George Papaioannou

• IPTO

Characterizing imaging performance requires a multidisciplinary approach that evaluates various interconnected parameters, including dosage optimization and dynamic accuracy. Radiation dose and dynamic accuracy are challenged by patient motion that results in poor image quality. These challenges are more prevalent in the brain/cardiac pediatric pat...

We investigate the impact of several critical events associated with the Russo Ukrainian war, started officially on 24 February 2022 with the Russian invasion of Ukraine, on ten European electricity markets, two natural gas markets (the European reference trading hub TTF and N.Y. NGNMX market) and how these markets interact to each other and with U...

Increasing the generation of electric power from renewable energy sources (RESs) creates important challenges to transmission system operators (TSOs) for balancing the power system. To address these challenges, adequate system flexibility is required. In this context, TSOs carry out flexibility assessment studies to evaluate the flexibility level o...

This paper presents a detailed flexibility and cost assessment study of the Greek power system for the time period 2021–2025 where for the first time the reserve requirements are determined based on the statistical analysis of the residual load variability and forecast error at hourly steps. In particular, the long-term uncertainties are modeled vi...

Transmission line monitoring and power flow control in meshed networks have become major concerns for Transmission System Operators due to the heavily stressed electrical power systems caused by the increased renewable energy penetration. Upgrading the existing transmission lines and/or building new ones are traditional approaches to solving conges...

Congestion issues are becoming more prevalent as the share of variable renewable energy increases. Conventional methods to mitigate them, such as building new lines, require significant lead time and upfront investment costs. Thus, alternative approaches that deal with congestion problems faster and in a more efficient manner have gained significan...

Transmission line monitoring and power flow control in meshed networks have become major concerns for Transmission System Operators due to the heavily stressed electrical power systems caused by the increased renewable energy penetration. Upgrading the existing transmission lines and/or building new ones are traditional approaches to solving conges...

We aim to investigate whether EEG dynamics differ in adults with ASD (Autism Spectrum Disorders) and ADHD (attention-deficit/hyperactivity disorder) compared with healthy subjects during the performance of an innovative cognitive task, Aristotle’s valid and invalid syllogisms, and how these differences correlate with brain regions and behavioral da...

The increasing share of variable renewable energy (VRE) generation can lead to transmission congestion issues, which in turn could result in curtailment of VRE generation as well as prevent further VRE integration. Traditionally, congestion issues were dealt through grid expansion or upgrading existing transmission lines; these solutions, however,...

Objective We aim to investigate whether EEG dynamics differ in adults with ASD (Autism Spectrum Disorders), ADHD (attention-deficit/hyperactivity disorder), compared with healthy subjects during the performance of an innovative cognitive task: Aristotle's valid and invalid syllogisms. We follow the Neuroanatomical differences type of criterion in a...

The continuous penetration of renewable energy resources (RES) into the energy mix and the transition of the traditional electric grid towards a more intelligent, flexible and interactive system, has brought electrical load forecasting to the foreground of smart grid planning and operation. Predicting the electric load is a challenging task due to...

The European Commission’s Target Model’s main objective is to integrate European electricity markets, leading to a single internal energy market and guaranteeing the instantaneous balance between electricity generation and demand. According to the target model for electricity trading, proposed by the European Network Transmission System Operators f...

This paper focuses on the potential future breakthroughs of TSO/DSO coordination in enhancing the transmission system reliability without further extensions or upgrades of the power system infrastructure. The demonstration site of Kefalonia is selected for the case study. Simulations are carried out through PSS ® E in order to investigate the prosp...

Congestion issues are becoming more prevalent as the share of variable renewable energy increases. Conventional methods to mitigate them, such as building new lines, require significant lead time and upfront investment costs. In order to deal with congestion problems faster and in a more efficient manner, the Greek Transmission System Operator inst...

Italy, Greece, and, to a lesser degree, Bulgaria have experienced fast growth in their renewable generation capacity (RESc) over the last several years. The consequences of this fact include a decrease in spot wholesale prices in electricity markets and a significant effect on cross border trading (CBT) among neighboring interconnected countries. I...

The high proliferation of converter-dominated Distributed Renewable Energy Sources (DRESs) at the distribution grid level has gradually replaced the conventional synchronous generators (SGs) of the transmission system, resulting in emerging stability and security challenges. The inherent characteristics of the SGs are currently used for providing a...

The large-scale integration of variable renewable energy (VRE) in power systems, such as wind and solar, increases the flexibility needed to maintain the load-generation balance. In order for the power operators to plan for secure and reliable operation, they must examine whether there exists sufficient power system flexibility to meet ramps caused...

In this work, a hybrid model that combines Singular Spectrum Analysis (SSA) and Long Short-Term Memory (LSTM) Neural Networks is proposed for day-ahead hourly load forecasting. First, the coordinates of the phase space are defined by constructing the trajectory matrix. Afterwards, Singular Value Decomposition (SVD) is performed, allowing us to extr...

The large-scale integration of variable renewable energy (VRE) in power systems, such as wind and solar, increases the flexibility needed to maintain the load-generation balance. In order for the power operators to plan for secure and reliable operation, they must examine whether there exists sufficient power system flexibility to meet ramps caused...

The large-scale integration of variable renewable energy (VRE) in power systems, such as wind and solar, increases the flexibility needed to maintain the load-generation balance. In order for the power operators to plan for secure and reliable operation, they must examine whether there exists sufficient power system flexibility to meet ramps caused...

Forecasting electricity load is an important task for the safe and reliable operation of the power system and has been a prominent area of research for years. Whether the forecasting tasks concern daily or hourly values the relevant literature is mostly focused on comparing the performance of different models. Regardless model selection, when consi...

In this paper we examine and compare the efficiency of four European electricity markets (NordPool, Italian, Spanish and Greek) of different microstructure and level of maturity, by testing the weak form of the Efficient Market Hypothesis (EMH). To quantify the level of efficiency deviation of each market from the ‘ideal’ or ‘benchmark market of ra...

The purpose of this study is to investigate short and long run relationships between electricity spot prices in Greece, Brent oil, natural gas, lignite fuel cost and carbon allowances using daily data from 2007 to 2014. Static and dynamic Johansen test are applied in order to identify long run relations and also to assess the evolution over time in...

Utilization of non-linear tools to characterize the state of development of the electricity markets in Italy and Greece. This is equivalent to testing the Efficient Market Hypothesis on these markets. The tools include a variety of complexity measures like Maximal Lyapunov and Hurst exponents and HHI index for market concentration and Entropy, a me...

This work aims to detect the impact of fundamentals and regulatory reforms on the Greek Wholesale Electricity Market, applying SARMAX/GARCH models. The System Marginal Price (SMP) is considered a stochastic, nonlinear process, reflecting not only the effects of endogenous/fundamental market factors but also the effects of exogenous variables includ...

Liberalization of electricity markets has increasingly created the need for understanding the volatility and correlation structure between electricity and financial markets. This work reveals the existence of structural changes in correlation patterns among these two markets and links the changes to both fundamentals and regulatory conditions preva...

Liberalization of electricity markets has increasingly created the need for understanding the volatility and correlation structure between electricity and financial markets. This work reveals the existence of structural changes in correlation patterns among these two markets and links the changes to both fundamentals and regulatory conditions preva...

In this work we propose a new hybrid model, a combination of the manifold learning Principal Components (PC) technique and the traditional multiple regression (PC-regression), for short and medium-term forecasting of daily, aggregated, day-ahead, electricity system-wide load in the Greek Electricity Market for the period 2004–2014. PC-regression is...

We study the co-evolution of the dynamics or co-movement of two electricity markets, the Italian and Greek, by studying the dynamics of their wholesale day-ahead prices, simultaneously in the time-frequency domain. Co-movement is alternatively referred as market integration in financial economics and markets are internationally integrated if the re...

This work presents the results of an empirical research with the target of modeling the stylized facts of the daily expost System Marginal Price (SMP) of the Greek wholesale electricity market, using data from January 2004 to December of 2011. SMP is considered here as the footprint of an underline stochastic and nonlinear process that bears all th...

The Efficient Market Hypothesis (EMH) is widely accepted to hold true under certain assumptions. One of its implications is that the prediction of stock prices at least in the short run cannot outperform the random walk model. Yet, recently many studies stressing the psychological and social dimension of financial behavior have challenged the valid...

Conference code: 86196, Export Date: 24 October 2012, Source: Scopus, Art. No.: 5954848, doi: 10.1109/IWBP.2011.5954848, Language of Original Document: English, Correspondence Address: Kanellos, G.T.; Informatics and Telematics Institute, Centre for Research and Technology Hellas, Thessaloniki, Greece; email: gtkanellos@gmail.com, References: www.i...

It is apparent that socket fit is the most common source of dissatisfaction in amputees and part of a growing medical and socioeconomic problem. Even the most up to date trans-tibial socket designs are not capable of coping with the issue of continuous stump volume change that is apparent within a day, week, month or season of socket use. Intellige...

Optimal performance of artificial limbs is still largely dependent on the accurate evaluation of their biomechanical behavior. The accumulated expertise of the prosthetist and indirect measurements of socket and joint kinematics are currently used in a trial and error format for prosthesis-socket performance maximization. The accurate direct unobtr...

The design, construction, and fitting of artificial limbs remain to this day an art, dependent on the accumulated expertise of the practitioner/prosthetist. Socket fitting is cost ineffective, time consuming, and a source of inconvenience for the amputee. Stump-skin slippage within the socket can cause discomfort, internal limb pain, and eventually...

We report on the development of a flexible 2D optical fiber-based pressure sensing surface suitable for biomedical applications. The sensor comprises of highly-sensitive Fiber Bragg Grating elements embedded in a thin polymer sheet to form a 2x2 cm² sensing pad with a minimal thickness of 2.5mm, while it is easily expandable in order to be used as...

Daily volume loss of the residual limp is reported as one of the greatest challenges in socket fitting. Assisted vacuum socket systems were developed to prevent stump's volume loss and maintain sufficient socket fit. There is however very little quantitative biomechanical research for the evaluation of below knee sockets with assisted vacuum system...

We report on the application perspectives of optical fiber strain and shear sensor configurations in the fields of orthopedic biomechanics and rehabilitation. The principle of operation of Fiber Bragg Grating (FBG) sensing elements is presented revealing their potential for introducing intelligence in biotechnological products for orthopedics and r...

The apparent correlation between bone density and susceptibility to fracture was evaluated using finite element modeling. Based on computed tomography data of an actual femur bone, a versatile virtual model was created and modified in order to simulate different bone geometries and densities. Under typical load conditions the highest strains were c...

Dynamic Roentgen Stereogrammetric Analysis (DRSA) provides a highly accurate research and clinical tool in human movement sciences. Essential for the respective DRSA measurements is proper alignment and calibration of the device. An improved method for determining the sufficiency of those preparations is introduced and discussed.

An adaptable bedding surface for the prophylaxis and treatment of decubitus ulcers was developed and evaluated in a number of preclinical studies. The new bed reduced the average contact pressure peaks in prolonged supine bed rest while significantly decelerating the onset and progression of pressure sores. A special advantage of the surface is its...

The new Wound Diagnostics Tool (WDT) software package presented here aims to produce wound progress statistics that have clinical significance by linking digital image-based and three-dimensional (3D) geometry maps of the ulcer with existing traditional risk assessment techniques and other wound progress tracking information. All this information i...

Successful focal articular surface injury (FAI) repair depends on appropriate matching of the geometrical/material properties of the repaired site, and on the overall dynamic response of the knee to in-vivo loading. There is evidence linking the pathogenesis of lesion progression (e.g. osteoarthritis) to weightbearing site and defect size. The pape...

Conventional motion measurement techniques are unable to measure knee arthrokinematics during dynamic knee motion to clinically significant levels of accuracy. Assessment with Biplane Dynamic Roentgen Stereogrammetric Analysis (DRSA) overcomes the problem but previous attempts report challenges with motion blur, dynamic accuracy, image quality, exc...

Little is known about in vivo menisci loads and displacements in the knee during strenuous activities. A new method that combines high-speed kinematics measured with biplane dynamic Roentgen stereogrammetric analysis (DRSA) and a subject-specific finite element (FE) model for studying in vivo meniscal behavior is presented here. Further model calib...

Bones in the skeleton join to form segments or links that provide for the attachment of muscles, ligaments, tendons, and so on. Altogether, these systems of bones and soft tissues, called joints, produce movement for the organism. Joint biomechanics traditionally is a division of biomechanics that studies the effect of forces on the joints of livin...

Wavelets are used for the processing of signals that are non-stationary and time varying. The electromyogram (EMG) contains transient signals related to muscle activity. Wavelet coefficients are proposed as features for identifying muscle fatigue. By observing the approximation coefficients it is shown that their amplitude follows closely the muscl...

Several finite element models have been developed for estimating the mechanical response of joint internal structures, where direct or indirect in vivo measurement is difficult or impossible. The quality of the predictions made by those models is largely dependent on the quality of the experimental data (e.g. load/displacement) used to drive them....