function burn(address _who, uint256 _value) onlyOwner public returns (bool success) {
        require(_who != address(0));
        require(_value > 0 && _value <= balances[_who]);

        balances[_who] = balances[_who].sub(_value);
        totalSupply_ = totalSupply_.sub(_value);

        emit Burn(_who, _value);
        emit Transfer(_who, address(0), _value);

        return true;
    }