Search results for "MAGNETIC FIELD"
showing 10 items of 1488 documents
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
2008
We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst. We analyse RXTE observations that monitored A 0535+26 during the outburst. We complete spectral and timing analyses of the data. We study the evolution of the pulse period, present energy-dependent pulse profiles both at the initial pre-outburst flare and close to outburst maximum, and measure how the cyclotron resonance-scattering feature (hereafter CRSF) evolves. We present three main results: a constant period P=…
YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppress fluctuations of X-ray emission
2013
Context. Theoretical arguments and numerical simulations of radiative shocks produced by the impact of the accreting gas onto young stars predict quasi-periodic oscillations in the emitted radiation. However, observational data do not show evidence of such periodicity. Aims. We investigate whether physically plausible perturbations in the accretion column or in the chromosphere could disrupt the shock structure influencing the observability of the oscillatory behavior. Methods. We performed local 2D magneto-hydrodynamical simulations of an accretion shock impacting a chromosphere, taking optically thin radiation losses and thermal conduction into account. We investigated the effects of seve…
Are pulsars born with a hidden magnetic field?
2015
The observation of several neutron stars in the center of supernova remnants and with significantly lower values of the dipolar magnetic field than the average radio-pulsar population has motivated a lively debate about their formation and origin, with controversial interpretations. A possible explanation requires the slow rotation of the proto-neutron star at birth, which is unable to amplify its magnetic field to typical pulsar levels. An alternative possibility, the hidden magnetic field scenario, considers the accretion of the fallback of the supernova debris onto the neutron star as responsible for the submergence (or screening) of the field and its apparently low value. In this paper …
Magnetic fields of relativistic jets in active galactic nuclei
2011
The motivation of my work is to understand the role played by the magnetic field in the dynamics and emission of relativistic jets. In order to achieve this objective I have been carrying it out in two parallel ways. In the first of them I have performed numerical magnetohydrodynamic and emission (eRMHD) simulations of relativistic jets. The simulations have been performed in collaboration with the Relativistic Astrophysics Group in the University of Valencia, using a numerical code that solves the RMHD equations in conservative form and cylindrical coordinates with axial symmetry (see Leismann et al., 2005, for more details). I have focused the study on the role played by the magnetic fiel…
Intermittent release of transients in the slow solar wind: 1. Remote sensing observations
2010
[1] The Heliospheric Imager (HI) instruments on board the STEREO spacecraft are used to analyze the solar wind during August and September 2007. We show how HI can be used to image the streamer belt and, in particular, the variability of the slow solar wind which originates inside and in the vicinity of the streamer belt. Intermittent mass flows are observed in HI difference images, streaming out along the extension of helmet streamers. These flows can appear very differently in images: plasma distributed on twisted flux ropes, V-shaped structures, or “blobs.” The variety of these transient features may highlight the richness of phenomena that could occur near helmet streamers: emergence of…
Measurement of untruncated nuclear spin interactions via zero- to ultralow-field nuclear magnetic resonance
2015
Zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the coupling averages to zero under isotropic molecular tumbling. Under partial alignment, this information is retained in the form of so-called residual dipolar couplings. We report zero- to ultra-low-field NMR measurements of residual dipolar couplings in acetonitrile…
Polarization-driven spin precession of mesospheric sodium atoms
2018
We report experimental results on the first on-sky observation of atomic spin precession of mesospheric sodium driven by polarization modulation of a continuous-wave laser. The magnetic resonance was remotely detected from the ground by observing the enhancement of induced fluorescence when the driving frequency approached the precession frequency of sodium in the mesosphere, between 85 km and 100 km altitude. The experiment was performed at La Palma, and the uncertainty in the measured Larmor frequency ($\approx$260 kHz) corresponded to an error in the geomagnetic field of 0.4 mG. The results are consistent with geomagnetic field models and with the theory of light-atom interaction in the …
Sidebands in Optically Detected Magnetic Resonance Signals of Nitrogen Vacancy Centers in Diamond
2013
We study features in the optically detected magnetic resonance (ODMR) signals associated with negatively charged nitrogen-vacancy (NV) centers coupled to other paramagnetic impurities in diamond. Our results are important for understanding ODMR line shapes and for optimization of devices based on NV centers. We determine the origins of several side features to the unperturbed NV magnetic resonance by studying their magnetic field and microwave power dependences. Side resonances separated by around 130 MHz are due to hyperfine coupling between NV centers and nearest-neighbor C-13 nuclear spins. Side resonances separated by approximately {40, 260, 300} MHz are found to originate from simultan…
Corrosion Phenomena of Eurofeer Steel in Pb-17Li Stationary Flow at Magnetic Field
2006
Search of new energy sources draws the increasing attention to use for this purpose of reactors. In the Europe some years the program EUROATOM uniting scientific of the many countries for the decision of constructive problems at designing of fusion reactors operates. One of the main things in this program is the problem of liquid metals breeder blanket behaviour. Structural material of blanket should meet high requirements because of extreme operating conditions. Therefore the knowledge of the effect of metals flow velocity, temperatures and also a neutron irradiation and a magnetic field on the corrosion processes are necessary. At the moment the eutectic lead -lithium (Pb-17Li) is conside…
Investigation of inductive coupling solutions for E-bike wireless charging
2015
Wireless charging of electric vehicle batteries is a major topic for academic and industrial research. The wireless charging is based on the inductive coupling between a primary coil, connected to the grid, and a secondary coil, connected to the vehicle battery. Wireless battery charging provides benefits in terms of comfort for the drivers, who should just park to start the charging operation, without needing to plug in the vehicle. Wireless charging is particularly convenient for E-bike users. For the bicycle charging, the inductive coupling should be implemented through a compact and light-weight solution. In this paper, different options of inductively coupled coils for E- bike charging…