Thus by 1803 there were two known rare earth elements, yttrium and cerium, although it took another 30 years for researchers to determine that other elements were contained in the two ores ceria and yttria (the similarity of the rare earth metals' chemical properties made their separation difficult).
For instance, students who pursue a Ph.D. in psychology usually take from five to seven years depending upon required coursework as well as internship and supervised residency requirements.
A doctorate in nursing degree takes, on average, four to six years to complete. You will spend a great deal of time focusing on an area of research that you choose. For students who have the time and resources, there is the chance to finish your program sooner.bout a doctoral degree in nursing. Completing a doctoral degree in nursing (DNP) program will take anywhere from three to five years and has the ability to propel you further in your career.