$A$	self-defined function
$a$	self-defined function
$B$	self-defined function
$b$	self-defined function
$C$	self-defined function
$C_i$	heat leakage coefficient ($J/K$)
$c$	self-defined function
$F$	external load
$f$	dimensionless external load
$G$$H$, $I$	some defined functions
$J$	steady current
$k$	temperature ratio
$k_B$	Boltzmann constant ($J/K$)
$L$	length of potential field ($m$)
$n$	the ratio of barrier height
$P$	power output ($W$)
$Q$	heat flow rate ($W$)
$q_{kin}$	kinetic energy ($W$)
$q_L$	heat leakage rate ($W$)
$T$	temperature ( $K$)
$U$	barrier height ($J$)
$v$	drift velocity of particle
$x$, $y$	self-defined functions
$z$	the position of particle
Greek symbols
$\gamma$	friction coefficient
$\eta$	efficiency
$\mu$	asymmetry of the potential
$\omega$, $\tau$	temperature ratio
$\beta$	dimensionless heat leakage coefficient
Abbreviations
CR	cold reservoir
FTT	Finite time thermodynamics
HE	heat engine
HR	hot reservoir
TBHE	thermal Brownian heat engine
VM	viscous medium