期刊文献+
共找到37篇文章
< 1 2 >
每页显示 20 50 100
Shim coil design for Halbach magnet by equivalent magnetic dipole method 被引量:1
1
作者 Jia-Min Wu Zheng Xu +2 位作者 Pan Guo Jin-Feng Qi Yu-Cheng He 《Chinese Physics B》 SCIE EI CAS CSCD 2018年第10期300-307,共8页
Low-field nuclear magnetic resonance magnet(2 MHz) is required for rock core analysis. However, due to its low field strength, it is hard to achieve a high uniform B0 field only by using the passive shimming. Theref... Low-field nuclear magnetic resonance magnet(2 MHz) is required for rock core analysis. However, due to its low field strength, it is hard to achieve a high uniform B0 field only by using the passive shimming. Therefore, active shimming is necessarily used to further improve uniformity for Halbach magnet. In this work, an equivalent magnetic dipole method is presented for designing shim coils. The minimization of the coil power dissipation is considered as an optimal object to minimize coil heating effect, and the deviation from the target field is selected as a penalty function term. The lsqnonlin optimization toolbox of MATLAB is used to solve the optimization problem. Eight shim coils are obtained in accordance with the contour of the stream function. We simulate each shim coil by ANSYS Maxwell software to verify the validity of the designed coils. Measurement results of the field distribution of these coils are consistent with those of the target fields.The uniformity of the B0 field is improved from 114.2 ppm to 26.9 ppm after using these shim coils. 展开更多
关键词 equivalent magnetic dipole method shim coils magnetic resonance Halbach magnet
下载PDF
Feasibility Research on Fatigue Damage Evaluation Based on Magnetic Memory Method 被引量:1
2
作者 王翔 秦晔 +1 位作者 陈铭 王成焘 《Journal of Donghua University(English Edition)》 EI CAS 2005年第5期9-11,共3页
To confirm whether Magnetic Memory Method can be used to evaluate the fatigue damage of ferromagnetic part or not,this paper stated the principle of magnetic memory method.Also, the relationship between testing parame... To confirm whether Magnetic Memory Method can be used to evaluate the fatigue damage of ferromagnetic part or not,this paper stated the principle of magnetic memory method.Also, the relationship between testing parameter of magnetic memory method and fatigue damage was analyzed based on the experiment. The results show that magnetic memory method can be used to evaluate the fatigue damage represented by stress concentration. However, the relationship between the parameter of magnetic memory method and fatigue damage still needs to be studied. 展开更多
关键词 magnetic memory method fatigue damage stress concentration
下载PDF
SIMUUTION OF ELECTROMAGNETIC TUBE BULGING BASED ON LOOSE COUPLING METHOD 被引量:6
3
作者 LI Zhong LI Chunfeng 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2006年第4期566-569,共4页
A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radi... A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM, The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpicces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored, The calculated results show well agreements with the experimental results. 展开更多
关键词 Loose coupling method Electromagnetic tube bulging Excitation Magnetic pressure
下载PDF
Equivalent magnetic dipole method used to design gradient coil for unilateral magnetic resonance imaging
4
作者 Zheng Xu Xiang Lil +1 位作者 Pan Guo Jia-Min Wu 《Chinese Physics B》 SCIE EI CAS CSCD 2018年第5期545-550,共6页
The conventional magnetic resonance imaging(MRI)equipment cannot measure large volume samples nondestructively in the engineering site for its heavy weight and closed structure.In order to realize the mobile MRI,this ... The conventional magnetic resonance imaging(MRI)equipment cannot measure large volume samples nondestructively in the engineering site for its heavy weight and closed structure.In order to realize the mobile MRI,this study focuses on the design of gradient coil of unilateral magnet.The unilateral MRI system is used to image the local area above the magnet.The current density distribution of the gradient coil cannot be used as a series of superconducting nuclear magnetic resonance gradient coils,because the region of interest(ROI)and the wiring area of the unilateral magnet are both cylindrical side arc surfaces.Therefore,the equivalent magnetic dipole method is used to design the gradient coil,and the algorithm is improved for the special case of the wiring area and the ROI,so the X and Y gradient coils are designed.Finally,a flexible printed circuit board(PCB)is used to fabricate the gradient coil,and the magnetic field distribution of the ROI is measured by a Gauss meter,and the measured results match with the simulation results.The gradient linearities of x and y coils are 2.82%and 3.56%,respectively,less than 5%of the commercial gradient coil requirement. 展开更多
关键词 unilateral MRI equivalent magnetic dipole method gradient coil current density distribution
下载PDF
AN EXPERIMENTAL RESEARCH ON BUBBLE PROPERTIES OF MAGNETIC FLUIDIZED BEDS BY MAGNETIC INDUCTIVE METHOD
5
作者 蔡崧 邢春礼 《Journal of Southeast University(English Edition)》 EI CAS 1991年第2期95-102,共8页
In view of the fact that the existing methods of measuring bubble propertiesare difficult to be realized in magnetic fluidized beds,a new method,the magnetic induc-tive method,has been developed.With the help of this ... In view of the fact that the existing methods of measuring bubble propertiesare difficult to be realized in magnetic fluidized beds,a new method,the magnetic induc-tive method,has been developed.With the help of this method the bubble properties inmagnetic fluidized beds were studied successfully,which concerned mainly with the influ-ence of magnetic intensity,single jet gas flow rate and main fluidizing gas flow rate onbubble frequency,velocity volume and coalescence or splitting. 展开更多
关键词 fluidized BEDS BUBBLE MEASUREMENT methods/magnetic fluidized BEDS bubblc charactcristics
下载PDF
Calculating magnetic shielding effectiveness for high-power dc comparator by magnetic circuit method
6
作者 WANG Xiao-wei REN Shi-yan 《Journal of Chongqing University》 CAS 2007年第2期113-118,共6页
Magnetic shielding is very important in the design of a high-power dc comparator. This paper addressed the application of magnetic circuit method to calculate the magnetic shielding effectiveness of high-power dc comp... Magnetic shielding is very important in the design of a high-power dc comparator. This paper addressed the application of magnetic circuit method to calculate the magnetic shielding effectiveness of high-power dc comparators when an external radial magnetic field is added. The mathematical relationship between the magnetic shielding effectiveness and the parameters of the magnetic shielding body were obtained. To verify the validity of the calculation method, we developped a procedure to measure the magnetic shielding effectiveness of the magnetic body by measuring the induction voltage of the detection winding instead of the magnetic intensity at a point in the magnetic shielding body, making the manipulation much easier. The result calculated with the magnetic circuit method turns out to be closer to the measured one compared with that calculated with a conventional algorithm proposed by Ren, suggesting that the magnetic circuit method is an applicable tool for estimating the toroidal cavity magnetic shielding effectiveness of a heavy current comparator when a radial magnetic field is added. 展开更多
关键词 radial magnetic field magnetic shielding effectiveness magnetic circuit analysis method magnetic potential
下载PDF
Reconnaissance investigation of geothermal resources in parts of the Middle Benue Trough, Nigeria using remote sensing and geophysical methods
7
作者 Tochukwu Ngene Manoj Mukhopadhyay Suame Ampana 《Energy Geoscience》 2022年第4期360-371,共12页
In Nigeria,the basement complex and the sedimentary basins house many thermal springs which are physical manifestations of geothermal energy.However,there are difficulties in accessing the sustain-ability of these res... In Nigeria,the basement complex and the sedimentary basins house many thermal springs which are physical manifestations of geothermal energy.However,there are difficulties in accessing the sustain-ability of these resources due to ethical and security issues as well as limited data in Nigeria.Thus,identifying the precise location,temperature,and energy potential on a large scale has been a major drawback.This paper is the preliminary investigation of geothermal potential in parts of the Middle Benue Trough using satellite imagery,geology,regional gravity,and high-resolution aeromagnetic data.Landsat 8 scene was used to estimate the Land Surface Temperature(LST)in ArcGIS^(TM).Selected sites were classified as very low,low,moderate,and high LST.The intermediate and high classes happen to be possible geothermal zones,and they occupy 49% of the study area(38,077 km^(2)).The Riverline was superimposed on the LST,and the high-temperature sites were located by the identification tool.Streams/river data overlapped on the selected sites were regarded as thermal/warm springs.Remarkably,the LST results show lower temperatures(<36℃)at the famous thermal springs(Awe and Wukari)than some unknown rivers/streams found in Kwande(38℃),Ussa,(38℃),Gwer East(37℃),Yola Cross and Ogoja(36℃).Furthermore,the geophysical datasets,regional gravity,and high-resolution aeromagnetic data were interpolated to delineate the subsurface features associated with geothermal manifestations.The four layers from the LST were further evaluated using the geophysical approach.Gravity and mag-netic values revealed variations that could be linked to geothermal alterations.The correlation of the geophysical anomalies and LST with the geology of the study area uncovers essential information on energy potentials.Therefore,further investigation is required to estimate the depth of the causative body,the geothermal gradients,and the reservoir volumes. 展开更多
关键词 ARCMAP Gravity and magnetic methods Geothermal resources Landsat 8 Land surface temperature
下载PDF
APPLICATION OF HIGH-RESOLUTION MAGNETIC METHOD AND GRADIENT METHOD TO LOCATE ABANDONED BRINE-WELLS IN HUTCHINSON, KANSAS, U.S.A.
8
作者 CHEN Chao XIA Jianghai +2 位作者 XIA Sihao David Laflen Stephen L. Williams 《工程地球物理学报》 2004年第1期17-25,共9页
After successfully locating one abandoned brine well by an electromagnetic method during testing in 2001 and five abandoned brine wells by a high resolution magnetic method during 2002, a high resolution magnetic meth... After successfully locating one abandoned brine well by an electromagnetic method during testing in 2001 and five abandoned brine wells by a high resolution magnetic method during 2002, a high resolution magnetic method was again proposed to search for wells in 2003 when a second sensor was employed to acquire data for calculating the pseudo vertical gradient of magnetic fields. Total area surveyed in 2003 was 1,024,000 ft 2, which was divided into grids with an average size of 10,000 ft 2 and distributed across eight different sites. Magnetic anomalies and their vertical gradients from known brine wells were first recorded as signatures to identify anomalies caused by possible buried brine wells. Of fifty one verified anomalies, thirty one anomalies were due to wells buried at depths from 0 to 8.5 ft: twenty one 6 to 9 inch abandoned brine wells, seven 1.5 to 3 inch probable water wells, one 16 inch dewatering well for a construction site at a depth of 3 ft, and two 4 inch wells on the ground surface. Approximate monopole shaped anomalies were observed from all these wells after data corrections. However, the range of amplitudes of magnetic anomalies from 7,000 to 28,000 nT from these abandoned brine wells was measured. This range of anomalies is mainly due to the thickness and depth of buried wells. Anomaly amplitudes from 1.5 to 3 inch wells are 4,000 to 8,000 nT and linearly correlate with the buried depth. One 3 inch well that caused an anomaly of 13,000 nT could be the inner pipe of a brine well. Gradient anomalies are roughly in a range of 100 to 200 nT/inch for 1.5 to 3 inch wells and 200 to 300 nT/inch for brine wells.As indicated by the potential field theory, gradient data possess higher horizontal resolution than the magnetic field itself. Gradient data provide valuable assistance in determining horizontal locations of anomaly sources for excavation. In practice, however, improvement in the horizontal resolution is limited by survey line spacing. If only one sensor is used in a survey, there is rapid decrease in the horizontal resolution when sensor height increases from 14 to 44 inches. This indicates that it is critical to keep the sensor as close to the ground as possible when hunting buried wells that are close to each other. It also suggests that the downward continuation is useful to increase the horizontal resolution in well hunting. 展开更多
关键词 High resolution magnetic method Magnetic gradient method Brine Well
下载PDF
ANALYSIS OF HUMAN PLACENTA BY ^(31)P NUCLEAR MAGNETIC RESONANCE AND THIN-LAYER CHROMATOGRAPHY SCANNING COMBINED WITH THE CORRECTIVE METHOD OF ABSORBANCE PROPORTIONAL COEFFICIENT
9
作者 Rong GUO Jian wei CHEN Yi Min XU AiHua ZHANG Nanjing College of Traditional Chinese Medicine,Nanjing 210029 《Chinese Chemical Letters》 SCIE CAS CSCD 1993年第12期1081-1084,共4页
Five phospholipids in human placenta were determined by phosphorus 31 nuclear magnetic resonance(^(31)P NMR)spectroscopy and thin-layer chromatography(TLC) scanning combined with the corrective method of absorbance pr... Five phospholipids in human placenta were determined by phosphorus 31 nuclear magnetic resonance(^(31)P NMR)spectroscopy and thin-layer chromatography(TLC) scanning combined with the corrective method of absorbance proportional coefficient. The NMR spectrometer used this investigation was a Bruker AM-500 spectrometer operating at 202.4 MHz for ^(31)P chemical shifts are relative to 85% phosphoric acid. TIC was carried out by silica gel H plate developed in chloroform-methanol-glacial acetic acid-ethanol-water(25:4:6:2:0.5),with Vaskovsky reagent as colour -developing agent of phospholipids. 展开更多
关键词 P NUCLEAR MAGNETIC RESONANCE AND THIN-LAYER CHROMATOGRAPHY SCANNING COMBINED WITH THE CORRECTIVE method OF ABSORBANCE PROPORTIONAL COEFFICIENT ANALYSIS OF HUMAN PLACENTA BY LPC TLC
下载PDF
Numerical and experimental studies on the effectiveness of time-varying electromagnetic fields in reducing electron density
10
作者 郭韶帅 谢楷 +2 位作者 徐晗 付麦霞 牛营营 《Plasma Science and Technology》 SCIE EI CAS CSCD 2023年第6期30-40,共11页
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 tim... 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. 展开更多
关键词 BLACKOUT magnetic window method time-varying E×B fields
下载PDF
Reconnaissance Geophysical Study on the Southeastern Part of Al-Qashah Aera, KSA
11
作者 Ali Y. Al-Bakri Mohammed Sazid 《World Journal of Engineering and Technology》 2023年第3期424-433,共10页
The investigated study area locates about 72 km from Jeddah City, Makkah District, Kingdom of Saudi Arabia. The study mainly aimed to define the most significant zones of possible mineralization and outline their subs... The investigated study area locates about 72 km from Jeddah City, Makkah District, Kingdom of Saudi Arabia. The study mainly aimed to define the most significant zones of possible mineralization and outline their subsurface parameters (location and strike) in the southeast of Jabal Al-Qashah. Several geophysical methods have been conducted to carry out the goal, including ground magnetic, self-potential (SP), and induced polarization (IP) methods. Integrating these methods aims to help delineate the possible mineralization in the study area. The magnetic survey was conducted along 17 profiles where these profiles were chosen to be perpendicular to the strike of the quartz shear zone. Self-potential was applied along with five profiles covering the study area. At the same time, induced polarization was used along with one profile located at the western side of the study area corresponding to some magnetic and SP profiles. The most interesting zones of mineralization were successfully determined by comparing the results of residual magnetic profile (3), SP profile (1), and IP profile, where geological structures control some mineralization. 展开更多
关键词 Geophysical methods Magnetic method Self-Potential (SP) Induced Polarization (IP) Jabal Al-Qashah
下载PDF
Quantitative Detection of Corrosion State of Concrete Internal Reinforcement Based on Metal Magnetic Memory
12
作者 Zhongguo Tang Haijin Zhuo +3 位作者 Beian Li Xiaotao Ma Siyu Zhao Kai Tong 《Structural Durability & Health Monitoring》 EI 2023年第5期407-431,共25页
Corrosion can be very harmful to the service life and several properties of reinforced concrete structures.The metal magnetic memory(MMM)method,as a newly developed spontaneous magnetic flux leakage(SMFL)non-destructi... Corrosion can be very harmful to the service life and several properties of reinforced concrete structures.The metal magnetic memory(MMM)method,as a newly developed spontaneous magnetic flux leakage(SMFL)non-destructive testing(NDT)technique,is considered a potentially viable method for detecting corrosion damage in reinforced concrete members.To this end,in this paper,the indoor electrochemical method was employed to accelerate the corrosion of outsourced concrete specimens with different steel bar diameters,and the normal components Bz and its gradient of the SMFL fields on the specimen surfaces were investigated based on the metal magnetic memory(MMM)method.The experimental results showed that the SMFL experimental Bz curves are consistent with the analytical results of the theoretical model.Furthermore,the crest-to-trough behavior on the Bz signal curve and its zero-point gradient spacing can more accurately indicate the corroded area’s extent.Then,a magnetic characteristic parameter W based on a large amount of experimental data was established to characterize the degree of corrosion of the steel bars.The magnetic characteristic parameter W is linearly related to the maximum cross-sectional area loss rateof the corroded reinforcement.This paper will lay the foundation for future research on corrosion detection of reinforced concrete structures based on the MMM method and provide a feasible way for non-destructive detection of corrosion independent of the influence of reinforcement diameter and magnetization history. 展开更多
关键词 Reinforcing steel metal magnetic memory(MMM)method spontaneous magnetic flux leakage(SMFL) nondestructive testing local corrosion
下载PDF
Design Optimization for Generating a High Static Magnetic Field
13
作者 Hussien A. Elharati Salma Ahmed Alharati +1 位作者 Ziad Omar Wareg Mohamed Amro Waregh 《World Journal of Engineering and Technology》 2023年第4期793-806,共14页
This paper details the creation of a device capable of generating a powerful and consistent static magnetic field. This apparatus serves the purpose of quantifying the magnetostrictive strain found in materials like a... This paper details the creation of a device capable of generating a powerful and consistent static magnetic field. This apparatus serves the purpose of quantifying the magnetostrictive strain found in materials like annealed cobalt ferrite and Terfenol-D, specifically those shaped as cylindrical rods. In our investigation, the use of static magnetic fields proves most advantageous. This choice is made to mitigate the generation of eddy currents, which would inevitably occur if the magnetic field intensity were varied. The fundamental idea behind this design involves employing a C-shaped iron core constructed from low-carbon mild steel. On this core, three coils are mounted, each capable of producing one-third of the required 9000 Oersted (Oe) magnetic field strength. The test specimen is situated within the “jaws” of the C-shaped core, thus completing the magnetic circuit. To manage the heat generated by each coil, a cooling system consisting of copper tubes is employed. These tubes facilitate the flow of air to dissipate the heat. To model and predict the magnetic field strength produced by the coils, finite element analysis (FEMM) software is utilized, and the results align closely with the anticipated outcomes. This design effectively generates a robust and unchanging magnetic field measuring a stable 9000 Oe in total. Consequently, this equipment finds utility in characterizing the magnetic properties of specific materials. 展开更多
关键词 Static Magnetic Field Magnetostrictive Strain Eddy Currents Magnetic Field Strength Finite Element method Magnetics (FEMM)
下载PDF
2D joint inversion of CSAMT and magnetic data based on cross-gradient theory 被引量:5
14
作者 Wang Kun-Peng Tan Han-Dong Wang Tao 《Applied Geophysics》 SCIE CSCD 2017年第2期279-290,324,共13页
A two-dimensional forward and backward algorithm for the controlled-source audio-frequency magnetotelluric (CSAMT) method is developed to invert data in the entire region (near, transition, and far) and deal with ... A two-dimensional forward and backward algorithm for the controlled-source audio-frequency magnetotelluric (CSAMT) method is developed to invert data in the entire region (near, transition, and far) and deal with the effects of artificial sources. First, a regularization factor is introduced in the 2D magnetic inversion, and the magnetic susceptibility is updated in logarithmic form so that the inversion magnetic susceptibility is always positive. Second, the joint inversion of the CSAMT and magnetic methods is completed with the introduction of the cross gradient. By searching for the weight of the cross-gradient term in the objective function, the mutual influence between two different physical properties at different locations are avoided. Model tests show that the joint inversion based on cross-gradient theory offers better results than the single-method inversion. The 2D forward and inverse algorithm for CSAMT with source can effectively deal with artificial sources and ensures the reliability of the final joint inversion algorithm. 展开更多
关键词 CSAMT magnetic method data space inversion cross-gradient joint inversion
下载PDF
Quantitative analysis of magnetic anomaly of reinforcements in bored in-situ concrete piles 被引量:3
15
作者 Sun Bin Dong Ping Wang Chong Pu Xiaoxuan Wu Yongjing 《Applied Geophysics》 SCIE CSCD 2009年第3期275-286,301,共13页
We quantitatively study magnetic anomalies of reinforcement rods in bored insitu concrete piles for the first time and summarized their magnetic anomaly character. Key factors such as measuring borehole orientation, b... We quantitatively study magnetic anomalies of reinforcement rods in bored insitu concrete piles for the first time and summarized their magnetic anomaly character. Key factors such as measuring borehole orientation, borehole-reinforcement distance, and multiple-section reinforcement rods are discussed which contributes valid and quantitative reference for using the magnetic method to detect reinforcement rods. Through tests with model piles, we confirm the accuracy of theoretical computations and then utilize the law discovered in theoretical computations to explain the characteristics of the actual testing curves. The results show that the Za curves of the reinforcement rod reflect important factors regarding the reinforcement rods, such as rod length, change of reinforcement ratio, length of overlap, and etc. This research perfects the magnetic method for detecting reinforcement rods in bored in-situ concrete piles and the method has great importance for preventing building contractor fraud. 展开更多
关键词 Applied geophysics concrete piles reinforcement rods magnetic method
下载PDF
Identification of suitable sites for open and bore well using ground magnetic survey 被引量:1
16
作者 A Muthamilselvan 《Journal of Groundwater Science and Engineering》 2021年第3期256-268,共13页
The study aims to identify a suitable site for open and bore well in a farmhouseusing ground magnetic survey in south India.It also aims to define depth to granitoid and structural elements which traverse the selected... The study aims to identify a suitable site for open and bore well in a farmhouseusing ground magnetic survey in south India.It also aims to define depth to granitoid and structural elements which traverse the selected area.Magnetic data(n=84)measured,processed and interpreted as qualitative and quantitatively.The results of total magnetic intensities indicate that the area is composed of linear magnetic lows trending NE-SW direction and circular to semi-circular causative bodies.The magnetic values ranged from-137 nT to 2345 nT with a mean of 465 nT.Reduction to equator shows significant shifting of causative bodies in the southern and northern directions.Analytical signal map shows exact boundary of granitic bodies.Cosine directional filter has brought out structural element trending NE-SW direction.Results of individual profile brought to light structurally weak zone between 90 m and 100 m in all the profile lines.Sudden decrease of magnetic values from 2042 nT to 126 nT noticed in profile line 6 between 20 m and 30 m indicates fault occurrence.Magnetic breaks obtained from these maps were visualized,interpreted and identified two suitable sites for open and bore well.Radially averaged power spectrum estimates depth of shallow and deep sources in 5 m and 50 m,respectively.Euler method has also been applied to estimate depth of granitoid and structural elements using structural indexes 0,1,2,and 3 and found depth ranges from<10 m to>90 m.Study indicates magnetic method is one of the geophysical methods suitable for groundwater exploration and site selection for open and borewells. 展开更多
关键词 Magnetic method Groundwater exploration Euler deconvolution Open well
下载PDF
Some tests and improvements to the VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager 被引量:1
17
作者 Fei Teng Yuan-Yong Deng 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2014年第11期1469-1480,共12页
Some experimental tests and improvements to the Very Fast Inversion of the Stokes Vector program, which is designed for the inversion calculation used by the Helioseismic and Magnetic Imager instrument on the Solar Dy... Some experimental tests and improvements to the Very Fast Inversion of the Stokes Vector program, which is designed for the inversion calculation used by the Helioseismic and Magnetic Imager instrument on the Solar Dynamics Observatory, are given. On one hand, the interpolation for calculating the Voigt function is not smooth, which may occasionally cause the iteration process to converge to different minima although they are very close to initial values. This problem can be solved by a smoother interpolation. On the other hand, in order to improve the performance of this program, we have tried to abandon the randomly-jump-out strategy and set the initial value properly to avoid non-global minima. The resulting method costs only 1//4 of the computational time, and will be very competitive when the users are only interested in the vectorial magnetic fields and the velocities along the line of sight. 展开更多
关键词 SUN magnetic fields -- methods numerical -- techniques polarimetric
下载PDF
Solar flare prediction using highly stressed longitudinal magnetic field parameters 被引量:3
18
作者 Xin Huang Hua-Ning Wang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2013年第3期351-358,共8页
Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for ... Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for 1055 active regions. We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples. Using the long-term accumulated MDI data, we build the solar flare prediction model by using a data mining method. Furthermore, the decision boundary, which is used to divide flaring from non-flaring samples, is determined by the decision tree algorithm. Finally, the performance of the prediction model is evaluated by 10-fold cross validation technology. We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method. 展开更多
关键词 Sun: magnetic fields -- Sun: flares -- methods: statistical
下载PDF
A Non-axisymmetric Spherical α~2-Dynamo 被引量:1
19
作者 Jie Jiang Jing-Xiu Wang 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2006年第2期227-236,共10页
Using the Chebyshev-tau method, the generation of oscillatory nonaxisymmetric stellar magnetic fields by the α^2-dynamo is studied in spherical geometry. Following the boundary conditions given by Schubert & Zhang, ... Using the Chebyshev-tau method, the generation of oscillatory nonaxisymmetric stellar magnetic fields by the α^2-dynamo is studied in spherical geometry. Following the boundary conditions given by Schubert & Zhang, the spherical α^2-dynamo consists of a fully convective spherical shell with inner radius ri and outer radius ro. A comparison of the critical dynamo numbers of axisymmetric and φ-dependent modes for different thicknesses of the convective shell and different α- profiles leads to the following qualitative results: (i) when the angular factor of α- profile is sin^n θ cosθ (n= 1, 2, 4) the solutions of the α^2dynamo are oscillatory and non-axisymmetric, (ii) the thinner the convective shell, the more easily is the nonaxisymmetric mode excited and the higher is the latitudinal wave number, (iii) the thickness of the outer convective shell has an effect on the symmetries of the magnetic fields. 展开更多
关键词 stars: magnetic fields - methods: numerical
下载PDF
Preprocessing photospheric vector magnetograms for nonlinear force-free field extrapolation of the global corona 被引量:1
20
作者 Ai-Ying Duan Huai Zhang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2018年第7期113-124,共12页
Nonlinear force-free magnetic field (NLFFF) extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric mag... Nonlinear force-free magnetic field (NLFFF) extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric magnetograms contain magnetic forces and small-scale noises, and fail to be consistent with the force-free assumption of NLFFF models. The procedure for removing the forces and noises in observed data is called preprocessing. In this paper, we extend the preprocessing code of Jiang & Feng to spherical coordinates for a full sphere. We first smooth the observed data with Gaussian smoothing, and then split the smoothed magnetic field into a potential field and a non-potential field. The potential part is computed by a numerical potential field model, and the non-potential part is prepro- cessed using an optimization method to minimize the magnetic forces and magnetic torques. Applying the code to synoptic charts of the vector magnetic field from SDO/HMI, we find it can effectively reduce the noises and forces, and improve the quality of data for a better input which will be used for NLFFF extrapolations applied to the global corona. 展开更多
关键词 magnetic fields - magnetohydrodynamics (MHD) - methods numerical - Sun CORONA
下载PDF
上一页 1 2 下一页 到第
使用帮助 返回顶部