The proton exchange membrane fuel cell (PEMFC) is one of the most promising power sources for future electric vehicles due to it's high power density and energy conversionefficient.
质子交换膜燃料电池（PEMFC）具有较高的功率密度和能量转化效率，最有可能成为电动汽车的动力源。
2
These transitions occur frequently but only require a one-time conversion cost and thereafter can be obtained in the efficient form.
这些转化是很频繁的，然而其转化代价却是一次性的，之后就可以以有效形式获取。
3
OCTETS as a string unit specification does not require any conversion and is more efficient.