Effective mass (solid-state physics) from both sides gives where is the th element of , is the th element of , and are the th and th elements of , respectively, and is the total energy of the particle according to the Planck–Einstein relation. The index is contracted by the use of Einstein notation (there is an implicit summation over ). Since Newton's second law uses the inertial mass (not the gravitational mass), we can identify the inverse of this mass in the equation above as the tensor This tensor expresses the change in group velocity due to a change in crystal momentum. Its
This Is What Rock n' Roll Looks Like week, the song went up two spots, peaking at number forty-four. The following two weeks, "This Is What Rock n' Roll Looks Like" remained stationary at number forty-four on the weeks ending August 1, 2011 and August 8, 2011, respectively. A music video for "This Is What Rock n' Roll Looks Like" was shot and directed by Sanaa Hamri at Citrus College in Glendora, California. Porcelain Black discussed the idea behind the music video for "This Is What Rock n' Roll Looks Like" with AOL's Carlos Ramirez, stating it was based on real life experiences. After Porcelain Black's mother had