To obtain such positron microbeam, it is necessary to use objective lenses, which are commonly used in the electron microscopy. We also attempted to form the positron microbeam using a positron beam for the positron diffraction experiment and a SEM optics [6]; [7] ; [8].
Publicly Traded Companies that Benefited from Forced or Slave Labor, 1929-1945 CalPERS
Although slaves had been sold in the American colonies since at least 1619, slave labor did not come to represent a significant proportion of the labor force in any part of North America until the last quarter of the 17th century.