1,800 research outputs found
Spot activity of the RS CVn star {\sigma} Geminorum
We model the photometry of RS CVn star Geminorum to obtain new
information on the changes of the surface starspot distribution, i.e., activity
cycles, differential rotation and active longitudes. We use the previously
published Continuous Periods Search-method (CPS) to analyse V-band differential
photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated
Telescope at the Fairborn Observatory. The CPS-method divides data into short
subsets and then models the light curves with Fourier-models of variable orders
and provides estimates of the mean magnitude, amplitude, period and light curve
minima. These light curve parameters are then analysed for signs of activity
cycles, differential rotation and active longitudes. We confirm the presence of
two previously found stable active longitudes, synchronised with the orbital
period d and find eight events where the active longitudes
are disrupted. The epochs of the primary light curve minima rotate with a
shorter period d than the orbital motion. If the
variations in the photometric rotation period were to be caused by differential
rotation, this would give a differential rotation coefficient of . The presence of two slightly different periods of active regions may
indicate a superposition of two dynamo modes, one stationary in the orbital
frame and the other one propagating in the azimuthal direction. Our estimate of
the differential rotation is much higher than previous results. However,
simulations show that this can be caused by insufficient sampling in our data.Comment: 10 pages, 6 figures. Submitted to A&
Effects of Scots pine paternal genotypes of two contiguous seed orchards on the budset and frost hardening of first-year progeny
In Scots pine (Pinus sylvestris L.), it has been shown that the parental conditions have a role in the phenological variation among first-year seedlings. For this reason, it is argued that they should be comprehensively controlled before estimating the parental genotype effects. This controlled-cross study examined the effects of a set of fathers of Scots pines on the timing of budset and autumn frost hardening of first-year seedlings. The paternal genotypes had either a northern or southern provenance, but had spent a period of over 25 years as grafts in a shared climatic environment in two closely located southern orchards. Pollen applied in the crosses was collected from these orchards in one year and all the maternal genotypes were pollinated in only one seed orchard. The results of freeze tests and budset observations of the consequent progeny were analysed and additionally compared with results obtained using seedlings from seed lots of natural forests in order to estimate the ability of northern paternal genotypes to maintain a northern effect under southern conditions. This environmentally controlled study demonstrated a significant effect of the paternal genotype on the budset and autumn frost hardening of first-year seedling of Scots pine. With the applied study design, no significant indication of an environmental influence on the effect of the paternal genotype was obtained. The accuracy of the observations is discussed. It is concluded that the results suggest a minor role of mutability in the effects of Scots pine paternal genotypes.Peer reviewe
Rediscovery of Geophilus carpophagus Leach (Chilopoda: Geophilomorpha) from Finland
Geophilus carpophagus Leach, 1815 has long been listed as regionally extinct from Finland. Here we report its rediscovery after decades of absence
Surface distribution of small-scale magnetic field on the active cool star LQ Hydrae
It is well known that small-scale magnetism dominates the surface magnetic
field topologies of active late-type stars. However, little information is
available on the spatial distribution of this key magnetic field component.
Here, we take advantage of the recently developed magnetic field diagnostic
procedure relying on the magnetic intensification of iron atomic lines in the
optical. We extend this methodology from measuring a single average field
strength value to simultaneous Doppler imaging reconstruction of the
two-dimensional maps of temperature and magnetic field strength. We applied
this novel surface mapping approach to two spectroscopic data sets of the young
active Sun-like star LQ Hya. For both epochs, we found a fairly uniform field
strength distribution, apart from a latitudinal trend of the field strength
increasing from 1.5-2.0 kG at low latitudes to 3.0-3.5 kG, close to the
rotational poles. This distribution of the small-scale field does not display a
clear correlation with the locations of temperature spots or the global
magnetic field structure reconstructed for the same epochs.Comment: 7 pages, 6 figures; accepted for publication in A&
The quantum phase slip phenomenon in superconducting nanowires with high-impedance environment
Quantum phase slip (QPS) is the particular manifestation of quantum
fluctuations of the order parameter of a current-biased quasi-1D
superconductor. The QPS event(s) can be considered a dynamic equivalent of
tunneling through conventional Josephson junction containing static in space
and time weak link(s). At low temperatures T<<Tc the QPS effect leads to finite
resistivity of narrow superconducting channels and suppresses persistent
currents in tiny nanorings. Here we demonstrate that the quantum tunneling of
phase may result in Coulomb blockade: superconducting nanowire, imbedded in
high-Ohmic environment, below a certain bias voltage behaves as an insulator.Comment: 3 pages, 3 figure
Direct Observation of Josephson Capacitance
The effective capacitance has been measured in the split Cooper pair box
(CPB) over its phase-gate bias plane. Our low-frequency reactive measurement
scheme allows to probe purely the capacitive susceptibility due to the CPB band
structure. The data are quantitatively explained using parameters determined
independently by spectroscopic means. In addition, we show in practice that the
method offers an efficient way to do non-demolition readout of the CPB quantum
state.Comment: 4 page
Hidden magnetic fields of young suns
Global magnetic fields of active solar-like stars are, nowadays, routinely detected with spectropolarimetric measurements and are mapped with Zeeman Doppler imaging (ZDI). However, due to the cancellation of opposite field polarities, polarimetry only captures a tiny fraction of the magnetic flux and cannot assess the overall stellar surface magnetic field if it is dominated by a small-scale component. The analysis of Zeeman broadening in high-resolution intensity spectra can reveal these hidden complex magnetic fields. Historically, there were very few attempts to obtain such measurements for G dwarf stars due to the difficulty of disentangling the Zeeman effect from other broadening mechanisms affecting spectral lines. Here, we developed a new magnetic field diagnostic method based on relative Zeeman intensification of optical atomic lines with different magnetic sensitivity. By using this technique, we obtained 78 field strength measurements for 15 Sun-like stars, including some of the best-studied young solar twins. We find that the average magnetic field strength Bf drops from 1.3-2.0 kG in stars younger than about 120 Myr to 0.2-0.8 kG in older stars. The mean field strength shows a clear correlation with the Rossby number and with the coronal and chromospheric emission indicators. Our results suggest that magnetic regions have roughly the same local field strength B approximate to 3.2 kG in all stars, with the filling factor f of these regions systematically increasing with stellar activity. In comparing our results with the spectropolarimetric analyses of global magnetic fields in the same stars, we find that ZDI recovers about 1% of the total magnetic field energy in the most active stars. This figure drops to just 0.01% for the least active targets.Peer reviewe
Why the Realist-Instrumentalist Debate about Rational Choice Rests on a Mistake
Within the social sciences, much controversy exists about which status should be ascribed to the rationality assumption that forms the core of rational choice theories. Whilst realists argue that the rationality assumption is an empirical claim which describes real processes that cause individual action, instrumentalists maintain that it amounts to nothing more than an analytically set axiom or ‘as if’ hypothesis which helps in the generation of accurate predictions. In this paper, I argue that this realist-instrumentalist debate about rational choice theory can be overcome once it is realised that the rationality assumption is neither an empirical description nor an ‘as if’ hypothesis, but a normative claim
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