26 research outputs found
Magnetic cycles at different ages of stars
We study the different patterns of interannual magnetic variability in stars
on or near the lower main sequence, approximately solar-type (G-K dwarf) stars
in time series of 36 years from the Mount Wilson Observatory Ca\,{\sc ii}\,H\&K
survey. Our main aim is to search for correlations between cycles, activity
measures and ages. Time-frequency analysis has been used to discern and reveal
patterns and morphology of stellar activity cycles, including multiple and
changing cycles, in the datasets. Both the results from short-term Fourier
transform and its refinement using the Choi-Williams distribution, with better
frequency resolution, are presented in this study. Rotational periods of the
stars were derived using multi-frequency Fourier analysis.From the studied 29
stars we found at least one activity cycle on 28 of them. Twelve stars, with
longer rotational periods ( days) have simple, smooth cycles, and
the rest of the stars, with on-average much faster rotation (
days) show complex and sometimes vigorously changing, multiple cycles. The
cycles are longer and quite uniform in the first group ( years),
while are generally shorter and with greater variety in the second one
(). There is a clear age division between stars with smooth and
complex cycles that follows the known separation between the older and younger
stars at around 2 to 3~Gyr of age.Comment: Accepted to Astronomy and Astrophysic
New skeletal tuberculosis cases in past populations from Western Hungary (Transdanubia)
The distribution, antiquity and epidemiology of tuberculosis (TB) have previously been studied in osteoarchaeological material in the eastern part of Hungary, mainly on the Great Plain. The purpose of this study is to map the occurrence of skeletal TB in different centuries in the western part of Hungary, Transdanubia, and to present new cases we have found. Palaeopathological analysis was carried out using macroscopic observation supported by radiographic and molecular methods. A large human osteoarchaeological sample (n = 5684) from Transdanubian archaeological sites ranging from the 2nd to the 18th centuries served as a source of material. Spinal TB was observed in seven individuals (in three specimens with Pott's disease two of which also had cold abscess) and hip TB was assumed in one case. The results of DNA for Mycobacterium tuberculosis were positive in seven of the eight cases identified by paleopathology, and negative in the assumed case of hip TB. However, the molecular results are consistent with highly fragmented DNA, which limited further analysis. Based on the present study and previously published cases, osteotuberculosis was found in Transdanubia mainly during the 9th–13th centuries. However, there are no signs of TB in many other 9th–13th century sites, even in those that lie geographically close to those where osteotuberculous cases were found. This may be due to a true absence of TB caused by the different living conditions, way of life, or origin of these populations. An alternative explanation is that TB was present in some individuals with no typical paleopathology, but that death occurred before skeletal morphological features could develop
Token Jumping in minor-closed classes
Given two -independent sets and of a graph , one can ask if it
is possible to transform the one into the other in such a way that, at any
step, we replace one vertex of the current independent set by another while
keeping the property of being independent. Deciding this problem, known as the
Token Jumping (TJ) reconfiguration problem, is PSPACE-complete even on planar
graphs. Ito et al. proved in 2014 that the problem is FPT parameterized by
if the input graph is -free.
We prove that the result of Ito et al. can be extended to any
-free graphs. In other words, if is a -free
graph, then it is possible to decide in FPT-time if can be transformed into
. As a by product, the TJ-reconfiguration problem is FPT in many well-known
classes of graphs such as any minor-free class
A case of spinal tuberculosis from the Middle Ages in Transylvania (Romania)
Study Design: Case report. Objective: To characterise the paleopathology presented in the skeleton of a 45-50-year-old male indicative of tuberculous spondylitis and to confirm by the detection of ancient DNA. Summary of Background Data: Tuberculosis (TB) is an infectious disease prevalent in both present and ancient human populations. The disease is primarily located within the lungs, so although characacteristic bone lesions can lead to a clear diagnosis, skeletal TB occurs in only 5-6% of TB infections, even in historical cases. In addition, the visual appearance of human skeletal remains may be influenced by the environmental conditions at the burial site. However, it is important to recognise ancient skeletal TB, because this can provide important data on the history of Mycobacterium tuberculosis and gives an unique opportunity for physicians to observe the natural outcome of the infection from the pre-antibiotic era. Methods: Paleopathological analysis was carried out using careful visual observation supported by ancient DNA analysis. Approximately 60 mg of bone powder from rib fragments was examined and DNA from the M. tuberculosis complex was detected by PCR targeting specific genetic loci of the IS6110 and IS1081 regions. Results: The skeleton is part of a human osteoarchaeological collection (n=274) from the 12th-13th century Transylvanian archaeological site of Peteni, in modern-day Romania. The individual, a 45-50-year-old male, showed gross pathology typical of tuberculous spondylitis. The paleopathological diagnosis was supported by analysis for M. tuberculosis complex ancient DNA. Conclusions: This case demonstrates that TB was present in Transylvania (Romania) during the 12-13th century and adds to the growing body of knowledge on the history of this disease
Superflares on the late-type giant KIC 2852961 -- Scaling effect behind flaring at different energy levels
The most powerful superflares reaching 10erg bolometric energy are
from giant stars. The mechanism behind flaring is supposed to be the magnetic
reconnection, which is closely related to magnetic activity including
starspots. However, it is poorly understood, how the underlying magnetic dynamo
works and how the flare activity is related to the stellar properties which
eventually control the dynamo action. We analyse the flaring activity of KIC
2852961, a late-type giant star, in order to understand how the flare
statistics are related to that of other stars with flares and superflares and
what the role of the observed stellar properties in generating flares is. We
search for flares in the full Kepler dataset of the star by an automated
technique together with visual inspection. We set a final list of 59 verified
flares during the observing term. We calculate flare energies for the sample
and perform a statistical analysis. The stellar properties of KIC 2852961 are
revised and a more consistent set of parameters are proposed. The cumulative
flare energy distribution can be characterized by a broken power-law, i.e. on
the log-log representation the distribution function is fitted by two linear
functions with different slopes, depending on the energy range fitted. We find
that the total flare energy integrated over a few rotation periods correlates
with the average amplitude of the rotational modulation due to starspots.
Flares and superflares seem to be the result of the same physical mechanism at
different energetic levels, also implying that late-type stars in the main
sequence and flaring giant stars have the same underlying physical process for
emitting flares. There might be a scaling effect behind generating flares and
superflares in the sense that the higher the magnetic activity the higher the
overall magnetic energy released by flares and/or superflares.Comment: 14 pages, 17 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
The history of degenerate (bipartite) extremal graph problems
This paper is a survey on Extremal Graph Theory, primarily focusing on the
case when one of the excluded graphs is bipartite. On one hand we give an
introduction to this field and also describe many important results, methods,
problems, and constructions.Comment: 97 pages, 11 figures, many problems. This is the preliminary version
of our survey presented in Erdos 100. In this version 2 only a citation was
complete
Eclipsing spotted giant star with K2 and historical photometry
Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10% of their MS lifetime on the giant branch. Due to their rapid evolution it is difficult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims: We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods: We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRCIC photometric observations, to find the binary system parameters as well as robust spot models for the giant at two different epochs. Results: We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung-Russell diagram. We find that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions: We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic field, since we see greater differences in more active stars. Data presented in this paper are based on observations obtained at the HAT station at the Submillimeter Array of SAO, and the HAT station at the Fred Lawrence Whipple Observatory of SAO
Ischemic preconditioning protects the heart against ischemia-reperfusion injury in chronic kidney disease in both males and females
Highlights 1. There was no difference in the severity of chronic kidney disease (CKD) between male and female rats based on serum urea and creatinine levels as well as creatinine clearance. 2. As compared to females, males developed a more severe uremic cardiomyopathy characterized by left ventricular hypertrophy and fibrosis in CKD based on echocardiography and histology. 3. Following ischemia/reperfusion, infarct size was significantly smaller in females than in males, both in the sham-operated and CKD groups. 4. The infarct size-limiting effect of ischemic preconditioning (IPRE) was preserved in both sexes in CKD despite the more severe uremic cardiomyopathy in male CKD rats. 5. IPRE significantly increased the phospho-STAT3/STAT3 ratio in sham-operated, but not in CKD animals in both sexes
Investigation of the Antihypertrophic and Antifibrotic Effects of Losartan in a Rat Model of Radiation-Induced Heart Disease
Radiation-induced heart disease (RIHD) is a potential late side-effect of thoracic radiotherapy resulting in left ventricular hypertrophy (LVH) and fibrosis due to a complex pathomechanism leading to heart failure. Angiotensin-II receptor blockers (ARBs), including losartan, are frequently used to control heart failure of various etiologies. Preclinical evidence is lacking on the anti-remodeling effects of ARBs in RIHD, while the results of clinical studies are controversial. We aimed at investigating the effects of losartan in a rat model of RIHD. Male Sprague-Dawley rats were studied in three groups: (1) control, (2) radiotherapy (RT) only, (3) RT treated with losartan (per os 10 mg/kg/day), and were followed for 1, 3, or 15 weeks. At 15 weeks post-irradiation, losartan alleviated the echocardiographic and histological signs of LVH and fibrosis and reduced the overexpression of chymase, connective tissue growth factor, and transforming growth factor-beta in the myocardium measured by qPCR; likewise, the level of the SMAD2/3 protein determined by Western blot decreased. In both RT groups, the pro-survival phospho-AKT/AKT and the phospho-ERK1,2/ERK1,2 ratios were increased at week 15. The antiremodeling effects of losartan seem to be associated with the repression of chymase and several elements of the TGF-β/SMAD signaling pathway in our RIHD model