陈家庄铀矿同位素地质年代学特征

陈家庄铀矿床铀单矿物U-Pb及黑云母K-Ar、全岩Rb-Sr同位素定年结果,成矿时期为423—382Ma,主成矿年龄406Ma,矿床形成至今仍保持半封闭系统,未遭受明显后期改造。本区早古生代时期发生的区域动力热流变质作用的年龄为457Ma,热液活动的上限为378Ma,冷却年龄为373—350Ma,伟晶状花岗岩原岩丰龄452Ma。并提出了本区主要地质事件时序及演化模式。     

利用遥感技术进行大熊猫栖息环境的调查研究

本文利用陆地卫星图像和航空像片判读,结合地面采样调查,对既能从遥感图像上提取又是影响大熊猫主食竹类生长的环境因子,建立多元回归的数学模型。根据多元回归求算各个地块的得分值,以评价主食竹类的立地质量等级。得出位于中高海拔东北向缓坡下部兼有针阔混交林覆盖的厚土层地段,是主食竹类的最适生长环境和大熊猫的最佳栖息环境。因此,利用遥感技术进行立地质量分类和编制大熊猫环境质量分布图,将对恢复和改善其栖息环境以及管理保护工作起到积极的作用。     

日本沼虾受精卵核行为的初步研究

研究了日本沼虾受精卵的核行为。结果表明 :日本沼虾在 2 1℃水箱中培养时 ,雌虾交配产卵后 0 .5 h,受精卵内仅出现 1个雌原核 ,未见雄原核 ;产卵后 1 .5 h,卵内同时出现雌原核和雄原核 ;产卵后 3 .5 h,雌原核和雄原核接近 ;产卵后 4h,雌原核和雄原核联合 ,形成合子核 ;产卵后 4.5 h,开始第一次有丝分裂 ;产卵后 7h,形成 2个核 ;产卵后 8h,形成 4个核     

Periodicity in the crater formation rate and implications for astronomical modeling

Claim for periodicity in the crater formation rate is reinvestigated using a criterion proposed by Broadbent, and data sets of Rampino and Stothers and of Grieve are shown to satisfy the periodicity criterion (P 30 Myr).On the other hand, currently observed impactors are mainly asteroids, while long and short periodic comets whose fluxes may vary by external disturbances occupy only a small fraction. Using a Monte Carlo simulation, constraints are obtained for the dispersion Q(Myr) from an exact periodicity and for the periodic components (F _tp) in the signals for their periodicity to be detected. It is found that for = 5, 6 and 7 Myr, F _tp, would have to be 40% or greater, 60% or greater and 80% or greater, respectively. These constraints are used to discuss whether the giant molecular cloud perturbations can give rise to the periodicity in the impact events. The amplitude of the solar Z-motion need to be some 100pc for = 6 Myr, which requires the periodic component (SP and LP comets, if the former originate from the latter) to be 60%, while for = 7 Myr, the periodic component need to be 80%. The GMC perturbation model consistent with the periodicity appears to be the one where the amplitude is 100pc and the periodic component - 60% of the impactors. If SP comets mainly originate from a source such as the hypothetical Kuiper belt, the GMC perturbation would not be consistent with the periodicity.     

The shape, topography, and geology of Tempel 1 from Deep Impact observations

Deep Impact images of the nucleus of Comet Tempel 1 reveal pervasive layering, possible impact craters, flows with smooth upper surfaces, and erosional stripping of material. There are at least 3 layers 50-200 m thick that appear to extend deep into the nucleus, and several layers 1-20 m thick that parallel the surface and are being eroded laterally. Circular depressions show geographical variation in their forms and suggest differences in erosion rates or style over scales >1 km. The stratigraphic arrangement of these features suggests that the comet experienced substantial periods of little erosion. Smooth surfaces trending downslope suggest some form of eruption of materials from this highly porous object. The Deep Impact images show that the nucleus of Tempel 1 cannot be modeled simply as either an onion-layer or rubble pile structure.     

生物冰核Snomax成核性能分析测试

为了研究生物冰核Snomax的成核性能,在静态等温云室中对Snomax的成核性能进行测试分析,得出其成核率、核化速率、成核阈温等性能参数,结果表明在-4～-18℃,Snomax成核率在108/g～1011/g范围内变化,不同温度、过冷水含量、冰核浓度对Snomax催化产生的冰晶形态有重要影响。此外,对比分析测试了AgI焰剂与Snomax的成核性能,试验结果表明AgI焰剂成核率比Snomax高出3～4个数量级,但亲水性Snomax冰核蛋白具有更快的核化速率和环境友好性。通过对比两种冰核的成核特性,分析了生物冰核在人工影响天气作业中可能的应用。     

Geomorphology of a modern carbonate slope system and associated sedimentary processes: Example of the giant Great Abaco Canyon,Bahamas

The large acoustic data set acquired during the Carambar cruises is composed of high resolution bathymetry, backscatter data and very‐high resolution seismic lines which allow for an overview of the morphology and sediment transfer processes from the shallow upper slope to the abyssal plain of a modern carbonate system: the north‐eastern slope of the Little Bahama Bank. Surficial distribution of the acoustic facies and echofacies reflects a wide variety of sedimentary processes along and across the slope. The western sector of the Little Bahama Bank is dominated by depositional processes whereas its eastern sector, which is incised in the lower slope by giant canyons, is affected by erosion and bypass processes. Datasets suggest that currents play an important role both in along‐slope sedimentary processes and in the abyssal plain. The Antilles Current appears to affect a large part of the middle and lower slopes. The absence of sizeable present‐day channel/levée complexes or lobes at the mouth of the canyon – revealed by the bathymetric map – indicates that the southward flowing Deep Western Boundary Current influences modern abyssal sediment deposition. Based on depositional processes and indicators of canyon maturity observed in facies distribution, the current study proposes that differential subsidence affects the eastern versus western part of the bank. The morphology of the Great Abaco Canyon and Little Abaco Canyon, which extend parallel to the platform, and the Little Bahama Bank slope appears to be related to the Great Abaco Fracture Zone.     

Rotation and color properties of the nucleus of Comet 2P/Encke

We present results from CCD observations of Comet 2P/Encke acquired at Steward Observatory's 2.3 m Bok Telescope on Kitt Peak. The observations were carried out in October 2002 when the comet was near aphelion. Rotational lightcurves in B-, V-, and R-filters were acquired over two nights of observations, and analysed to study the physical and color properties of the nucleus. The average apparent R-filter magnitude across both nights corresponds to a mean effective radius of 3.95±0.06 km, and this value is similar to that found for the V- and B-filters. Taking the observed brightness range, we obtain a/b?1.44±0.06 for the semi-axial ratio of Encke's nucleus. Applying the axial ratio to the R-filter photometry gives nucleus semi-axes of [3.60±0.09]×[5.20±0.13] km, using the empirically-derived albedo and phase coefficient. No coma or tail was seen despite deep imaging of the comet, and flux limits from potential unresolved coma do not exceed a few percent of the total measured flux, for standard coma models. This is consistent with many other published data sets taken when the comet was near aphelion. Our data includes the first detailed time series multi-color measurements of a cometary nucleus, and significant color variations were seen on October 3, though not repeated on October 4. The average color indices across both nights are: (V−R)=0.39±0.06 and (B−V)=0.73±0.06 (). We analysed the R-filter time-series photometry using the method of Harris et al. [Harris, A.W., Young, J.W., Bowell, E., Martin, L.J., Millis, R.L., Poutanen, M., Scaltriti, F., Zappala, V., Schober, H.J., Debehogne, H., Zeigler, K.W., 1989. Icarus 77, 171-186] to constrain the rotation period of the comet's nucleus, and find that a period of ∼11.45 h will satisfy the data, however the errors bars are large. We have successfully linked our data with the September 2002 data from Fernández et al. [Fernández, Y.R., Lowry, S.C., Weissman, P.R., Mueller, B.E.A., Samarasinha, N.H., Belton, M.J.S., Meech, K.J., 2005. Icarus 175, 194-214]—taken just 2-3 weeks before the current data set—and we show that a rotation period of just over 11 h works extremely well for the combined data set. The resulting best-fit period is 11.083±0.003 h, consistent with the Fernández et al. value.