Aris and Amundson studied a chemical reactor and obtained the two equationsDaoud showed that at most one limit cycle may exist in the region of interest. Itis showed in this paper that other singular points exist and ...Aris and Amundson studied a chemical reactor and obtained the two equationsDaoud showed that at most one limit cycle may exist in the region of interest. Itis showed in this paper that other singular points exist and that a stable limitt cycle existsaround the singularity (1/2, 2) when K∈(9-δ, 9).展开更多
In this paper, by making use of Duan＇s topological current theory, the evolution of the vortex filaments in excitable media is discussed in detail. The vortex filaments are found generating or annihilating at the lim...In this paper, by making use of Duan＇s topological current theory, the evolution of the vortex filaments in excitable media is discussed in detail. The vortex filaments are found generating or annihilating at the limit points and encountering, splitting, or merging at the bifurcation points of a complex function Z（x, t）. [t is also shown that the Hopf invariant of knotted scroll wave filaments is preserved in the branch processes （splitting, merging, or encountering） during the evolution of these knotted scroll wave filaments. Furthermore, it also revealed that the ＂exclusion principle＂ in some chemical media is just the special case of the Hopf invariant constraint, and during the branch processes the ＂exclusion principle＂ is also protected by topology.展开更多
To solve the increasing model complexity due to several input variables and large correlations under variable load conditions,a dynamic modeling method combining a kernel extreme learning machine(KELM)and principal co...To solve the increasing model complexity due to several input variables and large correlations under variable load conditions,a dynamic modeling method combining a kernel extreme learning machine(KELM)and principal component analysis(PCA)was proposed and applied to the prediction of nitrogen oxide(NO_(x))concentration at the outlet of a selective catalytic reduction(SCR)denitrification system.First,PCA is applied to the feature information extraction of input data,and the current and previous sequence values of the extracted information are used as the inputs of the KELM model to reflect the dynamic characteristics of the NO_(x)concentration at the SCR outlet.Then,the model takes the historical data of the NO_(x)concentration at the SCR outlet as the model input to improve its accuracy.Finally,an optimization algorithm is used to determine the optimal parameters of the model.Compared with the Gaussian process regression,long short-term memory,and convolutional neural network models,the prediction errors are reduced by approximately 78.4%,67.6%,and 59.3%,respectively.The results indicate that the proposed dynamic model structure is reliable and can accurately predict NO_(x)concentrations at the outlet of the SCR system.展开更多
Realizing low contact resistance between graphene and metal electrodes remains a well-known challenge for building high-performance graphene devices. In this work, we attempt to reduce the contact resistance in graphe...Realizing low contact resistance between graphene and metal electrodes remains a well-known challenge for building high-performance graphene devices. In this work, we attempt to reduce the contact resistance in graphene transistors and further explore the resistance limit between graphene and metal contacts. The Pd/graphene contact resistance at room temperature is reduced below the 100 Ω·μm level both on mechanically exfoliated and chemical-vapor-deposition graphene by adopting high-purity palladium and high-quality graphene and controlling the fabrication process to not contaminate the interface. After excluding the parasitic series resistances from the measurement system and electrodes, the retrieved contact resistance is shown to be systematically and statistically less than 100 Ω·μm, with a minimum value of 69 Ω·μm, which is very close to the theoretical limit. Furthermore, the contact resistance shows no clear dependence on temperature in the range of 77-300 K; this is attributed to the saturation of carrier injection efficiency between graphene and Pd owing to the high quality of the graphene samples used, which have a sufficiently long carrier mean-free-path.展开更多
Strain engineering is a promising method for tuning the electronic properties of two-dimensional(2 D)materials,which are capable of sustaining enormous strain thanks to their atomic thinness.However,applying a large a...Strain engineering is a promising method for tuning the electronic properties of two-dimensional(2 D)materials,which are capable of sustaining enormous strain thanks to their atomic thinness.However,applying a large and homogeneous strain on these 2D materials,including the typical semiconductor MoS_(2),remains cumbersome.Here we report a facile strategy for the fabrication of highly strained MoS_(2) via chalcogenide substitution reaction(CSR)of MoTe_(2) with lattice inheritance.The MoS_(2)resulting from the sulfurized MoTe_(2) sustains ultra large in-plane strain(approaching its strength limit~10%)with great homogeneity.Furthermore,the strain can be deterministically and continuously tuned to~1.5%by simply varying the processing temperature.Thanks to the fine control of our CSR process,we demonstrate a heterostructure of strained MoS_(2)/MoTe_(2)with abrupt interface.Finally,we verify that such a large strain potentially allows the modulation of MoS_(2) bandgap over an ultra-broad range(~1 e V).Our controllable CSR strategy paves the way for the fabrication of highly strained 2D materials for applications in devices.展开更多
文摘Aris and Amundson studied a chemical reactor and obtained the two equationsDaoud showed that at most one limit cycle may exist in the region of interest. Itis showed in this paper that other singular points exist and that a stable limitt cycle existsaround the singularity (1/2, 2) when K∈(9-δ, 9).
基金Supported by the National Natural Science Foundation of China under Grant No.10275030the Cuiying Programm of Lanzhou University under Grant No.22500-582404
文摘In this paper, by making use of Duan＇s topological current theory, the evolution of the vortex filaments in excitable media is discussed in detail. The vortex filaments are found generating or annihilating at the limit points and encountering, splitting, or merging at the bifurcation points of a complex function Z（x, t）. [t is also shown that the Hopf invariant of knotted scroll wave filaments is preserved in the branch processes （splitting, merging, or encountering） during the evolution of these knotted scroll wave filaments. Furthermore, it also revealed that the ＂exclusion principle＂ in some chemical media is just the special case of the Hopf invariant constraint, and during the branch processes the ＂exclusion principle＂ is also protected by topology.
基金The National Natural Science Foundation of China(No.71471060)the Natural Science Foundation of Hebei Province(No.E2018502111)。
文摘To solve the increasing model complexity due to several input variables and large correlations under variable load conditions,a dynamic modeling method combining a kernel extreme learning machine(KELM)and principal component analysis(PCA)was proposed and applied to the prediction of nitrogen oxide(NO_(x))concentration at the outlet of a selective catalytic reduction(SCR)denitrification system.First,PCA is applied to the feature information extraction of input data,and the current and previous sequence values of the extracted information are used as the inputs of the KELM model to reflect the dynamic characteristics of the NO_(x)concentration at the SCR outlet.Then,the model takes the historical data of the NO_(x)concentration at the SCR outlet as the model input to improve its accuracy.Finally,an optimization algorithm is used to determine the optimal parameters of the model.Compared with the Gaussian process regression,long short-term memory,and convolutional neural network models,the prediction errors are reduced by approximately 78.4%,67.6%,and 59.3%,respectively.The results indicate that the proposed dynamic model structure is reliable and can accurately predict NO_(x)concentrations at the outlet of the SCR system.
基金This work was supported by the Ministry of Sdence and Technology of China （Grant Nos. 2011CB933001 and 2011CB933002）, National Natural Science Foundation of China （Grant Nos. 61322105, 61271051, 61321001, and 61390504）, and Beijing Municipal Science and Technology Commission （Grant Nos. Z131100003213021 and D141100000614001）.
文摘Realizing low contact resistance between graphene and metal electrodes remains a well-known challenge for building high-performance graphene devices. In this work, we attempt to reduce the contact resistance in graphene transistors and further explore the resistance limit between graphene and metal contacts. The Pd/graphene contact resistance at room temperature is reduced below the 100 Ω·μm level both on mechanically exfoliated and chemical-vapor-deposition graphene by adopting high-purity palladium and high-quality graphene and controlling the fabrication process to not contaminate the interface. After excluding the parasitic series resistances from the measurement system and electrodes, the retrieved contact resistance is shown to be systematically and statistically less than 100 Ω·μm, with a minimum value of 69 Ω·μm, which is very close to the theoretical limit. Furthermore, the contact resistance shows no clear dependence on temperature in the range of 77-300 K; this is attributed to the saturation of carrier injection efficiency between graphene and Pd owing to the high quality of the graphene samples used, which have a sufficiently long carrier mean-free-path.
基金supported by the National Natural Science Foundation of China(21825103,52001165)Natural Science Foundation of Hubei Province(2019CFA002)+2 种基金Natural Science Foundation of Jiangsu Province(BK20200475)the Fundamental Research Funds for the Central Universities(2019kfy XMBZ018,30921011215)supports from Analytical and Testing Center in Huazhong University of Science and Technology as well as Nanostructure Research Center(NRC)supported by the Fundamental Research Funds for the Central Universities(WUT:2019III012GX,2020III002GX)。
文摘Strain engineering is a promising method for tuning the electronic properties of two-dimensional(2 D)materials,which are capable of sustaining enormous strain thanks to their atomic thinness.However,applying a large and homogeneous strain on these 2D materials,including the typical semiconductor MoS_(2),remains cumbersome.Here we report a facile strategy for the fabrication of highly strained MoS_(2) via chalcogenide substitution reaction(CSR)of MoTe_(2) with lattice inheritance.The MoS_(2)resulting from the sulfurized MoTe_(2) sustains ultra large in-plane strain(approaching its strength limit~10%)with great homogeneity.Furthermore,the strain can be deterministically and continuously tuned to~1.5%by simply varying the processing temperature.Thanks to the fine control of our CSR process,we demonstrate a heterostructure of strained MoS_(2)/MoTe_(2)with abrupt interface.Finally,we verify that such a large strain potentially allows the modulation of MoS_(2) bandgap over an ultra-broad range(~1 e V).Our controllable CSR strategy paves the way for the fabrication of highly strained 2D materials for applications in devices.
