A direct current power system according to one non-limiting embodiment includes a direct current power source operable to distribute a direct current voltage throughout at least one structure, and at least one controller operable to selectively couple a direct current load to the direct current voltage in response to a wireless signal from an energy-harvesting switch. These devices are used to test for a variety of analytes, such as drugs of abuse, hormones, proteins, urine or plasma components and the like. The waveguide core has a waveguide core face such that the waveguide core face is aligned with the substrate face. The video display is pivotable between a stowed position and a viewing position. The serial ATA interface is configured to transfer standard disk-drive commands from the host computer to the disk control system and is configured to not transfer nonstandard disk-drive commands from the host computer to the disk control system. The thermally conductive composition absorbs or reflects electro magnetic interference waves and prevents their transmission into and through the heat pipe to the electronic components being cooled by the heat pipe.