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1.
Determining the thermal conductivity of iron alloys at high pressures and temperatures are essential for understanding the thermal history and dynamics of the Earth''s metallic cores. The authors summarize relevant high-pressure experiments using a diamond-anvil cell and discuss implications of high core conductivity for its thermal and compositional evolution.The thermal conductivity of iron alloys is a key to understanding the mechanism of convection in the Earth''s liquid core and its thermal history. The Earth''s magnetic field is formed by a dynamo action that requires convection in the liquid core. Present-day outer core convection can be driven by the buoyancy of light-element-enriched liquid that is released upon inner core solidification in addition to thermal buoyancy associated with secular cooling. In contrast, before the birth of the inner core, the core heat loss must be more than the heat conducted down the isentropic gradient in order to drive convection by thermal buoyancy alone, which can be a tight constraint upon the core thermal evolution.Recent mineral physics studies throw the traditional value of the Earth''s core thermal conductivity into doubt (Fig. (Fig.1).1). Conventionally the thermal conductivity of the outer core had been considered to be ∼30 W m−1 K−1, an estimate based on shock experiments and simple physical models including the Wiedemann-Franz law: κel = LTρ−1, where κel, L, T and ρ are electronic thermal conductivity, Lorenz number, temperature and electrical resistivity, respectively [1]. Such relatively low core conductivity indicates that liquid core convection could have been driven thermally even with relatively slow cooling rate. However, in 2012–2013, our conventional view was challenged by both computational and experimental studies showing much higher core conductivity [2–4].Open in a separate windowFigure 1.(a) Electrical resistivity and (b) thermal conductivity values at the top of the Earth''s core in the literature [1,2,4–7,9,16]. Filled symbols were calculated on the basis of the Wiedemann-Franz law with ideal Lorenz number (L0 = 2.44 × 10−8 W Ω K−2). Gray bands indicate (a) the range of saturation resistivity [9] and (b) thermal conductivity computed from the saturation resistivity and the Wiedemann-Franz law.Since then, experimental determinations of the thermal conductivity of iron and alloys have been controversial (Fig. (Fig.1).1). Ohta et al. [5] measured the electrical resistivity of iron under core conditions in a laser-heated diamond-anvil cell (DAC). The results demonstrate relatively high thermal conductivity of ∼90 W m−1 K−1 for liquid Fe-Ni-Si alloy based on their measured resistivity for pure iron, Matthissen''s rule and Wiedemann-Franz law, which is compatible with ab initio simulations [2,4]. On the other hand, flash laser-heating and fast thermal radiation detection experiments demonstrated the low core conductivity of 20–35 W m−1 K−1 based on finite element method simulations [6,7], in accordance with the traditional estimate [1]. Since transport properties that describe non-equilibrium phenomena are difficult to measure, the fact that determinations of the iron conductivity under core conditions have become viable these days is a remarkable success in mineral physics. Nevertheless, the discrepancy in core conductivity makes a big difference in the expected age of the inner core, mechanism of liquid core convection and thermal history [3].Despite a number of subsequent studies based on a variety of different techniques, we still see a dichotomy of proposed core conductivity values (Fig. (Fig.1).1). The ‘saturation’ resistivity, which is derived from the fact that the mean free path of electron–phonon interaction cannot be longer than the interatomic distance, gives the lower bound for conductivity. Such saturation resistivity lies between two clusters of reported high and low resistivity values. While the resistivity saturation is important in highly resistive transition metals and their alloys [3,8] (Fig. (Fig.2),2), the conventional estimate [1] did not include the effect of saturation in their models, which resulted in much higher resistivity than the saturation value and hence low core conductivity. The core electrical resistivity measured by recent DAC experiments [3,5,9] shows resistivity saturation (Fig. (Fig.2),2), demonstrating the high core conductivity as far as the Wiedemann-Franz law holds with ideal Lorenz number (Fig. (Fig.1).1). Additionally, since temperature has a large effect on resistivity, temperature gradient in a laser-heated sample is an issue. An internally-resistance-heated DAC provides homogenous and stable sample heating and is thus a promising technique for conductivity measurements at high pressure and temperature (P–T) [9]. The validity of the Wiedemann-Franz law under extreme conditions has also been an issue. Simultaneous measurements of the electrical resistivity and the thermal conductivity of iron alloy under core high P–T conditions will provide decisive evidence for it.Open in a separate windowFigure 2.Temperature response of the electrical resistivity of (a) fcc iron estimated at 1 bar [8] (blue curve) and (b) hcp iron at 115 GPa [5]. Red curve and black line with gray uncertainty band indicate the predicted resistivity based on the Bloch-Grüneisen model with and without the resistivity saturation, respectively.As introduced above, the most recent high P–T measurements for Fe containing 2, 4, 6.5 wt.% Si using an internally-resistance-heated DAC have demonstrated that the thermal conductivity of Fe-12.7 wt.% (22.5 at.%) Si is ∼88 W m−1 K−1 at core-mantle boundary (CMB) conditions when the effects of resistivity saturation, melting and crystallographic anisotropy at measurements are taken into account [9] (Fig. (Fig.1).1). Thermal conductivity of Fe-10 at.% Ni-22.5 at.% Si alloy, a possible outer core composition, could be ∼79 W m−1 K−1 considering the impurity effect of Ni [10]. Si exhibits the largest ‘impurity resistivity’, indicating that the 79 W m−1 K−1 is the lower bound for the thermal conductivity of the Earth''s liquid core. The core thermal evolution models by Labrosse [11] demonstrated that if liquid core convection has been driven by thermal buoyancy with the core thermal conductivity of 79 W m−1 K−1 at the CMB and no radiogenic heating in the core, the CMB temperature is calculated to be ∼5500 K at 3.2 Ga and ∼4800 K at 2.0 Ga. Such high CMB temperature suggests that the whole mantle was fully molten until 2.0–3.2 Ga. It is not consistent with geological records, calling for a different mechanism of core convection.Chemical buoyancy may be an alternate means of driving convection in the core from the early history of the Earth. It has been proposed that the compositional buoyancy in the core could arise from the exsolution of MgO, SiO2 or both [12–14]. Recent core formation models based on the core-mantle distributions of siderophile elements suggest that core metals segregated from silicate at high temperatures, typically at 3000–4000 K and possibly higher [13,15], which enhances the incorporation of lithophile elements including Si and O, and possibly Mg into metals. It is suggested that the (Si, O)-rich liquid core may have become saturated with SiO2 upon secular cooling [14]. Indeed, the original core compositions proposed in recent core formation models include Si and O beyond the saturation limit at CMB conditions [15], i.e. 136 GPa and 4000 K, leading to SiO2 crystallization [13]. The rate of SiO2 crystallization required to sustain geodynamo is as low as 1 wt.% per 109 years, which corresponds to a cooling rate of 100–200 K Gyr−1 [14]. The most recent model of the core compositional evolution by Helffrich et al. [13] showed that MgO saturation follows SiO2 saturation only when >1.7 wt.% Mg in the core. If this is the case, in addition to solid SiO2, (Mg, Fe)-silicate melts exsolve from the core and transfer core-hosted elements such as Mo, W and Pt to the mantle. The core-derived silicate melts may have evolved toward FeO-rich compositions and now represent the ultra-low velocity zones above the CMB. 相似文献
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Solar irradiance has been universally acknowledged to be dominant by quasi-decadal variability, which has been adopted frequently to investigate its effect on climate decadal variability. As one major terrestrial energy source, solar-wind energy flux into Earth''s magnetosphere (Ein) exhibits dramatic interannual variation, the effect of which on Earth''s climate, however, has not drawn much attention. Based on the Ein estimated by 3D magnetohydrodynamic simulations, we demonstrate a novelty that the annual mean Ein can explain up to 25% total interannual variance of the northern-hemispheric temperature in the subsequent boreal winter. The concurrent anomalous atmospheric circulation resembles the positive phase of Arctic Oscillation/North Atlantic Oscillation. The warm anomalies in the tropic stratopause and tropopause induced by increased solar-wind–magnetosphere energy persist into the subsequent winter. Due to the dominant change in the polar vortex and mid-latitude westerly in boreal winter, a ‘top-down’ propagation of the stationary planetary wave emerges in the Northern Hemisphere and further influences the atmospheric circulation and climate. 相似文献
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生物多样性与人类生活息息相关,同时赋予人类一些大自然的馈赠,是人类社会赖以生存和发展的物质基础。因此,生物多样性的可持续发展对人类的健康和生命安全至关重要。然而,随着人类社会和经济的发展,人类活动以及气候变化等已经对生物多样性产生深远的影响;甚至开始造成地球上第6次生物大灭绝。随着人口数量和消费速率的增长,生物多样性丧失的速率正在急剧增加,一系列威胁地球上维持生命系统可持续发展的因素正在凸显。目前,中国在发展经济的同时正在采取积极的措施,出台相关的政策等对生物多样性进行保护。中国政府的决心、"一带一路"建设、对基础研究的资助力度加大以及中国科学院海外科教基地对生物多样性研究的布局等,将对全球生物多样性研究与保护作出积极的贡献。 相似文献
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Jin Liu Chenxu Wang Chaojia Lv Xiaowan Su Yijin Liu Ruilian Tang Jiuhua Chen Qingyang Hu Ho-Kwang Mao Wendy L Mao 《国家科学评论(英文版)》2021,8(4)
As the reaction product of subducted water and the iron core, FeO2 with more oxygen than hematite (Fe2O3) has been recently recognized as an important component in the D” layer just above the Earth''s core-mantle boundary. Here, we report a new oxygen-excess phase (Mg, Fe)2O3+δ (0 < δ < 1, denoted as ‘OE-phase’). It forms at pressures greater than 40 gigapascal when (Mg, Fe)-bearing hydrous materials are heated over 1500 kelvin. The OE-phase is fully recoverable to ambient conditions for ex situ investigation using transmission electron microscopy, which indicates that the OE-phase contains ferric iron (Fe3+) as in Fe2O3 but holds excess oxygen through interactions between oxygen atoms. The new OE-phase provides strong evidence that H2O has extraordinary oxidation power at high pressure. Unlike the formation of pyrite-type FeO2Hx which usually requires saturated water, the OE-phase can be formed with under-saturated water at mid-mantle conditions, and is expected to be more ubiquitous at depths greater than 1000 km in the Earth''s mantle. The emergence of oxygen-excess reservoirs out of primordial or subducted (Mg, Fe)-bearing hydrous materials may revise our view on the deep-mantle redox chemistry. 相似文献
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The effect of an electrical double layer (EDL) on microchannel flow has been studied widely, and a constant bulk electric conductivity is often used in calculations of flow rate or pressure drop. In our experimental study of pressure-driven micropipette flows, the pipette diameter is on the same order of magnitude as the Debye length. The overlapping EDL resulted in a much higher electric conductivity, lower streaming potential, and lower electroviscous effect. To elucidate the effect of overlapping EDL, this paper developed a simple model for water flow without salts or dissolved gases (such as CO2) inside a two-dimensional microchannel. The governing equations for the flow, the Poisson, and Nernst equations for the electric potential and ion concentrations and the charge continuity equation were solved. The effects of overlapping EDL on the electric conductivity, velocity distribution, and overall pressure drop in the microchannel were quantified. The results showed that the average electric conductivity of electrolyte inside the channel increased significantly as the EDL overlaps. With the modified mean electric conductivity, the pressure drop for the pressure-driven flow was smaller than that without the influence of the EDL on conductivity. The results of this study provide a physical explanation for the observed decrease in electroviscous effect for microchannels when the EDL layers from opposing walls overlap. 相似文献
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The traditional view of a dry, volatile-poor Moon has been challenged by the identification of water and other volatiles in lunar samples, but the volatile budget delivery time(s), source(s) and temporal evolution remain poorly constrained. Here we show that hydrogen and chlorine isotopic ratios in lunar apatite changed significantly during the Late Accretion (LA, 4.1–3.8 billion years ago). During this period, deuterium/hydrogen ratios in the Moon changed from initial carbonaceous-chondrite-like values to values consistent with an influx of ordinary-chondrite-like material and pre-LA elevated δ37Cl values drop towards lower chondrite-like values. Inferred pre-LA lunar interior water contents are significantly lower than pristine values suggesting degassing, followed by an increase during the LA. These trends are consistent with dynamic models of solar-system evolution, suggesting that the Moon''s (and Earth''s) initial volatiles were replenished ∼0.5 Ga after their formation, with their final budgets reflecting a mixture of sources and delivery times. 相似文献
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针对贫困地区妇女的扶贫工作是脱贫攻坚不可或缺的重要组成部分。妇女脱贫对于阻断贫困代际传递,增进妇女福祉,建设和谐幸福家庭具有至关重要的作用。2020年是全国贫困地区从脱贫走向振兴的关键节点,在此背景下,深入研究新时代妇女脱贫问题具有重要意义。文章首先指出了当前妇女脱贫面临的4个问题——乡村性别歧视,“数字鸿沟”,社会救助力量薄弱,以及扶贫工作中的性别意识欠缺。进而在介绍理论基础、国际妇女脱贫经验和国内妇女脱贫典型案例的基础上,提出4点建议：（1）将性别平等内化为乡村社会行为规范;（2）增加培训以弥合“数字鸿沟”;（3）提高家庭劳动社会化水平;（4）建设包容、弹性、可持续的妇女扶贫长效机制。 相似文献
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安徽蒙城地球物理国家野外科学观测研究站的主要任务是开展地震、重力、形变、电磁等多种固体地球物理观测与研究,以及开展中高层大气和电离层多物理量的近地空间环境观测与研究。地球内部到外部空间的综合地球物理观测对认识地球本体和近地空间环境的结构、形成与演化,以及各种自然灾害的孕育发生规律及预警和预报具有非常重要的意义。通过不同尺度地球物理台阵观测资料,获得了郯庐—大别构造带多尺度结构、变形和孕震构造特征。基于近地空间环境观测数据,揭示了中高层大气与电离层的精细结构和变化机制。这些研究为区域地震监测和地震灾害研究、近地空间环境监测和空间灾害研究等提供了重要的基础。 相似文献
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Qingyang Hu Jin Liu Jiuhua Chen Bingmin Yan Yue Meng Vitali B Prakapenka Wendy L Mao Ho-Kwang Mao 《国家科学评论(英文版)》2021,8(4)
Understanding the mineralogy of the Earth''s interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H2O to form a previously unknown (Mg, Fe)O2Hx (x ≤ 1) phase. The (Mg, Fe)O2Hx has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg0.6Fe0.4)O or beyond 2300 km for (Mg0.7Fe0.3)O. The (Mg, Fe)O2Hx is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg2+, Fe3+ and H+). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere. 相似文献
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基于诱致性技术创新理论,从偏向性技术进步的视角分析玉米产业节本增效途径。研究发现：2004-2018年玉米产业的生产率为降低趋势,主要是因为其技术进步率的降低导致生产率的损失。技术进步对玉米产出增长的贡献率达到40%以上,机械投入对产出增长的贡献率超过30%。玉米产业表现出较强的机械要素替代劳动力要素,但生物化学要素对土地要素的替代效应并没有很显著。玉米产业的技术进步路径表现为从提高土地生产率的生物化学型向提高劳动生产率的机械型技术进步模式转变,这与我国玉米产业技术发展趋势和地理特征有关。研究价值：为玉米产业实现技术进步和节本增效提供参考依据,对促进我国区域玉米技术进步、保证我国粮食安全具有重要理论和现实意义。 相似文献
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The oxygenation of Earth''s atmosphere is widely regarded to have played an important role in early-life evolution. Chromium (Cr) isotopes recorded in sedimentary rocks have been used to constrain the atmospheric oxygen level (AOL) over geological times based on the fact that a positive Cr isotopic signature is linked to the presence of Cr(VI) as a result of oxidative continental weathering. However, there is no direct evidence of the presence of Cr(VI) in sedimentary rocks yet. Carbonates are most widely distributed over geological times and were thought to have incorporated Cr(VI) directly from seawater. Here, we present results of Cr valence states in carbonates which show Cr(III) is the dominant species in all samples spanning a wide range of geological times. These findings indicate that Cr(VI) in seawater was reduced either before or after carbonate precipitation, which might have caused Cr isotopic fractionation between seawater and carbonates, or marine carbonates preferentially uptake Cr(III) from seawater. As Cr(III) can come from non-redox Cr cycling, which also can cause isotopic fractionation, we suggest that positively fractionated Cr isotopic values do not necessarily correspond to the rise in AOL. 相似文献
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随着科技体制改革的不断深入，新型研发机构逐渐在我国创新体系中崭露头角。本文基于巴斯德象限理论模型，以江苏省产业技术研究院膜科学技术所为例，研究了江苏省新型研发机构的共建模式，剖析其在组织机构、管理体制、协同机制以及运作机理等方面的建设规律，探索科技与产业化结合的路径，为解决科技与经济“两张皮”难题提供新思路。最后，本文总结了研究所的科技成果转化成效，提出其共建的启示，以期形成科技体制改革的示范效应，带动江苏省域及其它省份地区的新型研发机构建设。 相似文献
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探讨如何激活农业企业绿色创业以解决日益窘迫的环境问题,以我国207家农业企业为案例样本,基于集合论思想,运用模糊集定性比较分析方法(fsQCA),从环境、组织两个层面分析政府环境规制、市场压力、管理者环境认知以及绿色价值观等4个条件因素对绿色创业导向形成的多重因果机制。研究发现:缺乏市场压力是导致非高绿色创业导向的必要条件;高绿色创业导向的驱动机制分为3条路径,非高绿色创业导向的驱动机制分为2条路径,且与高绿色创业导向的驱动机制呈非对称关系。研究结论对推动农业企业绿色创业实践的启示包括:政府必须进一步做好政策宣传,企业要引进有绿色创业愿景的管理者,学校也要加强对学生生态文明意识的教育以及培养其社会责任感;在推动绿色创业中要把握好关键核心要素;企业管理者应当根据内部价值观和文化以及外部规制和市场竞争状况选择适合的绿色创业提升方向。 相似文献
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Yanwei Huang Yu He Howard Sheng Xia Lu Haini Dong Sudeshna Samanta Hongliang Dong Xifeng Li Duck Young Kim Ho-kwang Mao Yuzi Liu Heping Li Hong Li Lin Wang 《国家科学评论(英文版)》2019,6(2):239
Lithium titanium oxide (Li4Ti5O12, LTO), a ‘zero-strain’ anode material for lithium-ion batteries, exhibits excellent cycling performance. However, its poor conductivity highly limits its applications. Here, the structural stability and conductivity of LTO were studied using in situ high-pressure measurements and first-principles calculations. LTO underwent a pressure-induced amorphization (PIA) at 26.9 GPa. The impedance spectroscopy revealed that the conductivity of LTO improved significantly after amorphization and that the conductivity of decompressed amorphous LTO increased by an order of magnitude compared with its starting phase. Furthermore, our calculations demonstrated that the different compressibility of the LiO6 and TiO6 octahedra in the structure was crucial for the PIA. The amorphous phase promotes Li+ diffusion and enhances its ionic conductivity by providing defects for ion migration. Our results not only provide an insight into the pressure depended structural properties of a spinel-like material, but also facilitate exploration of the interplay between PIA and conductivity. 相似文献
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作为"亚洲水塔"重要组成部分的冰川,对气候变化的响应极其敏感。研究全球变暖背景下青藏高原及周边地区冰川变化的时空格局特征,有助于识别"亚洲水塔"的主要储水与供水区域,这对水资源的合理规划与利用具有重要意义。文章通过综合分析,揭示出"喀喇昆仑异常"现象在昆仑山西部和帕米尔高原地区亦有不同程度的表现,分布在这些区域以外的青藏高原及周边地区山地冰川近期大多处于加速消融状态;同时,阐明了近50年来以及未来不同气候变化情景下青藏高原及周边地区冰川变化对流域水资源状况和海平面上升的影响;并指出,要系统开展青藏高原及周边地区冰川的调查与观测,建立气候-冰川-水文过程耦合模型,准确评估变化环境下的冰川水资源状况及其影响,以服务于中国社会经济发展和"绿色丝绸之路"建设。 相似文献
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本文通过构建平台和借贷双边用户的演化博弈基准模型,引入平台竞争和监管机构,研究P2P网贷平台信用风险的控制策略.研究结果表明：完善的征信体系有助于提高借款人违约成本;平台是否合规经营的决策受平台声誉、合规经营收益和违约经营收益等多方面因素的影响,违约借款人的比例越低,则平台合规经营的可能性越高,信用风险越低;平台的自我约束和自我激励均有限,平台竞争不利于平台控制信用风险,政府监管对控制平台信用风险、推动行业可持续发展具有重要作用.基于此,本文提出构建政府—平台—用户的双层信用风险控制体系,并提出具体信用风险控制策略建议. 相似文献
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应用分子动力学模拟的方法,研究了纳米金刚石颗粒的导热系数对温度和颗粒尺寸的依存关系。为了得到较为准确的模拟结果,采用了平衡态分子动力学模拟的方法。计算了较长时间的热流自相关函数,并得到了导热系数的收敛结果。结果表明,纳米金刚石颗粒由于尺寸的影响,导热系数低于体材料金刚石的导热系数;随温度的升高,导热系数出现一个峰值,该峰值点的温度小于体材料金刚石出现峰值点的温度;随颗粒尺寸的增大,导热系数增加,我们预测导热系数将在一定的颗粒尺寸时收敛于体材料金刚石的导热系数。 相似文献