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1.
地幔主要矿物橄榄石［(Mg089Fe011)2SiO4］的相变与深源地震的解释以及俯冲带和周围地幔的相互作用相关. 其中,形核率和长大率是刻画其相变动力学的两个重要参数. 因为实验技术的原因,目前人们还没有基于实验数据给出橄榄石的形核率. 本文首先通过对挤碰物理图像的分析,对边界形核情形的相变动力学理论中表征挤碰程度的无量纲参数进行了修正. 在此基础上,根据已有的实验资料,首次对橄榄石相变的形核率进行了估计. 通过对形核率数据的拟合,可以得到形核率参数K0和γ1/3. 得到两个形核率参数的变化范围分别为K0=55×1021～87×1027s-1·m-2·K-1,γ1/3=0～020 J·m-2,最佳拟合值为：K0=69×1024s-1·m-2·K-1,γ1/3=016 J·m-2. 相似文献
2.
Early stage of critical clusters growth in phenomenological and molecular dynamics simulation models
Romuald Puzyrewski Jaros&#x;aw Rybicki Micha&#x; Bia&#x;oskrski 《Atmospheric Research》2006,82(3-4):465
The growth of critical clusters is discussed in the paper according to the classical and molecular dynamics (MD) approaches. A new formula for molecule numbers in critical clusters has been derived within the framework of the classical approach. A set of equations controlling the early stage of growth in a neighborhood of a critical size is presented. As far as molecular dynamics simulation is concerned, a computational technique based on the DL_POLY code is described in brief. Computation results are presented concerning cluster formation of H2O vapor, distribution of clusters versus time, cluster growth and radial density distribution of isolated clusters. A comparison with the classical results is made for a case of dense vapor, where the mechanism of strong condensation is predominant. The Hertz–Knudsen formula seems to be verified by the molecular dynamics results. 相似文献
3.
Maurizio Bucca Martin Dietzel Jianwu Tang Albrecht Leis Stephan Jürgen Khler 《Chemical Geology》2009,266(3-4):152-165
Otavite, witherite, calcite, strontianite, hydrozincite and hydrocerussite nucleation was induced by CO2 diffusion through a polyethylene membrane into a metal bearing solution. Nucleation and ongoing precipitation was followed at 25 ± 1 °C by the chemical evolution of the solution and the consumption of sodium hydroxide (pH-stat conditions). X-ray diffraction patterns as well as FT-infrared and Raman spectra confirmed the formation of well crystallized solids, except for less crystalline hydrozincite. In several experiments simonkolleite and laurionite precipitated concurrently with hydrozincite and hydrocerussite. The carbonate end-member minerals, smithsonite and cerussite, however were not formed. Carbonate minerals crystallized as spherical aggregates of thin layered otavite, spherical orientated witherite needles, rhombohedral calcite, pseudo-hexagonal strontianite laths, fibrous lumps of hydrozincite and planar hexagonal hydrocerussite crystals. Crystal and aggregate sizes range between 1 and 100 μm. Nucleation occurred at well defined reaction times and distinct critical supersaturation indices (SIcrit). The time for nucleation at constant pH decreased as the initial metal concentration increased for a given solid. The SIcrit values decreased in the order of hydrocerussite (3.2), otavite (2.5), strontianite (1.6), witherite (0.9) and calcite (0.7). 相似文献
4.
Toshikazu Ebisuzaki Hiroko Miyahara Ryuho Kataoka Tatsuhiko Sato Yasuhiro Ishimine 《Gondwana Research》2011,19(4):1054-1061
Volcanoes with silica-rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment. We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%. This relationship is not observed for eruptions from volcanoes with relatively silica-poor magma, such as Izu-Ohshima. It is well known that the cosmic-ray flux is negatively correlated with solar magnetic activity, as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system. The strong negative correlation observed between the timing of silica-rich eruptions and solar activity can be explained by variations in cosmic-ray flux arising from solar modulation. Because silica-rich magma has relatively high surface tension (~ 0.1 Nm?1), the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution, even when located relatively close to the surface, within the penetration range of cosmic-ray muons (1–10 GeV). These muons can contribute to nucleation in supersaturated magma, as documented by many authors studying a bubble chamber, via ionization loss. This radiation-induced nucleation can lead to the pre-eruptive exsolution of H2O in the silica-rich magma. We note the possibility that the 1991 Mt. Pinatubo eruption was triggered by the same mechanism: an increase in cosmic-ray flux triggered by Typhoon Yunya, as a decrease in atmospheric pressure results in an increase in cosmic-ray flux. We also speculate that the snowball Earth event was triggered by successive large-scale volcanic eruptions triggered by increased cosmic-ray flux due to nearby supernova explosions. 相似文献
5.
冰晶核化对雷暴云微物理过程和起电影响的数值模拟研究 总被引：2，自引：0，他引：2
本文在已有的二维对流云模式中采用了一种与气溶胶有关的冰晶核化方案替代原有的冰晶核化经验公式, 并选取个例, 分别就两种方案进行了模拟对比试验。模拟结果表明:(1)新方案所得冰晶比含水量主要分布在-0.1~-7.6℃温区之间, 高于原方案所得的-50.1~-24.2℃温区;在整个雷暴云的发展过程中新方案冰晶的分布高度、温度区间以及最大浓度值均大于原方案。(2)在新方案中, 温度相对较高的过冷区产生大量冰晶, 其争食云中水汽抑制了云滴、雨滴的增长。此外, 与原方案相比, 霰增长受雨滴大幅减小的影响进一步得到限制, 导致生成的霰小于原方案, 且空间分布具有较大区别。(3)两方案在雷暴云初期形成的电荷结构不同;在发展旺盛与消散阶段新方案中电荷空间分布区域和电荷量均大于原方案, 此外, 在不同时刻主正电荷区和主负电荷区的中心高度存在差异。本文对云微物理过程及起电的分析为后继探讨气溶胶与雷暴云起放电过程、电荷结构之间的相互关系提供了有利条件。 相似文献
6.
Development of crystallographic preferred orientations by nucleation and growth of new grains in experimentally deformed quartz single crystals 总被引：1，自引：1，他引：0
Deformation experiments have been carried out to investigate the effect of dynamic recrystallisation on crystallographic preferred orientation (CPO) development. Cylindrical samples of natural single crystals of quartz were axially deformed together with 1 vol.% of added water and 20 mg of Mn2O3 powder in a Griggs solid medium deformation apparatus in different crystallographic orientations with compression direction: (i) parallel to <c>, (ii) at 45° to <c> and 45° to <a> and (iii) parallel to <a>. The experiments were performed at a temperature of 800 °C, a confining pressure of 1.2 GPa, a strain rate of 10− 6 s− 1, to bulk finite strains of 14–36%. The deformed samples were analysed in detail using optical microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Two different microstructural domains were distinguished in the deformed samples: (i) domains with undulatory extinction and deformation lamellae, and (ii) domains with new recrystallised grains. Within the domains of undulatory extinction, crystal-plastic deformation caused gradual rotations of the crystal lattice up to 30° away from the host orientation. New recrystallised grains show a strong CPO with c-axis maxima at 45° to the compression direction. This is the case in all experiments, irrespective of the initial crystallographic orientation. The results show that c-axes are not continuously rotated towards the new maxima. The new grains thus developed through a mechanism different from subgrain rotation recrystallisation. New grains have a subeuhedral shape and numerous microcavities, voids, fluid channels and fluid inclusions at their grain boundaries. No host control is recorded in misorientation axes across their large angle grain boundaries. New grains might have been created by nucleation from solution in the μm-scale voids and microfractures. The CPO most likely developed due to preferred growth of the freshly precipitated grains with orientations suitable for intracrystalline deformation at the imposed experimental conditions. 相似文献
7.
This paper summarises the development and principal results of fifty years of research on aerosols in the marine atmosphere at Mace Head Atmospheric Research Station on the west coast of Ireland. It concentrates on the sources, physico-chemical properties, number and mass concentrations, size range, volatility and chemical composition of aerosols in different air masses. It also examines optical properties of the aerosols and their long-range transport. 相似文献
8.
The kinetics of crystallization of strontium carbonate (strontianite) from strontium bicarbonate solutions were examined. CO2 was stripped from a slightly acidic solution of Sr(HCO3)2 by stirring resulting in critical supersaturation and precipitation of strontianite. The reduction of the Sr2+ concentration was recorded as a function of time by measuring the electrolytic conductivity and the pH value.
Homogeneous primary nucleation is dominant at high supersaturations, whereas heterogeneous primary nucleation prevails at low supersaturations. The crystal growth rate increases with increasing supersaturation. This effect is less pronounced at higher supersaturations. The growth rate is mostly transport-controlled at high supersaturation. At lower supersaturation the crystal growth is mainly determined by integration of ions into the crystal lattice. These results may be used to explain the deposition of strontianite in natural systems. 相似文献
9.
Ions can speed up the formation of aerosol particles. The former studies have mainly concerned on the role of the ion charge itself. We have studied the possible (additional) role of the actual small air ion spectrum shape, and the quantitative role of ion–ion recombination pathway. By means of our ion evolution model, formation of new species (H2SO4)n(NH3)m(HNO3)k via ion–ion recombination was investigated. The model shows how the generation rate of the new species depends on the concentrations of H2SO4 and NH3, and how it depends on the tropospheric background aerosol situation. The rate can be up to a few new neutral complexes per cubic centimeter and per second. New particle generation via ion–ion recombination provides an extra channel, especially for the clean atmosphere. Former results have shown that such situations are often present in Antarctica. Our aerosol spectrum measurements reveal a number of similar non-Antarctic results. Sometimes, such situations are followed by aerosol bursts, which may be (partly) due to an ion–ion recombination channel. 相似文献
10.
三维冰雹云催化数值模式 总被引：89，自引：10，他引：79
为了研究冰雹形成机制、催化防雹机制和通过数值试验获得冰雹云优化催化技术,在以前工作的基础上,发展了一个３维弹性冰雹云催化数值模式。模式考虑了冰雹云中详细的微物理过程,各种粒子采用双变参数谱,将云中水物质分成水汽、云水、雨水、冰晶、雪、霰、冻滴和雹８类,可以预报粒子的比浓度和比含量,尤其可以计算以霰或冻滴为胚胎的雹块的数量,非常适合研究冰雹的形成机制。此外,建立了催化剂ＡｇＩ的守恒方程,考虑了人工冰核的凝华核化及与云、雨滴接触的冻结核化过程,并用地面降雹动能通量检验催化防雹效果,因此,也可以研究催化防雹机制和对雹云的催化技术。 相似文献