In this study, the spatiotemporal distributions of monthly and annual temperature minima (Tmin) and maxima (Tmax), extreme Tmin and Tmax, the highest (lowest) Tmin (Tmax), frost day (FD), icing day (ID), summer day (SD) and tropical night (TR) at 112 stations and over the ten large river basins on the Tibetan Plateau and its surroundings (TPS) during 1963–2015 are examined. Mann-Kendall test is applied for the trends. The analyses show: the northwest experiences the hottest summer while the central TPS has the coldest winter and most frequent frost and icing days. The northwest (southeast) features the highest (lowest) monthly extreme temperature ranges. The northwest has the most frequent hot summer days, whereas the southeast has the least frequent frost and icing days. The entire TPS displays few tropical nights. Most stations show positive trends for all monthly and annual Tmin and Tmax variables. February displays the most positive trends for both monthly Tmin and Tmax variables while April shows the highest number of stations with decreasing trends in monthly Tmax. The trends of FD and ID are negative, whereas the trends of SU and TR are positive. Over river basins, the trends of monthly Tmin are all positive and statistically significant and the trends of monthly Tmax are all positive except for one negative trend and around 1/3 of the positive trends are statistically significant. Relatively larger increases in monthly Tmin and Tmax are noted for the cold season than the warm. The monthly and annual Tmin variables increase more than Tmax variables.

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With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with doublenegativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.Currently, acoustic metamaterials are extensively studied owing to unprecedented characteristics, which exhibit application potentials in various fields [1][2][3][4][5][6] . However, with the development of acoustic metamaterials, the limitations of passive metamaterials have been observed. First, the characteristic frequency bands related to extraordinary acoustic performance are restricted into narrow bands induced by resonance. In addition, since the unique characteristics of metamaterials are created by artificial structures, they cannot be freely changed once the metamaterials are fabricated. Therefore, tunable acoustic metamaterials with adjustable characteristic frequency bands are urgently required treading on the heels of their counterparts in electromagnetics and optics [7][8][9][10] . Different mechanisms were adopted to realize tunable metamaterials. First, tunable features arose from nonlinear effects in acoustic metamaterials, in which the constitutive parameters could be changed with the intensities of input acoustic fields, and they were considered to be self-modulation metamaterials [11][12][13] . On the other hand, actively tunable metamaterials, which could be controlled by an external source other than input acoustic fields, were presented. As an example, by mechanically changing the volumes of Helmholtz resonators in a metamaterial, the resonant frequency was adjusted, which could change the corresponding characteristic frequency bands 11,14 . A similar method on the analogy of the split-ring resonators in electromagnetic metamaterials was introduced into acoustic metamaterials, in which the resonant frequency of a split hollow sphere was tuned by filling water into the sphere to change the volume 15 . Similarly, the equivalent sound speed could be changed by filling a fluid into the intermediate gaps of a metamaterial 16 . Generally, an external electric signal is preferred as the control signal in tuning the performance of a metamaterial. Piezoelectric materials, which...

Solution‐processed intrinsic ZnO and Al‐doped ZnO (ZnO:Al) were spin coated on textured n‐type c‐Si wafer to replace the phosphorus‐doped amorphous silicon as the electron selective transport layer (ESTL) of the Si heterojunction (SHJ) solar cells. Besides the function of electron selective transportation, the nondoped ZnO was found to possess certain passivation effect on c‐Si wafer. The SHJ solar cells with different combinations of passivation layer (intrinsic a‐Si:H, SiOx, and nondoped ZnO) and electron transport layer (nondoped ZnO and ZnO:Al) were fabricated and compared. An efficiency up to 18.46% was achieved on a SHJ solar cell with an a‐Si:H/ZnO:Al double layer back structure. And, all the solution‐processed nondoped ZnO/ZnO:Al combination layers present fairly good electron selective transportation property for SHJ solar cell, resulting in an efficiency of 17.13%. The carrier transport based on energy band diagrams of the rear side of the solar cells has been discussed related to the performance of the SHJ solar cells.

Insulating against low-frequency sound (below 500 Hz) remains challenging despite the progress that has been achieved in sound insulation and absorption. In this work, an acoustic metamaterial based on membrane-coated perforated plates is presented for achieving sound insulation in a low-frequency range, even covering the lower audio frequency limit, 20 Hz. Theoretical analysis and finite element simulations demonstrate that this metamaterial can effectively block acoustic waves over a wide low-frequency band regardless of incident angles. Two mechanisms, non-resonance and monopolar resonance, operate in the metamaterial, resulting in a more powerful sound insulation ability than that achieved using periodically arranged multi-layer solid plates.

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases which lacks ideal treatment options. Kaempferol and kaempferide, two natural flavonol compounds isolated from Hippophae rhamnoides L., were reported to exhibit a strong regulatory effect on lipid metabolism, for which the mechanism is largely unknown. In the present study, we investigated the effects of kaempferol and kaempferide on oleic acid (OA)-treated HepG2 cells, a widely used in vitro model of NAFLD. The results indicated an increased accumulation of lipid droplets and triacylglycerol (TG) by OA, which was attenuated by kaempferol and kaempferide (5, 10 and 20 μM). Western blot analysis demonstrated that kaempferol and kaempferide reduced expression of lipogenesis-related proteins, including sterol regulatory element-binding protein 1 (SREBP1), fatty acid synthase (FAS) and stearoyl-CoA desaturase 1 (SCD-1). Expression of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT enhancer binding proteins β (C/EBPβ), two adipogenic transcription factors, was also decreased by kaempferol and kaempferide treatment. In addition, western blot analysis also demonstrated that kaempferol and kaempferide reduced expression of heme oxygenase-1 (HO-1) and nuclear transcription factor-erythroid 2-related factor 2 (Nrf2). Molecular docking was performed to identify the direct molecular targets of kaempferol and kaempferide, and their binding to SCD-1, a critical regulator in lipid metabolism, was revealed. Taken together, our findings demonstrate that kaempferol and kaempferide could attenuate OA-induced lipid accumulation and oxidative stress in HepG2 cells, which might benefit the treatment of NAFLD.

Physical phenomena induced by nonlinear effects in an acoustic metamaterial with double-negativity based on two types of scatterers, side holes and membrane, located along a pipe are theoretically and experimentally studied. We find that the pass and forbidden bands related to double-negativity and single-negativity effects in the metamaterial vary with the input acoustic intensities because of the nonlinearities of both types of scatterers. The nonlinearities can disrupt the unique features associated with these characteristic frequency bands of the metamaterial; however, the nonlinear effects may also lead to applications as automatically triggered acoustic isolators, tunable acoustic metamaterials, and so on.

Investigating the changes in the extreme temperature indices is crucial for the assessment of climate change and to recommend practical adaptation strategies particularly in countries like Nepal, which is highly prone to the impacts of extreme climatic events. This study analyses the mean temperatures and the changes of extreme temperature indices at 25 stations located in different physiographic regions in Nepal at monthly and annual time scales for 1986–2015. Ten extreme temperature indices recommended by ETCCDI are selected and examined. Quality control is first conducted for original daily maximum and minimum temperature data. In Nepal, it is warming in general with maximum temperature (0.04°C year−1) increasing faster than minimum temperature (0.02°C year−1) on countrywide average which is contrary to the changes in the Tibetan Plateau and its surroundings and the global average. The changes in extreme temperatures are spatiotemporally heterogeneous and unique. Annually, cold extremes increase but the percentage of days below 10th percentile becomes less frequent. Terai and Siwalik plain regions show negative annual trends in cold indices (TNn and TXn), but mixed changes in other extreme indices. There are strong correlations between the trends of maximum temperature‐related variables and elevation. This analysis also adds the evidence of pronounced warming in higher elevation only for day‐time extreme temperatures but not for temperature minima in Nepal which differs from the other studies around the world. This study also reveals that December and January tend to have colder days in the Terai. However, summer months are getting hotter in each region across the country. Kathmandu, the most urbanized city in Nepal shows a significant increase in minimum temperature (Tmin) and minimum Tmin (TNn) indicating the influence of urbanization in temperature change ‐ an urban heat island effect.