Photon splitting in atomic fields

Photon splitting due to vacuum polarization in the electric field of an atom is considered. We survey different theoretical approaches to the description of this nonlinear QED process and several attempts of its experimental observation. We present the results of the lowest-order perturbation theory as well as those obtained within the quasiclassical approximation being exact in the external field strength. The experiment where photon splitting was really observed for the first time is discussed in details. The results of this experiment are compared with recent theoretical estimations.Comment: 45 pages, 24 figure

Statistical Channel Model for 60 GHz WLAN Systems in Conference Room Environment

In this work, a methodology of statistical channel modeling for 60 GHz WLAN systems is proposed and a channel model for the office conference room environment is developed. The proposed methodology takes into account the most important properties of the indoor 60 GHz propagation channel such as large propagation loss and necessity to use steerable directional antennas by the WLAN stations, quasi-optical propagation nature, clustering structure of the channel, and significant impact of the polarization characteristics. A general mathematical structure of the channel model that supports all the described 60 GHz propagation channel properties is suggested. Then the conference room scenario for 60 GHz WLAN systems is introduced. Development of the inter cluster, intra cluster, and polarization impact modeling parameters is considered in details first explaining the used methodology for each channel modeling aspect and then followed by its application to the conference room scenario. The raw data for the channel model development include the experimental results [1], [2] and ray-tracing simulations for the conference room scenario. The proposed channel modeling methodology and the developed conference room channel model were adopted by the IEEE 802.11ad committee for 60 GHz WLAN systems standardization

Polarization ququarts

We discuss the concept of polarization states of four-dimensional quantum systems based on frequency non-degenerate biphoton field. Several quantum tomography protocols were developed and implemented for measurement of an arbitrary state of ququart. A simple method that does not rely on interferometric technique is used to generate and measure the sequence of states that can be used for quantum communication purposes.Comment: 13 pages, 10 figure

Experimental investigation of high-energy photon splitting in atomic fields

The new data analysis of the experiment, where the photon splitting in the atomic fields has been observed for the first time, is presented. This experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, the statistics of $1.6\cdot 10^9$ photons incident on the BGO target was collected. About 400 candidates to the photon splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the cross section calculated exactly in an atomic field. The predictions obtained in the Born approximation significantly differ from the experimental results.Comment: 11 pages, 6 figures, LaTe

ТИПОЛОГИЯ СРЕДНЕВЕКОВЫХ ТОПОРОВ C СЕВЕРА ЗАПАДНОЙ СИБИРИ

The paper presents the results of the research on the Middle Ages iron axes found in different years in the north of Western Siberia and the Urals, excluding pole-axe (berdysh Rus.) that appear in large numbers in the study area with the growing of the Russian population. The relevance of such study has matured, since there are enough sources that need to be generalized and critically compiled. Taking into account the morphological features of the archaeological evidence, the authors propose to classify all currently known axes by 2 groups and 13 types. The first group including 3 types of minting axes were made exclusively for combat use. The second group includes 10 types of axes, classified as universal, which served both for the military and for economic purposes. The text with the description of the sites contains also table with the data on the basic parameters of axes (item length, blade width) and the time of their use (existence). For the first time, a new type of battle axe (type 13), accidentally found in the Khanty-Mansi Autonomous Okrug - Ugra, is published. We present analogues of this subject among the products of Russian blacksmiths of the 13th-14th centuries and explain the position on the dating and on origin of the axe. The paper discusses the evolution of certain types of objects, describes plots concerning the origin of certain items (imports from Volga Bulgaria, Russian lands, etc.) and the special attitude of the local population to this type of weapon, which could be stored for centuries in the holy places of the Ob Ugrians. The authors come to the conclusion that imported axes of the second group were used as a standard for Siberian blacksmiths. But local products, characterized by primitive technology (a multilayer package), low quality welding of iron strips and an abundance of slag inclusions, can be finally identified only after metallographic microstructural analysis. This research should be prolonged, because annual archaeological investigations replenish the source base, and, with no doubt, the typology of axes proposed in the article will be supplemented and adjusted. © 2020 Tyumen Scientific Centre of Siberian Branch of the Russian Academy of Sciences. All rights reserved.Работа выполнена по Программе УрО РАН № 18-6-6-15 «Археологические памятники как источники по реконструкции развития древних обществ Урала и севера Западной Сибири» (рук. д.и.н. А.Ф. Шорин)

МОДИФИКАЦИЯ БЮДЖЕТНЫХ ПРАВИЛ ДЛЯ ИНВЕСТИЦИОННОГО РАЗВИТИЯ ЭКОНОМИКИ РОССИИ

The article analyzes the problem of modifying the budget rules while facing a slowdown of the economic growth in Russia in the context of high levels of natural rent. It was revealed that the main disadvantage of the current fiscal rules is the lack of coordination with the investment and monetary policy. Modifying the existing budget rules is proven to be necessary for the transfer of the natural rent in the infrastructure development and the diversification of the economy.The basis of the new fiscal rules is the mechanism for maintaining a balance between cash flows in consumption funds, investment, and savings. This requires formation of an Investment fund for the development of the national economy, filled not only by the state rental revenues, but the Bank of Russia as well (especially in the period of low oil prices). В статье анализируется проблема модификации бюджетных правил в условиях замедления роста экономики России на фоне высокого уровня природной ренты. Выявлено, что основным недостатком действующего бюджетного правила является его нескоординированность с инвестиционной и денежно-кредитной политикой государства. Обосновывается, что для перевода природной ренты в развитие инфраструктуры и диверсификацию экономики необходимо модифицировать действующие бюджетные правила.В основе новых бюджетных правил предлагается механизм поддержания оптимального соотношения между денежными потоками в фонды потребления, инвестирования и накопления. Для этого необходимо формирование Инвестиционного фонда развития национальной экономики, наполняемого не только за счет рентных доходов государства, но и средств Банка России (особенно в период низких цен на нефть).

Interplay Between Mixed and Pure Exciton States Controls Singlet Fission in Rubrene Single Crystals

Singlet fission (SF) is a multielectron process in which one singlet exciton S converts into a pair of triplet excitons T+T. SF is widely studied as it may help overcome the Shockley-Queisser efficiency limit for semiconductor photovoltaic cells. To elucidate and control the SF mechanism, great attention has been given to the identification of intermediate states in SF materials, which often appear elusive due to the complexity and fast timescales of the SF process. Here, we apply 10fs-1ms transient absorption techniques to high-purity rubrene single crystals to disentangle the intrinsic fission dynamics from the effects of defects and grain boundaries and to identify reliably the fission intermediates. We show that above-gap excitation directly generates a hybrid vibronically assisted mixture of singlet state and triplet-pair multiexciton [S:TT], which rapidly (<100fs) and coherently branches into pure singlet or triplet excitations. The relaxation of [S:TT] to S is followed by a relatively slow and temperature-activated (48 meV activation energy) incoherent fission process. The SF competing pathways and intermediates revealed here unify the observations and models presented in previous studies of SF in rubrene and propose alternative strategies for the development of SF-enhanced photovoltaic materials

The Energetics of Li Off-Centering in K1−x_{1-x}Lix_xTaO3_3; First Principles Calculations

K$_{1-x}$Li$_{x}$TaO$_3$ (KLT) solid solutions exhibit a variety of interesting physical phenomena related to large displacements of Li-ions from ideal perovskite A-site positions. First-principles calculations for KLT supercells were used to investigate these phenomena. Lattice dynamics calculations for KLT exhibit a Li off-centering instability. The energetics of Li-displacements for isolated Li-ions and for Li-Li pairs up to 4th neighbors were calculated. Interactions between nearest neighbor Li-ions, in a Li-Li pair, strongly favor ferroelectric alignment along the pair axis. Such Li-Li pairs can be considered "seeds" for polar nanoclusters in KLT. Electrostriction, local oxygen relaxation, coupling to the KT soft-mode, and interactions with neighboring Li-ions all enhance the polarization from Li off-centering. Calculated hopping barriers for isolated Li-ions and for nearest neighbor Li-Li pairs are in good agreement with Arrhenius fits to experimental dielectric data.Comment: 14 pages including 10 figures. To Physical Review B. Replaced after corrections due to referees' remark