ABSTRACT
The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report 60 bursts detected with the ...Effelsberg telescope at 1.4 GHz. We observe large variations in the burst rate, and report the first FRB 20200120E ‘burst storm’, where the source suddenly became active and 53 bursts (fluence ≥0.04 Jy ms) occurred within only 40 min. We find no strict periodicity in the burst arrival times, nor any evidence for periodicity in the source’s activity between observations. The burst storm shows a steep energy distribution (power-law index α = 2.39 ± 0.12) and a bimodal wait-time distribution, with log-normal means of 0.94$^{+0.07}_{-0.06}$ s and 23.61$^{+3.06}_{-2.71}$ s. We attribute these wait-time distribution peaks to a characteristic event time-scale and pseudo-Poisson burst rate, respectively. The secondary wait-time peak at ∼1 s is ∼50 × longer than the ∼24 ms time-scale seen for both FRB 20121102A and FRB 20201124A – potentially indicating a larger emission region, or slower burst propagation. FRB 20200120E shows order-of-magnitude lower burst durations and luminosities compared with FRB 20121102A and FRB 20201124A. Lastly, in contrast to FRB 20121102A, which has observed dispersion measure (DM) variations of ΔDM > 1 pc cm−3 on month-to-year time-scales, we determine that FRB 20200120E’s DM has remained stable (ΔDM < 0.15 pc cm−3) over >10 months. Overall, the observational characteristics of FRB 20200120E deviate quantitatively from other active repeaters, but it is unclear whether it is qualitatively a different type of source.
The article introduces the results of studying the magnetic field distribution in the alternator inductor with an axial arrangement of open magnetic cores (OMC) and external closure of magnetic ...fluxes. The study compares the efficiency of using magnetic fluxes from permanent magnets (PM) on the example of two model variants of inductors with OMC developed by the authors. The analysis of the density distribution of magnetic fluxes in OMC was carried out by 3D modelling of the magnetic field using EMWorks software. It has been shown that such generators can be manufactured using a waste-free technology for strip of OMC. This technology significantly reduces the production costs of OMC. By modelling the distribution of magnetic fluxes in the OMC of the inductor, the results of experimental studies and analysis of the created device show that the capacity of generator can be varied by changing its dimensions and the number of the toggle switches on the rotor. This allows the alternator to be adapted to the load requirements – power banks and bicycle electronics.
The article investigates the properties and potential of compressed hydrogen as one of the most promising energy carriers in order to facilitate the development of energy storage capabilities and lay ...down a stable foundation for the future of a sustainable energy sector. The study considers the use of hydrogen, compressed at high pressure from 50 MPa to 100 MPa, at refuelling stations to supply electric cars. The technical properties of modern hydraulic compressors used for hydrogen accumulation in high pressure buffer containers are considered. The study shows that the design of hydraulic compressors in terms of their technical characteristics optimally corresponds to the primary requirements for their use as booster compressors at refuelling stations. The authors conclude with the proposal of an enhanced design of the hydraulic compressor with the use of fluid flow counters in a control system of a hydrogen compression cycle. The proposed technical solution provides for continuous monitoring of the hydrogen compression process that increases the reliability of control system operation.
ABSTRACT
Torsional Alfvén waves in coronal plasma loops are usually considered to be non-collective, i.e. consist of cylindrical surfaces evolving independently, which significantly complicates their ...detection in observations. This non-collective nature, however, can get modified in the non-linear regime. To address this question, the propagation of non-linear torsional Alfvén waves in straight magnetic flux tubes has been investigated numerically using the astrophysical MHD code Athena++ and analytically, to support numerical results, using the perturbation theory up to the second order. Numerical results have revealed that there is radially uniform-induced density perturbation whose uniformity does not depend on the radial structure of the mother Alfvén wave. Our analysis showed that the ponderomotive force leads to the induction of the radial and axial velocity perturbations, while the mechanism for the density perturbation is provided by a non-equal elasticity of a magnetic flux tube in the radial and axial directions. The latter can be qualitatively understood by the interplay between the Alfvén wave perturbations, external medium, and the flux tube boundary conditions. The amplitude of these non-linearly induced density perturbations is found to be determined by the amplitude of the Alfvén driver squared and the plasma parameter β. The existence of the collective and radially uniform density perturbation accompanying non-linear torsional Alfvén waves could be considered as an additional observational signature of Alfvén waves in the upper layers of the solar atmosphere.
The article presents a hydraulic hydrogen compression solution designed to serve as a booster compressor. It can be adapted to changing parameters of the inlet pressure of hydrogen and allows ...stabilising the hydrogen accumulation process in the high-pressure storage.
The main results of this study were obtained using a numerical model developed to explore the thermodynamic processes that occur during the hydraulic compression of hydrogen. The modelling was carried out using COMSOL Multiphysics® 6.0 software with the CFD and heat transfer modules. The compression chamber in the form of a cylinder with a volume of 1.14
and wall thickness of 5 mm was used in the computational model. The aim of these simulations was to investigate the temperature change limits of hydrogen, cylinder walls and working fluid, as well as to estimate the actual value of pressure inside the cylinder. The considered process of pressure increase in the cylinder chamber was modelled as a continuous change of volume filled with working fluid with discrete time step of 0.01
, taking into account the increase of temperature inside the cylinder. The derived modelling results for different durations of compression stroke t
from 0.5 to 20.0
were presented. The curves of energy consumption and temperature rise during the compression process were calculated for initial hydrogen pressures P
= 3.0, 10.0, 15.0 and 20.0
and compression ratio Kc = 5.0.
The results of simulation of thermodynamic processes and their analysis allowed estimating energy consumption in the system of hydraulic compression and determining conditions which would lead to the increase in efficiency of hydrogen compression operation systems under consideration.
The article studies magnetic field distribution in the alternator inductors with an axial arrangement of open magnetic cores (OMC) and an external closure of the magnetic flux. The study compares the ...efficiency of magnetic flux utilization for four models with different modifications of the geometry of the magnetic circuit of inductors. The analysis of the density distribution of magnetic flux in OMC is carried out by 3D modelling of the magnetic field using EMWorks software. Based on the experimental study of the properties of the base model, the influence of the configuration of the magnetic circuit of the inductor on the efficiency of the alternator is shown. The results are presented in the form of tables and diagrams characterising changes in magnetic fluxes and electromotive force (EMF) in relative units. The results provide the grounds for assessing the potential and possible limits of optimization with respect to the size of air gaps and dimensions of the magnetic flux toggle switches. The study indicates that the proposed alternator can be adapted for various load requirements and optimized for various applications, such as charging power banks and powering bicycle electronics. The study also demonstrates that for such generators, OMC can be manufactured using a waste-free strip production technology.
The authors perform a comparative analysis of the efficiency of two types of low-power wind energy conversion systems with horizontal and vertical axis in the meteorological conditions of Latvia. The ...analysis is based on long-term wind speed measurements over the period of two years conducted by a network of 22 observation stations at the height of 10
above the ground. The study shows that in the conditions of Latvia wind turbines with a horizontal axis are expected to work with greater efficiency than similar installations with a vertical axis. The paper presents the models of the spatial distribution of average wind speed, Weibull wind speed frequency distribution parameters and the values of the expected operational efficiency for small wind turbine generators. The modelling results are presented in the form of colour contour maps. Overall, the results of the study can serve as a tool for forecasting annual energy production and for estimating the feasibility of commercial use of wind energy at the height of 10
in the territory of Latvia.
The article introduces two new designs of flux switching permanent magnet alternators with a radial and an axial arrangement of the inductor relative to the magnetic flux switch. The study presents ...the results of 3D magnetic flux modelling along with the outcomes of physical experiments. In the course of laboratory experiments, the results of theoretical estimations are compared with actual physical performance parameters. The results are presented in the form of power and output voltage curves in relation to the frequency and load current. The study proposes the practical application of the alternators based on the magnetic flux switching principle in the development of a bicycle generator. Laboratory test models are made of a laminated steel using a waste-free technology.
Aims.
Molecular masers, including methanol and hydroxyl masers, and in particular the ones in excited rotational states (ex-OH masers), are one of the most informative tools for studying star-forming ...regions. So, the discovery, of new maser sources in these regions is of great importance. Many studies and surveys of ex-OH maser sources have been carried out in the southern celestial hemisphere, but only a few have been done in the northern hemisphere. The specific aim of this work is to close this gap.
Methods.
The star-forming regions in the northern hemisphere with known active methanol masers were observed to search for new ex-OH maser sources with the 32 m and 16 m radio telescopes of the Ventspils International Radio Astronomy Centre (VIRAC).
Results.
Three OH maser lines in the excited state at the 6035 MHz in three northern hemisphere star-forming regions are detected. The maser 189.030+0.783 was previously known, but we suggest this maser is a possible variable. We confirm recent detections of the ex-OH masers 85.41+0.00 and 90.92+1.49 by other authors. The magnetic field strength in the masering regions is estimated by using right circular polarization and left circular polarization pair splitting. The high-velocity resolution provides us with an estimation of a comparatively small magnetic field strength for the 189.030+0.783 and 90.92+1.49 star-forming regions.
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