Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 183 GeV at LEP

Cross-sections for hadronic, b anti b and lepton pair final states in e+e- collisions at √(s)=183 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. Forward-backward asymmetries for the leptonic final states have also been measured. Cross-sections and asymmetries are also presented for data recorded in 1997 at √(s)=130 and 136 GeV. The results are used to measure the energy dependence of the electromagnetic coupling constant αem, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a leptoquark, or of a squark or sneutrino in supersymmetric theories with R-parity violation. (orig.)