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September 23, 2018
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To see why these recent advances are so exciting and what impact they may have on the world, it’s important to understand how superconducting materials work.
Most materials offer resistance when electricity runs through them and heat up. Resistance is how filaments in an incandescent lightbulb produce light Ulfbastel/Wikimedia Commons, CC BY-SA
A resistance-free material
A superconductor is any material that conducts electricity without offering any resistance to the flow of the electric current.
This resistance-free attribute of superconductors contrasts dramatically with standard conductors of electricity – like copper or aluminum – which heat up when current passes through them. This is similar to quickly sliding your hand across a smooth, slick surface compared to sliding your hand over a rough rug. The rug generates more friction and, therefore, more heat, too. Electric toasters and older-style incandescent lightbulbs use resistance to produce heat and light, but resistance can pose problems for electronics. Semiconductors have resistance below that of conductors, but still higher than that of superconductors.
Superconductive materials repel magnetic fields, making it possible to levitate a magnet above a superconductor.
Another characteristic of superconductors is that they repel magnetic fields. You may have seen videos of the fascinating result of this effect: It is possible to levitate magnets above a superconductor.
How do superconductors work?
All superconductors are made of materials that are electrically neutral – that is, their atoms contain negatively charged electrons that surround a nucleus with an equal number of positively charged protons.
If you attach one end of a wire to something that is positively charged, and the other end to something that is negatively charged, the system will want to reach equilibrium by moving electrons around. This causes the electrons in the wire to try to move through the material.
At normal temperatures, electrons move in somewhat erratic paths. They can generally succeed in moving through a wire freely, but every once in a while they collide with the nuclei of the material. These collisions are what obstruct the flow of electrons, cause resistance and heat up the material.
The nuclei of all atoms are constantly vibrating. In a superconducting material, instead of flitting around randomly, the moving electrons get passed along from atom to atom in such a way that they keep in sync with the vibrating nuclei. This coordinated movement produces no collisions and, therefore, no resistance and no heat.
The colder a material gets, the more organized the movement of electrons and nuclei becomes. This is why existing superconductors only work at extremely low temperatures.
Superconducting materials would allow engineers to fit many more circuits onto a single computer chip. David Carron/Wikimedia Commons, CC BY-SA
Benefits to electronics
If scientists can develop a room-temperature superconducting material, wires and circuitry in electronics would be much more efficient and produce far less heat. The benefits of this would be widespread.
If the wires used to transmit electricity were replaced with superconducting materials, these new lines would be able to carry up to five times as much electricity more efficiently than current cables.
The speed of computers is mostly limited by how many wires can be packed into a single electric circuit on a chip. The density of wires is often limited by waste heat. If engineers could use superconducting wires, they could fit many more wires in a circuit, leading to faster and cheaper electronics.
Finally, with room-temperature superconductors, magnetic levitation could be used for all sorts of applications, from trains to energy-storage devices.
With recent advances providing exciting news, both researchers looking at the fundamental physics of high-temperature superconductivity as well as technologists waiting for new applications are paying attention.
Mishkat Bhattacharya, Professor of Physics and Astronomy, Rochester Institute of Technology
This article is republished from The Conversation under a Creative Commons license. Read the original article.
These evolutionary experiments happened in animals scattered all across the mammalian family tree – including flying squirrels, marsupial possums and the colugo (cousin of the primates). But they all have something in common. It’s a special skin structure between their limbs called a patagium, or flight membrane.
The fact these similar structures have arisen so many times (a process called convergent evolution) hints that the genetic underpinnings of patagia might predate flight. Indeed, they could be shared by all mammals, even those living on the ground.
If this is true, studying patagia can help us to better understand the incredible adaptability of mammals. We might also discover previously unknown aspects of human genetics.
Sugar gliders are one of several mammals that have independently evolved the ability to fly through the air. apiguide/Shutterstock
A deceptively simple membrane
Despite being seemingly simple skin structures, patagia contain several tissues, including hair, a rich array of touch-sensitive neurons, connective tissue and even thin sheets of muscle. But in the earliest stages of formation, these membranes are dominated by the two main layers of the skin: the inner dermis and outer epidermis.
The patagium in sugar gliders (red arrow) forms after birth when the newborn, or joey, is in its marsupial mother’s pouch. Charles Feigin, Author provided
At first, they hardly differ from neighboring skin. But at some point, the skin on the animal’s sides starts to rapidly change, or differentiate. The dermis undergoes a process called condensation, where cells bunch up and the tissue becomes very dense. Meanwhile, the epidermis thickens in a process called hyperplasia.
In some mammals, this differentiation happens when they are still an embryo in the uterus. Incredibly though, in our main model species – the marsupial sugar glider (Petaurus breviceps) – this process begins after birth, while they are in the mother’s pouch. This provides us with an incredible window into patagium formation.
Starting with the sugar glider, we examined the behaviors of thousands of genes active during the early development of the patagium, to try and figure out how this chain of events is kicked off.
From gliders to bats
We discovered that levels of a gene called Wnt5a are strongly correlated with the onset of those early skin changes – condensation and hyperplasia. Through a series of experiments involving cultured skin tissues and genetically engineered laboratory mice, we showed that adding extra Wnt5a was all it took to drive both of these early hallmarks of patagium formation.
Interestingly, when we extended our work to bats, we found extremely similar patterns of Wnt5a activity in their developing lateral patagia to that in sugar gliders. This was surprising, since bats (placental mammals) last shared a common ancestor with the marsupial sugar glider around 160 million years ago.
Perhaps even more remarkably, we found a nearly identical pattern in the outer ear (or pinna) of lab mice. The pinna is a nearly universal trait among mammals, including innumerable species with no flying ancestry.
Seba’s short-tailed bat has a lateral patagium (connected to the flank of the body) activated by Wnt5a. Irineu Cunha/iNaturalist, CC BY-NC
A molecular toolkit
Together, these results suggest something profound. Wnt5a’s role in ushering in the skin changes needed for a patagium likely evolved long before the first mammal ever took to the air.
Originally, the gene had nothing to do with flight, instead contributing to the development of seemingly unrelated traits. But because of shared ancestry, most living mammals today inherited this Wnt5a-driven program. When species like gliders and bats started on their separate journeys into the air, they did so with a common “molecular toolkit”.
Not only that, but this same toolkit is likely present in humans and working in ways we don’t fully understand yet.
There are definite limits to our recent work. First, we haven’t made a flying mouse. This may sound like a joke, but demonstrates we still don’t fully understand how a region of dense, thick skin becomes a thin and wide flight membrane. Many more genes with unknown roles are bound to be involved.
Second, while we’ve shown a cause-and-effect relationship between Wnt5a and patagium skin differentiation, we don’t know precisely how Wnt5a does it. Moving forward, we hope to fill in these gaps by broadening the horizons of our cross-species comparisons and by conducting more in-depth molecular studies on patagium formation in sugar gliders.
For now though, our study presents an exciting new view of flight in mammals. We may not be the strongest fliers, but trying is in our DNA.
Charles Feigin, Postdoctoral Fellow in Genomics and Evolution, The University of Melbourne
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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