Balancing The Budget Through Revenue or Spending Adjustments? The Case of Greece

Panagiotis T. Konstantinou 중앙대학교 경제연구소 2004 Journal of Economic Development Vol.29 No.2

This paper examines the solvency of the Greek fiscal policy. Employing a cointegrated VAR as a benchmark, evidence of a long-run link between revenues and spending is presented, although intertemporal solvency is violated. Utilizing Granger-causality tests, a test for fiscal adjustment neutrality and Generalized Impulse Responses, this paper provides evidence in favor of the ‘tax and spend’ hypothesis for Greece. Additionally, the empirical evidence indicates that fiscal adjustment should take place through spending rather than revenue adjustment.

Operation of a Modular Multilevel Converter with Selective Harmonic Elimination PWM

Georgios S. Konstantinou,Mihai Ciobotaru,Vassilios G. Agelidis 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

The modular multilevel converter (MMC) is based on the cascaded interconnection of half-bridge switching sub-modules and features modular characteristics that allow its expandability while providing high quality voltage and current output waveforms and removing the need for filtering. The switching frequency of each of the individual converter sub modules being maintained low and the balancing of the capacitor voltages are important requirements for the operation of the converter. Two different modulation approaches of the converter are discussed. Selected simulation and experimental results taken from a low-power laboratory prototype are presented.

Grid-Converter Stability Analysis Based on Bus Admittance Phase

Shan Jiang,Georgios Konstantinou 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-

Impedance-based stability analysis method is widely used for stability demonstration of interconnected converter systems. Prior work dominantly adopts the minor-loop gain, also known as the return-ratio matrix (RRM), as the stability indicator. However, this approach complicates the analysis by relying on both the magnitude and phase information. By alternatively selecting the total bus admittance as the stability indicator, this paper demonstrates that the number of phase shifting points (purely based on the phase information) in the eigenloci of total bus admittance, directly reflects the overall system stability for any interconnected converter system. Moreover, this paper establishes the relationship between the proposed method and two existing methods, i.e. the RRM-based method and passivity theory. The proposed method overcomes the conservative nature of the passivity theory and is effective for the stability analysis of non-minimum phase systems, where the RRM-based method cannot be directly applied. The comparative study is validated by the control hardware-in-the-loop model of an interconnected converter system.

Influence of heat treatment on the microstructure and the physical and mechanical properties of dental highly translucent zirconia

Konstantinos Dimitriadis,Athanasios Konstantinou Sfikas,Spyros Kamnis,Pepie Tsolka,Simeon Agathopoulos 대한치과보철학회 2022 The Journal of Advanced Prosthodontics Vol.14 No.2

PURPOSE. Microstructural and physico-mechanical characterization of highly translucent zirconia, prepared by milling technology (CAD-CAM) and repeated firing cycles, was the main aim of this in vitro study. MATERIALS AND METHODS. Two groups of samples of two commercial highly-translucent yttria-stabilized dental zirconia, VITA YZ-HTWhite (Group A) and Zolid HT + White (Group B), with dimensions according to the ISO 6872 “Dentistry - Ceramic materials”, were prepared. The specimens of each group were divided into two subgroups. The specimens of the first subgroups (Group A1 and Group B1) were merely the sintered specimens. The specimens of the second subgroups (Group A2 and Group B2) were subjected to 4 heat treatment cycles. The microstructural features (microstructure, density, grain size, crystalline phases, and crystallite size) and four mechanical properties (flexural strength, modulus of elasticity, Vickers hardness, and fracture toughness) of the subgroups (i.e. before and after heat treatment) were compared. The statistical significance between the subgroups (A1/A2, and B1/B2) was evaluated by the t-test. In all tests, P values smaller than 5% were considered statistically significant. RESULTS. A homogenous microstructure, with no residual porosity and grains sized between 500 and 450 nm for group A and B, respectively, was observed. Crystalline yttria-stabilized tetragonal zirconia was exclusively registered in the X-ray diffractograms. The mechanical properties decreased after the heat treatment procedure, but the differences were not statistically significant. CONCLUSION. The produced zirconia ceramic materials can be safely (i.e., according to the ISO 6872) used in extensive fixed prosthetic restorations, such as substructure ceramics for three-unit prostheses involving the molar restoration and substructure ceramics for prostheses involving four or more units. Consequently, milling technology is an effective manufacturing technology for producing zirconia substructures for dental fixed all-ceramic prosthetic restorations.

Evaluation of Arm Reliability in Modular Multilevel Converters with Multiple Sub-modules for MVDC Applications

Yumeng Tian,Georgios Konstantinou 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-

Since the reduced number of sub-modules (SMs) in modular multilevel converters (MMCs) for medium-voltage DC (MVDC) applications cannot provide the same redundant design as high-voltage DC (HVDC) systems, reliability becomes a significant issue in MVDC systems. To evaluate the reliability performance of converters, arm reliability in MMC requires to be analysed and the design of redundancy can be further optimised. Considering the number of redundant SMs, redundancy operation schemes, and correlation coefficient between SMs, arm reliability are analysed in MMC for MVDC systems with multiple SM topologies. The aim of this paper is to provide a comprehensive evaluation of arm reliability in MMC with multiple SMs and identify the high-reliability options for SMs in different scenarios for MVDC applications.

Power-Flow-Related Admittance Characterization of Two-Level and Modular Multilevel Converters

Ye Zhu,Shan Jiang,Georgios Konstantinou 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-

This paper investigates and compares the admittance shaping effects of power flow in two-level converters and modular multilevel converters (MMCs), based on sequence admittance models. Due to the significant harmonic coupling in the MMC and the linearization in the small-signal modeling process, the steady-state harmonics of the state variables, which are influenced by power flow, are included in the MMC model. It is demonstrated that the low-frequency admittance of the MMC changes with power flow, because of the power-variant steady-state harmonics in the impedance model. This is different to the low-frequency admittance of two-level converters, which is independent of power. The phase-locked loop has the same admittance shaping effect on both converters around the fundamental frequency, dominated by the fundamental component in the output current. Based on the analysis, stable operation area maps for both converters are defined to demonstrate the stability influence of power flow, further validated by simulation case studies. Understanding the converter characteristics under different power flow can help to facilitate the controller design to guarantee system stability, especially in MMCs due to their internal dynamics.

Decoupled Sequential Power Flow Study in MT-MVDC Distribution Systems based on Novel NR/Estimation-Correction Algorithm

Pingyang Sun,Rongcheng Wu,Gen Li,Muhammad Khalid,Graham Town,Georgios Konstantinou 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-

In order to address the gap in comprehensive power flow (PF) analysis of multi-terminal medium-voltage direct current (MT-MVDC) distribution systems, this paper proposes a novel decoupled sequential PF algorithm based on Newton- Raphson (NR)/estimation-correction method. The presented algorithm is designed for an MT-MVDC distribution network and takes into account the PF equations of both generic ac/dc and dc/dc converters. The MVDC PF study is the main focus and the power losses of voltage source converters (VSCs) & dc/dc converters are considered for accurately deriving the dc powers at MVDC links. The proposed algorithm only requires to define a single dc power or current bus type, hence the bus type definition is simplified and the solution of multiple sub-Jacobian matrices can be avoided. A binary search method is employed to correct the estimated initial dc power/current values, which contributes to the searching time reduction. Although an external correction iteration is required in the dc PF derivation, the proposed algorithm still improves on the computation efficiency in comparison with coupled sequential ac/dc PF algorithms. An MT-MVDC distribution network incorporated into IEEE 14 bus system verifies the validity and efficiency of the proposed algorithm.

Reinforcement of Power System Performance Through Optimal Allotment of Distributed Generators Using Metaheuristic Optimization Algorithms

Mirsaeidi Sohrab,Li Shangru,Devkota Subash,He Jinghan,Li Meng,Wang Xiaojun,Konstantinou Charalambos,Said Dalila Mat,Muttaqi Kashem M. 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.5

Owing to the acute shortage of electric power in the majority of countries, short-term measures such as installation of Distributed Generators (DGs) have attracted much attention in recent decades. Employment of DGs can provide numerous advantages for the power systems through reduction of losses, escalation of the voltage profi le, as well as mitigation of pollutant emissions. However, in case they are not optimally allotted, they may even lead to aggravation of the network operation from diff erent aspects. The aim of this paper is to explore the optimal size and location of DGs using metaheuristic optimization algorithms so that the network performance is enhanced. The salient feature of the proposed strategy compared to the previous works is that it contemplates optimal allotment of DGs under various objectives, i.e. minimization of total network active and reactive power losses, and Cumulative Voltage Deviation (CVD), with diff erent weight values. Furthermore, the impact of enhancement in the number of DGs on diff erent aspects of power system performance is investigated. Finally, to increase the accuracy of the results, three diff erent nature-inspired optimization algorithms, i.e. Genetic Algorithm (GA), Grey Wolf Optimizer (GWO), and Particle Swarm Optimization (PSO) are deployed, and their speed in approaching the global optimum is compared with each other. The simulation results on IEEE 14-bus system indicate that the proposed strategy not only can reinforce the overall network performance through reduction of active and reactive power losses, and voltage deviation but also lead to the improvement of network voltage profi le.

Impact of HER2 and PTEN Simultaneous Deregulation in Non-small Cell Lung Carcinoma: Correlation with Biological Behavior

Panagiotou, Ioannis,Georgiannos, Stavros N.,Tsiambas, Evangelos,Karameris, Andreas,Konstantinou, Marios,Lazaris, Andreas C.,Kavantzas, Nikolaos,Vilaras, George,Patsouris, Efstratios Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.12

Background: HER2/neu overexpression due to gene amplification is an important factor in breast cancer, modifying the sensitivity to anti-HER2 monoclonal antibody therapy. The clinical significance of HER2 expression in non small cell lung carcinoma (NSCLC) is currently under evaluation. The tumor suppressor gene PTEN negatively regulates the HER2/PI3K/Akt signalling pathway. The purpose of this study was to evaluate the role of simultaneous alteration in HER2 and PTEN protein expression in relation to biological behaviour of NSCLCs. Materials and Methods: Protein expression was determined by immunohistochemistry in sixty-one (n=61) NSCLC cases along with CISH for HER2 gene analysis and detection of chromosome 17 aneuploidy. Patients were followed-up for a period of 34 to 41 months after surgery. Results: HER2 overexpression (2+/3+score) was detected in 17 (27.9%) patients while loss of PTEN expression was observed in 24 (39.3%) cases, low expression in 29 (47.6%) and overexpression in 8 (13.1%). Simultaneous HER2 overexpression and PTEN low/loss of expression were correlated with metastasis (71.4% vs 36.2% p=0.03). Analysis in the subgroup of 22 patients of pTNM stage III with lymph node status N1 or N2 revealed that there was a relationship between the number of positive regional lymph node groups and simultaneous deregulation of the two genes (p=0.04). Multivariate analysis determined that HER2 overexpression was associated with an increasing risk of developing metastases (OR: 4.3; 95%CI: 1.2-15.9; p: 0.03) while PTEN overexpression was associated with lower risk (OR: 0.1; 95%CI: 0.1, 1.0; p: 0.05). Conclusions: Simultaneous HER2/PTEN deregulation is a significant genetic event that leads to a more aggressive phenotype of NSCLC.

Thermal Performance of Modular Multilevel Converters in HVDC Applications under Offset PWM

Harith R. Wickramasinghe,Weiyao Wang,Ke Ma,Georgios Konstantinou 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

The total number of submodules (SMs) in a modular multilevel converter (MMC) can be utilized by considering an offset in the arm currents in order always operate at the maximum duty cycle. This article presents the thermal performance of an MMC for an HVDC application when considering its operation under offset PWM. It is demonstrated that the reduction of the total energy in the SM capacitors and the improved performance under faults with lower overall losses but with a variation in the distribution of losses among the devices within an SM. Simulation results based on detailed thermal models as well as experimental cases with thermal behavior demonstrate the impact of offset PWM in an MMC for HVDC applications.