Morphological instabilities in pattern formation by precipitation and crystallization processes

Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.     

Grain size and chemical controls on the ductile properties of mostly frictional faults at low-temperature hydrothermal conditions

A conceptually simple process which establishes a steady grain size distribution is envisioned to control the ductile creep properties of fault zones that mainly slip by frictional processes. Fracture during earthquakes and aseismic frictional creep tend to reduce grain size. However, sufficiently small grains tend to dissolve so that larger grains grow at their expense, a process called Ostwald ripening. A dynamic stedy state is reached where grain size reduction by fracture is balanced by grain growth from Ostwald ripening. The ductile creep mechanism within fault zones in hard rock is probably pressure solution where the rate is limited by diffusion along load-bearing grain-grain contacts. The diffusion paths that limit Ostwald repening are to a considerable extent the same as those for pressure solution. Active Ostwald ripening thus implies conditions suitable for ductile creep. An analytic theory allows estimation of the steady-state mean grain size and the viscosity for creep implied by this dynamic steady state from material properties and from the width, shear traction, and long-term slip velocity of the fault zone. Numerical models were formulated to compute the steady state grain size distribution. The results indicate that ductile creep, as suggested in the companion paper, is a plausible mechanism for transiently increasing fluid pressure within mostly sealed fault zones so that frictional failure occurs at relatively low shear tractions, 10 MPa. The relevant material properties are too poorly known, however, for the steady state theory (or its extension to a fault that slips in infrequent large earthquakes) to have much predictive value without additional laboratory experiments and studies of exhumed faults.     

小麦雨后青枯逼熟中期农业天气的分析及预报

利用北半球５００ｈＰａ候平均高度资料，对小麦雨后青枯逼熟的中期环流特征进行分析，建立小麦雨后青枯逼熟的预报方法，经１９９１－１９９３年应用，效果较好。     

Understanding mafic-felsic magma interactions in a subvolcanic magma chamber using rapakivi feldspar: A case study from the Bathani volcano-sedimentary sequence,eastern India

The Ghansura Rhyolite Dome of the Bathani volcano-sedimentary sequence in eastern India originated from a subvolcanic felsic magma chamber that was intruded by volatile-rich basaltic magma during its evolution leading to the formation of a porphyritic andesite. The porphyritic andesite consists of rapakivi feldspars, which are characterized by phenocrysts of alkali feldspar mantled by plagioclase rims. Results presented in this work suggest that intimate mixing of the mafic and felsic magmas produced a homogeneous hybrid magma of intermediate composition. The mixing of the hot volatile-rich mafic magma with the relatively colder felsic magma halted undercooling in the subvolcanic felsic system and produced a hybrid magma rich in volatiles. Under such conditions, selective crystals in the hybrid magma underwent textural coarsening or Ostwald ripening. Rapid crystallization of anhydrous phases, like feldspars, increased the melt water content in the hybrid magma. Eventually, volatile saturation in the hybrid magma was reached that led to the sudden release of volatiles. The sudden release of volatiles or devolatilization event led to resorption of alkali feldspar phenocrysts and stabilizing plagioclase, some of which precipitated around the resorbed phenocrysts to produce rapakivi feldspars.     

SPATIAL AND TEMPORAL CLIMATOLOGY OF SNOWSTORMS IN THE DEEP SOUTH

Significant snowstorm events occurring during the winters from 1948/49 through 1989/90 are studied using a network of 100 weather stations across the southern states of Mississippi, Alabama, Georgia and South Carolina. To qualify for entry into the snowstorm inventory, at least 10 out of the 100 sites need a minimum of 25 mm (1 inch) of snowfall. A total of 69 events are identified and further categorized into four magnitudes based upon areal coverage or total snowfall amount. The storms are also classified into regional categories based upon the dominant part of the study area affected. The spatial characteristics of the snowstorms are discussed and illustrated with maps showing snowfall distributions for representative storms. Most events impact the northern portions of the study area although some very major storms fit into a Miscellaneous category with unique snowfall distributions in the southern or central parts of the Deep South. The temporal character of snowstorm frequency reveals that a very low number of events occurred during the 1950s with peak occurrence during the 1960s. Snowstorms generally remained more frequent during the 1970s and 1980s compared to the 1950s.     

珠母贝、亲贝人工促熟培育与催产的研究

从23 ~24℃开始,每4~5d升高水温1℃,终至26~27℃,并用亚心形扁藻(Platymonassubcordiformis)、三角褐指藻(Phaeodactylartriconrutum)及辅助饲料投喂培育,促进珠母贝[Pinctadamargaritifera(Linne) ]亲贝性腺发育成熟。用阴干刺激、异性产物刺激及浓扁藻液结合诱导,催产率达100%。     

Experimental investigation of Ostwald-ripening rates of forsterite in the haplobasaltic system

The rate of Ostwald ripening of forsterite is experimentally measured in a haplobasaltic melt (SiO₂–Al₂O₃–CaO–MgO). The goal of the experiments is to determine if the rate of Ostwald ripening is sufficient to affect textural development in crystallizing magmas of a basaltic composition. With preequilibrated charges, experiments were run isothermally so that all textural changes could be ascribed to Ostwald ripening. An increase of crystal size from 3.5 μm to 14 μm (in average) has been observed during 10 days. Glass compositions were identical in all charges, indicating that the observed increase in average crystal size is not the results of chemical disequilibrium but the results of Ostwald ripening. Due to the constraints on experimental duration, the rate-limiting process (i.e., diffusion control or reaction control) could not be determined. Our experimental results, however, demonstrate that the rate of Ostwald ripening in basaltic rocks is sufficient to be of fundamental importance in the development of textures in igneous rocks. These results strongly suggest that Ostwald ripening, as well as nucleation and crystal growth, should be considered in analyses of textures in igneous rocks.     

日本对虾卵巢促熟技术研究

利用卵巢未发育的海捕日本对虾Ｐｅｎａｅｕｓｊａｐｏｎｉｃｕｓ，采用综合措施，进行切除眼柄前、后两个阶段培育，促进卵巢发育和成熟。结果：切除眼柄前分别在ｔ＝１５．０—１８℃和２０．０─２３．０℃经１７ｄ左右的培育，卵巢发育率为６２％—６５％；切除眼柄后在ｔ＝２５．０—２５．５℃经４—５ｄ的培育，亲虾成批成熟和产卵，成熟率为９６％。先后两批共育出了３０２０万尾苗种。