Search results for "MAGNETIC FIELD"
showing 10 items of 1488 documents
Magnetic field and temperature dependent correlations in the singlet ground state system CsFeBr3
1992
Abstract In the singlet ground state system CsFeBr 3 the temperature and magnetic field dependence of the magnetic dispersion curves have been measured by inelastic neutron scattering. At a field of 4.1 T magnetic Bragg peaks appear at (⅓ ⅓ 1) and (⅔ ⅔ 1). The correlation lengths were derived from the experimental data by integrating the constant Q -scans over the energy transfer. The Q -dependence was fitted to Lorentzians and correlations lengths were extracted for different directions in the lattice. These correlation lengths decrease with increasing temperature and increase with increasing field. Above the phase transition the correlation lengths decrease again.
Magnetic excitations and phase transition of CsFeBr3 in an external magnetic field
1990
In CSFeBr3 the Fe2+ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Lande factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgard describe the ex…
Renormalization of the Fröhlich constant for electrons in a quantum dot
2002
Recent experimental investigations of far-infrared attenuation in GaAs/InAs quantum dot in magnetic field and measurements of photoluminescence features for smaller pyramid-shape GaAs/InAs quantum dots indicated an enhancement of coupling of longitudinal optical phonons with confined electrons, which manifested itself in a significant increase of the effective Frohlich constant in comparison to its bulk value. We give a simple quasiclassical explanation of this enhancement and relate the renormalization of the Frohlich constant with the dot diameter.
Resolution changes of MCP-PMTs in magnetic fields
2016
Micro-channel plate photomultiplier tubes (MCP-PMTs) are chosen in many applications that have to cope with strong magnetic fields. The DIRC detectors of the PANDA experiment plan to employ them as they show excellent timing characteristics, radiation hardness, relatively low dark count rates and sufficient lifetime. This article mainly focuses on the performance of the position reconstruction of detected photons. Two different MCP-PMTs with segmented anode geometries have been tested in magnetic fields of different strengths. The variation of their performance has been studied. The measurements show improved position resolution and image shifts with increasing magnetic field strength.
Some physical appearances of vector coherent states and coherent states related to degenerate Hamiltonians
2005
In the spirit of some earlier work on the construction of vector coherent states over matrix domains, we compute here such states associated to some physical Hamiltonians. In particular, we construct vector coherent states of the Gazeau-Klauder type. As a related problem, we also suggest a way to handle degeneracies in the Hamiltonian for building coherent states. Specific physical Hamiltonians studied include a single photon mode interacting with a pair of fermions, a Hamiltonian involving a single boson and a single fermion, a charged particle in a three dimensional harmonic force field and the case of a two-dimensional electron placed in a constant magnetic field, orthogonal to the plane…
Modulating magnetar emission by magneto-elastic oscillations
2014
We present a new numerical tool to calculate the emission of highly magnetized neutron stars (magnetars) and apply it to describe the quasi-periodic oscillations (QPOs) observed in magnetar giant flares. In previous work we have developed a model of magneto-elastic oscillations of magnetars that allows to reproduce the observed frequencies. These QPOs can couple to the star's exterior through the magnetic field and induce currents in the magnetosphere that provide scattering targets for resonant cyclotron scattering of the photons. The scattering is calculated with a Monte-Carlo approach and it is coupled to a code that calculates the momentum distribution of the charge carriers as an one-d…
Photospheric response to an ellerman bomb-like event—an analogy of Sunrise/IMaX observations and MHD simulations
2017
S. Danilovic et. al.
The pulsations of the B5IVe star HD 181231 observed with CoRoT and ground-based spectroscopy
2009
International audience; Context: HD 181231 is a B5IVe star, which has been observed with the CoRoT satellite during ~5 consecutive months and simultaneously from the ground in spectroscopy and spectropolarimetry. Aims: By analysing these data, we aim to detect and characterize as many pulsation frequencies as possible, to search for the presence of beating effects possibly at the origin of the Be phenomenon. Our results will also provide a basis for seismic modelling. Methods: The fundamental parameters of the star are determined from spectral fitting and from the study of the circumstellar emission. The CoRoT photometric data and ground-based spectroscopy are analysed using several Fourier…
FULLY RESOLVED QUIET-SUN MAGNETIC FLUX TUBE OBSERVED WITH THE SUNRISE/IMAX INSTRUMENT
2010
Until today, the small size of magnetic elements in quiet Sun areas has required the application of indirect methods, such as the line-ratio technique or multi-component inversions, to infer their physical properties. A consistent match to the observed Stokes profiles could only be obtained by introducing a magnetic filling factor that specifies the fraction of the observed pixel filled with magnetic field. Here, we investigate the properties of a small magnetic patch in the quiet Sun observed with the IMaX magnetograph on board the balloon-borne telescope Sunrise with unprecedented spatial resolution and low instrumental stray light. We apply an inversion technique based on the numerical s…
Supersonic Magnetic Upflows in Granular Cells Observed with Sunrise/IMaX
2010
Using the IMaX instrument on-board the Sunrise stratospheric balloon-telescope we have detected extremely shifted polarization signals around the Fe I 5250.217 {\AA} spectral line within granules in the solar photosphere. We interpret the velocities associated with these events as corresponding to supersonic and magnetic upflows. In addition, they are also related to the appearance of opposite polarities and highly inclined magnetic fields. This suggests that they are produced by the reconnection of emerging magnetic loops through granular upflows. The events occupy an average area of 0.046 arcsec$^2$ and last for about 80 seconds, with larger events having longer lifetimes. These supersoni…