Effect of switching stresses on domain evolution during quasi-static crack growth in a ferroelastic single crystal

The present paper demonstrates the effect of switching stresses on domain evolution and fracture toughening during quasi-static crack growth in elastically isotropic ferroelastic single crystals with transversally isotropic ferroelastic strains. With a simple switching algorithm and crack propagation procedure, domain evolution is simulated in an exemplary material with semi-infinite crack under mode I loading, starting from a mono-domain configuration. Domain reorientation is found to be strongly affected by switching stresses, which therefore have to be considered in the context of domain evolution modelling and fracture toughening. Before the onset of crack growth a needle-like domain is formed at the tip of the stationary crack, but this does not effect the crack tip stress intensity factor. Elongation of this domain during the onset of crack growth causes a large increase of the fracture toughness. Domain separation in a later stage results in toughness reduction. The subsequent domain evolution indicates a periodic formation of needle-like domains as observed in soft ferroelastic materials.     

Influence of short-term heat treatment on the microstructure and mechanical properties of EN AW-6060 T4 extrusion profiles—Part B

In the automotive industry aluminium and its corresponding semi-finished products contribute an essential part to the aim of weight reduction in car body structures. Aluminium alloys of the 6000 series with Mg and Si contents are preferred because of the possibility to increase strength by ageing processes. However, the cold formability in comparison to other materials like mild steels is quite low and due to this, complex parts are only producible at higher temperatures. Therefore, the so called Tailor Heat Treatment was developed to improve the cold formability of aluminium alloys. In this approach, a short-term heat treatment is conducted to achieve a local softening of the material due to dissolution of Mg and Si clusters (retrogression). This effect is used to improve the material flow, relief critical forming zones and enhance the overall formability of the material. Afterwards, strength can be increased again by ageing processes. However, up till now a holistic process understanding, taking into account all process parameters as well as a microstructural explanation is missing. Therefore, the focus of the fundamental investigations lies on connections between the mechanical properties and short-term heat treatment with industry-relevant heating rates as well as natural and artificial ageing process. Conclusively, the evolution of the mechanical properties with regard to the natural ageing process is compared with findings of DSC analysis, which were discussed in Part A. Based on these results, a process window is derived for the subsequent forming process and the final mechanical properties of the final part in dependency of the forming history as well as the artificial ageing process, are identified.     

Cancer-Associated Fibroblasts Modify the Response of Prostate Cancer Cells to Androgen and Anti-Androgens in Three-Dimensional Spheroid Culture

Androgen receptor (AR) targeting remains the gold standard treatment for advanced prostate cancer (PCa); however, treatment resistance remains a major clinical problem. To study the therapeutic effects of clinically used anti-androgens we characterized herein a tissue-mimetic three-dimensional (3D) in vitro model whereby PCa cells were cultured alone or with PCa-associated fibroblasts (CAFs). Notably, the ratio of PCa cells to CAFs significantly increased in time in favor of the tumor cells within the spheroids strongly mimicking PCa in vivo. Despite this loss of CAFs, the stromal cells, which were not sensitive to androgen and even stimulated by the anti-androgens, significantly influenced the sensitivity of PCa cells to androgen and to the anti-androgens bicalutamide and enzalutamide. In particular, DuCaP cells lost sensitivity to enzalutamide when co-cultured with CAFs. In LAPC4/CAF and LNCaP/CAF co-culture spheroids the impact of the CAFs was less pronounced. In addition, 3D spheroids exhibited a significant increase in E-cadherin and substantial expression of vimentin in co-culture spheroids, whereas AR levels remained unchanged or even decreased. In LNCaP/CAF spheroids we further found increased Akt signaling that could be inhibited by the phosphatidyl-inositol 3 kinase (PI3K) inhibitor LY294002, thereby overcoming the anti-androgen resistance of the spheroids. Our data show that CAFs influence drug response of PCa cells with varying impact and further suggest this spheroid model is a valuable in vitro drug testing tool.     

Identification of New QTLs for Dietary Fiber Content in Aegilops biuncialis

Grain dietary fiber content is an important health-promoting trait of bread wheat. A dominant dietary fiber component of wheat is the cell wall polysaccharide arabinoxylan and the goatgrass Aegilops biuncialis has high β-glucan content, which makes it an attractive gene source to develop wheat lines with modified fiber composition. In order to support introgression breeding, this work examined genetic variability in grain β-glucan, pentosan, and protein content in a collection of Ae. biuncialis. A large variation in grain protein and edible fiber content was revealed, reflecting the origin of Ae. biuncialis accessions from different eco-geographical habitats. Association analysis using DArTseq-derived SNPs identified 34 QTLs associated with β-glucan, pentosan, water-extractable pentosan, and protein content. Mapping the markers to draft chromosome assemblies of diploid progenitors of Ae. biuncialis underlined the role of genes on chromosomes 1M^b, 4M^b, and 5M^b in the formation of grain β-glucan content, while other QTLs on chromosome groups 3, 6, and 1 identified genes responsible for total- and water-extractable pentosan content. Functional annotation of the associated marker sequences identified fourteen genes, nine of which were identified in other monocots. The QTLs and genes identified in the present work are attractive targets for chromosome-mediated gene transfer to improve the health-promoting properties of wheat-derived foods.     

De-Brominating Flame-Retardant Polystyrene by Utilizing Basic Oxides in Chemical Recycling

Chemical recycling is a method to close the recycling loop for polymers. This is particularly applicable for polystyrene (PS), where the monomer styrene is directly formed by depolymerization and subsequently utilized for the production of new PS. However, some waste sources contain critical additives as legacies, such as brominated flame retardants. There is a profound need to remove these substances from the material, as current thresholds do not allow such additives above certain limits in new products. In this work we present the beneficial use of basic oxides during the thermal depolymerization of a mixture of PS and 1,2,5,6,9,10-hexabromocyclododecane. It was demonstrated that especially barium oxide and calcium oxide allowed the reduction of bromine up to 96 % in the crude styrene oil.     

Investigations on the polymorphism of K4CaSi6O15 at elevated temperatures

In the present study, single crystals and polycrystalline material of K₄CaSi₆O₁₅ were prepared from solid-state reactions between stoichiometric mixtures of the corresponding oxides/carbonates. Heat capacity (C_p) measurements above room temperature using a differential scanning calorimeter indicated that two thermal effects occurred at approximately T₁ = 462 K and T₂ = 667 K, indicating the presence of structural phase transitions. The standard third-law entropy of K₄CaSi₆O₁₅ was determined from low-temperature C_p’s measured by relaxation calorimetry using a Physical Properties Measurement System and amounts to S°(298K) = 524.3 ± 3.7 J·mol⁻¹·K⁻¹. For the 1^st transition, the enthalpy change ΔH^tr1 = 1.48 kJ·mol and the entropy change ΔS^tr1 = 3.25 J·mol⁻¹·K⁻¹, whereas ΔH^tr2 = 3.33 kJ·mol⁻¹ and ΔS^tr2 = 5.23 J·mol⁻¹·K⁻¹ were determined for the 2^nd transition. The compound was further characterized by in-situ single-crystal X-ray diffraction between ambient temperature and 1063 K. At 773 K, the high-temperature phase stable above T₂ has the following basic crystallographic data: monoclinic symmetry, space group P2₁/c, a = 6.9469(4) Å, b = 9.2340(5) Å, c = 12.2954(6) Å, β = 93.639(3)°, V = 787.13(7) ų, Z = 2. It belongs to the group of interrupted framework silicates and is based on tertiary (Q³-type) [SiO₄]-tetrahedra. Together with the octahedrally coordinated Ca-cations, a three-dimensional mixed polyhedral network structure is formed, in which the remaining K-ions provide charge balance by occupying voids within the net. The intermediate temperature modification stable between T₁ and T₂ shows a (3+2)-dimensional incommensurately modulated structure that is characterized by the following q-vectors: q₁ = (0.057, 0.172, 0.379), q₂ = (-0.057, 0.172, -0.379). The crystal structures of the high- and the previously studied ambient temperature polymorph (space group Pc) are topologically equivalent and show a group-subgroup relationship. The index of the low- in the high-symmetry group is six and involves both, losses in translation as well as point group symmetry. The distortion is based on shifts of the different atom species and tilts of the 4- and 6-fold coordination polyhedra. Actually, for some of the oxygen atoms, the displacements exceed 0.5 Å. A more detailed analysis of the distortions relating to both structures has been performed using mode analysis, which revealed that the primary distortion mode transforms according to the Λ₁ irreducible representation of P2₁/c. However, other modes with smaller distortion amplitudes are also involved.     

Reel-to-reel wet coating as an efficient up-scaling technique for the production of bulk-heterojunction polymer solar cells

In this paper we report for the first time very promising results in up-scaling coating processes for thin flexible polymer solar cell (PSC) application. Two functional layers for PSC devices, the conducting poly- (3,4-ethylene-dioxythiophene):polystyrenesulfonate and the photoactive one (poly-3-hexylthiophene/[6,6]-phenyl-C61-butyric acid methyl ester), could be successfully prepared by continuous reel-to-reel (R2R) wet coating of low-viscosity solutions and dispersions on ITO-coated PET substrates. A laboratory coating machine (LBA-200) was used for R2R slot die coating (1-4 m/min). Out of this R2R-produced bilayer-system PSCs were accomplished and tested. Light power conversion efficiencies up to 1.7% under AM 1.5 illumination (100 mW/cm²) could be obtained.     

Electron Holography at Atomic Dimensions—Present State

An electron microscope is a wave optical instrument where the object information is carried by an electron wave. However, an important information, the phase of the electron wave, is lost, because only intensities can be recorded in a conventional electron micrograph. Off-axis electron holography solves this “phase problem” by encoding amplitude and phase information in an interference pattern, the so-called hologram. After reconstruction, a rather unrestricted wave optical analysis can be performed on a computer. The possibilities as well as the current limitations of off-axis electron holography at atomic dimensions are discussed, and they are illustrated at two applications of structure characterization of ε-NbN and YBCO-1237. Finally, an electron microscope equipped with a Cs-corrector, a monochromator, and a Möllenstedt biprism is outlined for subangstrom holography.