It's been enough where I end up automatically ignoring MDPI papers unless someone I respect recommends one to me. For better or worse. But MDPI made it's own bed in many ways.
Again, this is my one and only experience with them. I'd be interested if others have any...
most papers are worthless, but when they are first written, it is too early to tell which ones they are; of course reviewers' suggestions are often helpful in improving the quality of a paper, but they cannot improve a worthless paper into a groundbreaking one
pre-publication peer review was instituted mostly in the mid-twentieth century and should be regarded as a failed experiment belonging to the age of paper. most peer-reviewed papers are worthless, and peer review often serves merely to retard progress
most of the papers i see on mdpi are mediocre, but some are useful, and it certainly isn't vixra-style garbage
It is obtuse to think that a few people can read a paper and know it's validity. It's falsifiable but even that's fuzzy. The problem then comes down to the incentive structures. Why do people cheat? Because we're lazy evaluators. It's odd to me that we won't read the works of peers in a department, lab, whatever. But doing that would be a much stronger form of evaluation than anything that could be inferred from citations, h-index, conference ranking, etc. Plus, the structure is to push novelty fast and frequently. That's not only not possible but ignores a fundamental aspect of science: reproducibility.
But this also doesn't mean there aren't scam publishers and publishers scammers prefer. But I'd say that those are a result of the former issue. Because metrics are not being treated as guides. It's just Goodhart's Law in action.
i don't think mdpi is a scam publisher, but then, i don't read mdpi papers from following some kind of latest-mdpi-papers feed; i read them because other papers cite them, so i couldn't tell you if the utter-bullshit-paper percentage on mdpi is 1% or 99%
i just know i heave a sigh of relief when the paper i'm looking for turns out to be on mdpi, because i know that not only will i be able to read it without hassle, it will have a clearly marked creative-commons license that permits me to archive and redistribute the paper. same with hindawi actually, though i'm mmaybe a bit prejudiced against hindawi papers
http://www.mdpi.com/1996-1073/9/8/622/htm a 2016 #paper on #solar #energy payback times and EROEI (“EROI”) and life-cycle analysis (LCA) and net energy analysis (NEA). In particular fixed ground-mounted “multicrystalline” silicon #photovoltaic cells have EPBT of 0.9 to 2.1 years depending on irradiation (insolation), and an EROEI of 15 to 35. This is surprising because that’s pretty much what it was when NREL published an EPBT analysis around 2001 or so.
https://www.mdpi.com/1996-1073/2/1/1/htm “#Energy Inputs in #Food Crop Production in Developing and Developed Nations,” Pimentel’s #EROEI #paper where he found about four joules returned per joule spent on industrialized #agriculture, #CC-BY, Energies 2009, 2(1), 1-24; https://doi.org/10.3390/en20100001
https://www.mdpi.com/1424-8220/21/2/438 Elfring, Torta, and van de Molengraft’s more comprehensive #particle-filters #tutorial #paper (with #PDF) which supposedly has example code that I can’t find. This is recent (02021) and open-access (#CC BY, I think), and many pages long, and has an overview of a lot of the motivation, but in some sense not very approachable.
https://www.mdpi.com/2075-163X/12/2/220 #CC #paper describes various excavation methods (plasma, foam injection, etc.) including #expanding-grout, which it says works by hydrating lime under confinement and also producing ettringite, but lists four different types: type K (4CaO·3Al₂O₃·SO₃ + 8CaSO₄⋅H₂O + 6Ca(OH)₂ + 74H₂0 → 3(3CaO⋅Al₂O₃⋅3 CaSO₄⋅32H₂O, can be enhanced with silica fume and plasticizer), type M (CaO⋅Al₂O₃ + 3CaSO₄⋅H₂O + 2Ca(OH)₂ + 24H₂O → 3CaO⋅Al₂O₃⋅3CaSO₄⋅32H₂O), type S (3CaO⋅Al₂O₃ + 3CaSO₄⋅H₂O + 26H₂O → 3CaO⋅Al₂O₃⋅3CaSO₄⋅32H₂O), and class [sic] G (CaO + H₂O → Ca(OH)₂). Calls it “SCDA” and mentions ASTM C 845 “Standard Specification for Expansive Hydraulic Cement”. It says they work too slowly (12h) to replace explosives in the usual mining cycle, but I suspect that’s not true of class G, where the main problem is keeping it from reacting to completion before you can pour it into the hole.
https://en.wikipedia.org/wiki/Predatory_publishing
the claim is that they are ripping off the scientists. Note
https://en.wikipedia.org/wiki/Jeffrey_Beall
was forced to retract his claim that MDPI was predatory.
You can't just look at the publisher.
A quick shortcut is to look at who are the editors/organizers. If you don't see affiliations from the West, it's unfortunately a very bad sign.
MDPI is the most active RSS feed by far in my collection, they publish a lot of stuff. I'd be interested in getting feeds of Open Access papers on other journals (say from Science) but so far no dice.