function burn(uint256 _value) onlyOwner public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);   
        balanceOf[msg.sender] = sub( balanceOf[msg.sender],_value);            
        totalSupply =sub(totalSupply,_value);                      
        Burn(msg.sender, _value);
        return true;
    }