Earth

Lensless imaging technology introduces computing power into the conventional optical imaging system. The lensless camera becomes compact and easy-to-build. The earliest lensless camera could be pinhole camera, but the low light throughput limits its popularization. Then coded aperture cameras extend the idea of a pinhole camera by replacing the pinhole with a mask which allows more light throughput. Since the image reconstruction in lensless imaging is susceptible to the noise, current implementations need multiple shots or strict calibrations to enhance robustness.

In a new research article published in Light Science & Application, the researchers from Tsinghua University in China and MIT in the US introduce a Fresnel zone plate which is called Fresnel zone aperture (FZA) to develop a thin lensless camera. Though the Fresnel zone plate could be used as an imaging element similar to the lens, its long focal length could not support thin structure.

"The function of lens is modulating the light field, and converging the incoming light onto the focal plane. If we can obtain the light field on the exit plane of lens, the light field on the focal plane could be reconstructed by numerical propagation. Then the length of imaging system can be significantly shortened." said the first author, Jiachen Wu, from Tsinghua University.

It is not easy to obtain the light field because the sensor can only record the intensity while the phase information is lost. Since holography can record an interference pattern to reproduce the light field, the researchers seek to extend the concept of holography for incoherent illumination. It is interesting that the shadow of Fresnel zone plate has the same form with the point source hologram. That means the object could be encoded into hologram by Fresnel zone plate under the incoherent illumination. Then the image could be reconstructed by backpropagation method.

In FZA imaging system, the Fresnel zone plate is placed only three millimeters from the sensor. Jiachen and his colleagues took a series of pictures which are displayed on an LCD monitor. The incident light rays from a point on the object pass through the FZA and cast the shadow of FZA on the sensor. The resulting image from the camera sensor show distinct fringe characteristic similar to a hologram.

How to reconstruct the image from the single-shot 'hologram'? This problem looks challenging. It is well known that twin-image effect is the inherent problem in holography. The twin image likes a defocused image superimposes on the original image, and reduces the reconstructed image quality. The phase shifting is a valid method to eliminate twin image but it needs at least four captures. Inspired by compressive holography, the researchers introduced the total variation (TV) constraint into image reconstruction so that the twin image which does not satisfy the constraint of minimum TV could be effectively eliminated. Thanks to the compressive sensing algorithm, the single-shot imaging without any calibration could be realized for the thin lensless camera.

This computational imaging architecture can significantly drive down the cost of camera. Since the camera could be tightly integrated by depositing the FZA pattern on the cover glass of sensor, the assembly of camera could be reduced into the fabrication of sensor. This thin lensless camera has great potential for super-thin smart phones, home security cameras, autonomous cars, etc.

"We try to open a door for high quality lensless cameras free of noise. The presented technique provides a prototype for the integration of cameras and smart devices. Through a partnership between academia and industry, this technique could become practical," Prof. George Barbastathis says.

For the subsequent works, the researchers will further develop an updated version with hardware and software for the potential customers.

The simulations show that the asteroid hit Earth at an angle of about 60 degrees, which maximised the amount of climate-changing gases thrust into the upper atmosphere.

Such a strike likely unleashed billions of tonnes of sulphur, blocking the sun and triggering the nuclear winter that killed the dinosaurs and 75 per cent of life on Earth 66 million years ago.

Drawn from a combination of 3D numerical impact simulations and geophysical data from the site of the impact, the new models are the first ever fully 3D simulations to reproduce the whole event - from the initial impact to the moment the final crater, now known as Chicxulub, was formed.

The simulations [2] were performed on the Science and Technology Facilities Council (STFC) DiRAC High Performance Computing Facility.

Lead researcher Professor Gareth Collins, of Imperial's Department of Earth Science and Engineering, said: "For the dinosaurs, the worst-case scenario is exactly what happened. The asteroid strike unleashed an incredible amount of climate-changing gases into the atmosphere, triggering a chain of events that led to the extinction of the dinosaurs. This was likely worsened by the fact that it struck at one of the deadliest possible angles.

"Our simulations provide compelling evidence that the asteroid struck at a steep angle, perhaps 60 degrees above the horizon, and approached its target from the north-east. We know that this was among the worst-case scenarios for the lethality on impact, because it put more hazardous debris into the upper atmosphere and scattered it everywhere - the very thing that led to a nuclear winter."

The results are published today in Nature Communications.

Crater creation

The upper layers of earth around the Chicxulub crater in present-day Mexico contain high amounts of water as well as porous carbonate and evaporite rocks. When heated and disturbed by the impact, these rocks would have decomposed, flinging vast amounts of carbon dioxide, sulphur and water vapour into the atmosphere.

The sulphur would have been particularly hazardous as it rapidly forms aerosols - tiny particles that would have blocked the sun's rays, halting photosynthesis in plants and rapidly cooling the climate. This eventually contributed to the mass extinction event that killed 75 per cent of life on Earth.

The team of researchers from Imperial, the University of Freiburg, and The University of Texas at Austin, examined the shape and subsurface structure of the crater using geophysical data to feed into the simulations that helped diagnose the impact angle and direction. Their analysis was also informed by recent results from drilling into the 200 km-wide crater, which brought up rocks containing evidence of the extreme forces generated by the impact.

Peak performance

Pivotal to diagnosing the angle and direction of impact was the relationship between the centre of the crater, the centre of the peak ring - a ring of mountains made of heavily fractured rock inside the crater rim - and the centre of dense uplifted mantle rocks, some 30 km beneath the crater.

At Chicxulub, these centres are aligned in a southwest-northeast direction, with the crater centre in between the peak-ring and mantle-uplift centres. The team's 3D Chicxulub crater simulations at an angle of 60 degrees reproduced these observations almost exactly.

The simulations reconstructed the crater formation in unprecedented detail and give us more clues as to how the largest craters on Earth are formed. Previous fully 3D simulations of the Chicxulub impact have covered only the early stages of impact, which include the production of a deep bowl-shaped hole in the crust known as the transient crater and the expulsion of rocks, water and sediment into the atmosphere.

These simulations are the first to continue beyond this intermediate point in the formation of the crater and reproduce the final stage of the crater's formation, in which the transient crater collapses to form the final structure (see video). This allowed the researchers to make the first comparison between 3D Chicxulub crater simulations and the present-day structure of the crater revealed by geophysical data.

Co-author Dr Auriol Rae of the University of Freiburg said: "Despite being buried beneath nearly a kilometre of sedimentary rocks, it is remarkable that geophysical data reveals so much about the crater structure - enough to describe the direction and angle of the impact."

The researchers say that while the study has given us important insights into the dinosaur-dooming impact, it also helps us understand how large craters on other planets form.

Co-author Dr Thomas Davison, also of Imperial's Department of Earth Science and Engineering, said: "Large craters like Chicxulub are formed in a matter of minutes, and involve a spectacular rebound of rock beneath the crater. Our findings could help advance our understanding of how this rebound can be used to diagnose details of the impacting asteroid."

Enzymes from cold-loving organisms that live at low temperatures, close to the freezing point of water, display highly distinctive properties. In a new study published in Nature Communications, scientists at Uppsala University have used large-scale computations to explain why many cold-adapted enzymes stop functioning at around room temperature.

Enzymes are the "machines" that maintain metabolism in all living cells, but unfortunately all biochemical reactions normally stop at low temperatures. Evolution has solved this problem by developing cold-adapted enzymes in species whose internal cell temperature is the same as in the cold external environment. This applies to countless organisms, from bacteria to certain plants and cold-blooded vertebrates, such as fish that live in very cold water. These cold-adapted enzymes have special thermodynamic properties that enable them to function in freezing conditions. Evidently, they also melt at lower temperatures than ordinary enzymes; but it makes no difference if they melt at approximately 40 degrees Celsius, since they never need to work in such a warm environment.

However, one major unsolved enigma has been why many cold-adapted enzymes stop functioning even at around room temperature, long before they start melting. Researchers Jaka Socan, Miha Purg and Johan Åqvist have now, for the first time, succeeded in explaining this by means of extensive computer simulations.

The scientists simulated the chemical reaction in a starch-degrading enzyme from an Antarctic bacterium at various temperatures, and compared this with calculations relating to the same enzyme from an ordinary, warm-blooded pig. The Antarctic enzyme then proved to start breaking up locally even at room temperature, and this defect makes the starch molecules adhere much less well to the enzyme. This phenomenon gives rise to a maximum reaction speed at 25 degrees Celsius, and takes place at some 15 degrees Celsius below the melting point. In the pig enzyme, on the other hand, the reaction speed just keeps increasing until the enzyme finally melts at roughly 60 degrees Celsius.

With computer calculations, it is thus possible to identify which parts of the cold-adapted enzymes give rise to their special properties.

"Both our new results and earlier ones from computer simulations of various cold-adapted enzymes, and their mutants, show that we've now reached a stage where one can rationally redesign enzymes to change their properties in a predictable way. This approach has long been an aim, but to date it hasn't been able to compete with random laboratory evolution of enzymes, for which Frances Arnold was awarded the Nobel Prize in 2018," says Johan Åqvist, Professor of Theoretical Chemistry at the Department for Cell and Molecular Biology, Uppsala University.

"Directed evolution" is the process by which scientists produce tailor-made proteins for cell biology, physiology and biomedicine in the laboratory. Based on this method, Max Planck researchers from Martinsried have now developed a method to optimize proteins directly in mammalian cells. Using the new method, the scientists have produced the fluorescent protein mCRISPRred, which fluoresces brightly in lysosomes - very acidic, all-decomposing cell vesicles - which were previously difficult to label.

In the directed evolution of proteins, vast numbers of slightly altered variants of a starting protein are produced. This creates a large pool of potential candidates for later use in biomedical research. In a second step, researchers select the protein variants with improved, desired properties. The characterization of suitable protein candidates takes place in the test tube or in microbial cells. Overall, the process is very successful for many applications. However, protein variants that are supposed to function under the specific conditions of the mammalian cell or its organelles are difficult to identify in this way.

Together with colleagues from the neighboring Max Planck Institute of Biochemistry, researchers from Oliver Griesbeck's group developed a new, CRISPR-Cas9 based, method for directed protein evolution: "Our technique has nothing to do with the genome editing for which CRISPR is so well known," explains Arne Fabritius, one of the two first authors of the study. "We use the method to separate the DNA strand at a specific location. Errors in the repair mechanism then lead to genetic diversity - and this, directly in a living mammalian cell."

The new method introduces the gene of the desired protein into the cell's genome as a single copy. Here, it is stably embedded and is passed on to daughter cells during cell division. Using the CRISPR-Cas9 gene scissors, the researchers are able to cut at specific sites at the gene of the inserted protein. By adding specially made building blocks, planned errors occurring during the repair of the cut can lead to altered and, with a bit of luck, improved variants of the original protein.

In this way, the researchers from Martinsried have developed the protein mCRISPRed, which fluoresces brighter at the acidic pH in lysosomes and is much more robust than all previously designed proteins.

Lysosomes are the waste-disposal organelles of the cell. Their acidic pH dissolves almost everything they come in contact with. For quite some time, researchers had been looking for a way to introduce brightly fluorescing proteins into lysosomes to label them and thus to improve their investigation within cells.

The newly developed protein mCRISPRed shows that the properties of a protein can be adapted even to very specific conditions such as those of the lysosome. "The new application of CRISPR-Cas9 opens up completely different possibilities for advancing the development of biosensors, receptors, therapeutic proteins or signaling proteins," enthuses Oliver Griesbeck. "For me, this is definitely the next step in protein engineering!"

Fibroblasts are the most common connective tissue cells. They produce the structural framework for animal tissues, synthesise the extracellular matrix and collagen, and play a critical role in wound healing. However, during the cellular aging process, fibroblasts lose their ability to contract, leading to stiffness due to reduced connective tissues.

A study from the Mechanobiology Institute at the National University of Singapore has shown that these fibroblasts can be rejuvenated, or redifferentiated, by being geometrically confined on micropatterns. The above shows microscopic imaging of the control (left) and rejuvenated fibroblasts (right), with fluorescent labels highlighting the nucleus (blue), nuclear envelope (green), and cytoskeleton (in magenta). The presence of more contractile proteins (in red) in the rejuvenated fibroblasts indicates that they have recovered their ability to contract. These rejuvenated cells were observed to have reduced DNA damage, and enhanced cytoskeletal gene expression.

The results of this study were first published in the Proceedings of the National Academy of Sciences on 29 April 2020.

The research team believes that their mechanical reprogramming approach can overcome the shortcomings of conventional rejuvenation methods, including generation of short-lived or oncogenic fibroblasts. These mechanically rejuvenated fibroblasts could potentially be used as clinical implants in regenerative medicine and stem cell engineering.

How can patterns in the marine biodiversity of the past help us to understand how it may change in the future? A recent research by Drs Moriaki Yasuhara and Timothy C Bonebrake (School of Biological Sciences and Swire Institute of Marine Science, the University of Hong Kong) and numerous international collaborators finds that the tropical diversity decline now seen in the ocean is not purely human induced, but nonetheless will worsen considerably if we do not limit anthropogenic climate warming.

The research, published in Proceedings of the National Academy of Sciences of the United States of America, used fossil records to reconstruct global oceanic biodiversity patterns of the last ice age (~20,000 years ago) and the pre-industrial period (before 1800s), and used these to build ecological models for projecting global marine biodiversity in the near future (2090s). Using fossil protozoan foraminifera (Images 1, 2) as a "window" to see into past pelagic ecosystems through their rich fossil records, the authors discovered an equatorial "dip" in diversity during the pre-industrial period and projected for the end of this century, but not during the last ice age (Image 3).

"Biodiversity is usually high in the tropics and low at the poles. We call this important pattern the 'latitudinal diversity gradient'. Yet, recent studies have found that global marine biodiversity patterns often show an equatorial 'dip' of diversity. We wanted to explore what caused this, and whether it was a recent pattern," said lead author Dr Moriaki Yasuhara.

The modern decline of tropical diversity likely started during post-ice-age warming around 15,000 years ago. However, the magnitude of decline is projected to be amplified by anthropogenic warming. By the end of the 21st century, tropical diversity may decrease to levels not seen for millions of years if our future aligns with the "business-as-usual" CO2 emission scenario.

"By using fossil records we discovered that the diversity 'dip' in equatorial regions of the ocean is caused by species distribution shifts driven by post-ice-age ocean warming," continued co-lead author Dr Chih-Lin Wei, Associate Professor at Institute of Oceanography, National Taiwan University. The pelagic ocean covers the vast majority of Earth's surface and is the largest ecosystem on Earth (Images 4, 5). It is home to planktons that play a key role in food chain, top predators and economically important species that are increasingly under threat from climate change.

"These clear links between warming and reduced tropical biodiversity mean that by the end of this century, oceanic diversity at the equator may dip to a level unprecedented in human history," co-author Dr Derek P Tittensor, Associate Professor at Dalhousie University, concluded.

In 2018, around 16 million people were displaced by extreme climate events. People from poorer countries flee more often as a result of climate events. Scientists at the Max Planck Institutes for Evolutionary Biology in Plön and Meteorology in Hamburg have used a climate game to investigate how extreme climate events combined with poverty affect the migration of people to rich countries if the participants are also expected to finance measures against climate change. In this economic experiment, the representatives of the wealthy countries were rarely able to stop climate change and migration. In contrast, the representatives of the poorer countries are prepared to support a minimum level of climate protection by the rich.

Climate change is accompanied by extreme events such as floods, heat waves, and tropical hurricanes. "Such events will become more frequent and intense. This will also increase climate-induced migration", says Jochem Marotzke from the Max Planck Institute for Meteorology in Hamburg. Climate change and the resulting events affect poorer population groups the most. But combating it is a global challenge. This is partly why effective climate protection is difficult to implement.

To investigate the connection between climate protection measures, climate-induced migration, and poverty, the scientists recruited 410 students from the Universities of Hamburg and Kiel to participate in a climate game. The players represented the inhabitants of either a wealthy or a poor country. As starting capital, the representatives of the rich country received €40 each. Those of the poor country received €20.

The participants were able to invest this and any money earned through harvesting in the prevention of "dangerous" climate change simulated in the game. This is the case, for example, when a certain average temperature is exceeded. The participants were allowed to keep the remaining amount for themselves provided that the goal of averting "dangerous" climate change was achieved by the respective group after 20 rounds of play.

Investment in climate protection

Each participant could contribute €2 or €4 per round for the environment or nothing at all. The climate goal was achieved if everyone invested an average of €2. Such a system favours freeloaders who do not want to spend anything on climate protection but benefit from the successful climate protection by others.

At the beginning, representatives of the wealthy country achieved a crop yield twice that of the poorer country per round. In each round, the poor inhabitants were able to try to migrate to the rich country. At least four "rich" participants were able to jointly achieve a fixed sum to block migration. Here too, freeloaders were able to try to benefit from the efforts of others.

But this often led to not meeting the target sum for blocking the migration, which then took place. With each migrant, the crop yield decreased in the rich country and increased in the poor country until there was a distribution of two inhabitants in the poor country and eight in the rich country. The yields per inhabitant were then equal, and there was no longer any poverty migration. This "Nash equilibrium" - in which no participant can gain by a unilateral change of behaviour if the behaviours of the others remain unchanged - was always achieved, albeit delayed by the occasional successful blocking.

In the game, only the representatives of the poor country suffered from climate events with a probability of ten or 20 percent. This resulted in a crop failure for them in each of three consecutive rounds. When a climate event was announced, the number of migrants also increased in equilibrium beyond pure poverty migration. The representatives of the rich countries tried to block the migrants. During the climate event, the efforts for climate protection of the poor decreased, while those of the rich increased - but not to the necessary extent.

Missed goal

Most groups did not achieve the climate goal and lost their money, although the rich had far greater financial reserves than the poor. "As long as there is hope that others will raise money while you save, some people will obviously run the risk of losing in the end", says Manfred Milinski.

Surprisingly, once a certain minimum contribution by the rich is exceeded, the poor are at least willing to try to raise the missing amount to achieve the climate protection goal. Global cooperation could therefore be possible as long as the economically powerful make efforts to slow climate change.

Graphene analogues, such as graphene oxide (GO) and its reduced forms (rGO), are fascinating carbon materials due to the complementary properties endowed by the sp3-sp2 interconversion, revealing the substitutability and potential for industrialization of integrated graphene devices. Appropriate micro/nanostructural design of GO and rGO for controlling the energy band gap and surface chemical activity is important for developing strategic applications. The femtosecond laser plasmonic lithography (FPL) technology is a qualified candidate for generating the required structures due to its efficiency, high-quality, flexibility and controllability. However, as both the theoretical and experimental explorations of this method are still in their infancy, micro/nanoprocessing of graphene materials using FPL has not been realized. The feasibility of implementing the technique in practical applications is still questionable because most related studies only highlight the characteristics of the structure obtained from the processing but often ignore the complementary changes in the properties of the material itself.

In a new paper published in Light Science & Application, scientists from the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, China, and co-workers presented a high-quality, efficient and large-area periodic micro/nanoripple manufacturing (~680 nm period) and photoreduction of GO films (~140 nm thickness) on a silicon substrate by using the FPL method. Interestingly, unlike most of the reported laser-induced periodic surface structures (LIPSS) in which the pattern alignment is perpendicular to the polarization of the incident light, they are found to have the extraordinary uniform distribution with orientation parallel to each other in this case. Such a phenomenon cannot be explained by the conventional theory of LIPSS, i.e., the interference between the incident light with TM mode and the excited surface plasmon (SP) wave. The analysis demonstrated that the laser-induced gradient reduction of GO film from its surface to the interior plays a key role, and it leads to an inhomogeneous slab with the maximum dielectric permittivity (DP) at the surface and a smaller DP in the interior that allows excitation of TE-mode surface plasmons (TE-SPs) and the subsequent uncommon interference. Due to the diverse physical mechanisms involved in the laser-rGO interaction, the LIPSS formation also exhibited unique characteristics such as strong robustness against a range of perturbations. Because the microprocessing contains no assistant operations, such as chemical etching, the properties of the graphene material are retained, which allows them for optoelectronic applications. As a matter of fact, through modulation of the photoreduction degree and structural design of the rGO surface, they realized the enhanced light absorption (~ 20%), thermal radiation (> 10°C) and anisotropic conductivities (anisotropy ratio ~ 0.46) from this film material. Based on it, they designed an on-chip, broadband photodetector with stable photoresponsivity (R ~ 0.7 mA W-1) even when exposed to light with the low power (0.1 mW). The authors of the paper summarize the significance of this work as follows:

"(1) The FPL technology is used for the first time to realize the preparation of high-quality, efficient and large-scale periodic micro/nanostructures on the surface of graphene materials; (2) The physical mechanisms of the laser-material interaction involved in FPL technology is further improved; (3) Both the structural characteristics and the properties of the processed material itself are taken into account in the application of photoelectric devices."

"Compared to laser direct writing adopting the same incident laser parameters, our FPL strategy takes only ~1/14000 of the time to process a centimetre-sized sample (1×1.2 cm2). At the same time, due to the possible nonlinear optical property, the FPL strategy induces an obvious 'self-repairing' phenomenon, which can effectively guarantee the processing quality. For example, we can prepare rGO-LIPSS films on different substrates and nondestructively transfer them onto other substrates."

"Our explanation of the experimental phenomena is markedly different from most of the principles at present. This will give us a clearer understanding of the relevant physical processes and lay a solid foundation for the further development of FPL technologies."

"The structured graphene materials by FPL technology present excellent photoelectric performance. The photoresponsivity is numerically comparable to the response of the samples obtained by other reduction methods (e.g., chemical and thermal) and is much larger than that of typical photoreduced ones. The anisotropy ratio is even larger than that of some natural anisotropic crystals. Our work combines the experimental exploration with the in-depth understanding of high-speed micro/nanopatterning of the regular rGO-LIPSS, which not only benefits fundamental physics but also facilitates the practical development of graphene analogues on the industrial scale. "

Alterations to chromosomes are considered important in speciation (the process by which new species are formed). In a new paper in the journal Molecular Biology and Evolution, researchers from the University of Konstanz, Harvard University and La Sapienza University of Rome study wild house mice (Mus musculus domesticus) from several islands in the Aeolian archipelago off the coast of Sicily, Southern Italy. Their findings provide empirical support to the idea that a specific type of large-scale chromosomal rearrangements called "Robertsonian (Rb) fusions" play an active role in speciation.

Read the full story on the website of the University of Konstanz at: https://www.uni-konstanz.de/en/university/news-and-media/current-announcements/press-releases/press-releases-in-detail/chromosomale-artbildung-bei-wildlebenden-hausmaeusen/

Facts:

New genome-wide study of wild house mice (Mus musculus domesticus) in Southern Italy suggests that a specific type of large-scale chromosomal rearrangements called Robertsonian fusions play an active role in speciation.

Using a range of powerful genetic approaches, researchers from the University of Konstanz, Harvard University and La Sapienza University of Rome traced the demographic patterns and karyotypic distributions of wild house mouse populations in the Aeolian archipelago.

Original publication: Paolo Franchini, Andreas F. Kautt, Alexander Nater, Gloria Antonini, Riccardo Castiglia, Axel Meyer, Emanuela Solano, Reconstructing the evolutionary history of chromosomal races on islands: a genome-wide analysis of natural house mouse populations, Molecular Biology and Evolution, msaa118, 25 May 2020. DOI: https://doi.org/10.1093/molbev/msaa118

Focussing on three identical chromosomal rearrangements found in the island and in mainland populations, the researchers were able to show that, contrary to previous suggestions, large-scale genetic mutations are occurring more readily than anticipated and independently from one another.

For the first time, scientists have introduced minuscule tracking devices directly into the interior of mammalian cells, giving an unprecedented peek into the processes that govern the beginning of development.

This work on one-cell embryos is set to shift our understanding of the mechanisms that underpin cellular behaviour in general, and may ultimately provide insights into what goes wrong in ageing and disease.

The research, led by Professor Tony Perry from the Department of Biology and Biochemistry at the University of Bath, involved injecting a silicon-based nanodevice together with sperm into the egg cell of a mouse. The result was a healthy, fertilised egg containing a tracking device.

The tiny devices are a little like spiders, complete with eight highly flexible 'legs'. The legs measure the 'pulling and pushing' forces exerted in the cell interior to a very high level of precision, thereby revealing the cellular forces at play and showing how intracellular matter rearranged itself over time.

The nanodevices are incredibly thin - similar to some of the cell's structural components, and measuring 22 nanometres, making them approximately 100,000 times thinner than a pound coin. This means they have the flexibility to register the movement of the cell's cytoplasm as the one-cell embryo embarks on its voyage towards becoming a two-cell embryo.

"This is the first glimpse of the physics of any cell on this scale from within," said Professor Perry. "It's the first time anyone has seen from the inside how cell material moves around and organises itself."

WHY PROBE A CELL'S MECHANICAL BEHAVIOUR?

The activity within a cell determines how that cell functions, explains Professor Perry. "The behaviour of intracellular matter is probably as influential to cell behaviour as gene expression," he said. Until now, however, this complex dance of cellular material has remained largely unstudied. As a result, scientists have been able to identify the elements that make up a cell, but not how the cell interior behaves as a whole.

"From studies in biology and embryology, we know about certain molecules and cellular phenomena, and we have woven this information into a reductionist narrative of how things work, but now this narrative is changing," said Professor Perry. The narrative was written largely by biologists, who brought with them the questions and tools of biology. What was missing was physics. Physics asks about the forces driving a cell's behaviour, and provides a top-down approach to finding the answer.

"We can now look at the cell as a whole, not just the nuts and bolts that make it."

Mouse embryos were chosen for the study because of their relatively large size (they measure 100 microns, or 100-millionths of a metre, in diameter, compared to a regular cell which is only 10 microns [10-millionths of a metre] in diameter). This meant that inside each embryo, there was space for a tracking device.

The researchers made their measurements by examining video recordings taken through a microscope as the embryo developed. "Sometimes the devices were pitched and twisted by forces that were even greater than those inside muscle cells," said Professor Perry. "At other times, the devices moved very little, showing the cell interior had become calm. There was nothing random about these processes - from the moment you have a one-cell embryo, everything is done in a predictable way. The physics is programmed."

The results add to an emerging picture of biology that suggests material inside a living cell is not static, but instead changes its properties in a pre-ordained way as the cell performs its function or responds to the environment. The work may one day have implications for our understanding of how cells age or stop working as they should, which is what happens in disease.

The study is published this week in Nature Materials and involved a trans-disciplinary partnership between biologists, materials scientists and physicists based in the UK, Spain and the USA.

Glass frogs are well known for their see-through skin but, until now, the reason for this curious feature has received no experimental attention.

A team of scientists from the University of Bristol, McMaster University, and Universidad de Las Américas Quito, sought to establish the ecological importance of glass frog translucency and, in doing so, have revealed a novel form of camouflage.

Using a combination of behavioural trials in the field, computational visual modelling and a computer-based detection experiment, the study published in PNAS reveals that, while glass frog translucency does act as camouflage, the mechanism differs from that of true transparency.

Lead author, Dr James Barnett who began the research while a PhD student at the University of Bristol and is now based at McMaster University in Canada, said:

"The frogs are always green but appear to brighten and darken depending on the background. This change in brightness makes the frogs a closer match to their immediate surroundings, which are predominantly made up of green leaves. We also found that the legs are more translucent than the body and so when the legs are held tucked to the frog's sides at rest, this creates a diffuse gradient from leaf colour to frog colour rather than a more salient sharp edge. This suggests a novel form of camouflage: 'edge diffusion'."

Dr Barnett said scientific debate had often been skeptical of the degree to which glass frogs can be called transparent.

"Transparency is, at face value, the perfect camouflage. It is relatively common in aquatic species where animal tissue shares a similar refractive index to the surrounding water. However, air and tissue are quite different in their refractive indices, so transparency is predicted to be less effective in terrestrial species. Indeed, terrestrial examples are rare. Although glass frogs are one commonly cited example of terrestrial transparency, their sparse green pigmentation means they are better described as translucent," said Dr Barnett.

Dr Barnett's PhD was supervised by Professor Nick Scott-Samuel, an expert in visual perception from the University of Bristol's School of Psychological Sciences, and Innes Cuthill, Professor of Behavioural Ecology from Bristol's School of Biological Sciences. Professor Scott-Samuel said:

"Our study addresses a question that has been the topic of much speculation, both among the public and the scientific community. We now have good evidence that the frogs' glass-like appearance is, indeed, a form of camouflage."

Professor Cuthill said: "Animal camouflage has long been a textbook example of the power of Darwinian natural selection. However, in truth, we are only beginning to unravel how different forms of camouflage actually work. Glass frogs illustrate a new mechanism that we hadn't really considered before."

The world's deep oceans are warming at a slower rate than the surface, but it's still not good news for deep-sea creatures according to an international study.

The research, led by University of Queensland PhD student Isaac Brito-Morales, looked at how ocean life was responding to climate change.

"We used a metric known as climate velocity which defines the likely speed and direction a species shifts as the ocean warms," Mr Brito-Morales said.

"We calculated the climate velocity throughout the ocean for the past 50 years and then for the rest of this century using data from 11 climate models.

"This allowed us to compare climate velocity in four ocean depth zones - assessing in which zones biodiversity could shift their distribution the most in response to climate change."

The researchers found climate velocity is currently twice as fast at the surface because of greater surface warming, and as a result deeper-living species are less likely to be at risk from climate change than those at the surface.

"However by the end of the century, assuming we have a high-emissions future, there is not only much greater surface warming, but also this warmth will penetrate deeper," Mr Brito-Morales said.

"In waters between a depth of 200 and 1000 metres, our research showed climate velocities accelerated to 11 times the present rate.

"And in an interesting twist, not only is climate velocity moving at different speeds at different depths in the ocean, but also in different directions which poses huge challenges to the ways we design protected areas."

Senior researcher UQ's Professor Anthony Richardson said the team believed action must be taken to aggressively manage carbon emissions.

"Significantly reducing carbon emissions is vital to control warming and to help take control of climate velocities in the surface layers of the ocean by 2100," he said.

"But because of the immense size and depth of the ocean, warming already absorbed at the ocean surface will mix into deeper waters.

"This means that marine life in the deep ocean will face escalating threats from ocean warming until the end of the century, no matter what we do now.

"This leaves only one option - act urgently to alleviate other human-generated threats to deep-sea life, including seabed mining and deep-sea bottom fishing.

"The best way to do this is to declare large, new protected areas in the deep ocean where damage to ocean life is prohibited, or at least strictly managed."

Global warming is causing species to search for more temperate environments in which to migrate to, but it is marine species - according to the latest results of a Franco-American study mainly involving scientists from the CNRS, Ifremer, the Université Toulouse III - Paul Sabatier and the University of Picardy Jules Verne (1) - that are leading the way by moving up to six times faster towards the poles than their terrestrial congeners. By analysing the speed of change in the distribution range of more than 12,000 animal and plant species, according to isotherm shifts in latitude and altitude, the researchers have shown that under certain conditions marine species are capable of following the invisible migration of temperatures towards the poles. This unbridled race against global warming is modulated by the pressure of human activities (fishing, aquaculture, agriculture, silviculture, urban planning) speeding up or slowing down the movement of species in their pursuit of more favourable climatic conditions. These results, published in the journal Nature Ecology & Evolution on 25 May 2020, raise questions about the capacity of terrestrial organisms to adapt to anticipated global warming temperatures in the 21st century.

The diagnosis of cancer in a child can be devastating to parents and other loved ones, but in a recent study from Denmark, having a child with cancer did not appear to impact parents' risk of separation or divorce or affect future family planning. The findings are published early online in CANCER, a peer-reviewed journal of the American Cancer Society (ACS).

Childhood cancer can cause feelings of fear and uncertainty among parents and burden them with many practical challenges related to caregiving and work-related obligations. To assess the impact of childhood cancer on parental relationships, Luzius Mader, PhD, of the Danish Cancer Society Research Center, and his colleagues examined data from several registries in Denmark, linking information on parents of children diagnosed with cancer in 1982-2014 (7,066 children and 12,418 case parents) with 10 comparison parents of children without cancer (69,993 children and 125,014 comparison parents). Parents were followed until 10 years after diagnosis, separation or divorce, death, emigration, or the end of 2017, whichever came first.

Overall, parents of children with cancer had a four percent lower risk of separation and an eight percent lower risk of divorce compared with parents of children without cancer. Among parents of children with cancer, those who were younger, had less education, and were unemployed had elevated risks for separation and divorce. Risks were also higher among parents of children diagnosed at a younger age.

The investigators also evaluated how the diagnosis of cancer in a child affects parents' decisions on having another child. They expected that parents of a child with cancer would have fewer children than parents of children without cancer, and that they would postpone having another child. This was not the case, however, as the researchers found that the childhood cancer experience did not negatively affect parents' future family planning in Denmark.

Dr. Mader noted that health care providers should communicate these reassuring and encouraging findings to parents, but that support should be offered if needed to improve family life in the long term. "Currently, family support services are largely limited to the child's in-patient treatment including support by hospital staff such as social workers or psycho-oncologists as well as through community organizations; however, while more general support services such as marital counselling are widely available, cancer-specific family support services are often lacking after the child's treatment," he said.

Varennes, May 25 2020 - Australian and Canadian researchers led by Prof David J. Moss at Swinburne University of Technology and honorary professor at the Institut National de la Recherche Scientifique (INRS) was able to achieve world record-high data transmission over 75 km of standard optical fibre using a powerful class of micro-comb called soliton crystals.

"This is one of the most efficient transmission systems implemented in a standard telecom network, given the record amount of information that can be encoded and propagated in an optical fibre with minimum loss of data," says Professor Roberto Morandotti of the INRS, co-author of the study published on May 22 in Nature Communications and long-term collaborator of Prof Moss.

Telecommunication networks use many different frequencies, or colours, to transfer as much information as possible. Current networks need typically a separate laser for every colour, which is difficult and costly to set up properly. "Here, we decided to use a micro-comb to replace the multiple lasers. Like a hair comb, we can generate a set of frequencies which are equally distant, and the phase and amplitude of which can be easily and precisely controlled," explains Morandotti. The ability to supply all wavelengths with a single, compact integrated chip, replacing many parallel lasers, offers the greatest benefit, in terms of performance, scalability and power consumption.

"We took advantage of the fact that a frequency comb could be created with a device known as a micro-ring resonator. Previous to this work, a well-behaved comb, resulting in a so-called cavity soliton, required a special and unique balance between colour dispersion and non-linearity. Such combs are typically difficult to generate and stabilize, and not really power efficient even under ideal conditions, so the researchers have developed a new way to achieve them for telecom purposes. In particular, if the microresonator is properly designed, it is possible to get a cross point between the optical modes supported by the device, which in turn creates the right condition for realizing a different type of micro-comb, leading to so-called crystal solitons, which is both robust and user-friendly," explains Professor Morandotti.

This work demonstrates the capability of optical micro-combs to perform in demanding and practical optical communications networks. According to Professor Morandotti, the proposed mechanism could be commercially implemented in 5 years from now since similar micro-ring resonators, intended for less demanding applications such as filtering, are already well known and commercially available.