Roof structures including safety stanchions for mounting directly to the roof of a building are disclosed. The driver circuit is so configured that a circuit element affected by stray capacitance formed between the conductive seal and the driver circuit is disposed apart from the conductive seal. Further, the systems may identify tailored content based upon a consumer profile, communicate the tailored content to a web client, andor receive a selection of the tailored content. The output point of the midpoint electric potential of the second series circuit is provided at a midpoint between two temperature sensor resistors, and the second midpoint connection is provided on the center line of the heater resistor. The present invention is also directed to an enriched or purified population of immortalized progenitor cells. The system provides a plurality of camp tools that are integral to a shovel, so as to provide the intended function without interfering with the normal usage of the shovel.