Enhancement of Kerr nonlinearity with vanishing absorption in a tripod scheme

The giant enhancement of Kerr nonlinearity in a four-level tripod type system is investigated theoretically. By tuning the value of the Rabi frequency of the coherent control field, owing to the double dark resonances, the giant-enhanced Kerr nonlinearity can be achieved within the right transparency window. The in fluence of Doppler broadening is also discussed.

中国黑龙江省嘉荫地区乌云组古果实学研究

白垩纪末至第三纪初（K/T界限，距今约65Ma），恐龙大规模灭绝，爬行类的优势地位被哺乳动物所取代;裸子植物和蕨类急剧衰退，被子植物蓬勃发展，并逐渐成为地表植被的主体，研究这一时期的植物群的结构和特征进而揭示植物演化和环境变迁的规律及其相互关系是当今地球科学、生命科学和环境科学的重要研究内容。黑龙江省嘉荫地区的乌云组产有丰富的植物化石，其地质时代虽未定论，但不超出晚白垩世马斯特里赫特期至早第三纪古新世的范围，处于K/T界限，对其植物群的研究意义重大。乌云植物群以往的研究在古果实学研究方面明显不足、在植物群的性质的认识及乌云组时代的确定等方面存在很大争议。本文重点研究了乌云组的果实和种子化石，增添了新的植物类群，丰富了此植物群的研究内容，对乌云组的时代问题的确定提供了新的证据。 本文研究了乌云组的Nordenskioldia borealis（昆兰树科）、Nyssidium jianyinense sp. nov. （连香树科）、Hypericum zhuii sp. nov. （金丝桃科）、Amersinia obtrullate（广义山茱萸科）、Acer wuyunense sp. nov.（槭树科）等5种果实和种子化石。Nordenskioldia borealis的果无柄、为分果、小果瓣环绕中央柱轮状排列。Nyssidium jianyinense的果序为圆锥果序、蓇葖对生、蓇葖腹缝相对、果皮三层。Hypericum zhuii的种子外形呈长椭圆形、端部具乳突、表面网状、种脊明显、种皮两层、外种皮细胞的垂周壁明显加厚。Amersinia obtrullate果序头状、果镘形、3果室。Acer wuyunense果为翅果、小坚果被明显侧翼、翅强烈下延，包围小坚果。经修订和补充，乌云植物群目前共有维管植物48属60种，其中，蕨类植物4属6种、裸子植物7属7种、被子植物37属48种，被子植物占总种数的80%、占总属数的77%，被子植物占绝对优势。当时的群落类型湿生群落和中生群落类型为主，湿生群落主要有：由Sequoia���Metasequoia���Taxodium、Glyptostrobus等组成的针叶林;以Nyssidium、Trochodendroides占优势的阔叶林。 以Metasequoia���优势的针叶林和以Nyssidium、Trochodendroides等占优势的阔叶林。乌云植物群中热带和亚热带成分占种子植物总属数的54%，而温带成分则占36%，亚热带成分占优势，当时的气候-植被类型为亚热带常绿林或常绿夏绿混交林。Nordenskioldia、Nyssidium、Amersinia、Acer化石的地质分布不早于古新世的地层，这—证据不支持乌云组的地质时代划为晚白垩世，而支持划归古新世的观点。

濒危物种保护、生境破碎化及其恢复

保护区是否真的能起保护作用？保护区究竟如何布局？这是自然保护区的建设一直争论不休的课题。就大熊猫保护而言，目前面临的最紧迫问题可能不是保护区数量多少的问题，而是这些多个保护区组成的保护区群的配置或格局是否合理。因此，本研究以岷山大熊猫保护区群为研究对象，分析现有大熊猫及栖息地及其保护现状，指出目前保护区存在的问题，并对岷山大熊猫自然保护区群合理布局提出建议性设计，以期为大熊猫保护及自然保护区建设的理论提供借鉴。 到目前，为了保护大熊猫，在岷山地区已经建立了1 7个自然保护区，这些保护区的建立对大熊猫的保护起到了非常重要的重要。但是，大熊猫栖息地仍然持续下降。就其原因有两方面，即岷山地区人为活动的干扰，如旅游业的盲目发展。但，同时大熊猫自然保护区本身的布局存在一定的不合理性。最后，从景观尺度上提出岷山大熊猫保护区群合理建设的布局，即在分析现有保护布局基础上，找到优先保护的敏感地带建立廊道，将所有保护区连成布局合理的保护区群。 大熊猫受威胁的关键因子并不是竹子，而是森林．竹子复合系统的破碎化或质量的退化，故保护大熊猫应从保护森林、恢复森林．竹子复合生态系统的质量入手。但是，具体实践中究竞采取什么模式来恢复退化的大熊猫栖息地？选取不同模式的科学依据是什么？如何评判不同恢复模式的成本和效益？这些方面的工作到目前缺少系统研究。本研究在分析了岷山地区自然、社会与经济条件的基础上，从荒山荒地造林、天然林保护与低效林地改造主要植被恢复措施着手，全面分析各类植被恢复措施所形成植被的生态效益（保持水土、涵养水源、保持肥力等）、经济收益（木材、果品和林副特产品）、社会效益（种植结构、劳动力再分配等），总结出植被恢复成本和效益的构成要素，计算主要植被恢复模式的成本和效益，为选择适宜的植被恢复措施、典型植被恢复模式和合理确定植被恢复技术提供科学依据，从而推动岷山植被快速健康地恢复，为大熊猫提供适宜的生存空间。 三峡大坝的建设使其固有水域的人为改造导致水位上升，使原本连续的山地生态系统被分割成大小不等的岛屿。水位变化导致的这种生境岛屿化为栖息地破碎化和岛屿生物地理学提供了十分难得的实证研究的机会。然而，同时，这种栖息地的片段化无疑对三峡库区生物多样性保护和生态系统的完整性造成威胁。到目前，为了监测库区建设对生态环境的影响，已经建立了22个定位观测站，但没有一个是生境破碎化方面的，为此建议尽快建立生境破碎化方面的定位研究站。三峡库区生物多样性丰富，但保护区面积仅仅占库区面积的6.9%，而同期我国已经建立了1 999个自然保护区，占国土面积的15%，因此，非常迫切建立更多的保护区（至少达到全国平均水平）。为了从宏观尺度上加强对库区的综合保护，建议从景观生态学的角度出发，将库区作为一个自然、社会和经济复合生态系绕对待。

Interspecies implantation and mitochondria fate of panda-rabbit cloned embryos

Somatic cell nuclei of giant pandas can dedifferentiate in enucleated rabbit ooplasm, and the reconstructed eggs can develop to blastocysts. In order to observe whether these interspecies cloned embryos can implant in the uterus of an animal other than th

Phylogeny and biogeography of the Petaurista philippensis complex (Rodentia : Sciuridae), inter- and intraspecific relationships inferred from molecular and morphometric analysis

With modified DNA extraction and Purification protocols, the complete cytochrome b gene sequences (1140 bp) were determined from degraded museum specimens. Molecular analysis and morphological examination of cranial characteristics of the giant flying squirrels of Petaurista philippensis complex (P. grandis, P. hainana, and P. yunanensis) and other Petaurista species yielded new insights into long-standing controversies in the Petaurista systematics. Patterns of genetic variations and morphological differences observed in this study indicate that P. hainana, P. albiventer, and P. yunanensis can be recognized as distinct species, and P. grandis and P. petaurista are conspecific populations. Phylogenetic relationships reconstructed by using parsimony, likelihood, and Bayesian methods reveal that, with P. leucogenys as the basal branch, all Petaurista groups formed two distinct clades. Petaurista philippensis, P. hainana, P. yunanensis, and P. albiventer are clustered in the same clade, while P. grandis shows a close relationship to P. petaurista. Deduced divergence times based on Bayesian analysis and the transversional substitution at the third codon suggest that the retreating of glaciers and upheavals or movements of tectonic plates in the Pliocene-Pleistocene were the major factors responsible for the present geographical distributions of Petaurista groups. (c) 2005 Elsevier Inc. All rights reserved.

Rapid and parallel chromosomal number reductions in muntjac deer inferred from mitochondrial DNA phylogeny

Muntjac deer (Muntiacinae, Cervidae) are of great interest in evolutionary studies because of their dramatic chromosome variations and recent discoveries of several new species. In this paper, we analyze the evolution of karyotypes of muntjac deer in the context of a phylogeny which is based on 1,844-bp mitochondrial DNA sequences of seven generally recognized species in the muntjac subfamily. The phylogenetic results support the hypothesis that karyotypic evolution in muntjac deer has proceeded via reduction in diploid number. However, the reduction in number is not always linear, i.e., not strictly following the order: 46-->14/13-->8/9-->6/7. For example, Muntiacus muntjak (2n = 6/7) shares a common ancestor with Muntiacus feae (2n = 13/14), which indicates that its karyotype was derived in parallel with M. feae's from an ancestral karyotype of 2n greater than or equal to 13/14. The newly discovered giant muntjac (Muntiacus vuquangensis) may represent another pa;allel reduction lineage from the ancestral 2n = 46 karyotype. Our phylogenetic results indicate that the giant muntjac is relatively closer to Muntiacus reevesi than to other muntjacs and may be placed in the genus Muntiacus. Analyses of sequence divergence reveal that the rate of change in chromosome number in muntjac deer is one of the fastest in vertebrates. Within the muntjac subfamily, the fastest evolutionary rate is found in the Fea's lineage, in which two species with different karyotypes diverged in around 0.5 Myr.

中国巨松鼠Ratufa bicolor(Sciuridae:Ratufinae)头骨形态的地理学变异

巨松鼠(Ratufa bicolor)是东洋界的特有类群.中国仅有一种,分布于海南、广西西南部、云南南部、西南部、西部和西北部,关于其亚种的分化结论过去主要依据其皮毛的颜色特征.本研究共测取75个巨松鼠头骨,每号头骨标本测取23个变量,运用统计分析软件SPSS 11.0对巨松鼠的可测量变量进行主成分分析、判别分析及聚类分析,以探讨巨松鼠各亚种地位的有效性及其头骨形态的地理学变异.研究结果显示阿萨姆亚种R.b.gigantea和海南亚种R.b.hainana均为有效亚种,前者分布自广西西南部向西经云南南部、西南部、西部达西北部,后者分布于海南.同时,本研究结果不支持滇南亚种R.b.stigmosa作为一个有效的亚种.

常用鱼药漂白粉和氯杀宁对背角无齿蚌的毒性影响

试验以洱海流域的背角无齿蚌为研究对象,确定常用鱼药:漂白粉、氯杀宁对湖泊大型底柄动物背角无齿蚌的毒性影响.试验得出漂白粉作用下,背角无齿蚌24 h、48 h、72 h、96 h、120 h、144 h、168 h的半致死率;氯杀宁作用下,背角无齿蚌24 h、48 h、72 h、96 h的半致死率;漂白粉有效氯安全浓度95.25～108.86 mg/L;氯杀宁有效氯安全浓度3.32～3.55 mg/L.通过显微镜观察,漂白粉和氯杀宁的主要作用部位为背角无齿蚌的呼吸系统,在其鳃上可见明显病变.

罗氏沼虾卵子在授精时的变化(英文)

<正> The freshwater giant prawn, Macrobrachium rosenbergii is of great economic importance in many coun-tries. It's farmed production is recorded globally. We examine the fertilization cytology in the hope that theymay serve to augment the previous reports

Extraordinarily thick-boned fish linked to the aridification of the Qaidam Basin (northern Tibetan Plateau)

Scattered with numerous salt lakes and approximate to 2,700-3,200 m above sea level, the giant Qaidam inland basin on the northern Tibetan Plateau has experienced continuing aridification since the beginning of the Late Cenozoic as a result of the India-Asia plate collision and associated uplift of the Tibetan Plateau. Previous evidence of aridification comes mainly from evaporite deposits and salinity-tolerant invertebrate fossils. Vertebrate fossils were rare until recent discoveries of abundant fish. Here, we report an unusual cyprinid fish, Hsianwenia wui, gen. et sp. nov., from Pliocene lake deposits of the Qaidam Basin, characterized by an extraordinarily thick skeleton that occupied almost the entire body. Such enormous skeletal thickening, apparently leaving little room for muscles, is unknown among extant fish. However, an almost identical condition occurs in the much smaller cyprinodontid Aphanius crassicaudus (Cyprinodonyiformes), collected from evaporites exposed along the northern margins of the Mediterranean Sea during the Messinian desiccation period. H. wui and A. crassicaudus both occur in similar deposits rich in carbonates (CaCO3) and sulfates (CaSO4), indicating that both were adapted to the extreme conditions resulting from the ariclification in the two areas. The overall skeletal thickening was most likely formed through deposition of the oversaturated calcium and was apparently a normal feature of the biology and growth of these fish.

Uniaxial Strain Effects on Optical Properties of c-plane Wurtzite GaN

We investigate the uniaxial strain effect in the c-plane on optical properties of wurtzite GaN based on k center dot p theory, the spin-orbit interactions are also taken into account. The energy dispersions show that the uniaxial strain in the c-plane gives an anisotropic energy splitting in the k(x) - k(y) plane, which can reduce the density of states. The uniaxial strain also results in giant in-plane optical polarization anisotropy, hence causes the threshold carrier density reduced. We clarify the relations between the uniaxial strain and the optical polarization properties. As a result, it is suggested that the compressive uniaxial strain perpendicular to the laser cavity direction in the c-plane is one of the preferable approaches for the effcient improvement of GaN-based laser performance.

Strain Effects on the Optical Polarization Properties of R-Plane Wurtzite GaN

Using the effective-mass Hamiltonian for an arbitrary direction wurtzite semiconductor on the basis of k.p theory, we investigate the strain effects on the transition energies and optical properties in the R-plane ([1012]-oriented plane) GaN. The results show that (1) the transition energies decrease with the biaxial strains changing from -0.5 to 0.5%; and (2) giant optical anisotropy appears in the R-plane which is significantly affected by the biaxial strains. We clarify the relation between the strains and the polarization properties. Finally, we discuss the application of these properties to the R-plane GaN based devices. (c) 2009 The Japan Society of Applied Physics

Ballistic electron transport in hybrid ferromagnet/two-dimensional electron gas sandwich nanostructure: Spin polarization and magnetoresistance effect

We have theoretically investigated ballistic electron transport through a combination of magnetic-electric barrier based on a vertical ferromagnet/two-dimensional electron gas/ferromagnet sandwich structure, which can be experimentally realized by depositing asymmetric metallic magnetic stripes both on top and bottom of modulation-doped semiconductor heterostructures. Our numerical results have confirmed the existence of finite spin polarization even though only antisymmetric stray field B-z is considered. By switching the relative magnetization of ferromagnetic layers, the device in discussion shows evident magnetoconductance. In particular, both spin polarization and magnetoconductance can be efficiently enhanced by proper electrostatic barrier up to the optimal value relying on the specific magnetic-electric modulation. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3041477]

Interlayer segregation in magnetic multilayers and its influence on exchange coupling

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. X-ray photoelectron spectroscopy shows that Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. While studying Ta/X(X=Bi,Pb,Ag,In)/NiFe/FeMn multilayers, we also find that X atoms segregate to the NiFe/FeMn interface, which results in a decrease of the H-ex. However, a small amount of Bi, Pb, etc. deposited between Cu and pinned NiFe layer for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers can increase H-ex. (C) 2003 American Institute of Physics.

Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (H-ex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta. (C) 2002 American Institute of Physics.