1,828 research outputs found
A genetic assessment of parentage in the blackspot sergeant damselfish, Abudefduf sordidus (Pisces: Pomacentridae)
Microsatellite markers were used to investigate the reproductive behavior of the damselfish Abudefduf sordidus at Johnston Atoll, Central Pacific Ocean. Genetic results indicated that ten males maintained guardianship over their nest territories for up to nine nest cycles during a 3.5 month period. Genotypes of 1025 offspring sampled from 68 nests (composed of 129 clutches) were consistent with 95% of the offspring being sired by the guardian male. Offspring lacking paternal alleles at two or more loci were found in 19 clutches, indicating that reproductive parasitism and subsequent alloparental care occurred. Reconstructed maternal genotypes allowed the identification of a minimum of 74 different females that spawned with these ten territorial males. Males were polygynous, mating with multiple females within and between cycles. Genetic data from nests, which consisted of up to four clutches during a reproductive cycle, indicated that each clutch usually had only one maternal contributor and that different clutches each had different dams. Females displayed sequential polyandry spawning with one male within a cycle but switched males in subsequent spawning cycles. These results highlight new findings regarding male parasitic spawning, polygyny, and sequential polyandry in a marine fish with exclusive male paternal care.Published versio
Damselfish embryos as a bioindicator for military contamination on Coral Reefs at Johnston Atoll, Pacific Ocean
This study investigated the association between sediment contamination, PCB accumulation in adult nesting males and the occurrence of embryonic abnormalities in the damselfish, Abudefduf sordidus, from two sites with high PCB contamination and three âreferenceâ sites (contaminants very low or not measurable) within Johnston Atoll, Central Pacific Ocean. Developmental abnormalities were assessed in damselfish embryos collected in the field during four natural spawning seasons (1996, 1998, 1999, and 2001). Laboratory incubations of abnormal embryos demonstrated that the observed abnormalities were lethal. PCBs were measured in fish collected in three years. Mean whole-body concentrations of total PCBs ranged from 364.6 to 138,032.5 ng/g lipid. A significant residueâeffect relationship was found between total PCB concentration and embryo abnormalities. The occurrence of embryo abnormalities was positively related to fish PCB concentration (other contaminants were also evaluated including metals and dioxins). This study demonstrates the utility of using damselfish embryos as a bioindicator tool for monitoring coral reefs. It also provides baseline-monitoring criteria and evaluates sediment quality benchmarks used for ecological risk assessments on coral reefs.Published versio
FUSE Observations of the Dwarf Nova SW UMa During Quiescence
We present spectroscopic observations of the short-period cataclysmic
variable SW Ursa Majoris, obtained by the Far Ultraviolet Spectroscopic
Explorer (FUSE) satellite while the system was in quiescence. The data include
the resonance lines of O VI at 1031.91 and 1037.61 A. These lines are present
in emission, and they exhibit both narrow (~ 150 km/s) and broad (~ 2000 km/s)
components. The narrow O VI emission lines exhibit unusual double-peaked and
redshifted profiles. We attribute the source of this emission to a cooling flow
onto the surface of the white dwarf primary. The broad O VI emission most
likely originates in a thin, photoionized surface layer on the accretion disk.
We searched for emission from H_2 at 1050 and 1100 A, motivated by the
expectation that the bulk of the quiescent accretion disk is in the form of
cool, molecular gas. If H_2 is present, then our limits on the fluxes of the
H_2 lines are consistent with the presence of a surface layer of atomic H that
shields the interior of the disk. These results may indicate that accretion
operates primarily in the surface layers of the disk in SW UMa. We also
investigate the far-UV continuum of SW UMa and place an upper limit of 15,000 K
on the effective temperature of the white dwarf.Comment: 21 Pages, 3 figures, to be published in Ap
The value of closed-circuit rebreathers for biological research
Closed-circuit rebreathers have been used for underwater biological research since the late 1960s,
but have only started to gain broader application within scientific diving organizations within the
past two decades. Rebreathers offer certain specific advantages for such research, especially for
research involving behavior and surveys that depend on unobtrusive observers or for a stealthy
approach to wildlife for capture and tagging, research that benefits from extended durations
underwater, and operations requiring access to relatively deep (>50 m) environments (especially in
remote locations). Although many institutions have been slow to adopt rebreather technology
within their diving programs, recent developments in rebreather technology that improve safety,
standardize training requirements, and reduce costs of equipment and maintenance, will likely
result in a trend of increasing utilization of rebreathers for underwater biological research.Published versio
From <i>extractive</i> to <i>transformative</i> industries:paths for linkages and diversification for resource-driven development
A Binary Orbit for the Massive, Evolved Star HDE 326823, a WR+O System Progenitor
The hot star HDE 326823 is a candidate transition-phase object that is
evolving into a nitrogen-enriched Wolf-Rayet star. It is also a known
low-amplitude, photometric variable with a 6.123 d period. We present new, high
and moderate resolution spectroscopy of HDE 326823, and we show that the
absorption lines show coherent Doppler shifts with this period while the
emission lines display little or no velocity variation. We interpret the
absorption line shifts as the orbital motion of the apparently brighter star in
a close, interacting binary. We argue that this star is losing mass to a mass
gainer star hidden in a thick accretion torus and to a circumbinary disk that
is the source of the emission lines. HDE 326823 probably belongs to a class of
objects that produce short-period WR+O binaries.Comment: 32 pages, 10 figures, accepted to the Astronomical Journa
Tunable Depletion Potentials Driven By Shape Variation Of Surfactant Micelles
Depletion interaction potentials between micron-sized colloidal particles are induced by nanometer-scale surfactant micelles composed of hexaethylene glycol monododecyl ether (C12E6), and they are measured by video microscopy. The strength and range of the depletion interaction is revealed to arise from variations in shape anisotropy of the surfactant micelles. This shape anisotropy increases with increasing sample temperature. By fitting the colloidal interaction potentials to theoretical models, we extract micelle length and shape anisotropy as a function of temperature. This work introduces shape anisotropy tuning as a means to control interparticle interactions in colloidal suspensions, and it shows how the interparticle depletion potentials of micron-scale objects can be employed to probe the shape and size of surrounding macromolecules at the nanoscale
The Magnetised Bellows of Betelgeuse
We present calculations for a magnetised hybrid wind model for Betelegeuse
(Orionis). The model is a direct application of our previously
derived theory, combining a canonical Weber-Davis (WD) stellar wind with dust
grains in the envelope of an AGB star \citep[see][]{Thirumalai2010}. The
resulting hybrid picture provides a mechanism for solving the problem of
lifting stellar material up from the photosphere \citep[e.g.][]
{Harper2009,Guandalini2006,Jura1984} and into the circumstellar envelope. It
also predicts wind velocities in agreement with current estimates. Our approach
reveals that magnetic fields in supergiant stars like Betelgeuse
\citep[see][]{Auriere2010}, may play a vital role in determining the nature of
the stellar outflow and consequently, opens a new avenue of investigation in
the field of hybrid stellar winds.Comment: 13 pages, 4 figure
On the Dynamic Stability of Cool Supergiant Atmospheres
We have developed a new formalism to compute the thermodynamic coefficient
Gamma1 in the theory of stellar and atmospheric stability. We generalize the
classical derivation of the first adiabatic index, which is based on the
assumption of thermal ionization and equilibrium between gas and radiation
temperature, towards an expression which incorporates photo-ionization due to
radiation with a temperature T_rad different from the local kinetic gas
temperature.Our formalism considers the important non-LTE conditions in the
extended atmospheres of supergiant stars. An application to the Kurucz grid of
cool supergiant atmospheres demonstrates that models with T_rad =~ T_eff
between 6500 K and 7500 K become most unstable against dynamic perturbations,
according to Ledoux' stability integral . This results from Gamma1 and
acquiring very low values, below 4/3, throughout the entire stellar
atmosphere, which causes very high gas compression ratios around these
effective temperatures. Based on detailed NLTE-calculations, we discuss
atmospheric instability of pulsating massive yellow supergiants, like the
hypergiant rho Cas (Ia+), which exist in the extension of the Cepheid
instability strip, near the Eddington luminosity limit.Comment: 54 pages including figures and the Appendix, 7 figures, Accepted for
The Astrophysical Journal, Main Journal, 558, Sept. 200
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