The Six Kingdoms. When Linnaeus developed his system of classification, there were only two kingdoms, Plants and Animals. But the use of the microscope led to the discovery of new organisms and the identification of differences in cells.A two-kingdom system was no longer useful.Today the system of classification includes six kingdoms.he Six Kingdoms. When Linnaeus developed his system of classification, there were only two kingdoms, Plants and Animals. But the use of the microscope led to the discovery of new organisms and the identification of differences in cells.
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PTC stands for âPositive Temperature Coefficientâ. PTC thermistors are resistors with a positive temperature coefficient, which means that the resistance increases with increasing temperature. PTC thermistors are divided into two groups, based on the materials used, their structure and the manufacturing process. The first group of PTC thermistors is comprised of silistors, which use silicon as the semiconductive material. They are used as PTC temperature sensors for their linear characteristic. The second group is the switching type PTC thermistor. This type of PTC thermistors is widely used in PTC heaters, sensors etc. Polymer PTC thermistors, made of a special plastic, are also in this second group, often used as resettable fuses. The switching type PTC thermistor has a highly nonlinear resistance-temperature curve.