北极新奥尔松(Ny-lesund)地区环境中有机碳组成来源的初步分析

对2010年8月从北极新奥尔松地区(Ny-lesund)中国黄河站附近所采集的土壤、沉积物和苔藓进行整体指标[OC%,TN%,δ13C(‰)]和木质素(lignin-derived phenols)分析;并对土壤和沉积物进行粒度分析。结果显示OC%与TN%具有相同的来源;但是粒度并不是控制有机物分布的主要因素。数据显示当地木质素主要来自当地的维管植物和苔藓,但是可能会受到当地动物或者微生物的影响。木质素的降解参数(Ad/Al)v值的大小顺序为沉积物土壤苔藓,可能是由于苔藓的表面吸附了细颗粒的煤炭,但是缺少14C数据,无法定量计算煤炭对环境中有机碳的贡献;另外一个降解参数肉桂基酚类两种单体(CAD/FAD)比值由苔藓、土壤、沉积物依次降低,反映出成岩作用增强,木质素降解程度增加。综合OC%、TN%、δ13C(‰)和木质素数据,中国北极黄河站周围环境中的有机碳来源主要为当地的苔藓和维管植物,也有可能吸附了一些煤颗粒,但是由于技术手段的限制,煤炭的贡献在当前的数据解析下无法定量评估。     

Extinction curves expected in young galaxies

We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). We adopt Nozawa et al. (2003) for compositions and size distribution of grains formed in SNe II and PISNe. We find that the extinction curve is quite sensitive to internal metal mixing in supernovae (SNe). The extinction curves predicted from the mixed SNe are dominated by SiO₂ and are characterized by a steep rise from infrared to ultraviolet (UV). The dust from unmixed SNe shows a shallower extinction curve, because of the contribution from large-sized (∼0.1 μm) Si grains. However, the progenitor mass is important in unmixed SNe II: if the progenitor mass is smaller than  ∼20 M_⊙  , the extinction curve is flat in UV; otherwise, the extinction curve rises towards the short wavelength. The extinction curve observed in a high-redshift quasar  ( z = 6.2)  favours the dust production by unmixed SNe II. We also provide some useful observational quantities, so that our model might be compared with future high- z extinction curves.     

对OH/IR星演化的模型研究

渐近巨星分支恒星 (AGB星 )是一种晚期演化恒星 ,它是恒星作为以核反应释能为发光能源的天体的最后演化阶段。AGB星阶段的恒星具有许多有趣的性质 ,如很大的质量损失率 (因此形成很厚的拱星尘埃气体包层 ) ,光变 ,热脉动 (或He闪耀 ) ,强的红外超量发射 ,分子脉泽发射等 ,弄清AGB星的演化规律是研究恒星演化理论的重要任务。目前人们所知道的AGB星的演化图景是 ,恒星经过漫长的主序演化之后 ,将经过红巨星 (RGB)阶段 ,然后才进入AGB阶段 ,在其演化过程中AGB星的光度和质量损失率要逐渐增大 ,它的光变周期也逐渐变长 ,在其中心星经历了一系列的由He核反应不稳定性引起的热脉动之后 ,它的质量损失很快停止 ,恒星开始向行星状星云 (PN)演化 ,最后行星状星云将会变成一个白矮星 ,这将是许多初始质量不很大的恒星的最终结局。OH/IR星阶段是AGB星演化的一个阶段 ,OH/IR星是那些质量稍大的恒星在AGB阶段后期演化而成的天体。现阶段人们对OH/IR星的具体演化过程还知道得很少。我们利用了球对称包层中的尘埃辐射转移模型来研究OH/IR星的演化性质 ,并且收集了尽量多的具有可靠距离的OH/IR星来研究他们的光度和质量损失率的演化性质。在本文的研究工作中 ,我们主要讨论了OH/IR星在远红外双色图中的分布规律 ,还发现     

萤火一号火星探测器的轨道设计和STK仿真

研究了行星际轨道的基本设计参数和设计方法。首先介绍了Lambert问题及其对基本设计参数的求解,然后利用Lambert问题解生成的PCP图搜索了全局最优的2009~2010年发射窗口,并利用卫星软件工具包(STK)模拟了萤火一号(YH-1)在复杂力模型下主要飞行轨道的全过程。计算和仿真结果表明,Lambert问题解与STK相结合,可以有效地建立行星际飞行的复杂设计轨道。     

Factors affecting levels of aerosol sulfate and nitrate on the Western Mediterranean coast

The present study was carried out between October 2003 and September 2004 at an urban background station near the Mediterranean coast in southeastern Spain. The sulfate and nitrate content was determined in 332 PM10 and PM2.5 daily samples. The results show that the seasonal variation of nitrate measured in PM10 does not correspond with what has been observed at other locations in the Iberian Peninsula, where the minima are reached during the summer months due to decomposition of ammonium nitrate at high temperatures. The recorded levels of PM10 nitrate were slightly higher in summer due to an increase in the concentrations of coarse mode nitrate. On the contrary, both the concentrations and the percentages of nitrate in PM2.5 were lowest from June to September. The sulfate levels in both PM10 and PM2.5 were maxima in summer because the oxidation rate of SO₂ increases with solar radiation. An elevated correlation (0.72 < r < 0.92) between the monthly average concentrations and percentages of sulfate and solar radiation has been found. We have also investigated the influence that Saharan dust intrusions and high pollution episodes have upon the sulfate and nitrate concentrations. Both types of events increased NO₃⁻ and SO₄²⁻ levels, particularly the high pollution episodes.     

西安市灰尘循环模式及搬运沉积

城市灰尘的搬运沉积方式与其粒径组成密切相关.一般说来,粗颗粒物多以滚动方式搬运;中细颗粒物多以跳跃方式搬运;极细颗粒物多以悬浮方式搬运.西安市灰尘颗粒物主要来源于以跳跃方式搬运的中远距离颗粒物,其次为以滚动方式搬运的近源颗粒物,而以悬浮方式搬运的远距离颗粒物约占12%.     

ULTRACAM observations of the black hole X-ray transient XTE J1118+480 in quiescence

We present 450- and 850-μm maps of R Coronae Australis. We compare the maps with previous surveys of the region, and shed new light on the previously unknown nature of the protostellar sources at the centre of the cloud. We clarify the nature of two millimetre sources previously discovered in lower-resolution data. We identify one new Class 0 protostar, which we label SMM 1B, and we measure the envelope masses of a number of more evolved protostars. We identify two new pre-stellar cores, which we call SMM 1A and SMM 6.     

The role of dispersed ash in orbital-scale time-series studies of explosive arc volcanism: insights from IODP Hole U1437B,Northwest Pacific Ocean

ABSTRACT

Tephra fallout beds in marine sediments provide chronologically precise and highly resolved records of volcanism at time scales relevant to Quaternary climate cycles. While the record of discrete (visible) thin tephra beds is readily accessible, the significance of the dispersed (invisible) tephra record remains unclear. Here we evaluate the role of dispersed tephra for orbital-scale volcanic time variations in the Quaternary (<1.2 Ma) carbonate mud of IODP Hole U1437B (Northwest Pacific). The carbonate mud contains cyclic series of discrete fallout tephra beds from the oceanic Izu Bonin (~85% of tephra beds) and the continental Japan (~15%) volcanic arcs, respectively. Our results show the inorganic aluminosilicate (lithogenic) fraction is a mixture of dispersed Izu Bonin and Japan ash, and Asian dust. The time distribution of the Izu Bonin ash with its distinct composition appears to confirm and enhance the cyclic time variation of the discrete ash beds at Hole U1437B. Dispersed Japan ash resembles Asian dust in trace elements and is only distinguishable in Sr-Nd isotope space. Collectively, our results confirm the existence of periodic, orbital-scale fluctuations of arc volcanic frequency. Orbital-scale time variations of marine ash may be best established by series of discrete marine ash beds, yet the concomitant dispersed ash flux must also be recorded in order to understand the total flux of arc volcanic ash into the ocean basins and thus the role of the volcanism-climate link.     

Dust variation recorded by lacustrine sediments from arid Central Asia since ~ 15 cal ka BP and its implication for atmospheric circulation

A long dust history established using geological archives from dust provenance areas is necessary to understand the role of atmospheric dust in the global climate system better. Core sediments from a closed-basin groundwater-recharged lake in arid Central Asia were investigated using a multi-proxy approach (e.g. ¹⁴C AMS dating, pollen, and grain size) to trace the dust history since ~ 15 cal ka BP. Pollen analysis showed that before 7.9 cal ka BP, the vegetation was of desert type. After 7.9 cal ka BP, vegetation density increased, probably due to slightly increased moisture. The Chenopodiaceae-dominated desert expanded rapidly at 4.2–3.8 cal ka BP. Grain-size analysis was conducted for samples of lake deposits, modern aeolian dust, and dust trapped in snow, and the data showed that there was strong aeolian dust deposition at 11.8–11.1, 10.6–8, 6.1–4.9, and after 3.3 cal ka BP. This timing corresponds well with periods of increased terrestrial dust fluxes recorded by Greenland ice cores. Our study may document changes in the location and intensity of the Siberia High. These changes may play a more important role in the history of dust emission in arid Central Asia than previously thought.