Here you find all contributions made by external authors to JUnQ. This includes peer-reviewed articles and editorial board reviewed open questions.
Sometimes they come and go with a bang, sometimes they are silent. They glow bright as a lightning in white, yellow, red or blue. They fly freely through the room and some of them even permeate solid matter. They all have in common that they appear mostly during stormy weather, are somewhat spherically shaped and have a lifetime of several seconds. For many centuries people report about observations of lightning balls as depicted in figure 1.Clearly, ball lightnings cannot be the same phenomenon as a strong electric discharge like a bolt lightning since their effect is not as dramatic. A full scientific explanation is not yet found. Do they really exist or are they only the product of frightened people’s minds?
Sure, bolts can cause phosphenes, impressions in the focus of the eye that remain some moments after looking into bright lights. But during the last years scientist came up with some experiments that deliver plausible explanations of their formation:
Abrahamson and J. Dinniss found out that after the impact of a bolt into the soil a cloud of Silicon (Si), Silicon carbide (SiC) and Silicon monoxide (SiO) nanoparticles evaporates and oxidizes in a timespan of several seconds. During this time the energy is released as a bright ball-shaped light.
At the IPP in Garching, Germany, Prof. Dr. Gerd Fu?mann vaporized and ionized a tiny amount of water by an electrical discharge between two electrodes above a water surface. The glowing plasma cloud, called plasmoid, has a spherical or mushroom-like shape (shown in figure 2) and a lifetime below one second. The appearance of these plasmoids is demonstrated in a short video on their web page: http://www.ipp.mpg.de/2977926/kugelblitzeStill these experiments lack to explain all the observed properties of a ball lightning: the free movement, the ability to permeate matter and the long lifetime of several seconds. It is plausible that there might occur spherical light phenomena during bolt impacts. An explanation of the rather vivid properties of a ball lightning is yet to come. But maybe they belong to the section of narrative decor.
– Tatjana Daenzer
 Smirnov, B. M., Phys. Rep. 1987, 152, 177-226.
 Peer, J., Kendl, A., Physics Letters A, 2010, 374, 4797-4799.
 Abrahamson, J., Dinniss, J., Nature, 2000, 403, 519-521.
 Fussmann, G., Phys. Unserer Zeit. 2008, 5, 246-252.
Put a raw egg on a flat table, and give it a good spin with two fingers. The egg spins, however, rather slowly because the liquid inside poorly exchanges momentum with the outside shell. Thus, when you spin the egg by applying force to the shell, most of the inside resists the motion and the friction forces between the inside (immobile) and the shell (mobile) will be slowing down the egg’s speed. But if you consider a cooked egg, proteins contained inside the egg are now forming a solid phase that is tightly joint to the shell. In that case, there are no friction forces in the “egg system” and the movement is not slowed down.
In this case now, the only existing friction forces are those between egg and the support (the table) and the air (which can be reasonably neglected). If your initial momentum transfer is strong enough, you observe a strange phenomenon: the spinning egg starts to rotate upright.
The physical concept used to explain this phenomenon is inertia. Spinning ice skaters can reduce their moment of inertia by pulling in their arms, allowing them to spin faster. You can also sit on a swivel chair and spin on yourself. Extend your arms horizontally and you will slow down. The same is happening with the egg. Friction forces tend to slow down the egg, and decrease overall energy. To save energy, like the skater, the egg stands up and the momentum of inertia consequently decreases.
To spin upright, the egg needs some energy, exactly as one needs some energy to get up in the morning, fighting against gravity. The necessary energy is provided by the rotation itself, and the change of orientation of the egg will only happen if the spinning is fast enough.
— Adrien THUROTTE
Bou-Rabee, N. M., J. E. Marsden, and L. N. Romero, A geometric treatment of Jellett’s egg, Angew. Math. Mech. (ZAMM) 85, (2005), 618-642
Ordinary glass as it is used for windows can exhibit exceptional behaviors and even shred a rifle bullet to pieces, furthermore it can help to make car windows safer and to understand the inner processes in volcanos.
Key to all these fascinating properties are the so-called Prince Rupert’s Drops. These structures are solidified drops of glass, which are produced by letting a drop of molten glass fall into a bucket of water. The sudden shock caused by the massive temperature drop on the surface of the glass basically locks in the outer shape of the drop, preserving main body and tail. (Fig. 1) [1,2,3].This object has now very unique properties: If the main body of the droplet is hit by a hammer, it practically never breaks. It even withstands a direct hit of a rifle bullet, whereas the bullet can be completely shred to pieces. All this the main body of the glass droplet can stand without breaking. However, if there is too much force applied to the fragile tail of the Prince Rupert’s Drop, or if it is even just nicked, the whole drop explodes into tiny pieces of glass that can spread over several meters. [4,5]
To understand how this fascinating behavior is created, we have to have a closer look at how the drop is created. Everything starts with a drop of hot, molten glass, suddenly getting in contact with water. As mentioned, the outer layer of the drop immediately solidifies and locks in the characteristic drop or tear shape. The thin tail is created when the drop detaches from its origin (e.g. the glass rod) and starts falling and also gets locked into its shape when touching the water for the first time. While the outer layers are now already solid glass, the interior of the drop is still a hot liquid (Fig. 2 top). Consequently, this glass contracts while cooling down and starts pulling the solid outer layers inward, stressing them just like an arch bridge is stressed (compressive strain) and thereby stabilizes the structure. Along the axis of the drop, however, the strain is not compressive but tensile, because the shrinking material tries to pull along the tail.These stresses make the round shaped main body of the drop extremely resistant to external disruptions, whereas the tail constitutes a weak spot (Fig. 2 bottom). If the latter is now damaged in any way, the energy stored in the mechanical stress can be released and a mechanical failure front runs through the material, destroying more and more of it until the main body is shredded into dust. This process can happen with a speed of around 1600m/s, just like an explosion, and it usually only ends with the pulverization of the whole drop. Thus, this is the secret of the Prince Rupert’s Drop; it is always experiencing extreme internal stress that makes the convex part so extremely stable (like an arch bridge) that even rifle bullets shatter on them.
Finally, in its cooled state, the drop represents a system that exhibits extreme internal stresses. These stresses make the round shaped main body of the drop extremely resistant to external disruptions, whereas the tail constitutes a weak spot (Fig. 2 bottom). If the latter is now damaged in any way, the energy stored in the mechanical stress can be released and a mechanical failure front runs through the material, destroying more and more of it until the main body is shred to dust. This process can happen with a speed of around 1600m/s, just like an explosion, and it usually only ends with the pulverization of the whole drop. Thus, this is the secret of the Prince Rupert’s Drop; it is always experiencing extreme internal stress that makes the convex part so extremely stable (like an arch bridge) that even rifle bullets shatter on them.
So, we can ask whether this effect can be useful for anything. The answer is yes, indeed. Exactly the same principle is used in tempered glass like it is used e.g. in car windows. This glass does not shatter into sharp shards, but instead produces relatively smooth and small pieces and therefore is less harmful for the passengers of the car in case of an accident. Currently, Prince Robert’s Drops are even researched to understand better the quick cooling of volcanic lava under certain circumstances and therefore the inner processes within a volcano. Thus, all in all, these fascinating objects are full of wonders.
— Kai Litzius
“I try to interact with context, so I place in the streets elements and characters that belong especially to the streets. I like to show things and people that society aims at keeping hidden: homeless people, smokers, street kids, bench lovers for example” – C215
Read more about his work here: C215
The pursuit of the unobserved and the unfathomable in scientific research often affords the scientist glimpses of unrivaled visual experiences. The Princeton University Art of Science exhibition provides an avenue where scientists have the opportunity to present their images obtained during their research. The exhibition helps to spread awareness of the scientific technique and the artistic brilliance that research is replete with, to artists as well as to the common demographic. The exhibition attempts to forge a strong connection between Art and Science. The exchange with artists reveals a different way for scientists to visualize and contemplate their own research.
Read more about the exhibition here: Princeton Art of Science Exhibition
JUnQ, 7, 1, XIV–XV, 2017
Is it possible to know everything in every discipline? Surely not, especially not in modern times in which it is increasingly important to have experts of an explicit field of knowledge. We all remember some real whiz kids from our school years but only a very few of us can be outstanding experts in widely varied fields. Just imagine the time you would need to learn all of it.
Read the full article here: Scholars Then and Now
JUnQ, 7, 1, X–XIII, 2017
Science fair demonstrations are something that I always look forward to. I was there this other day at one such fair for gifted youngsters. I was demonstrating an experiment on densities. The experiment was quite a familiar one. The one where liquids with different densities do not mix. And where liquids with a lower value of density stay on top of liquids with larger densities, as distinct layers. To make it more vivid and interesting for the kids, I added a different color to each layer. A young boy came up to me after the demonstration and said…“It would be so boring if we did not invent colors to begin with”. His observation struck me and got me thinking. With our academic training in Science, we take a lot of stuff for granted. We rarely stop to wonder at the beauty and artistry inherent in the everyday experiments that we do and in the things that are around us.
Read the full article here: A Tale of Art and Science
Have you ever regretted not to have your camera to immortalize a beautiful, dreamlike or poetic scene in the lab?
Is there a funny, challenging or even profound situation in your lab, office, studio. . . that combines Science and Art?
Look for all the details here: JUnQ Photo Contest
Tyler Thrasher is an artist using many different techniques to express himself. He is a musician, a painter, an illustrator, a photographer and, not least, to some extent a scientist. For one of his current projects, he grows crystal clusters on collected, inanimate objects, like dead insects and skulls. By transforming deceased creatures into something beautiful, often mystical, he attempts to follow the approach of alchemists. Nevertheless, his art builds on “hard science” and follows the physical rules of crystallization. His results offer a different, inspiring view on a well-known method and teach not only science but also the inherent beauty of their studied objects.
Find the Interview here: Insect Alchemy