The Carnot cycle is a theoretical thermodynamic cycle that represents the most efficient engine possible. It consists of four reversible processes: two isothermal processes and two adiabatic processes.

The Carnot cycle can be represented on a temperature-entropy (T-s) diagram. The cycle starts at state A, where the working substance is in contact with a high-temperature reservoir at temperature T_h. In the first process, isothermal expansion (process AB), the working substance absorbs heat Q_h from the high-temperature reservoir, and its temperature remains constant at T_h. The working substance expands and does work on the surroundings.

Next, in the adiabatic expansion (process BC), the working substance does work on the surroundings without exchanging heat with the surroundings. As a result, the temperature of the working substance decreases from T_h to T_c.

In the third process, isothermal compression (process CD), the working substance is in contact with a low-temperature reservoir at temperature T_c. Heat Q_c is rejected to the low-temperature reservoir, and the temperature of the working substance remains constant at T_c. The working substance contracts and work is done on it by the surroundings.

Finally, in the adiabatic compression (process DA), the working substance is compressed without exchanging heat with the surroundings. The temperature of the working substance increases from T_c to T_h.

The Carnot cycle is reversible, meaning that it can be operated in reverse to act as a heat pump or refrigerator. The efficiency of the Carnot engine is given by:

Efficiency = 1 - (T_c / T_h)

Where T_c is the temperature of the low-temperature reservoir and T_h is the temperature of the high-temperature reservoir.

In the specific case you mentioned, the Carnot engine operates between temperatures T_h = 727 K and T_c = ??? (the temperature of the low-temperature reservoir is not specified). With this information, the efficiency of the Carnot engine can be calculated using the equation mentioned above.