Substances of cometary grains estimated from evaporation and radiation pressure mechanisms

The shape and intensity distribution of tails for several large comets are estimated on the basis of grain properties in the solar radiation field. The following results are obtained: (1) The ratio of the maximum radiation pressure force to the gravitaional force acting on dust grains in cometary tails is found to be less than 2.5. This means that grains such as graphite particles in the size range 0.02–0.2 μm do not exist in them, because such particles would allow forces greater than 2.5 (2) Tail substances supplied near the time of perihelion passage for the Sun-grazing comet Ikeya-Seki (1965 VIII) and Comet Seki-Lines (1962 III) were composed of particular grains which had values of radiation pressure ratio less than 1.0. Therefore, it is concluded that the material was composed of silicate grains only, since iron grains had sublimated and there were no graphite particles.     

Oceanic crust production and climate during the last 100 Myr

In order to evaluate the possible influence of oceanic crust production on climatic changes during the past 100Myr variations in total oceanic crust for this period including production at mid-ocean ridges, oceanic plateaus, and back-arc basins were calculated using the most recent and accurate time-scales. The rates presented here differ from those of Larson (1991a, b) on Cenozoic fluctuations and show that (1) maximum production values occurred during the Cenomanian, Palaeocene, and late Oligocene-early Miocene and (2) minimum values occurred in Campanian-Maastrichtian, late Eocene, and middle Miocene. Significantly, variations of oceanic crust production correspond with variations in the δ¹⁸O of deep-water benthic foraminifera: maximum values of oceanic crust production correspond with minimum values of δ¹⁸O, and minimum production values with maximum values of δ¹⁸O. This latter synchronism suggests that changes in land-sea relationships and atmospheric CO₂ related to major fluctuations in oceanic crust production were the main cause of mid-Cretaceous warming and Late Cretaceous cooling, and of climatic quasi-cycles having a periodicity of 33–38 million years over the last 100 Myr. This is the first report showing variations of ocean crust production synchronized with the Cenozoic climate changes.     

Partial derivative of love numbers

We present a simple formula for the partial derivatives of Love numbers with respect to density, bulk modulus and rigidity without urging the Adams-Williamson condition in the liquid core. Partials of the second degree Love numbers are computed for model 1066 A. Love numbers prove to be either completely or virtually independent of the elastic profile within the whole core. Delta-function-like changes occur in Love numbers when we perturb the density of the top and bottom layers of the outer core.     

东亚东倾地形格局的形成与季风系统演化历史寻踪——综合大洋钻探计划683号航次建议书简介

围绕IODP 683号建议书,介绍东亚东倾地形格局与季风系统演化历史的相关研究。新生代全球宏观环境格局发生了一系列重大变化,表现为岩石圈活动强烈,板块漂移导致海陆格局和地貌格局的变化,并引发洋流和大气环流的改组,最终导致全球气候的重大变化。新生代岩石圈运动和气候变化表现最为典型的地区是亚洲,其中最具标志性和全球意义的地质事件是喜马拉雅山和青藏高原的隆升及亚洲季风系统的形成与演化。青藏高原隆升最直接的结果是亚洲地区现代地貌格局的形成,大江大河的发育,并在很大程度上影响了亚洲季风系统的形成与演化。综合大洋钻探计划683号航次建议书,计划在长江中下游盆地和东海陆架盆地实施钻探,以获得长江历史演化和东亚季风演化的地质记录,并为研究青藏高原的演化提供新的证据。     

浅层包气带水汽昼夜运移规律及其数值模拟研究

西北干旱、半干旱地区,浅层包气带水分通量主要由水汽组成,而水汽在运移过程中产生的能量转换和质量迁移是地表质能平衡计算不可缺少的重要源汇项。在野外进行一个沙坑实验,发现土壤水在中午(12:00—15:00)达到最大值(10cm深度,5.9~6.1cm3/cm3;30cm深度,11.9~13.1cm3/cm3),而在凌晨(02:00—05:00)出现最小值(10cm深度,4.4~4.5cm3/cm3;30cm深度,10.4~10.8cm3/cm3)。为进一步验证该实验条件下的土壤水运移及分布规律,考虑了土壤水、汽、热耦合运移的HYDRUS-1D模型被用来对实验过程进行模拟,模拟结果与实测结果吻合较好。为描述土壤水分昼夜运移模式,笔者将土壤水耦合运移的时间信息和空间信息进行同步分析;并根据土壤水运移的不同驱动力,分别对温度梯度、基质势梯度作用下的液态水及汽态水通量进行了分析。     

Rapid and Simple Measurement of H2 Emission from Active Faults Using Compact Sampling Equipments

Smaller equipment has been developed for sampling and measuring H₂ in fault zones. A considerable volume of hydrogen emission, suggesting the presence of fluid paths along fault zones, was detected within a 1‐h simple field procedure at an active fault in Central Japan, the Atotsugawa Fault. The equipment enabled measurements in a thin fault gouge with a thickness of 10 mm; this led to pervasive sampling from small fault zones hosted in harder rocks. A rapid evaluation of the spatio‐temporal heterogeneity of hydrogen emissions along the faults, using the present method, would increase knowledge of fluid circulation around faults.     

A coronal condensation observed at the total solar eclipse of June 11, 1983 and a related transient prominence

A coronal condensation was observed simultaneously with Fexiv 5303, Fex 6374, Fe xi 7892, and H filtergraphs. The size and shape of the condensation in 5303 are different from those in other filtergrams. H filtergrams taken around the eclipse time show that a small transient prominence exists in close proximity to the condensation core and behaves like a post-flare loop system, though the appearance is quite different and no flare-report exists. A small-scale energetic phenomenon seems to have occurred at the top of magnetic loops.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 285.     

Seasonal variation of bromocarbons at Hateruma Island,Japan: implications for global sources

High-frequency measurements of dibromomethane (CH₂Br₂) and bromoform (CHBr₃) at Hateruma Island, in the subtropical East China Sea, were performed using automated preconcentration gas chromatography/mass spectrometry. Their baseline concentrations, found in air masses from the Pacific Ocean, were 0.65 and 0.26 ppt, respectively, in summer and 1.08 and 0.87 ppt, respectively, in winter. Air masses transported from Southeast Asia were rich in bromocarbons, suggesting strong emissions in this area. The passage of cold fronts from the Asian continent was associated with sharp increases in observed concentrations of bromocarbons derived from coastal regions of the continent. Comparison of the relationships between [CH₂Br₂]/[CHBr₃] and [CHBr₃] in the Hateruma Island data with those in monthly mean data from 14 globally distributed U.S. National Oceanic and Atmospheric Administration ground stations suggested that these gases are produced primarily from a common process on a global scale.     

Numerical analysis on seepage failures of dike due to water level-up and rainfall using a water–soil-coupled smoothed particle hydrodynamics model

For seepage failures of dike due to water level-up and rainfall, surface infiltration and strength change induced by suction reduction are important factors; thus, numerical analysis should consider the coupling of water and soil, as well as the effect of saturation to obtain more precise failure mechanism. Based on the advanced smoothed particle hydrodynamics (SPH) method, this work proposed a two-phase-coupled SPH model in coordination with a novel constitutive model for unsaturated soils. Then, a triaxial compression test is simulated to check the applicability of the SPH method on the soil phase. After that, the failure test of a dike due to water level-up is discretized and simulated, from which the seepage process, the distribution of maximum shear strain, the slip surface, and pore water pressure are obtained. The two-phase-coupled SPH model is also applied to a slope failure test of heavy rainfall, and the results are compared to the model test. Finally, a dike failure test due to rainfall is analyzed using the proposed SPH model to reproduce the surface infiltration and suction reduction. The proposed SPH model provides several insights of seepage failures and can be a helpful tool for the analysis of dike failures induced by water level-up and rainfall.     

Study of the structure of silica film by infrared spectroscopy and electron diffraction analyses

Amorphous silicon oxide films have been studied on the basis of electron diffraction (ED) analyses and infrared (IR) spectroscopy in order to elucidate the relationship between the structures. After the heat treatment of the film in air at 300 and 500°C, the ED pattern showed halo rings, and the IR spectra clearly changed. Intensity analysis of the ED pattern provided evidence for the structural change of the amorphous film. It was concluded that the spectral changes in the ranges of 9.2–10.2, 12.5–13.5 and 19.5–22.5 μm were the result of phase transitions of the microcrystallites of α-cristobalite to β-cristobalite, and α- or β-quartz. Astrophysical implications have been discussed.