About: http://webisa.webdatacommons.org/69137731

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	However, difficulties in implementation, in particular in connection with providing for the necessary high frequency on and off switching of the source tube, prevented this type of system from attaining widespread usage.
http://www.w3.org/ns/prov#wasQuotedFrom	google.com