Perhaps you should try some spelling variations:
"medium connectivity" » "media connectivity", "maximum connectivity", "minimum connectivity"
"model directivity" » "model directive", "model directives", "model directionality"
"edge directivity" » "edge connectivity", "_ directivity", "edge directions"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("edge directivity") OR ("model directivity"))) OR ("medium connectivity")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"edge directivity\") OR (\"model directivity\"))) or (\"medium connectivity\"))".
• Removing quotes may allow a broader search: (((( edge directivity ) OR ( model directivity ))) or ( medium connectivity )).
• Adding a wildcard symbol may retrieve word variants: (((("edge directivity") OR ("model directivity"))) or ("medium connectivity"))*.