IUCrJ 11 (2024): 977-990

https://doi.org/10.1107/S2052252524009722

Regolith draws intensive research attention because of its importance as the basis for fabricating materials for future human space exploration. Martian regolith is predicted to consist of defect-rich crystal structures due to long-term space weathering. The present report focuses on the structural differences between defect-rich and defect-poor forsterite (Mg₂SiO₄) – one of the major phases in Martian regolith. In this work, forsterites were synthesized using reverse strike co-precipitation and high-energy ball milling (BM). Subsequent post-processing was also carried out using BM to enhance the defects. The crystal structures of the samples were characterized by X-ray powder diffraction and total scattering using Cu and synchrotron radiation followed by Rietveld refinement and pair distribution function (PDF) analysis, respectively. The structural models were deduced by density functional theory assisted PDF refinements, describing both long-range and short-range order caused by defects. The Raman spectral features of the synthetic forsterites complement the ab initio simulation for an in-depth understanding of the associated structural defects.

 © 2024 Attribution 4.0 International (CC BY 4.0)

Frontiers in Space Technologies 5 (2024) 

doi: 10.3389/frspt.2024.1352213

With increasing relevance for lunar activities, the location selection for in situ resource utilization (ISRU) facilities is a necessary step to identify the most suitable configuration during mission planning. To raise information about the dominant location dependencies, a scenario was set up where an ISRU product is exported to an orbital depot and mass costs are used for classification.In the selected scenario, Oxygen is produced by an Ilmenite reduction plant and subsequently exported to the Lunar Gateway via an Oxygen-Hydrogen fueled launcher running in a round-trip, refueling Oxygen at the lunar surface and Hydrogen at the Lunar Gateway. It showed that the variations in transport costs can be either entirely avoided or have a recessive influence on the mission's total costs over an extended amount of time, such as 20 years. The identification of the top 10 most optimal locations for various resolutions were only slightly altered under consideration of flight costs compared to only considering the ISRU factors, which concludes the insignificance of flight cost dependencies for the analysed case.

© 2024, The Authors, CC BY 4.0

The Journal of Chemical Physics 160 (2023): 152501

doi: 10.1063/5.0199247

Stretching or compression can induce significant energetic, geometric, and spectroscopic changes in materials. To fully exploit these effects in the design of mechano- or piezo-chromic materials, self-healing polymers, and other mechanoresponsive devices, a detailed knowledge about the distribution of mechanical strain in the material is essential. Within the past decade, Judgement of Energy DIstribution (JEDI) analysis has emerged as a useful tool for this purpose. Based on the harmonic approximation, the strain energy in each bond length, bond angle, and dihedral angle of the deformed system is calculated using quantum chemical methods. This allows the identification of the force-bearing scaffold of the system, leading to an understanding of mechanochemical processes at the most fundamental level. Here, we present a publicly available code that generalizes the JEDI analysis, which has previously only been available for isolated molecules. Now, the code has been extended to two- and three-dimensional periodic systems, supramolecular clusters, and substructures of chemical systems under various types of deformation. Due to the implementation of JEDI into the Atomic Simulation Environment, the JEDI analysis can be interfaced with a plethora of program packages that allow the calculation of electronic energies for molecular systems and systems with periodic boundary conditions. The automated generation of a color-coded three-dimensional structure via the Visual Molecular Dynamics program allows insightful visual analyses of the force-bearing scaffold of the strained system.

© 2024 Author(s). Published under an exclusive license by AIP Publishing.

npj computational materials 10 (2024): 55

doi: 10.1038/s41524-024-01236-3

Infrared and Raman spectroscopies are ubiquitous techniques employed in many experimental laboratories, thanks to their fast and non-destructive nature able to capture materials' features as spectroscopic fingerprints. Nevertheless, these measurements frequently need theoretical and computational support in order to unambiguously decipher and assign complex spectra. Linear response theory provides an effective way to obtain the higher-order derivatives needed, but its applicability to modern exchange-correlation functionals and pseudopotential formalism remains limited. Here, we devise an automated, open-source, user-friendly approach based on density-functional theory and the electric-enthalpy functional to allow seamless calculation from first principles of infrared absorption and reflectivity, together with zone-center phonons, static dielectric tensor , and Raman spectra. By employing a finite-displacement and finite-field approach, we allow for the use of any functional, as well as an efficient treatment of large low-symmetry structures. Additionally, we propose a simple scheme for efficiently sampling the Brillouin zone at different electric fields. To demonstrate the capabilities of the present approach, we study ferroelectric LiNbO ₃  crystal as a paradigmatic example, and predict infrared and Raman spectra using various (semi)local, Hubbard corrected, and hybrid functionals. Our results also show how PBE0 and extended Hubbard functionals (PBEsol+U+V) yield for this case the best match in terms of peak positions and intensities, respectively.

© The Authors, CC BY 4.0

Frontiers in Space Technologies 4 (2023): 1328341  

doi: 10.3389/frspt.2023.1328341

Over the past few years, the international space industry has focused extensively on advancing technologies to enable prolonged human space exploration missions. The primary limiting factor for these endeavors is the spacecraft’s capacity to transport and store essential supplies from Earth to support human life and mission equipment throughout the mission’s duration. In-situ resource utilization (ISRU) is the preferred solution for this challenge. Previous lunar missions have identified the presence of oxygen within the lunar regolith, which is an important resource for human space exploration missions. Oxygen is present in many different minerals within the lunar regolith out of which, ilmenite provides the highest yield of oxygen per unit mass using hydrogen reduction. However, the distribution of ilmenite is neither high nor uniform throughout the lunar surface and therefore, needs beneficiation, which is an important intermediate step for ilmenite-based oxygen production. A regolith beneficiation testbed was developed at DLR Bremen which is a TRL 4 level representation of the technology. The testbed has multiple process parameters that can be adjusted to produce the desired feedstock. This work focuses on the optimization of this testbed to produce a feedstock with higher ilmenite content than the input regolith. The testbed comprises three beneficiation techniques, viz. gravitational, magnetic and electrostatic beneficiation that work sequentially to produce the desired feedstock. The optimized parameter configuration achieved up to three-fold increase in the ilmenite grade relative to the input with about 32 wt% of the total ilmenite being recovered in the enriched output. These experiments have highlighted other underlying factors that influenced the experimental research such as the design of testbed components, system residuals and limited availability for Off-the-shelf components. The observations made from these experiments have also provided insights into the further development of the technology. The work has thus produced evidence for the effectiveness of the beneficiation testbed in producing an enriched feedstock while outlining avenues for future improvements.

© 2024, The Authors, CC BY 4.0

Physical Review B 108 (2023): 235171

doi: 10.1103/PhysRevB.108.235171

We present a first-principles study of the low-temperature rhombohedral phase of BaTiO3 using Hubbard corrected density-functional theory. By employing density-functional perturbation theory, we calculate the onsite HubbardU for Ti(3d) states and the intersite HubbardV between Ti(3d) and O(2p) states. We show that applying the onsite Hubbard U correction alone to Ti(3d) states proves detrimental, as it suppresses the Ti(3d)–O(2p) hybridization and drives the system towards a cubic phase. Conversely, when both onsite U and intersite V are considered, the localized character of the Ti(3d) states is maintained, while also preserving the Ti(3d)–O(2p) hybridization, restoring the rhombohedral phase of BaTiO3. The generalized PBEsol+U+V functional yields good agreement with experimental results for the band gap and dielectric constant, while the optimized geometry is slightly less accurate compared to PBEsol. Zone-center phonon frequencies and Raman spectra are found to be significantly influenced by the underlying geometry. PBEsol and PBEsol+U+V provide satisfactory agreement with the experimental Raman spectrum when the PBEsol geometry is used, while PBEsol+U Raman spectrum diverges strongly from experimental data highlighting the adverse impact of the U correction alone in BaTiO3. Our findings underscore the promise of the extended Hubbard PBEsol+U+V functional with first-principles U and V for the investigation of other ferroelectric perovskites with mixed ionic-covalent interactions.

©2023, American Physical Society

Wireless Networks   2 8  (2022) :  3275-3292

doi: 10.1007/s11276-022-03008-7

Nowadays, the exploitation of Wireless Underground Sensor Networks (WUSNs) remains challenging because of the attenuation of wireless underground communications. This issue widely affects the reliability of communications in such network since the quality of links depends on changing soil conditions. To address this problem, several path loss models have been proposed to predict the attenuation of an electromagnetic wave in soil. However, this prediction has to be done  in-situ  by the sensor nodes themselves so that they can avoid wasting energy when transmissions are not possible due to bad soil conditions. In this paper, we propose a link channel optimization for reliable communications in WUSNs based on Sugeno Fuzzy Inference System (FIS). The proposed approach enables a transmitting node to check whether its environment allows it to reliably send data to a receiver. The proposed FIS consists of 4 inputs, one output and 36 inference rules. The inputs give information on the node's environment, the output gives the probability that data to be sent by a transmitter will be received or not by the receiver. To evaluate the proposed approach, we consider the dataset composed of 140 measurements in dry and moist soil configurations performed at the Cheikh Anta Diop University of Dakar in Senegal. For the validation, we compared our proposal with a recent path loss model called WUSN-PLM according to performance metrics. The results show that our proposal outperforms the WUSN-PLM with higher balanced accuracy (88.21% against 81.061%) and higher Matthews Correlation Coefficient (0.798 against 0.643).

© The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature 2022

44th COSPAR Scientific Assembly. Held 16-24 July, 2022. Online at https://www.cosparathens2022.org/. Abstract PEX.2-0002-22.

Bibcode: 2022cosp...44.3186A

Leading space agencies have the intention to bring humans to Mars in the next decades, and some private companies push for sooner deadlines. In fact, promises and plans to land humans on Mars have recurrently been announced since the end of the Apollo era, but have remained largely incomplete or even abandoned. At the University of Bremen, we are convinced that human Mars exploration will happen and that it will have a huge impact on both humankind and on the Martian environment. Given that even optimists do not see humans on Mars before the 2030s, we believe that now is the right moment to research possible scenarios for human Mars exploration and settlement, and to study the consequences for Earth, Mars and humankind. To this end, we have formed a new research initiative "Humans on Mars - Pathways to a long-term sustainable human presence" at the University of Bremen. Our approach to human Mars exploration is transdisciplinary and human-centered. On one hand, humankind has experienced tremendous progress and increase in welfare since the Apollo era. On the other hand, we see unambiguously the immense impact of increasing population and welfare on the environmental pollution and associated climate changes. In a nutshell, while the development of new technologies has been the main driver of progress, it has also put Earth in danger. We here argue that human Mars exploration can be instrumental in leading a change from a technology-centered toward a human-centered society, thereby solving our most pressing problems on Earth. Specifically, the thin CO2 Martian atmosphere, the scarcity of energy sources and water, the difficulties to produce food and consumables, and the need for cooperative human-robotic crews, pose challenges whose solutions will enormously benefit Earth. In short, the mindset emerging from thinking under the severe constraints on Mars could be the key to making our presence on Earth sustainable. In this talk, we will present our vision and report on the progress made in selected areas, starting with the shifts in experience and demands on new ways of interaction which come with humankind's expansion to Mars. These include the interactions of the humans on Mars with the humans on Earth on one hand and their habitat and swarm of robots on the other. We will present our efforts in in-situ resource utilization, which focus on sustainable bioproduction, the extraterrestrial fabrication of metal alloys, the production with impure materials and the harvesting of energy from space radiation. 

Electrochimica Acta 406 (2022), 139847

doi: https://doi.org/10.1016/j.electacta.2022.139847

The Point Defect Model (PDM) is known for over 40 years and has brought deeper insight to the understanding of passivity. During the last decades it has seen several changes and refinements, and it has been widely used to analyze growth kinetics of different alloys. Nevertheless, the model has been based on still unconfirmed assumptions, as constant and potential independent electric field strength. To overcome this limitation, we introduce a Refined PDM (R-PDM) in which we replace those assumptions by using additional equations for charge distribution including new physically valid boundary conditions based on considering finite dimensions for the defects by introduction of two defect layer at the film boundaries and by calculating the potential drop at the surface of the film towards the solution over the compact double layer. The calculations by the R-PDM show that the original PDM assumptions are only valid for very specific parameter combinations of oxide film growth and vacancies transport and cannot generally be taken for granted. We believe our findings of electric field and potential drop dependency on the external potential to pave the way for a more realistic description of passive layer formation.

© 2022 Elsevier Ltd. All rights reserved.

Faraday Discussions Advance Article (2023)

doi: https://doi.org/10.1101/2021.10.25.465696 preprint available open access: doi: http://biorxiv.org/lookup/doi/10.1101/2021.10.25.465696

The electrosynthesis of valuable compounds by biofilms on electrodes is being intensively studied since few years. However, so far, the actual biofilms growing on cathodes produce mainly small and relatively inexpensive compounds such as acetate or ethanol. Recently, a novel Knallgas bacterium, Kyrpidia spormannii EA-1 has been described to grow on cathodes under thermophilic and microaerophilic conditions, producing significant amounts of PolyHydroxyAlkanoates (PHAs). These PHA are promising sustainable bioplastic polymers with the potential to replace petroleum-derived plastics in a variety of applications. However, the effect of culture conditions and electrode properties on the growth of K. spormannii EA-1 biofilms and PHA production is still unclear. In this study, we report on the optimization of growth and PHA production in liquid culture and on the cathode of a Microbial Electrosynthesis System. Optimization of the preculture allows to obtain high cell density of up to 8.5 Log10 cells∙ml-1 in 48h, decreasing the time necessary by a factor of 2.5. With respect to cathodic biofilm formation, this study was focused on the optimization of three main operating parameters, which are the applied cathode potential, buffer pH, and the oxygen concentration in the feed gas. Maximum biofilm formation and PHA production was observed at an applied potential of -844mV vs. SCE, pH 6.5, O2 saturation of 2.5%. The PHA concentration in the biofilm reached a maximum of ≈26.8 μg·cm-2 after optimization, but at 2.9% the coulombic efficiency remains relatively low. We expect that further nutrient limitation will allow the accumulation of more PHA, based on a dense biofilm growth. In conclusion, these findings take microbial electrosynthesis of PHA a step forward towards practical implementation.

@ The Authors (2021) licensed under CC BY-NC 4.0