2维和2.5维起伏地表直流电法有限差分数值模拟

起伏地表直流电场数值模拟现多采用有限元法,主要是因为其有灵活的处理曲边界的能力,然而有限元法比有限差分法要复杂,如果让有限差分法也同样具有较好的处理曲边界的能力,那数值模拟将变得更为简单.本文通过在非正则内点处采用不等距差分,在起伏地表点处直接实现边界条件,克服转移法人为改变地表形状的弊端,使得基于笛卡尔网格的有限差分法有了较强的处理曲边界的能力.通过2维和2.5维的水平地表数值解和解析解的对比,以及2维起伏地表情况下数值解和保角变换理论解的对比,均说明该方法的有效性.最后例举了一些数值计算实例.

双相介质瑞雷面波有限差分正演模拟

为了研究双相介质瑞雷面波的形成机制及传播规律,促进瑞雷面波资料处理方法的发展。文章根据弹性波动方程,采用交错网格有限差分算法,对二维各向同性弹性介质做解析解与数值解的对比,在此基础上,将PML吸收边界条件,改进的镜像法应用于双相介质波动方程中,并作了稳定性分析,对双相介质水平层状、起伏分界面等典型模型瑞雷面波及体波在内的全波场进行研究。结果表明:基于弹性介质解析解与数值解的对比,在误差接受范围内,研究双相介质是可行的;把稍作改进的镜像法应用于双相介质中,能够有效地处理瑞雷面波自由边界问题;通过详细分析双相介质瑞雷面波及体波在内的全波场的信息,对以双相介质为基础的地震波勘探有一定的指导作用。

起伏地表条件下的弹性波叠前逆时偏移

目前,地震勘探条件复杂、地下地质构造多样的"双复杂"地区的地震勘探面临着诸多挑战,特别是地表起伏条件给地下复杂构造精确成像带来了困难。通过研究起伏地表条件下的弹性波叠前逆时偏移方法,采用简洁有效的处理方法解决起伏地表的自由边界条件;利用有效边界的边界存储策略解决弹性波叠前逆时偏移中存储量大的问题。数值实验结果证明该方法能够准确地重建震源波场,SEG加拿大起伏地表逆掩断层模型进一步验证了提出方法的有效性。

Deep mantle hydrogen in the pyrite-type FeO_(2)–FeO_(2)H system

The pyrite-type FeO_(2)and FeO_(2)H were synthesized at the pressure-temperature conditions relevant to Earth’s deep lower mantle.Through the water-iron reaction,the pyrite-phase is a good candidate to explain the chemical heterogeneities and seismological anomalies at the bottom of the mantle.The solid solution of pyrite-type FeO_(2)and FeO_(2)H,namely the FeO_(2)Hx(0≤x≤1),is particularly interesting and introduces puzzling chemical states for both the O and H atoms in the deep mantle.While the role of H in the FeO_(2)–FeO_(2)H system has been primarily investigated,discrepancies remain.In this work,we summarize recent progress on the pyrite-phase,including FeO_(2),FeO_(2)H,and FeO_(2)Hx,which is critical for understanding the water cycling,redox equilibria,and compositional heterogenicities in the deep lower mantle.

Application of superconductive gravity technique on the constraints of core-mantle coupling parameters

The parameters, i.e. the Period and the Quality factor, of the Earth's free core nutation (FCN) are closely related to the dissipative coupling between the core and the mantle. Based on the FCN parameters obtained from the actual observations and theoretical simulation, significantly constrained in this study were several key parameters near the core-mantle boundary (CMB), related to the core and mantle coupling, including viscosity at the top of liquid core, conductivity at the bottom of the mantle, and dynamic ellipticity of the CMB. In order to choose high quality observations from global stations of the superconducting gravimeters (SG) on the Global Geodynamics Project (GGP) network, we adopted two criteria, the standard deviations of harmonic analysis on tidal observations and the quality of the FCN parameters calculated with the observations from single station. After the mean ocean tidal effects of the recent ocean tidal models were removed, the FCN parameters were retrieved by stacking the tidal gravity observations from the GGP network. The results were in a good agreement with those in the recent research by using the SG and/or the VLBI observations. Combined with an FCN theoretical model deduced by angular momentum method, the viscous and electromagnetic coupling parameters near the CMB were evaluated. Numerical results indicated that the viscosity at the top of the liquid core was in the range from 6.6×102 to 2.6×103 Pa·s, which was in good agreement with those obtained from the Earth's nutation, the FCN and variations in the length of day (LOD). The conductivity at the bottom of the mantle should be as large as 2.6×106-1.0×107 S m-1 to match the FCN quality factors from the actual observations. The dissipative coupling had a little influence of 1-2 sidereal days for the FCN period.

Morphology and possible origins of the Perm anomaly in the lowermost mantle of Earth

We have constrained a small-scale,dome-shaped low-velocity structure near the core-mantle boundary(CMB)of Earth beneath Perm(the Perm anomaly)using travel-time analysis and three-dimensional(3-D)forward waveform modeling of seismic data sampling of the mantle.The best-fitting dome-shaped model centers at 60.0°E,50.5°N,and has a height of 400 km and a radius that increases from 200 km at the top to 450 km at the CMB.Its velocity reduction varies from 0%at the top to–3.0%at 240km above the CMB to–3.5%at the CMB.A surrounding 240-km-thick high-velocity D''structure has also been detected.The Perm anomaly may represent a stable smallscale chemical pile in the lowermost mantle,although the hypothesis of a developing mantle plume cannot be ruled out.

Research on the comprehensive performance of PrFeB magnets for synchrotron radiation and free electron laser

PrFeB magnets, which possess excellent magnetic properties at low temperatures, have important application value as cryogenic permanent magnet undulators for synchrotron radiation sources and free electron lasers. In this research study, several high-performance PrFeB magnets(P42H, P48SH, and P48UH) were prepared, and their performance was comprehensively examined, including evaluations of their magnetic properties,microstructures, uniformity, and stability. Next,their application prospects were analyzed and discussed. In China, the first cryogenic permanent magnet undulators(CPMUs) with P48SH magnets with 18 mm cycle lengths have been developed. When the temperature is 80 K and the gap is 6.0 mm,the magnetic field measurement results of the CPMU showed that the effective magnetic field peak was approximately 0.92 T, yielding an increase of 11.76% relative to operation at 300 K, with an RMS phase error of about 4.99°.

THE OPTIMAL MOTION OF TWO-DIMENSIONAL UNDULATING PLATE SWIMMING IN FLUID FLOW

The optimum shape of a two-dimensional undulatory plate in its motion in fluid flow is analyzed and the physical parameters（the thrust and the power）are calculated by the boundary element method.With the commonly used Lagrange multiplier method,only a saddle point of the optimum solution can be obtained,but not the solution itself due to the singularity of the problem.To eliminate the singularity,a method is proposed by adding an amplitude constraint.The new method is a generalization of that proposed by Wu,and it can be applied to more complex cases.The optimum shape of the linearly varying amplitude motion is studied in detail.It is shown that both the maximum and the minimum solutions exist when the frequency is higher than a critical value.For a high frequency,the maximum efficient motion with a large amplitude at the leading edge and a small amplitude at the trailing edge induces a large leading edge suction force.As the frequency decreases,the leading edge suction force decreases to a minimum and then increases.For high wavenumbers,there exists an optimum frequency with the maximum efficiency.High efficiency holds over a large range of frequency.The optimum efficiency increases as the wavenumber increases.The increase of the wavenumber can also reduce the leading edge suction force.The optimization method can also be applied to a quadratically varying amplitude motion.It is found that the optimum efficiency is larger than that for the linearly varying amplitude motion.However,the additional efficiency is relatively small,especially as the original efficiency is already high enough.

Magnetic field stability of PrFeB magnets developed by GBD for cryogenic permanent magnet undulators

The magnetic field stability of the PrFeB magnets is one of the key points which affect its application in such devices as cryogenic permanent magnet undulators. In this study, the magnetic properties and micro structure of PrFeB magnets, which were developed by the grain boundary diffusion, were examined. The demagnetizing field distribution of the cryogenic permanent magnet undulator made using the PrFeB magnets was simulated by Radia, and the change mechanism of the irreversible demagnetization following treatments at high temperatures was experimentally studied, The results show that the intrinsic coercivity of the PrFeB magnets can be increased by diffusion of Tb. Meanwhile, the remanence of the magnets displays almost no loss, and the increasing range is closely related to the orientation thickness of the PrFeB magnet, Therefore, the PrFeB magnets developed using grain boundary diffusion are found to have extremely high comprehensive magnetic properties, The irreversible demagnetization of the PrFeB magnets developed by grain boundary diffusion for the CPMU is determined to be significantly improved following high-temperature treatments.

Effects of depth-and composition-dependent thermal conductivity and the compositional viscosity ratio on the long-term evolution of large thermochemical piles of primordial material in the lower mantle of the Earth:Insights from 2-D numerical modeling

Thermal conductivity plays an important role in the thermochemical evolution of Earth’s mantle.Recent mineral physics studies suggest that the thermal conductivity of the mantle varies with pressure and composition,and this may play an important role in the evolution of the Earth’s mantle.Meanwhile,the rheology of the deep mantle is also supposed to be composition-dependent.However,the dynamic influences of these factors remain not well understood.In this study,we performed numerical experiments of thermochemical mantle convection in 2-D spherical annulus geometry to systematically investigate the effects of depth-and composition-dependent thermal conductivity and the compositional viscosity ratio on the long-term evolution of the large thermochemical structure of primordial material in Earth’s mantle.Our results show that increasing the depth-dependent thermal conductivity leads to a larger core-mantle boundary(CMB)heat flow and allows the formation of more stable large thermochemical piles(e.g.,Large Low Shear Velocity Provinces,LLSVPs);while decreasing the composition-dependent thermal conductivity would slightly destabilize the primordial thermochemical piles,increase the altitude of these piles and the temperature differences between the piles and the ambient mantle.If the primordial mantle material is compositionally more viscous(e.g.,20 times than that of the ambient mantle),the long-term stability of the thermochemical piles of primordial material decreases,and this destabilizing effect will be enhanced by decreasing the composition-dependent thermal conductivity.As a result,the thermochemical piles would be unstable in the core-mantle boundary region.Therefore,our study indicates that the combined effects of depth-and composition-dependent thermal conductivity and compositional viscosity ratio are pronounced to the thermochemical evolution of the mantle.

利用低阶大地水准面异常反演大尺度核幔边界起伏

核幔边界（core-mantle boundary,CMB）是地球内部最重要的物理化学界面之一,地核和地幔通过核幔边界发生多种相互作用,这对地球重力场、地球自转及地磁场等都能产生重要影响。大地水准面异常是地球重力场的重要观测量,反映了地球内部的物质密度异常及界面变化等重要信息。推导了通过大地水准面异常反演核幔边界起伏的公式,利用2-4阶大地水准面异常反演了大尺度核幔边界起伏形态。结果显示,核幔边界起伏的径向幅度达±5km、与Morelli的地震层析成像结果的幅度接近,但在形态上略有差异。以高为5km、底边长为1 000km的棱柱体模型模拟计算了核幔边界密度异常引起的大地水准面异常响应,结果与观测大地水准面异常比较接近。

SH-wavefield simulation for a laterally heterogeneous whole-Earth model using the pseudospectral method

We present a scheme to simulate SH-wave propagation in a whole-Earth model with arbitrary lateral heterogeneities employing the Fourier pseudospectral method. Wave equations are defined in two-dimensional cylindrical coordinates and the model is taken through a great circle of the Earth. Spatial derivatives in the wave equations are calculated in the wavenumber domain by multiplication, and the transformation between spatial and wavenumber domains is performed via fast Fourier transformation. Because of the high accuracy and high speed of the Fourier pseudospectral method, the scheme enables us to calculate a short-wavelength global SH-wavefield with accurate waveforms and arrival times for models with heterogeneities that can be approximated as azimuthally symmetric. Comparing with two-dimensional simulation methods based on an axisymmetric model, implementing the seismic source in the present scheme is more convenient. We calculated the global SH-wavefield for the preliminary reference Earth model to identify the generation, reflection and refraction of various seismic phases propagating in the Earth. Applications to a heterogeneous global model with low-velocity perturbation above the core-mantle boundary were conducted to analyze the effect of lateral heterogeneity on global SH-wave propagation.

Investigation of the SA evolution by using the CHAOS-4 model over 1997–2013

The temporal and spatial evolution characteristics of the geomagnetic secular acceleration(SA) are investigated, based on CHAOS-4 core field model during the period of 1997–2013. The SA evolution on a short time scale is associated with the phenomenon of the geomagnetic jerk. More details of the global extent and the occurrence time of the successive jerks(the 1999, 2003, 2007, and 2011 jerks) are obtained. The location, size and reversed polarity pattern for the 1999 jerk are similar to those for the 2003 jerk in the Asian-Indian sector. While the 2007 and 2011 jerks mainly take place in the Atlantic sector. The direction and speed of the shift for the four jerks are different, identified by the occurrence time of the jerks. The zonal motions of the SA patches exhibit an oscillation pattern in the Asian-Indian sector, whereas a purely westward drifting pattern is along the equator in the Atlantic sector. It is believed that the shift of the jerks is related to the motion of SA-B_r patches observed at the core-mantle boundary(CMB).

香港粤语强调焦点句语调的音高表现

本文基于语调格局及语调系统的思路[6,7],用音高起伏度的计算方法 [8],对四位香港粤语发音人的三组不同位置的强调焦点句进行系统分析,并以自然焦点句作为参照。从四位发音人的平均结果发现:(1)舒声、入声自然焦点句音高的最高点在句首调域的上线,最低点在句末调域的下线。句末词调域最宽,具有句末焦点句的特征。(2)舒声强调焦点句音高的最高点在强调焦点所在词调域的上线,最低点在句末的下线。焦点所在的调域最宽。(3)不同焦点位置的入声句,焦点调域的最大值在调域的上线。入声短促,下线提高,承载边界调的能力显著减弱。(4)四组实验句调域宽窄的顺序为:句末>句首>自然焦点>句中(84%>75%>71%>66%)。(5)香港粤语强调焦点句,句中焦点所在词调域未出现最大化扩展,焦点后音高无骤降,焦点后调域没有出现急剧压缩的现象(PFC)[22]。这一结果与北京普通话焦点所在词域的特点不同。本研究结果对于粤语教学和研究都具有重要意义。

下地幔侧向不均匀及绝对板块运动对大地水准面的影响

本文提出并研究了板块上大地水准面受下地幔侧向不均匀性及板块绝对运动的影响而随时间变化的问题。利用已有的下地幔侧向不均匀性模型、板块绝对运动速度模型进行了计算,并分核幔边界不存在起伏和存在起伏两种情况进行了讨论。结果表明,在相当长时间内,其垂直变化绝对幅度可达 200米。确定古大地水准面应考虑这一变化。

Reversed polarity patches at the CMB and geomagnetic field reversal

The International Geomagnetic Reference Field models (IGRF) for 1900-2000 are used to calculate the geomagnetic field distribution in the Earth' interior from the ground surface to the core-mantle boundary (CMB) under the assumption of insulated mantle. Four reversed polarity patches, as one of the most important features of the CMB field, are revealed. Two patches with +Z polarity (downward) at the southern African and the southern American regions stand out against the background of -Z polarity (upward) in the southern hemisphere, and two patches of -Z polarity at the North Polar and the northern Pacific regions stand out against the +Z background in the northern hemisphere. During the 1900-2000 period the southern African (SAF) patch has quickly drifted westward at a speed of 0.2-0.3°/a; meanwhile its area has expanded 5 times, and the magnetic flux crossing the area has intensified 30 times. On the other hand, other three patches show little if any change during this 100-year period. Extending upward, each of the reversed polarity patches at the CMB forms a chimney-shaped 'reversed polarity column' in the mantle with the bottom at the CMB. The height of the SAF column has grown rapidly from 200km in 1900 to 900km in 2000. If the column grows steadily at the same rate in the future, its top will reach to the ground surface in 600-700 years. And then a reversed polarity patch will be observed at the Earth's surface, which will be an indicator of the beginning of a magnetic field reversal. On the basis of this study, one can describe the process of a geomagnetic polarity reversal, the polarity reversal may be observed firstly in one or several local regions; then the areas of these regions expand, and at the same time, other new reversed polarity regions may appear. Thus several poles may exist during a polarity reversal.

VLBI Observations of Nearly Diurnal Free Wobble

Theories of the Earth’s nutation show that the couplings between the core andmantle can give rise to an additional rotational normal mode,except for the Chandlerwobble(CW),due to the ellipsoidal core-mantle boundary and the fluid core of the Earth.The normal mode has often been referred to as the nearly diurnal free wobble(NDFW)with a period of nearly one sidereal day as viewed from the terrestrial reference system.The nutation of this mode relative to inertial reference system is retrograde free corenutation(RFCN).The theoretical value of the period is about 460 sidereal days.