Direct Evidence of Two Superconducting Gaps in FeSe0.5_{0.5}Te0.5_{0.5}: SnS-Andreev Spectroscopy and Lower Critical Field

We present direct measurements of the superconducting order parameter in nearly optimal FeSe$_{0.5}$Te$_{0.5}$ single crystals with critical temperature $T_C \approx 14$ K. Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy and measurements of lower critical field, we directly determined two superconducting gaps, $\Delta_L \approx 3.3 - 3.4$ meV and $\Delta_S \approx 1$ meV, and their temperature dependences. We show that a two-band model fits well the experimental data. The estimated electron-boson coupling constants indicate a strong intraband and a moderate interband interaction

Refining of metal melts by filtration method

The article describes the prerequisites of filtration refining of metal melts. When filtering the liquid metals the refining effect is caused by the deposition on the filter surface of suspended non-metallic particles in the melt, and by the release of the non-metallic phase directly from the melt. Along with this the mechanism of melt refining from a superequilibrium dissolved impurity is realized when filtering as a result of the reaction course of chemical binding of the impurity element

Signal recognition and background suppression by matched filters and neural networks for Tunka-Rex

The Tunka Radio Extension (Tunka-Rex) is a digital antenna array, which measures the radio emission of the cosmic-ray air-showers in the frequency band of 30-80 MHz. Tunka-Rex is co-located with TAIGA experiment in Siberia and consists of 63 antennas, 57 of them are in a densely instrumented area of about 1 km\textsuperscript{2}. In the present work we discuss the improvements of the signal reconstruction applied for the Tunka-Rex. At the first stage we implemented matched filtering using averaged signals as template. The simulation study has shown that matched filtering allows one to decrease the threshold of signal detection and increase its purity. However, the maximum performance of matched filtering is achievable only in case of white noise, while in reality the noise is not fully random due to different reasons. To recognize hidden features of the noise and treat them, we decided to use convolutional neural network with autoencoder architecture. Taking the recorded trace as an input, the autoencoder returns denoised trace, i.e. removes all signal-unrelated amplitudes. We present the comparison between standard method of signal reconstruction, matched filtering and autoencoder, and discuss the prospects of application of neural networks for lowering the threshold of digital antenna arrays for cosmic-ray detection.Comment: ARENA2018 proceeding

Current Status and New Challenges of The Tunka Radio Extension

The Tunka Radio Extension (Tunka-Rex) is an antenna array spread over an area of about 1~km$^2$. The array is placed at the Tunka Advanced Instrument for cosmic rays and Gamma Astronomy (TAIGA) and detects the radio emission of air showers in the band of 30 to 80~MHz. During the last years it was shown that a sparse array such as Tunka-Rex is capable of reconstructing the parameters of the primary particle as accurate as the modern instruments. Based on these results we continue developing our data analysis. Our next goal is the reconstruction of cosmic-ray energy spectrum observed only by a radio instrument. Taking a step towards it, we develop a model of aperture of our instrument and test it against hybrid TAIGA observations and Monte-Carlo simulations. In the present work we give an overview of the current status and results for the last five years of operation of Tunka-Rex and discuss prospects of the cosmic-ray energy estimation with sparse radio arrays.Comment: Proceedings of E+CRS 201

First analysis of inclined air showers detected by Tunka-Rex

The Tunka Radio Extension (Tunka-Rex) is a digital antenna array for the detection of radio emission from cosmic-ray air showers in the frequency band of 30 to 80 MHz and for primary energies above 100 PeV. The standard analysis of Tunka-Rex includes events with zenith angle of up to 50$^\circ$. This cut is determined by the efficiency of the external trigger. However, due to the air-shower footprint increasing with zenith angle and due to the more efficient generation of radio emission (the magnetic field in the Tunka valley is almost vertical), there are a number of ultra-high-energy inclined events detected by Tunka-Rex. In this work we present a first analysis of a subset of inclined events detected by Tunka-Rex. We estimate the energies of the selected events and test the efficiency of Tunka-Rex antennas for detection of inclined air showers.Comment: ARENA2018 proceeding

МЕТОДИКА РАСЧЕТА НЕСТАЦИОНАРНОГО ОТРЫВНОГО ОБТЕКАНИЯ СИСТЕМЫ ПРОФИЛЕЙ, ДВИЖУЩИХСЯ ВБЛИЗИ НЕПОДВИЖНОГО ЭКРАНА

In this article an attempt is made to explain the nature of differences in measurements of forces and moments, which influence an aircraft at take-off and landing when testing on different types of stands. An algorithm for numerical simulation of unsteady separated flow around airfoil is given. The algorithm is based on the combination of discrete vortex method and turbulent boundary layer equations. An unsteady flow separation modeling has been used. At each interval vortex method was used to calculate the potential flow around airfoils located near a screen. Calculated pressures and velocities were then used in boundary layer calculations to determine flow separation points and separated vortex in- tensities. After that calculation were made to determine free vortex positions to next time step and the process was fulfilled for next time step. The proposed algorithm allows using numeric visualization to understand physical picture of flow around airfoil moving close to screen. Three different ways of flow modeling (mirror method, fixed or movable screens) were tested. In each case the flow separation process, which determines pressure distribution over airfoil surface and influ- ences aerodynamic performance, was viewed. The results of the calculations showed that at low atitudes of airfoil over screen mirror method over predicts lift force compared with movable screen, while fixed screen under predicts it. The data obtained can be used when designing equipment for testing in wind tunnels.В работе сделана попытка объяснить часто встречающиеся в экспериментальной практике различия в измерениях сил и моментов, действующих на профиль на режимах взлета и посадки при испытаниях на различных типах стендов. Предложен алгоритм расчета нестационарного отрывного обтекания профилей вблизи твердой поверхности. Алгоритм основан на сочетании метода дискретных особенностей и уравнений турбулентного пограничного слоя. Задача решалась в нестационарной постановке. На каждом временном шаге метод дискретных вихрей применялся для расчета невязкого течения во внешней по отношению к профилям области (давлений и скоростей на профилях и экране) и определения динамики движения вихрей следа. Уравнения турбулентного пограничного слоя использовались для расчета положений точек отрыва на профилях и экране и интенсивностей сходящих в этих точках вихрей. Предложенный алгоритм позволяет с помощью численной визуализации понять физическую картину течения в приэкранной области. Моделирование экрана тремя различными способами зеркальный метод, неподвижный и подвижный экраны - дало возможность проследить процесс возникновения отрыва, который определяет распределение давления на профиле и, следовательно, влияет на аэродинамические характеристики, для каждой модели экрана. По результатам расчетов дан сравнительный анализ этих способов моделирования профиля над экраном, который позволяет утверждать, что аэродинамические характеристики профилей при малых высотах над экраном существенно зависят от модели экрана. Зеркальный метод дает завышенное значение подъемной силы по сравнению с прямым методом, а результаты расчетов в обращенном движении при малых высотах над экраном дают заниженные результаты. Полученные данные могут быть использованы при проектировании стендов для испытания моделей в аэродинамических трубах

Application of Thin Piezoelectric Films in Diamond-Based Acoustoelectronic Devices

The theory of external loading influence on acoustic parameters of piezoelectric five-layered structure as “Al/(001) AlN/Mo/(001) diamond/Me” has been developed. Oscillations in diamond-based high-overtone bulk acoustic resonators (HBARs) have been investigated in terms of 3D FEM simulation. Peculiarities of technology of aluminum-scandium nitride (ASN) films have been discussed. Composition Al0.8Sc0.2N was obtained to create the diamond-based HBAR and SAW resonator. Application of ASN films has resulted in a drastic increasing an electromechanical coupling up to 2.5 times in comparison with aluminum nitride. Development of ASN technology in a way of producing a number of compositions with the better piezoelectric properties has a clear prospective. SAW resonator based on “Al IDT/(001) AlN/(001) diamond” structure has been investigated in the band 400–1500 MHz. The highest-quality factor Q ≈ 1050 was observed for the Sezawa mode at 1412 MHz. Method of measuring HBAR’s parameters within 4–400 K at 0.5–5 GHz has been developed. Results on temperature dependence of diamond’s Q-factor at relatively low frequencies were quite different in comparison with the ones at the frequencies up to 5 GHz. Difference could be explained in terms of changing mechanism of acoustic attenuation from Akhiezer’s type to the Landau-Rumer’s one at higher frequencies in diamond