Search results for " Magnetic field"
showing 10 items of 165 documents
Complete mapping of the spin-wave spectrum in vortex state nano-disk
2016
© 2016 American Physical Society.We report a study on the complete spin-wave spectrum inside a vortex-state nanodisk. Transformation of this spectrum is continuously monitored as the nanodisk becomes gradually magnetized by a perpendicular magnetic field and encounters a second-order phase transition to the uniformly magnetized state. This reveals the bijective relationship that exists between the eigenmodes in the vortex state and the ones in the saturated state. It is found that the gyrotropic mode can be continuously viewed as a uniform phase precession, which uniquely softens (its frequency vanishes) at the saturation field to transform above into the Kittel mode. By contrast, the other…
Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305
2007
We perform a timing analysis on RXTE data of the accreting millisecond pulsar XTE J1751-305 observed during the April 2002 outburst. After having corrected for Doppler effects on the pulse phases due to the orbital motion of the source, we performed a timing analysis on the phase delays, which gives, for the first time for this source, an estimate of the average spin frequency derivative = (3.7 +/- 1.0)E-13 Hz/s. We discuss the torque resulting from the spin-up of the neutron star deriving a dynamical estimate of the mass accretion rate and comparing it with the one obtained from X-ray flux. Constraints on the distance to the source are discussed, leading to a lower limit of \sim 6.7 kpc.
Timing of the Accreting Millisecond Pulsar XTE J1814-338
2006
We present a precise timing analysis of the accreting millisecond pulsar XTE J1814-338 during its 2003 outburst, observed by RXTE. A full orbital solution is given for the first time; Doppler effects induced by the motion of the source in the binary system were corrected, leading to a refined estimate of the orbital period, P_orb=15388.7229(2)s, and of the projected semimajor axis, a sini/c= 390.633(9) lt-ms. We could then investigate the spin behaviour of the accreting compact object during the outburst. We report here a refined value of the spin frequency (nu=314.35610879(1) Hz) and the first estimate of the spin frequency derivative of this source while accreting (nu^dot=(-6.7 +/- 0.7) 1…
Dynamics of an elongated magnetic droplet in a rotating field
2002
A model is proposed for the dynamics of an elongated droplet under the action of a low frequency rotating magnetic field. This model determines a set of critical frequencies at which the transitions to more complex bent shapes take place. These transitions occur through propagation of jumps of the droplet's axial tangent angle described by a nonlinear singularly perturbed partial differential equation with the intrinsic viscosity of the droplet playing the regularizing role.
Effect of a Steady Magnetic Field and Imposed Rotation of Vessel on Heat and Mass Transfer in Swirling Recirculating Flows
1999
A simplified theoretical model for the solidification interface shape prediction is introduced and tested. We linearised a coupled hydrodynamic-solidification problem about the state with a flat interface. In such a way we split the problem into a hydrodynamic part with a flat solid-liquid front and a solidification part with a calculated heat flux from the liquid phase. The method allows obvious conclusions on optimum heat conditions near the solidification interface providing its flatness and maximum pulling velocity at the same time. Comparison to the results by FLUENT package showed that the method provides a reasonable accuracy even for a noticeably deformed interface shape. Another pa…
Linear and non-linear stability of a thermally stratified magnetically driven rotating flow in a cylinder
2010
The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by the rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilise the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. It is known from earlier studies that these rolls can be only excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this non-linear bypass instability into …
Observation of the cosmic ray moon shadowing effect with the ARGO-YBJ experiment
2011
Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the obser…
On magnetic guidance of charged particles
2016
High precision beta decay experiments with polarized neutrons, employing magnetic guiding fields for the decay electrons in combination with energy dispersive detectors, initiated detailed studies of the point spread function (PSF) for homogeneous magnetic fields. A PSF describes the radial probability distribution of mono-energetic electrons at the detector plane which were emitted from a point-like source. With regard to accuracy considerations for high-precision experiments unwanted singularities occur as function of the radial detector coordinate which have recently been discussed in detail by Dubbers (2015) [3]. In the present article mathematical inconsistencies in the approximations …
From My Postdoc at the “Abteilung Cardona”
2015
Before finishing my Ph.D. in September 1986, I had already a non permanent position at the University of Valencia, it was called at this time assistant professor (profesor ayudante), with a lot of teaching. I sent a letter to Manuel at the beginning of 1987 and, after receiving the letter, he called immediately by phone my thesis advisor, Prof. Alfredo Segura. Manuel told him: I have a lot of people at the moment, but if he is very good, I will accept him. Finally, he sent me an acceptation letter and I got a fellowship from the local government and the Ministry of Education. I did my postdoc from December 87 to 89.
Magnetic imaging of a late Bronze Age tumulus in France before and during excavation
2002
Geophysical surveying is taking place in the Chatillon-sur-Seine area in France to examine and map prehistoric settlements and the structure of tumuli (grave-mounds which originally reached a height of up to 5 m but which are now almost level). The magnetic survey discussed here was conducted to detect archaeological structures within a late La Tene (100-50 bce) necropolis, in particular the preexcavation recording of a late Bronze Age round barrow. During the excavation, additional surveys were carried out to analyze the influence of immediate subsurface soil layers on the magnetic anomalies originating from the deeper archaeological features. Additional radar surveys made use of a 500 MHz…