2,508 research outputs found
Coronal X-ray emission and planetary irradiation in HD 209458
HD 209458 is one of the benchmark objects in the study of hot Jupiter
atmospheres and their evaporation through planetary winds. The expansion of the
planetary atmosphere is thought to be driven by high-energy EUV and X-ray
irradiation. We obtained new Chandra HRC-I data, which unequivocally show that
HD 209458 is an X-ray source. Combining these data with archival XMM-Newton
observations, we find that the corona of HD 209458 is characterized by a
temperature of about 1 MK and an emission measure of 7e49 cm^-3, yielding an
X-ray luminosity of 1.6e27 erg/s in the 0.124-2.48 keV band. HD 209458 is an
inactive star with a coronal temperature comparable to that of the inactive Sun
but a larger emission measure. At this level of activity, the planetary
high-energy emission is sufficient to support mass-loss at a rate of a few
times 1e10 g/s.Comment: Accepted for publication in A&
Fifteen years in the high-energy life of the solar-type star HD 81809. XMM-Newton observations of a stellar activity cycle
Aims. The data set of the long-term XMM-Newton monitoring program of HD 81809
is analyzed to study its X-ray cycle, to investigate if the latter is related
to the chromospheric one, to infer the structure of the corona of HD 81809, and
to explore if the coronal activity of HD 81809 can be ascribed to phenomena
similar to the solar ones and, therefore, considered an extension of the solar
case. Methods. We analyze the observations of HD 81809 performed with
XMM-Newton with a regular cadence of 6 months from 2001 to 2016 and
representing one of the longest available observational baseline (~yr)
for a solar-like star with a well-studied chromospheric cycle (with a period of
~yr). We investigate the modulation of coronal luminosity and
temperature and its relation with the chromospheric cycle. We interpret the
data in terms of a mixture of solar-like coronal regions, adopting a
methodology originally proposed to study the Sun as an X-ray star. Results. The
observations show a well-defined regular cyclic modulation of the X-ray
luminosity that reflects the activity level of HD 81809. The data covers
approximately two cycles of coronal activity; the modulation has an amplitude
of a factor of (excluding evident flares, as in the June 2002
observation) and a period of ~yr, consistent with that of the
chromospheric cycle. We demonstrate that the corona of HD 81809 can be
interpreted as an extension of the solar case and it can be modeled with a
mixture of solar-like coronal regions along the whole cycle. The activity level
is mainly determined by a varying coverage of very bright active regions,
similar to cores of active regions observed in the Sun. Evidence of unresolved
significant flaring activity is present especially in proximity of cycle
maxima.Comment: 11 pages, 5 Figures, A&A accepte
Quality assurance in higher education - meta-evaluationof multi-stage evaluation procedures in Germany
Systematic procedures for quality assurance and improvement through evaluation have been in place in Western Europe since the mid 1980s and in Germany since the mid 1990s. As studies in Europe and beyond show that multi-stage evaluation procedures as the main quality assurance instrument for evaluation of teaching and learning in higher education institutions have proved reliable and have gained acceptance, in Germany (as well as in other countries) the evaluation of teaching and learning through internal and external evaluations has long come under the fire of criticism. Our results of the first comprehensive and representative investigation of procedures for the evaluation of teaching and learning in Germany show that former participants in the evaluations (reviewers and those reviewed) are satisfied all in all with the multi-stage procedure. They are convinced that the goals of quality assurance and improvement were achieved. Suggestions for improving the procedures target individual aspects, such as, for example, the composition of the review panel. Against this background, it makes sense to perform regular quality assessments of the procedures for quality assurance and improvemen
Psychophysiological correlates of peritraumatic dissociative responses in survivors of life-threatening cardiac events
The psychophysiological startle response pattern associated with peritraumatic dissociation (DISS) was studied in 103 survivors of a life-threatening cardiac event (mean age 61.0 years, SD 13.95). Mean time period since the cardiac event was 37 (79 IQD) months. All patients underwent a psychodiagnostic evaluation (including the Peritraumatic Dissociative Experiences Questionnaire) and a psychophysiological startle experience which comprised the delivery of 15 acoustic startle trials. Magnitude and habituation to trials were measured by means of electromyogram (EMG) and skin conductance responses (SCR). Thirty-two (31%) subjects were indexed as patients with a clinically significant level of DISS symptoms. High-level DISS was associated with a higher magnitude of SCR (ANOVA for repeated measures p = 0.017) and EMG (p = 0.055) and an impaired habituation (SCR slope p = 0.064; EMG slope p = 0.005) in comparison to subjects with no or low DISS. In a subgroup analysis, high-level DISS patients with severe post-traumatic stress disorder (PTSD; n = 11) in comparison to high-level DISS patients without subsequent PTSD (n = 19) exhibited higher EMG amplitudes during all trials (repeated measures analysis of variance IF = 5.511, p = 0.026). The results demonstrate exaggerated startle responses in SCR and EMG measures - an abnormal defensive response to high-intensity stimuli which indicates a steady state of increased arousal. DISS patients without PTSD exhibited balanced autonomic responses to the startle trials. DISS may, therefore, unfold malignant properties only in combination with persistent physiological hyperarousability. Copyright (C) 2002 S. Karger AG, Basel
Validation of coupled neutronic/thermal-hydraulic codes for VVER reactors - final report - FIKS-CT-2001-00166
Noninvasive monitoring of liver fat during treatment with GLPâ1 analogues and SGLTâ2 inhibitors in a realâworld setting
Introduction: Patients with NAFLD have a twoâfold increased risk of diabetes, and conversely, NAFLD affects up to 80% of patients with type 2 diabetes. Due to the coâoccurrence of both diseases and the lack of approved pharmacotherapy for NAFLD, the antiâsteatogenic potential of diabetesârelated drugs is being explored. In this study, we aim to monitor liver fat noninvasively during treatment with SGLTâ2 inhibitors or GLPâ1 analogues in a realâworld setting. Methods: Overall, 39 patients (49% women, age 57.7 ± 10.9 years) with type 2 diabetes and hepatic steatosis (defined by controlled attenuation parameter [CAP] values â„ 215 dB/m) were observed for 6 months and routinely monitored with respect to hepatic fat contents and liver stiffness (VCTE); body composition (BIA); and blood biochemistry, including liver function tests (LFTs), serum lipids and glucose metabolism markers. Results: Median liver fat contents were significantly (P = .026) reduced by 9% in patients taking either SGLTâ2 (n = 22) or GLPâ1 (n = 17) for 6 months (absolute median CAP decrease: â32 dB/m [â58 to 32 dB/m]). In parallel, serum ALT and ÎłâGT activities decreased significantly (P = .002 and P = .049, respectively). These improvements were accompanied by significant (P < .0001) changes to body weight and BMI (â2.5 ± 3.3 kg and â0.9 ± 1.2 kg/m2, respectively) and glucose homeostasis, with significant reductions in HbA1c and fasting plasma glucose (FDG) (both P < .0001). Of note, significant reductions of intrahepatic lipid contents occured in patients receiving SGLTâ2 inhibitors only. Conclusions: In this realâworld observational evaluation of fatty liver monitored noninvasively in patients with type 2 diabetes treated with either SGLT2 or GLPâ1, improvements in measures of hepatic steatosis, glucose and weight parameters were observed after 6 months, with significant reductions of intrahepatic lipid contents seen specifically in the SGLT2 subgroup
Image restoration using the chiral Potts spin-glass
We report on the image reconstruction (IR) problem by making use of the
random chiral q-state Potts model, whose Hamiltonian possesses the same gauge
invariance as the usual Ising spin glass model. We show that the pixel
representation by means of the Potts variables is suitable for the gray-scale
level image which can not be represented by the Ising model. We find that the
IR quality is highly improved by the presence of a glassy term, besides the
usual ferromagnetic term under random external fields, as very recently pointed
out by Nishimori and Wong. We give the exact solution of the infinite range
model with q=3, the three gray-scale level case. In order to check our
analytical result and the efficiency of our model, 2D Monte Carlo simulations
have been carried out on real-world pictures with three and eight gray-scale
levels.Comment: RevTex 13 pages, 10 figure
A multi-wavelength view of the multiple activity cycles of ~Eridani
Eridani is a highly active young K2 star with an activity cycle of
about three years established using Ca II H & K line index measurements
(S_MWO). This relatively short cycle has been demonstrated to be consistent
with X-ray and magnetic flux measurements. Recent work suggested a change in
the cyclic behaviour. Here we report new X-ray flux and S_MWO measurements and
also include S_MWO measurements from the historical Mount Wilson program. This
results in an observational time baseline of over 50 years for the S_MWO data
and of over 7 years in X-rays. Moreover, we include Ca II infrared triplet
(IRT) index measurements (S_IRT) from 2013-2022 in our study. With the extended
X-ray data set, we can now detect the short cycle for the first time using a
periodogram analysis. Near-simultaneous S_MWO data and X-ray fluxes, which are
offset by 20 days at most, are moderately strongly correlated when only the
lowest activity state (concerning short-term variability) is considered in both
diagnostics. In the S_MWO data, we find strong evidence for a much longer cycle
of about 34 years and an 11-year cycle instead of the formerly proposed
-year cycle in addition to the known 3-year cycle. The superposition of the
three periods naturally explains the recent drop in S_MWO measurements. The two
shorter cycles are also detected in the S_IRT data, although the activity
cycles exhibit lower amplitudes in the S_IRT than in the S_MWO data. Finally,
the rotation period of Eri can be found more frequently in the S_MWO
as well as in the S_IRT data for times near the minimum of the long cycle. This
may be explained by a scenario in which the filling factor for magnetically
active regions near cycle maximum is too high to allow for notable short-term
variations.Comment: accepted to A&
Thyroid Hormones Regulate Selenoprotein Expression and Selenium Status in Mice
Impaired expression of selenium-containing proteins leads to perturbed thyroid hormone (TH) levels, indicating the central importance of selenium for TH homeostasis. Moreover, critically ill patients with declining serum selenium develop a syndrome of low circulating TH and a central downregulation of the hypothalamus-pituitary-thyroid axis. This prompted us to test the reciprocal effect, i.e., if TH status would also regulate selenoprotein expression and selenium levels. To investigate the TH dependency of selenium metabolism, we analyzed mice expressing a mutant TH receptor α1 (TRα1+m) that confers a receptor-mediated hypothyroidism. Serum selenium was reduced in these animals, which was a direct consequence of the mutant TRα1 and not related to their metabolic alterations. Accordingly, hyperthyroidism, genetically caused by the inactivation of TRÎČ or by oral TH treatment of adult mice, increased serum selenium levels in TRα1+m and controls, thus demonstrating a novel and specific role for TRα1 in selenium metabolism. Furthermore, TH affected the mRNA levels for several enzymes involved in selenoprotein biosynthesis as well as serum selenoprotein P concentrations and the expression of other antioxidative selenoproteins. Taken together, our results show that TH positively affects the serum selenium status and regulates the expression of several selenoproteins. This demonstrates that selenium and TH metabolism are interconnected through a feed-forward regulation, which can in part explain the rapid parallel downregulation of both systems in critical illness
Variational method and duality in the 2D square Potts model
The ferromagnetic q-state Potts model on a square lattice is analyzed, for
q>4, through an elaborate version of the operatorial variational method. In the
variational approach proposed in the paper, the duality relations are exactly
satisfied, involving at a more fundamental level, a duality relationship
between variational parameters. Besides some exact predictions, the approach is
very effective in the numerical estimates over the whole range of temperature
and can be systematically improved.Comment: 20 pages, 5 EPS figure
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