A method for repelling insects from the skin of a subject by applying thiamine to the skin in a transdermal patch in an effective amount for systemic absorption through the skin. Each block has two longitudinal lateral surfaces bounding two corresponding longitudinal grooves, and two transverse lateral surfaces bounding two corresponding transverse grooves. A service is a category of work hosted on a subset of multi-node database servers, such as work that is performed for an online order entry application. Identification of the node is stored for use in tracing a route of the tracer packet through the data processing system in response to receiving a message from a node indicating receipt of the tracer packet. The third antiferromagnetic layers are disposed on the second antiferromagnetic layer at the two side portions.