Great sand sea and selima sand sheet, eastern sahara: geochronology of desertification

The relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the Great Sand Sea. Active dune formation corresponds with interpluvial periods of hyperaridity; dune stability corresponds with semiarid pluvial periods. Archeological sites associated with truncated paleosols in the Selima Sand Sheet suggest a similar climatic relation and indicate that the isohyets of central Sudan shifted at least 400 kilometers northward during the peak of pluvials.     

Circular feature among dunes of the great sand sea, egypt

A circular crater, about 4 kilometers in diameter and located at 24.2 degrees N, 26.4 degrees E, was discovered in Landsat images among the linear dunes of the Great Sand Sea, Egypt. The crater has a sharp and crenulated rim crest, a terraced wall, a discontinuous inner structure (approximately 1.6 kilometers in diameter), and a few rim blocks. Its morphological and morphometric characteristics are similar to those of meteorite impact craters and other circular structures on the moon and the terrestrial planets. Because of its interaction with windblown sand, it is particularly comparable with craters on Mars.     

大规模筛选表达序列标签(ESTs)方法的改进

介绍一种改进的大规模ESTs筛选的方法。以SMARTTM cDNA Library Construction Kit所构建的毛冠鹿大脑cDNA文库为研究材料,基于该文库噬菌体可自发转化为质粒的特点,直接把噬菌体文库转化为质粒文库。随机选取平板中转化后的质粒cDNA文库克隆,振荡培养后运用菌液电泳的方法代替传统的PCR筛选法,对重组克隆进行筛选。改进的菌液电泳法可以准确鉴定出重组的质粒,并估计出插入片段的大小。该方法能更好地保持SMARTTM cDNA Library Construction Kit所构建文库的完整性,是一种简单、高效、适用于大规模表达序列标签筛选的有效方法。     

科尔沁沙地古榆树资源的收集保存及其繁殖技术的研究

经该研究项目调查 ,在以榆树疏林草地为主要植物群落、总面积约 1175 5 9万hm2 的科尔沁沙地上 ,百年以上的古榆树 (Ulmuspumila)现仅存 30余株 .为了使这些长期经受自然选择、对逆境适应能力特别强的宝贵优良基因资源得以保存 ,该项目正在营建全国规模最大的榆树基因库 ,该基因库的重点是对科尔沁沙地古榆树资源进行收集与保存 ,同时也收集国内分布区内有代表性的能适应该地的榆树种、品种及类型 .至 2 0 0 0年底 ,该基因库已收集种质资源 88份 .预期到 2 0 0 2年该基因库建成时 ,总面积可达 7hm2 ,收集各种种质资源 10 0份 .为长期利用古榆树资源 ,该研究还对收集到的榆树资源进行了扩繁 (扦插、嫁接 )技术试验     

科尔沁沙地古榆树资源的收集保存及其繁殖技术的研究

经该研究项目调查,在以榆树疏林草地为主要植物群落、总面积约1 175.59万hm2的科尔沁沙地上,百年以上的古榆树(Ulmus pumila)现仅存30余株.为了使这些长期经受自然选择、对逆境适应能力特别强的宝贵优良基因资源得以保存,该项目正在营建全国规模最大的榆树基因库,该基因库的重点是对科尔沁沙地古榆树资源进行收集与保存,同时也收集国内分布区内有代表性的能适应该地的榆树种、品种及类型.至2000年底,该基因库已收集种质资源88份.预期到2002年该基因库建成时,总面积可达7!hm2,收集各种种质资源100份.为长期利用古榆树资源,该研究还对收集到的榆树资源进行了扩繁(扦插、嫁接)技术试验.     

项目管理承包模式在工程项目管理中的应用

介绍了近年来国际工程界应用的一种新型的工程建设项目承包模式、项目管理承包模式及其相关背景.从项目管理承包模式适用范围、分类及与其它模式相比具有的优势等方面对其进行了特性分析.结合大型工程项目的特点,提出了应用项目管理承包模式中应着重考虑的问题及实施步骤.     

Kom ombo: preliminary report on the fauna of late paleolithic sites in upper egypt

A Late Pleistocene fauna comprising 3 fish, 1 reptile, 22 birds, and 14 mammals is identified from sites containing Sebilian, Sebekian, Silsilian, Menchian, and Halfan industries. It is remarkable for its variety, especially of birds, and gives evidence for year-round occupation of these sites.     

咪唑离子液体在砂土中的吸附与运移

研究了三种咪唑离子液体([C_2MIM][PF_6],[C_4MIM][PF_6]和[C_4MIM][BF_4])在砂土环境中的静态吸附与动态运移规律,讨论了离子液体阴/阳离子结构变化对其吸附/运移行为的影响。结果表明:三种离子液体的砂土吸附系数(Kd)介于4.3~7.7 L·kg~(-1)之间,整体吸附量偏低,暗示其环境迁移能力强。在静态吸附中,随着阳离子碳链长度从C2增加到C4,离子液体的吸附能力得到提升,迁移能力随之下降,相比而言,阴离子(PF_6~-和BF_4~-)的改变对Kd几乎没有影响;然而在动态柱实验中,阴离子变化能影响阻滞系数R值的大小,这得益于离子液体在土柱中经历反复的吸附-脱附过程,从而使阴离子之间的差异得以放大。首次采用CXTFIT软件对离子液体的运移进行数值模拟发现,其观察值和模拟值高度吻合,表明非平衡模型适合定量描述和预测离子液体在环境中的运移规律。     

Genome-wide identification of the CONSTANS-LIKE(COL) family and mechanism of fruit senescence regulation by PpCOL8 in sand pear(Pyrus pyrifolia)

Pyrus pyrifolia Nakai ‘Whangkeumbae’ is a sand pear fruit with excellent nutritional quality and taste. However, the industrial development of pear fruit is significantly limited by its short shelf life. Salicylic acid(SA), a well-known phytohormone, can delay fruit senescence and improve shelf life. However, the mechanism by which SA regulates CONSTANS-LIKE genes(COLs) during fruit senescence and the role of COL genes in mediating fruit senescence in sand pear are poorly understood. In this stu...     

Changes in the west antarctic ice sheet

The portion of the West Antarctic ice sheet that flows into the Ross Sea is thinning in some places and thickening in others. These changes are not caused by any current climatic change, but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability. The near-future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet, and not so much to the threat of a possible greenhouse warming. Thus the near-term future of the ice sheet is already determined. However, too little of the ice sheet has been surveyed to predict its overall future behavior.     

Large-scale variations in the obliquity of Mars

Large-scale variations in the obliquity of the planet Mars are produced by a coupling between the motion of its orbit plane due to the gravitational perturbations of the other planets and the precession of its spin axis which results from the solar torque exerted on the equatorial bulge of the planet. The obliquity oscillates on a time scale of approximately 1.2 x 10(5) years. The amplitude of this oscillation itself varies periodically on a time scale of 1.2 X 10(6) years. The present-day obliquity is approximately 25.1 degrees. The maximum possible variation is from about 14.9 to 35.5 degrees. Signtificant climatic effects must be associated with the phenomenon.     

海滨沙滩单叶蔓荆对沙埋的生理响应特征

海滨沙滩单叶蔓荆(Vitex trifolia L.var.simplicifolia)是优良的抗沙埋地被植物.以烟台海岸沙地单叶蔓荆为材料,通过不同厚度沙埋过程中沙上和沙下叶片抗逆生理指标的测定以揭示其抗沙埋生理调控机制.结果表明,轻度和中度沙埋5d,成株和幼株整株叶片细胞膜透性增大、POD和SOD活力增高、MDA和脯氨酸含量和叶片相对含水量(RWC)增加、可溶性糖含量下降.但同株沙上叶片细胞膜透性、MDA含量、SOD和POD活力和可溶性糖含量均高于沙下,而沙上叶片脯氨酸含量低于沙下叶片.在轻度和中度沙埋lOd,沙上叶片细胞膜透性、MDA和可溶性糖含量、叶片POD活力降低,叶片SOD活力仍有小幅度增高,但脯氨酸含量增加,沙上叶片生长旺盛.研究表明,沙埋下叶片抗氧化酶活力和脯氨酸含量与细胞膜透性和膜脂过氧化成正相关.沙埋使植株上部叶片接近沙表面而经受干旱和地面热辐射胁迫引起细胞膜脂过氧化加剧和细胞膜透性加大.同时沙埋也使沙下叶片遭遇黑暗和缺氧胁迫诱导细胞内膜脂过氧化,但也激活了叶片抗氧化酶保护系统和叶片脯氨酸的积累抑制细胞膜脂过氧化维护细胞膜的稳定.因此在沙埋过程中,叶片快速响应沙埋胁迫激活叶片抗氧化酶系统抑制膜脂过氧化作用维持氧自由基和抗氧化酶系统的动态平衡在单叶蔓荆适应轻度和中度沙埋,维护沙上叶片旺盛生长中起重要作用,也是重度全埋下沙下植株茎顶端能快速延伸弯曲生长最后顶出沙面再生的主要生理保护原因.     

Large-scale copy number polymorphism in the human genome

The extent to which large duplications and deletions contribute to human genetic variation and diversity is unknown. Here, we show that large-scale copy number polymorphisms (CNPs) (about 100 kilobases and greater) contribute substantially to genomic variation between normal humans. Representational oligonucleotide microarray analysis of 20 individuals revealed a total of 221 copy number differences representing 76 unique CNPs. On average, individuals differed by 11 CNPs, and the average length of a CNP interval was 465 kilobases. We observed copy number variation of 70 different genes within CNP intervals, including genes involved in neurological function, regulation of cell growth, regulation of metabolism, and several genes known to be associated with disease.     

帐幕熏蒸技术的研究进展

论述了近些年我国帐幕熏蒸技术方面的研究与应用概况。     

可食性涂膜对冷藏过程中上海蜜梨品质的影响

利用羧甲基壳聚糖涂膜和森帕尔保鲜涂膜处理上海蜜梨,4℃冷藏并定时检测梨品质.结果表明:与直接冷藏处理的对照组相比,涂膜处理降低了上海蜜梨的呼吸速率,减少了储藏过程中上海蜜梨的可溶固形物、可滴定酸、抗坏血酸、硬度和果肉相对电导率的变化.相对于市售的森帕尔涂膜,羧甲基壳聚糖涂膜对上海蜜梨的保鲜效果更好.     

Large-scale,decelerating, relativistic x-ray jets from the microquasar XTE J1550-564

We have detected, at x-ray and radio wavelengths, large-scale moving jets from the microquasar XTE J1550-564. Plasma ejected from near the black hole traveled at relativistic velocities for at least 4 years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high-energy (up to 10 tera-electron volts) particles that were accelerated in the shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium. XTE J1550-564 offers a rare opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of relativistic jets from Galactic x-ray binaries and active galactic nuclei.     

宁夏野生固沙优良耐旱树种杠柳的繁育技术研究

通过对宁夏天然固沙旱生植物——杠柳的选优驯化和硬枝扦插、嫩枝扦插、营养袋扦插等苗木繁育试验,总结成了一套切实可行的苗木繁育技术,应用实践后取得了良好效果.对宁夏利用天然野生树木资源,进行荒山开发、沟坡绿化和水土保持及治沙造林,具有很好的利用价值.     

不同用量保水剂对沿海沙地麻竹生理特征的影响

[目的]探究施用保水剂对麻竹(Dendrocalamus latiflorus)夏季叶片生理特征的影响,为其在沿海防护竹林经营中推广应用提供科学依据.[方法]以2年生麻竹为试验材料,于4月分别沟施30.0、60.0和90.0 kg/ha保水剂,以不施用保水剂为对照(CK),7、8和9月测定麻竹叶片的生理指标和叶绿素荧光参数等指标,并通过主成分分析法和隶属函数法对保水剂施用效果进行综合评价.[结果]随保水剂用量的增加,在同一月份(分别为7、8和9月)测定麻竹叶片的叶绿素、可溶性糖和可溶性蛋白含量均呈先增加后减少的变化趋势,过氧化物酶(POD)和超氧化物歧化酶(SOD)活性呈先升高后降低的变化趋势,电解质渗透率和丙二醛(MDA)含量呈降低趋势.在相同用量保水剂处理下,7、8和9月麻竹叶片的叶绿素和可溶性糖含量呈逐渐增加趋势,POD活性呈逐渐升高趋势,可溶性蛋白含量呈先减少后增加的变化趋势,SOD活性呈先降低后升高的变化趋势,电解质渗透率呈先升高后降低的变化趋势,MDA含量呈先增加后减少的变化趋势.在同一测定月份,麻竹叶片的最大光化学效率(Fv/Fm)、实际光化学效率(ΦPSI)、光化学淬灭(qP)和非光化学淬灭(qN)均随保水剂用量增加呈逐渐升高的变化趋势.相同用量保水剂处理麻竹叶片的Fv/Fm、ΦPSI、qP和qN在7、8和9月均呈先降低后升高的变化趋势.主成分分析和综合评价结果表明,不同用量保水剂对夏季生长麻竹的保水效果排序为60.0 kg/ha>90.0 kg/ha>30.0 kg/ha>CK.[结论]利用隶属函数法可综合评价不同用量保水剂对麻竹的保水效果;沟施60.0 kg/ha保水剂对麻竹的保水效果最佳,可在沿海沙地竹林栽培中推广使用.