Influence of misalignments on performance of externally occulted solar coronagraphs. Application to PROBA-3/ASPIICS

ASPIICS is a novel externally occulted coronagraph that will be launched onboard the PROBA-3 mission of ESA. The external occulter (EO) will be placed on one satellite ~150 m ahead of the second satellite with an optical instrument. During part of each orbit, the satellites will fly in a precise formation, constituting a giant externally occulted coronagraph. Large distance between the EO and the primary objective will allow observations of the white-light solar corona starting already from ~1.1RSun. We analyze influence of shifts of the satellites and misalignments of optical elements on diffracted light. Based on the quantitative influence of misalignments on diffracted light, we will provide a "recipe" for choosing the size of the internal occulter (IO) to achieve a trade-off between the minimal height of observations and sustainability to possible misalignments. We implement a numerical model of the diffracted light and its propagation through the optical system, and compute intensities of diffracted light throughout the instrument. Our numerical model extends axi-symmetrical model of Rougeot et al. 2017 to non-symmetrical cases. The computations fully confirm main properties of the diffracted light obtained from semi-analytical consideration. Results: relative influences of various misalignments are significantly different. We show that: the IO with R=1.1RSun is large enough to compensate possible misalignments in ASPIICS, apodizing the edge of the IO leads to additional suppression of the diffracted light. Conclusions: the most important misalignment is the tilt of the telescope WRT the line connecting the center of the EO and the entrance aperture. Special care should be taken to co-align the EO and the coronagraph, i.e. co-aligning the diffraction fringe from the EO and the IO. We suggest that the best orientation strategy is to point the coronagraph to the center of the EO.Comment: 13 pages, 15 figure

Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph

Context: ASPIICS is a novel externally occulted solar coronagraph, which will be launched onboard the PROBA-3 mission of the European Space Agency. The external occulter will be placed on the first satellite approximately 150 m ahead of the second satellite that will carry an optical instrument. During 6 hours per orbit, the satellites will fly in a precise formation, constituting a giant externally occulted coronagraph. Large distance between the external occulter and the primary objective will allow observations of the white-light solar corona starting from extremely low heights 1.1RSun. Aims: To analyze influence of optical ghost images formed inside the telescope and develop an algorithm for their removal. Methods: We implement the optical layout of ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential regimes. We identify sources of the ghost contributions and analyze their geometrical behaviour. Finally we develop a mathematical model and software to calculate ghost images for any given input image. Results: We show that ghost light can be important in the outer part of the field of view, where the coronal signal is weak, since the energy of bright inner corona is redistributed to the outer corona. However the model allows to remove the ghost contribution. Due to a large distance between the external occulter and the primary objective, the primary objective does not produce a significant ghost. The use of the Lyot spot in ASPIICS is not necessary.Comment: 14 pages, 13 figure

Orientation and symmetry control of inverse sphere magnetic nanoarrays by guided self-assembly

Inverse sphere shaped Ni arrays were fabricated by electrodeposition on Si through the guided self-assembly of polystyrene latex spheres in Si/SiO2 patterns. It is shown that the size commensurability of the etched tracks is critical for the long range ordering of the spheres. Moreover, noncommensurate guiding results in the reproducible periodic triangular distortion of the close packed self-assembly. Magnetoresistance measurements on the Ni arrays were performed showing room temperature anisotropic magnetoresistance of 0.85%. These results are promising for self-assembled patterned storage media and magnetoresistance devices

Problems of Data Collection for the Application of the Data Mining Methods in Analyzing Threshold Levels of Indicators of Economic Security

Determining threshold values of key economic security indices describing an economic situation in any country is an important stage in the assessment of the country’s economic stability. A research was undertaken to determine how this problem can be effectively solved with such Data Mining algorithm as decision trees. According to the results of the research the effectiveness of the method was proved, but only with sufficient amount of data available. However, such data collection has a number of significant problems. These problems can be attributed to the following factors: the data for the analysis are presented with varying frequency, there is no possibility to use data over longer time intervals, the lack of a common list of indicators of economic security, which are used in different countries. The purpose of this paper is to analyze the existing problems of the data collection and to submit proposals of solving them. Keywords: Economic security, Issues of data collection, Data Mining, thresholds

From Coulomb excitation cross sections to non-resonant astrophysical rates in three-body systems: 17^{17}Ne case

Coulomb and nuclear dissociation of $^{17}$Ne on light and heavy targets are studied theoretically. The dipole E1 strength function is determined in a broad energy range including energies of astrophysical interest. Dependence of the strength function on different parameters of the $^{17}$Ne ground state structure and continuum dynamics is analyzed in a three-body model. The discovered dependence plays an important role for studies of the strength functions for the three-body E1 dissociation and radiative capture. The constraints on the $[s^2]/[d^2]$ configuration mixing in $^{17}$Ne and on $p$-wave interaction in the $^{15}$O+$p$ channel are imposed based on experimental data for $^{17}$Ne Coulomb dissociation on heavy target.Comment: 12 pages, 13 figure

The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance

The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to mid-ultraviolet) solar radiometer onboard the European Space Agency PROBA2 mission that was launched in November 2009. LYRA acquires solar irradiance measurements at a high cadence (nominally 20 Hz) in four broad spectral channels, from soft X-ray to MUV, that have been chosen for their relevance to solar physics, space weather and aeronomy. In this article, we briefly review the design of the instrument, give an overview of the data products distributed through the instrument website, and describe the way that data are calibrated. We also briefly present a summary of the main fields of research currently under investigation by the LYRA consortium

Orthogonality of Biphoton Polarization States

Orthogonality of two-photon polarization states belonging to a single frequency and spatial mode is demonstrated experimentally, in a generalization of the well-known anti-correlation 'dip' experiment.Comment: Submitted to Phys.Rev.Let

Модель балансування паралельної обробки фото- відеокадрів в обчислювальному кластері для БПЛА

In solving some problems that are common to the system of operating UAVs, for example, parallelprocessing tasks of photo and video-frames, it seems appropriate the operative design of the computing cluster for UAV. The computing cluster for UAV is characterized by a dynamic structure(field) telecommunication system. This circumstance makes it necessary, for management purposes, tosynthesize such model of the cluster what allows, on the one hand, to calculate the effective plan forthe organization of the computation process, and on the other hand - to spend on these calculationsthe minimum resources (particularly - time). It is proposed, in the case of cluster for UAV, the classic,with criteria "cost - performance", (linear) V.Leontyev’s model. Figs:2. Refs:3 titles.При решении некоторых проблем, общих для системы действующих БПЛА, например задач параллельной обработки фото и видеокадров, представляется целесообразным оперативное проектирование вычислительного кластера для БПЛА. Вычислительный кластер для БПЛА характеризуется динамической структурой (полевой) телекоммуникационной системы. Это обстоятельство делает необходимым, для целей управления, синтезировать такую модель кластера, которая позволяет, с одной стороны, вычислить эффективный план организации вычислительного процесса, а с другой - затратить на эти вычисления минимальные ресурсы (вчастности - время). Предлагается, в случае кластера для БПЛА, модель в терминах «стоимость - производительность» на основе (линейной) модели В. Леонтьева. Рис.2. Библиогр.:3назв.При розв’язанні деяких проблем, загальних для системи діючих БПЛА, наприклад завданьпаралельної обробки фото і відео кадрів, представляється доцільним оперативне проектування обчислювального кластера для БПЛА. Обчислювальний кластер для БПЛА характеризується динамічною структурою (польової) телекомунікаційної системи. Ця обставина робить необхідним для цілей управління синтезувати таку модель кластера, яка дозволяє,з одного боку, обчислити ефективний план організації обчислювального процесу, а з іншого -витратити на ці обчислення мінімальні ресурси (зокрема - час). Пропонується, у випадку кластера для БПЛА, класична модель за критерієм «вартість - продуктивність» на основі(лінійної) моделі В. Леонтьєва. Рис.2. Бібліогр.:3 наз

Development of High Granulated Straw Chambers of Large Sizes

We have developed the baseline design for the straw drift tube tracking detectors for high rate environment application. The low-mass inner straw elements and the technology of the multianode straws assembly was devised and checked. The prototype chamber was constructed and studied the granularity of similar chambers can be reduced to one cm2. Submitted to Physics of Elementary Particles and Atomic Nuclei, LettersComment: 6 pages, 10 figure

Characteristic features of the temperature dependence of the surface impedance in polycrystalline MgB2_2 samples

The real $R_s(T)$ and imaginary $X_s(T)$ parts of the surface impedance $Z_s(T)=R_s(T)+iX_s(T)$ in polycrystalline MgB$_2$ samples of different density with the critical temperature $T_c\approx 38$ K are measured at the frequency of 9.4 GHz and in the temperature range $5\le T<200$ K. The normal skin-effect condition $R_s(T)=X_s(T)$ at $T\ge T_c$ holds only for the samples of the highest density with roughness sizes not more than 0.1 $\mu$m. For such samples extrapolation $T\to 0$ of the linear at $T<T_c/2$ temperature dependences $\lambda_L(T)=X_s(T)/\omega\mu_0$ and $R_s(T)$ results in values of the London penetration depth $\lambda_L(0)\approx 600$ \AA and residual surface resistance $R_{res}\approx 0.8$ m$\Omega$. In the entire temperature range the dependences $R_s(T)$ and $X_s(T)$ are well described by the modified two-fluid model.Comment: 7 pages, 3 figures. Europhysics Letters, accepted for publicatio