Faraday ghosts: depolarization canals in the Galactic radio emission

Narrow, elongated regions of very low polarized intensity -- so-called canals -- have recently been observed by several authors at decimeter wavelengths in various directions in the Milky Way, but their origin remains enigmatic. We show that the canals arise from depolarization by differential Faraday rotation in the interstellar medium and that they represent level lines of Faraday rotation measure RM, a random function of position in the sky. Statistical properties of the separation of canals depend on the autocorrelation function of RM, and so provide a useful tool for studies of interstellar turbulence.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Pink Page

Non-local effects in the mean-field disc dynamo. II. Numerical and asymptotic solutions

The thin-disc global asymptotics are discussed for axisymmetric mean-field dynamos with vacuum boundary conditions allowing for non-local terms arising from a finite radial component of the mean magnetic field at the disc surface. This leads to an integro-differential operator in the equation for the radial distribution of the mean magnetic field strength, $Q(r)$ in the disc plane at a distance $r$ from its centre; an asymptotic form of its solution at large distances from the dynamo active region is obtained. Numerical solutions of the integro-differential equation confirm that the non-local effects act similarly to an enhanced magnetic diffusion. This leads to a wider radial distribution of the eigensolution and faster propagation of magnetic fronts, compared to solutions with the radial surface field neglected. Another result of non-local effects is a slowly decaying algebraic tail of the eigenfunctions outside the dynamo active region, $Q(r)\sim r^{-4}$, which is shown to persist in nonlinear solutions where $\alpha$-quenching is included. The non-local nature of the solutions can affect the radial profile of the regular magnetic field in spiral galaxies and accretion discs at large distances from the centre.Comment: Revised version, as accepted; Geophys. Astrophys. Fluid Dyna

A Pan-European model of the Neolithic

We present a mathematical model, based on a compilation of radiocarbon dates, of the transition to the Neolithic, from about 7000 to 4000 BC in Europe. With the arrival of the Neolithic, hunting and food gathering gave way to agriculture and stock breeding in many parts of Europe; pottery-making spread into even broader areas. We use a population dynamics model to suggest the presence of two waves of advance, one from the Near East, and another through Eastern Europe. Thus, we provide a quantitative framework in which a unified interpretation of the Western and Eastern Neolithic can be developed.Predstavljamo matematični model, ki temelji na kompilaciji radiokarbonskih datumov med 7000 in 4000 BC. Ti datumi so v Evropi povezani s prehodom v neolitik, ko sta poljedelstvo in živinoreja v mnogih regijah zamenjala lov in nabiralništvo; lončarstvo pa se je širilo še dlje. S pomočjo modela populacijske dinamike predstavljamo dva vala napredovanja, enega iz Bližnjega Vzhoda in drugega preko Vzhodne Evrope. Z njim zagotavljamo kvantitavni okvir, v katerem lahko razvijamo enovito interpretacijo 'zahodnega' in 'vzhodnega' neolitika

The Holocene Environment and Transition to Agriculture in Boreal Russia (Serteya Valley Case Study)

This article outlines the results of one of the aspects of a multidisciplinary project currently conducted in the upper part of the basin of the Western Dvina River in North-Western Russia. The project was targeted at prehistoric lake dwelling sites in the valley of Serteya River, a small tributary of the Western Dvina, and aimed at the precise dating of the initial transition from hunting-gathering to agriculture in that area. The methods used included pollen, diatom and geochemical analyses under strict time control provided by radiocarbon dating. The initial settlement emerged at c. 6200 cal. BC, when the valley was filled by a fresh water lake with a relatively high lake-level. The initial indices of agriculture became perceptible in the deposits of Usvyatian Culture (4600-3400 cal. BC), featuring large-scale constructions of pile-dwellings. Indices of swidden type agriculture became apparent in the deposits of Zhizhitsian Culture, 2300-2200 cal. BC

The Spread of the Neolithic in the South East European Plain: Radiocarbon Chronology, Subsistence, and Environment

Newly available radiocarbon dates show the early signs of pottery-making in the North Caspian area, the Middle-Lower Volga, and the Lower Don at 8-7 kyr cal BC. Stable settlements, as indicated by "coeval subsamples," are recognized in the Middle-Lower Volga (Yelshanian) at 6.8 kyr cal BC and the Caspian Lowland at about 6 kyr cal BC. The ages of the Strumel-Gostyatin, Surskian, and Bug-Dniesterian sites are in the range of 6.6-4.5 kyr BC, overlapping with early farming entities (Starčevo-Krs-Criş and Linear Pottery), whose influence is perceptible in archaeological materials. Likewise, the 14C-dated pollen data show that the spread of early pottery-making coincided with increased precipitation throughout the forest-steppe area.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202