Free-free Gaunt factors: comparison of various models

We develop the general theory of free-free absorption processes in terms of basic quantum mechanical principles. We perform calculations of the free-free Gaunt factor for several models of the electron-atom (ion) interaction in a variety of systems including rare gases, alkali, and aluminum. In addition, we investigate plasma-screening effects in such models as the Yukawa potential. Our calculations compare well with those of other authors, and our comparative study of various models allows a more thorough understanding of their range of validity. 38 refs., 2 figs., 14 tabs

Population genomics of post-glacial western Eurasia.

Western Eurasia witnessed several large-scale human migrations during the Holocene <sup>1-5</sup> . Here, to investigate the cross-continental effects of these migrations, we shotgun-sequenced 317 genomes-mainly from the Mesolithic and Neolithic periods-from across northern and western Eurasia. These were imputed alongside published data to obtain diploid genotypes from more than 1,600 ancient humans. Our analyses revealed a 'great divide' genomic boundary extending from the Black Sea to the Baltic. Mesolithic hunter-gatherers were highly genetically differentiated east and west of this zone, and the effect of the neolithization was equally disparate. Large-scale ancestry shifts occurred in the west as farming was introduced, including near-total replacement of hunter-gatherers in many areas, whereas no substantial ancestry shifts happened east of the zone during the same period. Similarly, relatedness decreased in the west from the Neolithic transition onwards, whereas, east of the Urals, relatedness remained high until around 4,000 BP, consistent with the persistence of localized groups of hunter-gatherers. The boundary dissolved when Yamnaya-related ancestry spread across western Eurasia around 5,000 BP, resulting in a second major turnover that reached most parts of Europe within a 1,000-year span. The genetic origin and fate of the Yamnaya have remained elusive, but we show that hunter-gatherers from the Middle Don region contributed ancestry to them. Yamnaya groups later admixed with individuals associated with the Globular Amphora culture before expanding into Europe. Similar turnovers occurred in western Siberia, where we report new genomic data from a 'Neolithic steppe' cline spanning the Siberian forest steppe to Lake Baikal. These prehistoric migrations had profound and lasting effects on the genetic diversity of Eurasian populations

Production of {\pi}+ and K+ mesons in argon-nucleus interactions at 3.2 AGeV

First physics results of the BM@N experiment at the Nuclotron/NICA complex are presented on {\pi}+ and K+ meson production in interactions of an argon beam with fixed targets of C, Al, Cu, Sn and Pb at 3.2 AGeV. Transverse momentum distributions, rapidity spectra and multiplicities of {\pi}+ and K+ mesons are measured. The results are compared with predictions of theoretical models and with other measurements at lower energies.Comment: 29 pages, 20 figure

Integrated scattering of microwaves by small metal spheres

When electromagnetic radiation falls upon a material body of any kind, the associated electric field induces periodic oscillations of the electrons of the material synchronous with the incident radiation. The material serves as a secondary source and emits energy in the form of scattered radiation with a frequency equal to that of the incident electromagnetic wave. The polarization and intensity of the scattered radiation are determined by the size, shape, electric constants, and interactions among the scattering elements. The scattering of electromagnetic waves is an old problem in physics. Such names as Rayleigh, Debye, and Mie have become associated with scattering, in recognition of their contribution to the subject. Because of the complexity of the general solution, applying to particles of arbitrary size, shape, orientation, and index of refraction, the complete solution probably will never be obtained. In some special cases however, notably the case of plane electromagnetic waves scattered by independent isotropic spherical particles as treated by Mie, a complete and rigorous solution has been obtained --Introduction, page 1

Akmeolinguistic in the context of individual education

Die innovativen Prozesse in der Gesellschaft, Wirtschaft und im Bildungswesen von heute fordern neue Standards und Ausbildungsansätze. Die methodisch-didaktischen Möglichkeiten der Ausbildung tragen dazu bei, dass die Kenntnisse zugänglicher und die Studenten selbsständiger werden. Das Thema des autonomen Lernens ist zwar nicht neu, aber gerade heute wird es immer aktueller. Akmeologischer Ansatz im modernen Ausbildungssystem besteht darin, Erfolg zu erreichen. Dazu führt professionelle Motivation, Entwicklung des kreativen Potenzials und anderer persönlichen Ressourcen. Akmelinguistik beschreibt Faktoren, Mechanismen und Gesetzmäßigkeiten der Entwicklung und Selbstaktualisierung der erwachsenen Lernenden für die besten Ergebnisse beim Sprachenlernen

Comparison of models for the free-free Gaunt factor at low temperatures and frequencies

We perform calculations for the free-free Gaunt factor at electron and photon energies below 1 Ry in the dipole approximation to the radiation field for a variety of representations of the scattering potential. We consider the static-exchange, static-exchange + model polarization, model exchange, and static models. Within each model, the resulting Schroedinger equation is solved exactly using a linear algebraic prescription. We investigate the rare gas and alkali systems. We find great sensitivity to the models for energies below four electron volts (4 eV). Above this energy, the Gaunt factors for the various models come into better agreement. 31 refs., 3 figs., 1 tab