Webometrics benefitting from web mining? An investigation of methods and applications of two research fields

Webometrics and web mining are two fields where research is focused on quantitative analyses of the web. This literature review outlines definitions of the fields, and then focuses on their methods and applications. It also discusses the potential of closer contact and collaboration between them. A key difference between the fields is that webometrics has focused on exploratory studies, whereas web mining has been dominated by studies focusing on development of methods and algorithms. Differences in type of data can also be seen, with webometrics more focused on analyses of the structure of the web and web mining more focused on web content and usage, even though both fields have been embracing the possibilities of user generated content. It is concluded that research problems where big data is needed can benefit from collaboration between webometricians, with their tradition of exploratory studies, and web miners, with their tradition of developing methods and algorithms

Barrier diameter effect on the behaviour of transformer oil submitted to AC voltage

International audienceDielectric interfaces can have a significant effect on the insulating performances of HV apparatus. The oil/solid interface represents a relatively weak component of an insulation system in power transformer. Therefore, when we are considering the effect of oil breakdown in oil filled transformer, we should consider the interactions which electrical discharges may have with solid surfaces. This work is devoted to the influence of insulating barrier on the behaviour of transformer oil under ac voltage in point-plane electrode configuration. The influence of the characteristics of barrier such as its position between electrodes, and its diameter on the pre-breakdown and breakdown phenomena is investigated. It is shown that the insertion of barrier near the point electrode increases the breakdown voltage and leads to decrease the pre-breakdown charge. The increase of breakdown voltage is due to the channel elongation of the disruptive charge. By determination of the pre-breakdown charge and breakdown voltage, we can estimate the optimal position of the barrier. The barrier diameter influences the breakdown voltage, the pre-breakdown charge and the trajectory of discharge

Pre-breakdown current in long point-plane transformer oil gaps with insulating barrier under AC voltage

International audienceIn this paper we present results of carried out investigations on the influence of insulating barriers on AC prebreakdown current of long point-plane transformer oil gaps up to 12cm. The insertion of an insulating barrier leads to an important prebreakdown current decrease. The barrier acts as a geometrical and electrostatic obstacle for the disruptive discharge. We present in the paper a comparison between the prebreakdown current in the system with barrier to that one without barrier. We have considered the parameters of the barrier such as its position between the electrodes, and its nature. We observe that the evolution of the pre-breakdown current versus the applied voltage has a capacitive behavior. The equivalent impedance of the oil gap is deduced from the experimental current-voltage characteristics

Determination of the capacitance of long transformer oil gaps with insulating barriers

International audienceThis work is aimed at the effect of insulating barriers on the variation of the capacitance of long transformer oil gap systems submitted to AC Voltage. The tests are carried out in point-plane electrode arrangement by considering the influence of the parameters of barriers such as its position with respect to the electrodes and its thickness. The capacitances of the system with barrier and that one without barrier are compared. It’s shown that the evolution of the pre-breakdown charge versus the applied voltage has a capacitive behavior. The insertion of barrier increases the capacitance of the system resulting in a decrease of the impedance of the system. The determination of the capacitance provides a correlation between the electrical charge and the dielectric strength

Barrier effect on breakdown of point-plane oil gaps under alternating current voltage

International audienceThis study deals with the influence of insulating barriers on AC dielectric strength of transformer oil in point-plane electrode configuration. The influence of the characteristics of barrier such as its position with regard to the point electrode, its thickness and dimension as well as its constituting material is investigated. It is shown that the insertion of barrier near the point electrode generally leads to the increase of breakdown voltage; this later also increases with the dimensions of barrier. The optimal position of barrier is at about 20% of gap starting from the sharp electrode (i.e. the point). The barrier acts as a geometrical obstacle against the direct propagation of discharge. There is an equivalency between distances of systems with barrier and without barrier

Effective web log mining and online navigational pattern prediction

NoAccurate web log mining results and efficient online navigational pattern prediction are undeniably crucial for tuning up websites and consequently helping in visitors' retention. Like any other data mining task, web log mining starts with data cleaning and preparation and it ends up discovering some hidden knowledge which cannot be extracted using conventional methods. In order for this process to yield good results it has to rely on some good quality input data. Therefore, more focus in this process should be on data cleaning and pre-processing. On the other hand, one of the challenges facing online prediction is scalability. As a result any improvement in the efficiency of online prediction solutions is more than necessary. As a response to the aforementioned concerns we are proposing an enhancement to the web log mining process and to the online navigational pattern prediction. Our contribution contains three different components. First, we are proposing a refined time-out based heuristic for session identification. Second, we are suggesting the usage of a specific density based algorithm for navigational pattern discovery. Finally, a new approach for efficient online prediction is also suggested. The conducted experiments demonstrate the applicability and effectiveness of the proposed approach. (C) 2013 Elsevier B.V. All rights reserved

Transformer oil reclamation by combining several strategies enhanced by the use of four adsorbents

From an environmental perspective, petroleum-based aged oils removed from power transformers are source of several pollutants and therefore cannot be disposed of without due care. The degradation of oil in in-service transformers is due to various factors concurrent with the operation of the units over several years. The present study proposes a new strategy to rejuvenate used mineral oils by combining centrifugation, dehydration and sorption with four different adsorbents: activated carbon (ACH), silica gel (SG), magnesium oxide (MO) and activated bentonite (AB). The process of regeneration proposed in this study resulted in a level of restoration that saw the used oil take on the characteristics of new oil (colour, dissipation factor, resistivity, permittivity, acid number). The results also showed that the optimum form of the re-refined base oil can be attributed to a 10% (w/w) quaternary mixture of the adsorbents, itself comprised of 1% ACH, 6% SG, 1% MO and 2% AB. The anticipated benefits are reduced risk of dielectric breakdown blamed for over 75% of extra high-voltage (EHV) power transformer failures and extended transformer life expectancy by retarding the solid insulation aging processes