222 research outputs found
Matching times of leading and following suggest cooperation through direct reciprocity during V-formation flight in ibis
One conspicuous feature of several larger bird species is their annual migration in V-shaped or echelon formation. When birds are flying in these formations, energy savings can be achieved by using the aerodynamic up-wash produced by the preceding bird. As the leading bird in a formation cannot profit from this up-wash, a social dilemma arises around the question of who is going to fly in front? To investigate how this dilemma is solved, we studied the flight behavior of a flock of juvenile Northern bald ibis (Geronticus eremita) during a human-guided autumn migration. We could show that the amount of time a bird is leading a formation is strongly correlated with the time it can itself profit from flying in the wake of another bird. On the dyadic level, birds match the time they spend in the wake of each other by frequent pairwise switches of the leading position. Taken together, these results suggest that bald ibis cooperate by directly taking turns in leading a formation. On the proximate level, we propose that it is mainly the high number of iterations and the immediacy of reciprocation opportunities that favor direct reciprocation. Finally, we found evidence that the animals' propensity to reciprocate in leading has a substantial influence on the size and cohesion of the flight formations
Quantitative atomic spectroscopy for primary thermometry
Quantitative spectroscopy has been used to measure accurately the
Doppler-broadening of atomic transitions in Rb vapor. By using a
conventional platinum resistance thermometer and the Doppler thermometry
technique, we were able to determine with a relative uncertainty of
, and with a deviation of from the
expected value. Our experiment, using an effusive vapour, departs significantly
from other Doppler-broadened thermometry (DBT) techniques, which rely on weakly
absorbing molecules in a diffusive regime. In these circumstances, very
different systematic effects such as magnetic sensitivity and optical pumping
are dominant. Using the model developed recently by Stace and Luiten, we
estimate the perturbation due to optical pumping of the measured value
was less than . The effects of optical pumping on atomic and
molecular DBT experiments is mapped over a wide range of beam size and
saturation intensity, indicating possible avenues for improvement. We also
compare the line-broadening mechanisms, windows of operation and detection
limits of some recent DBT experiments
Comments on alternative calculations of the broadening of spectral lines of neutral sodium by H-atom collisions
With the exception of the sodium D-lines recent calculations of line
broadening cross-sections for several multiplets of sodium by Leininger et al
(2000) are in substantial disagreement with cross-sections interpolated from
the tables of Anstee and O'Mara (1995) and Barklem and O'Mara (1997). The
discrepancy is as large as a factor of three for the 3p-4d multiplet. The two
theories are tested by using the results of each to synthesize lines in the
solar spectrum. It is found that generally the data from the theory of Anstee,
Barklem and O'Mara produce the best match to the observed solar spectrum. It is
found, using a simple model for reflection of the optical electron by the
potential barrier between the two atoms, that the reflection coefficient is too
large for avoided crossings with the upper states of subordinate lines to
contribute to line broadening, supporting the neglect of avoided ionic
crossings by Anstee, Barklem and O'Mara for these lines. The large
discrepancies between the two sets of calculations is a result of an
approximate treatment of avoided ionic crossings for these lines by Leininger
et al (2000).Comment: 18 pages, 5 ps figures included, to appear in J Phys B: At. Mol. Opt.
Phy
The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees
This paper reports on the spectroscopic investigation of 238 Cepheids in the
northern sky. Of these stars, about 150 are new to the study of the galactic
abundance gradient. These new Cepheids bring the total number of Cepheids
involved in abundance distribution studies to over 400. In this work we also
consider systematics between various studies and also those which result from
the choice of models. We find systematic variations exist at the 0.06 dex level
both between studies and model atmospheres. In order to control the systematic
effects our final gradients depend only on abundances derived herein. A simple
linear fit to the Cepheid data from 398 stars yields a gradient d[Fe/H]/dRG =
-0.062 \pm 0.002 dex/kpc which is in good agreement with previously determined
values. We have also reexamined the region of the "metallicity island" of Luck
et al. (2006). With the doubling of the sample in that region and our
internally consistent abundances, we find there is scant evidence for a
distinct island. We also find in our sample the first reported Cepheid (V1033
Cyg) with a pronounced Li feature. The Li abundance is consistent with the star
being on its red-ward pass towards the first giant branch.Comment: 66 pages including tables, 12 figures, Accepted Astronomical Journa
HD 65949: Rosetta Stone or Red Herring
HD 65949 is a late B star with exceptionally strong Hg II at 3984[A], but it
is not a typical HgMn star. The Re II spectrum is of extraordinary strength.
Abundances, or upper limits are derived here for 58 elements based on a model
with Teff = 13100K, and log(g) = 4.0. Even-Z elements through nickel show minor
deviations from solar abundances. Anomalies among the odd-Z elements through
copper are mostly small. Beyond the iron peak, a huge scatter is found. The
abundance pattern of the heaviest elements resembles the N=126 r-process peak
of solar material, though not in detail. We find a significant correlation of
the abundance excesses with second ionization potentials for elements with Z >
30. This indicates the relevance of photospheric or near-photospheric
processes. We explore a model with mass accretion of exotic material followed
by the more commonly accepted differentiation by diffusion. That model leads to
a number of predictions which challenge future work.
Likely primary and secondary masses are near 3.3 and 1.6 M(solar), with a
separation of ca. 0.25 AU. New atomic structure calculations are presented in
two appendices.Comment: Accepted by MNRAS: 16 pages, 5 figure
Falsification Of The Atmospheric CO2 Greenhouse Effects Within The Frame Of Physics
The atmospheric greenhouse effect, an idea that many authors trace back to
the traditional works of Fourier (1824), Tyndall (1861), and Arrhenius (1896),
and which is still supported in global climatology, essentially describes a
fictitious mechanism, in which a planetary atmosphere acts as a heat pump
driven by an environment that is radiatively interacting with but radiatively
equilibrated to the atmospheric system. According to the second law of
thermodynamics such a planetary machine can never exist. Nevertheless, in
almost all texts of global climatology and in a widespread secondary literature
it is taken for granted that such mechanism is real and stands on a firm
scientific foundation. In this paper the popular conjecture is analyzed and the
underlying physical principles are clarified. By showing that (a) there are no
common physical laws between the warming phenomenon in glass houses and the
fictitious atmospheric greenhouse effects, (b) there are no calculations to
determine an average surface temperature of a planet, (c) the frequently
mentioned difference of 33 degrees Celsius is a meaningless number calculated
wrongly, (d) the formulas of cavity radiation are used inappropriately, (e) the
assumption of a radiative balance is unphysical, (f) thermal conductivity and
friction must not be set to zero, the atmospheric greenhouse conjecture is
falsified.Comment: 115 pages, 32 figures, 13 tables (some typos corrected
Quantum oscillations in the kinetic energy density: Gradient corrections from the Airy gas
BNP controls early load-dependent regulation of SERCA through calcineurin
Heart failure is characterised by reduced expression of sarcoplasmic reticulum calcium-ATPase (SERCA) and increased expression of B-type natriuretic peptide (BNP). The present study was performed to investigate causality of this inverse relationship under in vivo conditions in the transversal aortic constriction mouse model (TAC). Left ventricular SERCA-mRNA expression was significantly upregulated in TAC by 32% after 6 h, but not different from sham after 24 h. Serum proANP and BNP levels were increased in TAC after 24 h (BNP +274%, p < 0.01; proANP +60%, p < 0.05), but only proANP levels were increased after 6 h (+182%, p < 0.01). cGMP levels were only increased 24 h after TAC (+307%, p < 0.01), but not 6 h after TAC. BNP infusion inhibited the increase in SERCA expression 6 h after TAC. In BNP-receptor-knockout animals (GC-A), the expression of SERCA was still significantly increased 24 h after TAC at the mRNA level by 35% (p < 0.05), as well as at the protein level by 25% (p < 0.05). MCIP expression as an indicator of calcineurin activity was regulated in parallel to SERCA after 6 and 24 h. MCIP-mRNA was increased by 333% 6 h after TAC, but not significantly different from sham after 24 h. In the GC-A-KO mice, MCIP-mRNA was significantly increased in TAC compared to WT after 24 h. In mice with BNP infusion, MCIP was significantly lower 6 h after TAC compared to control animals. In conclusion, mechanical load leads to an upregulation of SERCA expression. This is followed by upregulation of natriuretic peptides with subsequent suppression of SERCA upregulation. Elevated natriuretic peptides may suppress SERCA expression by inhibition of calcineurin activity via activation of GC-A
Net emission coefficients of argon iron plasmas with electron Stark widths scaled to experiments
Detecting Sunyaev-Zel'dovich clusters with PLANCK: II. Foreground components and optimised filtering schemes
The PLANCK mission is the most sensitive all-sky CMB experiment currently
planned. The High Frequency Instrument (HFI) will be especially suited for
observing clusters of galaxies by their thermal Sunyaev-Zel'dovich (SZ) effect.
In order to assess PLANCKs SZ-capabilities in the presence of spurious signals,
a simulation is presented that combines maps of the thermal and kinetic
SZ-effects with a realisation of the cosmic microwave background (CMB), in
addition to Galactic foregrounds (synchrotron emission, free-free emission,
thermal emission from dust, CO-line radiation) as well as the sub-millimetric
emission from celestial bodies of our Solar system. Additionally, observational
issues such as the finite angular resolution and spatially non-uniform
instrumental noise of PLANCKs sky maps are taken into account, yielding a set
of all-sky flux maps, the auto-correlation and cross-correlation properties of
which are examined in detail. In the second part of the paper, filtering
schemes based on scale-adaptive and matched filtering are extended to spherical
data sets, that enable the amplification of the weak SZ-signal in the presence
of all contaminations stated above. The theory of scale-adaptive and matched
filtering in the framework of spherical maps is developed, the resulting filter
kernel shapes are discussed and their functionality is verified.Comment: 23 pages, 22 figures, 1 table, submitted to MNRAS, 05.Jul.200
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