The purpose of this thesis is to study the characteristics of turbulent plasma in magnetic confinement devices (tokamaks, stellarators). A variety of plasma instabilities caused by the magnetic topology of fusion devices are driven by radial temperature gradients and end up destabilizing plasma. We study the statistical properties of turbulence, the nature of turbulent transport for various observables e.g. heat and particle fluxes. Also we examine the conditions under which plasma self – organizes in such devices. Numerical plasma simulations are preformed for this purpose with the use of the GENE gyrokinetic code.
The purpose of this PhD is the study of the large scale structures. We investigate the cosmological
evolution of the dark matter halo bias, i.e., the ratio of the fluctuations of mass tracers to those of the
underlying mass. We study the six most popular dark matter halo bias models using recent bias data of
Luminous Red Galaxies (LRGs) from the Dark Energy Survey (DES) and the 2-point correlation
function data of LRGs from SDSS (2SLAQ). From the above procedure we also determine the free
parameter of the models, the dark matter halo mass in which the LRGs live.
Moreover, we examine the relationship between the turnaround radius and the virial mass of cosmic
structures in the context of ΛCDM model and an f(T) model of modified gravity. The turnaround radius
is the distance from the center of the cosmic structure to the shell that is detaching from Hubble flow,
while the virial mass is defined as the mass enclosed within the volume, where the density is 200 time
the background density. Additionally, in this process we question dark energy models through
We study the possible dependence of the dark matter halo physical properties (morphology, spin, dynamical status, etc.) on their environment, local and large-scale, in order to understand to what extend the environment or/and the cosmological initial conditions affect the evolution, shape and dynamics of cosmic structure. Since the conclusions of several relevant works in the bibliography have been contradicting, due to the different methodologies used for the classification of different halo-environments, we develop new structure finding algorithms based on simulated annealing, previously applied in robotic-vision problems. Our algorithms will be applied on N-body cosmological simulation data, in order to clarify which the main factor defining the physical parameters of cosmic structure is. Is it their environment or the different initial conditions ?
With this dissertation we expect to find periodic orbits and their families, in severely disturbed gravitational systems such as the three body problem, with bodies of random mass distribution, with rotation around their axes, influenced by solar radiation pressure and other similar disturbances. This PhD aims to study such complex dynamic systems, one of which could be a real asteroid. The search for periodic orbits will be done not via conventional methods such as differential corrections, but using genetic-evolutionary algorithms or minimization methods that simulate natural processes without necessarily knowing apriori the neighborhood of their whereabouts. The basic model used is a uniformly rotating triaxial ellipsoid which serves as a starting point before simulating the shape of the real asteroid.
Paspaliaris Evangelos - Dimitrios
Astrophysics of Black Holes (Cosmological Observations: Stellar populations in distant galaxies and the contribution of over-massive black holes to the properties of the Interstellar medium)
The Laplace Resonance is a major case of three-body resonances. A prominent example in our solar system refers to the configuration of the three Galilean satellites Io, Europa and Ganymede. The goal of this project is to study in detail the dynamical endstates allowed in the framework of the Laplace resonance under the action of dissipation, caused either by tidal effects or by the interaction of the bodies with a disc. This goal will be approached by understanding the structure of periodic orbits, as well as of other low-dimensional invariant objects (e.g. invariant tori), and subsequently by understanding the evolutionary path of systems under the action of dissipation. Focusing on particular systems e.g. the Jovian satellite system and the TRAPPIST-1, it is expected to address the question of whether dissipative effects can lead to the observed final configurations, and will provide a modelling interpreting as close as possible the observations.
Orbital dynamics and diffusion at resonances in the near-Earth space environment
Large Scale Peculiar Flows
The subject of the current dissertation is the development of novel data analysis techniques for current and future gravitational wave detectors, with particular emphasis on techniques suitable for the detection and analysis of binary neutron star mergers. We will construct surrogate models of gravitational-wave template banks, making use of machine learning techniques. Our models will serve as template banks for accurate parameter estimation (with a particular emphasis on extracting the tidal deformability parameter) for the upcoming observations with the current LIGO-Virgo-KAGRA network of detectors as well as with their near-term upgrades beyond design sensitivity.
Transport Phenomena, with emphasis on spreading and diffusion, in complex systems
The ATLAS experiment, one of the four major experiments of the LHC at CERN, aims to study among others physics models beyond the Standard Model. In the context of this PhD thesis, time has been devoted to the installation, operation and maintenance of the Fast Tracker project, which is an upgrade of the triggering system of the ATLAS experiment, and in parallel there is an ongoing analysis on the experimental data, collected by the ATLAS experiment during its running period 2015 – 2018, aiming at setting limits to the contribution of new physics models on the four-leptons channel and particularly to anomalous gauge-boson couplings where the final-state particles are leptons originating from Z-boson decays.
One of the most prominent ideas, originally coming from String Theory, that led to the creation of a rapidly evolving new area in theoretical Physics in the last twenty years is holographic duality. In the core of this field lies the observation that a n+1 – dimensional Anti-deSitter spacetime that describes a gravity theory, corresponds under certain limits to a n-dimensional gauge field theory living on the boundary of the AdS space. The theory, which is known as AdS/CFT correspondence gives rise to a map between fields and physical quantities of the two dual spaces and provides the opportunity to investigate properties of the one system by studying the other. My thesis examines the properties of a Taub-Nut 4-dimensional AdS spacetime, which corresponds to a 3-dimensional fluid that lives on its boundary. By analysing scalar field fluctuations that propagate in the Taub-Nut AdS spacetime, we have produced novel results regarding the nature of the boundary fluid and its relation to the Nut charge, that is encompassed by the dynamics of the bulk theory.
Aim of this PhD thesis is to assess the feasibility of individualized kidney dosimetry in patients treated for differentiated thyroid cancer (DTC). Kidneys because they are a primary route of excretion conjugates potential radiation dose-limiting organs in radionuclide therapies. Knowing that radiopharmaceuticals passing though the kidneys results in a differential dose rate to suborgan elements, presenting a significant challenge in assessing an accurate dose–response relationship that is predictive of toxicity in future patients. To minimize this possibility, it is essential to calculate dose before administration. The originality of this dissertation lies in the fact that dose that allocated to kidneys it not considered before administration. Goal is to plan a useful formula that physicians and physicists will easily use in order to individually calculate the absolute dosage that have to be administered to each patient.
The larger effective dose per person of the population from diagnostic medical examinations in the Greek population is is due to CT scans. According to Greek Atomic Energy Commission (GAEC) from 2013 until now, the number of established CT scans systems in Greece is increased by 16%. Based on the above, there is a need for a further theoretical and clinical study of the radiation dose in Computed tomography departments using thermoluminescence detectors (TLDs). The aim of this work is to study (a) the awareness of radiation protection issues and dose levels of imaging procedures among public and clinical doctors using a questionnaire (b) the calibration of TLD dosimeters in CT beams and (c) performing in vivo measurements. By appropriate placement of dosimeters in the patient, the dose of specific radiosensitive organs will be evaluated depending on the clinical application and patient size.
Τα ραδιενεργά αεροζόλς ως ιχνηθέτες στη μελέτη της ατμοσφαιρικής ρύπανσης
The present study aims at the exploration on the relation of 137Cs, as the most important radioactive pollutant in the marine environment, with marine parameters observed from remote sensing satellites. These parameters are Sea Surface Temperature (SST), Sea Surface Salinity (SSS) and Ocean Color (OC) that includes Chlorophyll-A concentration (Chlor_A), Particulate Inorganic and Organic Carbon concentration (PIC, POC) and Daily and Instantaneous Photosynthetically Available Radiation (PAR and iPAR). The above parameters are correlated directly or indirectly with 137Cs activity concentrations in sea water. These relations, algorithms and raw data will be illustrated in a geographic information system (GIS) for the creation of an innovative tool (GIS platform), able to use remote sensing for the detection and forecast of 137Cs activity concentrations in the marine ecosystem. Therefore, this tool will be used for the radiological risk assessment, in terms of the radiation protection of man and marine ecosystem.
The proposed doctoral dissertation aims to develop a method of calculating the therapeutic dose in patients undergoing radionuclide therapy with radium dichloride (Ra-223). The treatment is applied to patients with bone metastases, especially to castration-resistant late stage prostate cancer. Sophisticated image analysis techniques such as pattern recognition and computational vision will be used to achieve the goal. The planar images will be improved and analyzed for the purpose of automatically locating bone metastases and determining regions of interest around them. The expected results of the above study are the development of an algorithm for the automatic calculation of doses in patients receiving the treatment, the design of a practice that will be applied at all stages of the study, the calculation of the doses received each patient's organ and the creation of a database of absorbed doses.
This doctoral program involves many areas of modern research, namely: particle physics, experimental high-energy physics and, finally, high-volume data science and Artificial Intelligence - Machine Learning. The objective of the final work and research is the efficient processing of data collected from the ATLAS experiment of the CERN LHC Accelerator, using and developing machine learning techniques and algorithms. Its completion will have contributed to the management of the colossal volume of data generated within seconds in the ATLAS detector of the LHC accelerator at CERN, the most accurate experimental search for new physics in observed interactions and the reduction of the use of computational power through intelligent algorithms based on Machine and Deep Learning.
The scope of this PhD thesis is to study, compare and evaluate the dosimetric impact of different calculation algorithms, Acuros XB (AXB) and Anisotropic Analytical Algorithm (AAA) in body areas with heterogeneities (lung, breast etc). Tissue heterogeneities can be a challenge in the treatment planning process concerning the clinical dose calculation algorithms, can affect the accuracy of dose delivery and lead to overestimation or underestimation of dose. The aim of this project is to use calculated plans with AAA and recalculate them with AXB, comparing and evaluating the Planning Target Volume (PTV) coverage and the doses to Organs At Risk (OARs) for plans with Volumetric Modulated Arc Therapy (VMAT) and Intensity-Modulated Radiotherapy (IMRT) techniques.
A major issue most countries are facing is how to effectively deal with raw radioactive waste without having sufficient data about the radionuclides they contain and their chemical and physical characteristics. This waste is named raw Historical Radioactive Waste. The storage, treatment and disposal of radioactive waste can pose a significant environmental and health risk, without the proper radiological characterization and segregation regarding the activity and half-life of radionuclides in classes of different management routes. The Historical Radioactive Waste can be fully characterized by radiological characteristics (radionuclides, specific activities), composition and other harmful/ toxic substances.
This thesis concerns the development of a technique for radiological characterization and segregation of raw Historical Radioactive Waste in different management routes. The technique will be a combination of non-destructive measurements and sampling techniques. The radionuclides in radioactive waste can be: either (a) gamma emitters which can easily be detected by a gamma spectrometry system; or (b) alpha or beta emitters without emitting gamma rays (difficult to detect radionuclides)and therefore can only be determined by sampling and costly radiochemical analyses. The samples should be taken from items of the same origin in order to determine the scaling factor (the ratio of difficult to detect radionuclides to key radionuclides which are gamma emitters). The total activity is determined by non-destructive measurement, based on gamma spectrometry as well as by the use of the scaling factors.
In the Large Hadron Collider (LHC), incoherent collective effects, and in particular beam-beam and electron cloud effects, pose significant challenges to the preservation of the beam quality, determining in particular transverse emittance growth and particle losses. These phenomena involve strong non-linearities in the particle motion and their modelling and understanding rely heavily on numerical simulations based on tracking codes. The simulation of realistic scenarios requires long simulation time-spans (millions of turns), which result in a significant computational burden. The tools routinely used at CERN for these studies, allow a first characterization of the non-linear motion, for example through tune-spreads and Dynamic Aperture estimations. Nevertheless, direct predictions of beam-lifetime and emittance growth-rates are often out of reach. In this thesis, novel tools and techniques will be developed, aiming at realistic simulation of the non-linear dynamics for an LHC bunch, in the presence of head-on and long-range beam-beam forces as well as of electron clouds. To tackle the associated computational burden, the usage of GPU-based super-computers in particle tracking simulations will be explored. The developed tools and techniques will be compared against semi-analytical calculations, existing simulation codes and experimental data collected during LHC operation and in dedicated tests. After these validation steps, the beam and machine configurations foreseen for the High-Luminosity LHC upgrade project will also be studied, to identify possible performance limitations coming from beam-beam and electron cloud effects and to define possible mitigation strategies.
Polychronis Koliogiannis Koutmiridis
Neutron stars are extraordinary cosmic laboratories, as they allow us to probe aspects of all fundamental interactions at extremes of density and gravity that are impossible to reproduce in terrestrial laboratories. In the present dissertation, a systematic study of the effects of the dense nuclear matter equation of state on the basic properties of neutron stars, will be carried out. In addition, the upper limit to the angular velocity of rotation of the rapidly rotating neutron stars will be studied, while in any case, constraints will be introduced to the structure of the equation of state by means of observational data. The equations of state that will be studied, will concern both cold and hot nuclear matter. Finally, the above research will be linked to the detection of gravitational waves from binary neutron star mergers, by using the tidal polarizability, and attempts will be made in order to establish constraints on the dense nuclear matter equation of state in the high density region.
Subject of the Thesis is a study of new nuclear models of infinite nuclear matter through forming respective Equations of State (EoS). Emphasis will be given to the density area from saturation density and above in the condensed matter phase diagram. Equations of State that will be developed have to be adjusted in order to use them in realistic nuclear systems (for example, finite nuclei, relativistic nuclear reactions), where there are experimental data available for comparison. Subsequently, an application will be done on nuclear astrophysics systems (for example, static neutron stars, neutron stars binaries). In these cases the EoS will be adapted to energy densities/pressures, but now for systems in β-equilibrium or in dynamic states consisted of nucleons, hyperons and leptons. Additionally, EoS will be investigated not only as functions of baryonic density but also versus temperature and isospin asymmetry as well.
In this dissertation, we systematically study the effect of the nuclear symmetry energy in the basic properties of finite nuclei. More specifically, a study takes place of this effect on neutron-rich, heavy nuclei, where symmetry energy plays a dominant role. There is a calculation of the differences in the neutron and proton radii, as well as a calculation of the distribution of neutron matter inside nuclei. Furthermore, symmetry energy is associated with various surface properties of the finite nuclei, while there is also a comparison with experimental data (where available) and when not available, there are relevant estimations. The calculations are within the Thomas-Fermi model.
In this PhD thesis, long-time air filters of 45 years will be analyzed. The filters will be analyzed with the X-ray (XRF) technique to determine the composition of the suspended particulates retained on the filters and with the gamma-spectroscopy technique to determine the 210Pb radioactive isotope attached to the suspended particles. In addition, thanks to the Positive Matrix Factorization model (PMF), it will be possible to determine the individual sources of all pollutants.
The aim of the PhD thesis is to study the change in concentrations of radioactive isotopes and heavy metals over a long period of time in order to determine the parameters that affect the concentrations of these elements, whether meteorological conditions or man-made activities, as well as precise sources of pollutants.
The existence of air filters of such a long time series (45 years) is a rare primary experimental material, and for the first time a radioactive isotope, 210Pb, will be used as a tracer to determine the effect of human activity. Finally, there will be a credible database that can form the basis for the study and for additional measures to reduce pollutants in areas with similar environmental conditions.
A Study of the simultaneous production of two WZ bozons in assosiation with two jets in a proton-proton collision at the ATLAS experiment. A study of dimension-8 operators in the range of an effective field theory and how they influence the simultaneous production of two boons, as the first study in search of Physics beyond the Standard Module. Furthermore the required qualification task, for the acquisition of the writer’s capacity at the ATLAS experiment, is devised. This work includes the simulation of two subdetectors of the New small wheel, of the Micromegas and sTGC detectors.
Development of innovative instrumentation of new methods for selection and analysis of experimental data towards searching New Physics at the High Luminosity Large Hadron Collider
The ultimate goal of the dissertation is to study various artificial and natural materials for their possible use as passive or active dosimeters in various applications. In order for each of these materials to become a dosimeter, it must undergo a thorough investigation that includes 3 parts: (1) Firstly, study of its structure, through typical solid material characterization techniques. (2) Study of its energy levels, which is achieved with the thermally stimulated luminescence (Thermoluminescence, TL). (3) Finally, research is done on whether the material has dosimetric conditions, as determined by practical needs and applications. In order to investigate this, various methodologies will be used, such as: thermally stimulated luminescence (Thermoluminescence, TL), optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL).
The radiological characterization of activated components of nuclear reactor - as a result of neutron activation - which always appeared with surface contamination, is essential for the decision making process on their management during decommissioning. The need of decontamination, the appropriate method selected before the dismantling / cutting process, as well as the cutting techniques to be followed in order to reduce the production of secondary radioactive waste and limit the doses to personnel, must be based on accurate radiological characterization of the radionuclides inside the material and also those which are settled as surface contamination.
The increasing global interest concerning environmental issues has led both the scientific community and the industrial sector to the demand of adopting new materials from renewable resources, able to be incorporated in polymer matrices and to provide them improved properties and "green" character. The most innovative materials, which are considered to be the most important next generation nanofillers are nanocrystalline cellulose (CNC) and nanofibrillated cellulose (CNF). The aim of the dissertation is the preparation and study of new "green" nanocellulose polymer nanocomposites of high performance and functionality, able to be adopted in a variety of applications.
In this PhD thesis, bibliographic research was conducted on students' attitude towards STEAM (Science, Technology, Engineering, Arts and Mathematics) and how these can be altered with the help of educational robotics. According to the international literature it has been observed that students are drown away from natural sciences due to the difficulty of the subject, the non-connection of the subject with their every day life and the non-involvement of students with the essence of natural sciences. It is also reported that students would like to know more about the true essence of it and not just solve exercises. The results of the research show that students' involvement with programmable robots attract students' interest, allow children to create, enter the world of programming and learn about natural sciences by exploring. The method used is learning by inquiry (inquiry continuum). At the same time two series of different kind of activities were also created. The one had to do with co-creation of digital games and the other with co-creation of a panic room that also have to do with STEAM. The question is whether and how the students' attitudes towards STEAM change through their engagement with these activities and if their perception about STEAM is enhanced.
The main purpose of this PhD is the computational study of the structural and electronic properties of prototype organic semiconductors and inorganic materials, as well as of their interactions, for Organic Electronics (OE) technology applications. OE is a rapidly growing field due to the remarkable device properties such as low cost and flexibility. However, current efficiencies and lifetimes are significantly lower compared to traditional electronic devices. Further development requires to address open issues, such as stability and low performance. The morphology and the structural details of the active layer of an OE device, responsible of the charge carrier generation, must be well controlled even in atomic scale. Therefore, it is important to study the atomic mechanisms and fundamental phenomena that govern the layer, as well as its interface with other layers of the device. In this study, quantum-mechanical first-principles calculations are applied to provide atomic-scale details that are inaccessible by experimental techniques. Specifically, Density Functional Theory (DFT) based methods provide satisfactory description of the structural and electronic properties of this type of physical systems.
Recent years, research has intensified in the new interdisciplinary technological field of TEXTRONICS (Textile-Electronics). This PhD dissertation aims at the realization of a textile organic field effect transistor (TOFET) which operates under a safe voltage (less than 10V) and can be incorporated into fabric-structure circuits leading to practical wearable applications.
During this PhD research, fibrous textile organic transistors will be studied, designed, manufactured and optimized. In order to fulfill this purpose, the electrical performance and variability of the textile transistors as well as their reliability and durability according to selected textile tests will be evaluated. Based on the findings, a simple circuit that exploits the characteristics of the textile transistor and highlights the capabilities of its use in basic electronic applications will be built.
Within the framework of the Doctoral Thesis, optimization of printed layers for the construction of organic photovoltaic cells will be carried out in order to improve their structural, optical and electrical characteristics. The basic parameters to be studied are the thickness of the films, the printing and drying temperature, the concentration and the ratio of the solutions as well as the influence of the solvents.
Moreover, P1, P2, P3 lasers scribing processes will be studied to find optimal parameters to increase Geometric Fill Factor and minimize leakage currents. The main parameters to be studied are the effects of wavelength, pulse energy and the pulse to pulse overlap on the scribing quality. The scribed samples will be studied by optical microscopy, electron scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (EDX).
Thermoelectric materials are promising alternative energy sources, suitable for applications in thermoelectric generators and refrigerators, due to their low cost and environmentally friendly heat to power generation. However, their wide scale utilization is limited because of their low efficiency, which is directly related to the figure of merit ZT. The structural properties of these materials are of key importance for their performance, making their structural characterization extremely crucial. In this PhD thesis, a structural characterization will be performed in a series of samples, comprising bulk and nanostructured materials (eg PbSe, PbS), by using TEM electron microscopy methods (Electron Diffraction, High Resolution TEM microscopy-HRTEM, advanced microscopy techniques). These samples will be grown at the Department of Chemistry of Northwestern University (Illinois-USA). The analysis of the experimental results by using the appropriate software, will allow us to propose the appropriate structural models.
Scope of this doctoral thesis is the growth and investigations by optical spectroscopic techniques (Spectroscopic Ellipsometry, Raman, Photoluminescence, Absorption spectroscopy etc.) of the properties of thin-film materials that compose the structures of organic electronic devices. Appropriate theoretical optical models and methodologies will be established for the extraction of the thin films optical properties, the determination of electronic transitions, the thickness calculation as well as the characterization of homogeneity, composition, crystallinity, defects and morphology. The above along with the employment of spectroscopic In-Situ, In-Line and Real-Time monitoring during the synthesis of the films will lead to the understanding of the material growth mechanisms and better comprehension on the experimental synthesis parameters of the nano-materials, emerging to the optimization of the thin-films desirable properties.
In the present thesis, high performance (μmax = 0.21 cm2/Vs, low threshold voltages, on/off current ratios in the range of 103–104) Organic Field-Effect Transistors (OFETs) on flexible polymeric substrates (e.g. polyethylene terephthalate, PET) will be developed. To achieve the abovementioned OFET devices, low-cost and Roll-to-Roll (R2R) compatible solution-processing techniques will be utilized. In particular, the slot-die method will be used to print stripes of the flexible polymeric dielectric cPVP over a large substrate area (15 X 90 cm2), while subsequently the TIPS-PEN small molecule organic semiconductor will be deposited over the previous layer by spray-coating technology. The morphological and structural characteristics of the individual layers will be studied. Further, for the fabrication of fully printed OFET devices, the ink-jet printing method will be integrated for the deposition of the source and drain contacts over the slot-die-coated cPVP stripes. The same method will be also tried for printing the TIPS-PEN organic semiconductor. A process optimization study will be carried out to obtain the optimal morphological, structural and electrical characteristics of the produced OFETs.
The last step of this thesis concerns the fabrication of fully printed and flexible biosensors devices by screen-printing technology. The fabricated biosensors will be bio-functionalized for the early and accurate detection of the AMI (Acute Myocardial Infarction)-related biomarkers (Cardiac Troponin biomarkers). The functional characteristics of the produced biosensors will also be studied, such as the sensitivity, limit of detection (LoD), time to results and selectivity.
Two-dimensional (2D) materials, such as Transition Metal Dichalcogenides (TMDs), have unique structures and optical properties, being of great importance in novel low-dimensional optoelectronic devices. The present PhD thesis focuses on the study of the optical properties of different 2D-TMDs (e.g. MoS2, WS2, SnS2), including their heterostructures with graphene, both at ambient and elevated pressures as well as a function of temperature. Samples are grown by mechanical exfoliation and chemical vapour deposition (CVD), while the prepared 2D crystals are characterized, with respect to their quality and the number of layers, by means of optical spectroscopic techniques (Raman, Photoluminescence), as well as AFM, SEM and XRD.
The subject of this PhD thesis is the synthesis and study of nanocomposite polymers with different carbon structures with the objective of reducing the use of fossil fuels and the plastic waste reduction. The polymeric matrices studied are commonly used in geothermal heat pumps and food packaging respectively. The insertion of different carbon structures (graphene, carbon black, carbon nanotubes) as nanofillers aims at enhancing the desirable properties of polymeric matrices (thermal conductivity, mechanical properties, etc.) to improve the performance of their application systems, combined with the low cost. After the composition of the materials, the extensive study of their individual properties is achieved through the structural characterization, thermal analysis and the study of their mechanical properties. The study focuses on the effect of different filler contents and different carbon nanostructures on the properties of polymeric materials.
The present ongoing thesis involves the study of nanoscale phenomena by means of atomistic simulations along with Monte Carlo techniques, aiming towards the design of novel, optimized nanostructured materials with the desired properties for cutting edge technological applications on the one hand and the investigation of the underlying principles of the aforementioned phenomena, on the other. Atomistic simulations that are used in this study are divided into two main categories, Molecular Dynamics (MD) and ab initio. MD simulations are based on numerical solutions of Newtonian mechanics, were interactions between atoms in the systems under investigation are expressed via an empirical interatomic potential, whose parameters are calculated based on experimental measurements. Ab initio calculations are based on numerical solutions of equations derived from first principles. In particular, in this study the Density Functional Theory (DFT) family of algorithms is being employed, which allows the determination of the physical properties of a system based on a proper expression of the charge density via the solution of the Kohn-Sham equations. DFT simulations provide more accurate results at an elevated computational cost and for smaller orders of magnitude of the size of the system under investigation, along with information about its electronic configuration, which is not provided by standard MD algorithms.
The PhD thesis is focused on the synthesis of oxide nanostructures with photoluminescent properties, using Nanosphere Lithography method, and the development of nanostructured polymeric photoactive thin films, using wet processes and printing techniques, in order to fabricate light emitting diodes (LED) and organic LED (OLED) devices. The nanostructured films will be characterized in terms of their structural and morphological properties, the chemical bonding and their optical properties. The ultimate aim of this thesis will be the correlation between the chemical composition and structure of periodic nanostructures with the enhancement of their photoluminescence activity and in general their optical response. Finally, a comparative study will be carried out between the parameters of synthesis (growth) towards the development of functional LED and OLED devices.
Alkali metal, alkaline and rare earth doped C60 fullerenes, as well as their π-electron open-shell counterparts (polycyclic aromatic and anti-aromatic hydrocarbons, PAHs), will be investigated by spectroscopic techniques. These systems have drawn the scientific interest due to their fascinating physical properties, which can be applied to a variety of fields for basic and applied research. In particular, the strong electron correlations present in both systems is the key factor for discovering new electronic states of matter, such as non-conventional superconductivity, intermediate valence states of the cations, quantum-spin liquids, topological magnetic insulators etc. Spectroscopy (Raman, photoluminescence, X-ray absorption) is a very strong and helpful tool, especially when combined with the change of the external pressure and temperature conditions, leading to the comprehension of the mechanisms behind the response of these systems to external perturbations and may also lead to the synthesis of new materials with improved or novel electronic properties.
This thesis examines various biomedical applications of magnetic nanoparticles. Indicatively, the reduction in side effects in cancer patients is studied, that is, a reduction in the eddy currents caused by the electric fields being developed, using pulsed magnetic field (PMF) instead of alternating magnetic field (AMF) during magnetic nanoparticles hyperthermia and the magnetomechanical activation of magnetic nanoparticles (MNPs) as a strategy for the treatment of cancer. In the first case, multiple on-offs will be carried out in the shortest possible time and also, simultaneous relative movement of the coil towards the sample by which successive heat losses due to eddy currents are spread over a larger volume of tissue. This will allow the increase of the Ho magnetic field amplitude, i.e. an increase in the tumor volume heating rate, exceeding the clinically acceptable limit, Hof <4.85X108 Am-1s-1 (Brezovich Criterion), defined due to these side effects. In the second case, magnetomechanical strains will be exerted in cell lines, both cancerous and non-cancerous, combining different modes of fields (static, pulsed, alternating) of very low frequencies, allowing MNPs to function and bind specifically to cell membranes, malignant and non-malignant, in order to cause damage only to cancerous tissues.
In this PhD dissertation, we seek for nanostructures with geometries and materials that will provide them with desirable properties for use in a variety of applications. The results will be sorted in order to compute the excellent combinations for applications in fields such as: solar technology, detection and bioassay, biomedicine and biotechnology.
The purpose of this PhD thesis is to correlate the structure of complex nanostructures mainly with their optical properties. In order to achieve this goal, a theoretical study of the nanostructures energy will be made and it will be correlated with their experimental study by electron microscopy. The study of optical properties related to Localized Surface Plasmon Resonances (LSPR) will be done by solving Maxwell's equations using the Finite Element Method (FEM) and a suitable choice of dielectric function. For the energy study of nanostructures we will use suitable diatomic potentials combined with molecular dynamics, while for optical properties related to plasmons we will use the COMSOL Multiphysics software, based on the 3D Finite Element Method (FEM). In this way we will be able to construct geometry; introduce the properties of materials and study the behavior of nanostructures related to energy and light scattering.
The purpose of this research is to find out the elements and methodology that S.T.E.A.M. educational activities should include to develop skills that are necessary for 21st century citizens. More specifically, I will create and evaluate S.T.E.A.M. activities in cross-curricular learning environments aiming at differentiated teaching. At second level, the possibilities of introducing them into the school environment will be studied. I will study the teaching areas and the ways of convergence with curriculum characterized by distinct objects, distinct objectives and matter as opposed to STEAM methodology that includes complex use of tools and theories and transversal interdisciplinarity. Finally, I will study the views of Teachers, Students and Parents on the existing STEAM activities and I will produce and evaluate a teacher training material for primary and secondary education.
The subject of this PhD thesis is the study of cultural heritage artifacts, ceramics and paintings, with the use of physical-chemical techniques. As far as ceramics are concerned, the study aims at the determination of their main components and manufacturing conditions (heating temperature and atmosphere). Initially, an estimation of their type and manufacturing technology is made with the optical microscope. Morphological and stoichiometric analysis of their ceramic paste takes place with the use of SEM and EDS respectively. XRD and FTIR are used for the mineralogical study and the determination of their composition. For an estimation of the ceramics’ heating temperature and concentration of calcite in the original ceramic paste, TGA is used. Regarding paintings, analysis of the pigments’ composition is important to the understanding of the technique used for their production, and in combination with the examination of their preservation condition, it constitutes the basis for any intervention, cleaning or restoration. For the determination of the substrate’s composition and the components of the painting surface’s pigments, the techniques of XRD, SEM-EDS and FTIR are supplementary used. Moreover, the application of FTIR spectroscopy at the study of pigments, is useful for the identification of any organic binders possibly used.
The PhD thesis aims to the structural investigation of predominantly semiconducting nanostructures and heterostructures with high technological importance, especially for nanoelectronic and nanophotonic applications. The chemical composition and the morphological characteristics, such as the quality of interfaces and the appearance of structural defects are characterized and correlated to the growth conditions. Strain relaxation mechanisms through the introduction of defects, as well as defect introduction from other sources are thoroughly investigated both experimentally and theoretically. Experimental techniques include the structural characterization of a series of samples with conventional Transmission/Scanning-Transmission Electron Microscopy (TEM/STEM) and High Resolution (HR) TEM/STEM, combined with Energy Dispersive X-ray Spectroscopy (EDX). Quantitative experimental strain determination at the nanoscale is performed using Geometric Phase Analysis (GPA). The elastoplastic behavior of the heterostructures is further investigated through Molecular Dynamic (MD) simulations using empirical potentials, continuum elasticity calculations and the Finite Elements Method (FEM).
Thessaloniki possesses a fine collection of high value wall mosaics, covering a chronological range from the 4th to the 14th century. The rich archaeological material has been studied for decades without, although, a systematic scientific approach conserning the technology and materials science. The present PhD thesis investigate the technology and manufacture of numerous color glass tesserae and glass tesserae with metal leaf from four byzantine monuments of Thessaloniki. The aim is to contribute to the study of the byzantine wall mosaic art and production using analytical methods (XRD, SEM-EDS, TG-DTA, FTIR, UV/Vis, ΟΜ) for material's characterization, identification of manufacture and technology characteristics, evaluation of the pathology and degradation degree of the glass tesserae.
The aim of this doctoral thesis is the design through simulations of novel photonic integrated components and circuits on polymer and III-V materials platform. The integrated components will target the efficient management and guiding of light, including simple waveguide elements, optical power splitting components and multimode interference (MMI) couplers, polarization beam splitting and rotation components (PBS/PBR), spot size converters (SSC) and interfaces between different platforms for efficient light coupling and transition, as well as waveguide frontends (WFE) for emission in the free space and beamforming capabilities. 2D Eigenmode Analysis and 3D Finite Difference Time Domain (3D-FDTD) method will be used extensively for components optimization. Finally, the possibility of connecting integrated components on a circuit level will be investigated through simulations using circuit model analysis.
The dielectric silicon nitride (SiN) waveguide platform for photonic integrated circuits presents a variety of assets compared to other standard photonic integrated platforms in the industry like silicon (Si) or III-V materials: Lower propagation losses, low cost, and CMOS compatibility. Nevertheless, a great challenge has always been the design of active devices with the SiN photonic platform. This thesis targets at the development of novel integrated photonic devices and circuits through the design of coupling interfaces for the co-integration of the SiN photonic platform with alternative photonic and plasmonic technologies. In addition, novel passive devices and circuits utilizing the SiN material will be presented. The design analysis will utilize Computational Electromagnetic Techniques, such as the Finite-Difference Time-Domain (FDTD) Method and the Finite Elements Method (FEM), while analytical and semi-analytical models describing the physical operation of the designed integrated photonic devices and circuits will also be developed.
Experimental evaluation of photonic integrated circuits
Students find it difficult to understand the concepts and principles of Physics, partly because they differ in their epistemological approaches to truth. Inquiry-Based Learning is based on the belief that learning Physics is more than just remembering information and data and is more about understanding scientific methods and concepts. In Inquiry-Based Learning, students are instructed to work autonomously using their previous experiences and the capabilities of their environment. The aim of this study is to answer how students' attitudes and beliefs about Physics change with respect to various types of Inquiry-Based Learning.
Experimental Evaluation of Photonic Integrated Circuits
Nowadays, multiferroic materials comprise a huge reservoir of technological applications due to their tunable magnetic, electric/dielectric, thermal, and optical properties. Moreover, these features can be combined, giving rise to interesting cross-coupling effects (ferromagnetism, ferroelectricity) that further enhance the versatility of multiferroics for technological applications, such as information storage, spintronics and sensors.
This Ph.D. Thesis focuses on the study of biominerals and biopigments which are found in terrestrial and aquatic organisms. Parts of the exoskeletons of arthropods, gastropod shells, bivalve shells and byssi, as well as cephalopod, arthropod and gastropod pigments and fish scales will be investigated. The samples will be characterized with Raman, visible reflectance, X-ray absorption fine structure (XAFS) and X-ray fluorescence (XRF) spectroscopies and with low-angle X-ray scattering (SAXS). The main objectives of the Thesis are: (i) the study of the characteristics (size, symmetry, content, preferred orientation) and the composition of the biominerals in invertebrate shells and structural tissues and in fish scales, as the specific materials are biomimetic models and promising raw material for biocompatible materials, (ii) the identification of pigments found in shells and exoskeletons or released by cephalopods, (iii) the effect of environmental conditions like the intensity of solar radiation on the biominerals and biopigments as for example in gastropods (in order to understand the protective mechanisms from the solar radiation in species that adapt equally well to cold and hot climates) and (iv) the effect of climate change such as the acidification of the oceans into bivalve shells.
The purpose of this PhD thesis consists of basic research on Schottky contact Phonovoltaic devices and/or related structures, simulations of those with theoretical and real materials (inorganic and organic) and finally, sample(s) implementation by gathering and/or developing technical know-how. The final deliverables will include a functional prototype(s) with the best performance, as proof of concept.
The doctoral thesis investigates the implementation context of the inquiry method with the use of digital mobile devices as experimental tools in the teaching of Physics in Secondary Education. The interventions deploy experimentation and take advantage of either the built-in sensors of the portable digital devices, or the portable wireless external sensors and devices, which communicate with the portable digital devices through appropriate software.
The main objectives of the work are the development of High-Order Thinking Skills & critical thinking of the students, their awareness of the nature & methodologies of Physics, the improvement of students' interest in physics and the investigation of the degree of improvement of students' skills in experimentation.
This doctoral dissertation studies the design, development and implementation of internet simulations on current Physics subjects.
Initially, exploratory learning scenarios of current Physics subjects (Relativity, Quantum Mechanics, Nonlinear systems) will be created and afterwards implemented and evaluated.
These scenarios will be based on interactive simulations, which will be created for this purpose. With the simulations, students will be able to perform experiments to verify the laws that govern the phenomena.
Questions, as to whether the use of well-designed simulations can promote exploratory learning in the Modern Physics educational process, as well as to whether they can help students acquire 21st century skills, will be explored.
For their evaluation, data will be collected through questionnaires, interviews and worksheets.
This doctorate dissertation aims to study Nanomagnetic Bioceramics in a multidisciplinary framework, initiating from tailoring the synthesis for reliable and reproducible binary nanoparticles consisting of magnetic and ceramic counterparts. With respect to tunable physiochemical features, they will be implemented in nanocomposite scaffolds and their performance will be evaluated under realistic conditions. Eventually, they may be proposed as multifunctional biomedical agents combining diverse therapeutic probes in certain tumor treatments, such as bone regeneration, magnetic hyperthermia and drug delivery.
This PhD thesis concerns the development of applications on cyber-physical systems. The term cyber-physical system refers to the combination of a physical system and a network in order for an integrated entity to be implemented. The function of a cyber-physical system includes data acquisition from several nodes of the system, the transfer of these data among the nodes (through the network), as well as the processing of the data by proper units of the system. The implementation of a smart sensor system for the detection of leaks in pipelines carrying petroleum products in industrial environment has been chosen as an application in the field of cyber-physical systems. This system relies on the Acoustic Emission method, based on which the detection and localization of a leak can be achieved by the help of a network consisting of acoustic sensors (mounted on the external surface of the pipeline) and by the use of proper signal processing algorithms.
The Cyber-Physical systems are a development of computational systems, as they bridge the fields of cyberspace, informatics, telecommunications and distributed control with the physical world. They are consisted of individual systems that contribute their resources to create a new, more complex system. The new system offers significantly greater functionality and performance compared to the sum of the performance of the individual components that make up the system. In addition, it has the ability to interact and expand the capabilities of the physical world through its monitoring, computation, communication, coordination and decision making mechanisms.
The aim of the PhD thesis is the development of Cyber-Physical systems at hardware and software level. The proposed solution is developed by hardware and software co-design techniques in reconfigurable architectures (FPGAs) using high-level techniques and synthesis tools.
The aim of the PhD thesis is the design of low power consumption, voltage converting and energy harvesting circuits, that take advantage of the ambient energy (solar, thermal, mechanical etc.) and convert it to electrical. The provided energy can expand the lifetime of the battery or can eliminate the need for using one. Those circuits offer an alternative energy source for supplying electronic devices at remote and isolated from the power grid regions. Such circuits are used in autonomous systems (telemetry systems, control and observation systems etc.) which they supply with the needed energy.
Within the context of this Dissertation, the effective application of approximate computing will be utilized for the purposes of developing a tool which, given an implementation of an error-free application (“accurate solution”) and an heterogeneous platform composed of conventional computing resources and specialized hardware accelerators, produces in an automated way an approximated equivalent of an application that leads to maximization of design objectives, while guaranteeing the satisfaction of the maximum error bound.
The research activity within the framework of this doctoral thesis includes:
The research activity in the PhD thesis includes the design, fabrication, implementation and characterization of solar cell arrays (organic or dye-sensitized solar cells) in different alternative geometries with target to optimize their performance per unit area. The framework of this research includes the study and optimization of three different thin-film fabrication techniques (medium scale solar cells) and their implementation in a laboratory environment without specific purity conditions. Optical characterization will be performed of the photoanode, of the thin film sensitization as well as of the thin film devices and fully implemented solar cells. The constructed solar cells will be undergo optoelectronic characterization in a solar simulation to evaluate and compare their performance in direct and alternative solar cell array geometries in order to establish the corresponding structure-performance relationships.
Our aim is to study and parameterize the factors that affect the direct sun irradiance reaching the ground, in the area of Thessaloniki. The main parameters that interact with direct sunlight are aerosols, clouds and atmospheric humidity. In our study, we use measurements of aerosols optical depth, from various spectral instruments, and modeling the solar radiation in the atmosphere with numerical computational models. To study the effect of the atmosphere on solar radiation, we have installed a pyrheliometer, which constantly follows the Sun and records the direct component of the radiation.
Some expected results from this work are a better understanding of the effect of clouds and aerosols on solar radiation, the quantification of their role in the Thessaloniki region and the modeling of the mechanism of interaction of direct broad spectrum solar radiation. The general contribution of these results is related with the fields of Climate Change, Solar energy production and atmospheric quality.
The amount of ozone (O3) and sulfur dioxide (SO2) in the atmosphere are of great interest as variously affect the quality of human life, the environment and climate. The aim of this thesis is to investigate the total atmospheric column of these two gases (O3 & SO2) and their changes during the period 2013-2020 in the area of Thessaloniki, utilizing measurements of the terrestrial passive remote sensing systems named Phaethon. The determination of the total column is based on spectral measurements analysis of direct solar radiation using the differential optical absorption spectroscopy method, including also the quantification of uncertainty sources of the produced product. The quality of the measurements of Phaethon remote sensing systems will be evaluated by comparison with measurements from the Brewer standard spectrophotometer. Finally, the resulting products will be used to certify satellite observations.
In order to determine the temperature rise in patients, due to various implants (pacemakers, cochlear implants) during MRI exposure, a standard procedure has been established according to ISO TS 10974 Ed. 2.0, which consists of a four-tier approach. Tier 1 is the most conservative and computationally simple whereas Tier 2 and 3 provide successively less overestimation of test field magnitudes adding however to the computational burden. Tier 4 provides the least overestimation with the trade-off bigger computational time and resources. In our study, we are aiming in combining the advantages of Tier 3 approach with the computational results acquired from Tier 4.
Transcranial brain stimulation is a non-invasive and painless brain stimulation technique. Transcranial direct current stimulation (TDCS) and transcranial magnetic stimulation (TMS) are widely adopted non-invasive techniques used to stimulate regions of the brain. TDCS induces neuroplasticity and modulate cortical function by applying weak direct current (~ 2 mA) over the scalp via electrodes, while TMS involves placing a coil over the scalp through which an electric charge is passed, generating a magnetic field, which can induce an electric pulse in the brain sufficient to activate cortical neurons. Both non-invasive techniques can be applied for the treatment of various psychiatric and neurological disorders, including depression, epilepsy, chronic pain and stroke recovery.
The aim of the PhD thesis is to estimate the electric field distribution in cerebral tissues of interest, to calculate the maximum electric field intensity as well as to estimate the stimulation of a specific brain region for individualized treatment.
To achieve these objectives, simulations will be created with realistic anatomical models and electrode montages according to existing clinical studies. In addition, for the personalized treatment, high resolution MRI images will be used to construct realistic 3D human models.
Finally, the low frequency solver will be used in order to solve the electrostatic problem. The affected volume and the maximum electric field distributions will be computed and analysed in tissues of interest. From the results, the most effective electrode montage can be chosen as an individualized treatment plan for the patients.
Recently, the European Union has adopted a Directive (European Directive 2013/35 / EU) to protect workers from exposure to electromagnetic fields. However, this Directive does not give details on how to deal with cases where the worker carries either an active or passive (e.g., nails or plates, spinal fusion components) implant in his/her body. The aim of this dissertation is to study the distribution of induced electromagnetic fields from industrial sources within the tissues of workers, with special emphasis on workers bearing medical implants.
In the last decade, the subject of robotic vehicles and in particular the autonomous ones, has attracted the interest of the research community due to its many applications. Autonomous robotic vehicles are designed for use in rescue missions, firefighting, surveillance, mine detection, etc. A decisive role for the success of autonomous robotic vehicles in these missions is the route that they follow in their area of responsibility, which in most cases is totally unknown, with a goal for the fastest possible coverage, in an unpredictable way. A probable solution to this would be the use of linear and nonlinear systems in order to control the movement of autonomous robotic vehicles. Therefore, in the framework of this dissertation, several linear and nonlinear models will be designed, tested and further studied at the level of simulation to control the movement of autonomous robotic vehicles in order to find the best solutions for faster and complete coverage of an area of responsibility.
The subject of the doctoral thesis is the synthesis of high-efficiency thermoelectric materials that are based on metal silicides, applying an alternative preparation method that is pack cementation. Metal silicides have attracted the interest as especially economic and eco-friendly materials finding application in thermoelectric systems for waste heat recovery. Pack cementation, which is simple, ecological and of low cost, is used for the first time in synthesis of thermoelectric silicides enhanced with the suitable dopants, as well as of their solid solutions. The structure, the composition and the morphology of the synthesized materials are studied by X-ray techniques (XRD, XPS) and electron microscopy (SEM, ΤΕΜ/HRTEM). The efficiency of the materials is estimated with thermoelectric measurements, while the operating temperature limits and their oxidation resistance are determined by thermogravimetric analysis (TGA).
The main objective of the PhD thesis is the retrieval of trace-gas concentrations in the troposphere, focusing on sulfur dioxide (SO2), by analyzing spectra with the differential optical absorption spectroscopy (DOAS) technique. The spatial and temporal distribution of SO2 and other pollutants’ concentrations will be compared between an urban site (Laboratory of Atmospheric Physics, AUTH, in the center of Thessaloniki) and a rural site (KEDEK). In addition, ship emissions will be examined by installing a MAX-DOAS system at the port of the city of Thessaloniki. Moreover, the retrieved ground-based SO2 concentrations will be compared with satellite observations, in order to validate their products. Finally, optical and microphysical properties of aerosols in the atmosphere will be retrieved, using Multi-Axis DOAS (MAX-DOAS) measurements, since this is a novel, promising technique and very few publications are available.
The present PhD thesis focuses on studying the combinatorial effects of atmospheric pollution and thermal stress on anthropogenic and natural environment, focusing particularly on living organisms. In this context, a combined utilization of a meteorological and a photochemical model (WRF and CAMx) will be implemented, to numerically simulate meteorology and atmospheric composition. To describe the consequences, existing indices will be used while a new one will be produced. This innovative new index will express the combined effect of atmospheric pollution and thermal stress. In addition, the Urban Heat Island Effect (UHI) in Thessaloniki area will be examined, along with its impact on air quality. The ultimate goal of the present thesis is to deeply understand and substantiate the way air quality and thermal stress combine, and investigate the impact of this synergy on human health.
Transcranial magnetic stimulation (TMS) is a non-invasive technique for brain stimulation, with diagnostic and therapeutic applications, during which, a magnetic field induced by an electromagnetic coil placed above the head creates an intracranial electric current through electromagnetic induction. However, the differences in tissue geometry among patients along with the diversity in regions of interest require a personalized treatment plan for each patient. The present thesis aims to investigate and establish a computational procedure to allow the quantification of the induced electric field in the brain, based on each patient’s medical imaging data. Specifically, it intends to use the magnetic resonance imaging (MRI) and electroencephalogram (EEG) data to provide a three-dimensional head model per patient through a segmentation method, in order to adapt TMS application to the individual needs of each patient and optimize its performance.
The purpose of this PhD thesis is to design, experimentally synthesize and study the structural and magnetic properties of compounds with suitable characteristics, in order to be used as raw materials in the production of advanced permanent magnets. Existing bibliography covering a wide range of compounds will be studied, from which some will be selected for experimental implementation depending on prospects and implementation possibilities. Stoichiometry will be calculated based on semi-empirical data and literature, as well as computational methods. The manufacturing processes will include molding or solid state processes while further processing will take place with powder metallurgy and heat treatment techniques. The magnetic properties of the samples will be studied following magnetic and structural characterization. The expected results include the creation of new compounds with little or no rare-earth content, in various forms (intermetallic compounds, oxides, nanocomposites), suitable to be used in permanent magnet applications exhibiting improved properties compared to the cheap existing permanent magnets without the high cost of today's top performance magnets.
he PhD thesis concerns the estimation of the emission inventories of major air pollutants by the synergetic use of satellite observations with air quality modelling systems. The methodology is based on the inverse modelling of gaseous emissions, using satellite measurements, model simulations and the apriori bottom-up emission inventories, while the errors of the model and the retrievals are both taken into account. Satellite observations from TROPOMI instrument on the polar orbiting Sentinel 5-Precursor (S5P) platform will be acquired and the open source LOTOS-EUROS chemical transport model, which runs in the Aristotelis HPC cluster, will be used for the simulations. As a result an improved, continuously updated and high spatiotemporal top-down emission inventory will be produced by satellite observations.
The aim of the Phd thesis is the study of optical and microphysical properties of aerosol particles using remote sensing techniques. Measurements will be used for LIDAR ground-based stations, which are members of EARLINET European network, including the station of the Laboratory of Atmospheric Physics in Thessaloniki (LAP/AUTH). Passive and active remote sensing methods will be used synergistically with in-situ measurements. The systematic observations will allow, valid statistical results that are related to the search for spatial and seasonal dependencies of these properties and to their association for areas with different characteristics of natural and human activities emissions. Also, we will try to retrieve vertical distribution of the basic microphysical aerosol properties using inversing algorithms already used by the scientific community. The algorithms will adapt to LIDAR optical data by a combination of optical data from sunphotometers. In the context of the PhD thesis, a technical upgrade of the LAP LIDAR system is expected, with the aim of further operating characteristic improvement as well as the abillity for reliable retrieve measurements with ability of backscatter laser beam depolarization. The results from this thesis will highlight the spatial and temporal distribution of aerosols layers over Europe, as well as improve a data validation from satellite measurements.
Physical, optical and chemical properties of atmospheric aerosols under background conditions using remote sensing and in situ techniques
Metrology is the integrated science of measurement. It includes the definition and realisation of base units of measurement, ensuring their traceability at all levels of use, according to the uncertainty requirements at each level and calibrations in devices and systems to ensure their operation within certain frames and to calculate their uncertainty. It is a foundation stone in the service of scientific research and discovery, industrial development and education. This dissertation focuses on the study of electrical quantities and frequency-time measurements with the support and collaboration of the Hellenic Institute of Metrology. As well as possible changes with the implementation of the new International System of Units (SI). It aims to implement educational scenarios of exploratory and discovering learning in secondary and higher education based on the logic of metrological provisions and calibrations. Finally, the case of "virtual" metrology is studied with the use of computational tools and its new applications.
The objective of this thesis is the study of wireless systems with radio wave energy harvesting mechanisms. Towards this end, new technologies and innovative design techniques will be used for wireless sensors with minimal possible power consumption through multiband RF energy harvesting mechanisms. Α multiband antenna as well as a multiband rectifier will be designed using a new optimization technique. Optimization techniques for the overall sensor network will also be applied to minimize energy consumption.
This thesis focuses on the study of biomedical applications of magnetic nanoparticles. Specifically, the aim is to reduce the adverse side effects in patients with cancer treated with hyperthermia, while the use of magnetic resonance imaging in the application of magnetomechanical cell therapy using magnetic nanoparticles, is also studied. In the framework of this study, theoretical models will also be developed for simulation purposes.
Phd candidate in the Department of Physics (AUTH) with research subject remote sensing of Greenhouse Gases through Fourier Transform Infrared Spectroscopy by measuring the full atmospheric gas column from the ground, where the system (EM27/SUN) is faced up to the space. The EM27/SUN spectrometer is intended to measure direct solar radiation in the near infrared (NIR) spectral range. The recorded spectra contain signatures of atmospheric constituents (
The aim of this dissertation is to study problems in wireless communications using machine learning methods. Machine learning models will be studied for waveform classification in wireless networks. The application of machine learning models for supporting user mobility in 5G networks will be examined. Moreover, the use of evolutionary algorithms in machine learning models will be evaluated. Surrogate modeling methods will be applied in antenna design problems. Finally, federated learning methods for IoT networks will be studied.
Research in recent years in various fields of science has confirmed that nonlinear dynamical systems, especially those with chaotic behavior, can explain the occurrence of many and complex phenomena. The same has happened, since the 1980s, in the field of economic theory, as several chaotic phenomena have been observed in the study of known economic indicators. Therefore, the need arose for a new approach to economic theory that led in the last decade to the development of a new scientific field, "Econophysics". In this direction, an attempt is made to interpret the main features of economic theory, such as structural changes, irregular micro- and macroeconomic fluctuations using tools of non-linear dynamics. Therefore, in the framework of this dissertation will be studied the application of non-linear dynamical systems (continuous or discrete) for the interpretation and prediction of phenomena related to modern economic theory.
The presence of allergens from trees and plants degrades the quality of the air and significantly affects the quality of life of citizens, causing various allergic reactions such as allergic rhinitis and asthma. Monitoring and predicting pollen concentrations is vital to protecting health and improving quality of life, especially in urban areas. The present dissertation aims to develop a modeling system for calculating emissions and dispersion of pollen grains into the atmosphere for the study and forecast of biological weather. The system will include the WRF, NEMO and CAMx models. The results of the WRF meteorological model will be initial values for NEMO, which will be modified accordingly to include pollen emissions. CAMx will examine the dispersion of pollen into the atmosphere. The modeling system will be suitable for the operational forecast of the average daily concentrations of the most allergenic taxa of pollen. Nested domains will be used which will cover Europe and with high resolution the Eastern Mediterranean and Greece. An important part of the dissertation is the evaluation of the results produced through the comparison with measurements of pollen concentrations from existing monitoring stations.
In this doctoral dissertation the emissions from maritime transport and navigation as well as the air quality in ports of the wider Mediterranean region using synergistic methods of satellite remote sensing and air quality models will be studied. Specifically, an assessment of the current situation and new air quality patterns will be made using satellite observations from the TROPOMI (TROPOspheric Monitoring Instrument) located in orbit on the Sentinel-5 Precursor satellite. Simulations of air quality models from the LOTOS-EUROS chemical transfer model will be used to update emission fields in the Mediterranean as well as to develop a new upgraded emission inventory.
The aim of the thesis is the study of future changes of UV and visible (UV/Vis) radiation reaching the troposphere and Earth’s surface, with a view to calculate quantities affecting life on Earth (biologically relevant) and the environment. In order to interpret and calculate the radiation changes, new datasets of ozone, aerosols, clouds and the Earth’s reflectivity, will be used as input in radiative transfer model. The new datasets will be extracted from recent simulations performed by Earth System and Chemistry-Climate Models (CMIP6 and CCMI), as well as from regional models and they will cover the period of recent past and future projections through the whole course of the 21st century. Finally, appropriate weighting functions (Action Spectra) will be applied to study the effects on ecosystems, human health) and agriculture.
Assessment of anthropogenic and natural aerosols' impact on the radiation budget and climate
Binary neutron star mergers can have different outcomes, depending on the neutron star masses and on the equation of state of high density matter. One possible outcome of such a merger is a long-lived (τ>10ms) compact remnant, a hypermassive neutron star (HMNS), supported by strong differential rotation. Studying the oscillation frequencies of the merger remnant, it is expected that two discrete frequencies of the remnant may be observable by the upgraded generation of gravitational wave detectors. The main work of the project is to analyze binary neutron star merger configurations, exploring different options for the differential rotation law in the process, in order to arrive at practical empirical relations for these two frequencies, which can then be used for inferring information on the equation of state.
Vasileia Aspasia Masoura
Studies of recent decades have led to the conclusion that there is an inextricable link between the galaxies and the Supermassive Black Holes (SMBHs) located in their centre. However, it is still unclear how the activity of the SMBH affects the properties of the host galaxy. The first part of my PhD thesis addresses this question by studying the correlation between the SMBH activity and the SFR of the host galaxy (Masoura et al. 2018). Specifically, we use X-ray observations from the XMM-XXL and the XMM-ATLAS fields, to compose the largest sample (~3,500) of X-ray Active Galactic Nuclei (AGN). These sources have been observed in a wide range of the electromagnetic spectrum, from ultraviolet to far infrared wavelengths. Our analysis shows that the AGN can either enhance or suppress the SFR depending on its power. The second part of my thesis studies the correlation between the star-formation and the AGN absorption. There is a scientific debate as to whether the absorption we observe in some AGN is a geometric effect or an evolutionary phase in the galaxy’s lifetime. Investigating whether there is a correlation between star-formation and absorption will shed light on this issue.
This doctoral dissertation includes both a qualitative as well as quantitative correlation between different luminescence methods in different geological materials, in order to investigate the luminescence phenomenon. Initially, a correlation was made between the thermoluminescence-TL curve after bleaching and the components of both linearly modulated optically stimulated luminescence (LM-OSL) and continuous wave optically stimulated luminescence OSL (CW-OSL) in natural calcium fluoride. A correlation study between continuous wave OSL and infared stimulated luminescence (IRSL) was amplified in various materials of geological origin such as one K-feldspar, two different grain size fractions of Durango apatite and one gypsum, by investigating the influence of IR stimulation to the OSL signal. As a follow-up of previous studies, a correlation between OSL and IRSL was attempted in different types of potassium feldspars using two different protocols. The purpose of this study is to investigate the luminescence mechanism within the crystalline lattice of these materials. This work continues to this day.
This research focuses on the search for New Physics in the Large Hadron Collider at CERN with the ATLAS experiment. The search is indirect, kinematic bosonic distributions that are known from simulations and from previous experiments, are under study. Possible shape distortions or increased cross section, compared to the Standard Model, serve as a probe for New Physics. In addition, the performance of the muon reconstruction efficiency, specifically in the forward region of the detector is being studied. Finally, there is active participation in the data taking in the ATLAS experiment.
In the present dissertation we study the equation of state (EoS) of nuclear matter along with its respective effects on static and rotating neutron stars. Firstly, we study the constraints that are imposed by the upper bound of the speed of sound on the EoS of hadronic matter in high densities and its effects both on the upper bound of the mass and the tidal polarizability of neutron stars. Subsequently, we are dealing with the effects of the EoS through the symmetry energy on the crust-core interface (low densities) of slowly rotating neutron stars. Lastly, we study the speed of sound effects on rotating neutron stars.
Terrestrial mosses can be used as bioindicators. They obtain most of their nutrients directly from wet and dry deposition. The simplicity and the low cost of the moss biomonitoring technique make them ideal for the determination of heavy metals and radionuclides concentrations.
This was the first time that moss technique was applied in Greece and the obtained data were included in the database of UNECE ICP-Vegetation European moss survey.
Within the framework of this PhD study, ninety-five (95) samples of Hypnum cupressiforme Hedw., were collected during the summer 2016. They were analyzed by gamma-spectrometry for the determination of 7Be, 210Pb, 137Cs and 40K concentrations, as well as by Neutron Activation Analysis (NAA) for the determination of the elemental concentrations of thirty-three elements.
The analysis enabled the definition of factors such as soil dust, vehicular traffic, heavy oil combustion and mining activities that contributed to the heavy metal concentrations. Possible transboundary transports of elements were also studied. The transfer factor from air and soil to mosses was studied too.
This thesis is the result of a constant search in pedagogical and technological level of an effective way of teaching physics from distance. We developed this kind of learning environments, because it is the only way to create a communication bridge and direct cooperation with all the other educational levels & sectors in different geographical areas.
It focuses on the design and implementation of distance learning modules, that deal with modern complex physics themes and have been approached in a variety of ways using a number of learning tools (virtual experiments, remote experiments, simulations, learning managements systems, educational websites) and various learning methods (e-learning, blended learning, learning object theory).
The thesis describes the attitude of students studying in the first grade of Lyceum in Cyprus towards the course of Physics as well as the correlation of this attitude with their performance as defined both in terms of the knowledge gained as well as in relation to the development of basic competences. For this purpose, properly-designed questionnaires and essays are given to a large number of pupils for many years. Innovative teaching approaches such as games, quizzes, etc. are being developed and implemented in learning environments in order to improve the attitude, the performance and the learning satisfaction of the students towards the course of Physics. The impact of these approaches on experimental groups is investigated and recorded in relation to the objectives of the curriculum.
Study of diffusion and reaction-diffusion processes on multilevel networks. One of the most important problems in modern network theory is the topological and dynamic characterization of systems consisting of two or more interconnected networks. We will study the influence that their mesoscopic organization has on the collective behaviors of diffusion and reaction-diffusion processes acting on them. For this purpose extensive simulations will be performed for both multilevel and isolated networks. Many network types, cross-system interactions and initial conditions will be used. Simple diffusion, A + A = 0 and A + B = 0 processes will be studied.
Magnetic nanomaterials represent one of the most important and emerging classes of materials in nanotechnology due to a range of potential applications. In particular, magnetic nanoparticles have been envisaged for various biological and biomedical applications. This thesis deals with the synthesis, characterization as well as with the biological in vitro application of ferrite nanoparticles. Interestingly, single, functionalized and core shell ferrites are thoroughly studied. This thesis work shows that the improvement of ferrites’ intrinsic properties (both structural and magnetic) has a crucial impact to their potential use as heating or magnetomechanical stress agents in magnetic hyperthermia and magnetomechanical cell triggering applications respectively. Meanwhile, magnetic hyperthermia standardization, one of the main objectives of this thesis, is an absolute obligatory step to highlight with certainty the series of novel nanoparticle systems with the greatest heating performance for in vitro magnetic hyperthermia.
My area of PhD thesis is magnetism and magnetic materials, starting from systematic synthesis and robust investigation of physical properties and concluding to technological applicability of nanomagnetism on diverse aspects, such as information storage, biomedicine and sustainable growth. More specifically, my thesis has to do with arranging at the nanoscale magnetic nanoparticles, aiming to enhance their collective magnetic features. Magnetic nanoparticles may be organized in nanostructures assemblies with emerging properties, distinctly different both from those of isolated nanoparticles and/or of the corresponding bulk phases. The macroscopic magnetic features of such nanoscale assemblies are determined by particle interactions, giving rise, for example, to unique electrical, optical, or magnetic properties.
Aim of the present doctoral thesis is the development, the implementation and the evaluation of a methodology that creates motivation to learn Physics in the secondary education and specifically for the topic of energy. The development of the methodology is based on the theories of the motivational components, interest and self-efficacy. A teaching intervention targeting desirable learning outcomes by enhancing students’ interest and self-efficacy was developed and implemented. The design and the composition of the activities were according to Renninger & Hidi (2006) model and Bandura’s (1997) socio-cognitive theory. The teaching intervention was carried out in a public school during the physics lessons in the second class of high school. A software was designed and used for the purposes of the intervention. In order to evaluate the intervention data collection was conducted through self-report questionnaires, work sheets and interviews.
The present doctoral thesis studies the design, the development and the evaluation of a Teaching Learning Sequence (TLS) in upper secondary education for the teaching of concepts related to Atomic Physics and Light through the study of Stellar Spectra. The Sequence was designed utilizing the Model of Education Reconstruction (MER) and the approach of structured inquiry. In the context of the thesis the preconceptions of the students are investigated and experimental activities are implemented. The research is carried out in the second class of Lyceum and comprises consecutive redesigned implementations of the Learning Sequence. Students’ learning outcomes after the implementation of the Sequence, are evaluated each time with questionnaires, interviews and worksheets. Moreover, they are compared with those achieved by the students of the control group in which the teaching is done according to the approach defined by the Curriculum.
In the present PhD thesis, the painting and ground layers of works of art are being in-depth studied, as a contribution to the documentation, dating, restoration and preservation of paintings. The research conducted within the scope of the PhD thesis includes the following sub-topics:
A. Thermal degradation of paintings: The alteration of painting layers in the case of extreme thermal incidents is being studied, by means of physicochemical methods.
B. Luminescence study of calcium sulfates for their use as dating dosimeter: Calcium sulfates are basic components of artifacts, and have been used as substrates and structural materials of paintings and monuments, respectively. The three types of calcium sulfate (dihydrate, hemihydrate and anhydrous) are being studied, by means of Thermoluminescence, Optically Stimulated Luminescence and Infrared Stimulated Luminescence.
C. Case studies: Characterization and documentation of materials and techniques of post-Byzantine painting artifacts (wall-paintings/portable icons).
The subject of the PhD is the study of nanoscale multi-gate MOSFETs, which are the most promising candidates for the next generation of integrated circuits according to the International Technology Roadmap for Semiconductors (ITRS). This thesis is focused on the study of triple-gate junctionless transistors (JLTs). The goal of the research is to develop analytical compact models for the drain current and transconductances of the JLTs, implement these models to a commercial circuit simulation tool and investigate their variability and reliability. The simulation tool will be evaluated in analog CMOS circuits with transistors down to 25nm channel length.
The treatment of choice of bone defects with the transplantation of autologous graft has particular problems such as painful surgeries and necrosis or graft failure caused by insufficient vascularization within the graft. In addressing these issues, bone tissue engineering with 3D scaffolds and modern developments in regenerative medicine provide the appropriate framework for the formation of new functional tissues.
Thus the aim of the present PhD thesis is the fabrication of bioactive polymeric–ceramic hybrid 3D scaffolds focused on the enhancement of osteogenesis and angiogenesis, using mesoporous nanocarriers for the development of local drug delivery systems to prolonged and sustained release of growth factors in-vitro.
In the current thesis, real systems will be studied by considering them as networks. Specifically, patent citations (patent data filed in EPO and PCT) and scientific collaborations that derive from European funding Programs (FP5-7, HORIZON2020) will be studied. At the beginning, some basic network properties will be studied, such as the size, the diameter, the clustering coefficient and the degree distribution of the networks. Next, the k-shell decomposition and the percolation methods will be applied in order to extract characteristics that basic properties do not allow. Finally, a multilayer network will be created by considering the two databases as a separate layer. This will allow us to understand how these layers interact and how changes in the one layer can affect the other.
The magnetic nanoparticles synthesis by the liquid chemistry method is the main goal of the present PhD thesis. The conditions of the chemical reactions were selected for the purpose of optimization of their structural and magnetic properties in relation to the application that they are foreordained. The structural characterization is carried out by X-ray powder diffraction (XRD) and TEM, while the magnetic one by VSM or SQUID magnetometry. Raman spectroscopy and/or IR spectroscopy and thermogravimetric analysis (TGA) are performed complementary. Finally, magnetic hyperthermia measurements are carried out in order to evaluated the thermal capability of a tissue by the produced nanoparticles, via the estimation of SLP factor, as well as fluorescence measurements in order to ascertained their potential use as fluorescence agents.
The aim of this thesis is the performance evaluation of an air quality numerical model, i.e., the Comprehensive Air Quality Model with Extensions (CAMx). The area of study is the Eastern Mediterranean region. At first, the results of the model will be evaluated against surface measurements from the available air quality monitoring networks, operating at local, national and international level. The ability of the model to accurately reproduce the individual physical and chemical atmospheric processes that determine the air quality will be examined as well. Furthermore, a post-processing filter will be developed, applied to the model's results in order to improve the accuracy of predictions.
Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a well-established and widely applied method for the monitoring of air quality species in the atmosphere. Moreover, it is considered as a reference technique for the validation of satellite observations. The development and optical characterization of ground-based MAX-DOAS systems (Phaethon), as well as the spectral analysis of their measurements are investigated in this thesis. Proper algorithms are developed and used for the retrieval of vertical profiles and tropospheric and stratospheric vertical columns of trace gases such as nitrogen dioxide (NO2) and formaldehyde (HCHO) from observations in the city center of Thessaloniki. In addition, field measurements are performed over sub-urban and rural areas near Thessaloniki. These observations performed over the greater area of Thessaloniki are compared with corresponding satellite-derived products. The different spatial representativeness of ground-based and space-borne retrievals and the effect of spatial variability of tropospheric gases on the comparisons are under investigation. The retrieval algorithms and the operational performance of Phaethon system are validated against other well-characterized MAX-DOAS instruments.
Recently, there has been a growing interest in thermally conductive polymeric materials. Carbon-based nanomaterials, such as graphene nanoplatelets have been proposed to be the next generation of multifunctional nanofillers for the improvement of properties of polymers. Graphene nanoplatelets are ultrathin particles of graphite that can be thought of as short stacks of graphene sheets. A series of graphene nanoplatelets-reinforced thermoplastic high-density polyethylene were prepared by the melt-mixing method, with the introduction of graphene nanoplatelets of different sizes (5, 15 and 25 μm in diameter) at various filler contents (0.5-5 wt.%). Several methods were used to study the structure, morphology, thermal and mechanical properties of nanocomposites. It was found that the graphene nanoplatelets with the higher diameter size affect more the thermal and mechanical properties of matrix than the smaller ones.
In this PhD thesis, the dynamic behavior of non-linear circuits is studied by controlling them by microcontroller systems. We study the ways in which the chaotic behavior of dynamic systems can be confirmed. These include Lyapunov exponents, system dimensions, Poincaré map, bifurcation diagram and the power spectrum. Two ways of approximate solving non-linear systems using the computer are studied, the Euler method and the fourth-order Runge-Kutta method. Moreover, ways to solve circuits with non-linear elements are being described. The proposal of an experimental method of imaging of the three basic diagrams (phasic portrait, Poincaré map and bifurcation diagram) on the oscilloscope, with the development of an appropriate microcontrolled device, is one of the aims of this PhD thesis. This device will be used to analyze several of the well-known chaotic dynamic systems as well as newly proposed chaotic dynamic systems for educational purposes at undergraduate and postgraduate level.
Research activities in various fields of science have confirmed that nonlinear dynamical systems, especially those with chaotic behavior, can explain the appearance of complex phenomena. The same has happened since the 1980s in the field of economic theory, as chaotic phenomena have been observed in the study of well-known economical models. Therefore the need for a new approach to economic theory has emerged, which led in the last decades to the development of a new interdisciplinary field, known as "Econophysics". To this direction, an attempt is made to interpret the main features of economic theory, such as structural changes, irregular micro- and macro-economic fluctuations with the use of tools from nonlinear dynamics. Consequently, in this thesis the application of nonlinear dynamical systems to the interpretation and prediction of economical models will be studied.
The Large scale phenomena on the summer atmospheric circulation over East Mediterranean is studied in this doctoral thesis. The analysis focuses on the Aegean basin over the summer period (from May to September). In the frame of this work the teleconnections (Indian summer Monsoon and ENSO) which influence the summer atmospheric circulation over East Mediterranean are studied. For the analysis, ESMs data (Earth System Models) available from the fifth Phase of Coupled Model Intercomparison Project (CMIP5) in frame of Intergovernmental on Climate Change (IPCC, AR5) are used. Furthermore, data from European Center for Medium-Range Weather Forecasts (ECMWF) and observations are analysed, according to the availability. This study focuses on a better understanding of atmospheric circulation mechanism over the East Mediterranean, the Etesian winds phenomenon and the teleconnections among Etesians, summer Asian Monsoon and ENSO (El–Nino Southern Oscillation).
The present thesis includes the numerical quantification of in-vitro interactions between magnetic nanostructures and living matter, which is performed under the influence of external varying magnetic fields and frequencies. In this context, the conversion of magnetic energy a) to mechanical stress through magneto-mechanical forces in the frequency range <100 Hz and b) to heat through magnetic particle hyperthermia at 100-1000 kHz is studied. For the first case the theoretical and experimental effect of the field gradient on the movement of the nanostructures and also the activation of cellular mechanisms through the mechanical stresses produced is investigated. Moreover, in magnetic particle hyperthermia the induction of apoptosis in cancer cells by combining the alternating magnetic field with the magnetic nanostructures is being examined. In each case, simulation of both the magnetic response of nanostructures and the transfer of energy (mechanical or thermal) to the biological material is carried out, while the influence of various factors such as the properties of nanoparticles (size, shape, magnetic anisotropy), the magnetic field (frequency, width, steps) and the protocol (dosage: duration of application, concentration) on the whole process is studied.
The aim of the Phd Thesis is the investigation of the natural emissions and their impact in the atmospheric pollution. In this context, the Natural Emission MOdel (NEMO), initially developed at the Laboratory of Atmospheric Physics, will be updated to include desert dust from regions like Sahara and Middle East, as well pollen emissions from the vegetation. A sensitivity analysis will be realized to reveal the differences among the parameterizations. Several simulations will be realized with the aid of the meteorological model WRF for the production of the input fields in NEMO and the chemistry-transport model CAMx and for the calculation of the surface concentrations. NEMO will be evaluated indirectly with existing measurements and the output concentrations from CAMx. General recommendations will be given for the implementation of the schemes and the advantages/disadvantages of each one will be highlighted.