The optical and structure properties of the PbS nanoclusters in the Langmuir-Blodgett matrix as well as their properties after the matrix removal in the ammonium atmospheres have been studied. ...According to the electron microscopy data, it has been established that there are PbS nanoclusters formed on the surface of the samples. It has been found that the matrix removal results in a significant enlargement of the PbS nanocrystals accompanied by the shift of the luminescence into the infra-red range. It has been shown that the PL intensity of PbS quantum dots (QDs) in the matrix decreases with the temperature decrease due to the carrier transfer into defect QDs whereas the the luminescence intensity of the PbS nanocrystals without a matrix grows at the temperature increase.
Single crystals of earlier unknown hydroxonium monoaquatrisulfatodiuranylate 6.86-hydrate (H
3
O)
2
(UO
2
)
2
(SO
4
)
3
(H
2
O) · 6.86H
2
O (
I
) have been synthesized via the evaporation of an ...aqueous UO
2
(NO
3
)
2
(H
2
O)
2
·
n
H
2
O (
n
= 2, 4) solution containing sulfuric and nitric acids in air at room temperature. The structure of complex I has been studied by X-ray diffraction. Crystals are monoclinic,
а
= 15.0903(12) Å,
b
= 9.9191(8) Å,
c
= 15.6099(13) Å, β = 112.560(1)°, space group
P
2
1
/
n
,
Z
= 4,
V
= 2157.7(3) Å
3
. The complex is formed due to electrostatic attraction forces between counterions and stabilized by hydrogen bonds. Its main structural element is the (UO
2
)
2
(SO
4
)
3
H
2
O
n
2-
framework. The structure contains two types of uranium atoms surrounded by oxygen atoms according to a pentagonal bipyramid motif. The coordination polyhedra of all the three crystallographically different S atoms are SO
4
2-
tetrahedra. The U(1) atom in the equatorial bipyramid plane is monodentately bonded to the oxygen atoms of five SO
4
2-
tetrahedra, while the U(2) atom is monodentately coordinated to four sulfate groups and one water molecule.
This work is a methodical study on hybrid reconstruction techniques for hybrid imaging/timing Cherenkov observations. This type of hybrid array is to be realized at the gamma-observatory TAIGA ...intended for very high energy gamma-ray astronomy (> 30 TeV). It aims at combining the cost-effective timing-array technique with imaging telescopes. Hybrid operation of both of these techniques can lead to a relatively cheap way of development of a large area array. The joint approach of gamma event selection was investigated on both types of simulated data: the image parameters from the telescopes, and the shower parameters reconstructed from the timing array. The optimal set of imaging parameters and shower parameters to be combined is revealed. The cosmic ray background suppression factor depending on distance and energy is calculated. The optimal selection technique leads to cosmic ray background suppression of about 2 orders of magnitude on distances up to 450 m for energies greater than 50 TeV.
The study of the cosmic ray mass composition in the energy range 1016 - 1018 eV is one of the main aims of Tunka-133. This EAS Cherenkov array started data acquisition in the Tunka Valley (50 km from ...Lake Baikal) in autumn 2009. Tunka-133 provides a measurement of the EAS maximum depth (Xmax) with an accuracy of about 30 g/cm2. Further mass composition analyses at the highest energies (1017 - 1018 eV) will be based on the comparison of primary energy measured by the radio method and the densities of charged particles measured by shielded and unshielded detectors. The high duty cycle of the common operation of the new scintillation array (Tunka-Grande) and the radio extension of the experiment (Tunka-REX) will provide a high statistics of events.
In this paper we propose a ‘knee-like’ approximation of the lateral distribution of the Cherenkov light from extensive air showers in the energy range 30–3000 TeV and study a possibility of its ...practical application in high energy ground-based gamma-ray astronomy experiments (in particular, in TAIGA-HiSCORE). The approximation has a very good accuracy for individual showers and can be easily simplified for practical application in the HiSCORE wide angle timing array in the condition of a limited number of triggered stations.
Some results of studies of cosmic rays obtained during the NUCLEON space experiment in 2015–2017 are presented. This experiment was intended for direct measurements of the energy spectra and chemical ...composition of cosmic rays (
Z
= 1−30) in the energy range 2–500 TeV. Results presented include energy spectra for various abundant nuclei measured using the new Kinematic Lightweight Energy Meter (KLEM). The primary energies are established using the spatial densities of secondary particles produced in inelastic interactions with a carbon target.
The main aims of the NUCLEON satellite experiment are direct measurement of the energy spectra of cosmic ray protons and nuclei in the 2–500 TeV range of energies by two different methods (an ...ionization calorimeter and the new Kinematic Lightweight Energy Meter (KLEM) technique). The energy spectra of protons and helium nuclei are presented, and their characteristics are discussed.
For dipalmitoylphosphatidylcholine (DPPC) lipid/water bilayers, a detailed temperature dependence of the Raman scattering spectra at the spectral range of the CH2-stretching modes was investigated. ...Below 150 K the ratio of intensities of the 2880 cm−1 antisymmetric vibration line and the 2850 cm−1 symmetric one was found to be nearly temperature-independent. Between 150 and 230 K it decreases slightly as temperature increases; and above 230 K it decreases remarkably. This decrease is accompanied with broadening of the antisymmetric line, from 4.2 cm−1 at 100 K to 5.7 cm−1 at 296 K. According to literature, the decrease of the antisymmetric line may be interpreted in two ways: (i) the appearance of a static conformational disorder (or of a disorder fluctuating at the time scale larger than picoseconds) and (ii) relaxation at the ps time scale, which is induced by coupling with temperature-activated librational-torsional motion of the lipid chain. Both these interpretations imply that obtained data evidence the appearance of molecular flexibility of lipids around ∼200 K. The observed effect is to be compared with low-temperature dynamical transition found in disordered media with neutron scattering, Mössbauer absorption, molecular dynamics simulations and other techniques. This transition implies that with temperature increase harmonic atomic motions are transformed to large-amplitude anharmonic (or stochastic) ones. The characteristic times of these motions lay at the ps time scale. The closeness of the temperature of the transition and of the time scale of motions with those found in this work by Raman scattering for lipid bilayers supports the dynamic nature of the 2880 cm−1 antisymmetric vibration line decrease (i.e., that it is induced by coupling with libration-torsion). To prove that the observed onset of flexibility is a property of a disordered state, Langmuir−Blodgett films of behenic acid were studied. These films contain, like lipids, long CH2-tails, but, in opposite to bilayers, they have a well-ordered crystalline-like structure. The relative intensity of the antisymmetric/symmetric CH2-stretching lines was found in these films to be temperature-independent in the whole temperature range studied, between 60 and 296 K.
The Tunka-Grande array is part of an experimental complex located in the Tunka Valley (Republic of Buryatia, Russia) about 50 km from Lake Baikal. This complex also contains the Tunka-133 and ...Tunka-Rex arrays. The aim of this complex is to study the primary cosmic ray energy spectrum and mass composition in the energy range of 10
16
–10
18
eV, and to search for diffuse gamma rays in the energy range of 5 × 10
16
–5 × 10
17
eV. The design of the Tunka-Grande array and the procedure for reconstructing the parameters of extensive air showers (EASes) are described, and preliminary results are presented from the search for diffuse gamma rays with energies of more than 5 × 10
16
eV.
•Model +7 with a large dispersion of CR maximum energy accelerated in SNRs of different types is studied.•List of potential nearby and young CR sources is compiled and their role in CR fluxes is ...investigated.•Experimental procedure of ‘two-dimensional’ anisotropy measurements is reproduced.•A fine structures of CR spectrum and general features of dipole anisotropy are explained.•Indication of the SNRs thatcan be responsible for the knee origin.
The role of nearby galactic sources, the supernova remnants, in formation of observed energy spectrum and large-scale anisotropy of high-energy cosmic rays is studied. The list of these sources is made up based on radio, X-ray and gamma-ray catalogues. The distant sources are treated statistically as ensemble of sources with random positions and ages. The source spectra are defined based on the modern theory of cosmic ray acceleration in supernova remnants while the propagation of cosmic rays in the interstellar medium is described in the frameworks of galactic diffusion model. Calculations of dipole component of anisotropy are made to reproduce the experimental procedure of “two-dimensional” anisotropy measurements. The energy dependence of particle escape time in the process of acceleration in supernova remnants and the arm structure of sources defining the significant features of anisotropy are also taken into account. The essential new trait of the model is a decreasing number of core collapse SNRs being able to accelerate cosmic rays up to the given energy, that leads to steeper total cosmic ray source spectrum in comparison with the individual source spectrum. We explained simultaneously the new cosmic ray data on the fine structure of all particle spectrum around the knee and the amplitude and direction of the dipole component of anisotropy in the wide energy range 1TeV–1EeV. Suggested assumptions do not look exotic, and they confirm the modern understanding of cosmic ray origin.
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