Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

Thermoelectric power and carrier concentration of La2−xSrxCuO4(0.03 <x <0.17) single crystals

Thermoelectric power (S) measurements have been systematically investigated in high-quality La2-x-Srx-CuO4 single crystals with different Sr concentrations (x =0.03, 0.05, 0.07, 0.1, 0.12). In this doping range studied, S remains positive, and with the increase of Sr concentration,room-temperature thermoelectric power S (290 K) decreases.An empirical formula which presents a relationship between hole concentration P and room-temperature thermoelectric power S (290 K) is reported in this note. Based on the theory of metallic diffusion model, the experimental results are discussed.     

非线性4n阶常微分方程的非线性三点边值问题解的存在性

利用“上下解”的方法，讨论了非线性4n阶常微分方程y^(4n)=f(t,y,y′，…，y^(4n-1)满足条件g2i(y^2i)(a),y^(2i 1)(a))=0 i=0,1,…，2n-3 g4n-4(y^4n-4(a),y^(4n-3)(a),y^(4n-2)(a),y^(4n-1)(a))=0 g4n-3(y(b),6′(b),…，y^(4n-6)(b))=0 g4n-2(y^4n-5)(b),y^(4n-4)(b))=0 g4n-1(y^4n-3)(b),y^(4n-2)(b))=0 g2i 1(y^2i 1)(c),y^(2i 2(c))=0 i=0,1,…，2n-4 g4n-5(y^(4n-5(c),y^(4n-4)(c),…,y^(4n-1)c(c))=0 的非线性三点边值问题解的存在性.     

非酸催化合成3,9-二苯基-2,4,8,10-四氧杂螺[5,5]-十一烷

利用苯甲醛与季戊四醇在非酸催化剂的作用下 ,合成了聚缩醛螺胞二醚的先导化合物3,9-二苯基 - 2 ,4,8,1 0 -四氧杂螺 [5 ,5 ]-十一烷 .考察了催化剂、反应物的摩尔比、带水剂、反应温度等对反应的影响 .利用FTIR、TG及HNMR对标题化合物的结构进行了表征 ,产品的最高收率可达 88%以上 .     

济阳坳陷永921地区沙四段可容空间变化速率与储层特征的关系

济阳坳陷永 92 1地区沙四段储层第Ⅳ油层组与第Ⅴ油层组具有相同的沉积微相 ,近似相同的埋深和构造位置 ,但其储层物性差异较大。第Ⅳ油层组储层物性差 ,非均质性强 ,含油性也差 ;第Ⅴ油层组储层连通性好 ,储层物性好 ,含油性也好。通过分析由构造因素所控制的可容空间的变化发现 ,第Ⅴ油层组沉积时期 ,可容空间的生长速率低 ,沉积物可以得到充分的分选 ,砂砾岩得以沉积 ,泥岩及杂基被进一步搬运到盆地中心沉积 ,因而其储层物性很好 ;第Ⅳ油层组沉积时期 ,可容空间的生长速率高 ,单位时间内有足够的空间接受几乎所有搬运来的沉积物的沉积 ,沉积物得不到充分的分选 ,砂砾岩、泥岩及杂基同时沉积 ,因而其储层物性很差。     

H+7团簇离子及其中性团簇产物H4和H5

报道了H7^ 团簇的实验研究结果，从H7^ 的分解能谱发现，可能存在H4和H5等中性团簇产物。分析讨论了H7^ 的形成方式和可能的分解途径。     

CDMA软切换的队列模式

针对移动通信系统的软切换技术，讨论了几种情况相应的算法思想，重点分析了基于方向的软切换模式，为更好地适应第三代、第四代移动通信系统的要求，提出基于方向的双队列模型，并定性地分析了该模型的性能，改善了系统的通信质量。     

MPEG-4视频编码的可分级技术研究

首先分析了MPGE 4视频分级编码的基本思想 ,讨论了如何实现时域和空域上的分级编码算法。在此基础上 ,结合MPEG 4的抗误码技术 ,提出了一种适应IP网络传输的精细粒度分级视频编码方案。     

8-氯-10,11-二氢-4-氮杂-5H-二苯并[a,d]-5-环庚酮的合成

以2-氰基-3-甲基吡啶为原料，通过Ritter反应、烷基化、腈化、水解、环化等五步反应成了氯雷他定的重要中间体8-氯-10，11-二氢杂-5H-二苯并[a,d]-5-环庚酮，总收率为25.6%，其结构经核磁共振、质谱等确证。