Stationary point approach to the phase transition of the classical XY chain with power-law interactions

The stationary points of the Hamiltonian H of the classical XY chain with power-law pair interactions (i.e., decaying like r^{-{\alpha}} with the distance) are analyzed. For a class of "spinwave-type" stationary points, the asymptotic behavior of the Hessian determinant of H is computed analytically in the limit of large system size. The computation is based on the Toeplitz property of the Hessian and makes use of a Szeg\"o-type theorem. The results serve to illustrate a recently discovered relation between phase transitions and the properties of stationary points of classical many-body Hamiltonian functions. In agreement with this relation, the exact phase transition energy of the model can be read off from the behavior of the Hessian determinant for exponents {\alpha} between zero and one. For {\alpha} between one and two, the phase transition is not manifest in the behavior of the determinant, and it might be necessary to consider larger classes of stationary points.Comment: 9 pages, 6 figure

Single-cell transcriptome analyses on developmental transitions in mouse pluripotent stem cells

Böttcher M. Single-cell transcriptome analyses on developmental transitions in mouse pluripotent stem cells. Bielefeld: Universität Bielefeld; 2020.We used an in vitro model of Pluripotent Stem Cell (PSC) development in mice to analyze dynamic changes in transcriptomes of hundreds of individual cells which were undergoing an induced transition from naïve mouse Embryonic Stem Cells (mESC) towards primed pluripotent Epiblast Stem Cells (EpiSC). The differentiation of mESCs to EpiSC-like cells takes about five days after induction. We collected cell samples in 24-hour intervals for four days after induction as well as untreated mESCs and primed state EpiSCs. Single-cell isolation and scRNA-seq library preparation for each time point were done on the commercial Fluidigm C1 platform. In addition, we sampled C1-Cap Analysis of Gene Expression (C1-CAGE) libraries for the same set of time points to enable detection of non- coding RNAs (ncRNAs) such as anti-sense RNAs or enhancer RNAs. This C1-CAGE protocol was new and still undergoing optimization at the beginning of our experiments. C1-CAGE was first published by Kouno *et al.* (2019) and the author of this thesis contributed as a co-author. Throughout the work on this project a data management platform called SCPortalen was developed to share all data among project collaborators. SCPortalen’s publication was also co-authored by the author of this thesis (Abugessaisa et al., 2018). The combination of transcriptome datasets from two different protocols allowed the elucidation of expression dynamics of the naïve- to-primed stem cell conversion. We independently identified two subpopulations of cells during the transition process with both the Fluidigm scRNA-seq and C1-CAGE dataset. Pseudotime analysis revealed the developmental trajectory of cells and is a powerful tool to reliably identify developmental stages of cells without prior knowledge of their actual stage. Among these two transition phase subpopu- lations, one showed wide-spread repression of gene expression. The small nuclear RNA (snRNA) *Rn7sk* was identified as one potential regulator of this population specific phenomenon. The second subpop- ulation shared some characteristics with primed EpiSCs such as cell morphology and the expression of known primed state marker genes, but it could be shown that cells from this population were still undergoing Epithelial-Mesenchymal Transition (EMT). That is a clear sign that these cells have not yet fully transitioned to primed pluripotent stem cells. Interestingly, the characteristics of this subpopulation largely match a predicted third pluripotency state called “formative” (Smith, 2017). Therefore, we believe that our dataset not only contains naïve and primed pluripotent stem cells, but also formative pluripotent stem cells. Thus, our dataset represents a unique resource to compare and study this proposed formative pluripotency state. Last but not least, we found several marker gene candidates for all developmental stages of the naïve-to-primed transition, which will facilitate classification of cells in future experiments. For example, we propose *Cd59a* as a highly specific marker gene for primed EpiSCs. The results of this thesis project have also been compiled into a manuscript for publication in a peer reviewed journal and will be submitted soon after the submission of this thesis

Sulphur and Carbon Isotopes as Tracers of Past Sub-seafloor Microbial Activity

Microbial life below the seafloor has changed over geological time, but these changes are often not obvious, as they are not recorded in the sediment. Sulphur (S) isotope values in pyrite extracted from a Plio- to Holocene sequence of the Peru Margin (Ocean Drilling Program, ODP, Site 1229) show a down-core pattern that correlates with the pattern of carbon (C) isotopes in diagenetic dolomite. Early formation of the pyrite is indicated by the mineralogical composition of iron, showing a high degree of pyritization throughout the sedimentary sequence. Hence, the S-record could not have been substantially overprinted by later pyrite formation. The S- and C-isotope profiles show, thus, evidence for two episodes of enhanced microbial methane production with a very shallow sulphate-methane transition zone. The events of high activity are correlated with zones of elevated organic C content in the stratigraphic sequence. Our results demonstrate how isotopic signatures preserved in diagenetic mineral phases provide information on changes of past biogeochemical activity in a dynamic sub-seafloor biosphere

Detail CFD simulation of the integrated reactor pressure vessel of SMART

This paper presents a detailed analysis of the full Reactor Pressure Vessel (RPV) of SMART with ANSYS CFX 20.2. SMART is a water-cooled SMR designed by KAERI for an operation with forced convection. The thermal power of SMART amounts to 330 MW$_{th}$. In the integrated SMR-concept, the main primary loop components such as the helical steam generators, pressurizer and canned pumps are located inside the RPV. The CFD model uses a concept of full geometrical detail resolution with partial boundary inflation of the mesh and porous media modelling with sources for momentum and energy for components like the core, pumps and steam generators. The detailed results obtained with a steady-state RANS simulation using ANSYS CFX 20.2 are very promising as the comparison of selected core parameters of the CFD-simulation with the ones of the system thermal hydraulic code TRACE have shown

Patient-Specific Synthetic Osteochondral Resurfacing of an Extensive Shoulder OCD Lesion in a Dog

The aim of this study was to describe template-guided implantation and clinical outcome of a patient-specific resurfacing implant for an extensive humeral head osteochondritis in a client-owned dog. An 8-month-old intact female Irish Wolfhound, weighing 45 kg, exhibiting lameness in the right thoracic limb, and diagnosed with an extensive caudocentral humeral head osteochondritis. Based on computed tomography data, an anatomically contoured patient-specific implant (Ø 25 mm) was created. The implant consisted of a trabecular titanium base and a polycarbonate urethane bearing cup. For intraoperative guidance, a surgical drill guide, models of the affected humeral head, and trial implants were 3D printed. The implantation procedure was performed using the modified Cheli approach. Orthopaedic and radiographic follow-up examinations were conducted at 6 weeks and 10 months postoperatively. The examination revealed stable implant position, and some mild residual lameness at 6 weeks. Furthermore, the mild osteophytosis, initially evident on the day of surgery, showed a progression during each subsequent follow-up. Complications were not observed at any time point. At 10 months, the dog was free of lameness and exhibited no functional impairment, even after strenuous exercise. This level of activity remained unchanged up to the latest follow-up at 18 months, as confirmed during a telephonic interview. The utilization of a patient-specific resurfacing implant using a guided approach was technically feasible and resulted in excellent short- to mid-term clinical outcome in this case of extensive caudocentral humeral head osteochondritis dissecans (OCD) lesion. However, it is crucial to note that the potential influence of the implant on osteoarthritis progression requires further investigation

Packaging of up to 240 subunits of a 17 kDa nuclease into the interior of recombinant hepatitis B virus capsids

AbstractThe icosahedral nucleocapsid of hepatitis B virus (HBV) consists of multiple subunits of a single 183 amino acids (aa) core protein encasing the viral genome. However, recombinant core protein alone also forms capsid-like particles. We have recently shown that a 238 aa protein centrally inserted into the core protein can be displayed on the particle surface. Here we demonstrate that replacement of the C-terminal basic domain by the 17 kDa Staphylococcus aureus nuclease also yields particles but that in these the foreign domains are located in the interior. The packaged nuclease is enzymatically active, and the chimeric protein forms mosaic particles with the wild-type core protein. Hence the HBV capsid is useful as a molecular platform which, dependent on the fusion site, allows foreign protein domains to either be packaged into or be exposed on the exterior of the particle. These results are of relevance for the use of the HBV capsid as a vaccine carrier, and as a target for antiviral therapy