3,369 research outputs found
Verification of time-reversibility requirementfor systems satisfying the Evans-Searles fluctuation theorem
The Evans-Searles fluctuation theorem (ESFT) has been shown to be applicable in the near- and far-from-equilibrium regimes for systems with both constant and time-dependent external fields. The derivations of the ESFT have assumed that the external field has a definite parity under a time-reversal mapping. In the present paper, we confirm that the time-reversibility of the system dynamics is a necessary condition for the ESFT to hold. The manner in which the ESFT fails for systems that are not time-reversible is presented, and results are shown which demonstrate that systems which fail to satisfy the ESFT may still satisfy the Crooks relation (CR)
Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars
The connection between stellar rotation, stellar activity, and convective
turnover time is revisited with a focus on the sole contribution of magnetic
activity to the Ca II H&K emission, the so-called excess flux, and its
dimensionless indicator R in relation to other stellar
parameters and activity indicators. Our study is based on a sample of 169
main-sequence stars with directly measured Mount Wilson S-indices and rotation
periods. The R values are derived from the respective S-indices
and related to the rotation periods in various -colour intervals. First,
we show that stars with vanishing magnetic activity, i.e. stars whose excess
flux index R approaches zero, have a well-defined,
colour-dependent rotation period distribution; we also show that this rotation
period distribution applies to large samples of cool stars for which rotation
periods have recently become available. Second, we use empirical arguments to
equate this rotation period distribution with the global convective turnover
time, which is an approach that allows us to obtain clear relations between the
magnetic activity related excess flux index R, rotation
periods, and Rossby numbers. Third, we show that the activity versus Rossby
number relations are very similar in the different activity indicators. As a
consequence of our study, we emphasize that our Rossby number based on the
global convective turnover time approaches but does not exceed unity even for
entirely inactive stars. Furthermore, the rotation-activity relations might be
universal for different activity indicators once the proper scalings are used.Comment: 13 pages, 7 figures, accepted for publication in A&
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&
The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
Aims. A large number of Calcium Infrared Triplet (IRT) spectra are expected
from the GAIA- and CARMENES missions. Conversion of these spectra into known
activity indicators will allow analysis of their temporal evolution to a better
degree. We set out to find such a conversion formula and to determine its
robustness.
Methods. We have compared 2274 Ca II IRT spectra of active main-sequence F to
K stars taken by the TIGRE telescope with those of inactive stars of the same
spectral type. After normalizing and applying rotational broadening, we
subtracted the comparison spectra to find the chromospheric excess flux caused
by activity. We obtained the total excess flux, and compared it to established
activity indices derived from the Ca II H & K lines, the spectra of which were
obtained simultaneously to the infrared spectra.
Results. The excess flux in the Ca II IRT is found to correlate well with
and , as well as , if the
-dependency is taken into account. We find an empirical conversion formula
to calculate the corresponding value of one activity indicator from the
measurement of another, by comparing groups of datapoints of stars with similar
B-V.Comment: 16 pages, 15 figures. Accepted for publication in Astronomy &
Astrophysic
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
Fluctuation Theorem in Rachet System
Fluctuation Theorem(FT) has been studied as far from equilibrium theorem,
which relates the symmetry of entropy production. To investigate the
application of this theorem, especially to biological physics, we consider the
FT for tilted rachet system. Under, natural assumption, FT for steady state is
derived.Comment: 6 pages, 2 figure
Fluctuation Theorem for Hamiltonian Systems - Le Chatelier's Principle
For thermostatted dissipative systems the Fluctuation Theorem gives an
analytical expression for the ratio of probabilities that the time averaged
entropy production in a finite system observed for a finite time, takes on a
specified value compared to the negative of that value. Hitherto it had been
thought that the presence of some thermostatting mechanism was an essential
component of any system which satisfies a Fluctuation Theorem. In the present
paper we show that a Fluctuation Theorem can be derived for purely Hamiltonian
systems, with or without applied dissipative fields.Comment: 10 pages including 4 figures, submitted for publicatio
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
Negative Entropy Production in Oscillatory Processes
Linear irreversible thermodynamics asserts that the instantaneous local
spontaneous entropy production is always nonnegative. However for a
viscoelastic fluid this is not always the case. Given the fundamental status of
the Second Law, this presents a problem. We provide a new derivation of the
Second Law, from first principles, which is valid for the appropriately time
averaged entropy production allowing the instantaneous entropy production to be
negative for short intervals of time. We show that time averages (rather than
instantaneous values) of the entropy production are nonnegative. We illustrate
this using molecular dynamics simulations of oscillatory shear.Comment: 5 pages 2 figure
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