'unco'-'vola'
- uncontrolled alternating current arc
- uncontrolled high-voltage spark generator
- undercritically damped oscillating discharge
- unidirectional discharge
- unidirectional spark
- unpolarized
- unresolvable band spectra
- unresolved band spectra
- untergrund
- UPS
- uptake rate
- vacuum phototube
- vacuum sparks
- vacuum-cup electrode
- valence electrons
- value of a division
- vaporization