In this article, we consider the non-linear difference equation(f(z + 1)f(z)-1)(f(z)f(z-1)-1) =P(z, f(z))/Q(z, f(z)),where P(z, f(z)) and Q(z, f(z)) are relatively prime polynomials in f(z) with rational coefficients....In this article, we consider the non-linear difference equation(f(z + 1)f(z)-1)(f(z)f(z-1)-1) =P(z, f(z))/Q(z, f(z)),where P(z, f(z)) and Q(z, f(z)) are relatively prime polynomials in f(z) with rational coefficients. For the above equation, the order of growth, the exponents of convergence of zeros and poles of its transcendental meromorphic solution f(z), and the exponents of convergence of poles of difference △f(z) and divided difference △f(z)/f(z)are estimated. Furthermore, we study the forms of rational solutions of the above equation.展开更多
Distillation is the most common separation technology utilized in the petroleum and chemistry industries.Due to the wide usage of the distillation column,even a small improvement in performance may result in significa...Distillation is the most common separation technology utilized in the petroleum and chemistry industries.Due to the wide usage of the distillation column,even a small improvement in performance may result in significant energy cost savings.Aiming to improve the hydrodynamics and mass transfer performance,the flow-guided trapezoid spray-packing tray(FTS-PT)was designed by combining flow-guided holes and trapezoidal caps with structured packing.And the experimental measurements of the FTSPT,including pressure drop,clear liquid height,weeping,entrainment,and tray efficiency,were conducted in a 500 mm diameter plexiglass column with the air-water-oxygen system.Moreover,the performance of the FTS-PT was compared with that of new vertical sieve tray(New VST)and F1 valve tray.The results show that FTS-PT has a significant advantage in pressure drop,entrainment,and capacity.Furthermore,the calculation model of the pressure drop was derived and used for the FTS-PT with a relative deviation of less than 5%.展开更多
With the rapid development of knowledge pal malto:wangliye@cuc.edu.cn with a large number of knowledge products when purchasing,leading to the need for an effective recommendation system.However,existing recommendatio...With the rapid development of knowledge pal malto:wangliye@cuc.edu.cn with a large number of knowledge products when purchasing,leading to the need for an effective recommendation system.However,existing recommendation systems cannot accurately and adequately represent paid knowledge products with implicit but specialized features and sparse interactive histories,and thus are deemed not suitable for such products.In this paper,we propose a novel recommendation system for knowledge products,the core of which is the designed customer oriented representation of knowledge products.Specifically,we utilize customer activity information on the free knowledge sharing platform as the knowl-edge document for each customer of paid knowledge products,to extract customer knowledge background and preference.Then,a deep learning based model Doc2vec is adopted to transfer knowledge documents to customer knowledge background vectors.Such vectors of a particular paid knowledge product are further aggregated to a product-level vector for customer-oriented product representation,based on which two recommendation results are generated with product ratings and similarities of paid knowledge prod-ucts,respectively.Extensive comparative experiments are conducted to demonstrate the ffectiveness of the proposed system for the representation and recommendation of paid knowledge products.This paper will contribute to the literature of knowledge payment and recommendation systems,as well as provide practical implications for the information service and the operation of knowledge products on knowledge payment platforms.展开更多
Plutonium(Pu)is an anthropogenic radionuclide which mainly derived from atmospheric nuclear tests in the environment.In this study,the Pu isotopes(^(239)Pu and^(240)Pu)in aerosol samples collected during the sandstorm...Plutonium(Pu)is an anthropogenic radionuclide which mainly derived from atmospheric nuclear tests in the environment.In this study,the Pu isotopes(^(239)Pu and^(240)Pu)in aerosol samples collected during the sandstorm and non-sandstorm period were measured by accelerator mass spectrometry(AMS)and the behavior of Pu was studied.The activity concentrations of ^(239)Pu and ^(240)Pu in the aerosol samples of Beijing were ranged from 0.62 nB q/m^(3)to 99.6 n Bq/m^(3)for ^(239)Pu and 3.51 nBq/m^(3)to 60.23 n Bq/m^(3)for ^(240)Pu,respectively.^(239)Pu and ^(240)Pu concentrations exhibited a remarkable seasonal variation trend,with the higher results showed in spring,and the relatively lower concentrations in winter.The observed higher concentration of^(239)Pu and^(240)Pu detected in sandstorm samples further indicated Pu was closely related to the occurrence of sandstorms.The global fallout characteristics of^(240)Pu/^(239)Pu atom ratios(average0.20,ranging from 0.16 to 0.27)in aerosol samples indicating that global fallout was the major source of Pu in the atmosphere.Using aluminum(Al)as an indicator of soil resuspension,significant positive correlation between^(239)Pu and Al(r^(2)=0.934),240Pu and Al(^(r)2=0.525)revealed that soil resuspension was a primary source of atmospheric Pu in Beijing.These results implied that the combination of^(239)Pu,^(240)Pu and Al could be used as the potential tracer of sandstorm.展开更多
基金supported by the National Natural Science Foundation of China(11371225)National Natural Science Foundation of Guangdong Province(2016A030313686)
文摘In this article, we consider the non-linear difference equation(f(z + 1)f(z)-1)(f(z)f(z-1)-1) =P(z, f(z))/Q(z, f(z)),where P(z, f(z)) and Q(z, f(z)) are relatively prime polynomials in f(z) with rational coefficients. For the above equation, the order of growth, the exponents of convergence of zeros and poles of its transcendental meromorphic solution f(z), and the exponents of convergence of poles of difference △f(z) and divided difference △f(z)/f(z)are estimated. Furthermore, we study the forms of rational solutions of the above equation.
基金supported by National Natural Science Foundation of China(22008004)Fundamental Research Funds for the Central Universities(ZY2017)。
文摘Distillation is the most common separation technology utilized in the petroleum and chemistry industries.Due to the wide usage of the distillation column,even a small improvement in performance may result in significant energy cost savings.Aiming to improve the hydrodynamics and mass transfer performance,the flow-guided trapezoid spray-packing tray(FTS-PT)was designed by combining flow-guided holes and trapezoidal caps with structured packing.And the experimental measurements of the FTSPT,including pressure drop,clear liquid height,weeping,entrainment,and tray efficiency,were conducted in a 500 mm diameter plexiglass column with the air-water-oxygen system.Moreover,the performance of the FTS-PT was compared with that of new vertical sieve tray(New VST)and F1 valve tray.The results show that FTS-PT has a significant advantage in pressure drop,entrainment,and capacity.Furthermore,the calculation model of the pressure drop was derived and used for the FTS-PT with a relative deviation of less than 5%.
基金This work is supported by the National Natural Science Foundation of China under Grant Nos.71772177,72072177,72202221the Open Research Project of the State Key Laboratory of Media Convergence and Communication,Communication University of China under Grant No.SKLMCC2021KF005the"Double First-Class"Major(Key)lconic Project of Bejjing Foreign Studies University(Study on the globalization risk in post epidemic period:From the perspective of financial s-curity and business risk under Grant No.2022SYLZD001),and the Fundamental Resea rch Funds for the Central Universities.
文摘With the rapid development of knowledge pal malto:wangliye@cuc.edu.cn with a large number of knowledge products when purchasing,leading to the need for an effective recommendation system.However,existing recommendation systems cannot accurately and adequately represent paid knowledge products with implicit but specialized features and sparse interactive histories,and thus are deemed not suitable for such products.In this paper,we propose a novel recommendation system for knowledge products,the core of which is the designed customer oriented representation of knowledge products.Specifically,we utilize customer activity information on the free knowledge sharing platform as the knowl-edge document for each customer of paid knowledge products,to extract customer knowledge background and preference.Then,a deep learning based model Doc2vec is adopted to transfer knowledge documents to customer knowledge background vectors.Such vectors of a particular paid knowledge product are further aggregated to a product-level vector for customer-oriented product representation,based on which two recommendation results are generated with product ratings and similarities of paid knowledge prod-ucts,respectively.Extensive comparative experiments are conducted to demonstrate the ffectiveness of the proposed system for the representation and recommendation of paid knowledge products.This paper will contribute to the literature of knowledge payment and recommendation systems,as well as provide practical implications for the information service and the operation of knowledge products on knowledge payment platforms.
基金supported by the financial supports from the National Natural Science Foundation of China(Nos.U1932103,U1832212,11875266)Key Deployment Projects of Chinese Academy of Sciences(No.ZDRW-CN-2018–1)Beijing Natural Science Foundation(No.7191008)。
文摘Plutonium(Pu)is an anthropogenic radionuclide which mainly derived from atmospheric nuclear tests in the environment.In this study,the Pu isotopes(^(239)Pu and^(240)Pu)in aerosol samples collected during the sandstorm and non-sandstorm period were measured by accelerator mass spectrometry(AMS)and the behavior of Pu was studied.The activity concentrations of ^(239)Pu and ^(240)Pu in the aerosol samples of Beijing were ranged from 0.62 nB q/m^(3)to 99.6 n Bq/m^(3)for ^(239)Pu and 3.51 nBq/m^(3)to 60.23 n Bq/m^(3)for ^(240)Pu,respectively.^(239)Pu and ^(240)Pu concentrations exhibited a remarkable seasonal variation trend,with the higher results showed in spring,and the relatively lower concentrations in winter.The observed higher concentration of^(239)Pu and^(240)Pu detected in sandstorm samples further indicated Pu was closely related to the occurrence of sandstorms.The global fallout characteristics of^(240)Pu/^(239)Pu atom ratios(average0.20,ranging from 0.16 to 0.27)in aerosol samples indicating that global fallout was the major source of Pu in the atmosphere.Using aluminum(Al)as an indicator of soil resuspension,significant positive correlation between^(239)Pu and Al(r^(2)=0.934),240Pu and Al(^(r)2=0.525)revealed that soil resuspension was a primary source of atmospheric Pu in Beijing.These results implied that the combination of^(239)Pu,^(240)Pu and Al could be used as the potential tracer of sandstorm.
