Tag Archives: University of Kiel

Similarities between a moth’s eye and snakeskin

Finding patterns in nature that are repeated seems to be the order of the day although there is a twist to this particular story. This time, researchers at Kiel University (also known as, University of Kiel or Christian-Albrechts University of  Kiel [Germany]) have found superficial similarities between a moth’s eye and snakeskin according to a May 4, 2016 news item on Nanowerk,

One thing is obvious: moth’s eyes and snake’s skin are entirely different. Researchers at Kiel University have taken a closer look, however, and have now brought the supposed ‘apples and oranges’ to a common denominator. They have opened up a completely new, comparative view of biological surfaces using a newly developed method, and have thus come closer to the solution of how these surfaces work. Dr. Alexander Kovalev, Dr. Alexander Filippov and Professor Stanislav Gorb from the Zoological Institute at Kiel University have published their findings in the current edition of the scientific journal Applied Physics A (“Correlation analysis of symmetry breaking in the surface nanostructure ordering: case study of the ventral scale of the snake Morelia viridis”).

A May 3, 2016 Kiel University press release, which originated the news item, describes the scientists’ first approach to the research,

One surface demonstrates reduced light reflection, the other is water repellent and resistant to abrasion. Surfaces in the animal world are evolved to adapt to their environments and give the animal they cover the greatest possible evolutionary advantage. Scientists are today still puzzled by exactly how and why these different structures develop in detail.

Current research looks right into the surface nano-structures using the latest research techniques. Normally, we would limit ourselves to comparisons within closely related species and just look thoroughly at small areas of the surface, says Gorb: “That is why we asked ourselves which structural differences can be found between completely different species. To do so, we changed biology’s typical perspective and addressed larger surface areas from various species.” These types of cross-species or cross-material studies of nanostructures are common in other technical or inorganic fields. In Biology, however, this method is completely new, Gorb continues.

They got the idea from the decorations in the hallway of their own institute, where scanning electron microscope images of moth’s eyes and snake’s skin are displayed. At some point, theoretical physicist Filippov noticed similarities between the images, which showed the surfaces at a resolution of a few millionths of a millimetre. Nipples and dimples could be seen which seemed to the human eye to follow a certain pattern. Using methods that are normally used in crystallography, the scientists were finally able to recognise the particular patterns that distinguish the two species. “The structure of moth’s eyes is perfectly organised. Nipples are highly ordered, and preferred directions are exhibited in the structural organisation”, explains Kovalev, biophysicist and main author of the study. The scientists were already aware of the eye structure’s strict symmetry. However, the fact that this goes right through to the nano-level and is repeated across the entire surface in so-called domains, is an important new finding.

So which symmetry does snake’s skin have, which at first glance appears similar, perhaps even more perfectly organised? “Compared to the structure of the moth’s eye, the structure of the snake’s skin is unorganised”, explains Kovalev. He continued: “If we concentrate on one dimple in the skin, like one nipple in the eye, we only see a diffuse cloud of further dimples in the close surroundings. Neither particular directions nor the regular arrangement can be defined. This unorganised structure continues across the entire surface.”

On concluding there were significant differences as well as similarities, the scientists took a closer look,

On their own, these findings about the organised eye structure on the one hand and the unorganised skin structure on the other hand are not especially significant. But by taking the common denominator, i.e. investigating both structures with the same degree of resolution, it is possible for the first time to compare fundamentally different structures, explains Gorb: “However, the ‘coincidental’ degree of organisation is not coincidental, but a result of evolution. That would mean that the perfect organisation gives the moth its incredible night vision, while the imperfect organisation in snake’s skin ensures the best friction properties.” That sounds logical, when you consider the laws of physics, that a symmetrical structure is necessary for good vision and good friction properties require the surface ordering in the contact with the ground to be as low as possible.

If the Kiel-based researchers had followed the usual approaches and compared snakes to snakes and moths to moths, the organisation of the elements at nano-level would have hardly been considered significant. “By comparing evolutionary distant species, we now see that the key to understanding surface functions must be right at the smallest level. Every biological surface is adapted to its environment, and these adaptations are reflected in the organisation of their smallest elements in a certain perfect or imperfect degree”, Gorb concludes.

This is the snakeskin,

Scanning electron microscopy image of the tail ventral scale in the snake Morelia viridis. The black shadowed gray circle marks a typical hexagonal arrangement of dimples, whereas both white and black circles mark five- and sevenfold symmetrical arrangement of dimples, respectively. Credit: research group Gorb

Scanning electron microscopy image of the tail ventral scale in the snake Morelia viridis. The black shadowed gray circle marks a typical hexagonal arrangement of dimples, whereas both white and black circles mark five- and sevenfold symmetrical arrangement of dimples, respectively. Credit: research group Gorb

This is the moth’s eye,

 

Scanning electronmicroscopy image of a single ommatidium surface of an eye in the moth Manduca sexta. Credit: research group Gorb

Scanning electronmicroscopy image of a single ommatidium surface of an eye in the moth Manduca sexta.
Credit: research group Gorb

Here’s a link to and a citation for the paper,

Correlation analysis of symmetry breaking in the surface nanostructure ordering: case study of the ventral scale of the snake Morelia viridis by A. Kovalev, A. Filippov, S. N. Gorb. Applied Physics A March 2016, 122:253 DOI:  10.1007/s00339-016-9795-2 First online: 03 March 2016

This paper is behind a paywall.

Memristors and dogs

They’ve managed to recreate Pavlov’s classic experiment with dogs and feeding bells using an electronic circuit and teaching it to respond to a stimulus just as the dogs learned to respond. From the May 8, 2012 news item on Science Daily,

The bell rings and the dog starts drooling. Such a reaction was part of studies performed by Ivan Pavlov, a famous Russian psychologist and physiologist and winner of the Nobel Prize for Physiology and Medicine in 1904. His experiment, nowadays known as “Pavlov’s Dog,” is ever since considered as a milestone for implicit learning processes. By using specific electronic components scientists form the Technical Faculty and the Memory Research at the Kiel University together with the Forschungszentrum Jülich were now able to mimic the behavior of Pavlov`s dog.

I found this image on the May 8, 2012 news release webpage at the University of Kiel (Germany) website,

The experiment called “Pavlov’s Dog” shows that acoustic stimulations can cause physical reactions. Scientists of Kiel University redesigned this mental learning process. Source: Kohlstedt

Also from the May 8, 2012 news release on the University of Kiel website,

“We used memristive devices in order to mimic the associative behaviour of Pavlov’s dog in form of an electronic circuit”, explains Professor Hermann Kohlstedt, head of the working group Nanoelectronics at the University of Kiel.

Memristors are a class of electronic circuit elements which have only been available to scientists in an adequate quality for a few years. They exhibit a memory characteristic in form of hysteretic current-voltage curves consisting of high and low resistance branches. In dependence on the prior charge flow through the device these resistances can vary. Scientists try to use this memory effect in order to create networks that are similar to neuronal connections between synapses. “In the long term, our goal is to copy the synaptic plasticity onto electronic circuits. We might even be able to recreate cognitive skills electronically”, says Kohlstedt. The collaborating scientific working groups in Kiel and Jülich have taken a small step toward this goal.

The project set-up consisted of the following: two electrical impulses were linked via a memristive device to a comparator. The two pulses represent the food and the bell in Pavlov’s experiment. A comparator is a device that compares two voltages or currents and generates an output when a given level has been reached. In this case, it produces the output signal (representing saliva) when the threshold value is reached. In addition, the memristive element also has a threshold voltage that is defined by physical and chemical mechanisms in the nano-electronic device. Below this threshold value the memristive device behaves like any ordinary linear resistor. However, when the threshold value is exceeded, a hysteretic (changed) current-voltage characteristic will appear.

“During the experimental investigation, the food for the dog (electrical impulse 1) resulted in an output signal of the comparator, which could be defined as salivation. Unlike to impulse 1, the ring of the bell (electrical impulse 2) was set in such a way that the compartor’s output stayed unaffected – meaning no salivation”, describes Dr. Martin Ziegler, scientist at the Kiel University and the first-author of the publication. After applying both impulses simultaneously to the memristive device, the threshold value was exceeded. The working group had activated the memristive memory function. Multiple repetitions led to an associative learning process within the circuit – similar to Pavlov’s dogs. “From this moment on, we had only to apply electrical impulse 2 (bell) and the comparator generated an output signal, equivalent to salivation”, says Ziegler and is very pleased with these results. Electrical impulse 1 (feed) triggers the same reaction as it did before the learning. Hence, the electric circuit shows a behaviour that is termed classical conditioning in the field of psychology. Beyond that, the scientists were able to prove that the electrical circuit is able to unlearn a particular behaviour if both impulses were not longer applied simultaneously.

My most recent posting (and I have many) on memristors is from April 19, 2012 where I mentioned an artificial synapse developed with them at the University of Michigan and also noted that HP Labs has claimed it will be releasing ‘memristor-based’ products in2013.

The May 8, 2012 news item on Science Daily includes the full citation for the team’s paper and a link to it (the paper is behind a paywall).