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As a simple and effective force tracking control method, impedance control is widely used in robot contact operations. The internal control parameters of traditional impedance control are constant and cannot be corrected in real time, which will lead to instability of control system or large force tracking error. Therefore, it is difficult to be applied to the occasions requiring higher force accuracy, such as robotic medical surgery, robotic space operation and so on. To solve this problem, this paper proposes a model reference adaptive variable impedance control method, which can realize force tracking control by adjusting internal impedance control parameters in real time and generating a reference trajectory at the same time. The simulation experiment proves that compared with the traditional impedance control method, this method has faster force tracking speed and smaller force tracking error. It is a better force tracking control method.

Forest canopies are the functional interface between ecosystem and the atmospheric nitrogen (N) deposition. However, the sources of spatio‐temporal variability and intra‐event variation of N deposition via throughfall (TF) remain ambiguous. Here, we analysed TF samples for concentrations and fluxes of ammonium (NH4+) and nitrate (NO3−) using an array of 20 fixed‐position collectors on an event and within event basis throughout the 2019 growing season in a Chinese pine plantation, Northern China. Results showed that the volume weighted mean concentrations of NH4+ and NO3− in TF were significantly higher than those in bulk precipitation (BP) during the study period. A canopy budget model indicated that canopy uptake was more dominant than dry deposition for NH4+, while the reverse was true for NO3−. This caused a comparable TF NH4+ flux but an enhanced TF NO3− fluxes compared to BP. The intra‐event trend and magnitude of TF NH4+ and NO3− concentrations were influenced by the antecedent dry period and rainfall intensity, and indicated that biological nitrification may occur in the canopies. In addition, due to the larger of canopy NH4+ uptake that counteracted the amplifying effect of dry deposition, the spatial variability of TF NH4+ concentration was significantly lower than that of TF NO3− concentration, and exhibited more temporal persistence. No relationship was found between the spatial distribution of TF NH4+ concentration and the TF amount, the distance to the nearest trunk, nor the canopy cover, whereas the TF NO3− concentration was significantly related to the TF amount and the canopy cover. These findings can enhance our understanding of N processes within canopies, and have important implications for evaluating the impacts of N deposition in forest ecosystems. [ABSTRACT FROM AUTHOR]

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS−), and becomes underwater superaerophobic as the PFOS− are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices. [ABSTRACT FROM AUTHOR]

An increasing number of studies have examined the effects of various biotic and abiotic factors on stemflow production. Of those that have ascribed the importance of canopy structure to stemflow production, there has been a bias towards field studies. Coupling Bayesian inference with the NIED (National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan) large‐scale rainfall simulator, this study leveraged a unique opportunity to control rainfall amounts and intensities to pinpoint the canopy structural metrics that differentially influence stemflow funnelling ratios for three common tree species between leafed and leafless canopy states. For the first time, we examined whether canopy structure metrics exert a static control on stemflow funnelling ratios or whether different elements of canopy structure are more or less important under leafed or leafless states, thereby allowing us to determine if tacit assumptions about the static influence of canopy structure on stemflow production (and funnelling) are valid (or not). Rainfall simulations were conducted at 15, 20, 30, 40, 50, and 100 mm h−1 under both leafed and leafless tree conditions (12 simulations in total) to detect any differential effects on the presence or absence of foliage on stemflow funnelling ratios. For leafed conditions, the highest percentages of best‐fitting models (ΔDIC ≤2) indicated that stemflow funnelling ratios were mainly controlled by total dry aboveground biomass (Ball), diameter at breast height (DBH), total dry foliar biomass (Bf), tree height (H), and woody to foliar dry biomass ratio (BR). Whilst for the leafless state, the highest percentages of best‐fitting models (ΔDIC ≤2) indicated that total dry branch biomass (Bbr) was relatively dominant as was the interaction effects between crown projection area and species (CPA:species). These results compel us to reject any assumption of a static effect of different elements of canopy structure on stemflow funnelling. [ABSTRACT FROM AUTHOR]

Although we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multinational data set of >120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared with leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops (D50_DR, 50th cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees (D50_DR of 4.32 mm). Canopy drip was much larger in diameter under woody drip points (D50_DR of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points (p ranged from <0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size‐dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor. [ABSTRACT FROM AUTHOR]

Abstract: Spatial variability of throughfall (TF) isotopic composition, used as tracer input, influences isotope hydrological applications in forested watersheds. Notwithstanding, identification of the dominant canopy factors and processes that affect the patterns of TF isotopic variability remains ambiguous. Here, we examined the spatio‐temporal variability of TF isotopic composition in a Japanese cypress plantation, in which intensive strip thinning was performed and investigated whether canopy structure at a fine resolution of canopy effect analysis is related to TF isotopic composition and how this is affected by meteorological factors. Canopy openness, as an index of canopy structure, was calculated from hemispherical photographs at different zenith angles. TF samples were collected in a 10 × 10 m experimental plot in both pre‐thinning (from July to November 2010) and post‐thinning (from May 2012 to March 2013) periods. Our results show that thinning resulted in a smaller alteration of input δ18O of gross precipitation, whereas the changes in deuterium excess varied in both directions. Despite the temporal stability of spatial patterns in TF amount, the spatial variability of TF isotopic composition was not temporally stable in both pre‐ and post‐thinning periods. Additionally, after thinning, the isotopic composition of TF was best related to canopy openness calculated at the zenith angle of 7°, exhibiting three different relationships, that is, significantly negative, significantly positive, and nonsignificant. Changes in meteorological factors (wind speed, rainfall intensity, and temperature) were found to affect the relationships between TF δ18O and canopy openness. The observed shifts in the relationships reveal different dominant factors (partial evaporation and the selection), and canopy water flowpaths control such differences. This study provides useful insights into the spatial variability of TF isotopic composition and improves our understanding of the physical processes of interception through canopy passage. [ABSTRACT FROM AUTHOR]

Throughfall ( TF ) is a critical component of the hydrological and biogeochemical cycles and is greatly influenced by stand structures in forested watersheds. Previous studies have examined the relationships between TF and stand structures for different species and regions. However, there remains acknowledged difficulty in estimation of TF with changing stand structures due to forest management (e.g., thinning) for specific species and regions. This study conducted intensive thinning with 43–50% stem removal at seven experimental plots with various structures (e.g., stand density, canopy cover and basal area) across Japan that were covered by Japanese cypress ( Chamaecyparis obtusa Endl.) and cedar ( Cryptomeria japonica D. Don) plantations. TF was measured by a set of 20 tipping-bucket rain gauges placed in a lattice-like pattern within the plots before and after thinning. Results showed that during the study periods, thinning caused an increase in the mean TF rate from 63.2 ± 7.0% to 75.4 ± 6.0%. The TF rate was significantly negatively correlated with stand density, canopy cover, and basal area on a stand scale. Additionally, the slope ( a TF ) of event-based linear TF - P g (gross rainfall) equation was significantly higher in post-thinning (0.782 ± 0.077) than that in pre-thinning (0.663 ± 0.078), whereas it’s intercept ( b TF ) showed no significant difference (−0.707 ± 0.810 mm in pre-thinning and −0.441 ± 0.607 mm in post-thinning). The a TF significantly decreased with increasing stand density and canopy cover, whereas the b TF was not significantly correlated with any forest-structure variables. Further, the TF rate and a TF were estimated, respectively, by their related stand-structural variables in multiple regression models with high determination coefficients and moderate relative errors. The b TF was assumed to be a constant and its mean value obtained from all the experimental plots in each (pre- and post-thinning) period. Thus, the models of stand-scale TF rate and event-based TF amount were developed with input of commonly forest inventories. These models were validated by using the dataset of this study and earlier publications for Japanese cedar and cypress plantations, and showed good fit between the estimated and measured values. These models are practical tools that can be readily used for assessing the changes in TF with changing stand structures at both stand and event-based scales, and have also potential implications in evaluating the spatial TF patterns at catchment scale and exploiting similar models in other species and regions. [ABSTRACT FROM AUTHOR]

We examined the effect of strip thinning on the spatio-temporal variability of throughfall (TF) in a mature Japanese cypress (Chamaecyparis obtusa) stand. Strip thinning, which removed 50% of stems, was performed in a catchment in October 2011. TF was examined by setting up 20 tipping-bucket rain gauges in an experimental plot. Canopy interception parameters were derived from high-temporal-resolution TF data. Observations were obtained during the growing season in the pre-thinning and postthinning periods. The results demonstrated that after thinning, the TF rate increased from 64.3 to 76.2%, and the mean coefficient of variation of the TF rate significantly decreased from 27.3 ± 9.7 to 22.5 ± 6.8%. The spatial TF patterns were largely related to the rainfall class. There was no significant difference in the TF rate for the rainfall amount >25mm between the periods. The temporal persistence of the normalized TF was slightly stable in the post-thinning period and was not significantly related to canopy cover or the distance to the nearest trunk of each rain gauge in either period. Additionally, thinning resulted in an increase in the proportion of direct TF (from 0.14 ± 0.07 to 0.33 ± 0.11) and a decrease in canopy water storage (from 2.4 ± 0.7 to 1.5 ± 0.5 mm). The quantification of the canopy interception parameters can aid in modelling the changes in interception loss and its processes induced by thinning. These findings also help recognize the changes in spatial TF patterns under different forest management practices. [ABSTRACT FROM AUTHOR]

• Spring wheat was 15N-labeled via a split-root technique. • The NdfR was estimated by the isotope ratio and isotope mass balance approaches. • The isotope ratio approach underestimated NdfR before plant maturity. • The two approaches had no difference for estimation of NdfR after plant maturity. • Selecting appropriate calculation approach to quantify NdfR should be considered. Accurate quantification of nitrogen (N) derived from rhizodeposition (NdfR) is crucial to assess N stored in plants and the total N balance in plant-soil systems. However, there remains uncertainty in the estimates of NdfR for 15N-labeled plants with the split-root technique using the isotope ratio approach and the isotope mass balance approach. Here, we examined the two calculation approaches that estimate NdfR from 15N-urea (99 atom%) labeling of spring wheat (Triticum aestivum L.) using the split-root technique in a pot experiment over plant growth, and assessed the causative factors of their potential bias. The results showed that independent of the approach, the total amount of NdfR was 5.3–9.8 mg plant−1 and contributed up to 19.9–26.3% of total plant N throughout the growth period. At the heading and filling stages after labeling, the amounts of NdfR using the isotope ratio approach (5.3 and 6.6 mg plant−1, respectively) were significantly lower than those (7.1 and 7.8 mg plant−1, respectively) using the isotope mass balance approach, due to soil N losses and an uneven distribution of 15N. At the ripening stage after labeling, however, the differences in the amount of NdfR between the two approaches disappeared (9.8 and 9.6 mg plant−1, respectively). This indicated that the isotope ratio approach underestimates the amount of NdfR during the plant developmental period, while both approaches can be used to quantify the amount of NdfR at plant maturity. [ABSTRACT FROM AUTHOR]

• TF or SF base cations fluxes had no significant differences between UP and LP. • Relative contributions of DD and CE to NTF were different at the two slope plots. • NTF K+ flux was dominated by CE regardless of slope position. • NTF Ca2+ and Mg2+ fluxes were dominated by DD in UP, while CE in LP. • ANC and ALK of TF and SF were significantly higher compared to BP. Atmospheric deposition of base cations in contact with the canopy alters their chemical characteristics and plays a vital role in offsetting soil acidification and nutrient imbalance by replenishing the base cationic pool in forest ecosystems. However, the effects of site characteristics on deliveries of base cations fluxes via throughfall (TF) and stemflow (SF) across topographic gradients within a watershed remain less understood. Here, we examined the concentrations and fluxes of base cations (potassium (K+), calcium (Ca2+), magnesium (Mg2+) and sodium (Na+)), acid neutralizing capacities (ANC) and alkalinity (ALK) in bulk precipitation (BP), TF and SF in an upper slope plot (UP) and a lower slope plot (LP) in a subtropical broadleaved montane forest, Southeast China. In addition, a canopy budget model was applied to distinguish the relative contributions of dry deposition (DD) and canopy exchange (CE) to net TF + SF (NTF) flux. Results showed that annual volume weighted mean concentrations of base cations in TF and SF were significantly higher than those in BP in both UP and LP. Annual fluxes of TF or SF base cations had no significant differences between UP and LP, resulting in a comparable of the NTF fluxes. However, the relative contributions of DD and CE to NTF were different at the two slope plots. NTF K+ flux was dominated by CE regardless of slope position. Unlike K+, NTF Ca2+ and Mg2+ fluxes were dominated by DD in UP, while CE in LP. In addition, ANC and ALK of TF and SF were significantly higher compared to BP , suggesting rainwater beneath the canopy became less acidic and may mitigate in part the risk of soil acidification, especially in the dormant season. This study can provide insights into the spatial variability of chemical characteristics of base cations, and improve our understanding of the quantities and controls of external and internal nutrient inputs occurring within the canopy in forest watershed. [ABSTRACT FROM AUTHOR]

Knowledge of the characteristics of chemical components transported in the xylem sap of trunks remains deficient and limited because no appropriate method exists to extract the xylem sap from this part of the tree. We thus explored the differences in xylem sap components extracted by means of centrifugation and water displacement methods and depicted the level and behavior of chemical components in the xylem sap of trunks and branches of different aged trees from a pine forest in northern China. There were no significant differences between the two methods with respect to nitrogen (N) compounds and inorganic ions in the xylem sap. Potassium concentrations obtained by the methods were similar and consistent with the values obtained from earlier publications on woody species. This suggests that contamination of the xylem sap by the centrifugation method is negligible, and this method would be a reliable and robust tool for collection of the trunk xylem sap. Dissolved organic N was the dominant component of total N followed by nitrate (NO 3 −) and ammonium (NH 4 +). Potassium and chloride were the predominant cation and anion, respectively, of the xylem sap. The NO 3 − concentration basically did not change, whereas the NH 4 + concentration was larger transported from the trunk to branches for the large tree class during foliage senescence. More inorganic N components (mainly NO 3 −) were found in young trees than in old trees. Our study contributes to improve the diagnostic assessments of tree physiological processes and growth in mature forest trees under environmental changes. • A centrifugation method was proposed to collect the trunk xylem sap of forest trees. • DON was the dominant component of TN in trunk xylem sap followed by NO 3 − and NH 4 +. • K+ and Cl− were the predominant cation and anion, respectively, of trunk xylem sap. • NO 3 − and NH 4 + had different behaviors when transported from the trunk to branches. • More inorganic N components (mainly NO 3 −) were found in young trees. [ABSTRACT FROM AUTHOR]

A wide area of paddy fields was contaminated by radiocesium derived from the Fukushima nuclear accident. Implement of agricultural countermeasures is one of the principle methods to reduce the contamination of rice plants. In this study, the effect of topsoil removal measure and fertilizer application on radiocesium uptake by rice plants was investigated over a four-year period. Some other available countermeasures carried out after the Fukushima nuclear accident were also summarized. The results indicate that the effect of topsoil removal measure on the accumulation of radiocesium in rice plants was effective, but the concentration ratio of radiocesium activity concentration between rice plant and soil increased. This may be correlated with the radiocesium imported from irrigation water and relatively high exchangeable radiocesium proportion of plowing soil in the topsoil removal paddy. We summarized four year's data to further confirm that potassium and nitrogen fertilizers had an opposite effect on the accumulation of radiocesium in rice plants. Increasing potassium and reducing nitrogen fertilizer conditions tended to inhibit the radiocesium uptake by rice plants. Moreover, of all the available countermeasures applied in the paddy fields, the most effective countermeasure was the application of phlogopite. However, further analyses are required to confirm the effectiveness of application of phlogopite considering the limited available information. [ABSTRACT FROM AUTHOR]

The effects of a 50% forest thinning intensity on Fukushima-derived 137 Cs deposition by litterfall and its discharge by runoff in hillslope coniferous forest were monitored using four litterfall traps and a hillslope erosion plot. The observation was underway during the pre-and post-thinning periods. Results demonstrated that during the pre-thinning period a total 150 ± 13 g m -2 of litterfall deposited about 924 ± 69 Bq m -2 of 137 Cs. This accounts for 11% of the local 137 Cs fallout recorded for the study site in the aftermath of the accident. After thinning, both litterfall and 137 Cs increased by more than six- and two-fold, respectively. This is possibly owing to the slow individual tree recovery rate assisted by the change on the running space provided by canopy openings, which can accelerate even the normal gust wind to gain damaging power on the unshielded mechanically injured parts of the contaminated residual trees. In both cases, litterfall generally transferred about 37% (3 ± 0.2 kBq m -2 ) of the local 137 Cs fallout onto the forest floor over the observation period. The eroded litter-associated 137 Cs increased by about a factor of two after thinning, which only accounted for less than 1% of 137 Cs deposited by litterfall. This implies that the forest floor retains 137 Cs and remains contaminated regardless of the size of the eroded litter material. But this could become a potential secondary contamination source for the downstream resources such as water bodies and villages, especially at the time of flooding, which in turn calls a serious attention in designing decontamination schemes., (Copyright © 2019 Elsevier Ltd. All rights reserved.)