrusion length and height are varied and their effect on the flow is examined. Periodic boundary conditions are imposed in the streamwise and spanwise directions. Bounce-back reflecting boundary conditions are enforced at the fluid–solid wall interface. Simulations are performed for a range of values of the external driving force.Analysis of fluid particle trajectories and average residence time reveals temporary trapping of fluid inside the upper wall cavities for a considerable amount of time. This trapping affects macroscopic quantities such as density, velocity, pressure and temperature distribution inside and close to the cavities as well as the functional relations between the flow friction factor and the flow Reynolds number. When compared to the channel with flat walls, lower flow velocities are observed in the core region of the channel. The reduction of velocities as the protrusion size varies is quantified. Density, pressure and temperature remain almost constant in the core of the channel and their distribution near and inside the cavities depend on the protrusion size. For all channel cases, the friction factor/Reynolds number relationship, follows a power law relation of the form, f Re = A = const, i.e. the Poiseuille number of the flow is constant. The value of constant A increases as the protrusion length decreases and the protrusion height increases, and represents the dependence of the flow resistance on the protrusion size.
In the present work we expand our previous work in [1] by introducing the Julia Deviation Distanc... more In the present work we expand our previous work in [1] by introducing the Julia Deviation Distance and the Julia Deviation Plot in order to study the stability of the Julia sets of noiseperturbed Mandelbrot maps. We observe a power-law behaviour of the Julia Deviation Distance of the Julia sets of a family of additive dynamic noise Mandelbrot maps from the Julia set of the Mandelbrot map as a function of the noise level. Additionally, using the above tools, we support the invariance of the Julia set of a noise-perturbed Mandelbrot map under different noise realizations.
In this work, we propose new applications of analytic and non-analytic perturbations of the Mande... more In this work, we propose new applications of analytic and non-analytic perturbations of the Mandelbrot map as expressed in a two-parameter deformation family of it. The influence of alternative applications of noise for specific choices of a Mandelbrot set is also provided. Hence, we are in a position of examining the stability of this set under stochastic perturbations.
Journal of Water Supply: Research and Technology-Aqua
The ability of heavy metals to accumulate in living organisms, combined with the fact that they a... more The ability of heavy metals to accumulate in living organisms, combined with the fact that they are not biodegradable, necessitates an expansion and improvement of the existing water purification methods. An effective mixing of contaminated water with heavy metals and magnetic nanoparticles is crucial for water treatment applications. In the present work, electromagnetic and shear mixing are combined to explore optimization mixing strategies. Mixing is studied through simulations under various initial conditions for two streams that are loaded with nanoparticles and one contaminated water stream that lies between the nanoparticle streams. In the present work, magnetic mixing is superimposed with a time-modulated gradient external magnetic field. The results show that as the radius ratio between the nanoparticles and the heavy metals increases, the external magnetic field is more effective insofar as the mixing of the nanoparticles is concerned. Moreover, for simulations where the ra...
Smoothed Particle Hydrodynamics (SPH) is a promising simulation technique in the family of Lagran... more Smoothed Particle Hydrodynamics (SPH) is a promising simulation technique in the family of Lagrangian mesh-free methods, especially for flows that undergo large deformations. Particle methods do not require a mesh (grid) for their implementation, in contrast to conventional Computational Fluid Dynamics (CFD) methods. Conventional CFD algorithms have reached a very good level of maturity and the limits of their applicability are now fairly well understood. In this paper we investigate the application of the SPH method in Poiseuille and transient Couette flow along with a free surface flow example. Algorithmically, the method is viewed within the framework of an atomic-scale method, Molecular Dynamics (MD). In this way, we make use of MD codes and computational tools for macroscale systems.
We present molecular dynamics simulation results on fluid and transport properties for nanochanne... more We present molecular dynamics simulation results on fluid and transport properties for nanochannel flows. The upper channel wall is constructed from periodic roughness elements and flows are simulated both in longitudinal (ribs) and transverse (grooves) direction and are compared to respective flat-wall channel flows. Various wall/fluid interaction strength ratios are considered for the simulations, covering typical hydrophilic and hydrophobic channels. We show that groove orientation (ribs and grooves) has a primitive effect on flow mainly due to slip length increase in a ribbed-wall channel. The transport properties of the fluid are significantly affected by wall wettability, as, in flows past an hydrophobic wall, the diffusion coefficient presents anisotropy, shear viscosity attains a minimum value and thermal conductivity increases.
Abstract: The study of genetic sequences is of great importance in biology and medicine. Sequence... more Abstract: The study of genetic sequences is of great importance in biology and medicine. Sequence analysis and taxonomy are two major fields of application of bioinformatics. In this survey, we present results concerning genetic sequences and Chou's pseudo amino acid composition as well as methodologies developed based on this concept along with elements of fuzzy set theory, and emphasize on fuzzy clustering and its application in analysis of genetic sequences.
Physica A: Statistical Mechanics and its Applications, 2019
• Recurrence Plots (RPs) of velocity data in a turbulent MHD channel flow are analyzed. • Differe... more • Recurrence Plots (RPs) of velocity data in a turbulent MHD channel flow are analyzed. • Different time scale and location underlying mechanisms are identified. • The RPs analysis identifies the spatial effect of the magnetic field on the flow. • The methodology has potential applications in spatiotemporal phenomena.
We present non-equilibrium molecular dynamics simulations of liquid argon flow through nano-chann... more We present non-equilibrium molecular dynamics simulations of liquid argon flow through nano-channels formed by two infinite krypton plates. Density, velocity and temperature distributions across the channel are studied for channels widths in the range 2.65sigma-18.58sigma (sigma is the argon atom diameter). For small channels (2.65sigma-7.9sigma) the fluid is ordered in layers and this ordering persists close to the walls even
Journal of Environmental Science and Health, Part A, 2001
An advanced statistical analysis technique using the fuzzy clustering method was employed in this... more An advanced statistical analysis technique using the fuzzy clustering method was employed in this work, for the evaluation of PCDD/F emissions during solid waste combustion. In addition, this technique was applied for the assessment of the effect of an inhibitor (urea) on the toxic compound releases and on the various isomer distributions. Municipal solid wastes were combusted in a lab-scale reactor and the toxic gas emissions were measured at the unit outlet. Combustion tests of urea-fuel mixtures were classified in the same group, indicating that urea affected the formation mechanisms of toxic gases. Combustion tests of single fuel were not included in the same group. Furthermore, urea ability to modify the gas emissions pathways was not affected by the method of its addition to the fuel.
The main parameters influencing the mechanical performance of glass-ceramic materials are the sha... more The main parameters influencing the mechanical performance of glass-ceramic materials are the shape and mean size of the ceramic phase, i.e. the crystalline inclusions. The aim of the present work is twofold: first, to study the effect of the above parameters on the modes of fracture in two kinds of glass-ceramic materials by the use of the static microindentation technique; second, to interpret the experimental results by the application of a simple physical model. It was found that reduction in the size of granularly shaped crystallite inclusions or reduction of the width of needle-like crystalline inclusions results in an increase of the extent of crack propagation, while the fracture mode shifts from intergranular to transgranular. These observations were successfully interpreted in terms of energetic arguments related to the size of the crystalline inclusions with respect to the width of a disordered zone acting as an interface between them and the amorphous matrix.
International Journal of Decision Support System Technology
The sensor-era has brought rapid changes in transportation; the abundance of data has started cha... more The sensor-era has brought rapid changes in transportation; the abundance of data has started changing the traditional way in which planners and engineers approach mobility. Nowadays, traffic monitoring and information provision systems heavily rely on floating car data usually of special vehicles (e.g., trucks, taxi), and the question that arises is whether such sources can provide reliable data for the whole traffic in a complex urban environment. The current paper, through Thessaloniki's (GR) case study, seeks to evaluate the reliability of taxi data compared to the overall traffic. The analysis reveals that for the examined critical urban road paths, there is a strong relation among floating taxi data with the overall traffic that is additionally influenced by other significant factors (e.g., number of lanes, day, time period). Furthermore, a modelling approach with a generalized linear model (gamma with log link) seems appropriate when dealing with skewed and heteroscedasti...
Using molecular dynamics and a rigid ion potential, we studied the vibrational and structural pro... more Using molecular dynamics and a rigid ion potential, we studied the vibrational and structural properties of the NiO(001) surface with and without cationic adatoms. We found that the bulk phonon density of states (DOS) is altered by the presence of the surface and that the adatom introduces new frequency modes. From the relaxed positions of the surface ions, it came
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Papers by T. Karakasidis