Numerical aeroacoustic analysis of propeller designs

As propeller-driven aircraft are the best choice for short/middle-haul flights but their acoustic emissions may require improvements to comply with future noise certification standards, this work aims to numerically evaluate the acoustics of different modern propeller designs. Overall sound pressure level and noise spectra of various blade geometries and hub configurations are compared on a surface representing the exterior fuselage of a typical large turboprop aircraft. Interior cabin noise is also evaluated using the transfer function of a Fokker 50 aircraft. A blade design operating at lower RPM and with the span-wise loading moved inboard is shown to be significantly quieter without severe performance penalties. The employed Computational Fluid Dynamics (CFD) method is able to reproduce the tonal content of all blades and its dependence on hub and blade design features

Antimultipath communication by injecting tone into null in signal spectrum

A transmitter for digital radio communication creates a null by balanced encoding of data modulated on an RF carrier, and inserts a calibration tone within the null. This is accomplished by having the calibration tone coincide in phase and frequency with the transmitted radio frequency output, for coherent demodulation of data at the receiver where the tone calibration signal is extracted and used for multipath fading compensation

A Comparison between the staggered position one-angle screening method and the multi-angle screening method in terms of misregistration when printing process color on newsprint

The multi-angle screening configuration is by far the most widely used screening configuration for process color printing, but there are alternative screening configurations which may be preferable in certain situations. Color separations made using the Staggered Position One-Angle screening configuration are reported to provide printed reproductions on newsprint which appear sharper, offer improved color reproduction, produce smoother color reproduction, and preserve color better in the shadows. The staggered position technique can be generated with high-end scanners and prepress equipment, as well as with desktop publishing workstations using the Flamenco screening algorithm. However, the staggered position method may be subject to greater color variation than the multi-angle method due to random misregistration which can occur during a newspaper press run. This study investigated printed process color reproductions produced by the staggered position screening technique in comparison to reproductions produced by the multi-angle screening technique at two commonly used screen rulings, 85 and 100 lpi, on newsprint. During a press run, one printing plate at a time was laterally misregistered in eight increments. A total of 32 sample press sheets and an OK standard press sheet were taken during the press run. A series of printed color patches on each press sheet were measured with a computerized spectrophotometer to determine if the color difference (AE) between the sample and the OK standard press sheet was significant or not. The two screening methods were also evaluated for consistency of color reproduction. Using a two sample t-test, it was determined that color misregistration resulted in a significant statistical difference between the staggered position test target and the multi- angle test target for the same screen frequency. On an individual patch-by-patch comparison, there were certain patches which did not exhibit a significant statistical difference between the two screen configurations. It was also determined that the multiangle screening method produced consistent, acceptable color variation with every increment of misregistration. The staggered position technique produced unpredictable and often unacceptable amounts of color variation which varied with misregistration and the number of overprinting inks

A Comparison of staggered position one angle process color printing with four angle and one angle process color printing

The Staggered Position One Angle method of preparing color separations does not adjust the dot angle for each color. The dot pattern is staggered horizontally or vertically by half a row of dots for each separation maintaining the same angle. The investigation compared the Staggered Position method to the four angle method and to the dot-on-dot method. Newsprint was the substrate, and 65, 85, and 100 lines per inch were the rulings. Experienced judges viewed the representative prints and scored each for sharpness, color variability, and overall acceptance. They were also asked to indicate the evidence of rosette and moire patterns. Densitometric and spectrophotometer readings were used for objective analysis. The judges found the Staggered Position to be equal or better than both four angle and dot-on-dot printing in most instances. A non existant rosette pattern and a minimal risk of moire\u27 patterns also resulted. The Staggered Position printing excelled in the ability to produce a sharp reproduction, and its tone reproduction was found to be equivalent to the four angle and dot-on-dot printing. The use of Delta E for the visual rejection or acceptance of an image was found not to be a good indicator in this particular study. The study opens up a number of areas for further research into this new separation method, but because of its good performance on newsprint, it should be considered as an alternative to the four angle method for newspapers

Single-Frequency Network Terrestrial Broadcasting with 5GNR Numerology

L'abstract è presente nell'allegato / the abstract is in the attachmen