Effect of Helix Angle on the Performance of Helical Vertical Axis Wind Turbine

The energy crisis has forced researchers to look for various non-conventional energy sources. Wind energy is one of the potential sources, and researchers have invested resources in developing different kinds of wind turbines. Vertical axis wind turbines (VAWT) have received less attention than their horizontal-axis counterparts. A helical-bladed VAWT is preferred because it makes perfect sense as an improvement in design, as they have higher azimuth angles of power generation capabilities. This paper studies the effects of the helix angle of blades in the aerodynamic performance of VAWT using 3D numerical simulations. Three different helix angles of 60°, 90°, and 120° of a three-bladed VAWT operating across different tip speed ratios were studied. Turbulence is modelled using a four-equation transition SST k-ω model (shear stress transport). The 60° helical-bladed VAWT was found to be better performing in comparison with all other helical-bladed and straight-bladed VAWT. The ripple effects on the shaft are also analysed using a standard deviation plot of the moment coefficient generated by a single blade over one complete cycle of its rotation. It was observed that the greater the helix angle, the lower the standard deviation. The paper also tries to analyse the percentage of power generated by each quartile of flow and the contribution of each section of the blade. Ansys FLUENT was employed for the entire study. A comparative study between different helical-bladed VAWT and straight-bladed VAWT was carried out along with wake structure analysis and flow contours for a better understanding of the flow field.

Outer retinal layer thickness in patients with glaucoma with horizontal hemifield visual field defects

Background/AimsTo determine the effect of glaucoma on outer retinal layer thickness in eyes with horizontal hemifield visual field (VF) defects.MethodsWe conducted a cross-sectional study in glaucomatous eyes with repeatable (in three or examinations) horizontal hemifield VF (programme 24–2) defect defined as: all five nasal VF locations immediately either above or below the horizontal midline abnormal in the pattern deviation plot with p<0.5%; no mirror-image adjacent 5 VF locations abnormal in the pattern deviation plot and no non-edge VF locations in the non-affected hemifield abnormal in the pattern deviation plot with p<1%. We used optical coherence tomography to measure thickness of each retinal layer in the temporal macula (12° horizontally and 24° vertically) and computed the absolute (µm) and relative (%) intraindividual asymmetry between the perimetrically normal and abnormal hemimacula.ResultsWe included 10 eyes of 8 patients with median age of 67 years and median VF mean deviation of −8.85 dB. The nerve fibre, ganglion cell and inner plexiform layers were significantly thinner in the perimetrically abnormal hemimacula (median asymmetry of –6.4, –11.5 and −3.8 µm, (corresponding to –27.7, –40.5 and −15.7 %), respectively, all p≤0.01). The inner nuclear layer was slightly thicker in the perimetrically abnormal hemimacula (median asymmetry of 1.3 µm (5.0 %), p=0.01). The outer plexiform, outer nuclear and photoreceptor layers asymmetry values were negligible.ConclusionOur study showed no evidence that glaucoma has an effect on the outer retinal layer thickness. In contrast, a large impact was observed in inner layer thickness.

Η συμβολή της swap περιμετρίας στην πρώιμη διάγνωση του χρόνιου γλαυκώματος

Σκοπός: Η σύγκριση των δυο περιμετριών, SWAP και SAP την στιγμή της μετατροπής στο γλαύκωμα. Ασθενείς και Μέθοδοι: Πρόκειται για μια προοπτική μελέτη ασθενών με οφθαλμική υπερτονία. Διακόσιοι ογδόντα δυο ασθενείς με οφθαλμική υπερτονία συμπεριελήφθησαν διαδοχικά και εξετάστηκαν με SAP και SWAP κάθε χρόνο για 5 χρόνια ή μέχρι την μετατροπή σε γλαύκωμα. Τόσο η SAP όσο και η SWAP πραγματοποιήθηκαν με το Humphrey Field Analyzer II χρησιμοποιώντας το 24-2 full threshold. Η ανωμαλία τόσο για την SAP όσο και για την SWAP καθορίστηκε από το διάγραμμα της pattern deviation plot και ορίστηκε ως: α) ένα σημείο κάτω από το 0,5% επίπεδο στατιστικής σημαντικότητας ή β) ένα σύμπλεγμα 2 ή περισσοτέρων σημείων κάτω από το 1% ή γ) ένα σύμπλεγμα από 3 ή περισσότερα σημεία κάτω από 5%. Τα παθολογικά τεστ έπρεπε να επαληθευτούν μέσα σε ένα χρόνο για να θεωρηθούν ως μετατροπή. Αποτελέσματα: Από τους 282 που συμπεριελήφθησαν αρχικά, 32 ασθενείς εξαιρέθηκαν. Από τους 250 που παρέμειναν στην μελέτη, ένα σύνολο από 38 ασθενείς μετατράπηκαν κατά την διάρκεια της παρακολούθησης. 36,8% των μετατροπών ανιχνεύτηκαν νωρίτερα με την SWAP, 29% ταυτόχρονα και 34,2% δεν ανιχνεύτηκαν με την SWAP κατά την διάρκεια της περιόδου παρακολούθησης. 2,4% των ασθενών παρουσίασαν ελλείμματα στην SWAP που δεν κατέληξαν σε μετατροπή κατά την διάρκεια της παρακολούθησης. Συζήτηση: Υπήρξαν ασθενείς με πρώιμη, ταυτόχρονη η καθόλου μετατροπή στη SWAP χρησιμοποιώντας την SAP για το κριτήριο αναφοράς. Καθώς η κάθε μέθοδος ανιχνεύει το γλαύκωμα σε ένα υποσύνολο ασθενών και αυτά τα υποσύνολα επικαλύπτονται μερικώς ίσως να ήταν δόκιμο να γίνεται έλεγχος τόσο με την SWAP όσο και με την SAP με επανάληψη όταν είναι εμφανής η απώλεια οπτικών πεδίων.

Source Camera Identification Based on Sensor Readout Noise

A digitally developed image is a viewable image (TIFF/JPG) produced by a camera’s sensor data (raw image) using computer software tools. Such images might use different colour space, demosaicing algorithms or by different post processing parameter settings which are not the one coded in the source camera. In this regard, the most reliable method of source camera identification is linking the given image with the sensor of camera. In this paper, the authors propose a novel approach for camera identification based on sensor’s readout noise. Readout noise is an important intrinsic characteristic of a digital imaging sensor (CCD or CMOS) and it cannot be removed. This paper quantitatively measures readout noise of the sensor from an image using the mean-standard deviation plot, while in order to evaluate the performance of the proposed approach, the authors tested against the images captured at two different exposure levels. Results show datasets containing 1200 images acquired from six different cameras of three different brands. The success of proposed method is corroborated through experiments.

Source Camera Identification Based on Sensor Readout Noise

A digitally developed image is a viewable image (TIFF/JPG) produced by a camera’s sensor data (raw image) using computer software tools. Such images might use different colour space, demosaicing algorithms or by different post processing parameter settings which are not the one coded in the source camera. In this regard, the most reliable method of source camera identification is linking the given image with the sensor of camera. In this paper, the authors propose a novel approach for camera identification based on sensor’s readout noise. Readout noise is an important intrinsic characteristic of a digital imaging sensor (CCD or CMOS) and it cannot be removed. This paper quantitatively measures readout noise of the sensor from an image using the mean-standard deviation plot, while in order to evaluate the performance of the proposed approach, the authors tested against the images captured at two different exposure levels. Results show datasets containing 1200 images acquired from six different cameras of three different brands. The success of proposed method is corroborated through experiments.

Evaluation of Threshold Estimation and Learning Effect of two Perimetric Strategies, Sita Fast and Clip, in Damaged Visual Fields

Purpose The threshold estimation, learning effect, and between-algorithm differences of the Fast Swedish Interactive Thresholding Algorithm (SITA Fast), of the Humphrey Field Analyzer (HFA), and the Continuous Light Increment Perimetry (CLIP) strategy of the Oculus Twinfield perimeter were evaluated in damaged visual fields. Methods Twenty-one glaucomatous patients with damaged visual fields (MD worse than −8 dB) underwent Oculus Full Threshold (FT), Humphrey FT, SITA Fast, and CLIP 30–2 perimetric examinations. All the tests were repeated in a second session at least 3 days later. The point-wise differences in absolute sensitivity and of the total deviation plot values between FT and fast algorithms, between fast algorithms and the learning effect were evaluated (Wilcoxon test and Bland-Altman analysis). Results The average point-wise sensitivity difference between SITA Fast and HFA FT strategy (0.84 dB) was significantly lower than that found between CLIP and Oculus FT strategy (1.71 dB). Between-algorithm point-wise differences of the total deviation plot values of the fast strategies were not significantly different. Learning effect for SITA Fast (0.67 dB) was higher than that found for CLIP (0.39 dB). Test time for SITA (367±71 sec) and CLIP (453±98 sec) were about 55% and 35%, respectively, shorter (pp<0.001) than those found with FT algorithms. The acceptance for fast algorithms and particularly for CLIP was significantly better. Conclusions The two fast strategies, even though using very different algorithms, showed good threshold estimation compared to FT strategies with a consistent time saving in damaged visual fields.