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This study describes traction behaviours of lubricant films having anomalous shapes under elastohydrodynamic lubrication conditions. The traction generated at a point contact area between a glass or sapphire disc and a steel ball was measured by changing the slide-to-roll ratio. Three alcohols, 1-dodecanol, ethylene glycol and glycerol, and two alkanes of n-tetradecane and n-hexadecane were used as lubricants. Lubricants developing anomalous film shapes exhibited a solid-like behaviour with a sharp traction peak at low slide-to-roll ratios. On the contrary, other lubricants having conventional film shapes indicated a gradual increase in traction coefficient with increasing slide-to-roll ratios. The similarity of the traction behaviour to that of traction fluids supports the solidification of the film, which developed anomalous film shapes.

Extreme pressure (EP) additives are used to reduce friction and improve the wear resistance of lubricants that are used in engine and gear systems in vehicles and cold working process. Sulfur-containing EP additives react with the metal surface to form inorganic tribofilms, such as those containing iron sulfide, with a relatively low shearing strength that prevents scuffing. In this study, tribofilms formed under boundary lubrication via the reaction of a polysulfide additive on carbon steel (S45C) and stainless steel (SUS304) surfaces were investigated using four ex situ techniques, namely, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction analysis, and transmission electron microscopy, to understand the causes of scuffing in stainless steel. In the tests conducted with the SUS304 disc, the friction coefficient increased more slowly compared to that of the S45C disc and showed fluctuations. The tribofilm on the S45C disc comprised the outermost and inner layers of FeS2 (pyrite) and FeS (troilite) structures, respectively. Conversely, the tribofilm on the SUS304 disc surface possessed an FeS2 structure in both the outermost and inner layers. The tribofilm on the SUS304 disc exhibited poor crystallinity in the outermost layer and was thinner than that formed on the S45C disc. The formation of a weaker tribofilm on the SUS304 disc probably introduced instability of the friction coefficient and scuffing.

A solid contact model with high accuracy is required for mixed lubrication calculation to predict friction loss and wear in sliding parts by computer-aided engineering; however, existing models hav...

Paddy fields are considered as one of the most important sources of anthropogenic methane (CH4) and nitrous oxide (N2O) emissions. While several technical options have been proposed to reduce these...

Scuffing is a catastrophic failure that causes significant surface damages such as plastic flow and welding with a marked increase in friction, wear, temperature and noise. In this study, variations in the crystal grain structure of a steel surface was analysed in situ during the scuffing process using a synchrotron X-ray diffraction system, combined with a visible camera and a near-infrared thermometer. The in situ observation system was synchronously operated to capture a contact area between a rotating sapphire ring and a stationary bearing steel pin. The Debye–Scherrer ring diffracted from the contact area was captured by a two-dimensional detector. The scuffing behaviour could be classified as either micro scuffing or macro scuffing. During the micro scuffing period, plastic flow occurred intermittently with a significant temperature rise of approximately 1000 °C. During the macro scuffing period, heat was continuously generated over the contact area. When plastic flow occurred, the captured Debye–Scherrer ring indicated the orientation of crystal grains as well as a phase transformation from martensite to austenite. This study constitutes the first in-situ observation of the behaviour of crystal grains in the dynamic recrystallisation process occurring during the scuffing process.

The atmospheric concentration of methane has increased rapidly in recent years. Because it is a radiative trace gas and takes part in atmospheric chemistry, the rapid increase could be of significant environmental consequence. Of the wide variety of sources, rice fields are considered an important source of atmospheric methane because the harvest area of rice has increased greatly in the last 50 years. Because of the possibility of controlling the emission by agronomic practices, rice cultivation must be one of the most hopeful sources for mitigating methane emission.

Rice cultivation has long been known as one of the dominant anthropogenic contributors to methane (CH4) emissions, yet there is still uncertainty when estimating its emissions at the global or regional scale. An increasing number of rice field measurements have been conducted globally, which allow us to reassess the major variables controlling CH4 emissions and develop region- and country-specific emission factors (EFs). The results of our statistical analysis show that the CH4 flux from rice fields was closely related to organic amendments, the water regime during and before the rice-growing season, soil properties and agroecological conditions. The average CH4 fluxes from fields with single and multiple drainage were 71 % and 55 % that of continuously flooded rice fields. The CH4 flux from fields that were flooded in the previous season were 2.4 and 2.7 times that of fields previously drained for a short and long season, respectively. Rice straw applied at 6 t ha−1 in the preseason can decrease CH4 emissions by half when compared to that applied shortly before rice transplanting. The global default EF was estimated to be 1.19 kg CH4 ha−1 day−1 with a 95 % confidence interval of 0.80 to 1.76 kg CH4 ha−1 day−1 for continuously flooded rice fields without organic amendment and with a preseason water status of short drainage. The lower EFs were found in countries from South Asia (0.85 kg CH4 ha−1 day−1) and North America (0.65 kg CH4 ha−1 day−1) relative to other regions, indicative of geographical variations at sub-regional and country levels. In conclusion, these findings can provide a sound basis for developing national inventories and mitigation strategies of CH4 emission from rice fields.

We conduct in-situ observations of the wear process of metals in dry conditions. To this end, we constructed an experiment to observe the wear process of a point contact area, created between a rotating sapphire disc and a metal pin. The experimental setup included a microscope and a camera with visible-light and near-infrared detectors. Several steels, including stainless steel, and copper alloys were tested as pin materials. The wear comprised plastic flow, formation of transfer layers from the metal pin onto the sapphire disc, and expansion of the contact area. The influences of metal compositions and base metals on the wear behaviour were discussed.

Methane (CH4) is a greenhouse gas, and paddy fields are one of its main anthropogenic sources. In Japan, country-specific emission factors (EFs) have been applied since 2003 to estimate national-scale CH4 emission from paddy field. However, these EFs did not consider the effects of factors that influence CH4 emission (e.g., amount of organic C inputs, field drainage rate, climate) and can therefore produce estimates with high uncertainty. To improve the reliability of national-scale estimates, we revised the EFs based on simulations by the DeNitrification-DeComposition-Rice (DNDC-Rice) model in a previous study. Here, we estimated total CH4 emission from paddy fields in Japan from 1990 to 2010 using these revised EFs and databases on independent variables that influence emission (organic C application rate, paddy area, proportions of paddy area for each drainage rate class and water management regime). CH4 emission ranged from 323 to 455ktCyr-1 (1.1 to 2.2 times the range of 206 to 285ktCyr-1 calculated using previous EFs). Although our method may have overestimated CH4 emissions, most of the abovementioned differences were presumably caused by underestimation by the previous method due to a lack of emission data from slow-drainage fields, lower organic C inputs than recent levels, neglect of regional climatic differences, and underestimation of the area of continuously flooded paddies. Our estimate (406ktC in 2000) was higher than that by the IPCC Tier 1 method (305ktC in 2000), presumably because regional variations in CH4 emission rates are not accounted for by the Tier 1 method.

The objective of this study is to better understand the scuffing phenomenon using a specially designed in-situ observation system. The developed in-situ observation system comprises four sets of a digital CCD camera and a xenon flashing lamp. The independent operation of the capture devices could capture four successive images over short time intervals during a long-duration experiment. Scuffing behaviour that occurs in a friction surface between a rotating sapphire disc and a stationary martensitic steel pin in dry conditions was observed by the developed in-situ observation system. The results showed the behaviour of plastic flow that occurred in the frictional contact area. Plastic flow was observed to occur immediately after the transfer layer passed through the contact area. Each instance of plastic flow was a few milliseconds long. The speed of plastic flow was much less than the sliding speed. At the end of the fast plastic flow process, the brightness of the area of the plastic flow increased, which could be attributed to the oxidation of the steel surface.

This study describes the effect of textured patterns on the lubrication performance in starved hydrodynamic lubrication. A friction test rig including an in-situ observation system is used with controlled lubricant quantity to create point contact between a convex glass lens and rotating steel disc. The in-situ observation system captures the meniscus pattern around the lubricated area as well as optical interferograms of the film thicknesses. Longitudinal or transverse grooves are created on discs, which improve lubricant supply into the lubricated area at high sliding conditions, compared to a flat disc. Mechanisms for improving the lubricant supply through textured patterns are discussed based on the in-situ observation results.

Field experiments of two consecutive years (2010–2011) were conducted to investigate the effect of crop-rice rotation systems on greenhouse gas (GHG) emissions, soil carbon sequestration, and rice yield. Rotation crops were cultivated in the dry season, while rain-fed rice was grown in the wet season. Four different treatments were investigated: fallow-rice (RF), rice–rice (RR), corn-rice (RC) and sweet sorghum-rice (RS). The closed-chamber method was used for flux measurements of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) in the field. Parameters such as soil carbon budgets (SCBs), soil organic carbon (SOC) stocks, and crop yields were also measured. In this study, it was found that RC and RS rotations reduced CH4 emissions by 78–84%, and reduced net CO2 equivalent emissions (CH4 and N2O) by 68–78%, as compared with RR. After two consecutive years of crop cultivation, SCBs were reclaimed by positive values in the RC and RR treatments. The SOC stocks were maintained in the RR, RC and RS treatments, but decreased in the RF. Although RF also reduced the net CO2 equivalent emissions by 72–84% as compared with RR, there were losses in soil carbon sequestration and agricultural land utilization. The rice grain yields of RC and RS were stable in both years, while RF fell slightly by 11%, and RR significantly reduced by 39% from the first year.

This study investigates the relationship between the molecular structure of lubricants and the appearance of anomalous film shapes in elastohydrodynamic lubrication conditions. A ball-on-disc type test rig was used, which produced a point contact area between a rotating glass disc and rotating steel ball. Several pure liquids such as alkanes, alcohols, and others with a single polar site were used as lubricants. Linear chain lubricants caused solid-like behaviour in the film formation, traction coefficient and flow out time of entrapped lubricant in shock loading tests whereas complexly shaped lubricants caused liquid-like behaviour. The clear dependence on lubricant type appears to indicate that the anomalous film shapes formed due to the solidification of the lubricant.

This study investigated the relationship between the chemical reaction film formation derived from engine oil additives and crystal grain structure of a steel surface. Variations in the contact area between a rotating sapphire disc and a stationary steel pin were captured by a monochromatic high-speed camera. A fully formulated low viscosity engine oil was used as the lubricant. After friction tests, the elements on the surface were analysed using energy dispersive X-ray spectroscopy and the crystal grain structure of the top surface layer by electron backscatter diffraction. In-situ and ex-situ analyses revealed that plastic flow changed the crystal grain structure of the surface, inhibiting the formation of the chemical reaction film derived from additives.

Application of biochar to the soil has been reported as one of the mitigation technologies of CH4 emission from rice cultivation due to its unique characteristics of high porosity and surface area. The application of small particle size of biochar is rich in surface area that may enhance the mitigation potential. Rice cultivation and soil incubation experiments were conducted to evaluate the effect of two groups of biochar particle size on CH4 emission and production in order to show the mitigation potential. This experiment consists of three treatments including no biochar (CT), small particle size (0.5-2 mm) biochar (SB), and large particle size (2-4 mm) biochar (LB). Both biochar sizes were amended at 10 t ha−1 equivalent rate and all treatments were applied chemical fertilizer at 100 kg N ha−1 equivalent rate. The results demonstrated that SB and LB reduced cumulative CH4 emission by 24.0% and 17.1% and cumulative CH4 production by 24.6% and 15.0% as compared to CT, respectively. Our results showed that SB achieved higher mitigation potential than LB by an average of 8.47%, although it was not significant. The mitigation of both biochar sizes was supported by the significant change of soil methanogens and methanotrophs abundances. The suppression of methanogens abundance and the stimulation of methanotrophs abundance indicated in the ratio of mcrA to pmoA was significantly reduced in SB (68.0%) which higher than in LB (56.3%) as compared to CT. Both application sizes also increased soil oxidation capacity through soil Eh increase which no difference between SB and LB. In term of grain yield, SB and LB were not different and both did not show the significant change as relative to CT. The application of small size biochar in this study affected more mitigation potential of CH4 emission as compared to larger size, therefore there is a need of further study on typical size of biochar in order to recommend the most mitigation potential of biochar application.

In the current study, the heat generation behaviour at plastic flow area in the contact area during a scuffing process was observed in situ using a monochrome high-speed camera that detected both visible and near-infrared light. The scuffing test was conducted using a pin-on-disc test rig comprising a rotating sapphire disc and a fixed martensitic steel pin. Engine oil was supplied as a lubricant. The images captured by the high-speed camera clearly showed changes in the contact area and the heat generation behaviour. It was found that the heat generation behaviour could be classified into three stages during scuffing. In the first stage, local heat generation occurred intermittently at local severe contact points, such as the passing of transfer layers on the sapphire disc and the trailing edge of the contact area. In the second stage, heat generation occurred intermittently over larger areas in which heat had been generated until that time. When the entire contact area had previously generated heat, heat generation became continuous throughout the contact area in the third stage. During the third stage, the contact area was increased rapidly, which caused catastrophic failure. These results highlight important questions regarding material phenomena that remain to be investigated.

In a previous study, we developed a novel in situ analysis and observation system that allows for simultaneous synchrotron X-ray diffraction (XRD) and optical observations of a frictional surface. This in situ system was used to investigate the scuffing phenomena of SUJ2 bearing steel (AISI 52100); characteristic surface deteriorations occurred during the scuffing process, including plastic flow, heat-spot formation, austenite transformation, and a decrease in the width of the XRD peaks (indicating a decrease of dislocations and strain). These surface deteriorations are not observed during normal wear, hence it is possible that they cause catastrophic wear during the scuffing of steel. In this study, to elucidate the scuffing mechanism of steel, we focused on the following two points: (1) whether the above surface deteriorations are unique to SUJ2 steel or whether they occur in general steels as well, and (2) the extent to which these surface deteriorations contribute to the wear amount. To achieve these objectives, we performed scuffing tests on four types of steel using the previously developed in situ system. In particular, we focused on the first stage of the scuffing process. The present test results suggest that these surface deteriorations also occur in general steels, and that plastic flow and heat-spot formation, which originate from the same phenomenon, are the dominant contributors to the wear amount during the scuffing of steel. Furthermore, the wear amount per unit plastic flow appears to be independent of steel composition.

Rice cultivation has long been known as one of the dominant anthropogenic contributors to methane (CH 4 ) emissions, yet there is still uncertainty when estimating its emissions at the global/regional scale. An increasing number of rice field measurements have been conducted globally, which allow us to assess the major variables controlling CH 4 emissions and develop the region- and country-specific emission factors (EFs). Results shown that the CH 4 flux from rice fields were closely related to organic amendment, water regime during and before the rice-growing season, soil properties and climate. The average CH 4 flux from fields with single and multiple drainages were 71 % and 55 % of that from continuously flooded rice fields. The CH 4 flux from fields that were flooded in the previous season were 2.4 and 2.7 times that from fields previously drained for a short and long season. Contrary to the previously reported optimum soil pH of around neutrality, paddy soils with pH of 5.0–5.5 gave the maximum CH 4 emission. Rice straw applied at 6 t ha −1 shortly before rice transplanting can increase CH 4 emission by 3.2 times, while it increases CH 4 emission by only 1.6 times when applied in the previous season. The default EF was estimated to 1.19 kg CH 4 ha −1 d −1 with a 95 % confidence interval of 0.80 to 1.76 kg CH 4 ha −1 d −1 for continuously flooded rice fields without organic amendment and with a preseason water status of short drainage. The default EFs at sub-regional and country levels were also estimated. We conclude that these default EFs and scaling factors can be used to develop national or regional emission inventories.

This chapter provides results of the simultaneous measurements of emission, production, and oxidation of methane (CH4) in a Japanese rice paddy field during an entire cultivation period. It focuses on seasonal changes of CH4 production and oxidation in different depths of paddy soil, and their relationship to CH4 emission, in order to understand factors controlling this process in paddy fields. A field study was carried out in an experimental paddy field of the Ryugasaki Branch of the Ibaraki Agricultural Experiment Station during the 1991 growing season. The soil of the paddy field is classified as Gley soil. The closed chamber method was used for the measurements of the CH4 emissions from paddy fields into the atmosphere. Temperature of air and paddy soil at the depths of 0, 2, 5, and 10 cm was continuously recorded during the cultivation periods by using Pt-resistance thermometers and a data logger.

The use of N fertilizers for agricultural production acts as a sources of atmospheric $$\hbox {N}_2\hbox {O}$$ . Fertilizer induced $$\hbox {N}_2\hbox {O}$$ emission considerably varies in accordance with environmental factors. We conducted a $$\hbox {N}_2\hbox {O}$$ flux measurement campaign across 10 different experimental sites with various soil types throughout Japan and investigated the fertilizer induced $$\hbox {N}_2\hbox {O}$$ emission factors (FIEFs) of synthetic fertilizers (mainly urea) in multiple growing periods at each experimental site. FIEFs considerably varied among the 10 sites, and measurement periods ranged from 0.00 to 7.13 % in 40 total observations. Soil profile information divided the experimental sites into two major groups through cluster analysis, which are volcanic or non-volcanic soils. According to this classification, FIEFs were clearly differentiated into high and low FIEF groups (mean values: 2.67 and 0.59 %, respectively). Regression trees selected total soil carbon, the depth to the Fe mottling horizon, and mean air temperature as the key parameters to determine the strength of FIEFs out of 10 explanatory variables (e.g., N fertilizer application rates, fertilizer application times, clay content, total precipitation during measurement periods, pH, total soil carbon, and total soil nitrogen). The existence of shallow Fe mottling layer (up to 42.5 cm) induced high FIEFs in this model, suggesting that upward $$\hbox {N}_2\hbox {O}$$ emissions derived from the intermediate Fe mottling layers presumably contributed high $$\hbox {N}_2\hbox {O}$$ emissions in such soils. Our results suggest that the soil profile information associated with the water regime is an important index for synthetic fertilizer induced $$\hbox {N}_2\hbox {O}$$ emissions.

Planting winter wheat with rice straw application (WS) after rice harvest is a typical practice in Jiangsu Province, China. However, in the past decades quite a large area of paddy fields appeared to be left in fallow in the winter season, letting abundant weeds incorporated prior to rice transplanting (FSW) during the following rice season. Little is known about the effects of WS and FSW on the process of CH4 emission and on relative contribution of acetate to total CH4 production (Fac) and fraction of CH4 oxidized (Fox). Results show that FSW significantly increased CH4 production potential of paddy soil, CH4 concentration in soil solution, and CH4 emission from the fields (P

This study investigates a hydrodynamic lubrication mechanism of textured surfaces, termed “balancing wedge action”, found in pivoted pad bearings. The analytical model is a one-dimensional pivoted ...

Cultivated wetland rice fields are a source of methane (CH4) emissions. To estimate CH4 emissions and develop policies to reduce such emissions, information on water management at the farm level is crucial. It is known that farmers implement midseason drainage (MD) to increase rice yields and save water. However, little is known about whether MD is carried out in soils where CH4 emissions are high and how part-time status will influence management. The objective of this study is to identify factors that determine MD implementation using a binomial logistic regression model based on a farm-level survey in Japan and to indicate possible changes in estimates of CH4 emissions, accounting for current water management practices. The implementation rates were significantly higher where the soil types were classified as having the potential for high CH4 emissions. Under current water management practices, the duration of MD and the percentage of continuous flooding were 5 to 7 days longer and approximately 7 % higher, respectively, than the values used by the Greenhouse Gas Inventory Office of Japan, which in turn are used to report greenhouse gas emissions to the United Nations Framework Convention on Climate Change. By accounting for current water conditions with the Tier 2 method, this study indicates that national estimates of CH4 emissions from rice straw application areas could be lowered by 12.7 %. These results may contribute to the development of a mitigation policy that will help to further reduce CH4 emissions.

This study comprises a comprehensive assessment, integration, and synthesis of data gathered from a 3-year field experiment conducted at four sites in Southeast Asia, namely Hue, Vietnam; Jakenan, Indonesia; Prachin Buri, Thailand; and Muñoz, Philippines, to assess the site-specific feasibility of alternate wetting and drying (AWD) as a greenhouse gas (GHG) mitigation option in irrigated rice fields. AWD effectively reduced water use compared to continuous flooding (CF) but did not significantly reduce rice grain yield and soil carbon content in all sites. Methane (CH4) emissions varied significantly among sites and seasons as affected by soil properties and water management. AWD reduced CH4 emissions relative to CF by 151 (25%), 166 (37%), 9 (31%), and 22 (32%) kg CH4 ha−1 season−1 in Hue, Jakenan, Prachin Buri, and Muñoz, respectively. In Prachin Buri and Muñoz, AWD reduced CH4 emissions only during the dry season. Site-specific CH4 emission factors (EFs) ranged 0.13–4.50 and 0.08–4.88 kg CH4 ha−1 d−1 under CF and AWD, respectively. The mean AWD scaling factors (SFs) was 0.69 (95% confidence interval: 0.61–0.77), which is slightly higher than the Intergovernmental Panel on Climate Change (IPCC)’ SF for multiple aeration of 0.52 (error range: 0.41–0.66). Significant reductions in the global warming potential (GWP) of CH4+nitrous oxide (N2O) by AWD were observed in Hue and Jakenan (27.8 and 36.1%, respectively), where the contributions of N2O to the total GWP were only 0.8 and 3.5%, respectively. In Muñoz, however, CH4 emission reduction through AWD was offset by the increase in N2O emissions. The results indicate that the IPCC’s SF for multiple aeration may only be applied to irrigated rice fields where surface water level is controllable for a substantial period. This study underscores the importance of practical feasibility and appropriate timing of water management in successful GHG reductions by AWD.

In contrast to upland croplands, carbon dioxide (CO2) emission from soils has rarely been investigated previously in fields with paddy rice cultivation. In this study, we hypothesized that CO2 emission from paddy soils is suppressed to be a low level due the soil submergence for months for paddy rice cultivation and conducted a continuous measurement of net CO2 flux from the soil/water surface of a paddy field throughout the year, including both the submerged and drained periods. The net CO2 flux was generally near zero during the submerged period with paddy rice cultivation and showed a slight CO2 influx in the daytime and efflux at nighttime, indicating dominance of photosynthetic CO2 uptake and respiratory CO2 release by aquatic weeds and algae in paddy water. The diurnal variations in net CO2 flux and dissolved CO2 concentration had negative correlations with the pH of paddy water. A remarkably high CO2 efflux was observed during the period with intermittent drainage in summer. Unexpectedly, the cumulative CO2 emissions throughout the year were not considerably lower than those reported in upland croplands ranging from 1309 to 2160 g CO2 m−2 yr−1, of which 41–48% was emitted from the first drainage in summer to the rice harvest in autumn. In summary, in this study, we revealed that CO2 emission from soil in paddy fields is strictly suppressed during the submerged period, but considerably enhanced by the succeeding drainage, which may negate the suppressed CO2 emission during the submerged period.