Magnetic domain walls and domains in thin films, nano stripes and 3D structures

In this thesis we image domains and domain walls by spin-polarised scanning electron microscopy (spin-SEM) in three different magnetic material systems. Spin-SEM is a powerful technique for that purpose because it allows the direct probing of the magnetisation in a specimen with the spatial resolution of a SEM which is around 10 nm in our system. The first chapter is devoted to the basic theoretical background necessary to understand the experiments. A brief discussion about the spin-orbit interaction highlights the importance of this interaction for the field of magnetism. A section about domain walls reminds the reader about the domain wall types in perpendicularly magnetised materials. Finally the Dzyaloshinskii-Moriya interaction (DMI) and its influence on domain walls are discussed. Chapter 3 details the experimental set-up, in particular the spin-SEM tool used for our experimental investigations. We look at how we measure the magnetisation of a specimen, in order to correctly interpret the recorded magnetic patterns. It turns out that it is often crucial to be capable to determine all three magnetization components. To this end, we have built a spin rotator, i.e., an extension to the microscope which allows us to measure all three components of the magnetisation vector. In the 4th chapter, differently arranged stacks of nickel and iron on top of the (100) surface of copper are investigated. The magnetic materials are evaporated in-situ onto the copper crystal which guarantees a high purity of the ferromagnetic materials. The domain walls in this system with perpendicular magnetisation are imaged and we find Néel, Bloch and intermediate domain walls. From the results we can conclude that the symmetry is broken in such a way that a chiral interaction is obtained, i.e., DMI. We estimate the strength of this interaction and compare our results with literature values. Chapter 5 deals with perpendicularly magnetised nanowires, which exhibit distinct domain wall types depending on the geometry. Nanowires with different width are shaped out of a sputtered cobalt/nickel multilayer by an electron beam lithography process. The transition of the domain wall type in the nanowires is investigated by direct imaging of the wall structure. We discover an achiral intermediate wall type that is unpredicted by established theoretical models. With the help of micromagnetic simulations, the formation of this novel wall type is explained. We discuss why this intermediate wall should occur in all perpendicularly magnetised materials for appropriate wire dimensions and we exclude DMI as a possible cause for this novel wall type. Finally, in chapter 6, three-dimensional magnetic cobalt structures are investigated, which are the first step towards three-dimensional, extended, magnetic spin ice networks. We show that two-photon lithography in combination with electroplating is capable of producing large arrays of three dimensional magnetic structures in the submicrometre range by imaging the domain pattern in these structures. Additionally, we show how a detailed analysis by spin-SEM can be used to improve the production process of samples

Two-photon Lithography for 3D Magnetic Nanostructure Fabrication

Ferromagnetic materials have been utilised as recording media within data storage devices for many decades. Confinement of the material to a two dimensional plane is a significant bottleneck in achieving ultra-high recording densities and this has led to the proposition of three dimensional (3D) racetrack memories that utilise domain wall propagation along nanowires. However, the fabrication of 3D magnetic nanostructures of complex geometry is highly challenging and not easily achievable with standard lithography techniques. Here, by using a combination of two-photon lithography and electrochemical deposition, we show a new approach to construct 3D magnetic nanostructures of complex geometry. The magnetic properties are found to be intimately related to the 3D geometry of the structure and magnetic imaging experiments provide evidence of domain wall pinning at a 3D nanostructured junction

A minimal Beta Beam with high-Q ions to address CP violation in the leptonic sector

In this paper we consider a Beta Beam setup that tries to leverage at most existing European facilities: i.e. a setup that takes advantage of facilities at CERN to boost high-Q ions (8Li and 8B) aiming at a far detector located at L = 732 Km in the Gran Sasso Underground Laboratory. The average neutrino energy for 8Li and 8B ions boosted at \gamma ~ 100 is in the range E_\nu = [1,2] GeV, high enough to use a large iron detector of the MINOS type at the far site. We perform, then, a study of the neutrino and antineutrino fluxes needed to measure a CP-violating phase delta in a significant part of the parameter space. In particular, for theta_13 > 3 deg, if an antineutrino flux of 3 10^19 useful 8Li decays per year is achievable, we find that delta can be measured in 60% of the parameter space with 6 10^18 useful 8B decays per year.Comment: 19 pages, 10 figures, added references and corrected typo

Wnt secretion is required to maintain high levels of Wnt activity in colon cancer cells

Aberrant regulation of the Wnt/β-catenin pathway has an important role during the onset and progression of colorectal cancer, with over 90% of cases of sporadic colon cancer featuring mutations in APC or β-catenin. However, it has remained a point of controversy whether these mutations are sufficient to activate the pathway or require additional upstream signals. Here we show that colorectal tumours express elevated levels of Wnt3 and Evi/Wls/GPR177. We found that in colon cancer cells, even in the presence of mutations in APC or β-catenin, downstream signalling remains responsive to Wnt ligands and receptor proximal signalling. Furthermore, we demonstrate that truncated APC proteins bind β-catenin and key components of the destruction complex. These results indicate that cells with mutations in APC or β-catenin depend on Wnt ligands and their secretion for a sufficient level of β-catenin signalling, which potentially opens new avenues for therapeutic interventions by targeting Wnt secretion via Evi/Wls

The EU Center of Excellence for Exascale in Solid Earth (ChEESE): Implementation, results, and roadmap for the second phase

publishedVersio

Anterior deltoid muscle tension quantified with shear wave ultrasound elastography correlates with pain level after reverse shoulder arthroplasty

INTRODUCTION: Reverse shoulder arthroplasty (RSA) leads to medialization and distalization of the centre of rotation of the shoulder joint resulting in lengthening of the deltoid muscle. Shear wave ultrasound elastography (SWE) is a reliable method for quantifying tissue stiffness. The purpose of this study was to analyse if deltoid muscle tension after RSA correlates with the patients’ pain level. We hypothesized that higher deltoid muscle tension would be associated with increased pain. MATERIAL AND METHODS: Eighteen patients treated with RSA were included. Constant score (CS) and pain level on the visual analogue scale (VAS) were analysed and SWE was performed on both shoulders. All three regions of the deltoid muscle were examined in resting position and under standardized isometric loading. RESULTS: Average patient age was 76 (range 64–84) years and average follow-up was 15 months (range 4–48). The average CS was 66 points (range 35–89) and the average pain level on the VAS was 1.8 (range 0.5–4.7). SWE revealed statistically significant higher muscle tension in the anterior and middle deltoid muscle region in patients after RSA compared to the contralateral non-operated side. There was a statistically significant correlation between pain level and anterior deltoid muscle tension. CONCLUSION: SWE revealed increased tension in the anterior and middle portion of the deltoid muscle after RSA in a clinical setting. Increased tension of the anterior deltoid muscle portion significantly correlated with an increased pain level. SWE is a powerful, cost-effective, quick, dynamic, non-invasive, and radiation-free imaging technique to evaluate tissue elasticity in the shoulder with a wide range of applications. LEVEL OF EVIDENCE: Diagnostic study, Level III

Associations between Bone Mineral Density and Longitudinal Changes of Vertebral Bone Marrow and Paraspinal Muscle Composition Assessed Using MR-Based Proton Density Fat Fraction and T2* Maps in Patients with and without Osteoporosis

Background: Proton-density fat fraction (PDFF) and T2* of the vertebrae, as well as the cross-sectional area (CSA) of the paraspinal musculature (PSM), have been suggested as biomarkers for bone fragility. The aim of this study was to longitudinally assess changes in PDFF, T2* and CSA of the PSM over 6 months in patients with and without osteoporosis. Methods: Opportunistic bone mineral density (BMD) measurements (BMD < 120 mg/cm3) were obtained from a CT acquired during the clinical routine work up in osteoporotic/osteopenic patients (n = 29, mean age 72.37 ± 10.12 years, 16 women). These patients were frequency-matched for age and sex to subjects with normal BMD values (n = 29). All study patients underwent 3T MR imaging at baseline and 6-month follow up, including spoiled gradient echo sequences for chemical shift encoding-based water-fat separation, from which T2* and PDFF values of the lumbar spine and the PSM were obtained. Moreover, the CSA of the PSM was assessed longitudinally. Changes in T2*, PDFF and CSA over 6 months were calculated for the vertebrae and PSM and associations with baseline BMD values were assessed. Results: The change in CSA of the PSM over 6 months was significantly lower in the osteoporotic/osteopenic group (−91.5 ± 311.7 mm2), compared to the non-osteoporotic group, in which the CSA increased (29.9 ± 164.0 mm2, p = 0.03). In a further analysis, patients with higher vertebral PDFF at baseline showed a significantly stronger increase in vertebral T2*, compared to those patients with lower vertebral PDFF at baseline (0.9 ± 1.6 ms vs. 0.0 ± 1.8 ms, p = 0.04). Moreover, patients with higher PSM PDFF at baseline showed a significantly stronger increase in vertebral T2*, compared to those patients with lower PSM PDFF at baseline (0.9 ± 2.0 ms vs. 0.0 ± 1.3 ms, p = 0.03). Conclusion: The PSM CSA decreased significantly longitudinally in patients with osteoporosis/osteopenia, compared to those without. Additionally, higher vertebral and PSM PDFF at baseline were associated with stronger changes in vertebral bone marrow T2*. Therefore, longitudinal PDFF and T2* mapping may be useful quantitative radiation-free tools for the assessment and prediction of muscle and bone health in patients with suspected osteoporosis/osteopenia

Cathepsin A contributes to left ventricular remodeling by degrading extracellular superoxide dismutase in mice

In the heart, the serine carboxypeptidase cathepsin A (CatA) is distributed between lysosomes and the extracellular matrix (ECM). CatA-mediated degradation of extracellular peptides may contribute to ECM remodeling and left ventricular (LV) dysfunction. Here, we aimed to evaluate the effects of CatA overexpression on LV remodeling. A proteomic analysis of the secretome of adult mouse cardiac fibroblasts upon digestion by CatA identified the extracellular antioxidant enzyme superoxide dismutase (EC-SOD) as a novel substrate of CatA, which decreased EC-SOD abundance 5-fold.In vitro, both cardiomyocytes and cardiac fibroblasts expressed and secreted CatA protein, and only cardiac fibroblasts expressed and secreted EC-SOD protein. Cardiomyocyte-specific CatA overexpression and increased CatA activity in the LV of transgenic mice (CatA-TG) reduced EC-SOD protein levels by 43%. Loss of EC-SOD-mediated antioxidative activity resulted in significant accumulation of superoxide radicals (WT, 4.54 mu mol/mg tissue/min; CatA-TG, 8.62 mu mol/mg tissue/min), increased inflammation, myocyte hypertrophy (WT, 19.8 mu m; CatA-TG, 21.9 mu m), cellular apoptosis, and elevated mRNA expression of hypertrophy-related and profibrotic marker genes, without affecting intracellular detoxifying proteins. In CatA-TG mice, LV interstitial fibrosis formation was enhanced by 19%, and the type I/type III collagen ratio was shifted toward higher abundance of collagen I fibers. Cardiac remodeling in CatA-TG was accompanied by an increased LV weight/body weight ratio and LV end diastolic volume (WT, 50.8 mu l; CatA-TG, 61.9 mu l). In conclusion, CatA-mediated EC-SOD reduction in the heart contributes to increased oxidative stress, myocyte hypertrophy, ECM remodeling, and inflammation, implicating CatA as a potential therapeutic target to prevent ventricular remodeling.</p