Question: How can I separate the exponent of an expression?

I've written a procedure which currently outputs, for example, 3/8*2^(1/3)*k^(4/3). However when I plot this it doesn't give me the correct graph that I'm looking for. I've found that rewriting the equation as  3/8*2^(1/3)*(k^2)^2/3 will give me the proper function in Maple, however I don't know how to get my procedure to output the equation in terms of k^2. I'm sure there's a fairly straightforward solution- does anyone know what I'm missing?

Cheers.

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