How does the "portal particle screens" improvement work?

I'm playing as Vaulters, and I'm having difficulty parsing what the hell the "portal particle screens" system improvement does:

Specifically:

1. What is "construction effects"? Does it mean that during construction, my empire has reduced science? What if I'm building more than one of these at once? Does this penalty go away when construction is complete?
2. What does "per constructed aperture" mean? I'm guessing per portal, since portals have in their description "+1 Vaulter aperture on star system". Is there anything else which is an "aperture"?
3. How does the science bonus work? Does it mean the system's science output improves by (1 science per portal)%?
4. What does it mean "not affected by additional improvements, not cumulative"? I'm guessing the former is that portals built after that improvement is built do not count, but what does the latter mean?
5. And finally, a bit more high level: even if I have like 20 portals, how can +20% science bonus on a single system be worth -66% science on the entire empire for 15 turns?

Solution 1:

OK, so I experimented with it and I think I can now answer all of the questions:

1. It means the during the construction, empire-wide science output is decreased by 66% of what it would otherwise be. When building more than one of these improvements in parallel, empire science output goes down to 0%. However, there's no benefit in building more than one of these in parallel - see below.
2. It's per portal, as far as I can tell.
3. It's a an empire modifier, not a system one. It adds a +x% science from empire line to the "empire wide factors" list - for example, here's my modifier after building one while owning 24 portals:
   
   And here's how it appears on a sample system:
   
   The second line, the "from empire" one, is from the improvement. It's roughly 24% of the "from planets" value. I'm not quite sure why it's not exactly 24%, maybe it's due to some interaction with one of the many other system- or empire-level modifiers.
   Again, this bonus will now appear on every system, not just the ones on which this improvement was built.
4. It means:
   • "Not affected by additional improvements" - additional copies of the "portal particle screens" improvement will have no further beneficial effects. Unlike my original assumption, portals built after that improvement is completed do count, and they increase the modifier.
   • "Not cumulative" - the bonuses are added together and then applied as one bonus, not multiplying each other.
5. Math time! If your total science output is S, over the 15 turns you build this improvement you lose 15*0.66*S = 10S science. Owning P portals does not exactly translate to an empire-wide P% bonus because it's a modifier on the base value (science from planets) and not final value (entire system science). Let's estimate that the base value is roughly 3/4 of the total value, which means the total science bonus per turn due to the improvement is 0.01*P*0.75*S = 0.0075PS, so the time it will take to get back the investment is 10S/0.0075PS = 1333.33/P. Here's how it looks plotted against the number of portals (axes don't matter since it's symmetric):
   
   So, for example, with 20 systems it will take 67 turns to return the investment, while with 40 systems it will take 34 turns. So even with 40 systems, it will mean 34+15 = 49 turns before you catch up and start seeing a benefit, meaning 49 turns in which you get new technologies slower than if you would not have built the improvement - that's quite a lot! Overall I'd say that building this improvement is highly situational, and generally not worth it unless your empire spans many dozens of systems - and even then, don't expect any quick returns.