Comparative Analysis of AC and DC Distribution System with Respect to Harmonic Distortion Considering Daily Load Profile

Electrical energy is the most efficient and the cleanest form of energy at the moment that is being transmitted and distributed amongst end-users. From its earlier days, the AC system was preferred as an economical solution for transmission and distribution. However, the development in the power electronics technology and the evolution of highly efficient power electronic converters have established the resurgence of DC power system. Furthermore, the trend is shifting towards DC loads as various energy efficient appliances, such as DC inverter air conditioners, operate on DC nowadays. This further advocates the shift towards the DC power system. This research works is an effort to perform the comparative analysis of AC Distribution System (ACDS) and DC Distribution System (DCDS), with regards to power quality and harmonic distortion in particular. The comparison is performed considering load profile and load variation on daily basis. Simulations are performed in MATLAB. It has been concluded at the end that ACDS is better than DCDS in terms of power quality as total harmonic distortion of the DCDS under the same loading and same load variation during the whole day was significantly higher than that of ACDS.

A Histological Study of Human Olfactory Mucosa: Regional Distribution and Age Related Changes

The present study on the morphology of human olfactory mucosa was carried out with emphasis on its regional distribution, and changes related with age and gender. Eighty tissue samples (forty for either sex) were collected from cadavers ranging from 30 to 82 years of age, available in the mortuary of King Edward Medical College, Lahore. Individual age groups of males and females included 10 specimens from each sex. The histological study of the mucosa included morphology, regional distribution, quantitative analysis of all four major types of epithelial cells, height of epithelium and thickness of lamina propria in the roof, medial and lateral walls of both nasal cavities. A detailed study of the epithelium revealed the presence of classically known three cells: olfactory cells, sustentacular cells and basal cells and a fourth type, microvillar cells. In the age group 30-39 years (male and female) the mucosa was seen in the roof lying next to cribriform plate of the ethmoid bone and extending on both sides of the nasal septum and on the lateral walls of both nasal cavities. At places the respiratory epithelium was seen in the area of the olfactory epithelium which was much thicker. In the age group of 40-49 years, early age related changes were observed in the shape of occasional short epithelial invaginations, and disturbance of the zonal distribution of olfactory and supporting cells. In the age group 50-59 years, major morphological changes were observed like substantial reduction in the number of nuclei resulting in decreased height of the epithelium, disturbance of zonal distribution and presence of epithelial invaginations. The age group of 60 years onwards showed gradual thinning of the epithelium, epithelial invaginations, and in few cases atrophied olfactory epithelium devoid of olfactory cells. ANOVA showed significant age related decrease in the number of olfactory and sustentacular cells and in the height of the olfactory epithelium among the male and female groups. There was no significant age related decrease in the number of basal cells and thickness of the lamina propria. The number of microvillar cells was markedly less when compared to other cells of the epithelium. These results suggest that loss of olfactory and sustentacular cells becomes pronounced in individuals of both sexes of 50+ years of age. The results of the present study suggest that the reduction in the number of olfactory receptors and in the height of neuroepithelium with advancing age is associated iiwith impairment of olfactory sensibility. There was no evidence of significant sex related differences in the olfactory mucosa. These results are in the accordance with the previous observations in humans and other mammals showing a decline in the olfactory capacity with aging, mostly attributable to a decline in the number of olfactory cells. Contrary to earlier observations, the present study did not reveal any conclusive evidence that females had an increased sense of smell based on histological observations alone.