Strain controlled fatigue of P92 steel with various strain hold dwells introduced at the peak loading point were conducted at 625 °C. Two features which depend on the cycle and strain range level ...were observed under the fatigue-creep condition for the viscous and cyclic softening material. The first one is the accelerated cyclic softening response which is ascribed to the accumulated inelastic strain transformation from the creep mechanism during the strain dwell period and becomes more significant with the decrease of strain ranges. The second one is the decelerated stress relaxation behavior which is caused by the reduced viscous stress related to the continuous cyclic softening and fades with the decrease of cyclic strain ranges. Accordingly, a new unified viscoplastic constitutive model within the framework of Chaboche model was developed by improving the nonlinear isotropic hardening rule and the kinematic hardening rule with a cyclic softening parameter. As a result, the accelerated cyclic softening and decelerated stress relaxation response of fatigue-creep interaction was finely reproduced by the proposed model.
•Strain controlled fatigue of P92 with various strain hold dwells introduced at the peak loading point were conducted at 625 °C.•The accelerated cyclic softening response increases with the decrease of strain ranges due to the strain dwell.•The decelerated stress relaxation behavior fades with the decrease of cyclic strain ranges due to the continuous cyclic softening.•A unified viscoplastic constitutive model was developed by improving the kinematic hardening rule with a cyclic softening parameter.
A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z‐scheme heterojunctions for artificial photosynthesis is ...presented. A series of COF–semiconductor Z‐scheme photocatalysts combining water‐oxidation semiconductors (TiO2, Bi2WO6, and α‐Fe2O3) with CO2 reduction COFs (COF‐316/318) was synthesized and exhibited high photocatalytic CO2‐to‐CO conversion efficiencies (up to 69.67 μmol g−1 h−1), with H2O as the electron donor in the gas–solid CO2 reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic‐semiconductor systems utilizing the Z‐scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor‐to‐COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO2 reduction and holes in the semiconductor for H2O oxidation, thus mimicking natural photosynthesis.
Here comes the sun: A strategy to covalently connect covalent organic frameworks with semiconductors to create organic–inorganic Z‐scheme heterojunctions was developed and applied for the CO2 photoreduction with H2O. This work delivers new insights for the future design of Z‐scheme organic–inorganic heterojunctions for artificial photosynthesis.
In this work, we rationally designed a series of crystalline and stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs; MPc‐TFPN COF, M=Ni, Co, Zn) under the guidance of ...reticular chemistry. As a novel single‐site catalysts (SSCs), NiPc/CoPc‐TFPN COF exhibited outstanding activity and selectivity for electrocatalytic CO2 reduction (ECR; Faradaic efficiency of CO (FECO)=99.8(±1.24) %/ 96.1(±1.25) % for NiPc/CoPc‐TFPN COF). More importantly, when coupled with light, the FECO and current density (jCO) were further improved across the applied potential range (−0.6 to −1.2 V vs. RHE) compared to the dark environment for NiPc‐TFPN COF (jCO increased from 14.1 to 17.5 A g−1 at −0.9 V; FECO reached up to ca. 100 % at −0.8 to −0.9 V). Furthermore, an in‐depth mechanism study was established by density functional theory (DFT) simulation and experimental characterization. For the first time, this work explored the application of COFs as photo‐coupled electrocatalysts to improve ECR efficiency, which showed the potential of using light‐sensitive COFs in the field of electrocatalysis.
A series of stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs) were developed and applied for photo‐coupled electrocatalytic CO2 reduction. This work represents a new insight for the future rational design of light sensitive crystalline materials for CO2 reduction.
Ultrathin ferroelectric materials could potentially enable low-power perovskite ferroelectric tetragonality logic and nonvolatile memories
. As ferroelectric materials are made thinner, however, the ...ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides-the archetypal ferroelectric system
. Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes
. Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO
), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems-that is, from perovskite-derived complex oxides to fluorite-structure binary oxides-in which 'reverse' size effects counterintuitively stabilize polar symmetry in the ultrathin regime.
The critical size limit of voltage-switchable electric dipoles has extensive implications for energy-efficient electronics, underlying the importance of ferroelectric order stabilized at reduced ...dimensionality. We report on the thickness-dependent antiferroelectric-to-ferroelectric phase transition in zirconium dioxide (ZrO
) thin films on silicon. The emergent ferroelectricity and hysteretic polarization switching in ultrathin ZrO
, conventionally a paraelectric material, notably persists down to a film thickness of 5 angstroms, the fluorite-structure unit-cell size. This approach to exploit three-dimensional centrosymmetric materials deposited down to the two-dimensional thickness limit, particularly within this model fluorite-structure system that possesses unconventional ferroelectric size effects, offers substantial promise for electronics, demonstrated by proof-of-principle atomic-scale nonvolatile ferroelectric memory on silicon. Additionally, it is also indicative of hidden electronic phenomena that are achievable across a wide class of simple binary materials.
The relationship between Mechanical Specific Energy (MSE) and the Rate of Penetration (ROP), or equivalently the depth of cut per revolution, provides an important measure for strategizing a drilling ...operation. This study explores how MSE evolves with depth of cut, and presents a concerted effort that encompasses analytical, computational and experimental approaches. A simple model for the relationship between MSE and cutting depth is first derived with consideration of the wear progression of a circular cutter. This is an extension of Detournay and Defourny's phenomenological cutting model. Wear is modeled as a flat contact area at the bottom of a cutter referred to as a wear flat, and that wear flat in the past is often considered to be fixed during cutting. But during a drilling operation by a full bit that consists of multiple circular cutters, the wear flat length may increase because of various wear mechanisms involved. The wear progression of cutters generally results in reduced efficiency with either increased MSE or decreased ROP. Also, an accurate estimate of removed rock volume is found important for the evaluation of MSE. The derived model is compared with experiment results from a single circular cutter, for cutting soft rock under ambient pressure with actual depth measured through a micrometer, and for cutting high strength rock under high pressure with actual cutting area measured by a confocal microscope. Finally, the model is employed to interpret the evolution of MSE with depth of cut for a full drilling bit under confining pressure. The general form of equation of the developed model is found to describe well the experiment data and can be applied to interpret the drilling data for a full bit.
All-natural plant protein-based high internal phase emulsion gels (HIPE-Gels) have attracted increasing attention recently in food, cosmetic, pharmaceutical, and other fields. Herein, HIPE-Gels were ...simultaneously fabricated by natural Quillaja saponin (QS) and soy protein isolate (SPI), and investigated the effects of environmental factors i.e., storage, acidic, ionic strength, heating and freeze-thawing on their physical stability. The combination of SPI and QS enabled the highly stable O/W emulsion gels with a shear-thinning behavior. At the appropriate concentration (i.e., 1.5% SPI and 0.09% QS), the emulsion gels exhibited high tolerance toward long-term storage and destabilizing environments. Although poor stability at a pH close to the isoelectric point of SPI, incorporating QS provided excellent acidic stability of plant-based emulsion gels. The strong electrostatic repulsion provided by QS would reduce the aggregation between droplets under acid environment and the electrostatic shielding of salt ions, improving the acid tolerance and salt tolerance of SPI-based emulsion gels. In addition, QS had also improved their thermal stability and freeze-thaw stability. These findings demonstrated that the combination of SPI and QS could provide an effective strategy to fabricate all-natural plant protein-based mayonnaise to withstand several environmental factors, developing label-friendly novel food products.
Display omitted
•All-natural plant-based HIPE-Gels simultaneously stabilized by Quillaja saponin (QS) and soy protein isolate (SPI).•Influence of environmental stresses (i.e., storage, acidic, NaCl, thermal and freeze-thawing) on stability was systematically investigated.•HIPE-Gels simultaneously stabilized by SPI and QS showed a better physical stability.•These plant-based emulsifiers had synergistic effects on improving emulsion stability.•Providing important information about the formation of stable plant protein-based foods.
The synthesis of fully epitaxial ferroelectric Hf0.5Zr0.5O2 (HZO) thin films through the use of a conducting pyrochlore oxide electrode that acts as a structural and chemical template is reported. ...Such pyrochlores, exemplified by Pb2Ir2O7(PIO) and Bi2Ru2O7(BRO), exhibit metallic conductivity with room‐temperature resistivity of <1 mΩ cm and are closely lattice matched to yttria‐stabilized zirconia substrates as well as the HZO layers grown on top of them. Evidence for epitaxy and domain formation is established with X‐ray diffraction and scanning transmission electron microscopy, which show that the c‐axis of the HZO film is normal to the substrate surface. The emergence of the non‐polar‐monoclinic phase from the polar‐orthorhombic phase is observed when the HZO film thickness is ≥≈30 nm. Thermodynamic analyses reveal the role of epitaxial strain and surface energy in stabilizing the polar phase as well as its coexistence with the non‐polar‐monoclinic phase as a function of film thickness.
Metallic pyrochlore oxide electrodes are introduced to create epitaxial Hf0.5Zr0.5O2 thin films. The emergence of the non‐polar‐monoclinic phase from the polar‐orthorhombic phase is observed when the film thickness is ≥≈30 nm. Further tuning through such an epitaxial stabilization process can lead to the orthorhombic phase being stable over an even larger thickness range.
Odd-chain fatty acids (OCFAs) naturally occur in bacteria, higher animals, and in plants. During recent years, they have received increasing attention due to their unique pharmacological properties ...and usefulness for agricultural and industrial applications. Recently, OCFAs have been identified and quantified in a few organisms, and new pharmacological functions of OCFAs have been reported. Some of the publications are related to the optimization of OCFA production through fermentation and genetic engineering. The present review aims to provide a summary on the recent progress in the field of microbial-derived OCFAs. More specifically, we outline the publications of OCFAs related to (i) different sources of OCFAs; (ii) endogenous synthesis of OCFAs; (iii) production of OCFAs through fermentation; (iv) genetic engineering related to OCFA; and (v) role of OCFAs in human health and disease. Finally, some areas that require further research are discussed.
With the scaling of lateral dimensions in advanced transistors, an increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the ...operating voltage1. This led to a fundamental change in the gate stack in 2008, the incorporation of high-dielectric-constant HfO2 (ref. 2), which remains the material of choice to date. Here we report HfO2-ZrO2 superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors, and scaled down to approximately 20 angstroms, the same gate oxide thickness required for high-performance transistors. The overall equivalent oxide thickness in metal-oxide-semiconductor capacitors is equivalent to an effective SiO2 thickness of approximately 6.5 angstroms. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO2-based high-dielectric-constant gate stacks without scavenging the interfacial SiO2, which has adverse effects on the electron transport and gate leakage current3. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. This work demonstrates that ultrathin ferroic HfO2-ZrO2 multilayers, stabilized with competing ferroelectric-antiferroelectric order in the two-nanometre-thickness regime, provide a path towards advanced gate oxide stacks in electronic devices beyond conventional HfO2-based high-dielectric-constant materials.
PDF
