1 Routine screening of average-risk women should begin at age 50, instead of age 40. 2  Routine screening should end at age 74. 3  Women should get screening mammograms every two years instead of every year.4  Breast self-exams have little value, based on findings from several large studies. Routine screening of average-risk women should begin at age 50, instead of age 40. 2  Routine screening should end at age 74. 3  Women should get screening mammograms every two years instead of every year.
in chemical compound: Alkynes. Molecules that contain a triple bond between two carbon atoms are known as alkynes. The triple bond is made up of one Ï bond and two Ï bonds. As in alkenes, the Ï bonds constitute regions of increased electron density lying parallel to the carbon-carbon bond axis.
Alkenes: Nomenclature . An alkene is a hydrocarbon characterized by a double bond between two constituent carbon atoms. Obviously, the name alkene is very close to alkane, and for good reason. Consider, for instance, ethane (an alkane having two carbon atoms) versus ethene (an alkene having two carbon atoms):