3,369 research outputs found

    Verification of time-reversibility requirementfor systems satisfying the Evans-Searles fluctuation theorem

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    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

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    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 RHK+^{+}_{\rm{HK}} 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 RHK+^{+}_{\rm{HK}} values are derived from the respective S-indices and related to the rotation periods in various B−VB-V-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index RHK+^{+}_{\rm{HK}} 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 RHK+^{+}_{\rm{HK}}, 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

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    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

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    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 RHK′R_\mathrm{HK}' and RHK+R_\mathrm{HK}^{+}, as well as SMWOS_\mathrm{MWO}, if the B−VB-V-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

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    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 (∼15\sim 15~yr) for a solar-like star with a well-studied chromospheric cycle (with a period of ∼8\sim 8~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 ∼5\sim 5 (excluding evident flares, as in the June 2002 observation) and a period of 7.3±1.57.3\pm 1.5~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

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    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

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    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

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    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

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    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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