In this article, we determine all homogeneous two-spheres in the complex Grassmann manifold G(2, 5; C) by theory of unitary representations of the 3-dimensional special unitary group SU(2).
The pre-modern history of population change in the Fuping County(Shaanxi Province, China)during the Ming and Qing Dynasties(AD 1368-1911) was reconstructed using historical sources.The Fuping County experienced two ma...The pre-modern history of population change in the Fuping County(Shaanxi Province, China)during the Ming and Qing Dynasties(AD 1368-1911) was reconstructed using historical sources.The Fuping County experienced two major population collapses, i.e. the late Ming Dynasty(1550-1640 s) and the 1860-1880 s. The first one was caused by the great AD 1556 earthquake and the extreme droughts and warfare in the 1630-1640 s. The second one was caused by warfare and extreme droughts. As a whole, natural disasters, including extreme drought and great earthquake, were the key direct causes of population collapse, and climatic cooling would be a potential indirect cause. It is very interesting that population collapses occurred almost synchronously in the Fuping County and whole China, and the trends of population change were also very similar. Climate-population relationship in China would be valid at finer geographic level,and climatic cooling could be a potential indirect cause of population collapse.展开更多
In this paper we completely classify the homogeneous two-spheres,especially,the minimal homogeneous ones in the quaternionic projective space HPn.According to our classification,more minimal constant curved two-sphere...In this paper we completely classify the homogeneous two-spheres,especially,the minimal homogeneous ones in the quaternionic projective space HPn.According to our classification,more minimal constant curved two-spheres in HPnare obtained than what Ohnita conjectured in the paper"Homogeneous harmonic maps into complex projective spaces.Tokyo J Math,1990,13:87–116".展开更多
Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Compos...Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials.The results indicate that the skeleton density,total pore area,average pore diameter,and porosity of the materials increase after chemical foaming treatment,showing a more open pore structure.The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly.Consequently,the thermal stability of the materials improves significantly,and the hardness and elastic modulus of the matrix increase by 73.7%and 49.4%,respectively.The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure.The wear rate,in particular,decreases by 47.7%from 2.83×10^(−8) to 1.48×10^(−8)cm^(3)/J as the foaming agent content increases.Most importantly,this study provides an effective method to regulate the pore structure of wet friction materials,which is conducive to achieving the desired tribological properties.展开更多
We study a superminimal surface M immersed into a hyperquadric Q2 in several cases classified by two global defined functions TX and TY,which were introduced by X.X.Jiao and J.Wang to study a minimal immersion f:M→Q2...We study a superminimal surface M immersed into a hyperquadric Q2 in several cases classified by two global defined functions TX and TY,which were introduced by X.X.Jiao and J.Wang to study a minimal immersion f:M→Q2.In case both TX and TY are not identically zero,it is proved that fis superminimal if and only if f is totally real or io f:M→CP3 is also minimal,where i:Q2→CP^3 is the standard inclusion map.In the rest case that TX=0 or TY=0,the minimal immersion f is automatically superminimal.As a consequence,all the superminimal two-spheres in Q2 are completely described.展开更多
We prove that if φ is a homogeneous harmonic map from a Riemann surface M into a complex Grassmann manifold G（k, n）, then the maps of the harmonic sequences generated by φ are all homogeneous.
文摘目的:比较老年轻度认知障碍(mild cognitive impairment,MCI)者与老年认知正常对照(normal control,NC)者的听配能差异,探索其与抑郁、焦虑程度的相关性。方法:纳入老年MCI患者35例,NC组46例,采用言语、空间与听觉质量量表(speech,spatial and qualities of hearing scale,SSQ)评估其听配能各维度,同时对其认知功能与焦虑抑郁情况进行测评。结果:MCI组SSQ量表的言语理解与空间听觉维度分别显著低于NC组。两组言语理解能力均与抑郁程度显著负相关,MCI组的空间听觉能力与焦虑程度显著负相关(均为P<0.05)。结论:老年MCI患者的总体听配能弱于认知正常者,且听配能情况与抑郁焦虑程度相关,提升听配能可能有助于改善老年MCI患者认知功能与情绪状态。
基金supported by the National Natural Science Foundation of China(11401481)
文摘In this article, we determine all homogeneous two-spheres in the complex Grassmann manifold G(2, 5; C) by theory of unitary representations of the 3-dimensional special unitary group SU(2).
基金supported by the National Natural Science Foundation of China[Grant No.41672180]the Ministry of Science and Technology of China[Grant No.2017FY101002]
文摘The pre-modern history of population change in the Fuping County(Shaanxi Province, China)during the Ming and Qing Dynasties(AD 1368-1911) was reconstructed using historical sources.The Fuping County experienced two major population collapses, i.e. the late Ming Dynasty(1550-1640 s) and the 1860-1880 s. The first one was caused by the great AD 1556 earthquake and the extreme droughts and warfare in the 1630-1640 s. The second one was caused by warfare and extreme droughts. As a whole, natural disasters, including extreme drought and great earthquake, were the key direct causes of population collapse, and climatic cooling would be a potential indirect cause. It is very interesting that population collapses occurred almost synchronously in the Fuping County and whole China, and the trends of population change were also very similar. Climate-population relationship in China would be valid at finer geographic level,and climatic cooling could be a potential indirect cause of population collapse.
基金supported by National Natural Science Foundation of China(Grant Nos.11471299,11401481 and 11331002)。
文摘In this paper we completely classify the homogeneous two-spheres,especially,the minimal homogeneous ones in the quaternionic projective space HPn.According to our classification,more minimal constant curved two-spheres in HPnare obtained than what Ohnita conjectured in the paper"Homogeneous harmonic maps into complex projective spaces.Tokyo J Math,1990,13:87–116".
基金This research was supported by the National Natural Science Foundation of China(Nos.51872176 and 52172102)the Shaanxi Key Industry Innovation Chain Project(No.2021ZDLGY14-04)+1 种基金the Science Fund for Distinguished Young Scholars of Shaanxi Province(No.2019JC-32)the Fundamental Research Funds for the Central Universities(No.G2020KY05130).
文摘Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials.The results indicate that the skeleton density,total pore area,average pore diameter,and porosity of the materials increase after chemical foaming treatment,showing a more open pore structure.The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly.Consequently,the thermal stability of the materials improves significantly,and the hardness and elastic modulus of the matrix increase by 73.7%and 49.4%,respectively.The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure.The wear rate,in particular,decreases by 47.7%from 2.83×10^(−8) to 1.48×10^(−8)cm^(3)/J as the foaming agent content increases.Most importantly,this study provides an effective method to regulate the pore structure of wet friction materials,which is conducive to achieving the desired tribological properties.
基金supported by the National Natural Science Foundation of China(Grant No.11301273)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(17KJA110002)+2 种基金the Natural Science Foundationof Jiangsu Province(BK20181381)The second author was supported by the NationalNatural Science Foundation of China(Grant No.11401481)the Research Enhancement Fund and Continuous Support Fund of Xi'an Jiaotong-Liverpool University(REF-18-O1-03,RDF-SP-43).
文摘We study a superminimal surface M immersed into a hyperquadric Q2 in several cases classified by two global defined functions TX and TY,which were introduced by X.X.Jiao and J.Wang to study a minimal immersion f:M→Q2.In case both TX and TY are not identically zero,it is proved that fis superminimal if and only if f is totally real or io f:M→CP3 is also minimal,where i:Q2→CP^3 is the standard inclusion map.In the rest case that TX=0 or TY=0,the minimal immersion f is automatically superminimal.As a consequence,all the superminimal two-spheres in Q2 are completely described.
基金This work was supported in part by the National Natural Science Foundation of China （Grant No. 11401481） and the Research Development Fund of XJTLU （Grant No. RDF13-01-14）.
文摘We prove that if φ is a homogeneous harmonic map from a Riemann surface M into a complex Grassmann manifold G（k, n）, then the maps of the harmonic sequences generated by φ are all homogeneous.
