35 research outputs found
From polyhistory to subversion: the philological foundations of Hermann Samuel Reimarus's (1694-1768) radical enlightenment
No full textThis dissertation focuses on the distinguished scholar Hermann Samuel Reimarus (1694-1768) who, alongside Lessing, Kant, Mendelssohn, and Wolff, is one of the most significant and influential figures of the German Enlightenment. Reimarus is perhaps best known for his subversive critique of revelation, known as the Apologie oder Schutzschrift für die vernünftigen Verehrer Gottes [Apology or the Defense of the Reasonable Worshippers of God], which was published posthumously by Lessing and spurred the fragment controversy, one of the most important disputes of the German Enlightenment.
Generally, this controversy has provided the context for existing scholarship on Reimarus, and by labeling him a deist and radical Wolffian, modern scholars have primarily emphasized the philosophical nature of his criticism. An intensive examination of the Reimarus Nachlass, with its numerous handwritten drafts of the Apology, lecture notes, adversaria, and bibliographies, paired with an understanding of his education, the influence of his mentors, and his teaching career as professor of Oriental languages at the Gymnasium illustre in Hamburg reveals, however, why such an approach ultimately ignores who Reimarus really was: a classical scholar and skilled Hebraist, raised and bred in the world of the polyhistors.
By focusing on Reimarus's use of philology, antiquarianism, and Semitic languages I show how these fields, developed by humanists and reformers and perfected in the course of the seventeenth century, influenced Reimarus's "Radical Enlightenment." Therefore, this project will significantly contribute to discussions of the Radical Enlightenment and the creation of the modern world by illustrating how its proponents - such as Reimarus - remained indebted to the tradition of the humanists.Ph.D.Includes bibliographical references
Micro- and nanomechanics of mineralised collagen fibre elasto-plasticity
No full textMusculoskeletal diseases such as osteoporosis, osteoarthritis and bone cancer pose
a significant social and economic challenge in ageing societies worldwide. In digital
healthcare, computational models could be a cornerstone in mitigating these challenges
by facilitating, for example, personalised bone strength analyses or manufacturing
of bespoke implants. Such models, however, critically depend on understanding the
complex characteristics of bone as a material. Currently, there is limited knowledge
on the elasto-plastic behaviour of bone’s fundamental mechanical building block, the
mineralised collagen fibre. Especially the load transfer between mineralised collagen
fibrils and mineral particles, its main mechanical components, is unclear. Therefore, we
aimed at (i) simultaneously quantifying the fibre, fibril and mineral deformation using
a micro- and nanomechanical testing protocol, (ii) formulating a statistical constitutive
model to explain the fibre behaviour and the load transfer between its constituents as
well as (iii) using (i) and (ii) to test under quasi-physiologic conditions.
Laser manufacturing and focused ion beam milling were used to extract micrometre sized
samples from individual mineralised collagen fibres of mineralised turkey leg tendon, a
model system for bone. These micropillars were tested in an experimental set-up that
combined micropillar compression and X-ray scattering or diffraction under dry and
rehydrated conditions. An elasto-plastic statistical constitutive model was developed in
which two shear lag models simulate the stress transfer between fibre, fibril and mineral.
Ultrastructural features were included based on nanoscale imaging data.
Experimental data show small fibril and mineral strains compared to the fibre strain.
This was related to localised strains and heterogeneous fibril deformations due to a
gradual nonlinear fibril recruitment. By incorporating this recruitment, the model can
explain the elasto-plastic fibre behaviour as seen in dry and rehydrated experiments
including the load transfer between fibre, fibrils and mineral particles with an accuracy
of 95% for dry and 89% for rehydrated conditions. The model provides distributions
for the micro- and nanomechanical responses and, thus, directly simulates strain ratios
determined experimentally by in-situ mechanical testing and X-ray scattering/diffraction
measurements. Experiment and model allowed it to identify the micro- and nanome-chanical behaviour of the fibril array. Rehydration decreased fibre stiffness by 60%,
yield and compressive strength by 75%, and fibril stiffness by 25%.
The new insights into the micro- and nanoscale elasto-plastic behaviour of bone’s fundamental mechanical building block help to understand bone’s hierarchical material
mechanics. Results may be used to inform computational models for nonlinear bone
strength analyses as well as the design of tissue engineered bio-inspired implants.Engineering and Physical Sciences Research Council (EPSRC
Uniform asymptotic regularity for Mann iterates
No full textIn [16] we obtained an effective quantitative analysis of a theorem due to Borwein, Reich and Shafrir on the asymptotic behavior of general Krasnoselski-Mann iterations for nonexpansive self-mappings of convex sets C in arbitrary normed spaces. We used this result to obtain a new strong uniform version of Ishikawa's theorem for bounded C. In this paper we give a qualitative improvement of our result in the unbounded case and prove the uniformity result for the bounded case under the weaker assumption that C contains a point x whose Krasnoselski-Mann iteration (x k ) is bounded. We also consider more general iterations for which asymptotic regularity is known only for uniformly convex spaces (Groetsch). We give uniform effective bounds for (an extension of) Groetsch's theorem which generalize previous results by Kirk/Martinez-Yanez and the author
An experimentally informed statistical elasto-plastic mineralised collagen fibre model at the micrometre and nanometre lengthscale
No full textBone is an intriguingly complex material. It combines high strength, toughness and lightweight via an elaborate hierarchical structure. This structure results from a biologically driven self-assembly and self-organisation, and leads to different deformation mechanisms along the length scales. Characterising multiscale bone mechanics is fundamental to better understand these mechanisms including changes due to bone-related diseases. It also guides us in the design of new bio-inspired materials. A key-gap in understanding bone's behaviour exists for its fundamental mechanical unit, the mineralised collagen fibre, a composite of organic collagen molecules and inorganic mineral nanocrystals. Here, we report an experimentally informed statistical elasto-plastic model to explain the fibre behaviour including the nanoscale interplay and load transfer with its main mechanical components. We utilise data from synchrotron nanoscale imaging, and combined micropillar compression and synchrotron X-ray scattering to develop the model. We see that a 10-15% micro- and nanomechanical heterogeneity in mechanical properties is essential to promote the ductile microscale behaviour preventing an abrupt overall failure even when individual fibrils have failed. We see that mineral particles take up 45% of strain compared to collagen molecules while interfibrillar shearing seems to enable the ductile post-yield behaviour. Our results suggest that a change in mineralisation and fibril-to-matrix interaction leads to different mechanical properties among mineralised tissues. Our model operates at crystalline-, molecular- and continuum-levels and sheds light on the micro- and nanoscale deformation of fibril-matrix reinforced composites.</p
Assessing minipig compact jawbone quality at the microscale
No full textPreclinical studies often require animal models for in vivo experiments. Particularly in dental research, pig species are extensively used due to their anatomical similarity to humans. However, there is a considerable knowledge gap on the multiscale morphological and mechanical properties of the miniature pigs’ jawbones, which is crucial for implant studies and a direct comparison to human tissue. In the present work, we demonstrate a multimodal
framework to assess the jawbone quantity and quality for a minipig animal model that could be further extended to humans.
Three minipig genotypes, commonly used in dental research, were examined: Yucatan, G ̈ottingen, and Sinclair. Three animals per genotype were tested. Cortical bone samples were extracted from the premolar region of the mandible, opposite to the teeth growth. Global morphological, compositional, and mechanical properties were assessed using micro-computed tomography (micro-CT) together with Raman spectroscopy and nano-
indentation measurements, averaged over the sample area. Local mineral-mechanical relationships were investigated with the site-matched Raman spectroscopy and micropillar compression tests. For this, a novel femtosecond laser ablation protocol was developed, allowing high-throughput micropillar fabrication and testing without exposure to high vacuum.
At the global averaged sample level, bone relative mineralization demonstrated a significant difference between the genotypes, which was not observed from the complementary micro-CT measurements. Moreover, bone hardness measured by nanoindentation showed a positive trend with the relative mineralization. For all genotypes, significant differences between the relative mineralization and elastic properties were more pronounced within the osteonal regions of cortical bone. Site-matched micropillar compression and Raman spectroscopy highlighted the differences between the genotypes’ yield stress and mineral to matrix ratios.
The methods used at the global level (averaged over sample area) could be potentially correlated to the medical tools used to assess jawbone toughness and morphology in clinics. On the other hand, the local analysis methods can be applied to quantify compressive bone mechanical properties and their relationship to bone mineralization
Uniform Asymptotic Regularity for Mann Iterates
No full textIn a previous paper we obtained an effective quantitative analysis of a theorem due to Borwein, Reich and Shafrir on the asymptotic behavior of general Krasnoselski-Mann iterations for nonexpansive self-mappings of convex sets C in arbitrary normed spaces. We used this result to obtain a new strong uniform version of Ishikawa's theorem for bounded C . In this paper we give a qualitative improvement of our result in the unbounded case and prove the uniformity result for the bounded case under the weaker assumption that C contains a point x whose Krasnoselski-Mann iteration (x_n) is bounded. We also consider more general iterations for which asymptotic regularity is known only for uniformly convex spaces (Groetsch). We give uniform effective bounds for (an extension of) Groetsch's theorem which generalize previous results by Kirk/Martinez-Yanez and the author
qPRS analysis code
No full text<p>Code for the quantitative Polarized Raman spectra (qPRS) analysis.</p>
<p>When using this code in your work, please cite:</p>
<ol>
<li>Kochetkova Tatiana, Peruzzi Cinzia, Braun Oliver, Overbeck Jan, Maurya Anjani K, Neels Antonia, Calame Michel, Michler Johann, Zysset Philippe, Schwiedrzik Jakob. Combining polarized Raman spectroscopy and micropillar compression to study microscale structure-property relationships in mineralized tissues. Acta Biomaterialia 2021, 119, 390-404; DOI: 10.1016/j.actbio.2020.10.034</li>
<li>Kochetkova Tatiana, Groetsch Alexander, Indermaur Michael, Peruzzi Cinzia, Remund Stefan, Neuenschwander Beat, Bellon Benjamin, Michler Johann, Zysset Philippe, Schwiedrzik Jakob. Assessing minipig compact jawbone quality at the microscale. Journal of the Mechanical Behavior of Biomedical Materials 2022,134,105405; DOI: 10.1016/j.jmbbm.2022.105405</li>
</ol>
<p>In case of further question please contact <a href="mailto:[email protected]">[email protected]</a> (Tatiana).</p>
<p>All of the codes were written by Tatiana Kochetkova during her PhD thesis work at Empa, Swiss Federal Laboratories for Materials Science and Technology.</p>
<p>This work was funded by the Special Focus Area Personalized Health and Related Technologies (SFA PHRT) iDoc Project 2017-304.</p>
Extrafibrillar matrix yield stress and failure envelopes for mineralised collagen fibril arrays
No full textBone metabolic diseases such as osteoporosis constitute a major socio-economic challenge. A detailed understanding of the structure-property relationships of bone's underlying hierarchical levels has the potential to improve diagnosis and the ability to treat those diseases, especially with regards to the onset of failure. Therefore, elastic and yield properties of mineralised turkey leg tendon (MTLT), a mineralised tissue that is similar to bone but has a simpler multiscale structure, were investigated. Elastic properties were identified using a multiscale micromechanical model. The input parameters include constituent mechanical properties, volume fractions and inclusion aspect ratios and these were obtained from a wide variety of literature sources. The determined elastic properties were used to formulate micromechanically informed yield surfaces and to identify yield properties of MTLT at the nanometre length scale where failure is first reported to occur. This was done in conjunction with experimental results from the compression of micropillars extracted from individual mineralised collagen fibres. This data was then used to identify micromechanically informed failure envelopes. The shear yield stress of the extrafibrillar matrix, associated with interfibrillar sliding, was identified as 137.65 MPa. The ratio between tensile and compressive yield stress in the Drucker-Prager yield criterion was 0.65. For both criteria apparent yield stress of the mineralised collagen fibril decreased to 25.3–31.4% when varying fibril orientation from 0° to 90°. This study identified yield properties of extrafibrillar matrix using an aligned mineralised tissue. The ability to obtain yield stress data and unloading stiffness from micropillar compression tests of MTLT at the level of the mineralised collagen fibril array and downscaling these into the EM mitigates against possible errors associated with macroscopic stiffness predictions and proved to be an invaluable advantage compared to similar modelling approaches. Results may help to improve computational models that may then be used in pre-clinical testing or development of personalised treatment strategies
