Tag: TechStories

Two and a half years ago, I printed this phone holder on an SLA printer, a holder of my own design. And then my cat broke it with its paw. I started to glue it together with superglue, and realized that this plastic does not bond very well (but it still bonded after sanding). I began to investigate why, and found a lot of interesting information about superglue.

How does superglue work? Inside the tube, it remains liquid and consists of molecules of ethyl cyanoacrylate monomers. When the glue is applied to a surface, it fills the pores and cracks, which must be present for the glue to work—hence the importance of roughly sanding the surface. The polymerization reaction begins due to contact with water (including moisture in the air). Therefore, you should not wash off the glue with water, as it will set even faster. Acetone can be used—unless the glue is in the eyes. And it does get into the eyes, often because it is packaged in a container that resembles eye drops. The molecules begin to connect with each other, forming long polymeric chains, transforming from a liquid to a solid state.

Thanks to rapid polymerization, the glue sets in 10–30 seconds.

The glue also poorly bonds hydrophobic surfaces, such as polyethylene, polypropylene, Teflon. They lack free electrons for the glue to interact with and do not absorb moisture, which is necessary to initiate the reaction.

Impacts and shearing—superglue works excellently under tension, but is very brittle under impacts and shearing. This is its weak spot.

– Cyanoacrylate was discovered accidentally by the photo company Eastman Kodak (specifically by Harry Coover), who was trying to create a transparent plastic for gun sights.

– Unlike most plastics, which deteriorate after being recycled, superglue can be heated to 210°C and decomposed back into monomers. These monomers can then be reassembled to create a new, durable material. This allows for the recycling of plastic without loss of quality.

– The properties of the glue caught the interest of the US Army, particularly during the height of the Vietnam War. Transportation of the wounded took just minutes, but many soldiers died from uncontrollable bleeding. Therefore, in 1966, the US Army sent a special surgical brigade to South Vietnam, armed with aerosol sprays of cyanoacrylate. Although this method was used in a limited number of cases, out of 30 documented cases of using the glue to stop bleeding, it was successful in 26. A safer surgical glue was invented in 1998.

And the green sphere at the bottom is also an interesting object, I also printed it. It is a spherical section of a gyroid. A gyroid is a continuous (without self-intersections) infinitely repeating structure in three dimensions without any reflection symmetries. It is, incidentally, the only such structure known to science. Overall, it’s a way to create elements with minimum weight and maximum strength. Inside, essentially, it consists of sinusoids along three coordinates.

Look at how interestingly the glass has cracked. The crack goes in a circle. Usually, on glass, cracks tend to spread towards the nearest edge because that’s where the stress can be minimal. However, in this case, it seems that the crack stopped before reaching the edge of the glass, which is quite unusual.

Unfortunately, this is already the third glass with a similar crack; in the other two, the crack indeed completed the circle. The dishwasher, which torments the glass with its temperature, is to blame for everything. The second photo shows how it was originally

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I was thinking this morning about how to explain what a programmer’s job interview is like. I think I came up with a great analogy. It’s as if, when hiring a cook for a cafeteria, they were asked to describe the process of protein denaturation in a chicken egg at the molecular level. When hiring a salesperson, it would be essential to know how a reduction in the refinancing rate would affect aggregate demand in the long term.

You can’t just hire a welder. He needs to know how many valence electrons are in an iron atom and be able to derive the equation for the chemical reaction during welding.

A plumber must definitely know Bernoulli’s law and be able to calculate the water flow through a pipe using the Navier-Stokes equation.

Undoubtedly, you can’t just hire a hairdresser—you need one who can explain in detail how disulfide bonds work in the structure of hair and why, on a molecular level, a perm is a crime against keratin.

A carpenter should be asked about the ideal number of hammer strikes per minute to secure a nail considering the thickness of the wood. Even if he cannot name the exact number, he must demonstrate a thought process in the right direction (towards the interviewers).

Of course, once a programmer is hired, the very first task will involve reversing a string without using built-in functions. By recursion. Right after writing a module where two 100-digit numbers are added without using the addition operation. And the result is displayed in the console, formatted like a diamond. And certainly, a Java programmer will be using volatile, transient, strictfp at least every other day.

You should hire someone whose eyes sparkle with passion, or if not, someone who, like a tank, confidently plows through to a solution. Someone who understands exactly where to hit the code with a sledgehammer to make it work and keeps duct tape in their pocket in case that doesn’t help. Someone capable of fixing a bug and explaining to the client why the bug is a “feature” and not a mistake. Someone who says “that’s an interesting problem, I’ll think about it” instead of “it’s impossible”, and is already Googling how to do it. Someone who writes patches with such inspiration that they look like part of the architecture. And most importantly — you should hire someone who isn’t afraid to ask during the interview: “Why do I need to solve problems reversing strings, when in real life I have reverse()? Like in Python s[::-1] or ”.join(reversed(s)).”