O/O ratios in anhydrous spinel lherzolite xenoliths from the Shavaryn-Tsaram volcano, Mongolia

Anhydrous spinel lherzolite xenoliths from the Shavaryn-Tsaram volcano, which represent unusually clinopyroxenerich samples of upper mantle beneath the Tariat Depression in north-central Mongolia, have particularly low δ¹⁸O values of +4.9 to +5.7‰ SMOW. Constituent minerals exhibit small (ca. 0.5–0.7‰) variations in¹⁸O content (olivine = +4.6 to +5.3‰, clinopyroxene = +5.6 to +6.1‰, orthopyroxene = +5.8 to +6.5‰), that are unrelated to xenolith modal mineralogy, chemical composition, radiogenic isotope character, or pyroxene equilibration temperature. This O-isotope character of the Tariat xenoliths is interpreted to reflect the closed-system distribution of oxygen isotopes in a slowly cooling mantle diapir emplaced into the lithosphere from a relatively primitive region of the asthenosphere.     

High-pressure disproportionation of Co2SiO4 spinel and implications for Mg2SiO4 spinel

Co₂SiO₄ spinel has been found to disproportionate into its isochemically mixed oxides with rocksalt and rutile structures at pressures between 170 and 190 kbar and temperatures between 1400 and 1800°C in a diamond-anvil press. The exact disproportionation pressure is not certain due to transient increases in pressure during the local and rapid heating by a continuous YAG laser. The slope of the phase boundary between the spinel phase and the mixed oxides is calculated to be?33 ± 20bar/deg. This negative slope is consistent with the observed anomalously large entropy of CoO (relative to its isostructural oxides) in entropy vs.(MV)^?1/2 systematics, whereM is the formula weight andV the molar volume. The sign of the slope for a phase boundary in the disproportionation of spinel depends on the values of entropy of the rocksalt oxides as well as the inverse character exhibited in the spinel phases. The normal entropy of MgO suggests that the phase boundary for the disproportionation of Mg₂SiO₄ spinel has positive slope.     

Effects of cation disordering in a natural MgAl2O4 spinel observed by rectangular parallelepiped ultrasonic resonance and Raman measurements

At moderate temperatures, the elastic properties of natural MgAl₂O₄ spinel differ in several significant ways from properties of synthetic spinels. Below 1000 K, the ultrasonic resonant frequencies of an ordered natural spinel change significantly after heat treatment; at higher temperatures, both types of spinels have similar resonant responses. The temperature derivatives of the elastic constants of an ordered spinel also differ from those of disordered spinels at moderate temperatures; again, at higher temperatures, both types of spinels have similar behaviors. The Raman spectra also differ below 1000 K for ordered natural and disordered spinels and are similar at higher temperatures and after cooling to ambient temperature. We associate these changes in ultrasonic resonance and Raman spectra of spinel with cation disordering at high temperature which may be quenched by cooling. We deduce estimates of the inversion parameter from the relative intensities of the two A_1g Raman modes in very good agreement with estimates made from other measurements. We find thatC ₁₁ andC ₁₂ decrease by 4 and 8%, respectively, with 20% inversion in spinel;C ₄₄ is less sensitive to cation order. These results imply that previous measurements of the adiabatic elastic constants of spinels at ambient conditions have been affected by the state of cation disorder of the specimen.     

Molecular simulation of the CH4/CO2/H2O adsorption onto the molecular structure of coal

Clarification of the molecular mechanism underlying the interaction of coal with CH₄, CO₂, and H₂O molecules is the basis for an in-depth understanding of the states of fluid in coal and fluid-induced coal swelling/contraction. In terms of instrumental analysis, molecular simulation technology based on molecular mechanics/dynamics and quantum chemistry is a powerful tool for revealing the relationship between the structure and properties of a substance and understanding the interaction mechanisms of physical-chemical systems. In this study, the giant canonical ensemble Monte Carlo (GCMC) and molecular dynamics (MD) methods were applied to investigate the adsorption behavior of a Yanzhou coal model (C₂₂₂H₁₈₅N₃O₁₇S₅). We explored the adsorption amounts of CH₄, CO₂, and H₂O onto Yanzhou coal, the adsorption conformation, and the impact of oxygen-containing functional groups. Furthermore, we revealed the different adsorption mechanisms of the three substances using isosteric heat of adsorption and energy change data. (1) The adsorption isotherms of the mono-component CH₄, CO₂, and H₂O were consistent with the Langmuir model, and their adsorption amounts showed an order of CH₄<CO₂<H₂O. In addition, high temperatures were non-conducive to adsorption. When the three components of CH₄/CO₂/H₂O were mixed (at a molar ratio of 1:1:1) for adsorption, only the adsorption curve of H₂O was consistent with the Langmuir model. (2) The mean values of the isosteric heat of adsorption of CH₄, CO₂, and H₂O were 22.54, 36.90, and 37.82 kJ/mol, respectively; that is, H₂O>CO₂>CH₄. In addition, at higher temperatures, the isosteric heat of adsorption decreased; pressure had no significant effect on the heat of adsorption. (3) CH₄ molecules displayed an aggregated distribution in the pores, whereas CO₂ molecules were cross arranged in pairs. Regarding H₂O molecules, under the influence of hydrogen bonds, the O atom pointed to surrounding H₂O molecules or the H atoms of coal molecules in a regular pattern. The intermolecular distances of the three substances were 0.421, 0.553, and 0.290 nm, respectively. The radial distribution function (RDF) analysis showed that H₂O molecules were arranged in the most compact fashion, forming a tight molecular layer. (4) H₂O molecules showed a significantly stratified distribution around oxygen-containing functional groups on the coal surface, and the bonding strength showed a descending order of hydroxyl> carboxyl>carbonyl. In contrast, CO₂ and CH₄ showed only slightly stratified distributions. (5) After the adsorption of CH₄, CO₂, and H₂O, the total energy, the energy of valence electrons, and the non-bonding interaction of the system in the Yanzhou coal model all decreased. The results regarding the decrease in the total energy of the system indicated an order of H₂O>CO₂>CH₄ in terms of the adsorption priority of the Yanzhou coal model. The results regarding the decrease in the energy of valence electrons showed that under certain geological conditions, a pressure-induced “coal strain” could lead to a structural rearrangement during the interaction of coal with fluid to form a more stable conformation, which might be the molecular mechanism of coal swelling resulting from the interaction between fluid and coal. An analysis of the contribution of Van der Waals forces, electrostatic interactions and hydrogen bonds to the decrease in non-bonding interactions revealed the mechanism underlying the interactions between coal molecules and the three substances. The interaction between coal molecules and CH₄ consisted of typical physical adsorption, whereas that between coal molecules and CO₂ consisted mainly of physical adsorption combined with weak chemical adsorption. The interaction between coal molecules and H₂O is physical and chemical.     

Prediction of the Shear Wave Velocity from Compressional Wave Velocity for Gachsaran Formation

Shear and compressional wave velocities, coupled with other petrophysical data, are very important for hydrocarbon reservoir characterization. In situ shear wave velocity (Vs) is measured by some sonic logging tools. Shear velocity coupled with compressional velocity is vitally important in determining geomechanical parameters, identifying the lithology, mud weight design, hydraulic fracturing, geophysical studies such as VSP, etc. In this paper, a correlation between compressional and shear wave velocity is obtained for Gachsaran formation in Maroon oil field. Real data were used to examine the accuracy of the prediction equation. Moreover, the genetic algorithm was used to obtain the optimal value for constants of the suggested equation. Furthermore, artificial neural network was used to inspect the reliability of this method. These investigations verify the notion that the suggested equation could be considered as an efficient, fast, and cost-effective method for predicting Vs from Vp.     

Effects of elevated CO2 concentration on CH4 and N2O emissions from paddy fields: A meta-analysis

The inevitable rise of atmospheric CO₂ concentration plays an important role in regulating the carbon(C)and nitrogen(N)cycling in the rice-cropping system.Elucidating the effects of elevated CO₂ concentration(ECO₂)on CH₄ and N₂O emissions from paddy fields is essential for evaluating agricultural production in response to global climate change.In this study,we conducted a global meta-analysis to assess the overall effect of ECO₂ on CH₄ and N₂O emissions from paddy fields,aiming at providing a guideline for sustainable C and N management in paddy fields under future climate conditions.The results showed that,overall,ECO₂ significantly increased CH₄ emissions from rice fields by 23%(P<0.05),but reduced N₂O emissions by 22%(P<0.05).With a long duration(>10 yr)of ECO₂ ,ECO₂ significantly reduced CH₄ and N₂O emissions from paddy fields by 27%and 53%,respectively(P<0.05).Along with the increasing levels of ECO₂ ,the stimulating effect of ECO₂ on CH₄ emissions showed a trend of"weakening firstly and then strengthening",while its effect on N₂O emissions changed from stimulation to inhibition.Agronomy managements(e.g.,N application rates,straw incorporations,water regimes,and rice cultivars)affected the effects of ECO₂ on CH₄ and N₂O emissions from paddy fields.With no or half amount of straw incorporation,ECO₂ increased CH₄ emissions by 27% or 49%(P<0.05)from paddy fields,respectively,while non-significant effects on CH₄ emissions from paddy fields were observed under full straw incorporation.With the increasing amount of straw incorporation,the reductions in N₂O emissions from paddy fields were enhanced by ECO₂.Compared with a continuous flooding regime,intermittent irrigation weakened the promoted effect on CH₄ emissions but stimulated the inhibited effect on N₂O emissions from paddy fields under ECO₂.Therefore,under the future condition of ECO₂,it is recommended to adopt the appropriate agricultural management measures,such as combining straw incorporation and intermittent irrigation,and optimizing N application and using rice cultivars of high-yield with lower emissions.In addition,it is necessary to conduct comprehensive studies at multiscale,with multi-factor,and by multi-method to effectively reduce the uncertainty of quantifying the response of CH₄ and N₂O emissions from paddy fields to future ECO₂ .     

The fluxes and controlling factors of N_2O and CH_4 emissions from freshwater marsh in Northeast China

Nitrous oxide (N2O) and methane (CH4) emissions were measured using a static chamber method in two adjacent plots of freshwater marsh predominated by Calamagrostis angustifolia, one is seasonal waterlogged (SW) and the other without surface water accumulation (NW), in Sanjiang Plain wetland (47°35′N, 133°31′E), northeast China, during 2002-2004. The diurnal and seasonal flux variations of both gases were significantly correlated with 5-cm-soil temperature. The NW marsh is a source of N2O and sink of CH4, wh...     

Thermodynamic properties of calcium ferrite-type MgAl2O4: A first principles study

The diamond anvil cell experiments have revealed that the calcium ferrite(CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt(MORB) in the lower mantle. In this study, we have performed first principles lattice dynamics calculations for the Mg Al_2O_4 end-member of the aluminous phase based on density functional perturbation theory using two functionals within the local density approximation(LDA) and generalized gradient approximation(GGA) for bracketing the calculated properties at their lower and upper limits, respectively. A simple empirical pressure correction at zero temperature has been applied to both LDA and GGA. The results of room-temperature equation of state(EOS) and zero-pressure thermal expansion calculated by GGA with pressure correction have shown the best agreement with available experimental data. The high-pressure and temperature thermodynamic properties have been obtained using the GGA with correction method. The pressure-volume relations are fitted with a third-order high-temperature Birch-Murnaghan EOS. The isobaric heat capacity, the coefficient of thermal expansion and isothermal bulk modulus are fitted with polynomials and their coefficients are reported in the range of 0–40 GPa and 300–2000 K. The density profile of MORB estimated using the computational thermo-elastic constants supports the hypothesis that the subducted oceanic slabs could gain enough downwelling forces into the lower mantle.     

Elastic properties of the olivine and spinel polymorphs of Mg2GeO4, and evaluation of elastic analogues

The single-crystal elastic moduli of the olivine and spinel phases of Mg₂GeO₄ have been measured using Brillouin scattering spectra. The moduli for the olivine phase are: C₁₁ = 3.12, C₂₂ = 1.87, C₃₃ = 2.17, C₆₆ = 0.71, C₂₃ = 0.66, C₃₁ = 0.65 and C₁₂ = 0.60. The moduli for the spinel phase are: C₁₁ = 3.00, C₄₄ = 1.26 and C₁₂ = 1.18.These data are analyzed to define the best type of elastic analogue for magnesium orthosilicates. The character of the many-bodied, non-central force associated with the divalent cation is found to significantly influence the relative magnitudes of the elastic moduli. Since the nature of the many-bodied, non-central force is quite different for alkaline earth cations than for transition metal cations, we conclude that materials which contain one of these cation types is not a good analogue for materials with the other type. Magnesium orthogermanate, however, is a good analogue of magnesium orthosilicate. On the other hand, the high elastic anisotropy of the spinel phase of the germanate suggests that the germanium tetrahedron is less rigid under shear than the corresponding silicon tetrahedron. The success of the magnesium orthogermanate to model the magnesium orthosilicate is probably a result of the mechanical isolation of the tetrahedra, thus requiring the conclusions of this study to be further tested before applying them to other silicate systems.     

Experimental study on N_2O and CH_4 fluxes from the dark coniferous forest zone soil of the Gongga Mountain, China

The increasing concentration of greenhouse gas in the atmosphere and their resultant climatic and environmental changes have been drawing much attention of the governments of various countries in recent years. The sphere of global influence and the comp…     

另类显式逐步积分格式性态的数值模拟研究

通过初始条件激励下多自由度体系动力响应数值模拟以及对不同模拟方法加速度序列模拟结果的比较分析,研究了PJ方法、BW方法和LL方法的性态,如收敛性、稳定性、精度以及相关问题.取得的主要研究结果是:积分步长Δt=0.1T2min可以作为保证BW方法数值精度和稳定性的充分条件;在该条件得到满足情况下,BW方法较之PJ和LL方法均有显著的综合优势,特别是相对精度方面的优势可以达到数量级水平.研究结果表明,显式方法可在大型有限元动力分析软件中逐渐起到更加重要的作用.     

Nonlinear behavior simulation of soil-structure interaction system via real-time hybrid testing

Bulletin of Earthquake Engineering - Soil-structure interaction (SSI) can potentially compromise structures that are subjected to seismic excitation. In recent years, real-time hybrid testing...     

Fractional crystallization trends in the system Mg2SiO4-CaAl2Si2O8-FeO-Fe2O3-SiO2 over the range of oxygen partial pressures of 10−11 to 10−0.7 atm

A brief report is made of current laboratory investigations on phase relations among olivine, pyroxene, anorthite, magnetite, tridymite, liquid and gas in the system Mg₂SiO₄-CaAl₂Si₂O₈-FeO-Fe₂O₂-SiO₂ over a wide range of oxygen partial pressures. Courses of fractional crystallization under various conditions of oxygen partial pressure are depicted using an anorthite saturation diagram. Starting with a basalt-like composition in the system, fractional crystallization at a moderate oxygen partial pressure (10 atm.) results in an andesite-like residual liquid of composition 55 SiO₂, 14 iron oxide, 6 MgO, 9 CaO, 16 Al₂O₃ at a temperature of 1155°C. With fractional crystallization in a closed system, the end liquid approaches the composition of 45 SiO₂, 38 iron oxide, 6 CaO and 11 Al₂O₃, at a temperature of 1050°C and oxygen partial pressure of about 10^?12 atm. The andesitic final liquid in this system would be expected to further differentiate toward dacitic and rhyolitic compositions if alkalies and water were present in the system. On the basis of these studies, the derivation of liquids of andesitic, dacitic or rhyolitic composition from primary basalts by fractional crystallization seems entirely possible if the oxygen partial pressure is maintained at a moderate or high level.     

断层系统摩擦动力学行为的有限元模拟分析

绝大多数大地震发生在先存断层构造上,被广泛认为是一种断层摩擦失稳行为.研究断层上的摩擦动力学行为对地震数值预报具有重要意义.本文围绕地震断层动力学行为,首先回顾了断层摩擦动力学有限元模拟相关的进展,尤其是有限元模拟过程中断层摩擦行为的处理方法,重点分析比较了不同时间积分方案在有限元模拟计算中的差异,探讨了传统有限元方法在模拟断层摩擦失稳非线性的收敛性等难题.考虑到相关差异及问题,本文主要简明介绍了基于R-minimum策略自适应地控制时间步长方案及其有限元计算算法和相关软件,其兼顾了静态隐式与动态显式的优点,将不稳定的隐式迭代计算转变为显式计算;同时利用库仑摩擦定律及速率和状态相关的摩擦本构方程,通过节点-点任意接触单元模拟变形体之间的三维非线性接触摩擦动力学行为,并小结了相关的成功应用实例.此外,为了构建刻画复杂断层形态的有限元网格模型,本文在总结了相关有限元网格生成算法基础上,举例说明了我们最近发展的基于图像的复杂断层约束下非连续四边形和六面体网格的生成方法.最后以此为例,对生成的复杂断层系统模型进行了有限元数值模拟分析.

     

Greenhouse gas emissions (CO2, CH4, and N2O) from several perialpine and alpine hydropower reservoirs by diffusion and loss in turbines

We investigated greenhouse gas emissions (CO₂, CH₄, and N₂O) from reservoirs located across an altitude gradient in Switzerland. These are the first results of greenhouse gas emissions from reservoirs at high elevations in the Alps. Depth profiles were taken in 11 reservoirs located at different altitudes between the years 2003 and 2006. Diffusive trace gas emissions were calculated using surface gas concentrations, wind speeds and transfer velocities. Additionally, methane entering with the inflowing water and methane loss at the turbine was assessed for a subset of the reservoirs. All reservoirs were emitters of carbon dioxide and methane with an average of 970?±?340?mg?m^?2?day^?1 (results only from four lowland and one subalpine reservoir) and 0.20?±?0.15?mg?m^?2?day^?1, respectively. One reservoir (Lake Wohlen) emitted methane at a much higher rate (1.8?±?0.9?mg?m^?2?day^?1) than the other investigated reservoirs. There was no significant difference in methane emissions across the altitude gradient, but average dissolved methane concentrations decreased with increasing elevation. Only lowland reservoirs were sources for N₂O (72?±?22???g?m^?2?day^?1), while the subalpine and alpine reservoirs were in equilibrium with atmospheric concentrations. These results indicate reservoirs from subalpine/alpine regions to be only minor contributors of greenhouse gases to the atmosphere compared to other reservoirs.     

A sophisticated simulation for the fracture behavior of concrete material using XFEM

The development of a powerful numerical model to simulate the fracture behavior of concrete material has long been one of the dominant research areas in earthquake engineering.A reliable model should be able to adequately represent the discontinuous characteristics of cracks and simulate various failure behaviors under complicated loading conditions.In this paper,a numerical formulation,which incorporates a sophisticated rigid-plastic interface constitutive model coupling cohesion softening,contact,friction and shear dilatation into the XFEM,is proposed to describe various crack behaviors of concrete material.An effective numerical integration scheme for accurately assembling the contribution to the weak form on both sides of the discontinuity is introduced.The effectiveness of the proposed method has been assessed by simulating several well-known experimental tests.It is concluded that the numerical method can successfully capture the crack paths and accurately predict the fracture behavior of concrete structures.The influence of mode-Ⅱ parameters on the mixed-mode fracture behavior is further investigated to better determine these parameters.     

O2 density and temperature profiles retrieving from direct solar Lyman-alpha radiation measurements

The resonance transition ²P-²S of the atomic hydrogen (Lyman-alpha emission) is the strongest and most conspicuous feature in the solar EUV spectrum. The Lyman-alpha radiation transfer depends on the resonance scattering from the hydrogen atoms in the atmosphere and on the O₂ absorption. Since the Lyman-alpha extinction in the atmosphere is a measure for the column density of the oxygen molecules, the atmospheric O₂ density and temperature profiles can be calculated thereof. A detector of solar Lyman-alpha radiation was manufactured in the Stara Zagora Department of the Solar-Terrestrial Influences Laboratory (STIL). Its basic part is an ionization camera, filled in with NO. A 60 V power supply is applied to the chamber. The produced photoelectric current from the sensor is fed to a two-channel amplifier, providing analog signal. The characteristics of the Lyman-alpha detector were studied. It passed successfully all tests and the results showed that the so-designed instrument could be used in rocket experiments to measure the Lymanalpha flux. From the measurements of the detector, the Lyman-alpha vertical profile can be obtained. Programs are created to compute the O₂ density, atmospheric power and temperature profiles based on Lymanalpha data. The detector design appertained to ASLAF project (Attenuation of the Solar Lyman-Alpha Flux), a scientific cooperation between STIL—Bul.Acad.Sci., Stara Zagora Department and the Atmospheric Physics Group at the Department of Meteorology (MISU), Stockholm University, Sweden. The joint project was part of the rocket experiment HotPay I, in the ALOMAR eARI Project, EU’s 6th Framework Programme, Andøya Rocket Range, Andenes, Norway. The project is partly financed by the Bulgarian Ministry of Science and Education.