Transition-metal catalyzed cross-coupling is one of the basic strategies for the C-C bond formation.However,it is difficult to achieve satisfactory results when terminal alkynes with electron-withdrawing group such as...Transition-metal catalyzed cross-coupling is one of the basic strategies for the C-C bond formation.However,it is difficult to achieve satisfactory results when terminal alkynes with electron-withdrawing group such as propiolate esters are used.The reason behind this might be the easy polymerization of this type of alkynes in the presence of base.A tetrahydroxydiboron and copper sulfate co-promoted cross-coupling/cyclization of propiolate esters and o-iodobenzoic acid for the facile and efficient construction of phthalides is described.Preliminary mechanism study indicates that tetrahydroxydiboron can inhibit the polymerization of propiolate esters and increase the reaction rate.This method is characterized by high regio-and stereoselectivities,mild reaction conditions,short reaction time,broad substrate scope,and excellent functional group compatibility.展开更多
In this paper,we study the topology of moment-angle manifolds and prove a conjecture of S.Gitler and S.Lopez de Medrano concerned with the behavior of the moment-angle manifold under the surgery’cutting off a vertex...In this paper,we study the topology of moment-angle manifolds and prove a conjecture of S.Gitler and S.Lopez de Medrano concerned with the behavior of the moment-angle manifold under the surgery’cutting off a vertex’on a simple polytope.Let P be a simple polytope of dimension n with m facets and Pv be a poly tope obtained from P by cutting off one vertex v.Let Z=Z(P)and Zv=Z(Pv)be the corresponding moment-angle manifolds.S.Gitler and S.Lopez de Medrano conjectured that:Zv is diffeomorphic to δ[(Z(-D^n+m)×D^2]##^m-n/j=1(m-n/j)(S^j+2×S^m+n-j-1),and they proved the conjecture in the case m<3 n.In this paper we prove the conjecture in the general case.展开更多
In this paper, the authors consider the problem of which(generalized) momentangle manifolds admit Ricci positive metrics. For a simple polytope P, the authors can cut off one vertex v of P to get another simple polyto...In this paper, the authors consider the problem of which(generalized) momentangle manifolds admit Ricci positive metrics. For a simple polytope P, the authors can cut off one vertex v of P to get another simple polytope P_v, and prove that if the generalized moment-angle manifold corresponding to P admits a Ricci positive metric, the generalized moment-angle manifold corresponding to P_v also admits a Ricci positive metric. For a special class of polytope called Fano polytopes, the authors prove that the moment-angle manifolds corresponding to Fano polytopes admit Ricci positive metrics. Finally some conjectures on this problem are given.展开更多
The connected sum is a fundamental operation in geometric topology and combinatorics.In this paper,we study the connection between connected sums of simplicial spheres and the algebraic topology of their corresponding...The connected sum is a fundamental operation in geometric topology and combinatorics.In this paper,we study the connection between connected sums of simplicial spheres and the algebraic topology of their corresponding moment-angle manifolds.The cohomology rings of moment-angle manifolds corresponding to connected sums of simplicial spheres are computed,which leads to a conjecture on the topology of such moment-angle manifolds.展开更多
To the Editor:Coronavirus disease 2019(COVID-19),caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),is a serious public health crisis threatening human health and survival worldwide.[1]Reportedly,la...To the Editor:Coronavirus disease 2019(COVID-19),caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),is a serious public health crisis threatening human health and survival worldwide.[1]Reportedly,laboratory characteristics such as C-reactive protein,lactate dehydrogenase,D-dimer,plasma cytokines,blood platelets,and leukocytes are abnormal in patients with SARS-CoV-2 infections.[2,3]To enhance the protective immune response against SARS-CoV-2,vaccines have been rapidly developed and administered to healthy individuals or patients with various diseases in several countries.[4,5]However,some healthy individuals have still become infected with SARS-CoV-2 despite vaccination.Changes in the clinical and laboratory indices of vaccinated patients with COVID-19 remain unknown.In the present study,we report the effects of vaccination in patients with COVID-19.展开更多
This paper deals with homology groups induced by the exterior algebra generated by the simplicial compliment of a simplicial complex K. By using ech homology and Alexander duality, the authors prove that there is a du...This paper deals with homology groups induced by the exterior algebra generated by the simplicial compliment of a simplicial complex K. By using ech homology and Alexander duality, the authors prove that there is a duality between these homology groups and the simplicial homology groups of K.展开更多
文摘Transition-metal catalyzed cross-coupling is one of the basic strategies for the C-C bond formation.However,it is difficult to achieve satisfactory results when terminal alkynes with electron-withdrawing group such as propiolate esters are used.The reason behind this might be the easy polymerization of this type of alkynes in the presence of base.A tetrahydroxydiboron and copper sulfate co-promoted cross-coupling/cyclization of propiolate esters and o-iodobenzoic acid for the facile and efficient construction of phthalides is described.Preliminary mechanism study indicates that tetrahydroxydiboron can inhibit the polymerization of propiolate esters and increase the reaction rate.This method is characterized by high regio-and stereoselectivities,mild reaction conditions,short reaction time,broad substrate scope,and excellent functional group compatibility.
基金supported by National Natural Science Foundation of China(Grant Nos.11571186,11701411,11801580 and 11871284)。
文摘In this paper,we study the topology of moment-angle manifolds and prove a conjecture of S.Gitler and S.Lopez de Medrano concerned with the behavior of the moment-angle manifold under the surgery’cutting off a vertex’on a simple polytope.Let P be a simple polytope of dimension n with m facets and Pv be a poly tope obtained from P by cutting off one vertex v.Let Z=Z(P)and Zv=Z(Pv)be the corresponding moment-angle manifolds.S.Gitler and S.Lopez de Medrano conjectured that:Zv is diffeomorphic to δ[(Z(-D^n+m)×D^2]##^m-n/j=1(m-n/j)(S^j+2×S^m+n-j-1),and they proved the conjecture in the case m<3 n.In this paper we prove the conjecture in the general case.
基金supported by the National Natural Science Foundation of China(Nos.11471167,11571186,11701411,11801580)
文摘In this paper, the authors consider the problem of which(generalized) momentangle manifolds admit Ricci positive metrics. For a simple polytope P, the authors can cut off one vertex v of P to get another simple polytope P_v, and prove that if the generalized moment-angle manifold corresponding to P admits a Ricci positive metric, the generalized moment-angle manifold corresponding to P_v also admits a Ricci positive metric. For a special class of polytope called Fano polytopes, the authors prove that the moment-angle manifolds corresponding to Fano polytopes admit Ricci positive metrics. Finally some conjectures on this problem are given.
基金supported by National Natural Science Foundation of China(Grant Nos.11801580 and 11871284)supported by National Natural Science Foundation of China(Grant Nos.11871284 and 11761072).
文摘The connected sum is a fundamental operation in geometric topology and combinatorics.In this paper,we study the connection between connected sums of simplicial spheres and the algebraic topology of their corresponding moment-angle manifolds.The cohomology rings of moment-angle manifolds corresponding to connected sums of simplicial spheres are computed,which leads to a conjecture on the topology of such moment-angle manifolds.
基金supported by grants from the Emergency Prevention and Control Scientific Research Project of Henan Province(Nos.211100310700 and 211100310900)Major Public Welfare Projects in Henan Province(No.201300310400).
文摘To the Editor:Coronavirus disease 2019(COVID-19),caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),is a serious public health crisis threatening human health and survival worldwide.[1]Reportedly,laboratory characteristics such as C-reactive protein,lactate dehydrogenase,D-dimer,plasma cytokines,blood platelets,and leukocytes are abnormal in patients with SARS-CoV-2 infections.[2,3]To enhance the protective immune response against SARS-CoV-2,vaccines have been rapidly developed and administered to healthy individuals or patients with various diseases in several countries.[4,5]However,some healthy individuals have still become infected with SARS-CoV-2 despite vaccination.Changes in the clinical and laboratory indices of vaccinated patients with COVID-19 remain unknown.In the present study,we report the effects of vaccination in patients with COVID-19.
基金supported by the National Natural Science Foundation of China(Nos.11371093,11261062,11471167)
文摘This paper deals with homology groups induced by the exterior algebra generated by the simplicial compliment of a simplicial complex K. By using ech homology and Alexander duality, the authors prove that there is a duality between these homology groups and the simplicial homology groups of K.
