材料界的轻骑兵——环烯烃类共聚物

通过一名普通大学生在国庆期间的武汉之旅,描述了她与华为Mate 60、食品包装袋和医疗器械的几次偶遇,并借此以生动活泼的方式向读者介绍了环烯烃类共聚物(COC)材料及其在光学器件、塑料包装和生物医学领域的典型应用。

Analysis of anomalous transport with temporal fractional transport equations in a bounded domain

Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with respect to time is a fraction. In this case, the Caputo fractional derivative relative to time is utilized, because it preserves the form of the initial conditions. A numerical calculation reveals that the fractional order of the temporal derivative α(α ∈(0, 1), sub-diffusive regime) controls the diffusion rate. The temporal fractional derivative is related to the fact that the evolution of a physical quantity is affected by its past history, depending on what are termed memory effects. The magnitude of α is a measure of such memory effects. When α decreases, so does the rate of particle diffusion due to memory effects. As a result,if a system initially has a density profile without a source, then the smaller the α is, the more slowly the density profile approaches zero. When a source is added, due to the balance of the diffusion and fueling processes, the system reaches a steady state and the density profile does not evolve. As α decreases, the time required for the system to reach a steady state increases. In magnetically confined plasmas, the temporal fractional transport model can be applied to off-axis heating processes. Moreover, it is found that the memory effects reduce the rate of energy conduction and hollow temperature profiles can be sustained for a longer time in sub-diffusion processes than in ordinary diffusion processes.

Effects of Ulva prolifera dissipation on the offshore environment based on remote sensing images and field monitoring data

Outbreaks of Ulva prolifera have continued in the South Yellow Sea of China(SYS)since 2007,becoming a serious marine ecological disaster.Large amounts of U.prolifera drift to the coast of the Shandong Peninsula to dissipate under the action of southeast monsoons and ocean surface currents.This causes serious harm to the ecological environment and economic activities of coastal cities.To investigate the impact of U.prolifera dissipation,this study extracted the spatiotemporal distribution of U.prolifera in the SYS from 2012 to 2020 based on the Google Earth Engine.The outbreak cycle of U.prolifera was determined by fitting analysis of outbreak time and coverage area through MATLAB.This study also looked at the effect of U.prolifera dissipation on water quality through field monitoring data.The results showed that the growth curve of the U.prolifera has a significant Gaussian distribution.The U.prolifera dissipates in Haiyang,China,in July and August every year and affects the offshore environment.Water quality parameters of seawater at different depths had significant differences after the U.prolifera dissipation.Changes in pH,chemical oxygen demand,nitrite nitrogen,nitrate nitrogen,ammonia nitrogen,chlorophyll a,total phosphorus,and suspended solids were more significant in surface seawater than in deeper water.Changes in the concentrations of dissolved oxygen and total nitrogen were more significant in the deep seawater(1.63 and 1.1 times higher than those in the surface seawater,respectively).The dissipation of U.prolifera releases a large amount of carbon and nitrogen into the seawater,which provides rich nutrients for phytoplankton and may cause secondary disasters such as red tide.These findings are useful for further understanding the rules of U.prolifera dissipation,as well as preventing and controlling green tide disasters.

Cytoprotective effect of amniotic membrane extracts on human corneal epithelial cells exposed to benzalkonium chloride in vitro

Background:The goal was to explore the protective effect and potential mechanism of amniotic membrane extracts(AME)on the ocular surface exposed to benzalkonium chloride(BAC).Methods:The human corneal epithelial cell(HCEC)line SD-HCEC1s was cultured in 5 groups:normal control(NC),NC+AME,BAC,BAC+NC,and BAC+AME.Cell viability analysis,flow cytometry analysis,real-time polymerase chain reaction(PCR),and western blot were employed to measure changes in cell function.Matrix metalloproteinases(MMPs)and inflammatory cytokines were assayed by enzyme-linked immunosorbent assay(ELISA)and activity assays.Results:Real-time PCR and western blot analysis demonstrated that the expressional level of caspase-8 was increased while the levels of Muc1,Muc4,and Muc16 were decreased after treatment with 0.02%BAC for 1 h.When the SD-HCEC1s were withdrawn from the BAC and switched to media containing 10%AME for 2 days,the expression level of capsase-8 was decreased while the levels of Muc1,Muc4,and Muc16 were increased.Real-time PCR and ELISA demonstrated that the mRNA and protein levels of MMP-1,MMP-3,MMP-13,CXCL1,interleukin(IL)-1β,IL-6,and tumor necrosis factor-alpha(TNF-α)were significantly increased after treatment with 0.02%BAC,whereas those of MMP-8 were decreased.When the 0.02%BAC was withdrawn and the SD-HCEC1s were cultured in 10%AME,the mRNA and protein levels of MMP-1,MMP-3,MMP-13,CXCL1,IL-1β,IL-6,and TNF-αwere decreased,while those of MMP-8 were increased.MMP-8 activity assays confirmed that IL-1βand TNF-αdownregulated the protein levels of MMP-8.Conclusions:AME protects SD-HCEC1s when stressed in BAC via upregulation of MMP-8 and downregulation of IL-1βand TNF-α.AME may have the potential functions to be employed as a topical adjunctive therapy in eyes chronically exposed to BAC.

Research and Practice of Flexibility in Distribution Systems:A Review

Flexibility in energy systems can support the operation of the electricity grid by providing active and reactive power to avoid voltage limit violations or congestion.Active distribution networks can provide this flexibility by implementing systems to control distributed generators,storage or loads.Additionally,power flow controlling devices can be used to implement operational flexibility in the energy system.This paper presents concepts for planning and forecasting of flexibility,monitoring of energy systems and control of flexibility from active distribution networks(ADNs)to enable the use of flexibility in future power systems.

Comparative Analysis on the Stability Mechanism of Droop Control and VID Control in DC Microgrid

Voltage resonance and fluctuation deteriorate the stability of DC microgrids(DC-MGs)and restrict their popularization.Conventional droop control cannot suppress voltage fluctuation and damp oscillations.Therefore,new control methods,namely,droop+filter control and virtual inertia and damping control,are proposed.These methods differ owing to the addition of low pass filter(LPF)and virtual inertia loop.In this study,the stability of these control methods is investigated comprehensively to understand their differences arising from the use of LPF and inertia loop as well as the underlying dynamic stability mechanism.The leading causes of voltage instability in DC-MGs regulated by droop control are first presented.Subsequently,control methods for solving this issue are compared and their simplified small-signal models are constructed.Based on eigenvalue analysis,the DC-MG is equivalent to a third-order system.Different control effects can be acquired by changing the control parameters and the location of the eigenvalues;furthermore,they can be used to understand the dynamic stability.Eigenvalue analysis can provide parameter design guidelines.Finally,the simulation results verify the validity of the theoretical analysis.

Power,Society,and Living Space: Evolution and Formation Mechanism of Urban Streets in China

Being one of the most important elements of urban public space, streets have contained rich social lives as well as the social and political connotations in Chinese cities with specific local characteristics, while most of them have been long neglected in the researches focusing on grand narratives and center-based perspectives. The paper retrospectively analyzes the evolution process of urban streets in China, dividing it into four critical periods. With the perspective of socio-spatial analysis, the unique formation mechanisms of Chinese urban streets are summarized in different contexts including power system, social domain, and living space, thus to provide references for the exploration of street development mode and revitalization mechanism facing the multiple challenges of globalization, modernity, as well as local social and cultural traditions.