Max Planck Society

The Social Systems Citations Theory (SSCT) is the most recent theory of citations integrating previous theories. It focuses on communications in science that are formally manifested as publications and citations in scientific communication networks. These networks can be observed and empirically studied by using science maps. Science maps typically visualize networks of communication elements such as key words, cited references, and subject areas. In this study, a procedure to create global overlay maps using OpenAlex is proposed. It is an important advantage of OpenAlex publication and citation data that they are freely available. Overlay maps visualize how the overlaid data (e.g., research of an institution) are positioned in the whole science system (the base map). Six different base maps are provided to the user for their own applications. Using one of these base maps, example overlay maps for two individuals (the authors of this paper) and four research institutions are shown and discussed. A method for normalizing the overlay data is also proposed that can be used for the comparison of two different overlaid units. Overlay maps using raw overlay data display general concepts more pronounced than specific concepts. It is the other way around with their counterparts using normalized overlay data. Advantages and limitations of the proposed overlay approach based on OpenAlex are discussed.

The identification of key materials’ parameters correlated with the performance can accelerate the development of heterogeneous catalysts and unveil the relevant underlying physical processes. However, the analysis of correlations is often hindered by inconsistent data. Besides, nontrivial, yet unknown relationships may be important, and the intricacy of the various processes may be significant. Here, we tackle these challenges for the CO oxidation catalyzed by perovskites using a combination of rigorous experiments and artificial intelligence. A series of 13 ABO3 (A=La, Pr, Nd, Sm; B=Cr, Mn, Fe, Co) perovskites was synthesized, characterized, and tested in catalysis. To the resulting dataset, we applied the symbolic‐regression SISSO approach. We identified an analytical expression correlated with the activity that contains the normalized unit‐cell volume, the Pauling electronegativity of the elements A and B, and the ionization energy of the element B. Therefore, the activity is described by crystallographic distortions and by the chemical nature of A and B elements. The generalizability of the identified descriptor is confirmed by the good quality of the predictions for 3 additional ABO3 and 16 chemically more complex AMn(1‐x)B’xO3 (A=La, Pr, Nd; B’=Fe, Co, Ni, Cu, Zn) perovskites.

In our work, we demonstrate that X-ray photons can initiate a “molecular catapult” effect, leading to the dissociation of chemical bonds and the formation of heavy fragments within just a few femtoseconds. We reconstruct the momenta of fragments from a three-body dissociation in bromochloromethane using the ion pair average (IPA) reference frame, demonstrating how light atomic groups, such as alkylene and alkanylene, can govern nuclear dynamics during the dissociation process, akin to projectiles released by a catapult. Supported by ab initio calculations, this work highlights the crucial role of low-reduced-mass vibrational modes in driving ultrafast chemical processes.

Sialic acids are monosaccharide residues involved in several biological processes. Controlling the stereoselectivity of sialylation reactions is challenging and mechanistic studies on the structure of its intermediate, the sialyl cation, are scarce. Here it is shown that a sialyl cation can be generated and isolated from an ionized sialic acid precursor. This short‐lived species is structurally characterized for the first time using cryogenic infrared spectroscopy. In combination with quantum chemical calculations, the results reveal that the positive charge at the anomeric carbon of the sialyl cation is stabilized by remote participation of the C5‐NHAc group leading to the formation of a bridged structure. In this structure, the β‐side is shielded from nucleophilic attack, potentially explaining the α‐selectivity of this building block in SN1‐type sialylation reactions. Other modes of participation are energetically unfavored and cannot be observed experimentally.

Liquid-jet photoelectron spectroscopy (LJ-PES) and electronic-structure theory were employed to investigate the chemical and structural properties of the amino acid l-proline in aqueous solution for its three ionized states (protonated, zwitterionic, and deprotonated). This is the first PES study of this amino acid in its biologically relevant environment. Proline’s structure in the aqueous phase under neutral conditions is zwitterionic, distinctly different from the nonionic neutral form in the gas phase. By analyzing the carbon 1s and nitrogen 1s core levels as well as the valence spectra of aqueous-phase proline, we found that the electronic structure is dominated by the protonation state of each constituent molecular site (the carboxyl and amine groups) with small yet noticeable interference across the molecule. The site-specific nature of the core-level spectra enables the probing of individual molecular constituents. The valence photoelectron spectra are more difficult to interpret because of the overlapping signals of proline with the solvent and pH-adjusting agents (HCl and NaOH). Yet, we are able to reveal subtle effects of specific (hydrogen-bonding) interaction with the solvent on the electronic structure. We also demonstrate that the relevant conformational space is much smaller for aqueous-phase proline than for its gas-phase analogue. This study suggests that caution must be taken when comparing photoelectron spectra for gaseous- and aqueous-phase molecules, particularly if those molecules are readily protonated/deprotonated in solution.

Borders are ubiquitous. As invisible lines, they contribute to a functioning world order and guarantee security for the people. In the form of walls and fences, they divide society and establish strongholds of prosperity that are not accessible to everyone. A similar effect can be observed in connection with the concept of citizenship, which binds people fatefully to a particular territory and thus significantly determines an individual’s life chances. This article shows how borders and their protection as well as the concept of citizenship challenge fundamental ideas of justice and traces discourses that seek to evolve the current border and citizenship regimes into a more universal and just form of human coexistence.

We report a fully differential study of ionization of the Ne L shell by Compton scattering of 20 keV photons. We find two physical mechanisms that modify the Compton-electron emission. Firstly, we observe scattering of the Compton electrons at their parent nucleus. Secondly, we find a distinct maximum in the electron momentum distribution close-to-zero momentum that we attribute to a focusing of the electrons by the Coulomb potential.

We use ab initio molecular dynamics simulations based on density-functional theory to revisit the enigmatic capacitance peak of the electrified Pt(111)/water interface around the potential of zero charge. We demonstrate that counterbalancing the electronic excess charges with partially charged hydrogen atoms constitutes a computationally efficient approach to converged interfacial water structures. The thus enabled detailed analysis of the interfacial water response clarifies that the peak in the capacitance is predominantly due to structural reorientation, although its magnitude is significantly increased by strong internal electronic polarization, also known as charge transfer (CT). We find that CT is more complex than previously thought, resulting from the interplay between chemisorbed water and depolarization effects from the surrounding water. Finally, we demonstrate that quantitative agreement with the experimental peak can be achieved through inclusion of the interfacial response into an implicit solvent model for the extended part of the double layer. This suggests that such models can accurately reproduce screened interfacial fields as a function of potential, despite their notoriously small native capacitance.

Several diatomic transition metal oxides, rare-earth metal oxides, and fluorides have the unusual property that their bond dissociation energy is larger than their ionization energy. In these molecules, bound levels above the ionization energy can be populated via strong, resonant transitions from the ground state. The only relevant decay channel of these levels is autoionization; predissociation is energetically not possible and radiative decay is many orders of magnitude slower. Starting from translationally cold neutral molecules, translationally cold molecular ions can thus be produced with very high efficiency. By populating bound levels just above the ionization energy, internally cold molecular ions, exclusively occupying the lowest rotational level, are produced. This is experimentally shown here for the dysprosium monoxide molecule DyO, for which the lowest bond dissociation energy is determined to be 0.0831(6) eV above the ionization energy. Published by the American Physical Society 2024

The identification of key materials’ parameters correlated with the performance can accelerate the development of heterogeneous catalysts and unveil the relevant underlying physical processes. However, the analysis of correlations is often hindered by inconsistent data. Besides, nontrivial, yet unknown relationships may be important, and the intricacy of the various processes may be significant. Here, we tackle these challenges for the CO oxidation catalyzed by perovskites using a combination of rigorous experiments and artificial intelligence. A series of 13 ABO3 (A = La, Pr, Nd, Sm; B = Cr, Mn, Fe, Co) perovskites was synthesized, characterized, and tested in catalysis. To the resulting dataset, we applied the symbolic‐regression SISSO approach. We identified an analytical expression correlated with the activity that contains the normalized unit‐cell volume, the Pauling electronegativity of the elements A and B, and the ionization energy of the element B. Therefore, the activity is described by crystallographic distortions and by the chemical nature of A and B elements. The generalizability of the identified descriptor is confirmed by the good quality of the predictions for 3 additional ABO3 and of 16 chemically more complex AMn(1‐x)B’xO3 (A = La, Pr, Nd; B’ = Fe, Co Ni Cu, Zn) perovskites.

Hypervelocity white dwarfs (HVWDs) are stellar remnants moving at speeds exceeding the Milky Way's escape velocity ¹⁻⁶ . The origins of the fastest HVWDs are enigmatic, with proposed formation scenarios facing challenges explaining both their extreme velocities and observed properties ⁷⁻⁸ . Here we report a three-dimensional hydrodynamic simulation of a merger between two hybrid helium-carbon-oxygen white dwarfs (HeCO WDs with masses of 0.68 and 0.62 M_sun). We find that the merger leads to a partial disruption of the secondary WD, coupled with a double-detonation explosion of the primary WD. This launches the remnant core of the secondary WD at a speed of ~2000 km s ⁻¹ , consistent with observed HVWDs. The low mass of the ejected remnant and its heating from the primary WD's ejecta explain the observed luminosities and temperatures of hot HVWDs, which are otherwise difficult to reconcile with previous models. This discovery establishes a new formation channel for HVWDs and points to a previously unrecognized pathway for producing peculiar Type Ia supernovae and faint explosive transients.

Imaging ultrafast atomic and molecular hydrogen motion with femtosecond time resolution is a challenge for ultrafast spectroscopy due to the low mass and small scattering cross section of the moving neutral hydrogen atoms and molecules. Here, we propose time- and momentum-resolved photoelectron diffraction (TMR-PED) as a way to overcome limitations of existing methodologies and illustrate its performance using a prototype molecular dissociation process involving the sequential ejection of a neutral hydrogen molecule and a proton from the methanol dication. By combining state-of-the-art molecular dynamics and electron-scattering methods, we show that TMR-PED allows for direct imaging of hydrogen atoms in action. More specifically, the fingerprint of hydrogen dynamics reflects the time evolution of polarization-averaged molecular-frame photoelectron angular distributions (PA-MFPADs) as would be recorded in X-ray pump/X-ray probe experiments with few-femtosecond resolution. We present the results of two precursor experiments that support the feasibility of this approach.

We propose the concept of short-term mindsets as an alternative to self-control as envisioned in Gottfredson & Hirschi's self-control theory (SCT). We lay out a competing perspective, short-term mindsets theory (STMT), based on this novel concept. STMT assumes that short-term mindsets are partly rooted in enduring individual differences and in part develop in response to criminogenic environments, events, and experiences. STMT connects individual-level perspectives to sociogenic views by explaining how several risk factors of crime (e.g., negative parenting, delinquent peers, substance use) all impact on short-term mindsets. Exposure to one risk factor encourages short-term mindsets that, in turn, make exposure to other risk factors more likely, thereby increasing the likelihood of crime. We show that STMT enjoys stronger empirical support than SCT, better aligns with other theory, and can account for phenomena typically considered at odds with, or outside the purview of, SCT.

Using high-resolution flat-field spectrographs at the LLNL SuperEBIT electron beam ion trap, we have observed extreme ultraviolet spectra (λ 32–43 Å) of highly charged ions of Eu (Z = 63) under a range of production conditions suitable for Na- through Zn-like ions. Almost 30 lines were identified with the aid of Flexible Atomic Code computations and spectral modeling. While some of the wavelength measurements are among the most accurate in this wavelength range, some of the identifications are still tentative. We discuss how experimental conditions and spectral complexity interact in the analysis process.

We use one-photon excitation to promote K -shell electrons of formic acid (which has a planar equilibrium structure) to an antibonding π * orbital. The excited molecule is known to have a (chiral) pyramidal equilibrium structure. In our experiment, we determine the handedness of the excited molecule by imaging the momenta of charged fragments, which occur after its Coulomb explosion triggered by Auger-Meitner decay cascades succeeding the excitation. We find that the handedness of the excited molecule depends on its spatial orientation with respect to the propagation (or polarization) direction of the exciting photon. The effect is largely independent of the exact polarization properties of the light driving the 1 s → π * excitation. Published by the American Physical Society 2024

The hippocampus is a central modulator of the HPA-axis, impacting the regulation of stress on brain structure, function, and behavior. The current study assessed whether three different types of 3 months mental Training Modules geared towards nurturing (a) attention-based mindfulness, (b) socio-affective, or (c) socio-cognitive skills may impact hippocampal organization by reducing stress. We evaluated mental training-induced changes in hippocampal subfield volume and intrinsic functional connectivity, by combining longitudinal structural and resting-state fMRI connectivity analysis in 332 healthy adults. We related these changes to changes in diurnal and chronic cortisol levels. We observed increases in bilateral cornu ammonis volume (CA1-3) following the 3 months compassion-based module targeting socio-affective skills ( Affect module), as compared to socio-cognitive skills ( Perspective module) or a waitlist cohort with no training intervention. Structural changes were paralleled by relative increases in functional connectivity of CA1-3 when fostering socio-affective as compared to socio-cognitive skills. Furthermore, training-induced changes in CA1-3 structure and function consistently correlated with reductions in cortisol output. Notably, using a multivariate approach, we found that other subfields that did not show group-level changes also contributed to changes in cortisol levels. Overall, we provide a link between a socio-emotional behavioural intervention, changes in hippocampal subfield structure and function, and reductions in cortisol in healthy adults.

Liquid-jet photoemission spectroscopy (LJ-PES) directly probes the electronic structure of solutes and solvents. It also emerges as a novel tool to explore chemical structure in aqueous solutions, yet the scope of the approach has to be examined. Here, we present a pH-dependent liquid-jet photoelectron spectroscopic investigation of ascorbic acid (vitamin C). We combine core-level photoelectron spectroscopy and ab initio calculations, allowing us to site-specifically explore the acid–base chemistry of the biomolecule. For the first time, we demonstrate the capability of the method to simultaneously assign two deprotonation sites within the molecule. We show that a large change in chemical shift appears even for atoms distant several bonds from the chemically modified group. Furthermore, we present a highly efficient and accurate computational protocol based on a single structure using the maximum-overlap method for modeling core-level photoelectron spectra in aqueous environments. This work poses a broader question: to what extent can LJ-PES complement established structural techniques such as nuclear magnetic resonance? Answering this question is highly relevant in view of the large number of incorrect molecular structures published.