The enhancement of the functional properties of materials at reduced dimensions is crucial for continuous advancements in nanoelectronic applications. Here, we report that the scale reduction leads ...to the emergence of an important functional property, ferroelectricity, challenging the long-standing notion that ferroelectricity is inevitably suppressed at the scale of a few nanometers. A combination of theoretical calculations, electrical measurements, and structural analyses provides evidence of room-temperature ferroelectricity in strain-free epitaxial nanometer-thick films of otherwise nonferroelectric strontium titanate (SrTiO3). We show that electrically induced alignment of naturally existing polar nanoregions is responsible for the appearance of a stable net ferroelectric polarization in these films. This finding can be useful for the development of low-dimensional material systems with enhanced functional properties relevant to emerging nanoelectronic devices.
High-β_{θe} (a ratio of the electron thermal pressure to the poloidal magnetic pressure) steady-state long-pulse plasmas with steep central electron temperature gradient are achieved in the ...Experimental Advanced Superconducting Tokamak. An intrinsic current is observed to be modulated by turbulence driven by the electron temperature gradient. This turbulent current is generated in the countercurrent direction and can reach a maximum ratio of 25% of the bootstrap current. Gyrokinetic simulations and experimental observations indicate that the turbulence is the electron temperature gradient mode (ETG). The dominant mechanism for the turbulent current generation is due to the divergence of ETG-driven residual flux of current. Good agreement has been found between experiments and theory for the critical value of the electron temperature gradient triggering ETG and for the level of the turbulent current. The maximum values of turbulent current and electron temperature gradient lead to the destabilization of an m/n=1/1 kink mode, which by counteraction reduces the turbulence level (m and n are the poloidal and toroidal mode number, respectively). These observations suggest that the self-regulation system including turbulence, turbulent current, and kink mode is a contributing mechanism for sustaining the steady-state long-pulse high-β_{θe} regime.
Abstract Objective Multi-mode universal adhesives offer clinicians the choice of using the etch-and-rinse technique, selective enamel etch technique or self-etch technique to bond to tooth ...substrates. The present study examined the short-term in vitro performance of five universal adhesives bonded to human coronal dentine. Methods Two hundred non-carious human third molars were assigned to five groups based on the type of the universal adhesives (Prime&Bond Elect, Scotchbond Universal, All-Bond Universal, Clearfil Universal Bond and Futurabond U). Two bonding modes (etch-and-rinse and self-etch) were employed for each adhesive group. Bonded specimens were stored in deionized water for 24 h or underwent a 10,000-cycle thermocycling ageing process prior to testing ( N = 10). Microtensile bond testing (μTBS), transmission electron microscopy (TEM) of resin–dentine interfaces in non-thermocycled specimens and scanning electron microscopy (SEM) of tracer-infused water-rich zones within hybrid layers of thermocycled specimens were performed. Results Both adhesive type and testing condition (with/without thermocycling) have significant influences on μTBS. The use of each adhesive in either the etch-and-rinse or self-etch application mode did not result in significantly different μTBS to dentine. Hybrid layers created by these adhesives in the etch-and-rinse bonding mode and self-etch bonding mode were ∼5 μm and ≤0.5 μm thick respectively. Tracer-infused regions could be identified within the resin–dentine interface from all the specimens prepared. Conclusion The increase in versatility of universal adhesives is not accompanied by technological advances for overcoming the challenges associated with previous generations of adhesives. Therapeutic adhesives with bio-protective and bio-promoting effects are still lacking in commercialized adhesives. Clinical significance Universal adhesives represent manufacturers’ attempt to introduce versatility in product design via adaptation of a single-bottle self-etch adhesive for other application modes without compromising its bonding effectiveness.
Stimulation with ultrafast light pulses can realize and manipulate states of matter with emergent structural, electronic and magnetic phenomena. However, these non-equilibrium phases are often ...transient and the challenge is to stabilize them as persistent states. Here, we show that atomic-scale PbTiO
/SrTiO
superlattices, counterpoising strain and polarization states in alternate layers, are converted by sub-picosecond optical pulses to a supercrystal phase. This phase persists indefinitely under ambient conditions, has not been created via equilibrium routes, and can be erased by heating. X-ray scattering and microscopy show this unusual phase consists of a coherent three-dimensional structure with polar, strain and charge-ordering periodicities of up to 30 nm. By adjusting only dielectric properties, the phase-field model describes this emergent phase as a photo-induced charge-stabilized supercrystal formed from a two-phase equilibrium state. Our results demonstrate opportunities for light-activated pathways to thermally inaccessible and emergent metastable states.
Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of ...characterization techniques, and simulations, we observe that in PbTiO
/SrTiO
superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a
/a
phase. At room temperature, the coexisting vortex and ferroelectric phases form a mesoscale, fibre-textured hierarchical superstructure. The vortex phase possesses an axial polarization, set by the net polarization of the surrounding ferroelectric domains, such that it possesses a multi-order-parameter state and belongs to a class of gyrotropic electrotoroidal compounds. Finally, application of electric fields to this mixed-phase system permits interconversion between the vortex and the ferroelectric phases concomitant with order-of-magnitude changes in piezoelectric and nonlinear optical responses. Our findings suggest new cross-coupled functionalities.
The complex interplay of spin, charge, orbital and lattice degrees of freedom provides a plethora of exotic phases and physical phenomena. In recent years, complex spin topologies have emerged as a ...consequence of the electronic band structure and the interplay between spin and spin-orbit coupling in materials. Here we produce complex topologies of electrical polarization--namely, nanometre-scale vortex-antivortex (that is, clockwise-anticlockwise) arrays that are reminiscent of rotational spin topologies--by making use of the competition between charge, orbital and lattice degrees of freedom in superlattices of alternating lead titanate and strontium titanate layers. Atomic-scale mapping of the polar atomic displacements by scanning transmission electron microscopy reveals the presence of long-range ordered vortex-antivortex arrays that exhibit nearly continuous polarization rotation. Phase-field modelling confirms that the vortex array is the low-energy state for a range of superlattice periods. Within this range, the large gradient energy from the vortex structure is counterbalanced by the corresponding large reduction in overall electrostatic energy (which would otherwise arise from polar discontinuities at the lead titanate/strontium titanate interfaces) and the elastic energy associated with epitaxial constraints and domain formation. These observations have implications for the creation of new states of matter (such as dipolar skyrmions, hedgehog states) and associated phenomena in ferroic materials, such as electrically controllable chirality.
Ubiquitously distributed in different plant species, plant lectins are highly diverse carbohydrate‐binding proteins of non‐immune origin. They have interesting pharmacological activities and ...currently are of great interest to thousands of people working on biomedical research in cancer‐related problems. It has been widely accepted that plant lectins affect both apoptosis and autophagy by modulating representative signalling pathways involved in Bcl‐2 family, caspase family, p53, PI3K/Akt, ERK, BNIP3, Ras‐Raf and ATG families, in cancer. Plant lectins may have a role as potential new anti‐tumour agents in cancer drug discovery. Thus, here we summarize these findings on pathway‐ involved plant lectins, to provide a comprehensive perspective for further elucidating their potential role as novel anti‐cancer drugs, with respect to both apoptosis and autophagy in cancer pathogenesis, and future therapy.
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A multiscale model is developed to investigate the evolution mechanisms of site-specific grain structures during additive manufacturing (AM) of metallic alloys, using the selective ...electron beam melting (SEBM) fabrication of Ti-6Al-4V as an example. Specifically, finite-element method is utilized to predict the thermal response at macroscale during SEBM, and the extracted thermal information is then input into a temperature-dependent phase-field model to simulate the grain growth at mesoscale. The grain epitaxial growth, grain selection, grain nucleation and layer-by-layer manufacturing fashion are incorporated, in order to accurately predict grain structure development and relevant physical processes during AM. It is found that, the development of the predominant grain structures in the thick and thin walls, i.e., the large vertical columnar β//Nz grains and slanted columnar grains with various grain orientations, respectively, can be attributed to the competition and collaboration between the thermal gradient and the crystallographically preferred grain growth, as shown from the different growth stages in the simulations. Good agreements in the final grain structures and textures are achieved between the experimental observations and numerical simulations. The present study potentially offers valuable insights and guidance toward designing AM conditions to tailor the grain structures and textures.
A fast Fourier transform (FFT) based computational approach integrating phase-field method (PFM) and crystal plasticity (CP) is proposed to model recrystallization of plastically deformed ...polycrystals in three dimensions (3-D). CP at the grain level is employed as the constitutive description to predict the inhomogeneous distribution of strain and stress fields after plastic deformation of a polycrystalline aggregate while the kinetics of recrystallization is obtained employing a PFM in the plastically deformed grain structure. The elasto-viscoplastic equilibrium is guaranteed during each step of temporal phase-field evolution. Static recrystallization involving plasticity during grain growth is employed as an example to demonstrate the proposed computational framework. The simulated recrystallization kinetics is compared using the classical Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. This study also gives us a new computational pathway to explore the plasticity-driven evolution of 3D microstructures.
The unique immunomodulatory properties of mesenchymal stem cells (MSCs) make them an invaluable cell type for the repair of tissue/ organ damage caused by chronic inflammation or autoimmune ...disorders. Although they hold great promise in the treatment of immune disorders such as graft versus host disease (GvHD) and allergic disorders, there remain many challenges to overcome before their widespread clinical application. An understanding of the biological properties of MSCs will clarify the mechanisms of MSC-based transplantation for immunomodulation. In this review, we summarize the preclinical and clinical studies of MSCs from different adult tissues, discuss the current hurdles to their use and propose the future development of pluripotent stem cell-derived MSCs as an approach to immunomodulation therapy.
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