JETP Letters最新文献

In this work, for the first time, a comprehensive experimental and theoretical study was carried out on the influence of copper substitution with magnetically active metals TM = Mn, Fe, Co, Ni on the thermoelectric and magnetic properties of tetrahedrites of the composition Cu₁₁TM₁Sb₄S₁₃. Maximum value of thermoelectric figure of merit (z{{T}_{{max }}} = 1.34) at 735 K was achieved for the unalloyed sample. It was established that doping (3d)-metals leads to a decrease (zT) due to a decrease in electrical conductivity and an increase in thermal conductivity. Experimental data show that with decreasing charge number (3d)-ion, an increase in the magnetic moment at the substitution position is observed. However, for the entire series of compositions, no significant increase in magneto-thermoEMF was detected. The calculations carried out within the framework of the density functional theory qualitatively reproduce the experimental data and confirm that the contribution of spin entropy, magnon drag and other spin-caloritron mechanisms to the thermoelectric properties in tetrahedrites with substitutions 3d-metals is insignificant.

A generalization of the Fäldt–Wilkin formalism, which relates the meson production cross sections with the emission of a deuteron to those with the emission of a nucleon pair in the final state, is proposed for higher excitation energies of the final pair of nucleons. To derive the relationship between the cross sections, a model of interaction with an additional non-nucleon channel is used, in which the relationship between the corresponding amplitudes is determined by the energy dependence of the non-nucleon component of the (NN)-system wavefunction. It is shown that the obtained cross section ratio is practically independent of the interaction model at excitation energies of the nucleon pair from 0 to 40–50 MeV. As an example, the ratios of total and differential cross sections of the reaction (pp to pn{{pi }^{ + }}) to the corresponding cross sections of (pp to d{{pi }^{ + }}) are considered. It is shown that the proposed generalized formalism for taking into account the final-state interaction of nucleons describes well the experimental data at energies of incident protons below 600 MeV.

The results of research on a new type of microscopy—ghost imaging microscopy, which has the advantages of ghost imaging—are presented. A consistent theory of ghost imaging microscopy with an incoherent light source has been developed. The optical scheme of the ghost imaging microscope includes two objective lenses in the object channel and one lens in the reference channel. The calculation of the mutual spatial correlation function of channel intensities containing information about the object under study is presented. It is shown that visualization using ghost imaging microscopy is possible when the lens condition in the object channel is not met, which distinguishes this type of microvisualization from optical one. A source of pseudo-thermal radiation was used in experimental studies. Ghost images of biological preparations of ascomycete fungi of Aspergillus genus and animal epidermal cells have been reconstructed. The resulting images demonstrate the transmission of the main structural elements of the objects under study.

Excitation of the nucleus ²²⁹Th to a low-lying isomeric state 3/2+ (8.356 eV) during the transition of an electron between bound states in a Th ion in the case of proximity of energies and coincidence of the multipolarities of the nuclear and electronic transitions can lead to multiple coherent transfer of excitation energy from the electron shell to the nucleus and back. Thus, the electron shell plays the role of a kind of resonator for the virtual photon emitted by the nucleus. At the same time, it “breathes,” periodically decreasing and increasing in size. Such energy oscillations between the doublet of nuclear levels and the electron shell are a consequence of the relatively large interaction energy of the electron and nuclear currents. Due to the coherent nature of the phenomenon, the process under consideration becomes the main, but at the same time reversible, channel for the “decay” of both the nuclear isomer and the excited ion.

The results of a study of the extraction of a proton beam circulating in the U-70 accelerator by a crystal using the phenomenon of volume particle capture in the channeling mode are presented. When aiming a primary beam of intensity at a crystal in the ring of the U-70 accelerator (3 times {{10}^{{11}}}) p/cycle at the SPASCHARM installation, the intensity was observed up to (6 times {{10}^{6}}) p/cycle. This method was implemented for the first time in global accelerator practice. Despite the lower intensity of the extracted beam compared to traditional extraction based on end-capture of particles, extraction using the volume capture phenomenon provides more stable parameters of the extracted.

The measurement results (A)-dependences of the relative yields of neutral mesons ({{pi }^{0}}), (omega (782)), ({{f}_{2}}(1270)) and (K_{S}^{0}) in relation to (eta )-meson produced in ({{pi }^{ + }}A)-interactions at a momentum of 7 GeV/c are presented. The measurements were performed on six nuclear targets (Be, C, Al, Cu, Sn, Pb) in the Hyperon-M experiment at the U-70 accelerator complex. Mesons were identified by their photon decays using the LGD2 wide-aperture electromagnetic calorimeter. The yield ratios of the mesons under study to the yield (eta )-mesons were measured in the beam fragmentation region (({{x}_{F}} > 0.6) in the center of mass system (pi N)-reactions). It is shown that the relative yields of non-strange mesons (({{pi }^{0}}), (omega (782)), ({{f}_{2}}(1270))) decrease with increasing the mass number of the target nucleus. At the same time, the yield ratio (K_{S}^{0}{text{/}}eta ) demonstrates a steady statistically significant increase with increasing (A). The obtained results are important for the study of hadron–nucleus interactions at intermediate energies, including testing and fine-tuning transport models such as GiBUU, PHSD, UrQMD, SMASH, regarding the influence of collective effects in the nucleus on the production of mesons with different quark compositions.

In the temperature range (T = 30{-} 300) K, the process of magnetization reversal of ultrathin Co layers, isolated and exchange-coupled through a Pd layer, was experimentally studied, and the nucleation fields ({{H}_{N}}) were determined. It was found that a crossover is observed in the ({{H}_{N}}(T)) dependences of exchange-coupled films. In the high temperature region, where the layers undergo magnetization reversal independently of each other, as in single-layer films, ({{H}_{N}} sim {{T}^{{ - 1}}}), in the low temperature region, where the layers undergo a correlated magnetization reversal, ({{H}_{N}} sim ln ({{T}^{{ - 1}}})). The performed numerical calculations showed interlayer exchange interaction is the key factor driving nucleation in the heterostructure, qualitatively explaining the observed dependence ({{H}_{N}}(T)).

A diffraction spectrograph for the soft X-ray range with a grazing angle of 1.5°, which is compatible with modern CCD and CMOS detectors, has been developed and tested. Spectral decomposition is performed by a high-frequency spherical varied line-space grating, which produces a flat field in the wavelength range of 10‒60 Å. The spectrograph has been tested recording line spectra of multiply charged ions excited in laser plasmas of Teflon, aluminum, and titanium.

It has been shown that the relativistic self-trapping regime of an intense ultrashort laser pulse propagating in a plasma of a near-critical density can be used to create a highly efficient source of laser-accelerated ions. Practically significant characteristics of protons accelerated mainly due to the directed Coulomb explosion of a charged cavity upon reaching the rear edge of the target during relativistic self-trapping have been obtained in the three-dimensional numerical simulation of proton acceleration. In comparison with the most efficient method of accelerating protons by laser irradiation of ultrathin films, the studied mechanism has demonstrated the possibility of achieving the same, or even slightly higher, record energy of accelerated particles, without requiring ultra-high radiation contrast.

A method has been developed to analyze noncollinear schemes of highly nondegenerate parametric down-conversion, taking into account the transverse limitation of the pump region such that low-frequency idler photons leave the nonlinear interaction region before signal photons, crossing the boundaries of the pump beam or the side of a nonlinear crystal. General expressions have been obtained for the second and fourth moments of the fields in schemes with losses of idler photons generated under spatial phase matching conditions at various angles to the pump propagation direction. It has been shown that the effects of leakage of idler photons through the side with increasing scattering angle lead to an overall decrease in the numbers of photons detected in the signal and idler channels. A counterintuitive result has been obtained, indicating that the considered loss mechanism can lead to a significant increase in the biphoton correlation function, determined not only by a decrease in the total number of generated photons, but also by the ratio of the projections of the idler and signal wave vectors on the pump direction.