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Abnormal vibration and noise, originated from friction and wear, are often found in water-lubricated stern-tube bearings, which seriously threatens the safety and concealment of underwater vehicles. In order to better understand the friction-induced vibration in water-lubricated stern-tube bearings, friction pairs of rubber specimens matched with ZQSn10-2 brass were tested on the water-lubricated bearing test rig SBB-100. A high-speed camera was used to track the micro images that focused on of the rubber layer vibration motion, while a machine vision technique also was employed to extract the friction-induced vibration of the test bearings. The experimental analysis results demonstrate that the bearing vibration was mainly induced by stick-slip. Furthermore, the orthogonal experiment method was used to distinguish the key factors that induce the bearing vibration among rotating speed, contact pressure, rubber layer hardness and thickness, and lubrication condition. The analysis results indicate that the importance of factors is sorted in the order of lubrication condition, contact pressure, hardness and thickness of rubber layers. In normal lubrication condition, the intensity of friction-induced vibration of the rubber bearings can be reduced by increasing the hardness of the rubber layer, decreasing the contact pressure, and the thickness of the rubber layer.

The mixture powder of Ultra-high molecular weight polyethylene (UHMWPE) and graphite was blended into nitrile–butadiene rubber (NBR) to be modified to develop a new kind of compound water lubricated rubber bearing with cost-effective, low-friction performance. In order to study the tribological and vibration performance of the new material, a series of experiments were carried out on the test rig SSB-100. Friction coefficient and vibration characteristics under different working conditions: speed, specific pressure and temperature were acquired and analyzed by torque meter and B&K Pulse. The mechanical physical performance of the compound rubber material SPB-N has reached the requirements of Chinese ship standard CB/T769-2008. The results showed that a better tribological performance of the new material met the U.S. military standard (MIL-DTL-17901C (SH)). Stick-slip effect of the new material was induced with critical speed of 0.27 m/s, which showed excellent low-speed performance. Moreover, its friction coefficient reached a minimum value at the speed of 0.54 m/s. Local specific pressure of the new material was 0.7 MPa. The new composite rubber material was served as a kind of water-lubricated bearing material with excellent all-round performances.

Nitrile-butadiene rubber (NBR) and another polymer with an excellent self-lubricating property are blended to develop a new kind of polymer used for water-lubricated stern bearings. The tribological performance of the new Polymer Blend of NBR (PBN), with the comparison of a rubber common used for most stern bearings, was studied using a stern bearing test rig of SSB-100. The results showed that the friction coefficients of PBN are lower than those of NBR under water-lubricated conditions. And the difference is the most evident at speeds of 0.1 ~ 2.0m/s. So PBN will change to Plasto-Elastohydrodynamic (PEH) Lubrication at lower speed to reduce the critical speed of bearing squeal. This indicates blending rubber with other polymers is an effective means to develop low-friction stern bearing materials. Furthermore, test results revealed that reducing the rubber layer thickness and hardness will reduce the friction coefficients. So in the structure design of water-lubricated rubber bearings, selecting proper structural parameter will improve the tribological performance.

CO2 fixation is the central mechanism of primary production in almost all ecosystems,and plays a major role in regulating the concentration of atmospheric CO2.Carbon dioxide accounts for about 50% of the current global warming potential.Soil microorganisms that assimilate CO2 are widely distributed,and have a great ability to adapt to environmental extremes,such as within volcanic sediments,lake wetlands and the submarine realm.Microbial CO2 assimilation is of great significance to climate change mitigation and sustainable development for human beings. It has now been well established that atmospheric concentration of CO2 can be reduced significantly by adopting management practices to enhance CO2 sequestration(storage) in cropland soils.Among the approaches for increasing CO2 sequestration of croplands are soil fertilization management practices,such as returning crop residues to the soil,planting temporarily retired land with grass for stabilization,and integrating nutrient management strategies to diversified cropping systems. Paddy soils are distributed widely throughout the world,and generally are known for their production of greenhouse gasses(N2O and CH4).Numerous studies have used molecular techniques to investigate these microbial driving mechanisms.However,few studies have addressed the importance of microbial CO2 fixation processes in paddy soils.Investigation of the impacts of long-term fertilization on the structure and abundance of CO2 assimilating bacteria in paddy soils can provide a theoretical basis for the application of information on fertilization of paddy-rice fields.This type of research also may benefit the reduction of greenhouse gas emissions and increase carbon sequestration. Although carbon fixating microorganisms exhibit a wide range of physiological and ecological traits,most photo-and chemoautotrophic bacteria use ribulose-1,5-biphosphate carboxylase/oxygenase(RubisCO),which catalyzes the first rate-limiting step in the Calvin cycle to incorporate atmospheric CO2.The cbbL gene,which encodes the large subunit of the form I RubisCO is especially useful as a functional marker for significant phylogenetic analyses of CO2 fixating microorganisms in different ecological systems. In this study,soil samples were collected from a long-term fertilization experiment,which included a station that received no fertilization(CK),one treated with chemical fertilization(NPK),and one with NPK plus crop residue return(NPKS).The abundance,diversity,and composition of soil-CO2 fixating bacteria were determined using Polymerase Chain Reaction(PCR),cloning and sequencing,and real-time quantitative PCR of the cbbL gene to explore the effects of long-term fertilization on the structure and abundance of the CO2 fixation bacterial community.Based on sequence libraries of cbbL genes,our results clearly demonstrate that there was a significant response difference in community composition with respect to long-term fertilization regimes.A total of 165 cbbL genotypes from three different treatment soils were divided into 14 bacterial cbbL gene phylotypes,mainly including Bradyrhizobium,Ralstonia,and Thiobacillus.Facultative autotrophic bacteria,such as Bradyrhizobium and Ralstonia,dominated both in NPK and NPKS treatment soils,while growth of the obligate autotrophic bacteria,such as Thiobacillus and Nitrosospira,were suppressed.LUBSHUFF statistical analyses also demonstrated that cbbL gene libraries of CK,NPK and NPKS treatments were significantly different from one another.The Rarefaction curve indicated that fertilizer addition increases cbbL gene diversity.Thus,the NPK treatment had the highest curve.The abundance of the bacterial cbbL gene ranged from 3.35×108—5.61×108 copies g-1 soil.Crop residue return NPKS had the highest abundance of bacterial cbbL gene,which was about one half the value of CK.Finally,application of chemicals and organic fertilizers in paddy ecosystems significantly influenced the CO2 fixating bacterial community structure,and increased bacterial abundance and diversity.These results provide a strong basis for further investigation of fertilization on soil carbon sequestration potential and its related microbial mechanisms.

Nitrogen(N) loss via nitrate(NO-3) leaching from soil is one of the major contributors to environmental degradation.Vegetable soil is characterized by intensive fertilization with low nitrogen usage efficiency as a result of NO-3 leaching.Nitrification and de-nitrification are the most important processes in NO-3 formation and transformation,and are driven by functional microorganism in soil.The use of nitrification inhibitors,such as DCD,may play a key role in mitigating N loss. Investigations were conducted on the inhibitory effect of DCD to the functional microorganisms among the processes of nitrification and de-nitrification,and the relationship between DCD and nitrogen transformation.In this research,two kinds of vegetable soils were selected from Huangxing country,Changsha,reflecting long-term(about 20 years) and short-term vegetable cropping(1 year).Each sample was a mixture of 5 cores(0—20cm top soil) randomly taken in the same field.Two treatments for each soil sample were conducted: CK treatment(urea at 0.2g N/kg),and DCD treatment(urea at 0.2g N/kg with DCD 0.02g/g),each treatment with 3 replicates.The pots were incubated for 64 days at 25℃,and systematically measured NH+4 and NO-3 concentrations.According to the dynamics of NH+4 transformation,three soil samples were taken at the 3rd,7th and 64th days,which represented the increasing,peak and decreasing status of NH+4 concentration.The abundances of nitrifying gene amoA and denitrifying gene nirK were analyzed by Real-time PCR,. Results indicated that NH+4 concentrations of DCD treatments increased 248% and 225% compared to the CK treatment in the long-term and short term vegetable soils,respectively.NO-3 concentrations of DCD treatments decreased 31% and 20% compared to the CK treatment in the long-term and short-term vegetable soils separately.Furthermore,NH+4 concentration of DCD treated short term soil decreased slightly while long term soil remained the same level,suggesting that DCD had a better effect on long-term vegetable soil.The abundances of 16S rRNA gene and nirK gene had no significant difference between two treatments.However,the amoA gene abundance of DCD treatment for the long-term vegetable soil and the short-term vegetable soil had significantly decreased compared to the CK treatment,61% and 48% respectively on the 3rd day,71% and 54% respectively on the 7th day,but no differences were observed between two treatments after 64 days incubation.There was extremely significant correlation between NO-3 concentration and the amoA gene abundance. The results showed that the process of nitrification could be inhibited by DCD through restraining the growth of nitrifying bacteria.In addition,intensive application of inorganic fertilizer accelerated N element cycle in soil through the shift of composition and abundance of nitrogen-transformation functional microorganism.Thus,it might be better to use DCD together with suitable amount of fertilizer to improve nitrogen fertilizer usage efficiency and reduce nitrate loss.