This is because most fraternities and sororities are named after a series of Greek letters, such as Alpha Delta Pi or Sigma Phi.

VOA: special.2009.09.25

So we can also name this orbital, and this orbital we're going to call sigma 1 s star.

我们也可以，给这个轨道命名。

麻省理工公开课 - 化学原理课程节选

And so it has what? In contrast to the sigma, it has a nodal plane containing both nuclei.

这是什么，和sigma相反，它是包覆在核上的平面电子云，有一个界面。

麻省理工公开课 - 固态化学导论课程节选

The SIGMA DP1 Merrill is designed for wide angle images, the SIGMA DP2 Merrill is for standard range, while the DP3 Merrill rounds out the series with a camera for all shooting situations.

ENGADGET: Sigma DP3 Merrill packs a Foveon X3 sensor and a fixed F2.8, 75mm-equivalent lens

The SIGMA DP3 Merrill is equipped with a hot shoe, allowing use of the dedicated external flashgun EF-140 DG (optional) as well as SIGMA electronic flashguns for SD series such as EF-610 DG Super (optional) and EF-610 DG ST (optional).

ENGADGET: Sigma DP3 Merrill packs a Foveon X3 sensor and a fixed F2.8, 75mm-equivalent lens

Interest in Six Sigma meanwhile is an area where the United States scores highly.

FORBES: Why America Is Second Best With Its Innovation Culture