Search

The authors consider a model of charged semi-hard-core bosons on a square lattice with possible occupation number at each site. Temperature phase diagrams of the model are obtained using quantum Monte Carlo calculations, and the effect of local charge correlations is studied. It is shown that local charge correlations increase the role of quantum fluctuations in the formation of phase states. [ABSTRACT FROM AUTHOR]

Estimates of doses inside the spacecraft were carried out for flights to the Moon using low-thrust engines. The characteristics of the trajectory, which is significantly different from the Hohmann trajectory, are taken into account. Such a trajectory causes a long stay inside the radiation belts, which can cause disruptions in the operation of onboard equipment. It turned out that, during long-term transportation of food products, they may be damaged under the influence of radiation. This is extremely important in the case of the creation of habitable stations on the Moon surface or near-Moon orbit. The presented results can be used in the preparation of future space experiments. [ABSTRACT FROM AUTHOR]

The High Energy Cosmic Ray Observatory (HERO) is an experimental design for the direct study of cosmic rays based on the use of an ultraheavy ionization calorimeter. The effective geometric factor of the facility will be at least 12 m sr for cosmic-ray protons and at least 16–20 m sr for nuclei and electrons. During 5–7 years of exposure, this mission will allow measuring the energy spectra of all common and rare cosmic-ray nuclei in the energy range of eV/particle with element-by-element resolution of the charge of nuclei and with sufficiently high energy resolution. It is planned to study not only the cosmic ray nuclei with charges , but also the superheavy nuclei beyond the iron peak, as well as high-energy electrons, positrons, and gamma rays. The main objectives, design appearance, and characteristics of the space mission are discussed. [ABSTRACT FROM AUTHOR]

Results of great astrophysical importance are obtained in processing data collected in the NUCLEON space experiment. The GALPROP package is used to solve the inverse problem of cosmic ray (CR) propagation from a source (a nearby supernova) to the observer. A component-by-component spectrum of the source is plotted, and a systematic change in its spectral index is revealed. This can be interpreted as incomplete ionization of cosmic rays at the moment they are accelerated at the front of the supernova's shock wave. Fluxes of nitrogen nuclei and the total spectrum of rare nuclei with odd charges of 9 to 19 (F, Na, Al, P, Cl, K) are investigated in analyzing the spectra in terms of magnetic rigidity. The ratios of the flows of odd and even nuclei are plotted. The spectrum of rare odd nuclei is found to be harder than that of abundant even nuclei (Z = 10–20) in the 300–10 000 GV range of magnetic rigidities. [ABSTRACT FROM AUTHOR]

A wide-angle Cerenkov array TAIGA-HiSCORE (FOV 0.6 sr), was originally created as a part of TAIGA installation for high-energy gamma-ray astronomy and cosmic ray physics. Array now consist on nearly 100 optical stations on the area of 1 km . Due to high accuracy and stability ( 1 ns) of time synchronization of the optical stations the accuracy of EAS arrival direction reconstruction is reached 0.1 . It was proven that the array can also be used to search for nanosecond events of the optical range. The report discusses the method of searching for optical transients using the HiSCORE array and demonstrates its performance on a real example of detecting signals from an artificial Earth satellite. The search for this short flares in the HiSCORE data of the winter season 2018–2019 is carried out. One candidate for double repeater has been detected, but the estimated probability of random simulation of such a transient by background EAS events is not less than 10 , which does not allow us to say that the detected candidate corresponds to a real astrophysical transient. An upper bound on the frequency of optical spikes with flux density of more than and a duration of more than 5 ns is established as events/sr/h. [ABSTRACT FROM AUTHOR]

The inhomogeneity of the spectrum of cosmic rays in the region of 10 TV (small knee), observed in the data of direct experiments of cosmic rays, is considered in terms of isotropic diffusion from a single close source. It is shown that such a description is possible. The area of possible space-time localization of the source and its energetics are determined. [ABSTRACT FROM AUTHOR]

A report is given on the main results from the NUCLEON space experiment. The composition and spectrum of cosmic rays is measured in the range of 2 to 500 TeV. Spectra of particular nuclei, including nickel and secondary nuclei, are obtained. The dependence of the ratio between the fluxes of protons and helium nuclei on magnetic rigidity is investigated. A universal knee is found in the magnetic rigidity spectra of different nuclei. [ABSTRACT FROM AUTHOR]

In this paper, the authors present the composition of a prototype of the Detector Part of the Station (DPS) that uses a novel method for studying the integrated circuit durability to single-event effects (SEEs) during operation in outer space. The prototype operability is verified using Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

The aim of the NUCLEON space experiment was to measure spectra of high-energy cosmic rays. Direct measurements of energy spectra of protons and nuclei of cosmic rays which allow separating particles in charge are required to solve important astrophysical problems. The satellite was launched on December 26, 2014, and operated for three years. Measured spectra of protons and alpha particles in the energy range of 2–500 TeV per particle have been presented. The results have been analyzed and compared to other experimental data for lower energies. The ratio of fluxes of protons and alpha particles is nearly constant in a wide range of magnetic rigidities (3–100 TV). Thus, the behavior of the ratio of the spectra is significantly different from a similar dependence in the region of lower magnetic rigidities measured in other experiments. One of the possible explanation of this effect can be given within a model with one close source. [ABSTRACT FROM AUTHOR]

The problem of competing orderings in the high-temperature cuprate materials is widely discussed for the last years. We present the mean-field approximation results for the spin-pseudospin model accounting for the on-site and inter-site correlations, the antiferromagnetic exchange coupling, the one- and two-particle transport. The explicit form of the equations for the critical temperatures of the most significant order parameters of the model are given. [ABSTRACT FROM AUTHOR]

We make use of the S = 1 pseudospin formalism to describe the charge degree of freedom in a model high- T c cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu 1 + , 2 + , 3 + . Starting with a parent cuprate as an analog of the quantum paramagnet ground state and using the Schwinger boson technique, we found the pseudospin spectrum and conditions for the pseudomagnon condensation with phase transition to a superconducting state. [ABSTRACT FROM AUTHOR]

In this work, we address a topical problem of a competition of charge and spin ordering for high-T cuprates. We have studied a simplified static 2D spin-pseudospin model on a square lattice, which takes into account both conventional antiferromagnetic spin exchange coupling and the on-site and intersite charge correlations in the CuO2 planes with the on-site Hilbert space reduced to only three effective valent states. We compared an analytical results for the ground state and for the temperature phase diagrams obtained in a mean field approximation and a large amount of the classical Monte Carlo calculations. Numerical results show that homogeneous ground state antiferromagnetic solutions found in a mean field approximation are unstable for the "strong" exchange limit with respect to phase separation with the charge and spin subsystems behaving like immiscible quantum liquids. We found an analytical expression for critical temperature of phase separation and performed the comparison with the Monte Carlo results. [ABSTRACT FROM AUTHOR]

In 2015–2016 regular observations within the SETI program were carried out at the RATAN-600 radio telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The aim of observations was to search for artificial signals from about 30 Sun-like stars and two metal-rich globular clusters. The main underlying idea of these studies was to perform multiple repeated observations (monitoring) of the same objects. The data were analyzed using three methods: we (1) searched for a strong single signal, (2) estimated the flux averaged over the entire observing time, and (3) analyzed the correlations between signals at different frequencies. Collecting the data over two observing years made it possible to perform a search for weak signals at the detection level of several mJy at 2.7 and 6.3 cm wavelengths. The power limits on the signals of extraterrestrial civilizations averaged over the entire data set lie in the 1016–1020 Winterval practically for all objects, whereas the upper luminosity limits for single observations (the beam crossing time was 7–19 s) are 1017–1021 W and the effective isotropic emitted power of the hypothetical transmitters of the said civilizations do not exceed 2 × 109–2 × 1013 W, which is close to the corresponding parameter for the biggest planetary radars. The resulting luminosity limits are indicative of the absence of radio emission from the observed Sun-like stars, which is stationary on average and exhibits flare-like behavior during some observing sessions. [ABSTRACT FROM AUTHOR]

Numerous experimental data point to cuprates as d-d charge transfer unstable systems whose description implies the inclusion of the three many-electron valence states CuO47−,6−,5− (nominally Cu1+,2+,3+) on an equal footing as a well-defined charge triplet. We introduce a minimal model to describe the charge degree of freedom in cuprates with the on-site Hilbert space reduced to only the three states and make use of the S = 1 pseudospin formalism. The formalism constitutes a powerful method to study complex phenomena in interacting quantum systems characterized by the coexistence and competition of various ordered states. Overall, such a framework provides a simple and systematic methodology to predict and discover new kinds of orders. In particular, the pseudospin formalism provides the most effective way to describe different topological structures, in particular, due to a possibility of a geometrical two-vector description of the on-site states. We introduce and analyze effective pseudospin Hamiltonian with on-site and inter-site charge correlations, two types of a correlated one-particle transfer and two-particle, or the composite boson transfer. The latter is of a principal importance for the HTSC perspectives. The 2D S = 1 pseudospin system is prone to a creation of different topological structures, which form topologically protected inhomogeneous distributions of the eight local S = 1 pseudospin order parameters. We present a short overview of localized topological structures, typical for S = 1 (pseudo)spin systems, focusing on unexpected antiphase domain walls in parent cuprates and so-called quadrupole skyrmion, which are believed to be candidates for a topological charge excitation in parent or underdoped cuprates. Puzzlingly, these unconventional structures can be characterized by an uniform distribution of the mean on-site charge, that makes these invisible for X-rays. Quasi-classical approximation and computer simulation are applied to analyze localized topological defects and evolution of the domain structures in "negative-U" model under charge order-superfluid phase transition. [ABSTRACT FROM AUTHOR]

We address a minimal model to describe the charge degree of freedom in the CuO2 planes with the on-site Hilbert space reduced to only a charge triplet of the three effective valence centers, nominally Cu1+;2+;3+, and made use of the S = 1 pseudospin formalism. The 2D S = 1 pseudospin system is prone to a creation of different topological structures which form topologically protected inhomogeneous distributions of the eight local S = 1 pseudospin order parameters including charge density and superfluid order parameters. We focus on the so-called quadrupole skyrmion which is believed to be a candidate for a topological charge excitation in parent or underdoped cuprates. Puzzlingly, such an unconventional structure is characterized by a uniform distribution of the mean on-site charge that makes the quadrupole skyrmion texture to be invisible for X-rays. We suppose that the parent insulating antiferromagnetic cuprates may be unstable with regard to nucleation of topological defects in the unconventional form of the one- or multi-center skyrmion-like object with ring-shaped superfluid regions. [ABSTRACT FROM AUTHOR]

The NUCLEON space observatory was developed to measure the spectra of cosmic ray nuclei with individual charge resolution in the energy range of several TeV to 1 PeV per particle. The NUCLEON was launched into a heliosynchronous orbit as an additional load on the Resurs-2P production satellite on December 28, 2014, and it is still in operation (2019). This work is a brief review of the results from the NUCLEON observatory over three years of operation in orbit. The spectra of the main primary abundant nuclei and product nuclei of cosmic rays (CRs) are presented. Some new interesting features of the CR spectra found in the NUCLEON data are discussed. [ABSTRACT FROM AUTHOR]

It is shown that the structure of antiphase domain boundaries in the antiferromagnetic (AFM) phase of a highly anisotropic magnet with S = 1 on a two-dimensional square lattice depends greatly on single-ion anisotropy parameter D. Computer modeling on large square lattices illustrates the changes in the boundary structure from the quantum paramagnet (QP) to the XY phase, including the intermediate QP–XY phase at fairly small variations in positive D. [ABSTRACT FROM AUTHOR]

The aims and scientific tasks of the space High-Energy Ray Observatory experiment are determined. The design of the scientific equipment is described. It is characterized by an unprecedently high geometric factor (~20 m2 sr) and fairly high accuracy of measurement. The performance of the equipment allows precise study of cosmic rays in a wide range of energies, including the completely unstudied region of 1015–1016 eV. The current status of the space experiment is determined. [ABSTRACT FROM AUTHOR]

Titanium is a rare, secondary nucleus among Galactic cosmic rays. Using the Silicon matrix in the ATIC experiment, Titanium has been separated. The energy dependence of the Ti to Fe flux ratio in the energy region from 5 GeV per nucleon to about 500 GeV per nucleon is presented. [ABSTRACT FROM AUTHOR]

Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants. All components of the cosmic rays show an intensity that decreases as a power law with increasing energy (for example as E-2.7). Electrons in particular lose energy rapidly through synchrotron and inverse Compton processes, resulting in a relatively short lifetime (about 105 years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away). Here we report an excess of galactic cosmic-ray electrons at energies of ∼300–800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar or micro-quasar) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza–Klein particle with a mass of about 620 GeV). [ABSTRACT FROM AUTHOR]

We analyze the characteristics of the albedo, or the backscatter current, which constitutes a background for charge measurements in calorimetric experiments in high-energy cosmic rays. We compare the experimental data obtained in the flights of the ATIC spectrometer with the simulations performed using the GEANT 3.21 code. We discuss the influence of the backscatter on the charge resolution in the ATIC experiment.© 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Nominally electron doped antiferromagnetic tetragonal nonsuperconducting Nd2 – xCexCuO4 + δ(x=0.12) has been shown to manifest strong angular dependence of the in-plane magnetoresistance on the orientation of the external magnetic field within the ab plane in many aspects similar to that observed in hole doped YBa2Cu3O7 – δ and La2 – xSrxCuO4. Specific fourfold angular magnetoresistance anisotropy amounting to several percents was observed in oxygen annealed films at low temperatures and in an external magnetic field up to 5.5 T. The strong temperature dependence and fourfold symmetry observed in our sample points to a specific role of rare-earth (Nd) ions in magnetoresistance anisotropy. At low temperature T = 1.4 K, we observed the unusual transformation of magnetoresistance response with increasing the external magnetic field, which seems to be a manifestation of a combined effect of a crossover between first and second order spin-flop transitions and a field-dependent rare-earth contribution to quasiparticle magnetotransport. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The main mechanism in homogeneous broadening and relaxation of crystal-field excitations for R-ions in cuprates is believed to be provided by the fluctuations of crystalline electric field induced by a static and dynamic charge inhomogeneity generic to doped cuprates. Such an inhomogeneity is assumed to be the result of topological phase separation. We address the generalized granular model as one of the model scenarios for describing the static and dynamic charge inhomogeneity in cuprates. The charge subsystem is believed to be similar to that of a Wigner crystal with melting transition and phononlike positional excitation modes. We consider a simple model of charge inhomogeneity that allows us to elucidate the main universal features of the density of CF states and the respective inhomogeneous broadening. The formal description of R-ion relaxation mainly coincides with that of the recently suggested magnetoelastic mechanism by Lovesey and Staub. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A new approach to the study of phase separation in lanthanum manganites is proposed based on the combined investigation of their optical and magnetooptical characteristics providing information about the conducting and ferromagnetic regions, respectively. Effects of the [sup 18]O isotope substitution for [sup 16]O in the epitaxial films of (La[sub 0.5]Pr[sub 0.5])[sub 0.7]Ca[sub 0.3]MnO[sub 3] (grown on SrTiO[sub 3] or LaAlO[sub 3] substrates) upon the IR absorption spectra and the equatorial Kerr effect measured in the 1.5–3.8 eV range were studied. A giant drop in the temperature of maximum resistance of the film grown on SrTiO[sub 3] and disappearance of the metal-insulator transition in the film on LaAlO[sub 3] , observed upon the isotope exchange, are accompanied by a decrease in the contribution of free charge carriers to the absorption spectra, by the appearance of bands due to localized states, and by a decrease in magnitude of the equatorial Kerr effects. Measurements of the Kerr effect and the temperature variation of the optical transmission show evidence of the presence of ferromagnetic metal regions in the [sup 18]O-isotope-substituted (La[sub 0.5]Pr[sub 0.5])[sub 0.7]Ca[sub 0.3]MnO[sub 3]/LaAlO[sub 3] film at low temperatures, with a general semiconductor character of the resistivity behavior in the entire temperature range studied. Changes observed in the absorption spectra are explained based on a model of the pseudo-Jahn–Teller polar centers and phase separation. The optical and magnetooptical data show evidence of a percolation nature of the giant isotope effect in manganites. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Combined measurements of conversion electron spectra and the decay constant (76.5 eV, (1/2)[sup +] 7rarr; (7/2)[sup -]) of the E3-isomeric transition of the uranium-235 nucleus have been performed with collection of the isomer atoms on an indium surface. The conversion spectra are interpreted as corresponding to a mixture of two different oxides A and B of uranium, one of which (A) is similar to UO[sub 2], and the other (B) consists of a uranium-oxygen cluster based on the linear uranyl group O-U-O. From a set of mixed experimental spectra conversion spectra have been found corresponding to the chemical states A and B of the isomer atoms, and the variation of the absolute intensities of the conversion lines has been quantitatively investigated for them by varying the chemical composition of the isomer atoms and the ratio between the intensities of various conversion lines of the B spectrum. Experimental ratios between the intensities of the conversion lines are compared with the expected ratios in accordance with the distribution of the 6p electron density in the uranyl group. It is concluded that the experimental data agree with the calculation and that abrupt violations of proportionality of the partial probabilities of conversion of the electron density near the nucleus are absent. In accordance with the hypothesis of proportionality of the partial probabilities of conversion, an experimental estimate is given of the degree of localization of the deep-lying uranium 6p[sub ½] shell during formation of the chemical bond in the uranyl group: around 70% of the 6p[sub ½] electron density remains in the quasi-atomic uranium shell and around 30% is transferred to hybrid molecular orbitals. [ABSTRACT FROM AUTHOR]

We examine the isotope effect in copper-oxygen high-T[sub c] superconductors using the model of polar Jahn-Teller centers, a variant of the local-boson model. The isotope-effect exponents for oxygen and copper depend on the structure of Jahn-Teller centers and its variation due to boson motion. A number of YBa2Cu[sub 3]O[sub 7-δ]-based compounds are used to illustrate the feasibility of quantitatively describing the experimentally observed values of α[sub Cu] and α[sub O] and their relationship to T[sub c]. [ABSTRACT FROM AUTHOR]

The NUKLON-2 experiment is aimed at measuring the isotope and charge composition of cosmic rays for medium, heavy, and superheavy ions (Z < 82) with energies between 300 MeV/nucleon and 1 GeV/nucleon. The design of the planned satellite-borne NUKLON-2 cosmic-ray detector is presented. Modeling of the detector's performance indicates the adopted isotope-separation techniques are effective. [ABSTRACT FROM AUTHOR]

Nominally electron doped antiferromagnetic tetragonal nonsuperconducting Nd2 – xCexCuO4 + δ(x=0.12) has been shown to manifest strong angular dependence of the in-plane magnetoresistance on the orientation of the external magnetic field within the ab plane in many aspects similar to that observed in hole doped YBa2Cu3O7 – δ and La2 – xSrxCuO4. Specific fourfold angular magnetoresistance anisotropy amounting to several percents was observed in oxygen annealed films at low temperatures and in an external magnetic field up to 5.5 T. The strong temperature dependence and fourfold symmetry observed in our sample points to a specific role of rare-earth (Nd) ions in magnetoresistance anisotropy. At low temperature T = 1.4 K, we observed the unusual transformation of magnetoresistance response with increasing the external magnetic field, which seems to be a manifestation of a combined effect of a crossover between first and second order spin-flop transitions and a field-dependent rare-earth contribution to quasiparticle magnetotransport. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]