Sentence:  Essentially these birefringence studies show that at low rates of shear a <WSD>tension</WSD> is 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:  (physics) a stress that produces an elongation of an elastic physical body