Search results for "waves"
showing 10 items of 1766 documents
Modeling the long duration rise phase of a flare detected on the M star TWA 11 B
2009
We present preliminary results from the analysis of a long duration flare that was observed in a serendipitous XMM-Newton detection of the M star CD-39 7717 B (TWA 11 B), member of the young stellar association TW Hya. Only the rise phase (with a duration of ~35 ks) and possibly the flare peak are present in the light-curve. The decay phase was not monitored. The fluorescent iron emission line at 6.4 keV was observed during this event. As far as we are concerned, since TWA 11 B seems to have no disk, this is only the third detection of Fe photospheric fluorescence. During the flare, the X-ray flux increased a factor of ~4. Taking the light curve and the evolution of the hardness ratio into …
From scalar to polar active matter: Connecting simulations with mean-field theory
2019
We study numerically the phase behavior of self-propelled elliptical particles interacting through the ``hard'' repulsive Gay-Berne potential at infinite P\'eclet number. Changing a single parameter, the aspect ratio, allows us to continuously go from discoid active Brownian particles to elongated polar rods. Discoids show phase separation, which changes to a cluster state of polar domains, which then form polar bands as the aspect ratio is increased. From the simulations, we identify and extract the two effective parameters entering the mean-field description: the force imbalance coefficient and the effective coupling to the local polarization. These two coefficients are sufficient to obta…
Vorticity Determines the Force on Bodies Immersed in Active Fluids
2021
When immersed into a fluid of active Brownian particles, passive bodies might start to undergo linear or angular directed motion depending on their shape. Here we exploit the divergence theorem to relate the forces responsible for this motion to the density and current induced by--but far away from--the body. In general, the force is composed of two contributions: due to the strength of the dipolar field component and due to particles leaving the boundary, generating a non-vanishing vorticity of the polarization. We derive and numerically corroborate results for periodic systems, which are fundamentally different from unbounded systems with forces that scale with the area of the system. We …
Sum Frequency Generation Spectra from Velocity–Velocity Correlation Functions
2017
We developed an expression for the calculation of the sum frequency generation spectra (SFG) of water interfaces that is based on the projection of the atomic velocities on the local normal modes. Our approach permits one to obtain the SFG signal from suitable velocity-velocity correlation functions, reducing the computational cost to that of the accumulation of a molecular dynamics trajectory, and therefore cutting the overhead costs associated with the explicit calculation of the dipole moment and polarizability tensor. Our method permits to interpret the peaks in the spectrum in terms of local modes, also including the bending region. The results for the water-air interface, obtained usi…
Optical Harmonic Generation Parametric Devices
1999
The sections in this article are 1 Nonlinear Optics: an Actual and Wide Field Of Optics Research 2 Main Applications of Parametric Devices 3 Induced Macroscopic Polarization 4 Electromagnetic Energy Exchange 5 Nonlinear Materials 6 Propagation of the Waves in the Nonlinear Medium 7 Second Harmonic Generation 8 Optical Parametric Generators and Amplifiers 9 Optical Parametric Oscillators 10 Recent Advances in Frequency Conversion
Penumbral oscillations in Na D lines
1990
Penumbral oscillations were measured in two opposite parts in the penumbra of a spot, using photographic spectra of Na D lines. Power spectra of velocities show the presence of the 5-min oscillation with lowv rms. Coherence and phase analyses between the velocity fluctuations of the lines are also studied. The results seem to show that the 5-min oscillation is still surviving as a standing or evanescent wave at the height of formation of Na D lines.
Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors
2018
In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. Fo ...
THE OPEN BCS MODEL, ITS STOCHASTIC LIMIT AND SOME GENERALIZATIONS
2005
In this paper we use the stochastic limit approach as a tool to discuss the open BCS model of low temperature superconductivity. We also briefly discuss the role of a second reservoir interacting with the first one (but not with the system) in the computation of the critical temperature corresponding to the transition from a normal to a superconducting phase.
THE ACCELERATING JET OF 3C 279
2012
Analysis of the proper motions of the subparsec scale jet of the quasar 3C 279 at 15 GHz with the Very Long Baseline Array shows significant accelerations in four of nine superluminal features. Analysis of these motions is combined with the analysis of flux density light curves to constrain values of Lorentz factor and viewing angle (and their derivatives) for each component. The data for each of these components are consistent with significant changes to the Lorentz factor, viewing angle, and azimuthal angle, suggesting jet bending with changes in speed. We see that for these observed components Lorentz factors are in the range Γ = 10-41, viewing angles are in the range = 0.°1-5.°0, and in…
High Precision Differential Astrometry in Large Angular Separation Pairs of Radiosources
1994
We show preliminary results of three of the four radiosource pairs with angular separations ranging from 0.01° to 6° where we have determined such a separation with a typical fractional precision of 10-8using phase delays corrected for structural and ionospheric contributions. In the radiosource 4C39.25 we measure a motion with respect to an external radiosource which is compatible with previously reported internal superluminal motion.