1,255 research outputs found
Eddy heat fluxes from direct current measurements of the Antarctic Polar Front in Shag Rocks Passage
Determining meridional heat flux in the Southern Ocean is critical to the accurate understanding and model simulation of the global ocean. Mesoscale eddies provide a significant but poorly-defined contribution to this transport. An eighteen-month deep-water current meter array deployment in Shag Rocks Passage (53°S, 48°W) between May 2003 and November 2004 provides estimates of the eddy flux of heat across the Polar Front. We calculate a statistically nonzero (99% level), vertically coherent local poleward heat flux of 12.0 ± 5.8 kW m-2 within the eddy frequency band at ~2750 m depth. Exceeding previous deep-water estimates by up to an order of magnitude, this highlights the large spatial variation in flux estimates and illustrates that constriction of circumpolar fronts facilitates large eddy transfers of heat southwards
Development of lateralization of the magnetic compass in a migratory bird
The magnetic compass of a migratory bird, the European robin (Erithacus rubecula), was shown to be lateralized in favour of the right eye/left brain hemisphere. However, this seems to be a property of the avian magnetic compass that is not present from the beginning, but develops only as the birds grow older. During first migration in autumn, juvenile robins can orient by their magnetic compass with their right as well as with their left eye. In the following spring, however, the magnetic compass is already lateralized, but this lateralization is still flexible: it could be removed by covering the right eye for 6 h. During the following autumn migration, the lateralization becomes more strongly fixed, with a 6 h occlusion of the right eye no longer having an effect. This change from a bilateral to a lateralized magnetic compass appears to be a maturation process, the first such case known so far in birds. Because both eyes mediate identical information about the geomagnetic field, brain asymmetry for the magnetic compass could increase efficiency by setting the other hemisphere free for other processes
The Taurus Boundary of Stellar/Substellar (TBOSS) Survey II. Disk Masses from ALMA Continuum Observations
We report 885m ALMA continuum flux densities for 24 Taurus members
spanning the stellar/substellar boundary, with spectral types from M4 to M7.75.
Of the 24 systems, 22 are detected at levels ranging from 1.0-55.6 mJy. The two
non-detections are transition disks, though other transition disks in the
sample are detected. Converting ALMA continuum measurements to masses using
standard scaling laws and radiative transfer modeling yields dust mass
estimates ranging from 0.3-20M. The dust mass shows a
declining trend with central object mass when combined with results from
submillimeter surveys of more massive Taurus members. The substellar disks
appear as part of a continuous sequence and not a distinct population. Compared
to older Upper Sco members with similar masses across the substellar limit, the
Taurus disks are brighter and more massive. Both Taurus and Upper Sco
populations are consistent with an approximately linear relationship in
to , although derived power-law slopes depend strongly
upon choices of stellar evolutionary model and dust temperature relation. The
median disk around early M-stars in Taurus contains a comparable amount of mass
in small solids as the average amount of heavy elements in Kepler planetary
systems on short-period orbits around M-dwarf stars, with an order of magnitude
spread in disk dust mass about the median value. Assuming a gas:dust ratio of
100:1, only a small number of low-mass stars and brown dwarfs have a total disk
mass amenable to giant planet formation, consistent with the low frequency of
giant planets orbiting M-dwarfs.Comment: 41 pages and 32 figures, with all tables and appendices presented
here in their entirety. Accepted for publication in AJ (November 26, 2017
On disc driven inward migration of resonantly coupled planets with application to the system around GJ876
We consider two protoplanets gravitationally interacting with each other and
a protoplanetary disc. The two planets orbit interior to a tidally maintained
disc cavity while the disc interaction indices inward migration. When the
migration is slow enough, the more rapidly migrating outer protoplanet
approaches and becomes locked in a 2:1 commensurability with the inner one.
This is maintained in subsequent evolution. We study this evolution using a
simple anaytic model, full hydrodynamic 2D simulations of the disc planet
system and longer time N body integrations incorporating simple prescriptions
for the effect of the disc on the planet orbits. The eccentricity of the
protoplanets are found to be determined by the migration rate induced in the
outer planet orbit by the external disc. We apply our results to the recently
discovered resonant planets around GJ876. Simulation shows that a disc with
parameters expected for protoplanetary discs causes trapping in the 2:1
commensurability when the planets orbit in an inner cavity and that
eccentricities in the observed range may be obtained.Comment: 8 pages, 5 figures, submitted to A&A on 30/03/200
Physioacoustic therapy: placebo effect on recovery from exercise-induced muscle damage
We evaluated claims that physioacoustic therapy can enhance muscle healing following damaging exercise. Untrained subjects were randomly assigned to control (C), placebo (P) or treatment (T) groups. All groups performed 70 eccentric triceps contractions followed by; no treatment (C), sham physioacoustic treatment (P), or actual physioacoustic therapy (T) on days 1–4 post-exercise. Muscle soreness and isometric and concentric triceps peak torque were determined pre-exerciseand on days 1–4 and 7 post-exercise. The T group received physioacoustic therapy for 30 min/day on the treatment days. The P group believed they received physioacoustic therapy, although the chairs were turned off. Peak torques were depressed (P < 0.05) on days 1–3 in all groups and returned to pre-exercise values by days 4–7 in both P and T groups. C group peak torques remained depressed (P < 0.05) through day 7. Soreness was elevated (P < 0.05) in all groups on days 1–2 post-exercise. P and T groups reported no soreness by day 3 while the C group remained sore (P < 0.05) through days 3–4. The T group recovered soreness and force faster than C but at a similar rate to the P group. The effectiveness of physioacoustic therapy in enhancing post-exercise muscle healing may be attributable to a placebo effect
Hydrodynamic Simulations of Propagating Warps and Bending Waves In Accretion Discs
We present the results of a study of propagating warp or bending waves in
accretion discs. Three dimensional hydrodynamic simulations were performed
using SPH, and the results of these are compared with calculations based on the
linear theory of warped discs. We consider primarily the physical regime in
which the dimensionless viscosity parameter `alpha' < H/r, the disc aspect
ratio, so that bending waves are expected to propagate. We also present
calculations in which `alpha' > H/r, where the warps are expected to behave
diffusively. Small amplitude perturbations are studied in both Keplerian and
slightly non Keplerian discs, and we find that the SPH results can be
reasonably well fitted by those of the linear theory. The main results of these
calculations are: (1) the warp in Keplerian discs when `alpha' < H/r propagates
with little dispersion and damps at a rate expected from estimates of the code
viscosity, (2) warps evolve diffusively when `alpha' > H/r, (3) the non
Keplerian discs exhibit a substantially more dispersive behaviour of the warps.
Initially imposed higher amplitude nonlinear warping disturbances were studied
in Keplerian discs. The results indicate that nonlinear warps can lead to the
formation of shocks, and that the evolution of the warp becomes less wave-like
and more diffusive in character. This work is relevant to the study of the
warped accretion discs that may occur around Kerr black holes or in misaligned
binary systems. The results indicate that SPH can accurately model the
hydrodynamics of warped discs, even when using rather modest numbers of
particles.Comment: 14 pages, 9 figures, to appear in MNRA
<i>Herschel</i> observations of the debris disc around HIP 92043
Context. Typical debris discs are composed of particles ranging from several micron sized dust grains to km sized asteroidal bodies, and their infrared emission peaks at wavelengths 60-100 μm. Recent Herschel DUNES observations have identified several debris discs around nearby Sun-like stars (F, G and K spectral type) with significant excess emission only at 160 μm.
Aims. We observed HIP 92043 (110 Her, HD 173667) at far-infrared and sub-millimetre wavelengths with Herschel PACS and SPIRE. Identification of the presence of excess emission from HIP 92043 and the origin and physical properties of any excess was undertaken through analysis of its spectral energy distribution (SED) and the PACS images.
Methods. The PACS and SPIRE images were produced using the HIPE photProject map maker routine. Fluxes were measured using aperture photometry. A stellar photosphere model was scaled to optical and near infrared photometry and subtracted from the far-infared and sub-mm fluxes to determine the presence of excess emission. Source radial profiles were fitted using a 2D Gaussian and compared to a PSF model based on Herschel observations of α Boo to check for extended emission.
Results. Clear excess emission from HIP 92043 was observed at 70 and 100 μm. Marginal excess was observed at 160 and 250 μm. Analysis of the images reveals that the source is extended at 160 μm. A fit to the source SED is inconsistent with a photosphere and single temperature black body.
Conclusions. The excess emission from HIP 92043 is consistent with the presence of an unresolved circumstellar debris disc at 70 and 100 μm, with low probability of background contamination. The extended 160 μm emission may be interpreted as an additional cold component to the debris disc or as the result of background contamination along the line of sight. The nature of the 160 μm excess cannot be determined absolutely from the available data, but we favour a debris disc interpretation, drawing parallels with previously identified cold disc sources in the DUNES sample
The effect of active immunization against adrenocorticotropic hormone on cortisol, beta-endorphin, vocalization, and growth in pigs
Because the poor growth performance of intensively housed pigs is associated with increased circulating glucocorticoid concentrations, we investigated the effects of glucocorticoid suppression by inducing a humoral immune response to ACTH on physiological and production variables in growing pigs. Grower pigs (28.6 0.9 kg) were immunized with amino acids 1 through 24 of ACTH conjugated to ovalbumin and suspended in diethylaminoethyl (DEAE) dextran-adjuvant or adjuvant alone (control) on d 1, 28, and 56. The ACTH-specific antibody titers generated suppressed increases in cortisol concentrations on d 63 in response to an acute stressor (P = 0.002; control = 71 +/- 8.2 ng/ mL; ACTH-immune = 43 +/- 4.9 ng/mL) without altering basal concentrations. Plasma beta-endorphin concentrations were also increased (P < 0.001) on d 63 (control = 18 +/- 2.1 ng/mL; ACTH-immune = 63 +/- 7.3 ng/mL), presumably because of a release from negative feedback on the expression of proopiomelanocortin in pituitary corticotropes. Immunization against ACTH did not alter ADG (P = 0.120; control = 1,077 25; ACTH-immune = 1,143 25 g) or ADFI (P = 0.64; control = 2,719 42; ACTH-immune = 2,749 42 g) and did not modify behavior (P = 0.681) assessed by measuring vocalization in response to acute restraint. In summary, suppression of stress-induced cortisol responses through ACTH immunization increased beta-endorphin concentrations, but it did not modify ADG, ADFI, or restraint vocalization score in growing pigs
Hubble and Spitzer Space Telescope Observations of the Debris Disk around the Nearby K Dwarf HD 92945
[ABRIDGED] We present the first resolved images of the debris disk around the
nearby K dwarf HD 92945. Our F606W (V) and F814W (I) HST/ACS coronagraphic
images reveal an inclined, axisymmetric disk consisting of an inner ring
2".0-3".0 (43-65 AU) from the star and an extended outer disk whose surface
brightness declines slowly with increasing radius 3".0-5".1 (65-110 AU) from
the star. A precipitous drop in the surface brightness beyond 110 AU suggests
that the outer disk is truncated at that distance. The radial surface-density
profile is peaked at both the inner ring and the outer edge of the disk. The
dust in the outer disk scatters neutrally but isotropically, and it has a low
V-band albedo of 0.1. We also present new Spitzer MIPS photometry and IRS
spectra of HD 92945. These data reveal no infrared excess from the disk
shortward of 30 micron and constrain the width of the 70 micron source to < 180
AU. Assuming the dust comprises compact grains of astronomical silicate with a
surface-density profile described by our scattered-light model of the disk, we
successfully model the 24-350 micron emission with a minimum grain size of
a_min = 4.5 micron and a size distribution proportional to a^-3.7 throughout
the disk, but with a maximum grain size of 900 micron in the inner ring and 50
micron in the outer disk. Our observations indicate a total dust mass of ~0.001
M_earth. However, they provide contradictory evidence of the dust's physical
characteristics: its neutral V-I color and lack of 24 micron emission imply
grains larger than a few microns, but its isotropic scattering and low albedo
suggest a large population of submicron-sized grains. The dynamical causes of
the disk's morphology are unclear, but recent models of dust creation and
transport in the presence of migrating planets indicate an advanced state of
planet formation around HD 92945.Comment: 29 pages, 10 figures; to be published in The Astronomical Journa
Target Selection for the LBTI Exozodi Key Science Program
The Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS)
on the Large Binocular Telescope Interferometer will survey nearby stars for
faint emission arising from ~300 K dust (exozodiacal dust), and aims to
determine the exozodiacal dust luminosity function. HOSTS results will enable
planning for future space telescopes aimed at direct spectroscopy of habitable
zone terrestrial planets, as well as greater understanding of the evolution of
exozodiacal disks and planetary systems. We lay out here the considerations
that lead to the final HOSTS target list. Our target selection strategy
maximizes the ability of the survey to constrain the exozodi luminosity
function by selecting a combination of stars selected for suitability as
targets of future missions and as sensitive exozodi probes. With a survey of
approximately 50 stars, we show that HOSTS can enable an understanding of the
statistical distribution of warm dust around various types of stars and is
robust to the effects of varying levels of survey sensitivity induced by
weather conditions.Comment: accepted to ApJ
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