7,789 research outputs found
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
High precision studies of soft dipole mode in two-neutron halo nuclei: He case
The "soft dipole" E1 strength function is calculated for the transition from
the He ground state to the continuum He++. The
calculations were performed within the hyperspherical harmonics formalism. The
sensitivity of the results to the He ground state structure and to final
state interactions, are analyzed. The large-basis calculations show the
reliably converged results for soft dipole strength function and for momentum
correlations of the ^{6}\mbox{He} \rightarrow \, ^{4}He++ dissociation
products. Transition mechanisms are analyzed based on the momentum
correlations. The comparison with experimental data is provided.Comment: 16 pages, 17 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
СONCEPT AND CALCULATION OF THE LIMIT TRANSVERSE SIZE OF CAPILLARIES
Porous medium are products of processing in food, agricultural, chemical and many other industries. Calculations of processes with wet porous medium are based on capillary properties of the liquid in a pore space. The capillary properties of liquids in porous media are established in pore models in the form of thin tubes of circular or slit transverse sections. The intensity of the processes occurring in it depends on the nature of the filling of the pore space with liquid. Filling with liquid and the formation of a capillary layer is possible only in small pores. However, there is no analytical justification for the transverse pore size, more than which it cannot be filled with liquid by capillary forces. With this in mind, the concept of the limiting transverse size of a capillary for a liquid under conditions of complete wetting is introduced. The limiting size calculation is based on two conditions: the shape of the axial section of the meniscus surface has the appearance of a semicircle and its extremum point is located at the level of the free surface of the fluid supplying the capillary. A capillary column cannot form in larger pores. The absence of formulas for calculating capillaries of the limiting sizes can introduce a significant error into the analytical calculation of the moisture content in the capillary layer of a liquid in porous media and moisture transfer processes. The aim of the study was to obtain formulas for calculating the limiting (largest) sizes of capillaries of a circular, flat slit section and annular transverse sections with complete wetting of their walls. For the conditions above, it was identified that the limiting distance between the walls was independent from annular capillary diameter. The formulas for the limiting transverse sizes of the flat slit and annular capillaries turned out to be the same under the assumptions above. This indicates a weak dependence of the limiting size of a slit capillary on the curvature of its transverse section. Examples of calculations of capillaries of the limiting sizes are performed.Porous medium are products of processing in food, agricultural, chemical and many other industries. Calculations of processes with wet porous medium are based on capillary properties of the liquid in a pore space. The capillary properties of liquids in porous media are established in pore models in the form of thin tubes of circular or slit transverse sections. The intensity of the processes occurring in it depends on the nature of the filling of the pore space with liquid. Filling with liquid and the formation of a capillary layer is possible only in small pores. However, there is no analytical justification for the transverse pore size, more than which it cannot be filled with liquid by capillary forces. With this in mind, the concept of the limiting transverse size of a capillary for a liquid under conditions of complete wetting is introduced. The limiting size calculation is based on two conditions: the shape of the axial section of the meniscus surface has the appearance of a semicircle and its extremum point is located at the level of the free surface of the fluid supplying the capillary. A capillary column cannot form in larger pores. The absence of formulas for calculating capillaries of the limiting sizes can introduce a significant error into the analytical calculation of the moisture content in the capillary layer of a liquid in porous media and moisture transfer processes. The aim of the study was to obtain formulas for calculating the limiting (largest) sizes of capillaries of a circular, flat slit section and annular transverse sections with complete wetting of their walls. For the conditions above, it was identified that the limiting distance between the walls was independent from annular capillary diameter. The formulas for the limiting transverse sizes of the flat slit and annular capillaries turned out to be the same under the assumptions above. This indicates a weak dependence of the limiting size of a slit capillary on the curvature of its transverse section. Examples of calculations of capillaries of the limiting sizes are performed
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
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