美国对清洁能源研发的探讨

美国能源部高级研究计划署(the Depart ment of Energy’s Advanced Research Projects Agency-Energy,简称为ARPA-E)在2011年2月28日到3月2日召开了第二届年会.与会人员达2000多人.在会上有许多人发表了重要的讲话,其中有前加州州长A.Schwarzenegger,现任能源部长朱棣文和ARPA-E主任A.Majum-dar等.A.Schwarzenegger州长在会议上说,根据我的经验,新能源的研发不仅能使美国在国际上保持一定的竞争力,而且能使美国的经济持续增长并在国内提供充足的就业机会.他还说,加州的政策已经使其人均用     

地幔矿石的超塑性

超塑性是指某些材料在加热时可将自身的长度拉伸几倍左右.在地球地幔中的矿石一般是不能忍受这样的拉伸长度,但最近日本Tokyo大学的Takebiko Hiraga教授和日本国家新材料研究所的Hidehiro Yoshida教授所领导的研究组已找到了直接的证据,证明地幔矿石都应是超塑性的.它们的特性与其他真实的或预期的可塑性     

地幔矿石的超塑性

超塑性是指某些材料在加热时可将自身的长度拉伸几倍左右.在地球地幔中的矿石一般是不能忍受这样的拉伸长度,但最近日本Tokyo大学的Takebiko Hiraga教授和日本国家新材料研究所的Hidehiro Yoshida教授所领导的研究组已找到了直接的证据,证明地幔矿石都应是超塑性的.它们的特性与其他真实的或预期的可塑性材料一样是一种多晶聚集结     

Grain Growth During Superplastic Deformation

Significant grain growth occurring during superplastic deformation is related to the micro-mechanism of superplastic flow. Observations performed on the deformed surface of superplastically deformed tensile and shear Pb-62%Sn samples and bi-axially formed AA7475 samples directly indicate that cooperative grain boundary sliding, i.e. sliding of grain groups, is accompanied by cooperative grain boundary migration that can result in an enhanced grain growth. Such a long range correlation in migration of sliding grain boundaries is related to movement of grain boundary dislocations having a step associated with its core. Observed correlation between grain size and strain measured in different regions of a superplastically formed Ti-alloy part and alignment of grain boundaries along shear surfaces support coupling of grain boundary sliding and migration. A model of grain growth considering climb of cellular dislocations, topological defects in a grain array, has been expanded to incorporate gliding and mixed cellular dislocations.     

Structure of the mantle discontinuities

Abstract

The results of thermodynamic calculations in the FeO-MgO-SiO₂ (FMS) system show that the elastic properties and density across the 400-km discontinuity might be consistent with a transition zone of isochemical pyrolite composition and do not require chemical stratification. However, phase changes in pyrolite do not explain the 650-km discontinuity.     

Superplastic Deformation of Titanium Alloy with Different Structure and Phase Composition

Russian Physics Journal - The α+β titanium alloy Ti-6Al-4V having different structure and phase composition is investigated in this paper under the tensile deformation in the temperature...     

纳米多晶铜的超塑性变形机理的分子动力学探讨

在聚能装药爆炸压缩形成射流的过程中, 伴随着金属药型罩的晶粒细化, 从原始晶粒30-80 μm细化到亚微米甚至纳米量级, 从微观层面研究其细化机理和动态超塑性变形机理具有很重要的科学意义. 采用分子动力学方法模拟了不同晶粒尺寸下纳米多晶铜的单轴拉伸变形行为, 得到了不同晶粒尺寸下的应力-应变曲线, 同时计算了各应力-应变曲线所对应的平均流变应力. 研究发现平均流变应力最大值出现在晶粒尺寸为14.85 nm时. 通过原子构型显示, 给出了典型的位错运动过程和晶界运动过程, 并分析了在不同晶粒尺寸下纳米多晶铜的塑性变形机理. 研究表明: 当晶粒尺寸大于14.85 nm时, 纳米多晶铜的变形机理以位错运动为主; 当晶粒尺寸小于14.85 nm时, 变形机理以晶界运动为主, 变形机理的改变是纳米多晶铜出现软化现象即反常Hall-Petch关系的根本原因. 通过计算结果分析, 建立了晶粒合并和晶界转动相结合的理想变形机理模型, 为研究射流大变形现象提供微观变形机理参考.     

Electromagnetic exploration of the oceanic mantle

Electromagnetic exploration is a geophysical method for examining the Earth’s interior through observations of natural or artificial electromagnetic field fluctuations. The method has been in practice for more than 70 years, and 40 years ago it was first applied to ocean areas. During the past few decades, there has been noticeable progress in the methods of instrumentation, data acquisition (observation), data processing and inversion. Due to this progress, applications of this method to oceanic regions have revealed electrical features of the oceanic upper mantle down to depths of several hundred kilometers for different geologic and tectonic environments such as areas around mid-oceanic ridges, areas around hot-spot volcanoes, subduction zones, and normal ocean areas between mid-oceanic ridges and subduction zones. All these results estimate the distribution of the electrical conductivity in the oceanic mantle, which is key for understanding the dynamics and evolution of the Earth together with different physical properties obtained through other geophysical methods such as seismological techniques.     

Transient creep in the upper mantle

Summary The rheological properties of the upper mantle are examined on the basis of recent advances in the study of the rheology of partially melted rocks. The presence of a few percent liquid phase in the lowvelocity zone, which is indicated but not required by the geophysical evidence, does not affect the long-term creep properties of the material. Thus, while partial melting in the upper mantle can easily account for a variety of geodynamic processes, it cannot alter the rheology which is in all likelihood non-Newtonian. This conclusion is only apparently at odds with the most commonly accepted interpretation of postglacial isostatic rebound, which is taken to be compatible with a Maxwellian earth with Newtonian viscosity. It is pointed out here that neither the total strain, nor the time since deglaciation are such that the widespread assumption of steady-state rheology is necessarily justified. Under the assumption that transient creep, and not steady-state creep, governs the behaviour of the upper mantle during postglacial rebound, the inferred transient-creep viscosities are shown to be of the expected order of magnitude and to grade into the usually accepted steady-state viscosities at larger strains.

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Riassunto Si esaminano le proprietà reologiche del mantello superiore tenendo conto di recenti sviluppidella reologia di rocce parzialmente fuse. La presenza di una piccola percentuale di fase liquida nella zona a bassa velocità, che è indicata ma non richiesta dalla prova geofisica, non influenza le proprietà di scorrimento a lungo termine del materiale. Così, mentre la parziale fusione nel mantello superiore può facilmente render conto di una varietà di processi geodinamici, essa non può alterare la reologia che è con tutte le probabbilità non newtoniana. Questa conclusione è solo apparentemente in disaccordo con l'interpretazione più comunemente accettata di contraccolpo postglaciale isostatico che è considerato compatibile con una terra maxwelliana con viscosità newtoniana. Si mette qui in evidenza che nè lo sforzo totale, nè il tempo dalla deglaciazione sono tali che l'ipotesi diffusa di reologia di stato stazionario è necessariamente giustificata. Considerando che lo scorrimento transitorio, e non lo scorrimento di stato stazionario, regola il comportamento del mantello superiore durante il contraccolpo postglaciale, si mostra che le viscosità dedotte di scorrimento transitorio sono dell'ordine di grandezza previsto e si distribuiscono nelle viscosità di stato stazionario usualmente accettate per sforzi maggiori.

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Резуме Исследуются реолгические свойства верхней мантии на основе недавних успехов при исследовании реологии частично расплавленных скал. Наличие нескольких процентов жидкой фазы в низкоскоростной зоне, о чем свидетельствуют геофизические данные, не затрагивают продолжительных свойств ползучести материала. Хотя частичное плавление в верхней мантии может легко объяснить многообразие геодинамических процессов, оно не может изменить реологию, которая, вероятно, является неньютоновской. Этот вывод является очевидным при сопоставлении с обычно принятой интерпретацией послеледникового изостатического отскока, который является совместимым с максвелловской землей с ньютоновской вязкостью. В работе отмечается, что ни полная деформация, ни время с момента исчезновения ледникового покрова не являются такими, что широко распространенное предположение об стационарной реологии безусловно оправдывается. В предположении, что переходная ползучесть, а на стационарная ползучесть, определяет поведение верхней мантии в течение послеледникового периода, показывается, что вязкости при переходной ползучести имеют ожидаемый порядок магнитуды и переходят в обычные стационарные вязкости при больших деформациях.

     

The Influence of Structure and Phase Composition of Titanium Alloy on Superplastic Deformation

Russian Physics Journal - The paper presents research into the behavior of high-temperature plastic deformation of titanium alloy Ti–4.74 wt.% Al–5.57 wt.% Mo–5.04 wt.% V alloy...     

Ilmenite: mantle reservoir for nitrogen?

Five ilmenite megacrysts from the Premier kimberlite pipe have been analysed by Mössbauer spectroscopic and electron microprobe techniques for their Fe³⁺/Fe²⁺ ratio; and by nuclear bombardment techniques for their N₂ content. Comparison of the Fe³⁺/Fe²⁺ ratio determined from electron microprobe analysis for total Fe assuming stoichiometry with the direct determination of this ratio by Mössbauer techniques is sufficiently good that the former method which is very widely used may be considered reliable. The N₂ content of the ilmenite samples ranges from 0.5 to 2.0%, considerably in excess of that for most minerals. Heating experiments suggest that the N₂ is not located in liquid inclusions. Isotopic analysis of ilmenite is not available and so its origin is uncertain, but these results suggest that ilmenite could be a major reservoir for N₂ in the earth's mantle.     

Lagrangian avenues of transport in the Earth's mantle

A method of visualizing and characterizing stirring structures of high Rayleigh number geophysical flows whose time dependence is strongly aperiodic is presented. To this end, the system is leaked by defining a smaller region of the flow, so that a particle is considered to be escaped if it enters this region. By means of an ensemble of nonescaped tracers, we are able to characterize stirring and transport processes by visualizing the converging and stretching filamentations (stable and unstable manifolds) in the flow. The method indicates that the present-day Earth's mantle is not well stirred because the time that has passed since the formation of the Earth has not been long enough for the flow of the mantle to generate efficient stirring, and observations reveal indeed the existence of reservoirs of different materials.     

Mineralogical analysis of a weathering mantle derived from tuffite

Mössbauer spectra are presented at 15 and 298 K for magnetically-separated extracts of magnetic soils from a tuffite-derived weathering mantle from Minas Gerais, Brazil. The principal iron-bearing mineral is maghemite in which the degree of Ti or Mg substitution is found to vary with depth. The Mg-maghemite, with lattice parametera ₀=0.838 nm, is a new natural mineral. It is associated with anatase in the magnetic-separates.On leave of absence from Departamento de Química, UFV, 36570-000 ViÇosa (MG), Brazil.