Digital receivers for low-frequency radio telescopes UTR-2, URAN, GURT

This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. Since 1998, digital receivers performing on-the-fly dynamic spectrum calculations or waveform data recording without data loss have been used at the UTR-2 radio telescope, the URAN VLBI system, and the GURT new generation radio telescope. Here we detail these receivers developed for operation in the strong interference environment that prevails in the decameter wavelength range. Data collected with these receivers allowed us to discover numerous radio astronomical objects and phenomena at low frequencies, a summary of which is also presented.Comment: 24 pages, 15 figure

Results of lumbar interbody fusion in elderly patients with lumbar spinal stenosis associated with cauda equina syndrome

Background: Currently, there are no clear recommendations on the timing of surgical intervention for the slow development of cauda equina syndrome (CES) against the background of lumbar spinal stenosis (LSS) at the lumbar level in elderly patients. The information on the long-term effectiveness of decompressive and stabilizing interventions (DSI) in the lumbar spine in this pathology is also limited.Objective: To conduct a comparative analysis of the results of surgical treatment of elderly patients with LSS associated with CES after open and low-traumatic DSI.Material and methods: The retrospective study included 37 patients operated on between 2000 and 2020 for CES caused by LSS. Two groups were distinguished: in the first group (n = 17), an open DSI was performed with the median approach, in the second group (n = 20) a low-traumatic DSI was performed according to the author’s method. Technical features of interventions and specificity of the postoperative period, preoperative instrumental data, clinical parameters in dynamics, and complications were compared.Results: In a comparative analysis in the group of patients operated on with author’s low-traumatic DSI, smaller parameters were registered: the duration of the operation (p = 0.02), the blood loss (p = 0.003), the duration of inpatient treatment (p = 0.002), and the postoperative need for opioid analgesics (p < 0.05). In catamnesis, statistically significantly better clinical parameters of bladder sphincter control (p = 0.02) and motor function recovery (p = 0.01), Oswestry Disability Index (ODI) (p = 0.03) and the Short Form-36 (SF-36) (p = 0.01) were observed in patients of the group II, compared with the group I. A greater number of complications were noticed in the group of open DSI (p = 0.003), with a comparable frequency of reoperations in the follow-up period (p = 0.79).Conclusion: In elderly patients with CES-associated LSS, the advantages of the author’s low-traumatic DSI in comparison with open DSI were established of less blood loss and duration of hospitalization, low need for postoperative analgesia, the minimum number of complications, and the dynamics of neurological symptoms, better recovery of ODI and SF-36 in catamnesis

Spallative ablation of dielectrics by X-ray laser

Short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron-ion equilibrium and rises pressure in a heated layer. The case where pulse duration $\tau_L$ is shorter than acoustic relaxation time $t_s$ is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless to wavelength. While the physics of electron-ion relaxation on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse

Влияние молекулярной массы на процесс электроформования волокнистых материалов, полученных из растворов полиакрилонитрила

In the article influence of the molecular weight of polyacrylonitrile on electrospinning process and also on the diameter and mechanical properties of the obtained fibers and fiber materials are considered. Polymers with molecular weight from 280 000 to 700 000 were investigated. Fibers with a diameter from 200 to 1100 nm were obtained.В статье рассматривается влияние молекулярной массы полиакрилонитрила на диаметр и механические свойства полученных волокон и волокнистых материалов. Исследованы полимеры с молекулярной массой от 280 000 до 700 000. Получены волокна с диаметром от 200-1100 нм

Исследование процесса растяжения жидкой полимерной струи в электрическом поле из растворов полиакрилонитрила

The article considers stretching of liquid polyacrylonitrile jet in electrostatic field. Polymers with molecular weight from 130 000 to 700 000 were investigated. Regularities of stretching of the jet based on polyacrylonitrile solutions were determined.В статье рассматривается процесс растяжения жидкой полимерной струи растворов полиакрилонитрила (ПАН) находящейся в электрическом поле. Исследованы полимеры с молекулярной массой от 130 000 до 700 000. Установлены основные закономерности процесса растяжения струи на основе растворов ПАН

Grain refinement of magnesium alloys: a review of recent research, theoretical developments and their application

This paper builds on the ‘‘Grain Refinement of Mg Alloys’’ published in 2005 and reviews the grain refinement research onMg alloys that has been undertaken since then with an emphasis on the theoretical and analytical methods that have been developed. Consideration of recent research results and current theoretical knowledge has highlighted two important factors that affect an alloy’s as-cast grain size. The first factor applies to commercial Mg-Al alloys where it is concluded that impurity and minor elements such as Fe and Mn have a substantially negative impact on grain size because, in combination with Al, intermetallic phases can be formed that tend to poison the more potent native or deliberately added nucleant particles present in the melt. This factor appears to explain the contradictory experimental outcomes reported in the literature and suggests that the search for a more potent and reliable grain refining technology may need to take a different approach. The second factor applies to all alloys and is related to the role of constitutional supercooling which, on the one hand, promotes grain nucleation and, on the other hand, forms a nucleation-free zone preventing further nucleation within this zone, consequently limiting the grain refinement achievable, particularly in low solute-containing alloys. Strategies to reduce the negative impact of these two factors are discussed. Further, the Interdependence model has been shown to apply to a broad range of casting methods from slow cooling gravity die casting to fast cooling high pressure die casting and dynamic methods such as ultrasonic treatment