Sentence:  Essentially these birefringence studies show that at low rates of shear a tension <WSD>is</WSD> present at 45 ` to the direction of shear , and as the rate of shear increases , the direction of the maximum tension moves asymptotically toward the direction of shear . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)