Values Of Magnetic Intensity Research Articles

Effect of pulsed magnetic field on microstructure of 1Cr18Ni9Ti austenitic stainless steel

The aim of this paper is to investigate the effects of pulsed magnetic field on the microstructure of 1Cr18Ni9Ti austenitic stainless steel. Experimental results indicate that during the solidification of 1Cr18Ni9Ti austenitic stainless steel, applications of pulsed magnetic field can significantly refine its microstructure. And there is an optimal value of magnetic intensity under which the grain size is the finest. Moreover, applications of pulsed magnetic field can significantly reduce the solidification time, and also lead to increase of the initiation and finishing solidification temperature.

Determination of the parameters of compact ferro-metallic objects with transforms of magnitude magnetic anomalies

The transforms based on magnitude of the magnetic anomaly (MMA), or absolute value of anomalous magnetic intensity, are relatively insensitive to the direction of the source magnetisation vector and show high centricity. Obtaining them requires calculation of only first-order horizontal derivatives of the component magnetic anomalies X, Y and Z, obtained through transformation of total magnetic anomalies Δ T (TMA). We studied the use of the magnetic transforms based on the MMA of a dipole source and that of their ratios for determining the geometric and physical parameters of compact environmental ferro-metallic sources. Analytical formulas for all the parameters of the magnetic dipole based on calculation of MMAs, their gradients and Laplacian, and their ratios were obtained. The horizontal position of the dipole source is determined by the maximum of the Laplacian of the MMA, which is the transform with the highest centricity. We applied the approach on model data and on magnetic anomalies over environmental sources, represented by unexploded ordnance (UXO) and clutter from the Badlands Bombing Range, USA. The obtained parameter values were compared with those estimated through Euler deconvolution using unprescribed structural index and linear model of the background, and through inversion. The comparison showed that the proposed method produced similar depth results to that of the Euler deconvolution method for the objects with estimated structural index over and around 2.5, i.e., for the sources, which to a great extent can be approximated with a dipole. The inversion for the dipole parameters using as initial parameters the estimated with the MMA transform method ones confirmed the results of the MMA transform method for the dipole coordinates and magnetisation for all items.

Spectral variability and transient injection of relativistic electrons for BL Lac objects

The spectral hardening with increasing intensity in optical range for four BL Lac objects have been found by analyzing our observed data. Making use of the synchrotron loss of transient injection of relativistic electrons, we succeeded in explaining the phenomenon of the spectral hardening in the outburst phase. The value of magnetic intensity and the limit condition of the transient injection of relativistic electrons seem to be reasonable.

Tectonic rotation and diverse remanence carriers revealed by the paleomagnetism of Eo-Oligocene turbidites from two Ultrahelvetic units (Western Alps, Haute-Savoie, France)

Our paleomagnetic study of two Ultrahelvetic units from the Western Alps shows that: (1) one unit has experienced an important vertical-axis tectonic rotation, and (2) in turbidite deposits, the nature of the remanence carrier can differ between coarse-grained and fine-grained intervals. Samples were collected at close intervals from weakly deformed turbidites in two different areas (Dérochoir and Marais). Characteristic remanent magnetization (ChRM) was measured with alternating field and thermal demagnetization, whereas clues for identifying the main remanence carrier were provided by coercivity spectra analysis. In the Dérochoir area, the bulk of the section consists of fine-grained rocks. Magnetic intensity values are small, directions are scattered and no polarity reversals were detected. Remanence was probably acquired during late diagenesis or regional tectonic deformation. In coarser lithologies, depositional ChRM has probably been preserved by an early phase of cementation. In the Marais turbidites, remanent magnetization is mainly carried by magnetite. Although some samples show clustered directions, several polarity inversions have been observed, suggesting that remanence was acquired soon after sediment deposition. Magnetic directions values indicate a counterclockwise rotation of about 110° of the Marais sediments with respect to the stable European craton. This movement, which partly affects the underlying Subalpine chains, is probably related to sinistral strike–slip motion along a major regional accident during the Late Oligocene or Miocene.

On the problem of magnetic field generation by helical turbulence

Abstract Mean-field electrodynamics, including both the α-effect and the effect of Lorentz forces damping action on small-scale helical fluid motions (the latter taken in the limit of low magnetic Reynolds number values) is formulated for the electrically conducting, rotating, inviscid Boussinesq fluid. A self-consistent system of two coupled ordinary differential equations in terms of mean magnetic field intensity and helicity bulk density is derived for the case of spatial homogeneity and isotropy. The mean-field induction equation takes into account both the α-effect and the effect of magnetic viscosity. The helicity balance equation contains the helicity source due to buoyant forcing and the helicity sink because of Ohmic dissipation. This system has the unique stationary solution, which is the global attractor, and describes the saturated values of mean magnetic field intensity and helicity. Possible implications to the problem of the terrestrial magnetism are discussed briefly.

Proterozoic crustal boundary in the southern part of the Illinois Basin

Recently acquired COCORP and proprietary seismic reflection data in the southern part of the Illinois Basin, combined with other geological and geophysical data, indicate that a WNW-trending Proterozoic terrane boundary (40 km wide) lies within basement. The boundary is characterized by the termination of subhorizontal Proterozoic reflectors and associated diffraction patterns along a line coinciding with the major magnetic lineament in this region (South Central Magnetic Lineament). North of the boundary, where reflectors thought to represent a sequence of layered Proterozoic rocks in the upper crust are widespread and as much as 11 km thick, total magnetic intensity values are relatively high, suggesting layers of rock with high magnetic susceptibility. To the south, the Proterozoic rocks are acoustically transparent on seismic reflection sections and total magnetic intensity values are relatively low. Moreover, relatively high Bouguer gravity anomaly values to the south may be caused by a dense, altered, lower crustal layer similar to that interpreted from deep seismic refraction studies to underlie the northern Mississippi Embayment. The boundary lies along the projected trend of the northern margin of the Early Proterozoic Central Plains orogen and we suggest that it marks the convergent margin of this orogen. Reactivation of the boundary and the associated zone of weakness during late Paleozoic times apparently resulted in structural deformation in the southern part of the Illinois Basin, including movement along the Cottage Grove Fault System and Ste. Genevieve Fault Zone and igneous activity at Hicks Dome. In addition to the role played by this crustal boundary in the evolution of the Illinois Basin, its location between the Wabash Valley Seismic Zone to the northeast and the New Madrid Seismic Zone to the southwest may be a significant factor in present-day seismicity.

Extension of the Narmada — Son lineament on the continental margin off Saurashtra, Western India as obtained from magnetic measurements

Magnetic total intensity values and bathymetric data collected on the continental margin off Saurashtra were, used to prepare magnetic anomalies and bathymetric contour maps. The magnetic anomalies are considered to have been caused by the Deccan Trap flood basalts which underlie the Tertiary sediments. Interpretation of the magnetic data using two-dimensional modelling method suggests that the magnetic basement is block faulted and deepens in steps from less than 1.0 km in the north to about 8.0 km towards the southern portion of the study area. The WNW-ESE trending faults identified in the present study extend across the Saurashtra continental margin between Porbandar and Veraval and appear to represent a major linear tectonic feature. The relationship of these fault lineaments with the regional tectonic framework have been discussed to indicate that they conform better as the northern boundary faults of the Narmada rift graben on the continental margin off Saurashtra.

Practical Application of Theoretical Models to Magnetometer Surveys on Hazardous Waste Disposal Sites — A Case History

AbstractWastes were to be exhumed and removed from a hazardous and chemical waste disposal site. The major disposal practice was shallow burial of wastes in metal drums in parallel trenches. The actual boundaries of the trenches beneath the landscaped cover were not accurately known.Theoretical two‐dimensional models were used to evaluate the application of magnetic methods to define trench boundaries on the disposal site. The models predicted that both the total field and the vertical component anomalies were diagnostic; however, the vertical component anomaly was more focused on the trench boundaries.A survey with a vertical component fluxgate magnetometer was successful in defining trench boundaries. Observations made along traverses that trended perpendicular to the long axis of the parallel trenches indicated vertical magnetic intensity values with a cyclical pattern of large positive values over trenches and large negative values over intertrench corridors. Vertical magnetic intensity values determined with theoretical two‐dimensional models compared favorably to the observed vertical magnetic values. The models were used to constrain the interpretation of the field observations to define trench boundaries; the magnetic survey defined trench boundaries with an accuracy within ± 2 feet.

Cross-over analysis of Marine magnetic anomalies

Using cross-over analysis the reduction of total magnetic intensity values to magnetic anomalies was studied in an area with ship-tracks which have been made over a period of several years. Under these circumstances the secular variation becomes important. At first we used the old IGRF 1975. This reference field does not correct the secular variation accurately. In the period 1969–1980 the mean values of the differences of the magnetic anomalies at crossing rise to more than 150 nT. The recently adopted reference fields DGRF 1965, DGRF 1970, DGRF 1975 and PGRF 1975 correct the secular variation much better. The mean values now only rise to about 50 nT over the same period. A reduction using a regional determined by filtering along the track removes the secular variation completely. The latter reduction has the disadvantage that the standard deviations of the mean values at the intersections increase, because the regional depends on the orientation of the track line. Calculation of average secular variation in subareas of 4×4 degrees yields a decrease from the northeast to the southwest.

Sequicentenary of Gauss's first measurement of the absolute value of magnetic intensity

The geomagnetic field and its changes with time are major tools for probing the Earth’s deep interior. It is therefore particularly appropriate that the Royal Society Discussion Meeting on the Earth’s core should coincide with the 150th anniversary of the first absolute measurement of the intensity of the geomagnetic field. This was only one of Carl Friedrich Gauss’s many contributions, both direct and indirect, to geomagnetism. For example, it was Gauss who devised the methods of least squares and of spherical harmonic analysis. With Weber, he applied these to the geomagnetic field to show that it was nearly all of internal origin. Gauss was also the initiator of, and an active participant in, the ‘Gottingen Magnetic Union’, a scheme for the simultaneous observation of the magnetic field at widespread sites from which has developed the present worldwide network of magnetic observatories. The particular achievement that we commemorate here was the determination by Gauss of the horizontal intensity of the geomagnetic field in units related to the millimetre, milligram and second. (This was one tenth of the unit that subsequently bore his name.) At that time he was working towards a universal system of units for all physical quantities and conceived the original idea that magnetic intensity can be measured in terms of mass, length and time.

Lunar and solar daily variations of the geomagnetic field at Toolangi

Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Toolangi during two ten year periods (1924–1933 and 1949–1958) have been analysed to determine their solar and luni-solar diurnal components. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. It is shown that there are marked differences in the dependence ofS andL on the various parameters and a tentative explanation of this phenomenon is given.

Delineation of geothermal deposits by means of long-spacing resistivity and airborne magnetics

In geothermal provinces such as the Imperial Valley of California useful information regarding the temperature distribution at depth can be obtained by comparing the apparent resistivity values obtained from long-spacing resistivity profiles with magnetic intensity values obtained from similar profiles generated from the airborne magnetic map. In Basin and Range « hotspring å type geothermal provinces long-spacing apparent resistivity data help in identifying zones of greater permeability and/or temperature along the faults discernible on the airborne magnetic maps. Examples of surveys conducted in each type of geothermal province are presented. To obtain reliable apparent resistivity data in highly conductive geothermal provinces it is necessary to resort to real-time cross-power analysis. The instrumentation used to compute these statistics in the field is described.

Observations of proton gyro-effects in the topside ionosphere

The electron-resonance spikes on the Alouette 1 ionograms often exhibit distinctive spurs, and these are suggested to be a proton gyro-effect of some kind. The absolute values, and also the latitude variation, of the total magnetic intensity derived from the spurs on the assumption that they are a proton gyro-resonance effect agree with the actual values of magnetic intensity to about one per cent, which is better than the estimated accuracy of measurement. The occurrence of the spurs is shown to be closely associated with the satellite orientation.

Comparison of some recently defined geomagnetic field models to the Vanguard 3 (1959η) data

This letter forms part of a continuing effort of comparing magnetic intensity values defined by geomagnetic field models with satellite magnetic observation [Heuring, 1964]. Recent harmonic descriptions reduced to the Vanguard 3 epoch have been compared with the Vanguard 3 magnetic data [Cain et al., 1962] for the altitude range 2500–4000 km, the highest of the four ranges used in the earlier study. The data selected for comparison were those obtained during times when the planetary magnetic index was Kp ≤ 5 and those for which Cain et al. [1962] assigned a quality index of L = 0 and defined as ‘best data.’ (In Heuring [1964] the quality index was used as L < 7.

The interaction between elastic wave motions and a magnetic field in electrical conductors

The propagation of elastic waves in an electrically conducting solid permeated by a uniform, static magnetic field is discussed. In the case of plane wave motions, two systems of waves arise: simple uncoupled systems and a trimodal coupled system of waves. In the uncoupled case, in which polarizations are unaltered, two dispersive, complex phase velocities exist. For a weak impressed magnetic field, one of these velocities is close to the elastic wave velocity of the polarized wave in the absence of the field. The other wave, called an eddy current wave, although strongly attenuated, cannot be neglected in the solution of boundary value problems. When the theory of magnetoelastic interactions is applied to seismic motions in the conducting core of the earth, it is found that compressional waves are virtually unattenuated in the core for the pertinent values of frequency, conductivity, and magnetic intensity. It is concluded that magnetoelastic interactions are not a significant mechanism in the earth's core.

Magnetic work of the United States Coast and Geodetic Survey from July 1, 1949 to June 30, 1950

Geomagnetic information is an essential element of navigational charts. It is also required to surveyors in retracing old property lines originally defined by compass bearings. Important collateral uses occur in geophysical exploration for oil‐bearing structures, in the study and prediction of radio propagation affecting communications and radio navigational aids, in the study of sunspot activities and of auroral and ionospheric disturbances, and in certain military applications.The magnetic survey of the United States has required the accumulation, over many years, of observed values of magnetic declination, intensity, and dip at several thousand places in the United States and territorial areas. The declination in the United States, directly needed for navigational and surveying uses, varies from 22° West in Maine to 24° East in the Pacific Northwest. To evaluate the constantly changing components of the magnetic field, repeat observations at a limited number of key stations are made on a regular schedule, whereas continuous readings of the changing components are made at fixed observatories.

A note on the relationship between the horizontal components of Dm and Dst

IntroductionBy DmiH is designated the difference obtained by subtracting the daily mean value of horizontal magnetic intensity, H, on five international quiet days from the corresponding value on five international disturbed days in each month. This difference represents in average a certain storm‐time effect of 5, or less, strongest disturbances occurring in each month, but it lacks an exact physical meaning. It might be only said that DmiH is a result of the storm‐time changes of H being of a form similar to that expressed by the curves given by Chapman as the average effects of 40 moderate magnetic storms [see p. 276 and Fig. 4 of 1 of “References” at end of paper], because a local‐time effect and that of an irregular part of storms included are removed in DmiH by averaging. Let Chapman's curves be designated by fcsH(t) and the storm‐time changes, if referred to the storms occurring on international disturbed days, by fisH(t). DmiH is somewhat associated with fisH(t) but it is not quite clear what relation DmiH exists to any element defined on the basis of fisH(t), which is derived from the same storms as DmiH.

The application of new instruments to magnetic field‐work

In past years, magnetic land‐surveys have consisted essentially of the determination of the absolute values of magnetic declination (D), dip (I), and intensity (H, Z, or F ), at marked or unmarked stations. In later years, it has usually been the practice to measure horizontal intensity (H), rather than total intensity (F). Standard instruments for this work consist of field‐magnetometers for the measurement of declination and intensity, and either earth‐inductors or dip‐circles for dip.In observing declination, it is necessary first to determine by astronomical observations a true azimuth or bearing to some object that can be used as a mark of reference. An adequate number of pointings of a suspended magnet are then made, and from their mean value, the true bearing of the reference‐mark, and the instrumental correction, declination is determined. If a magnetometer is used, the magnet is suspended by either a silk or metallic fiber, so that when the magnet is in the meridian, there is no torsion in the suspension. Another instrument used to measure declination, where great accuracy is not required, is known as a compass‐declinometer. It consists essentially of a compass‐needle supported on a steel pivot bearing on a jewel. Peep‐sights are used to line the instrument on the mark.