检索结果-南通市图书馆

Total synthesis of a putative yuzurimine-type Daphniphyllum alkaloid C_(14)–epi-deoxycalyciphylline H

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Chemical Letters 2024年第4期35卷 336-339页

作者： Jingping Hu Jing xu Shenzhen Grubbs Institute and Department of Chemistry and Guangdong Provincial Key Laboratory of Catalysis and Shenzhen Key Laboratory of Small Molecule Drug Discovery and Synthesis Southern University of Science and TechnologyShenzhen 518055China

One of the largest subfamilies within the famous Daphniphyllum alkaloid family is made up of the yuzurimine-type(or macrodaphniphyllamine-type) alkaloids. Their complex aza-polycyclic caged structures, several contiguous stereogenic centers, and vicinal all-carbon quaternary centers make these alkaloids formidable challenge for synthetic chemists. Recently, synthesis of these alkaloids has received extensive attention from our community. Herein, we wish to report the total synthesis of C_(14)–epideoxycalyciphylline H, a putative member of yuzurimine-type alkaloid subfamily. Key transformations employed in our approach include an intramolecular Prins reaction and a Pd-catalyzed enyne cycloisomerization. In addition, synthesis of a daphnezomine L-type alkaloid, paxdaphnidine A, was also studied.

关键词： Total synthesis Daphniphyllum alkaloids Yuzurimine-type alkaloids Prins reaction Enyne cycloisomerization

Hawking–Page transition and the dual relations of anti-de Sitter black holes surrounded by dark energy in general dimensions

在线全文

学校读者我要写书评

暂无评论

Communications in Theoretical Physics 2024年第7期76卷 96-106页

作者： Zhang Xin xu Wei School of Mathematics and Physics China University of Geosciences

Recently, a dual relation T0（n + 1） = THP（n） between the minimum temperature(T0（n + 1）)black hole phase and the Hawking–Page transition(THP（n）) black hole phase in two successive dimensions was introduced by Wei et al（2020 Phys. Rev. D 102 10411）; this was reminiscent of the anti-de Sitter/conformal field theory（AdS/CFT） correspondence, as the Hawking–Page transition temperature could be treated as the temperature of the dual physical quantity on the boundary and the latter corresponds to that in the bulk. In this paper, we discuss the Hawking–Page transition and the dual relations in AdS black holes surrounded by dark energy in general dimensions. Our findings reveal the occurrence of the Hawking–Page transition between the thermal AdS radiation and thermodynamically stable large AdS black holes, in both the spacetime surrounded by phantom dark energy and the spacetime surrounded by quintessence dark energy. We discuss the effects of the phantom dark energy and quintessence dark energy on the Hawking–Page transition temperature. For the dual relation in particular, it works well for the case of an AdS black holes surrounded by phantom dark energy. For the case of an AdS black hole surrounded by quintessence dark energy, the dual relation should be modified under an open assumption that the state parameter and the density parameter of the quintessence dark energy depend on the dimensions of the spacetime.

关键词： black hole thermodynamics dark energy Hawking-Page transition

Crystal facet-dependent CO_(2) cycloaddition to epoxides over ZnO catalysts

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Frontiers of Chemical Science and Engineering 2024年第5期18卷 49-59页

作者： Yongjian Wei Ying Li Yunfei xu Yinghui Sun Tong xu Haiou Liang Jie Bai Inner Mongolia Key Laboratory of Industrial Catalysis Hohhot 010051China College of Chemical Engineering Inner Mongolia University of TechnologyHohhot 010051China

With regard to green chemistry and sustainable development,the fixation of CO_(2) into epoxides to form cyclic carbonates is an attractive and promising pathway for CO_(2) *** oxides,renowned as promising eco-friendly catalysts for industrial production,are often undervalued in terms of their impact on the CO_(2)addition *** this work,we successfully developed ZnO nanoplates with(002)surfaces and ZnO nanorods with(100)surfaces via morphology-oriented regulation to explore the effect of crystal faces on CO_(2) *** quantitative data obtained from electron paramagnetic resonance spectroscopy indicated that the concentration of oxygen vacancies on the ZnO nanoplate surfaces was more than twice that on the ZnO nanorod *** functional theory calculations suggested that the(002)surfaces have lower adsorption energies for CO_(2) and epichlorohydrin than the(100)*** a result,the yield of cyclochloropropene carbonate on the ZnO nanoplates(64.7%)was much greater than that on the ZnO nanorods(42.3%).Further evaluation of the reused catalysts revealed that the decrease in the oxygen vacancy concentration was the primary factor contributing to the decrease in catalytic *** on these findings,a possible catalytic mechanism for CO_(2) cycloaddition with epichlorohydrin was *** work provides a new idea for the controllable preparation of high-performance ZnO catalysts for the synthesis of cyclic carbonates from CO_(2) and epoxides.

关键词： carbon dioxide cycloaddition zinc oxide crystal face oxygen vacancy

Women’s empowerment and food consumption:Evidence from female-headed households in Tanzania

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Integrative Agriculture 2024年第2期23卷 457-467页

作者： Mosses Lufuke xu Tian College of Economics and Management Nanjing Agricultural UniversityNanjing 210095China Department of Economics The University of DodomaDodoma 41218Tanzania College of Economics and Management China Agricultural UniversityBeijing 100083China Academy of Global Food Economics and Policy China Agricultural UniversityBeijing 100083China

Despite the growing recognition of women’s increasing role in the household and corresponding empowerment programs in sub-Saharan Africa,intensive research on the relationship between women’s influence and household food consumption is *** the most recent(2017-2018)national household survey data from Tanzania,this study examined the influence of women’s empowerment on household food ***,we compared the monthly consumption of eight food categories between female-headed households(FHHs)and male-headed households(MHHs)using both descriptive statistics and the propensity score matching(PSM)***,we adopted the two-stage Linear Expenditure System and Almost Ideal Demand System model(LES-AIDS)to estimate income and price elasticities for the two household *** results show that FHHs consume bread and cereals,fish,oils and fats,vegetables,and confectionery(sugar,jam,honey,chocolate,etc.)more than ***,FHHs have a significantly higher income elasticity of demand for all food groups than *** are also more price elastic than MHHs in meat,fish,oils,fats,sugar,jam,honey,chocolate,etc.

关键词： women’s empowerment food consumption income elasticity price elasticity

Evidence-based practices in sustainable travel behavior intervention: A knowledge graph-based systematic review

在线全文

学校读者我要写书评

暂无评论

Journal of Traffic and Transportation Engineering(English Edition) 2024年第2期11卷 293-311页

作者： Jian Li Chenjie xu Key Laboratory of Road and Traffic Engineering of the Ministry of Education College of Transportation EngineeringTongji UniversityShanghai 201804China

Sustainable travel behavior intervention is an essential strategy to promote the development of urban *** interventions offer personalized strategies based on certain scenario and participants to promote its effectiveness over hard travel ***,personalized strategies may also bring about difficulties to identify the actual effect of the ***,based on current practice,to make full use of travel behavior interventions,it is necessary to construct a unified methodological evidencebased framework to assess the reliability and effectiveness of travel behavior intervention *** response to these issues,we applied evidence-based knowledge graph to the field of sustainable travel behavior interventions to help decision supporters design sustainable travel behavior interventions wisely and in turn avoid excessive use of hard travel *** introduced concept of evidence-based practice to conduct a systematic analysis concerning reliability and validity of current full volume empirical studies by dimensions of scenarios,types of interventions and *** addition,we took advantage of high extensivity and integrability of knowledge graph to organize evidence-based related *** of the systematic analysis shows that in terms of reliability of evidence,school intervention is the best scenario,knowledge incentive is the best intervention type and promoting public transit and walking proportion are the best ***,the reliability of interventions in workplace,belonging to reward and threat along with aiming at changing travel patterns generally and lowering travel carbon emission need to be *** the study,various research prospects are raised to promote evidence quality in the field of travel behavior intervention *** a pioneer study,our research contributes to the field of urban transportation in introducing concepts of evidence-based practice and enabling optimization and

关键词： Evidence-based decision-making Evidence assessment Knowledge graph Travel behavior intervention Sustainable travel

Resource Allocation for Channel Estimation in Reconfigurable Intelligent Surface-Aided Multi-Cell Networks

在线全文

学校读者我要写书评

暂无评论

Journal of Communications and Information Networks 2024年第1期9卷 64-79页

作者： Yining xu Sheng Zhou Department of Electronic Engineering Beijing National Research Center for Information Science and TechnologyTsinghua UniversityBeijing 100084China

Reconfigurable intelligent surface(RIS)is a promising solution to deal with the blockage-sensitivity of millimeter wave band and reduce the high energy consumption caused by network densification. However, deploying large scale RISs may not bring expected performance gain due to significant channel estimation overhead and non-negligible reflected *** this paper,we derive the analytical expressions of the coverage probability, area spectrum efficiency(ASE)and energy efficiency (EE)of a downlink RIS-aided multi-cell *** order to optimize the network performance, we investigate the conditions for the optimal number of training symbols of each antenna-to-antenna and antenna-to-element path (referred to as the optimal unit training overhead) in channel *** study shows that:1)RIS deployment is not“the more, the better”, only when blockage objects are dense should one deploy more RISs;2) the coverage probability is maximized when the unit training overhead is designed as large as possible;3)however,the ASE-and-EE-optimal unit training overhead exists. It is a monotonically increasing function of the frame length and a monotonically decreasing function of the average signal-to-noise-ratio (in the high signal-to-noise-ratio region). Additionally,the optimal unit training overhead is smaller when communication nodes deploy particularly few or many antennas.

关键词： reconfigurable intelligent surface multi-cell network directional transmissions channel estimation resource allocation stochastic geometry

The symmetric space,strong isotropy irreducibility and equigeodesic properties

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science China Mathematics 2024年第1期67卷 129-148页

作者： Ming xu Ju Tan School of Mathematical Sciences Capital Normal UniversityBeijing 100048China School of Microelectronics and Data Science Anhui University of TechnologyMa'anshan 243032China

A smooth curve on a homogeneous manifold G/H is called a Riemannian equigeodesic if it is a homogeneous geodesic for any G-invariant Riemannian *** homogeneous manifold G/H is called Riemannian equigeodesic,if for any x∈G/H and any nonzero y∈Tx(G/H),there exists a Riemannian equigeodesic c(t) with c(0)=x and ■(0)=*** two notions can be naturally transferred to the Finsler setting,which provides the definitions for Finsler equigeodesics and Finsler equigeodesic *** prove two classification theorems for Riemannian equigeodesic spaces and Finsler equigeodesic spaces,***,a homogeneous manifold G/H with a connected simply connected quasi compact G and a connected H is Riemannian equigeodesic if and only if it can be decomposed as a product of Euclidean factors and compact strongly isotropy irreducible ***,a homogeneous manifold G/H with a compact semisimple G is Finsler equigeodesic if and only if it can be locally decomposed as a product,in which each factor is Spin(7)/G2,G2/SU (3) or a symmetric space of compact *** results imply that the symmetric space and the strongly isotropy irreducible space of compact type can be interpreted by equigeodesic *** an application,we classify the homogeneous manifold G/H with a compact semisimple G such that all the G-invariant Finsler metrics on G/H are *** suggests a new project in homogeneous Finsler geometry,i.e.,to systematically study the homogeneous manifold G/H on which all the G-invariant Finsler metrics satisfy a certain geometric property.

关键词： equigeodesic equigeodesic space flag manifold orbit type stratification symmetric space strongly isotropy irreducible space

Distributed Stochastic Optimization with Compression for Non-Strongly Convex Objectives

在线全文

学校读者我要写书评

暂无评论

Computer Modeling in Engineering & Sciences 2024年第4期139卷 459-481页

作者： xuanjie Li Yuedong xu School of Information Science and Technology Fudan UniversityShanghaiChina

We are investigating the distributed optimization problem,where a network of nodes works together to minimize a global objective that is a finite sum of their stored local *** nodes exchange optimization parameters through the wireless network,large-scale training models can create communication bottlenecks,resulting in slower training *** address this issue,CHOCO-SGD was proposed,which allows compressing information with arbitrary precision without reducing the convergence rate for strongly convex objective ***,most convex functions are not strongly convex(such as logistic regression or Lasso),which raises the question of whether this algorithm can be applied to non-strongly convex *** this paper,we provide the first theoretical analysis of the convergence rate of CHOCO-SGD on non-strongly convex *** derive a sufficient condition,which limits the fidelity of compression,to guarantee ***,our analysis demonstrates that within the fidelity threshold,this algorithm can significantly reduce transmission burden while maintaining the same convergence rate order as its no-compression *** experiments further validate the theoretical findings by demonstrating that CHOCO-SGD improves communication efficiency and keeps the same convergence rate order *** experiments also show that the algorithm fails to converge with low compression fidelity and in time-varying ***,our study offers valuable insights into the potential applicability of CHOCO-SGD for non-strongly convex ***,we provide practical guidelines for researchers seeking to utilize this algorithm in real-world scenarios.

关键词： Distributed stochastic optimization arbitrary compression fidelity non-strongly convex objective function

The fate of eclogites in the lithosphere

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science China Earth Sciences 2024年第3期67卷 879-884页

作者： Zhensheng WANG Yixian xu State Key Laboratory of Geological Processes and Mineral Resources China University of GeosciencesWuhan 430074China Key Laboratory of Geoscience Big Data and Deep Resource of Zhejiang Province School of Earth SciencesZhejiang UniversityHangzhou 310058China

1. Eclogites and the concept of viscous drainage Eclogites are a distinctive rock type, mainly composed of garnet and omphacite and formed through ultra-high-pressure metamorphism, wherein oceanic or continental crust... 详细信息

关键词： crustal garnet rock

同方期刊数据库