高寒矮嵩草草甸不同退化演替阶段植物地上部氮磷元素比较

本研究旨在比较高寒草甸草地不同退化演替阶段下植物地上部氮磷元素含量、吸收速率以及单位面积累计重量.结果表明:植物生长季内(5～9月),3个样地植物地上部N、P含量都是在生长初期最高,随植物生长季节的推移以及地上生物量的增加,其含量逐渐稀释直到生长季节结束,全氮含量范围为36.90～14.90 g/kg,全磷的含量范围是2.22～1.06 g/kg.不同退化演替阶段由于植物组成的不同,其N、P含量有明显的差异,P的含量中度退化样地最高(1.91%),重度退化样地最低(1.51%);N的含量则恰恰相反,重度退化样地最高(26.40%),中度退化样地最低(18.60%);原生植被样地介于两者之间,其生长季P的平均含量为1.63%,N的平均含量为20.80%.植物N、P的吸收速率和单位面积累计重量都是随退化程度的加剧而降低,即原生植被样地>中度退化样地>重度退化样地,并且植物营养元素吸收速率与地上生物量生长速率呈正相关关系.

祁连山北坡河谷农业区苜蓿引种试验

在祁连山北坡肃南裕固族自治县河谷农业区进行引种试验，结果表明：筛选出的9个参试苜蓿Medicngo sativa品种均可在当地安全越冬，播种后第2年即可每年收获2茬，鲜草总产量为59.8～81.5 t／hm~2。因此，这9个苜蓿品种具有较好的生产性能，适合在该地区推广种植。

小麦品种群体的细胞学研究

对9个小麦品种群体进行了细胞学观察。结果表明, 4. 53% 的细胞含有至少一对不配对的染色体, 2. 31% 的细胞里, 染色体偏离正常的数目。显然, 这种自然的不规则性可能导致非整倍体后代的产生。3. 57% 的细胞发生了易位, 群体的2. 22% 为单体植株。

春小麦植株高度与灰翅麦茎蜂危害率的关系

试验表明,春小麦植株高度与灰翅麦茎蜂危害率呈极显著正相关,回归方程为Y = - 11.2462 +0.2966 X , r = 0.7821。植株高度100 cm 以上,断茎率普遍在22 %以上,70 cm 以下,断茎率仅有2.65 %～4.07 %。

Characterizing evapotranspiration over a meadow ecosystem on the Qinghai-Tibetan Plateau

To characterize evapotranspiration (ET) over grasslands on the Qinghai-Tibetan Plateau, we examined ET and its relevant environmental variables in a Kobresia meadow from 2002 to 2004 using the eddy covariance method. The annual precipitation changed greatly, with 554, 706, and 666 mm a(-1) for the three consecutive calendar years. The annual ET varied correspondingly to the annual precipitation with 341, 407, and 426 mm a(-1). The annual ET was, however, constant at about 60% of the annual precipitation. About 85% annual ET occurred during the growing season from May to September, and the averaged ET for this period was 1.90, 2.23, and 2.22 mm/d, respectively for the three consecutive years. The averaged ET was, however, very low (< 0.40 mm/d) during the nongrowing season from October to April. The annual canopy conductance (gc) and the Priestley-Taylor coefficient (a) showed the lowest values in the year with the lowest precipitation. This study first demonstrates that the alpine meadow ecosystem is characterized by a low ratio of annual ET to precipitation and that the interannual variation of ET is determined by annual precipitation.

CIMS——工业腾飞的翅膀

工业腾飞的翅膀中科院沈阳自动化所研究员中国ＣＩＭＳ　专家组成员薛劲松人类社会经历了农业时代、工业时代的历史过变，而今已进入以计算机、多媒体技术为标志的电子时代，逐步迈进信息社会。ＣＩＭＳ则是信息时代新工业革命的核心。时至今日，国家“８６３”高技术发展..。

中新世以来中国北方风尘堆积的粘土矿物组成及其古环境意义

In northern China, the loess-soil sequence of the last 2.6 Ma, the Hipparion Red-Earth of eolian origin and recently reported Pliocene-Miocene loess-soil sequence provide a near continuous continental eolian record of climatic history for the past 22.0 Ma. This work aims to investigate the composition and structure of clay minerals contained in deposits, and to explore their implications for environmental evolutions over the last 22.0 Ma. Clay minerals, which were extracted from eolian samples collected at Xifeng (0-6.2 MaBP) and Qinan (6.2-22.0 MaBP) sections, were analyzed qualitatively and semi-quantitatively by using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TG) and chemical analysis. The main conclusions are as follows: Over the last 22.0 Ma, the clay mineral assemblage among Quaternary loess-soils, Hipparion Red-Earth, and Miocene loess-soils shows similar components, mainly consisting of illite (55-80%), kaolinite (7-20%), chlorite (4-13%), smectite (2-23%) as results calculated by comparing major peak areas. There are no obvious differences in both types and amounts of clay minerals between loess and interbedded soils, suggesting that overwhelming part of the clay minerals is derived from the source. According to the components of clay minerals, the whole sequence of eolian deposits in the Loess Plateau can be divided into ten clay mineral assemblage zones over the last 22.0 Ma, whose corresponding ages are: 22.0-21.0 MaBP, 21.0-18.0 MaBP, 18-16.2 MaBP, 16.2-13.0 MaBP, 13.0-10.0 MaBP, 10.0-5.5 MaBP, 5.5-4.4 MaBP, 4.4-2.8 MaBP, 2.8-1.0 MaBP, 1.0-0 MaBP, respectively. This may imply that dust supply changed at least nine times over the past 22.0 Ma. The loess illite has a better crystaliinity, higher value of the FWHM and IC, than the interbedd soils. Previous studies indicated that irregular mixed layer minerals could form under relatively warm and humid conditions (Han, 1982). According to the general distribution of clay minerals of zonal soil (Chamley, 1989), the clay mineral assemblage of eolian deposits in Xifeng and Qinan sections is typical of temperature-humid and warm-subarid environment. Therefore, our results indicate climatic environment in Loess Plateau did not change remarkably since 22.0 Ma, and fluctuated between temperature-humid and warm-subarid climate. 4. The illite generally presents poorer crystaliinity during the period of 22.0 to 2.8 MaBP than in the last 2.8 Ma BP, especially at the intervals of 3.5-4.5 Ma BP, 14.0-17.0 MaBP and 20.0-22.0 Ma BP, which indicates that the weathering intensity was stronger in Neogene than in Quaternary. 5. The relatively low ice volume and high global temperature may be responsible for the strange weathering intensity during the interval of the 3.5-4.5 Ma BP, 14.0-17.0 Ma BP and 20.0-22.0 Ma BP.

High-performance 2 mm gate width GaNHEMTs on 6H-SiC with output power of 22.4 W @ 8 GHz

Optimized AlGaN/AlN/GaN high electron mobility transistors (HEMTs) structures were grown on 2-in semi-insulating (SI) 6H-SiC substrate by metal-organic chemical vapor deposition (MOCVD). The 2-in. HEMT wafer exhibited a low average sheet resistance of 305.3 Omega/sq with a uniformity of 3.85%. The fabricated large periphery device with a dimension of 0.35 pm x 2 nun demonstrated high performance, with a maximum DC current density of 1360 mA/mm, a transconductance of 460 mS/mm, a breakdown voltage larger than 80 V, a current gain cut-off frequency of 24 GHz and a maximum oscillation frequency of 34 GHz. Under the condition of continuous-wave (CW) at 9 GHz, the device achieved 18.1 W output power with a power density of 9.05 W/mm and power-added-efficiency (PAE) of 36.4%. While the corresponding results of pulse condition at 8 GHz are 22.4 W output power with 11.2 W/mm power density and 45.3% PAE. These are the state-of-the-art power performance ever reported for this physical dimension of GaN HEMTs based on SiC substrate at 8 GHz. (c) 2008 Elsevier Ltd. All rights reserved.