Bulletin of the Russian Academy of Sciences: Physics最新文献

An experimental study was performed to analyze the emission of runaway electrons in atmospheric gaps in the presence of an advanced pulse, preceding the subnanosecond leading edge of the main voltage pulse, during which the electric field at the cathode reaches a strength sufficient for the occurrence of runaway electrons. The pulses of the runaway electron current vary due to the appearance and dynamics of the cathode plasma layer from the boundary of which the electrons run away. Plasma is generated by ionization of the gas by field emission electrons as early as during the advance pulse. It is shown that the characteristics of the runaway electron flow depend on the amplitude and duration of this pulse, as well as on the presence of an interval between it and the leading edge of the main voltage pulse.

We presented a description of various configurations of a plasma-chemical reactor for the synthesis of lanthanum hexaboride. The experimental and analytical results of this study demonstrate the possibility of synthesizing lanthanum hexaboride with a cubic crystal lattice. The recommended configuration of an arc reactor for the maximum yield of the desired phase is shown. The characteristics of the energy parameters and X-ray phase analysis data for the obtained synthesis products are presented using two different configurations of the plasma-chemical reactor.

Synthetic glycolipids and similar amphiphils with peptide and other head groups have been designed for labeling/modification of living cells under mild physiological conditions. Under-standing the mechanism of their penetration through the cellular glycocalyx and subsequent insertion into the plasma membrane opens up the prospect of improving the recently found anti-tumor properties of such constructs. In this work, we applied small-angle X-ray scattering (SAXS) technique to characterize structure of nanoparticles formed by self-assembly of synthetic glycolipid A (type 2)-Ad-DE and to estimate its dependence on the glycolipid concentration. The studies were performed at a range of SAXS-applicable concentrations. The obtained results indicate that self-assembly process leads to formation of monodisperse nanoparticles with micelle-like architecture, which is maintained regardless of concentration, indicating absence of the nanoparticle’s positive interaction with their glycopart. We applied ab initio modeling that showed a good agreement with experimental data, and found that the ellipsoid monodisperse nanoparticles have a size of about 14 nm. Quasi-atomic modeling visualised that glycan ligands are well accessed for biological recognition. This knowledge will facilitate further study of the formation of the supramolecular form(s) of A(type 2)-Ad-DE and other glycolipids within the glycocalyx and its further fate in new therapeutic strategies.

We have used a planar magnetron discharge to form emission plasma in a forevacuum plasma electron source (FPES) generating pulsed low-energy (up to 10 keV) electron beam at gas pressure of 4–16 Pa (Ar, N₂). The operation features of the magnetron discharge and emission properties of its plasma in the FPES have been investigated. Initiation voltage and delay time of initiation of the magnetron discharge decrease with increasing accelerating voltage, gas pressure, and acceleration gap length, as well as when Ar is used instead of N₂. The observed decrease in the initiation voltage and delay time is due to influence of a “parasitic” high-voltage glow discharge appearing in an accelerating gap, when high voltage is applied. An increase in pressure leads to higher emission current (beam current), that is typical for FPESs based on other discharge types. This increase in emission current is caused by a “back-streaming” ion flow from beam-produced plasma. Operating voltage of the planar magnetron discharge is lower during electron beam generation at gas pressure more than 4 Pa, which is also due the influence of the “back-streaming” ion flow penetrating into discharge system of the planar magnetron. The use of the planar magnetron discharge in the FPES provides generation of the wide-aperture (with radius of up to about 40 mm) low-energy electron beam with rather high homogeneity, pulse duration up to 10 ms and current up to 15 A.

The products resulting from the oxidative modification of petroleum asphaltenes were studied by Raman spectroscopy. Oxidizing agents such as peroxyacetic acid, potassium dichromate, and ammonium persulfate were used. Raman spectroscopy data indicated that the diameter of the aromatic sheets in asphaltenes varies widely depending on the calculation method applied. During chemical modification, the number of aromatic sheets decreases by several folds compared to native asphaltenes. The average number of aromatic rings per asphaltene sheet was found to be 8–10.

A new method of nonresonant selective spectroscopy was proposed for studying the low-frequency dynamics of molecules in liquids. The method is based on the nonresonant two-pulse laser excitation of the ultrafast optical Kerr effect. The first pulse induces anisotropy of the medium exclusively due to the orientational response of molecules. Theoretical calculations showed that, under these conditions, one can send a second pulse, which excites other vibrational and rotational responses, but suppresses the induced orientational anisotropy. It was shown that this scenario corresponds to conventional single-pulse excitation of the ultrafast optical Kerr effect, which does not include the contribution from orientational anisotropy. This allows for accurate determination of the spectral characteristics of intermolecular dynamics.

The spectral and kinetic characteristics of conjugates of Ce_0.50Y_0.35Tb_0.15F₃ nanoparticles with chlorin e-6 (Photoran) were studied. Effective nonradiative energy transfer from nanoparticles to e-6 chloride molecules is shown. Cytotoxic properties of conjugates induced by exposure to X-ray radiation against human lung adenocarcinoma cells A549 have been characterized.

We presented the results of a numerical analysis of frequency entanglement in the context of generating multidimensional hybrid-entangled states of biphotons, proposed by the authors earlier. The results presented will be useful for researchers in the field of quantum optics to understand the internal structure of entanglement of hybrid two-photon states of light and the possibility of controlling these states.

An optical quantum memory protocol is implemented in schemes of silenced echo revival in a ¹⁶⁷Er³⁺:Y₂SiO₅ crystal at a telecommunication wavelength. The signal pulse recovery efficiency is 13% at a storage time of 60 μs for the optimum intensity of rephasing laser pulses. With a further increase in the laser pulse intensity, a superradiance pulse appears, causing a decrease in the signal pulse recovery efficiency. A way of improving the quantum memory efficiency by further increasing the pulse area of rephasing pulses is discussed.

The authors propose and test a quantum key distribution scheme with independent detection using sideband encoding and a Sagnac interferometer. The scheme provides automatic compensation for phase fluctuations in optical channels and demonstrates stable interference of weak coherent states over a 25-km link with a low error rate, confirming it can be used to build secure quantum networks.