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Experimental and Theoretical Force Constants as Meaningful Indicator for Interatomic Bonding Characteristics and the Specific Case of Elemental Antimony
No full textStable Sb exhibits a rhombohedral structure, often referred to as distortedprimitive cubic, with each Sb atom having three short and three longer firstneighbor bonds. However, this crystal structure can also be interpreted asbeing layered, putting emphasis on only three short first neighbor bonds.Therefore, temperature-dependent extended X-ray absorption fine structure(EXAFS) spectroscopy is carried out at the Sb K-edge in order to obtain moredetailed information on local structural and vibrational properties. Evaluationof the temperature-dependent bond lengths provides thetemperature-dependent Peierls distortion while the temperature dependenceof the variance of the interatomic distance distribution yields the EXAFS forceconstants. Ab initio density functional theory (DFT) calculations are used fordetermining projected force constants. Both EXAFS and DFT force constantsare compared to those of other materials with different bondingcharacteristics, including two-center covalently bonded semiconductors,multicenter bonded IV–VI and V2VI3 compounds, and metallic Cu. Clearly, Sbexhibits characteristics of both localized covalent bonding and delocalizedmulticenter bonding. This suggests a continuous transition between thesetwo bonding scenarios and adds to the understanding of bonding inelemental Sb in particular and in IV–VI and V2VI3 materials ingeneral
Proteorhodopsin insights into the molecular mechanism of vectorial proton transport
No full textBacterial proton pumps, proteorhodopsins (PRs), are a major group of light-driven membrane proteins found in marine bacteria. They are functionally and structurally distinct from archaeal and eukaryotic proton pumps. To elucidate the proton transfer mechanism by PRs and understand the differences to nonbacterial pumps on a molecular level, high-resolution structures of PRs’ functional states are needed. In this work, we have determined atomic-resolution structures of MAR, a PR from marine actinobacteria, in various functional states, notably the challenging late O intermediate state. These data and information from recent atomic-resolution structures on an archaeal outward proton pump bacteriorhodopsin and bacterial inward proton pump xenorhodopsin allow for deducing key universal elements for light-driven proton pumping. First, long hydrogen-bonded chains characterize proton pathways. Second, short hydrogen bonds allow proton storage and inhibit their backflow. Last, the retinal Schiff base is the active proton donor and acceptor to and from hydrogen-bonded chains
Structural and Functional Analysis of the Lectin-like Protein Llp1 Secreted by Ustilago maydis upon Infection of Maize
No full textThe biotrophic fungus Ustilago maydis, which causes smut disease in maize, secretes numerous proteins upon plant colonization. Some of them, termed effectors, help to evade plant defenses and manipulate cellular processes within the host. The function of many proteins specifically secreted during infection remains elusive. In this study, we biochemically characterized one such protein, UMAG_00027, that is highly expressed during plant infection. We show that UMAG_00027 is a secreted protein with a lectin-like fold and therefore term it Llp1 (lectin-like-protein 1). Llp1 decorated the fungal cell wall of cells grown in axenic culture or proliferating in planta, which is in agreement with its potential sugar-binding ability. We were unable to identify the precise sugar moieties that are bound by Llp1. CRISPR/Cas9-mediated deletion of llp1 reveals that the gene is not essential for fungal virulence. A structural search shows the presence of several other lectin-like proteins in U. maydis that might compensate for the function of Llp1 in ∆llp1 mutants. We therefore speculate that Llp1 is part of a family of lectin-like proteins with redundant functions
A novel method of preparation of YAlO:Cr ceramics and its structural and optical characterization
No full textYAlO:Cr ceramics were prepared by a new method of electron beam synthesis. Special features of thismethod are the fast speed of synthesis, high phase purity and stoichiometry. The samples were characterized bySEM and XRD methods. After the samples structure was confirmed, the optical measurements of the excitation/emission spectra and luminescence kinetics were performed in a wide temperature range. Characteristic excitation and emission spectral features of the 6-fold coordinated Cr ions were detected and investigated; theirpresence is solid proof of successful doping of the prepared ceramics samples with the trivalent chromium ions.The developed technique of ceramics synthesis can be applied to other samples with different chemicalcompositions
Charge conduction and relaxation in CaDyBaFeO
No full textThe paper presents in-depth studies of the dielectric properties and conduction dynamics of Dy-doped CaBaFeO which is a recently characterized magnetoelectric material with strong potentials for technological applications as it shows a near-room-temperature ferrimagnetic transition along with strong ferrimagnetic moment, and gigantic electric polarization change. This work demonstrates the direct correlation of the dielectric and electrical transport properties of CaDy_BaFeO (=0, 0.01, 0.03, and 0.05) with structural distortion through various dc, ac conduction, high-energy x-ray diffraction studies, and modeling of the data. CaBaFeO has a unique structure characterized by alternate stacking of FeO4 tetrahedra in triangular and kagomé layers. Large structural distortion, competing magnetic interactions, exchange striction effects, and possible charge ordering are expected to play a major role in the dielectric and electrical properties of the material. We report observation of short-range polaron hopping conduction mechanism in the low-temperature regime and signature of large polaronic nature of charge carriers. Modeling of the electric modulus using Havriliak-Negami equation points out both distribution and cooperativeness in the polaron dynamics which can be correlated to the interplay of structural distortion, and the background electric field due to the polar nature of the materials. The Havriliak-Negami parameters closely follow orthorhombic distortion of the structures
A novel high-performance Al-6Zn-4Ni-2Mg-1Cu-Fe alloy for wire-arc directed energy deposition
No full textDirected energy deposition processes are increasingly incorporated in modern industrial manufacturing chains.Aluminum alloys often fall short either of mechanical properties, or of processability. Therefore, the need for newalloy compositions emerges that show both robust and versatile processability as well as high mechanical performance.Here, an alloy composition that has not been tested yet for directed energy deposition is investigated:Al-6Zn-4Ni-2Mg-1Cu-Fe. To achieve the required properties, the positive effects of intermetallic phases formingduring solidification and subsequent heat treatment are jointly utilized in this alloy system. After wire fabricationand processing by directed energy deposition, the specimens were characterized in detail and the effects of apost-process heat treatment were assessed. Characterization results evidence the absence of crystallographictexture and the presence of various intermetallic phases in combination with high mechanical strength values:485 MPa yield strength and 545 MPa ultimate tensile strength after a solution heat treatment followed by anartificial aging heat treatment. The systematic investigations of a new high-performance aluminum alloy shedlight upon the complex microstructures in as-built and heat-treated material conditions and their relevance tomechanical properties
Neutrino Electromagnetic Properties and the Weak Mixing Angleat the LHC Forward Physics Facility
No full textThe LHC produces an intense beam of highly energetic neutrinos of all three flavors in the forwarddirection, and the Forward Physics Facility (FPF) has been proposed to house a suite of experimentstaking advantage of this opportunity. In this study, we investigate the FPF’s potential to probe theneutrino electromagnetic properties, including neutrino millicharge, magnetic moment, and chargeradius. We find that, due to the large flux of tau neutrinos at the LHC, the FPF detectors willbe able to provide the strongest laboratory-based sensitivity to the tau neutrino magnetic momentand millicharge by searching for excess in low recoil energy electron scattering events. We alsofind that, by precisely measuring the rate of neutral current deep inelastic scattering events, theFPF detectors have the potential to obtain the strongest experimental bounds on the neutrinocharge radius for the electron neutrino, and one of the leading bounds for the muon neutrino flavor.The same signature could also be used to measure the weak mixing angle, and we estimate thatsin2θW could be measured to about 3% precision at a scale Q ∼ 10 GeV, shedding new light on thelong-standing NuTeV anomal
Computing Excited States of Molecules Using Normalizing Flows
No full textCalculations of highly excited and delocalizedmolecular vibrational states are computationally challenging tasks,which strongly depend on the choice of coordinates for describingvibrational motions. We introduce a new method that leveragesnormalizing flows, i.e, parametrized invertible functions, to learnoptimal vibrational coordinates that satisfy the variational principle.This approach produces coordinates tailored to the vibrational problem at hand, significantly increasing the accuracy and enhancingthe basis set convergence of the calculated energy spectrum. The efficiency of the method is demonstrated in calculations of the 100lowest excited vibrational states of HS, HCO, and HCN/HNC. The method effectively captures the essential vibrational behaviorof molecules by enhancing the separability of the Hamiltonian and hence allows for an effective assignment of approximate quantumnumbers. We demonstrate that the optimized coordinates are transferable across different levels of basis set truncation, enabling acost-efficient protocol for computing vibrational spectra of high-dimensional systems
The RÅC International Summer School 2023: Six days on “Cutting-edge Neutron and X-ray Research for a Sustainable Future”
No full textAfter the RÅC Summer School in 2022 had taken place in Varberg, Sweden, the research centre DESY organised this year’s edition of the Röntgen-Ångström International Summer School – or RÅC-2023 in short –, as a six-day-event from 20 to 27 August 2023, in Lüneburg, Germany (https://www.rac-school.org/rac2023). This year’s focal theme of the school was “Cutting-edge Neutron and X-ray Research for a Sustainable Future”. The school in Lüneburg brought together 52 young scientists in materials research from Sweden, Germany and various other European countries, such as Estonia, Latvia, Lithuania, France, Greece, as well as Ukraine and Israel. They all have very much enjoyed participating in a program ranging from high-level scientific lectures by international experts to social activities and an excursion.The RÅC International Summer School is a German-Swedish collaboration, under the umbrella of the bilateral Röntgen-Ångström Cluster. The cluster as well as the school are co-funded by the Swedish Research Council, Vetenskapsrådet, and the Federal Ministry of Education and Research (BMBF). During the last years, 2020–2022, the school has undergone several changes and adaptations of its format. After the Russian military attack on Ukraine in February 2022, and in consequence of applying EU-wide sanctions against Russia, the German and Swedish partners of the RÅC School Steering Committee have decided to halt the former trilateral German-Swedish-Russian summer school cooperation, and to adapt the school’s format to a bilateral format, and to open it further to young scientists affiliated to institutions not only from Sweden, Germany, but also from many other countries in the EU or even beyond
All hard X-ray Transient Grating Spectroscopy
No full textThe understanding of matter requires the study of excitations across the entire kinematic region. The regime with nanometer length scales (i.e. wave vectors in the nm-1 range) is crucial for transport phenomena in liquids and crystals and holds the key to understanding phenomena including charge, spin and heat diffusion transitioning between diffusive and ballistic regimes. Optical transient gratings (TG) demonstrated access to all relevant quantum degrees of freedom (e.g. charge, lattice and spin), but are limited to typically micron-size grating steps. Extreme-Ultraviolet TG spectroscopy has represented a major leap forward in this respect as it allows access to mesoscopic scales. Using hard X-rays for excitation and probing would extend TG spectroscopy into the nm-1 range and beyond. While the generation of hard X-ray excited TG’s and their probing by optical pulses was recently reported here we present an all X-ray TG (XTG) study, which uses hard X-ray pulses for both excitation and probing, demonstrating key ingredients that allow reaching previously inaccessible kinematic regions. Thus, ultrafast XTG promises to overcome the resolution limitations of neutron and X-ray based inelastic scattering techniques