Using HI to probe large scale structures at z∼3

The redshifted 1420 MHz emission from the HI in unresolved damped Lyman-α clouds at high z will appear as a background radiation in low frequency radio observations. This holds the possibility of a new tool for studying the universe at high-z, using the mean brightness temperature to probe the HI content and its fluctuations to probe power spectrum. Existing estimates of the HI density atz−3 imply a mean brightness temperature of 1 mK at 320 MHz. The cross-correlation between the temperature fluctuation across different frequencies and sight lines is predicted to vary from 10⁻⁷ K² to 10⁻⁸ K² over intervals corresponding to spatial scales from 10 Mpc to 40 Mpc for some of the currently favoured cosmological models. Comparing this with the expected sensitivity of the GMRT, we find that this can be detected with ∼ 10 hrs of integration, provided we can distinguish it from the galactic and extragalactic foregrounds which will swamp this signal. We discuss a strategy based on the very distinct spectral properties of the foregrounds as against the HI emission, possibly allowing the removal of the foregrounds from the observed maps.     

Effect of dust polarity on dust ion-acoustic localized structures in a superthermal dusty plasma

The effects of dust polarity and superthermal electrons are incorporated in the study of dust ion-acoustic (DIA) solitary waves (SWs) as well double layers (DLs) in a dusty plasma containing warm adiabatic ions, superthermal electrons, and arbitrarily (positively or negatively) charged immobile dust. Based on the energy-like integral equation, a new relationship between the localized electrostatic disturbances and dust polarity is derived. It is shown that there exists rarefactive SWs and DLs with qualitatively different structures in a way that depends on the population of superthermal electrons. As the electrons evolve their thermodynamic equilibrium, the localized structures are found with larger amplitude. It is also found that their amplitude increases (decreases) with the increase in the negative (positive) dust number density.     

Diagnostics of Near-Solar Plasma Turbulence Parameters Using the Radio Sounding Technique at Small Heliocentric Distances

We investigate the temporal correlation function and the mean intensity of monochromatic radio emission in the neighborhood of a regular caustic produced by radio sounding of near-solar plasma. Using asymptotic analysis and numerical simulation, we determine conditions under which the temporal correlation function is related to the temporal structure function by a relation similar to that used for the solar wind diagnostics (Coles and Harmon, Astrophys. J. 337, 1023, 1989) in the case of weak refraction of radio waves. Information on the correlation function and on the mean intensity in the caustic shadow region can be used to determine the parameters of the electron density fluctuation spectrum at small heliocentric distances.     

Behavior of the Rayleigh-Taylor mode in a dusty plasma with rotational and shear flows

The stability of a dusty plasma with sheared rotational flows is investigated. Using the fluid model together with the Bayly nonmodal approach, the inhomogeneous partial differential equations governing short-wavelength perturbations at the center of a rotational flow field or vortex structure are obtained. The effects of flow eccentricity, strength of the flow shear, as well as concentration of dust grains on the stability of the perturbations are investigated numerically. It is found that flow shear can cause secondary Rayleigh-Taylor instability of a rotational flow.     

The example of effective plasma acceleration in a magnetosphere

The problem of effective transform of Poynting flux energy into the kinetic energy of relativistic plasma outflow in a magnetosphere is considered. In this article we present an example of such acceleration. In order to perform it, we use the approach of ideal axisymmetric magnetohydrodynamics (MHD). For highly magnetized plasma outflow we show that a linear growth of Lorentz factor with a cylindrical distance from the rotational axis is a general result for any field configuration in the sub-magnetosonic flow. In the far region the full magnetohydrodynamics problem for one-dimensional flow is considered. It turns out that the effective plasma outflow acceleration is possible in the paraboloidal magnetic field. It is shown that such an acceleration is due to the drift of charged particles in the crossed electric and magnetic field. The clear explanation of the absence of acceleration in the monopole magnetic field if given.      

Optimized spectral bandwidth in high angular resolution imaging effect of a finite spatial-coherence outer scale

In the case of high angular resolution techniques (speckle interferometry, long baseline Michelson interferometry), one has studied how varies the signal-to-noise ratio (SNR) in terms of the spectral bandwidth . For values of varying from 0 up to 100 nanometers, it is shown that the SNR, contrary to the predictions, has no maximum value. In addition, in the case of the high frequency approximation, the effects of a finite spatial-coherence outer scale, the influence of the turbulence model used and of the optical energy of the turbulence on the optimal spectral bandwidth have been analyzed and discussed.     

Contraction of near-Earth satellite orbits using uniformly regular KS canonical elements in an oblate atmosphere with density scale height variation with altitude

A new non-singular analytical theory for the contraction of near-Earth satellite orbits under the influence of air drag is developed in terms of uniformly regular Kustaanheimo and Stiefel (KS) canonical elements using an oblate atmosphere with variation of density scale height with altitude. The series expansions include up to fourth power in terms of eccentricity and c (a small parameter dependent on the flattening of the atmosphere). Only two of the nine equations are solved analytically to compute the state vector and change in energy at the end of each revolution, due to symmetry in the equations of motion. It is observed that the analytically computed values of the semi-major axis and eccentricity are consistent with the numerically integrated values up to 500 revolutions over a wide range of the drag-perturbed orbital parameters. The theory can be effectively used for re-entry of near-Earth objects.     

Estimating the redshift distribution of photometric galaxy samples – II. Applications and tests of a new method

In Lima et al. we presented a new method for estimating the redshift distribution,   N ( z )  , of a photometric galaxy sample, using photometric observables and weighted sampling from a spectroscopic subsample of the data. In this paper, we extend this method and explore various applications of it, using both simulations and real data from the Sloan Digital Sky Survey (SDSS). In addition to estimating the redshift distribution for an entire sample, the weighting method enables accurate estimates of the redshift probability distribution,   p ( z )  , for each galaxy in a photometric sample. Use of   p ( z )  in cosmological analyses can substantially reduce biases associated with traditional photometric redshifts, in which a single redshift estimate is associated with each galaxy. The weighting procedure also naturally indicates which galaxies in the photometric sample are expected to have accurate redshift estimates, namely those that lie in regions of photometric-observable space that are well sampled by the spectroscopic subsample. In addition to providing a method that has some advantages over standard photo- z estimates, the weights method can also be used in conjunction with photo- z estimates e.g. by providing improved estimation of   N ( z )  via deconvolution of   N ( z _phot)  and improved estimates of photo- z scatter and bias. We present a publicly available   p ( z )  catalogue for ∼78 million SDSS DR7 galaxies.