This work is devoted to the experimental study and symmetry analysis of the Raman-active vibration modes in MnBi
2
Te
4
·
n
(Bi
2
Te
3
) van der Waals topological insulators, where
n
is the number of ...Te–Bi–Te–Bi–Te quintuple layers between two neighboring Te–Bi–Te–Mn–Te–Bi–Te septuple layers. Confocal Raman spectroscopy is applied to study Raman spectra of crystal structures with
, and ∞. The experimental frequencies of vibration modes of the same symmetry in the structures with different
n
are compared. The lattice dynamics of free-standing one, three, and four quintuple layers, as well as of bulk Bi
2
Те
3
and MnBi
2
Te
4
, is considered theoretically. Vibrational modes of the last two systems have the same symmetry, but different displacement fields. These fields in the case of a Raman-active mode do not contain displacements of manganese atoms for any finite
. It is shown that two vibrational modes in the low-frequency region of the spectrum (35–70 cm
–1
) of structures with
, and 6 practically correspond to the lattice dynamics of
n
free quintuple Bi
2
Те
3
layers. For this reason, the remaining two vibration modes, which are observed in the high-frequency region of the spectrum (100–140 cm
–1
) and are experimentally indistinguishable in the sense of belonging to quintuple or septuple layer or to both layers simultaneously, should also be assigned to vibrations in quintuple layers under immobile atoms of septuple layers.
A comprehensive comparative study of the structure, phase composition, and mechanical properties of heat-resistant nickel-based Ni–Cr–(X) alloys produced by the methods of traditional metallurgy and ...self-propagating high-temperature synthesis (SHS metallurgy) is carried out. With the purpose of formation of the submicrocrystalline structure, a longitudinal rolling and post-deformation annealing of the cast alloy is performed. The microstructure of the heat-resistant alloys is investigated by the SEM and TEM methods. It is shown that the cast alloy has a recrystallized structure with the mean grain size of ~1 μm and the particles of chromium carbides have a size of ~1–3 μm. After rolling and subsequent annealing (750°C/1 h), the average grain size is reduced to 0.43 μm and the formation of dispersed particles of carbides 100 nm in size is observed. The structure of the alloy obtained by SHS metallurgy is dendritic, and particles of W and Cr are absent. When 0.1 wt % carbon powder is added to the initial powder mixture for SHS synthesis, formation of the network of W and Cr particles is observed along the boundaries of dendrite colonies. It is found that the SHS Ni-based heat-resistant alloy similar in composition to commercial cast alloy is characterized by improved mechanical properties and increased heat resistance compared to the cast alloy in both the coarse-grained and the submicrocrystalline state. Adding the carbon powder to the powder mixture for SHS leads to a further increase in the resistance to high-temperature deformation owing to formation of the carbide phase impeding the movement of dislocations and grain boundary creeping processes.
Additives are actively used to improve the quality of liquid fuels. Effective mixing of the additive with fuel with high reliability and efficiency of the boiler is ensured by the choice of ...technological dosing scheme liquid additive which will allow to organize automatically preparation of the additive, adding it to the oil and stirring.
The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs
1 –
x
Sb
x
structures (
x
= 0.43 and 0.38) in a wide temperature range of 5–300 K and magnetic fields up to 8 T are ...studied. From the thermal-activation dependence of the electrical conductivity, the band gap of the composition InAs
0.57
Sb
0.43
is estimated as 120 meV. The electron concentration in InAs
1 –
x
Sb
x
(6 × 10
16
cm
–3
for InAs
0.62
Sb
0.38
and 5 × 10
16
cm
–3
for InAs
0.57
Sb
0.43
) determined from the Hall effect agrees well with the electron concentration calculated from the Shubnikov–de-Haas oscillations. We also carry out the spectral ellipsometric studies of unrelaxed heteroepitaxial structures of InAs
1 –
x
Sb
x
(
x
= 0.43 and 0.38) in the photon energy range of 1–6 eV. The spectral dependences of the imaginary and real parts of the dielectric constant are determined. The dispersion dependences of the refractive index and the extinction coefficient are calculated and presented.
Long-term observational data on a small, shallow Lake Vendyurskoe (Karelia) were used to analyze the space and time dissolved-oxygen dynamics in winter. Biochemical consumption was found to play a ...leading role in the reduction of dissolved-oxygen concentration in lake water in winter. The total decrease in the amount of dissolved oxygen since the beginning of under-ice period until mid-April was shown to amount to one third of the initial value. The year-to-year variations in winter oxygen consumption are ~10%, suggesting the process to be stable in the years of observations. The rate of oxygen consumption and variations in dissolved oxygen content of lake water in winter were evaluated. The analysis and literary data allow us to conclude that the hydrophysical processes taking place in shallow lakes in winter have a considerable effect on their oxygen regime.
The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs{sub 1 –x}Sb{sub x} structures (x = 0.43 and 0.38) in a wide temperature range of 5–300 K and magnetic fields up to 8 T ...are studied. From the thermal-activation dependence of the electrical conductivity, the band gap of the composition InAs{sub 0.57}Sb{sub 0.43} is estimated as 120 meV. The electron concentration in InAs{sub 1 –x}Sb{sub x} (6 × 10{sup 16} cm{sup –3} for InAs{sub 0.62}Sb{sub 0.38} and 5 × 10{sup 16} cm{sup –3} for InAs{sub 0.57}Sb{sub 0.43}) determined from the Hall effect agrees well with the electron concentration calculated from the Shubnikov–de-Haas oscillations. We also carry out the spectral ellipsometric studies of unrelaxed heteroepitaxial structures of InAs{sub 1 –x}Sb{sub x} (x = 0.43 and 0.38) in the photon energy range of 1–6 eV. The spectral dependences of the imaginary and real parts of the dielectric constant are determined. The dispersion dependences of the refractive index and the extinction coefficient are calculated and presented.
High-throughput 16S rRNA sequencing was performed to compare the microbiomes inhabiting two contrasting soil types-sod-podzolic soil and chernozem-and the corresponding culturome communities of ...potentially cellulolytic bacteria cultured on standard Hutchinson media. For each soil type, soil-specific microorganisms have been identified: for sod-podzolic soil-Acidothermus, Devosia, Phenylobacterium and Tumebacillus, and for chernozem soil-Sphingomonas, Bacillus and Blastococcus. The dynamics of differences between soil types for bulk soil samples and culturomes varied depending on the taxonomic level of the corresponding phylotypes. At high taxonomic levels, the number of common taxa between soil types increased more slowly for bulk soil than for culturome. Differences between soil-specific phylotypes were detected in bulk soil at a low taxonomic level (genus, species). A total of 13 phylotypes were represented both in soil and in culturome. No relationship was shown between the abundance of these phylotypes in soil and culturome.
Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium, which is referred to as a ...'secondary source'. Positrons might also originate in objects such as pulsars and microquasars or through dark matter annihilation, which would be 'primary sources'. Previous statistically limited measurements of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref. 8). Here we report a measurement of the positron fraction in the energy range 1.5-100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.
The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs1 –xSbx structures (x = 0.43 and 0.38) in a wide temperature range of 5–300 K and magnetic fields up to 8 T are studied. ...From the thermal-activation dependence of the electrical conductivity, the band gap of the composition InAs0.57Sb0.43 is estimated as 120 meV. The electron concentration in InAs1 –xSbx (6 × 1016 cm–3 for InAs0.62Sb0.38 and 5 × 1016 cm–3 for InAs0.57Sb0.43) determined from the Hall effect agrees well with the electron concentration calculated from the Shubnikov–de-Haas oscillations. We also carry out the spectral ellipsometric studies of unrelaxed heteroepitaxial structures of InAs1 –xSbx (x = 0.43 and 0.38) in the photon energy range of 1–6 eV. The spectral dependences of the imaginary and real parts of the dielectric constant are determined. The dispersion dependences of the refractive index and the extinction coefficient are calculated and presented.
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