The politicians internal divisions have led to fears that a political vacuum could give Sunni militants a chance to revive the sectarian violence that roiled the nation in 2006 and 2007.

VOA: standard.2010.04.04

This is titanium sponge that comes out of the bottom of this reactor, and it subsequently re-melted in a vacuum arc furnace.

海绵状的钛,从反应器的底部出来，随后在真空炉中重新熔炼。

麻省理工公开课 - 固态化学导论课程节选

In addition to that, we have that epsilon nought value, remember that's the permittivity constant in a vacuum, and basically that is what we use as a conversion factor to get from units. We don't want namely coulombs to units, we want that will allow us to cancel out in this equation.

这是电子的电荷，此外，我们有epsilon零，记住这是真空的介电常数，这是我们用来转换单位的转换常数,我们不想用库伦单位，我们希望这个可以在方程中约去它。

麻省理工公开课 - 化学原理课程节选