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Third‐order nonlinear optical (NLO) absorption properties and ultra‐fast carrier dynamics of organic 4‐N,N‐dimethylamino‐4'‐N'‐methyl‐stilbazolium tosylate (DAST) at the wavelength of 520 nm are investigated by femtosecond open‐aperture Z‐scan technique and transient absorption spectroscopy, respectively. Z‐scan measurements indicate that DAST solution exhibits ultra‐high nonlinear saturable absorption (SA) responses with a figure of merit of 4.57 × 10−13 esu cm and a saturation strength of 3.20 GW cm−2, far superior to those of the most known 2D SA materials under similar excitations. Transient absorption results reveal that the outstanding SA performances of the solution‐phase DAST are rooted in ultra‐fast ground‐state bleaching based on the Pauli blocking effect. The subsequent excited state carrier relaxation processes are dominated by rapid intraband carrier cooling and defect‐assisted interband Auger recombination. Moreover, high‐quality DAST−polyvinyl alcohol composite films prepared by solution casting exhibit similar ultra‐high SA responses and reliable long‐term stability without any degradation of their SA responses even after exposure to air moisture for 100 days. These findings establish an experimental and theoretical foundation for the development of high‐performance ultra‐fast optoelectronic devices based on organic NLO materials in the future. [ABSTRACT FROM AUTHOR]

Self-healing anti-corrosion materials are widely regarded as a promising long-term corrosion protection strategy, and this is even more significant if the damage can be monitored in real-time and consequently repaired. Inspired by the hierarchical structure of human skin, self-healing, solvent-free polyurethane/carbon nanotubes composites (SFPUHE-HTF-CNTs) with a skin-like bilayer structure were constructed. The SFPUHE-HTF-CNTs were composed of two layers, namely, a hydrophobic solvent-free polyurethane (SFPUHE-HTF) containing disulfide bonds and fluorinated polysiloxane chain segments consisting of a self-healing layer and CNTs with good electrical conductivity consisting of a corrosion protection layer, which also allowed for the real-time monitoring of damage. The results of corrosion protection experiments indicated that the SFPUHE-HTF-CNTs had a low corrosion current density (8.94 × 10−9 A·cm−2), a positive corrosion potential (−0.38 V), and a high impedance modulus (|Z| = 4.79 × 105 Ω·cm2). The impedance modulus could still reach 4.54 × 104 Ω·cm2 after self-healing, showing excellent self-healing properties for anti-corrosion protection. Synchronously, the SFPUHE-HTF-CNTs exhibited a satisfactory damage sensing performance, enabling the real-time monitoring of fractures at different sizes. This work realized the effective combination of self-healing with corrosion protection and damage detection functions through a bionic design, and revealed the green, and low-cost preparation of advanced composites, which have the advantage of scale production. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has presented unprecedented disruptions to human society worldwide since late 2019, and lockdown policies in response to the pandemic have directly and drastically decreased human socioeconomic activities. To quantify and assess the extent of the pandemic's impact on the economy of Hebei Province, China, nighttime light (NTL) data, vegetation information, and provincial quarterly gross domestic product (GDP) data were jointly utilized to estimate the quarterly GDP for prefecture-level cities and county-level cities. Next, an autoregressive integrated moving average model (ARIMA) model was applied to predict the quarterly GDP for 2020 and 2021. Finally, economic recovery intensity (ERI) was used to assess the extent of economic recovery in Hebei Province during the pandemic. The results show that, at the provincial level, the economy of Hebei Province had not yet recovered; at the prefectural and county levels, three prefectures and forty counties were still struggling to restore their economies by the end of 2021, even though these economies, as a whole, were gradually recovering. In addition, the number of new infected cases correlated positively with the urban NTL during the pandemic period, but not during the post-pandemic period. The study results are informative for local government's strategies and policies for allocating financial resources for urban economic recovery in the short- and long-term. [ABSTRACT FROM AUTHOR]

In this paper, the spatial-temporal dynamics of a delayed reaction-diffusion Hopfield's neural network model (HNNM) under a Neumann boundary condition is considered. Our main concern is the absolute, also called the delay-independent, global or local stability of the trivial and nontrivial steady states of the HNNM with non-monotone activation functions. The dissipativity of the semiflow generated by HNNM is first proved and then the absolute attractivity of both the trivial and the nontrivial steady states is obtained by adopting the idea of connecting the spatial-temporal dynamics of the HNNM with the asymptotic behaviors of a finite-dimensional discrete dynamical system. Specifically, it is shown that the strong attractors of the finite-dimensional discrete dynamical system generated by the nonlinear activation function of the HNNM are indeed the attractors of the corresponding delayed reaction-diffusion HNNM. Numerical simulations are also conducted at last to illustrate the effectiveness of our established results. [ABSTRACT FROM AUTHOR]