What is the optimal sequence of departures and arrivals on a single runway? When in a peak load scenario with plenty of departing &amp; arriving aircraft to keep the ATC pipeline full, are there considerations that make a certain sequence of Departures / Arrivals that optimizes throughput?

For specificity, let us assume a single runway in use and no general aviation aircraft with predominantly jet traffic and multiple runway entry &amp; exit taxiways available. Including high speed exit turnoffs. 

I typically see a sequence something like:

 Dep-Dep-Arr-Dep-Dep-Arr


But an alternative optimum might turn out to be:

Dep-Arr-Dep-Arr-Dep-Arr


etc.

I realize that the specifics will depend on the exact aircraft etc. but just to use an idealized model what would result from typical operating constraints. e.g. You need to allow a certain separation during approach but you can have multiple aircraft lined up for take off. So is the potential to squeeze departures into the "holes" higher? Also, you can clear a second departure after a first far more rapidly, than the landing-to-landing interval right?

Just wondering, if you had to set up a formal optimization model what sort of parameters &amp; constraints should go into the model as inputs. 

A follow up question: Say you had two runways available in parallel &amp; widely spaced apart. Does it make sense (for throughput) to dedicate one to landings &amp; another to takeoffs or is it more efficient to mix landings &amp; takeoffs on both runways? 

R18L: Dep-Dep-Dep-Dep-Dep-Dep-Dep-Dep-Dep
R18R: Arr-Arr-Arr-Arr-Arr-Arr-Arr-Arr-Arr


vs 

R18L: Dep-Dep-Arr-Dep-Dep-Arr-Dep-Dep-Arr
R18R: Dep-Dep-Arr-Dep-Dep-Arr-Dep-Dep-Arr


PS. If further simplifying assumptions are necessary, let's imagine a hypothetical airport serving a single aircraft type, say A320 only. Or assume any type you will to be representative of a wide class of aircraft just to get the modelling started.
Usually a mixed usage runway is more efficient than a dedicated arrival runway(s). Arrivals are harder to get closer together than departures as well. Running a final with 5 mile gaps(for wake and all departures) is a good way to do dep-arr-dep-arr.

With dedicated Dep-Arr runways, and assuming you have aircraft ready to go, your expected hourly rate for Arrival only runways is usually around 30, whereas with a departure only runway the rate is about 45 or so(assuming minimal spacing, and have decent fan headings, and the departure routes are split decently to allow good separation heading to the center).