Layered double hydroxide (LDH) nano‐ and microstructures with controllable size and morphology have been fabricated on “bivalent metal” substrates such as zinc and copper by a one‐step, room‐temperature process, in which metal substrates act as both reactants and supports. By manipulating the concentration of NH3 · H2O, the thickness and lateral size of the LDH materials can be tuned from several tens of nanometers to several hundreds of nanometers and from several hundreds of nanometers to several micrometers, respectively. This method is general and may be readily extended to any other alkali‐resisted substrate coated with Zn and Cu. As an example, Zn‐covered stainless steel foil has been shown to be effective for the growth of a ZnAl LDH film. After calcinating the as‐grown LDH at high temperature (650 °C) in argon gas, a ZnO/ZnAl2O4 porous nanosheet film is obtained, which is then directly used for the first time as the anode material for Li‐ion batteries with the operating voltage window of 0.05–2.5 V (vs. Li). The result demonstrates that ZnO/ZnAl2O4 has higher discharge and charge capacities and considerably better cycling stability compared to pure ZnO (Li insertion/extraction rate: 200 or 500 mA g−1). The improved electrochemical performance can be ascribed to the buffering effect of the inactive matrix ZnAl2O4 by relieving the stress caused by the volume change during charge–discharge cycling. This work represents a successful example for the development of promising ZnO‐based anode materials for Li‐ion batteries.
Bi2WO6 uniform hierarchical microspheres were grown on a large scale at 180 °C by a simple hydrothermal method
with the help of the surfactant poly(vinyl pyrrolidone) (PVP). X-ray diffraction (XRD), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to characterize
the product. The result indicated that three-dimensional (3D) Bi2WO6 microspheres were constructed layer-by-layer from a large
number of two-dimensional (2D) sheets, which were composed of numerous interconnected square nanoplates with a mean side
length of 65 nm. Pore-size distribution analysis showed that both mesopores and macropores existed in the 3D microstructures. The
formation mechanism was discussed on the basis of the results of time-dependent experiments. It was demonstrated that PVP played
a key role in the formation of such hierarchical microspheres. By adjusting the amount of PVP, Bi2WO6 with different morphologies
can be attained accordingly. UV−vis spectroscopy was further employed to estimate the band gap energy of the hierarchical structures.
Our work may shed some light on the design of other well-defined complex nanostructures, and the as-grown architectures may
have potential applications.
Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential.
Predator-induced stress shows pronounced effects on prey by inducing behavioural, morphological, and physiological responses. Increasing evidence shows that these antipredator responses may also lead to changes in life-history traits such as aging and lifespan. However, little is known about how predator cues influence the fitness of preys and their transgenerational effects. Parental spider mites (Tetranychus urticae) were either raised on a leaf disc with or without cues from a natural predator (Phytoseiulus persimilis). The results showed that predator cues prolonged the development of both sexes, shortened female adult lifespan but not that of males, and reduced lifetime reproductive outputs of the females. The studies with offspring from both cuesexposed and control mothers demonstrated that parental effects were significant in the early developmental stage of offspring, but not in later life stages. The lifespan of offspring was strongly negatively affected by the predator-induced stress when they were directly exposed but not the stress-experienced by their mothers. Additionally, the parental effects in the earlier life stage were sex-specific, with delayed hatching in daughters (but not sons) when parents were exposed to predator-induced stress. This crosstransgenerational study indicated that there were deleterious effects of predator-induced stress on aging and lifespan of prey for both parents and their offspring, although the parental effects appeared to be weak (in the early stage of offspring but diminished in adult stage). This study highlighted the sexdifference of prey in response to predator-induced stress and sex-dependent parental effects on the offspring.
Mesenchymal stem cells (MSCs) play important roles in tissue regeneration due to their self-renewal, multilineage differentiation and immunosuppression abilities. MSCs can be isolated from various kinds of tissue, such as umbilical cord, cord blood and placenta. Human placenta mesenchymal stem cells (hPMSCs) possess stronger immunosuppressive properties, such as the ability to inhibit T-cell activation and proliferation, than human bone marrow MSCs. We have investigated that the roles of the programmed death ligands 1 and 2 (PDL1 and PDL2) in hPMSC adhesion, migration and immunosuppression were investigated. PDL1 and PDL2 were highly expressed by hPMSCs. Knockdown of PDL1 and/or PDL2 by siRNA increased hPMSC adhesion, but greatly decreasing migration. PDL1 and PDL2 expressed on hPMSCs inhibited T-cell proliferation by arresting the cell cycle. Knockdown of PDL1 and/or PDL2 in hPMSCs, however, had no effect on the expression of CD69, a T-cell early activation marker found on both CD4(+) and CD8(+) T-cell subsets. In summary, the roles of the negative co-stimulators PDL1 and PDL2 is on the adhesion, migration and immunosuppression of hPMSCs. These findings may be useful regarding the potential use of hPMSCs in clinical cell.
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