33 research outputs found
Improved transmission line protection performance concerning high resistance faults.
No full textThesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.ESKOM has relied primarily on impedance-based measurement protection relays for the protection of transmission lines. One of the main disadvantages of distance relays is the limited fault resistance measurement capability. High-resistance faults are characterised by low fault currents, therefore the impedance calculated would be much bigger and so the fault will appear to be beyond the protected line. The main aim of the study is to gain clear understanding of the capability of the existing relays used in Eskom Transmission network, to be able to give recommendations on the refinements to the transmission line protection philosophy required to improve future protection performance. Omicron relay tests, showed that the dynamic characteristics of the three selected relays which were tested covers more fault resistance than that of the normal static impedance and also that the effect of DC offset is negligible with regards to fault resistance measurement capability. Normally the relays have built in algorithms which are able to filter nuisance signals. Theoretical case study that compared the most used relays in Eskom Transmission was done and the results are documented. Settings recommendations to improve fault resistance coverage were deduced from the above study. Fault investigation by using digital simulations (Matlab simulations) has proven the lack of capability to operate for some impedance relays in some fault conditions, as the fault resistance sometimes moves fault impedance beyond relay characteristic even when actual . polarization of the relay is considered. Analysis of the protection performance in transmission proved that high resistance faults accounts for at least half of protection equipment performance index (PEPI) incidents. Finally the author made recommendations to improve the protection performance concerning high resistance faults
Plato, Machiavelli and machiavellism
No full textThroughout this paper the author questions Machiavelli’s Machiavellism, i.e. the position that Machiavelli’s political theory takes stance of immoralism. The first part of the paper compares Plato’s and Machiavelli’s political philosophy, analyzing differences as well as similarities between these two philosophers. Author finds Plato’s views on politics and political community more malignant than Machiavelli’s. Machiavelli’s views on politics, state, laws and liberty are in fact closer to the basic principles of liberalism then to the tenets of tyranny or totalitarianism. The second part of the paper deals with the concept of the autonomy of politics and the use of cruelties and evils as the instruments of rule in Machiavelli’s work. In this part of the paper, author denies that Machiavelli was the philosopher of evil or the proponent of political gangsterism
Benchmark footbridge for vibration serviceability assessment under the vertical component of pedestrian load
No full textThis is the author accepted manuscript. The final version is available from American Society of Civil Engineers via the DOI in this recordData availability: the electronic format of the data used is available at www.warwick.ac.uk/go/civileng/crg/structures/publications/dataVibration serviceability criteria are governing the design and determining the cost of modern, slender footbridges. Efficient and reliable evaluation of dynamic performance of these structures usually requires a detailed insight into the structural behavior under human-induced dynamic loading. Design procedures are becoming ever more sophisticated and versatile, and for their successful use, a thorough verification on a range of structures is required. The verification is currently hampered by a lack of experimental data that are presented in the form directly usable in the verification process. This study presents a comprehensive experimental data set acquired on a box-girder footbridge that is lively in the vertical direction. The data are acquired under normal operating conditions and are presented using a range of descriptors suitable for easy extraction of desired information. This will allow researchers and designers to use this bridge as a benchmark structure for vibration serviceability checks under the vertical component of the pedestrian loading. In addition, capabilities of a sophisticated force model (developed for walking over rigid surfaces) to predict vibrations on this lively bridge are investigated. It was found that there are discrepancies between computed and measured responses. These differences most likely are a consequence of the pedestrian-structure interaction on this lively bridge. The interaction was then quantified in the form of pedestrian contribution to the overall damping of the human-structure system. © 2012 American Society of Civil Engineers.Engineering and Physical Sciences Research Council (EPSRC
NAUČNO - STRUČNI DISKURS ENGLESKOG JEZIKA U REGISTRU SPORTA
No full textRhetorics is in the lime light again because the orator is attracting the attention of the audience when creating texts using scientific style that noone could use before (E. Hinkel, 2002). It is almost compulsory to publish widely scientific articles and papers in English if the author claims to be accepted by his respective academic discourse community. Many an author has been diminished by the panel of scientific referees and reviewers who decide on the acceptability of the paper. This norm of publishing in English starts a race that is usually dictated by the anglosaxon norms of writing. That is why we have to find out the norms of writing so that they can be taught and transferred to our students
NAUČNO - STRUČNI DISKURS ENGLESKOG JEZIKA U REGISTRU SPORTA
No full textRhetorics is in the lime light again because the orator is attracting the attention of the audience when creating texts using scientific style that noone could use before (E. Hinkel, 2002). It is almost compulsory to publish widely scientific articles and papers in English if the author claims to be accepted by his respective academic discourse community. Many an author has been diminished by the panel of scientific referees and reviewers who decide on the acceptability of the paper. This norm of publishing in English starts a race that is usually dictated by the anglosaxon norms of writing. That is why we have to find out the norms of writing so that they can be taught and transferred to our students
Comparative analysis of the efficacy and biocompatibility of various methods of dialysis
No full textBackground/Aim. The efficacy and biocompatibility of hemodialysis have a singnificant impact on dialysis patient morbidity and mortality rate. The aim of our study was to compare the efficacy and biocompatibility of different hemodialysis modalities in our patients. Methods. A total of 55 patients were included in the study, and on the basis of dialysis modality, they were divided in four groups: group I - postdilution on-line hemodiafiltration (n = 15), group II - bicarbonate high-flux polysulphone hemodialysis (n = 15), group III - bicarbonate low-flux polysulphone hemodialysis (n = 15), and groupe IV - bicarbonate cuprophane hemodialysis (n = 10). The efficacy was evaluated on the basis of urea reduction rate (URR), urea Kt/V index and serum β2-microglobuline reduction rate, and the biocompatibility was evaluated on the basis of the leukocyte count fall during the first fifteen minutes of dialysis session, and of the serum C-reactive protein (CRP) level. Results. The highest mean URR was achieved in the group I (70.53 ± 6.49 %), and it was significantly higher in comparison with the average URR in the group IV (54.8 ± 6.35%) (p = 0.001). The average value of urea Kt/V index in the group I (1.48 ± 0.22) was significantly higher in comparison with the average value in the groupe II 1.30 ± 0.22 (p < 0.05), group III (1.05 ± 0.22), and group IV (0.98 + 0.22) (p = 0.001). Serum β2-microglobuline reduction rate was 68.93 ± 8.25% in the group I, and 58.86 ± 7.98% in the groupe II (p = 0.01). During the first 15 minutes of hemodialysis the leukocyte number was decreased by 12.57 ± 9.35% in the group I, 13.61 ± 9.64% in the group II, 18.3 ± 13.24 in the group III and 62.3 ± 15.4 in the group IV, on average. The mean serum level of CRP was 9.4 ± 6.47 mg/l in the group IV, and less than 3.5 mg/l in the group I of the patients (p = 0.001). Conclusion. Postdilution on-line hemodiafiltration in comparison with standard hemodialysis provided the more effective elimination of small and middle uremic toxins molecules and a significantly higher degree of biocompatibility. The patients treated with standard hemodialysis frequently do not achieve the minimal value of urea Kt/V index prescribed by National Kidney Foundation - Dialysis Outcomes Quality Inatiatives standards. These patients also have significantly higher serum CRP values which suggest the state of chronic microinflammation
Temperature-Compensated Microstrip Antenna for Ice Measurement and Wireless Sensor Network
No full textRÉSUMÉ: L'objectif principal de cette thèse est de concevoir et de développer une technique de compensation de température liée à la fréquence de résonance d'une antenne microruban. Une telle antenne microruban compensée en température, capable de résister à une variation importante de température, est utilisée comme une partie d'un capteur pour mesurer l'épaisseur de la charge de la glace. Les antennes microruban conçues de cette manière sont utilisées dans un réseau de capteurs de température sans fil en relation avec ses applications critiques d'un système de dégivrage d'hélicoptère. Un prototype de réseau de capteurs de température sans fil qui contrôle à distance la mise en marche ou l'arrêt des appareils de chauffage destinés au dégivrage est développé. Parmi toutes les autres antennes, l'antenne microruban est sélectionnée en raison de sa polyvalence. Aussi, sa fréquence de résonance souffre d'un problème de stabilité due à sa susceptibilité à des facteurs externes tels que les fluctuations de température. En plus, sa résonance provoquant une largeur de bande de fréquence étroite ne conduit pas à une solution directement préférée. Pour minimiser l'instabilité de fréquence induite par la température et aussi pour éviter de perdre le signal ou les interférences des canaux adjacents, on a besoin de développer une technique de compensation de température très efficace et pratique. Dans ce travail, une technique de compensation de la température efficace et pratique est conçue pour les antennes microruban. La technique de compensation imagée est supérieure à la technique existante, tant dans sa simplicité que dans sa stabilité en fréquence. A notre, connaissance, rien de semblable n'a été fait auparavant. Pour la première fois, la dépendance de la fréquence de résonance de l'antenne microruban en fonction de la température est étudiée à l'aide d'une formulation mathématique de la déviation de fréquence pour les géométries rectangulaires, circulaires et triangulaires. Le modèle de circuit est adopté pour l'analyse de l'impact de la température sur la fréquence de résonance de l'antenne microruban appropriée pour les procédures de CAO (conception assistée par ordinateur). Les simulations électromagnétiques sur les résultats de la théorie de déviation du modèle de circuit adopté. Les résultats de l'impact de la température sur la dérive de fréquence des antennes microruban résonnant à 2,4 GHz modélisées sur différents substrats sont présentés et comparés. ABSTRACT: The primary goal of this thesis is to devise and develop a technique of temperature compensation related to the resonant frequency of a microstrip patch antenna (MPA). Such a temperature-compensated microstrip patch antenna capable of standing against a substantial variation of temperature is exploited as part of an ice-sensor for measuring ice loading thickness. Microstrip antennas designed in this way are used in a wireless temperature sensor network in connection with its critical applications of a helicopter de-icing system. A prototype of wireless temperature sensor network which remotely controls turning-on or turning-off heaters intended for de-icing is developed. Among all other antennas, the microstrip antenna is selected due to its versatility. Thanks to the susceptibility of the microstrip patch antenna to external factors, such as temperature fluctuations, its resonant frequency suffers from a stability issue. In addition to that, its resonance causing a narrow frequency bandwidth does not lead to a straightforwardly preferred solution. To minimize the temperature-induced frequency instability and also to prevent losing signal or interferences from adjacent channels, one needs to develop a very efficient and practical temperature compensation technique. In this work, an efficient and practical technique through a resonant frequency temperature compensation for microstrip patch antennas is devised, which is superior to existing counterparts both in its simplicity and frequency stability. To the best of the author`s knowledge, nothing similar was done before. For the first time, a temperature dependence of microstrip antenna resonant frequency is investigated through a mathematical formulation of frequency drift for rectangular, circular, and triangular patch geometries. The circuit model for analyzing temperature impact on microstrip antenna resonant frequency suitable for computer-aided design (CAD) procedures is adopted. Electromagnetic simulations along with results of the adopted circuit model support the derived theory. Results of temperature impact on the frequency drift of microstrip antennas resonant at 2.4 GHz modelled on different substrates are shown and compared. Analysis, simulation, and experimental results show that antennas built on thicker substrates exhibit a better temperature behaviour of the resonant frequency. Based on a theoretically formulated frequency drift, a temperature compensation condition for the rectangular patch geometry of MPA is derived
Heart failure with preserved left ventricular ejection fraction in patients undergoing hemodialysis
No full textAssociation between age and cardiovascular status by echosonography in asymptomatic predialysis patients with chronic kidney disease
No full textAge is an important risk factor for cardiovascular disease in the general population and in dialysis patients. The aim of this study is to investigate the influence of age on the cardiovascular status of asymptomatic predialysis patients with chronic kidney disease (CKD). Echocardiography and carotid ultrasound were performed in 61 patients with CKD stages 4–5, who were divided by age into two groups: group 1 (≥65 years, n = 31) and group 2 (<65 years, n = 30). Data were compared with those of control group (≥65 years, n = 20). Group 1 patients had significantly higher left ventricular mass index (LVMI), (P <0.001), worse LV diastolic function (lower E/A ratio: P<0.05, E’ velocities: P< 0.001, E’/A’ ratio: P <0.001, and a higher ratio E/E’: P <0.05) and a higher prevalence of aortic (P <0.01) and mitral calcification (P <0.001) compared to group 2 patients. Elderly patients also had significantly increased intima-media thickness (IMT, P <0.001) and a greater prevalence of carotid plaques (P <0.05) and calcifications (P <0.001) than younger patients. Multiple regression analysis showed that IMT, LVMI, and E/A ratio were independent variables associated with aging (R2 = 0.605). We concluded that older CKD patients demonstrated more profound structural and functional abnormalities of the myocardium, as well as more prominent vascular changes compared to younger CKD patients. The changes in IMT, LVMI, and E/A ratio are independently associated with aging of CKD patients
