@phdthesis{Walther2008, author = {Walther, Markus}, title = {Simulation of strain-induced and defect-controlled self-organization of nanostructures}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-27931}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2008}, abstract = {In this PhD thesis, the effect of strain on heteroepitaxial growth is investigated by means of Kinetic Monte Carlo simulations. In this context the lattice misfit, arising from the different lattice constants of the adsorbate and the substrate material, is of particular interest. As a consequence, this lattice misfit leads to long-range elastic strain effects having strong influence on the entire growing crystal and its resulting surface morphology. The main focus of this work is the investigation of different strain relaxation mechanisms and their controlling parameters, revealing interesting consequences on the subsequent growth. Since epitaxial growth is carried out under conditions far away from thermodynamic equilibrium, it is strongly determined by surface kinetics. At this point the relevant kinetic microscopic processes are described, followed by theoretical considerations of heteroepitaxial growth disclosing an overview over several independent methodological streams, used to model epitaxy in different time and length scales, as well as the characterization of misfit dislocations and the classification of epitaxial growth modes based on thermodynamic considerations. The epitaxial growth is performed by means of Kinetic Monte Carlo simulations which allows for the consideration of long range effects in systems with lateral extension of few hundred atoms. By using an off-lattice simulation model the particles are able to leave their predefined lattice sites, which is an indispensable condition for simulating strain relaxation mechanisms. The main idea of our used model is calculating the activation energy of all relevant thermally activated processes by using simple pair potentials and then realizing the dynamics by performing each event according to its probability by means of a rejection-free algorithm method. In addition, the crystal relaxation procedure, the grid-based particle access method, which accelerates the simulation enormously, and the efficient implementation of the algorithm are discussed. To study the influence of long range elastic strain effects, the main part of this work was realized on the two dimensional triangular lattice, which can be treated as a cross section of the real three dimensional case. Chapter 4 deals with the formation of misfit dislocations as a strain relaxation mechanism and the resulting consequences on the subsequent heteroepitaxial growth. We can distinguish between two principally different dislocation formation mechanisms, depending strongly on the sign as well as on the magnitude of the misfit, but also the surface kinetics need to be taken into account. Additionally, the dislocations affect the lattice spacings of the crystal whose observed progression is in qualitative good agreement with experimental results. Furthermore, the dislocations influence the subsequent growth of the adsorbate film, since the potential energy of an adatom is modulated by buried dislocations. A clear correlation between the lateral positions of buried dislocations and the positions of mounds grown on the surface can be observed. In chapter 5, an alternative strain relaxation mechanism is studied: the formation of three dimensional islands enables the particles to approach their preferred lattice spacing. We demonstrate that it is possible to adjust within our simulation model each of the three epitaxial growth modes: Volmer-Weber, Frank-van der Merve or layer-by-layer, and Stranski-Krastanov growth mode. Moreover, we can show that the emerging growth mode depends in principle on two parameters: on the one hand the interaction strength of adsorbate particles with each other, compared to the interaction of adsorbate with substrate particles, and on the other hand the lattice misfit between adsorbate and substrate particles. A sensible choice of these two parameters allows the realization of each growth mode within the simulations. In conclusion, the formation of nanostructures controlled by an underlying dislocation network can be applied in the concept of self-organized pattern formation as well as by the tendency to form ordered arrays of strain-induced three dimensional grown islands. In chapter 6, we extend our model to three dimensions and investigate the effect of strain on growth on bcc(100) surfaces. We introduce an anisotropic potential yielding a stable bcc lattice structure within the off-lattice representation. We can show that the strain built up in submonolayer islands is mainly released at the island edges and the lattice misfit has strong influence on the diffusion process on the plane surface as well as on the situation at island edges with eminent consequences on the appearance of submonolayer islands.}, subject = {Kristallwachstum}, language = {en} } @article{HoertererBaumbachLemperleetal.2019, author = {H{\"o}rterer, Hubert and Baumbach, Sebastian Felix and Lemperle, Stefan and Altenberger, Sebastian and Gottschalk, Oliver and Mehlhorn, Alexander Tobias and R{\"o}ser, Anke and Walther, Markus}, title = {Clinical outcome and concomitant injuries in operatively treated fractures of the lateral process of the talus}, series = {BMC Musculoskeletal Disorders}, volume = {20}, journal = {BMC Musculoskeletal Disorders}, doi = {10.1186/s12891-019-2603-3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-321207}, year = {2019}, abstract = {Background The aim of this study was to review the patient rated outcome (PROM) of surgically treated fractures to the lateral process of the talus (LPTF) and identify factors influencing the outcome. Methods Retrospective study with a current follow-up. Eligible were all patients treated surgically for a LPTF (n = 23) with a minimum follow-up of one year. Demographics, medical history, trauma mechanism, fracture characteristics, concomitant injuries, treatment details, complications, return to work and sports were assessed retrospectively. The current follow-up included the VAS FA, Karlsson Score, and SF-12. The primary outcome was the VAS FA. Secondary aim was the identification of parameters influencing the PROMs. Results 22 patients (96\% follow-up) with a mean age of 32 ± 9 (18 to 49) years were included. 73\% suffered a Hawkins Type 1, 23\% a Type 2, and one patient a Type 3 fracture. 82\% suffered concomitant injuries. 9\% suffered minor surgical side infections, 50\% developed symptomatic subtalar osteoarthritis. At final follow-up (44 ± 2 (12 to 97) months), the mean VAS FA Overall was 77 ± 21 (20 to 100), the Karlsson Score 72 ± 21 (34 to 97), and for the SF 12 the PCS 53 ± 8 (36 to 64) and the MCS 53 ± 7 (32 to 63). 50\% of patients returned to their previous level of sports. Hawkins Type 1 fractures resulted in better VAS FA Overall score than Type 2 fractures. Posttraumatic subtalar osteoarthritis was the independent factor associated to a poor patient rated outcome (VAS FA, Karlsson Score). Conclusion After a follow-up of over 3.5 years, surgically treated LPTF resulted in only moderate results. 50\% suffered posttraumatic symptomatic subtalar osteoarthritis, which was the primary independent parameter for a poor outcome following LPTF. Level of evidence Level III.}, language = {en} } @article{BaumbachHoertererOppeltetal.2022, author = {Baumbach, Sebastian Felix and H{\"o}rterer, Hubert and Oppelt, Sonja and Szeimies, Ulrike and Polzer, Hans and Walther, Markus}, title = {Do pre-operative radiologic assessment predict postoperative outcomes in patients with insertional Achilles tendinopathy?: a retrospective database study}, series = {Archives of Orthopaedic and Trauma Surgery}, volume = {142}, journal = {Archives of Orthopaedic and Trauma Surgery}, number = {11}, issn = {1434-3916}, doi = {10.1007/s00402-021-03897-x}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-307963}, pages = {3045-3052}, year = {2022}, abstract = {Introduction Diagnosis and treatment of insertional tendinopathy of the Achilles tendon (IAT) remains a challenge. The aim of this study was to assess the influence of pre-operative radiological pathologies on the patient-reported outcomes following open debridement of all pathologies for IAT. Materials and methods In this IRB-approved retrospective correlation and comparative study, patients with pre-operative imaging were identified from the authors' retrospective IAT database comprising of 118 patients. All were treated by a standardized surgical treatment strategy utilizing a midline, transachillary approach and debridement of all pathologies. A total of fifteen radiologic parameters were measured on radiographs (RX) and MRI. The patient-reported outcomes were assessed using the Victorian Institute of Sport Assessment-Achilles questionnaire (VISA-A-G) and the general health questionnaire SF-12 at a minimum follow-up of 12 months. The data are presented as mean ± SD (95\% CI). Results 88 patients (74.6\%) with an average age of 50 ± 12 (47-52) years were included. Radiographs were available in 68 patients and MRI in 53. The mean follow-up was 3.8 ± 1.9 (3.4-4.3) years. The overall VISA-A-G was 81 ± 22 (77-86), the SF-12 PCS 54 ± 7 (52-55), and the SF-12 MCS 52 ± 9 (50-54) points. None of the assessed radiological parameters had a significant influence on the patient-reported outcome following surgical treatment for IAT. Conclusion In this retrospective correlation study, no significant association was found between preoperative radiographic and MRI radiologic parameters for IAT and postoperative patient-reported outcomes (VISA-A-G and SF-12).}, language = {en} }