557 research outputs found
A photometric study of the hot exoplanet WASP-19b
Context: When the planet transits its host star, it is possible to measure
the planetary radius and (with radial velocity data) the planet mass. For the
study of planetary atmospheres, it is essential to obtain transit and
occultation measurements at multiple wavelengths.
Aims: We aim to characterize the transiting hot Jupiter WASP-19b by deriving
accurate and precise planetary parameters from a dedicated observing campaign
of transits and occultations.
Methods: We have obtained a total of 14 transit lightcurves in the r'-Gunn,
IC, z'-Gunn and I+z' filters and 10 occultation lightcurves in z'-Gunn using
EulerCam on the Euler-Swiss telescope and TRAPPIST. We have also obtained one
lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring
an occultation at 1.19 micron. We have performed a global MCMC analysis of all
new data together with some archive data in order to refine the planetary
parameters and measure the occultation depths in z'-band and at 1.19 micron.
Results: We measure a planetary radius of R_p = 1.376 (+/-0.046) R_j, a
planetary mass of M_p = 1.165 (+/-0.068) M_j, and find a very low eccentricity
of e = 0.0077 (+/-0.0068), compatible with a circular orbit. We have detected
the z'-band occultation at 3 sigma significance and measure it to be dF_z'= 352
(+/-116) ppm, more than a factor of 2 smaller than previously published. The
occultation at 1.19 micron is only marginally constrained at dF_1190 = 1711
(+/-745) ppm.
Conclusions: We have shown that the detection of occultations in the visible
is within reach even for 1m class telescopes if a considerable number of
individual events are observed. Our results suggest an oxygen-dominated
atmosphere of WASP-19b, making the planet an interesting test case for
oxygen-rich planets without temperature inversion.Comment: Published in Astronomy & Astrophysics. 11 pages, 11 figures, 4 table
Collective synchronization in populations of globally coupled phase oscillators with drifting frequencies
We generalize the Kuramoto model for coupled phase oscillators by allowing
the frequencies to drift in time according to Ornstein-Uhlenbeck dynamics. Such
drifting frequencies were recently measured in cellular populations of
circadian oscillator and inspired our work. Linear stability analysis of the
Fokker-Planck equation for an infinite population is amenable to exact solution
and we show that the incoherent state is unstable passed a critical coupling
strength K_c(\ga, \sigf), where \ga is the inverse characteristic drifting
time and \sigf the asymptotic frequency dispersion. Expectedly agrees
with the noisy Kuramoto model in the large \ga (Schmolukowski) limit but
increases slower as \ga decreases. Asymptotic expansion of the solution for
\ga\to 0 shows that the noiseless Kuramoto model with Gaussian frequency
distribution is recovered in that limit. Thus varying a single parameter allows
to interpolate smoothly between two regimes: one dominated by the frequency
dispersion and the other by phase diffusion.Comment: 5 pages, 5 figures, accepted in Phys. Rev.
Reactive Hall response
The zero temperature Hall constant R_H, described by reactive
(nondissipative) conductivities, is analyzed within linear response theory. It
is found that in a certain limit, R_H is directly related to the density
dependence of the Drude weight implying a simple picture for the change of sign
of charge carriers in the vicinity of a Mott-Hubbard transition. This novel
formulation is applied to the calculation of R_H in quasi-one dimensional and
ladder prototype interacting electron systems.Comment: 4 pages, 3 Postscript figure
Replica Symmetry Breaking in Attractor Neural Network Models
The phenomenon of replica symmetry breaking is investigated for the retrieval
phases of Hopfield-type network models. The basic calculation is done for the
generalized version of the standard model introduced by Horner [1] and by
Perez-Vicente and Amit [2] which can exhibit low mean levels of neural
activity. For a mean activity the Hopfield model is recovered. In
this case, surprisingly enough, we cannot confirm the well known one step
replica symmetry breaking (1RSB) result for the storage capacity which was
presented by Crisanti, Amit and Gutfreund [3] (\alpha_c^{\hbox{\mf
1RSB}}\simeq 0.144). Rather, we find that 1RSB- and 2RSB-Ans\"atze yield only
slightly increased capacities as compared to the replica symmetric value
(\alpha_c^{\hbox{\mf 1RSB}}\simeq 0.138\,186 and \alpha_c^{\hbox{\mf
2RSB}}\simeq 0.138\,187 compared to \alpha_c^{\hbox{\mf RS}}\simeq
0.137\,905), significantly smaller also than the value \alpha_c^{\hbox{\mf
sim}} = 0.145\pm 0.009 reported from simulation studies. These values still
lie within the recently discovered reentrant phase [4]. We conjecture that in
the infinite Parisi-scheme the reentrant behaviour disappears as is the case in
the SK-spin-glass model (Parisi--Toulouse-hypothesis). The same qualitative
results are obtained in the low activity range.Comment: Latex file, 20 pages, 8 Figures available from the authors upon
request, HD-TVP-94-
Transport and conservation laws
We study the lowest order conservation laws in one-dimensional (1D)
integrable quantum many-body models (IQM) as the Heisenberg spin 1/2 chain, the
Hubbard and t-J model. We show that the energy current is closely related to
the first conservation law in these models and therefore the thermal transport
coefficients are anomalous. Using an inequality on the time decay of current
correlations we show how the existence of conserved quantities implies a finite
charge stiffness (weight of the zero frequency component of the conductivity)
and so ideal conductivity at finite temperatures.Comment: 6 pages, Late
Nuclear Spin Relaxation in Hole Doped Two-Leg Ladders
The nuclear spin-lattice relaxation rate () has been measured in the
single crystals of hole doped two-leg ladder compounds
SrCaCuO and in the undoped parent material
LaCaCuO. Comparison of at the Cu and the two
distinct oxygen sites revealed that the major spectral weight of low frequency
spin fluctuations is located near for most of the
temperature and doping ranges investigated. Remarkable difference in the
temperature dependence of for the two oxygen sites in the heavily doped
=12 sample revealed reduction of singlet correlations between two legs in
place of growing antiferromagnetic correlations along the leg direction with
increasing temperature. Such behavior is most likely caused by the dissociation
of bound hole pairs.Comment: 4 pages. to appear in J. Phys. Soc. Jpn. Vol. 6
Investigating the role of auditory and visual sensory inputs for inducing relaxation during virtual reality stimulation
Stress is a part of everyday life which can be counteracted by evoking the relaxation response via nature scenes presented using immersive virtual reality (VR). The aim of this study was to determine which sensory aspect of immersive VR intervention is responsible for the greatest relaxation response. We compared four conditions: auditory and visual combined (audiovisual), auditory only, visual only, and no artificial sensory input. Physiological changes in heart rate, respiration rate, and blood pressure were recorded, while participants reported their preferred condition and awareness of people, noise, and light in the real-world. Over the duration of the stimulation, participants had the lowest heart rate during the audiovisual and visual only conditions. They had the steadiest decrease in respiration rate and the lowest blood pressure during the audiovisual condition, compared to the other conditions, indicating the greatest relaxation. Moreover, ratings of awareness indicated that participants reported being less aware of their surroundings (i.e., people, noise, light, real environment) during the audiovisual condition versus the other conditions (p < 0.001), with a preference for audiovisual inputs. Overall, the use of audiovisual VR stimulation is more effective at inducing a relaxation response compared to no artificial sensory inputs, or the independent inputs
The CORALIE survey for southern extra-solar planets. X. A Hot Jupiter orbiting HD73256
Recent radial-velocity measurements obtained with the CORALIE spectrograph on
the 1.2-m Euler Swiss telescope at La Silla unveil the presence of a new
Jovian-mass Hot Jupiter around HD 73256. The 1.85-M_Jup planet moves on an
extremely short-period (P=2.5486 d), quasi-circular orbit. The best Keplerian
orbital solution is presented together with an unsuccessful photometric
planetary-transit search performed with the SAT Danish telescope at La Silla.
Over the time span of the observations, the photometric follow-up of the
candidate has nevertheless revealed a P=14-d photometric periodicity
corresponding to the rotational period of the star. This variation as well as
the radial-velocity jitter around the Keplerian solution are shown to be
related to the fair activity level known for HD 73256.Comment: 7 pages, 7 figures. Accepted in A&
Memory and relatedness of transcriptional activity in mammalian cell lineages
Phenotypically identical mammalian cells often display considerable variability in transcript levels of individual genes. How transcriptional activity propagates in cell lineages, and how this varies across genes is poorly understood. Here we combine live-cell imaging of short-lived transcriptional reporters in mouse embryonic stem cells with mathematical modelling to quantify the propagation of transcriptional activity over time and across cell generations in phenotypically homogenous cells. In sister cells we find mean transcriptional activity to be strongly correlated and transcriptional dynamics tend to be synchronous; both features control how quickly transcriptional levels in sister cells diverge in a gene-specific manner. Moreover, mean transcriptional activity is transmitted from mother to daughter cells, leading to multi-generational transcriptional memory and causing inter-family heterogeneity in gene expression
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