Multi-object spectroscopy of stars in the CoRoT fields I: Early-type stars in the CoRoT-fields IRa01, LRa01, LRa02

Observations of giant stars indicate that the frequency of giant planets is much higher for intermediate-mass stars than for solar-like stars. Up to now all known planets of giant stars orbit at relatively far distances from their host stars. It is not known whether intermediate-mass stars also had many close-in planets when they were on the main sequence, which were then engulfed when the star became a giant star. To understand the formation and evolution of planets it is therefore important to find out whether main-sequence stars of intermediate-mass have close-in planets or not. A survey for transiting planets of intermediate-mass stars would be ideal to solve this question, because the detection of transiting planets is not affected by the rapid rotation of these stars. As a first step for an efficient survey we need to identify intermediate-mass stars in the CoRoT-fields, which can then be used as an input list. To compile the input list we derived the spectral types of essentially all O, B and A stars down to 14.5 mag in the CoRoT fields IRa01, LRa01, LRa02 taken with the multi-object spectrograph AAOmega. We determined the spectral types by comparing the spectra with template spectra from a library. In total we identify 1856 A and B stars that have been observed with CoRoT. Given the number of planets that have been detected in these fields amongst late-type stars, we estimate that there are one to four transiting planets of intermediate-mass stars waiting to be discovered. Our survey not only allows us to carry out a dedicated planet search programme but is also essential for any types of studies of the light curves of early-type stars in the CoRoT database. We also show that it would be possible to extend the survey to all fields that CoRoT has observed using photometrically determined spectral types.Comment: 57 pages, 12 figures, accepted for publication in Astronomy and Astrophysic

The influence of thermal evolution in the magnetic protection of terrestrial planets

Magnetic protection of potentially habitable planets plays a central role in determining their actual habitability and/or the chances of detecting atmospheric biosignatures. Here we develop a thermal evolution model of potentially habitable Earth-like planets and super-Earths (SEs). Using up-to-date dynamo-scaling laws, we predict the properties of core dynamo magnetic fields and study the influence of thermal evolution on their properties. The level of magnetic protection of tidally locked and unlocked planets is estimated by combining simplified models of the planetary magnetosphere and a phenomenological description of the stellar wind. Thermal evolution introduces a strong dependence of magnetic protection on planetary mass and rotation rate. Tidally locked terrestrial planets with an Earth-like composition would have early dayside magnetopause distances between 1.5 and 4.0 Rp , larger than previously estimated. Unlocked planets with periods of rotation ~1 day are protected by magnetospheres extending between 3 and 8 Rp . Our results are robust in comparison with variations in planetary bulk composition and uncertainties in other critical model parameters. For illustration purposes, the thermal evolution and magnetic protection of the potentially habitable SEs GL 581d, GJ 667Cc, and HD 40307g were also studied. Assuming an Earth-like composition, we found that the dynamos of these planets are already extinct or close to being shut down. While GL 581d is the best protected, the protection of HD 40307g cannot be reliably estimated. GJ 667Cc, even under optimistic conditions, seems to be severely exposed to the stellar wind, and, under the conditions of our model, has probably suffered massive atmospheric losses

Exploitation Perspective Index as a support of the management of the transformer fleet

This paper presents an alternative approach to the Transformer Assessment Index (TAI) by proposing a relatively simple rating method called the Exploitation Perspective Index (EPI). The method provides two numerical indicators: the first reflects the overall technical condition of the particular unit, and the second shows the condition of the unit in the context of the entire fleet. The objective of the EPI method is to support the decision-making process regarding the technical condition assessment of each of the transformers in the target population, considering not only technical but also economic aspects of transformer maintenance. Application of the method is described step by step, including input data, parametrization of the weights, and interpretation of the output results it provides. The proposed method is evaluated by two representative use cases and compared with two other methods. As a result, EPI confirms its applicability, and it has already been successfully implemented by the electric power industry. EPI can be potentially freely adopted for any transformer fleet, as well as for the specific situation of the utility, by adjusting the relevant parameters.Web of Science2321art. no. 868

The Application of Selected Hierarchical Clustering Methods for Classification the Acoustic Emission Signals Generated by Partial Discharges

The paper presents the results of the application of the hierarchical clustering methods for the classification of the acoustic emission (AE) signals generated by eight basic forms of partial discharges (PD), which can occur in paper-oil insulation of power transformers. Based on the registered AE signals from the particular PD forms, using a frequency descriptor in the form of the power spectral density (PSD) of the signal, their representation in the form of the set of points on plane XY was created. Next, these sets were subjected to analysis using research algorithms consisting of selected clustering methods. Based on the suggested numeric performance indicators, the analysis of the degree of reproduction of the actual distribution of points showing the particular time waveforms of the AE signals from eight adopted PD forms (PD classes) in the obtained clusters was carried out. As a result of the analyses carried out, the clustering algorithms of the highest effectiveness in the identification of all eight PD classes, classified simultaneously, where indicated. Within the research carried out, an attempt to draw general conclusions as to the selection of the most effective hierarchical clustering method studied and the similarity function to be used for classification of the selected basic PD forms

Application of Selected Machine Learning Techniques for Identification of Basic Classes of Partial Discharges Occurring in Paper-Oil Insulation Measured by Acoustic Emission Technique

The paper reports the results of a comparative assessment concerned with the effectiveness of identifying the basic forms of partial discharges (PD) measured by the acoustic emission technique (AE), carried out by application of selected machine learning methods. As part of the re-search, the identification involved AE signals registered in laboratory conditions for eight basic classes of PDs that occur in paper-oil insulation systems of high-voltage power equipment. On the basis of acoustic signals emitted by PDs and by application of the frequency descriptor that took the form of a signal power density spectrum (PSD), the assessment involved the possibility of identifying individual types of PD by the analyzed classification algorithms. As part of the research, the results obtained with the use of five independent classification mechanisms were analyzed, namely: k-Nearest Neighbors method (kNN), Naive Bayes Classification, Support Vector Machine (SVM), Random Forests and Probabilistic Neural Network (PNN). The best results were achieved using the SVM classification tuned with polynomial core, which obtained 100% accuracy. Similar results were achieved with the kNN classifier. Random Forests and Naïve Bayes obtained high accuracy over 97%. Throughout the study, identification algorithms with the highest effectiveness in identifying specific forms of PD were established

Influence of the Cable Accessories Installing Method on the Partial Discharge Activity in Medium Voltage Cables

This article proposes a method to modify the construction of a medium voltage (MV) heat shrinkable cable termination in cases of atypical damage to the shields of cross-linked polyethylene (XLPE) insulated cables. The proposed solutions include a modified method of assembling electric field control coating. An attempt was made to check the effect of such damage to the shields of MV cables with XLPE insulation on the level of occurrence of partial discharges within the cable termination. The investigations included testing the XRUHAKXS 1 × 240/25 cable type using the electric method (ME) and high frequency (HF) method with sinusoidal AC test voltage. As a result of the measurements, the values of total charges in the period and phase-resolved partial discharge (PRPD) patterns were obtained. The presented experimental results show the influence of the damage of the semiconducting coating surface on the occurrence of a defect in the cable termination without a modified method of control mantissa pinning. We suggest new methods of assembling MV cable accessories in the case of the presented coating damage in MV cable insulation

Eosinophilic pulmonary vasculitis as a manifestation of the hyperinflammatory phase of COVID-19.

No abstract availabl

A planet in a polar orbit of 1.4 solar-mass star

Although more than a thousand transiting extrasolar planets have been discovered, only very few of them orbit stars that are more massive than the Sun. The discovery of such planets is interesting, because they have formed in disks that are more massive but had a shorter life time than those of solar-like stars. Studies of planets more massive than the Sun thus tell us how the properties of the proto-planetary disks effect the formation of planets. Another aspect that makes these planets interesting is that they have kept their original orbital inclinations. By studying them we can thus find out whether the orbital axes planets are initially aligned to the stars rotational axes, or not. Here we report on the discovery of a planet of a 1.4 solar-mass star with a period of 5.6 days in a polar orbit made by CoRoT. This new planet thus is one of the few known close-in planets orbiting a star that is substantially more massive than the Sun