1,721,173 research outputs found
Unfolding Low-Energy Gamma-Ray Spectrum Obtained with NaI(Tl) in Air Using Matrix Inversion Method
No full textMatrix inversion method is presented to unfold the gamma-ray spectrum obtained with an NaI(Tl) detector using several standard gamma-ray sources. The method is based on response matrix generated by Monte Carlo simulation of mono-energy gamma-ray photon ranging from 10 keV to 1 MeV in step of 10 keV. The comparison of the measured and simulated response function was also performed in order to validate the simulation response function. Good agreement was achieved around the photo-peak region of the spectrum, but slight deviation was observed at low energy region especially at Compton continuum region. The Compton continuum count was significantly transferred into the corresponding photo-peak and consequently the peak to background ratio was improved substantially by the application of the unfolding method. Therefore, small peak can be identified and analyzed that would otherwise be lost in the background
Identification of partial discharge sources and their location within high voltage transformer windings
No full textThis thesis is concerned with developing a new approach to high voltage transformers condition monitoring, which involve partial discharge (PD) measurement and localisation within high-voltage transformer windings. This is an important source of information for both diagnosis and prognosis of the health of power transformers. Generally, Partial discharges (PDs) existence in transformer windings are normally due to ageing processes, operational over stressing or defects introduced during manufacture. Although, the presence of PDs does not necessarily indicate imminent failure of a transformer, it is however, a serious insulation degradation or ageing mechanism which can be considered as a precursor of transformer failure. The initial approach taken in this thesis is based on a lumped parameter network model. The model was created and its parameters were approximated using analytical solutions based on the geometrical dimensions of transformer windings. Based on the lumped parameter network model, theoretically the rational function should be a positive-real (PR) function and it is shown later on in this thesis that the model does hold the theoretical assumptions. Nevertheless, impulse response of actual transformer windings constructed for laboratory assessment was shown differently although different methods were used to find rational functions with positive-real (PR). Due to the fact that real transformer windings do not hold the characteristic of positive real transfer function, thus, this thesis finds an alternative and proposes a different approach for PD localisation which is based on energy distribution and features extraction methods for localisation, particularly Wavelet Transform (WT) and Principal Component Analysis (PCA). The idea of the developed approach is based on the fact that any discharge occurring at any point along windings produce an electrical signal that will propagate as a travelling wave towards both ends of the windings. During the propagation of the PD signals along transformer windings, the response with respect to the propagation path taken and termination characteristics will cause attenuation and distortion to the waveforms, ultimately produced changes in the energy characteristics of the PD pulses when they reach measurement sensors
Reynolds number effect on 3D turbulent offset jet reattaching to a free surface
No full textExperimental study was carried out to investigate the effect of Reynolds number on 3D offset jet reattaching to above free surface. Sharp edged square nozzle was used to produce the jets, and the measurements were performed at the following six different Reynolds numbers: 2300, 3700, 5100, 7900, 10300 and 11900. Detailed velocity measurements were made in the symmetry plane. From the PIV data, the mean velocity and turbulence statistics were obtained to study the effects of Reynolds number on the salient features of the jet flow. Preliminary results on streamwise mean velocity decay along the nozzle centerline, contours of streamwise mean velocity and Reynolds shear stress are presented herein
Partial discharge propagation inside a high voltage transformer winding: comparison of measurement and simulation
No full textPartial discharge (PD) analysis, based on measurement data, assumes that PD signals propagate inside a transformer winding from the PD source to the measurement points. In this paper, signals are injected via an external connection into specific points along the winding of a transformer experimental model. The measurement data obtained using radio frequency current transducers (RFCT) connected to the external bushing tap and the neutral to earth connections are illustrative of the propagation of signals inside a transformer winding. Thus, this paper reports on the development of a simulation model based on a lumped parameter network approach and compares simulation results with experimental measurements of PD signal propagation inside a high voltage transformer winding model. The physical model is an interleaved disc type winding which consists of eight sections and is modeled as having internal winding series resistances (R), inductances (L), series capacitances (K) and shunt capacitances (Cg), the model also includes the effect of their mutual inductances. The parameters are calculated using analytical calculations based on geometrical dimensions and the winding is modeled using a commercially available mathematics package. The simulation creates PD signals at both ends of the winding i.e. at terminal 1 and terminal 8, which are grounded through a small capacitive and resistive element to represent the bushing end and neutral to earth connection respectively. An experiment has been developed that can be used to validate the simulation data and hence determine the accuracy of the derived model and ultimately its use as a PD localisation approac
A small gamma camera combined with a uniformly redundant array (URA) collimator: the performance comparison with a pinhole gamma camera
No full textComparative study of partial discharge localisation techniques within transformer windings
Full text linkPartial discharge (PD) activity may occur inside power transformers and the existence of this activity produces a negative effect on the transformer until eventually there is catastrophic failure. Therefore, partial discharge detection and measurement within a transformer winding have become an important research area to provide asset health information enabling the maintenance and replacement processes to be carried out effectively. A modern condition monitoring system for PD activity inside HV transformers may use any observable phenomena but here we concentrate on an electrical detection method. The fundamental localization technique uses wavelet multi-resolution analysis for calculating the energy at different frequency ranges and Principal Component Analysis as dimensional reduction tool that produces the output that ultimately can be used as an indicator of PD location inside a transformer winding. However, an alternative method has been developed to using corresponding 3 dimensional filters to enable the localisation process. Both approaches are compared and obtained results are presented in this paper
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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