Write Python functions to capture the process descriptions given below. All functions must have at least one function call to demonstrate that the function is working correctly. 

1. A function of one argument that returns double the value of the argument. 

2. A function of two arguments that returns the smaller of them. 

3. A function of two arguments that returns 1 if the first argument is negative but the second argument otherwise. 

4. Write a function called calculate_circle_area that takes the radius of a circle as an argument and returns its area. 

5. Create a second function called calculate_rectangle_area that calculates the area of a rectangle given its length and width. 

6. Implement a function that converts temperature from Celsius to Fahrenheit and vice versa, and demonstrate its usage.

The use of any IA involvement is prohibited.