Symmetrical Gear Spins One-Way, Harvesting Surrounding Chaos

August 30, 2024 by Donald Papp 12 Comments

Here’s a novel ratchet mechanism developed by researchers that demonstrates how a single object — in this case a gear shaped like a six-pointed star — can rectify the disordered energy of its environment into one-way motion.

5x speed video of gear in agitated water bath.

The Feynman–Smoluchowski ratchet has alternating surface treatments on the sides of its points, accomplished by applying a thin film layer to create alternating smooth/rough faces. This difference in surface wettability is used to turn agitation of surrounding water into a ratcheting action, or one-way spin.

This kind of mechanism is known as an active Brownian ratchet, but unlike other designs, this one doesn’t depend on the gear having asymmetrical geometry. Instead of an asymmetry in shape, there’s an asymmetry in the gear tooth surface treatments. You may be familiar with the terms hydrophobic and hydrophilic, which come down to a difference in surface wettability. The gear’s teeth having one side of each is what rectifies the chaotic agitation of the surrounding water into a one-way spin. Scaled down far enough, these could conceivably act as energy-harvesting micromotors.

Want more detail? The published paper is here, and if you think you might want to play with this idea yourself there are a few different ways to modify the surface wettability of an object. High voltage discharge (for example from a Tesla coil) can alter surface wettability, and there are off-the-shelf hydrophobic coatings we’ve seen used in art. We’ve even seen an unusual clock that relied on the effect.

Demonstrating The Photoelectric Effect Using Neon Lamps

August 28, 2024 by Dave Rowntree 30 Comments

Neon lamps are fun to play with. These old-school indicators were once heavily utilized in many types of equipment for indication purposes but now seem largely relegated to mains voltage indication duties. Here’s a fun video by [Ashish Derhgawen], discussing the photoelectric effect of neon lamps with some simple demonstrations.

[Ashish] demonstrates the well-known photoelectric effect by triggering a sub-biased neon lamp with visible light from an LED. Neon bulbs work on the principle of voltage-induced ionization, creating a visible glowing plasma. If the applied voltage is high enough, around 60 to 80 V, electrons get knocked off the neutral neon atoms. The now free electrons, roaming around highly energized, will eventually come across a neon ion (missing an electron) and recombine to make it neutral again.

The results are a lower total energy state, and the difference in energy is resolved by the emission of a photon of light, which, in the case of neon, is a dull reddish-orange. Nothing unusual there. However, nothing will happen if the applied voltage bias is just below this device-specific threshold. There’s not enough energy to strip electrons.

Apply an external light source, and this threshold can be exceeded. The photons from the LED are just energetic enough to strip a small number of electrons from the surface of the electrodes, and this causes a cascade, or avalanche effect, lighting up the plasma and turning on the neon lamp. ~~Take away the external light source, and it dies down and goes dark.~~

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Setup of a small lightbulb passing light through a thin film

Experimenting With Interference On Thin Layers

August 26, 2024 by Heidi Ulrich No comments

[Stoppi] has taken on a fascinating project involving the interference of thin layers, a phenomenon often observed in everyday life but rarely explored in such depth. This project delves into the principles of interference, particularly focusing on how light waves interact with very thin films, like those seen in soap bubbles or oil slicks. The post is in German, but you can easily translate it using online tools.

Interference occurs when waves overlap, either reinforcing each other (constructive interference) or canceling each other out (destructive interference). In this project, [Stoppi] specifically examines how light behaves when passing through thin layers of air trapped between semi-transparent mirrors. When light waves reflect off these mirrors, the difference in path length leads to interference patterns that depend on the layer’s thickness and the wavelength of the light.

To visualize this, [Stoppi] used an interferometer made from semi-transparent mirrors and illuminated it with a bulb to ensure a continuous spectrum of light. By analyzing the transmitted light spectrum with a homemade spectrometer, he observed clear peaks corresponding to specific wavelengths that could pass through the interferometer. These experimental results align well with theoretical predictions, confirming the effectiveness of the setup.

If you like pretty patterns, soap bubbles are definitely good for several experiments. Don’t forget: pictures or it didn’t happen.

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Intuitive Explanation Of Arithmetic, Geometric & Harmonic Mean

August 24, 2024 by Maya Posch 8 Comments

The simple definition of a mean is that of a numeric quantity which represents the center of a collection of numbers. Here the trick lies in defining the exact type of numeric collection, as beyond the arithmetic mean (AM for short, the sum of all values divided by their number) there are many more, with the other two classical Pythagorean means being the geometric mean (GM) and harmonic mean (HM).

The question that many start off with, is what the GM and AM are and why you’d want to use them, which is why [W.D.] wrote a blog post on that topic that they figure should be somewhat intuitive relative to digging through search results, or consulting the Wikipedia entries.

Compared to the AM, the GM uses the product of the values rather than the sum, which makes it a good fit for e.g. changes in a percentage data set. One thing that [W.D] argues for is to use logarithms to grasp the GM, as this makes it more obvious and closer to taking the AM. Finally, the HM is useful for something like the average speed across multiple trips, and is perhaps the easiest to grasp.

Ultimately, the Pythagorean means and their non-Pythagorean brethren are useful for things like data analysis and statistics, where using the right mean can reveal interesting data, much like how other types using something like the median can make a lot more sense. The latter obviously mostly in the hazy field of statistics.

No matter what approach works for you to make these concepts ‘click’, they’re all very useful things to comprehend, as much of every day life revolves around them, including concepts like ‘mean time to failure’ for parts.

Top image: Cycles of sunspots for the last 400 years as an example data set to apply statistical interpretations to. (Credit: Robert A. Rohde, CC BY-SA 3.0)

Creating Customized Diffraction Lenses For Lasers

August 23, 2024 by Bryan Cockfield 3 Comments

[The Thought Emporium] has been fascinated by holograms for a long time, and in all sorts of different ways. His ultimate goal right now is to work up to creating holograms using chocolate, but along the way he’s found another interesting way to manipulate light. Using specialized diffraction gratings, a laser, and a few lines of code, he explores a unique way of projecting hologram-like images on his path to the chocolate hologram.

There’s a lot of background that [The Thought Emporium] has to go through before explaining how this project actually works. Briefly, this is a type of “transmission hologram” that doesn’t use a physical object as a model. Instead, it uses diffraction gratings, which are materials which are shaped to light apart in specific ways. After some discussion he demonstrates creating diffraction gratings using film. Certain diffraction patterns, including blocking all of the light source, can actually be used as a lens as the light bends around the blockage into the center of the shadow where there can be focal points. From there, a special diffraction lens can be built.

The diffraction lens can be shaped into any pattern with a small amount of computer code to compute the diffraction pattern for a given image. Then it’s transferred to film and when a laser is pointed at it, the image appears on the projected surface. Diffraction gratings like these have a number of other uses as well; the video also shows a specific pattern being used to focus a telescope for astrophotography, and a few others in the past have used them to create the illusive holographic chocolate that [The Thought Emporium] is working towards.

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Citizen Scientists Spot Super Fast Moving Object In NASA Data

August 22, 2024 by Lewin Day 18 Comments

When you were five, you probably spotted your best friend running at “a million miles an hour” when they beat everybody at the local athletics meet. You probably haven’t seen anything that fast snice. According to NASA, though, a group of citizen scientists spotted a celestial object doing just that!

The group of citizen scientists were involved in a NASA program called Backyard Worlds: Planet 9. They were working on images from NASA’s Wide-field Infrared Explorer mission. Scanning through stored images, Martin Kabatnik, Thomas P. Bickle, and Dan Caselden identified a curiously speedy object termed CWISE J124909.08+362116.0. There are lots of fast-moving objects out in space, but few quite as fast as this one. It’s quite literally zooming through the Milky Way at about 1 million miles per hour.

It’s unclear exactly what the object is. It appears light enough to be a low-mass star, or potentially a brown dwarf—somewhere in between the classification of gas giant and star. It also has suspiciously low iron and metallic content. The leading hypothesis is that CWISE J1249 might have been ejected from a supernova, or that it got flung around a pair of black holes.

For now, it remains a mystery. It’s a grand discovery that really highlights the value of citizen science. If you’ve been doing your own rigorous scientific work—on NASA’s data or your own—do let us know!

WOW! It Wasn’t Aliens After All!

August 20, 2024 by Jenny List 21 Comments

There may not be many radio astronomy printouts that have achieved universal fame, but the one from Ohio State University’s Big Ear telescope upon which astronomer [Jerry R. Ehman] wrote “WOW!” is definitely one of them. It showed an intense one-off burst that defied attempts to find others like it, prompting those who want to believe to speculate that it might have been the product of an extraterrestrial civilization. Sadly for them the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo has provided an explanation by examining historical data from the Arecibo telescope.

The radio signal in question lay on the hydrogen line frequency at 1420 MHz, and by looking at weaker emissions from cold hydrogen clouds they suggest that the WOW! signal may have come from a very unusual stimulation of one of these clouds. A magnetar is a type of neutron star which can create an intense magnetic field, and their suggestion is that Big Ear was in the lucky position of being in the right place at the right time to see one of these through a hydrogen cloud. The field would excite the hydrogen atoms to maser-like emission of radiation, leading to the unexpected blip on that printout.

There’s a question as to whether speculation about aliens is helpful to the cause of science, but in answer to that we’d like to remind readers that we wouldn’t be talking about magnetars now without it, and that the WOW! signal was in fact part of an early SETI experiment. Better keep on searching then!

Meanwhile readers with long memories will recollect us looking at the WOW! signal before.