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五阶全对称幻方
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作者 郑格于 《嘉应大学学报》 1996年第6期7-12,共6页
本文解决五阶全对称幻方的一切解及所具有的性质。
关键词 全对称幻方 广义全对称幻方 幻方理论 矩阵 广义对称线 组性组合
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Studies on Genetic Polymorphism of Different Biotypeswith RAPD Analysis1
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作者 吴玉萍 贾方钧 吴清江 《Developmental and Reproductive Biology》 1999年第2期25-31,共7页
In the present paper, RAPD was used to study the genetic polymorphism of fisheswith different genome combinations. Our results indicated that four of the 26 random primersproduced distinct and reproducible electrophor... In the present paper, RAPD was used to study the genetic polymorphism of fisheswith different genome combinations. Our results indicated that four of the 26 random primersproduced distinct and reproducible electrophoretic patterns which were genome-specific andcould distinguish different biotypes. This enabled us to derive a diagnostic profile, from whichwe constructed a molecular marker key for different biotypes. By the analysis of the data ofRAPD patterns, the genetic relationship was constructed with UPGMA (unweighted pair-groupmethod with arithmetical averages). Our experiments also concluded that RAPD was moresuccessful in variety identification than protein polymorphism analysis and serohematology for itstechnological simplicity and sensitivity. 展开更多
关键词 genome addition RAPD genetic polymorphism
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EVALUATION OF INTERNATIONAL CLASSIFICATION CRITERIA (2002) FOR PRIMARY SJGREN'S SYNDROME IN CHINESE PATIENTS 被引量:4
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作者 Yan Zhao Jian Kang +4 位作者 Wen-jie Zheng Wei Zhou Xiao-ping Guo Yan Gao Yi Dong 《Chinese Medical Sciences Journal》 CAS CSCD 2005年第3期190-193,共4页
Objective To evaluate the sensitivity and specificity of international classification criteria (2002) for primary Sjogren's syndrome (pSS) and the role of lower lip biopsy in diagnosis of pSS in Chinese patients.... Objective To evaluate the sensitivity and specificity of international classification criteria (2002) for primary Sjogren's syndrome (pSS) and the role of lower lip biopsy in diagnosis of pSS in Chinese patients. Mothoda Patients who were diagnosed by the experts/rheumatologists as pSS during 1990-2002 from the Department of Rheumatology, Peking Union Medical College Hospital were retrospectively collected as experimental group. Patients who were diagnosed as non-pSS connective tissue diseases or non-connective tissue diseases served as control group. Those with a history of head-neck radiation, hepatitis C virus infection, AIDS, lymphoma, sarcoidosis, graft versus host disease (GVHD), and anti-acetylcholine drug use were exempted. Both groups were required to complete questionnaires about symptoms such as dry eyes and dry mouth, and complete the objective tests of keratoconjunctivitis and xerostomia including Schirmer test, corneal staining, unstimulated salivary flow, sialography, lower lip biopsy, and antinuclear antibodies (including anti-SSA/SSB antibodies) test. Results A total of 330 pSS patients were included in experimental group and 185 non-pSS patients in control group. The mean age of both groups matched (47.8 ± 10.9 years vs. 46.2±13.6 years, P 〉 0.05). The sensitivities of the criteria in pSS patients with lower lip biopsy and in pSS patients without lower lip biopsy were 89.2% and 87.2%, respectively; the overall sensitivity was 88.5%. The specificity was 97.3%. A total of 11.3% pSS patients with negative anti-SSA/SSB antibodies were diagnosed as pSS by lower lip biopsy. Coadwion The international classification criteria (2002) for pSS is feasible in Chinese patients. It has high sensitivity and specificity, and may serve as diagnosis criteria in routine clinical practice. 展开更多
关键词 primary Sjogren's syndrome CRITERIA CLASSIFICATION
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Effects of calcium addition on as-cast microstructure and mechanical properties of Mg-5Zn-5Sn alloy 被引量:9
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作者 杨明波 程亮 潘复生 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2010年第5期769-775,共7页
The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction,%) alloy were investigated.The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to t... The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction,%) alloy were investigated.The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to the Mg-5Zn-5Sn alloy not only refines the as-cast microstructure of the alloy but also causes the formation of the primary and/or eutectic CaMgSn phases with high thermal stability;an increase in Ca amount from 0.5% to 1.5% (mass fraction) increases the amount and size of the CaMgSn phase.In addition,Ca addition to the Mg-5Zn-5Sn alloy improves not only the tensile properties at room temperature and 150 ℃ but also the creep properties.Among the Ca-containing Mg-5Zn-5Sn alloys,the one added 0.5% (mass fraction) Ca obtains the optimum ultimate tensile strength and elongation at room temperature and 150 ℃,however,the alloy added 1.5% (mass fraction) Ca exhibits the optimum yield strength and creep properties. 展开更多
关键词 magnesium alloy Mg-5Zn-5Sn alloy microstructure and properties Ca addition
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Movement-assisted service composition optimization in dynamic networks
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作者 赵耀培 Yang Yang Mi Zhenqiang 《High Technology Letters》 EI CAS 2013年第2期176-181,共6页
The mobility of service providers brings new features into the research of dynamic network based service composition.From an optimistic perspective,the mobility of services could benefit the optimization of service co... The mobility of service providers brings new features into the research of dynamic network based service composition.From an optimistic perspective,the mobility of services could benefit the optimization of service composition,if properly handled.Therefore,the impacts of node mobility on the dynamic network based service composition are investigated.Then,a movement-assisted optimization method,namely MASCO,is proposed to improve the performance of the composited services by minimizing the length of data stream and the hop-counts of the service routes in the underlying networks.The correctness and efficiency of the proposed method are then verified through theoretical analysis and computer simulations. 展开更多
关键词 service composition dynamic networks motion control service optimization re-versed current
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Effect of Al and Sc on deformation behavior of FeCoNi multi-element alloys
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作者 Rui ZHOU Mou LI +4 位作者 Jing-wen QIU Si-hui OUYANG Di PAN Cheng-shang ZHOU Yong LIU 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2019年第10期2109-2116,共8页
The effects of Al and Sc on mechanical properties of FeCoNi multi-element alloys(MEAs) were investigated by compressive tests. The microstructures of FeCoNi MEAs with different contents of Al and Sc were characterized... The effects of Al and Sc on mechanical properties of FeCoNi multi-element alloys(MEAs) were investigated by compressive tests. The microstructures of FeCoNi MEAs with different contents of Al and Sc were characterized and the strengthening mechanisms were discussed. The results show that FeCoNi MEA with a low content of Al has a face-centered cubic(FCC) structure. The yield strength increases linearly with the increase of Al content, which is largely caused by solid solution hardening. Further addition of Sc can promote the formation of a new phase in(FeCoNi)1-xAlx MEAs. A minor addition of Sc can significantly increase the yield strengths of(FeCoNi)1-xAlx MEAs with a low Al content and improve the compressive plasticity of(FeCoNi)1-xAlx MEAs with a high Al content. 展开更多
关键词 FeCoNi multi-element alloys mechanical properties MICROSTRUCTURE strengthening mechanism
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An Introduction to China Electricity Council
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《Electricity》 2004年第1期3-5,共3页
China Electricity Council is a trade federation of enterprises and institutions of Chinese power industry and a non-profit social-economic organization. The paper briefs its nature, main responsibilities and organizat... China Electricity Council is a trade federation of enterprises and institutions of Chinese power industry and a non-profit social-economic organization. The paper briefs its nature, main responsibilities and organization framework of service network. 展开更多
关键词 power industry ENTERPRISE organization framework
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Inheritance of Main Morphological Traits and Chemical Parameters' Analysis of Oriental Tobacco
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作者 Vesselina Masheva Maria Kasheva 《Journal of Agricultural Science and Technology(A)》 2016年第6期417-422,共6页
This study was conducted to evaluate four different parental oriental varieties with their F1 crosses to estimate inheritance of some morphological traits, such as plant hight, number of leaves, total dry weigh and ch... This study was conducted to evaluate four different parental oriental varieties with their F1 crosses to estimate inheritance of some morphological traits, such as plant hight, number of leaves, total dry weigh and chemical compounds, especially nicotine and sugars during sun-curing period. The oriental varieties Kozarsko 541, Plovdiv 50 and Krumovgrad 17 from Bulgaria and Basma Xanthi 101 from Greece and their respective crosses with Basma Xanthi 101 were studied. The study was set up in 2014 and 2015 in experimental field of the Tobacco and Tobacco Products Institute, Plovdiv, using randomized block design with four replications. Common agricultural practices were applied during the growing season. The result indicated that in hybrid combination with parental varieties Kozarsko 541 and Plovdiv 50, except total dry weight, additive gene effects are important for traits height of plant and number of leaves. Height of plant and number of leaves are inherited partially dominant to parent with higher value and total dry weight inheritance was over dominant. In hybrid combination Krumovgrad 17 x Basma Xanthi 101, inheritance of the plant height and leaves number were over dominant type. Total dry weight is inherited partially dominant. In a word, prevailing mode for inheritance of plant hight and total dry weight was the over dominance and for number of leaves it was partial dominance. In sun-curing with yellowing stage, nicotine decreased and sugars increased in all tested varieties with a highest percentage in variety Kozarsko 541 (nicotine) and Krumovgrad 17 (sugars). 展开更多
关键词 Oriental tobacco inhedtanee character morphological traits chemical parameters.
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Development of an Efficient Plant Regeneration System for Pelargonium×Citrosum Vanleenii
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作者 LIAO Fang-lei DAI Ya-juan WANG Pan-pan SONG Qing LU Hong-fei 《Agricultural Science & Technology》 CAS 2011年第5期678-682,780,共6页
[Objective]As a mosquito-repelling ornamental plant,Pelargonium×Citrosum Vanleenii(P.× Citrosum Vanleenii)is hard to be acquired because of its hybrid background,the paper was to a new regeneration system of... [Objective]As a mosquito-repelling ornamental plant,Pelargonium×Citrosum Vanleenii(P.× Citrosum Vanleenii)is hard to be acquired because of its hybrid background,the paper was to a new regeneration system of(P.× Citrosum Vanleenii).[Method] By studying the influence of plant growth regulators(PGRs)on explant type(leaves and petioles),the optimal combinations of PGRs to maximize SELSs(somatic embryo-like structure)and buds were established.[Result]0.2 mg/L NAA+1.0 mg/L BA was best for LS(leaves segments)and 0.2 mg/L NAA + 1.5 mg/L BAs was best for PS(petioles segments).Cultured plantlets were successfully acclimatized in soil where they grew normally without any morphological variation.Although both LS and PS were usable,the leaf was a better explant for induction of embryogenic calli,somatic embryo-like structures and buds.[Conclusion]This work offered a rapid and efficient system for plant regeneration of P.×Citrosum Vanleenii. 展开更多
关键词 Pelargonium×Citrosum Vanleenii Regeneration system Embryo-like embryogenesis Somatic embryo-like structures NAA BA
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Effect of Different Hormone Combinations on Somatic Embryogenesis in Cotton Cultivar Xinluzao 33(Gossypium hirsutum L.)
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作者 Panpan MA Zongming XIE +2 位作者 Quansheng LI Yousheng TIAN Youzhong LI 《Agricultural Science & Technology》 CAS 2015年第10期2174-2178,共5页
[Objective] This study was conducted to evaluate the efficiency of somatic embryogenesis and plant regeneration for an upland cotton cultivar Xinluzao33 under the induction of different hormone combinations and thus t... [Objective] This study was conducted to evaluate the efficiency of somatic embryogenesis and plant regeneration for an upland cotton cultivar Xinluzao33 under the induction of different hormone combinations and thus to determine the optimal hormone combination. [Method] Calli of Xinluzao33(Gossypium hirsutum L.) were induced from seedling hypocotyl tissue by a range of DK and BK combinations. Embryogenic calli and embryos were induced on callus-inducing medium(CIM) without any hormones. Callus appearance and quality were compared to determine which medium was the optimal for callus induction. Embryogenesis ratio was calculated to determine which medium was the best for somatic embryogenesis and plant regeneration. [Result] Callus induction rate was 100% in all the 12 hormone combinations.The calli were yellow or kelly, and their texture was loose or soft under low concentrations of DK combinations, green or white, variably compact under high concentrations of DK combinations. The calli induced by BK combinations were kelly or green, covering creamy white substance. The best medium for callus induction was DK6(0.05 mg/L 2, 4-D and 0.10 mg/L KT). Embryogenic calli were successfully induced from all the combinations. The efficiency of embryogenic callus induction,embryogenesis, and plantlet regeneration were significantly different among the 12 combinations. The result showed that the embryogenesis ratio was the highest in BK3 combination(0.50 mg/L IBA and 0.50 mg/L KT), 72.86% of embryogenic calli differentiated into somatic embryos after being cultured on CIM for 80 d, and80.93% of the somatic embryos finally regenerated into plants on SEM(somatic embryo induction medium). [Conclusion] These results indicate that hormone combination BK3(0.50 mg/LIBA and 0.50 mg/L KT) was the best medium for somatic embryogenesis and plant regeneration from Xinluzao33. 展开更多
关键词 embryogenesis somatic Gossypium regeneration callus Cotton induction cotton upland cultivar
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The sexual dimorphism displayed by the roots of mulberry(Morus alba)saplings depends on the sex of the neighboring plants 被引量:2
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作者 Chunyan Zhang Juan Zhu +3 位作者 Gang Liu Youyou Huang Gaiqun Huang Xiao Xu 《Journal of Plant Ecology》 SCIE CSCD 2021年第6期1037-1046,共10页
Aims Dioecious plants present sexual dimorphism,but how the root traits and nutrient uptake of female and male plants in dioecious species response to the sexual identity change of the neighbor plants are poorly under... Aims Dioecious plants present sexual dimorphism,but how the root traits and nutrient uptake of female and male plants in dioecious species response to the sexual identity change of the neighbor plants are poorly understood.Methods Mulberry(Morus alba L.),a dioecious plant widely distributed in China,was employed in our study.Male and female plants were grown with neighbors of the same and opposite sex for 3 months.At harvest,the root anatomy,root morphology,nutrient concentrations and biomass accumulation were measured.Important Findings When grown with the opposite sex,the males showed decreases in root xylem size,biomass of root and stem and increases in root N,P and K concentrations compared with grown with the same sex.By contrast,females showed significant increases in xylem size,fine root system(e.g.fine root length,root surface area and root volume),root carbon isotope composition(δ13C)and root N,P and K concentrations.The changes in theδ13C and N,P and K concentrations in male and female plants were associated with the changes of root traits.These results demonstrated that the sexual identity of the neighboring plants affected root anatomy and morphology of female and male mulberry plants.Meanwhile,the responses of female and male plants to the sex change of the neighboring plants showed sexual dimorphism,which influenced water-use efficiency and resource acquisition.These findings are important for understanding the population dynamics of other dioecious species in forestry and natural systems. 展开更多
关键词 dioecious plant intersexual combination intrasexual combination Morus alba NUTRITION root traits
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BDS triple-frequency carrier-phase linear combination models and their characteristics 被引量:18
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作者 ZHANG XiaoHong HE XiYang 《Science China Earth Sciences》 SCIE EI CAS CSCD 2015年第6期896-905,共10页
An investigation has been made on the models and characteristics of triple-frequency carrier-phase linear combinations for the Bei Dou Navigation Satellite System(BDS). Based on the three frequencies of the BDS, three... An investigation has been made on the models and characteristics of triple-frequency carrier-phase linear combinations for the Bei Dou Navigation Satellite System(BDS). Based on the three frequencies of the BDS, three categories of combinations are developed: ionosphere-free combinations(i.e., those that eliminate the ionospheric effect), minimum-noise combinations(those that mitigate the effects of thermal noise and multiple paths), and troposphere-free combinations(those that mitigate tropospheric effects). Both the ionosphere-free and troposphere-free combinations can be expressed as planes, whereas the minimum-noise combinations can be expressed as a line. The relationships between these three categories of linear combinations are investigated from the perspective of geometry. The angle between the troposphere-free plane and ionosphere-free plane is small, while the angles between the troposphere-free plane and the minimum-noise line, and between the ionosphere-free plane and the minimum-noise line, are large. Specifically, the troposphere-free plane is orthogonal to the minimum-noise line. By introducing the concepts of lane number and integer ionosphere number, the characteristics of the long-wavelength integer combinations and ionosphere-free integer combinations are investigated. The analysis indicates that the longest wavelength that can be formed for integer combinations is 146.53 m, and the ionosphere-free integer combinations all have large noise amplification factors. The ionosphere-free integer combination with minimum noise amplification factor is(0, 62, 59). According to the lane number, integer ionosphere number, and noise amplification factor, optimal integer combinations with different characteristics are presented. For general short baselines and long baselines, three independent integer combinations are suggested. 展开更多
关键词 BeiDou Navigation Satellite System triple-frequency linear combination long wavelength ionosphere-free minimum noise
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Spherical Scattered Data Quasi-interpolation by Gaussian Radial Basis Function 被引量:2
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作者 Zhixiang CHEN Feilong CAO 《Chinese Annals of Mathematics,Series B》 SCIE CSCD 2015年第3期401-412,共12页
Since the spherical Gaussian radial function is strictly positive definite, the authors use the linear combinations of translations of the Gaussian kernel to interpolate the scattered data on spheres in this article. ... Since the spherical Gaussian radial function is strictly positive definite, the authors use the linear combinations of translations of the Gaussian kernel to interpolate the scattered data on spheres in this article. Seeing that target functions axe usually outside the native spaces, and that one has to solve a large scaled system of linear equations to obtain combinatorial coefficients of interpolant functions, the authors first probe into some problems about interpolation with Gaussian radial functions. Then they construct quasi- interpolation operators by Gaussian radial function, and get the degrees of approximation. Moreover, they show the error relations between quasi-interpolation and interpolation when they have the same basis functions. Finally, the authors discuss the construction and approximation of the quasi-interpolant with a local support function. 展开更多
关键词 Scattered data APPROXIMATION Spherical Gaussian radial basis function Modulus of continuity
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The essential rate of approximation for radial function manifold 被引量:1
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作者 LIN ShaoBo CAO FeiLong XU ZongBeni 《Science China Mathematics》 SCIE 2011年第9期1985-1994,共10页
In this paper, we investigate the radial function manifolds generated by a linear combination of radial functions. Let Wp^r(B^d) be the usual Sobolev class of functions on the unit ball 54. We study the deviation fr... In this paper, we investigate the radial function manifolds generated by a linear combination of radial functions. Let Wp^r(B^d) be the usual Sobolev class of functions on the unit ball 54. We study the deviation from the radial function manifolds to WP^r(b^d). Our results show that the upper and lower bounds of approximation by a linear combination of radial functions are asymptotically identical. We also find that the radial function manifolds and ridge function manifolds generated by a linear combination of ridge functions possess the same rate of approximation. 展开更多
关键词 radial function rate of approximation Sobolev class ridge function
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Graded microstructures of Al-Li-Mg-Zn-Cu entropic alloys under supergravity 被引量:4
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作者 Ruixuan Li Zhe Wang +4 位作者 Zhancheng Guo Peter K. Liaw Tao Zhang Lugee Li Yong Zhang 《Science China Materials》 SCIE EI CSCD 2019年第5期736-744,共9页
Investigating the microstructures and properties of gradient materials has been regarded as a promising way to accelerate the identification of optimal compositions for applications. Herein, a supergravity method is a... Investigating the microstructures and properties of gradient materials has been regarded as a promising way to accelerate the identification of optimal compositions for applications. Herein, a supergravity method is applied to prepare the graded entropic alloys Al-Zn-Li-Mg-Cu. Through carefully optimizing the experimental conditions, the graded microstructures and hardness values appear after the supergravity technique. The morphology of the alloy significantly changes from the bulk intermetallics to eutectic structures along the supergravity force direction, which results from the crushed and graded aluminum oxide combined with the extremelystrong force. The results show that with this supergravity method, a performance-enhanced alloy can potentially be achieved through the centrifugation in a short time span and thus it paves the way for designing and synthesizing entropic alloys with intriguing properties. 展开更多
关键词 entropic alloys SUPERGRAVITY graded microstructures grain refinement viscosity
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Positive combinations of projections in von Neumann algebras and purely infinite simple C*-algebras 被引量:1
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作者 KAFTAL Victor NG PingWong ZHANG Shuang 《Science China Mathematics》 SCIE 2011年第11期2383-2393,共11页
We give an overview of the question: which positive elements in an operator algebra can be written as a linear combination of projections with positive coefficients. A special case of independent interest is the ques... We give an overview of the question: which positive elements in an operator algebra can be written as a linear combination of projections with positive coefficients. A special case of independent interest is the question of which positive elements can be written as a sum of finitely many projections. We focus on von Neumann Mgebras, on purely infinite simple C^*-algebras, and on their associated multiplier algebras. 展开更多
关键词 C^*-algebras linear combinations positive combinations projections
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Finite particle method for kinematically indeterminate bar assemblies 被引量:14
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作者 Ying YU Yao-zhi LUO 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2009年第5期669-676,共8页
This study presents a structural analysis algorithm called the finite particle method (FPM) for kinematically indeterminate bar assemblies. Different from the traditional analysis method, FPM is based on the combina... This study presents a structural analysis algorithm called the finite particle method (FPM) for kinematically indeterminate bar assemblies. Different from the traditional analysis method, FPM is based on the combination of the vector mechanics and numerical calculations. It models the analyzed domain composed of finite particles. Newton's second law is adopted to describe the motions of all particles. A convected material flame and explicit time integration for the solution procedure is also adopted in this method. By using the FPM, there is no need to solve any nonlinear equations, to calculate the stiffness matrix or equilibrium matrix, which is very helpful in the analysis of kinematically indeterminate structures. The basic formulations for the space bar are derived, following its solution procedures for bar assemblies. Three numerical examples are analyzed using the FPM. Results obtained from both the straight pretension cable and the suspension cable assembly show that the FPM can produce a more accurate analysis result. The motion simulation of the four-bar space assembly demonstrates the capability of this method in the analysis ofkinematically indeterminate structures. 展开更多
关键词 Finite particle method (FPM) Vector mechanics Convected material frame Explicit time integrations Kinematicallyindeterminate bar assemblies
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DYNAMIC PORTFOLIO CHOICE UNDER THE TIME-VARYING,JUMPS,AND KNIGHT UNCERTAINTY OF ASSET RETURN PROCESS 被引量:4
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作者 Chaolin HE Weidong MENG 《Journal of Systems Science & Complexity》 SCIE EI CSCD 2012年第5期896-908,共13页
By introducing a stochastic element to the double-jump diffusion framework to measure the Knight uncertainty of asset return process, this paper builds the model of dynamic portfolio choice, which maximizes the expect... By introducing a stochastic element to the double-jump diffusion framework to measure the Knight uncertainty of asset return process, this paper builds the model of dynamic portfolio choice, which maximizes the expected utility of terminal portfolio wealth. Through specifying the state function of uncertainty-aversion, it utilizes the max-min method to derive the analytical solution of the model to study the effect of the time-varying, jumps, and Knight uncertainty of asset return process on dynamic portfolio choice and their interactions. Results of comparative analysis show: The time-varying results in positive or negative intertemporal hedging demand of portfolio, which depends on the coefficient of investor's risk aversion and the correlation coefficient between return shift and volatility shift; the jumps in asset return overall reduce investor's demand for the risky asset, which can be enhanced or weakened by the jumps in volatility; due to the existing of the Knight uncertainty, the investor avoids taking large position on risky asset, and the resulting is the improving of portfolio's steady and immunity. At last, an empirical study is done based on the samples of Shanghai Exchange Composite Index monthly return data from January 1997 to December 2009, which not only tests the theoretical analysis but also demonstrates that the proposed method in the paper is useful from the aspect of portfotio's equivalent utility. 展开更多
关键词 Conditional characteristic function dynamic portfolio JUMPS Knight uncertainty spec-tral generalized method of moments time-varying.
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Balancing selection and recombination drive genetic variation at MHC class I genes in the giant panda
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作者 于方鉴 朱英 +2 位作者 熊铁一 万秋红 张和民 《Science Bulletin》 SCIE EI CAS CSCD 2015年第1期136-138,共3页
Major histocompatibility complex (MHC) is a family of highly polymorphic genes activating adaptive immunity in vertebrates. However, the underlying mecha- nism of MHC evolution is still not fully understood. In this... Major histocompatibility complex (MHC) is a family of highly polymorphic genes activating adaptive immunity in vertebrates. However, the underlying mecha- nism of MHC evolution is still not fully understood. In this study, we investigated genetic variation of three classical MHC class I genes in the giant panda (Ailuropoda mela- noleuca) and tested for selection effect and recombination event across exonic and intronic sequences to understand maintenance mechanism of polymorphism at Aime-MHC class I genes. In total, we isolated 21 MHC class I haplotypes (exon 2-intron 2-exon 3) from 46 captive giant pandas, of which eight were for Aime-C, seven for Aime-I and six for Aime-L; however, we only identified six unique sequences from these haplotypes. The subsequent maximum-likeli- hood and Chi-square analyses both detected evidence of recombination acting on the 21 haplotypes. These results indicate that the giant panda still retains a relatively high adaptive variation at Aime-MHC-I genes, and that the intronic segments have been homogenized along evolu- tionary time by recombination and subsequent genetic drift.We calculated nucleotide substitution rates of the antigen- binding regions (exons 2 and 3) and the noncoding intron 2, and found two pieces of evidence supporting the presence of balancing selection in the giant panda: an excess of nonsynonymous over synonymous substitutions at the antigen-binding sites, and an obviously higher synonymous substitutions in the exons than nucleotide substitutions in the intron. Thus, this study reveals that balancing selection and recombination together shape the diversity pattern at Aime- MHC-I loci of the giant panda. 展开更多
关键词 dN/ds Intron homogenization Recombination MHC Giant panda
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