Thermal-buble initiated breakdown characteristics of liquid helium and nitrogen at atmospheric pressure
Experiments show that electric field promotes to form a vapor locking in a gap with a hot spot and in turn the formation of locked vapor produces the serious reduction of breakdown voltage. Especially it is argued that the dielectric strength of liquid helium under serious hot spot conditions decreases below that for saturated gas.
D.c. electrical breakdown of saturated liquid helium at 0.1 MPa in the presence of thermally induced bubbles
Abstract Breakdown phenomena initiated by thermally generated bubbles in liquid helium are investigated experimentally. The process is considered to be of importance for the design of electrical insulation of superconducting devices. The results of the investigations show that the boiling processes are significantly affected by the application of an electrostatic field and that the bubble shape varies complicatedly with the magnitude of electric field, heater power for generation of bubble and the arrangement of electrode system. Thus the breakdown voltage of liquid helium in a parallel plane gap depends on those experimental conditions. It is argued that the breakdown strength of saturated liquid helium at atmospheric pressure in the presence of thermal bubbles becomes lower than that of saturated helium vapour at the same pressure.
An automated retinal image quality grading algorithm
This paper introduces an algorithm for the automated assessment of retinal fundus image quality grade. Retinal image quality grading assesses whether the quality of the image is sufficient to allow diagnostic procedures to be applied. Automated quality analysis is an important preprocessing step in algorithmic diagnosis, as it is necessary to ensure that images are sufficiently clear to allow pathologies to be visible. The algorithm is based on standard recommendations for quality analysis by human screeners, examining the clarity of retinal vessels within the macula region. An evaluation against a reference standard data-set is given; it is shown that the algorithm's performance correlates closely with that of clinicians manually grading image quality.