A fluid flow detecting apparatus is disclosed for detecting a characteristic of fluid flowing in a fluid passage. The cathode includes a plurality of electrically conductive carriers and a plurality of field emitters formed thereon. The light detection unit illuminates the correction image on the image carrying member and detects light reflected thereby. If required, the second application may access the one or more network services via the first network, using the retrieved network address. In one embodiment, lead ion-detecting microspheres are provided that can detect nanomolar levels of lead ions with response times on the order of minutes.