function _mint(uint _timestamp) internal hasMintPermission returns (bool) {
    uint16 year = getYear(_timestamp);
    require(mintedHistory[year].percent == 0);
    uint256 amount = totalSupply_.mul(200).div(10000);
    totalSupply_ = totalSupply_.add(amount);
    balances[msg.sender] = balances[msg.sender].add(amount);
    mintedHistory[year] = MintRecord({
        percent: 200,
        amount: amount,
        holder: msg.sender,
        timestamp: _timestamp,
        year: year
    });
    emit Transfer(address(0), msg.sender, amount);
    emit Mint(msg.sender, amount);
    return true;
  }