Interplanetary scintillation and pulsar pulse statistics

The effect of interplanetary plasma on pulsed pulsar radiation passing through is considered. The pulses of two rotating radio transients (J0609+16, J1132+25) and a pulsar (B0320+39) detected on the Large Phased Array (Pushchino observatory) were analyzed. It is shown that in observations at the frequency of 111 MHz, on elongations of 20o-40o, both an increase and a decrease in the number of received pulses are observed. The change in the number of pulses is explained by the distortion of the energy distribution of pulses due to interplanetary scintillation. These changes in the number of observed pulses are in qualitative agreement with the expected dependence of the scintillation index on the observed sources elongation. Analytical expressions are obtained that allow estimating the effective modulation index from observations of individual pulses for the power distribution of pulses by energy.Comment: accepted to MNRAS, 5 pages, 3 figure

Mapping of periodically poled crystals via spontaneous parametric down-conversion

A new method for characterization of periodically poled crystals is developed based on spontaneous parametric down-conversion. The method is demonstrated on crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled structures, obtained directly under Czochralski growth procedure and designed for application of OPO in the mid infrared range. Infrared dispersion of refractive index, effective working periods and wavelengths of OPO were determined by special treatment of frequency-angular spectra of spontaneous parametric down-conversion in the visible range. Two-dimensional mapping via spontaneous parametric down-conversion is proposed for characterizing spatial distribution of bulk quasi-phase matching efficiency across the input window of a periodically poled sample.Comment: 19 pages, 6 figure

Study of Bright Compact Radio Sources of the Northern Hemisphere at the frequency of 111 MHz

The search for compact components of strong ($S_{int} \ge 5$ Jy at 102.5 MHz) discrete radio sources from the Pushchino catalogue was carried out using the method of interplanetary scintillation. A total of 3620 sources were examined, and 812 of them were found to compact (scintillating) components. Estimates of fluctuations of the flux density of these compact components were derived from the scintillation index ($m_{max}$) corresponding to an elongation of $25^o$. The angular size and compactness of 178 sources with compact components were estimated. Scintillation indices of sources corresponding to the compact component ($m_{max}$) and flux densities of compact components were determined. It was demonstrated that slow variations of the spatial distribution of interplanetary plasma, which are related to the 11-year cycle of solar activity, may exert a systematic influence on the estimates of angular sizes of sources. Coefficients compensating the deviation from the spherical symmetry of solar wind in the estimates of angular sizes were found using the coefficient of asymmetry of the statistical distribution of intensity fluctuations. The study of correlations between the parameters of sources in the sample revealed that the maximum value of the scintillation index decreases as the integrated flux increases, while the angular size has no marked dependence on the integrated flux.Comment: published in Astronomy Report, translated by Yandex translator with correction of scientific lexis, 16 pages, 6 figures, 3 table, appendi

The selection of an electric propulsion subsystem architecture for high-power space missions

The arise of high-power electric propulsion is paving the way towards new horizons of space exploration. Hall thrusters represent a promising propulsion concept, able to fulfil challenging mission requirements for both commercial and exploration applications. This technology offers several benefits in terms of flexibility of operation, extensive lifetime and high reliability. However, the design of a high-power electric propulsion subsystem (E-PROP) still presents challenges to address. Filling the corresponding technological gaps will open new market opportunities, owing mainly to the extension of mission capabilities and the reduction of the overall mission costs. Therefore, investigations of innovative technology alternatives will allow to identify the most promising E-PROP architectures for various high-power mission scenarios. One of the most critical trade-off to perform is between a high-power monolithic thruster and a cluster of thrusters of lower power. Another criticality is the amount of propellant necessary to perform high delta-v missions. The high price of xenon prompted the investigation on alternative propellants, such as krypton. The propellant selection should consider the impact on different aspects of the platform design, including performance, system complexity and mission costs. Last, due to the high-power levels that the E-PROP shall manage, a different architecture can be implemented by adopting the direct-drive approach, i.e. a direct and non-isolated connection between the solar array and the thruster. However, even if the disruptive direct-drive technology allows a significant reduction in the EP system mass and cost, its implementation rises additional challenges to the design of the spacecraft power subsystem. This paper analyses the impact of innovative architecture solutions on the design of a high-power E-PROP. In the framework of this research, we first carried out an extensive investigation of possible mission scenarios and we derived corresponding mission requirements and constrains. Then, we performed three technological trade-offs: monolithic 20 kW vs 5 kW cluster configuration, Xe vs Kr propellant and direct-drive vs standard PPU. All the analysis are based on the experimental data obtained during the 5 kW and 20 kW thrusters development and characterisation at SITAEL. We characterized each design option through several figures of merit, evaluating them for each identified mission scenario. We exploited an Analytical Hierarchy Process for the trade-off analyses and a Monte Carlo method to perform the preliminary evaluation of the trade-off weights. The analyses are based on the research activities that are currently ongoing at SITAEL and PoliTo in the framework of 20 kW E-PROP development programmes. The results of the work highlight the effects of each architecture alternative on both platform design and mission performance

Biphoton compression in standard optical fiber: exact numerical calculation

Generation of two-photon wavepackets, produced by spontaneous parametric down conversion in crystals with linearly chirped quasi-phase matching grating, is analyzed. Although being spectrally broad, two-photon wavepackets produced this way are not Fourier transform limited. In the paper we discuss the temporal compression of the wavepackets, exploiting the insertion of a standard optical fiber in the path of one of the two photons. The effect is analyzed by means of full numerical calculation and the exact dispersion dependencies in both the crystal and the fiber are considered. The study opens the way to the practical realization of this idea.Comment: 10 pages, 16 figure

Revisiting Pushchino RRAT search using neural network

The search for rotating radio transients (RRAT) at declination from -9o to +42o was carried out in the semi-annual monitoring data obtained on the Large Phased Array (LPA) radio telescope at the frequency of 111 MHz. A neural network was used to search for candidates. 4 new RRATs were detected, having dispersion measures (DM) 5-16 pc/cm3. A comparison with an earlier RRAT search conducted using the same data shows that the neural network reduced the amount of interference by 80 times, down to 1.3% of the initial amount of interferences. The loss of real pulsar pulses does not exceed 6% of their total number.Comment: 7 pages, 2 figures, submitted to A&

Pushchino multibeams pulsar search. IV. Detection of new pulsars at declinations -9o < \delta < +55o

The search for pulsars in monitoring data obtained at the radio telescope Large Phased Array (LPA) at a frequency of 111 MHz was carried out. Daily round-the-clock observations were carried out for about 3,000 days. The duration of the observation session for each direction in the sky was 3.5 minutes per day. The search for pulsars was carried out using power spectra. To search for weak pulsars, power spectra were summed up. The expected increase in sensitivity was 35-40 times compared to observations in one session. In a blind search, 330 pulsars with regular radiation were detected, with periods (P) from 0.0333 to 3.7455 s and dispersion measures (DM) up to 249 pc/cm3. 39 pulsars turned out to be new. Average profiles were obtained for 6 pulsars. The DM for 7 pulsars previously detected on the LPA have been clarified.Comment: published in MNRAS, 13 pages, 4 figures, 4 tables, 4 appendixe

Twin-photon techniques for photo-detector calibration

The aim of this review paper is to enlighten some recent progresses in quantum optical metrology in the part of quantum efficiency measurements of photo-detectors performed with bi-photon states. The intrinsic correlated nature of entangled photons from Spontaneous Parametric Down Conversion phenomenon has opened wide horizons to a new approach for the absolute measurement of photo-detector quantum efficiency, outgoing the requirement for conventional standards of optical radiation; in particular the simultaneous feature of the creation of conjugated photons led to a well known technique of coincidence measurement, deeply understood and implemented for standard uses. On the other hand, based on manipulation of entanglement developed for Quantum Information protocols implementations, a new method has been proposed for quantum efficiency measurement, exploiting polarisation entanglement in addition to energy-momentum and time ones, that is based on conditioned polarisation state manipulation. In this review, after a general discussion on absolute photo-detector calibration, we compare these different methods, in order to give an accurate operational sketch of the absolute quantum efficiency measurement state of the art