3,064 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&
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
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
Role of intralaminar thalamic neurons during spike and wave discharges in a genetic rat model of absence epilepsy
Absence Epilepsie ist eine nicht konvulsive Form der Epilepsie. Während eines Anfalls treten im Elektroenzephalogramm (EEG) Spitze-Welle-Entladungen (SWDs) auf. Die vorliegende Studie untersuchte die Rolle des centrolateralen Nucleus (CL) und paracentralen Nucleus (PC) während SWDs. Die Experimente wurden in vivo an Wistar albino Glaxo Ratten von Rijswijk (WAG/Rij) durchgeführt. Extrazelluläre Ableitungen zeigen, dass während SWDs die Neurone im CL burst-ähnliche Aktivität aufweisen. Die Neurone im PC zeigen tonische Aktivität, die während der Spikekomponente der SWDs gehemmt wird. Mikroiontophoreseexperimente weisen nach, dass GABAA und GABAB Rezeptoren an der neuronalen Aktivität während der SWD beteiligt sind. Mikrostimulationsexperimente zeigen, dass im PC SWDs in Abhängigkeit von der Frequenz entweder hervorgerufen oder unterdrückt werden können. Insgesamt zeigen die Ergebnisse, dass neuronale Aktivität im PC unterdrückt werden muss, damit SWDs auftreten können
Perfect magnetohydrodynamics as a field theory
We propose the generally covariant action for the theory of a self-coupled
complex scalar field and electromagnetism which by virtue of constraints is
equivalent, in the regime of long wavelengths, to perfect magnetohydrodynamics
(MHD). We recover from it the Euler equation with Lorentz force, and the
thermodynamic relations for a prefect fluid. The equation of state of the
latter is related to the scalar field's self potential. We introduce 1+3
notation to elucidate the relation between MHD and field variables. In our
approach the requirement that the scalar field be single valued leads to the
quantization of a certain circulation in steps of ; this feature leads,
in the classical limit, to the conservation of that circulation. The
circulation is identical to that in Oron's generalization of Kelvin's
circulation theorem to perfect MHD; we here characterize the new conserved
helicity associated with it. We also demonstrate the existence for MHD of two
Bernoulli-like theorems for each spacetime symmetry of the flow and geometry;
one of these is pertinent to suitably defined potential flow. We exhibit the
conserved quantities explicitly in the case that two symmetries are
simultaneously present, and give examples. Also in this case we exhibit a new
conserved MHD circulation distinct from Oron's, and provide an example.Comment: RevTeX, 16 pages, no figures; clarifications added and typos
corrected; version to be published in Phys. Rev.
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&
The grand canonical ABC model: a reflection asymmetric mean field Potts model
We investigate the phase diagram of a three-component system of particles on
a one-dimensional filled lattice, or equivalently of a one-dimensional
three-state Potts model, with reflection asymmetric mean field interactions.
The three types of particles are designated as , , and . The system is
described by a grand canonical ensemble with temperature and chemical
potentials , , and . We find that for
the system undergoes a phase transition from a
uniform density to a continuum of phases at a critical temperature . For other values of the chemical potentials the system
has a unique equilibrium state. As is the case for the canonical ensemble for
this model, the grand canonical ensemble is the stationary measure
satisfying detailed balance for a natural dynamics. We note that , where is the critical temperature for a similar transition in
the canonical ensemble at fixed equal densities .Comment: 24 pages, 3 figure
Non-commuting coordinates, exotic particles, & anomalous anyons in the Hall effect
Our previous ``exotic'' particle, together with the more recent anomalous
anyon model (which has arbitrary gyromagnetic factor ) are reviewed. The
non-relativistic limit of the anyon generalizes the exotic particle which has
to any .When put into planar electric and magnetic fields, the Hall
effect becomes mandatory for all , when the field takes some critical
value.Comment: A new reference added. Talk given by P. Horvathy at the International
Workshop "Nonlinear Physics: Theory and Experiment. III. July'04, Gallipoli
(Lecce, Italy). To be published in Theor. Math. Phys. Latex 9 pages, no
figure
The relation between stellar magnetic field geometry and chromospheric activity cycles – II The rapid 120-day magnetic cycle of <i>τ</i> Bootis
One of the aims of the BCool programme is to search for cycles in other stars and to understand how similar they are to the Sun. In this paper, we aim to monitor the evolution of τ Boo’s large-scale magnetic field using high-cadence observations covering its chromospheric activity maximum. For the first time, we detect a polarity switch that is in phase with τ Boo’s 120-day chromospheric activity maximum and its inferred X-ray activity cycle maximum. This means that τ Boo has a very fast magnetic cycle of only 240 days. At activity maximum τ Boo’s large-scale field geometry is very similar to the Sun at activity maximum: it is complex and there is a weak dipolar component. In contrast, we also see the emergence of a strong toroidal component which has not been observed on the Sun, and a potentially overlapping butterfly pattern where the next cycle begins before the previous one has finished
Corner Exponents in the Two-Dimensional Potts Model
The critical behavior at a corner in two-dimensional Ising and three-state
Potts models is studied numerically on the square lattice using transfer
operator techniques. The local critical exponents for the magnetization and the
energy density for various opening angles are deduced from finite-size scaling
results at the critical point for isotropic or anisotropic couplings. The
scaling dimensions compare quite well with the values expected from conformal
invariance, provided the opening angle is replaced by an effective one in
anisotropic systems.Comment: 11 pages, 2 eps-figures, uses LaTex and eps
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