Seismic data from man-made impacts on the moon

Unusually long reverberations were recorded from two lunar impacts by a seismic station installed on the lunar surface by the Apollo 12 astronauts. Seismic data from these impacts suggest that the lunar mare in the region of the Apollo 12 landing site consists of material with very low seismic velocities near the surface, with velocity increasing with depth to 5 to 6 kilometers per second (for compressional waves) at a depth of 20 kilometers. Absorption of seismic waves in this structure is extremely low relative to typical continental crustal materials on earth. It is unlikely that a major boundary similar to the crustmantle interface on earth exists in the outer 20 kilometers of the moon. A combination of dispersion and scattering of surface waves probably explains the lunar seismic reverberation. Scattering of these waves implies the presence of heterogeneity within the outer zone of the mare on a scale of from several hundred meters (or less) to several kilometers. Seismic signals from 160 events of natural origin have been recorded during the first 7 months of operation of the Apollo 12 seismic station. At least 26 of the natural events are small moonquakes. Many of the natural events are thought to be meteoroid impacts.     

First-principles determination of elastic anisotropy and wave velocities of MgO at lower mantle conditions

The individual elastic constants of magnesium oxide (MgO) have been determined throughout Earth's lower mantle (LM) pressure-temperature regime with density functional perturbation theory. It is shown that temperature effects on seismic observables (density, velocities, and anisotropy) are monotonically suppressed with increasing pressure. Therefore, at realistic LM conditions, the isotropic wave velocities of MgO remain comparable to seismic velocities, as previously noticed in athermal high-pressure calculations. Also, the predicted strong pressure-induced anisotropy is preserved toward the bottom of the LM, so lattice-preferred orientations in MgO may contribute substantially to the observed seismic anisotropy in the D" layer.     

棉花吸收稀土元素的动态研究

以鲁棉６号及棕壤、褐土、潮土和砂姜黑土为试验材料，进行棉花自然吸收稀土的动态研究。结果表明，在棉花生长发育的早中期，叶中的稀土含量和吸收量均高于茎和根。在成熟期根中的稀土含量和吸收量均达最高值。叶和茎的稀土含量在不同的生育期中变化较平缓，而根的稀上含量变幅较大，呈前高中低后又高的变化趋势。稀土在棉花发育的花龄期有较强的活力，提示我们施用稀土应在生长的早期。土壤的稀土含量状况和其他农化性状也影响着棉花对稀土的吸收。与棉花叶片稀土含量的临界值相比较，４种土壤均需要施用稀土元素肥料。     

Post-perovskite phase transition in MgSiO3

In situ x-ray diffraction measurements of MgSiO3 were performed at high pressure and temperature similar to the conditions at Earth's core-mantle boundary. Results demonstrate that MgSiO3 perovskite transforms to a new high-pressure form with stacked SiO6-octahedral sheet structure above 125 gigapascals and 2500 kelvin (2700-kilometer depth near the base of the mantle) with an increase in density of 1.0 to 1.2%. The origin of the D" seismic discontinuity may be attributed to this post-perovskite phase transition. The new phase may have large elastic anisotropy and develop preferred orientation with platy crystal shape in the shear flow that can cause strong seismic anisotropy below the D" discontinuity.     

Seismic determination of elastic anisotropy and mantle flow

When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.     

土的弹性抗力与墩顶固结结构物的联合计算

将土、基础及上部结构物视为一个整体，在计入土的弹性抗力后对多跨无铰拱和连续刚构的上下部结构进行联合计算，并给出了算例，可供设计参考。     

"数字地球"与"数字农业"

“数字地球”就是信息化的地球，它包括全部地球资料的数字化、网络化、智能化和可视化的过程在内。数字地球的核心思想是用数字化手段整体性地解决地球问题并最大限度地利用信息资源。“数字农业”是实施“数字地球”战略的重要组成部分。本文分别论述了“数字地球”、“数字农业”的源起、概念、内涵、特点及中国的发展战略。     

福建省武夷山地区土壤与武夷岩茶中稀土元素的研究

通过福建省武夷山地区的茶园土壤样品与及生长的茶叶样品的采集,采用ICP-MS对茶叶与土壤样品进行16种稀土元素含量的分析,对茶叶与土壤稀土元素进行统计分析,结果表明:武夷山地区武夷岩茶对土壤中的稀土元素Ce、La有富集作用,与茶叶稀土含量具有正相关性,而茶叶对土壤稀土元素Sc的吸收率为0.5%～5.0%,与Ce、La的吸收率相比较,处于低水平的吸收富集。     

Long-Period Seismic Waves from Nuclear Explosions in Various Environments

Large nuclear explosions in the solid earth, the hydrosphere, and the lower and upper atmosphere have generated seismic waves of periods greater than about 5 seconds which have been detected at great distances from the source.     

Velocity structure of a gas hydrate reflector

Seismic reflection profiles across many continental margins have imaged bottom-simulating reflectors (BSRs) parallel to the seabed; these are often interpreted as the base of a zone in which methane hydrate "ice" is stable. Waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a BSR and its thickness. A test of this method at a drill site of the Ocean Drilling Program predicts that sediment pores beneath the BSR contain free methane for approximately 30 meters. The hydrate and underlying gas represent a large global reservoir of methane, which may have economic importance and may influence global climate.     

SMA智能控制装置及结构地震反应控制分析

为了获得一种性能优良的结构抗震用控制装置,通过利用SMA(Shape Memory Alloy)弹性模量随温度变化特性,设计了一种新型SMA智能控制装置,并给出了SMA智能控制装置最大输出控制力和等效刚度的计算公式。最后,针对某3层框架结构,分别在未控、主动控制和SMA智能控制3种情况下,进行了地震时程仿真分析。计算结果表明:SMA智能控制装置可以有效降低结构地震反应幅值,控制效果接近主动控制效果,是一种较好的结构抗震用控制装置。     

Elasticity of MgSiO3 in the Perovskite Structure

The single-crystal elastic moduli of MgSiO(3) in the perovskite structure, the high-pressure polymorph of MgSiO(3) pyroxene, have been determined. The data indicate that a mantle with either pyrolite or pyroxene stoichiometry is compatible with the seismic models appropriate to the earth's lower mantle, provided that the shear modulus of MgSiO(3) perovskite exhibits a strong negative temperature derivative. Such a temperature derivative falls outside of the range expected for a well-behaved refractory ceramic and could result if the pressure-temperature regime of the earth's lower mantle is near that required for a ferroelastic phase transformation of the perovskite phase.     

水稻土的研究 Ⅷ.江苏丘陵冲田水稻土的腐殖质和络合态铁

本文对宁镇丘陵十个剖面和里下河圩田二个剖面的腐殖质含量及其组成和络合态铗含量进行了研究。试验结果如下:(1)冲田水稻土耕层腐殖质含量高于旱地黄刚土,低于圩田水稻土,腐殖质积累层厚度随水稻土发育程度而逐渐加深;(2)冲田水稻土腐殖质组成以富里酸占优势,胡敏酸碳/富里酸碳比值高于早地黄刚土,但比圩田水稻土低;(3)冲田水稻土胡敏酸的E_(465)低于圩田水稻土;(4)络合态铁含量在全剖面上的分布与腐殖质含量密切相关。     

High-Pressure Elasticity of Iron and Anisotropy of Earth's Inner Core

A first principles theoretical approach shows that, at the density of the inner core, both hexagonal [hexagonal close-packed (hcp)] and cubic [face-centered-cubic (fcc)] phases of iron are substantially elastically anisotropic. A forward model of the inner core based on the predicted elastic constants and the assumption that the inner core consists of a nearly perfectly aligned aggregate of hcp crystals shows good agreement with seismic travel time anomalies that have been attributed to inner core anisotropy. A cylindrically averaged aggregate of fcc crystals disagrees with the seismic observations.     

Earth Strain Measurements with a Laser Interferometer: An 800-meter Michelson interferometer monitors the earth's strain field on the surface of the ground

The development of the laser as a source of coherent optical radiation has permitted the application of interferometric techniques to the problem of earth strain measurement. By use of this technology, an 800-meter laser strain meter has been developed which operates above the surface of the ground. The instrument has a strain least count of 10(-10), requires no calibration, and has a flat and linear response from zero frequency to 1 megahertz. The linearity and large dynamic range of the laser strain meter offer unprecedented versatility in the recording of seismic strains associated with earthquakes and nuclear blasts. The extremely wide bandwidth opens new areas of the strain spectrum to investigation. A key to the understanding of the state of stress of the earth and the association phenomona of tectonic activity and earthquakes is a knowledge of the spatial distribution of the earth strain. Measurements of secular strain and earth tides indicate that, even at these long periods, surface strain measurements are valid representations of earth strain at depth. The LSM thus provides a means of making crustal strain measurements at points selected for maximum geophysical interest and ultimately allow the mapping of strain field distributions.     

Seismic-wave attenuation associated with crustal faults in the new madrid seismic zone

The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones.     

苎麻对钙素营养的吸收与分配特征

以湘苎三号和多倍体二号为材料，采用土培方法，研究了钙在苎麻植株体内的吸收和分配特征．结果表明：施钙能促进苎麻对钙的吸收；高钙处理时钙的吸收集中于生育中期和后期，低钙和不施钙处理时钙的吸收集中于生育前期和中期；苎麻以叶中钙的含量最高，叶是钙的主要累积部位，叶中钙的分配比例随着生育期的推进而下降．     

The manganese site of the photosynthetic water-splitting enzyme

As the originator of the oxygen in our atmosphere, the photosynthetic water-splitting enzyme of chloroplasts is vital for aerobic life on the earth. It has a manganese cluster at its active site, but it is poorly understood at the molecular level. Polarized synchrotron radiation was used to examine the x-ray absorption of manganese in oriented chloroplasts. The manganese site, in the "resting" (S1) state, is an asymmetric cluster, which probably contains four manganese atoms, with interatomic separations of 2.7 and 3.3 angstroms; the vector formed by the 3.3-angstrom manganese pair is oriented perpendicular to the membrane plane. Comparisons with model compounds suggest that the cluster contains bridging oxide or hydroxide ligands connecting the manganese atoms, perhaps with carboxylate bridges connecting the 3.3-angstrom manganese pair.     

Earth's Viscosity

Seismic methods are now being used to determine not only Earth's elastic properties, but also by how much it departs from a perfectlyelastic body. The seismic anelasticity (Q) varies by several orders of magnitude throughout the mantle, the main feature being an extremely dissipative zone in the upper mantle above 400 kilometers. Recent determinations of viscosity by McConnell show a similar trend. The two sets of data indicate that the ratio of viscosity to Q is roughly a constant, at least in the upper mantle of Earth. On the assumption that this relation is valid for the rest of Earth, viscosities are estimated in regions that are inaccessible for direct measurement. The implied presence of a low-viscosity zone in the upper mantle, overlying a more viscous, less deformable, lower mantle, reconciles viscosites calculated from the shape of Earth and from postglacial uplift. The mismatch of the deformational characteristics at various levels in Earth, coupled with the changing rate of rotation, may be pertinent to the rate of release of seismic energy as a function of depth.