Creation of 3-D Crystals from Single Cobalt Nanoparticles in External Magnetic Fields

2001 ◽  
Vol 54 (8) ◽  
pp. 497 ◽  
Author(s):  
Michael Hilgendorff ◽  
Bernd Tesche ◽  
Michael Giersig
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Colloidal Dispersions ◽  
Cobalt Nanoparticles ◽  
Dipole Interactions ◽  
Carbon Coated ◽  
Perfect Symmetry ◽  
The Magnetic Field ◽  
Applied External Magnetic Field

Using monodisperse nanocrystalline cobalt (Co) particles in non-polar colloidal dispersions, large areas of symmetric multi-dimensional structures were created using magnetophoretic deposition (MPD). To overcome the van der Waals and magnetic dipole–dipole interactions, the particles were stabilized with hydrophobic amines, phosphines, carboxylates and/or polymers. Depending on the preparation parameters, our particles had either bcc or ε-Co crystalline structures. Using MPD with magnetic fields up to 1 T, it was possible to create two-dimensional (2-D) arrays of near-perfect symmetry up to 1 m2 in size on various substrates, e.g. carbon-coated copper grids, silicon, or glass. Growth of the 2-D crystal was shown to be dependent on the direction of the applied external magnetic field. Three-dimensional (3-D) crystals could be created by increasing the magnetic field strength up to 6 T.

Changes in the Magnetic Fields of Star-Shaped JIS-SKS93 Plates Embedded in Clear Acrylic Cold Mounting Resin under Tensile Stress

2012 ◽  
Vol 457-458 ◽  
pp. 884-890
Author(s):  
Megumi Uryu ◽  
Katsuyuki Kida ◽  
Takashi Honda ◽  
Kenichi Saruwatari ◽  
Edson Costa Santos ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Stress Concentration ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Steel Specimen ◽  
Acrylic Resin ◽  
Steel Sample ◽  
Hall Probe ◽  
Film Sensor ◽  
The Magnetic Field

Fatigue failure of machine components occurs when cracks form in the stress concentration area and propagate under continued loading during component work. In order to understand the relation between the phenomena of stress concentration and crack propagation, non-destructive evaluation methods using in-situ measurements in the stress concentration areas are necessary. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was developed and the three dimensional magnetic fields were observed at room temperature in air. The effect of stress on the changes in the magnetic field in steel components is reported. A steel specimen (JIS SKS93) embedded in acrylic resin were strained at different loads and the magnetic field before and after straining were observed. The obtained magnetic images clearly corresponded with the shape of the steel plate. It was possible to measure the changes in the magnetic field of the steel sample after straining under tensile loading, by neutralizing the initial magnetic field of the specimens prior to testing.

On the stability of parallel flows with parallel magnetic fields

1966 ◽  
Vol 293 (1434) ◽  
pp. 342-358 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Parallel Magnetic Field ◽  
Parallel Flows ◽  
The Mean ◽  
The Stability ◽  
The Magnetic Field ◽  
Parallel Magnetic Fields

The first part of the paper is a physical discussion of the way in which a magnetic field affects the stability of a fluid in motion. Particular emphasis is given to how the magnetic field affects the interaction of the disturbance with the mean motion. The second part is an analysis of the stability of plane parallel flows of fluids with finite viscosity and conductivity under the action of uniform parallel magnetic fields. We show that, in general, three-dimensional disturbances are the most unstable, thus disagreeing with the conclusion of Michael (1953) and Stuart (1954). We show how results obtained for two-dimensional disturbances can be used to calculate the most unstable three-dimensional disturbances and thence we prove that a parallel magnetic field can never completely stabilize a parallel flow.

scholarly journals Analytical Three-dimensional Magnetohydrostatic Equilibrium Solutions for Magnetic Field Extrapolation Allowing a Transition from Non-force-free to Force-free Magnetic Fields

Solar Physics ◽  
2019 ◽  
Vol 294 (12) ◽  
Author(s):  
Thomas Neukirch ◽  
Thomas Wiegelmann
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Model Parameters ◽  
Extrapolation Methods ◽  
Equilibrium Solutions ◽  
Flexible Modeling ◽  
New Family ◽  
Cheap Method ◽  
The Magnetic Field

AbstractFor the extrapolation of magnetic fields into the solar corona from measurements taken in the photosphere (or chromosphere) force-free magnetic fields are typically used. This does not take into account that the lower layers of the solar atmosphere are not force-free. While some numerical extrapolation methods using magnetohydrostatic magnetic fields have been suggested, a complementary and numerically comparatively cheap method is to use analytical magnetohydrostatic equilibria to extrapolate the magnetic field. In this paper, we present a new family of solutions for a special class of analytical three-dimensional magnetohydrostatic equilibria, which can be of use for such magnetic field extrapolation. The new solutions allow for the more flexible modeling of a transition from non-force-free to (linear) force-free magnetic fields. In particular, the height and width of the region where this transition takes place can be specified by choosing appropriate model parameters.

scholarly journals Magnetic Fields in Young Galaxies

2002 ◽  
Vol 12 ◽  
pp. 706-708 ◽  
Author(s):  
Åke Nordlund ◽  
Örnólfur Rögnvaldsson
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Magnetic Fields ◽  
Thermal Energy ◽  
Three Dimensional ◽  
Initial Ratio ◽  
Cooling Flow ◽  
Halo Gas ◽  
The Magnetic Field

AbstractWe have studied the fate of initial magnetic fields in the hot halo gas out of which the visible parts of galaxies form, using three-dimensional numerical MHD-experiments. The halo gas undergoes compression by several orders of magnitude in the subsonic cooling flow that forms the cold disk. The magnetic field is carried along and is amplified considerably in the process, reaching μG levels for reasonable values of the initial ratio of magnetic to thermal energy density.

Three-dimensional MHD flows in rectangular ducts with internal obstacles

2000 ◽  
Vol 418 ◽  
pp. 265-295 ◽  
Author(s):  
B. MÜCK ◽  
C. GÜNTHER ◽  
U. MÜLLER ◽  
L. BÜHLER
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Magnetic Fields ◽  
Interaction Parameter ◽  
Hartmann Number ◽  
Three Dimensional ◽  
Side Length ◽  
Two Dimensional ◽  
The Magnetic Field

This paper presents a numerical simulation of the magnetohydrodynamic (MHD) liquid metal flow around a square cylinder placed in a rectangular duct. In the hydrodynamic case, for a certain parameter range the well-known Kármán vortex street with three-dimensional flow patterns is observed, similar to the flow around a circular cylinder. In this study a uniform magnetic field aligned with the cylinder is applied and its influence on the formation and downstream transport of vortices is investigated. The relevant key parameters for the MHD flow are the Hartmann number M, the interaction parameter N and the hydrodynamic Reynolds number, all based on the side length of the cylinder. The Hartmann number M was varied in the range 0 [les ] M [les ] 85 and the interaction parameter N in the range 0 [les ] N [les ] 36. Results are presented for two fixed Reynolds numbers Re = 200 and Re = 250. The magnetic Reynolds number is assumed to be very small. The results of the numerical simulation are compared with known experimental and theoretical results. The hydrodynamic simulation shows characteristic intermittent pulsations of the drag and lift force on the cylinder. At Re = 200 a mix of secondary spanwise three-dimensional instabilities (A and B mode, rib vortices) could be observed. The spanwise wavelength of the rib vortices was found to be about 2–3 cylinder side lengths in the near wake. At Re = 250 the flow appears more organized showing a regular B mode pattern and a spanwise wavelength of about 1 cylinder side length. With an applied magnetic field a quasi-two-dimensional flow can be obtained at low N ≈ 1 due to the strong non-isotropic character of the electromagnetic forces. The remaining vortices have their axes aligned with the magnetic field. With increasing magnetic fields these vortices are further damped due to Hartmann braking. The result that the ‘quasi-two-dimensional’ vortices have a curvature in the direction of the magnetic field can be explained by means of an asymptotic analysis of the governing equations. With very high magnetic fields the time-dependent vortex shedding can be almost completely suppressed. By three-dimensional visualization it was possible to show characteristic paths of the electric current for this kind of flow, explaining the action of the Lorentz forces.

scholarly journals Three-dimensional magnetohydrodynamic equilibria with continuous magnetic fields

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
S. R. Hudson ◽  
B. F. Kraus
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Energy Functional ◽  
Equilibrium States ◽  
Equilibrium Solutions ◽  
Magnetic Islands ◽  
Continuity Properties ◽  
Rotational Transform ◽  
The Magnetic Field

A brief critique is presented of some different classes of magnetohydrodynamic equilibrium solutions based on their continuity properties and whether the magnetic field is integrable or not. A generalized energy functional is introduced that is comprised of alternating ideal regions, with nested flux surfaces with an irrational rotational transform, and Taylor-relaxed regions, possibly with magnetic islands and chaos. The equilibrium states have globally continuous magnetic fields, and may be constructed for arbitrary three-dimensional plasma boundaries and appropriately prescribed pressure and rotational-transform profiles.

scholarly journals Semiclassical bounds in magnetic bottles

2016 ◽  
Vol 28 (01) ◽  
pp. 1650002 ◽  
Author(s):  
Diana Barseghyan ◽  
Pavel Exner ◽  
Hynek Kovařík ◽  
Timo Weidl
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Dirichlet Boundary ◽  
Three Dimensional ◽  
Local Change ◽  
Two Dimensional ◽  
Magnetic Systems ◽  
Spectral Estimates ◽  
The Magnetic Field

The aim of the paper is to derive spectral estimates into several classes of magnetic systems. They include three-dimensional regions with Dirichlet boundary as well as a particle in [Formula: see text] confined by a local change of the magnetic field. We establish two-dimensional Berezin–Li–Yau and Lieb–Thirring-type bounds in the presence of magnetic fields and, using them, get three-dimensional estimates for the eigenvalue moments of the corresponding magnetic Laplacians.

scholarly journals Magnetism and the Invisible Man: The mysteries of coronal cavities

2013 ◽  
Vol 8 (S300) ◽  
pp. 139-146 ◽  
Author(s):  
Sarah Gibson
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Interplanetary Space ◽  
Three Dimensional ◽  
Field Measurements ◽  
Coronal Magnetic Field ◽  
Magnetic Structures ◽  
Coronal Magnetic Fields ◽  
Multiple Wavelengths ◽  
The Magnetic Field

AbstractMagnetism defines the complex and dynamic solar corona. Twists and tangles in coronal magnetic fields build up energy and ultimately erupt, hurling plasma into interplanetary space. These coronal mass ejections (CMEs) are transient riders on the ever-outflowing solar wind, which itself possesses a three-dimensional morphology shaped by the global coronal magnetic field. Coronal magnetism is thus at the heart of any understanding of the origins of space weather at the Earth. However, we have historically been limited by the difficulty of directly measuring the magnetic fields of the corona, and have turned to observations of coronal plasma to trace out magnetic structure. This approach is complicated by the fact that plasma temperatures and densities vary among coronal magnetic structures, so that looking at any one wavelength of light only shows part of the picture. In fact, in some regimes it is the lack of plasma that is a significant indicator of the magnetic field. Such a case is the coronal cavity: a dark, elliptical region in which strong and twisted magnetism dwells. I will elucidate these enigmatic features by presenting observations of coronal cavities in multiple wavelengths and from a variety of observing vantages, including unprecedented coronal magnetic field measurements now being obtained by the Coronal Multichannel Polarimeter (CoMP). These observations demonstrate the presence of twisted magnetic fields within cavities, and also provide clues to how and why cavities ultimately erupt as CMEs.

Reduced MHD in nearly potential magnetic fields

1997 ◽  
Vol 57 (1) ◽  
pp. 83-87 ◽  
Author(s):  
H. R. STRAUSS
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Potential Field ◽  
Three Dimensional ◽  
Pressure Effects ◽  
Mhd Equations ◽  
Dimensional Structure ◽  
Three Dimensional Structure ◽  
The Magnetic Field

Reduced, approximate MHD equations are derived for the case where the magnetic field is close to a potential field. The potential field can have an arbitrary three-dimensional structure, as long as it is non-vanishing. Finite current and pressure effects are included.

scholarly journals Selection of optimum device parameters for permanent magnetic field generation

2021 ◽  
Vol 22 (6) ◽  
pp. 176-187
Author(s):  
R. T. Khazieva ◽  
M. D. Ivanov
Keyword(s):  
Magnetic Field ◽  
Energy Efficiency ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Design Parameters ◽  
Programming System ◽  
Power Circuit ◽  
Three Dimensional Modeling ◽  
Dimensional Modeling ◽  
The Magnetic Field

THE PURPUSE. To consider the fields of application of electromagnetic treatment of water systems. To analyze the modern literature on the use of constant magnetic fields for dehydration of oil-water emulsions. To develop the design of a device for generating constant magnetic fields and select its parameters. To select the electrical circuit for powering the device. To determine how the energy efficiency of the device changes with an increase in its overall dimensions. METHODS. When solving the problem, the KOMPAS-3D three-dimensional modeling system was used, the magnetic field induction was calculated using the PascalABC programming system, the optimal device parameters were selected using the Microsoft Excel program. RESULTS. The article describes the relevance of the topic, considers the distribution of the magnetic field in the device under development, determines the optimal design parameters for this device and selects the electrical power circuit. CONCLUSION. Calculations have shown that the coefficient taking into account the inhomogeneous distribution of the magnetic field in the device is 0.883. Using the KOMPAS-3D three-dimensional modeling system, a model of the device under development was builttaking into account the obtained relationships.When using a circuit with an uncontrolled rectifier and autotransformer, the power consumed by the device is 2.67 times lower than the power consumed by the device when using a circuit with a controlled rectifier and a transformer. Energy efficiency increases significantly with the increase in device performance.

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