Multi-Conjugate Adaptive Optics with laser guide stars: performance in the infrared and visible

The assumption of the Gaussianity of primordial perturbations plays an important role in modern cosmology. The most direct test of this hypothesis consists of testing the Gaussianity of cosmic microwave background (CMB) maps. Counting the pixels with the temperatures in given ranges and thus estimating the one-point probability function of the field is the simplest of all the tests. Other usually more complex tests of Gaussianity generally use a great deal of the information already contained in the probability function. However, the most interesting outcome of such a test would be the signal of non-Gaussianity independent of the probability function. It is shown that the independent information has purely morphological character i.e. it depends on the geometry and topology of the level contours only. As an example we discuss in detail the quadratic model   v = u + α ( u ²-1)  ( u is a Gaussian field with   u¯ =0  and  〈 u ²〉=1  , α is a parameter) that may arise in slow-roll or two-field inflation models. We show that in the limit of small amplitude α the full information about the non-Gaussianity is contained in the probability function. If other tests are performed on this model they simply recycle the same information. A simple procedure allowing us to assess the sensitivity of any statistics to the morphological information is suggested. We provide an analytic estimate of the statistical limit for detecting the quadratic non-Gaussianity α _c as a function of the map size in the ideal situation when the scale of the field is resolved. This estimate is in a good agreement with the results of the Monte Carlo simulations of 256² and 1024² maps. The effect of resolution on the detection quadratic non-Gaussianity is also briefly discussed.     

Structure and kinematics of the interstellar medium around WR 134 and WR 135

Based on our H _α interferometry and 21-cm and CO observations, we analyze the structure and kinematics of the interstellar medium around the stars WR 134 and WR 135. We conclude that the HI bubble found here previously is associated with WR 135, not with WR 134. High-velocity motions of ionized gas that can be interpreted as expansion of the gas swept up by the stellar wind with a velocity up to 50–80 km s^?1 are observed around both stars. The line-of-sight velocity field of the ionized hydrogen in the Cygnus arm is shown to agree with the large-scale line-of-sight velocity distribution of the CO emission.     

Relativistic reference frames including time scales: Questions and answers

The subject of relativistic reference frames in astronomy is discussed with respect to the problems and needs of the various user groups. For didactical reasons the discussion is presented in form of a sequence of questions and answers.     

Reach-scale suspended sediment balance downstream from dams in a large Mediterranean river

Abstract

This paper presents a reach-scale sediment balance of a large impounded Mediterranean river (the lower Ebro, 1998–2008). Multi-temporal sediment storage and the influence of floods and tributaries on the sediment load were examined using continuous discharge and turbidity records. The mean annual suspended sediment load at the reach outlet (Xerta) is 0.12?×?10⁶ t, corroborating previous results. Suspended sediment concentrations were low (SSC_mean?=?13 mg L^-1), attaining a maximum of 274 mg L^-1. Erosion processes (channel-scour, bank erosion) are dominant, and net export of sediment occurs over the long term. Unexpectedly, ephemeral tributaries were found to contribute significantly: sediment delivered during torrential events attained 5% of the Ebro annual load, and was even larger than that in flushing flows. Overall, most of the suspended sediment load is transported by floods (up to 65% in some years). The results constitute basic information to underpin current management actions aiming to achieve the sustainability of the riverine and deltaic system.

Editor D. Koutsoyiannis; Associate editor D. Hughes

Citation Tena, A., Batalla, R.J. and Vericat, D., 2012. Reach-scale suspended sediment balance downstream from dams in a large Mediterranean river. Hydrological Sciences Journal, 57 (5), 831–849.     

On the Structure of Small-Scale Motion in the Core of the Earth

In 1996, St Pierre (1996) reported numerical simulations of a buoyant blob migrating across the earth's outer core and subject to the combined effects of rotation and an azimuthal magnetic field. He noted that the blob rapidly fragments into a series of plate-like structures. Quite independently, Davidson (1995, 1997) discovered a similar behaviour in the context of low- R m turbulence (without a Coriolis force) and showed that this phenomenon has its roots in the destruction of angular momentum by the Lorentz force. The purpose of this paper is to pull together these earlier studies and, in particular, to determine whether or not St. Pierre's platelets are also a consequence of the destruction of angular momentum. We confirm that this is indeed the case.     

Paleolatitudes of the Kerguelen hotspot: new paleomagnetic results and dynamic modeling

The Kerguelen Plateau, a Large Igneous Province in the southern Indian Ocean, was formed as a product of the Kerguelen hotspot in several eruptive phases during the last 120 Myr. We obtained new paleolatitudes for the central and northern Kerguelen Plateau from paleomagnetic investigations on basalts, which were drilled during ODP Leg 183 to the Kerguelen Plateau-Broken Ridge. The paleolatitudes coincide with paleolatitudes from previous investigations at the Kerguelen Plateau and Ninetyeast Ridge (the track of the Kerguelen hotspot) and indicate a difference between paleolatitudes and present position at 49°S of the Kerguelen hotspot. We show that true polar wander, the global motion between the mantle and the rotation axis, cannot explain this difference in latitudes. We present numerical model results of plume conduit motion in a large-scale mantle flow and the resulting surface hotspot motion. A large number of models all predict southward motion between 3° and 10° for the Kerguelen hotspot during the last 100 Myr, which is consistent with our paleomagnetic results.     

Hydrotroilite as a bioindicator of paleohydrological and paleoclimatic processes in the Caspian basin

The results of studying the distribution of hydrotroilite (a product of bacterial sulfate-reduction) in deep-water bottom sediments in the Southern and Middle Caspian Sea are considered and its relationships with paleoclimatic and paleohydrological processes in the sea basin are analyzed.