Perovskites Understood

November 27, 2021 by Al Williams 9 Comments

The usual solar cell is made of silicon. The better cells use the crystalline form of the element, but there are other methods to obtain electric energy from the sun using silicon. Forming silicon crystals, though, can be expensive so there is always interest in different solar technologies. Perovskite is one of the leading candidates for supplanting silicon. Since they use lead salts, they are cheap and simple to construct. The efficiency is good, too, even when the material is not particularly well ordered. The problem is every model science has on what should make a good solar cell predicted that orderly compounds would perform better, even though this is not true for perovskite. Now scientists at Cambridge think they know why these cells perform even in the face of structural defects.

Perovskites take their name from a natural mineral that has the same atomic structure. In 2009, methylammonium lead halide perovskites were found to act as solar cells. Conversion rates can be as high as 25.5% according to sources and — apparently — the cells could be as much as 31% efficient, in theory. Solar cells top out — again, in theory — at 32.3% although in the real world you are lucky to get into the high twenties.

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PFAS: The Organofluorines Your Biochemist Warned You About

November 22, 2021 by Maya Posch 49 Comments

Sometimes it begins to feel like a tradition that a certain substance or group of substances become highly popular due to certain highly desirable chemical or physical properties, only for these chemicals then to go on to turn out to form a hazard to the biosphere, human life, or both. In the case of per- and polyfluoroalkyl substances (PFAS) it’s no different. Upon the discovery that a subgroup of these – the fluorosurfactants – have the ability to reduce water surface tension significantly more than other surfactants, they began to be used everywhere.

Today, fluorosurfactants are being used in everything from stain repellents to paint, make-up, and foam used by firefighters. In a recent study of 231 cosmetic products bought in the US and Canada (Whitehead et al., 2021), it was found that all of them contained PFAS, even when not listed on the packaging. The problematic part here is that PFASs are very stable, do not decay after disposal, and bioaccumulate in the body where they may have endocrine-disrupting effects.

Some areas have now at least partially banned PFAS, but the evidence for this is so far mixed. Let’s review what we do know at this point, and which alternatives we have to continuing to use these substances. Continue reading “PFAS: The Organofluorines Your Biochemist Warned You About” →

Tomatoes Are Not Guncotton

November 22, 2021 by Zoe Skyforest 14 Comments

[Integza] hates tomatoes, but loves rocketry. Thus, he decided to see if he could process his most-loathed fruit into some sort of rocket fuel, or at least something relatively flammable. The experiment ended poorly, but the science behind it is interesting.

The basic idea is that tomatoes are largely made up of water, sugar, and cellulose. Thus, if you nitrate that cellulose, it becomes nitrocellulose, also known as guncotton. Guncotton is was once used to replace gunpowder in firearms, though today it’s often used by magicians to create ashless flashes of flame.

To achieve this, [Integza] first attempted to make regular guncotton using a 50:50 mixture of nitric acid and sulfuric acid. The cotton was then neutralized with a baking soda and water mixture to remove excess acid, and the cotton dried. Once tested, it burned quickly as you’d expect from guncotton.

After removing the sugars from tomatoes with water, soap, hydrogen peroxide, and bleach, the tomatoes were then dried to remove excess water before also getting the acid treatment. They were then similarly neutralized, dried, and tested. One tomato did burn rather quickly, while the others merely fizzled.

One of the reasons behind this may have been due to the composition of the tomatoes. Tomatoes often consist of a mixture of cellulose, hemicellulose, and lignin, these latter components are known for producing inferior guncotton. The ramshackle preparation may have had some effect on the results. Let’s just say and it’s not advisable to work with fuming acids without protective gear and a fume hood, either.

The video’s title claims that the tomatoes were turned into rocket fuel, which is far beyond the actual results of the experiment. However, with some more advanced chemical processing, we could certainly see the fruit becoming a mite more flammable than it was. You’re probably better off just sticking to straight cotton though, for the best results. Video after the break.

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Magic In VR That Depends On Your Actual State Of Mind

November 21, 2021 by Donald Papp 10 Comments

[Cangar]’s excitement is palpable in his release of a working brain-computer interface (BCI) mod for Skyrim VR, in which the magic system in the game is modified so that spell effectiveness is significantly boosted when the player is in a focused mental state. [Cangar] isn’t just messing around, either. He’s a neuroscientist whose research focuses on assessing mental states during task performance. Luckily for us, he’s also an enthusiastic VR gamer, and this project of his has several interesting aspects that he’s happy to show off in a couple of videos.

User wearing VR headset — The Muse 2 fits under the VR headset easily.

It all starts with the player wearing a Muse 2 meditation device; a type of passive, off-the-shelf electroencephalography (EEG) unit aimed primarily at guiding a user towards better relaxation and focus. [Cangar] reads data using the Brainflow library and processes it into a final value on a scale between “not focused” and “focused”. [Cangar] makes a point of explaining that his system ultimately has the goal of modeling the player’s state of mind, which is different from modeling just the brain activity. As such, motion data is considered as well, and holding still confers a small bonus to the process.

How is this data actually used in the game? In VR, this “focus” value is shown as a small bar on the player’s wrist, and spell effectiveness (for example, damage for attack spells) scales along with the size of the bar. When the bar is full a player would be very powerful, with spells doing double damage. If the bar is empty, spells will do little to no damage.

[Cangar] demonstrates the mod in two videos (both embedded below), but you won’t see him blasting enemies with fireballs. Presumably, VR gamers already know what that looks like, so what he does instead is explain how the system looks and works (first video, cued to 4:12), and in the second, he video demonstrates how the focus meter changes depending on his activity and mental state.

The results look exciting, and the potential uses of a system like this are pretty interesting to think about. Taking a few deep breaths and calming one’s body and mind before launching a magical attack will have a tangible effect in the world, and because things rarely go according to plan, there is also a clear survival benefit to learning to focus while under pressure. But if a brain monitor isn’t your cup of tea, maybe consider a leisurely bike ride through Skyrim, instead.

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Microplastics Are Everywhere: Land, Sea And Air

November 16, 2021 by Zoe Skyforest 65 Comments

Plastics took off in the 20th century, with the new class of materials finding all manner of applications that metal, wood and paper simply couldn’t deliver on. Every field from electronics to the packaging of food found that plastics could play a role.

Now, over 150 years since the development of Parkesine in 1867, we’re now realizing that plastics come with more than a few drawbacks. They don’t break down well in nature, and now microplastics are beginning to appear all over the Earth, even in places where humans rarely tread. It seems they may even spread via the air, so let’s take a look at this growing problem and what can be done about it.

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Vacuum “Tube” Might Replace GPS One Day

November 15, 2021 by Al Williams 27 Comments

GPS and similar satellite navigation systems changed everything. The modern generation is far less likely to have had to fold a service station map or ask someone for directions on the side of the road. But GPS isn’t perfect. You need to see the sky, for one thing. For another, an adversary could jam or take down your satellites. Even a natural disaster could temporarily or permanently knock out your access to the satellites.

The people at Sandia National Labs worry about things like that and they want to replace GPS with quantum accelerometers and gyroscopes. The problem: those things take expensive and bulky vacuum systems and lasers. Sandia, however, has had a sealed device about the size of an avocado that weighs about a pound that could possibly do the job. Their goal is to see it work without maintenance for four more years.

This is no ordinary vacuum tube, though. It is made of titanium and sapphire. By itself, the device doesn’t do much of anything, but it shows that rubidium can be contained in a sealed chamber with no additional pumping. These quantum sensors aren’t anything new, but a tiny self-contained cold-atom sensor can pave the way for putting these sensors in vehicles like ships, aircraft, and ground vehicles. Submarines, which don’t usually have a clear shot at the sky without floating an antenna, are also candidates for the new technology.

A navigation system based on this technology uses a laser to cool the subject atoms and then measures their movements. This allows very precise determination of acceleration and rotation which allows for a more precise inertial navigation system.

If you need a refresher on how GPS works, we can explain it. If you think the idea of a module containing rubidium is far-fetched, don’t forget you can already get them for precision clock work.

Mining And Refining: Pure Silicon And The Incredible Effort It Takes To Get There

November 15, 2021 by Dan Maloney 30 Comments

Were it not for the thin sheath of water and carbon-based life covering it, our home planet would perhaps be best known as the “Silicon World.” More than a quarter of the mass of the Earth’s crust is silicon, and together with oxygen, the silicate minerals form about 90% of the thin shell of rock that floats on the Earth’s mantle. Silicon is the bedrock of our world, and it’s literally as common as dirt.

But just because we have a lot of it doesn’t mean we have much of it in its pure form. And it’s only in its purest form that silicon becomes the stuff that brought our world into the Information Age. Elemental silicon is very rare, though, and so getting appreciable amounts of the metalloid that’s pure enough to be useful requires some pretty energy- and resource-intensive mining and refining operations. These operations use some pretty interesting chemistry and a few neat tricks, and when scaled up to industrial levels, they pose unique challenges that require some pretty clever engineering to deal with.

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