Reply to I. R. Qureshi by the Authors

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 663-663
Author(s):  
B. K. Bhattacharyya ◽  
M. E. Navolio
Keyword(s):  
Magnetic Field ◽  
General Practice ◽  
Gravitational Field ◽  
Potential Field ◽  
Gravity Anomalies ◽  
The Body ◽  
Point Mass ◽  
Convolution Approach ◽  
Magnetic And Gravity Anomalies

In order to determine expressions for magnetic and gravity anomalies generated by a body of known shape, it is the general practice to integrate the dipolar magnetic field or the gravitational field due to a point mass over the volume occupied by the body. The digital convolution approach, as discussed in the above paper, makes it unnecessary to perform the integration analytically and to use a complicated expression for computing the anomalous potential field.

Discussion on “Digital Convolution of Computing Gravity and Magnetic Anomalies Due to Arbitrary Bodies,” by B. K. Bhattacharyya and M. E. Navolio (GEOPHYSICS, December 1975, p. 981–992)

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 663-663
Author(s):  
I. R. Qureshi
Keyword(s):  
Magnetic Field ◽  
Gravitational Field ◽  
Numerical Integration ◽  
Magnetic Anomalies ◽  
Point Mass ◽  
Mathematical Approach ◽  
Gravity And Magnetic ◽  
Small Side

I congratulate the authors on their elegant mathematical approach to the computation of gravity and magnetic anomalies due to arbitrary bodies. But I consider their concluding remark, “In this approach, it is not necessary to perform integration of the dipolar magnetic field or the gravitational field due to a point mass,” to be inaccurate and misleading. The method proposed by the authors represents, in effect, the division of arbitrary bodies into cubes of a small side and numerical integration [their equations (20) and (25)] of the effects of “equivalent” dipoles or point masses located at the centers of these cubes. Hence, the smaller the side of the cube, the better the accuracy of the method.

An Augmented Iteratively Re-weighted and Refined Least Squares Method for lp Minimization Problem in Inverse Modeling of Potential Field Magnetic Data

2020 ◽  
Vol 1 (3) ◽  
Author(s):  
Maysam Abedi
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Least Squares ◽  
Minimization Problem ◽  
Potential Field ◽  
Field Data ◽  
Least Squares Method ◽  
Porphyry Copper ◽  
Magnetic Data ◽  
Magnetic Field Data

The presented work examines application of an Augmented Iteratively Re-weighted and Refined Least Squares method (AIRRLS) to construct a 3D magnetic susceptibility property from potential field magnetic anomalies. This algorithm replaces an lp minimization problem by a sequence of weighted linear systems in which the retrieved magnetic susceptibility model is successively converged to an optimum solution, while the regularization parameter is the stopping iteration numbers. To avoid the natural tendency of causative magnetic sources to concentrate at shallow depth, a prior depth weighting function is incorporated in the original formulation of the objective function. The speed of lp minimization problem is increased by inserting a pre-conditioner conjugate gradient method (PCCG) to solve the central system of equation in cases of large scale magnetic field data. It is assumed that there is no remanent magnetization since this study focuses on inversion of a geological structure with low magnetic susceptibility property. The method is applied on a multi-source noise-corrupted synthetic magnetic field data to demonstrate its suitability for 3D inversion, and then is applied to a real data pertaining to a geologically plausible porphyry copper unit.  The real case study located in  Semnan province of  Iran  consists  of  an arc-shaped  porphyry  andesite  covered  by  sedimentary  units  which  may  have  potential  of  mineral  occurrences, especially  porphyry copper. It is demonstrated that such structure extends down at depth, and consequently exploratory drilling is highly recommended for acquiring more pieces of information about its potential for ore-bearing mineralization.

scholarly journals ELECTROMAGNETIC FIELDS OF CHARGED AND MAGNETIZED CYLINDRICAL CONDUCTORS IN NUT SPACE

2005 ◽  
Vol 14 (03n04) ◽  
pp. 687-695 ◽  
Author(s):  
B. J. AHMEDOV ◽  
A. V. KHUGAEV ◽  
N. I. RAKHMATOV
Keyword(s):  
Magnetic Field ◽  
Gravitational Field ◽  
Electromagnetic Fields ◽  
Electric Charge ◽  
Maxwell Equations ◽  
Analytic Solutions ◽  
Vertical Magnetic Field ◽  
General Relativistic ◽  
Azimuthal Current ◽  
Cylindrical Conductors

We present analytic solutions of Maxwell equations for infinitely long cylindrical conductors with nonvanishing electric charge and currents in the external background spacetime of a line gravitomagnetic monopole. It has been shown that vertical magnetic field arising around cylindrical conducting shell carrying azimuthal current will be modified by the gravitational field of NUT source. We obtain that the purely general relativistic magnetic field which has no Newtonian analog will be produced around charged gravitomagnetic monopole.

THREE DIMENSIONAL INTERPRETATION OF GRAVITATIONAL ANOMALIES

Geophysics ◽  
1952 ◽  
Vol 17 (2) ◽  
pp. 344-364 ◽  
Author(s):  
Fraser S. Grant
Keyword(s):  
Gravitational Field ◽  
Mass Distribution ◽  
Three Dimensional ◽  
Relaxation Method ◽  
The Body ◽  
Multipole Moments ◽  
Size And Shape ◽  
Surface Field ◽  
Derivatives Of

A method is developed for determining the approximate size and shape of the three‐dimensional mass distribution that is required to produce a given gravitational field. The first few reduced multipole moments of the distribution are calculated from the derivatives of the surface field, and the approximative structure is determined from the values of these moments and a knowledge of the density contrast between the body and its surroundings. A system of classification of problems by symmetry is introduced and its practical usage discussed. A relaxation method is described which may be used to adjust the initial solution systematically to give agreement over the whole field. A descriptive discussion is appended.

Initial Results On Medium Frequency Electromagnetic Field Penetration In Biological Soft Tissue

2012 ◽  
Author(s):  
Zulkarnay Zakaria ◽  
Mohd Fahajumi Jumaah ◽  
Mohd Saiful Badri Mansor ◽  
Khairi Mat Daud ◽  
Mohd Hafiz Fazalul Rahiman ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Soft Tissue ◽  
Soft Tissues ◽  
Low Cost ◽  
The Body ◽  
Small Scale ◽  
Medium Frequency ◽  
Magnetic Field Penetration ◽  
Magnetic Induction Tomography ◽  
Field Penetration

Terapi merupakan antara teknik perubatan tertua dalam mengekalkan kesihatan badan terutama daripada aliran darah yang tidak baik, strok dan beberapa penyakit yang lain. Teknik ini termasuklah akupuntur, guasa dan juga urutan. Terdapat juga teknik terapi moden seperti terapi warna, terapi ozon, terapi dadah dan banyak lagi. Kertas kajian ini akan mengetengahkan penjana terapi elektromagnet, satu alat yang mempunyai potensi aplikasi terapi dalam bidang perubatan. Alat ini menghasilkan medan magnet berfrekuensi sederhana sebagai sumber terapi. Perkakasan yang berskala kecil berfrekuensi sederhana dan berkos rendah ini telah dibangunkan dan telah diuji pada tisu biologi bagi mengukur tahap ketembusan medan magnet. Ujian ini telah membuktikan bahawa medan magnet yang telah dihasilkan mampu menembusi tisu lembut bersaiz sehingga 2 cm dengan jarak 7 cm daripada sumber. Kebolehan penembusan sistem ini terhadap tisu lembut memberikan peluang yang cerah kepada kajian ini memandangkan medan magnet telah menunjukkan potensi sebagai sebahagian daripada terapi untuk memulihkan migraine, strok, kekejangan dan beberapa yang lain selain boleh diaplikasikan dalam pengimejan tomografi induksi magnet. Kata kunci: Terapi elektromagnet, medan magnet, penembusan, tisu lembut, aplikasi perubatan Therapy is among the oldest medication technique in maintaining the health of the body especially from bad blood circulation, stroke and several others. This technique includes acupuncture, guasa and also massage. There are also modern therapy techniques like colour therapy, water therapy, ozone therapy, drug therapy and others. This paper will highlight electromagnetic therapy generator, a device which has the potential of therapy application in medical field. This device produce medium frequency magnetic field as a therapy source. This small scale medium frequency and low cost hardware that has been developed was tested on the biological tissue for the purpose of measuring the magnetic field penetration. The testing has proven that the generated magnetic field is able to penetrate the soft tissue up to 2 cm with distance from the source up to 7 cm. The capability of the system penetrations through the soft tissues provide the bright future of this research since magnetic field have shown the potential as being part of the therapy for curing migraine, stroke, cramp and several others besides the application in the magnetic induction tomography imaging. Key words: Electromagnetic therapy, magnetic field, penetration, soft tissue; medical applications

COMPARISON OF CARDIAC MAGNETIC FIELD DISTRIBUTIONS DURING DEPOLARIZATION AND REPOLARIZATION

2003 ◽  
Vol 13 (12) ◽  
pp. 3783-3789 ◽  
Author(s):  
F. E. SMITH ◽  
P. LANGLEY ◽  
L. TRAHMS ◽  
U. STEINHOFF ◽  
J. P. BOURKE ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Distribution ◽  
Normal Subjects ◽  
The Body ◽  
Magnetic Field Distribution ◽  
T Wave ◽  
High Magnetic Field Strength ◽  
The Magnetic Field

Multichannel magnetocardiography measures the magnetic field distribution of the human heart noninvasively from many sites over the body surface. Multichannel magnetocardiogram (MCG) analysis enables regional temporal differences in the distribution of cardiac magnetic field strength during depolarization and repolarization to be identified, allowing estimation of the global and local inhomogeneity of the cardiac activation process. The aim of this study was to compare the spatial distribution of cardiac magnetic field strength during ventricular depolarization and repolarization in both normal subjects and patients with cardiac abnormalities, obtaining amplitude measurements by magnetocardiography. MCGs were recorded at 49 sites over the heart from three normal subjects and two patients with inverted T-wave conditions. The magnetic field intensity during depolarization and repolarization was measured automatically for each channel and displayed spatially as contour maps. A Pearson correlation was used to determine the spatial relationship between the variables. For normal subjects, magnetic field strength maps during depolarization (R-wave) showed two asymmetric regions of magnetic field strength with a high positive value in the lower half of the chest and a high negative value above this. The regions of high R-wave amplitude corresponded spatially to concentrated asymmetric regions of high magnetic field strength during repolarization (T-wave). Pearson-r correlation coefficients of 0.7 (p<0.01), 0.8 (p<0.01) and 0.9 (p<0.01) were obtained from this analysis for the three normal subjects. A negative correlation coefficient of -0.7 (p<0.01) was obtained for one of the subjects with inverted T-wave abnormalities, suggesting similar but inverted magnetic field and current distributions to normal subjects. Even with the high correlation values in these four subjects, the MCG was able to identify differences in the distribution of magnetic field strength, with a shift in the T-wave relative to the R-wave. The measurement of cardiac magnetic field distribution during depolarization and repolarization of normal subjects and patients with clinical abnormalities should enable the improvement of theoretical models for the explanation of the cardiac depolarization and repolarization processes.

Geologic structure of the northern New Caledonia Ridge, as inferred from magnetic and gravity anomalies

Tectonics ◽  
1988 ◽  
Vol 7 (5) ◽  
pp. 991-1013 ◽  
Author(s):  
J. Y. Collot ◽  
P. Rigolot ◽  
F. Missègue
Keyword(s):  
New Caledonia ◽  
Gravity Anomalies ◽  
Geologic Structure ◽  
Magnetic And Gravity Anomalies

scholarly journals Magnetic behaviour of supraconducting tin spheres

1935 ◽  
Vol 151 (873) ◽  
pp. 316-333 ◽  
Author(s):  
K. Mendelssohn ◽  
J. D. Babbitt ◽  
Frederick Alexander Lindemann
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Force ◽  
Magnetic Behaviour ◽  
The Body ◽  
Whole Body ◽  
Measured Field ◽  
Lines Of Force ◽  
As If ◽  
Field Strengths

Until a year ago it was generally accepted that if a body is made supraconducting while in a magnetic field the lines of magnetic force were "frozen in," i. e ., whatever lines of force passed through the body at the time when it became supraconducting remained there afterwards, unaffected by any change in the external field, so long as the body was supraconducting. Meissner and Ochsenfeld, however, showed that this supposition was not true. They measured field strengths in the immediate neighbourhood of cylinders which had been cooled to supraconductivity in an external magnetic field, and found that the field of force was then of the same nature as that to be expected in the neighbourhood of perfectly diamagnetic bodies. Thus it appeared that when a body becomes supraconducting in a magnetic field the lines of force are all pressed out of the body, and the induction inside the body falls to zero. At the same time, however, these authors report on another experiment, the result of which appears to us not entirely in accordance with the assumption that the induction in the whole body became zero. They measured the field strengths inside and outside a hollow cylinder, after it had become supraconducting in a field perpendicular to its axis, and found again that the field strength outside was as if the cylinder were almost perfectly diamagnetic, but the field inside was appreciably the same as if the cylinder were non-supraconducting. We therefore made a number of experiments, hoping to find out more exactly the nature of the phenomenon.

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