Advent Calendar 2020

Time for a little mental exercise: today's image shows a spatial, geometric structure, the so-called three-dimensional resonance arrangement. Each of the coloured surfaces represents a circular disc. These all meet in the centre of the sphere and partially cover each other. There are numerous chambers between the circular discs; the space between the yellow, the purple and the orange disc is most clearly visible in the picture. How many chambers does the structure house in total? Mathematicians also address this question, but they do not limit themselves to three dimensions. While in the three-dimensional case, imagination or a little crafting skill help, it becomes more difficult with each additional dimension. An exact formula for the number of chambers of the resonance arrangement in any dimension is not known, but Lukas Kühne of the Max Planck Institute for Mathematics in the Sciences recently managed a new estimate. The resonance arrangement and its chambers occur in various contexts both within mathematics and in application areas such as quantum field theory or game theory. Incidentally, the solution for the three-dimensional case is 32 - 16 chambers above the green equatorial plane and 16 chambers below.

Graphic

Some microbes are capable of producing methane - a highly potent greenhouse gas and biofuel. These so-called methanogens gain their energy through various chemical reactions that take place in an oxygen-free environment. They are possibly among the earliest forms of life on earth. At the same time, we can use them today for new biotechnologies, for example to bind carbon dioxide and produce methane. This is used as a source of energy - as in the case of natural gas, for example, which consists mainly of methane. The researchers are therefore focusing on the chemical reactions involved in methane production. What here resembles an origami butterfly  is a crystallized enzyme that can produce methane and is found in all methanogens. The green-yellowish colour comes from a special nickel-containing molecule. This molecule is buried deep in the enzyme nucleus, but is of immense importance: it orchestrates the formation of methane and is therefore the key to the entire process.

Stereo Light Microscopy

Refrigerator magnet - in the future, this could no longer mean an ornament on the appliance, but a less energy-intensive cooling technology based on the magnetocaloric effect: some materials placed in a magnetic field absorb a lot of heat when they change from the non-magnetic to the ferromagnetic state and cool down when the field is removed. In most cases, this effect cannot be exploited because this heat-absorbing change in magnetic state usually involves atoms arranging themselves differently. This makes the cooling cycle deteriorate after multiple repetitions. However, in a compound of the rare-earth metal europium with the metal indium, a large magnetocaloric effect occurs without such losses. The image is part of a simulation that illustrates how this is possible. The effect can be explained here solely by the fact that magnetic interactions of the electrons change strongly, but not the atomic structure. The golden lines mark the limits of the states that the electrons assume, which are significantly involved in building up the magnetic order. Understanding the effect helps in the search for new magnetic materials that could replace today's inefficient and polluting refrigerators.

Computersimulation

The thale cress (Arabidopsis thaliana) is one of the most famous plants in the world ˗ yet it neither looks spectacular, nor is it important for agriculture. In plant research, however, the small annual wild herb is the most important model organism: it is undemanding, grows quickly and produces large quantities of seeds. Above all, it has already been well studied and its genome is completely known. Researchers at the Max Planck Institute for Developmental Biology have uncovered a signalling pathway in thale cress that explains why some plants flower even on short, dark days. Micro RNAs play a central role in this - small RNA snippets that are involved in gene regulation. When their concentration in the plant drops, this triggers flower formation, even without external influence. This ensures that the plant can flower and reproduce even when temperature or light conditions are not favourable. This images allows us a view into an Arabidopsis flower shows a stamen with almost ripe pollen grains inside.

Scanning electron microscopy

Some bacteria possess an ability that - while practical for them - is rather unpleasant for humans: in order to defy environmental influences and to be able to colonise inhospitable habitats, they combine with other microbes and form a common protective layer of mucus. This creates biofilms that are extremely resistant and can only be removed with difficulty - a major problem in medicine as well as in food production. To be able to combat biofilms more effectively, researchers want to understand the rules by which they are constructed. To this end, they cultivate E. coli bacteria on nutritious agar gels where the cells deposit a fibrous matrix. To monitor the growth of the resulting biofilm, the researchers start by mixing fluorescent beads under the cells. As the biofilm grows, the beads are entrained. For our "fireworks", a fluorescence image was taken every hour for five days, after which all images were superimposed.

Stereomicroscopy

One million X-ray sources - that is the impressive yield of the first complete sky survey with the eRosita telescope on board the space probe Spectrum X-ray Gamma (SRG). The image of the hot and energy-rich universe is a completely different one than that offered by optical or radio observatories. Outside our home galaxy, most X-ray sources are active centres of distant galaxies containing supermassive black holes. There are also clusters of galaxies that appear as extended X-ray halos and glow thanks to the hot gas trapped in huge accumulations of dark matter. To create this image, the telescope rotated continuously on its own axis, providing a uniform exposure of about 150 to 200 seconds over most of the sky. The entire firmament was projected onto an ellipse, with the centre of the Milky Way in the middle and the galactic disc in the horizontal. The colours correspond to different energies of the received X-ray photons.

Read more: Our deepest view of the X-ray sky

Under the microscope, crystals on the microscope slide show up like ice flowers on a poorly insulated windowpane. The "small" difference lies in the temperature: these iridescent structures are formed when hydroxyquino cools and crystallises from a 150°C hot melt. Scientists at the Max Planck Institute for the Dynamics of Complex Technical Systems are investigating the suitability of the benzene derivative as a so-called co-former for a potential active pharmaceutical ingredient:

BDMC (bisdemethoxycurcumin), one of the three main ingredients of the turmeric plant, is considered a potential active ingredient for the prevention of Alzheimer's disease and cancer. However, it is very poorly soluble in water and therefore poorly absorbed by the human body. However, if two chemical substances - here hydroxyquino and BDMC - crystallize together, co-crystals with new physico-chemical properties can form. The scientists are interested in the extent to which co-crystallisation can increase the water solubility and thus the bioavailability of BDMC.

Polarisation microscopy

Squid, cuttlefish and octopus can change their appearance at lightning speed. This ability allows them to camouflage themselves from predators or to swim unnoticed to prey. Mating is different: here, some species let conspicuous, almost psychedelic dynamic patterns travel over their bodies. Millions of tiny elastic pigment cells in the skin provide the necessary colour changes. Each pigment cell is surrounded by radial muscles. When those muscles contract, the pigment cell expands, revealing the pigment. When they relax, the pigment cell shrinks and the coloured “pixel” disappears. The muscles are controlled directly by neurons in the brain. Researchers study how the animals interpret what they see to decide what patterns to generate in response and how. This image shows a newly hatched bobtail squid Euprymna berryi, stained with fluorescent antibodies to reveal a dense network of peripheral nerve cells. The colour palette reflects different depths of the nerves in the tissue.

Confocal microscopy

Scientists from the Max Planck Institutes for Biogeochemistry in Jena and for Chemistry in Mainz are researching the CO2 cycle in the largest continuous forest area on earth at the Amazon Tall Tower Observatory - ATTO for short - in the middle of the Brazilian rainforest. In their work, the researchers are not only looking turning their eyes upwards - mosses cover large parts of the trees and shrubs in the Amazon rainforest. They are only metabolically active when it is humid enough, because they cannot regulate their water content themselves. They survive long dry periods in a desiccated, inactive state. As the researchers have now discovered, mosses close to the forest floor react reliably to rain events. For mosses within the canopy of trees, on the other hand, humidity and dew seem to be the more important water sources. When they have enough water to wake up from their dormant state, light availability becomes most important to determine how productive they are in their photosynthetic activity. And also if they absorb more carbon dioxide from the atmosphere than they release through respiration.

Photography

More: Welcome to the Amazon

The four-legged robotic "dog" Solo 8 is capable of jumping and down  - like an excitable young dog. The lightweight and torque-controlled robot from the Max Planck Institute for Intelligent Systems is built for highly dynamic motion sequences. For example, it can jump waist high or topple over and come back onto its feet. The new research robot was developed as an open source project. The goal of the participating researchers is to create an easily accessible and affordable platform for research and teaching in the field of robot locomotion. Solo 8 is inexpensive and easy to build. Most of the parts that make up the robot are 3D-printed, and the few remaining ones are purchasable off-the-shelf. The design instructions and robot software are freely available, so the developers hope that other scientists will pick up the ideas and build on them.

Photography

Read more: Four-legged robot makes research comparable worldwide

The snowy landscape in this picture is literally out of this world – it is a picture of the Occator Crater on Ceres. The dwarf planet was once the scene of cryovolcanic eruptions: subsurface brine pushed upward; the water evaporated, leaving behind these bright, salty deposits. At about 950 kilometres in diameter, Ceres is the largest body in the asteroid belt that stretches between the orbits of Mars and Jupiter. From 2015 to 2018, NASA's unpiloted Dawn space probe explored this the unusual body up close. The scientific camera system on board, from the Max Planck Institute for Solar System Research in Göttingen, played an important role. Again and again, there are new insights: one of the most exciting regions turned out to be the huge Occator crater, which measures about 92 kilometres in diameter. This small dome, 340 metres high and covered with salt deposits, is at its centre. Images like this one help decipher the crater's exact geology and thus its evolutionary history.

Read more: Cryovolcanism on Ceres

3D reconstruction

Wouldn't it be practical if mammals grew in eggs? It would make births so much easier. Also, it would have advantages for research: as with fish, amphibians or birds, researchers could observe the development from fertilisation to the "finished" animal. However, in the case with mammals, that ends as soon as the embryo has nested in the uterus. Now it is hidden from all eyes. But this is when things get really exciting: the organs are laid out, the embryo changes its shape profoundly. Millimetre-sized squiggles like the one in the picture could help: If clumps of mouse stem cells are cultivated in a special supporting gel, structures grow that resemble at least part of the embryo. Within five days, spherical cell clusters develop into structures with annexes for nerve, bone, cartilage and muscle tissue. In applied research, this would make it possible to effectively study the effects of pharmacological agents more effectively in the future – and on a scale that would not be possible in living organisms. And basic research could possibly unravel the mystery of how a mammalian embryo takes shape.

 Fluorescence microscopy

Read more here: Embryonic development in a petri dish

Read more here: Another major step towards room-temperature superconductivity

Digital photography

We usually associate optical fibres with fast internet. But depending on the structure and material, glass fibres can not only conduct light, but also influence and alter it. Researchers at the Max Planck Institute for the Science of Light make use of this ability to generate light with special properties. For example, the researchers can genera white light from infrared laser pulses that extends spectrally from the ultraviolet to the infrared range in hollow-core fibres. This white light still has essential properties of laser light and is called supercontinuum. It is used, among other things, in medical technology. To do this, the scientists first produce a suitable fibre: firstly, they manually arrange individual quartz glass rods and capillaries in the desired shape. The preliminary stage of the glass fibre shown here is then drawn in several steps at temperatures of up to 2000°C to produce the finished fibre, which is only 150 micrometres thick. The diameter becomes 200 times smaller in the process, but the complex structure remains intact and the special light-guiding properties are created.

Photography

This kindergarten in Bamako, the capital of Mali, has a very scientific purpose: Rainer Polak and Nori Jacoby from the Max Planck Institute for Empirical Aesthetics have rented the premises to research traditional dance and music in West Africa. To this end, they have engaged several groups of local professional artists. Involved are a drum ensemble with three musicians, two singers and several dancers. During the live session, all aspects of the performance are captured in multimedia. One of the dancers wears a motion-capture suit that incorporates 17 so-called inertial-based sensors. They record acceleration, rotation and magnetic field values. In this way, all movements can be precisely documented. The Frankfurt scientists regularly collect data in field research situations in Mali and Bolivia and, for comparison, also in Germany, Bulgaria, the USA, Great Britain and Uruguay. The goal of the project is to empirically compare the perception and performance of musical rhythm in different cultures.

Photography

Recognising movements and their direction is vital: it is the only way, for example, to recognise an approaching enemy in time to adapt one's own movements accordingly. Max Planck researchers are using fruit flies to study how a nerve cell detects movement. Although their eyes are constructed quite differently from those of mammals, the visual processing in insects and mammals shows astonishing parallels. In the flies, the neurobiologists discovered that certain cells that process movement information occur in four subgroups. Each group reacts only to movements in one direction: to the right, left, upwards or downwards. The nerve cells of these direction-selective groups pass on their information to separate layers of the subsequent nerve tissue, for example, when instructions for course correction are passed on to the flight muscles. The picture shows the visual system of a developing fly brain. The direction-sensitive cells glow green. The organising processing layers can be seen in blue and red.

Fluorescence microscopy

Unequal siblings also exist in space. A particularly strange pair were captured by the LIGO and Virgo detectors. The two observatories search the sky for gravitational waves - those ripples in space-time that Albert Einstein predicted a century ago. The waves originate from cosmic collisions and occur when, for example, black holes approach each other in a wild dance and eventually merge. Usually, the two black holes have quite similar masses. But the message with the designation GW190814 poses a mystery: never before have researchers measured a gravitational wave from a system in which the individual masses are distributed so differently. According to the models that gave rise to this visualisation, a normal black hole with 23 solar masses and an object of only 2.6 times the mass of the sun have collided. But what is behind this mysterious companion? The lightest black hole known so far or the heaviest neutron star found in a binary system?

Read more: A black hole with a puzzling companion

Computer simulation

An exciting cycle can be observed in bacteria of the species Pseudomonas fluorescens: If the cells are cultivated in a nutrient solution, they rise to the surface because they need oxygen to grow. If oxygen is available, the genetic constellation changes so that the cells produce cellulose. This acts like an adhesive that attaches the bacteria together. This creates a "mat" that becomes thicker and thicker as the bacteria population continues to grow. But at some point the mat becomes so heavy that it collapses and breaks apart. The bacteria sink down and the cellulose production stops. But their hunger for oxygen drives them back up and the cycle starts again. A look at a Petri dish shows the final stage of the cellulose mat just before it collapses. Researchers at the Max Planck Institute for Evolutionary Biology want to find out which signals from the environment boost cellulose production and which strategies the cells develop to break out of the community and thus choose new and more effective ways of survival.