2,820 research outputs found
Stream-field interactions in the magnetic accretor AO Piscium
UV spectra of the magnetic accretor AO Psc show absorption features for half
the binary orbit. The absorption is unlike the wind-formed features often seen
in similar stars. Instead, we attribute it to a fraction of the stream that
overflows the impact with the accretion disk. Rapid velocity variations can be
explained by changes in the trajectory of the stream depending on the
orientation of the white-dwarf's magnetic field. Hence we are directly
observing the interaction of an accretion stream with a rotating field. We
compare this behavior to that seen in other intermediate polars and in SW Sex
stars.Comment: Accepted for ApJ; 6 page
Promoting kangaroo as a sustainable option for meat production on the rangelands of Australia
Implications
•As kangaroo meat is sourced from native wildlife, conservation of the species is important in developing sustainable meat harvesting. Landholders, conservationists, and commercial meat producers need to work together to achieve this goal.
•The production of high quality meat products from field-harvested carcasses can be augmented through a better understanding of the impact that field conditions and carcass handling have on final meat eating quality.
•Food safety is also paramount, with measures taken to minimize the impacts of parasitism and microbial contamination. Any breaches of inspection protocols can only serve to undermine consumer confidence and viability of the industry
Cooling of the Cassiopeia A neutron star and the effect of diffusive nuclear burning
The study of how neutron stars cool over time can provide invaluable insights
into fundamental physics such as the nuclear equation of state and
superconductivity and superfluidity. A critical relation in neutron star
cooling is the one between observed surface temperature and interior
temperature. This relation is determined by the composition of the neutron star
envelope and can be influenced by the process of diffusive nuclear burning
(DNB). We calculate models of envelopes that include DNB and find that DNB can
lead to a rapidly changing envelope composition which can be relevant for
understanding the long-term cooling behavior of neutron stars. We also report
on analysis of the latest temperature measurements of the young neutron star in
the Cassiopeia A supernova remnant. The 13 Chandra observations over 18 years
show that the neutron star's temperature is decreasing at a rate of 2-3 percent
per decade, and this rapid cooling can be explained by the presence of a proton
superconductor and neutron superfluid in the core of the star.Comment: 7 pages, 7 figures; to appear in the AIP Conference Proceedings of
the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the
Era of Gravitational Wave Astronomy (January 3-7, 2019, Xiamen, China
Explaining the imbalance in δ13C between soil and biomass in fire-prone tropical savannas
Currently, models of terrestrial 13C discrimination indicate that about one quarter of the gross primary productivity (GPP - total carbon fixed as biomass by plants) by the terrestrial biosphere is attributable to tropical savanna/grassland plants that use the C, photosynthetic pathway. However, the fraction of C,-derived biomass in soil organic carbon in savanna systems is much lower than these GPP estimates imply. Determining this imbalance has significant implications for correctly interpreting soil and palaeosol carbon isotope data, and for modelling studies that use variations in the atmospheric δ13CO, record to apportion sources and sinks of carbon. Here, we present preliminary results using hydrogen pyrolysis (HyPy) for quantifying the abundance and identifying the source of pyrogenic carbon (PC) in tropical savannas of North Queensland (Australia). We collected sediment from a series of micro-catchments covering the broadest possible range of C, and C, environments, and compared the abundances and stable isotope compositions of the total organic carbon (TOC) and pyrogenic carbon (PC) fractions.
Hydrogen pyrolysis (HyPy) can be used to quantify the production, fate and stable isotope composition of PC produced by vegetation burning. HyPy is pyrolysis (up to ~600°C) under high hydrogen pressures (>10 MPa) in the presence of a catalyst, and when applied to sediments, soils, or organic samples results in the reductive removal of labile organic matter. Therefore, this technique offers great potential to effectively isolate and quantify pyrogenic carbon in a rapid and cost effective manner. Moreover, comparison of the stable carbon isotope composition of PC with bulk carbon has the potential to discern if there is a dominant vegetation source contributing to burning.
The results indicate that the δ13C value of PC in the sediments is up 6‰ higher than the 613C value of TOC. There is a larger difference when TOC abundances in the sediments are lowest. This suggests a significant component of C,-derived PC is present in the sediments, even when the proportion of C, biomass in the catchment is relatively low. This in turn, provides evidence for the preferential combustion and transport of C4-derived PC in tropical savannas. Savanna fires preferentially burn the grass understorey rather than large trees, leading to a bias toward the finer C,-derived PC being exported from a fire and accumulated in the sedimentary record while large particles of Crderived PC are more likely to remain at the site of burning. Our preliminary data suggest that application of HyPy in environmental studies enables accurate quantification of an essential component of the terrestrial C cycle. Moreover, the use of HyPy also enables the reliable determination of the stable carbon isotope composition of PC, which will enable deeper understanding of the dynamic role of biomass burning in the global carbon cycle
The effectiveness of using the workplace to identify and address modifiable health risk factors in deprived populations
Objectives To establish whether a programme of targeted health screening, with referral to appropriate interventions, offered to an employed but socioeconomically deprived group was effective in overcoming barriers to uptake of such services and improving a range of surrogate health markers for participants. Methods Low-paid local government employees from socially and economically deprived areas in North-East England were invited to attend a free health check. Health checks were conducted within working hours and close to their worksite, and included assessment of a range of lifestyle and health-related risk factors, including those associated with cardiovascular disease (CVD). A range of additional interventions were offered where indicated. Participants were invited to repeat screening approximately 9 months later. Results 635 (20% response rate) employees in the target age group (≥40 years) attended the first check. Most health risk markers improved in those (N=427) attending both health checks, as did the mean CVD risk score (t=2.86, p=0.004). 269 referrals were made to the intervention programmes. Conclusions This workplace programme had a positive impact on cardiovascular health, but attendance rates were low. These findings suggest that workplace health screening activities may have the potential to improve health in a group often considered hard to reach by other routes, but do not offer a straightforward solution in overcoming barriers to access for such subgroups within the working population
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
The accretion flow in the discless intermediate polar V2400 Ophiuchi
RXTE observations confirm that the X-ray lightcurve of V2400 Oph is pulsed at
the beat cycle, as expected in a discless intermediate polar. There are no
X-ray modulations at the orbital or spin cycles, but optical line profiles vary
with all three cycles. We construct a model for line-profile variations in a
discless accretor, based on the idea that the accretion stream flips from one
magnetic pole to the other, and show that this accounts for the observed
behaviour over the spin and beat cycles. The minimal variability over the
orbital cycle implies that 1) V2400 Oph is at an inclination of only ~10 deg,
and 2) much of the accretion flow is not in a coherent stream, but is circling
the white dwarf, possibly as a ring of denser, diamagnetic blobs. We discuss
the light this sheds on disc formation in intermediate polars.Comment: 10 pages, 12 figures, To appear in MNRAS, includes low-res figures to
reduce siz
An alternative model of the magnetic cataclysmic variable V1432 Aquilae (=RX J1940.1-1025)
V1432 Aql is currently considered to be an asynchronous AM Her type system,
with an orbital period of 12116.3 s and a spin period of 12150 s. I present an
alternative model in which V1432 Aql is an intermediate polar with disk
overflow or diskless accretion geometry, with a spin period near 4040 s. I
argue that published data are insufficient to distinguish between the two
models; instead, I provide a series of predictions of the two models that can
be tested against future observations.Comment: 10 pages LaTeX including 3 Postscript Figures, to be published in Ap
Periodicities In The X-Ray Intensity Variations of TV Columbae: An Intermediate Polar
We present results from a temporal analysis of the longest and the most
sensitive X-ray observations of TV Columbae--an intermediate polar. The
observations were carried out with the RXTE PCA, ROSAT PSPC, and ASCA. Data
were analyzed using a 1-dimensional CLEAN and Bayesian algorithms. The presence
of a nearly sinusoidal modulation due to the spin of the white dwarf is seen
clearly in all the data, confirming the previous reports based on the EXOSAT
data. An improved period of 1909.7+/-2.5s is derived for the spin from the RXTE
data.The binary period of 5.5hr is detected unambiguously in X-rays for the
first time. Several side-bands due to the interaction of these periods are
observed in the power spectra, thereby suggesting contributions from both the
disk-fed and the stream-fed accretion for TV Col. The accretion disk could
perhaps be precessing as side-bands due to the influence of 4 day period on the
orbital period are seen. The presence of a significant power at certain
side-bands of the spin frequency indicates that the emission poles are
asymmetrically located. The strong power at the orbital side-bands seen in both
the RXTE and ROSAT data gives an indication for an absorption site fixed in the
orbital frame. Both the spin and the binary modulation are found to be
energy-dependent. Increased hardness ratio during a broad dip in the intensity
at binary phase of 0.75--1.0 confirms the presence of a strong attenuation due
to additional absorbers probably from an impact site of the accretion stream
with the disk or magnetosphere. Hardness ratio variations and the energy
dependent modulation depth during the spin modulation can be explained by
partially covered absorbers in the path of X-ray emission region in the
accretion stream.Comment: 34 pages, including 12 figures, Accepted for publication in
Astronomical Journal, scheduled for January 2004 issue (vol. 127
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