This paper is concerned with the enumeration of a special kind of labeled connected graphs of which the cutpoint-graphs are trees.A new method—treelization is introduced, by which the enumeration of this special kind...This paper is concerned with the enumeration of a special kind of labeled connected graphs of which the cutpoint-graphs are trees.A new method—treelization is introduced, by which the enumeration of this special kind of graphs can be solved. The enumerative formula with generating function is derived. The method of treelization is powerful in solving enumeration problems of graphs and deserves further research. For example, using the similar way, another special kind of labeled connected graphs of which the block-graphs are trees can be enumerated.展开更多
Objective: To investigate the effect of arsenic trioxide(As_2O_3)with three different concentration groups on the distribution and recruitment of dendritic cells(DCs)in the conducting airways of asthmatic mice. Metho...Objective: To investigate the effect of arsenic trioxide(As_2O_3)with three different concentration groups on the distribution and recruitment of dendritic cells(DCs)in the conducting airways of asthmatic mice. Methods: Fifty BALB/c mice were divided into 5 groups at random:control group,asthmatic group,therapeutic groups with low dose(1 mg/kg),moderate dose(5 mg/kg)and high dose(10 mg/kg)of As_2O_3.The immunohistochemistry,scanning electron microscope and computerized image analysis were applied to detect airway DCs,respectively. Results: We demonstrated from the control mice that all intraepithelial NLDC-145 + DCs throughout the respiratory tree could be accounted for a network of cells with dendritic cell morphology,and the density of DCs varied from(500±50)cells/mm 2 epithelial surface in the large airways,to(60±10)cells/mm 2 epithelial surface in the small airways(P<0.05).The DCs characteristic of spiny and long processes were impressively observed by the scanning electron microscope.Compared with the control mice,the density,but not the distribution of NLDC-145 + DCs was significantly upregulated in the conducting airways of asthmatic mice(P<0.01).Compared with the asthmatic mice,the densities,but not the distributions of NLDC-145 + DCs were significantly down regulated in the conducting airways of the therapeutic groups with three varying concentrations of As_2O_3(P<0.01)while there were no statistical differences between each other(P>0.05). Conclusion: Our findings suggest that it might be an important therapeutic mechanism of As_2O_3 to downregulate not the distribution but the density of DCs in the conducting airways of asthmatic mice,and low dose of As_2O_3 has potential value in treating asthma.展开更多
A facile and green approach has been developed for the in situ synthesis of hybrid nanomaterials based on dendrite-shaped Pd nanostructures supported on graphene （RG）. The as-synthesized hybrid nanomaterials （RG-Pd...A facile and green approach has been developed for the in situ synthesis of hybrid nanomaterials based on dendrite-shaped Pd nanostructures supported on graphene （RG）. The as-synthesized hybrid nanomaterials （RG-PdnDs） have been thoroughly characterized by high resolution transmission electron microscopy, X-ray photoelectron spectroscop）~ atomic force microscop）~ Raman spectroscopy and electrochemical techniques. The mechanism of formation of such dendrite- shaped Pd nanostructures on the graphene support has been elucidated using transmission electron microscopy （TEM） measurements. The RG induces the formation of, and plays a decisive role in shaping, the dendrite morphology of Pd nanostructures on its surface. Cyclic voltammetry and chronoamperometry techniques have been employed to evaluate the electrochemical performance of RG-PdnDs towards oxidation of methanol. The electrochemical （EC） activities of RG-PdnDs are compared with graphene-supported spherical-shaped Pd nanostructures, Pd nanodendrites alone and a commercial available Pd/C counterpart. The combined effect of the graphene support and the dendrite morphology of RG-PdnDs triggers the high electrocatalytic activity and results in robust tolerance to CO poisoning.展开更多
This paper demonstrates a one-pot approach to produce highly dispersed dendritic palladium-platinum bi- metallic nanoparticles （NPs） with small particle size, tunable composition and high catalytic activity. Herein,...This paper demonstrates a one-pot approach to produce highly dispersed dendritic palladium-platinum bi- metallic nanoparticles （NPs） with small particle size, tunable composition and high catalytic activity. Herein, the PdPt bi- metallic NPs have been obtained using bayberry tannin （BT） as both the reducing agent and surfactant. Additionally, the PdPt bimetallic NPs with different Pd/Pt atomic ratios can be prepared by just varying the amounts of the Pd and Pt pre- cursors. Most importantly, the as-prepared Pd52Pt4s catalyst exhibits the optimal catalytic activities compared with the other compositional PdPt NPs （Pds2Ptls, Pd69Ph~, and Pd36 Pt64） and commercial Pt/C （20 wt.%） catalyst for the methanol oxidation reaction （MOR）. Meanwhile, Pd52Pt4s also shows better CO tolerance, which can be attributed to the unique dendritic structure and the synergistic effect between Pd and Pt. With evident advantages of the facile preparation and enhanced catalytic performance, it holds great promise as a high-performance catalyst for electrochemical energy con- version.展开更多
The Bergman cyclization has strongly impacted on a number of fields including pharmaceutics, synthetic chemistry, and material science. The diradical intermediates stemmed from enediynes can not only cause DNA cleavag...The Bergman cyclization has strongly impacted on a number of fields including pharmaceutics, synthetic chemistry, and material science. The diradical intermediates stemmed from enediynes can not only cause DNA cleavage under physiological conditions but also function as monomer or initiator participants in polymer science. The homo-polymerization of enediynes through the Bergman cyclization to fabricate conjugated polymers is a fascinating strategy due to the advantages of facial operation, high efficiency, tailored structure, and catalyst-free operation. Moreover, conjugated polymers generated through the Bergman cyclization show many remarkable properties, such as excellent thermal stability, good solubility, and processability, which enables these polymers to be further manufactured into carbon-rich materials. Recent times have seen extensive efforts devoted to the application of the Bergman cyclization in polymer science and materials chemistry. A variety of synthetic strategies have been developed to fabricate structurally unique materials via the Bergman cyclization, including the fabrication of rod-like polymers with polyester, dendrimers and chiral imide side chains, functionalization of carbon nanomaterials by surface-grafting conjugated polymers, formation of nanoparticles by intramolecular collapse of single polymer chains, and the construction of carbon nanomembranes with different morphologies. Future developments involving the Bergman cyclization in polymer science, probably by altering the reaction mechanism to precisely control the microstructure of polymeric products, are also proposed in this review article.展开更多
Dendrimers are well-defined tree-like macromolecules possessing numerous chain ends emanating from a single core, which makes them attractive candidates for mimicking light-harvesting systems and hydrogenases. Photoin...Dendrimers are well-defined tree-like macromolecules possessing numerous chain ends emanating from a single core, which makes them attractive candidates for mimicking light-harvesting systems and hydrogenases. Photoinduced electron and energy transfers are main processes involved in light-harvesting and photocatalysis. In this review, the general concepts of design strategies and recent developments of photofunctional dendrimers in biomimics of light-harvesting systems and hydrogenases are discussed. The energy transfer and electron transfer processes in light-harvesting dendrimers and the effect of dendritic structures in photochemical hydrogen production are illustrated.展开更多
文摘This paper is concerned with the enumeration of a special kind of labeled connected graphs of which the cutpoint-graphs are trees.A new method—treelization is introduced, by which the enumeration of this special kind of graphs can be solved. The enumerative formula with generating function is derived. The method of treelization is powerful in solving enumeration problems of graphs and deserves further research. For example, using the similar way, another special kind of labeled connected graphs of which the block-graphs are trees can be enumerated.
文摘Objective: To investigate the effect of arsenic trioxide(As_2O_3)with three different concentration groups on the distribution and recruitment of dendritic cells(DCs)in the conducting airways of asthmatic mice. Methods: Fifty BALB/c mice were divided into 5 groups at random:control group,asthmatic group,therapeutic groups with low dose(1 mg/kg),moderate dose(5 mg/kg)and high dose(10 mg/kg)of As_2O_3.The immunohistochemistry,scanning electron microscope and computerized image analysis were applied to detect airway DCs,respectively. Results: We demonstrated from the control mice that all intraepithelial NLDC-145 + DCs throughout the respiratory tree could be accounted for a network of cells with dendritic cell morphology,and the density of DCs varied from(500±50)cells/mm 2 epithelial surface in the large airways,to(60±10)cells/mm 2 epithelial surface in the small airways(P<0.05).The DCs characteristic of spiny and long processes were impressively observed by the scanning electron microscope.Compared with the control mice,the density,but not the distribution of NLDC-145 + DCs was significantly upregulated in the conducting airways of asthmatic mice(P<0.01).Compared with the asthmatic mice,the densities,but not the distributions of NLDC-145 + DCs were significantly down regulated in the conducting airways of the therapeutic groups with three varying concentrations of As_2O_3(P<0.01)while there were no statistical differences between each other(P>0.05). Conclusion: Our findings suggest that it might be an important therapeutic mechanism of As_2O_3 to downregulate not the distribution but the density of DCs in the conducting airways of asthmatic mice,and low dose of As_2O_3 has potential value in treating asthma.
文摘A facile and green approach has been developed for the in situ synthesis of hybrid nanomaterials based on dendrite-shaped Pd nanostructures supported on graphene （RG）. The as-synthesized hybrid nanomaterials （RG-PdnDs） have been thoroughly characterized by high resolution transmission electron microscopy, X-ray photoelectron spectroscop）~ atomic force microscop）~ Raman spectroscopy and electrochemical techniques. The mechanism of formation of such dendrite- shaped Pd nanostructures on the graphene support has been elucidated using transmission electron microscopy （TEM） measurements. The RG induces the formation of, and plays a decisive role in shaping, the dendrite morphology of Pd nanostructures on its surface. Cyclic voltammetry and chronoamperometry techniques have been employed to evaluate the electrochemical performance of RG-PdnDs towards oxidation of methanol. The electrochemical （EC） activities of RG-PdnDs are compared with graphene-supported spherical-shaped Pd nanostructures, Pd nanodendrites alone and a commercial available Pd/C counterpart. The combined effect of the graphene support and the dendrite morphology of RG-PdnDs triggers the high electrocatalytic activity and results in robust tolerance to CO poisoning.
基金supported by the National Natural Science Foundation of China (51571151, 51701139, 51671143, 51371119 and U1601216)
文摘This paper demonstrates a one-pot approach to produce highly dispersed dendritic palladium-platinum bi- metallic nanoparticles （NPs） with small particle size, tunable composition and high catalytic activity. Herein, the PdPt bi- metallic NPs have been obtained using bayberry tannin （BT） as both the reducing agent and surfactant. Additionally, the PdPt bimetallic NPs with different Pd/Pt atomic ratios can be prepared by just varying the amounts of the Pd and Pt pre- cursors. Most importantly, the as-prepared Pd52Pt4s catalyst exhibits the optimal catalytic activities compared with the other compositional PdPt NPs （Pds2Ptls, Pd69Ph~, and Pd36 Pt64） and commercial Pt/C （20 wt.%） catalyst for the methanol oxidation reaction （MOR）. Meanwhile, Pd52Pt4s also shows better CO tolerance, which can be attributed to the unique dendritic structure and the synergistic effect between Pd and Pt. With evident advantages of the facile preparation and enhanced catalytic performance, it holds great promise as a high-performance catalyst for electrochemical energy con- version.
基金supported by the National Natural Science Foundation of China(21474027,91023008,20874026,20704013)Shanghai Shuguang Project(07SG33)+1 种基金New Century Excellent Talents in University,Ph D Programs Foundation of Ministry of Education of China,Shanghai Leading Academic Discipline Project(B502)the"Eastern Scholar Professorship"support from Shanghai Local Government
文摘The Bergman cyclization has strongly impacted on a number of fields including pharmaceutics, synthetic chemistry, and material science. The diradical intermediates stemmed from enediynes can not only cause DNA cleavage under physiological conditions but also function as monomer or initiator participants in polymer science. The homo-polymerization of enediynes through the Bergman cyclization to fabricate conjugated polymers is a fascinating strategy due to the advantages of facial operation, high efficiency, tailored structure, and catalyst-free operation. Moreover, conjugated polymers generated through the Bergman cyclization show many remarkable properties, such as excellent thermal stability, good solubility, and processability, which enables these polymers to be further manufactured into carbon-rich materials. Recent times have seen extensive efforts devoted to the application of the Bergman cyclization in polymer science and materials chemistry. A variety of synthetic strategies have been developed to fabricate structurally unique materials via the Bergman cyclization, including the fabrication of rod-like polymers with polyester, dendrimers and chiral imide side chains, functionalization of carbon nanomaterials by surface-grafting conjugated polymers, formation of nanoparticles by intramolecular collapse of single polymer chains, and the construction of carbon nanomembranes with different morphologies. Future developments involving the Bergman cyclization in polymer science, probably by altering the reaction mechanism to precisely control the microstructure of polymeric products, are also proposed in this review article.
基金supported by the National Basic Research Program of China(2013CB834703,2013CB834505)the National Natural Science Foundation of China(21173245,21273258,21233011,21472201,21302196)
文摘Dendrimers are well-defined tree-like macromolecules possessing numerous chain ends emanating from a single core, which makes them attractive candidates for mimicking light-harvesting systems and hydrogenases. Photoinduced electron and energy transfers are main processes involved in light-harvesting and photocatalysis. In this review, the general concepts of design strategies and recent developments of photofunctional dendrimers in biomimics of light-harvesting systems and hydrogenases are discussed. The energy transfer and electron transfer processes in light-harvesting dendrimers and the effect of dendritic structures in photochemical hydrogen production are illustrated.
