On the efficiency of production of the Fe Kα emission line in neutral matter

The absolute luminosity of the Fe Kα emission line from matter illuminated by X-rays in astrophysical sources is non-trivial to calculate except when the line-emitting medium is optically thin to absorption and scattering. We characterize the Fe Kα line flux using a dimensionless efficiency, defined as the fraction of continuum photons above the Fe K shell absorption edge threshold energy that appear in the line. The optically thin approximation begins to break down even for column densities as small as  2 × 10²² cm⁻²  . We show how to obtain reliable estimates of the Fe Kα line efficiency in the case of cold, neutral matter, even for the Compton-thick regime. We find that, regardless of geometry and covering factor, the largest Fe Kα line efficiency is attained well before the medium becomes Compton-thick. For cosmic elemental abundances it is difficult to achieve an efficiency higher than a few per cent under the most favourable conditions and lines of sight. For a given geometry, Compton-thick lines-of-sight may have Fe Kα line efficiencies that are orders of magnitude less than the maximum possible for that geometry. Configurations that allow unobscured views of a Compton-thick reflecting surface are capable of yielding the highest efficiencies. Our results can be used to estimate the predicted flux of the narrow Fe Kα line at  ∼6.4 keV  from absorption models in active galactic nucleus (AGN). In particular we show that contrary to a recent claim in the literature, absorption-dominated models for the relativistic Fe Kα emission line in  MCG−  6-30-15 do not overpredict the narrow Fe Kα line for any column density or covering factor.     

武汉中层大气温度特性的激光雷达观测研究

报道了升级改造后的WIPM瑞利散射激光雷达的技术状况,并通过与CIRA86标准大气模式和UARS卫星探测的比较,考察了其中层大气温度探测性能. 基于2002年至2003年激光雷达的系统观测数据,给出了武汉上空中层大气温度分布的年平均特性及在各种时间尺度下的变化规律,分析了标准大气模式在描述中层大气温度分布平均特性和变化规律上的局限.     

盆地构造地震地面运动速度和加速度分布特征的数值模拟

本文用错格实数傅里叶变换的拟谱法的数值模拟方法分析了地震波在冲积扇、盆地等不均匀地震构造体区域的传播过程和地面运动分布. 结果表明, 地震波由岩石区进入盆地结构后,在盆地内上下多次反射振荡,对地面建筑物可能形成多次连续的振动和破坏,仅有极少量地震波能量返回岩石区域中,这是防灾研究中值得注意的地面运动特征;地震波在盆地边界地质构造条件下,形成的地震波体波与次生面波动的叠加干涉形成了大振幅的地面运动,它可能导致建筑物的极大破坏;破坏峰值的空间位置可能远离岩石和盆地沉积层的边界或者地震断层的位置.     

Processing of Aerosol Particles in Convective Cumulus Clouds: Cases Study in the Mexican East Pacific

In the Mexican Intertropical Convergence Zone, particle size distributions within 500 m of cloud boundaries at altitudes of 1000, 2500, and 4200 m, were compared against size distributions at the same levels but 1500 m away from the clouds. The differences in the distributions near and far from the cloud are related to processes that may change particle properties inside the cloud. Chemical changes in the aerosols are deduced from the particles’ refractive index, as derived from comparisons with the scatter...     

Polycentric systems for coping with collective action and global environmental change

The 20th anniversary issue of Global Environmental Change provides an important opportunity to address the core questions involved in addressing “global environmental” problems—especially those related to climate change. Climate change is a global collective-action problem since all of us face the likelihood of extremely adverse outcomes that could be reduced if many participants take expensive actions. Conventional collective-action theory predicts that these problems will not be solved unless an external authority determines appropriate actions to be taken, monitors behavior, and imposes sanctions. Debating about global efforts to solve climate-change problems, however, has yet not led to an effective global treaty. Fortunately, many activities can be undertaken by multiple units at diverse scales that cumulatively make a difference. I argue that instead of focusing only on global efforts (which are indeed a necessary part of the long-term solution), it is better to encourage polycentric efforts to reduce the risks associated with the emission of greenhouse gases. Polycentric approaches facilitate achieving benefits at multiple scales as well as experimentation and learning from experience with diverse policies.     

禹城地区光合有效辐射的计算方法

利用2005年7月-2006年10月在山东禹城对太阳辐射（包括光合有效辐射PAR、可见光辐射VIS、总辐射Q等）、气象要素等进行的4次综合观测资料,初步得到了朋R,VIS的日、季节变化特征并对其进行了分析,结果表明：各辐射的小时累计之比vIS／Q,PAR／Q,PAR／VIS相对稳定,其平均值分别为0．39,1．95（mol／MJ）,4．97（mol／MJ）,但它们均有明显的日、逐日、季节变化,并受水汽、气溶胶、云等因素的影响。同时建立了实际天气PAR,VIS的小时累计经验公式及其转换关系,计算值与观测值均比较接近。当考虑水汽和散射因子时,PAR,VIS的计算值与观测值的相对偏差分别为11．1％,10．6％。限于实际情况,可以只考虑水汽因子的作用来计算PAR和VIS的小时累计值,它们的相对偏差分别为13．3％,12．6％。水汽因子对于PAR,VIS的传输和计算具有重要作用。     

两次冰雹过程多普勒天气雷达产品的对比分析

利用常规天气资料和长沙多普勒天气雷达产品,对2008年4月8日和2009年3月21日发生在湖南的两次春季冰雹天气对比分析发现:这两次过程前期形势均为500 hPa西风槽以阶梯槽的形势影响湖南,槽前配合有冷锋南下,锋前的西南倒槽明显发展,低槽、切变以及冷空气是其主要影响天气系统;通过雷达产品对比分析发现,4月8日过程是一次典型的超级单体过程,3月21日过程为一次强飑线过程,在降雹前VIL值均有明显的反应。     

Continuing current in multiple channel cloud-to-ground lightning

In this study we analyze the effects of continuing current initiated by strokes following a new channel to ground in multiple stroke flashes using high-speed video records, electric field measurements from a fast antenna and lightning detection network data. We observed that the long continuing current initiated by a stroke that follows a new channel also obeys the pattern in the initiation of long continuing current suggested by Rakov and Uman [Rakov, V.A., Uman, M.A., 2003. Lightning: Physics and Effects, 687pp., Cambridge Univ. Press, New York.]. We also verify that the statement of Rakov and Uman [Rakov, V.A. and Uman, M.A., 1990. Some properties of negative cloud-to-ground lightning flashes versus stroke order, Journal of Geophysical Research. 95, 5447–5453.] reporting that: “...strokes initiating long continuing currents tend to have lower initial electric field peak than regular strokes” is valid for strokes that create a new channel to ground and are followed by long continuing current (CC). Apparently the reduction of peak current value (I_p) when the stroke is followed by a long CC is stronger than the I_p increase that is commonly observed when strokes follow a new channel. We also find that the “exclusion zone” proposed by Saba et al. [Saba, M.M.F., Pinto, O. Jr., Ballarotti, M.G., 2006a. Relation between lightning return stroke peak current and following continuing current, Geophysical Research Letters 33, L23807, doi:10.1029/2006GL027455.] is valid for new channels initiating CC, and finally we verify that a number of strokes in the same channel larger than four or the existence of a long CC current do not always consolidate the channel in a multiple stroke flash.     

Upper limit on dimming of cosmological sources by intergalactic grey dust from the soft X-ray background

Active galactic nuclei (AGN) produce a dominant fraction  ( F _AGN∼ 80 per cent)  of the soft X-ray background (SXB) at photon energies  0.5 < E < 2 keV  . If dust pervaded throughout the intergalactic medium, its scattering opacity would have produced diffuse X-ray haloes around AGN. Taking account of known galaxies and galaxy clusters, only a fraction   F _halo≲ 10 per cent  of the SXB can be in the form of diffuse X-ray haloes around AGN. We therefore limit the intergalactic opacity to optical/infrared photons from large dust grains, with radii in the range   a = 0.2–2.0 μm  , to a level  τ_GD≲ 0.15( F _halo/10 per cent)(F_AGN/80 per cent)⁻¹  to a redshift   z ∼ 1  . Our results are only weakly dependent on the grain size distribution in this size range or the redshift evolution of the intergalactic dust. Stacking X-ray images of AGN can be used to improve our constraints and diminish the importance of dust as a source of systematic uncertainty for future supernova surveys which aim to improve the precision on measuring the redshift evolution of the dark energy equation-of-state.