What Influence Does Residual Magnetism Have on the Transformer Core?

Whenever a power or distribution transformer is isolated from the power system, it is very likely that residual magnetism remains in the core. Residual magnetism also occurs when performing winding resistance test which is also a routine test of the transformer manufacturers and onsite test. This paper discusses the influence of residual magnetism on some diagnostic measurement methods and on the inrush current. It also describes how to overcome the difculties of demagnetisation onsite with a mobile test equipment

Missing Heritability in the Tails of Quantitative Traits? A Simulation Study on the Impact of Slightly Altered True Genetic Models

Objective: Genome-wide association studies have identified robust associations between single nucleotide polymorphisms and complex traits. As the proportion of phenotypic variance explained is still limited for most of the traits, larger and larger meta-analyses are being conducted to detect additional associations. Here we investigate the impact of the study design and the underlying assumption about the true genetic effect in a bimodal mixture situation on the power to detect associations. Methods: We performed simulations of quantitative phenotypes analysed by standard linear regression and dichotomized case-control data sets from the extremes of the quantitative trait analysed by standard logistic regression. Results: Using linear regression, markers with an effect in the extremes of the traits were almost undetectable, whereas analysing extremes by case-control design had superior power even for much smaller sample sizes. Two real data examples are provided to support our theoretical findings and to explore our mixture and parameter assumption. Conclusions: Our findings support the idea to re-analyse the available meta-analysis data sets to detect new loci in the extremes. Moreover, our investigation offers an explanation for discrepant findings when analysing quantitative traits in the general population and in the extremes. Copyright (C) 2011 S. Karger AG, Base

ROOM TEMPERATURE INVESTIGATION OF SKYRMION- HOSTING PT/CO/TA MULTILAYERS

Multilayers composed of heavy metals and ferromagnetic materials with strong perpendicular anisotropy are potential candidates for magnetic memory applications [1,2]. In particular, magnetic skyrmions may enable ultra-dense storage devices due to the extremely low spin currents needed to move/manipulated them [2]. Skyrmions emerge from the competition between the Dzyaloshinskii–Moriya interaction and exchange interactions generated at the interface of thin ferromagnetic layers and heavy metals with large spin-orbit coupling [3]. Pt/Co-based multilayers generally exhibit worm domains, which can nucleate into skyrmions through breaking/nucleation processes [4]. Recent studies have demonstrated the nucleation of skyrmions by varying external magnetic field, temperature, and current in sputtered Pt/Co/Ta multilayers [4,5].In this work, [Pt/Co/Ta]x multilayers with perpendicular magnetic anisotropy were grown by molecular beam epitaxy. We have demonstrated the feasibility of manipulating magnetic domains in our multilayers by changing the number of repetitions x and the Co layer thickness between 5 Å to 21 Å. Using magnetic force microscopy (MFM), we observed worm domains or stripe domains. These domains can be broken into skyrmions, by applying an out- of-plane field or into stripe domains by applying in-plane fields. We achieved partially ordered skyrmions at a low external field of ~38 mT for the multilayer with a cobalt thickness of 17 Å (see Figure 1). Furthermore, isolated skyrmions in this multilayer remain even after the external magnetic field has been removed.References[1] A. Fert and V. Sampai (2013) Nat. Nanotechnol. 8, 152–156[2] C Wang C, Seinige H. and Tsoi M. (2013), J. Phys. D: Appl. Phys. 46, 285001[3] Xichao Zhang X., Zhou Y., Song K.M., Park T.E., Xia J., Ezawa M., Liu X., Zhao W., Zhao G. and Woo S. (2020), J. Phys. Condens. Matter 32, 143001[4] Ma M., Ang C., Li Y., Pan Z., Gan W., Lew W.S. and Ma F. (2020), J. Appl. Phys. 127, 223901[5] Brandao J., Dugato D.A., Puydinger dos Santos M.V., Berón F. and Cesar J.C. (2022), Appl. Surf. Sci. 585, 15259

Tuning of Room Temperature Skyrmions in Pt/Co/Ta Multilayers

Magnetic skyrmions are nanoscale topological objects which are promising for next-generation information storage technologies and computing. [1,2] In magnetic multilayers, they can be stabilized at room temperature. [3-5]. Skyrmions emerge due to an interplay between several magnetic contributions. Among them the interfacial Dzyaloshinskii-Moriya Interaction (DMI) drives the spins into non-collinear orientation, while the perpendicular magnetic anisotropy (PMA) favours the out-of-plane orientation and the shape anisotropy prefers in-plane spin orientation. To study this competition of energies and the appearance of skyrmions, we have varied the Co film thickness as well as the number of repetitions in [Pt/Co(x)/Ta]$_N$ multilayers. This multilayer system was chosen because it is an established multilayer system for skyrmions and results can be compared with existing investigations, like e.g. [3,6].Polycrystalline [Pt(40 Å)/Co(x)/Ta(19 Å)]$_N$ multilayers were fabricated in a molecular beam epitaxy setup by thermal deposition on oxidized Si(001) substrates with a buffer layer of 47 Å Ta and a 30 Å Pt cap layer. The Co film thickness was varied between 5 Å and 21 Å, the number of repetitions varied between 8 and 10.Magnetic force microscopy measurements reveal the existence of skyrmions at a Co thickness between 9Å and 17 Å. The figure below gives examples with varying thickness and number of repetitions in indicated magnetic field. The density of skyrmions as well as their size varies. In remanence, stable skyrmions form only for the 17 Å Co sample with N=10 otherwise worm domains develop. Topological Hall effect measurements confirm these observations. The relationship between these findings is discussed in this contribution.References [1] A. Fert, V. Cros, and J. Sampaio, Nature Nanotech 8 (2013) 152. [2] K. Raab, M.A. Brems, G. Beneke, et al., Nat Commun 13 (2022) 6982. [3] S. Woo, K. Litzius, B. Krüger, M.-Y. Im, L. Caretta, K. Richter et al., Nat. Mat. 15 (2016) 501 [4] A. Soumyanarayanan, M. Raju, A. Gonzalez Oyarce, et al., Nature Mater 16 (2017) 898. [5] T.Dohi, R.M.Reeve and M. Kläui, Annu Rev. Condens. Matter Phys. 13 (2022) 73. [6] S.Zhang, J.Zhang, Y.Wen, E.M.Chudnovsky, and Y.Zhang, Comms. Phys. 36 (2018) 1

Discovery of Novel MDR-Mycobacterium tuberculosis Inhibitor by New FRIGATE Computational Screen

With 1.6 million casualties annually and 2 billion people being infected, tuberculosis is still one of the most pressing healthcare challenges. Here we report on the new computational docking algorithm FRIGATE which unites continuous local optimization techniques (conjugate gradient method) with an inherently discrete computational approach in forcefield computation, resulting in equal or better scoring accuracies than several benchmark docking programs. By utilizing FRIGATE for a virtual screen of the ZINC library against the Mycobacterium tuberculosis (Mtb) enzyme antigen 85C, we identified novel small molecule inhibitors of multiple drug-resistant Mtb, which bind in vitro to the catalytic site of antigen 85C

Relation of sample stoichiometry and growth conditions in SrCoO3−δ_{3−\delta} thin films

Strontium cobaltite (SrCoO$_{3-\delta}$) exists in two topotactic phases, depending on the oxygen content. SrCoO$_3$ is a ferromagnetic metal (T$_C$ =305K) with perovskite structure while SrCoO$_{2.5}$ is an antiferromagnetic insulator (T$_N$ =570K) with brownmillerite tructure [1]. We aim at growing thin films of SrCoO$_{3−\delta}$ via molecular beam epitaxy, and thus investigate the influence of growth conditions like the elemental deposition rate of Sr and Co, substrate temperature and oxygen pressure on the sample toichiometry and surface topography. For this, we employ in-situ electron diffraction to monitor the sample growth and ex-situ X-ray reflectometry and atomic force microscopy to investigate the structural properties. The stoichiometry is determined by Rutherford backscattering spectrometry. We provide a comprehensive overview of the samples addressing the requirements to achieve a Sr:Co stoichiometry of 1:1. [1]C.K. Xie et al., Appl. Phys. Lett 99, 052503 (2011

Topotactic transition mechanisms in SrCoO2.5+x_{2.5+x} films

Transition metal oxides are a big research topic, because they offer a wide range of possible applications, particularly in information and energy technology. One such system is strontium cobaltite (SrCoO2.5+x), which exists in two distinct topotactic phases, depending on the oxygen content. SrCoO3 is a ferromagnetically ordered metal with a Curie temperature of 305 K, but the system becomes an antiferromagnetic insulator with a Néel temperature of 570 K, when the oxygen content is decreased to SrCoO2.5. Along with this magnetic transition, the structure changes from perovskite to the orthorhombic brownmillerite, with the missing oxygen atoms forming vacancy channels [1]. Because of the multivalent Co states and high oxygen mobility it is a promising material for device applications [2]. To control the oxygen content, several possibilities exist. We focus on annealing in oxidising conditions and applying variable strain with a piezoelectric substrate to the film.We grow thin films of SrCoO2.5 by molecular beam epitaxy on SrTiO3 and LSAT substrates for investigations of oxygen annealing induced transitions and 0.7(Pb(Mg1/3Nb2/3)O3)-0.3(PbTiO3) (PMN-PT), a piezoelectric substrate, to study the possibility of a strain dependent oxidation state.To be able to successfully control the oxidation state and transfer strain from the substrate to the film, a high sample quality and epitaxy is mandatory. Thus, we present the results of the film growth and quality, as well as first results of the magnetic characterisation by SQUID and neutron reflectometry for annealed and strained samples.[1] C.K. Xie et al., Appl. Phys. Lett. 99, 2011 [2] H. Jeen et al., Nature Materials 12, 201