3,107 research outputs found
Skyrmion ratchet propagation: utilizing the skyrmion Hall effect in AC racetrack storage devices
Magnetic skyrmions are whirl-like nano-objects with topological protection. When driven by direct currents, skyrmions move but experience a transverse deflection. This so-called skyrmion Hall effect is often regarded a drawback for memory applications. Herein, we show that this unique effect can also be favorable for spintronic applications: We show that in a racetrack with a broken inversion symmetry, the skyrmion Hall effect allows to translate an alternating current into a directed motion along the track, like in a ratchet. We analyze several modes of the ratchet mechanism and show that it is unique for topological magnetic whirls. We elaborate on the fundamental differences compared to the motion of topologically trivial magnetic objects, as well as classical particles driven by periodic forces. Depending on the exact racetrack geometry, the ratchet mechanism can be soft or strict. In the latter case, the skyrmion propagates close to the efficiency maximum
Beyond skyrmions: Review and perspectives of alternative magnetic quasiparticles
Magnetic skyrmions have attracted enormous research interest since their discovery a decade ago. The non-trivial real-space topology of these nano-whirls leads to fundamentally interesting and technologically relevant consequences â the skyrmion Hall effect of the texture and the topological Hall effect of the electrons. Furthermore, it grants skyrmions in a ferromagnetic surrounding great stability even at small sizes, making skyrmions aspirants to become the carriers of information in the future. Still, the utilization of skyrmions in spintronic devices has not been achieved yet, among other reasons, due to shortcomings in their current-driven motion. In this review, we present recent trends in the field of topological spin textures that go beyond skyrmions. The majority of these objects can be considered a combination of multiple subparticles, such as the bimeron, or the skyrmion analogues in different magnetic surroundings, such as antiferromagnetic skyrmions, as well as three-dimensional generalizations, such as hopfions. We classify the alternative magnetic quasiparticles â some of them observed experimentally, others theoretical predictions â and present the most relevant and auspicious advantages of this emerging field
Microscopic origin of the anomalous Hall effect in noncollinear kagome magnets
The anomalous Hall effect is commonly considered a signature of ferromagnetism. However, recently, an enormous anomalous Hall conductivity was measured in the compensated kagome magnets Mn3Sn and Mn3Ge. The occurrence of this effect is allowed by the magnetic point group of these materials; however, its emergence is still lacking a microscopic explanation. Herein we show that the spin-orbit coupling and an out-of-plane tilting of the texture are equivalent for several kagome magnets. Consequently, a coplanar system with spin-orbit coupling behaves as if it were virtually noncoplanar. We show via tight-binding model calculations that the Hall effect can mainly be interpreted as a topological Hall effect generated by the opening angle of the virtually tilted texture. Furthermore, upon tilting the fixed texture out of the kagome plane, we find a critical tilting angle for which the Hall conductivity vanishes for all energies. In this case, the Hamiltonian is invariant under a combined time-reversal and mirror symmetry, because the virtual texture is coplanar
Identification of a Candidate CD5 Homologue in the Amphibian Xenopus laevis
We identified a novel T cell Ag in the South African clawed toad (Xenopus laevis) by a mAb designated 2B1. This Ag is present in relatively high levels on most thymocytes, approximately 65% of splenocytes, 55% of PBL, and 65% of intestinal lymphocytes, but is rarely seen on IgM+ B cells in any of these tissues. Lymphocytes bearing the 2B1 Ag proliferate in response to stimulation with Con A or PHA, whereas the 2B1- lymphocytes are reactive to LPS. Biochemical analysis indicates that this Ag is a differentially phosphorylated glycoprotein of 71 to 82 kDa. The protein core of 64 kDa bears both N- and O-linked carbohydrate side chains. The amino-terminal protein sequence of the 2B1 Ag shares significant homology with both the macrophage scavenger receptor type 1 motif and the mammalian CD5/CD6 family. The biochemical characteristics and cellular distribution of the 2B1 Ag suggest that it represents the CD5 homologue in X. laevis. While T cells constitutively express this highly conserved molecule, Xenopus B cells acquire the CD5 homologue only when they are stimulated in the presence of T cell
Insights into intermetallic phases on pulse welded dissimilar metal joints
The Magnetic Pulse Welding (MPW) process has been developed to an industrially used joining method which is considered to be a fast, noncontact, clean and "cold" solid state welding process. Unlike fusion welding, the absence of direct heat during the welding cycle makes it possible to join dissimilar metals, for instance aluminium to copper or copper to steel, without noticeable detrimental metallurgical defects. This is very desirable, as today s industry lacks technologies to join often not fusion-weldable dissimilar materials effectively. However, current metallographic studies show that for many material combinations the formation of intermetallic seams in the joint region of magnetic pulse welds can not be completely avoided. Modern technical equipment for MPW is used to join aluminium with copper in order to study the microstructure and the intermetallic phases formed in the weld region in dependence of the processing parameters. The welds are analysed by means of metallographic and electron microscopic (SEM) methods. Relations between the parameters and the microstructures formed within the weld joints are shown. Based on the obtained results conclusions will be drawn with respect to the intermetallic phase formation process and the optimization of the weld microstructure and properties
Spin and orbital Edelstein effects in a two-dimensional electron gas: Theory and application to SrTiO<sub>3</sub> interfaces
The Edelstein effect produces a homogeneous magnetization in nonmagnetic materials with broken inversion symmetry which is generated and tuned exclusively electrically. Often the spin Edelstein effect-that is, a spin density in response to an applied electric field-is considered. In this paper we report on the electrically induced magnetization that comprises contributions from the spin and the orbital moments. Our theory for these spin and orbital Edelstein effects is applied to the topologically nontrivial two-dimensional electron gas at SrTiO3 interfaces. In this particular system the orbital Edelstein effect exceeds the spin Edelstein effect by more than one order of magnitude. This finding is explained mainly by orbital moments of different magnitude in the Rashba-like split band pairs, while the spin moments are of almost equal magnitude
Low-cost chamber design for simultaneous CO<sub>2</sub> and O<sub>2</sub> flux measurements between tree stems and the atmosphere
Interleukin-18 Mediates Immune Responses to Campylobacter jejuni Infection in Gnotobiotic Mice
Background Human Campylobacter jejuni infections are progressively rising
worldwide. Information about the molecular mechanisms underlying
campylobacteriosis, however, are limited. In the present study we investigated
whether cytokines such as IL-23, IL-22 and IL-18, which share pivotal
functions in host immunity, were involved in mediating intestinal and systemic
immunopathological responses upon C. jejuni infection. Methodology/Principal
Findings To assure stable infection, gnotobiotic (i.e. secondary abiotic) IL-
23p19-/-, IL-22-/- and IL-18-/- mice were generated by broad-spectrum
antibiotic treatment. Following peroral C. jejuni strain 81â176 infection,
mice of all genotypes harbored comparably high pathogenic loads in their
intestines. As compared to wildtype controls, however, IL-18-/- mice displayed
less distinct C. jejuni induced sequelae as indicated by less pronounced large
intestinal shrinkage and lower numbers of apoptotic cells in the colonic
epithelial layer at day 8 postinfection (p.i.). Furthermore, lower colonic
numbers of adaptive immune cells including regulatory T cells and B
lymphocytes were accompanied by less distinct secretion of pro-inflammatory
cytokines such as TNF and IFN-Îł and lower IL-17A mRNA expression levels in
colonic ex vivo biopsies of infected IL-18-/- as compared to wildtype mice.
Upon C. jejuni infection, colonic IL-23p19 expression was up-regulated in
IL-18-/- mice only, whereas IL-22 mRNA levels were lower in uninfected and
infected IL-23p19-/- as well as infected IL-18-/- as compared to respective
wildtype control mice. Remarkably, not only intestinal, but also systemic
infection-induced immune responses were less pronounced in IL-18-/- mice as
indicated by lower TNF, IFN-Îł and IL-6 serum levels as compared to wildtype
mice. Conclusion/Significance We here show for the first time that IL-18 is
essentially involved in mediating C. jejuni infection in the gnotobiotic mouse
model. Future studies need to further unravel the underlying regulatory
mechanisms orchestrating pathogen-host interaction
A systematic study of zooplankton-based indices of marine ecological change and water quality: Application to the European marine strategy framework Directive (MSFD)
Marine zooplankton are central components of holistic ecosystem assessments due to their intermediary role in the food chain, linking the base of the food chain with higher trophic levels. As a result, these organisms incorporate the inherent properties and changes occurring atall levels of the marine ecosystem, temporally integrating signatures of physical and chemical conditions. For this reason, zooplankton-based biometrics are widely accepted as useful tools for assessing and monitoring the ecological health and integrity of aquatic systems. The European Marine Strategy Framework Directive (EU-MSFD) requires the use of different types of bio-monitors, including zooplankton, to monitor progress towards achieving specific environmental and water quality targets in EU. However, there is currently no comprehensive synthesis of zooplankton indices development, use, and associated challenges. We addressed this issue with a two-step approach. First, we formulated the indicator-metrics-indices cycle (IMIC) to redefine the closely related but often ambiguously utilized terms - indicator, metric and index, highlighting the convergence between them and the iterative nature of their interaction. Secondly, we formulated frameworks for synthesizing, presenting and systematically applying zooplankton indices based on the IMIC framework. The main benefits of the IMIC are twofold: 1). to disambiguate the key elements: indicators, metrics, and indices, revealing their links to an operational ecological indicator system, and 2) to serve as an organizing tool for the coherent classification of indices according to the MSFD descriptors. Using the IMIC framework, we identified and described two broad categories of indices namely the core biodiversity indices already in use in the Baltic Sea and North Atlantic regions, including the âZooplankton Mean Size and Total Stock (zooplankton MSTS)â and 'Plankton Lifeforms index (PLI)', and stressor-response indices retrieved from the existing literature, elucidating their applicability to different MSFD descriptors. Finally, major challenges of developing new indices and applying existing ones in the context of the MSFD were critically addressed and some solutions were proposed
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