Sentence:  <WSD>Gas</WSD> injection through a porous anode ( transpiration cooling ) not only feeds back the energy transferred to the anode by the above mentioned processes , but also modifies the conditions in the arc itself . 
Meaning of the word marked with <WSD> tags:  the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container