The three-day U.S Africa Leaders Summit starts today amid concerns that African leaders are not fully prepared to meet U.S President Barack Obama and other American leaders at a time when Africa needs billions of dollars in foreign direct investment and help in curbing armed militant groups threatening to overrun the continent. The exclusion of long-time Zimbabwean ruler, President Robert Mugabe, from the summit has worsened the situation with some observers saying the country is set to lose millions of dollars in youth and other investments. VOA's Gibbs Dube reports …….