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Search Results: 1 - 10 of 3529 matches for " Vyas Prasad "
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Effect of oral acetazolamide on human aqueous and serum electrolytes
Sharma R,Prasad Jagdish,Mishra Y,Vyas S
Indian Journal of Ophthalmology , 1983,
Study of Novel Pyrrole Derivatives
Ashok Prasad,K. S. Nimavat,K. B. Vyas
International Journal For Pharmaceutical Research Scholars , 2012,
Abstract: Substituted benzaldehydes on simplistic condensation with 2-(5-((naphthalen-1-yloxy) methyl)-2-thioxo-1,3,4-oxadiazol-3(2H)-yl)aceto hydrazide(1) was give the consequent N'-arylidene-2-(5-((naphthalen-1-yloxy)methyl)-2-thioxo-1,3,4-oxadiazol-3(2H)-yl) aceto hydrazide (2a-e) in fine yield. Cyclo condensation of compounds (2a-e) with maleic anhydride yields 2-aryl-5-oxo-1-(2-(5-(phenoxymethyl)-2-thioxo-1,3,4-oxadiazol-3(2H)-yl) acetamido)-2,5-dihydro-1H-pyrrole-3-carboxylic acid (3a-e). The structures of these compounds were established on the basis of analytical and spectral data. All the newly synthesized compounds were evaluated for their antibacterial and antifungal activities.
Performance analysis of Fourier and Vector Matrix Multiply methods for phase reconstruction from slope measurements
M B Roopashree,Akondi Vyas,B Raghavendra Prasad
Physics , 2009,
Abstract: The accuracy of wavefront reconstruction from discrete slope measurements depends on the sampling geometry, coherence length of the incoming wavefronts, wavefront sensor specifications and the accuracy of the reconstruction algorithm. Monte Carlo simulations were performed and a comparison of Fourier and Vector Matrix Multiply reconstruction methods was made with respect to these experimental and computational parameters. It was observed that although Fourier reconstruction gave consistent accuracy when coherence length of wavefronts is larger than the corresponding pitch on the wavefront sensor, VMM method gives even better accuracy when the coherence length closely matches with the wavefront sensor pitch.
Effective coherence length estimation of optical wavefronts
Akondi Vyas,M. B. Roopashree,B. Raghavendra Prasad
Physics , 2009,
Abstract: In adaptive optics, the measurement of spatial coherence length helps in deciding the optimum design parameters of a Shack Hartmann Sensor (SHS). Two methods of estimating the spatial coherence length of optical wavefronts are presented. The first method is based on counting the number of Hough peaks in the wavefront. The second method is based on a simple data mining technique applied on the wavefronts. Optical wavefronts with different properties are simulated and used for statistical analysis. A comparison of the performance of the two methods is presented using Monte Carlo simulations. It is shown that both these methods can become efficient tools in estimating the effective coherence length of optical wavefronts.
Prediction of wavefronts in adaptive optics to reduce servo lag errors using data mining
Akondi Vyas,M B Roopashree,B Raghavendra Prasad
Physics , 2009,
Abstract: Servo lag errors in adaptive optics lead to inaccurate compensation of wavefront distortions. An attempt has been made to predict future wavefronts using data mining on wavefronts of the immediate past to reduce these errors. Monte Carlo simulations were performed on experimentally obtained data that closely follows Kolmogorov phase characteristics. An improvement of 6% in wavefront correction is reported after data mining is performed. Data mining is performed in three steps (a) Data cube Segmentation (b) Polynomial Interpolation and (c) Wavefront Estimation. It is important to optimize the segment size that gives best prediction results. Optimization of the best predictable future helps in selecting a suitable exposure time.
Digital long focal length lenslet array using spatial light modulator
Akondi Vyas,M B Roopashree,B Raghavendra Prasad
Physics , 2009,
Abstract: Under a thin lens and paraxial approximation, the phase transformation function of a lens was simulated on a Liquid Crystal (LC) based Spatial Light Modulator (SLM). The properties of an array of such lenses simulated on transmitting type and reflecting type SLMs were investigated and the limits of its operation in wavefront sensing applications are discussed.
Optimization of Existing Centroiding Algorithms for Shack Hartmann Sensor
Akondi Vyas,M B Roopashree,B R Prasad
Physics , 2009,
Abstract: Three centroiding techniques to estimate the position of the spots in a Shack Hartmann sensor: Normalized Centre of Gravity (CoG), Iteratively Weighted Centre of Gravity (IWCoG) and Intensity Weighted (IWC) centroiding are studied in comparison. The spot pattern at the focal plane of a Shack Hartmann sensor was simulated by including the effect of a background noise. We present the results of optimization of the performance of each of the centroiding techniques as a function of Signal to Noise Ratio (SNR) at different experimental conditions.
Extrapolating Zernike Moments to Predict Future Optical Wave-fronts in Adaptive Optics Using Real Time Data Mining
Akondi Vyas,M. B. Roopashree,B. Raghavendra Prasad
Physics , 2010,
Abstract: We present the details of predicting atmospheric turbulence by mining Zernike moment data obtained from simulations as well as experiments. Temporally correlated optical wave-fronts were simulated such that they followed Kolmogorov phase statistics. The wave-fronts reconstructed either by modal or zonal methods can be represented in terms of Zernike moments. The servo lag error in adaptive optics is minimized by predicting Zernike moments in the near future by using the data from the immediate past. It is shown statistically that the prediction accuracy depends on the number of past phase screens used for prediction and servo lag time scales. The algorithm is optimized in terms of these parameters for real time and efficient operation of the adaptive optics system. On an average, we report more than 3% improvement in the wave-front compensation after prediction. This analysis helps in optimizing the design parameters for sensing and correction in closed loop adaptive optics systems.
Performance of centroiding algorithms at low light level conditions in adaptive optics
Akondi Vyas,M. B. Roopashree,B. Raghavendra Prasad
Physics , 2010, DOI: 10.1109/ARTCom.2009.30
Abstract: The performance metrics of different centroiding algorithms at low light level conditions were optimized in the case of a Shack Hartmann Sensor (SHS) for efficient performance of the adaptive optics system. For short exposures and low photon flux, the Hartmann spot does not have a Gaussian shape due to the photon noise which follows Poissonian statistics. The centroiding estimation error was calculated at different photon levels in the case of changing spot size and shift in the spot using Monte Carlo simulations. This analysis also proves to be helpful in optimizing the SHS specifications at low light levels.
Denoising Shack Hartmann Sensor spot pattern using Zernike Reconstructor
Akondi Vyas,M B Roopashree,B Raghavendra Prasad
Physics , 2009,
Abstract: Shack Hartmann Sensor (SHS) is inflicted with significant background noise that deteriorates the wave-front reconstruction accuracy. In this paper, a simple method to remove the back ground noise with the use of Zernike polynomials is suggested. The images corresponding to individual array points of the SHS at the detector, placed at the focal plane are independently reconstructed using Zernike polynomials by the calculation of Zernike moments. Appropriate thresholding is applied on the images. It is shown with computational experiments that using Zernike Reconstructor along with usual thresholding improves the centroiding accuracy when compared to direct thresholding. A study was performed at different Signal to Noise ratio by changing the number of Zernike orders used for reconstruction. The analysis helps us in setting upper and lower bounds in the application of this denoising procedure.
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