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.
Influence of Coupling Agents on Partial Discharge and Electrical Breakdown of Syntactic Foams at LNT
In this paper, syntactic foam is investigated as an alternative solid insulation material for cryogenic applications. Compared to conventional insulation materials based on liquid nitrogen, syntactic foam offers advantages like higher dielectric strength and it maintains its dielectric properties even during quenching of superconductors. Being an inhomogeneous material, syntactic foam features numerous interfaces between materials with different dielectric constants, which might be temperature de-pendent. It has been shown in previous investigations that improving bonding quality between materials of syntactic foam can be beneficial for mechanical and electrical strength. A broader variety of foam modifications using coupling agents are investigated in electrical tests for breakdown voltage at both 293 K and 77 K. To examine the initiation of breakdown, partial discharge measurements are performed at both ambient and liquid nitrogen temperature (LNT), and the results are compared to the existing model of electrical breakdown. The application of coupling agents shows no significant overall improvement for ac- and dc-breakdown stress. At LNT, syntactic foams show a higher partial discharge inception field stress, when microspheres are being treated with a coupling agent compared to untreated microspheres.
The Intuitive Physics of the Equilibrium of the Lever and of the Hydraulic Pressures: Implications for the Teaching of Elementary Physics.
The research field of intuitive physics focuses on discrepancies between 
theoretical and intuitive physical knowledge. Consideration of these 
discrepancies can help in the teaching of elementary physics. However, 
evidence shows that theoretical and intuitive physical knowledge may also 
be congruent. Physics teaching could further benefit from understanding the 
reasons for this congruence. The present study explored these reasons by 
investigating the intuitive physics of the equilibrium of the lever and of the 
hydraulic pressures. It was found that the intuitive-physics law of the lever 
was multiplicative for all participants while the intuitive-physics law of the 
hydraulic pressures differed among participants. Since these laws are 
equally simple and the layman probably has had extensive experience with 
the lever and scarce or no experience with the hydraulic lift, these findings 
support the general hypothesis that physical laws and corresponding 
intuitive-physics laws are congruent when people have had experience with 
the respective phenomena. The results and theoretical considerations suggest 
two strategic principles for teaching elementary physics.