渤海悬浮颗粒物的三维输运模式 I.模式

为了长时间,大范围研究渤海中悬浮物的输运规律,研究应用并改造了备国汉堡大学的粒子追踪悬浮物输运的三维模式,模式中考虑了风、气压等气象要素以外海传入的潮波作用下的三维正压海流对悬浮颗粒物的输运．同时考虑了悬浮颗粒物的学降及再悬浮机制和底质中的细颗粒物的运动,将风浪的作用引入了悬浮物输运的计算,数值模式应用的粒五追踪方法,能较好地反映悬浮物浓度的迅速变化。     

Clustering of galaxy clusters in cold dark matter universes

We use very large cosmological N -body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model ( τ CDM) and a flat low density model with a cosmological constant (ΛCDM). Our simulations each use 10⁹ particles to follow the mass distribution within cubes of side 2  h ⁻¹ Gpc ( τ CDM) and 3  h ⁻¹ Gpc (ΛCDM) with a force resolution better than 10⁻⁴ of the cube side. We investigate how the predicted cluster correlations increase for samples of increasing mass and decreasing abundance. Very similar behaviour is found in the two cases. The correlation length increases from     for samples with mean separation     to     for samples with     The lower value here corresponds to τ CDM and the upper to ΛCDM. The power spectra of these cluster samples are accurately parallel to those of the mass over more than a decade in scale. Both correlation lengths and power spectrum biases can be predicted to better than 10 per cent using the simple model of Sheth, Mo & Tormen. This prediction requires only the linear mass power spectrum and has no adjustable parameters. We compare our predictions with published results for the automated plate measurement (APM) cluster sample. The observed variation of correlation length with richness agrees well with the models, particularly for ΛCDM. The observed power spectrum (for a cluster sample of mean separation     ) lies significantly above the predictions of both models.     

Modelling of oxygen-rich envelopes using corundum and silicate grains

A set of 31 oxygen-rich stars has been modelled using corundum and silicate grains. These stars were selected according to their dust-envelope class, as suggested by Little-Marenin and Little in 1990. Then 16 stars classified as Sil were modelled using silicate grains; 10 Broad class stars using corundum (Al₂O₃) grains; and 5 ' Intermediate ' class stars using two kinds of grain simultaneously: corundum and silicate. The temperature of the central stars and some characteristics of their circumstellar envelopes such as their extinction opacities and extensions were determined by fitting the flux curves. The corundum/silicate ratios as well as the energy distributions and temperature laws have been obtained. Based on the authors' results they suggest the existence of chemical and structural evolution of the modelled circumstellar dust shells. The temperature of the central stars and the temperature of the hottest grains decrease from Broad to Intermediate to Sil classes, while the inner radii and optical depths increase in this sequence.     

Dust formation and inhomogeneous mass-loss from asymptotic giant branch stars

We examine the flow from asymptotic giant branch (AGB) stars when along a small solid angle the optical depth resulting from dust is very large. We consider two types of flows. In the first, small cool spots are formed on the surface of slowly rotating AGB stars. Large quantities of dust are expected to be formed above the surface of these cool spots. We propose that if the dust formation occurs during the last AGB phase when the mass-loss rate is high, the dust shields the region above it from the stellar radiation. This leads to both further dust formation in the shaded region and, owing to lower temperature and pressure, the convergence of the stream toward the shaded region, and the formation of a flow having a higher density than its surroundings. This density contrast can be as high as ∼4. A concentration of magnetic cool spots toward the equator will lead to a density contrast of up to a few between the equatorial and polar directions. This process can explain the positive correlation between high mass-loss rate and a larger departure from sphericity in progenitors of elliptical planetary nebulae. In the second type of flow, the high density in the equatorial plane is formed by a binary interaction, where the secondary star is close to, but outside the AGB envelope. The shielding of the radiation by dust results in a very slow and dense flow in the equatorial plane. We suggest this flow as an alternative explanation for the equatorial dense matter found at several hundred astronomical units around several post-AGB binary systems.     

Star formation in the Cepheus Flare region – II. A-type stars associated with IRAS sources

In order to reveal the star-forming history of the molecular cloud complex we studied the intermediate mass stellar population in the Cepheus Flare region. (Paper I dealt with the distance and the young stellar object candidates of the region.) Correlating the IRAS Point Source Catalogue and Faint Source Catalogue positions with those of 1214 B8–A8 and 1760 F0–F5 type stars brighter than     and classified during an objective prism survey, we identified 19 stars showing far-infrared excess emission in the Cepheus Flare region. In addition to the 16 stars whose counterparts are given in the IRAS catalogues, we found three more stars with infrared excess not recognized before. In order to identify the young medium-mass stars associated with the Cepheus Flare molecular clouds we observed the optical spectra of the IR-excess stars, and using published optical photometry and the IRAS data we examined their spectral energy distributions (SEDs) and IRAS two-colour diagram. The observations resulted in the discovery of a new Herbig Ae/Be star, BD +68°1118, coinciding with IRAS 21169+6842. More evolved HAe/Be stars may be SAO 19953, BD +67°1314 and BD +69°1231, whose H α lines showed weak emission components. Possible β Pictoris- or Vega-type stars may be HD 203854, HD 212826 and HD 216486, whereas the far-infrared fluxes at the positions of BD +72°1018, HD 210806 and HD 217903 can be attributed to the heating of the interstellar environment. We used distances and radial velocities of the stars derived from the spectroscopy and published optical photometry as indicators of their relations to the clouds. Information on the environment of the observed stars deduced from the diffuse interstellar band at λ 6613 is briefly discussed.     

A WIMP detector with two-phase xenon

We describe an important new technique to search for WIMPs. This technique employs a method of background discrimination using double phase xenon as detector target. We describe the construction of a two-phase, 1-kg xenon detector. The detector will be installed at the underground laboratory in the Mt. Blanc tunnel, which provides a low background rate. A comparison between the sensitivity curve of our detector and the theoretical events limit from SUSY calculations is presented.     

A brief introduction to recent applications of several sediment-analysis techniques in palaeolimnological studies-dry bulk density and water content, mineral magnetism, carbonate content, and content of total organic carbon, nitrogen content and c

ChalacteriStics of lacustrine sediments are often capable of ~ring the hydrological regales of the lakeand its environment and human achvihes in itS catclunent during the sedimentahon of these sedimentS.Therefore, by identifying these characteristics of sedimentS, it is likely to postUlate the physicalconditions in and around the lake during geological periods. Such reconstrUction of palaeoenvironmentshas become an increasingly important branch of ear sciences as there has been an expanded n…     

错流超滤技术在海水胶体态铀、钍、镭同位素和有机碳研究中的应用

建立了由预过滤装置、蠕动泵、中空纤维超滤膜(AmiconH10P10-20,标称截留分子量10KDa)和连接管组成的错流超滤系统,利用荧光标记的40KDa葡聚糖和已知放射性活度的234Th示踪剂评估了超滤膜的截留和吸附性质,探讨了234Th在超滤过程中的渗透行为,考查了该系统用于实际海水样品时铀、钍、镭同位素和有机碳的质量平衡状况.结果表明,10Kda中空纤维超滤膜对40Kda葡聚糖具有良好的截留效率(85%),而吸附损失率为18%.铀、钍、镭同位素和有机碳在超滤过程中均达到极佳的质量平衡,回收率R=95%～98%,优于大多数文献报道的值.234Th在超滤过程中的渗透行为可以很好地用渗透模型加以描述.研究组分胶体态含量占“溶解”态含量的份额大小顺序如下:钍同位素、有机碳、镭同位素约等于铀同位素,这与钍为强颗粒活性元素、铀和镭为水溶性元素的地球化学性质相吻合.