Effect of the reverse shock wave on the evolution of young supernova remnants

McKee's model of reverse shock wave in young supernova remnants is further discussed and a more general formula for the fraction of swept up mass is derived. It is found that (i) in the supernova material swept by the reverse shock wave, the temperature increases, and the total X-radiation decreases monotonically with time and (ii) the presence of the reverse shock decreases the fractional decay rate of the radio flux of supernova remnants, and satisfactorily accounts for the difference between the observed and Shklovsky's predicted values for Cas A.     

本溪地区太古宙岩石中黑云母击象的发现及其地质意义

作者在辽宁省本溪地区大范围内发现黑云母击象,这在该区尚属首次。黑云母击象以及存在的地质环境表明,在地质演变史上,本溪地区曾存在至少一期影响普遍的快速构造变形—岩浆活动事件,它很可能代表一次古断裂地震活动。     

类星体QSO2000-330的重元素吸收线系统的证认

本文利用文[1]和文[2]所给出的高红移类星体吸收系统的证认方法,对目前最大红移类星体QS02000-330(z_e=3.78)的吸收光谱进行了吸收线红移系统的证认,并得到了六个重元素的吸收线系统:z_a=3.1881,3.1913,3.3335,3.5519以及z_a=1.3441,3.3459。前四个系统和Hunstead等人(1986)所得到的A、B、C、D系统(红移值分别是z_a=3.1881,3.1914,3.3332,3.5519)相符合;后两个是我们新发现的吸收系统。     

Recruitment of postlarval prawns,Penaeus Orientalis,to a tidal estuary of Jiaozhou Bay,China

PostlarvalPenaeus orientalis kishinouye were simultaneously sampled at three fixed stations near the mouth of the Dagu River estuary in northwestern Jiaozhou Bay, China, at hourly intervals over a 49-h period in mid-June, 1984. The purpose of this sampling was to investigate the prawn’s recruitment into estuaries from coastal areas. The abundance of the postlarvae varied considerably between stations and time, but they tended to concentrate at the surface. Maximum entropy spectral analysis was first applied in the study of prawn recruitment and it revealed that variations in abundance involved a pronounced 12.4 hr cycle. It was concluded that natural tidal cycles had a strong influence on the changes of postlarval abundance, in contrast with the minor effects of diet and other environmental cycles. A tidally varying cross-river gradient of postlarval density was found. During flood tides the postlarvae were more abundant in the axis of the channel than over the banks. The opposite held true during ebb tides. Mechanisms of the postlarval recruitment are discussed in terms of alternating movements of the postlarvae between the banks and the channels in response to tidal cycles. Contribution No. 1485 from the Institute of Oceanology, Academia Sinica     

虚拟天文台的技术进展

虚拟天文台是在望远镜和探测器的研制技术、计算机网络技术取得突破性进展的条件下产生的，与最新的信息技术紧密结合成为其发展最鲜明的特点。用可扩展标记语言（简称XML）技术封装天文数据，把虚拟天文台建立在网格的体系结构之上是当今虚拟天文台技术发展的主流。按照目前虚拟天文台具代表性的层次式体系结构分层介绍各个层次的相关技术，同时提出充分利用现有资源优势实施中国虚拟天文台计算的设想。     

The role of ground water in arid/semiarid ecosystems, Northwest China

Ground water plays an important role in water supply and the ecology of arid to semiarid areas such as Northwest China, where the landscape is fragile due to frequent drought in the past few decades. This paper discusses the role of ground water in these ecosystems, including the effect of condensation water and water table depth on the growth of plants and degree of soil salinity. The paper also discusses the controlling process for land desertification and soil salinization in Northwest China. Water table depth is a key factor controlling the water balance, ground water flow, and salt transport in the vadose zone. The suitable water table depth for vegetation growth, which can prevent land desertification and soil salinization, is within a range of 2 to 4 m; the optimal depth is approximately 3 m. As examples, changes in ecosystems owing to water resources development in Tarim and Manas basins, Xinjiang, China, are discussed.     

澜沧江流域农业灌溉需水的时空变化(英文)

Based on the data of eight meteorological stations from the 1950s to 2007, current cropping patterns, field water moisture management, we use the Mann-Kendall and the Re-scaled Range Analysis methods to research the changes of humidity and crop irrigation water requirements in the Lancang River Basin. The results show that the annual and dry season average temperatures significantly increased, and the dry season rainfall increased while wet season rainfall decreased. Evaportranspiration (ET0) increased during both dry and wet seasons at all stations except Dali, Jianchuan and Gengma, and the aridity-humidity index decreased at most of the stations. The turning points of weather factors, ET0, the arid-ity-humidity index, paddy irrigation requirements and total agricultural water requirements occurred from the 1960s to the 1990s. The spatial changing tendency of paddy irrigation quota increased with the increase of altitude and latitude, and the correlation coefficients are 0.513 and 0.610, respectively. The maximum value is observed in Weixi, while the minimum in Mengla.     

Study on characteristics and regeneration rules of Salix gordejevii in Hunshandak Sandland, China

Salix gordejevii, a species of dune-fixing pioneer shrub in the Hunshandak Sandland in China, plays a vital role in maintenance and improvement of the local ecological environment. Salix gordejevii has an r-type reproductive countermeasure, which means it produces large quantities of seeds that have a high germination rate but relatively low seedling viability. Our research on the seed regeneration and sprouting regeneration characteristics of Salix gordejevii shows that its sprouting regeneration process is more productive and efficient than its seed regeneration process. At the same time, growth of Salix gordejevii would decline when the drifting sand dune was fixed. To assess its sprouting regeneration process, we analyzed the number, length, and diameter of new shoots under different cutting treatments, and found significant differences based on various cutting heights and different cutting times (April vs. October). We conclude that cutting measures which take advantage of this species’ robust sprout tillering can increase the biomass of this shrub and also can improve its canopy density and its forage properties for livestock grazing, with the added benefits of improved sand-fixing and prevention of wind erosion.     

Soil CO2 efflux, carbon dynamics, and change in thermal conditions from contrasting clear-cut sites during natural restoration and uncut larch forests in northeastern China

With the implementation of the Chinese Natural Forest Conservation Program (NFCP) in 1998, over millions of hectares of forest in northeastern China have been protected through natural restoration (closure of hills). The impact of this program on the carbon budget of soil has not been evaluated until now. This paper presents results from a 6-year study of total CO₂ efflux from both soil and litter (R _total), CO₂ flux from soil (R _soil), soil organic matter (SOM), soil microbe density, and litter input and root biomass at an uncut larch (Larix gmelinii) forest and at a natural restoration site. The natural restoration area is a clear-cut site that was formerly part of a continuous portion of the uncut larch forest. Our objectives were to: (1) quantify the magnitude of CO₂ efflux from typical sites in northeastern China; (2) explore the changes in thermal conditions, SOM, and annual CO₂ flux during the 6-year natural restoration, and (3) evaluate the impact of NFCP on soil carbon processes. The annual R _soil at the clear-cut site (58.6–68.2 mol m^???2 year^???1) was 113.6–228.4% (mean 141.5%) higher than that at the uncut larch site (29.6–58.4 mol m^???2 year^???1). At the same time, annual CO₂ from litter at the clear-cut site (2.0–14.2 mol m^???2 year^???1) was only 23.5–84.5% (mean 52.5%) of that at the uncut larch site (5.4–16.8 mol m^???2 year^???1). SOM at the surface layer of the clear-cut site was 75% of that at the uncut larch site, but the soil microbial biomass (carbon) at the clear-cut site was much higher than that at the larch site (p?<?0.05). The percentage of bacteria, fungi and actinomycetes also were largely different between both sites. Natural restoration at the clear-cut site strongly affected thermal conditions. Although the soil temperature (T _soil) and effective accumulated $T_{\rm soil} > 0^{\circ}$ C at the clear-cut site was much higher, the temperature sensitivity (Q ₁₀) was much lower than that at the uncut larch site, and their differences decreased linearly from 2001 to 2006 (p?<?0.05). Moreover, Q ₁₀ at the clear-cut site significantly increased with the progress of natural restoration, which diminished the Q ₁₀ difference between the two sites (slope?=???0.2792, r ²?=?0.4744, p?<?0.05). These data imply that the NFCP natural restoration process has positively recovered the thermal condition of the clear-cut site to the level of uncut larch forest during the 6-year period. However, linear regression analysis showed that the 6-year natural restoration only slightly affected the annual soil CO₂ efflux and SOM at both sites, and also did not diminish the differences between the two sites (p?>?0.10), indicating that a much longer time is necessary to restore the soil carbon in the clear-cut site.