Shizuo Kambayashi/Associated Press In a stock-market filing in Japan, Toshiba said losses associated with Westinghouse Electric, its troubled US nuclear power subsidiary, had created "substantial uncertainty" over its ability to continue as a going concern. The declaration lifts the stakes as Toshiba seeks outside investors for its coveted microchip business, a portion of which it is selling off to raise cash and stave off disaster. Toshiba's uncertain fate represents another blow for a country that has seen its dominance in a range of technologies eclipsed by rivals in South Korea and China.