Showing papers on "Noise reduction published in 1970"

Techniques for the Measurement of Photoemission Energy Distribution Curves by the ac Method

Abstract: A new circuit for measuring photoemission energy distribution curves (EDC's) by the ac retarding potential method is described which offers greatly improved noise performance over earlier circuits. General techniques for EDC noise reduction are outlined and the noise performance expected from different electrometer detectors is compared. A method for quantitatively evaluating the noise performance of an EDC measurement system from an experimental EDC is presented and applied to EDC's obtained with this new measurement system. Equivalent noise currents in energy distribution curves obtained with this system are found to be as low as 2 to 3×10−15 A rms. This low noise allows the measurement of EDC's with total dc photocurrents of less than 10−13 A.

Reduction of noise from supersonic jet flows

Abstract: Interacting coaxial supersonic jet flows noise reduction based on noise distribution characteristics measurement in anechoic chamber

Compressors and expanders for noise reduction systems

Abstract: The invention concerns noise reduction systems and compressors and expanders therefor in which the overall characteristic is formed by combining the output of a further path additively or subtractively with the output of a main, straight-through path, the further path including a filter and limiter. In this improvement the filter is essentially all-pass at low levels and only becomes high- pass or low-pass at higher levels. At low levels noise reduction is therefore wide-band. Applicable to tape and disc audio noise reduction.

Integrating measurements with noise reduction

Abstract: Noise rejection in an integrating type of analogue to digital converter is improved by effecting the integration in accordance with a variable weighting function, preferably a step function. Functions are described which flatten the response versus frequency curve in the neighborhood of the zeroes and introduce more zeroes into this curve. The weighting may be introduced by scaling either on the analogue side or the digital side of the instrument.

Some applications of jet noise theory

Abstract: Jet noise theory application in noise prediction and reduction at source for subsonic and supersonic jets

Elimination of coherent noise in a coherent light imaging system

Abstract: Optical imaging systems using coherent light introduce objectionable noise into the output image plane. Dust and bubbles on and in lenses cause most of the noise in the output image. This noise usually appears as bull's-eye diffraction patterns in the image. By rotating the lens about the optical axis these diffraction patterns can be essentially eliminated. The technique does not destroy the spatial coherence of the light and permits spatial filtering of the input plane.

Enhanced MRA Images Quality Using Structure Adaptive Noise Filter And Edge Sharpening Methods

Abstract: MR imaging is an emerging and fast growing medical imaging technique which gives high quality images of the soft tissues. There are certain kinds of noise which contaminates these images and thus makes their interpretation difficult for both human and machine. Filtering is a mathematical technique in which intensities of each pixel of the input image are combined with the intensities of its neighboring pixels, to remove the noise and smooth the image. Filtering could be used with MR images for noise removal. The ordinary image filters blur the image and also remove important structural information like lines and edges. This loss of structural information could be dangerous in a clinical environment and could leads to incorrect diagnosis. To address this problem, a structure preserving noise filter is required. When images are processed for human vision, it is also desirable to make them pleasing by sharpening their edges. Such a structure adaptive noise (SAN) filter and an edge sharpening method is designed and implemented on our MRI Visualization toolkit. Our results show that the methods are effective in removing noise, preserving structure, and sharpening edges.

A study of the magnitude of transportation noise generation and potential abatement-train system noise

Abstract: The noise from an individual vehicle is a function of the physical characteristics of the vehicle, the way in which the vehicles is operated and the construction characteristics of the vehicle's guideway, e.g., rail condition, roadbed supporting structure. Noise reduction at the source can be obtained by altering the vehicle and/or the guideway and by changing the way the vehicle is operated. Analysis of contemporary mass transit vehicle noise indicates that the rank order of conventional rail vehicle noise sources is: (1) wheel and rail system, (2) propulsion system and (3) auxiliary equipment. Noise levels alongside the right-of-way, are a function of the vehicle type, its operation and the configuration of the roadbed and surrounding areas. For a given vehicle and guideway, the right-of-way configuration has the greatest impact on the sound levels received at a specific wayside location. Rail vehicle wayside noise levels can be reduced by interrupting the sound transmission paths between the vehicle and the receiver. To the extent that this is achieved, rail vehicle wayside noise levels can be reduced in a manner which is similar to that used for highway noise reduction.

Noise behavior of GaAs Schottky-Barrier field-effect transistors in the microwave region

Abstract: Recently it has been shown that GaAs FET's with a Schottky-barrier gate are very promising devices for microwave applications. Transistors with a maximum frequency of oscillation of 30 GHz have been reported. The noise behavior of such devices has been investigated theoretically and experimentally. Compared to silicon devices, an additional noise source has to be taken into account in the GaAs FET--the intervalley scattering noise. This kind of noise occurs if carriers are scattered from the central valley to a satellite valley where the mobility is considerably reduced. This noise is very similar to the well-known generation-recombination noise.

Correlation detection of impulse noise for FM threshold extension

Abstract: A correlation technique is used to detect frequency-modulation noise impulses. When implemented in an impulse-noise-cancellation system, this technique provides a 2-dB extension in the FM threshold. It also allows the impulse-detection system to be independent of the modulating signal level and frequency deviations.

A self adaptive automatic carrier landing system (ACLS)

Abstract: This paper describes the results of a simulation study carried out to demonstrate the feasibility of a Self Adaptive ACLS. Results indicate that such a system can successfully reduce system errors due to nonlinearities and noise effects.

Physical origins of burst noise in transistors

Abstract: Burst noise in bipolar junction transistors has been attributed to leakage current through crystallographic defects located in proximity to the base-emitter junction. The current is modulated by the random occupancy of a single flaw located near the defects. The previous theoretical work has only described defects located in the emitter-base space-charge region away from the surface. This paper extends the noise model to include the regions close to the surface where the high incidence of defects makes burst noise sources more likely. Experimental data is presented on typical devices, some of which were gold doped. The proposed model is in agreement with all experimental measurements. The data, in conjunction with the noise model, is used to determine physical parameters such as capture cross sections and energy level of the flaw which correlate well with published values. The investigation suggests several techniques which are useful in reducing the incidence ot burst noise.