East European Journal of Physics

18-33

Authors: Oksana L. Andreeva, Leonid A. Bulavin, Viktor I. Tkachenko

The stability of a rotating and heated from below horizontal cylindrical layer of a viscous, incompressible liquid with free boundaries was theoretically investigated. Neglecting the centrifugal forces, the equations of motion, thermal conductivity and incompressibility of the liquid were written, from which the well-known dispersion equation was derived in the linear approximation. The stability of a rotating cylindrical volume of a liquid with no heating from below was considered, provided that the temperature difference between the horizontal boundaries of the liquid was fixed and equal to zero. It was demonstrated, that with no heating from below the temperature difference between the horizontal boundaries of the rotating liquid was not fixed and not maintained from the outside, the perturbed liquid temperature would increase, but its final value did not exceed the phase transition temperature. The obtained result was used to explain the heating of water in Ranque – Hilsch vortex tubes. It was concluded that the water heating in Ranque -Hilsch tubes should be considered as the inverse Rayleigh problem, in which the temperature gradient can be determined from the known distribution of velocities inside the volume. The stability of a rotating cylindrical volume of a liquid when heated from below was analyzed. It was demonstrated, that the value of the specified temperature difference at cylinder boundaries, as well as the initial rate of its variation, determine the final heating temperature of the liquid. A comparison of the proposed theory and experimental data for water heating shows their good qualitative and quantitative agreement.

41-46

Authors: Volodymyr M. Kuklin, Eugen V. Poklonskiy

The paper shows that the waves of anomalous amplitude are long-lived formations. They drift in the direction of the wave motion with the group velocity of the wave packet, which is half the phase velocity of the main wave. The swing of the wave (the distance from the hump to the trough) of the anomalous amplitude is more than three times the average value of the sweep of the wave motion. The modulation instability of this wave form a perturbation spectrum, the energy of which is twice the energy of the main wave in the developed process mode. The spatial size of the wave packet practically does not change, the amplitude of the swing in the maximum first increases, then gradually decreases. The number of such waves in areas of strong wind exposure is much larger than the statistics of random interference processes allow. This is due to the influence of the main wave (its amplitude remains noticeably greater than the amplitudes of each of the modes of the wave packet) on the behavior of each pair of modes from the wave packet of the perturbation. In the laboratory system, the duration of the anomalous wave coincides qualitatively with the time of existence of the Peregrin autowave. Although the Peregrin autowave corresponds to a different physical reality, where the dispersion of the wave is weak. Gravitational surface waves have a strong dispersion, and the NSE equation in this case is noticeably modified. However, in rest system of the wave packet (moving relative to the laboratory system) the abnormal amplitude wave lifetime is much longer. The distance that the wave packet travels with a persisting anomalous sweep is at least equal to several hundred wavelengths and can reach hundreds of kilometers. A simple calculation of such waves by means of space monitoring due to the small viewing area (frame) may be inaccurate. Once formed, such waves are able to drift over considerable distances. However, they may well get into the next frame of view. That is, estimates of the number of such waves can be overestimated.

58-69

Authors: Uliana Tarabara, Mykhailo Shchuka, Kateryna Vus, Olga Zhytniakivska, Valeriya Trusova, Galyna Gorbenko, Nikolai Gadjev, Todor Deligeorgiev

The applicability of the three-step Förster resonance energy transfer (FRET) to detection of insulin amyloid fibrils was evaluated, using the chromophore system, containing Thioflavin T (ThT), 4-dimethylaminochalcone (DMC), and two squaraine dyes, referred to here as SQ1 and SQ4. The mediator chromophore DMC was found to enhance the fluorescence intensity of the terminal acceptor, SQ1, excited at 440 nm (at the absorption maximum of the principal donor, ThT), in fibrillar insulin compared to the system without DMC, providing the evidence for the cascade energy transfer in the chain ThT→DMC→SQ4→SQ1. Furthermore, the resulting Stokes shift in the four-chromophore system was 240 nm, as compared to 45 nm for the fibril-bound ThT, suggesting that higher signal-to-noise ratio is the advantage of amyloid fibril detection by multistep FRET. The maximum efficiencies of energy transfer in the insulin fibrils estimated from the quenching of the donor fluorescence in the presence of acceptor for the donor-acceptor pairs ThT-DMC, DMC-SQ4 and SQ4-SQ1 were 40%, 60% and 30% respectively, while negligible FRET occurred in the non-fibrillized protein. The most pronounced differences between fibrillar and non-fibrillized insulin were observed in the 3D fluorescence spectra. Specifically, two intensive spots centered at the emission wavelengths ~ 650 nm (SQ4) and ~ 685 nm (SQ1) were revealed at the excitation wavelength ~ 440 nm in the 3D patterns of insulin amyloid aggregates. In contrast, in the case of the non-fibrillized protein, the barely noticeable spots centered at the same wavelengths, as well as higher fluorescence intensities at the excitation above 550 nm were observed, suggesting the predominant impact of the direct excitation of SQ1 and SQ4 on their fluorescence responses. The inter-chromophore distances calculated from the experimental values of the energy transfer efficiency assuming the isotropic rotation of the dyes, were found to be 2.4, 4.5 and 4.3 nm for the ThT-DMC, DMC-SQ4 and SQ4-SQ1 pairs, respectively, revealing the different fibril binding sites for the examined dyes. The quantum-chemical calculations and simple docking studies provided evidence for the SQ1, SQ4 and ThT, DMC binding to the wet and dry interface of the insulin amyloid protofilament, respectively. The dye-protein complexes are likely to be stabilized by the hydrophobic, van der Waals, aromatic and electrostatic interactions. In summary, the above technique based on the multistep FRET can be employed for the identification and characterization of amyloid fibrils in vitro along with the classical ThT assay, allowing the increase of the amyloid detection sensitivity and lowering the probability of the pseudo-positive result. The applicability of the multistep FRET for amyloid visualization in vivo can be also tested by the involvement of the near-infrared fluorescent dyes to the cascade.

77-81

Authors: Aleksey B. Batrakov, Eugeniy G. Glushko, Andrey А. Zinchenko, Yuriy F. Lonin, Anatoliy G. Ponomarev, Sergei I. Fedotov

To ensure the controllability and high noise immunity while measuring the characteristics of the accelerators of relativistic electron beams (REB) “TEMP”, and parameters of the processes in them, triggering devices with galvanic isolation of input and output circuits, allowing to set up the pulse delays in the range from 1 μs to tens of milliseconds, have been developed. When they are used, the effect of loop currents, which flow in the common ground circuits and affect the operation of the measuring equipment, is eliminated. To synchronize the operation of the REB accelerator “TEMP” a triggering device was developed and assembled. It was assembled from blocks produced on the up-to-date elemental base and is a complete functional product. The triggering device comprises a trigger block and delay units. The trigger block is developed on the basis of an AND - NOT chip and a multivibrator. The delay units are built on single-shot vibrators K155AG1 and differ in the value of adjustable delays, which are determined by the external elements R and C, connected to the multivibrator. Unfortunately, in case the millisecond delays are set up, the pulse drop on the multivibrator is not stable. Therefore, a digital triggering device was developed. The digital triggering device is built on the basis of digital microcircuits and consists of the following blocks: binary-decimal counters, decoders, and one oscillator with quartz frequency stabilization, which is common to all four channels. It contains four identical channels with delay adjustment from one microsecond to one hundred milliseconds. Such a pattern of the circuit allows, if necessary, adding channels for starting other units. Pulse signals of the triggering device are fed to the ignitor unit of the spark-gaps. A pulse generator for igniting the spark-gaps of the REB accelerator “TEMP” has been developed. A generator, designed to control the spark gaps ignition in the High Voltage Pulse Generator (HVPG) and spark gaps ignition in the magnetic systems, which are used in switching systems of the capacitor banks with the energy of 60  150 kJ, has been described. The generator provides voltage pulses with the amplitude of up to 20 kV, at the current in the short circuit mode of 5 A, the pulse duration of the first half wave of 12 μs, and the pulse repetition frequency (PRF) of not more than 10 Hz.

91-94

Authors: Gennadiy M. Onyshchenko, Volodymyr D. Ryzhikov, Ivan I. Yakymenko, Oleksandr P. Shchus

In the present work we found the maximum discovery distance for 239Pu-Be source using the detectors based on ZWO (ZnWO4) and BGO (Bi4Ge3O12) oxide scintillators. Detection distance was defined by using the radiation monitoring system ”PORTAL”. This research gives us data for estimation of the contribution of low-energy cascade gamma quanta CGQ. The CGQ emitted by excited scintillator nuclei defined the effective discovery distance of the fast neutrons source. The maximum detection distance was obtained with PMT in a single-photon counting mode. The maximum discovery distance for a BGO scintillator of size Ø40×40 mm – 38 cm, ZWO scintillator of size Ø52×40 mm – 54 cm, with reliability about 0.001. The results of the experiment on the ZWO scintillator can be explained by the registration of additional gamma quanta from the inelastic scattering reaction and the CGQ arising from resonant neutron capture region. This two mechanisms further lead to increase the sensitivity of the detector and increase the detection distance of the monitoring system. The key features of the monitoring system are: ZWO oxide scintillator, wide band measuring path, utilize PMT in single photon mode. The obtained detection distance was about 1.4 times higher in comparison with the spectrometric recording mode and 1.9 times higher in values of efficiency. Our results demonstrate the advantages of the ZWO scintillator compared to the BGO and demonstrate the possibility of using the resonant capture mechanism by ZWO detector nuclei to increase the fast neutrons sensitivity. The resonance capture mechanism increase sensitivity and maximum detection distance of the monitoring system. The low-energy gamma-quanta, which discharge of compound nuclei, are substantially suppressed in comparison with the classic spectrometric recording mode.