scholarly journals Modeling of Two-Dimensional Light Bullets Propagation in an Array of Carbon Nanotubes Taking into Account the Mechanical Tension and Magnetic Field

2020 ◽  
pp. 36-44
Author(s):  
Natalia Konobeeva ◽  
Dmitry Skvortsov
Keyword(s):  
Magnetic Field ◽  
Carbon Nanotubes ◽  
Gauge Theory ◽  
Magnetic Fields ◽  
Electronic Spectrum ◽  
Acoustic Field ◽  
Two Dimensional ◽  
Mechanical Tension ◽  
Light Bullet ◽  
The Magnetic Field

In this paper, we study the influence of acoustic and magnetic fields on the propagation of twodimensional light bullet in an array of carbon nanotubes. The acoustic field is taken into account in the framework of the gauge theory. A magnetic field is applied along the nanotube axis and leads to a change in the electronic spectrum of ?electrons. It is shown, that the pulse stably propagates in the medium, taking into account both of these factors. In this case, the magnetic field and tension slows down the pulse, as well as changes its amplitude.

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 Band functions in the presence of magnetic steps

2015 ◽  
Vol 26 (01) ◽  
pp. 161-184 ◽  
Author(s):  
P. D. Hislop ◽  
N. Popoff ◽  
N. Raymond ◽  
M. P. Sundqvist
Keyword(s):  
Magnetic Field ◽  
Asymptotic Expansion ◽  
Magnetic Fields ◽  
Essential Spectrum ◽  
Effective Potential ◽  
Explicit Description ◽  
Natural Order ◽  
Two Dimensional ◽  
Piecewise Constant ◽  
The Magnetic Field

We complete the analysis of the band functions for two-dimensional magnetic Schrödinger operators with piecewise constant magnetic fields. The discontinuity of the magnetic field can create edge currents that flow along the discontinuity, which have been described by physicists. Properties of these edge currents are directly related to the behavior of the band functions. The effective potential of the fiber operator is an asymmetric double well (eventually degenerated) and the analysis of the splitting of the bands incorporates the asymmetry. If the magnetic field vanishes, the reduced operator has essential spectrum and we provide an explicit description of the band functions located below the essential spectrum. For non-degenerate magnetic steps, we provide an asymptotic expansion of the band functions at infinity. We prove that when the ratio of the two magnetic fields is rational, a splitting of the band functions occurs and has a natural order, predicted by numerical computations.

scholarly journals Self-magnetic field calculations in ray-tracing codes

2000 ◽  
Vol 18 (4) ◽  
pp. 601-610 ◽  
Author(s):  
STANLEY HUMPHRIES ◽  
JOHN PETILLO
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Ray Tracing ◽  
Field Calculation ◽  
Two Dimensional ◽  
Magnetic Forces ◽  
Iteration Cycle ◽  
Simple Rules ◽  
The Magnetic Field ◽  
Limited Accuracy

Beam-generated magnetic fields strongly influence the behavior of relativistic electron guns. Existing methods used in ray-tracing codes have limited accuracy and may not correctly represent nonlaminar beams. We describe a technique for the magnetic field calculation in a two-dimensional code based on the assignment of particle currents to the faces of elements in the mesh used for the electrostatic calculation. The balanced calculation of electric and magnetic forces in the same iteration cycle reduces the possibility of numerical filamentation instabilities. With simple rules of assignment on boundary faces, the method also handles field contributions of electrode currents. Several benchmark calculations performed on conformal meshes illustrate the versatility of the technique.

INFLUENCE OF MAGNETIC FIELDS ON THE INTRINSIC SPIN HALL EFFECT IN TWO-DIMENSIONAL SYSTEMS

2009 ◽  
Vol 23 (12n13) ◽  
pp. 2566-2572 ◽  
Author(s):  
O. E. RAICHEV
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Hall Effect ◽  
Berry Phase ◽  
Zeeman Splitting ◽  
Hall Conductivity ◽  
Spin Hall Effect ◽  
Two Dimensional ◽  
The Magnetic Field ◽  
Spin Hall Conductivity

The influence of magnetic fields on the electron spin in solids involves two basic mechanisms. First, any magnetic field introduces the Zeeman splitting of electron states, thereby modifying spin precession. Second, since the magnetic field affects the electron motion in the plane perpendicular to the field, the spin dynamics is also modified, owing to the spin-orbit interaction. The theory predicts, as a consequence of this influence, unusual properties of the intrinsic spin-Hall effect in two-dimensional systems in the presence of magnetic fields. This paper describes non-monotonic dependence of the spin-Hall conductivity on the magnetic field and its enhancement in the case of weak disorder, as well as multiple jumps of the spin-Hall conductivity owing to the topological transitions (abrupt changes of the Berry phase) induced by the parallel magnetic field.

TWO-DIMENSIONAL D- DONOR IN A STRONG MAGNETIC FIELD

2008 ◽  
Vol 22 (26) ◽  
pp. 2579-2585
Author(s):  
XIAOYAN ZHANG ◽  
GUOLIANG FAN ◽  
JINFENG WANG
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Variational Method ◽  
Bound State ◽  
Binding Energies ◽  
Triplet States ◽  
Two Dimensional ◽  
Threshold Values ◽  
Spin Triplet ◽  
The Magnetic Field

Two-dimensional negative donor ion in magnetic fields are investigated. Using a variational method, we calculated the binding energies of D- center for the spin-triplet states of L = -2 and L = -3 in this structure. The threshold values of the magnetic field which turn unbound state into bound state were obtained.

scholarly journals Two-dimensional ultra-short optical pulses in carbon nanotubes with acoustic field

2019 ◽  
Vol 220 ◽  
pp. 03029
Author(s):  
Dmitry Skvortsov ◽  
Natalia Konobeeva ◽  
Irina Zaporotskova ◽  
Mikhail Belonenko
Keyword(s):  
Carbon Nanotubes ◽  
Electromagnetic Field ◽  
Gauge Theory ◽  
Stress Field ◽  
Acoustic Field ◽  
Vector Potential ◽  
Two Dimensional ◽  
Optical Pulses ◽  
Effective Equation ◽  
External Strain

We investigate the dynamics of ultra-short optical pulses in carbon nanotubes under the influence of an acoustic field in two-dimensional geometry. We obtain an effective equation for the vector potential of the electromagnetic field, taking into account the stress field described in the framework of the gauge theory. And, we study the effects, which observed with a change of the magnitude of the external strain.

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 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 Photoelectric Measurements of Sunspot Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 190-191
Author(s):  
F.-L. Deubner ◽  
R. Göhring
Keyword(s):  
Magnetic Field ◽  
Vector Field ◽  
Magnetic Fields ◽  
Linear Polarization ◽  
Field Vector ◽  
Two Dimensional ◽  
Magnetic Vector ◽  
Umbral Dots ◽  
Photoelectric Measurements ◽  
The Magnetic Field

Photoelectric polarization measurements in a stable sunspot (type H) with a particularly dark umbra, where ‘umbral dots’ were virtually lacking, have been carried out with the Capri magnetograph. The measurements were evaluated in terms of Unno's theory to give the value and direction of the magnetic field vector. The parameters η0 = 5, β0 = 2.5 and ΔλD = 40mÅ have been adopted for the Fe I 5250 line. Taking the configuration of the sunspot into account as well as simple conditions of steadiness of the distributions to be obtained, it is possible to derive the magnetic vector field from two-dimensional records of circular and linear polarization without ambiguities.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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