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Specialization or Diversification:Which is More Conducive to Foreign Trade Resilience?Evidence from China-Russia Border Regions in Northeast China
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作者 LI Yuxin ZHANG Pingyu +1 位作者 YANG Qifeng CHU Nanchen 《Chinese Geographical Science》 SCIE CSCD 2024年第6期1144-1157,共14页
Under the background of complex international situation,how to build the special geo-economic space of China-Russia bor-der lies in strengthening their foreign trade resilience against external shocks.Based on empiric... Under the background of complex international situation,how to build the special geo-economic space of China-Russia bor-der lies in strengthening their foreign trade resilience against external shocks.Based on empirical evidence from ten prefecture-level China-Russia border regions in Northeast China,this paper analyzed the spatiotemporal evolution of foreign trade resilience under dif-ferent shocks.Furthermore,through the Panel Regression model,the mechanism of the industrial structure on the foreign trade resili-ence in contraction period and expansion period was discussed.The results showed that:1)from 2004 to 2021,foreign trade in China-Russia border regions experienced five phases.The overall foreign trade resilience was higher than expected,showing a rising volatility trend,but there was significant spatial heterogeneity in the ability of cities to cope with shocks.2)Highly specialized clusters were mainly concentrated in Yichun,Heihe and Da Hinggan Ling Prefecture,while Mudanjiang and Yanbian performed better in related and unrelated diversification.3)In different stages of economic system evolution,the response mode,degree and result of border foreign trade resilience to regional industrial structure showed obvious stage characteristics.During the contraction period,related diversifica-tion was more conducive to improving the resistance through risk spillovers.During the expansion period,specialization played a more significant role in improving regional resilience through self-reinforcing effect.These results are beneficial for expanding the resilience theory,ensuring border economic security and optimizing border industrial investment layout. 展开更多
关键词 foreign trade resilience industrial structure specialization Panel Regression model China-Russia border regions North-east China
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Effects of pooling,specialization,and discretionary task completion on queueing performance
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作者 JIANG Houyuan 《运筹学学报(中英文)》 CSCD 北大核心 2024年第3期81-96,共16页
Pooling,unpooling/specialization,and discretionary task completion are typical operational strategies in queueing systems that arise in healthcare,call centers,and online sales.These strategies may have advantages and... Pooling,unpooling/specialization,and discretionary task completion are typical operational strategies in queueing systems that arise in healthcare,call centers,and online sales.These strategies may have advantages and disadvantages in different operational environments.This paper uses the M/M/1 and M/M/2 queues to study the impact of pooling,specialization,and discretionary task completion on the average queue length.Closed-form solutions for the average M/M/2 queue length are derived.Computational examples illustrate how the average queue length changes with the strength of pooling,specialization,and discretionary task completion.Finally,several conjectures are made in the paper. 展开更多
关键词 queuing systems pooling specialization discretionary task completion average queue length
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Rural Development Transformation and Social Governance from the Perspective of Specialization:A Case Study of Ruiling Village in Guangzhou City,China 被引量:3
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作者 LIN Yuancheng YANG Ren LI Simeng 《Chinese Geographical Science》 SCIE CSCD 2023年第5期796-812,共17页
The reorganization of the global production network and the increased mobility of urban-rural elements have accelerated the differentiation of rural spaces,resulting in a trend towards specialization in rural areas.Th... The reorganization of the global production network and the increased mobility of urban-rural elements have accelerated the differentiation of rural spaces,resulting in a trend towards specialization in rural areas.This paper focuses on the concept of specialization,and takes a renowned bonsai specialized village in Guangzhou City,China as a typical case to explore its transformation and development process,action logic and coupling mechanism with the social governance.The results show that:1)the development of rural specialization in Ruiling Village is shaped by several key actors,such as local governments,grassroots organizations,villagers,social organizations,policies,markets and infrastructure.The transfer of these key actors and the reconstruction of actor-networks in different stages have an important influence on the transformation and realization of rural development goals.2)Through subjects-driven,organization management and resource connection,social governance supports the specialization of rural industrial organization,operation,technology and mode.The governance structure shifts from decentralization to networking,refinement and integration.A coupling community of social governance and specialization is created by the social governance system of‘local government-grassroots organizationseconomic cooperatives-villagers’,which links industries,industrial chains and cooperatives.3)Social governance integrates into the value chain extension process of rural specialized development with a central,multi-level organizational structure.It promotes the construction of the whole value chain through organizational planning,resource integration and image shaping,thus realizing the value,branding and organization of the industry,as well as the integration of rural sustainable development and governance mechanism.Social governance has a profound impact on the development of rural specialization in terms of subject,structure and mode,and participates in the construction of the whole value chain of rural areas.This paper provides a new perspective for understanding the coupling effect of social governance in the rural development transformation,and promotes the rural sustainable development and governance. 展开更多
关键词 rural specialization rural development transformation social governance rural differentiation actor-network theory(ANT) Ruiling Village
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The Hesitance of Nurses to Apply for Midwifery Specialization: Explorative Qualitative Study
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作者 Fahima Al Harthy Mudhar Al Adawi +5 位作者 Khalid Al Busaidi Aisha Al Mamari Asma Al Zaabi Zubaida Suliman Al Balushi Shakila Al Habsi Kamila Al-Alawi 《Open Journal of Nursing》 2023年第8期512-527,共16页
Background: Many countries across the world are facing an ongoing shortage of midwife practitioners due to several reasons such as increased workload, working overtime, poor-quality midwifery care, low staff morale, s... Background: Many countries across the world are facing an ongoing shortage of midwife practitioners due to several reasons such as increased workload, working overtime, poor-quality midwifery care, low staff morale, stress and burnout, lack of opportunity for training, lack of management support, financial issues and lack of recognition and compromised autonomy. Purpose: To explore the reasons behind nurses’ hesitance to apply for midwifery specialization. The objectives of this study were to understand the challenges that lie in front of Omani nurses and the motivational factors to apply for a midwifery programme. Method: Exploratory qualitative study was conducted at the largest tertiary hospital in Oman. Purposive sampling was applied for participant recruitment. Face-to-face interviews and focus group discussions were used as data collection methods. The study included general nurses, nurses in charge working in the maternity unit as well as nurses whose applications were accepted for midwifery education. Qualified midwives were excluded. The data collection process yielded twenty-five nurses. The interview protocol highlighted the impact and perception of the midwifery specialization on nurses’ careers. Thematic analysis was employed for data analysis. Results: Three over-arching major themes were identified. These are 1) nurses’ perceptions about the nature of work in maternity wards, the nurses have positive perception toward working in maternity wards and labor room because of working exclusively with female patients and their babies 2) factors influencing the decision to study midwifery specialization, work overload, stress, lack of support from administration were the most common reason behind the nurses not to apply for midwifery specialization and 3) support and recommendations required for midwives, the nurses mentioned that their identity, promotions and support from the administration will encourage them to apply for midwifery specialization. Conclusion: One of the main reasons that hindered nurses from applying to midwifery specialization is the false belief that midwives cannot work outside the delivery suite (DS). The second reason was the stress that midwives encounter at DS, and this was perceived by general nurses who did not work at DS. These challenges could be mitigated by leadership support, midwifery profession identity, as well as financial recognition for the midwives. 展开更多
关键词 Midwifery specialization Hesitancy CHALLENGES
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Intraclonal Resource Sharing and Functional Specialization of Ramets in Response to Resource Heterogeneity in Three Stoloniferous Herbs 被引量:8
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作者 于飞海 董鸣 张称意 《Acta Botanica Sinica》 CSCD 2002年第4期468-473,共6页
Environments with reciprocal patchiness of resources, in which the availability of two resources such as light and soil nutrients are patchily distributed in horizontal space and negatively correlated in each patch, a... Environments with reciprocal patchiness of resources, in which the availability of two resources such as light and soil nutrients are patchily distributed in horizontal space and negatively correlated in each patch, are common in many ecosystems. The strategies by which clonal plants adapt to this type of heterogeneous environment were examined in three stoloniferous herbs,Potentilla reptans L. var. sericophylla Franch., P. anserina L. and Halerpestes ruthenica (Jacq.) Qvcz., commonly inhabiting forest understories, grasslands and low saline meadows, respectively. As pairs of connected ramets were subjected to reciprocal patchiness of light and nutrients, stolon connection between the two ramets significantly enhanced biomass of both ramet growing in low light intensity but high soil nutrient condition (LH ramet) and ramet growing in high light intensity but low soil nutrient condition (HL ramet) as well as whole ramet pairs (consisting of LH ramets and HL ramets). Additionally, stolon connection greatly increased root/shoot ratio of LH ramet while significantly decreased that of HL ramet. The results indicate that a reciprocal transportation of resources between interconnected ramets and a functional specialization of ramets in uptake of abundant resources occurred. By resource sharing and functional specialization, clonal plants can efficiently acquire locally abundant resources and buffer the stress caused by reciprocal patchiness of resources. 展开更多
关键词 Halerpestes ruthenica Potentilla anserina P. reptans var. sericophylla functional specialization light intensity nutrient content reciprocal patchiness of resources resource sharing
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Pattern Specialization Based on Partial Evaluation
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作者 毛宏燕 黄林鹏 李明禄 《Journal of Shanghai Jiaotong university(Science)》 EI 2007年第5期633-638,共6页
Design pattern enables software architecture generality and reusability, but which depresses the high performance. The pattern specialization was built on partial evaluation technology to reduce the overheads of desig... Design pattern enables software architecture generality and reusability, but which depresses the high performance. The pattern specialization was built on partial evaluation technology to reduce the overheads of design pattern. The design patterns were classified to extract the common features, and the corresponding pattern specializations were constructed. In the pattern specialization, the optimization opportunities were identified, and the specialization methods and conditions were described. The syntax of binding time analysis was defined, and the semantic depicted the invariant of usage context. The virtual invocation and dispatch were eliminated, which enhances the running efficiency. This pattern specialization is a high-level specialization for improving the performance of software aimed at design level that is orthogonal with the low-level code optimization. 展开更多
关键词 design pattern pattern specialization partial evaluation specialization declaration binding time analysis
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Demographic variation and habitat specialization of tree species in a diverse tropical forest of Cameroon 被引量:1
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作者 David Kenfack George B Chuyong +2 位作者 Richard Condit Sabrina E Russo Duncan W Thomas 《Forest Ecosystems》 SCIE CAS 2014年第4期201-213,共13页
Background: Many tree species in tropical forests have distributions tracking local ridge-slope-valley topography. Previous work in a 50-ha plot in Korup National Park, Cameroon, demonstrated that 272 species, or 63%... Background: Many tree species in tropical forests have distributions tracking local ridge-slope-valley topography. Previous work in a 50-ha plot in Korup National Park, Cameroon, demonstrated that 272 species, or 63% of those tested, were significantly associated with topography. Methods: We used two censuses of 329,000 trees ≥1 cm dbh to examine demographic variation at this site that would account for those observed habitat preferences. We tested two predictions. First, within a given topographic habitat, species specializing on that habitat ('residents') should outperform species that are specialists of other habitats ('foreigners'). Second, across different topographic habitats, species should perform best in the habitat on which they specialize ('home') compared to other habitats ('away'). Species' performance was estimated using growth and mortality rates. Results: In hierarchical models with species identity as a random effect, we found no evidence of a demographic advantage to resident species. Indeed, growth rates were most often higher for foreign species. Similarly, comparisons of species on their home vs. away habitats revealed no sign of a performance advantage on the home habitat. Conclusions" We reject the hypothesis that species distributions along a ridge-valley catena at Korup are caused by species differences in trees _〉1 cm dbh. Since there must be a demographic cause for habitat specialization, we offer three alternatives. First, the demographic advantage specialists have at home occurs at the reproductive or seedling stage, in sizes smaller than we census in the forest plot. Second, species may have higher performance on their preferred habitat when density is low, but when population builds up, there are negative density-dependent feedbacks that reduce performance. Third, demographic filtering may be produced by extreme environmental conditions that we did not observe during the census interval. 展开更多
关键词 TREE Demographic variation and habitat specialization of tree species in a diverse tropical forest of Cameroon FIGURE
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Changes of Word Meaning in English-Generalization/Specialization and Pejoration/Amelioration 被引量:1
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作者 范存英 庞峰 《海外英语》 2019年第11期254-256,共3页
Changes of word meanings in English are often achieved by the processes of generalization/specialization and pejoration/amelioration.By generalization or specialization,the literal meanings of a word are broadened or ... Changes of word meanings in English are often achieved by the processes of generalization/specialization and pejoration/amelioration.By generalization or specialization,the literal meanings of a word are broadened or narrowed.While by pejoration or amelioration,the associations of a word go downhill or rise.Trough supplying certain examples,a brief picture about meaning changes of words in English is drawn. 展开更多
关键词 word MEANING GENERALIZATION specialization pejoration AMELIORATION
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Disruption of ectoplasmic specializations between Sertoli cells and maturing spermatids by anti-nectin-2 and anti-nectin-3 antibodies
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作者 Yoshiro Toyama Fumie Suzuki-Toyota Mamiko Maekawa Chizuru Ito Kiyotaka Toshimori 《Asian Journal of Andrology》 SCIE CAS CSCD 2008年第4期577-584,共8页
Aim: To understand the biological functions of the ectoplasmic specializations between Sertoli cells and maturing spermatids in seminiferous epithelia. Methods: In order to disrupt the function of the ectoplasmic sp... Aim: To understand the biological functions of the ectoplasmic specializations between Sertoli cells and maturing spermatids in seminiferous epithelia. Methods: In order to disrupt the function of the ectoplasmic specializations, nectin-2, which is expressed at the specialization, was neutralized with anti-nectin-2 antibody micro-injected into the lumen of the mouse seminiferous tubule. Anti-nectin-3 antibody was also micro-injected into the lumen in order to neutralize nectin-3, which is expressed at the specialization. Results: The actin filaments at the specialization disappeared, and exfoliation of maturing spermatids was observed by electron microscopy. Conclusion: Nectin-2 was neutralized by anti-nectin-2 antibody and nectin-3 was neutralized by anti-nectin-3 antibody, respectively. Inactivated nectin-2 and nectin-3 disrupted the nectin-afadin-actin system, and finally the actin filaments disappeared. As a result, the specialization lost the holding function and detachment of spermatids was observed. One of the functions of the specialization seems to be to hold maturing spermatids until spermiation. 展开更多
关键词 ectoplasmic specialization Sertoli cell spermatogenic cell TESTIS ACTIN NECTIN mice
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Catalyst Pellet Shape Specialization for Ethylene Acetoxidation to Vinyl Acetate
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作者 Ju Mengjoe Xu Ke +1 位作者 Wang Shangdi (Department of Chemical Engineering Zhejiang University)(Hangzhou,310027 China) 《高校化学工程学报》 EI CAS CSCD 1994年第S1期72-76,共5页
CatalystPelletShapeSpecializationforEthyleneAcetoxidationtoVinylAcetateJuMengjoe;XuKe;WangShangdi(Department... CatalystPelletShapeSpecializationforEthyleneAcetoxidationtoVinylAcetateJuMengjoe;XuKe;WangShangdi(DepartmentofChemicalEnginee... 展开更多
关键词 PELLET SHAPE specialization ETHYLENE Acetoxidation CATALYST Activity Distribution
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China's Industrial Upgrade in Global Factor Specialization
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作者 金京 戴翔 张二震 《China Economist》 2014年第5期40-55,共16页
China has operated as a proactive destination of technology transfer and diffusion from the Western world since reform and opening-up in 1978.This enabled the country to seize strategic opportunities of global factor ... China has operated as a proactive destination of technology transfer and diffusion from the Western world since reform and opening-up in 1978.This enabled the country to seize strategic opportunities of global factor specialization and helped it achieve great industrial development and upgrade.Nevertheless,the traditional path of integration into the global system of factor specialization has also brought about problems of imbalance and incoordination such as an excessive consumption of natural resources and environmental damage,making it necessary for China's industrial development to increase sustainability.Deepening of global factor specialization,increased cross-border liquidity,and the strategy of "reverse integration" of multinational firms based on developing economies are tendencies highly consistent with the direction of China's industrial development and upgrade and present new strategic opportunities for integration into global factor specialization and industrial transformation.Rather than simply acting passively as a destination of foreign investment,a new round of opening-up is required for China to take a more efficient route in the global system of factor specialization.Therefore,in the area of industrial development,China must keep a down-to-earth attitude,effectively utilize the existing comparative advantages,and follow a gradual and science-based approach.Only by following this course will China be able to take advantage of the new opportunities,foster advanced indigenous and international factors,and increase its capabilities of innovation and global operation on the basis of global resources integration. 展开更多
关键词 factor specialization industrial upgrade comparative advantage
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The Characteristics and Enlightenment of the Specialization and Professionalization of College Counselors since the Founding of the People’s Republic of China
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作者 Shuang Zhou 《Journal of Contemporary Educational Research》 2020年第11期104-109,共6页
Since the 1970s,the Chinese government has promulgated relevant policies and launched a series of corresponding measures,mainly to strengthen the professional building of efficient counselors.With the education reform... Since the 1970s,the Chinese government has promulgated relevant policies and launched a series of corresponding measures,mainly to strengthen the professional building of efficient counselors.With the education reform,the role and mission of college counselors are also changing,from dealing with solely political work at the beginning to being a political guide,conceptual mentor,administrative management leader and imparter of mental health knowledge for young college students and so on.This paper mainly analyzes the characteristics of the professionalization and specialization development of the counselor team since the founding of the People's Republic of China,analyzes the current development difficulties,derives inspiration from the law of historical development,and eliminates the difficulties. 展开更多
关键词 College counselors specialization PROFESSIONALIZATION Team building
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Research on the theories and methods of the specialization of the college counselor's work
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作者 Huang Wenwen 《International English Education Research》 2015年第1期34-36,共3页
The research proposition of this article is to do a brief analysis of the specialized theories and the systems of the methods of the college counselors' work under the perspective of the professional theories of the ... The research proposition of this article is to do a brief analysis of the specialized theories and the systems of the methods of the college counselors' work under the perspective of the professional theories of the college counselors, and discuss the way of the realization of the specialization of the college counseling work, to achieve the professional orientation of the work of the college counselors. With the use of the specialized ways of work, we can make the college counselors develop themselves in the strict professional training and the continuous autonomous learning. They should use their own professional knowledge to equip themselves, to be the teachers and management personnel able to correctly guide the healthy growth of the university students. 展开更多
关键词 College counselors specialization of the work working responsibilities methods theories professional personnel
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Specialization Produces More Cheese Interviewing with Wu Ying, CEO of UTStarcom (China) Co., Ltd.
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《中国电信业》 2006年第S1期50-,共1页
When telecom giants in the world propose strategic transformation, domestic and foreign telecom equipment manufacturers at upper industrial chain are also faced with the dilemma of transformation, because each section... When telecom giants in the world propose strategic transformation, domestic and foreign telecom equipment manufacturers at upper industrial chain are also faced with the dilemma of transformation, because each section on the telecom industrial chain is closely connected with each other. Wu Ying, 展开更多
关键词 CEO of UTStarcom China LTD specialization Produces More Cheese Interviewing with Wu Ying
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Internal Drivers and the Specialization Status of Under-developed Countries: Evidence from China's High-tech Industry 被引量:1
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作者 杨高举 黄先海 Huang Deyuan 《Social Sciences in China》 2014年第2期106-121,共16页
This study incorporates value-added ratio (VAR) and productivity into the analytical framework of intra-product specialization (IPS) as a globally comparable index for international specialization status (ISS), ... This study incorporates value-added ratio (VAR) and productivity into the analytical framework of intra-product specialization (IPS) as a globally comparable index for international specialization status (ISS), to analyze the effect of domestic technological innovation, labor force investment, capital investment and foreign direct investment (FDI) spillovers on the ISS of developing countries. It also tests the effects empirically against the data from Chinese high-tech industries and enterprises. The results show that domestic technological innovation and the improved coordination of material capital and human capital are key internal drivers in the improvement of the ISS of Chinese high-tech industries, whereas FDI spillovers play a relatively limited role therein. Therefore, the key to China's industry upgrading is to tap and nurture the internal motive forces rather than to rely on FDI spillovers. 展开更多
关键词 internal drivers intra-product specialization international specialization status high-tech industries
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Maxillofacial Surgery Education: Where Is It Heading?
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作者 Carlos Aurelio Andreucci 《Health》 2024年第5期405-424,共20页
Oral and maxillofacial surgery have a long history dating back to ancient civilizations such as the Egyptians. Since then, surgeons have treated craniofacial trauma and alveolodental fractures. In 1846, Hullihen perfo... Oral and maxillofacial surgery have a long history dating back to ancient civilizations such as the Egyptians. Since then, surgeons have treated craniofacial trauma and alveolodental fractures. In 1846, Hullihen performed a mandibular body osteotomy to correct prognathism, marking a significant milestone in the field. Over time, the specialty has evolved significantly. The field of craniofacial surgery has undergone several phases, including its involvement in conflicts during world wars and the treatment of craniofacial fractures and discrepancies. The process of learning and teaching specialties has evolved differently in various countries throughout the 20th century. Currently, there is no uniformity in the training and registration of specialized professionals, resulting in distinct scenarios. Considering the accessibility of scientific knowledge through technology and globalization, it is crucial to provide an objective overview of the current state of education in the field. This paper focuses on effective professional training as the primary subject of residency courses in this specialty. A proposal is presented for education, emphasizing the significance of providing quality professional training that is tailored to the specific legislation of each country. 展开更多
关键词 Maxillofacial Surgery Medical Residency OMS Education OMS specialization
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Relationship between the unique microstructures and behaviors of high-entropy alloys 被引量:2
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作者 Yaqi Wu Peter KLiaw +5 位作者 Ruixuan Li Weiran Zhang Guihong Geng Xuehui Yan Guiqun Liu Yong Zhang 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2024年第6期1350-1363,共14页
High-entropy alloys(HEAs),which were introduced as a pioneering concept in 2004,have captured the keen interest of nu-merous researchers.Entropy,in this context,can be perceived as representing disorder and randomness... High-entropy alloys(HEAs),which were introduced as a pioneering concept in 2004,have captured the keen interest of nu-merous researchers.Entropy,in this context,can be perceived as representing disorder and randomness.By contrast,elemental composi-tions within alloy systems occupy specific structural sites in space,a concept referred to as structure.In accordance with Shannon entropy,structure is analogous to information.Generally,the arrangement of atoms within a material,termed its structure,plays a pivotal role in dictating its properties.In addition to expanding the array of options for alloy composites,HEAs afford ample opportunities for diverse structural designs.The profound influence of distinct structural features on the exceptional behaviors of alloys is underscored by numer-ous examples.These features include remarkably high fracture strength with excellent ductility,antiballistic capability,exceptional radi-ation resistance,and corrosion resistance.In this paper,we delve into various unique material structures and properties while elucidating the intricate relationship between structure and performance. 展开更多
关键词 high-entropy alloys unique microstructure special properties alloy design
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CO_2 Emissions Embodied in China's Foreign Trade:An Investigation from the Perspective of Global Vertical Specialization 被引量:25
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作者 Yuhuan Zhao Zhonghua Zhang +1 位作者 Song Wang Shaojun Wang 《China & World Economy》 SCIE 2014年第4期102-120,共19页
In light of the growth in vertically specialized in global trade, the present paper uses input output tables from the World Input-Output Database to construct an environmental multi regional input-output model to calc... In light of the growth in vertically specialized in global trade, the present paper uses input output tables from the World Input-Output Database to construct an environmental multi regional input-output model to calculate the CO2 emissions embodied in China's international trade during 1995-2009. The advantage of this model lies in its incorporation of the re exported CO2 emissions component embodied in trade and its ability to differentiate domestic sourced CO2 emissions from foreign-sourced CO2 emissions in trade. The results show that carbon emissions embodied in both China's exports and imports increased significantly during 1995-2009. One important reason for this is that the re-exported carbon emissions embodied in China's imported intermediate inputs increased substantially during this period. Our research reveals that accelerating the transformation of trade pattern and upgrading processing trade should be emphasized in the formulation of policy to prompt CO 2 emissions abatement in China. 展开更多
关键词 Key words: China CO2 emission global vertical specialization international trade multi- regional input-output analysis
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Integrating ancient patterns and current dynamics of insect-plant interactions" Taxonomic and geographic variation in herbivore specialization 被引量:6
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作者 J. Mark Scriber 《Insect Science》 SCIE CAS CSCD 2010年第6期471-507,共37页
The search for pattern in the ecology and evolutionary biology of insect-plant associations has fascinated biologists for centuries. High levels of tropical (tow-latitude) plant and insect diversity relative to pole... The search for pattern in the ecology and evolutionary biology of insect-plant associations has fascinated biologists for centuries. High levels of tropical (tow-latitude) plant and insect diversity relative to poleward latitudes and the disproportionate abundance of host-specialized insect herbivores have been noted. This review addresses several aspects of local insect specialization, host use abilities (and loss of these abilities with specialization), host-associated evolutionary divergence, and ecological (including "hybrid") speciation, with special reference to the generation of biodiversity and the geographic and taxonomic identification of "species borders" for swallowtail butterflies (Papilionidae). From ancient phytochemically defined angiosperm affiliations that trace back millions of years to recent and very local specialized populations, the Papilionidae (swallowtail butterflies) have provided a model for enhanced tmderstanding of localized ecological patterns and genetically based evolutionary processes. They have served as a useful group for evaluating the feeding specialization/physiological efficiency hypothesis. They have shown how the abiotic (thermal) environment interacts with host nutritional suitability to generate "voltinisrn/suitability" gradients in specialization or preference latitudinally, and geographical mosaics locally. Several studies reviewed here suggest strongly that the oscillation hypothesis for speciation does have considerable merit, but at the same time, some species-level host specializations may lead to evolutionary dead-ends, especially with rapid environmental/habitat changes involving their host plants. Latitudinal gradients in species richness and degree of herbivore feeding specialization have been impacted by recent developments in ecological genetics and evolutionary ecology. Localized insect- plant associations that span the biospectrum from polyphenisms, polymorphisms, biotypes, demes, host races, to cryptic species, remain academically contentious, with simple definitions still debated. However, molecular analyses combined with ecological, ethological and physiological studies, have already begun to unveil some answers for many important ecological/evolutionary questions. 展开更多
关键词 evolutionary dead-ends key innovations latitudinal gradients oscillation hypothesis of speciation polyspecialists preference/performance specialization/physiological efficiency hypothesis voltinism-suitability hypothesis
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Fitness traits and underlying genetic variation related to host plant specialization in the aphid Sitobion avenae 被引量:3
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作者 Su-Xia Gao De-Guang Liu +1 位作者 Hui Chen Xiu-Xiang Meng 《Insect Science》 SCIE CAS CSCD 2014年第3期352-362,共11页
Sitobion avenae (E) is an important cereal pest worldwide that can survive on various plants in the Poaceae, but divergent selection on different host plants shouldpromote the evolution of specialized genotypes or h... Sitobion avenae (E) is an important cereal pest worldwide that can survive on various plants in the Poaceae, but divergent selection on different host plants shouldpromote the evolution of specialized genotypes or host races. In order to evaluate their resource use strategies, clones of S. avenae were collected from oat and barley. Host-transfer experiments for these clones were conducted in the laboratory to compare their fitness traits. Our results demonstrated that barley clones had significantly lower fecundityand tended to have longer developmental times when transferred from barley to oat. However, oat clones developed faster after they were transferred to barley. Clones fromoat and barley had diverged to a certain extent in terms of fecundity and developmental time of the nymphs. The separation of barley clones and oat clones of S. avenae was alsoevident in a principal component analysis. Barley clones tended to have higher broad-sense heritabilities for fitness traits than oat clones, indicating the genetic basis of differentiationbetween them. Barley clones showed significantly higher extent of specialization compared to oat clones from two measures of specialization (i.e., Xsp and Ysp). Therefore, barleyclones were specialized to a certain extent, but oat clones appeared to be generalized. The fitness of S. avenae clones tended to increase with higher extent of specialization. Theevolution toward ecological specialization in S. avenae clones, as well as the underlying genetic basis, was discussed. 展开更多
关键词 BIOTYPE ecological specialization population divergence sympatric speciation wheat aphid
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