Characterization of Degenerate Configurations in Attitude Determination of Three-Vehicle Heterogeneous Formations

The existence of multiple solutions to an attitude determination problem impacts the design of estimation schemes, potentially increasing the errors by a significant value. It is therefore essential to identify such cases in any attitude problem. In this paper, the cases where multiple attitudes satisfy all constraints of a three-vehicle heterogeneous formation are identified. In the formation considered herein, the vehicles measure inertial references and relative line-of-sight vectors. Nonetheless, the line of sight between two elements of the formation is restricted, and these elements are denoted as deputies. The attitude determination problem is characterized relative to the number of solutions associated with each configuration of the formation. There are degenerate and ambiguous configurations that result in infinite or exactly two solutions, respectively. Otherwise, the problem has a unique solution. The degenerate configurations require some collinearity between independent measurements, whereas the ambiguous configurations result from symmetries in the formation measurements. The conditions which define all such configurations are determined in this work. Furthermore, the ambiguous subset of configurations is geometrically interpreted resorting to the planes defined by specific measurements. This subset is also shown to be a zero-measure subset of all possible configurations. Finally, a maneuver is simulated to illustrate and validate the conclusions. As a result of this analysis, it is concluded that, in general, the problem has one attitude solution. Nonetheless, there are configurations with two or infinite solutions, which are identified in this work.

Зависимость характеристик узких линий люминесценции в наноалмазах от параметров возбуждения и температуры

The influence of the excitation parameters and temperature on the spectral characteristics of narrow photoluminescence lines in nanodiamonds obtained by chemical vapor deposition is investigated. It is shown that the ratio of the line intensities in the spectrum depends on the wavelength and power of the excitation radiation. For some lines, with increasing power, a shift in the position of their maximum and broadening is also observed. After irradiation of nanodiamonds with a laser beam with a power density of ~1.2·105 W/cm2, the relative line intensities change. With increasing temperature in the range 79 - 300 K, temperature quenching of their intensity is observed.

Impact of intrinsic polarization of Sgr A* historical flares on (polarization) properties of their X-ray echoes

ABSTRACT Reflection of X-ray emission on molecular clouds in the inner ∼100 pc of our Galaxy reveals that, despite being extremely quiet at the moment, our supermassive black hole Sgr A* should have experienced bright flares of X-ray emission in the recent past. Thanks to the improving characterization of the reflection signal, we are able to infer parameters of the most recent flare(s) (age, duration, and luminosity) and relative line-of-sight disposition of the brightest individual molecular complexes. We show that combining these data with measurements of polarization in the reflected X-ray continuum will not only justify Sgr A* as the primary source but also allow deriving intrinsic polarization properties of the flare emission. This will help to identify radiation mechanisms and underlying astrophysical phenomena behind them. For the currently brightest reflecting molecular complex, Sgr A, the required level of sensitivity might be already accessible with upcoming X-ray polarimeters.

Effects of electron distribution anisotropy in spectroscopic diagnostics of solar flares

Aims. We analyzed effects of the bi-Maxwellian electron distribution representing electron temperature anisotropy along and across the magnetic field on the ionization and excitation equilibrium with consequences on the temperature diagnostics of the flare plasma. Methods. The bi-Maxwellian energy distributions were calculated numerically. Synthetic X-ray line spectra of the bi-Maxwellian distributions were calculated using non-Maxwellian ionization, recombination, excitation and de-excitation rates. Results. We found that the anisotropic bi-Maxwellian velocity distributions transform to the nonthermal energy distributions with a high-energy tail. Their maximum is shifted to lower energies and contains a higher number of the low-energy particles in comparison with the Maxwellian one. Increasing the deviation of the parameter p = T∥/T⊥ from 1, changes the shape of bi-Maxwellian distributions and ionization equilibrium, and relative line intensities also increase. The effects are more significant for the bi-Maxwellian distribution with T∥ > T⊥. Moreover, considering different acceleration mechanisms and collisional isotropization it is possible that the bi-Maxwellian distributions with high deviations from the Maxwellian distribution are more probable for those with p > 1 than for those with p < 1. Therefore, distributions with p > 1 can be much more easily diagnosed than those with p < 1. Furthermore, we compared the effects of the bi-Maxwellian distributions on the ionization equilibrium and temperature diagnostics with those for the κ-distributions obtained previously. We found that they are similar and at the present state it is difficult to distinguish between the bi-Maxwellian and κ-distributions from the line ratios.

Rotational and gas temperatures of molecular deuterium in a hollow cathode glow discharge

We report the results of optical emission spectroscopy measurements of rotational Trot and translational (gas) temperature of deuterium molecules. The light source was a low-voltage high-pressure hollow cathode (HC) glow discharge with titanium cathode operated in deuterium. The rotational temperature of excited electronic states of D2 was determined from the intensity distribution in the rotational structure of Q-branches of the two Fulcher-α diagonal bands: [ν′ = ν″ = 2] and [ν′ =ν″ = 3]. The population of the excited energy levels, determined from relative line intensities, was used to derive the radial distributions of the temperature of the excited and the ground state of the deuterium molecule.

Transition probabilities, oscillator strengths, and test ofJ-file sum rule for the 2p53p → 2p53s transition array in the neon emission spectra

In this work experimental transition probabilities, line strengths, and atomic oscillator strengths of 30 spectral lines corresponding to the 2p53p → 2p53s transitions array of neon have been deduced using a neon-filled hollow cathode lamp in conjunction with two spectrographs covering the wavelength region from 500 to 1000 nm. The experimental absolute transition probabilities have been determined using the relative intensity method and lifetimes of the excited states. The transition probabilities have been converted to the line strengths data and used for testing the J-file sum rule. Relative line strengths of all the lines have been computed to determine the oscillator strength values. The measured transition probabilities, oscillator strengths, and relative line strengths agree well with the previously reported data.

Properties of satellite galaxies in nearby groups

We studied the variation of stellar mass and various star-formation characteristics of satellite galaxies in a volume limited sample of nearby groups as a function of their group-centric distance and of their relative line-of-sight velocity in the group rest frame. We found clear radial dependencies, e.g. massive, red and passive satellites being distributed predominantly near the center of composite group. We also found some evidence of velocity modulation of star-forming properties of satellite galaxies near the group virial radius. We conclude that using kinematical data, it should be feasible to separate dynamical classes of bound, in-falling and 'backsplash' satellite galaxies.

On the use of two hydrogen bands for spectroscopic temperature measurement in a low-pressure gas discharge

We report the results of the optical emission spectroscopy measurements of rotational Trot and translational temperature Ttr of hydrogen molecules. The light source was hollow cathode glow discharge with titanium cathode operated in hydrogen at low pressure. The rotational temperature of excited electronic states of H2 was determined either from the relative line intensities of R branch of the GK → B band or from the P, Q and R-branches of the Fulcher-α diagonal band. The population of excited energy levels, determined from the relative line intensities was used to derive rotational temperature of the ground state of hydrogen molecule.