Search for Leptoquarks and FCNC in e^+ e^- annihilations at sqrt{s}=183 GeV

A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector.These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 1/pb. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from $134 GeV/c^2$ to $171 GeV/c^2$ for electromagnetic type couplings) and couplings of the leptoquark states.A search for top-charm flavour changing neutral currents($e^+ e^- \to \bar t c$ or charge conjugate) used the semileptonic decay channel. A limit on the flavour changing cross-section via neutral currents was set at 0.55pb (95% confidence level).