Context and question: At a certain temperature, (usually between 1,500 F (820 C) and 1,600 F (870 C), depending on carbon content), the base metal of steel undergoes a change in the arrangement of the atoms in its crystal matrix, called allotropy. This allows the small carbon atoms to enter the interstices of the iron crystal, diffusing into the iron matrix. When this happens, the carbon atoms are said to be in solution, or mixed with the iron, forming a single, homogeneous, crystalline phase called austenite. If the steel is cooled slowly, the iron will gradually change into its low temperature allotrope. When this happens the carbon atoms will no longer be soluble with the iron, and will be forced to precipitate out of solution, nucleating into the spaces between the crystals. The steel then becomes heterogeneous, being formed of two phases; the carbon (carbide) phase cementite, and ferrite. This type of heat treatment produces steel that is rather soft and bendable. However, if the steel is cooled quickly the carbon atoms will not have time to precipitate. When rapidly cooled, a diffusionless (martensite) transformation occurs, in which the carbon atoms become trapped in solution. This causes the iron crystals to deform intrinsically when the crystal structure tries to change to its low temperature state, making it very hard and brittle.
What are the characteristics of steel if it is cooled to quickly?
Answer: very hard and brittle
Context and question: Predatory animals often use their usual methods of attacking prey to inflict or to threaten grievous injury to their own predators. The electric eel uses the same electric current to kill prey and to defend itself against animals (anacondas, caimans, egrets, jaguars, mountain lions, giant otters, humans, dogs, and cats) that ordinarily prey upon fish similar to an electric eel in size; the electric eel thus remains an apex predator in a predator-rich environment. A predator small enough to be prey for others, the domestic cat uses its formidable teeth and claws as weapons against animals that might confuse a cat with easier prey. Many non-predatory prey animals, such as a zebra, can give a strong kick that can maim or kill, while others charge with tusks or horns.
What method is used by giant otters to prevent their prey from attacking them?
Answer: unanswerable
Context and question: Anthropologists have contributed to the debate by shifting the focus of research: One of the first challenges for the researcher wishing to carry out empirical research in this area is to identify an appropriate analytical tool. The concept of boundaries is useful here for demonstrating how identity works. In the same way as Barth, in his approach to ethnicity, advocated the critical focus for investigation as being "the ethnic boundary that defines the group rather than the cultural stuff that it encloses" (1969:15), social anthropologists such as Cohen and Bray have shifted the focus of analytical study from identity to the boundaries that are used for purposes of identification. If identity is a kind of virtual site in which the dynamic processes and markers used for identification are made apparent, boundaries provide the framework on which this virtual site is built. They concentrated on how the idea of community belonging is differently constructed by individual members and how individuals within the group conceive ethnic boundaries.
What researcher advocated for focus on the boundaries of ethnic groups rather than the cultural aspects of ethnic groups?
Answer:
Barth