Climate warming must lead the mainly air temperature controlled permafrost to degrade.Based on the numerical simulation,the process of permafrost degradation can be divided into five stages,i.e.,starting stage,tempera...Climate warming must lead the mainly air temperature controlled permafrost to degrade.Based on the numerical simulation,the process of permafrost degradation can be divided into five stages,i.e.,starting stage,temperature rising stage,zero geothermal gradient stage,talic layers stage,and disappearing stage,according to the shape of ground temperature profile.Permafrost on the Qinghai-Tibet Plateau (QTP) is generally considered a relic from late Pleistocene,and has been degenerating as a whole during Holocene.According to spatial-temporal compensation,the present thermal state discrepancy of permafrost in different areas on the QTP may correspond with their degradation stages.On the QTP,permafrost in the high and middle mountains belongs to temperature rising stage,the permafrost thermal state is transiting from late rising temperature stage to zero geothermal gradient stage that is distributed in the middle-low-mountains.Permafrost that is in a zero gradient stage mainly appears in the high plateau and valley,whereas the transition from zero gradient stage to talic layers stage of permafrost is located in the vicinity of the lower limit of permafrost,and permafrost is disappearing from margin of perennially frozen ground.There are two modes of perennially frozen ground thawing,thawing from top to bottom and thawing from bottom to top respectively.During the temperature rising stage,when the heat flux in the perennially frozen soil layer is less than that in the unfrozen soil underlying frozen soil layer,the geothermal flux is partly used to thaw the base of permafrost,and permafrost thaws from bottom to top.With the decrease of thermal gradient in the perennially frozen ground,the heat that is used to thaw permafrost base increases,and geothermal heat will be entirely consumed to thaw the base of permafrost until the temperature gradient reaches zero thermal gradient state.On the other hand,the disappearance of permafrost may be delayed by "thermal offset" and "seasonal offset" effects in the upper of permafrost 展开更多
In order to improve the incipient fault sensitivity and stability of degradation index in the rolling bearing performance degradation evaluation process,an embedding selection-based neighborhood preserving embedding(E...In order to improve the incipient fault sensitivity and stability of degradation index in the rolling bearing performance degradation evaluation process,an embedding selection-based neighborhood preserving embedding(ESNPE)method is proposed.Firstly,the acquired vibration signals are decomposed by variational mode decomposition(VMD),and the singular value and relative energy of each intrinsic mode function(IMF)are extracted to form a high-dimensional feature set.Then,the NPE manifold learning method is used to extract the embedded features in the feature space.Considering the problem that useful embedding information is easily suppressed in NPE,an embedding selection strategy is built based on the Spearman correlation coefficient.The effectiveness of embeddings is measured by the coefficient absolute value,and useful embeddings are preserved in the early stage of bearing degradation by using the first-order difference method.Finally,the degradation index is established using the support vector data description(SVDD)model and bearing performance degradation evaluation is achieved.The proposed method was tested with the whole life experiment data of a rolling bearing,and the result was compared with the feature extraction methods of traditional principal component analysis(PCA)and NPE.The results show that the proposed method is superior in improving the incipient fault sensitivity and stability of the degradation index.展开更多
Through using a direct-current driven plasma jet operated underwater,degradation of methylene blue(MB)is investigated with air and oxygen used as working gases.With a low power voltage,a plasma plume extends from the ...Through using a direct-current driven plasma jet operated underwater,degradation of methylene blue(MB)is investigated with air and oxygen used as working gases.With a low power voltage,a plasma plume extends from the needle electrode,which is purple in air.It turns pink after it bridges the two electrodes.During the process,oxygen plasma remains white.Discharge operates in a pulsed mode or a continuous one,which depends on the magnitude of power voltage.For the pulsed mode,oxygen discharge has a shorter plume and a higher pulse frequency than air discharge under the same power voltage.For the same current of the continuous mode,both power and gap voltages of oxygen discharge are higher than those of air discharge.Moreover,MB degradation efficiency increases with increasing power voltage or initial concentration of MB solution.Compared with air discharge,oxygen discharge has a higher degradation efficiency with the same power voltage and treatment time.The pulsed oxygen discharge with power voltage of about 6.5 k V has the highest efficiency in degrading MB dye,reaching approximately 85.8%after 10 min treatment.As a comparison,after 10 min treatment in air discharge,the highest degradation efficiency is 63.7%,which appears in the continuous mode at a power voltage of 10.6 kV.Besides,optical spectra from the discharges are also compared for the two types of working gases.展开更多
基金supported by National Natural Science Foundation of China (Grant No.40871040)CAS Action Plan for the Development of Western China (Grant No.KZCX2-XB2-10)Research Projectof State Key Laboratory of Frozen Soil Engineering (Grant No.SKLFSE-ZQ-06)
文摘Climate warming must lead the mainly air temperature controlled permafrost to degrade.Based on the numerical simulation,the process of permafrost degradation can be divided into five stages,i.e.,starting stage,temperature rising stage,zero geothermal gradient stage,talic layers stage,and disappearing stage,according to the shape of ground temperature profile.Permafrost on the Qinghai-Tibet Plateau (QTP) is generally considered a relic from late Pleistocene,and has been degenerating as a whole during Holocene.According to spatial-temporal compensation,the present thermal state discrepancy of permafrost in different areas on the QTP may correspond with their degradation stages.On the QTP,permafrost in the high and middle mountains belongs to temperature rising stage,the permafrost thermal state is transiting from late rising temperature stage to zero geothermal gradient stage that is distributed in the middle-low-mountains.Permafrost that is in a zero gradient stage mainly appears in the high plateau and valley,whereas the transition from zero gradient stage to talic layers stage of permafrost is located in the vicinity of the lower limit of permafrost,and permafrost is disappearing from margin of perennially frozen ground.There are two modes of perennially frozen ground thawing,thawing from top to bottom and thawing from bottom to top respectively.During the temperature rising stage,when the heat flux in the perennially frozen soil layer is less than that in the unfrozen soil underlying frozen soil layer,the geothermal flux is partly used to thaw the base of permafrost,and permafrost thaws from bottom to top.With the decrease of thermal gradient in the perennially frozen ground,the heat that is used to thaw permafrost base increases,and geothermal heat will be entirely consumed to thaw the base of permafrost until the temperature gradient reaches zero thermal gradient state.On the other hand,the disappearance of permafrost may be delayed by "thermal offset" and "seasonal offset" effects in the upper of permafrost
基金The National Natural Science Foundation of Chin(No.51975117)
文摘In order to improve the incipient fault sensitivity and stability of degradation index in the rolling bearing performance degradation evaluation process,an embedding selection-based neighborhood preserving embedding(ESNPE)method is proposed.Firstly,the acquired vibration signals are decomposed by variational mode decomposition(VMD),and the singular value and relative energy of each intrinsic mode function(IMF)are extracted to form a high-dimensional feature set.Then,the NPE manifold learning method is used to extract the embedded features in the feature space.Considering the problem that useful embedding information is easily suppressed in NPE,an embedding selection strategy is built based on the Spearman correlation coefficient.The effectiveness of embeddings is measured by the coefficient absolute value,and useful embeddings are preserved in the early stage of bearing degradation by using the first-order difference method.Finally,the degradation index is established using the support vector data description(SVDD)model and bearing performance degradation evaluation is achieved.The proposed method was tested with the whole life experiment data of a rolling bearing,and the result was compared with the feature extraction methods of traditional principal component analysis(PCA)and NPE.The results show that the proposed method is superior in improving the incipient fault sensitivity and stability of the degradation index.
基金sponsored by National Natural Science Foundation of China (Nos. 11875121,11575050 and 51977057)the Midwest Universities Comprehensive Strength Promotion Project+3 种基金the Natural Science Foundation of Hebei Province,China (Nos. A2019201100 and A2016201042)College Hundred Outstanding Innovative Talent Support Program of Hebei Education Bureau (No. SLRC2017021)the 333 Talents Project of Hebei province,China (No. A2016005005)Post-graduate’s Innovation Fund Project of Hebei Province(Nos. CXZZBS2019023 and CXZZBS2019029)。
文摘Through using a direct-current driven plasma jet operated underwater,degradation of methylene blue(MB)is investigated with air and oxygen used as working gases.With a low power voltage,a plasma plume extends from the needle electrode,which is purple in air.It turns pink after it bridges the two electrodes.During the process,oxygen plasma remains white.Discharge operates in a pulsed mode or a continuous one,which depends on the magnitude of power voltage.For the pulsed mode,oxygen discharge has a shorter plume and a higher pulse frequency than air discharge under the same power voltage.For the same current of the continuous mode,both power and gap voltages of oxygen discharge are higher than those of air discharge.Moreover,MB degradation efficiency increases with increasing power voltage or initial concentration of MB solution.Compared with air discharge,oxygen discharge has a higher degradation efficiency with the same power voltage and treatment time.The pulsed oxygen discharge with power voltage of about 6.5 k V has the highest efficiency in degrading MB dye,reaching approximately 85.8%after 10 min treatment.As a comparison,after 10 min treatment in air discharge,the highest degradation efficiency is 63.7%,which appears in the continuous mode at a power voltage of 10.6 kV.Besides,optical spectra from the discharges are also compared for the two types of working gases.
基金supported by the National Key R&D Program of China(2021YFB2401800)the National Natural Science Foundation of China(22179008,21875022)+1 种基金the Natural Science Foundation of Chongqing,China(cstc2020jcyj-msxmX0654,cstc2020jcyjmsxmX0589,and cstc2021jcyj-msxm1125)China Postdoctoral Science Foundation(2021M700403)。
