Abstract: A computer implemented method of presenting search results, the method comprising the steps of receiving a search query from a client; using the search query, searching a first database of pay-per-click display items to generate a set of pay-per-click search results that match the search query; using the search query, searching a second database of cost-per-impression display items to generate a set of cost-per-impression search results that match the search query; sending returned pay-per-click search results, comprising at least a subset of the set of pay-per-click search results, if any, and returned cost-per-impression search results, comprising at least a subset of the set of cost-per-impression search results, if any, to the client.

Abstract: There is disclosed an ion mobility detector having a sample inlet membrane means for flowing a sample passing through the membrane over an ionisation source to an ion reaction region, with which two or more ion drift regions communicate, means for impressing a potential gradient on each drift region, an ion injection shutter at the entrance to each drift region whereby the drift region can be made accessible or inaccessible to ions of a particular sign located in the reaction region, an ion detector in each drift region, means for passing drift gas down each drift region to the reaction region and exit means in the reaction region remote from the ionisation source for venting drift gas from the reaction region, the ionisation source (26) being offset from the reaction region (27).