Partial discharge behavior under operational and anomalous conditions in HVDC systems

Power cables undergo various types of overstressing conditions during their operation that influence the integrity of their insulation systems. This causes accelerated ageing and might lead to their premature failure in severe cases. This paper presents an investigation of the impacts of various dynamic electric fields produced by ripples, polarity reversal and transient switching impulses on partial discharge (PD) activity within solid dielectrics with the aim of considering such phenomena in high voltage direct current (HVDC) cable systems. Appropriate terminal voltages of a generic HVDC converter were reproduced - with different harmonic contaminations - and applied to the test samples. The effects of systematic operational polarity reversal and superimposed switching impulses with the possibility of transient polarity reversal were also studied in this investigation. The experimental results show that the PD is greatly affected by the dynamic changes of electric field represented by polarity reversal, ripples and switching. The findings of this study will assist in understanding the behaviour of PDs under HVDC conditions and would be of interest to asset managers considering the effects of such conditions on the insulation diagnostics

Wound healing properties of Eucheuma cottonii extracts in Sprague-Dawley rats.

Wounds are unavoidable events of life and arise due to agents that induce stress or injury. Wound has been a menace the world over and healing is a survival mechanism and represents an adaptation to the maintenance of normal anatomical structure and function. The objective of this study was to evaluate the potential wound healing properties of ethanolic and aqueous extracts of Eucheuma cottonii. A two centimeter diameter of skin excision wound was made on normal rats. Treatment with honey (100 mg/kg body weight) was used as positive control and untreated rats as the negative control groups. Inflammation and proliferation phases of wound healing including wound contraction, re-epithelization and granulation tissue development were monitored. This study showed that both seaweed extracts increased the rate of wound contraction compared with the positive and negative control. Ethanolic extract of E. cottonii was more effective than the aqueous extract by 20% (P<0.05). Histopathological findings showed the ethanolic extracts enhanced epithelization and tissue granulation significantly compared with both control groups. E. cottonii possesses several antioxidant compounds, which may be responsible for the accelerated wound healing. The present study demonstrated that these seaweed extracts accelerated healing better if not comparable with honey

Fully automatic segmentation of left ventricle in a sequence of echocardiography images of one cardiac cycle by dynamic directional vector field convolution (DDVFC) method and manifold learning

In this paper, an automatic method for segmentation of the left ventricle in two-dimensional (2D) echocardiography images of one cardiac cycle is proposed. In the first step of this method, using a mean image of a sequence of echocardiography images and its statistical properties the approximate region of left ventricle (LV) is extracted. Then the coordinate of extracted rectangular (ROI) is applied on all frames of sequences automatically. The mean image extracted ROI is used for defining the initial contour by scanning from the center point in polar coordinate. In the next step, all the extracted ROIs from the frames are mapped in a 2D space using the nonlinear dimension reduction manifold learning method. Using the properties of the manifold map end diastole (ED) and end systole (ES) frames are determined. Segmentation of the frames begins from ES frame, utilizing the dynamic directional vector field convolution (DDVFC) level set method with the initial contour as mentioned above. Final contour of each segmented frame is used as the initial contour of the next frame. Maximum range of the active contour motion is limited by a percent of the Euclidean distance between the point corresponds the current frame and the previous one in the resultant manifold. The results obtained from our method are quantitatively evaluated to those obtained by the gold contours drawn by a cardiologist on 489 echocardiographic images of seven volunteers using four distance measures: Hausdorff distance, average distance, area difference and area coverage error. We have also compared our results with the results of applying only DDVFC method. Comparing the implementation of only the DDVFC method, the results show final contours by proposed method are more close to contours drawn by a cardiologist. © 2013 National Taiwan University