Tag Archives: #friction

Fingerprints Moisture-regulating Mechanism Strengthens Human Touch (Biology)

Human fingerprints have a self-regulating moisture mechanism that not only helps us to avoid dropping our smartphone, but could help scientists to develop better prosthetic limbs, robotic equipment and virtual reality environments, a new study reveals.

Fingerprints’ moisture mechanism could be boon to robotics experts © University of Birmingham

Primates – including humans, monkeys and apes – have evolved epidermal ridges on their hands and feet with a higher density of sweat glands than elsewhere on their bodies. This allows precise regulation of skin moisture to give greater levels of grip when manipulating objects.

Fingerprints help to increase friction when in contact with smooth surfaces, boost grip on rough surfaces and enhance tactile sensitivity. Their moisture-regulating mechanism ensures the best possible hydration of the skin’s keratin layer to maximise friction.

Researchers at the University of Birmingham worked with partners at research institutions in South Korea, including Seoul National University and Yonsei University – publishing their findings today in Proceedings of the National Academy of Sciences (PNAS).

Co-author Mike Adams, Professor in Product Engineering and Manufacturing, at the University of Birmingham commented: “Primates have evolved epidermal ridges on their hands and feet. During contact with solid objects, fingerprint ridges are important for grip and precision manipulation. They regulate moisture levels from external sources or the sweat pores so that friction is maximised and we avoid ‘catastrophic’ slip and keep hold of that smartphone.”

“Understanding the influence of finger pad friction will help us to develop more realistic tactile sensors – for example, applications in robotics and prosthetics and haptic feedback systems for touch screens and virtual reality environments.”

Ultrasonic lubrication is commonly used in touch screen displays that provide sensory ‘haptic’ feedback, but its effectiveness is reduced when a user has dry compared with moist finger pads. Moreover, being able to distinguish between fine-textured surfaces, such as textiles, by touch relies on the induced lateral vibrations but the absence of sliding friction inhibits our ability to identify what we are actually touching.

Fingerprints are unique to primates and koalas – appearing to have the dual function of enhancing evaporation of excess moisture whist providing a reservoir of moisture at their bases that enables grip to be maximised.

The researchers have discovered that, when finger pads are in contact with impermeable surfaces, the sweat from pores in the ridges makes the skin softer and thus dramatically increases friction. However, the resulting increase in the compliance of the ridges causes the sweat pores eventually to become blocked and hence prevents excessive moisture that would reduce our ability to grip objects.

Using hi-tech laser-based imaging technology, the scientists found that moisture regulation could be explained by the combination of this sweat pore blocking and the accelerated evaporation of excessive moisture from external wetting as a result of the specific cross-sectional shape of the epidermal furrows when in contact with an object.

These two functions result in maintaining the optimum amount of moisture in the fingerprint ridges that maximises friction whether the finger pad is initially wet or dry.

“This dual-mechanism for managing moisture has provided primates with an evolutionary advantage in dry and wet conditions – giving them manipulative and locomotive abilities not available to other animals, such as bears and big cats,” added Professor Adams.

Reference: Seoung-Mok Yum, In-Keun Baek, Dongpyo Hong, Juhan Kim, Kyunghoon Jung, Seontae Kim, Kihoon Eom, Jeongmin Jang, Seonmyeong Kim, Matlabjon Sattorov, Min-Geol Lee, Sungwan Kim, Michael J. Adams, Gun-Sik Park, “Fingerprint ridges allow primates to regulate grip”, Proceedings of the National Academy of Sciences Nov 2020, 202001055; DOI: 10.1073/pnas.2001055117 https://www.pnas.org/content/early/2020/11/24/2001055117

Provided by University of Birmingham

Notes to editors:

* The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers, teachers and more than 6,500 international students from over 150 countries.
* ‘Fingerprint ridges allow primates to regulate grip’ – Seoung-Mok Yum, In-Keun Baek, Dongpyo Hong, Juhan Kim, Kyunghoon Jung, Seontae Kim, Kihoon Eom, Jeongmin Jang, Seonmyeong Kim, Matlabjon Sattorov, Min-Geol Leed, Sungwan Kime, Michael J. Adams and Gun-Sik Parka is published in Proceedings of the National Academy of Sciences (PNAS)

UCF Researcher Zeroes In on Critical Point for Improving Superconductors (Physics)

A superconductor that can operate at room temperature would be a dream material able to efficiently power the cities of tomorrow and magnetically levitate cars.

The search for a superconductor that can work under less extreme conditions than hundreds of degrees below zero or at pressures like those near the center of the Earth is a quest for a revolutionary new power — one that’s needed for magnetically levitating cars and ultra-efficient power grids of the future.

A UCF researcher is working to help understand how to one day create a “room temperature” superconductor. Powerful superconductors can levitate heavy magnets, paving the way for practical and affordable magnetically levitating cars, trains and more. Photo credit: Adobe Stock

But developing this kind of “room temperature” superconductor is a feat science has yet to achieve.

A University of Central Florida researcher, however, is working to move this goal closer to realization, with some of his latest research published recently in the journal Communications Physics – Nature.

In the study, Yasuyuki Nakajima, an assistant professor in UCF’s Department of Physics, and co-authors showed they could get a closer look at what is happening in “strange” metals.

These “strange” metals are special materials that show unusual temperature behavior in electrical resistance. The “strange” metallic behavior is found in many high-temperature superconductors when they are not in a superconducting state, which makes them useful to scientists studying how certain metals become high-temperature superconductors.

This work is important because insight into the quantum behavior of electrons in the “strange” metallic phase could allow researchers to understand a mechanism for superconductivity at higher temperatures.

“If we know the theory to describe these behaviors, we may be able to design high-temperature superconductors,” Nakajima says.

Superconductors get their name because they are the ultimate conductors of electricity. Unlike a conductor, they have zero resistance, which, like an electronic “friction,” causes electricity to lose power as it flows through a conductor like copper or gold wire.

This makes superconductors a dream material for supplying power to cities as the energy saved by using resistance-free wire would be huge.

Powerful superconductors also can levitate heavy magnets, paving the way for practical and affordable magnetically levitating cars, trains and more.

To turn a conductor into a superconductor, the metal material must be cooled to an extremely low temperature to lose all electrical resistance, an abrupt process that physics has yet to develop a fully comprehensive theory to explain.

These critical temperatures at which the switch is made are often in the range of -220 to -480 degrees Fahrenheit and typically involve an expensive and cumbersome cooling system using liquid nitrogen or helium.

Some researchers have achieved superconductors that work at about 59 degrees Fahrenheit, but it was also at a pressure of more than 2 million times of that at the Earth’s surface.

In the study, Nakajima and the researchers were able to measure and characterize electron behavior in a “strange” metallic state of non-superconducting material, an iron pnictide alloy, near a quantum critical point at which electrons switch from having predictable, individual behavior to moving collectively in quantum-mechanical fluctuations that are challenging for scientists to describe theoretically.

The researchers were able to measure and describe the electron behavior by using a unique metal mix in which nickel and cobalt were substituted for iron in a process called doping, thus creating an iron pnictide alloy that didn’t superconduct down to -459.63 degrees Fahrenheit, far below the point at which a conductor would typically become a superconductor.

“We used an alloy, a relative compound of high temperature iron-based superconductor, in which the ratio of the constituents, iron, cobalt and nickel in this case, is fine-tuned so that there’s no superconductivity even near absolute zero,” Nakajima says. “This allows us to access the critical point at which quantum fluctuations govern the behavior of the electrons and study how they behave in the compound.”

They found the behavior of the electrons was not described by any known theoretical predictions, but that the scattering rate at which the electrons were transported across the material can be associated with what’s known as the Planckian dissipation, the quantum speed limit on how fast matter can transport energy.

“The quantum critical behavior we observed is quite unusual and completely differs from the theories and experiments for known quantum critical materials,” Nakajima says. “The next step is to map the doping-phase diagram in this iron pnictide alloy system.”

“The ultimate goal is to design higher temperature superconductors,” he says. “If we can do that, we can use them for magnetic resonance imaging scans, magnetic levitation, power grids, and more, with low costs.”

Unlocking ways to predict the resistance behavior of “strange” metals would not only improve superconductor development but also inform theories behind other quantum-level phenomena, Nakajima says.

“Recent theoretical developments show surprising connections between black holes, gravity and quantum information theory through the Planckian dissipation,” he says. “Hence, the research of ‘strange’ metallic behavior has also become a hot topic in this context.”

Co-authors included researchers from the University of Maryland; the National Institute of Standards and Technology Center for Neutron Research; the National High Magnetic Field Laboratory at Florida State University; the Leibniz Institute for Solid State and Materials Research in Dresden, Germany; the Shanghai Institute of Microsystem and Information Technology at the Chinese Academy of Sciences in China; and the Canadian Institute for Advanced Research in Toronto, Canada.

The research was funded by the National Science Foundation Division of Materials Research, the Gordon and Betty Moore Foundation’s EPiQS Initiative. Some of the work was performed at the National High Magnetic Field Laboratory, which is supported by an NSF cooperative agreement with the State of Florida. Pressure measurements were supported by the National Institute of Standards and Technology.

Nakajima received his doctorate in physics from the University of Tokyo in Japan and worked as a postdoctoral research associate at the Center for Nanophysics and Advanced Materials at the University of Maryland. He joined UCF’s Department of Physics, part of UCF’s College of Sciences, in 2016.

References: Nakajima, Y., Metz, T., Eckberg, C. et al. Quantum-critical scale invariance in a transition metal alloy. Commun Phys 3, 181 (2020). https://www.nature.com/articles/s42005-020-00448-5 https://doi.org/10.1038/s42005-020-00448-5

Provided by University of Central Florida

Why there is no speed limit in the superfluid universe? (Physics / Quantum)

Physicists from Lancaster University have established why objects moving through superfluid helium-3 lack a speed limit in a continuation of earlier Lancaster research.

Researchers found the reason for the absence of the speed limit: exotic particles that stick to all surfaces in the superfluid. Credit: Lancaster University

Helium-3 is a rare isotope of helium, in which one neutron is missing. It becomes superfluid at extremely low temperatures, enabling unusual properties such as a lack of friction for moving objects.

It was thought that the speed of objects moving through superfluid helium-3 was fundamentally limited to the critical Landau velocity, and that exceeding this speed limit would destroy the superfluid. Prior experiments in Lancaster have found that it is not a strict rule and objects can move at much greater speeds without destroying the fragile superfluid state.

Now scientists from Lancaster University have found the reason for the absence of the speed limit: exotic particles that stick to all surfaces in the superfluid.

The discovery may guide applications in quantum technology, even quantum computing, where multiple research groups already aim to make use of these unusual particles.

To shake the bound particles into sight, the researchers cooled superfluid helium-3 to within one ten thousandth of a degree from absolute zero (0.0001K or -273.15°C). They then moved a wire through the superfluid at a high speed, and measured how much force was needed to move the wire. Apart from an extremely small force related to moving the bound particles around when the wire starts to move, the measured force was zero.

Lead author Dr Samuli Autti said: “Superfluid helium-3 feels like vacuum to a rod moving through it, although it is a relatively dense liquid. There is no resistance, none at all. I find this very intriguing.”

PhD student Ash Jennings added: “By making the rod change its direction of motion we were able to conclude that the rod will be hidden from the superfluid by the bound particles covering it, even when its speed is very high.” “The bound particles initially need to move around to achieve this, and that exerts a tiny force on the rod, but once this is done, the force just completely disappears,” said Dr Dmitry Zmeev, who supervised the project.

This article is republished from science daily

References: S. Autti, S. L. Ahlstrom, R. P. Haley, A. Jennings, G. R. Pickett, M. Poole, R. Schanen, A. A. Soldatov, V. Tsepelin, J. Vonka, T. Wilcox, A. J. Woods, D. E. Zmeev. Fundamental dissipation due to bound fermions in the zero-temperature limit. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-18499-1 link: https://www.nature.com/articles/s41467-020-18499-1