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Emergence of non-trivial polar topologies hidden in singular stress field in SrTiO3: topological strain-field engineering
No full textDiscovery of non-trivial topological structures in condensed matters holds promise in novel technological paradigms. In contrast to ferromagnetics, where a variety of topological structures such as vortex, meron, and skyrmion have been discovered, only few topological structures can exist in ferroelectrics due to the lack of non-collinear interaction like the Dzyaloshinskii-Moriya interaction in ferromagnetics. Here, we demonstrate that polarization structures with a wide range of topological numbers (winding number n from -3 to +1) can be mechanically excited and designed by the mode-I singular stress field formed near the crack-tip in incipient ferroelectric SrTiO3. Our phase-field simulations based on Ginzburg-Landau theory successfully reveals that the near-tip polar topology is driven by the flexoelectric coupling with intense strain gradient at the tip, while a variety of the far-field topological structures is triggered by a collaboration between the electrostrictive and flexoelectric effects. The strain (gradient) field analysis further shows that the unexpected topological characters are implied in the singular stress field, which develops a variety of polar topologies near the crack tip. Therefore, our work provides a novel insight into the unusual interplay between mechanical- and ferroelectric-topologies, i.e. 'topological strain-field engineering', which paves the way to the mechanical design of functional topologies in the matter
Phase constitution, microstructure evolution and magnetocaloric properties of LaFe11.8Si1.2 strip-casting flakes
No full textThe phase composition, microstructural evolution and magnetocaloric properties of LaFe11.8S1.2 strip-casting flakes annealed at different temperatures and annealing times were investigated. The phase constitution and microstructure of strip-casting flakes are sensitive to annealing temperature, 1373K was found to be the optimum temperature for 1:13 phase formation. The microstructure and magnetocaloric properties changed with annealing time due to the diffusion of Fe and Si atoms. Samples annealed at 1373K for 10h reveal a high content (89.40 wt%) of the 1:13 phase and exhibited a maximum entropy change (-Delta S-M)(max) of 16.89J/(kg.K) at 187K. These annealed LaFe11.8S1.2 strip-casting flakes are ideal master alloys for powder metallurgy fabrication of the heat exchangers used inactive magnetic regenerator prototypes
Effects of bulky 2,2 '-substituents in dianhydrides on the microstructures and gas transport properties of thermally rearranged polybenzoxazoles
No full textThe chain interactions of hydroxyl polyimide (HPI) precursors, such as chain packing and 7C-7C stacking interactions, significantly affect the microstructures and gas separation performance of the resulting thermally rearranged polybenzoxazoles (TR-PBOs). In this study, HPIs with various 2,2'-substituents in their anhydrides (BPDA-AP, PBPDA-AP, and 12FPBPDA-AP) were prepared through polycondensation of three dianhydrides (4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2'-diphenyl-4,4',5,5'-biphenyltetracarboxylic dianhydride (PBPDA), and 2,2'-bis(3 '',5 ''-ditrifluommethylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (12FPBPDA)) with 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AP). The dihedral angles and rotational barriers for PBPDA and 12FPBPDA were considerably larger than those for BPDA. Thus, the inter- and intra-molecular chain interactions were more pronounced for BPDA-AP than for PBPDA-AP and 12FPBPDA-AP. Consequently, the glass transition and TR temperatures of the HPIs were in the order of BPDA-AP > PBPDA-AP > 12FPBPDA-AP, whereas fractional free volume (FFV) and interchain distances followed the opposite trend. After TR, the FFV and interchain distances of the TR-PBO from BPDA-AP increased more than those from PBPDA-AP and 12FPBPDA-AP, whereas the pi-pi stacking interactions in BPDA-AP were well maintained. Consequently, BPDA-AP-450 exhibited the highest increase in gas permeability relative to its HPI precursor but the poorest plasticization resistance among fully converted TR-PBOs. This work demonstrated that chain packing played a crucial role in the TR behavior, microstructures, and gas transport properties of TR-PBOs
The corrosion behaviors of multilayer diamond-like carbon coatings: influence of deposition periods and corrosive medium (vol 6, pg 28570, 2016)
No full textLespedeza danxiaensis (Fabaceae), a new species from Guangdong, China, based on molecular and morphological data
No full textLespedeza danxiaensis (Fabaceae), a new species from Danxiashan National Nature Reserve in Guangdong Province, is described and illustrated. The new species is morphologically similar to Lespedeza pilosa, but it can be easily distinguished by its thin leathery leaflets and long peduncles. Phylogenetic analysis based on ITS confirmed that the new species belongs to Lespedeza subg. Macrolespedeza. The new species is the first known species of Lespedeza endemic to Danxia landform and is currently only known from Mount Danxia, Guangdong
Immune Response to Silk Sericin-Fibroin Composites: Potential Immunogenic Elements and Alternatives for Immunomodulation
No full textThe unique properties of silk proteins (SPs), particularly silk sericin (SS) and silk fibroin (SF), have attracted attention in the design of scaffolds for tissue engineering over the past decades. Since SF has good mechanical properties, while SS displays bioactivity, scaffolds combining both proteins should exhibit complementary properties enhancing the potential of these materials. Unfortunately, SS-SF composites can generate chronic immune responses and their immunogenic element is not completely clear. The potential of SS-SF composites in tissue engineering, elements which may contribute to their immunogenicity, and alternatives for their preparation and design, to modulate the immune response and take advantage of their useful properties, are discussed in this review. It is known that SS can enhance beta-sheet formation in SF, which may act as hydrophobic regions with a strong affinity for adsorption proteins inducing the chronic recruitment of inflammatory cells. Therefore, tailoring the exposure of hydrophobic regions at the scaffold surface should represent a viable strategy to modulate the immune response. This can be achieved by coating SS-SF composites with SS or other hydrophilic polymers, to take advantage of their antibiofouling properties. Research is still needed to realize the full potential of these composites for tissue engineering
Crystal Orientations Dependent Polarization Reversal in Ferroelectric PbZr0.2Ti0.8O3 Thin Films for Multilevel Data Storage Applications
No full textDeterministic creation of multiple ferroelectric states with variant values of polarization in ferroelectric thin films is promising for multilevel data storage applications. However, the intrinsic bi-stability of ferroelectric switching makes it challenging to achieve. The deterministic ferroelectric states can be achieved by multistep switching through various means such as controlling domain structure and switching by inducing local disorder, and also by crystal orientations. However, to determine the effect of crystal directions on the stability of multistep polarization reversal requires investigation on different crystal directions. A high-throughput approach namely combinatorial substrate epitaxy (CSE) is utilized to fabricate La0.7Sr0.3MnO3 (LSMO) polycrystalline substrate to grow PbZr0.2Ti0.8O3 (PZT) films epitaxially with different crystal directions in a single sample. The polarization reversal area is determined as a function of applied voltage along different . From the analysis, it is found that all exhibit multilevel polarization states due to multistep switching events. Further the degree of multilevel polarization states shows a sawtooth-like oscillatory behavior with increase in [111] miscut angle, which is attributed to influence of local disorder on the domain structure. Therefore, the realization of multilevel data storage device based on deterministic polarization reversal can be achieved with appropriate crystal directed thin films