青土湖近6000年来沉积气候记录研究--兼论四五世纪气候回暖

对青土湖志云村剖面沉积气候记录和湖泊进退进行了研究,证实季风边缘区河西走廓东段存在暖湿,冷干气候变化的阶段性特征。根据湖相沉积的颜色,粒度,化学组成和有机质含量等气候代用指标的综合分析,提出公元四五世纪存在一次百年尺度上的气候回暖,这一气候回暖事件的发现,可得到历史文献记录和青海湖自然记录的佐证。     

M4–18: the planetary nebula and its WC10 central star

We present a detailed analysis of the planetary nebula M4–18 (G146.7+07.6) and its WC10-type Wolf–Rayet (WR) central star, based on high‐quality optical spectroscopy (WHT/UES, INT/IDS, WIYN/DensPak) and imaging ( HST /WFPC2). From a non-LTE model atmosphere analysis of the stellar spectrum, we derive T _eff=31 kK,     v _∞=160 km s⁻¹ and abundance number ratios of H/He<0.5, C/He=0.60 and O/He=0.10. These parameters are remarkably similar to those of He 2–113 ([WC10]). Assuming an identical stellar mass to that determined by De Marco et al. for He 2–113, we obtain a distance of 6.8 kpc to M4–18 [ E ( B−V )=0.55 mag from nebular and stellar techniques]. This implies that the planetary nebula of M4–18 has a dynamical age of ∼3100 yr, in contrast to ≥270 yr for He 2–113. This is supported by the much higher electron density of the latter. These observations may be reconciled with evolutionary predictions only if [WC]-type stars exhibit a range in stellar masses.
Photoionization modelling of M4–18 is carried out using our stellar WR flux distribution, together with blackbody and Kurucz energy distributions obtained from Zanstra analyses. We conclude that the ionizing energy distribution from the WR model provides the best consistency with the observed nebular properties, although discrepancies remain.     

水分胁迫对冷蒿和差不嘎蒿体内水分状况的影响

在土壤正常水分条件下,冷蒿的ψ_w,ψ_π和ψ_π100远远低于差不嘎蒿,RWD、Va及Va·Vs^-1远远大于差不嘎蒿,维系其生命活动的膨压只占差不嘎蒿的30%。土壤极端干旱时,差不嘎蒿的上述参数发生大幅度变化,抗旱能力随之提高。极旱的午后,二种灌木均遭旱害威胁,其水分状况参数值(ψ_w,ψ_O、Va和RWD)相差很小。旱后复灌的情况下,差不嘎蒿上述参数同样发生大幅度变化,各参数值可恢复到对照水平;冷蒿在干旱和复灌期间参数相对变化较小。多水环境使二种灌木束缚水含量明显提高,从外观生长状况看差不嘎蒿优于冷蒿。     

鄂尔多斯盆地奥陶系碳酸盐岩沥青 A 和沥青 C 的生物标志物特征

摘 要　 研究了鄂尔多斯奥陶系碳酸盐岩中沥青 A 和沥青 C 的生物标志物特征‚表明沥青 A 和沥青 C 之间在生物标志物组成上存在着明显的差异‚产生这些差异的原因主要是氧化还原 环境、成熟度及粘土矿物含量的不同。结合沉积相分析‚探讨了不同沉积环境中沥青 A 与沥 青 C 的分布规律。     

珠江口表层水中主要常量离子的研究

９９４年９月采集了珠江口表层海水水样,并对其溶解态的Ｋ＋、Ｎａ＋、Ｃａ２＋、Ｍｇ２＋、ＳＯ２－４、Ｃｌ等化学要素进行了测定。结果表明,珠江口调查海域表层水中溶解态的Ｋ＋、Ｎａ＋、Ｃａ２＋、Ｍｇ２＋、ＳＯ２－４主要受陆源淡水与外海水物理混合稀释的影响,与Ｃｌ具有良好的直线正相关;Ｃａ２＋／Ｃｌ、ＳＯ２－４／Ｃｌ明显高于大洋水相应比值,Ｎａ＋／Ｃｌ、Ｍｇ２＋／Ｃｌ略高,而Ｋ＋／Ｃｌ比大洋比值低;在与中国其它各主要河口表层水对应Ｃｌ比较中,珠江口的ＳＯ２－４／Ｃｌ较高,而Ｃａ２＋／Ｃｌ,Ｍｇ２＋／Ｃｌ比值居低;上述各主要常量离子和Ｃｌ的等值线均沿自北向南走向递增。     

Influence of Bottom Stress on the Two-layer Flow Induced by Gravity Currents in Estuaries

Baroclinic circulation in highly stratified and partially stratified estuaries is characterised by a two-layer flow: a bottom salt- water inflow and a surface brackish-water outflow. Tidal period variation of the thicknesses of a two-layer flow is observed to be associated with mixing, bottom stress and hydraulic characteristics of superposed tidal and gravity currents. Here, both analytical two-layer hydraulic equations with weak friction and a numerical model including a turbulence closure were utilised to understand the mechanism of the layer tendency within a two-layer flow under different barotropic flow conditions. It has been found that in the weak bottom friction case, a gravity current has two critical solutions at the layer thickness equal to 0·5Hand 0·292H. The layer thickness towards a particular critical solution is dependent on the sign of the bottom stress, i.e. when the bottom stress is opposite (favor) to the bottom gravity current, its layer thickness converges to 0·5H(0·292H). In the case of strong bottom stress and mixing opposing the gravity current, the solutions of the gravity current layer thickness at 0·5Hand 0·292Hwill not be valid. Both mixing and vorticity produced by bottom stress erode the halocline, and produce a high velocity core in the mid-depth, which leads to the thickness of a bottom gravity current greater than 0·5H. These internal hydraulic tendency and mixing processes, varying with time-dependent barotropic tidal current forcing, determine the tidal period variation of the gravity current structure.     

Satellite and ship observations of Kuroshio warm-core ring 93A off Sanriku, northwestern North Pacific, in spring 1997

Synoptic ship and satellite observations were performed of the Kuroshio warm-core ring (KWCR) 93A and its adjacent waters, off Sanriku, northwestern North Pacific, between early April and late June 1997. The temporal and spatial distribution of chlorophylla (Chl-a) and sea surface temperature in the study area were analyzed using data from ADEOS Ocean Color and Temperature Scanner (OCTS) and NOAA Advanced Very High Resolution Radiometer (AVHRR). The objective of this study was to describe the temporal and spatial variability of the spring bloom and understand its relationship with the changes in the hydrographic structure of these waters in and around KWCR 93A. The maximum value of Chl-a concentration in the ring was less than 1 mg/m³ during April. The spring bloom in the ring occurred early in May and the relatively high maximum (>1.0 mg/m³) continued from early in May to mid-June. In late June, a ship-observed surface Chl-a concentration of less than 0.4 mg/m³ suggests that the spring bloom had already declined in and around KWCR 93A. Double spiral structures of warm and cold streamers appeared from late April to mid-May, which may have an influence on the occurrence of the spring bloom in and around the ring. In this episodic event, the warm streamer can maintain the available potential energy of the ring and the strength of upwelling around the ring. The cold streamer provided water with a high Chl-a concentration to the surface layer of the ring. In order to understand the temporal and spatial variability of Chl-a distribution in the ring, the behavior of the warm and cold streamers needs to be taken into consideration.     

中华鳖气单胞菌疖疮病的研究

气单胞菌疖疮病是中华鳖的主要病害之一,其发病对象主要是稚鳖。将病鳖进行细菌分离,获得的菌株经人工感染、毒力测试和细菌学鉴定,确定致病菌为嗜水气单胞菌Ａｅｒｏｍｏｎａｓｈｙｄｒｏｐｈｉｌａ与豚鼠气单胞菌Ａ．ｃａｖｉａｅ。此两种致病菌不仅对健康鳖表现出较强的致病力,出现与自然病鳖相同的症状,且对健康小鼠亦有较强的致死力,半致死量ＬＤ５０分别为４．５×１０６个菌／只和１．５８×１０６个菌／只。此外,测定了病原菌对抗生素的敏感性,为科学防治提供依据。