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Tag: Universiteit van Amsterdam

  • Rembrandt innovated by infusing canvas with lead for The Night Watch.

    Rembrandt innovated by infusing canvas with lead for The Night Watch.

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    Newswise — New research has revealed that Rembrandt impregnated the canvas for his famous 1642 militia painting ‘The Night Watch’ with a lead-containing substance even before applying the first ground layer. Such lead-based impregnation has never before been observed with Rembrandt or his contemporaries. The discovery, published today in Science Advances, underlines Rembrandt’s inventive way of working,  in which he did not shy away from using new techniques.

    The surprising observation is yet another result from Operation Night Watch, the largest and most wide-ranging research and conservation project in the history of Rembrandt’s masterpiece. It resulted from advanced analysis of an actual paint sample taken from the historical painting. First author of the paper is Fréderique Broers, a researcher at the Rijksmuseum and PhD student with professors Katrien Keune (University of Amsterdam), Koen Janssens (University of Antwerp) and Florian Meirer (Utrecht University). Her research forms part of the research project 3D Understanding of Degradation Products in Paintings of the Netherlands Institute for Conservation+Art+Science+ (NICAS), funded by the Dutch Research Council NWO. Broers and coworkers employed a combination of x-ray fluorescence and ptychography to identify and visualize sub-microscale chemical compounds in the lower layers of the canvas. By sampling the small Night Watch paint fragment at DESY (Deutsches Elektronen-Synchrotron, Hamburg), they discovered the lead-rich layer below the quartz-clay ground layer of the canvas. 

    Protection against moisture

    It was already known from earlier studies that Rembrandt had used a quartz-clay ground on the Night Watch. In earlier paintings he had used double grounds, consisting of a first ground containing red earth pigments followed by a second lead white containing ground. The large size of The Night Watch may have motivated Rembrandt to look for a cheaper, less heavy and more flexible alternative for the ground layer. Another issue he had to overcome was that the large canvas was intended for a damp outer wall of the great hall of the Kloveniersdoelen (musketeers’ shooting range) in Amsterdam. It had been reported that under humid conditions the common method of preparing the canvas using animal glue could fail. A contemporary source on painting techniques written by Théodore de Mayerne suggested impregnation with lead-rich oil as an alternative. This may have inspired Rembrandt for his unusual impregnation procedure to improve the durability of his masterpiece.

    Computational imaging

    The presence of this lead-containing ‘layer’ was discovered by the first-ever use of correlated x-ray fluorescence and ptychographic nano-tomography on a historical paint sample. This was performed at the PETRA III synchrotron radiation source at DESY. X-ray fluorescence is used to investigate the distribution of relatively heavy elements (calcium and heavier). Ptychography, a computational imaging technique based on experimentally obtained datasets, is capable of visualizing even the lightest elements and organic fractions. 

    Analysis of the micro sample taken from The Night Watch revealed that on the side of the sample closest to the canvas support a homogenous layer of dispersed lead was present in the ground layer. Since lead components were not to be expected in the quartz-clay ground layer, this was a rather puzzling observation. The results were then combined with the lead distribution map of the full Night Watch, obtained by X-ray fluorescence scanning of the painting in the Rijksmuseum’s Gallery of Honour. This map reveals the presence of lead throughout the painting and suggests application using large semi-circular brushstrokes, supporting the assumption that it results from an impregnation procedure. Even an imprint of the original strainer onto which the canvas was stretched when the preparatory layers were applied, is visible in the lead distribution map. This brings us yet another step closer to understanding Rembrandt’s creative process in painting The Night Watch, as well as its current condition. 

    Publication details

    Fréderique T.H. Broers, Ige Verslype, Koen W. Bossers, Frederik Vanmeert, Victor Gonzalez, Jan Garrevoet, Annelies van Loon, Esther van Duijn, Anna Krekeler, Nouchka De Keyser, Ilse Steeman, Petria Noble, Koen Janssens, Florian Meirer, Katrien Keune: Correlated x-ray fluorescence and ptychographic nanotomography on Rembrandt’s The Night Watch reveals unknown lead “layer”. Science Advances, 15 December 2023. DOI: 10.1126/sciadv.adj9394

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  • 70 Extinct Fish Thriving Again

    70 Extinct Fish Thriving Again

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    Newswise — The houting, a fish species that lived in North Sea estuaries and is officially extinct, turns out to be alive and well. Researchers from the University of Amsterdam and the Natural History Museum London extracted DNA from multiple houtings conserved in the museum, up to 250+ years old. Next they compared the DNA of these museum fish with DNA from various currently occurring sibling species. The biologists found hardly any genetic difference between houting and a species called European whitefish. Since this species is still common, houting also isn’t extinct.

    In a recent publication in the journal BMC Ecology and Evolution, the researchers describe how they isolated mitochondrial DNA from the fish. They even managed to obtain a small piece of DNA from a dried North Sea houting from 1754 that was used by Linnaeus for the official species description. Next they used the DNA to create a phylogenetic tree, in which all examined houting (Coregonus oxyrinchus) ended up in the same group as the European whitefish (Coregonus lavaretus).

    Not extinct

    According to the researchers, houting is therefore not a separate species. First author Rob Kroes of the University of Amsterdam comments: ‘The European whitefish is fairly widespread in Western and Northern Europe, both in freshwater rivers and lakes, estuaries and the sea. Because we found no species difference between houting of the past and today’s European whitefish, we do not consider the houting to be extinct.’

    External traits vs DNA

    So, how is it possible that the houting was officially declared extinct in 2008? Kroes: ‘It often happens that there is confusion as to whether animals are one species or not. Especially when fish are involved. They often have a lot of variation in morphological traits within a species. In this case, biologists long thought that houting is a different species from the European whitefish due to the length of the snout and the number of gill rakers. But these traits are simply not suitable to say that houting is a different species. Our DNA research now clearly shows that it isn’t.’

    Name change

    A change of the official Latin species name seems to be in order. However, a definitive adjustment of the name requires a bit of additional research on the DNA of the dried fish from 1754. According to the researchers, this will be difficult to do. Kroes: ‘The DNA is old and damaged, but I think we should try. At the moment, the protected status of various coregonids is a mess. According to the IUCN, North Sea houting is extinct; at the same time, there are various European nature laws that state that both houting and European whitefish must be protected. So we are actually protecting an extinct species that is just swimming around at the moment.’

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  • Enhancing Chemical Identification Challenges

    Enhancing Chemical Identification Challenges

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    Newswise — What chemicals are we exposed to on a daily basis? That is the central question of ‘non-targeted analysis’ or NTA, an emerging field of analytical science that aims to identify all chemicals around us. A daunting task, because how can you be sure to detect everything if you don’t know exactly what you’re looking for? In a paper in Environmental Science and Technology, researchers at the Universities of Amsterdam (UvA, the Netherlands) and Queensland (UQ, Australia) assess this problem. In a meta-analysis of NTA results published over the past six years, they estimate that less than 2% of all chemicals have been identified.

    According to Viktoriia Turkina who performed the research as a PhD student with Dr Saer Samanipour  at the UvA’s Van ‘t Hoff Institute for Molecular Sciences, this limitation underscores the urgent need for a more proactive approach to chemical monitoring and management. “We need to incorporate more data-driven strategies into our studies to be able to effectively protect the human and environmental health”, she says.

    Samanipour explains that current monitoring of chemicals is rather limited since it’s expensive, time consuming, and requires specialized experts. “As an example, in the Netherlands we have one of the most sophisticated monitoring programs for chemicals known to be of concern to human health. Yet we target less than 1000 chemicals. There are far more chemicals out there that we don’t know about.”

    A vast chemical space

    To deal with those chemicals, some 15 to 20 years ago the concept of non-targeted analysis was introduced to look at possible exposure in an unbiased manner. The idea is to take a sample from the environment (air, water, soil, sewer sludge) or the human body (hair, blood, etc ) and analyse it using well-established analytical techniques such as chromatography coupled with high resolution mass spectroscopy. The challenge then is to trace the obtained signal back to the structures of chemicals that may be present in the sample. This will include already known  chemicals, but also chemicals of which the potential presence in the environment is yet unknown.

    In theory, this ‘chemical space’ includes as many as 1060 compounds, an incomprehensible number that exceeds the number of stars in the universe by far. On the other hand, the number of organic and inorganic substances published in the scientific literature and public databases is estimated at around 180 million. To make their research even more manageable, Turkina, Samanipour and co-workers focused on a subset of 60.000 well-described compounds from the NORMAN database. Turkina: “This served as the reference to establish what is covered in NTA studies, and more importantly, to develop an idea about what is being overlooked.”

    The vast ‘exposome’ of chemicals that humans are exposed to on a daily basis is a sign of our times, according to Samanipour. “These days we are soaking in a giant ocean of chemicals. The chemical industry is part of that, but also nature is running all a whole bunch of reactions that result in exposure. And we expose ourselves to chemicals by the stuff we use – think for instance of the problem of microplastics. To solve all this we have to be able to go beyond pointing fingers. With our research, we hope to contribute to finding a solution together. Because we all are in the same boat.”

    Much room for improvement

    The meta analysis, which included 57 NTA papers, revealed that only around 2% of the estimated chemical space was covered. This can indicate that the actual exposure to chemicals is indeed quite low, however, it can also point to shortcomings in the applied analyses. According to Turkina and Samanipour, the latter is indeed the case. They focused on NTA studies applying liquid chromatography coupled with high resolution mass spectrometry (LC-HRMS) -one of the most comprehensive methods for the analysis of complex environmental and biological samples.

    It turned out that there was much room for improvement. For instance in sample preparation, they observed a bias towards specific compounds rather than capturing a more diverse set of chemicals. They also observed poor selection and inconsistent reporting of LC-HRMS parameters and data acquisition methods. “In general”, Samanipour says, “the chemical analysis community is to a great extent driven by the available technology that vendors have developed for specific analysis purposes. Thus the instrumental set-up and data processing methods are rather limited when it comes to non-targeted analysis.”

    To Samanipour, the NTA approach is definitely worth pursuing. “But we need to develop it further and push it forward. Together with vendors we can develop new powerful and more versatile analytical technologies, as well as effective data analysis protocols.” He also advocates a data-driven approach were the theoretical chemical space is ‘back calculated’  towards a subset of chemicals that are highly likely to be present in our environment. “Basically we have to better understand what is the true chemical space of exposure. And once those boundaries are defined, then it becomes a lot easier to assess that number of 2% we have determined.”

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  • Song sounds convey its meaning

    Song sounds convey its meaning

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    Newswise — Can you tell what a song is used for when it is not in your language or from your culture? A new study finds that worldwide, people are pretty good at recognizing when an unfamiliar song is used for dancing, soothing babies, or healing sickness. And it does not matter if the song comes from a nearby culture or a far away one. Music around the world is diverse, but there are thus some universal things about it that we all seem to get.

    Singing is something all human cultures do, and it comes in many distinctive styles and forms around the world. But certain types of songs share acoustic characteristics. For example, songs for dancing are often loud with a strong beat, while lullabies are usually soft and melodic. Previous research suggested that people can pick up on these musical cues to understand the purpose of a song, regardless of the language or culture it comes from. But we were not sure yet if these musical interpretations were universal, because the previous studies focused only on English-speaking people and the Western world.

    How well can people guess the meaning or purpose of unfamiliar songs?

    The way we make music and what it means to us might come from our biology: how our minds have developed over the course of human evolution and across our own lifespans. This limits how music evolves in diverse cultures. So, even though music can be different in various places, it still has some common features because of our shared human nature. These common features help us understand what a song might be about, even if we have never heard it before.

    In a new study, a team of international researchers asked over 5,000 people in 48 societies to guess what songs from unfamiliar languages and cultures were used for. Participants came from societies with lots of internet and technology and also from smaller, isolated societies with less access to global media. The researchers played them songs that were used for dancing, soothing a baby, healing the sick and expressing love.

    People around the world can figure out the purpose of the song

    People from both types of societies were surprisingly good at figuring out if a song was for dancing, soothing a baby, or healing the sick, but struggled with identifying love songs. Living closer to where the song was from or speaking a similar language helped listeners guess the song’s purpose a little more accurately, but this boost was negligible: the real driving factor was the acoustic features of the song, which are shared universally.

    The researchers conclude that this tells us that there are some simple aspects about understanding music that everyone seems to get, no matter where they are from. ‘This research confirms what we suspected based on previous research with English-speakers in industrialised countries’, tells one of the lead researchers Lidya Yurdum of the University of Amsterdam. ‘It doesn’t matter where you live or what language you speak, or if you have never been exposed to foreign music. People around the world “understand” certain types of songs. We think it’s because we all share something fundamental in our biology that shapes how humans make music.’

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  • Synthetic black holes radiate like real ones

    Synthetic black holes radiate like real ones

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    Newswise — Research led by the University of Amsterdam has demonstrated that elusive radiation coming from black holes can be studied by mimicking it in the lab.

    Black holes are the most extreme objects in the universe, packing so much mass into so little space that nothing – not even light – can escape their gravitational pull once it gets close enough.

    Understanding black holes is key to unravelling the most fundamental laws governing the cosmos, because they represent the limits of two of the best-tested theories of physics: the theory of general relativity, which describes gravity as resulting from the (large-scale) warping of spacetime by massive objects, and the theory of quantum mechanics, which describes physics at the smallest length scales. To fully describe black holes, we would need to stitch these two theories together and form a theory of quantum gravity.

    Radiating black holes
    To achieve this goal, we might want to look at what manages to escape from black holes, rather than what gets swallowed. The event horizon is an intangible boundary around each black hole, beyond which there is no way of getting out. However, Stephen Hawking famously discovered that every black hole must emit a small amount of thermal radiation due to small quantum fluctuations around its horizon.

    Unfortunately, this radiation has never been directly detected. The amount of Hawking radiation coming from each black hole is predicted to be so small, it is impossible to detect (with current technology) among the radiation coming from all other cosmic objects.

    Alternatively, could we study the mechanism underlying the emergence of Hawking radiation right here on Earth? This is what researchers from the University of Amsterdam and IFW Dresden set out to investigate. And the answer is an exciting “yes”.

    Black holes in the lab
    “We wanted to use the powerful tools of condensed matter physics to probe the unattainable physics of these incredible objects: black holes,” says author Lotte Mertens.
    To do so, the researchers studied a model based on a one-dimensional chain of atoms, in which electrons can “hop” from one atomic site to the next. The warping of spacetime due to the presence of a black hole is mimicked by tuning how easily electrons can hop between each site.

    With the right variation of hopping probability along the chain, an electron moving from one end of the chain to the other will behave exactly like a piece of matter approaching the horizon of a black hole. And, analogous to Hawking radiation, the model system has measurable thermal excitations in the presence of a synthetic horizon.

    Learning by analogy
    Despite the lack of actual gravity in the model system, considering this synthetic horizon gives important insight into the physics of black holes. For instance, the fact that the simulated Hawking radiation is thermal (meaning the system appears to have a fixed temperature) only for a specific choice of spatial variation of the hopping probability, suggests that real Hawking radiation may also only be purely thermal in certain situations.

    Additionally, the Hawking radiation only occurs when the model system starts out without any spatial variation of hopping probabilities, mimicking flat spacetime without any horizon, before being changed into one hosting a synthetic black hole. The emergence of Hawking radiation therefore requires a change in the warping of spacetime, or a change in how an observer looking for the radiation is perceiving this warping.

    Finally, Hawking radiation requires some part of the chain to exist beyond the synthetic horizon. This means that the existence of the thermal radiation is intricately connected to the quantum-mechanical property of entanglement between objects on either side of the horizon.

    Because the model is so simple, it can be implemented in a range of experimental setups. This could include tuneable electronic systems, spin chains, ultracold atoms or optical experiments. Bringing black holes to the lab can bring us one step closer to understanding the interplay between gravity and quantum mechanics, and on our way to a theory of quantum gravity.

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