In the study, the characteristics of the phase transition from a face-centered cubic crystal to a homogeneous phase in helium were calculated based on the correlation cell–cluster extension. A comparison of theoretical data with experimental data was conducted, and good agreement was obtained. The use of data on phase transitions in helium for estimating the thermodynamic characteristics of the phase transition in a quantum system of hard spheres is discussed.
In this paper, the magnetic structure of the storage ring for an X-ray source based on the effect of Compton backscattering and designed for use in the electron beam energy range from 35 to 120 MeV is investigated. For this storage ring, the results of calculating the dynamics of the electron beam are presented, and the effects of radiation damping, quantum excitation, laser damping, and intrabeam scattering are considered. The dynamic aperture and energy acceptance of this ring are discussed. The results of calculating the magnitude of the spectral brightness of X-ray radiation and its change over time are provided.
The degree of DNA compaction in various regions of the cell nucleus determines whether the corresponding genes should be expressed and other crucial cellular processes, such as DNA replication and repair, should occur. Therefore, the development of approaches to the experimental assessment of DNA compactness in cell nuclei, as well as its indicator, dynamic disorder which determines the degree of thermal fluctuation in the position and mutual orientation of molecular fragments, is highly relevant. In this paper, using single-stranded guanine and cytosine oligonucleotides, as well as their double-stranded combination as an example, it is shown that dynamic disorder in DNA can be assessed based on low-frequency Raman scattering (RS) spectroscopy data. For the first time, Raman spectra of oligonucleotides have been measured over a wide frequency range, including the low-frequency (10–200 cm({}^{-1})) and high-frequency (200–2000 cm({}^{-1})) regions. It was found that the low-frequency Raman intensity is maximal in single-stranded oligocytosine and minimal in the double-stranded oligonucleotide, which is in full agreement with the magnitude of dynamic disorder estimated from molecular dynamics simulations. The obtained results indicate the promising application of low-frequency Raman spectroscopy for assessing dynamic disorder and DNA compactness. The use of such a technique is expected to contribute to the understanding of key cellular processes and the physical mechanisms that underlie them, which is necessary for the development of advanced methods in molecular biophysics and cell biology.
The features of methods for obtaining information on photonuclear reaction cross sections using beams of bremsstrahlung and quasimonoenergetic photons formed during the in-flight annihilation of relativistic positrons are discussed. These methods have provided the vast majority of data in the nuclear excitation energy up to ({sim}40) MeV. It is shown that significant disagreements between the results of such experiments, both in absolute value and shape, are due to certain shortcomings of both methods. These shortcomings can be to a certain extent eliminated by using beams of photons formed in the processes of backward Compton scattering.
The results of the study on the impact of continuous visible laser irradiation on the field emission properties of point cathodes which are diamond needle-like microsized crystallites with a nanometer tip radius, are presented. The measurements were conducted in a vacuum diode configuration with a flat metal anode using DC voltage source. An increase in the field emission current was observed when the diamond needle was illuminated by laser radiation. The magnitude of the current changes directly proportional to the power of the radiation. At a maximum power density value of about 400 W/cm({}^{2}), the relative increase in current under the action of laser irradiation was 13(%). The relative increase in current is determined by the parameters of the dark current–voltage characteristic and reaches its maximum value in the region corresponding to the minimal increase in dark current with voltage. It is shown that the most probable mechanism for the current increase is the change in the electrical resistance of the diamond microneedle as a result of the absorption of laser radiation with the involvement of electronic levels located in the bandgap of diamond, associated with impurities or structural defects in the near surface layer of the diamond microneedle.
In the Randall–Sundrum model stabilized with the help of the Goldberger–Wise scalar field, the lowest order vacuum quantum corrections to the energy-momentum tensor of the scalar and tensor fields are considered. It is shown that the corresponding vacuum energy density of the fields in the bulk leads to the Casimir effect. Using the dimensional regularization method and the Abel–Plana formula, the divergences have been isolated and the vacuum energy density has been renormalized. An analytical expression for the Casimir force is obtained and an estimate of its influence on the model parameters is made. It has been found that the quantum corrections lead only to a negligibly small decrease in the distance between the branes, i.e. the model possesses steadiness with respect to quantum corrections.
To create a compact beam scanning system along the conveyor, this paper considers the horizontal placement of the accelerator with a magnetic system for rotating the beam by 90({}^{circ}). Three-dimensional modelling of the magnetic system and electron dynamics within it was carried out. Dose distributions in the near-surface area of the irradiated object were also obtained, based on which the optimal laws of changing the current and voltage of the scanning magnet were determined, ensuring the required conditions for product irradiation.
Stability of gas flows generated by steady near-limit flames propagating in vertical tubes is studied numerically. Basic scenarios of the burnt gas flow evolution are identified in relation to the thermal gas expansion parameter and the normal flame speed. It is shown that the implementation of a specific scenario essentially depends on the stagnation zone width as well as on the distance travelled by the gas from the flame front to the tube end. In particular, it is found that for sufficiently short distances, the burnt gas flows are stable provided that the stagnation zone width is less than half the tube diameter. Otherwise, an unstable flow evolution can lead to the appearance of recirculation domains and acoustic perturbations.
In connection with the planned work program at the megascience facility ‘‘Intense Inverse Compton’’ (INOC) at the Scientific Center for Physics and Mathematics in Sarov, a brief overview of experimental and theoretical results in the energy range of pygmy and giant resonances is presented. Considered are: (1) the pygmy dipole resonance in ({}^{208})Pb, for which the experimental resolution limit has already been reached, and separate (1^{-}) levels have been identified; (2) the most important physical results of experiments with resolution 50–200 keV both for the gamma strength functions, which determine characteristics of nuclear reactions, and for the analysis of nonstatistical mechanisms of formation of the widths of giant resonances (‘‘doorway’’ states) within the framework of wavelet analysis. Some results in the energy excitation range 1–5 MeV are also discussed.
The results of numerical modelling of deep convection processes in Lake Baikal during the autumnal thermal bar are presented. Using the Boldakov River—the Maloye More Strait cross-section, characterized by great depths, as an example, an analysis of the space–time temperature distributions under various wind conditions was conducted. Simulations have shown the effectiveness of wind only in the upper 250-meter layer. However, the cabbeling instability generated by the thermal bar can lead to convective mixing down to depths of ({sim}600) m.
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