Comparison of frequency control concepts in isolated power systems with diesel generators and fully rated wind energy converters

Isolated power systems are usually small remote electrical power systems facing a range of technical challenges. Without possessing primary conventional energy resources of their own and being often situated long distances away from countries exporting fossil fuels, isolated power systems depend on expensive imports of primary energy for ensuring power generation. Integration of renewable energy sources would therefore seem to be both a practical and financially beneficial solution. Frequency stability is a crucial aspect for all electrical power systems. However, interconnected power systems have in comparison to isolated power systems the ability of maintaining frequency stable due to large conventional power plants and to power reserves, as well as mechanisms that prevent a system collapse in case of a sudden severe power loss. The isolated power systems mentioned in this thesis dispose usually an autonomous power station (APS) mostly comprised from diesel fired synchronous generators and some kind of renewable energy sources. Since this is the most usual case in this thesis, the challenge of ensuring frequency stability for this kind of IPSs is presented, analysed and further explored by proposing and comparing frequency control concepts improving dynamic system response. Primary and secondary frequency control in isolated power systems takes place in a different way as in interconnected power systems. Existing frequency control concepts are presented and two of them are selected. Their relation to the two most common used speed governors for diesel fired synchronous generators are implemented and tuned as well. With reference to several dynamic simulation events like load steps and three - phase short circuits, these frequency control concepts are compared before and after tuning, so as to be able to propose a best practice for a network operator of isolated power systems generally. Moreover, the integration of Renewable Energy Sources and especially of fully rated wind energy converters is further explored. The aim is to determine if the proposed frequency control concept presented and explored before the integration would have a further positive effect after the integration, or if a new frequency control concept should be considered. At last, a real case study validates the selected frequency control concept. IPS of Lesbos in Hellas has been modelled in detail and according to real data provided from the Hellenic electricity distribution network operator. The generalisation of conclusions enables proposing a frequency control concept for isolated power systems operators improving frequency stability

Dilemma: Organic Growth or Acquisition? A Greek Bank Crosses The Borders and Goes International. Two Case Studies: Acquisition in Serbia and Organic Growth in Albania. Compare and Construct

This paper intends to compare and contrast the strategy of organic growth against the one of acquisition in the case of a bank which decides to cross the borders and expand to foreign countries. In order to analyse this dilemma this study will examine which are the most important variables when an acquisition is under consideration, which are the factors that lead to the choice of organic growth, despite the fact that organic growth is most of the times translated into a slower paced growth and what is the role of the macroeconomic environment and the influence of the regulatory framework of each country. Furthermore, this paper discusses which are the most important data that a bank should take into account in order to make that decision and under which circumstances it is worth to take the chance to proceed to an acquisition or insist on organic growth. For that cause we will examine the case of Alpha Bank, which is a Greek bank and has faced this dilemma during its expansion to South East Europe

Prediction of Soil Moisture from Remote Sensing Data

AbstractThis study evaluates the capability of soil water content predicted from remote sensing to indicate the soil/canopy water content at short time and space scale, through comparisons with daily soil moisture data determined in situ, using dielectric devices. Daily aqua moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and the diurnal (daytime and night time) land surface temperature difference (DLST) are employed to retrieving daily volumetric soil moisture content (θ) at Sparta experimental station, during the period June-August, of the years 2010, 2011, 2012 and 2014. Using the concept of apparent thermal inertia (ATI) in the remotely sensed topsoil moisture saturation index, daily θ is obtained from DLST and the volumetric saturated and residual soil moisture content and is compared with the experimental values of volumetric soil moisture content (SM) measured at various depths (10, 20, 30, 40, 60, 80 and 100cm). Simple relationships are also calibrated between SM and ATI or DLST or NDVI during the years 2010, 2011 and 2014 and are tested for predicting θ, during the year 2012. Especially the three first models predict θ satisfactorily as compared with the measured SM and hence they can offer a considerable guidance in irrigated agriculture and other related fields

Burning Socrates’ School down with Aristophanes: Learning and Teaching under Clouds

In Clouds (Nubes) of Aristophanes, Socrates appears as a sophist school owner, the Phrontisterion (‘thinkery’), in which he hosts students of all ages, in order to teach them not only philosophy, literature, physics but also effective sophistic techniques. In Clouds opposed ideas can be found like the aims of historical Socrates’ educational method, combined with Sophists’ modern ones. Aristophanes by using specific educational techniques, points out the educational contrasts and disagreements (Just Cause Vs Unjust Cause) and highlights the chasm between the empty theoretical discourse of young intellectuals and the real educational practical needs (learning skills, practical adjustment etc.). In this comedy, Aristophanes deals with many educational issues, which are common in every culture. What is his goal, however, when he appears with the Socratic method of learning and teaching (use of initiation vocabulary and terminology, ‘borrowings’ from the philosophic activity at the Thinkery?) What are the benefits for an apprentice student at Aristophanes’ Socrates and what is the purpose of the critical view of Aristophanes educational system of his time

Successful management of acute thromboembolic disease complicated with heparin induced thrombocytopenia type II (HIT II): a case series

Heparin-induced thrombocytopenia type II (HIT II) is a rare immune-mediated complication of heparin. The diagnosis of HIT is considered in patients exposed to heparin, presenting with thrombocytopenia and thrombosis

Serum Levels of Surfactant Proteins in Patients with Combined Pulmonary Fibrosis and Emphysema (CPFE)

Introduction Emphysema and idiopathic pulmonary fibrosis (IPF) present either per se or coexist in combined pulmonary fibrosis and emphysema (CPFE). Serum surfactant proteins (SPs) A, B, C and D levels may reflect lung damage. We evaluated serum SP levels in healthy controls, emphysema, IPF, and CPFE patients and their associations to disease severity and survival. Methods 122 consecutive patients (31 emphysema, 62 IPF, and 29 CPFE) and 25 healthy controls underwent PFTs, ABG-measurements, 6MWT and chest HRCT. Serum levels of SPs were measured. Patients were followed-up for 1-year. Results SP-A and SP-D levels differed between groups (p = 0.006 and p= 26 ng/mL) presented a weak association with reduced survival (p = 0.05). Conclusion In conclusion, serum SP-A and SP-D levels were higher where fibrosis exists or coexists and related to disease severity, suggesting that serum SPs relate to alveolar damage in fibrotic lungs and may reflect either local overproduction or overleakage. The weak association between high levels of SP-B and survival needs further validation in clinical trials

The Role of Inflammation in Diabetes: Current Concepts and Future Perspectives

Diabetes is a complex metabolic disorder affecting the glucose status of the human body. Chronic hyperglycaemia related to diabetes is associated with end organ failure. The clinical relationship between diabetes and atherosclerotic cardiovascular disease is well established. This makes therapeutic approaches that simultaneously target diabetes and atherosclerotic disease an attractive area for research. The majority of people with diabetes fall into two broad pathogenetic categories, type 1 or type 2 diabetes. The role of obesity, adipose tissue, gut microbiota and pancreatic beta cell function in diabetes are under intensive scrutiny with several clinical trials to have been completed while more are in development. The emerging role of inflammation in both type 1 and type 2 diabetes (T1D and T1D) pathophysiology and associated metabolic disorders, has generated increasing interest in targeting inflammation to improve prevention and control of the disease. After an extensive review of the possible mechanisms that drive the metabolic pattern in T1D and T2D and the inflammatory pathways that are involved, it becomes ever clearer that future research should focus on a model of combined suppression for various inflammatory response pathways

Multidetector row CT for imaging the paediatric tracheobronchial tree

The introduction of multidetector row computed tomography (MDCT) scanners has altered the approach to imaging the paediatric thorax. In an environment where the rapid acquisition of CT data allows general hospitals to image children instead of referring them to specialist paediatric centres, it is vital that general radiologists have access to protocols appropriate for paediatric applications. Thus a dramatic reduction in the delivered radiation dose is ensured with optimal contrast bolus delivery and timing, and inappropriate repetition of the scans is avoided. This article focuses on the main principles of volumetric CT imaging that apply generically to all MDCT scanners. We describe the reconstruction techniques for imaging the paediatric thorax and the low-dose protocols used in our institution on a 16-slice detector CT scanner. Examples of the commonest clinical applications are also given