First-principles investigation of in-plane anisotropies in XYTe4 monolayers with X = Hf, Zr, Ti and Y = Si, Ge.

In-plane anisotropic materials can introduce additional degrees of freedom while tuning their physical properties, which expand the range of opportunities for designing novel semiconductor devices and exploring distinct applications. In this work, we investigate the in-plane anisotropic electronic, elastic, transport and piezoelectric properties in a family of isostructural telluride XYTe4 (X = Hf, Zr and Ti, Y = Si and Ge) monolayers based on first-principles calculations. Six types of structures are verified to harbor direct bandgaps at the Γ point ranging between 0.98 and 1.36 eV. The orientation-dependent in-plane elastic stiffness of XYTe4 reveals the anisotropic and ultrasoft nature. Superior dielectric constants and giant switching effects are found in TiGeTe4 monolayers because of giant in-plane anisotropy. Strikingly, the piezoelectric coefficients of XSiTe4 differ by an order of magnitude along the two main directions. The strong in-plane anisotropic elastic properties of XYTe4 monolayers together with outstanding piezoelectric responses show that these structures can compete with that of transition metal dichalcogenides for applications in the field of flexible electronic devices.

Interface-induced transition from Schottky-to-Ohmic contact in Sc2CO2-based multiferroic heterojunctions.

In order to achieve a multiferroic heterojunction with a low resistance contact, we investigated a series of Sc2CO2-based van der Waals (vdW) multiferroic heterojunctions in which the ferromagnetics (1T-MnSe2, 1T-VSe2, and 1T-VTe2) were selected as the contact electrodes in terms of first-principles calculations. By reversing the polarization state of Sc2CO2 from Sc-P↑ to Sc-P↓, we found that the heterojunctions converted from Schottky-to-Ohmic contact. Moreover, this conversion, accompanied by an interface charge transfer is intrinsic and is not regulated by the interlayer spacing and biaxial strain. This work provides an avenue for the design of two-dimensional Sc2CO2-based multiferroic electronics in the future.

Spontaneous flexoelectricity and band engineering in MS2 (M = Mo, W) nanotubes.

Spontaneous flexoelectricity in transition metal dichalcogenide (TMD) nanotubes is critical to the design of new energy devices. However, the electronic properties adjusted by the flexoelectric effect in TMD nanotubes remain vague. In this work, we investigate the effect of flexoelectricity on band engineering in single- and double-wall MS2 (M = Mo, W) nanotubes with different diameters based on first-principles calculations and an atomic-bond-relaxation method. We find that the energy bandgap reduces and the polarization and flexoelectric voltage increase with decreasing diameter of single-wall MS2 nanotubes. The polarization charges promoted by the flexoelectric effect can lead to a straddling-to-staggered bandgap transition in the double-wall MS2 nanotubes. The critical diameters for bandgap transition are about 3.1 and 3.6 nm for double-wall MoS2 and WS2 nanotubes, respectively, which is independent of chirality. Our results provide guidance for the design of new energy devices based on spontaneous flexoelectricity.

Investigation of Dopamine Analogues: Synthesis, Mechanistic Understanding, and Structure-Property Relationship.

Dopamine, perhaps the simplest molecule that covalently links catechol and amine, together with its derivatives, has shown impressive adhesive and coating properties with its polymers. However, the scope of the molecules is rather limited, and the polymerization mechanisms are still elusive. We designed a general synthetic scheme and successfully synthesized a series of dopamine analogues with different alkyl chain lengths between the catechol and amine. Taking these new dopamine analogues, together with the molecular systems that have separate catechol and alkyl amine, we show that having both catechol and amine in the molecular system, whether covalently linked via an alkyl chain or not, is sufficient to polymerize under a similar reaction condition to that of dopamine polymerization. However, the time-dependent UV-vis characterization of the individual polymerization indicates that the polymerization for individual molecular systems likely proceeds via different reaction intermediates, depending on the length of the alkyl chain and whether there is a covalent linkage. Interestingly, whereas the covalent linkage via an alkyl chain is not necessary for showing the adhesive property, it is required to achieve the impressive coating property. Our results offer new insights into the design and synthesis of dopamine analogues for future applications, as well as a further mechanistic understanding of the polymerization of these dopamine analogues.

Thermo- and light-regulated formation and disintegration of double hydrophilic block copolymer assemblies with tunable fluorescence emissions.

We report on thermo- and light-regulated formation and disintegration of double hydrophilic block copolymer (DHBC) micelles associated with tunable fluorescence emissions by employing two types of DHBCs covalently labeled with fluorescence resonance energy transfer (FRET) donor and acceptor moieties, respectively, within the light and temperature dually responsive block. Both DHBCs are molecularly soluble at room temperature in their aqueous mixture, whereas, upon heating to above the critical micellization temperature (CMT, ~31 °C), they coassemble into mixed micelles possessing hydrophilic coronas and mixed cores containing FRET donors and acceptors. Accordingly, the closer spatial proximity between the FRET pair (NBDAE and RhBEA moieties) within micellar cores leads to substantially enhanced FRET efficiency, compared to that in the non-aggregated unimer state. Moreover, upon UV irradiation, the light-reactive moieties undergo light-cleavage reaction and transform into negatively charged carboxylate residues, leading to elevated CMT (∼46 °C). Thus, thermo-induced mixed micelles in the intermediate temperature range (31 °C < T < 46 °C) undergo light-triggered disintegration into unimers, accompanied with the decrease of FRET efficiency. Overall, the coassembly and disassembly occurring in the mixed DHBC solution can be dually regulated by temperature and UV irradiation, and most importantly, these processes can be facilely monitored via changes in FRET efficiency and distinct emission colors.

Glucose-regulated insulin release from acid-disintegrable microgels covalently immobilized with glucose oxidase and catalase.

The fabrication of a novel type of positively charged acid-disintegrable microgel loaded with insulin by electrostatic interactions and covalently immobilized with glucose oxidase (GOx) and catalase by inverse emulsion polymerization is reported, aiming for glucose-regulated insulin release by utilizing GOx/catalase cascade enzymatic reactions to trigger local pH decrease and acid-cleavage of crosslinking moieties. At the same time, a local pH decrease within the microgels also leads to the diminishment of net surface negative charges of encapsulated insulin. The above two factors both synergistically contribute to the prominently enhanced insulin release at high glucose levels (∼10-20 mM) compared to that in the absence of glucose.

A Norm-Based Conditional Process Model of the Negative Impact of Optimistic Bias on Self-Protection Behaviors During the COVID-19 Pandemic in Three Chinese Cities.

Data were collected from 896 participants in three Chinese cities affected by the COVID-19 pandemic to varying degrees through an online survey platform. A conditional process model was then proposed for the impact of optimistic bias on self-protection behaviors during the COVID-19 pandemic from the perspective of social norms. Statistical analysis demonstrates that optimistic bias has a negative impact on self-protection behaviors through message acceptance. Perceived social norms moderate this relationship in the following ways: (1) The higher the perceptions of social norms, the smaller the negative impact of optimistic bias on message acceptance, and the smaller the positive impact of message acceptance on self-protection behaviors. (2) Within a certain range, the higher the perceptions of social norms, the smaller the negative impact, both direct and indirect, of optimistic bias on self-protection behaviors. (3) The direct and indirect effects of optimistic bias on self-protection behaviors become insignificant when perceptions of social norms are very strong. Comparing the data of the three cities shows that higher risk is associated with a stronger role of social norms in moderating the relationship between optimistic bias and self-protection behaviors. The above results suggest that there may be both internal (optimistic bias) and external (social norms) reference points in individual decision-making regarding health behaviors. The theoretical and practical significance of the dual reference points are discussed.

Black phosphorus-based van der Waals heterostructures for mid-infrared light-emission applications.

Mid-infrared (MIR) light-emitting devices play a key role in optical communications, thermal imaging, and material analysis applications. Two-dimensional (2D) materials offer a promising direction for next-generation MIR devices owing to their exotic optical properties, as well as the ultimate thickness limit. More importantly, van der Waals heterostructures-combining the best of various 2D materials at an artificial atomic level-provide many new possibilities for constructing MIR light-emitting devices of large tuneability and high integration. Here, we introduce a simple but novel van der Waals heterostructure for MIR light-emission applications built from thin-film BP and transition metal dichalcogenides (TMDCs), in which BP acts as an MIR light-emission layer. For BP-WSe2 heterostructures, an enhancement of ~200% in the photoluminescence intensities in the MIR region is observed, demonstrating highly efficient energy transfer in this heterostructure with type-I band alignment. For BP-MoS2 heterostructures, a room temperature MIR light-emitting diode (LED) is enabled through the formation of a vertical PN heterojunction at the interface. Our work reveals that the BP-TMDC heterostructure with efficient light emission in the MIR range, either optically or electrically activated, provides a promising platform for infrared light property studies and applications.

Perfluorocarbon-based O2 nanocarrier for efficient photodynamic therapy.

Tumor hypoxia is considered as one of the major factors that limit the efficiency of photodynamic therapy (PDT), in which oxygen (O2) is needed to generate singlet oxygen (1O2) for cell destruction. Inspired by the excellent O2 carrying ability of perfluorocarbon molecules in artificial blood, we prepared a series of polymer micelles with a perfluorocarbon core to carry both photo-sensitizer and O2 to the tumor site, aiming to improve PDT efficiency. We found that the accelerated generation of 1O2 correlated with the increased perfluorocarbon amount in solution. In vitro cell study further showed that the new perfluorocarbon formulation not only improved the production of 1O2, leading to enhanced photodynamic therapy efficiency, but also significantly reduced cell toxicity when compared with the one without these perfluoro units. This work provides a new option for improving PDT efficiency with the new perfluorocarbon-incorporated nanoplatform.

Synthetic control over orientational degeneracy of spacer cations enhances solar cell efficiency in two-dimensional perovskites.

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported. Here we demonstrate that the selection of spacer cations (i.e., selective fluorination of phenethylammonium) affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells (average n = 4). Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties. This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of two-dimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice.

Dramatic Improvement of the Mechanical Strength of Silane-Modified Hydroxyapatite-Gelatin Composites via Processing with Cosolvent.

Bone tissue engineering (BTE) requires a sturdy biomaterial for scaffolds for restoration of large bone defects. Ideally, the scaffold should have a mechanical strength comparable to the natural bone in the implanted site. We show that adding cosolvent during the processing of our previously developed composite of hydroxyapatite-gelatin with a silane cross-linker can significantly affect its mechanical strength. When processed with tetrahydrofuran (THF) as the cosolvent, the new hydroxyapatite-gelatin composite can demonstrate almost twice the compressive strength (97 vs 195 MPa) and biaxial flexural strength (222 vs 431 MPa) of the previously developed hydroxyapatite-gelatin composite (i.e., processed without THF), respectively. We further confirm that this mechanical strength improvement is due to the improved morphology of both the enTMOS network and the composite. Furthermore, the addition of cosolvents does not appear to negatively impact the cell viability. Finally, the porous scaffold can be easily fabricated, and its compressive strength is around 11 MPa under dry conditions. All these results indicate that this new hydroxyapatite-gelatin composite is a promising material for BTE application.

Applying Lean Six Sigma methodology to reduce cesarean section rate.

OBJECTIVES: This study aims to reduce cesarean section rate and increase rate of vaginal delivery. METHODS: By using Lean Six Sigma (LSS) methodology, the cesarean section rate was investigated and analyzed through a 5-phase roadmap consisting of Define, Measure, Analyze, Improve, and Control. The principal causes of cesarean section were identified, improvement measures were implemented, and the rate of cesarean section before and after intervention was compared. RESULTS: After patients with a valid medical reason for cesarean were excluded, the main causes of cesarean section were maternal request, labor pain, parturient women assessment, and labor observation. A series of measures was implemented, including an improved parturient women assessment system, strengthened pregnancy nutrition guidance, implementation of painless labor techniques, enhanced midwifery team building, and promotion of childbirth-assist skills. Ten months after introduction of the improvement measures, the cesarean section rate decreased from 41.83% to 32.00%, and the Six Sigma score (ie, Z value) increased from 1.706 to 1.967 (P < .001). CONCLUSION: LSS is an effective way to reduce the rate of cesarean section.

The role of temperature in forming sol-gel biocomposites containing polydopamine.

To further improve the physical strength and biomedical applicability of bioceramicsbuilt on hydroxyapatite-gelatin (HAp-Gel) and siloxane sol-gel reactions, we incorporated mussel adhesive inspired polydopamine (PD) into our original composite based on HAp-Gel cross-linked with siloxane. Surprisingly, with the addition of PD, we observed that the processing conditions and temperatures play an important role in the structure and performance of these materials. A systematic study to investigate this temperature dependence behavior discloses that the rate of crosslinking of silane during the sol-gel process is significantly influenced by the temperature, whereas the polymerization of the dopamine only shows minor temperature dependence. With this discovery, we report an innovative thermal process for the design and application of these biocomposites.