<http://webisa.webdatacommons.org/308668144>	<http://www.w3.org/ns/prov#wasQuotedFrom>	<google.com> .
<http://webisa.webdatacommons.org/308668144>	<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>	<http://www.w3.org/ns/prov#Entity> .
<http://webisa.webdatacommons.org/prov/288259295>	<http://www.w3.org/ns/prov#wasDerivedFrom>	<http://webisa.webdatacommons.org/308668144> .
<http://webisa.webdatacommons.org/308668144>	<http://www.w3.org/ns/prov#value>	"In accordance with the present invention, a void in backfill material, such as soil surrounding a buried conduit may be detected from an acoustic frequency response of the conduit resulting from acoustic excitation of the conduit." .