Soil is formed slowly. The constant freezing and thawing in the tundra helps to break the rocks into smaller pieces. Permafrost consists mostly of gravel and finer material. The arctic tundra is also a windy place and winds can blow between 48 to 97 kilometres. The tundra is basically like a desert when it comes to precipitation. Only about 150-250 millimetres of precipitation (mostly snow) fall each year. When water saturates the upper surface, bogs and ponds may form, providing moisture for plants, and breeding thousands of insects that attract many migrating birds. Animals are adapted to handle cold winters and to breed and raise young quickly in the very short and cool summers. Some animals have grown thick fur that turns white in the winter. Others find a place to hibernate during the winter months. Many plants have dark red leaves that allow the plant to absorb more heat from
current for various values of LED current. The CTR is dependent on the LED and phototransistor characteristics, and can vary widely from one device to the next. The current transfer ratio has several implications when you want to inter- face a switch to a microprocessor system. First, if you want to connect the switch directly to a digital input (Figure 3.8), the transistor output has to swing between valid logic levels. To insure that the phototransistor saturates, the value of the pullup resistor is limited. For example, if you are driving the LED with 10 ma and the CTR has a minimum value of .1, then the pullup resistor will be around 5000 W. A smaller resistor would provide better noise immu- nity (lower impedance) and possibly faster speed, but wouldn’t work with all devices because the transistor would not be able to sink enough current to insure a valid logic low level. To use a smaller pullup, you could use an optical
Figure 11.9. The arrangement of the air control unit. 228 Chapter 11 continuous, with relatively low velocity, or equilibrium can be reached, and sausages periodic. With the periodic system, the room with lower moisture content are then dried is rinsed through with relatively dry, high- further the traditional way. velocity air. Then air circulation stops, and In the Quick-Dry-Slice (QDS) technology the product saturates the air; then the rinse (Comaposada et al. 2008), sausages are comes again. In this system, the product reg- fermented, and, after fermentation, they are ulates its own drying, and case hardening can frozen and sliced; in this form, they are dried be avoided. by convection and vacuum drying. This Smoking needs lower humidity. The method of drying lasts 30 minutes only, and
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