An XMM–Newton observation of the galaxy group MKW 4

We present an X-ray study of the galaxy group or poor cluster MKW 4. Working with XMM–Newton data we examine the distribution and properties of the hot gas which makes up the group halo. The inner halo shows some signs of structure, with circular or elliptical beta models providing a poor fit to the surface brightness profile. This may be evidence of large-scale motion in the inner halo, but we do not find evidence of sharp fronts or edges in the emission. The temperature of the halo declines in the core, with deprojected spectral fits showing a central temperature of ∼1.3 keV compared to ∼3 keV at 100 kpc. In the central ∼30 kpc of the group, multitemperature spectral models are required to fit the data, but they indicate a lack of gas at low temperatures. Steady-state cooling flow models provide poor fits to the inner regions of the group and the estimated cooling time of the gas is long except within the central dominant galaxy, NGC 4073. Abundance profiles show a sharp increase in the core of the group, with mean abundance rising by a factor of 2 in the centre of NGC 4073. Fitting individual elements shows the same trend, with high values of Fe, Si and S in the core. We estimate that ∼50 per cent of the Fe in the central 40 kpc was injected by Type Ia supernovae, in agreement with previous ASCA studies. Using our best-fitting surface brightness and temperature models, we calculate the mass, gas fraction, entropy and mass-to-light ratio of the group. At 100 kpc (∼0.1 virial radius) the total mass and gas entropy of the system (  ∼2 × 10¹³ M_⊙  and ∼300 keV cm²) are quite comparable to those of other systems of similar temperature, but the gas fraction is rather low (∼1 per cent). We conclude that MKW 4 is a fairly relaxed group, which has developed a strong central temperature gradient but not a large-scale cooling flow.     

Central Configurations of the Symmetric Restricted 4-Body Problem

We consider the symmetric planar (3 + 1)-body problem with finite masses m ₁ = m ₂ = 1, m ₃ = µ and one small mass m ₄ = . We count the number of central configurations of the restricted case = 0, where the finite masses remain in an equilateral triangle configuration, by means of the bifurcation diagram with as the parameter. The diagram shows a folding bifurcation at a value consistent with that found numerically by Meyer [9] and it is shown that for small > 0 the bifurcation diagram persists, thus leading to an exact count of central configurations and a folding bifurcation for small m ₄ > 0.     

黑洞X射线双星的类氢类氦铁K_α发射线

用径移主导吸积流模型(ADAF)不仅可以成功解释很多低吸积率天体的连续谱辐射,也可以说明X射线波段的谱线发射,而后者目前尚少有讨论.以黑洞X射线双星GX339-4处在低吸积率的宁静态情况为例,计算了它的铁线发射,表明在ADAF情况下的确可以产生足够强的可以在观测上检测的类氢和类氦铁Kα线.     

Primary nitrogen production at low Z

Stellar models with axial rotation and very low metallicity Z, typical of the early star generations have been computed. These models account for the effects of rotation in the same way as previous grids which successfully reproduce the He- and N-enrichments observed at the surface of massive stars, and also the high numbers of red supergiants observed in low Z galaxies (Meynet and Maeder, 2000; Maeder and Meynet, 2001). At very low metallicity (Z = 0.00001, i.e. one two thousandth of the solar metallicity),these models naturally lead to the production of primary nitrogen. This revised version was published online in September 2006 with corrections to the Cover Date.     

面向不同环境背景的Landsat影像水体提取方法适用性研究

快速、准确地从卫星影像中提取水体信息一直是遥感应用的热点问题,在水资源管理、水环境监测和灾害应急管理等领域极具应用价值.虽然目前已有多种针对Landsat系列影像的水体提取方法,但由于地理位置、地形和水体形态等环境背景因素的影响,导致同种方法在不同的环境背景中呈现出不同的提取效果.本文针对人为影响严重、影像明暗对比强烈...     

春、秋季北黄海生源要素的平面分布特征

根据春季和秋季对北黄海2个航次的调查数据,分析了北黄海春秋两季节生源要素的平面分布特征,并简要讨论了其成因.结果表明:(1) 春季北黄海DIN,PO4-P,SiO3-Si的平均浓度分别为(3.46±2.66),(0.18±0.17)和(3.29±3.06)μmol·dm-3,含量较低;到秋季则分别升高至(6.45±3.64),(0.40±0.24)和(7.64±3.84)μmol·dm-3;DO则表现出了相反的变化,秋季较低,春季为秋季的1.42倍.(2) 春季DIN,PO4-P,SiO3-Si在各个层次的分布趋势较为类似,表层和10 m层表现为北黄海中部低,近岸较高,30 m层以下则在冷水团盘踞区及海域东部有高值.DO表层和10 m层变化趋势不显著,但在30 m以下表现出与营养盐相反的分布规律.秋季,DIN,PO4-P,SiO3-Si在各个层次分别具有相同的分布趋势,表层和10 m层表现为北黄海中部低,近岸较高,30 m层以下则在冷水团盘踞区含量较高.而DO由表到底都表现出与营养盐相反的趋势.     

长江三角洲北翼ZKA4钻孔剖面第四纪磁性地层特征及其意义

对长江三角洲北翼南通地区ZKA4钻孔岩心进行了磁性地层学研究,结果表明,302.7 m的岩心记录了布容正向极性时（Brunhes）、松山负向极性时（Matruyama）和部分高斯正极性时（Gauss）。在系统古地磁样品采集、处理和测试的基础上,应用磁性地层、AMS 14C加速器测年等方法,结合岩性特征,对ZKA4钻孔剖面进行了详细地层划分,分别确定了下更新统、中更新统、上更新统和全新统的埋深及沉积厚度,其中Q/N界线位于291.72 m处,Qp1/Qp2、Qp2/Qp3、Qp3/Qh界线分别定位于189.39 m、132.44 m和26.14 m处。本项研究结果为该区域第四纪地层划分对比、古地理环境演化及岸线变迁等相关研究提供了可靠的地层年代框架。     

基于不同模型的河口区水产养殖塘水-气界面CH4气体传输速率及扩散通量研究

模型估算法是水-气界面甲烷（CH₄）通量监测的主要方法.本研究选择6种不同的参数化模型方法估算了2015年6、8和10月两个亚热带河口养殖塘水-气界面CH₄传输速率（k_x）及其扩散通量,探讨了河口养殖塘k_x及CH₄扩散通量的变化特征和影响因子.结果表明：研究期间,不同模型估算下的k_x及其扩散通量均值在闽江河口养殖塘变化范围分别为1.60±0.75~6.29±1.30 cm/h和9.19±2.67~30.64±6.28 μmol/（m²·h）,在九龙江河口养殖塘的变化范围分别为0.89±0.19~6.07±0.61 cm/h和3.18±0.48~21.03±2.13 μmol/（m²·h）;k_x及其扩散通量在两个河口区均呈现随时间推移而升高的特征;整个养殖期间,养殖塘水-气界面平均CH₄传输速率k_x呈现闽江河口略高于九龙江河口（P>0.05）,但水-气界面平均CH₄扩散通量呈现闽江河口显著高于九龙江河口的特征（P<0.05）;风速、水体溶解CH₄浓度和盐度是调控河口区养殖塘水-气界面CH₄扩散通量变化的重要因子;不同模型估算出的河口养殖塘水-气界面CH₄传输速率k_x存在差异,表明模型估算法获得的水-气界面CH₄扩散通量存在一定的不确定性.     

湿碱消解-等离子体发射光谱法测定海洋沉积物中的生物硅

利用湿碱式化学提取技术和电感耦合等离子体发射光谱仪,优化样品碱式消解方法,确定仪器最佳工作条件,建立了测定海洋沉积物中不同含量级别生物硅的方法。结果表明,仪器检出限为0.724μmol/L,方法检出限为0.942μmol/L。用于测定硅酸盐-硅溶液成分分析国家一级标准物质(GBW08648和GBW 08649,标准值分别为50.0μmol/L和100.0μmol/L),测定值分别为(49.888±0.275)μmol/L、(99.578±0.651)μmol/L,相对标准偏差为0.443%、0.527%;对于不同生物硅含量级别海洋沉积物样品的平行、独立测量,其相对标准偏差8.9%。方法快速、简便、准确,可满足古海洋学不同时空尺度气候和环境分析的应用。     

从传统测绘产业发展到地理信息产业的意义

20世纪 90年代中后期 ,以“3S”技术和“4D”产品的普及推广为标志 ,我国的传统测绘产业开始了向现代地理信息产业的过渡 ,这对测绘行业本身、对其他行业、对整个社会发展都具有重大意义