Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seism...Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.展开更多
Generation of large strains upon Na^(+) intercalation is one of the prime concerns of the mechanical degradation of Prussian blue(PB)and its analogs.Structural construction from the atomic level is imperative to maint...Generation of large strains upon Na^(+) intercalation is one of the prime concerns of the mechanical degradation of Prussian blue(PB)and its analogs.Structural construction from the atomic level is imperative to maintain structural stability and ameliorate the long-term stability of PB.Herein,an inter nickel hexacyanoferrate(NNiFCN)is successfully introduced at the out layer of iron hexacyanoferrate(NFFCN)through ion exchange to improve structural stability through compressive stress locking by forming NNiFCN shell.Furthermore,the kinetics of sodium ion diffusion is enhanced through the built-in electric pathway.The electrochemical performance is therefore significantly improved with a remarkable long-term cycling stability over 3,000 cycles at 500 mA·g^(–1) in the full sodium-ion batteries(SIBs)with a maximum energy density of 91.94 Wh·g^(–1),indicating that the core-shell structured NNiFCN/NFFCN could be the low-cost and high-performance cathode for full SIBs in large-scale EES applications.展开更多
In this paper,the mechanical degradation of natural fiber composites is studied with the consideration of the relative humidity and the temperature.A nonlinear constitutive model is established,which employs an intern...In this paper,the mechanical degradation of natural fiber composites is studied with the consideration of the relative humidity and the temperature.A nonlinear constitutive model is established,which employs an internal variable to describe the mechanical degradation related to the energy dissipation during moisture absorption.The existing experimental researches demonstrated that the mechanical degradation is an irreversible thermodynamic process induced by the degradation of fibers and the damages of interfaces between fiber and matrix,both of which depend on the variation of the relative humidity or the temperature.The evolution of the mechanical degradation is obtained through the determination of dissipation rates as a function of the relative humidity and the temperature.The theoretically predicted mechanical degradations are compared with experimental results of sisal fiber reinforced composites subject to different relative humidity and temperatures,and a good agreement is found.展开更多
LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)layered oxides have been regarded as promising alternative cathodes for the next generation of high-energy lithium ion batteries(LIBs)due to high discharge capacities and energy ...LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)layered oxides have been regarded as promising alternative cathodes for the next generation of high-energy lithium ion batteries(LIBs)due to high discharge capacities and energy densities at high operation voltage.However,the capacity fading under high operation voltage still restricts the practical application.Herein,the capacity degradation mechanism of NCM811 at atomic-scale is studied in detail under various cut-off voltages using aberration-corrected scanning transmission electron microscopy(STEM).It is observed that the crystal structure of NCM811 evolution from a layered structure to a rock-salt phase is directly accompanied by serious intergranular cracks under 4.9 V,which is distinguished from the generally accepted structure evolution of layered,disordered layered,defect rock salt and rock salt phases,also observed under 4.3 and 4.7 V.The electron energy loss spectroscopy analysis also confirms the reduction of Ni and Co from the surface to the bulk,not the previously reported only Li/Ni interlayer mixing.The degradation mechanism of NCM811 at a high cut-off voltage of4.9 V is attributed to the formation of intergranular cracks induced by defects,the direct formation of the rock salt phase,and the accompanied reduction of Ni^(2+)and Co^(2+)phases from the surface to the bulk.展开更多
Lignin is a natural polymer,second only to cellulose in natural reserves.Degradation is one of the ways to achieve the high-value transformation of lignin.Deep eutectic solvent(DES)thermal degradation of lignin can be...Lignin is a natural polymer,second only to cellulose in natural reserves.Degradation is one of the ways to achieve the high-value transformation of lignin.Deep eutectic solvent(DES)thermal degradation of lignin can be used as an excellent green degradation method.This paper introduces the degradation mechanism and effect of the lactic acid-choline chloride DES system in dissolving and degrading alkaline lignin,and the final solvent recovery.It can also be found from the scanning electron microscope(SEM)images that the surface of the degraded solid product is transformed from smooth to disordered.Fourier transform infrared(FTIR)spectroscopy and 1H-NMR spectroscopy were used to characterize the changes in lignin functional groups during DES treatment.The results showed that the content of phenolic hydroxyl groups increased after degradation,indicating that theβ-O-4 ether bond was broken.The molecular weight of the degraded lignin was observed by gel permeation chromatography(GPC),and the lignin residue with low molecular weight and narrow polydispersity index was obtained.The lowest average molecular weight(Mw)reached 2512 g/mol.The ratio of oxygen to carbon atoms in lignin increased substantially during degradation as measured by X-ray photoelectron spectroscopy(XPS),probably because DES treatment was accompanied by many oxidation reactions,which led to significant structural changes in lignin and a large number of ether bond breakage reactions during the reaction.The main final degradation products are aromatic monomers,vanillin,butyrovanillone,etc.展开更多
The ever-increasing future demands of electrification and grid storage have spurred continued research to develop rechargeable battery chemistries for reliable energy storage[1].Beyond current lithium-ion batteries,li...The ever-increasing future demands of electrification and grid storage have spurred continued research to develop rechargeable battery chemistries for reliable energy storage[1].Beyond current lithium-ion batteries,lithium–sulfur battery represents a promising system due to its high energy density(2600 Wh kg^(-1))and low material cost[2].展开更多
The efficiency of the green inhibitors(sodium salts of fumarate,glycolate and gluconate)in suppressing corrosion of the structural MA8 magnesium alloy(Mg–Mn–Ce)and the biomedical Mg–0.8Ca alloy was studied using th...The efficiency of the green inhibitors(sodium salts of fumarate,glycolate and gluconate)in suppressing corrosion of the structural MA8 magnesium alloy(Mg–Mn–Ce)and the biomedical Mg–0.8Ca alloy was studied using the hydrogen evolution measurements,mass loss test,EIS,PDP,SVET/SIET.The analysis of the morphology,chemical composition,and growth kinetic of corrosion films formed in 0.9 wt%NaCl solution with and without corrosion inhibitors was carried out.The most compact surface film with the smallest thickness was formed in a saline solution with sodium fumarate.The Mg alloy samples exhibited the highest polarization resistance,the lowest localized electrochemical activity,and the lowest corrosion rate in saline with the addition of sodium fumarate and sodium glycolate.The efficiency of the applied inhibitors was up to 81%.The model of the corrosion mechanism based on the sorption of molecules of organic inhibitors is proposed.The results show the high compatibility of the used inhibitors with the calcium-phosphate PEO-matrix,indicating the possibility of forming a self-healing coating by means of these active substances.展开更多
This work made use of the Aalto University Otanano-Nanomicroscopy Center and RAMI infrastructures.Financial support from Business Finland NextGenBat[grant number 211849]is greatly acknowledged.The tomography experimen...This work made use of the Aalto University Otanano-Nanomicroscopy Center and RAMI infrastructures.Financial support from Business Finland NextGenBat[grant number 211849]is greatly acknowledged.The tomography experiment was performed at the beamline ID16B of the European Synchrotron Radiation Facility(ESRF),Grenoble,France,in the frame of proposal CH-6644.The patent titled“Stabilized Positive Electrode Material to Enable High Energy and Power Density Lithium-Ion Batteries”(IPD3173)is pertinent to this manuscript.It was filed by Zahra Ahaliabadeh and Tanja Kallio,and the patent rights are held by Aalto University.展开更多
Heterogeneous catalysts promoting efficient production of reactive species and dynamically stabilized electron transfer mechanisms for peroxomonosulfates(PMS)still lack systematic investigation.Herein,a more stable ma...Heterogeneous catalysts promoting efficient production of reactive species and dynamically stabilized electron transfer mechanisms for peroxomonosulfates(PMS)still lack systematic investigation.Herein,a more stable magnetic layered double oxides(CFLDO/N-C),was designed using self-polymerization and high temperature carbonization of dopamine.The CFLDO/N-C/PMS system effectively activated PMS to remove 99%(k=0.737 min^(-1))of tetracycline(TC)within 10 min.The CFLDO/N-C/PMS system exhibited favorable resistance to inorganic anions and natural organics,as well as satisfactory suitability for multiple pollutants.The magnetic properties of the catalyst facilitated the separation of catalysts from the liquid phase,resulting in excellent reproducibility and effectively reducing the leaching of metal ions.An electronic bridge was constructed between cobalt(the active platform of the catalyst)and PMS,inducing PMS to break the O-O bond to generate the active species.The combination of static analysis and dynamic evolution confirmed the effective adsorption of PMS on the catalyst surface as well as the strong radical-assisted electron transfer process.Eventually,we further identified the sites where the reactive species attacked the TC and evaluated the toxicity of the intermediates.These findings offer innovative insights into the rapid degradation of pollutants achieved by transition metals in SR-AOPs and its mechanistic elaboration.展开更多
The photocatalytic degradation of Rhodamine B （RhB） was carried out using TiO2 supported on activated carbon （TiO2-AC） under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X...The photocatalytic degradation of Rhodamine B （RhB） was carried out using TiO2 supported on activated carbon （TiO2-AC） under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM） and Brunauer-Emmett-Teller （BET）. In the process of microwave-enhanced photocatalysis （MPC）, RhB （30 mg/L） was almost completely decoloured in 10 min, and the mineralization efficiency was 96.0% in 20 min. The reaction rate constant of RhB in MPC using TiO2-AC by pseudo first-order reaction kinetics was 4.16 times of that using Degussa P25. Additionally, according to gas chromatography/mass spectrometry （GC/MS） and liquid chromatography/mass spectrometry （LC/MS） identification, the major intermediates of RhB in MPC included two kinds of N-de-ethylation intermediates （N,N-diethyl-N＇-ethyl-rhodamine （DER））, oxalic acid, malonic acid, snccinic acid, and phthalic acid, maleic acid, 3-nitrobenzoic acid, and so on. The degradation of RhB in MPC was mainly attributed to the destruction of the conjugated structure, and then the intermediates transformed to acid molecules which were mineralized to water and carbon dioxide.展开更多
The 2,4,6-trinitrotoluene （TNT） is a potential carcinogens and TNT contaminated wastewater, which could not be effectively disposed with conventional treatments. The supercritical water oxidation （SCWO） to treat T...The 2,4,6-trinitrotoluene （TNT） is a potential carcinogens and TNT contaminated wastewater, which could not be effectively disposed with conventional treatments. The supercritical water oxidation （SCWO） to treat TNT contaminated wastewater was studied in this article, The TNT concentration in wastewater was measured by high-performance liquid chromatograph （HPLC） and the degraded intermediates were analyzed using GC-MS. The results showed that SCWO could degrade TNT efficiently in the presence of oxygen. The reaction temperature, pressure, residence time and oxygen excess were the main contributing factors in the process. The decomposition of TNT was accelerated as the temperature or residence time increased. At 550℃, 24 MPa, 120 s and oxygen excess 300%, TNT removal rate could exceed 99.9%. Partial oxidation occured in SCWO without oxygen. It was concluded that supercritical water was a good solvent and had excellent oxidation capability in the existence of oxygen. The main intermediates of TNT during SCWO included toluene, 1,3,5-trinitrobenzene, nitrophenol, naphthalene, fluorenone, dibutyl phthalate, alkanes and several dimers based on the intermediate analysis. Some side reactions, such as coupled reaction, hydrolysis reaction and isomerization reaction may take place simultaneously when TNT was oxidized by SCWO.展开更多
The degradation and mineralization of aniline （AN） using ozone combined with Fenton reagent （O3/Fenton） in a rotating packed bed （RPB） was proposed in this study, and the process （RPB-O3/Fenton） was compared w...The degradation and mineralization of aniline （AN） using ozone combined with Fenton reagent （O3/Fenton） in a rotating packed bed （RPB） was proposed in this study, and the process （RPB-O3/Fenton） was compared with conventional O3/Fenton in a stirred tank reactor （STR-O3/Fenton） or single ozonation in an RPB （RPB-O3）, Effects of high gravity factor, H2O2 dosage, H2O2 dosing method and initial pH on the AN mineralization efficiency were investigated in the RPB-O3/Fenton process, In addition, the behavior of Fe（Ⅱ） was monitored at different H2O2 dosing methods and pH values. Finally, the optimal operation conditions were determined with high gravity factor of 100, initial pH of 5, Fe（Ⅱ） concentration of 0.8 mmol·L-1 and H2O2 dosage of 2.5 ml. Under these conditions, for aniline wastewater at the volume of I L and concentration of 200 mg· L- 1 ,a fast and thorough decay of AN was conducted in 10 min, and the TOC removal efficiency reached 89% in 60 min. The main intermediates of p-benzoquinone, nitrobenzene, maleic acid and oxalic acid were identified by liquid chromatography/mass spectroscopy （LC/MS）, and the degradation pathways of AN in RPB-O3/Fenton system were proposed based on experimental evidence. It could be envisioned that high-gravity technology combined with O3/Fenton processes would be promising in the rapid and efficient mineralization ofwastewater.展开更多
The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical b...The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components （β-carotene, lutein, neoxanthin, and violaxthin） decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing （T1） were relatively higher than the rapid heating curing （T2） accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments （P〉 0.05）. The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes＇ activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma.展开更多
Tetracycline(TC)is an antibiotic mainly used in livestock production and respiratory infection.Traditional methods are not effective in removing TC from solution.In this study,TC was degraded by gas–liquid plasma in ...Tetracycline(TC)is an antibiotic mainly used in livestock production and respiratory infection.Traditional methods are not effective in removing TC from solution.In this study,TC was degraded by gas–liquid plasma in the presence of rGO-TiO_(2)in solution.The rGO-TiO_(2)was prepared by modified hummers and hydrothermal method.The electrical and optical properties of the gas–liquid discharge plasma were studied and the produced long-lived reactive species were analyzed by spectrophotometer.The degradation efficiency of TC was improved by 41.4%after plasma treatment for 12 min in presence of 30 mg l-1 r GO-TiO_(2)compared to that with plasma alone.The degradation efficiency increased with increasing discharge power,but as the initial concentration was increased from 20 to 80 mg l-1,the degradation efficiency of TC decreased.The initial p H had no significant effect on the degradation of TC.The intermediate products were determined by UV–vis spectrophotometry and ESI(+)–MS,and the degradation mechanism was analyzed.The reactive species,including O_(3),·OH,and H_(2)O_(2),etc.,produced in the plasma/catalyst system attracted electron-rich functional groups(amino group,aromatic ring,and double bond).Therefore,the gas–liquid plasma/catalyst system could be an effective and promising method for pharmaceutical wastewater treatment in future.展开更多
Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease...Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT.展开更多
Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation con...Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation concerning land degradation and aeolian activity in the alpine realm. In this study,spectral information from two Landsat-5 TM scenes(04.08.1994 and 28.07.2009,respectively) was combined with reference information obtained in the field to run supervised classifications of eight landscape types for both time steps. Subsequently,the temporal and spatial patterns of the alpine wetlands/grasslands evolutions in the Zoige Basin were quantified and assessed based on these two classification maps. The most conspicuous change is the sharp increase of ~627 km^2 degraded meadow. Concerning other land-covers,shallow wetland increases ~107 km^2 and aeolian sediments(mobile dunes and sand sheets) have an increase of ~30 km^2. Considering the deterioration,an obvious decrease of ~440 km^2 degraded wetland can be observed. Likewise,decrease of deep wetland(~78 km^2),humid meadow(~80 km^2) and undisturbed meadow(~88 km^2) were determined. These entire evolution matrixes undoubtedly hint a deteriorating tendency of the Zoige Basin ecosystem,which is characterized by significantly declined proportion of intact wetlands,meadow,rangeland and a considerable increase ofdegraded meadow and larger areas of mobile dunes. In particular,not only temporal alteration of the landcover categories,the spatial and topographical characteristics of the land degradation also deserves more attention. In the alpine rangelands,the higher terraces of the river channels along with their slopes are more liable to the degradation and desertification. This tendency has significantly impeded the nomadic and agriculture activities. The set of anthropozoogenic factors encompassing enclosures,overgrazing and trampling,rodent damaging and exceedingly ditching in the wetlands are assumed to be the main controlling mechanisms for the landscape degradation. A suite of strict protection policies is urgent and indispensable for self-regulation and restoration of the alpine meadow ecosystem. Controlling the size of livestock,less ditching in the rangeland,and the launching of a more strict nature reserve management by adjacent Ruoergai,Maqu and Hongyuan Counties would be practical and efficacious in achieving these objectives.展开更多
Phenolic compounds are widely present in domestic and industrial sewage and have serious environmental hazards.Electrochemical oxidation(EO)is one of the most promising methods for sewage degradation because of its hi...Phenolic compounds are widely present in domestic and industrial sewage and have serious environmental hazards.Electrochemical oxidation(EO)is one of the most promising methods for sewage degradation because of its high efficiency,environmental compatibility,and safety.In this work,we present an in-depth overview of the mechanism and factors affecting the degradation of phenolic compounds by EO.In particular,the effects of treatment of phenolic compounds with different anode materials are discussed in detail.The non-active anode shows higher degradation efficiency,less intermediate accumulation,and lower energy consumption than the active anode.EO combined with other treatment methods(biological,photo,and Fenton)presents advantages,such as low energy consumption and high degradation rate.Mean-while,the remaining drawbacks of the EO process in the phenolic compound treatment system have been discussed.Furthermore,future re-search directions are put forward to improve the feasibility of the practical application of EO technology.展开更多
The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the c...The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stressσnand lateral stressσpto investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσnandσp,the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσn,while they first increase and then gradually decrease asσpincreases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσn,but shows no significant change withσp.Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion cjp,friction angleφjp,and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσnandσp,G first rapidly decreases and then tends to stabilize;cjp,φjp,andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.展开更多
The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell（PEMFC） stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and...The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell（PEMFC） stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and configuration of the gas intake manifold, which may lead to the maldistribution of flow and pressure. In order to find out the mechanisms of the accelerated degradation in the front cells, an extensive program of experimental and simulation work is initiated and the results are reported. It is found that after long-term lifetime tests the accelerated degradation in the front cells occurs in all three fuel cell stacks with different flow-fields under the U-type feed configuration. Compared with the rear cells of the stack, the voltage of the front cells is much lower at the same current densities and the membrane electrode assembly（MEA） has smaller active area, more catalyst particle agglomeration and higher ohmic impedance. For further investigation, a series of three dimensional isothermal numerical models are built to investigate the degradation mechanisms based on the experimental data. The simulation results reveal that the dry working condition of the membrane and the effect of high-speed gas scouting the MEA are the main causes of the accelerated degradation in the front cells of a PEM fuel cell stack under the U-type feed configuration. Several mitigation strategies that would mitigate these phenomena are presented： removing cells that have failed and replacing them with those of the same aging condition as the average of the stack; choosing a Z-type feed pattern instead of a U-type one; putting several air flow-field plates without MEA in the front of the stack; or exchanging the gas inlet and outlet alternately at a certain interval. This paper specifies the causes of the accelerated degradation in the front cells and provides the mitigation strategies.展开更多
Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to the...Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation.展开更多
基金Project of China International Science and Technology Cooperation under Grant No.2009DFA82480Science and Technology Project of Communications’ Construction in Western China,MOC under Grant No.2009318223094
文摘Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.
基金J.G.S.wants to thanks China Scholarship Council(CSC)for the scholarship support(No.201706050153)。
文摘Generation of large strains upon Na^(+) intercalation is one of the prime concerns of the mechanical degradation of Prussian blue(PB)and its analogs.Structural construction from the atomic level is imperative to maintain structural stability and ameliorate the long-term stability of PB.Herein,an inter nickel hexacyanoferrate(NNiFCN)is successfully introduced at the out layer of iron hexacyanoferrate(NFFCN)through ion exchange to improve structural stability through compressive stress locking by forming NNiFCN shell.Furthermore,the kinetics of sodium ion diffusion is enhanced through the built-in electric pathway.The electrochemical performance is therefore significantly improved with a remarkable long-term cycling stability over 3,000 cycles at 500 mA·g^(–1) in the full sodium-ion batteries(SIBs)with a maximum energy density of 91.94 Wh·g^(–1),indicating that the core-shell structured NNiFCN/NFFCN could be the low-cost and high-performance cathode for full SIBs in large-scale EES applications.
基金supported by National Natural Science Foundation of China(Grant No.11572227)
文摘In this paper,the mechanical degradation of natural fiber composites is studied with the consideration of the relative humidity and the temperature.A nonlinear constitutive model is established,which employs an internal variable to describe the mechanical degradation related to the energy dissipation during moisture absorption.The existing experimental researches demonstrated that the mechanical degradation is an irreversible thermodynamic process induced by the degradation of fibers and the damages of interfaces between fiber and matrix,both of which depend on the variation of the relative humidity or the temperature.The evolution of the mechanical degradation is obtained through the determination of dissipation rates as a function of the relative humidity and the temperature.The theoretically predicted mechanical degradations are compared with experimental results of sisal fiber reinforced composites subject to different relative humidity and temperatures,and a good agreement is found.
基金supported by the National Natural Science Foundation of China(U2032131)the Key R&D Program of Shaanxi Province(2021GY-118)the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(2022SX-TD012 and 2021SXTD012)。
文摘LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)layered oxides have been regarded as promising alternative cathodes for the next generation of high-energy lithium ion batteries(LIBs)due to high discharge capacities and energy densities at high operation voltage.However,the capacity fading under high operation voltage still restricts the practical application.Herein,the capacity degradation mechanism of NCM811 at atomic-scale is studied in detail under various cut-off voltages using aberration-corrected scanning transmission electron microscopy(STEM).It is observed that the crystal structure of NCM811 evolution from a layered structure to a rock-salt phase is directly accompanied by serious intergranular cracks under 4.9 V,which is distinguished from the generally accepted structure evolution of layered,disordered layered,defect rock salt and rock salt phases,also observed under 4.3 and 4.7 V.The electron energy loss spectroscopy analysis also confirms the reduction of Ni and Co from the surface to the bulk,not the previously reported only Li/Ni interlayer mixing.The degradation mechanism of NCM811 at a high cut-off voltage of4.9 V is attributed to the formation of intergranular cracks induced by defects,the direct formation of the rock salt phase,and the accompanied reduction of Ni^(2+)and Co^(2+)phases from the surface to the bulk.
基金This work was financially supported by the National Natural Science Foundation of China(31730106).
文摘Lignin is a natural polymer,second only to cellulose in natural reserves.Degradation is one of the ways to achieve the high-value transformation of lignin.Deep eutectic solvent(DES)thermal degradation of lignin can be used as an excellent green degradation method.This paper introduces the degradation mechanism and effect of the lactic acid-choline chloride DES system in dissolving and degrading alkaline lignin,and the final solvent recovery.It can also be found from the scanning electron microscope(SEM)images that the surface of the degraded solid product is transformed from smooth to disordered.Fourier transform infrared(FTIR)spectroscopy and 1H-NMR spectroscopy were used to characterize the changes in lignin functional groups during DES treatment.The results showed that the content of phenolic hydroxyl groups increased after degradation,indicating that theβ-O-4 ether bond was broken.The molecular weight of the degraded lignin was observed by gel permeation chromatography(GPC),and the lignin residue with low molecular weight and narrow polydispersity index was obtained.The lowest average molecular weight(Mw)reached 2512 g/mol.The ratio of oxygen to carbon atoms in lignin increased substantially during degradation as measured by X-ray photoelectron spectroscopy(XPS),probably because DES treatment was accompanied by many oxidation reactions,which led to significant structural changes in lignin and a large number of ether bond breakage reactions during the reaction.The main final degradation products are aromatic monomers,vanillin,butyrovanillone,etc.
基金supported by the Agency for Science,Technology and Research(Central Research Fund Award)。
文摘The ever-increasing future demands of electrification and grid storage have spurred continued research to develop rechargeable battery chemistries for reliable energy storage[1].Beyond current lithium-ion batteries,lithium–sulfur battery represents a promising system due to its high energy density(2600 Wh kg^(-1))and low material cost[2].
基金supported by the Grant of Russian Science Foundation,Russia(project no 20–13–00130,https://rscf.ru/en/project/20-13-00130/)supported by the Grant of Russian Science Foundation,Russia(project no 24–73–10008,https://rscf.ru/en/project/24-73-10008/)XRD data were obtained under the government assignments from the Ministry of Science and Higher Education of the Russian Federation,Russia(project no FWFN-2024-0001).
文摘The efficiency of the green inhibitors(sodium salts of fumarate,glycolate and gluconate)in suppressing corrosion of the structural MA8 magnesium alloy(Mg–Mn–Ce)and the biomedical Mg–0.8Ca alloy was studied using the hydrogen evolution measurements,mass loss test,EIS,PDP,SVET/SIET.The analysis of the morphology,chemical composition,and growth kinetic of corrosion films formed in 0.9 wt%NaCl solution with and without corrosion inhibitors was carried out.The most compact surface film with the smallest thickness was formed in a saline solution with sodium fumarate.The Mg alloy samples exhibited the highest polarization resistance,the lowest localized electrochemical activity,and the lowest corrosion rate in saline with the addition of sodium fumarate and sodium glycolate.The efficiency of the applied inhibitors was up to 81%.The model of the corrosion mechanism based on the sorption of molecules of organic inhibitors is proposed.The results show the high compatibility of the used inhibitors with the calcium-phosphate PEO-matrix,indicating the possibility of forming a self-healing coating by means of these active substances.
基金Financial support from Business Finland NextGenBat[grant number 211849]is greatly acknowledged.
文摘This work made use of the Aalto University Otanano-Nanomicroscopy Center and RAMI infrastructures.Financial support from Business Finland NextGenBat[grant number 211849]is greatly acknowledged.The tomography experiment was performed at the beamline ID16B of the European Synchrotron Radiation Facility(ESRF),Grenoble,France,in the frame of proposal CH-6644.The patent titled“Stabilized Positive Electrode Material to Enable High Energy and Power Density Lithium-Ion Batteries”(IPD3173)is pertinent to this manuscript.It was filed by Zahra Ahaliabadeh and Tanja Kallio,and the patent rights are held by Aalto University.
基金supported by the Natural Science Foundation of China(62105292)the Shaanxi Fundamental Science Research Project for Mathematics and Physics(Grant no.22JSY015)+3 种基金the Young Talent Fund of Xi’an Association for Science and Technology(959202313020)the National Natural Science Foundation of Shaanxi Province(No.2021GXLH-Z-0 and 2020JZ-02)the project of Innovative Team of Shaanxi Province(2020TD001)the China Fundamental Research Funds for the Central Universities
文摘Heterogeneous catalysts promoting efficient production of reactive species and dynamically stabilized electron transfer mechanisms for peroxomonosulfates(PMS)still lack systematic investigation.Herein,a more stable magnetic layered double oxides(CFLDO/N-C),was designed using self-polymerization and high temperature carbonization of dopamine.The CFLDO/N-C/PMS system effectively activated PMS to remove 99%(k=0.737 min^(-1))of tetracycline(TC)within 10 min.The CFLDO/N-C/PMS system exhibited favorable resistance to inorganic anions and natural organics,as well as satisfactory suitability for multiple pollutants.The magnetic properties of the catalyst facilitated the separation of catalysts from the liquid phase,resulting in excellent reproducibility and effectively reducing the leaching of metal ions.An electronic bridge was constructed between cobalt(the active platform of the catalyst)and PMS,inducing PMS to break the O-O bond to generate the active species.The combination of static analysis and dynamic evolution confirmed the effective adsorption of PMS on the catalyst surface as well as the strong radical-assisted electron transfer process.Eventually,we further identified the sites where the reactive species attacked the TC and evaluated the toxicity of the intermediates.These findings offer innovative insights into the rapid degradation of pollutants achieved by transition metals in SR-AOPs and its mechanistic elaboration.
基金supported by the National Natural Science Foundation of China (No. 20707009)the Jiangsu Province Social Development Foundation (No.BS2007051)+1 种基金the Opening Foundation (WTWER0713) of Engineering Research Center for Water Treatment and Water Remediation of the Ministry of Education of Chinathe State Key Laboratory of Pollution Control and Resource Reuse Opening Foundation (No. PCRRCF07003).
文摘The photocatalytic degradation of Rhodamine B （RhB） was carried out using TiO2 supported on activated carbon （TiO2-AC） under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM） and Brunauer-Emmett-Teller （BET）. In the process of microwave-enhanced photocatalysis （MPC）, RhB （30 mg/L） was almost completely decoloured in 10 min, and the mineralization efficiency was 96.0% in 20 min. The reaction rate constant of RhB in MPC using TiO2-AC by pseudo first-order reaction kinetics was 4.16 times of that using Degussa P25. Additionally, according to gas chromatography/mass spectrometry （GC/MS） and liquid chromatography/mass spectrometry （LC/MS） identification, the major intermediates of RhB in MPC included two kinds of N-de-ethylation intermediates （N,N-diethyl-N＇-ethyl-rhodamine （DER））, oxalic acid, malonic acid, snccinic acid, and phthalic acid, maleic acid, 3-nitrobenzoic acid, and so on. The degradation of RhB in MPC was mainly attributed to the destruction of the conjugated structure, and then the intermediates transformed to acid molecules which were mineralized to water and carbon dioxide.
基金Project supported by the Science Technology Foundation of Educational Department(No.204020).
文摘The 2,4,6-trinitrotoluene （TNT） is a potential carcinogens and TNT contaminated wastewater, which could not be effectively disposed with conventional treatments. The supercritical water oxidation （SCWO） to treat TNT contaminated wastewater was studied in this article, The TNT concentration in wastewater was measured by high-performance liquid chromatograph （HPLC） and the degraded intermediates were analyzed using GC-MS. The results showed that SCWO could degrade TNT efficiently in the presence of oxygen. The reaction temperature, pressure, residence time and oxygen excess were the main contributing factors in the process. The decomposition of TNT was accelerated as the temperature or residence time increased. At 550℃, 24 MPa, 120 s and oxygen excess 300%, TNT removal rate could exceed 99.9%. Partial oxidation occured in SCWO without oxygen. It was concluded that supercritical water was a good solvent and had excellent oxidation capability in the existence of oxygen. The main intermediates of TNT during SCWO included toluene, 1,3,5-trinitrobenzene, nitrophenol, naphthalene, fluorenone, dibutyl phthalate, alkanes and several dimers based on the intermediate analysis. Some side reactions, such as coupled reaction, hydrolysis reaction and isomerization reaction may take place simultaneously when TNT was oxidized by SCWO.
基金Supported by the National Natural Science Foundations of China(U1610106)Shanxi Excellent Talent Science and Technology Innovation Project(201705D211011)+1 种基金Specialized Research Fund for Sanjin Scholars Program of Shanxi ProvinceNorth University of China Fund for Distinguished Young Scholars
文摘The degradation and mineralization of aniline （AN） using ozone combined with Fenton reagent （O3/Fenton） in a rotating packed bed （RPB） was proposed in this study, and the process （RPB-O3/Fenton） was compared with conventional O3/Fenton in a stirred tank reactor （STR-O3/Fenton） or single ozonation in an RPB （RPB-O3）, Effects of high gravity factor, H2O2 dosage, H2O2 dosing method and initial pH on the AN mineralization efficiency were investigated in the RPB-O3/Fenton process, In addition, the behavior of Fe（Ⅱ） was monitored at different H2O2 dosing methods and pH values. Finally, the optimal operation conditions were determined with high gravity factor of 100, initial pH of 5, Fe（Ⅱ） concentration of 0.8 mmol·L-1 and H2O2 dosage of 2.5 ml. Under these conditions, for aniline wastewater at the volume of I L and concentration of 200 mg· L- 1 ,a fast and thorough decay of AN was conducted in 10 min, and the TOC removal efficiency reached 89% in 60 min. The main intermediates of p-benzoquinone, nitrobenzene, maleic acid and oxalic acid were identified by liquid chromatography/mass spectroscopy （LC/MS）, and the degradation pathways of AN in RPB-O3/Fenton system were proposed based on experimental evidence. It could be envisioned that high-gravity technology combined with O3/Fenton processes would be promising in the rapid and efficient mineralization ofwastewater.
基金supported by the Key Project of State Tobacco Monoply Administration of China(3300806156)
文摘The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components （β-carotene, lutein, neoxanthin, and violaxthin） decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing （T1） were relatively higher than the rapid heating curing （T2） accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments （P〉 0.05）. The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes＇ activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma.
基金financially supported by National Natural Science Foundation of China(Nos.51777206 and 51541807)Natural Science Foundation of Anhui Province(Nos.1908085MA29,1708085MB47 and 1708085MA13)+4 种基金Doctoral Fund of Ministry of Education of China(No.2017M612058)Specialized Research Fund for the Doctoral Program of Hefei University of Technology(No.JZ2016HGBZ0769)Chinese Academy of Sciences under Grant No.DSJJ-14-YY02Science and Technology Cooperation Program between China and Finland(No.2017YFE0115200)Hong Kong Research Grants Council(RGC)General Research Funds(GRF)(No.City U 11205617)。
文摘Tetracycline(TC)is an antibiotic mainly used in livestock production and respiratory infection.Traditional methods are not effective in removing TC from solution.In this study,TC was degraded by gas–liquid plasma in the presence of rGO-TiO_(2)in solution.The rGO-TiO_(2)was prepared by modified hummers and hydrothermal method.The electrical and optical properties of the gas–liquid discharge plasma were studied and the produced long-lived reactive species were analyzed by spectrophotometer.The degradation efficiency of TC was improved by 41.4%after plasma treatment for 12 min in presence of 30 mg l-1 r GO-TiO_(2)compared to that with plasma alone.The degradation efficiency increased with increasing discharge power,but as the initial concentration was increased from 20 to 80 mg l-1,the degradation efficiency of TC decreased.The initial p H had no significant effect on the degradation of TC.The intermediate products were determined by UV–vis spectrophotometry and ESI(+)–MS,and the degradation mechanism was analyzed.The reactive species,including O_(3),·OH,and H_(2)O_(2),etc.,produced in the plasma/catalyst system attracted electron-rich functional groups(amino group,aromatic ring,and double bond).Therefore,the gas–liquid plasma/catalyst system could be an effective and promising method for pharmaceutical wastewater treatment in future.
基金Project supported by the Program for New Century Excellent Talents in University (Grant No.NCET-12-0915)
文摘Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT.
基金funded by the German Research Foundation (DFG) for the fieldwork and China Scholarship Council (201306190112)
文摘Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation concerning land degradation and aeolian activity in the alpine realm. In this study,spectral information from two Landsat-5 TM scenes(04.08.1994 and 28.07.2009,respectively) was combined with reference information obtained in the field to run supervised classifications of eight landscape types for both time steps. Subsequently,the temporal and spatial patterns of the alpine wetlands/grasslands evolutions in the Zoige Basin were quantified and assessed based on these two classification maps. The most conspicuous change is the sharp increase of ~627 km^2 degraded meadow. Concerning other land-covers,shallow wetland increases ~107 km^2 and aeolian sediments(mobile dunes and sand sheets) have an increase of ~30 km^2. Considering the deterioration,an obvious decrease of ~440 km^2 degraded wetland can be observed. Likewise,decrease of deep wetland(~78 km^2),humid meadow(~80 km^2) and undisturbed meadow(~88 km^2) were determined. These entire evolution matrixes undoubtedly hint a deteriorating tendency of the Zoige Basin ecosystem,which is characterized by significantly declined proportion of intact wetlands,meadow,rangeland and a considerable increase ofdegraded meadow and larger areas of mobile dunes. In particular,not only temporal alteration of the landcover categories,the spatial and topographical characteristics of the land degradation also deserves more attention. In the alpine rangelands,the higher terraces of the river channels along with their slopes are more liable to the degradation and desertification. This tendency has significantly impeded the nomadic and agriculture activities. The set of anthropozoogenic factors encompassing enclosures,overgrazing and trampling,rodent damaging and exceedingly ditching in the wetlands are assumed to be the main controlling mechanisms for the landscape degradation. A suite of strict protection policies is urgent and indispensable for self-regulation and restoration of the alpine meadow ecosystem. Controlling the size of livestock,less ditching in the rangeland,and the launching of a more strict nature reserve management by adjacent Ruoergai,Maqu and Hongyuan Counties would be practical and efficacious in achieving these objectives.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52025041 and 51974021)the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-004B2Z),and the Beijing Excellent Talents Foundation.
文摘Phenolic compounds are widely present in domestic and industrial sewage and have serious environmental hazards.Electrochemical oxidation(EO)is one of the most promising methods for sewage degradation because of its high efficiency,environmental compatibility,and safety.In this work,we present an in-depth overview of the mechanism and factors affecting the degradation of phenolic compounds by EO.In particular,the effects of treatment of phenolic compounds with different anode materials are discussed in detail.The non-active anode shows higher degradation efficiency,less intermediate accumulation,and lower energy consumption than the active anode.EO combined with other treatment methods(biological,photo,and Fenton)presents advantages,such as low energy consumption and high degradation rate.Mean-while,the remaining drawbacks of the EO process in the phenolic compound treatment system have been discussed.Furthermore,future re-search directions are put forward to improve the feasibility of the practical application of EO technology.
基金the National Natural Science Foundation of China(Nos.52469019,52109119,and 52274145)the Chinese Postdoctoral Science Fund Project(No.2022M723408)+1 种基金the Major Project of Guangxi Science and Technology(No.AA23023016)the Technology Project of China Power Engineering Consulting Group Co.,Ltd.(No.DG2-T01-2023)。
文摘The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stressσnand lateral stressσpto investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσnandσp,the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσn,while they first increase and then gradually decrease asσpincreases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσn,but shows no significant change withσp.Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion cjp,friction angleφjp,and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσnandσp,G first rapidly decreases and then tends to stabilize;cjp,φjp,andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.
基金supported by National Basic Research Program of China(973 Program,Grant No.2012CB215500)National Hi-tech Research and Development Program of China(863 Program,Grant Nos.2012AA1106012,2012AA053402)+1 种基金National Natural Science Foundation of China(Grant No.20976095)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20090002110074)
文摘The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell（PEMFC） stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and configuration of the gas intake manifold, which may lead to the maldistribution of flow and pressure. In order to find out the mechanisms of the accelerated degradation in the front cells, an extensive program of experimental and simulation work is initiated and the results are reported. It is found that after long-term lifetime tests the accelerated degradation in the front cells occurs in all three fuel cell stacks with different flow-fields under the U-type feed configuration. Compared with the rear cells of the stack, the voltage of the front cells is much lower at the same current densities and the membrane electrode assembly（MEA） has smaller active area, more catalyst particle agglomeration and higher ohmic impedance. For further investigation, a series of three dimensional isothermal numerical models are built to investigate the degradation mechanisms based on the experimental data. The simulation results reveal that the dry working condition of the membrane and the effect of high-speed gas scouting the MEA are the main causes of the accelerated degradation in the front cells of a PEM fuel cell stack under the U-type feed configuration. Several mitigation strategies that would mitigate these phenomena are presented： removing cells that have failed and replacing them with those of the same aging condition as the average of the stack; choosing a Z-type feed pattern instead of a U-type one; putting several air flow-field plates without MEA in the front of the stack; or exchanging the gas inlet and outlet alternately at a certain interval. This paper specifies the causes of the accelerated degradation in the front cells and provides the mitigation strategies.
文摘Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation.
