新疆吐鲁番桃树园二叠-三叠系古地磁初步研究

通过对吐鲁番桃树园二叠—三叠系古地磁特征初步研究,建立了二叠—三叠系界线磁性层柱,将其界线置于锅底坑组中下部,即37—36层(采点66～65).对二叠、三叠系古地磁研究表明,其古纬度为北纬26°～35°,属热带—北温带古气候环境,与古生物资料和沉积相相一致,推断古生物灭绝与新生,可能与地磁的转化密切相关。     

Numerical modelling of flow structures over idealized transverse aeolian dunes of varying geometry

A Computational Fluid Dynamics (CFD) model (PHOENICS™ 3.5) previously validated for wind tunnel measurements is used to simulate the streamwise and vertical velocity flow fields over idealized transverse dunes of varying height (h) and stoss slope basal length (L). The model accurately reproduced patterns of: flow deceleration at the dune toe; stoss flow acceleration; vertical lift in the crest region; lee-side flow separation, re-attachment and reversal; and flow recovery distance. Results indicate that the flow field over transverse dunes is particularly sensitive to changes in dune height, with an increase in height resulting in flow deceleration at the toe, streamwise acceleration and vertical lift at the crest, and an increase in the extent of, and strength of reversed flows within, the lee-side separation cell. In general, the length of the separation zone varied from 3 to 15 h from the crest and increased over taller, steeper dunes. Similarly, the flow recovery distance ranged from 45 to >75 h and was more sensitive to changes in dune height. For the range of dune shapes investigated in this study, the differing effects of height and stoss slope length raise questions regarding the applicability of dune aspect ratio as a parameter for explaining airflow over transverse dunes. Evidence is also provided to support existing research on: streamline curvature and the maintenance of sand transport in the toe region; vertical lift in the crest region and its effect on grainfall delivery; relations between the turbulent shear layer and downward forcing of flow re-attachment; and extended flow recovery distances beyond the separation cell. Field validation is required to test these findings in natural settings. Future applications of the model will characterize turbulence and shear stress fields, examine the effects of more complex isolated dune forms and investigate flow over multiple dunes.     

The assemblage diaspore+quartz in metamorphic rocks: a petrological, experimental and thermodynamic study

The upper pressure limit of pyrophyllite is given by the equilibria (i) pyrophyllite=diaspore+quartz and (ii) pyrophyllite=diaspore+coesite. High- P experimental investigations carried out to locate equilibrium (i) yield brackets between 497 °C/24.8  kbar and 535 °C/25.1  kbar, and between 500 °C/23  kbar and 540 °C/23  kbar. Equilibrium (ii) was bracketed at 550 °C between 26.0 and 28.3  kbar. In the experimental P–T  range, equilibria (i) and (ii) are metastable with respect to kyanite. A stable P–T  grid is calculated using thermodynamic data derived under consideration of the present experimental results. According to these data, the lower pressure limit of the assemblage diaspore+quartz according to equilibrium (i) range from about 12  kbar/300 °C to 20  kbar/430 °C (in the presence of pure water). The upper stability of diaspore+quartz is limited by the reaction diaspore+quartz=kyanite+H₂O at about 450 °C (nearly independent of pressure) and, to higher pressure, by the quartz=coesite transition. Equilibrium (ii) is metastable over the whole P–T  range.
Natural occurrences600.S of the diaspore–quartz assemblage in metamorphic rocks in Sulawesi, New Caledonia, Amorgos and the Vanoise are characterized by minerals indicative of high- P such as ferro-magnesiocarpholite, glaucophane, sodic pyroxene and lawsonite. The metamorphic P–T  conditions of these rocks are estimated to be in the range 300–400 °C, >8  kbar. These data are compatible with the derived P–T  stability field of the diaspore+quartz assemblage. We conclude that, in metamorphic rocks, diaspore+quartz is, as ferrocarpholite, an indicator for unusual low- T  /very high- P settings.     

地形影响的飞机颠簸及其数值仿真实验

首先利用中尺度数值模式ARPS模拟气流过山生成飞行数值仿真所需要的风场，然后利用飞机载荷因数变量方程进行飞机飞行的数值仿真试验。研究结果表明，气流过山产生的山脉重力波由于风切变临界层破碎，一方面能在对流层产生较强的湍流引起晴空飞机颠簸，另一方面也能在山脉背风面产生强烈下坡风，背风转子环流及低空湍流，影响飞机的起飞和着陆。揭示了飞机在过山脉地形背风面所产生的大气湍流中飞行时引起飞机颠簸的物理机制，有助于增强飞机颠簸的预测能力和飞行气象保障能力。     

Magnetic field hyperactivity during the early Neoproterozoic: A paleomagnetic and cyclostratigraphic study of the Katav Formation,southern Urals,Russia

We present a detailed magnetostratigraphic and cyclostratigraphic profile through the Riphean (Tonian) Katav Formation in the southern Urals. The study confirms the primary nature of the magnetization in these rocks. The cyclostratigraphic study identified several orbital periods including the 405 ka long eccentricity. This allows us to quantify the reversal frequency in the Katav and our estimates range of 7–12 reversals per million years. Based on our study, we identify an interval of magnetic field reversal hyperactivity in the Neoproterozoic interval. Age estimates for the Katav are contentious and range somewhere between 800 Ma and 900 Ma based on carbonate Pb-Pb ages and stable isotope correlations. The paleomagnetic poles obtained in this study of the Katav (and overlying Inzer) Formation do not fit anywhere on the Baltica apparent polar wander path between 1100 Ma and 900 Ma. Furthermore, they lie 90° away from the 900 Ma segment of the path. We tentatively estimate their age to be closer to 800 Ma and perhaps confirm a previously hypothesized pulse of rapid true polar wander between 825 Ma and 790 Ma.     

Comparing the terrain reversal effect in satellite images and in shaded relief maps: an examination of the effects of color and texture on 3D shape perception from shading

Terrain reversal effect (TRE) causes reversed 3D shape perception in satellite images and shaded relief maps (SRMs), and introduces difficulties in identifying landforms such as valleys and ridges. With this paper, in a controlled laboratory experiment, we compare how well 27 participants could identify valleys and ridges over 33 locations using SRMs, color satellite images and grayscale satellite images. The main depth cue is shadow both in vertical-view images and SRMs. However, the presence of texture and color in images also affect 3D shape perception. All our participants experience the illusion strongly: with the SRMs, it is very severe (2% accuracy), with grayscale images low but considerably better than SRMs (17.6% accuracy), and slightly worse with color imagery (15.3% accuracy). These differences between SRMs and imagery suggest that the participants who are able to bypass the illusion consciously or subconsciously interpret the photographic information. We support this observation further with a cue-strength analysis. Furthermore, we provide exploratory analyses of the effects of expertise, global convexity bias, and bistable perception. Our original empirical observations serve towards a better understanding of this visual illusion, and contribute towards nuanced and appropriate solutions to correcting for TRE differently for satellite images and SRMs.     

企鹅珍珠贝生殖细胞的发生

对不同发育阶段的企鹅珍珠贝[Ptedapenguin(Rding)]的性腺结构、生殖细胞结构与分布进行组织学观察,描述精/卵子发生过程中各级精/卵细胞的特征。结果表明:根据雌性生殖细胞形态和卵黄的变化特点,卵子发生经历卵原细胞、无卵黄初级卵母细胞、卵黄形成期卵母细胞及成熟卵子阶段;依据雄性生殖细胞大小和细胞核形态变化,精子发生经历精原细胞、初级精母细胞、次级精母细胞、精子细胞和精子阶段,其中精原细胞存在形态上有差异的A型和B型两种类型。此外还观察到企鹅珍珠贝的性别转化现象。     

陀螺经纬仪定向系统误差研究

通过对不同观测者用逆转点法进行的陀螺经纬仪定向实验数据分析,确认不同观测者在用逆转点法进行陀螺经纬仪定向时存在着显著的系统误差,而且这种系统误差的大小还随所使用的仪器不同而不同。研究结果对制定陀螺经纬仪定向操作程序和提高定向精度有一定的指导意义。     

Dynamic instability of clays: an energy approach

The dynamic instability of any soil is based on the ability to accumulate from cycle to cycle a part of the energy to be dissipated. Using the general thermodynamic approach in combination with high resolution experiments it is possible to analyze the transformations of energy in soil under dynamic loading. Undisturbed specimens of two Norwegian clays, sufficiently different in their engineering properties, were used in a number of undrained cyclic triaxial tests to study the influence of confining stress, coefficient of earth pressure at rest (K₀), dynamic stress amplitude and frequency of loading in the development of instability in the clays. This paper discusses the unit dissipated energy and the unit activation energy as possible energy criteria for evaluation of dynamic instability in soils.     

地球磁极倒转的星地碰撞成因

地球磁场多次发生南北(正负)磁极位置的变换, 即极性倒转, 这已为大家所公认; 但造成这种极性倒转的原因, 则是迄今未能很好解答的一个难题.基于地球磁场的发电机效应理论和星地碰撞的动力效应研究, 探讨了外星撞击地球造成地磁场极性倒转的可能性.研究表明, 当外星沿与地球自转的正逆不同方向撞击地球时引起的地球转速快慢变化, 可导致地球内部核、幔圈层之间的转速相对快慢关系(相对运动方向)发生改变, 从而受其控制的液核涡旋方向及相应的地磁场方向也会随之改变, 于是就形成地磁极性倒转.这是一个新的思路, 它给地磁极性倒转提出了一个简明的动力机制解释.