Comparative Study of PI Controller and PID Controller for Power Quality Improvement

Power factor correction (PFC) is a mandatory functionality of electronic products in the industrial and commercial market in order to mitigate grid harmonics to improve power quality. Since the load characteristics of most PFC applications such as home appliances, battery chargers, switched mode power supplies and other digital products support unidirectional power flow, the general ac - dc boost converter is considered a popular topology. It is one of the low cost, simple methodologies and their performance is well - proven. Maintaining dc - link voltage constantly inside the system in order to feed loads at different power ratings is the main task. Active power filters (APF) is another approach capable of improving grid power quality to control input current with a pure sinusoidal waveform in phase with input voltage. Unlike PFC circuits, the APF is a system in itself which provides compensation of harmonics and reactive power in order to reduce undesirable effects from non-linear loads and uncontrolled passive loads in power systems. The paper introduces a versatile method for mitigating grid power quality using unidirectional ac ? dc boost converter. The additional focus of this paper is to measure the quantity of input current distortions by the unidirectional ac ? dc boost converter used for supplying active power to the load and reactive power. By using this method, the amount of reactive power injected due to input current distortion from an individual converter to the grid should be restricted. This paper presents, control strategy by using dual boost PFC converter. An improved simulation software using MATLAB was developed to study the proposed method to mitigate harmonics in order to improve power quality. Comparative results for power quality improvement by using PI controller and PID controller are observed

Effect of cylinder power and axis changes on vision in astigmatic participants

Purpose: To ascertain the impact of altering cylinder (cyl) power and axis on vision in astigmatism.Methods: In a prospective, randomized, participant-masked, crossover clinical trial, 28 astigmatic participants were tested for the following conditions on different days: full sphero-cyl correction and undercorrection by 0.25, 0.50, and 0.75 DC while maintaining spherical equivalence. Axis was also misaligned between -30° and +30°, in 10° steps. For each configuration, monocular high- and low-contrast visual acuities (HCVA, LCVA) were measured at 6 m, and participants rated vision clarity (1-10), vision satisfaction (1-10), and vision acceptability (yes/no). Linear mixed models were used to compare visual performance in the overall group and in low, medium, and high cyl subgroups.Results: Undercorrecting cyl power affected all groups equally (P≥0.073). Undercorrection by 0.75 DC was significantly different to full cyl power for all variables (P≤0.007), while 0.25 DC undercorrection did not cause any significant decreases (P&gt;0.05). Undercorrection by 0.50 DC was significantly different to full cyl power for HCVA (P=0.006, however not clinically significant) and vision acceptability (P=0.034). Axis misalignment affected the cyl groups differently (P&lt;0.001), with the greatest impact in the high cyl group, followed by the medium then the low-cyl group. Misalignment by ±30° caused significant decreases in almost all cases (P≤0.003), while misalignments by ±10° or ±20° caused significant decreases for some cyl groups and test variables.Conclusion: Undercorrection of cyl by ≤0.50 DC while maintaining spherical equivalence has no significant effect on HCVA, LCVA, vision clarity, and vision satisfaction, while the amount of axis misalignment that can be tolerated is dependent on the cyl power. These results may have practical ophthalmic applications, such as reducing the total number of stock keeping units of toric contact lenses.</p

Visual performance of myopia control soft contact lenses in non-presbyopic myopes

Purpose: To compare the visual performance of soft contact lenses reported to reduce myopia progression.Methods: In a double-blind, randomized, crossover trial, 30 non-presbyopic myopes wore MiSight™, center-distance Proclear® Multifocal (+2.00 D add), and two prototype lenses for 1 week each. High- and low-contrast visual acuities at 6 m, and 70 and 40 cm; stereopsis at 40 cm; accommodative facility at 33 cm; and horizontal phoria at 3 m and 33 cm were measured after 1 week. Subjective performance was assessed on a numeric rating scale for vision clarity, lack of ghosting, vision stability, haloes, overall vision satisfaction, and ocular comfort. Frequency of eye-strain symptoms and willingness to purchase lenses were also reported with categorical responses. Participants reported wearing times (total and visually acceptable). Linear mixed models and chi-square tests were employed in analysis with level of significance set at 5%. Theoretical optical performance of all lenses was assessed with schematic myopic model eyes (-1.00, -3.00, and -6.00 D) by comparing the slope of the edge spread function (ESF), an indicator for optical performance/resolution and the blur patch size of the line spread function, an indicator for contrast, between the lenses.Results: Proclear Multifocal and MiSight provided the best distance acuities. However, the prototype lenses were rated significantly higher for many subjective variables, and there were no subjective variables where commercial lenses were rated significantly higher than the prototypes. Theoretical optical performance showed steeper slopes of the ESF and greater blur patch sizes of the LSP with commercial lenses, supporting the clinical findings of better visual acuities but reduced subjective performance. Participants wore prototypes longer and reported their vision acceptable for longer each day compared to MiSight. Both prototypes had the highest willingness-to-purchase rate.Conclusions: The prototypes were better tolerated by myopes compared to the commercial soft contact lenses currently used for slowing myopia progression.</p

Context and Crowding in Perceptual Learning on a Peripheral Contrast Discrimination Task: Context-Specificity in Contrast Learning

Perceptual learning is an improvement in sensitivity due to practice on a sensory task and is generally specific to the trained stimuli and/or tasks. The present study investigated the effect of stimulus configuration and crowding on perceptual learning in contrast discrimination in peripheral vision, and the effect of perceptual training on crowding in this task. 29 normally-sighted observers were trained to discriminate Gabor stimuli presented at 9° eccentricity with either identical or orthogonally oriented flankers with respect to the target (ISO and CROSS, respectively), or on an isolated target (CONTROL). Contrast discrimination thresholds were measured at various eccentricities and target-flanker separations before and after training in order to determine any learning transfer to untrained stimulus parameters. Perceptual learning was observed in all three training stimuli; however, greater improvement was obtained with training on ISO-oriented stimuli compared to CROSS-oriented and unflanked stimuli. This learning did not transfer to untrained stimulus configurations, eccentricities or target-flanker separations. A characteristic crowding effect was observed increasing with viewing eccentricity and decreasing with target-flanker separation before and after training in both configurations. The magnitude of crowding was reduced only at the trained eccentricity and target-flanker separation; therefore, learning for contrast discrimination and for crowding in the present study was configuration and location specific. Our findings suggest that stimulus configuration plays an important role in the magnitude of perceptual learning in contrast discrimination and suggest context-specificity in learning

Sadvritta with special reference to Charak Samhita

Health, according to Ayurveda, is a balance of body, mental, social, and spiritual wellbeing. Ayurveda is the Sanskrit word for "life science”. It is a guide to living an optimal and healthy life style for every human being in the universe, not only a therapeutic science. Ayurveda's major goal is to maintain health rather than treat sickness. According to Ayurveda, everyone can enjoy healthy life by following certain rules laid by the science. These various rules are divided into Dincharya (a daily regimen), Ritucharya (seasonal routine) and Sadvritta (code of good conduct for mental health and social behavior). These rules are very important in prevention of disease and promotion of ideal health. According to Ayurveda, to maintain healthy and disease free life everyone should follow these rules. In Charak Samhita, Acharya Charak has prescribed a list of good conduct which is very necessary to follow if we want to control the sense organ and to obtain perfect health. Sadvritta give the detail knowledge about “what to do?” What should not to?” and also “how to live?” Following the codes of right conduct described in Ayurveda is highly effective in reducing the life disorders and helps to live healthy life. Sadvritta is being studied since long by all Ayurvedists but very few conceptual works have been carried out an it. Therefore, in this article attempts are made to explain Sadvritta in details as maintained in Ayurvedic literature and its overall effect on human body

Perceptual learning in foveal and peripheral contrast discrimination: exploring the effects of stimuli on learning and the effects of learning on spatial vision

Crowding is defined as the deleterious influence of surrounding elements on visual perception. The crowding effect is predominant in the normal periphery and in amblyopia. Perceptual learning has been shown to improve spatial vision in amblyopia but has not previously been employed to investigate crowding in amblyopia.The purpose of this work was to investigate the effect of surrounding stimuli parameters on crowding and perceptual learning (PL), and the effect of PL on discrimination thresholds and crowding in foveal and peripheral vision. Two main configurations of Gabor stimuli were employed in all experiments of the study: ISO (identically oriented target and flankers) and CROSS (orthogonally oriented target and flankers). Crowding was investigated in both orientation discrimination and contrast discrimination (CD) tasks in normally sighted and amblyopic observers, while PL was investigated only in CD in the normally sighted group. PL was conducted in five and three training groups defined on the basis of training stimuli in foveal and peripheral vision, respectively. In peripheral vision, CD thresholds were compared before and after training on untrained stimulus conditions in order to investigate any learning transfer.In general, the ISO configuration yielded crowding in most conditions, while the CROSS configuration yielded no or minimal crowding in both tasks in normally sighted observers. No crowding was found in our small group of mild amblyopes. There was an overall lack of learning in foveal vision. In peripheral vision, greater improvement was obtained on flanked training stimuli than training without flankers. Additionally, learning in the ISO configuration resulted in greater improvement than the CROSS configuration. However, there was no learning transfer and no reduction of crowding in any training group following PL in peripheral vision.The primary conclusions of the study are:&#149; Perceptual learning in contrast discrimination is dependent on the initial level of performance of observers in foveal and peripheral vision.&#149; Stimulus configuration has an impact on the amount of improvement in perceptual learning in peripheral contrast discrimination.&#149; Perceptual learning in peripheral contrast discrimination neither improves thresholds on untrained stimuli nor reduces crowding, using the training paradigm of the present study

Visual performance of myopia control soft contact lenses in non-presbyopic myopes

Jennifer Sha,1 Daniel Tilia,1,2 Jennie Diec,1 Cathleen Fedtke,1,2 Nisha Yeotikar,1 Monica Jong,1,2 Varghese Thomas,1 Ravi C Bakaraju1,2 1Brien Holden Vision Institute, Sydney, NSW, Australia; 2School of Optometry and Vision Science, University of New South Wales, Sydney, NSW, Australia Purpose: To compare the visual performance of soft contact lenses reported to reduce myopia progression. Methods: In a double-blind, randomized, crossover trial, 30 non-presbyopic myopes wore MiSight&trade;, center-distance Proclear&reg; Multifocal (+2.00 D add), and two prototype lenses for 1 week each. High- and low-contrast visual acuities at 6 m, and 70 and 40 cm; stereopsis at 40&nbsp;cm; accommodative facility at 33 cm; and horizontal phoria at 3 m and 33 cm were measured after 1 week. Subjective performance was assessed on a numeric rating scale for vision clarity, lack of ghosting, vision stability, haloes, overall vision satisfaction, and ocular comfort. Frequency of eye-strain symptoms and willingness to purchase lenses were also reported with categorical responses. Participants reported wearing times (total and visually acceptable). Linear mixed models and chi-square tests were employed in analysis with level of significance set at 5%. Theoretical optical performance of all lenses was assessed with schematic myopic model eyes (&minus;1.00, &minus;3.00, and &minus;6.00 D) by comparing the slope of the edge spread function (ESF), an indicator for optical performance/resolution and the blur patch size of the line spread function, an indicator for contrast, between the lenses. Results: Proclear Multifocal and MiSight provided the best distance acuities. However, the prototype lenses were rated significantly higher for many subjective variables, and there were no subjective variables where commercial lenses were rated significantly higher than the prototypes. Theoretical optical performance showed steeper slopes of the ESF and greater blur patch sizes of the LSP with commercial lenses, supporting the clinical findings of better visual acuities but reduced subjective performance. Participants wore prototypes longer and reported their vision acceptable for longer each day compared to MiSight. Both prototypes had the highest willingness-to-purchase rate. Conclusions: The prototypes were better tolerated by myopes compared to the commercial soft contact lenses currently used for slowing myopia progression. Keywords: accommodation, theoretical optical performance, extended depth of focu

Effect of cylinder power and axis changes on vision in astigmatic participants

J Sha,1 C Fedtke,1,2 D Tilia,1,2 N Yeotikar,1 M Jong,1,2 J Diec,1 V Thomas,1 RC Bakaraju1,2 1Brien Holden Vision Institute, Sydney, NSW, Australia; 2School of Optometry and Vision Science, University of New South Wales, Sydney, NSW, Australia Purpose: To ascertain the impact of altering cylinder (cyl) power and axis on vision in astigmatism. Methods: In a prospective, randomized, participant-masked, crossover clinical trial, 28 astigmatic participants were tested for the following conditions on different days: full sphero-cyl correction and undercorrection by 0.25, 0.50, and 0.75 DC while maintaining spherical equivalence. Axis was also misaligned between &ndash;30&deg; and +30&deg;, in 10&deg; steps. For each configuration, monocular high- and low-contrast visual acuities (HCVA, LCVA) were measured at 6 m, and participants rated vision clarity (1&ndash;10), vision satisfaction (1&ndash;10), and vision acceptability (yes/no). Linear mixed models were used to compare visual performance in the overall group and in low, medium, and high cyl subgroups. Results: Undercorrecting cyl power affected all groups equally (P&ge;0.073). Undercorrection by 0.75 DC was significantly different to full cyl power for all variables (P&le;0.007), while 0.25 DC undercorrection did not cause any significant decreases (P&gt;0.05). Undercorrection by 0.50 DC was significantly different to full cyl power for HCVA (P=0.006, however not clinically significant) and vision acceptability (P=0.034). Axis misalignment affected the cyl groups differently (P&lt;0.001), with the greatest impact in the high cyl group, followed by the medium then the low-cyl group. Misalignment by &plusmn;30&deg; caused significant decreases in almost all cases (P&le;0.003), while misalignments by &plusmn;10&deg; or &plusmn;20&deg; caused significant decreases for some cyl groups and test variables. Conclusion: Undercorrection of cyl by &le;0.50 DC while maintaining spherical equivalence has no significant effect on HCVA, LCVA, vision clarity, and vision satisfaction, while the amount of axis misalignment that can be tolerated is dependent on the cyl power. These results may have practical ophthalmic applications, such as reducing the total number of stock keeping units of toric contact lenses. Keywords: astigmatism, toric, sensitivity, misalignment, visual performanc