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

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

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

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&

Amino-nitrile cleavage in the electrochemical reduction of hydeazones of aromatic aldehydes

1. Factors which determine the possibility of amino-nitrile cleavage of hydrazones on electrochemical reduction (ECR) include the basicity of the anionic product formed in the course of the ECR and the mobility of the aldehyde hydrogen which depends on the character of the electron polarization of the hydrazone fragment and the polarity of the N-N bond. 2. The primary action in amino-nitrile cleavage under conditions of ECR is the deprotonation of the azomethine fragment in the unreduced molecule by electrochemically generated strong base (anion or dianion). © 1988 Plenum Publishing Corporation

Perturbative regime of terahertz high-harmonics generation in topological insulators

In this Letter, terahertz high harmonic generation processes in topological insulators of the bismuth and antimony chalcogenides family are investigated. Field conversion efficiencies are determined and clean cubic and quintic power-law scaling is observed for third and fifth harmonics, up to driving terahertz fields of 140 kV/cm. This is in contrast to all previous experiments on terahertz harmonics generation in Dirac materials where a non-perturbative regime has been observed already at few 10s kV/cm driving fields. Our nonlinear THz spectroscopy experiments are complemented by THz pump - optical probe measurements showing distinctly different relaxation dynamics of the carriers in the topologically-protected Dirac states at the surfaces and the bulk. The THz-induced dynamics of surface states reveal ultrafast relaxation that prevents accumulation effects, and results in a clear perturbative regime of THz harmonics generation that is different to graphene or Dirac semimetals with their slower relaxation times in the few ps regime

Production and Application of Multicistronic Constructs for Various Human Disease Therapies

The development of multicistronic vectors has opened up new opportunities to address the fundamental issues of molecular and cellular biology related to the need for the simultaneous delivery and joint expression of several genes. To date, the examples of the successful use of multicistronic vectors have been described for the development of new methods of treatment of various human diseases, including cardiovascular, oncological, metabolic, autoimmune, and neurodegenerative disorders. The safety and effectiveness of the joint delivery of therapeutic genes in multicistronic vectors based on the internal ribosome entry site (IRES) and self-cleaving 2A peptides have been shown in both in vitro and in vivo experiments as well as in clinical trials. Co-expression of several genes in one vector has also been used to create animal models of various inherited diseases which are caused by mutations in several genes. Multicistronic vectors provide expression of all mutant genes, which allows the most complete mimicking disease pathogenesis. This review comprehensively discusses multicistronic vectors based on IRES nucleotide sequence and self-cleaving 2A peptides, including its features and possible application for the treatment and modeling of various human diseases