Semi‐Solid Processing of Metal Alloys

Semi‐solid metal casting is an innovative technology for the production of near‐net‐shape parts with demanding mechanical properties. The paper describes different processing routes and materials for semi‐solid‐metal casting (SSM), which have been investigated and also partially developed at the Foundry‐Institute of Aachen University. The standard thixocasting process for aluminium, highly reactive magnesium alloys and steel alloys with high melting points was investigated under variation of a wide range of process parameters. Specially adapted pre‐material production and reheating methods were developed for different materials and their application and future potential is pointed out. The thixocasting experiments were executed on a modified high pressure die‐casting machine with a specially designed “step‐die” providing wall thicknesses from 0.5 to 25 mm. The mechanical properties were tested in dependence of the wall thickness and the metal velocity. The results of these examination show high tensile strength values in combination with very good elongations. The rheocasting process is a new SSM‐forming method with liquid melt as feed‐stock and a high recycling potential. The research results of RCP‐technology (Rheo‐Container‐Process) invented at the Foundry‐Institute and of the Cooling‐Channel‐Process for aluminium and magnesium alloys are promising and are presented in this paper. Studies on semi‐solid processing of magnesium alloys and mixtures of them were conducted by Thixomolding^TM. To establish the most adequate process parameters, the temperature and the mixture relations were varied. Using a mould for tensile test specimens, the mechanical properties and the microstructure evolution could be evaluated. The chemical composition of the different phases was determined using SEM and EDX technologies. Evaluations of the flowing properties were conducted using a spiral mould with a total length of 2m and a cross section of 20mm x 1.5mm.     

Electrically Tunable Nanoporous Carbon Hybrid Actuators

A novel nanoporous carbon/electrolyte hybrid material is reported for use in actuation. The nanoporous carbon matrix provides a 3D network that combines mechanical strength, light weight, and low cost with an extremely high surface area. In contrast to lower dimensional nanomaterials, the nanoporous carbon matrix can be prepared in the form of macroscopic monolithic samples that can be loaded in compression. The hybrid material is formed by infiltrating the free internal pore volume of the carbon with an electrolyte. Actuation is prompted by polarizing the internal interfaces via an applied electric bias. It is found that the strain amplitude is proportional to the Brunauer‐Emmett‐Teller (BET) mass specific surface area, with reversible volume strain amplitudes up to the exceptionally high value of 6.6%. The mass‐specific strain energy density compares favorably to reported values for piezoceramics and for nanoporous metal actuators.     

Mathematical models of the transitions between endocrine therapy responsive and resistant states in breast cancer

Endocrine therapy, targeting the oestrogen receptor pathway, is the most common treatment for oestrogen receptor-positive breast cancers. Unfortunately, these tumours frequently develop resistance to endocrine therapies. Among the strategies to treat resistant tumours are sequential treatment (in which second-line drugs are used to gain additional responses) and intermittent treatment (in which a ‘drug holiday’ is imposed between treatments). To gain a more rigorous understanding of the mechanisms underlying these strategies, we present a mathematical model that captures the transitions among three different, experimentally observed, oestrogen-sensitivity phenotypes in breast cancer (sensitive, hypersensitive and independent). To provide a global view of the transitions between these phenotypes, we compute the potential landscape associated with the model. We show how this oestrogen response landscape can be reshaped by population selection, which is a crucial force in promoting acquired resistance. Techniques from statistical physics are used to create a population-level state-transition model from the cellular-level model. We then illustrate how this population-level model can be used to analyse and optimize sequential and intermittent oestrogen-deprivation protocols for breast cancer. The approach used in this study is general and can also be applied to investigate treatment strategies for other types of cancer.     

Orientation Gradients at Boundaries in Micron‐Sized Bicrystals

In micron‐sized Ni bicrystals, after compression tests, orientation gradients are measured by electron back scattering diffraction (EBSD). The results clearly show that EBSD can be used to study dislocation pile‐ups at boundaries. Using bicrystals with single and multiple slip orientations our results show that with decreasing the size of the pillars the orientation changes due to cross‐slip decreases and the orientation changes at the boundary increases. This directly indicates a change in the hardening mechanism when the probability of dislocation–dislocation interaction decreases due to source‐limited plasticity in the bicrystals with diameters below approximately two microns.     

Model-based test case generation and prioritization: a systematic literature review

Software and Systems Modeling - Model-based test case generation (MB-TCG) and prioritization (MB-TCP) utilize models that represent the system under test (SUT) for test generation and...     

Electrospinning and Imaging

Polymer processing via electrospinning is a cost effective and scalable method for preparing nanofibers with industrial, electrical, and biomedical applications, particularly tissue engineering and drug delivery. Characterization methods for these fibers include microscopy techniques for vitro surface morphology information, spectroscopy methods to determine in vitro chemical composition, and medical imaging tools for in vivo assessment of morphology and efficacy of implanted material. The focus of this paper is be on recent applications for electrospun nanofibers, in vitro characterization methods, and medical imaging modalities that can be used for in vivo assessment of the fibers, as well as insights in how to adapt existing techniques toward the characterization of electrospun materials.