sentences:  In the United States, utilities and oil and gas companies have used data diodes for several years, and regulators have encouraged their use to protect equipment and processes in SISs.The Nuclear Regulatory Commission (NRC) now mandates the use of data diodes and many other sectors, in addition to electrical and nuclear, also use data diodes effectively.In Europe, regulators and operators of several safety-critical systems started recommending and implementing regulations on the use of unidirectional gateways.