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81.
82.
83.
The peculiar galaxy NGC 4650 A (α=12h 42m. 1; = δ—40° 26′; 1950·0) has been studied by means of direct and spectral observations with the ESO 3·6-m telescope. It is
interpreted as a prolate, elliptical galaxy surrounded by a warped ring of H II regions, dust and stars. The distance is 47
Mpc (H
0=55 km s−1 Mpc−1). The ring is seen nearly edge-on (inclination 85°) and it rotates. It has a diameter of about 21 kpc and is bluer than the
elliptical galaxy for which the (M/L
v) ratio is ∼12 in solar units. The observed configuration may be the result of interaction with the nearby galaxy, NGC 4650. 相似文献
84.
Effects of Temperature and Humidity upon the Entrainment of Sedimentary Particles by Wind 总被引:2,自引:0,他引:2
Cheryl Mckenna Neuman 《Boundary-Layer Meteorology》2003,108(1):61-89
Aeolian transport of sedimentary particles is a well-recognized phenomenon in cold regions, but the effect of low temperature (T) and specific humidity (q) upon particle entrainment has not previously been investigated. This study reports on wind-tunnel experiments (-12 °C T 32 °C, and 1 g kg-1 q 10 g kg-1) that suggest the aerodynamic drag required to entrain sand sized particles can be 30% lower in cold or high latitude settings, as compared to hot deserts. For any given regional wind velocity, this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature.The influence of air temperature and humidity upon the threshold for particle motion is determined by three physical processes: (1) The effect of air viscosity and density on the fluid drag force acting to dislodge sedimentary particles; (2) the effect of viscosity on the turbulent wake shed from these particles, and the frequency and magnitude of burst-sweep events; and (3) the development of inter-particle cohesion via adsorbed water. This study considers the relative importance of each of these processes. The threshold friction velocity model of Shao and Lu is revised to incorporate the inter-particle force associated with hygroscopic water. It is found to perform well when tested against the experimental data obtained for this study. 相似文献
85.
福建省地震重点视防御区城市防震减灾体系工程以中国地震局关于建立健全地震监测预报、震灾预防和紧急救援三大体系为主要目标 ,以国家和福建省确定的地震重点监视防御区为主要目标区 ,尤以切实加强重点监视防御内城市的防震减灾措施 ,强化城市对地震灾害的综合防御能力为主要建设内容。该项目得到中国地震局、福建省委、省政府和有关地市大力支持 ,已列为福建省“十五”重点项目 ,省委、省政府为民办实事重点项目 相似文献
86.
Economic transition in central and eastern Europe (CEE) has had a particularly strong impact on industrial cities and regions. Following their economic collapse, most of them are now confronted with serious problems such as high unemployment and vast ecological damage. The paper presents findings from a pan European research project that investigated the problems of these cities and regions as well as the strategies being adopted to cope with structural change. It examines the differences in approaches and addresses the question whether existing EU policy is suitable for supporting the redevelopment of old industrial cities and regions in CEE countries. The paper concludes with recommendations for future directions in policy making. 相似文献
87.
88.
青藏高原雷暴云降水与地面电场的观测和数值模拟 总被引:4,自引:7,他引:4
在2003年青藏高原那曲地区夏季雷暴云的观测试验中,三次伴有降水的过程中都出现了地面电场(Egnd)随降水的漂移现象,而且固态和液态降水对Egnd的极性改变并不相同。为了模拟再现高原雷暴云降水和Egnd之间的关系,选取了8月13日这次具有高原雷暴代表性特征的过程,模拟了雷暴云移经观测点上空期间,测站固、液态降水与Egnd的变化以及雷暴云下部正电荷区的空间分布。模拟的Egnd及固、液态降水与其的对应关系与观测事实较一致。分析结果表明,固态降水主要携带正电荷,液态降水主要携带负电荷,各类带不同极性和数量电荷的降水粒子常共存在雷暴云中,Egnd主要受携带电荷量占主导地位的降水粒子的影响,地面出现强正电场时正好是云在当顶并且地面出现强固态降水的时间。 相似文献
89.
The impacts of the seasonal and interannual SST variability in the East Asia coastal regions (EACRSST) on the East Asian summer monsoon (EASM) have been examined using a regional climate model (PδRCM9) in this paper. The simulation results show that the correlation between the EACRSST and the EASM is strengthened after the mid-1970s and also the variability of the EACRSST forcing becomes much more important to the EASM interannual variability after the mid-1970s. The impacts of the EACRSST on the summer precipitation over each sub-region in the EASM region become weak gradually from south to north, and the temporal evolution features of the summer precipitation differences over North and Northeast China agree well with those of the index of EASM (IEASM) differences.
The mechanism analyses show that different EACRSST forcings result in the differences of sensible and latent heat flux exchanges at the air-sea interface, which alter the heating rate of the atmosphere. The heating rate differences induce low level air temperature differences over East Asia, resulting in the differences of the land-sea thermal contrast (LSTC) which lead to 850 hPa geopotential height changes. When the 850 hPa geopotential height increases over the East Asian continent and decreases over the coast of East China and the adjacent oceans during the weakening period of weakens consequently. On the contrary, the EASM enhances during the strengthening period of the LSTC. 相似文献
The mechanism analyses show that different EACRSST forcings result in the differences of sensible and latent heat flux exchanges at the air-sea interface, which alter the heating rate of the atmosphere. The heating rate differences induce low level air temperature differences over East Asia, resulting in the differences of the land-sea thermal contrast (LSTC) which lead to 850 hPa geopotential height changes. When the 850 hPa geopotential height increases over the East Asian continent and decreases over the coast of East China and the adjacent oceans during the weakening period of weakens consequently. On the contrary, the EASM enhances during the strengthening period of the LSTC. 相似文献
90.
Studies of ultracompact H ii regions — II. High-resolution radio continuum and methanol maser survey
A. J. Walsh M. G. Burton A. R. Hyland & G. Robinson 《Monthly notices of the Royal Astronomical Society》1998,301(3):640-698
High spatial resolution radio continuum and 6.67-GHz methanol spectral line data are presented for methanol masers previously detected by Walsh et al. (1997). Methanol maser and/or radio continuum emission is found in 364 cases towards IRAS -selected regions. For those sources with methanol maser emission, relative positions have been obtained to an accuracy of typically 0.05 arcsec, with absolute positions accurate to around 1 arcsec. Maps of selected sources are provided. The intensity of the maser emission does not seem to depend on the presence of a continuum source. The coincidence of water and methanol maser positions in some regions suggests there is overlap in the requirements for methanol and water maser emission to be observable. However, there is a striking difference between the general proximity of methanol and water masers to both cometary and irregularly shaped ultracompact (UC) H ii regions, indicating that, in other cases, there must be differing environments conducive to stimulating their emission. We show that the methanol maser is most likely present before an observable UC H ii region is formed around a massive star and is quickly destroyed as the UC H ii region evolves. There are 36 out of 97 maser sites that are linearly extended. The hypothesis that the maser emission is found in a circumstellar disc is not inconsistent with these 36 maser sites, but is unlikely. It cannot, however, account for all other maser sites. An alternative model which uses shocks to create the masing spots can more readily reproduce the maser spot distributions. 相似文献