Showing papers by "Academy of Sciences of the Czech Republic published in 2022"

Anomalous Hall antiferromagnets

Abstract: The Hall effect, in which a current flows perpendicular to an electrical bias, has been prominent in the history of condensed matter physics. Appearing variously in classical, relativistic and quantum guises, the Hall effect has — among other roles — contributed to the establishment of the band theory of solids, to research on new phases of interacting electrons and to the phenomenology of topological condensed matter. The dissipationless Hall current requires time-reversal symmetry breaking. When this symmetry breaking is due to an externally applied magnetic field, the effect is referred to as the ordinary Hall effect; when it is due to a non-zero internal magnetization (ferromagnetism), it is referred to as the anomalous Hall effect. The Hall effect has not usually been associated with antiferromagnetic order. More recently, however, theoretical predictions and experimental observations have identified large Hall effects in some compensated magnetic crystals, governed by neither of the global magnetic-dipole symmetry-breaking mechanisms mentioned above. The goal of this Review is to systematically organize the present understanding of anomalous antiferromagnetic materials that generate a Hall effect — which we call anomalous Hall antiferromagnets — and to discuss this class of materials in a broader fundamental and applied research context. Our motivation is twofold: first, because Hall effects that are not governed by magnetic-dipole symmetry breaking are at odds with the traditional understanding of the phenomenon, the topic deserves attention on its own. Second, this new incarnation of the Hall effect has placed it again in the middle of an emerging field in physics, at the intersection of multipole magnetism, topological condensed matter and spintronics.

Interface failure and delamination resistance of fiber-reinforced geopolymer composite by simulation and experimental method

Abstract: Fiber-reinforced geopolymer matrix composites (FRGC) have the potential areas of application to bridge the gap between the performances of polymer matrix and ceramic matrix composites. One of the major drawbacks of the geopolymer matrix is the extreme brittleness and weak interlaminar strength. To improve the interlaminar strength of composites, reinforcement of fibers such as carbon and E-glass are considered as fillers in the matrix. The study aimed to evaluate the inner strength and delamination behavior of carbon and E-glass fiber-reinforced composite. The inner structure of the delaminated area of the impacted composite is examined based on the microstructural images and internal areas. The study is being evaluated by simulation method and experimental observation was correlated. The effect of fiber reinforcement was evaluated using three-point flexural methods to obtain strength and modulus of rupture. Results indicate that the interlaminar strength of carbon fiber reinforced geopolymer composite is stronger than E-glass fiber-reinforced composite. The fibers are more intact in carbon fiber reinforced geopolymer composite with better delamination resistance and less impact area. However interlaminar strength of E-glass fiber reinforced is weak, leads to less delamination resistance, with more slippery behavior and more damage area.

Microtubule lattice spacing governs cohesive envelope formation of tau family proteins

Abstract: Tau is an intrinsically disordered microtubule-associated protein (MAP) implicated in neurodegenerative disease. On microtubules, tau molecules segregate into two kinetically distinct phases, consisting of either independently diffusing molecules or interacting molecules that form cohesive 'envelopes' around microtubules. Envelopes differentially regulate lattice accessibility for other MAPs, but the mechanism of envelope formation remains unclear. Here we find that tau envelopes form cooperatively, locally altering the spacing of tubulin dimers within the microtubule lattice. Envelope formation compacted the underlying lattice, whereas lattice extension induced tau envelope disassembly. Investigating other members of the tau family, we find that MAP2 similarly forms envelopes governed by lattice spacing, whereas MAP4 cannot. Envelopes differentially biased motor protein movement, suggesting that tau family members could spatially divide the microtubule surface into functionally distinct regions. We conclude that the interdependent allostery between lattice spacing and cooperative envelope formation provides the molecular basis for spatial regulation of microtubule-based processes by tau and MAP2.

Soil organic carbon content and mineralization controlled by the composition, origin and molecular diversity of organic matter: A study in tropical alpine grasslands

Abstract: The consensus for mechanisms controlling soil organic matter (SOM) persistence has shifted from traditional views based on SOM recalcitrance to a new paradigm based on SOM stabilization controlled by soil minerals and aggregates. Recent studies indicate that the origin, composition and molecular diversity of SOM are crucial to the decomposition and stabilization of SOM. However, it is not fully understood how the decomposition and stabilization of SOM are controlled at the molecular level. The objectives of this study were to investigate whether soil organic carbon (SOC) contents and mineralization are controlled by the composition, origin and molecular diversity of SOM. Soil samples were collected from contrasting bedrocks with different precipitation levels at tropical alpine grasslands of the Peruvian Andes. We applied a combination of a 76-day soil incubation experiment and pyrolysis-GC/MS assisted by thermochemolysis to investigate SOM decomposition and stabilization at the molecular level. The results indicated that soil samples with high SOC contents (92.6 ± 7.6 g kg−1 soil) and low SOC mineralization had abundant derivates of lignin, polysaccharides and n-alkanes. After the incubation, we observed neither a selective decomposition of any compound groups nor a decline of molecular diversity. In contrast, soil samples with low SOC contents (30.7 ± 2.8 g kg−1 soil) and higher SOC mineralization showed a depletion of plant-derived compounds, an accumulation of microbial-derived compounds and declined molecular diversity after the incubation. Furthermore, the SOC mineralization of these samples was positively correlated to the depletion of unsaturated fatty acids and the decrease in molecular diversity after the incubation. Therefore, we proposed that SOC contents and mineralization in our soils are (1) controlled by selective preservation of SOM molecular groups (e.g. plant-derived compounds), and (2) associated with changes in molecular diversity of SOM during microbial decomposition. Due to the selective preservation of organic compounds under different environmental conditions, we propose that environmental factors should be considered for the management of ecosystem services such as SOC sequestration in the studied region.

Atomically sharp domain walls in an antiferromagnet

Abstract: The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its physical fundamentals to applications in information technologies. Here, we explore antiferromagnetic CuMnAs in which imaging by x-ray photoemission reveals the presence of magnetic textures down to nanoscale, reaching the detection limit of this established microscopy in antiferromagnets. We achieve atomic resolution by using differential phase-contrast imaging within aberration-corrected scanning transmission electron microscopy. We identify abrupt domain walls in the antiferromagnetic film corresponding to the Néel order reversal between two neighboring atomic planes. Our work stimulates research of magnetic textures at the ultimate atomic scale and sheds light on electrical and ultrafast optical antiferromagnetic devices with magnetic field-insensitive neuromorphic functionalities.

Challenges in keeping annual killifish

Abstract: Turquoise killifish, Nothobranchius furzeri, is a naturally short-lived fish with applications across biomedical, ecotoxicological, and evolutionary research. In this chapter, we describe the challenges for their captive breeding and discuss current approaches to mitigate them. We first present the availability of different strains of N. furzeri (and of other Nothobranchius species) for experimental work and outline their differences. We then provide updates on the existing laboratory maintenance and breeding protocols, describe the course, peculiarities, and potential pitfalls of N. furzeri embryo development, summarize the current stage of approach to diet standardization, and define major health issues associated with keeping N. furzeri and other Nothobranchius species.

Heterogeneity in economic relationships: Scale dependence through the multivariate fractal regression

Abstract: Heterogeneity of effects between economic variables has been a frequently discussed topic for many years now. However, the estimation of such scale-dependent effects has proved challenging. Here, we propose a multivariate multiscale regression approach based on the combination of detrended fluctuation analysis and detrended cross-correlation analysis, but the idea can be easily translated into other time and frequency domain frameworks. As illustrations, we pick two classic economic models – the Taylor’s rule and the money demand function for the USA and Japan – and we uncover evident scale-dependence in the individual effects not visible by the simple regression tools. Importantly, the proposed framework can be used in any discipline where studying the effects at various scales is of interest. Further applications are thus certainly at hand.

Sex chromosome differentiation via changes in the Y chromosome repeat landscape in African annual killifishes Nothobranchius furzeri and N. kadleci

Abstract: Homomorphic sex chromosomes and their turnover are common in teleosts. We investigated the evolution of nascent sex chromosomes in several populations of two sister species of African annual killifishes, Nothobranchius furzeri and N. kadleci, focusing on their under-studied repetitive landscape. We combined bioinformatic analyses of the repeatome with molecular cytogenetic techniques, including comparative genomic hybridization, fluorescence in situ hybridization with satellite sequences, ribosomal RNA genes (rDNA) and bacterial artificial chromosomes (BACs), and immunostaining of SYCP3 and MLH1 proteins to mark lateral elements of synaptonemal complexes and recombination sites, respectively. Both species share the same heteromorphic XY sex chromosome system, which thus evolved prior to their divergence. This was corroborated by sequence analysis of a putative master sex determining (MSD) gene gdf6Y in both species. Based on their divergence, differentiation of the XY sex chromosome pair started approximately 2 million years ago. In all populations, the gdf6Y gene mapped within a region rich in satellite DNA on the Y chromosome long arms. Despite their heteromorphism, X and Y chromosomes mostly pair regularly in meiosis, implying synaptic adjustment. In N. kadleci, Y-linked paracentric inversions like those previously reported in N. furzeri were detected. An inversion involving the MSD gene may suppress occasional recombination in the region, which we otherwise evidenced in the N. furzeri population MZCS-121 of the Limpopo clade lacking this inversion. Y chromosome centromeric repeats were reduced compared with the X chromosome and autosomes, which points to a role of relaxed meiotic drive in shaping the Y chromosome repeat landscape. We speculate that the recombination rate between sex chromosomes was reduced due to heterochiasmy. The observed differences between the repeat accumulations on the X and Y chromosomes probably result from high repeat turnover and may not relate closely to the divergence inferred from earlier SNP analyses.

The role of complement in the tick cellular immune defense against the entomopathogenic fungus Metarhizium robertsii.

Abstract: Entomopathogenic fungi (EPF) have been widely explored for their potential in the biological control of insect pests and as an environmentally friendly alternative to acaricides for limiting tick infestation in the field. The arthropod cuticle is the main barrier against fungal infection, however, an understanding of internal defense mechanisms after EPF intrusion into the invertebrate hemocoel is still rather limited. Using an infection model of the European Lyme borreliosis vector Ixodes ricinus with the EPF Metarhizium robertsii, we demonstrated that ticks are capable of protecting themselves to a certain extent against mild fungal infections. However, tick mortality dramatically increases when the capability of tick hemocytes to phagocytose fungal conidia is impaired. Using RNAi-mediated silencing of tick thioester-containing proteins (TEPs), followed by in vitro and/or in vivo phagocytic assays, we found that C3-like complement components and α2-macroglobulin pan-protease inhibitors secreted to the hemolymph play pivotal roles in M. robertsii phagocytosis.