“Il sito comprato da Ama per realizzare l’inceneritore alla cifra astronomica di sette milioni e mezzo di euro è oggetto di indagini della Procura di Roma e della Corte dei conti è contaminato” è quanto dichiara in una nota l’Unione dei Comitati contro l’inceneritore.

“A metterlo nero su bianco – precisa la nota dell’Unione dei Comitati - sono le indagini di caratterizzazione ambientale del suolo svolte nel primo semestre del 2024 da Acea Infrastrutture che hanno evidenziato molteplici superamenti delle CSC per idrocarburi pesanti e degli IPA.
Appaiono particolarmente gravi – incalzano dall’Unione dei Comitati - le omissioni di Ama e dell’Amministrazione capitolina. La municipalizzata ha omesso di avviare le procedure obbligatorie attuando le misure di prevenzione stabilite dall'articolo 242 del codice dell’ambiente mentre l’amministrazione capitolina guidata da Gualtieri ha proseguito l’iter che ha portato alla validazione del progetto in un sito contaminato. L’amministrazione capitolina ha pertanto ignorato il principio di precauzione di derivazione europea stabilito che avrebbe imposto di indagare, origine, estensione e profondità della contaminazione la cui origine antropica in relazione agli idrocarburi pesanti e agli IPA è fuori discussione.
“Nell’ambito delle osservazioni alla VIA e sulla base del principio di precauzione stabilito dall’ articolo 191 del Trattato sul funzionamento dell’Unione europea – concludono dall’Unione – abbiamo pertanto chiesto di sospendere la VIA e il PAUR fin quando non fosse completato l’espletamento dell’insieme delle procedure obbligatorie necessarie alla caratterizzazione del sito. Infine, abbiamo sollecitato un intervento in autotutela finalizzato al previo espletamento delle procedure di caratterizzazione del sito accompagnato dalla sospensione della VIA e del PAUR evitando il danno erariale legato ai maggiori costi da sostenere per la bonifica per l’avvio in fasi successive”.

Bismuth is known for a few things: its low melting point, high density, and psychedelic hopper crystals. A literal deep-dive into any molten metal would be a terrible idea, regardless of low melting point, but [Electron Impressions]’s video on “Why Do Bismuth Crystals Look Like That” may be the most educational eight minutes posted to YouTube in the past week.

The whole video is worth a watch, but since spoilers are the point of these articles, we’ll let you in on the secret: it all comes down to Free Energy. No, not the perpetual motion scam sort of free energy, but the potential that is minimized in any chemical reaction. There’s potential energy to be had in crystal formation, after all, and nature is always (to the extent possible) going to minimize the amount left on the table.

In bismuth crystals– at least when you have a pot slowly cooling at standard temperature and pressure–that means instead of a large version of the rhombahedral crystal you might naively expect if you’ve tried growing salt or sugar crystals in beakers, you get the madman’s maze that actually emerges. The reason for this is that atoms are preferentially deposited onto the vertexes and edges of the growing crystal rather than the face. That tends to lead to more vertexes and edges until you get the fractal spirals that a good bismuth crystal is known for. (It’s not unlike the mechanism by which the dreaded tin whiskers grow, as a matter of fact.)

Bismuth isn’t actually special in this respect; indeed, nothing in this video would not apply to other metals, in the right conditions. It just so happens that “the right conditions” in terms of crystal growth and the cooling of the melt are trivial to achieve when melting Bismuth in a way that they aren’t when melting, say, Aluminum in the back yard. [Electron Impressions] doesn’t mention because he is laser-focused on Bismuth here, but hopper crystals of everything from table salt to gold have been produced in the lab. When cooling goes to quick, it’s “any port in a storm” and atoms slam into solid phase without a care for the crystal structure, and you get fine-grained, polycrystaline solids; when it goes slowly enough, the underlying crystal geometry can dominate. Hopper crystals exist in a weird and delightful middle ground that’s totally worth eight minutes to learn about.

Aside from being easy to grow into delightful crystals, bismuth can also be useful when desoldering, and, oddly enough, making the world’s fastest transistor.

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Try an experiment. Next time you are in a room with someone, ask them to name everything in the room. Only certain kinds of people will say “air” or “light.” For most people, those are just givens, and you don’t think about them unless, for some reason, you don’t have them. Resistance is like that in electronics. You use it constantly, but do you ever think much about what it is? For a resistor, the value in ohms really represents the slope of the line that describes the amount of voltage you’ll see across the component when it carries a certain amount of current. For resistors, that slope is — at least in theory — constant and positive. But [Void Electronics] made a video exploring negative resistance, and it is worth watching, below.

If you haven’t seen negative resistance before, you might wonder how that is possible. Ohm’s law is just a shorthand for calculating the slope of a graph with voltage on the Y axis and current on the X axis. It works because the voltage and current are always zero at the same time, so the slope is (V-0)/(I-0), and we just shorten that to the normal Ohm’s law equation.

But not everything has a linear response to current. Some devices will have different slopes over different current regions. And sometimes that slope can be negative, meaning that an increase in current through the device will cause it to drop less voltage. Of course, this is usually just over a narrow range and, as [Void] points out, most devices don’t specify that parameter on their data sheets. In fact, some transistors won’t even work in the circuit.

The circuit in question in the video below the break is an odd one. It uses two resistors, an LED, and a transistor. But the transistor’s base is left disconnected. No 555 needed. How does it work? Watch the video and you’ll see. There’s even a curve tracer if you don’t like to see hand-drawn graphs.

We’ve looked at negative resistance more than once. There are a few exotic devices, like tunnel diodes, that are explicitly used for the negative resistance property. When the gas in a neon bulb breaks down, you get the same effect.

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The fact that there exist in our world flat rocks that make lightning when you point them at the sun is one of the most unappreciated bits of wizardry in this modern age. As hackers, we love all this of techno-wizardry–but some of us abhor paying full price for it. Like cars, one way to get a great discount is to buy used. [Backyard Solar Project] helped a friend analyze some 14-year-old panels to see just how they’d held up over the years, and it was actually better than we might have expected.

The big polycrystalline panels were rated at 235 W when new, and they got 6 of them for the low, low price of “get this junk off my property”. Big panels are a bit of a pain to move, but that’s still a great deal. Especially considering that after cleaning they averaged 180 W, a capacity factor of 77%. Before cleaning 14 years worth of accumulated grime cost about eight watts, on average, an argument for cleaning your panels. Under the same lighting conditions, the modern panel (rated to 200 W) was giving 82% of rated output.

That implies that after 14 years, the panels are still at about 94% of their original factory output, assuming the factory wasn’t being overoptimistic about the numbers to begin with. Still, assuming you can trust the marketing, a half a percent power drop per year isn’t too bad. It’s also believable, since the US National Renewably Energy Laboratory (yes, they have one) has done tests that put that better than the average of 0.75 %/yr. Of course the average American solar panel lives in a hotter climate than [Backyard Solar Project], which helps explain the slower degradation.

Now, we’re not your Dad or your accountant, so we’re not going to tell you if used solar panels are worth the effort. On the one hand, they still work, but on the other hand, the density is quite a bit lower. Just look at that sleek, modern 200 W panel next to the old 235 W unit. If you’re area-limited, you might want to spring for new, or at least the more energy-dense monocrystalline panels that have become standard the last 5 years or so, which aren’t likely to be given away just yet. On the gripping hand, free is free, and most of us are much more constrained by budget than by area. If nothing else, you might have a fence to stick old panels against; the vertical orientation is surprisingly effective at higher latitudes.

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