Ferromagnetic domains in CrBr3, investigated with a liquid helium magnetic specimen stage

1978 ◽  
Vol 36 (1) ◽  
pp. 464-465
Author(s):  
H. Möllner ◽  
M. Schönauer ◽  
E.M. Hörl
Keyword(s):  
Magnetic Field ◽  
Liquid Helium ◽  
Curie Point ◽  
The Other ◽  
Horizontal Magnetic Field ◽  
Size And Shape ◽  
Other Hand ◽  
Ferromagnetic Domains ◽  
Electron Microscopical ◽  
Foil Orientation

In continuation of the electron microscopical work on CrBr3 done by Matricardi et. al. we have applied a special type of liquid helium specimen stage, which has permitted application of a horizontal magnetic field in the specimen region. During observation of the specimen we have been able to apply fields up to 60 Oe, without observation fields up to 600 Oe.In general the observations of Matricardi et.al. have been confirmed, especially the contrast, size and shape of the domains, their non-appearance in in-focus micrographs and micrographs taken above the Curie point. On the other hand occasional regions of the foil, where the contrast disappears (Fig. 1a] are not thought to be chemical inhomogeneities. Such regions can exhibit strong domain contrast if the foil orientation changes slightly, as in our case by the thermal strains occuring in warming-up the specimen to approx. 60 K and cooling it down again.

scholarly journals Elastic Properties of Magnetorheological Elastomers in a Heterogeneous Uniaxial Magnetic Field

2018 ◽  
Vol 19 (10) ◽  
pp. 3045 ◽  
Author(s):  
Takehito Kikuchi ◽  
Yusuke Kobayashi ◽  
Mika Kawai ◽  
Tetsu Mitsumata
Keyword(s):  
Magnetic Field ◽  
Elastic Properties ◽  
Uniform Magnetic Field ◽  
Large Strain ◽  
Small Strain ◽  
Experimental Results ◽  
The Other ◽  
Magnetorheological Elastomers ◽  
Other Hand ◽  
Strain Model

Magnetorheological elastomers (MREs) are stimulus-responsive soft materials that consist of polymeric matrices and magnetic particles. In this study, large-strain response of MREs with 5 vol % of carbonyl iron (CI) particles is experimentally characterized for two different conditions: (1) shear deformation in a uniform magnetic field; and (2), compression in a heterogeneous uniaxial magnetic field. For condition (1), dynamic viscoelastic measurements were performed using a rheometer with a rotor disc and an electric magnet that generated a uniform magnetic field on disc-like material samples. For condition (2), on the other hand, three permanent magnets with different surface flux densities were used to generate a heterogeneous uniaxial magnetic field under cylindrical material samples. The experimental results were mathematically modeled, and the relationship between them was investigated. We also used finite-element method (FEM) software to estimate the uniaxial distributions of the magnetic field in the analyzed MREs for condition (2), and developed mathematical models to describe these phenomena. By using these practicable techniques, we established a simple macroscale model of the elastic properties of MREs under simple compression. We estimated the elastic properties of MREs in the small-strain regime (neo–Hookean model) and in the large-strain regime (Mooney–Rivlin model). The small-strain model explains the experimental results for strains under 5%. On the other hand, the large-strain model explains the experimental results for strains above 10%.

Leibniz On Form and Matter

1997 ◽  
Vol 2 (3) ◽  
pp. 326-351 ◽  
Author(s):  
Daniel Garber
Keyword(s):  
Physical World ◽  
The Other ◽  
Middle Years ◽  
Size And Shape ◽  
Mechanical Philosophy ◽  
Other Hand

AbstractThis paper discusses the Aristotelian notions of matter and form as they are treated in the philosophy of Leibniz. The discussion is divided into three parts, corresponding to three periods in Leibniz's development. In the earliest period, as exemplified in a 1669 letter to his former mentor Jakob Thomasius, Leibniz argues that matter and form can be given straightforward interpretations in terms of size and shape, basic categories in the new mechanical philosophy. In Leibniz's middle years, on the other hand, as exemplified in the Discourse on Metaphysics and the correspondence with Arnauld, Leibniz seems to hold a more orthodox Aristotelian view of matter and form as the constituents of the corporeal substances that ground the reality of the physical world. In Leibniz's latest years, as discussed in the letters with Des Bosses, matter and form enter once again in connection with the vinculum substantiale, the substantial bond that is supposed to bind monads together to form corporeal substances.

Does draping aeromagnetic data reduce terrain‐induced effects?

Geophysics ◽  
1984 ◽  
Vol 49 (1) ◽  
pp. 75-80 ◽  
Author(s):  
V. J. S. Grauch ◽  
David L. Campbell
Keyword(s):  
Magnetic Field ◽  
Magnetic Behavior ◽  
The Other ◽  
Aeromagnetic Data ◽  
Total Magnetic Field ◽  
Vertical Derivative ◽  
Topographic Features ◽  
Other Hand ◽  
Terrain Effects ◽  
The Difference

Contrary to intuition, draped aeromagnetic surveys (when compared to typical level surveys) amplify, rather than reduce, the problem of magnetic‐terrain anomalies. Calculations of the total magnetic field of various simple magnetic topographies on level and draped surfaces support this conclusion. In cases where draped surfaces are lower than level surfaces, the draped profiles exhibit steeper gradients and deeper polarity lows over topography than do the level profiles. On the other hand, where draped surfaces are higher than level surfaces, all anomalies are attenuated, so that magnetic‐terrain effects might be reduced relative to subsurface sources (depending upon the magnetization of each). The difference in magnetic behavior between level and draped data can be explained by a contribution of a vertical derivative component in the draped case that is absent in the level case. The contribution is most significant near topographic features because both the observation surface and the topographic surface are changing vertically.

Analogue model studies of induction effects at auroral latitudes

1995 ◽  
Vol 13 (11) ◽  
pp. 1187-1196
Author(s):  
A. Viljanen ◽  
L. Szarka
Keyword(s):  
Magnetic Field ◽  
Thin Sheet ◽  
The Other ◽  
The Arctic ◽  
Field Observations ◽  
Analogue Model ◽  
Model Studies ◽  
Northern Fennoscandia ◽  
Horizontal Field ◽  
Other Hand

Abstract. In addition to field observations and numerical models, geomagnetic induction effects can be studied by scaled analogue model experiments. We present here results of analogue model studies of the auroral electrojet with an Earth model simulating the Arctic Ocean and inland conductivity structures in northern Fennoscandia. The main elements of the analogue model used were salt water simulating the host rock, an aluminium plate corresponding to the ocean and graphite pieces producing the inland highly conducting anomalies. The electrojet was a time-harmonic line current flowing at a (simulated) height of 100 km above northern Fennoscandia. The period simulated was 9 min. The analogue model results confirmed the well-known rapid increase of the vertical field when the coast is approached from the continent. The increase of the horizontal field due to induced ocean currents was demonstrated above the ocean, as well as the essentially negligible effect of these currents on the horizontal field on the continent. The behaviour of the magnetic field is explained with a simple two-dimensional thin-sheet model. The range, or the adjustment distance, of the ocean effect inland was found to be some hundreds of kilometers, which also agrees with earlier results of the Siebert-Kertz separation of IMAGE magnetometer data. The modelled inland anomalies evidently had too large conductivities, but on the other hand, their influence decayed on scales of only some tens of kilometers. Analogue model results, thin-sheet calculations, and field observations show that the induction effect on the horizontal magnetic field Bx near the electrojet is negligible. On the other hand, the vertical component Bz is clearly affected by induced currents in the ocean. Evidence of this is the shift of the zero point of Bz 0-1° southwards from the maximum of Bx. The importance of these results are discussed, emphasizing the determination of ionospheric currents.

scholarly journals Turbulent effects in flux-transport solar dynamos

2008 ◽  
Vol 4 (S259) ◽  
pp. 243-246
Author(s):  
G. A. Guerrero ◽  
E. M. de Gouveia Dal Pino ◽  
M. Dikpati
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
The Other ◽  
Toroidal Magnetic Field ◽  
Flux Transport ◽  
Other Hand ◽  
Magnetic Diffusivity

AbstractThe effects of turbulent pumping and η-quenching on Babcock-Leighton dynamo models are explored separately. Turbulent pumping seems to be important to solve several reported problems in these dynamo models related to the magnetic flux transport and to the parity. On the other hand, the suppression of the magnetic diffusivity, η, could help in the formation of long-lived, small and intense structures of toroidal magnetic field.

On double-roll convection in a rotating magnetic system

1975 ◽  
Vol 68 (3) ◽  
pp. 447-466 ◽  
Author(s):  
P. H. Robert ◽  
K. Stewartson
Keyword(s):  
Magnetic Field ◽  
Fluid Motion ◽  
Vertical Axis ◽  
Large Mass ◽  
The Other ◽  
Inviscid Fluid ◽  
Governing Equations ◽  
Horizontal Magnetic Field ◽  
Order Unity ◽  
Inertial Terms

Electrically and thermally conducting inviscid fluid rotating about a vertical axis is confined between two horizontal plates maintained a t different temperatures, the upper plate being the cooler. The fluid is permeated by a horizontal magnetic field that corotates with the fluid. In an earlier paper (Roberts & Stewartson 1974) the fluid is supposed to be in a state of near-marginal instability to convective overturning and the nonlinear evolution of single rolls is discussed. Inertial terms are neglected. However, if q < 2 and λ < 2/3½, where q and λ may be defined by equation (2.3) below, the principle of the exchange of stabilities holds and there is also a degeneracy in the linear stability problem. There are now two distinct unstable rolls equally possible and their nonlinear interaction leads to a violation of the governing equations. This difficulty has already been noted by Taylor (1963) and it is resolved in this paper by adding a geostrophic motion (the Taylor shear) parallel to the magnetic field and by restoring the inertial terms in the governing equations. We consider particularly instabilities in which one roll predominates and find that, if λ is sufficiently small, each of the rolls that can occur is stable with respect to the other, i.e. an initially weak roll of the other type dies out relative to it. This means that we can expect the fluid motion to consist of single rolls at large times. On the other hand when λ is near 2/3½ both rolls are unstable with respect to the other. The Taylor shear does not then die out and the two rolls become comparable in magnitude and modify each other's structure. At intermediate values of λ one of the rolls is stable in this way and the other unstable.The study is motivated by a desire to understand better the dynamical means by which a large mass of conducting fluid can create its own magnetism. It is argued that these instabilities suggest the existence of a mechanism of self-adjustment preventing λ from either increasing or decreasing indefinitely and noted that, very roughly, λ is of order unity in the earth's core.

scholarly journals Effects of strong magnetic field on the formation of wakes in thermal QCD

2021 ◽  
Vol 36 (06) ◽  
pp. 2150045
Author(s):  
Mujeeb Hasan ◽  
Binoy Krishna Patra
Keyword(s):  
Magnetic Field ◽  
Charge Density ◽  
Strong Magnetic Field ◽  
Finite Temperature ◽  
Fast Moving ◽  
The Other ◽  
Other Hand ◽  
Induced Charge Density ◽  
Induced Charge ◽  
The Magnetic Field

We have investigated how the wakes in the induced charge density and in the potential due to the passage of highly energetic partons through a thermal QCD medium get affected by the presence of strong magnetic field [Formula: see text]. For that purpose, we wish to analyze first the dielectric responses of the medium both in presence and absence of strong magnetic field. Therefore, we have revisited the general form for the gluon self-energy tensor at finite temperature and finite magnetic field and then calculate the relevant structure functions at finite temperature and strong magnetic field limit (SMF: [Formula: see text] as well as [Formula: see text], [Formula: see text] is the electric charge (mass) of [Formula: see text]th flavor). We found that for slow moving partons, the real part of dielectric function is not affected by the magnetic field whereas for fast moving partons, for small [Formula: see text], it becomes very large and approaches towards its counterpart at [Formula: see text], for large [Formula: see text]. On the other hand the imaginary part is decreased for both slow and fast moving partons, due to the fact that the imaginary contribution due to quark loop vanishes. With these ingredients, we found that the oscillation in the (scaled) induced charge density, due to the very fast partons becomes less pronounced in the presence of strong magnetic field whereas for smaller parton velocity, no significant change is observed. For the (scaled) wake potential along the motion of fast moving partons (which is of Lennard–Jones (LJ-)type), the depth of negative minimum in the backward region gets reduced drastically, resulting in the reduction of the amplitude of oscillation. On the other hand in the forward region, it remains as the screened Coulomb one, except the screening now becomes much stronger for higher parton velocity. Similarly for the wake potential transverse to the motion of partons in both forward and backward regions, the depth of LJ potential for fast moving partons gets decreased severely, but still retains the forward–backward symm etry. However, for lower parton velocity, the magnetic field does not affect it significantly.

Orientation of Prominence Microstructure Relative to the Direction of the Magnetic Field

1979 ◽  
Vol 44 ◽  
pp. 97-101
Author(s):  
O. Engvold ◽  
J.L. Leroy
Keyword(s):  
Magnetic Field ◽  
The Other ◽  
Optical Observations ◽  
High Quality ◽  
Hanle Effect ◽  
Other Hand ◽  
Solar Prominences ◽  
The Magnetic Field ◽  
Good Agreement ◽  
Field Strengths

Recent measurements of the polarization of the Hel D3 line (λ5876Å) in solar prominences (Hanle effect) have been used to infer new data about prominence magnetic field (Leroy 1977, Leroy et al. 1977, Sahal-Brèchot et al. 1977). The derived field strengths are in good agreement with previous magnetographic measurements obtained at several observatories in USA (Rust 1972). Using the Hanle effect also gives the direction of the magnetic field, which is a crusial parameter in theories of prominences (Kippenhahn and Schlüter 1957, Anzer 1968, Malville 1976). Some theories require a horizontal oriented magnetic field in the prominences. High quality optical observations, on the other hand, resolve predominantly vertically oriented prominence microstructure (Dunn 1972, Engvold 1976).

Strength and Conductivity of Deformed Cu-Fe Composites after Solidified with a Horizontal Magnetic Field

2010 ◽  
Vol 654-656 ◽  
pp. 1377-1380 ◽  
Author(s):  
Xiao Wei Zuo ◽  
En Gang Wang ◽  
Lei Qu ◽  
Peng Jia ◽  
Lin Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Quantitative Relationship ◽  
The Other ◽  
Drawing Ratio ◽  
Horizontal Magnetic Field ◽  
Fe Content ◽  
Fe Alloys ◽  
Solidification Microstructures ◽  
The Magnetic Field ◽  
Composite Wires

In this paper, the Cu-Fe alloys are fabricated by solidifying with and without a 1.0 Tesla horizontal magnetic field and they are drawn to composite wires under different drawing ratios, then their further strength and conductivity are investigated. The results show that, when the drawing ratio is lower, the strength of the Cu-Fe composites pre-solidified with a horizontal magnetic field is lower, which is caused by the coarser solidification microstructures induced by the injected magnetic field. However, the increase ratio in the strength of the Cu-Fe composites, which is plotted as a function of the Fe content and the drawing ratio, is higher in the case of the imposed magnetic field. It indicates that it is more efficient applying the magnetic field to fabricate Cu-Fe composites with high Fe contents and larger drawing ratio. A quantitative relationship is fitted to predict the influence of the Fe content on the strength of the Cu-Fe composites wires. On the other hand, the conductivity of the Cu-Fe composite wires is decreased with increasing Fe content. The injected magnetic field has no effect on the conductivity.

Finite-Amplitude Convection under the Combined Effect of Rotation and a Magnetic Field

1972 ◽  
Vol 2 (3) ◽  
pp. 147-148
Author(s):  
J. O. Murphy ◽  
R. Van der Borght
Keyword(s):  
Magnetic Field ◽  
Linear Theory ◽  
Thermal Convection ◽  
Finite Amplitude ◽  
Combined Effect ◽  
The Other ◽  
Inhibiting Effect ◽  
Other Hand ◽  
Non Linear

It is well known from linear theory that a magnetic field or rotation, acting separately, have an inhibiting effect on the onset of thermal convection. This has been confirmed by corresponding studies of finite amplitude convection. On the other hand, when both magnetic field and rotation act together, the linear theory predicts that they may have conflicting tendencies. It is the purpose of the present paper to report on the investigation of these effects in the case of non-linear thermal convection.

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