This paper examines an epidemic predator-prey model with prey dispersal and Holling type-II functional response. In this model, it is assumed that the predator population suffers a transmissible disease. By analyzing ...This paper examines an epidemic predator-prey model with prey dispersal and Holling type-II functional response. In this model, it is assumed that the predator population suffers a transmissible disease. By analyzing the corresponding characteristic equations, the local stability of each of feasible equilibria and the existence of Hopf bifurcations at the coexistence equilibrium is addressed. Using Lyapunov functionals and LaSalle's invariance principle, we obtained the sufficient conditions for the global stability of the trivial equilibrium, the predator-extinction equilibrium, the disease-free equilibrium and the coexistence equilibrium, respectively. The paper also includes numerical simulations to illustrate the analytical results.展开更多
Amino acids are the building blocks of proteins and play vital roles in both biological systems and drug development.In recent years,increasing attention has been given to the functionalization of amino acid derivativ...Amino acids are the building blocks of proteins and play vital roles in both biological systems and drug development.In recent years,increasing attention has been given to the functionalization of amino acid derivatives.Since the introduction of therapeutic insulin in the early 20th century,the conjugation of drug molecules with amino acids and peptides has been pivotal in driving advancements in drug discovery and become an integral part of modern medical practice.Currently,over a hundred peptide-drug conjugates have received global approval and are widely used to treat diseases such as diabetes,cancer,chronic pain,and multiple sclerosis.Key technologies for conjugating peptides with bioactive molecules include antibody-drug conjugates(ADCs),peptide-drug conjugates(PDCs),and proteolysis targeting chimeras(PROTACs).Significant efforts have been dedicated to developing strategies for the modification of amino acids and peptides,with particular focus on site-selective C-H alkylation/arylation reactions.These reactions are crucial for synthesizing bioactive molecules,as they enable the precise introduction of functional groups at specific positions,thereby improving the pharmacological properties of the resulting compounds.展开更多
The significant role of square root mapping in probability,statistics,physics,architecture and engineering motivates us to emphasize on a new radical functional equation arising from a square root and reciprocal squar...The significant role of square root mapping in probability,statistics,physics,architecture and engineering motivates us to emphasize on a new radical functional equation arising from a square root and reciprocal square root mappings.The interesting attribute of this equation is that it has both a square root mapping and a reciprocal square root mapping as solutions.We establish that the hyperstabilities of this equation exist using a fixed point alternative theorem.It is also demonstrated with an example that the stability may fail in special cases.展开更多
A predator-prey model with prey dispersal and Holling type-Ⅱ functional response is investigated.In this model,the time delay due to the gestation of the predator and stagestructure for the predator are considered.By...A predator-prey model with prey dispersal and Holling type-Ⅱ functional response is investigated.In this model,the time delay due to the gestation of the predator and stagestructure for the predator are considered.By analyzing the corresponding characteristic equations,the local stability of each of the nonnegative equilibria is discussed.The existence of Hopf bifurcations at the positive equilibrium is established.By using Lyapunov functionals and LaSalle’s invariance principle,sufficient conditions are obtained for the global stability of the positive equilibrium,the nonnegative boundary equilibrium and the trivial equilibrium of the model,respectively.Numerical simulations are carried out to illustrate the main results.展开更多
The difference of energy and electronic structure of V, Nb, and Ta in different crystalline structures were investigated by different methods in density functional theory （DFT）. Lattice constants, total energies, an...The difference of energy and electronic structure of V, Nb, and Ta in different crystalline structures were investigated by different methods in density functional theory （DFT）. Lattice constants, total energies, and densities of states of these metals were calculated using the plane-wave pseudopotential method in DFT. Results were compared with those of projector augmented wave method, CALPHAD method, and experiments. Total energy and electronic structure analyses showed that valence electrons mostly transferred from s to p or d state, changing obviously with both the crystal structure and the elemental period number from V to Ta and leading to stronger cohesion, higher cohesive energy and more stable lattice of heavier metals.展开更多
In this study,precise control over the thickness and termination of Ti3C2TX MXene flakes is achieved to enhance their electrical properties,environmental stability,and gas-sensing performance.Utilizing a hybrid method...In this study,precise control over the thickness and termination of Ti3C2TX MXene flakes is achieved to enhance their electrical properties,environmental stability,and gas-sensing performance.Utilizing a hybrid method involving high-pressure processing,stirring,and immiscible solutions,sub-100 nm MXene flake thickness is achieved within the MXene film on the Si-wafer.Functionalization control is achieved by defunctionalizing MXene at 650℃ under vacuum and H2 gas in a CVD furnace,followed by refunctionalization with iodine and bromine vaporization from a bubbler attached to the CVD.Notably,the introduction of iodine,which has a larger atomic size,lower electronegativity,reduce shielding effect,and lower hydrophilicity(contact angle:99°),profoundly affecting MXene.It improves the surface area(36.2 cm^(2) g^(-1)),oxidation stability in aqueous/ambient environments(21 days/80 days),and film conductivity(749 S m^(-1)).Additionally,it significantly enhances the gas-sensing performance,including the sensitivity(0.1119Ωppm^(-1)),response(0.2% and 23%to 50 ppb and 200 ppm NO_(2)),and response/recovery times(90/100 s).The reduced shielding effect of the–I-terminals and the metallic characteristics of MXene enhance the selectivity of I-MXene toward NO2.This approach paves the way for the development of stable and high-performance gas-sensing two-dimensional materials with promising prospects for future studies.展开更多
Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum m...Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum model with various radii for the solute cavity was used to study the relative stability in aqueous solution. The calculated molecular geometries for n=8 and 9 obtained in vacuo are consistent with those observed in experiments. It was found that while the nona-aqua complex is favored in the gas phase, in aqueous solution the octa-aqua conformation is preferred. This result, independent of the types of cavities employed, is in agreement with the experimental observation. The reliability of the present calculation was also addressed by comparing the calculated and experimental free energy of hydration, which revealed that the UA0, UAHF, and UAKS cavities are most appropriate when only the first solvation shell is treated explicitly.展开更多
Functional lipids,primarily derived through the modification of natural lipids by various processes,are widely acknowledged for their potential to impart health benefits.In contrast to chemical methods for lipid modif...Functional lipids,primarily derived through the modification of natural lipids by various processes,are widely acknowledged for their potential to impart health benefits.In contrast to chemical methods for lipid modification,enzymatic catalysis offers distinct advantages,including high selectivity,mild operating conditions,and reduced byproduct formation.Nevertheless,enzymes face challenges in industrial applications,such as low activity,stability,and undesired selectivity.To address these challenges,protein engineering techniques have been implemented to enhance enzyme performance in functional lipid synthesis.This article aims to review recent advances in protein engineering,encompassing approaches from directed evolution to rational design,with the goal of improving the properties of lipid-modifying enzymes.Furthermore,the article explores the future prospects and challenges associated with enzyme-catalyzed functional lipid synthesis.展开更多
In this paper, a diffusive predator-prey system with general functional responses and prey-tactic sensitivities is studied. Providing such generality, we construct a Lyapunov function and we show that the positive con...In this paper, a diffusive predator-prey system with general functional responses and prey-tactic sensitivities is studied. Providing such generality, we construct a Lyapunov function and we show that the positive constant steady state is locally and globally asymptotically stable. With an eye on the biological interpretations, a numerical simulation is performed to illustrate the feasibility of the analytical findings.展开更多
For functional difference equations with unbounded delay,we characterized the existence of totally stable and asymptotically almost periodic solution by using stability properties of a bounded solution in a certain li...For functional difference equations with unbounded delay,we characterized the existence of totally stable and asymptotically almost periodic solution by using stability properties of a bounded solution in a certain limiting equation.展开更多
A series of β-cyclodextrin （CDs） functionalized graphene nanohybrids have been successfully fabricated utilizing the classical covalent modification methods at different reaction temperatures. It is very interesti...A series of β-cyclodextrin （CDs） functionalized graphene nanohybrids have been successfully fabricated utilizing the classical covalent modification methods at different reaction temperatures. It is very interesting that although both CDs and graphene oxide （GO） could he easily decomposed, the effective combination of GO with CDs leads to significantly enhanced thermal stability of graphene derivatives （GO-CDs）. Moreover, the introduction of CDs could dramatically improve the dispersibility promotion of our products in both polar/protic and nonpolar/aprotic solvents, which will contribute to the preparation of polymer nanocomposites and increase of their thermal stability. The improved thermal degradation temperatures can be obtained for polyvinyl alcohol after filling with as little as 1 wt.% of the hybrid. The obtained products could be potentially used in heat-retardant or thermal-control materials.展开更多
In this paper,the stability of a class of impulsive functional differential equations with infinite delays is investigated.A uniform stability theorem and a uniform asymptotic stability theorem are established.
Sufficient condition for stochastic unifrom stability of a neutral stochastic functional differential equation is given, especially, new techniques are developed to cope with the neutral delay case, we obtained the su...Sufficient condition for stochastic unifrom stability of a neutral stochastic functional differential equation is given, especially, new techniques are developed to cope with the neutral delay case, we obtained the sufficient condition for asymptotic stability of neutral stochastic differential delay equations. Due to the new techniques developed in this paper, the results obtained arc very general and useful. The theory developed here gives a unified treatment for various asymptotic estimates e.g. exponential and polynomial bounds.展开更多
The Qinghai-Tibet Plateau(QTP),also known as the Third Pole of the Earth,is a vital ecological security barrier for China.It is a tremendously sensitive region affected by the impacts of global climate change.The esca...The Qinghai-Tibet Plateau(QTP),also known as the Third Pole of the Earth,is a vital ecological security barrier for China.It is a tremendously sensitive region affected by the impacts of global climate change.The escalating intensity of climate change has presented profound challenges to its ecosystem functions and stability.This study first analyzes the spatiotemporal variations of the QTP ecosystem patterns and the key functions of the Plateau including water conservation,soil conservation,and windbreak and sand fixation from 2000 to 2020.It clarifies the regional differences in ecosystem functions and their importance,further evaluates the stability of ecosystem functions,and lays a scientific foundation for an ecological civilization on the Plateau by implementing conservation and restoration projects.The main results show that:(1)From 2000 to 2020,the wetland area in the QTP increased,while the grassland area significantly decreased.There were improvements in water conservation and windbreak and sand fixation capacities,with annual rates of change being 3.57m~3·ha^(-1)·a^(-1)and 0.23 t·ha^(-1)·a^(-1),respectively.However,the overall soil conservation trend declined during the same period,with an annual change rate of-0.16 t·ha^(-1)·a^(-1).(2)The core areas of water conservation,soil conservation,and windbreak and sand fixation on the QTP accounted for 12.7%,13.9%,and 14.2%of the total area,respectively.The core water conservation areas are mainly the southeastern QTP,Sanjiangyuan,and Naqu,while the core windbreak and sand fixation areas were concentrated in the central and western parts of the Plateau.The core soil conservation areas surrounded the entire interior of the Plateau.(3)From 2000 to 2020,the water conservation,soil conservation,and windbreak sand-fixation function on the QTP had higher stability in the southeastern and central parts,while stability was lower in the western region.Considering the stability assessment and ecological protection and restoration practices,the QTP can be divided into three major categories and 16 ecological functional zones.Differentiated ecological protection and restoration efforts can be implemented based on the different core ecosystem functions and zoning.展开更多
In this paper, we considered a homogeneous reaction-diffusion predator-prey system with Holling type II functional response subject to Neumann boundary conditions. Some new sufficient conditions were analytically esta...In this paper, we considered a homogeneous reaction-diffusion predator-prey system with Holling type II functional response subject to Neumann boundary conditions. Some new sufficient conditions were analytically established to ensure that this system has globally asymptotically stable equilibria and Hopf bifurcation surrounding interior equilibrium. In the analysis of Hopf bifurcation, based on the phenomenon of Turing instability and well-done conditions, the system undergoes a Hopf bifurcation and an example incorporating with numerical simulations to support the existence of Hopf bifurcation is presented. We also derived a useful algorithm for determining direction of Hopf bifurcation and stability of bifurcating periodic solutions correspond to j ≠0 and j = 0, respectively. Finally, all these theoretical results are expected to be useful in the future study of dynamical complexity of ecological environment.展开更多
The paper presents an improved plane layout for stabilizing piles based on a proposed piecewise function expression for the irregular driving force. Based on the specific morphological characteristics of a highway lan...The paper presents an improved plane layout for stabilizing piles based on a proposed piecewise function expression for the irregular driving force. Based on the specific morphological characteristics of a highway landslide, the piecewise function is used to calculate the irregular driving force by dividing the landslide into several sub-areas.Furthermore, the reasonable layout range and pile spacing can be obtained based on the piecewise function expression of the irregular driving force and on relevant research results of the plane layout for stabilizing piles. Therefore, an improved plane layout of stabilizing piles is presented in consideration of a piecewise function expression of the irregular driving force. A highway landslide located in eastern Guizhou Province, China, is analyzed as a case study using the proposed method. The results demonstrate that the theory presented in this paper provides improved economic benefits and can reduce the requirednumber of stabilizing piles by 28.6% compared with the conventional plane layout scheme.展开更多
The dynamics, stability and control problem of a kind of infinite dimensional system are studied in the functional space with the method of modern Mathematics. First, the dynamical control model of the distributed par...The dynamics, stability and control problem of a kind of infinite dimensional system are studied in the functional space with the method of modern Mathematics. First, the dynamical control model of the distributed parameter system with multi-body flexible and multi-topological structure was established which has damping, gyroscopic parts and constrained damping. Secondly, the necessary and sufficient condition of controllability and observability, the stability theory and asymptotic property of the system were obtained. These results expand the theory of the field about the dynamics and control of the system with multi-body flexible structure, and have important engineering significance.展开更多
In this paper, we investigate the stability of a class of impulsive functional differential equations by using Lyapunov functional and Jensen＇s inequality. Some new stability theorems are obtained. Examples are given...In this paper, we investigate the stability of a class of impulsive functional differential equations by using Lyapunov functional and Jensen＇s inequality. Some new stability theorems are obtained. Examples are given to demonstrate the advantage of the obtained results.展开更多
In this study,the transverse vibration of a traveling beam made of functionally graded material was analyzed.The material gradation was assumed to vary continuously along the thickness direction of the beam in the for...In this study,the transverse vibration of a traveling beam made of functionally graded material was analyzed.The material gradation was assumed to vary continuously along the thickness direction of the beam in the form of power law exponent.The effect of the longitudinally varying tension due to axial acceleration was highlighted,and the dependence of the tension on the finite support rigidity was also considered.A complex governing equation of the functionally graded beam was derived by the Hamilton principle,in which the geometric nonlinearity,material properties and axial load were incorporated.The direct multiscale method was applied to the analysis process of an axially moving functionally graded beam with timedependent velocity,and the natural frequency and solvability conditions were obtained.Based on the conditions,the stability boundaries of subharmonic resonance and combination resonance were obtained.It was found that the dynamic behavior of axial moving beams could be tuned by using the distribution law of the functional gradient parameters.展开更多
We produced and analyzed oasis structure information, and evaluated oasis functional stability using the multiple indicators based on Remote Sensing(RS) and Geographical Information System(GIS) in the arid region of C...We produced and analyzed oasis structure information, and evaluated oasis functional stability using the multiple indicators based on Remote Sensing(RS) and Geographical Information System(GIS) in the arid region of China in 2015. The results showed that the oases area was 193,734 km^2, accounting for 8.17% of the arid region of China. The spatial difference in the functional stability of oases was obvious. The Beijiang zone had the highest functional stability and was relatively stable state, and the Hexi Corridor-Alashan Plateau zone had the lowest functional stability and was relatively unstable. The functional stability is dominated by production and ecological functions, which have regional differences. Increasing oasis agricultural output, strengthening highway infrastructure construction and paying attention to education will become important ways to improve oasis functional stability. Water resources determine the ecological function, thus affecting the oasis functional stability. The results provide references for the formulation of related policies according to local conditions.展开更多
基金Supported by the Social Science Foundation of Hebei Province(Grant No.HB23TJ003)the Science Research Project of Hebei Education Department(Grant No.BJK2024197)。
文摘This paper examines an epidemic predator-prey model with prey dispersal and Holling type-II functional response. In this model, it is assumed that the predator population suffers a transmissible disease. By analyzing the corresponding characteristic equations, the local stability of each of feasible equilibria and the existence of Hopf bifurcations at the coexistence equilibrium is addressed. Using Lyapunov functionals and LaSalle's invariance principle, we obtained the sufficient conditions for the global stability of the trivial equilibrium, the predator-extinction equilibrium, the disease-free equilibrium and the coexistence equilibrium, respectively. The paper also includes numerical simulations to illustrate the analytical results.
文摘Amino acids are the building blocks of proteins and play vital roles in both biological systems and drug development.In recent years,increasing attention has been given to the functionalization of amino acid derivatives.Since the introduction of therapeutic insulin in the early 20th century,the conjugation of drug molecules with amino acids and peptides has been pivotal in driving advancements in drug discovery and become an integral part of modern medical practice.Currently,over a hundred peptide-drug conjugates have received global approval and are widely used to treat diseases such as diabetes,cancer,chronic pain,and multiple sclerosis.Key technologies for conjugating peptides with bioactive molecules include antibody-drug conjugates(ADCs),peptide-drug conjugates(PDCs),and proteolysis targeting chimeras(PROTACs).Significant efforts have been dedicated to developing strategies for the modification of amino acids and peptides,with particular focus on site-selective C-H alkylation/arylation reactions.These reactions are crucial for synthesizing bioactive molecules,as they enable the precise introduction of functional groups at specific positions,thereby improving the pharmacological properties of the resulting compounds.
基金Supported by the Science and Engineering Research Board(SERB),India(MTR/2020/000534).
文摘The significant role of square root mapping in probability,statistics,physics,architecture and engineering motivates us to emphasize on a new radical functional equation arising from a square root and reciprocal square root mappings.The interesting attribute of this equation is that it has both a square root mapping and a reciprocal square root mapping as solutions.We establish that the hyperstabilities of this equation exist using a fixed point alternative theorem.It is also demonstrated with an example that the stability may fail in special cases.
基金Supported by the Social Science Foundation of Hebei Province(HB23TJO03)。
文摘A predator-prey model with prey dispersal and Holling type-Ⅱ functional response is investigated.In this model,the time delay due to the gestation of the predator and stagestructure for the predator are considered.By analyzing the corresponding characteristic equations,the local stability of each of the nonnegative equilibria is discussed.The existence of Hopf bifurcations at the positive equilibrium is established.By using Lyapunov functionals and LaSalle’s invariance principle,sufficient conditions are obtained for the global stability of the positive equilibrium,the nonnegative boundary equilibrium and the trivial equilibrium of the model,respectively.Numerical simulations are carried out to illustrate the main results.
基金ACKNOWLEDGMENTS This work was supported by the Doctoral Discipline Foundation of the Ministry of Education of China （No.20070533118） and the National Natural Science Foundation of China （No.50871124）. The authors acknowledge Dr. Y. Z. Nie for his useful discussion in calculations.
文摘The difference of energy and electronic structure of V, Nb, and Ta in different crystalline structures were investigated by different methods in density functional theory （DFT）. Lattice constants, total energies, and densities of states of these metals were calculated using the plane-wave pseudopotential method in DFT. Results were compared with those of projector augmented wave method, CALPHAD method, and experiments. Total energy and electronic structure analyses showed that valence electrons mostly transferred from s to p or d state, changing obviously with both the crystal structure and the elemental period number from V to Ta and leading to stronger cohesion, higher cohesive energy and more stable lattice of heavier metals.
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT)(No. 2021R1I1A1A0105621313, No. 2022R1F1A1074441, No. 2022K1A3A1A20014496, and No. 2022R1F1A1074083)supported by the Ministry of Education Funding (No. RIS 2021-004)supported by the Brain Pool program funded by the Ministry of Science and ICT through the National Research Foundation of Korea (RS-2023-00284318).
文摘In this study,precise control over the thickness and termination of Ti3C2TX MXene flakes is achieved to enhance their electrical properties,environmental stability,and gas-sensing performance.Utilizing a hybrid method involving high-pressure processing,stirring,and immiscible solutions,sub-100 nm MXene flake thickness is achieved within the MXene film on the Si-wafer.Functionalization control is achieved by defunctionalizing MXene at 650℃ under vacuum and H2 gas in a CVD furnace,followed by refunctionalization with iodine and bromine vaporization from a bubbler attached to the CVD.Notably,the introduction of iodine,which has a larger atomic size,lower electronegativity,reduce shielding effect,and lower hydrophilicity(contact angle:99°),profoundly affecting MXene.It improves the surface area(36.2 cm^(2) g^(-1)),oxidation stability in aqueous/ambient environments(21 days/80 days),and film conductivity(749 S m^(-1)).Additionally,it significantly enhances the gas-sensing performance,including the sensitivity(0.1119Ωppm^(-1)),response(0.2% and 23%to 50 ppb and 200 ppm NO_(2)),and response/recovery times(90/100 s).The reduced shielding effect of the–I-terminals and the metallic characteristics of MXene enhance the selectivity of I-MXene toward NO2.This approach paves the way for the development of stable and high-performance gas-sensing two-dimensional materials with promising prospects for future studies.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10804001, No.10674002, and No.20773024）, the National High Technology Research and Development Program of China （No.2006AA09Z243-3）, and the Program for Innovative Research Team in Anhui Normal University of China.
文摘Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum model with various radii for the solute cavity was used to study the relative stability in aqueous solution. The calculated molecular geometries for n=8 and 9 obtained in vacuo are consistent with those observed in experiments. It was found that while the nona-aqua complex is favored in the gas phase, in aqueous solution the octa-aqua conformation is preferred. This result, independent of the types of cavities employed, is in agreement with the experimental observation. The reliability of the present calculation was also addressed by comparing the calculated and experimental free energy of hydration, which revealed that the UA0, UAHF, and UAKS cavities are most appropriate when only the first solvation shell is treated explicitly.
基金supported by Natural Science Foundation of Sichuan Province(2023NSFSC0132)Fundamental Research Funds for Central Universities of the Sichuan University(YJ202308).
文摘Functional lipids,primarily derived through the modification of natural lipids by various processes,are widely acknowledged for their potential to impart health benefits.In contrast to chemical methods for lipid modification,enzymatic catalysis offers distinct advantages,including high selectivity,mild operating conditions,and reduced byproduct formation.Nevertheless,enzymes face challenges in industrial applications,such as low activity,stability,and undesired selectivity.To address these challenges,protein engineering techniques have been implemented to enhance enzyme performance in functional lipid synthesis.This article aims to review recent advances in protein engineering,encompassing approaches from directed evolution to rational design,with the goal of improving the properties of lipid-modifying enzymes.Furthermore,the article explores the future prospects and challenges associated with enzyme-catalyzed functional lipid synthesis.
文摘In this paper, a diffusive predator-prey system with general functional responses and prey-tactic sensitivities is studied. Providing such generality, we construct a Lyapunov function and we show that the positive constant steady state is locally and globally asymptotically stable. With an eye on the biological interpretations, a numerical simulation is performed to illustrate the feasibility of the analytical findings.
文摘For functional difference equations with unbounded delay,we characterized the existence of totally stable and asymptotically almost periodic solution by using stability properties of a bounded solution in a certain limiting equation.
基金supported by China Postdoctoral Science Foundation Funded Project(No.20100481146)Jiangsu Planned Projects for Postdoctoral Research Funds(No.1002015C)+2 种基金Natural Science Foundation of Jiangsu Province(No.BK2011712, BK20130575)National University Student Innovation Program(No.201210288036)NJUST Opening Measuring Fund of Large Precious Apparatus(No.2012-01-15)
文摘A series of β-cyclodextrin （CDs） functionalized graphene nanohybrids have been successfully fabricated utilizing the classical covalent modification methods at different reaction temperatures. It is very interesting that although both CDs and graphene oxide （GO） could he easily decomposed, the effective combination of GO with CDs leads to significantly enhanced thermal stability of graphene derivatives （GO-CDs）. Moreover, the introduction of CDs could dramatically improve the dispersibility promotion of our products in both polar/protic and nonpolar/aprotic solvents, which will contribute to the preparation of polymer nanocomposites and increase of their thermal stability. The improved thermal degradation temperatures can be obtained for polyvinyl alcohol after filling with as little as 1 wt.% of the hybrid. The obtained products could be potentially used in heat-retardant or thermal-control materials.
文摘In this paper,the stability of a class of impulsive functional differential equations with infinite delays is investigated.A uniform stability theorem and a uniform asymptotic stability theorem are established.
基金Supported by the National Natural Science Founda-tion of China (19531070) and the Major Project Foundation of HubeiProvince Education Department (2004Z001)
文摘Sufficient condition for stochastic unifrom stability of a neutral stochastic functional differential equation is given, especially, new techniques are developed to cope with the neutral delay case, we obtained the sufficient condition for asymptotic stability of neutral stochastic differential delay equations. Due to the new techniques developed in this paper, the results obtained arc very general and useful. The theory developed here gives a unified treatment for various asymptotic estimates e.g. exponential and polynomial bounds.
基金The Second Tibetan Plateau Scientific Expedition and Research Program,No.2019QZKK0404。
文摘The Qinghai-Tibet Plateau(QTP),also known as the Third Pole of the Earth,is a vital ecological security barrier for China.It is a tremendously sensitive region affected by the impacts of global climate change.The escalating intensity of climate change has presented profound challenges to its ecosystem functions and stability.This study first analyzes the spatiotemporal variations of the QTP ecosystem patterns and the key functions of the Plateau including water conservation,soil conservation,and windbreak and sand fixation from 2000 to 2020.It clarifies the regional differences in ecosystem functions and their importance,further evaluates the stability of ecosystem functions,and lays a scientific foundation for an ecological civilization on the Plateau by implementing conservation and restoration projects.The main results show that:(1)From 2000 to 2020,the wetland area in the QTP increased,while the grassland area significantly decreased.There were improvements in water conservation and windbreak and sand fixation capacities,with annual rates of change being 3.57m~3·ha^(-1)·a^(-1)and 0.23 t·ha^(-1)·a^(-1),respectively.However,the overall soil conservation trend declined during the same period,with an annual change rate of-0.16 t·ha^(-1)·a^(-1).(2)The core areas of water conservation,soil conservation,and windbreak and sand fixation on the QTP accounted for 12.7%,13.9%,and 14.2%of the total area,respectively.The core water conservation areas are mainly the southeastern QTP,Sanjiangyuan,and Naqu,while the core windbreak and sand fixation areas were concentrated in the central and western parts of the Plateau.The core soil conservation areas surrounded the entire interior of the Plateau.(3)From 2000 to 2020,the water conservation,soil conservation,and windbreak sand-fixation function on the QTP had higher stability in the southeastern and central parts,while stability was lower in the western region.Considering the stability assessment and ecological protection and restoration practices,the QTP can be divided into three major categories and 16 ecological functional zones.Differentiated ecological protection and restoration efforts can be implemented based on the different core ecosystem functions and zoning.
文摘In this paper, we considered a homogeneous reaction-diffusion predator-prey system with Holling type II functional response subject to Neumann boundary conditions. Some new sufficient conditions were analytically established to ensure that this system has globally asymptotically stable equilibria and Hopf bifurcation surrounding interior equilibrium. In the analysis of Hopf bifurcation, based on the phenomenon of Turing instability and well-done conditions, the system undergoes a Hopf bifurcation and an example incorporating with numerical simulations to support the existence of Hopf bifurcation is presented. We also derived a useful algorithm for determining direction of Hopf bifurcation and stability of bifurcating periodic solutions correspond to j ≠0 and j = 0, respectively. Finally, all these theoretical results are expected to be useful in the future study of dynamical complexity of ecological environment.
基金supported by the National Key R&D Program of China (2017YFC1501304)the National Natural Science Fund of China (No. 41472261)+1 种基金 the Key Technical Project of Shenzhen Science Technology Project (No. JSGG20160331154546471) the Open Fund of State Key Laboratory of Geohazard Prevention and Geoenviroment Protection (Grant No. SKLGP2017K017)
文摘The paper presents an improved plane layout for stabilizing piles based on a proposed piecewise function expression for the irregular driving force. Based on the specific morphological characteristics of a highway landslide, the piecewise function is used to calculate the irregular driving force by dividing the landslide into several sub-areas.Furthermore, the reasonable layout range and pile spacing can be obtained based on the piecewise function expression of the irregular driving force and on relevant research results of the plane layout for stabilizing piles. Therefore, an improved plane layout of stabilizing piles is presented in consideration of a piecewise function expression of the irregular driving force. A highway landslide located in eastern Guizhou Province, China, is analyzed as a case study using the proposed method. The results demonstrate that the theory presented in this paper provides improved economic benefits and can reduce the requirednumber of stabilizing piles by 28.6% compared with the conventional plane layout scheme.
文摘The dynamics, stability and control problem of a kind of infinite dimensional system are studied in the functional space with the method of modern Mathematics. First, the dynamical control model of the distributed parameter system with multi-body flexible and multi-topological structure was established which has damping, gyroscopic parts and constrained damping. Secondly, the necessary and sufficient condition of controllability and observability, the stability theory and asymptotic property of the system were obtained. These results expand the theory of the field about the dynamics and control of the system with multi-body flexible structure, and have important engineering significance.
基金supported by the National Natural Science Foundation of China (No. 10871063)Scientific Research Fund of Hunan Provincial Education Department (No. 07A038)
文摘In this paper, we investigate the stability of a class of impulsive functional differential equations by using Lyapunov functional and Jensen＇s inequality. Some new stability theorems are obtained. Examples are given to demonstrate the advantage of the obtained results.
基金The authors acknowledge the support of National Natural Science Foundation of China(Nos.11672187,11572182)Natural Science Foundation of Liaoning Province(201602573)+2 种基金the Key Research Projects of Shanghai Science and Technology Commission(No.18010500100)Innovation Program of Shanghai Education Commission(No.2017-01-07-00-09-E00019)Beiyang Young Scholars of Tian jin University(2019XRX-0027).
文摘In this study,the transverse vibration of a traveling beam made of functionally graded material was analyzed.The material gradation was assumed to vary continuously along the thickness direction of the beam in the form of power law exponent.The effect of the longitudinally varying tension due to axial acceleration was highlighted,and the dependence of the tension on the finite support rigidity was also considered.A complex governing equation of the functionally graded beam was derived by the Hamilton principle,in which the geometric nonlinearity,material properties and axial load were incorporated.The direct multiscale method was applied to the analysis process of an axially moving functionally graded beam with timedependent velocity,and the natural frequency and solvability conditions were obtained.Based on the conditions,the stability boundaries of subharmonic resonance and combination resonance were obtained.It was found that the dynamic behavior of axial moving beams could be tuned by using the distribution law of the functional gradient parameters.
基金This work was supported by the National Key Research and Development Program of China (2017YFC0504301)the Strategic Priority Research Program of Chinese Academy of Sciences,Pan-Third Pole Environment Study for a Green Silk Road (Pan-TPE)
文摘We produced and analyzed oasis structure information, and evaluated oasis functional stability using the multiple indicators based on Remote Sensing(RS) and Geographical Information System(GIS) in the arid region of China in 2015. The results showed that the oases area was 193,734 km^2, accounting for 8.17% of the arid region of China. The spatial difference in the functional stability of oases was obvious. The Beijiang zone had the highest functional stability and was relatively stable state, and the Hexi Corridor-Alashan Plateau zone had the lowest functional stability and was relatively unstable. The functional stability is dominated by production and ecological functions, which have regional differences. Increasing oasis agricultural output, strengthening highway infrastructure construction and paying attention to education will become important ways to improve oasis functional stability. Water resources determine the ecological function, thus affecting the oasis functional stability. The results provide references for the formulation of related policies according to local conditions.
