Charged domain walls in ferroelectrics exhibit a quasi-two-dimensional conduction path coupled to the surrounding polarization. They have been proposed for use as non-volatile memory with ...non-destructive operation and ultralow energy consumption. Yet the evolution of domain walls during polarization switching makes it challenging to control their location and conductance precisely, a prerequisite for controlled read-write schemes and for integration in scalable memory devices. Here, we explore and reversibly switch the polarization of square BiFeO
nanoislands in a self-assembled array. Each island confines cross-shaped, charged domain walls in a centre-type domain. Electrostatic and geometric boundary conditions induce two stable domain configurations: centre-convergent and centre-divergent. We switch the polarization deterministically back and forth between these two states, which alters the domain wall conductance by three orders of magnitude, while the position of the domain wall remains static because of its confinement within the BiFeO
islands.
The electronic conductivities of ferroelectric domain walls have been extensively explored over the past decade for potential nanoelectronic applications. However, the realization of logic devices ...based on ferroelectric domain walls requires reliable and flexible control of the domain-wall configuration and conduction path. Here, we demonstrate electric-field-controlled stable and repeatable on-and-off switching of conductive domain walls within topologically confined vertex domains naturally formed in self-assembled ferroelectric nano-islands. Using a combination of piezoresponse force microscopy, conductive atomic force microscopy, and phase-field simulations, we show that on-off switching is accomplished through reversible transformations between charged and neutral domain walls via electric-field-controlled domain-wall reconfiguration. By analogy to logic processing, we propose programmable logic gates (such as NOT, OR, AND and their derivatives) and logic circuits (such as fan-out) based on reconfigurable conductive domain walls. Our work might provide a potentially viable platform for programmable all-electric logic based on a ferroelectric domain-wall network with low energy consumption.
Iridescence in nematics Zeng, Minxiang; King, Daniel; Huang, Dali ...
Proceedings of the National Academy of Sciences - PNAS,
09/2019, Letnik:
116, Številka:
37
Journal Article
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Odprti dostop
Photonic materials with positionally ordered structure can interact strongly with light to produce brilliant structural colors. Here, we found that the nonperiodic nematic liquid crystals of ...nanoplates can also display structural color with only significant orientational order. Owing to the loose stacking of the nematic nanodiscs, such colloidal dispersion is able to reflect a broad-spectrum wavelength, of which the reflection color can be further enhanced by adding carbon nanoparticles to reduce background scattering. Upon the addition of electrolytes, such vivid colors of nematic dispersion can be fine-tuned via electrostatic forces. Furthermore, we took advantage of the fluidity of the nematic structure to create a variety of colorful arts. It was expected that the concept of implanting nematic features in photonic structure of lyotropic nanoparticles may open opportunities for developing advanced photonic materials for display, sensing, and art applications.
Room-temperature skyrmions in magnetic multilayers are considered to be promising candidates for the next-generation spintronic devices. Several approaches have been developed to control skyrmions, ...but they either cause significant heat dissipation or require ultrahigh electric fields near the breakdown threshold. Here, we demonstrate electric-field control of skyrmions through strain-mediated magnetoelectric coupling in ferromagnetic/ferroelectric multiferroic heterostructures. We show the process of non-volatile creation of multiple skyrmions, reversible deformation and annihilation of a single skyrmion by performing magnetic force microscopy with in situ electric fields. Strain-induced changes in perpendicular magnetic anisotropy and interfacial Dzyaloshinskii-Moriya interaction strength are characterized experimentally. These experimental results, together with micromagnetic simulations, demonstrate that strain-mediated magnetoelectric coupling (via strain-induced changes in both the perpendicular magnetic anisotropy and interfacial Dzyaloshinskii-Moriya interaction is responsible for the observed electric-field control of skyrmions. Our work provides a platform to investigate electric-field control of skyrmions in multiferroic heterostructures and paves the way towards more energy-efficient skyrmion-based spintronics.
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•Synthesis of Cu2+ responsive thermo-sensitive microgel (PNV).•Cu2+ softened and homogenized PNV microstructure with a great VPTT shift.•Demonstration of “smart” foams tunable by Cu2+ ...but insensitive to other cations.•Responsive foam destabilization was dominated by surface shear viscoelasticity.
Froth flotation has been a key chemical process extensively used in the recovery of heavy metal ions (e.g. Cu2+) from contaminated water, while often criticized by a secondary pollution of the added collectors, and a less selectivity to specific ions since the ion removal by particles is independent from the post-step of particle flotation. To facilitate the industrial operation, a “smart” flotation with foams responsively stabilized after selective adsorption of target ions from competitive ions are highly desired. In the current study, “smart” foams stabilized by Cu2+ responsive microgels were presented as a proof-of-concept.
Firstly, a Cu2+-responsive thermo-sensitive poly (N-Isopropylacrylamide-co-Vinyl imidazole) (PNV) microgel with a hydrodynamic radius (Rh) ∼ 334 nm and a fuzziness ∼ 37.2 nm was synthesized. Cu2+-imidazole complexation was demonstrated to enhance the microgel swelling with a softer and more homogenous microstructure, having the Rh increased by 30–50 nm for 0.005 M to 0.25 M Cu2+ and a significant volume phase transition temperature (VPTT) shift from ∼ 40 °C to ∼ 50 °C for 0.005 M Cu2+, ∼60 °C for 0.05 M Cu2+ and ≫ 60 °C for 0.25 M Cu2+.
Secondly, temperature responsive foams with a ultra-stability below VPTT of the microgel and a rapid collapse above the VPTT were readily produced based on PNV microgels. Cu2+ complexation enabled a modulation of temperature responsiveness of the foams, able to maintain a good foam stability in high temperatures (e.g. a life time > 6 h at 45 °C for 0.25 M Cu2+) where foams rapidly collapsed for other cations (e.g. ∼ 2 min, ∼10 min and ∼ 15 min at 45 °C for Na+, Mg2+, Zn2+, respectively), showing significance for selective recovery of Cu2+ from competitive ions via flotation.
Furthermore, an interfacial study at air–water interface revealed a better surface activity of Cu2+ -complexed PNV microgel with a less temperature dependence. An abrupt reduction of interfacial rheology around the VPTT with a G’s(25 °C)/G’s(70 °C) ratio ∼ 300.1 observed was believed to be the main reason of the responsive foam destabilization for PNV2, which was avoidable by entanglements between Cu2+-complexed PNV microgels, giving a G’s(25 °C)/G’s(70 °C) ratio ∼ 1.68. Ultimately, the good Cu2+ selectivity of PNV2 microgel was well demonstrated in mixed solutions of competitive ions Na+, Mg2+, Zn2+ in terms of Cu2+ sorption, particle swelling and foam stabillity. This study demonstrated a responsive Pickering foam stabilized by a Cu2+ tunable microgel, laying foundations to develop microgel-based flotation as a smart and green technology for Cu2+ recovery.
In a harsh environment, function aggregation of air-ground integrated network service function chaining (SFC) deployment can easily cause network load imbalance, which affects the network security ...and reliability. In this study, a task-similarity-based virtual network function (VNF) aggregation scheme was proposed. It considered air-ground network resource consumption and load balance before SFC mapping. A model for selecting VNFs to be aggregated based on task similarity was built. The tasks were classified based on their similarity. Furthermore, the VNFs to be aggregated were selected within the class under the constraints of the underlying physical resources. Load balancing was achieved by adjusting the similarity threshold. Moreover, an SFC mapping selection scheme based on network resource awareness was used to obtain the most suitable physical nodes for single-chain and multi-chain mapping according to various attributes of physical network nodes. The simulation results indicated that the proposed scheme with a better load balance design outperformed existing works on VNF aggregation. We also demonstrated that the task-similarity-based scheme was resource-consumption efficient and effective.
As an important thermosetting material, flame-retardant epoxy resin has various applications in the aerospace, chemical, and electronics industry, and other fields. However, the flame retardancy of ...epoxy resins is often improved at the expense of mechanical performance. The contradiction between flame retardancy and mechanical properties seriously impedes the practical applications of epoxy resin (EP). Herein, iron-loaded polydopamine functionalized montmorillonite (D-Mt-Fe
), which was prepared by dopamine, iron chloride and montmorillonite in an aqueous solution, was introduced to prepare iron-loaded polydopamine functionalized montmorillonite/epoxy resin composites (D-Mt-Fe
/EP). As expected, D-Mt-Fe
/EP-10 with 10 phr of D-Mt-Fe
passed the UL-94 V-0 rating, achieved a limiting oxygen index (LOI) value of 31.0% and reduced the smoke production rate (SPR) and total smoke production (TSP), indicating that the introduction of D-Mt-Fe
could endow EP with satisfactory flame retardancy through the radical scavenging function of dopamine in the gas phase and the catalytic charring effect of iron ions, respectively. Encouragingly, the mechanical property was also enhanced with the flexural strength increased by 25.5%. This work provided an attractive strategy for improving both the mechanical properties and fire resistance of EP, which greatly broadened their applications in the chemical industry and electronics field, etc.
Background:
Vitamins and carotenoids may be involved in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Previously related publications mainly focused on vitamin D and vitamin E, and ...studies on other vitamins and carotenoids and NAFLD are scarce.
Methods:
This study aimed to explore the clinical relevance of vitamin A, B vitamins (vitamin B1, vitamin B2, niacin, vitamin B6, folate, vitamin B12, and choline), vitamin C and carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lycopene, lutein + zeaxanthin) with liver steatosis and fibrosis in the 2017–2018 NHANES (
N
= 4,352). Liver steatosis and fibrosis were detected by transient elastography. Logistic regression, linear regression and restricted cubic splines were adopted to explore the non-linear dose-response relationships.
Results:
Higher intakes of vitamin C 0.68 (0.50–0.93) and β-carotene 0.71 (0.54–0.93) were inversely associated with liver steatosis. Higher levels of serum vitamin C 0.45 (0.32–0.62) were inversely associated with liver fibrosis, while higher intakes of choline 1.43 (1.04–1.98) and α-carotene 1.67 (1.01–2.74) were positively associated with liver fibrosis. In addition, marginally inverse association between lutein + zeaxanthin and liver steatosis and positive association between vitamin B12 and liver fibrosis were found. In linear regression, the above-mentioned associations between vitamin C, β-carotene, and lutein + zeaxanthin and liver steatosis, and serum vitamin C, choline, α-carotene, and vitamin B12 and liver fibrosis were also found. The above-mentioned associations were mainly linear, while the relationship between β-carotene and liver steatosis might be non-linear.
Conclusion:
Vitamin C, α-carotene, β-carotene, lutein + zeaxanthin, choline and vitamin B12 may be associated with liver steatosis and fibrosis.
Developing highly efficient and multifunctional epoxy resins (EPs) that overcome the shortcomings of flammability and brittleness is crucial for pursuing sustainable and safe application but remains ...a huge challenge. In this paper, a novel biomass-containing intumescent flame retardant containing a rigid–flexible and multi-siloxane bridge structure (DPB) was synthesized using siloxane; 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO); and biomass vanillin. DPB could facilitate the formation of a carbon residual with an intumescent structure, which effectively blocked the propagation of heat and oxygen. As a result, the peak heat release rate (pHRR) and total heat release (THR) of DPB/EP-7.5 decreased by 38.8% and 45.0%, respectively. In terms of mechanical properties, the tensile and flexural elongations at break of DPB/EP-7.5 increased by 77.2% and 105.3%, respectively. Impressively, DPB/EP-7.5 had excellent dielectric properties, with a dielectric constant of 2.5–2.9. This was due to the Si-O bonds (multi-siloxane bridges) contained in DPB/EP, which can quench the polarization behavior of the hydroxyl group. This paper provides a facile strategy for the preparation of multifunctional EP, which will pave the way for the promotion and application of EP in the high-end field.
To increase power rating, parallel-connected converters are widely used in power systems. However, it brings challenge to output harmonic current control. For active power filter, the harmonic ...current compensation performance worsens. A virtual resistor has significant effect on the amplitude and phase of the output current. Based on the analysis of current control loop with a virtual resistor, an enhanced current control method is proposed. The optimal value of a virtual resistor is used to stabilize the amplitude of the output harmonic current. The phase control of a filter capacitor harmonic voltage is used to regulate the phase of the output harmonic current. Finally, simulation and experimental results verify the correctness of theoretical analysis and effectiveness of the method. Load harmonic current compensation capability is guaranteed.
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