Since the Denali National Park and Preserve Visitor Center opened in summer 2005, many thousands of people have seen Heartbeats of Denali, a film that introduces visitors to the annual cycle of the park ecosystem. For a freshwater ice scientist, the segment that shows bare, heavily-cracked and wind-polished ice on the Nenana River is particularly interesting. Extending horizontally many tens of meters, the wide, snow-filled, thermal cracks give the ice cover the appearance of crazy paving. Thermal cracking also occurs under snow cover, on both river ice and lake ice, but the absence of snow amplifies the process and its effects. Without an insulating snow layer, the top of the ice becomes very cold, almost as cold as the air above, while the bottom, resting on water, remains at 32F (0C). The large temperature difference causes the ice to bend upwards and crack when it can no longer withstand the curvature (Metge 1976). If this process is repeated often enough, the entire ice cover is reduced to a series of smaller, angular plates defined by a dense network of inter-secting cracks; hence the appearance of crazy paving on the frozen Nenana River. The effectiveness of snow as an insulator is illustrated in Figure 1. It shows data obtained at Horseshoe Lake, 2.2 miles (3.5 km) north of the DNPP Visitor Center. On a cold (-5.7F, -20.95C) day in early December 2003, when the ice was 16.5 inches (0.42 m) thick, the average depth of snow on the ice was 6.3 in (0.16 m) (Figure 1a), and the average temperature at the base of the snow was 25.5F (-3.6C), a 31.2F (17.35C) difference (Figure 1b). The insu-lating effect of the snow is further illustrated by the almost linear relationship between ice surface temperature and snow depth values (Figure 1d), i.e., the deeper the snow, the higher the temperature on the ice surface at the bottom of the snow. The data in Figure 1 were obtained by third, fourth and fifth grade students from Tri-Valley School, Healy, about 8.1 miles (13 km) north of the lake. Since autumn 2003, a total of 60 different students have visited their frozen study site to measure ice thickness, and the depth, density and temperature of the snow on the ice. Because it is a mixed-grade class, some students have been making measurements for as many as three consecutive winters. Integrated into their science and language arts classes, the Horseshoe Lake project has taken students outdoors in winter to study their local ecosystem.
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Fuel injectors typically fail due to a buildup of contaminants such as carbon. Carbon build-up can cause a clogged or partially clogged injector, preventing the injector from closing all the way. This results in a drip that creates a misfire. Fuel injectors can also leak externally as a result of dry, cracked rubber seals, or cracks within the injector itself. Electrical portions of the injector are particularly vulnerable to age, heat, and damage from moisture. Symptoms of failure include:
An electric balance test for an electronic failure may be possible with the use of a scan tool. A technician will use this device to measure amp resistance on the injectors and test the volts on the wiring harness for electrical errors. If the fuel injector is clogged, a technician may have to remove the injectors and perform a flow test. A flow test will measure the condition and flow rate of your fuel injectors. 2ff7e9595c
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