Evaluation of Surface Roughness of Aluminum Alloy in Burnishing Process Based on Chaos Theory

Burnishing experiments with different burnishing parameters were performed on a computer numerical control milling machine to characterize the surface roughness of an aluminum alloy during burnishing.The chaos theory was employed to investigate the nonlinear features of the burnishing system.The experimental results show that the power spectrum is broadband and continuous,and the Lyapunov exponentλis positive,proving that burnishing has chaotic characteristics.The chaotic characteristic parameter,the correlation dimension D,is sensitive to the time behavior of the system and is used to establish the corresponding relationship with the surface roughness.The correlation dimension was the largest,when the surface roughness was the smallest.Furthermore,when the correlation dimension curve decreases,the roughness curve increases.The correlation dimension and surface roughness exhibit opposite variation trends.The higher the correlation dimension,the lower the surface roughness.The surface roughness of the aluminum alloy can be characterized online by calculating the correlation dimension during burnishing.

Investigation of Two-Dimensional Ultrasonic Surface Burnishing Process on 7075-T6 Aluminum

A novel two-dimensional ultrasonic surface burnishing process(2D-USBP)is proposed.7075-T6 aluminum samples are processed by a custom-designed 2D-USBP setup.Parameter optimization of 2D-USBP is conducted to determine the best processing strategy of 7075-T6 aluminum.A uniform design method is utilized to optimize the 2D-USBP process.U〔3(133)and 4(72)tables are established to conduct parameter optimization.Burnishing depth,spindle speed,and feed rate are taken as the control parameters.The surface roughness and Vickers hardness are taken as the evaluation indicators.It establishes the active control models for surface quality.Dry wear tests are conducted to compare the wear-resistance of the 2D-USBP treated sample and the original sample.Results show that the machining quality of 2D-USBP is best under 0.24 mm burnishing depth,5000 r/min spindle speed,and 25 mm/min feed rate.The surface roughness of the sample is reduced from 2517.758 to 50.878 nm,and the hardness of the sample surface is improved from 167 to 252 HV.Under the lower load,the wear mechanism of the 2D-USBP treated sample is mainly abrasive wear accompanied by delamination wear,while the wear mechanism of the original sample is mainly delamination wear.Under the higher load,the accumulation of frictional heat on the sample surface transforms the wear mechanisms of the original and the 2D-USBP treated samples into thermal wear.

Research on the mechanism of the two-dimensional ultrasonic surface burnishing process to enhance the wear resistance for aluminum alloy

The gradient nanostructure is machined on the aluminum(Al)alloy by the two-dimensional ultrasonic surface burnishing process(2D-USBP).The mechanism of why the gradient nanostructure enhances wear resistance is investigated.The mechanical properties and microstructure characterization for the gradient nanostructure are performed by operating a nanoindenter,transmission electron microscopy(TEM),and electron backscattered diffraction(EBSD).Dry wear tests are performed on the samples before and after machining to evaluate the wear resistance and mechanisms.The effect of the gradient nanostructure on the wear resistance is explored by developing the crystal plasticity(CP)finite element and molecular dynamics(MD)models.The characterization results show that the 2D-USBP sample prepared a gradient structure of~600μm thick on the aluminum surface,increasing the surface hardness from 1.13 to 1.71 GPa and reducing the elastic modulus from 78.84 to 70.14 GPa.The optimization of the surface microstructure and the increase of the mechanical properties effectively enhance the wear resistance of the sample,with 41.20%,39.07%,and 54.58% of the wear scar areas for the 2D-USBP treated samples to the original samples under 5,10,and 15 N loads,respectively.The gradient nanostructure hinders the slip of dislocations inside the sample during the wear process and reduces the size and scope of plastic deformation;meanwhile,the resistance to deformation,adhesion,and crack initiation and propagation of the sample surface is improved,resulting in enhanced wear resistance.

Dissimilatory iron reduction contributes to anaerobic mineralization of sediment in a shallow transboundary lake

Dissimilatory iron reduction(DIR)coupled with carbon cycling is increasingly being recognized as an influential process in freshwater wetland soils and sediments.The role of DIR in organic matter(OM)mineralization,however,is still largely unknown in lake sediment environments.In this study,we clarified rates and pathways of OM mineralization in two shallow lakes with seasonal hydrological connectivity and different eutrophic situations.We found that in comparison with the domination of DIR(55%)for OM mineralization in Lake Xiaoxingkai,the contribution of methanogenesis was much higher(68%)in its connected lake(Lake Xingkai).The differences in rates and pathways of sediment OM mineralization between the two lakes were attributed to higher concentrations of carbonate associated iron oxides(Fecarb)in Lake Xiaoxingkai compared to Lake Xingkai(P=0.002),due to better deposition mixing,more contributions of terrigenous detrital materials,and higher OM content in Lake Xiaoxingkai.Results of structural equation modeling showed that Fecarb and total iron content(TFe)regulated 25%of DIR in Lake Xiaoxingkai and 76%in Lake Xingkai,accompanied by a negative effect of TFe on methanogenesis in Lake Xingkai.The relative abundance and diversity of Fe-reducing bacteria were significantly different between the two lakes,and showed a weak effect on sediment OM mineralization.Our findings emphasize the role of iron minerals and geochemical characterizations in regulating rates and pathways of OM mineralization,and deepen the understanding of carbon cycling in lake sediments.

On the boundedness of running-in attractors based on recurrence plot and recurrence qualification analysis

A feature parameter was proposed to quantitatively explore the boundedness of running-in attractors;its variation throughout the friction process was also investigated. The enclosing radius R was built with recurrence plots(RPs) and recurrence qualification analysis(RQA) by using the time delay embedding and phase space reconstruction. Additionally, the typology of RPs and the recurrence rate(RR) were investigated to verify the applicability of R in characterizing the friction process. Results showed that R is larger at the beginning, but exhibits a downward trend in the running-in friction process;R becomes smooth and trends to small steady values during the steady-state friction period, and finally shows an upward trend until failure occurs. The evolution of R, which corresponded with the typology of RPs and RR during friction process, can be used to quantitatively analyze the variation of the running-in attractors and friction state identifacation. Hence, R is a valid parameter, and the boundedness of running-in attractors can offer a new way for monitoring the friction state of tribological pairs.

Chaotic characteristics and attractor evolution of friction noise during friction process

Friction experiments are conducted on a ring-on-disk tribometer, and friction noise produced during the friction process is extracted by a microphone. The phase trajectory and chaotic parameters of friction noise are obtained by phase-space reconstruction, and its attractor evolution is analyzed. The results indicate that the friction noise is chaotic because the largest Lyapunov exponent is positive. The phase trajectory of the friction noise follows a "convergence-stability-divergence" pattern during the friction process. The friction noise attractor begins forming in the running-in process, and the correlation dimension D increases gradually. In the stable process, the attractor remains steady, and D is stable. In the last step of the process, the attractor gradually disappears, and D decreases. The friction noise attractor is a chaotic attractor. Knowledge of the dynamic evolution of this attractor can help identify wear state changes from the running-in process to the steady and increasing friction processes.

Stretchable and self-healable spoof plasmonic meta-waveguide for wearable wireless communication system

Microwave transmission lines in wearable systems are easily damaged after frequent mechanical deformation,posing a severe threat to wireless communication.Here,we report a new strategy to achieve stretchable microwave transmission lines with superior reliability and durability by integrating a self-healable elastomer with serpentine-geometry plasmonic meta-waveguide to support the spoof surface plasmon polariton(SSPP).After mechanical damage,the self-healable elastomer can autonomously repair itself to maintain the electromagnetic performance and mechanical strength.Meanwhile,the specially designed SSPP structure exhibits excellent stability and damage resistance.Even if the self-healing process has not been completed or the eventual repair effect is not ideal,the spoof plasmonic meta-waveguide Can still maintain reliable performance.Self-healing material enhances strength and durability,while the SSPP improves stability and gives more tolerance to the self-healing process.Our design coordinates the structural design with material synthesis to maximize the advantages of the SSPP and self-healing material,signifcantly improving the relability and durability of stretchable microwave transmission lines.We also perform communication quality experiments to demonstrate the potential of the proposed meta-waveguide as interconnects in future body area network systems.

Photostable lysosomal imaging of living cell with hyperspectral stimulated Raman scattering microscopy using a probe based on bisarylbutadiyne

We designed a lysosome-selective Raman probe by conjugating bisphenylbutadiyne with morpholine, a well-known lysosome targeting moiety. This probe, named Lyso-BADY, has a Raman peak 28 times more intense than that of 5-ethynyl-2'-deoxyuridine. Lysosome in living cells was successfully visualized by hyperspectral stimulated Raman scattering (SRS) microscopy with this extracellular probe. Further study showed that the Raman signal of Lyso-BADY remained steady and strong even after a prolonged irradiation time. The photo-stability feature of Lyso-BADY rendered molecules of the similar structure as potentially versatile probe for continuous imaging in the future.

Linking changes of forage production and digestibility with grassland community assembly under nitrogen enrichment

Background:Forage production is the fundamental ecosystem service of grasslands.Although forage consumption occurs at community level,most studies focused on species-level changes of forage quality.The quantitative and qualitative changes of forage production are driven by species-specific trait,intra-specific plasticity,and species turnover.We examined the changes in forage production and digestibility after 5-year factorial treatments of nitrogen(N)addition and mowing in a temperate steppe and linked such changes to community assembly under the Price equation framework.Results:Nitrogen addition significantly reduced species richness,increased forage production,but did not change forage digestibility(indicated by the total Ca+Mg concentrations).Mowing did not affect forage production and digestibility.The positive effects of N addition on forage production were driven by the enhancement of abundance of the remaining species following N enrichment,rather than by species loss or species gain.The species identity effects could offset the effects of species richness loss or gain on forage production and digestibility.Conclusions:Our results highlight the importance of a community perspective in addressing the quantitative and qualitative changes of forage production under global change pressure of N enrichment.Species identity is important in determining the contribution of different processes of community assembly to ecosystem services.

Mowing weakens the positive effects of nitrogen deposition on fundamental ecosystem service of grassland

Forage yield is the fundamental ecosystem service of grasslands.While the quantitative responses of forage yield to nitrogen(N)enrichment are well known,its qualitative responses remain unclear.Even less known is the relative contribution of changes in community composition to the quality of the yield at the community level.We examined the quantitative and qualitative responses of forage yield at both plant functional group and community levels with factorial treatments of N addition and mowing in a temperate steppe.Nitrogen addition significantly enhanced the community-level yield by favoring the growth of rhizomatous grass.Mowing tended to mediate the impacts of N addition on the yield.Nitrogen addition increased the concentrations of crude protein and crude fat in forage at the community level.Neither the main effects of mowing nor its interactive effects with N addition affected forage quality.The N-induced shifts in plant species composition significantly contributed to the effects of N addition on forage quality at the community level.Our results suggest that mowing wound weaken the positive effects of N deposition on the quantity but not the quality of forage yield.Changes in plant community composition are important in driving the qualitative responses of yield to N deposition.

China’s Government Information Capacity,Medical Resource Allocation and COVID−19 Prevention and Control

The fight against the COVID−19 epidemic is a war against an“invisible enemy”.Access to accurate information and appropriate allocation of medical resources are key to containing the spread of the virus as soon as possible.The Chinese government has great power to collect information from individuals and basic-level organizations.It also has strong ability to pool and allocate medical resources.The fight against COVID−19 can be deemed as a quasi-natural experiment and based on this,we examine how government information capacity and medical resource allocation influence epidemic prevention and control in 286 Chinese cities(prefecture level and above).The fi ndings are as follows:(1)Government information capacities improve the effectiveness of prevention and control policies.At city level,for every 0.1 point of increase in government information capacity score,the number of confi rmed cases will reduce by 66.5,and the number of deaths per 10000 people will be down by 0.008.(2)The quantity of medical resources available has no direct influence on the effectiveness of epidemic prevention and control,but higher allocation efficiency does bring higher effectiveness.(3)The government can,on the one hand,allocate public resources based on information,and on the other hand guide the flow of social resources by releasing relevant information.Both can improve the allocation efficiency of medical resources.These fi ndings have some policy implications for improving global emergency management.