Thermal conductivity via magnetic excitations in spin-chain materials

We discuss the recent progress and the current status of experimental investigations of spin-mediated energy transport in spin-chain and spin-ladder materials with antiferromagnetic coupling. We briefly outline the central results of theoretical studies on the subject but focus mainly on recent experimental results that were obtained on materials which may be regarded as adequate physical realizations of the idealized theoretical model systems. Some open questions and unsettled issues are also addressed.Comment: 17 pages, 4 figure

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and x-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T, showing a minor but significant dependence of the dielectric constant on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.Comment: 10 pages, 11 figure

The transformation of the isis’s strategy in libya

The article analyzes the prospects of the presence of the terrorist organization “Islamic State” in Libya after the defeat of 2016. Although the Libyan authorities, with help of the international community, managed to deprive the ISIS of its stronghold in Sirte in 2016, the radical organization was able to recover, reorganize and once again claim to determine the future of Libya and the Sahel. The relevance of this study is due to the influence that the growth of radicalism in Libya has on international security, the environments in the Sahel and neighboring Arab and African countries. The situation is complicated by the fact that in Libya, from 2011 to the present time, there is a devastating civil war on calling into question the very existence of the Libyan state, creating a ground for the spread of radicalism and crime in the region and in the Mediterranean as a whole. Based on the analysis of reports from Libyan and Arab news agencies, data from European and American analytical centers, the authors draw conclusions about the prospects of the ISIS’s presence in Libya. Its future will depend on the success of state reconstruction. Organizations of this type emerge and can develop where national states are collapsing and a vacuum of power, chaos and lawlessness arise. The measures taken in the last year by the Libyan National Army to liberate southern Libya from terrorists and to open its oil fields may become a real obstacle for the ISIS there. If these measures have an effect, the “Islamic State” in Libya may face the impossibility of continuing its previous activities in the Libyan Fezzan. Conversely, if a new round of inter-tribal and inter-ethnic struggle breaks out in Fezzan as a result of the disruption of social and power balance due to the LNA campaign or inability of the Government of National Accord and Libyan National Army to work together, the “Islamic State” will only strengthen its positions. The ISIS has clearly demonstrated that it is able to gain and accumulate resources in conditions of instability. © 2019, Russian Academy of Sciences. All rights reserved

Chaotic Regime of Dicke Invertionless Super-Radiance in a High-Q Cavity

We investigate theoretically different regimes of Dicke superradiance of an ensemble of three-level emitters (L configuration of the operating transitions) placed in a cyclic high-Q cavity. It is shown, that different regimes of three-level Dicke superradiance can be realized: regular dynamics, quasiperiodic and even chaotic behavior

Chaotic Regime of Dicke Invertionless Super-Radiance in a High-Q Cavity

We investigate theoretically different regimes of Dicke superradiance of an ensemble of three-level emitters (L configuration of the operating transitions) placed in a cyclic high-Q cavity. It is shown, that different regimes of three-level Dicke superradiance can be realized: regular dynamics, quasiperiodic and even chaotic behavior

Chaotic Regime of Dicke Invertionless Super-Radiance in a High-Q Cavity

We investigate theoretically different regimes of Dicke superradiance of an ensemble of three-level emitters (L configuration of the operating transitions) placed in a cyclic high-Q cavity. It is shown, that different regimes of three-level Dicke superradiance can be realized: regular dynamics, quasiperiodic and even chaotic behavior