Opacity of relativistically underdense plasmas for extremely intense laser pulses

It is generally believed that relativistically underdense plasma is transparent for intense laser radiation. However, particle-in-cell simulations reveal abnormal laser field absorption above the intensity threshold about~$3 \times 10^{24}~\mathrm{W}\,\mathrm{cm}^{-2}$ for the wavelength of $1~\mu \mathrm{m}$. Above the threshold, the further increase of the laser intensity doesn't lead to the increase of the propagation distance. The simulations take into account emission of hard photons and subsequent pair photoproduction in the laser field. These effects lead to onset of a self-sustained electromagnetic cascade and to formation of dense electron-positron ($e^+e^-$) plasma right inside the laser field. The plasma absorbs the field efficiently, that ensures the plasma opacity. The role of a weak longitudinal electron-ion electric field in the cascade growth is discussed.Comment: 8 pages, 3 figure

In situ dating and investigation of remarkably depleted –27.3‰ SMOW “Slushball” Earth zircons

Paleoproterozoic amphibolites and gneisses - that are remarkably depleted in ^(18)O are found in the Belomorian Belt in Karelia, Russia [1,2]. We mapped their extent to exceed 200x20km and affect metamorphosed mafic intrusions (est. ~2.4 Ga intrusion age) and host 2.6Ga gneisses found in this 1.9 Ga collisional belt. δ^(18)O values of –7 to –27.3‰ characterize minerals and rocks from several of these localities; some of these rocks are also remarkably depleted with respect to δD (-212 to –235‰ amphiboles). All have typical terrestrial Δ^(17)O values of 0‰. Based on previous paleogeographic reconstructions, we attribute the origin of these exotic O and H isotope compositions to the hydrothermal alteration associated with subglacial rifting during the Paleoproterozoic panglobal ice ages, but discuss additional possibilities: extremely low-δ^(18)O Paleo- proterozoic sea water, and excursion of Karelia to polar latitudes. Given that at high-T hydrothermal exchange equilibrium Δ^(18)O(rockwater) is close to zero, but water-rock interaction is rarely 100% efficient, the lowest measured δ^(18)O value in silicates likely gives the upper δ^(18)O bound for the altering meteoric fluid; we thus continues our quest to find the lowest δ^(18)O material such as a mineral assemblage or a tiny zircon fragment that would provide record of δ^(18)Owater

Analytical description of the time-over-threshold method based on the time properties of plastic scintillators equipped with silicon photomultipliers

A new high-granular compact time-of-flight neutron detector for the identification and energy measurement of neutrons produced in nucleus-nucleus interactions at the BM@N experiment, Dubna, Russia, at energies up to 4 AGeV is under development. The detector consists of approximately 2000 fast plastic scintillators, each with dimensions of 40$\times$40$\times$25 mm$^3$, equiped with SiPM (Silicon Photomultiplier) with an active area of 6$\times$6 mm$^2$. The signal readout from these scintillators will employ a single-threshold multichannel Time-to-Digital Converter (TDC) to measure their response time and amplitude using the time-over-threshold (ToT) method. This article focuses on the analytical description of the signals from the plastic scintillator detectors equipped with silicon photomultipliers. This description is crucial for establishing the ToT-amplitude relationship and implementing slewing correction techniques to improve the time resolution of the detector. The methodology presented in this paper demonstrates that a time resolution at the 70 ps level can be achieved for the fast plastic scintillator coupled with silicon photomultiplier with epitaxial quenching resistors

Measurement of Time Resolution of Scintillation Detectors with EQR-15 Silicon Photodetectors for the Time-of-Flight Neutron Detector of the BM@N Experiment

To study the dependence of the equation of state of high density nuclear matter on the term characterizing the isospin (proton-neutron) asymmetry of nuclear matter, it is necessary to measure azimuthal flow of neutrons as well as azimuthal flow of charged particles from a dense nuclear matter in the nuclear-nuclear collisions. For this purpose INR RAS is developing a new high-granular neutron detector which will be used in the BM@N experiment at the extracted beam of the Nuclotron accelerator at JINR (Dubna). This detector will identify neutrons and measure their energies in the heavy-ion collisions up to 4 GeV per nucleon. This article presents the results of measurements of the time resolution and light yields of samples of scintillation detectors with sizes 40$\times$40$\times$25 mm$^3$ that will be used in a neutron detector based on the currently available fast plastic scintillator manufactured by JINR using an EQR15 11-6060D-S photodetector for light readout. For comparison, the results of measurements for a detector of the same size with a fast scintillator EJ-230 and with the same type of photodetector are given. The measurements were made on cosmic muons as well as on the electron synchrotron "Pakhra" of the Lebedev Physical Institute of the Russian Academy of Sciences located in Troitsk, Moscow

Methodology for building extraction templates for Russian language in knowledge-based IE systems

In this paper we describe methodology for building information extraction (IE) rules. Rules are usually developed by experts and are widely used in knowledge-based IE systems. They consist of two parts: the left-hand side (LHS) of a rule is a template that matches a certain syntactico-semantic structure (SSS) and the right-hand side is an action that is executed when LHS template is matched against a particular text fragment. In the paper we describe the process of building a more complex LHS part (further in the paper we will refer to LHS as template). This methodology was used for developing the information extraction system that extracts business events from news articles written in Russian language. © Copyright 2012 Hewlett-Packard Development Company, L.P

Dictionary and pattern-based recognition of organization names in Russian news texts

This paper describes a part of the event extraction system which has been developed in collaboration with HP Labs Russia. The domain of input texts is business news feeds. One of the most important event participant types is 'Organization'. This paper is focused on the problem of organization names recognition in Russian news texts. Two approaches have been implemented. The first is dictionary-based. We propose an algorithm to make a dictionary from a set of legal body full names gathered from a government registry. The main problems with the dictionary matching are incorrect stemming and significant fraction of ambiguous names among dictionary entries. The second recognition approach is based on usage of local context clues and internal name words. These words constitute patterns which are intrinsic to organization names. These patterns enable recognition of non-dictionary names. We propose an algorithm to derive such patterns from the original dictionary. © 2013 Hewlett-Packard Development Company, L.P

Проблемы семантической интеграции библиотечных данных

The Russian State Library and the National Library of Russia launched a joint project aimed at publishing the library data of the libraries that are the members of the National Digital Library, in accordance with the principles of Linked Open Data. This project will provide access to bibliographic information stored in several of the largest libraries of Russia, in the form suitable for automatic processing. The data set consists of tens of millions of records. A number of urgent problems have to be solved during the process of semantic integration, such as the development of the domain ontology, the conversion of library data from various MARC-formats to RDF, publication of data and provision of SPARQL access points to the data. Public access to one of the world's largest array of bibliographic information with the possibility to detect semantically related data will contribute to the development of culture as a whole and also of specific areas of publishing industry.В статье рассказывается о совместном проекте Российской государственной библиотеки и Российской национальной библиотеки. Его цель - публикация данных участников Национальной электронной библиотеки в соответствии с принципами Linked Open Data. Реализация проекта позволит получить доступ к библиографической информации, хранящейся в ряде крупнейших библиотек России, в виде, пригодном для машинной обработки. Перечислены принципиальные задачи, которые предстоит решить в процессе семантической интеграции библиотечных данных

Development of High Granular Neutron Time-of-Flight Detector for the BM@N experiment

The HGND (High Granular Neutron Detector) is developed for the BM@N (Baryonic Matter at Nuclotron) experiment on the extracted beam of the Nuclotron at JINR, Dubna. The HGND will be used to measure the azimuthal flow of neutrons produced with energies ranging from 300 to 4000 MeV in heavy-ion collisions at beam energies of 2--4 AGeV. The azimuthal flow of charged particles will be measured using the BM@N magnet spectrometer. The data on the azimuthal flow of neutrons will shed light on the study of the high-density Equation of State (EoS) of isospin-symmetric nuclear matter, which is crucial for studying astrophysical phenomena such as neutron stars and their mergers. The HGND has a highly granular structure with approximately 2000 plastic scintillation detectors (cells), each measuring 4$\times$4$\times$2.5 cm$^3$. These detectors are arranged in 16 layers, with 121 detectors in each layer, and are subdivided by copper absorber plates with a thickness of 3 cm. The light from each cell is detected with SiPM (Silicon Photomultiplier) with an active area of 6$\times$6 mm$^2$. Developed multi-channel TDC board based on the Kintex FPGA chip with a bin width of 100 ps will be used to perform precise timestamp and amplitude measurement using Time-over-Threshold (ToT) method. Good spatial resolution due to the high granularity together with a cell's time resolution of 100-150 ps ensures neutron reconstruction with good energy resolution. The design of the detector as well as the results from test measurements and simulations have been presented