3,152 research outputs found
A revised radiometric calibration for the Hinode/EIS instrument
A preliminary assessment of the in-flight radiometric calibration of the
Hinode EUV Imaging Spectrometer (EIS) is presented. This is done with the line
ratio technique applied to a wide range of observations of the quiet Sun,
active regions and flares from 2006 until 2012. The best diagnostic lines and
the relevant atomic data are discussed in detail. Radiances over the quiet Sun
are also considered, with comparisons with previous measurements. Some
departures in the shapes of the ground calibration responsivities are found at
the start of the mission. These shapes do not change significantly over time,
with the exception of the shorter wavelengths of the EIS short-wavelength (SW)
channel, which shows some degradation. The sensitivity of the SW channel at
longer wavelengths does not show significant degradation, while that of the
long-wavelength (LW) channel shows a significant degradation with time. By the
beginning of 2010 the responsivity of the LW channel was already a factor of
two or more lower than the values measured on the ground. A first-order
correction is proposed. With this correction, the main ratios of lines in the
two channels become constant to within a relative 20%, and the He II 256 A
radiances over the quiet Sun also become constant over time. This correction
removes long-standing discrepancies for a number of lines and ions, in
particular those involving the strongest Fe X, Fe XIII, Fe XIV, Fe XVII, and Fe
XXIV lines, where discrepancies of factors of more than two were found. These
results have important implications for various EIS science analyses, in
particular for measurements of temperatures, emission measures and elemental
abundances.Comment: Accepted for publication in A&A (under minor revision
Bonobos extract meaning from call sequences
This research was funded by a Leverhulme Trust Research Leadership Award and the Wissenschaftskolleg zu Berlin. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Studies on language-trained bonobos have revealed their remarkable abilities in representational and communication tasks. Surprisingly, however, corresponding research into their natural communication has largely been neglected. We address this issue with a first playback study on the natural vocal behaviour of bonobos. Bonobos produce five acoustically distinct call types when finding food, which they regularly mix together into longer call sequences. We found that individual call types were relatively poor indicators of food quality, while context specificity was much greater at the call sequence level. We therefore investigated whether receivers could extract meaning about the quality of food encountered by the caller by integrating across different call sequences. We first trained four captive individuals to find two types of foods, kiwi (preferred) and apples (less preferred) at two different locations. We then conducted naturalistic playback experiments during which we broadcasted sequences of four calls, originally produced by a familiar individual responding to either kiwi or apples. All sequences contained the same number of calls but varied in the composition of call types. Following playbacks, we found that subjects devoted significantly more search effort to the field indicated by the call sequence. Rather than attending to individual calls, bonobos attended to the entire sequences to make inferences about the food encountered by a caller. These results provide the first empirical evidence that bonobos are able to extract information about external events by attending to vocal sequences of other individuals and highlight the importance of call combinations in their natural communication system.Publisher PDFPeer reviewe
INTEREST RATES, PROMOTIONAL PRIZES AND COMPETITION IN THE BANKING INDUSTRY
Some Colombian commercial banks have used the strategy of offering promotional prizes in order to attract new savings customers. In this paper we develop a two-stage game model that allows us to understand the efects of this romotional strategy on the deposit interest rates, the deposit market shares and the intermediation spreads. We find that under this strategy it is possible for the bank that ofers the highest prize to segment the deposit market serving only customers that assign high subjective probabilities to winning prizes. More importantly we show that the bank that ofers the highest promotional prize not only pays the lowest deposit interest rate but also has the largest deposit market share and the widest intermediation spread.Banking Competition
GRMHD in axisymmetric dynamical spacetimes: the X-ECHO code
We present a new numerical code, X-ECHO, for general relativistic
magnetohydrodynamics (GRMHD) in dynamical spacetimes. This is aimed at studying
astrophysical situations where strong gravity and magnetic fields are both
supposed to play an important role, such as for the evolution of magnetized
neutron stars or for the gravitational collapse of the magnetized rotating
cores of massive stars, which is the astrophysical scenario believed to
eventually lead to (long) GRB events. The code is based on the extension of the
Eulerian conservative high-order (ECHO) scheme [Del Zanna et al., A&A 473, 11
(2007)] for GRMHD, here coupled to a novel solver for the Einstein equations in
the extended conformally flat condition (XCFC). We fully exploit the 3+1
Eulerian formalism, so that all the equations are written in terms of familiar
3D vectors and tensors alone, we adopt spherical coordinates for the conformal
background metric, and we consider axisymmetric spacetimes and fluid
configurations. The GRMHD conservation laws are solved by means of
shock-capturing methods within a finite-difference discretization, whereas, on
the same numerical grid, the Einstein elliptic equations are treated by
resorting to spherical harmonics decomposition and solved, for each harmonic,
by inverting band diagonal matrices. As a side product, we build and make
available to the community a code to produce GRMHD axisymmetric equilibria for
polytropic relativistic stars in the presence of differential rotation and a
purely toroidal magnetic field. This uses the same XCFC metric solver of the
main code and has been named XNS. Both XNS and the full X-ECHO codes are
validated through several tests of astrophysical interest.Comment: 18 pages, 9 figures, accepted for publication in A&
The EUV spectrum of the Sun: SOHO CDS NIS radiances during solar cycle 23
For the first time, we present and discuss EUV radiances of the solar
transition region (TR) and corona obtained during a solar cycle. The
measurements were obtained with the SOHO/coronal diagnostic spectrometer (CDS)
during the period from 1996 to 2010. We find that limb-brightening
significantly affects any characterisation of the solar radiances. We present
the limb-brightening function for the main lines and find that it does not
change measurably during the cycle. We confirm earlier findings that the
radiance histogram of the cooler lines have a well defined, log-normal
quiet-Sun component, although our results differ from previous ones. The width
of the lowest-radiance log-normal distribution is constant along the cycle.
Both the analysis of the centre-to-limb variation and of the radiance
statistical distribution point to a constant QS emission along solar cycle 23.
Lines formed above 1 MK are dramatically affected by the presence of active
regions, and indeed, no "quiet Sun" region can be defined during periods of
maximum activity. Much of the irradiance variability in lines formed below 1.5
MK is due to a change in the emitting area. For hotter lines, the emitting area
saturates to almost 100% of full solar disk at the maximum of activity, while
simultaneously the emission due to active regions increases by more than an
order of magnitude. We show that structures around active regions, sometimes
referred to as dark halos or dark canopies, are common and discuss their
similarities and differences with coronal holes. In particular, we show how
they are well visible in TR lines, contrary to coronal holes.Comment: 15 pages, 11 figures, 2 tables; in press in: Astronomy & Astrophysic
Solar microflares: a case study on temperatures and the Fe XVIII emission
In this paper, we discuss the temperature distribution and evolution of a
microflare, simultaneously observed by Hinode XRT, EIS, and SDO AIA. We find
using EIS lines that during peak emission the distribution is nearly isothermal
and peaked around 4.5 MK. This temperature is in good agreement with that
obtained from the XRT filter ratio, validating the use of XRT to study these
small events, invisible by full-Sun X-ray monitors such as GOES. The increase
in the estimated Fe XVIII emission in the AIA 94 {\AA} band can mostly be
explained with the small temperature increase from the background temperatures.
The presence of Fe XVIII emission does not guarantee that temperatures of 7 MK
are reached, as is often assumed. We also revisit with new atomic data the
temperatures measured by a SoHO SUMER observation of an active region which
produced microflares, also finding low temperatures (3 - 4 MK) from an Fe XVIII
/ Ca XIV ratio.Comment: 12-13 pages, 17 figures (22 eps-files), 4 tables, accepted by
Astronomy and Astrophysic
Modelling ion populations in astrophysical plasmas: carbon in the solar transition region
The aim of this work is to improve the modelling of ion populations in higher
density, lower temperature astrophysical plasmas, of the type commonly found in
lower solar and stellar atmospheres. Ion population models for these regions
frequently employ the coronal approximation, which assumes conditions more
suitable to the upper solar atmosphere, where high temperatures and lower
densities prevail. Using the coronal approximation for modelling the solar
transition region gives theoretical lines intensities for the Li-like and
Na-like isoelectronic sequences which can be factors of 2-5 times lower than
observed. The works of Burgess & Summers (1969) and Nussbaumer & Storey (1975)
showed the important part ions in excited levels play when included in the
modelling. Their models, however, used approximations for the atomic rates to
determine the ion balance. Presented here is the first stage in updating these
earlier models of carbon by using rates from up-to-date atomic calculations and
more recent photo-ionising radiances for the quiet Sun. Where such atomic rates
are not readily available, in the case of electron-impact direct ionisation and
excitation--auto-ionisation, new calculations have been made and compared to
theoretical and experimental studies. The effects each atomic process has on
the ion populations as density changes is demonstrated, and final results from
the modelling are compared to the earlier works. Lastly, the new results for
ion populations are used to predict line intensities for the solar transition
region in the quiet Sun, and these are compared with predictions from
coronal-approximation modelling and with observations. Significant improvements
in the predicted line intensities are seen in comparison to those obtained from
zero-density modelling of carbon.Comment: Draft accepted by A&A, 13 pages, 15 figure
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