网络地图服务传输机制的研究

就目前网络地图服务过程中所涉及的信息传输机制问题进行了研究.传统的地图传输模式主要偏向于信息的表达和获取之间的关系,特别是地图符号化以及使用者对地图表达的认识能力.在此基础上,提出网络地图服务传输的基本框架,探讨了网络地图服务传输的新模式.认为它们必须经过服务请求和服务响应两个过程,以及需求信息到数据描述语言的转换、需求描述到服务描述的转换、数据描述语言到地图数据提供的转换等3种信息转换.     

西北太平洋冷海温对东亚初夏大气环流影响的数值研究

利用改进的NCAR CCM3气候模式, 研究了1992年西北太平洋持续冷海温对东亚初夏季节大气环流的影响。西北太平洋冷海温不利于初夏东亚南支西风急流季节性北移, 引起亚洲东部沿海低槽明显加深, 东亚大槽平均高度场降低了4.66 dagpm, 从而也不利于西太平洋副热带高压的西伸加强。西北太平洋冷海温还不利于我国大陆初夏温度场回升, 特别是引起我国东北地区近地面温度下降2~5 ℃, 是影响东北冷夏现象的重要原因之一。模拟结果表明, 1992年初夏江淮入梅期较常年偏晚, 降水异常偏少, 与紧邻东亚大陆的西北太平洋持续冷海温有关。     

赤道东经90°海岭3.5Ma以来远洋记录反映的重大环境事件

通过对东经90°海岭ODP758钻孔岩心3.5Ma以来的浮游有孔虫远洋记录的研究,结合岩性地层、稳定同位素地层、碳酸盐地层等资料,探讨了喜马拉雅山加速隆升、"中更新世气候转型"、"中布容溶解"事件等重大构造、环境事件在研究区的表现及相关机制。通过对各项指标的分析和对比,根据ODP758岩心的有孔虫组合面貌、古温度、古盐度和古温跃层的变化情况,推断研究区在1.4～0.7Ma期间的气候变化可能是在"中更新世气候转型"条件下发生的。碳酸钙、碳酸钙沉积通量和非碳酸钙沉积通量曲线在1.7Ma时快速增长,与现有资料显示的青藏高原的隆升历史相符,分别与青藏高原隆升过程中的青藏运动A幕、B幕、C幕(1.7Ma)和昆仑-黄河运动(1.2～0.6Ma)相当。碳酸钙含量、大于150μm的粗组分含量、浮游有孔虫沉积通量和浮游有孔虫生物地层揭示出在0.5～0.4Ma期间研究区深海碳酸盐遭受了强烈溶解。此事件与大西洋、太平洋、印度洋及南沙海区沉积记录中的"中布容溶解"事件一致。     

CLIMATE ENVELOPES OF MIRE COMPLEX TYPES IN FENNOSCANDIA

Peatlands are characteristic features of the Fennoscandian landscape, about one‐quarter of the land surface being classified as peatland. The aim of this work was to determine the extent to which the distribution of four main mire complex types (aapa mire, blanket bog, palsa mire, raised bog) can be modelled on the basis of climatological parameters. Additionally, the relative importance of different climatological variables in influencing the distribution of different mire complex types was scrutinized using the variation partitioning method. Variation partitioning is a novel statistical approach that provides deeper understanding of the importance of different explanatory variable groups for geographical patterns than traditional regression methods. The variation in the distribution of mire complex types was decomposed into independent and joint effects of temperature, precipitation and spatial variables. The distributional limits of aapa mires, palsa mires and raised bogs were primarily associated with thermal factors, whereas moisture regime also played an obvious role for blanket bogs. A considerable amount of variation in the distribution of mire complex types was accounted for by the joint effects of explanatory variables and may thus be causally related to two or all three groups of variables. Although the present distribution of mire complex types corresponded well to the contemporary climate in Fennoscandia, our results indicate that the climate envelopes of palsa mires are narrow. Thus, they can be expected to be extremely sensitive to changes in future climatic conditions.     

Modelling of short-interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable–stable transition regime

Recent high-resolution observations of crustal movements have revealed silent slip events (SSEs) with propagation velocities of around 10–15 km d⁻¹ and with intervals of 3–14 months along the deeper parts of the Cascadia and Nankai subduction zones. This study develops 2-D and 3-D models of these short-interval SSEs considering the frictional behaviour that was confirmed experimentally by Shimamoto for the unstable–stable transition regime. To represent this frictional behaviour, a small cut-off velocity to an evolution effect is introduced in a rate- and state-dependent friction law. When the cut-off velocity to the evolution effect is significantly smaller than that to a direct effect, steady-state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities. At the deeper Cascadia and Nankai subduction interfaces, the pore pressure is inferred to be high because of the dehydration of materials in the descending plate. Under conditions where the pore-fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small, short-interval SSEs with propagation velocities and slip velocities of 4–8 km d⁻¹ and  2 − 4 × 10⁻⁷  m s⁻¹, respectively, can be reproduced. The propagation velocity of short-interval SSEs is in proportion to the slip velocity. The results also show that during the nucleation process of large earthquakes, the occurrence of short-interval SSEs becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone. Our results suggest that monitoring of short-interval SSEs might be useful for forecasting the main earthquakes.     

BaCO<Subscript>3</Subscript>: high-temperature crystal structures and the <Emphasis Type="Italic">Pmcn</Emphasis>→<Emphasis Type="Italic">R</Emphasis>3<Emphasis Type="Italic">m</Emphasis> phase transition at 811°C

The temperature (T) evolution of the barium carbonate (BaCO₃) structure was studied using Rietveld structure refinements based on synchrotron X-ray diffraction and a powdered synthetic sample. BaCO₃ transforms from an orthorhombic, Pmcn, α phase to a trigonal, R3m, β phase at 811°C. The orthorhombic BaCO₃ structure is isotypic with aragonite, CaCO₃. In trigonal R3m BaCO₃, the CO₃ group occupies one orientation and shows no rotational disorder. The average <Ba–O> distances increase while the <C–O> distances decrease linearly with T in the orthorhombic phase. After the 811°C phase transition, the <Ba–O> distances increase while C–O distances decrease. There is also a significant volume change of 2.8% at the phase transition.     

Topography of the mantle discontinuities beneath the South Pacific superswell as inferred from broadband waveforms on seafloor

We analyzed seismic waveforms recorded by the broadband ocean bottom seismographs deployed in the South Pacific superswell to determine the depths of the mantle discontinuities using a receiver function method. We estimated the thickness of the mantle transition zone (MTZ) to be 245 km on average beneath the superswell region, which is close to the global average. The MTZ is found to be thinned locally beneath the Society hot spot by 30 km. Temperature anomalies computed from the thinned transition zone and the Clapeyron slope of the olivine phase transformations are 150–200 K beneath the Society hot spot. Previous studies, using land-based data, suggested the presence of a hot MTZ beneath the Pitcairn hot spot. The locally hot transition zone beneath the hot spots is attributed to narrow mantle plumes probably rising from the lower mantle. The normal average thickness obtained from the present study indicates that there is no broad upwelling across the transition zone beneath the entire superswell region at present.     

Micro-and submicrostructural evidence for high-temperature brittle-ductile transition deformation of hornblende: Case study of high-grade mylonites from Diancangshan, western Yunnan

OM (optical microscope)/TEM (transmission electron microscope) micro- and submicrostructural analysis of hornblende rocks sheared at high temperatures from the Diancangshan area, western Yunnan reveals evidence for deformation in the brittle-ductile transition of hornblende at middle crustal level (about 637℃ and 0.653 GPa) and mechanisms of deformation in the transitional regime are further discussed. Sheared hornblende rocks at middle crustal level have typical mylonitic microstructures, shown by coarse porphyroclasts and fine matrix grains. Different mineral phases in the rocks show distinct deformation characteristics. Hornblende and feldspar grains are intensely deformed with ob- vious grainsize reduction, but quartz grains are recrystallized dominantly by grain growth. Hornblende grains show typical brittle-ductile transition nature. Initial crystallographic orientations of porphyro- clasts have strong effects on the behavior of grains during deformation. There are mainly two types of porphyroclasts, type I "hard" porphyroclasts and type II "soft" porphyroclasts, with [001] perpendicular and parallel to external shear stresses respectively. "Hard" porphyroclasts generally occur as compe- tent grains that are rarely deformed or sometimes deformed by fracturing and dislocation tangling. "Soft" porphyroclasts are highly deformed primarily by dislocation tangling (as shown in the cores of the porphyroclasts), but twinning, dislocation glide and climb probably due to hydrolytic weakening also contribute to dynamic recrystallization of the porphyroclasts into fine grains in the matrix. The micro- and submicrostructures of the two types of porphyroclasts and fine-grained matrix provide powerful evidence for the behavior of brittle-ductile transition of hornblende grains. It is concluded that twinning nucleation is one of the most important processes that operate during dynamic recrystalliza- tion of hornblende crystals at the brittle-ductile transition. (100) [001] twin gliding and dislocation creep (dislocation glide and climb) are mutually enhanced during twinning nucleation. As a newly discovered mechanism of dynamic recrystallization, it may have played more important roles than ever recognized during dynamic recrystallization of crystals with twins in the brittle-ductile transition.     

Earthquake source nucleation as self organization process

The theory of an earthquake source nucleation is discussed. Based on the assumption that self organization of damage process takes place in the zone of an earthquake source nucleation the theory incorporates the damage rheology framework of Lyakhovsky et al. and the approach of phenomenology theory of second-order phase transition. Namely, the free energy governing the process of an earthquake source nucleation depends on two collective variables α and φ in addition to the strain tensor ε_ij. The variable α quantifies the fracture of the medium and the variable φ quantifies the interaction effect of cracks. The region Ω_S is associated with a potential source of an earthquake if the damage variable α exceeds the critical value α_cr⁽¹⁾ inside Ω_S. The important feature of a potential source is that interaction of fractures causes acceleration of damage process inside the region of potential source and the material should lose stability primarily in this region. Interaction of fractures results also in occurrence of a residual stress caused by nonuniformity of fracture density. The appearance and development of the potential source result in increase of intensity of damage process not only in the region of potential source but also in a certain neighborhood of the last. It is compatible with such observed effects as acceleration of seismic energy release and growth of correlation length of weak seismicity before large earthquake. Transition of potential source to the stage of avalanche-unstable fracturing is associated with instability generated by explosive increase of interaction of fractures when the damage variable α exceeds the second critical value α_cr⁽²⁾ inside Ω_S.     

Laboratory measurements of the <Superscript>12</Superscript>C/<Superscript>13</Superscript>C kinetic isotope effects in the gas-phase reactions of unsaturated hydrocarbons with Cl atoms at 298 ± 3 K

The carbon kinetic isotope effects (KIEs) in the reactions of several unsaturated hydrocarbons with chlorine atoms were measured at room temperature and ambient pressure using gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). All measured KIEs, defined as the ratio of the rate constants for the unlabeled and labeled hydrocarbon reaction k ₁₂/k ₁₃, are greater than unity or normal KIEs. The KIEs, reported in per mil according to ^Cl ɛ = (k ₁₂/k ₁₃−1) × 1000‰ with the number of experimental determinations in parenthesis, are as follows: ethene, 5.65 ± 0.34 (1); propene, 5.56 ± 0.18 (2); 1-butene, 5.93 ± 1.16 (1); 1-pentene, 4.86 ± 0.63 (1); cyclopentene, 3.75 ± 0.14 (1); toluene, 2.89 ± 0.31 (2); ethylbenzene, 2.17 ± 0.17 (2); o-xylene, 1.85 ± 0.54 (2). To our knowledge, these are the first reported KIE measurements for reactions of unsaturated NMHC with Cl atoms. Relative rate constants were determined concurrently to the KIE measurements. For the reactions of cyclopentene and ethylbenzene with Cl atoms, no rate constant has been reported in refereed literature. Our measured rate constants are: cyclopentene (7.32 ± 0.88) relative to propene (2.68 ± 0.32); ethylbenzene (1.15 ± 0.04) relative to o-xylene (1.35 ± 0.21), all × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The KIEs in reactions of aromatic hydrocarbons with Cl atoms are similar to previously reported KIEs in Cl-reactions of alkanes with the same numbers of carbon atoms. Unlike the KIEs for previously studied gas-phase hydrocarbon reactions, the KIEs for alkene–Cl reactions do not exhibit a simple inverse dependence on carbon number. This can be explained by competing contributions of normal and inverse isotope effects of individual steps in the reaction mechanism. Implications for the symmetries of the transition state structures in these reactions and the potential relevance of Cl-atom reactions on stable carbon isotope ratios of atmospheric NMHC are discussed.