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Illuminating Rembrandt’s Chiaroscuro in The Night Watch: the painting process of Van Ruytenburch’s costume

Abstract\n This study examines Rembrandt’s use of chiaroscuro to depict the costume of Lieutenant Willem Van Ruytenburch, a prominently lit figure in The Night Watch (1642). As part of Operation Night Watch, the painting was analyzed using noninvasive imaging techniques, including reflectance imaging spectroscopy (RIS), macroscopic X-ray powder diffraction (MA-XRPD), and macroscopic X-ray fluorescence (MA-XRF). These methods enabled the mapping of the artist’s pigment palette, which includes lead white, lead-tin yellow, ochres, vermilion, arsenic sulfide pigments, red lakes, smalt, and azurite. Rembrandt applied these pigments in a consistent, systematic way, combining them in groups to achieve pictorial unity. Notably, arsenic-based pigments were used to capture the warm reflections of gold threads, unique to Van Ruytenburch’s costume. MA-XRPD also identified degradation products—mimetite, weddellite, and palmierite—associated with the original pigments. These results provide new insights into Rembrandt’s modus operandi and inform understanding of the current condition and implications for its conservation.

npj Herit. Sci.

Nouchka De Keyser et al.
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  • 2 min read

Active energy compression of a laser-plasma electron beam

Abstract\n Radio-frequency (RF) accelerators providing high-quality relativistic electron beams are an important resource enabling many areas of science, as well as industrial and medical applications. Two decades ago, laser-plasma accelerators1 that support orders of magnitude higher electric fields than those provided by modern RF cavities produced quasi-monoenergetic electron beams for the first time2–4. Since then, high-brightness electron beams at gigaelectronvolt (GeV) beam energy and competitive beam properties have been demonstrated from only centimetre-long plasmas5–9, a substantial advantage over the hundreds of metres required by RF-cavity-based accelerators. However, despite the considerable progress, the comparably large energy spread and the fluctuation (jitter) in beam energy still effectively prevent laser-plasma accelerators from driving real-world applications. Here we report the generation of a laser-plasma electron beam using active energy compression, resulting in a performance so far only associated with modern RF-based accelerators. Using a magnetic chicane, the electron bunch is first stretched longitudinally to imprint an energy correlation, which is then removed with an active RF cavity. The resulting energy spread and energy jitter are reduced by more than an order of magnitude to below the permille level, meeting the acceptance criteria of a modern synchrotron, thereby opening the path to a compact storage ring injector and other applications.

Nature

P. Winkler et al.
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A proteome-wide structural systems approach reveals insights into protein families of all human herpesviruses

AbstractStructure predictions have become invaluable tools, but viral proteins are absent from the EMBL/DeepMind AlphaFold database. Here, we provide proteome-wide structure predictions for all nine human herpesviruses and analyze them in depth with explicit scoring thresholds. By clustering these predictions into structural similarity groups, we identified new families, such as the HCMV UL112-113 cluster, which is conserved in alpha- and betaherpesviruses. A domain-level search found protein families consisting of subgroups with varying numbers of duplicated folds. Using large-scale structural similarity searches, we identified viral proteins with cellular folds, such as the HSV-1 US2 cluster possessing dihydrofolate reductase folds and the EBV BMRF2 cluster that might have emerged from cellular equilibrative nucleoside transporters. Our HerpesFolds database is available at https://www.herpesfolds.org/herpesfolds and displays all models and clusters through an interactive web interface. Here, we show that system-wide structure predictions can reveal homology between viral species and identify potential protein functions.

Nat Commun

Timothy K. Soh et al.
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Reinforcement learning-trained optimisers and Bayesian optimisation for online particle accelerator tuning

AbstractOnline tuning of particle accelerators is a complex optimisation problem that continues to require manual intervention by experienced human operators. Autonomous tuning is a rapidly expanding field of research, where learning-based methods like Bayesian optimisation (BO) hold great promise in improving plant performance and reducing tuning times. At the same time, reinforcement learning (RL) is a capable method of learning intelligent controllers, and recent work shows that RL can also be used to train domain-specialised optimisers in so-called reinforcement learning-trained optimisation (RLO). In parallel efforts, both algorithms have found successful adoption in particle accelerator tuning. Here we present a comparative case study, assessing the performance of both algorithms while providing a nuanced analysis of the merits and the practical challenges involved in deploying them to real-world facilities. Our results will help practitioners choose a suitable learning-based tuning algorithm for their tuning tasks, accelerating the adoption of autonomous tuning algorithms, ultimately improving the availability of particle accelerators and pushing their operational limits.

Sci Rep

Jan Kaiser et al.
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Real-time swelling-collapse kinetics of nanogels driven by XFEL pulses

Stimuli-responsive polymers are an important class of materials with many applications in nanotechnology and drug delivery. The most prominent one is poly- N -isopropylacrylamide (PNIPAm). The characterization of the kinetics of its change after a temperature jump is still a lively research topic, especially at nanometer-length scales where it is not possible to rely on conventional microscopic techniques. Here, we measured in real time the collapse of a PNIPAm shell on silica nanoparticles with megahertz x-ray photon correlation spectroscopy at the European XFEL. We characterize the changes of the particles diffusion constant as a function of time and consequently local temperature on sub-microsecond timescales. We developed a phenomenological model to describe the observed data and extract the characteristic times associated to the swelling and collapse processes. Different from previous studies tracking the turbidity of PNIPAm dispersions and using laser heating, we find collapse times below microsecond timescales and two to three orders of magnitude slower swelling times.

Sci. Adv.

Francesco Dallari et al.
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The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single x-ray free-electron laser (XFEL) pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R ≃ 0.8 μ, and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total x-ray phase shift which can be scaled with experimental parameters.

New J. Phys.

Hannes P Hoeppe et al.
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Using SXRF and LA-ICP-TOFMS to Explore Evidence of Treatment and Physiological Responses to Leprosy in Medieval Denmark

Leprosy, a chronic infectious disease, leads to blood mineral imbalances: low levels of zinc, calcium, magnesium, and iron and high levels of copper. Interestingly, in late medieval Europe, minerals were used to treat leprosy. We investigated physiological responses to leprosy and possible evidence of treatment in dental tissues of leprosy sufferers from medieval Denmark and early 20th century Romania when multidrug therapy was not then yet invented. Using Synchrotron Fluorescence (SXRF) and laser ablation (LA-ICP-TOFMS), we show marked covariations in the zinc, calcium, and magnesium distributions, which are compatible with clinical studies but cannot be directly attributed to leprosy. Minerals used historically as a treatment for leprosy show no detectable intake (arsenic, mercury) or a diffuse distribution (lead) related to the daily consumption of contaminated water and food. Intense lead enrichments indicate acute incorporations, potentially through the administration of lead-enriched medication or the mobilization of lead from bone stores to the bloodstream during intense physiological stress related to leprosy. However, comparisons with a healthy control group are needed to ascertain these interpretations. The positive correlations and the patterns observed between lead and essential elements may indicate underlying pathophysiological conditions, demonstrating the potential of the two techniques for investigating diseases in past populations. 

Biology. 2023; 12(2):184.

Brozou A, Mannino MA, Van Malderen SJM, Garrevoet J, Pubert E, Fuller BT, Dean MC, Colard T, Santos F, Lynnerup N, Boldsen JL, Jørkov ML, Soficaru AD, Vincze L, Cabec AL.
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Ultrafast light-induced dynamics in the microsolvated biomolecular indole chromophore with water

Interactions between proteins and their solvent environment can be studied in a bottom-up approach using hydrogen-bonded chromophore-solvent clusters. The ultrafast dynamics following UV-light-induced electronic excitation of the chromophores, potential radiation damage, and their dependence on solvation are important open questions. The microsolvation effect is challenging to study due to the inherent mix of the produced gas-phase aggregates. We use the electrostatic deflector to spatially separate different molecular species in combination with pump-probe velocity-map-imaging experiments. We demonstrate that this powerful experimental approach reveals intimate details of the UV-induced dynamics in the near-UV-absorbing prototypical biomolecular indole-water system. We determine the time-dependent appearance of the different reaction products and disentangle the occurring ultrafast processes. This approach ensures that the reactants are well-known and that detailed characteristics of the specific reaction products are accessible – paving the way for the complete chemical-reactivity experiment.

 Nat Commun 13, 7462

Onvlee, J., Trippel, S. & Küpper, J. 
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Speckle contrast of interfering fluorescence X-rays

With the development of X-ray free-electron lasers (XFELs), producing pulses of femtosecond durations comparable with the coherence times of X-ray fluorescence, it has become possible to observe intensity–intensity correlations due to the interference of emission from independent atoms. This has been used to compare durations of X-ray pulses and to measure the size of a focusedX-ray beam, for example. Here it is shown that it is also possible to observe the interference of fluorescence photons through the measurement of the speckle contrast of angle-resolved fluorescence patterns. Speckle contrast is often used as a measure of the degree of coherence of the incident beam or the fluctuations of the illuminated sample as determined from X-ray diffraction patterns formed by elastic scattering, rather than from fluorescence patterns as addressed here. Commonly used approaches to estimate speckle contrast were found to suffer when applied to XFEL-generated fluorescence patterns due to low photon counts and a significant variation of the excitation pulse energy from shot to shot. A new method to reliably estimate speckle contrast under such conditions, using a weighting scheme, is introduced. The method is demonstrated by comparing the speckle contrast of fluorescence observed with pulses of 3 fs to 15 fs duration.

J. Synchrotron Rad. 30.

Fabian Trost, Kartik Ayyer, Dominik Oberthuer, Oleksandr Yefanov, Saša Bajt, Carl Caleman, Agnes Weimer, Artur Feld, Horst Weller, Sébastien Boutet, Jason Koglin, Nicusor Timneanu, Joachim von Zanthier, Ralf Röhlsberger and Henry N. Chapman
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Genomic-Phenomic Reciprocal Illumination: Desyopone hereon gen. et sp. nov., an Exceptional Aneuretine-like Fossil Ant from Ethiopian Amber

Fossils are critical for understanding the evolutionary diversification, turnover, and morphological disparification of extant lineages. While fossils cannot be sequenced, phenome-scale data may be generated using micro-computed tomography (μ-CT), thus revealing hidden structures and
internal anatomy, when preserved. Here, we adduce the male caste of a new fossil ant species from Miocene Ethiopian amber that resembles members of the Aneuretinae, matching the operational definition of the subfamily. Through the use of synchrotron radiation for μ-CT, we critically test the aneuretine-identity hypothesis. Our results indicate that the new fossils do not belong to the Aneuretinae, but rather the Ponerini (Ponerinae). Informed by recent phylogenomic studies, we were able to place the fossils close to the extant genus Cryptopone based on logical character analysis, with the two uniquely sharing absence of the subpetiolar process among all ponerine genera. Consequently, we: (1) revise the male-based key to the global ant subfamilies; (2) revise the definitions of Aneuretinae, Ponerinae, Platythyreini, and Ponerini; (3) discuss the evolution of ant mandibles; and (4) describe the fossils as †Desyopone hereon gen. et sp. nov. Our study highlights the value of males
for ant systematics and the tremendous potential of phenomic imaging technologies for the study of ant evolution

 Insects 2022, 13, 796. https://doi.org/10.3390/insects13090796 

Boudinot, B.E.; Richter, A.K.; Hammel, J.U.; Szwedo, J.; Bojarski, B.; Perrichot, V.