Digital economy and high-quality development of the healthcare industry.

The high-quality development of the healthcare industry is of great significance for improving people's health and promoting the construction of a harmonious society. This paper focuses on the relationship between the development of China's digital economy and the high-quality development of the healthcare industry. Based on the panel data of 30 provinces in China from 2011 to 2020, this paper empirically studies whether the development of the digital economy promotes the high-quality development of the healthcare industry. This study finds that the development of digital economy has significantly promoted the high-quality development of the medical and health industry. The results of this study are still valid after a series of robustness tests including variable substitution, sample adjustment, and endogenous problem mitigation. Heterogeneity analysis shows that the effect of this policy is more significant in the eastern region and southern areas. The results of spatial econometric analysis show that the development of digital economy has obvious spatial spillover effect. The research in this paper can provide reference for developing countries to enhance the development level of digital health industry and improve people's lives.

Identification of a common ice nucleus on hydrophilic and hydrophobic close-packed metal surfaces.

Establishing a general model of heterogeneous ice nucleation has long been challenging because of the surface water structures found on different substrates. Identifying common water clusters, regardless of the underlying substrate, is one of the key steps toward solving this problem. Here, we demonstrate the presence of a common water cluster found on both hydrophilic Pt(111) and hydrophobic Cu(111) surfaces using scanning tunneling microscopy and non-contact atomic force microscopy. Water molecules self-assemble into a structure with a central flat-lying hexagon and three fused pentagonal rings, forming a cluster consisting of 15 individual water molecules. This cluster serves as a critical nucleus during ice nucleation on both surfaces: ice growth beyond this cluster bifurcates to form two-dimensional (three-dimensional) layers on hydrophilic (hydrophobic) surfaces. Our results reveal the inherent similarity and distinction at the initial stage of ice growth on hydrophilic and hydrophobic close-packed metal surfaces; thus, these observations provide initial evidence toward a general model for water-substrate interaction.

Spin-Enhanced O-H Cleavage in Electrochemical Water Oxidation.

Herein we report the vital role of spin polarization in proton-transfer-mediated water oxidation over a magnetized catalyst. During the electrochemical oxygen evolution reaction (OER) over ferrimagnetic Fe3 O4 , the external magnetic field induced a remarkable increase in the OER current, however, this increment achieved in weakly alkaline pH (pH 9) was almost 20 times that under strongly alkaline conditions (pH 14). The results of the surface modification experiment and H/D kinetic isotope effect investigation confirm that, at weakly alkaline pH, during the nucleophilic attack of FeIV =O by molecular water, the magnetized Fe3 O4 catalyst polarizes the spin states of the nucleophilic attacking intermediates. The spin-enhanced singlet O-H cleavage and triplet O-O bonding occur synergistically, which promotes the O2 generation more significantly than the strongly alkaline case involving only spin-enhanced O-O bonding.

Downregulation of nuclear STAT2 protein in the spinal dorsal horn is involved in neuropathic pain following chronic constriction injury of the rat sciatic nerve.

Regulation of gene transcription in the spinal dorsal horn (SDH) plays a critical role in the pathophysiology of neuropathic pain. In this study, we investigated whether the transcription factor STAT2 affects neuropathic pain and evaluated its possible mechanisms. A proteomic analysis showed that the nuclear fraction of STAT2 protein in the SDH was downregulated after chronic constriction injury of the rat sciatic nerve, which was associated with the development of neuropathic pain. Similarly, siRNA-induced downregulation of STAT2 in the SDH of naïve rats also resulted in pain hypersensitivity. Using RNA-sequencing analysis, we showed that reduction of nuclear STAT2 after chronic constriction injury was associated with increased expression of microglial activation markers, including the class II transactivator and major histocompatibility complex class II proteins. In addition, siRNA-induced downregulation of STAT2 promoted microglial activation and pro-inflammatory cytokine expression in the SDH. Taken together, these results showed that chronic constriction injury caused downregulation of nuclear STAT2 in the SDH, which may result in microglial activation and development of neuropathic pain. Our findings indicate that restoration of nuclear expression of STAT2 could be a potential pathway for the treatment of neuropathic pain.

Heat transport in Rayleigh-Bénard convection with linear marginality.

Recent direct numerical simulations (DNS) and computations of exact steady solutions suggest that the heat transport in Rayleigh-Bénard convection (RBC) exhibits the classical [Formula: see text] scaling as the Rayleigh number [Formula: see text] with Prandtl number unity, consistent with Malkus-Howard's marginally stable boundary layer theory. Here, we construct conditional upper and lower bounds for heat transport in two-dimensional RBC subject to a physically motivated marginal linear-stability constraint. The upper estimate is derived using the Constantin-Doering-Hopf (CDH) variational framework for RBC with stress-free boundary conditions, while the lower estimate is developed for both stress-free and no-slip boundary conditions. The resulting optimization problems are solved numerically using a time-stepping algorithm. Our results indicate that the upper heat-flux estimate follows the same [Formula: see text] scaling as the rigorous CDH upper bound for the two-dimensional stress-free case, indicating that the linear-stability constraint fails to modify the boundary-layer thickness of the mean temperature profile. By contrast, the lower estimate successfully captures the [Formula: see text] scaling for both the stress-free and no-slip cases. These estimates are tested using marginally-stable equilibrium solutions obtained under the quasi-linear approximation, steady roll solutions and DNS data. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'.

Thin liquid films down a vertical microfiber: Effect of curvature elasticity.

In this paper, we use a long-wave model to examine how the curvature elasticity modifies the famous Plateau-Rayleigh mechanism and the formation of viscous beads on a vertically placed fiber. By blending the analyses of linear stability, weakly nonlinear stability, exact nonlinear solutions, and numerical simulations, the effects of spontaneous curvature, surface bending rigidity, Gaussian curvature, and Van der Waals forces on the Plateau-Rayleigh mechanism and breakup of the liquid film are examined. The spontaneous curvature and surface bending rigidity are stabilizing the interface, which can reduce the amplitude and wave speed of nonlinear traveling waves and retard the breakup of film caused by Van der Waals attractions. However, the Gaussian curvature effect reinforces the Plateau-Rayleigh mechanism, which accelerates the rupture of film.

Designing Two-Dimensional Versatile Room-Temperature Ferromagnets via Assembling Large-Scale Magnetic Quantum Dots.

Two-dimensional (2D) ferromagnets possess astonishing potential in new-concept spintronics. However, most of the reported intrinsic 2D ferromagnets show a low Curie temperature far below room temperature. Here, we propose a series of 2D magnetic covalent and metal organic frameworks (COFs/MOFs) by assembling triangular zigzag graphene quantum dots (TZGDs) with various linkages, involving small-sized TZGDs, nonmetal atoms, magnetic metal atoms, and molecules. Upon first-principles calculations, we demonstrate 2D magnetic semiconductors with an enhanced Curie temperature of up to 472 K can be realized through the strong p(d)-p direct exchange interaction between TZGDs and linkages. Particularly, the TZGD size hardly affects the Curie temperature, whereas linkages can modulate the Curie temperature significantly. The TZGD size and linkages can regulate the electronic and magnetic properties of TZGD-based 2D ferromagnets. Our results confirm the possibility of designing 2D ferromagnets based on TZGDs and motivate the research of 2D ferromagnets on magnetic quantum dots and molecular magnets.

Are pyridinium ylides radicals?

Pyridinium ylides are usually considered nucleophiles that can undergo various reactions involving electron pairs. However, it was found that ylides resulting from deprotonation of N-alkyl-substituted pyridinium salts exhibit radical characters, with no discernable NMR signals but decent EPR spectra in both solution and the solid state. An observed correlation between lowered π* energy level of the pyridinium ring and increased EPR activity indicates that thermally induced electron-transfer processes could be involved, where the variable-temperature EPR spectrum indicates a singlet ground state and a thermally activated triplet state for the ylide. The fact that the high-resolution mass spectrum confirms the presence of oligomers of a less sterically hindered pyridinium ylide further points to a radical mechanism.

Two-dimensional Ca4N2 as a one-dimensional electride [Ca4N2]2+·2e- with ultrahigh conductance.

Electrides possess high electrical conductance and reactivity and are promising for novel applications in electronics and catalysis. Here, we predict a new thermodynamically and kinetically stable two-dimensional (2D) Ca4N2 using first-principles density functional theory (DFT) calculations. 2D Ca4N2 can serve as a one-dimensional (1D) electride [Ca4N2]2+·2e- with anionic electrons confined in the surface channels. In particular, we demonstrate that 2D Ca4N2 possesses high Fermi velocity (0.42 × 106 m s-1), electron effective Fermi mass (∼1me), ultrahigh charge density (1.14 × 1015 cm-2), and high carrier mobility (215 and 5.29 × 106 cm2 V-1 s-1 at a room temperature of 300 K and a low temperature of 2 K), resulting in ultrahigh conductance up to 0.039 and 966 S respectively for 300 and 2 K, compared to existing 2D materials and the best conductors (Cu and Ag). Furthermore, the first finding of 1D anionic electron behaviour on the surface of 2D materials can be used to stimulate the design of new kinds of electrides for exploring the physics of 1D and quasi-1D systems.

Accelerating Excitation Energy Computation in Molecules and Solids within Linear-Response Time-Dependent Density Functional Theory via Interpolative Separable Density Fitting Decomposition.

We present an efficient way to compute the excitation energies in molecules and solids within linear-response time-dependent density functional theory (LR-TDDFT). Conventional methods to construct and diagonalize the LR-TDDFT Hamiltonian require ultrahigh computational cost, limiting its optoelectronic applications to small systems. Our new method is based on the interpolative separable density fitting (ISDF) decomposition combined with implicitly constructing and iteratively diagonalizing the LR-TDDFT Hamiltonian and only requires low computational cost to accelerate the LR-TDDFT calculations in the plane-wave basis sets under the periodic boundary condition. We show that this method accurately reproduces excitation energies in a fullerene (C60) molecule and bulk silicon Si64 system with significantly reduced computational cost compared to conventional direct and iterative calculations. The efficiency of this ISDF method enables us to investigate the excited-state properties of liquid water absorption on MoS2 and phosphorene by using the LR-TDDFT calculations. Our computational results show that an aqueous environment has a weak effect on low excitation energies but a strong effect on high excitation energies of 2D semiconductors for photocatalytic water splitting.

Thermocapillary thin-film flows on a compliant substrate.

We study the dynamics of a thin liquid film on a compliant substrate in the presence of thermocapillary effect. A set of long-wave equations are derived to investigate the effects of fluid gravity (G), fluid inertia (Re), and Marangoni stresses (Ma) on the dynamics of the liquid film and the compliant substrate. By performing linear stability analysis and time-dependent computations of the long-wave equations, we examine two different cases: thin-film flows on a horizontally compliant substrate (ß=0, where ß is the inclined angle) and down a vertically compliant substrate (ß=π/2), respectively. For ß=0, we neglect fluid inertia and identify two different modes: (1) sinuous mode, where the deformations of liquid-air and liquid-substrate interfaces are in phase, which is induced by the fluid gravity, and (2) varicose mode, where the deformations of two interfaces are in phase opposition, which is induced by the Marangoni stresses. For ß=π/2, we consider a weak fluid inertia and only observe the varicose mode driven by fluid inertia and Marangoni stresses. However, because the gravity direction is parallel to the substrate, the fluid gravity modifies the varicose mode, making the deformations of two interfaces out of phase. In particular, we also seek the nonlinear traveling-wave solutions in the case of ß=π/2, revealing that fluid inertia and/or heating effect enhance the height and speed of the traveling waves. In both cases, the introduction of a strong wall heating gives rise to large deformations of both the thin liquid film and the compliant substrate.

Upper bound on angular momentum transport in Taylor-Couette flow.

We investigate the upper bound on angular momentum transport in Taylor-Couette flow theoretically and numerically by a one-dimensional background field method. The flow is bounded between a rotating inner cylinder of radius R_{i} and a fixed outer cylinder of radius R_{o}. A variational problem is formulated and solved by a pseudo-time-stepping method up to a Taylor number Ta=10^{9}. The angular momentum transport, characterized by a Nusselt number Nu, is bounded by Nu≤cTa^{1/2}, where the prefactor c depends on the radius ratio η=R_{i}/R_{o}. Three typical radius ratios are investigatedi.e., η=0.5,0.714,and0.909, and the corresponding prefactors c=0.0049,0.0075,and0.0086 are found to improve (lower) the rigorous upper bounds by Doering and Constantin [C. Doering and P. Constantin, Phys. Rev. Lett. 69, 1648 (1992)PRLTAO0031-900710.1103/PhysRevLett.69.1648] and Constantin [P. Constantin, SIAM Rev. 36, 73 (1994)SIREAD0036-144510.1137/1036004] by at least one order of magnitude. Furthermore, we show, via an inductive bifurcation analysis, that considering a three-dimensional background velocity field is unable to lower the bound.

Two-dimensional tessellation by molecular tiles constructed from halogen-halogen and halogen-metal networks.

Molecular tessellations are often discovered serendipitously, and the mechanisms by which specific molecules can be tiled seamlessly to form periodic tessellation remain unclear. Fabrication of molecular tessellation with higher symmetry compared with traditional Bravais lattices promises potential applications as photonic crystals. Here, we demonstrate that highly complex tessellation can be constructed on Au(111) from a single molecular building block, hexakis(4-iodophenyl)benzene (HPBI). HPBI gives rise to two self-assembly phases on Au(111) that possess the same geometric symmetry but different packing densities, on account of the presence of halogen-bonded and halogen-metal coordinated networks. Sub-domains of these phases with self-similarity serve as tiles in the periodic tessellations to express polygons consisting of parallelograms and two types of triangles. Our work highlights the important principle of constructing multiple phases with self-similarity from a single building block, which may constitute a new route to construct complex tessellations.

Observation of Gap Opening in 1T' Phase MoS2 Nanocrystals.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) manifest in various polymorphs, which deliver different electronic properties; the most prominent among them include the semiconducting 2H phase and metallic 1T (or distorted 1T' phase) phase. Alkali metal intercalation or interface strain has been used to induce semiconductor-to-metal transition in a monolayer MoS2 sheet, leading to exotic quantum states or improved performance in catalysis. However, the direct growth of 1T or 1T' phase MoS2 is challenging due to its metastability. Here, we report MBE growth of isolated 1T' and 2H MoS2 nanocrystals on a Au substrate; these nanocrystals can be differentiated unambiguously by their electronic states using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). By studying the initial stages of nucleation during molecular beam epitaxy (MBE) of MoS2, we could identify atomic clusters (30-50 atoms) with intralayer stacking corresponding to 1T' and 2H separately, which suggests a deterministic growth mechanism from initial nuclei. Furthermore, a topological insulator type behavior was observed for the 1T' MoS2 crystals, where an energy gap opening of 80 meV was measured by STS in the basal plane at 5 K, with the edge of the nanocrystals remaining metallic.

Atom-by-Atom Fabrication of Monolayer Molybdenum Membranes.

Fabrication of materials in the monolayer regime to acquire fascinating physical properties has attracted enormous interest during the past decade, and remarkable success has been achieved for layered materials adopting weak interlayer van der Waals forces. However, the fabrication of monolayer metal membranes possessing strong intralayer bonding remains elusive. Here, suspended monolayer Mo membranes are fabricated from monolayer MoSe2 films via selective electron beam (e-beam) ionization of Se atoms by scanning transmission electron microscopy (STEM). The nucleation and subsequent growth of the Mo membranes are triggered by the formation and aggregation of Se vacancies as seen by atomic resolution sequential STEM imaging. Various novel structural defects and intriguing self-healing characteristics are unveiled during the growth. In addition, the monolayer Mo membrane is highly robust under the e-beam irradiation. It is likely that other metal membranes can be fabricated in a similar manner, and these pure metal-based 2D materials add to the diversity of 2D materials and introduce profound novel physical properties.

Emergence of Droplets at the Nonequilibrium All-Aqueous Interface in a Vertical Hele-Shaw Cell.

The interfacial phenomena at liquid-liquid interfaces remain the subject of constant fascination in science and technology. Here, we show that fingers forming at the interface of nonequilibrium all-aqueous systems can spontaneously break into an array of droplets. The dynamic formation of droplets at the water-water (w/w) interface is observed when a less dense aqueous phase, for instance, the dextran solution, is placed on a denser aqueous phase, the polyethylene glycol solution, in a vertical Hele-Shaw cell. Because of the gradual diffusion of water from the upper phase into the lower phase, a dense layer appears at the nonequilibrium w/w interface. As a result, a periodic array of fingers emerge and sink. Remarkably, these fingers break up and an array of droplets are emitted from the interface. We characterize the wavelength of fingering by measuring the average distance between the dominant fingers. By varying the initial concentrations of the two nonequilibrium aqueous phases, we identify experimentally a phase diagram with a wide parameter space in which finger breaking occurs. Finally, plenty of droplets, spontaneously formed when one phase is continuously deposited onto another aqueous phase, further confirm the robustness of our experimental results. Our work suggests a simple yet efficient approach with a potential upscalability to generate all-aqueous droplets.

Absolute and convective instabilities of a film flow down a vertical fiber subjected to a radial electric field.

We consider the motion of a gravity-driven flow down a vertical fiber subjected to a radial electric field. This flow exhibits rich dynamics including the formation of droplets, or beads, driven by a Rayleigh-Plateau mechanism modified by the presence of gravity as well as the Maxwell stress at the interface. A spatiotemporal stability analysis is performed to investigate the effect of electric field on the absolute-convective instability (AI-CI) characteristics. We performed a numerical simulation on the nonlinear evolution of the film to examine the transition from CI to AI regime. The numerical results are in excellent agreement with the spatiotemporal stability analysis. The blowup behavior of nonlinear simulation predicts the formation of touchdown singularity of the interface due to the effect of electric field. We try to connect the blowup behavior with the AI-CI characteristics. It is found that the singularities mainly occur in the AI regime. The results indicate that the film may have a tendency to form very sharp tips due to the enhancement of the absolute instability induced by the electric field. We perform a theoretical analysis to study the behaviors of the singularities. The results show that there exists a self-similarity between the temporal and spatial distances from the singularities.

Strain Modulation by van der Waals Coupling in Bilayer Transition Metal Dichalcogenide.

Manipulation of lattice strain is emerging as a powerful means to modify the properties of low-dimensional materials. Most approaches rely on external forces to induce strain, and the role of interlayer van der Waals (vdW) coupling in generating strain profiles in homobilayer transition metal dichalcogenide (TMDC) films is rarely considered. Here, by applying atomic-resolution electron microscopy and density functional theory calculations, we observed that a mirror twin boundary (MTB) modifies the interlayer vdW coupling in bilayer TMDC films, leading to the development of local strain for a few nanometers in the vicinity of the MTB. Interestingly, when a single MTB in one layer is "paired" with another MTB in an adjacent layer, interlayer-induced strain is reduced when the MTBs approach each other. Therefore, MTBs are not just 1D discontinuities; they can exert localized 2D strain on the adjacent lattices.

Homoepitaxial Growth of Large-Scale Highly Organized Transition Metal Dichalcogenide Patterns.

Controllable growth of highly crystalline transition metal dichalcogenide (TMD) patterns with regular morphology and unique edge structure is highly desired and important for fundamental research and potential applications. Here, single-crystalline MoS2 flakes are reported with regular trigonal symmetric patterns that can be homoepitaxially grown on MoS2 monolayer via chemical vapor deposition. The highly organized MoS2 patterns are rhombohedral (3R)-stacked with the underlying MoS2 monolayer, and their boundaries are predominantly terminated by zigzag Mo edge structure. The epitaxial MoS2 crystals can be tailored from compact triangles to fractal flakes, and the pattern formation can be explained by the anisotropic growth rates of the S and Mo edges under low sulfur chemical potential. The 3R-stacked MoS2 pattern demonstrates strong second and third-harmonic-generation signals, which exceed those reported for monolayer MoS2 by a factor of 6 and 4, correspondingly. This homoepitaxial growth approach for making highly organized TMD patterns is also demonstrated for WS2 .

Mo-Terminated Edge Reconstructions in Nanoporous Molybdenum Disulfide Film.

The catalytic and magnetic properties of molybdenum disulfide (MoS2) are significantly enhanced by the presence of edge sites. One way to obtain a high density of edge sites in a two-dimensional (2D) film is by introducing porosity. However, the large-scale bottom-up synthesis of a porous 2D MoS2 film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. Here, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS2 films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS2 films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated edges leads to excellent activity for the hydrogen evolution reaction.