4,163 research outputs found
CP and related phenomena in the context of Stellar Evolution
We review the interaction in intermediate and high mass stars between their
evolution and magnetic and chemical properties. We describe the theory of
Ap-star `fossil' fields, before touching on the expected secular diffusive
processes which give rise to evolution of the field. We then present recent
results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that
magnetic fields of the kind seen on the main-sequence already exist during the
pre-main sequence phase, in agreement with fossil field theory, and that the
origin of the slow rotation of Ap/Bp stars also lies early in the pre-main
sequence evolution; we also present results confirming a lack of stars with
fields below a few hundred gauss. We then seek which macroscopic motions
compete with atomic diffusion in determining the surface abundances of AmFm
stars. While turbulent transport and mass loss, in competition with atomic
diffusion, are both able to explain observed surface abundances, the interior
abundance distribution is different enough to potentially lead to a test using
asterosismology. Finally we review progress on the turbulence-driving and
mixing processes in stellar radiative zones.Comment: Proceedings of IAU GA in Rio, JD4 on Ap stars; 10 pages, 7 figure
Evidence of large-scale amplitude modulation on the near-wall turbulence
The relationship between large- and small-scale motions remains a poorly understood process in wall-bounded turbulence. Such misunderstanding is perhaps, in part, due to the limited scale separation typical of many laboratory-scale facilities. A recent investigation performed by Hutchins and Marusic [11] in a high Reynolds number turbulent boundary layer has qualitatively shown the existence of a modulating influence of the large-scale log region motions on the small-scale near-wall cycle. For this study we build upon these observations, using the Hilbert transformation applied to the spectrally filtered smallscale component of fluctuating velocity signals, in order to quantitatively determine the degree of amplitude modulation imparted by the large-scale structures onto the near-wall cycle
Active particle in a harmonic trap driven by a resetting noise: an approach via Kesten variables
We consider an active particle trapped in a harmonic potential, and subjected
to a resetting noise. At some random times, the noise is reset to an arbitrary
position and restarts its motion. We focus on two resetting protocols: periodic
resetting, where the period is deterministic, and Poissonian resetting, where
times between resets are exponentially distributed with a rate . Between the
different resetting epochs, we can express recursively the position of the
particle. The random relation obtained takes a simple Kesten form that can be
used to derive an integral equation for the stationary distribution of the
position. We provide a detailed analysis of the distribution when the noise is
a resetting Brownian motion. In this particular instance, we also derive a
renewal equation for the full time dependent distribution of the position that
we extensively study. These methods are quite general and can be used to study
any process harmonically trapped when the noise is reset at random times.Comment: 52 pages, 17 figure
Genetic characterization of Strongyloides spp. from captive, semi-captive and wild Bornean orangutans (Pongo pygmaeus) in Central and East Kalimantan, Borneo, Indonesia
Orangutans (Pongo spp.), Asia's only great apes, are threatened in their survival due to habitat loss, hunting and infections. Nematodes of the genus Strongyloides may represent a severe cause of death in wild and captive individuals. In order to better understand which Strongyloides species/subspecies infect orangutans under different conditions, larvae were isolated from fecal material collected in Indonesia from 9 captive, 2 semi-captive and 9 wild individuals, 18 captive groups of Bornean orangutans and from 1 human working with wild orangutans. Genotyping was done at the genomic rDNA locus (part of the 18S rRNA gene and internal transcribed spacer 1, ITS1) by sequencing amplicons. Thirty isolates, including the one from the human, could be identified as S. fuelleborni fuelleborni with 18S rRNA gene identities of 98·5-100%, with a corresponding published sequence. The ITS1 sequences could be determined for 17 of these isolates revealing a huge variability and 2 main clusters without obvious pattern with regard to attributes of the hosts. The ITS1 amplicons of 2 isolates were cloned and sequenced, revealing considerable variability indicative of mixed infections. One isolate from a captive individual was identified as S. stercoralis (18S rRNA) and showed 99% identity (ITS1) with S. stercoralis sequences from geographically distinct locations and host species. The findings are significant with regard to the zoonotic nature of these parasites and might contribute to the conservation of remaining orangutan population
The envelope of IRC+10216 reflecting the galactic light: UBV surface brightness photometry and interpretation
We present and analyse new optical images of the dust envelope surrounding
the high mass-loss carbon star IRC+10216. This envelope is seen due to external
illumination by galactic light. Intensity profiles and colors of the nebula
were obtained in the UBV bandpasses. The data are compared with the results of
a radiative transfer model calculating multiple scattering of interstellar
field photons by dust grains with a single radius. The data show that the
observed radial shape of the nebula, especially its half maximum radius, does
not depend on wavelength (within experimental errors), suggesting that grains
scatter in the grey regime, etc, etc (this abstract has been shortened)Comment: accepted by A
Thermodynamically consistent description of the hydrodynamics of free surfaces covered by insoluble surfactants of high concentration
In this paper we propose several models that describe the dynamics of liquid
films which are covered by a high concentration layer of insoluble surfactant.
First, we briefly review the 'classical' hydrodynamic form of the coupled
evolution equations for the film height and surfactant concentration that are
well established for small concentrations. Then we re-formulate the basic model
as a gradient dynamics based on an underlying free energy functional that
accounts for wettability and capillarity. Based on this re-formulation in the
framework of nonequilibrium thermodynamics, we propose extensions of the basic
hydrodynamic model that account for (i) nonlinear equations of state, (ii)
surfactant-dependent wettability, (iii) surfactant phase transitions, and (iv)
substrate-mediated condensation. In passing, we discuss important differences
to most of the models found in the literature.Comment: 31 pages, 2 figure
Ocean acidification in the surface waters of the Pacific-Arctic boundary regions
Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 2 (2015): 122-135, doi:10.5670/oceanog.2015.36.The continental shelves of the Pacific-Arctic Region (PAR) are especially vulnerable to the effects of ocean acidification (OA) because the intrusion of anthropogenic CO2 is not the only process that can reduce pH and carbonate mineral saturation states for aragonite (Ωarag). Enhanced sea ice melt, respiration of organic matter, upwelling, and riverine inputs have been shown to exacerbate CO2 -driven ocean acidification in high-latitude regions. Additionally, the indirect effect of changing sea ice coverage is providing a positive feedback to OA as more open water will allow for greater uptake of atmospheric CO2 . Here, we compare model-based outputs from the Community Earth System Model with a subset of recent ship-based observations, and take an initial look at future model projections of surface water Ωarag in the Bering, Chukchi, and Beaufort Seas. We then use the model outputs to define benchmark years when biological impacts are likely to result from reduced Ωarag. Each of the three continental shelf seas in the PAR will become undersaturated with respect to aragonite at approximately 30-year intervals, indicating that aragonite undersaturations gradually progress upstream along the flow path of the waters as they move north from the Pacific Ocean. However, naturally high variability in Ωarag may indicate higher resilience of the Bering Sea ecosystem to these low-Ωarag conditions than the ecosystems of the Chukchi and the Beaufort Seas. Based on our initial results, we have determined that the annual mean for Ωarag will pass below the current range of natural variability in 2025 for the Beaufort Sea and 2027 for the Chukchi Sea. Because of the higher range of natural variability, the annual mean for Ωarag for the Bering Sea does not pass out of the natural variability range until 2044. As Ωarag in these shelf seas slips below the present-day range of large seasonal variability by mid-century, the diverse ecosystems that support some of the largest commercial and subsistence fisheries in the world may be under tremendous pressure.This project was funded by the National Science
Foundation (PLR- 1041102 and AGS-1048827)
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