ABSTRACT
The bulk of available stellar activity observations is frequently checked for the manifestation of signs in comparison with the known characteristic of solar magnetic modulation. The problem ...is that stellar activity records are usually an order of magnitude shorter than available observations of solar activity variation. Therefore, the resolved time-scales of stellar activity are insufficient to decide reliably that a cyclic variation for a particular star is similar to the well-known 11-yr sunspot cycles. As a result, recent studies report several stars with double or multiple cycles which serve to challenge the underlying theoretical understanding. This is why a consistent method to separate ‘true’ cycles from stochastic variations is required. In this paper, we suggest that a conservative method, based on the best practice of wavelet analysis previously applied to the study of solar activity, for studying and interpreting the longest available stellar activity record – photometric monitoring of V833 Tau for more than 100 yr. We find that the observed variations of V833 Tau with time-scales of 2–50 yr should be comparable with the known quasi-periodic solar mid-term variations, whereas the true cycle of V833 Tau, if it exists, should be of about a century or even longer. We argue that this conclusion does not contradict the expectations from the stellar dynamo theory.
The paper presents the results of studying light curves of the star HD 168443 obtained from the ground-based and space photometric observations within the ASAS, KWS surveys, and the
Hipparcos
mission ...from 1990 to 2020. During 30 years of observations, the average annual brightness of the star remained constant within the measurement errors, the mean
V
-value was 6
m
.96. Using the dense data series in 2007–2009, the photometric period of 34.7 days was found, and the low-amplitude brightness variability was studied with this period. We determined epochs and amplitude of rotational modulation produced by the development of active regions. These parameters do not change during 2–5 rotations of the star. The amplitude of the rotational modulation increases in 2007 before the epoch of maximum brightness. The star was the brightest in 2009, its
V
-magnitude was 6
m
.92. The location of starspots on the surface of the star during these epochs is also considered.
Exposure to stress activates the hypothalamic–pituitary–adrenal axis and leads to increased levels of glucocorticoid (GC) hormones. Prolonged elevation of GC levels causes neuronal dysfunction, ...decreases the density of synapses, and impairs neuronal plasticity. Decreased sensitivity to glucocorticoids (glucocorticoid resistance) that develops as a result of chronic stress is one of the characteristic features of stress-induced psychopathologies. In this article, we reviewed the published data on proposed molecular mechanisms that contribute to the development of glucocorticoid resistance in brain, including changes in the expression of the glucocorticoid receptor (GR) gene, biosynthesis of GR isoforms, and GR posttranslational modifications. We also present data on alterations in the expression of the
FKBP5
gene encoding the main component of cell ultra-short negative feedback loop of GC signaling regulation. Recent discoveries on stressand GRinduced changes in epigenetic modification patterns as well as normalizing action of antidepressants are discussed. GR and
FKBP5
gene polymorphisms associated with stress-induced psychopathologies are described, and their role in glucocorticoid resistance is discussed.
The International Geomagnetic Reference Field (IGRF) model is a combination of the several models developed by independent groups of scientists using different approaches for the selection of input ...data and methods for calculating harmonic coefficients. This approach allows for mutual comparison of individual models and for their combination to obtain the most reliable values of the harmonic coefficients. This letter provides a brief description of methods for building the IZMIRAN Earth’s main magnetic field model, submitted to the IAGA Working Group V-MOD for creating IGRF-13. Special efforts were made to obtain as uniform coverage of the entire Earth’s surface as possible with observations. The surface was divided into a grid of approximately equal cells. Then the data for geomagnetically quiet intervals were placed in the corresponding cells and a median filter was applied to select the data in each cell. Spherical harmonic coefficients up to degree 13 were calculated for the interval 2014-Jan to 2019-Aug with a time step of 10 days and extrapolated to 01.01.2010.
Chronic stress is the leading risk factor of a broad range of severe psychopathologies. Nonetheless, the molecular mechanisms triggering these pathological processes are not well understood. In our ...study, we investigated the effects of 15-day social defeat stress (SDS) on the genome-wide landscape of trimethylation at the 4th lysine residue of histone H3 (H3K4me3) and on the transcriptome in the prefrontal cortex of mice that were reared normally (group SDS) or subjected to maternal separation early in life (group MS+SDS). The mice with the history of stress early in life showed increased susceptibility to SDS in adulthood and demonstrated long-lasting genome-wide alterations in gene expression and splicing as well as in the H3K4me3 epigenetic landscape in the prefrontal cortex. Thus, the high-throughput techniques applied here allowed us to simultaneously detect, for the first time, genome-wide epigenetic and transcriptional changes in the murine prefrontal cortex that are associated with both chronic SDS and increased susceptibility to this stressor.
•Mice with a history of stress early in life showed increased susceptibility to SDS in adulthood•Stress early in life caused specific alterations in gene transcription, alternative splicing, and the H3K4me3 landscape in the prefrontal cortex under SDS in adulthood•The changes in the epigenetic landscape after SDS did not correlate with the level of gene expression
We have carried out a search for flares from the analysis of light curves for 12 active G, K, and M dwarfs. As sources of data we used ground-based observations in 2000–2020 from the photometric ...databases ASAS, SuperWASP, KWS. Events of low-amplitude brightening (∆
V
< 0.25 mag), which possibly could be flares, were revealed for 11 stars. A large number of such increases in brightness were found on K dwarfs. Events of increasing in
V
-magnitudes to 0.5 mag or more were detected on light curves of one G star, BE Cet, and two M dwarfs. For three flares we could follow their development with time. We have estimated the duration of these flares; they lasted more than an hour, but less than 3 hours. In most cases we could not determine a lifetime of the suggested flares, but we believe that most of the probable flares on the investigated cool dwarfs are short-lived, on the order of several minutes.
The behavior of the average annual luminosity of K–M dwarfs OU Gem, EQ Vir, V1005 Ori and AU Mic was studied at time intervals of several decades. The main sources of photometric data for 1989–2019 ...were the Hipparcos, ASAS, KWS databases. An analysis of long-term series showed that the average annual brightness of all stars varies cyclical. The durations of possible cycles for OU Gem, V1005 Ori and AU Mic are 40–42 years, for EQ Vir—16.6 years, and amplitudes of cycles are of 0.09–0.2
m
. The selected stars belong to the group of red dwarfs for which the average surface magnetic field 〈
B
〉 exceeds of several kilogauss. We examined the type of the relationship between the parameters of the cycle, its duration and amplitude, for 9 stars with 〈
B
〉 < 4 kG. A tendency to increasing of the amplitude and duration of the cycle when the value of 〈
B
〉 decrease has been noted. It may be suggested that with an increasing of the surface magnetic field, it becomes more uniform and the level of activity changes in this case in less degrees than on stars with strong local fields concentrated in large spots.
We consider a class of strictly pseudohyperbolic equations with lower order terms. The solvability of the Cauchy problem in Sobolev spaces with special weights is established. The uniqueness of the ...solution is proven and estimates are obtained.
The paper considers the creep of a textile-reinforced thermoplastic composite with a glass filler under the action of a combined short-term cyclic and long-term static tensile loads at room ...temperature. The investigations were carried out on glass-fabric-reinforced polypropylene specimens, which were made by autoclave molding. The creep of the composite was experimentally investigated under a cyclic load at different amplitudes. The creep kernel has been calculated from experimental data according to the Boltzmann superposition principle. Other creep models of materials have been analyzed based on data from a review. The laws governing the short-term creep of polypropylene under the action of a static load have been determined. A behaviorial model of the composite under investigation under the considered conditions is proposed. Numerical calculations have been made with the aid of the proposed model using experimental results taken from other works, and a good agreement between them has been established. The peculiarities of the creep of textile-reinforced polypropylene under the considered conditions have been determined. The range of application of the model has been determined.
Evolutionary status of the active star PZ Mon Pakhomov, Yu V; Chugai, N N; Bondar, N I ...
Monthly notices of the Royal Astronomical Society,
01/2015, Letnik:
446, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We use original spectra and available photometric data to recover the parameters of the stellar atmosphere of PZ Mon, formerly referred to as an active red dwarf. The derived effective temperature ...T... = 4700 K and gravity log g = 2.8 suggest that PZ Mon is a K2III giant. Stellar atmosphere parameters (T... and log g), along with evolutionary tracks, are used to estimate a stellar mass of ...1.5 M... and a radius of ...7.7 R... The angular radius derived by the infrared flux method, when combined with the linear radius, suggests a distance of 250 plus or minus 70 pc, a factor of 2.5 smaller than that suggested by the Hipparcos parallax. The red giant status of PZ Mon is confirmed by its carbon and nitrogen abundance. The spectrum reveals pronounced He i 5876-A absorption and H... emission, indicating a robust chromosphere. The International Ultraviolet Explorer (IUE) spectrum is found to contain a transition-layer emission line of C iv 1550 A. The C iv and X-ray luminosities are typical of RS CVn stars. The extended set of available photometric data confirms a period of 34.14 d, presumably related to stellar rotation. We found variations of radial velocity with amplitude of ...8 km s..., which could be caused by orbital motion. (ProQuest: ... denotes formulae/symbols omitted.)
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