The relaxed-polar mechanism of locally optimal Cosserat rotations for an idealized nanoindentation and comparison with 3D-EBSD experiments

The rotation ${\rm polar}(F) \in {\rm SO}(3)$ arises as the unique orthogonal factor of the right polar decomposition $F = {\rm polar}(F) \cdot U$ of a given invertible matrix $F \in {\rm GL}^+(3)$. In the context of nonlinear elasticity Grioli (1940) discovered a geometric variational characterization of ${\rm polar}(F)$ as a unique energy-minimizing rotation. In preceding works, we have analyzed a generalization of Grioli's variational approach with weights (material parameters) $\mu > 0$ and $\mu_c \geq 0$ (Grioli: $\mu = \mu_c$). The energy subject to minimization coincides with the Cosserat shear-stretch contribution arising in any geometrically nonlinear, isotropic and quadratic Cosserat continuum model formulated in the deformation gradient field $F := \nabla\varphi: \Omega \to {\rm GL}^+(3)$ and the microrotation field $R: \Omega \to {\rm SO}(3)$. The corresponding set of non-classical energy-minimizing rotations $${\rm rpolar}^\pm_{\mu,\mu_c}(F) := \substack{{\rm argmin}\\ R\,\in\,{\rm SO(3)}} \Big\{ W_{\mu, \mu_c}(R\,;F) := \mu\, || {\rm sym}(R^TF - 1)||^2 + \mu_c\, ||{\rm skew}(R^TF - 1)||^2 \Big\}$$ represents a new relaxed-polar mechanism. Our goal is to motivate this mechanism by presenting it in a relevant setting. To this end, we explicitly construct a deformation mapping $\varphi_{\rm nano}$ which models an idealized nanoindentation and compare the corresponding optimal rotation patterns ${\rm rpolar}^\pm_{1,0}(F_{\rm nano})$ with experimentally obtained 3D-EBSD measurements of the disorientation angle of lattice rotations due to a nanoindentation in solid copper. We observe that the non-classical relaxed-polar mechanism can produce interesting counter-rotations. A possible link between Cosserat theory and finite multiplicative plasticity theory on small scales is also explored.Comment: 28 pages, 11 figure

Describing and Simulating Dynamic Reconfiguration in SystemC Exemplified by a Dedicated 3D Collision Detection Hardware

The ongoing trend towards development of parallel software and the increased flexibility of state-of-the-art programmable logic devices are currently converging in the field of reconfigurable hardware. On the other hand there is the traditional hardware market, with its increasingly short development cycles, which is mainly driven by high-level prototyping of products. To enable the design community to conveniently develop reconfigurable architectures in a short time-to-market, this thesis introduces the library ReChannel, which extends SystemC with advanced language constructs for high level reconfiguration modelling. It combines IP reuse and high-level modelling with reconfiguration. The proposed methodology was tested on a hierarchical FPGA-based 3D collision detection accelerator, is also presented. To enable implementation of such a complex algorithm in FPGA logic it had to be implemented using fixed-point arithmetic. Therefore a special method was derived that enables rounding of the used bounding-volumes without incurring the correctness of the non-intersection reports. This guarantees a correct overall result. A bound on the rounding error was derived that gives a measure of the number of false intersection reports, and thus on the run-time. A triangle and a quadrangle intersection test were implemented as the second</p

Solvation free Energy Predictions from molecular Dynamics Simulations by improved alchemical Pathways and optimized Force Field Parameters

The rapid development of affordable medications relies on the knowledge of suitable solvents for potential active pharmaceutical ingredients. Molecular simulations can be interpreted as computational experiments and may complement laboratory experiments, as they not only enable the calculation of thermophysical properties but also allow for an insight into a systems behavior on the molecular level. Relative solubilities can be predicted by using molecular simulations to calculate the Gibbs free energy of solvation ΔGsolv. We developed algorithms to reduce the required computational effort and increase the statistical precision by improved alchemical pathways. However, the agreement between ΔGsolv predictions from simulations and experimental data depends on the molecular models (force fields) used. To consider polarization effects, we combined partial charges derived by the IPolQ-Mod method with the General Amber Force Field (GAFF) and found a comparable ΔGsolv accuracy to GAFF and its default RESP charges for a large set of compounds in various solvents. We initiated a parameter optimization to improve the accuracy of GAFF/IPolQ-Mod and present our current results of the refitting process

GAFF/IPolQ-Mod+LJ-Fit: Optimized force field parameters for solvation free energy predictions

Rational drug design featuring explicit solubility considerations can greatly benefit from molecular dynamics simulations, as they allow for the prediction of the Gibbs free energy of solvation and thus relative solubilities. In our previous work (A. Mecklenfeld, G. Raabe. J. Chem. Theory Comput. 13 no. 12 (2017) 6266–6274), we have compared solvation free energy results obtained with the General Amber Force Field (GAFF) and its default restrained electrostatic potential (RESP) partial charges to those obtained by modified implicitly polarized charges (IPolQ-Mod) for an implicit representation of impactful polarization effects. In this work, we have adapted Lennard-Jones parameters for GAFF atom types in combination with IPolQ-Mod to further improve the accuracies of solvation free energy and liquid density predictions. We thereby focus on prominent atom types in common drugs. For the refitting, 357 respectively 384 systems were considered for free energies and densities and validation was performed for 142 free energies and 100 densities of binary mixtures. By the in-depth comparison of simulation results for default GAFF, GAFF with IPolQ-Mod and our new set of parameters, which we label GAFF/IPolQ-Mod+LJ-Fit, we can clearly highlight the improvements of our new model for the description of both relative solubilities and fluid phase behaviour.</p

Intracranial pressure pulse amplitude during changes in head elevation: a new parameter for determining optimum cerebral perfusion pressure?

Objective: During short-term postural changes, the factors determining the amplitude of intracranial pulse pressure (ICPPA) remain constant, except for cerebrovascular resistance (CVR). Therefore, it may be possible to draw conclusions from the ICPPA onto the cerebrovascular resistance (CVR) and thus the relative change in cerebral perfusion pressure (CPP). Methods: Age, sex, disease, Glasgow Coma Scale score, placement of ventricular drain, blood gas analysis, and parameters of airway management were prospectively recorded in 40 patients. The changes in intracranial pressure (ICP), CPP, mean arterial pressure (MAP), and ICPPA at head elevations of 0°, 30°, and 60° were measured and analyzed online. Status of cerebrovascular autoregulation was checked using the pressure-reactivity index (PRx). Results: Altogether 36 subjects fulfilled the study conditions. Three patients had positive PRx indicating disturbed autoregulation and were excluded. Thus, 33 were left for analysis (18 females and 15 males). All of them were sedated and mechanically ventilated with Glasgow Coma scores ranging from 3-8. During change in head elevation from 0° to 60°, we found a significant (p < 0.05) improvement of the ICP, an increase of the ICCPA, a reduction of the MAP, and a decrease in the CPP. Increasing ICPPA was linked to decreasing CPP (0° to 60°, r = −0.42, p < 0.05). Conclusions: Head elevation is an important part of the ICP and CPP therapy in neurointensive care. When searching for the patient-specific optimum upper body position, ICPPA may provide additional information. Providing that the cerebral autoregulation is intact, the lowest ICPPA of a patient corresponds to the individual upper body position with the highest CP

Towards Phenomenon-driven Design Science Research

We propose a research approach that extends phenomenon-driven research – which is primarily aimed at producing descriptive and explanatory knowledge about novel phenomena – with a design-oriented focus. The resulting approach aims to develop not only explanatory knowledge about novel phenomena but also prescriptive knowledge about how to face corresponding novel challenges and does so in conjunction and in a mutually reinforcing way. We illustrate our approach with two examples to understand and produce design principles for the novel phenomena of organising the IT setups in Scaled Agile organisations and Digital Innovation Units, respectively. Researchers can draw on our approach to understand novel phenomena and simultaneously produce knowledge that is also relevant to practitioners facing novel practical challenges resulting from these novel phenomena