A rotation-driven pulsar radio emission mechanism

ABSTRACT We propose and discuss an alternative pulsar radio emission mechanism that relies on rotation-driven plasma oscillations, rather than on a beam-driven instability, and suggest that it may be the generic radio emission mechanism for pulsars. We identify these oscillations as superluminal longitudinal waves in the pulsar plasma and point out that these waves can escape directly in the O mode. We argue that the frequency of the oscillations is ω0 ≈ ωp(2〈γ〉)1/2/γs, where γs is the Lorentz factor of bulk streaming motion and 〈γ〉 is the mean Lorentz factor in the rest frame of the plasma. The dependence of the plasma frequency ωp on radial distance implies a specific frequency-to-radius mapping, ω0∝r−3/2. Escape of the energy in these oscillations is possible if they are generated in overdense, field-aligned regions that we call fibres; the wave energy is initially refracted into underdense regions between the fibres, which act as ducts. Some implications of the model for the interpretation of pulsar radio emission are discussed.

The abundance and structure of subhaloes near the free streaming scale and their impact on indirect dark matter searches

ABSTRACT The free streaming motion of dark matter particles imprints a cutoff in the matter power spectrum and set the scale of the smallest dark matter halo. Recent cosmological N-body simulations have shown that the central density cusp is much steeper in haloes near the free streaming scale than in more massive haloes. Here, we study the abundance and structure of subhaloes near the free streaming scale at very high redshift using a suite of unprecedentedly large cosmological N-body simulations, over a wide range of the host halo mass. The subhalo abundance is suppressed strongly below the free streaming scale, but the ratio between the subhalo mass function in the cutoff and no cutoff simulations is well fitted by a single correction function regardless of the host halo mass and the redshift. In subhaloes, the central slopes are considerably shallower than in field haloes, however, are still steeper than that of the NFW profile. Contrary, the concentrations are significantly larger in subhaloes than haloes and depend on the subhalo mass. We compare two methods to extrapolate the mass–concentration relation of haloes and subhaloes to z = 0 and provide a new simple fitting function for subhaloes, based on a suite of large cosmological N-body simulations. Finally, we estimate the annihilation boost factor of a Milky-Way-sized halo to be between 1.8 and 6.2.

Study of ion-acoustic solitary wave structures in multi-component plasma containing positive and negative ions and q-exponential distributed electron beam

Using reductive perturbation technique, small-amplitude ion-acoustic solitary wave has been investigated in multi-component dense plasma, in which an electron beam propagates along the general streaming motion. The electrons in plasma have the q-exponential distribution. The positive and negative ions follow a regular Maxwellian distribution. It has been found that the positive and negative ion densities as well as the beam concentration have significant effect on the formation and properties of solitary structures. The streaming velocities of corresponding particles also have pronounced effect on the features of the solitons.

The Enigmatic Enigma Illusion

As a visual illusion, the Enigma illusion is a pattern that in its original version consists of 120 black radial lines on a white background intercepted by three bicolored annuli and a central disk. The main illusory effect in the Enigma (leading to its name) occurs during fixation of the center of the static image. Then, quite intense streaming motion may be perceived on the different annuli. It is characterized by a traveling wave or some subtle motion on the annuli that may not be described in more detail by the observer. Sometimes the observers call it “a feeling of motion”. This perceived (illusory) motion can occur in either direction; clockwise or counterclockwise. This example shows that such illusions are an important means to psychophysically investigate human motion perception and its limits.

Steady streaming around a cylinder pair

The steady streaming motion that appears around a pair of circular cylinders placed in a small-amplitude oscillatory flow is considered. Attention is focused on the case where the Stokes layer thickness at the surface of the cylinders is much smaller than the cylinder radius, and the streaming Reynolds number is of order unity or larger. In that case, the steady streaming velocity that persists at the edge of the Stokes layer can be imposed as a boundary condition to numerically solve the outer streaming motion that it drives in the bulk of the fluid. It is investigated how the gap width between the cylinders and the streaming Reynolds number affect the flow topology. The results are compared against experimental observations.