Arrangement whereby a company employs only workers who are members in good standing of a specified labour union. It is the most rigid of the various schemes for protecting labour unions (more flexible arrangements include the union shop). Closed shops were declared illegal in the U.S. under the Taft-Hartley Act of 1947, but in practice they continue to exist in some industries, such as construction.
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An example of a closed-loop transfer function is shown below:
The summing node and the G(s) and H(s) blocks can all be combined into one block, which would have the following transfer function:
Using this figure we can write