Research on the tool influence function characteristics of magnetorheological precession finishing (MRPF).

Magnetorheological finishing (MRF) technology is characterized by its high convergence rate and minimal subsurface damage as advantages. However, the non-Gaussian type tool influence function (TIF) it generates may cause mid-frequency errors and oriented surface texture issues. Magnetorheological precession finishing (MRPF) technology capable of generating Gaussian-like removal functions, lacks a clearly defined removal function model. This study acquired polishing spots in tilted polishing, discrete precession, and continuous precession modes via fixed-point polishing experiments. Using Multiphysics simulation software, stress and velocity distribution in the contact area were simulated. A TIF model, incorporating the synergistic effects of pressure and shear force and multiple influence coefficients, was proposed based on velocity characteristics across the three modes. To accurately predict the TIF, surface topographies with varying coefficients were constructed using this model, analyzing the coefficients' impact on the TIF profile. Optimal coefficients were identified using a least fit error algorithm. Further analysis of the TIF's internal textures revealed that the precession mode of MRPF yields superior surface quality, thereby elucidating the material removal mechanism of MRPF and laying a theoretical groundwork for advancing processing technologies.

Detection and Evaluation for High-Quality Cardiopulmonary Resuscitation Based on a Three-Dimensional Motion Capture System: A Feasibility Study.

High-quality cardiopulmonary resuscitation (CPR) and training are important for successful revival during out-of-hospital cardiac arrest (OHCA). However, existing training faces challenges in quantifying each aspect. This study aimed to explore the possibility of using a three-dimensional motion capture system to accurately and effectively assess CPR operations, particularly about the non-quantified arm postures, and analyze the relationship among them to guide students to improve their performance. We used a motion capture system (Mars series, Nokov, China) to collect compression data about five cycles, recording dynamic data of each marker point in three-dimensional space following time and calculating depth and arm angles. Most unstably deviated to some extent from the standard, especially for the untrained students. Five data sets for each parameter per individual all revealed statistically significant differences (p < 0.05). The correlation between Angle 1' and Angle 2' for trained (rs = 0.203, p < 0.05) and untrained students (rs = -0.581, p < 0.01) showed a difference. Their performance still needed improvement. When conducting assessments, we should focus on not only the overall performance but also each compression. This study provides a new perspective for quantifying compression parameters, and future efforts should continue to incorporate new parameters and analyze the relationship among them.

Experimental warming altered plant functional traits and their coordination in a permafrost ecosystem.

Knowledge about changes in plant functional traits is valuable for the mechanistic understanding of warming effects on ecosystem functions. However, observations have tended to focus on aboveground plant traits, and there is little information about changes in belowground plant traits or the coordination of above- and belowground traits under climate warming, particularly in permafrost ecosystems. Based on a 7-yr field warming experiment, we measured 26 above- and belowground plant traits of four dominant species, and explored community functional composition and trait networks in response to experimental warming in a permafrost ecosystem on the Tibetan Plateau. Experimental warming shifted community-level functional traits toward more acquisitive values, with earlier green-up, greater plant height, larger leaves, higher photosynthetic resource-use efficiency, thinner roots, and greater specific root length and root nutrient concentrations. However, warming had a negligible effect in terms of functional diversity. In addition, warming shifted hub traits which have the highest centrality in the network from specific root area to leaf area. These results demonstrate that above- and belowground traits exhibit consistent adaptive strategies, with more acquisitive traits in warmer environments. Such changes could provide an adaptive advantage for plants in response to environmental change.

Development analysis of magnetorheological precession finishing (MRPF) technology.

Magnetorheological polishing (MRF) has emerged as a critical non-contact sub-aperture polishing technology due to its notable attributes of high precision and minimal damage. However, MRF's inherent D-shaped removal function leads to reduced convergence efficiency of surface form error and introduces mid-spatial-frequency (MSF) waviness. To address these challenges, we propose magnetorheological precession finishing (MRPF) technology, which ingeniously combines MRF with bonnet precession polishing to generate a Gaussian-like removal function. A pivotal component of what we believe to be a novel approach is the design and fabrication of a specialized hemispherical magnetorheological precession polishing head. The design process incorporates magnetostatic simulations and magnetic force analysis to determine the optimal generating conditions for magnetorheological ribbons. Spot polishing experiments confirm the suitability of a 30° precession angle. Experimental results demonstrate that 8-step polishing achieves a Gaussian-like removal function. Additionally, uniform polishing of fused quartz surfaces significantly reduces Ra from 0.7 µm to 2.14 nm. This research showcases the feasibility of MRPF as a new technical route to achieve Gaussian-like removal functions and nanometer-scaled surface roughness.

Spatially explicit estimate of nitrogen effects on soil respiration across the globe.

Soil respiration (Rs), as the second largest flux of carbon dioxide (CO2 ) between terrestrial ecosystems and the atmosphere, is vulnerable to global nitrogen (N) enrichment. However, the global distribution of the N effects on Rs remains uncertain. Here, we compiled a new database containing 1282 observations of Rs and its heterotrophic component (Rh) in field N manipulative experiments from 317 published papers. Using this up-to-date database, we first performed a formal meta-analysis to explore the responses of Rs and Rh to N addition, and then presented a global spatially explicit quantification of the N effects using a Random Forest model. Our results showed that experimental N addition significantly increased Rs but had a minimal impact on Rh, not supporting the prevailing view that N enrichment inhibits soil microbial respiration. For the major biomes, the magnitude of N input was the main determinant of the spatial variation in Rs response, while the most important predictors for Rh response were biome specific. Based on the key predictors, global mapping visually demonstrated a positive N effect in the regions with higher anthropogenic N inputs (i.e., atmospheric N deposition and agricultural fertilization). Overall, our analysis not only provides novel insight into the N effects on soil CO2 fluxes, but also presents a spatially explicit assessment of the N effects at the global scale, which are pivotal for understanding ecosystem carbon dynamics in future scenarios with more frequent anthropogenic activities.

Patterns and drivers of anaerobic nitrogen transformations in sediments of thermokarst lakes.

Significant attention has been given to the way in which the soil nitrogen (N) cycle responds to permafrost thaw in recent years, yet little is known about anaerobic N transformations in thermokarst lakes, which account for more than one-third of thermokarst landforms across permafrost regions. Based on the N isotope dilution and tracing technique, combined with qPCR and high-throughput sequencing, we presented large-scale measurements of anaerobic N transformations of sediments across 30 thermokarst lakes over the Tibetan alpine permafrost region. Our results showed that gross N mineralization, ammonium immobilization, and dissimilatory nitrate reduction rates in thermokarst lakes were higher in the eastern part of our study area than in the west. Denitrification dominated in the dissimilatory nitrate reduction processes, being two and one orders of magnitude higher than anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA), respectively. The abundances of the dissimilatory nitrate reduction genes (nirK, nirS, hzsB, and nrfA) exhibited patterns consistent with sediment N transformation rates, while α diversity did not. The inter-lake variability in gross N mineralization and ammonium immobilization was dominantly driven by microbial biomass, while the variability in anammox and DNRA was driven by substrate supply and organic carbon content, respectively. Denitrification was jointly affected by nirS abundance and organic carbon content. Overall, the patterns and drivers of anaerobic N transformation rates detected in this study provide a new perspective on potential N release, retention, and removal upon the formation and development of thermokarst lakes.

Stochastic processes regulate belowground community assembly in alpine grasslands on the Tibetan Plateau.

Understanding biogeographical patterns and underlying processes of belowground community assembly is crucial for predicting soil functions and their responses to global environmental change. However, little is known about potential differences of belowground community assembly among bacteria, fungi, protists and soil animals, particularly for alpine ecosystems. Based on the combination of large-scale field sampling, high-throughput marker-gene sequencing and multiple statistical analyses, we explored patterns and drivers of belowground community assembly in alpine grasslands on the Tibetan Plateau. Our results revealed that the distance-decay rates varied among trophic levels, with organisms of higher trophic level having weaker distance-decay pattern. The spatial and environmental variables explained limited variations of belowground communities. By contrast, the stochastic processes, mainly consisting of dispersal limitation and drift, played a primary role in regulating belowground community assembly. Moreover, the relative importance of stochastic processes varied among trophic levels, with the role of dispersal limitation weakening whereas that of drift enhancing in the order of bacteria, fungi, protists and soil animals. These findings advance our understanding of patterns and mechanisms driving belowground community assembly in alpine ecosystems and provide a reference basis for predicting the dynamics of ecosystem functions under changing environment.

Substantial non-growing season carbon dioxide loss across Tibetan alpine permafrost region.

One of the major uncertainties for projecting permafrost carbon (C)-climate feedback is a poor representation of the non-growing season carbon dioxide (CO2 ) emissions under a changing climate. Here, combining in situ field observations, regional synthesis and a random forest model, we assessed contemporary and future soil respired CO2 (i.e., soil respiration, Rs ) across the Tibetan alpine permafrost region, which has received much less attention compared with the Arctic permafrost domain. We estimated the regional mean Rs of 229.8, 72.9 and 302.7 g C m-2  year-1 during growing season, non-growing season and the entire year, respectively; corresponding to the contemporary losses of 296.9, 94.3 and 391.2 Tg C year-1 from this high-altitude permafrost-affected area. The non-growing season Rs accounted for a quarter of the annual soil CO2 efflux. Different from the prevailing view that temperature is the most limiting factor for cold-period CO2 release in Arctic permafrost ecosystems, precipitation determined the spatial pattern of non-growing season Rs on the Tibetan Plateau. Using the key predictors, model extrapolation demonstrated additional losses of 38.8 and 74.5 Tg C from the non-growing season for a moderate mitigation scenario and a business-as-usual emissions scenario, respectively. These results provide a baseline for non-growing season CO2 emissions from high-altitude permafrost areas and help for accurate projection of permafrost C-climate feedback.

Divergent Trajectory of Soil Autotrophic and Heterotrophic Respiration upon Permafrost Thaw.

Warming-induced permafrost thaw may stimulate soil respiration (Rs) and thus cause a positive feedback to climate warming. However, due to the limited in situ observations, it remains unclear about how Rs and its autotrophic (Ra) and heterotrophic (Rh) components change upon permafrost thaw. Here we monitored variations in Rs and its components along a permafrost thaw sequence on the Tibetan Plateau, and explored the potential linkage of Rs components (i.e., Ra and Rh) with biotic (e.g., plant functional traits and soil microbial diversity) and abiotic factors (e.g., substrate quality). We found that Ra and Rh exhibited divergent responses to permafrost collapse: Ra increased with the time of thawing, while Rh exhibited a hump-shaped pattern along the thaw sequence. We also observed different drivers of thaw-induced changes in the ratios of Ra:Rs and Rh:Rs. Except for soil water status, plant community structure, diversity, and root properties explained the variation in Ra:Rs ratio, soil substrate quality and microbial diversity were key factors associated with the dynamics of Rh:Rs ratio. Overall, these findings demonstrate divergent patterns and drivers of Rs components as permafrost thaw prolongs, which call for considerations in Earth system models for better forecasting permafrost carbon-climate feedback.

Crop Root Responses to Drought Stress: Molecular Mechanisms, Nutrient Regulations, and Interactions with Microorganisms in the Rhizosphere.

Roots play important roles in determining crop development under drought. Under such conditions, the molecular mechanisms underlying key responses and interactions with the rhizosphere in crop roots remain limited compared with model species such as Arabidopsis. This article reviews the molecular mechanisms of the morphological, physiological, and metabolic responses to drought stress in typical crop roots, along with the regulation of soil nutrients and microorganisms to these responses. Firstly, we summarize how root growth and architecture are regulated by essential genes and metabolic processes under water-deficit conditions. Secondly, the functions of the fundamental plant hormone, abscisic acid, on regulating crop root growth under drought are highlighted. Moreover, we discuss how the responses of crop roots to altered water status are impacted by nutrients, and vice versa. Finally, this article explores current knowledge of the feedback between plant and soil microbial responses to drought and the manipulation of rhizosphere microbes for improving the resilience of crop production to water stress. Through these insights, we conclude that to gain a more comprehensive understanding of drought adaption mechanisms in crop roots, future studies should have a network view, linking key responses of roots with environmental factors.

Phosphorus rather than nitrogen regulates ecosystem carbon dynamics after permafrost thaw.

Ecosystem carbon (C) dynamics after permafrost thaw depends on more than just climate change since soil nutrient status may also impact ecosystem C balance. It has been advocated that nitrogen (N) release upon permafrost thaw could promote plant growth and thus offset soil C loss. However, compared with the widely accepted C-N interactions, little is known about the potential role of soil phosphorus (P) availability. We combined 3-year field observations along a thaw sequence (constituted by four thaw stages, i.e., non-collapse and 5, 14, and 22 years since collapse) with an in-situ fertilization experiment (included N and P additions at the level of 10 g N m-2  year-1 and 10 g P m-2  year-1 ) to evaluate ecosystem C-nutrient interactions upon permafrost thaw. We found that changes in soil P availability rather than N availability played an important role in regulating gross primary productivity and net ecosystem productivity along the thaw sequence. The fertilization experiment confirmed that P addition had stronger effects on plant growth than N addition in this permafrost ecosystem. These two lines of evidence highlight the crucial role of soil P availability in altering the trajectory of permafrost C cycle under climate warming.

Above- and below-ground resource acquisition strategies determine plant species responses to nitrogen enrichment.

BACKGROUND AND AIMS: Knowledge of plant resource acquisition strategies is crucial for understanding the mechanisms mediating the responses of ecosystems to external nitrogen (N) input. However, few studies have considered the joint effects of above-ground (light) and below-ground (nutrient) resource acquisition strategies in regulating plant species responses to N enrichment. Here, we quantified the effects of light and non-N nutrient acquisition capacities on species relative abundance in the case of extra N input. METHODS: Based on an N-manipulation experiment in a Tibetan alpine steppe, we determined the responses of species relative abundances and light and nutrient acquisition capacities to N enrichment for two species with different resource acquisition strategies (the taller Stipa purpurea, which is colonized by arbuscular mycorrhizal fungi, and the shorter Carex stenophylloides, which has cluster roots). Structural equation models were developed to explore the relative effects of light and nutrient acquisition on species relative abundance along the N addition gradient. KEY RESULTS: We found that the relative abundance of taller S. purpurea increased with the improved light acquisition along the N addition gradient. In contrast, the shorter C. stenophylloides, with cluster roots, excelled in acquiring phosphorus (P) so as to elevate its leaf P concentration under N enrichment by producing large amounts of carboxylate exudates that mobilized moderately labile and recalcitrant soil P forms. The increased leaf P concentration of C. stenophylloides enhanced its light use efficiency and promoted its relative abundance even in the shade of taller competitors. CONCLUSIONS: Our findings highlight that the combined effects of above-ground (light) and below-ground (nutrient) resources rather than light alone (the prevailing perspective) determine the responses of grassland community structure to N enrichment.

Permafrost nitrogen status and its determinants on the Tibetan Plateau.

It had been suggested that permafrost thaw could promote frozen nitrogen (N) release and modify microbial N transformation rates, which might alter soil N availability and then regulate ecosystem functions. However, the current understanding of this issue is confined to limited observations in the Arctic permafrost region, without any systematic measurements in other permafrost regions. Based on a large-scale field investigation along a 1,000 km transect and a laboratory incubation experiment with a 15 N pool dilution approach, this study provides the comprehensive evaluation of the permafrost N status, including the available N content and related N transformation rates, across the Tibetan alpine permafrost region. In contrast to the prevailing view, our results showed that the Tibetan alpine permafrost had lower available N content and net N mineralization rate than the active layer. Moreover, the permafrost had lower gross rates of N mineralization, microbial immobilization and nitrification than the active layer. Our results also revealed that the dominant drivers of the gross N mineralization and microbial immobilization rates differed between the permafrost and the active layer, with these rates being determined by microbial properties in the permafrost while regulated by soil moisture in the active layer. In contrast, soil gross nitrification rate was consistently modulated by the soil NH 4 + content in both the permafrost and the active layer. Overall, patterns and drivers of permafrost N pools and transformation rates observed in this study offer new insights into the potential N release upon permafrost thaw and provide important clues for Earth system models to better predict permafrost biogeochemical cycles under a warming climate.

Unimodal Response of Soil Methane Consumption to Increasing Nitrogen Additions.

Nitrogen (N) status has a great impact on methane (CH4) consumption by soils. Modeling studies predicting soil CH4 consumption assume a linear relationship between CH4 uptake and N addition rate. Here, we present evidence that a nonlinear relationship may better characterize changes in soil CH4 uptake with increasing N additions. By conducting a field experiment with eight N-input levels in a Tibetan alpine steppe, we observed a unimodal relationship; CH4 uptake increased at low to medium N levels but declined at high N levels. Environmental and microbial properties jointly determined this response pattern. The generality of the unimodal trend was further validated by two independent analyses: (i) we examined soil CH4 uptake across at least five N-input levels in upland ecosystems across China. A unimodal CH4 uptake-N addition rate relationship was observed in 3 out of 4 cases; and (ii) we performed a meta-analysis to explore the N-induced changes in soil CH4 uptake with increasing N additions across global upland ecosystems. Results showed that the changes in CH4 uptake exhibited a quadratic correlation with N addition rate. Overall, we suggest that the unimodal relationship should be considered in biogeochemistry models for accurately predicting soil CH4 consumption under global N enrichment.

Changes in Methane Flux along a Permafrost Thaw Sequence on the Tibetan Plateau.

Permafrost thaw alters the physical and environmental conditions of soil and may thus cause a positive feedback to climate warming through increased methane emissions. However, the current knowledge of methane emissions following thermokarst development is primarily based on expanding lakes and wetlands, with upland thermokarst being studied less often. In this study, we monitored the methane emissions during the peak growing seasons of two consecutive years along a thaw sequence within a thermo-erosion gully in a Tibetan swamp meadow. Both years had consistent results, with the early and midthaw stages (3 to 12 years since thaw) exhibiting low methane emissions that were similar to those in the undisturbed meadow, while the emissions from the late thaw stage (20 years since thaw) were 3.5 times higher. Our results also showed that the soil water-filled pore space, rather than the soil moisture per se, in combination with the sand content, were the main factors that caused increased methane emissions. These findings differ from the traditional view that upland thermokarst could reduce methane emissions owing to the improvement of drainage conditions, suggesting that upland thermokarst development does not always result in a decrease in methane emissions.

Magnitude and Pathways of Increased Nitrous Oxide Emissions from Uplands Following Permafrost Thaw.

Permafrost thawing may release nitrous oxide (N2O) due to large N storage in cold environments. However, N2O emissions from permafrost regions have received little attention to date, particularly with respect to the underlying microbial mechanisms. We examined the magnitude of N2O fluxes following upland thermokarst formation along a 20-year thaw sequence within a thermo-erosion gully in a Tibetan swamp meadow. We also determined the importance of environmental factors and the related microbial functional gene abundance. Our results showed that permafrost thawing led to a mass release of N2O in recently collapsed sites (3 years ago), particularly in exposed soil patches, which presented post-thaw emission rates equivalent to those from agricultural and tropical soils. In addition to abiotic factors, soil microorganisms exerted significant effects on the variability in the N2O emissions along the thaw sequence and between vegetated and exposed patches. Overall, our results demonstrate that upland thermokarst formation can lead to enhanced N2O emissions, and that the global warming potential (GWP) of N2O at the thermokarst sites can reach 60% of the GWP of CH4 (vs ∼6% in control sites), highlighting the potentially strong noncarbon (C) feedback to climate warming in permafrost regions.

Micro-analysis model for material removal mechanisms of bonnet polishing.

There have been many researches concerning the modeling for material removal mechanisms of bonnet polishing (BP) based on the well-known Preston model. However, various parameters involved in the BP process are not formulated and considered in the classical model, such as slurry characteristics, pad properties, bonnet features, and processing conditions. In this paper, a micro-analysis model capturing those parameters is proposed based on the mutual interaction of the slurry, pad, and workpiece among the BP interfaces with the micro-contact theory and the tribology theory. The proposed model is validated by comparison with the experimental data, and good agreement can be obtained. According to the analysis of key parameters, the proposed model is capable of providing some insight into the material removal mechanisms of BP, and even those cannot be explained properly by the classical Preston model.

Improved analysis model for material removal mechanisms of bonnet polishing incorporating the pad wear effect.

Bonnet polishing technology has been widely applied in precision optical machining. Until now, most of the research concerning the modeling for material removal mechanisms of bonnet polishing have been presented based on the well-known Preston model. However, the various parameters involved in the bonnet polishing process are not formulated into that model, such as slurry characteristics, pad properties, bonnet sizes, processing conditions, etc. Recently, several analysis models capturing those various parameters have been developed and are even capable of interpreting non-Prestonian behaviors, but the pad wear effect has still not been taken into account. Hence, the purpose of this paper is to establish an improved analysis model by incorporating the pad wear effect with the cumulative polishing time. Compared with the previous analysis model and Preston model, the predicted results of the improved analysis model are much closer to the experimental data and become more acceptable. According to the analysis of key parameters, the understanding of material removal mechanisms in bonnet polishing is further completed, and the time-dependent pad wear effect should no longer be neglected.

Warming effects on permafrost ecosystem carbon fluxes associated with plant nutrients.

Large uncertainties exist in carbon (C)-climate feedback in permafrost regions, partly due to an insufficient understanding of warming effects on nutrient availabilities and their subsequent impacts on vegetation C sequestration. Although a warming climate may promote a substantial release of soil C to the atmosphere, a warming-induced increase in soil nutrient availability may enhance plant productivity, thus offsetting C loss from microbial respiration. Here, we present evidence that the positive temperature effect on carbon dioxide (CO2 ) fluxes may be weakened by reduced plant nitrogen (N) and phosphorous (P) concentrations in a Tibetan permafrost ecosystem. Although experimental warming initially enhanced ecosystem CO2 uptake, the increased rate disappeared after the period of peak plant growth during the early growing season, even though soil moisture was not a limiting factor in this swamp meadow ecosystem. We observed that warming did not significantly affect soil extractable N or P during the period of peak growth, but decreased both N and P concentrations in the leaves of dominant plant species, likely caused by accelerated plant senescence in the warmed plots. The attenuated warming effect on CO2 assimilation during the late growing season was associated with lowered leaf N and P concentrations. These findings suggest that warming-mediated nutrient changes may not always benefit ecosystem C uptake in permafrost regions, making our ability to predict the C balance in these warming-sensitive ecosystems more challenging than previously thought.

Linkages of plant stoichiometry to ecosystem production and carbon fluxes with increasing nitrogen inputs in an alpine steppe.

Unprecedented levels of nitrogen (N) have entered terrestrial ecosystems over the past century, which substantially influences the carbon (C) exchange between the atmosphere and biosphere. Temperature and moisture are generally regarded as the major controllers over the N effects on ecosystem C uptake and release. N-phosphorous (P) stoichiometry regulates the growth and metabolisms of plants and soil organisms, thereby affecting many ecosystem C processes. However, it remains unclear how the N-induced shift in the plant N:P ratio affects ecosystem production and C fluxes and its relative importance. We conducted a field manipulative experiment with eight N addition levels in a Tibetan alpine steppe and assessed the influences of N on aboveground net primary production (ANPP), gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem exchange (NEE); we used linear mixed-effects models to further determine the relative contributions of various factors to the N-induced changes in these parameters. Our results showed that the ANPP, GEP, ER, and NEE all exhibited nonlinear responses to increasing N additions. Further analysis demonstrated that the plant N:P ratio played a dominate role in shaping these C exchange processes. There was a positive relationship between the N-induced changes in ANPP (ΔANPP) and the plant N:P ratio (ΔN:P), whereas the ΔGEP, ΔER, and ΔNEE exhibited quadratic correlations with the ΔN:P. In contrast, soil temperature and moisture were only secondary predictors for the changes in ecosystem production and C fluxes along the N addition gradient. These findings highlight the importance of plant N:P ratio in regulating ecosystem C exchange, which is crucial for improving our understanding of C cycles under the scenarios of global N enrichment.