雷达信号的相关分析和谱分析

运动质点的多普勒效应使它们散射的雷达信号呈现为一种随机过程,对这随机过程的统计特性进行分析就能够推断云和降水的微物理或运动学的状况。本文由这种观点讨论了雷达气象的几种测量原理,它能够比较清楚地阐明每种方法的实质,也便于对各种方法的优缺点进行对比。文中还讨论了脉冲波列的谱分析问题,涉及了如何根据雷达测量结果去推断云和降水的微物理或运动学状况的问题。     

A reinterpretation of the entrainment process in some laboratory experiments

Pollard et al. (1973) proposed a closure hypothesis for the entrainment process in the stress-mixed layer of a stratified fluid. Some laboratory experiments suitable for testing the hypothesis were carried out by Kantha et al. (1977) and by Kato and Phillips (1969). In the early period of each experiment, before side-wall friction becomes important, these experiments support the closure hypothesis, with a critical Froude number close to 1, perhaps F = 1.2 ± 0.2.     

Age of the Laschamp paleomagnetic excursion revisited

The reverse paleomagnetism of the lava flows of Laschamp and Olby, already discovered by Bonhommet and Babkine, is confirmed. The ages of these flows, measured by¹⁴C, thermoluminescence and K-Ar dating are respectively36,000 ± 4000 and42,000 ± 5000years. VGP's comparison of the “Laschamp event” with those of the 30,000-year Lake Mungo excursion does not show evidence of coincidence between these two events.     

Cyclic triaxial tests on frozen sand

Strain-controlled cyclic triaxial tests were performed on a one-size silica (Ottawa) sand artificially frozen into 71.1-mm-diameter cylindrical samples. Ice-saturated samples with three different sand contents were tested under the following conditions: axial strains ranging from 3 × 10⁻³ to 3 X 10⁻²%, confining pressures from zero to 1.378 MPa, frequencies of 0.05–5.0 cps and temperatures from −1 to −10 °C.

Test equipment included (1) an MTS electrohydraulic closed-loop testing system which applies the load to the sample, (2) a triaxial cell completely immersed in a low-temperature coolant for temperature control, (3) a refrigeration unit for control of the coolant temperature and constant coolant circulation and (4) measuring devices including an LVDT and load cell, together with recording devices such as a digital multimeter, an oscilloscope, a strip-chart recorder and a minicomputer.

Test results indicate that the dynamic Young's modulus increases with increasing frequency, confining pressure and sand content, but decreases with increasing strain and temperature. The damping ratio decreases with increasing frequency, sand content and lower temperatures. The influence of confining pressures and axial strain on the damping ratio are less explicit for the ranges considered. The experimental results are compared with data from other sources.     

Alteration in CM carbonaceous chondrites inferred from modal and chemical variations in matrix

The modal abundance of matrix in CM chondrites appears to vary from 57–85 vol%. The concentrations of volatile elements that should occur in matrix remain approximately constant despite differences in the proportions of matrix, suggesting that the differing matrix contents may not be real primary variations but are optical effects due to aqueous alteration processes that make other petrologic components unrecognizable. Apparent matrix content can be used as a qualitative measure of the degree of alteration experienced by each CM chondrite. Fe/Si ratios in matrices decrease progressively with increasing alteration due to the formation of new phyllosilicate phases with higher Mg/Fe ratios and optically recognizable opaque minerals that are not counted as matrix. The aqueous alteration process in CM chondrites appears to have been largely isochemical if the bulk meteorites are considered as the reacting systems, although depletion patterns and isotopic anomalies indicate open-system behavior for a few highly mobile components.     

Spheroidal pyroxenite aggregates in the Bushveld Complex — a special case of silicate liquid immiscibility

Spherical aggregates of orthopyroxene are reported from some parts of the Bushveld Complex in a variety of host rocks.Detailed mapping has shown that these spherical aggregates, comprising pyroxenite spheroids in a quartz-norite matrix, are contact phenomena and not stratigraphic markers. Orthopyroxene, biotite and amphibole are enriched in spheroids relative to matrix; their mineral chemistry showing a fairly constant orthopyroxene and plagioclase composition through the spheroids and into the matrix, indicating in-situ formation.Bulk chemistry shows spheroid to matrix tie-lines orthogonal to those generally accepted for silicate liquid immiscibility, but other chemical information is consistent with the occurrence of immiscibility.The formation of the aggregates may be related to the industrial process of spherical agglomeration, by which spheroids are formed by the introduction of an immiscible “bridging liquid” to the melt — probably derived from the floor rocks in this case. The mechanism accounts for the field relationships, petrography and chemistry of the aggregate-matrix system. The petrology of the process equates with a special case of silicate liquid immiscibility induced by local contamination and ageing of the original magma.A similar “bridging liquid” mechanism could also account for the formation of the so-called “boulder bed” beneath the Merensky Reef.     

Laboratory experiments on the effects of crude oil on the Red Sea coral Stylophora pistillata

Sub-lethal detrimental effects of Iranian crude oil were studied on the hermatypic coral Stylophora pistillata in a long term laboratory experiment. The experimental system consisted of four 1500 l. capacity tanks, two of which were periodically polluted. A significant decrease in the number of female gonads per polyp were recorded in 75% of the colonies in the polluted tanks. It is concluded that chronic-oil pollution damages the reproductive system of scleractinian corals.     

Effects of bottom sediments on the survival of Enterobacter aerogenes in seawater

The survival of the coliform bacterium Enterobacter aerogenes in seawater was greatly affected by the underlying bottom sediments. The presence of sediments which contained higher concentrations of organic nutrients than the overlaying seawater prolonged the survival and even enabled growth of the bacterial cells. Results obtained from chemical analysis indicated that sediments of fine-grained, silt-clay type contained highest amounts of organic nutrients as compared with sediments with larger particle sizes such as silt and sand grains. Thus, nutrient contents of the sediments were found to be inversely proportional to sediment particle size. The degree of prolonged survival of E. aerogenes was also found to be inversely proportional to the size of the sediment particles presented. Release of the bound nutrients which became available to cells of E. aerogenes from sediments by action of waves and human activities can explain, at least in part, why high counts of coliform bacteria are obtained in coastal and beach waters.     

Axisymmetric seismic response of a thick circular plate supporting many rods by modal synthesis

Dynamic response of a thick, horizontal, circular plate supporting a large number of slender rods subjected to uniform boundary motion in the vertical direction has been studied by synthesizing component modes of continuous substructures. The excitation considered corresponds to the vertical component of boundary movement produced by earthquake disturbances and the axisymmetric response problem was solved. Mindlin theory was used to formulate the component equations of the plate which is treated as the main component in a modal synthesis technique. The slender rods, which are attached vertically to the plate, are handled as branch components. Vibration modes of a classical thin plate were used as the initial displacement functions for the Mindlin plate. These functions were subsequently modified by a component mode improvement process to obtain plate modes. System modes were generated by combining the improved plate modes with component modes of rods. Numerical results for the natural frequencies and time-history response of the coupled system are compared with those given by a three-dimensional finite element method.