Time-varying gravity field model of Sichuan-Yunnan region based on the equivalent mass source model

High-precision time-varying gravity field is an effective way to study the internal mass movement and understanding the spatio-temporal evolution process of the geodynamic system.Compared to the satellite gravity measurement,the repeated terrestrial gravity observation can provide a more high-order signal related to the shallow crust and subsurface.However,the suitable and unified method for gravity model estimation is a key problem for further applications.In this study,we introduce the spherical hexahedron element to simulate the field source mass and forward model the change of gravity field located at the Sichuan-Yunnan region(99—104°E,23—29°N)in the four epochs from 2015 to 2017.Compared to the experimental results based on Slepian or spherical harmonics frequency domain method,this alternative approach is suitable for constructing the equivalent mass source model of regional-scale gravity data,by introducing the first-order smooth prior condition of gravity time-varying signal to suppress the high-frequency component of the signal.The results can provide a higher spatial resolution reference for regional gravity field modeling in the Sichuan-Yunnan region.

Simultaneous resonance of an axially moving ferromagnetic thin plate under a line load in a time-varying magnetic field

In this paper,the simultaneous resonance of a ferromagnetic thin plate in a time-varying magnetic field,having axial speed and being subjected to a periodic line load,is studied.Based on the large deflection theory of thin plates and electromagnetic field theory,the nonlinear vibration differential equation of the plate is obtained by using the Hamilton′s principle and the Galerkin method.Then the boundary condition in which the longer opposite sides are clamped and hinged is considered.The dimensionless nonlinear differential equations are solved by using the method of multiple scales,and the analytical solution is given.In addition,the stability analysis is also carried out by using Lyapunov stability theory.Through numerical analysis,the variation curves of system resonance amplitude with frequency tuning parameter,magnetic field strength and external excitation amplitude are obtained.Different parameters that have significant effects on the response of the system,such as the thickness,the axial velocity,the magnetic field intensity,the position,and the frequency of external excitation,are considered and analyzed.The results show that the system has multiple solution regions and obvious nonlinear coupled characteristics.

Numerical and experimental studies on the effectiveness of time-varying electromagnetic fields in reducing electron density

When an aircraft or a hypersonic vehicle re-enters the atmosphere,the plasma sheath generated can severely attenuate electromagnetic wave signals,causing the problem of communication blackout.A new method based on time-varying E×B fields is proposed to improve on the existing static E×B fields and mitigate the radio blackout problem.The use of the existing method is limited by the invalid electron density reduction resulting from current density j=0 A m^(-2)in plasma beyond the Debye radius.The most remarkable feature is the introduction of a time-varying electric field to increase the current density in the plasma to overcome the Debye shielding effect on static electric field.Meanwhile,a magnetic field with the same frequency and phase as the electric field is applied to ensure that the electromagnetic force is always acting on the plasma in one direction.In order to investigate the effect of time-varying E×B fields on the plasma electron density distribution,two directions of voltage application are considered in numerical simulation.The simulation results indicate that different voltage application methods generate electromagnetic forces in different directions in the plasma,resulting in repulsion and vortex effects in the plasma.A comparison of the vortex effect and repulsion effect reveals that the vortex effect is better at reducing the electron density.The local plasma electron density can be reduced by more than 80%through the vortex effect,and the dimensions of the area of reduced electron density reach approximately 6 cm×4 cm,meeting the requirements of electromagnetic wave propagation.Besides,the vortex effect of reducing the electron density in RAM-C(radio attenuation measurements for the study of communication blackout)reentry at an altitude of 40 km is analyzed.On the basis of the simulation results,an experiment based on a rectangular-window discharge device is proposed to demonstrate the effectiveness of the vortex effect.Experimental results show that time-varying E×B fields can reduce the electron density in plasma of 3 cm thickness by 80%at B=0.07 T and U_(0)=1000 V.The investigations confirm the effectiveness of the proposed method in terms of reducing the required strength of the magnetic field and overcoming the Debye shielding effect.Additionally,the method is expected to provide a new way to apply a magnetic window in engineering applications.

A new algorithm based on the background field for red tide monitoring in the East China Sea

Remote sensing has been proven to be an effective means of monitoring red tides. The spectral information is an important basis for establishing a model to monitor red tides. The spectral curves of red tide events are analyzed and compared with multiyear monthly averaged spectral curves based on MODIS data from July 2002 to June 2012, as well as spectral differences at the same location during red tide presence and absence. A red tide monitoring algorithm is developed based on the background field to extract the red tide information of the East China Sea （ECS）. With the application of the algorithm in the ECS, the results reveal that the developed model can effectively determine the location of red tides, with good correspondence to the results from an official bulletin. This demonstrates that the algorithm can effectively extract the red tide information.

A numerical model study on multi-species harmful algal blooms coupled with background ecological fields

Based on systematized physical, chemical, and biological modules, a multi-species harmful algal bloom （HAB） model coupled with background ecological fields was established. This model schematically embod-ied that HAB causative algal species and the background ecological system, quantified as total biomass, were significantly different in terms of the chemical and biological processes during a HAB while the inter-action between the two was present. The model also included a competition and interaction mechanism between the HAB algal species or populations. The Droop equation was optimized by considering tempera-ture, salinity, and suspended material impact factors in the parameterization of algal growth rate with the nutrient threshold. Two HAB processes in the springs of 2004 and 2005 were simulated using this model. Both simulation results showed consistent trends with corresponding HAB processes observed in the East China Sea, which indicated the rationality of the model. This study made certain progress in modeling HABs, which has great application potential for HAB diagnosis, prediction, and prevention.

Determination of the degree 120 time-variable gravity field in the Sichuan-Yunnan region using Slepian functions and terrestrial measurements

The terrestrial time-variable gravity measurements are characterized by a high signal-to-noise ratio and sensitivity to the sources of mass change in the Earth's crust.These gravity data have many applications,such as surface deformation,groundwater storage changes,and mass migration before and after earthquakes.Based on repeated terrestrial gravity measurements at 198 gravity stations in the Sichuan-Yunnan region(SYR)from 2015 to 2017,we determine a time series of degree 120 gravity fields using the localized spherical harmonic(Slepian)basis functions.Our results show that adopting the first 6 Slepian basis functions is sufficient for effective localized Slepian modeling in the SYR.The differences between two gravity campaigns at the same time of year show an obvious correlation with tectonic features.The degree 120 timevariable gravity models presented in this paper will benefit the study of the regional mass migration inside the crust of the SYR and supplement the existing geophysical models for the China Seismic Experimental Site.

Density and temperature reconstruction of a flame-induced distorted flow field based on background-oriented schlieren(BOS) technique

An experimental system based on the background-oriented schlieren（BOS） technique is built to reconstruct the density and temperature distribution of a flame-induced distorted flow field which has a density gradient. The cross-correlation algorithm with sub-pixel accuracy is introduced and used to calculate the background-element displacement of a disturbed image and a fourth-order difference scheme is also developed to solve the Poisson equation. An experiment for a disturbed flow field caused by a burning candle is performed to validate the built BOS system and the results indicate that density and temperature distribution of the disturbed flow field can be reconstructed accurately. A notable conclusion is that in order to make the reconstructed results have a satisfactory accuracy, the inquiry step length should be less than the size of the interrogation window.

The X-ray Background (Deep Fields, Luminosity Functions and Type-Ⅱ Quasars)

Deep X ray surveys have shown that the cosmic X ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80% of the 0.1-10keV X ray background into discrete sources. Optical spectroscopic identifications show that the sources producing the bulk of the X ray background are a mixture of obscured (type 1) and unobscured (type 2) AGNs, as predicted by the XRB population synthesis models. A class of highly luminous type 2 AGN, so called QSO 2s, has been detected in the deepest Chandra and XMM Newton surveys. The new Chandra AGN redshift distribution peaks at much lower redshifts (z≈0.7) than that based on ROSAT data, indicating that Seyfert galaxies peak at significantly lower redshifts than QSOs.

Influence of regional background stress fields on the spontaneous rupture of the major faults around Xiluodu dam,China

Simulations of the spontaneous rupture of potential earthquakes in the vicinity of reservoir dams can provide accurate parameters for seismic resilience assessment,which is essential for improving the seismic performance of reservoir dams.In simulations of potential spontaneous ruptures,fault geometry,regional stress fields,constitutive parameters of the fault friction law,and many other factors control the slip rate,morphology,and dislocation of the rupture,thereby affecting the simulated ground motion parameters.The focus of this study was to elucidate the effects of the background stress field on the nucleation and propagation of spontaneous ruptures based on the factors influencing potential M>7 earthquake events on the Leibo Middle Fault(LBMF)and the Mabian-Yanjing Fault(MB-YJF)in the Xiluodu dam(XLD)region.Our simulation results show that the magnitude of the regional background stress field plays a decisive role in whether a destructive earthquake exceeding the critical magnitude will occur.We found that the direction and magnitude of the regional stress significantly affect the range of rupture propagation on the fault plane,and fault geometry affects the spatial distribution of the rupture range.Under the same regional stress field magnitude and orientation,a more destructive,high-magnitude earthquake is more likely to occur on the LBMF than on the MB-YJF.

Temperature Field Reconstruction in High-Temperature Gas by Using the Colored Background Oriented Schlieren Method

A 3D temperature field reconstruction method using the colored background oriented schlieren(CBOS)method is proposed to address image blurring due to the different refractive index of the multi-wavelength light and significant errors produced when the traditional background oriented schlieren(BOS)method is applied to high-temperature gas.First,the traditional method is employed to reconstruct the non-uniform 3D temperature field.Second,the CBOS method is applied to correct the distortion.Then,by analyzing the correlation coefficient among different color points of the colored background pattern,the non-uniform temperature field is reconstructed much more accurately.Finally,the experimental results are verified by applying the Runge-Kutta ray-tracing method and the thermocouple contact measurement method.The maximum average temperature error of the CBOS-reconstructed temperature field is 12.92°C,compared with the thermocouples.Therefore,an accurate three-dimensional reconstruction of the temperature field can be achieved by the proposed method effectively.

GRACE time-varying gravity field solutions based on PANDA software

The conventional dynamic approach for gravity filed modelling has been implemented in the PANDA(Position and Navigation Data Analyst) software. A variant of the so-called ’two-step’ method for gravity field modelling is adopted for this purpose, where the GRACE(Gravity Recovery and Climate Experiment)orbits are derived from the GPS(Global Positioning System) data in a first step followed by a simultaneous determination of dynamic orbit and gravity filed from the GPS-derived orbits and K-band rangerate measurements in a second step. In this way, the monthly gravity field solutions complete to degree and order 96 are produced for the period Jan. 2005 to Dec. 2010. Their performance is assessed by comparing them with the official solutions, i.e., CSR RL05, GFZ RL05 a and JPL RL05. A comparison in the spectral domain in terms of geoid heights reveals that the obtained solutions present the smallest degree amplitudes at degree 30-75. A further analysis of mass changes in the spatial domain demonstrates that the main signals observed from the obtained solutions are in great agreement with those from the official solutions. Remarkably, the correlation coefficients of mass changes in large river basins from the official solutions with respect to those from the obtained solutions are all above 0.97. These results demonstrate that the obtained solutions are comparable to the official solutions.

基于GPR-LSTM的地震热红外背景场的构建方法

地震监测是一项非常重要且具有挑战性的任务,遥感技术的不断发展加强了在宏观尺度上对地球表面的监测能力。研究表明,地震前通常都会出现地表温度异常升高的现象,因此各种异常提取算法被应用于地震热异常研究中。其中,基于背景场的提取方法由于具有较强的机理解释性而受到广泛应用。然而,以往基于背景场的异常提取方法更多将背景场限定于某一固定阈值,忽略了受外界因素(非震)影响导致的地表温度的小范围正常波动。据此,文中提出了一种基于GPR-LSTM的地震热红外背景场的构建方法。该方法包括两大部分:震期年变基准场的建立、实际LST的残差波动范围计算及背景场的构建。基于MODIS地表温度产品,以2008年四川汶川和新疆于田地震为研究对象,使用所述方法对地震前兆热异常信息进行提取与分析,经过实验得出以下结论:1)地震热异常通常沿青藏高原的断层分布,这不仅证明了文中方法能够减弱地表温度数据中噪声的干扰,同时也证明该方法在热异常信息提取方面的有效性;2)地震年份的构造活动比非地震年份更加活跃,导致地表温度的异常增温更加明显;3)不同地震案例震前的热异常时空特征各不相同。

基于雷达探测数据的尾涡危险区评估

针对尾涡危险区域的研究可以有效避免后机尾涡危险遭遇事件的发生,提出了一种基于激光雷达探测数据的尾涡危险区计算方法。根据雷达实测数据反演飞机尾涡的演化轨迹和速度环量;基于后机遭遇前机尾涡的空气动力学响应构建滚转力矩系数模型;考虑尾涡在实际场景下的演化情况,结合反演得到的尾涡特征参数,计算飞机遭遇尾涡时的滚转力矩并计算尾涡危险区。结果表明:基于激光雷达探测数据反演尾涡特征参数,左涡和右涡的位置、环量并不一致,据此结合滚转力矩系数模型计算得到的整体危险区域也具有不对称性,当单涡更稳定时,对应的危险区域也更大。以B738为后机,选取某一尾涡探测片段验证,对于涡心坐标位置为左涡(390 m,8.61°),右涡(435 m,8.85°)的尾涡,左涡、右涡的环量分别为256.83 m^(2)/s和223.35 m^(2)/s,左涡相对右涡实际划设的危险区覆盖范围更大,因此后机与前机左右尾涡的安全阈值区域不同,可据此对横向间隔做出不同调整,因此所提方法有利于为分析后机遭遇安全性、缩短尾流间隔提出重要参考。

基于现场可编程门阵列的水果识别系统设计

针对目前大多数水果识别系统实时性差和成本较高的问题,本文提出一种基于现场可编程门阵列(FPGA)的水果识别系统。整体硬件设计包含图像采集、检测识别和显示模块。软件部分通过图像采集平台将水果图像存储至双倍数据率同步动态随机存储器(DDR3)控制模块,进行图像灰度化处理,并创造性地提出背景帧差法对水果图像进行分割。通过融合水果颜色和几何特征,实现对水果数量、颜色和种类的识别。整个水果识别系统在不同光照下对常见水果进行了测试。实验结果表明,水果平均识别准确率达到93.25%,识别速度约为16.67 ms,FPGA硬件资源消耗率仅占28.02%,可以满足实时性需求。

不同遗传背景亲本及其杂交种对田间出苗率的影响

为了研究细胞质不同亲本及其杂交种对田间出苗率的影响,以29个AL型不育系和25个恢复系为亲本材料配制了双列杂交组合,以“同母多父”和“同父多母”的方式,对杂交种和亲本的田间出苗率进行比较分析。结果表明,细胞质遗传背景不同的恢复系、保持系、杂交种之间田间出苗率差异不显著。杂交种与双亲的田间出苗率间呈显著正相关,田间出苗率高的亲本所配置杂交种田间出苗率表现出较高杂种优势。杂交种田间出苗率应该作为优异亲本的重要指标得到重视。

基于等效磁路网络法的均匀正交磁场对环形磁芯等效电感的影响

电源中的磁性元件对外部磁场天然敏感,其工作特性直接影响电源的输出特性。实现背景磁场的建模是研究电源中磁性元件受强杂散磁场干扰问题的重要前提,但目前关注这一应用场景的相关研究较少,且常用的电磁场分析方法难以兼顾计算的精度和效率。基于等效磁路网络法提出了一种杂散磁场效应的分析方法,该方法将研究对象等效生成磁路单元,离散形成网络模型,并通过求解等效磁路系统方程得到模型的场量分布。以一款具体的环形铁氧体磁芯为例,利用等效磁路网络法计算了环形磁芯在直流激励和均匀正交磁场下的场量分布,分析了背景磁场对其等效电感的影响。通过对比等效磁路网络法与有限元法的计算结果,验证了该方法的准确性与高效性,且适用于电源受背景磁场干扰问题的分析。

基于合成场强仪的输电工程地面合成电场研究

高压直流(DC)输电线路交叉跨越是我国特高压(UHV)技术发展中出现的问题。由于两回DC线路相互影响,交叉跨越区域内合成电场呈复杂的三维分布,UHV DC输电工程地面合成电场计算较为困难。选取典型±800 kV UHV DC输电工程进行地面合成电场的实测研究。参照GB 39220—2020,采用HDEM-01合成场强仪进行野外现场实测。测量参数为有效期内的场磨传感器上积聚的电荷量。测量结果与运行初期实测数据的对比结果表明:±800 kV换流站周边运行初期合成电场强度略低于后期,且整体水平较低;沿线电磁环境敏感目标运行初期、后期的实测数据中,74%的数值小于5 kV/m。通过此次研究,明确了UHV DC输电工程合成电场不同时期的特性。该研究有助于推进UHV DC输电工程的快速建成,并提高其运行安全性,从而推动电力工程建设的发展。

邢台震区应力场特征及M_(L)3.5以上地震的发震背景分析

邢台老震区构造背景复杂,发育多组断裂,属构造较不稳定地带,且区域中小地震频发。2017年至2021年发生6次M_(L)3.5以上地震,其中有两次M L4以上地震。本文基于搜集的震源机制解资料,反演区域现今地壳应力场,模拟震源机制与地壳应力场的关系,计算地壳应力场在地震发震断层面上的相对剪应力和相对正应力,分析地震的发震背景。结果表明,6次M_(L)3.5以上地震中,有2次震源机制节面接近应力场的最大剪应力节面,有4次震源机制节面远离应力场的最大剪应力节面。说明地震不是完全按照震源机制节面上具有最大剪应力的破裂方向发生,有时可能发生在某些薄弱带上。因此,在进行地震预测时,不能只关注最大剪应力破裂方向,还应多关注其边缘的地质薄弱带,这一结果可能会为后续分析该区域的地震危险性,研究地震孕育机制及动力学过程提供一定的参考依据。

ARCADE 2 Spatial Roar, What Theory of Relation Reveals

The theory of Relation provides an explanation for the Arcade 2 excess. It assumes that the isotropic radio emission measured by the Arcade 2 Collaboration, which is 5 - 6 times brighter than the expected contributions from known extra-galactic sources, is the residue of an immense primitive energy of ordinary matter released by a relativistic bang almost 100 million years after the big bang, which gave the mass-energy the missing gravity to activate contraction. This relativistic bang, via a Lorentz energy transformation, would have released enormous energy held to be the source of the powerful radio noise detected by the NASA researchers. This transformation would have simultaneously triggered the formation of the first stars from dense gas and the reionization of less dense neutral gas. This departs from the idea that continuous reionization began after the formation of the first stars. We emphasize the importance of primordial magnetic fields, which would have generated significant density fluctuations during recombination and acted as a direct seed for cosmic structures. The first stars and galaxies were bathed in strong magnetic fields that gave rise to the radio microwave din (boom) discovered by Arcade 2. These intense magnetic fields alter the trajectory of charged particles zooming near the speed of light, triggering the space roar and emitting radiation that forms a synchrotron radio background. The theory of Relation offers an alternative to the Lambda-CDM cosmological model, which has become the standard model of the big bang, which leads straight to the vacuum catastrophe.

3-D finite element modeling for evolution of stress field and interaction among strong earthquakes in Sichuan-Yunnan region

Based on the latest achievement about activities of geological structure, a 3-D finite-element model containing four layers of upper crust, lower crust (two layers) and upper mantle is established in the paper. By repeated tests and revisions, the boundary conditions of the model are determined. And then the background stress field, the stress field caused by fault creep and the stress field triggered by strong earthquake in Sichuan-Yunnan region, as well as their dynamic variations are calculated. The results indicate that the latter earthquake often occurs in the area with positive Coulomb rupture stress change associated with the former one, the former earthquake has a triggering effect on the latter one to a certain extent, and strong earthquake often occur in groups under the background of high stress, which is of great significance for distinguishing seismic anomalies, as well as for improving the level of earthquake prediction.