2,734 research outputs found
Rings and arcs around evolved stars. II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009 and NGC 7027
We present a detailed comparative study of the arcs and fragmented ring-like
features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and
NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using
high-quality multi-epoch HST images. This comparison allows us to investigate
the connection and possible evolution between the regular patterns surrounding
AGB stars and the irregular concentric patterns around PNe. The radial proper
motion of these features, ~15 km/s, are found to be consistent with the AGB
wind and their linear sizes and inter-lapse times (500-1900 yr) also agree with
those found around AGB stars, suggesting a common origin. We find evidence
using radiative-hydrodynamic simulations that regular patterns produced at the
end of the AGB phase become highly distorted by their interactions with the
expanding PN and the anisotropic illumination and ionization patterns caused by
shadow instabilities. These processes will disrupt the regular (mostly spiral)
patterns around AGB stars, plausibly becoming the arcs and fragmented rings
observed in the haloes of PNe.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Dynamic analysis of a lithium-boiling potassium refractory metal Rankine cycle power system for the Jet Propulsion Laboratory
Lithium-boiling potassium refractory metal Rankine cycle power system heat transfer model
Submillimeter polarisation and magnetic field properties in the envelopes of proto-planetary nebulae CRL 618 and OH 231.8+4.2
We have carried out continuum and line polarisation observations of two
Proto-planetary nebulae (PPNe), CRL 618 and OH 231.8+4.2, using the
Submillimeter Array (SMA) in its compact configuration. The frequency range of
observations, 330-345 GHz, includes the CO(J=3-2) line emission. CRL 618 and OH
231.8+4.2 show quadrupolar and bipolar optical lobes, respectively, surrounded
by a dusty envelope reminiscent of their AGB phase. We report a detection of
dust continuum polarised emission in both PPNe above 4 sigma but no molecular
line polarisation detection above a 3 sigma limit. OH 231.8+4.2 is slightly
more polarised on average than CRL 618 with a mean fractional polarisation of
4.3 and 0.3 per cent, respectively. This agrees with the previous finding that
silicate dust shows higher polarisation than carbonaceous dust. In both
objects, an anti-correlation between the fractional polarisation and the
intensity is observed. Neither PPNe show a well defined toroidal equatorial
field, rather the field is generally well aligned and organised along the polar
direction. This is clearly seen in CRL 618 while in the case of OH 231.8+4.2,
the geometry indicates an X-shaped structure coinciding overall with a
dipole/polar configuration. However in the later case, the presence of a
fragmented and weak toroidal field should not be discarded. Finally, in both
PPNe, we observed that the well organised magnetic field is parallel with the
major axis of the 12CO outflow. This alignment could indicate the presence of a
magnetic outflow launching mechanism. Based on our new high resolution data we
propose two scenarios to explain the evolution of the magnetic field in evolved
stars.Comment: 11 pages, 8 figures and 1 table. Accepted for publication in the
Monthly Notices of the Royal Astronomical Societ
A Buffer Stocks Model for Stabilizing Price of Staple Food with Considering the Expectation of Non Speculative Wholesaler
This paper is a study of price stabilization in the
staple food distribution system. All stakeholders experience
market risks due to some possibility causes of price volatility.
Many models of price stabilization had been developed by
employing several approaches such as floor-ceiling prices,
buffer funds, export or import taxes, and subsidies. In the
previous researches, the models were expanded to increase the
purchasing price for producer and decrease the selling price
for consumer. Therefore, the policy can influence the losses for
non-speculative wholesaler that is reflected by the descending
of selling quantity and ascending of the stocks. The objective of
this model is not only to keep the expectation of both producer
and consumer, but also to protect non-speculative wholesaler
from the undesirable result of the stabilization policy. A
nonlinear programming model was addressed to determine the
instruments of intervention program. Moreover, the result
shows that the wholesaler behavior affects the intervention
costs.
Index Terms Buffer stocks, Price stabilization, Nonlinear
programming, Wholesaler behavior
The effects of age on associations between markers of HIV progression and markers of metabolic function including albumin, haemoglobin and lipid concentrations.
OBJECTIVES: We investigated whether age modified associations between markers of HIV progression, CD4 T lymphocyte count and HIV RNA viral load (VL), and the following markers of metabolic function: albumin, haemoglobin, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC).
METHODS: A retrospective analysis of data from the United Kingdom Collaborative HIV Cohort was carried out. Analyses were limited to antiretroviral-naĂŻve subjects to focus on the impact of HIV disease itself. A total of 16670 subjects were included in the analysis. Multilevel linear regression models assessed associations between CD4 count/VL and each of the outcomes. Statistical tests for interactions assessed whether associations differed among age groups.
RESULTS: After adjustment for gender and ethnicity, there was evidence that lower CD4 count and higher VL were associated with lower TC, LDL-C, haemoglobin and albumin concentrations but higher triglyceride concentrations. Age modified associations between CD4 count and albumin (P 50 years, a 50 cells/ÎŒL lower CD4 count correlated with a 2.4 [95% confidence interval (CI) 1.7-3.0], 3.6 (95% CI 3.2-4.0) and 5.1 (95% CI 4.0-6.1) g/L lower haemoglobin concentration and a 0.09 (95% CI 0.07-0.11), 0.12 (95% CI 0.11-0.13) and 0.16 (95% CI 0.13-0.19) g/L lower albumin concentration, respectively.
CONCLUSIONS: We present evidence that age modifies associations between CD4 count and plasma albumin and haemoglobin levels. A given reduction in CD4 count was associated with a greater reduction in haemoglobin and albumin concentrations among older people living with HIV. These findings increase our understanding of how the metabolic impact of HIV is influenced by age
Extended X-ray emission from the classic nova DQ Her -- On the possible presence of a magnetized jet
We present an analysis of archival Chandra and XMM-Newton observations of the
magnetically-active cataclysmic variable DQ Her and the shell around it ejected
in a nova event in 1934. A careful revision of the Chandra observations
confirms previous claims on the presence of extended X-ray emission around DQ
Her and reveals that it actually corresponds to a bipolar jet-like structure
extending 32 along a direction from NE to SW. Therefore, this X-ray
emission extends beyond the optical nova shell and is perpendicular to its
major axis. The XMM-Newton observations confirm the presence of the extended
X-ray emission detected by Chandra, suggesting the additional presence of a
diffuse X-ray emission from a hot bubble filling the nova shell. This hot
bubble was very likely produced by the explosion that created the nebular shell
detected in optical images. The bipolar feature can be modelled by the
combination of an optically thin plasma emission component with temperature
K and a power law component with a photon index of
. Its X-ray luminosity in the 0.3 - 5 keV energy range is
erg s, for an electron density
cm and a mass M. We suggest that the X-ray bipolar structure in DQ
Her is a jet and interpret its non-thermal X-ray emission in terms of a
magnetized jet.Comment: 8 pages, 4 figures, 1 table; accepted to MNRA
Transfinite thin plate spline interpolation
Duchon's method of thin plate splines defines a polyharmonic interpolant to
scattered data values as the minimizer of a certain integral functional. For
transfinite interpolation, i.e. interpolation of continuous data prescribed on
curves or hypersurfaces, Kounchev has developed the method of polysplines,
which are piecewise polyharmonic functions of fixed smoothness across the given
hypersurfaces and satisfy some boundary conditions. Recently, Bejancu has
introduced boundary conditions of Beppo Levi type to construct a semi-cardinal
model for polyspline interpolation to data on an infinite set of parallel
hyperplanes. The present paper proves that, for periodic data on a finite set
of parallel hyperplanes, the polyspline interpolant satisfying Beppo Levi
boundary conditions is in fact a thin plate spline, i.e. it minimizes a Duchon
type functional
Planetary nebulae with Wolf-Rayet-type central stars -- I. The case of the high-excitation NGC 2371
We present the analysis of the planetary nebula (PN) NGC 2371 around the
[Wolf-Rayet] ([WR]) star WD 0722295. Our Isaac Newton Telescope (INT)
Intermediate Dispersion Spectrograph (IDS) spectra, in conjunction with
archival optical and UV images, unveil in unprecedented detail the
high-ionisation of NGC 2371. The nebula has an apparent multipolar morphology,
with two pairs of lobes protruding from a barrel-like central cavity, a pair of
dense low-ionisation knots misaligned with the symmetry axis embedded within
the central cavity, and a high excitation halo mainly detected in He II. The
abundances from the barrel-like central cavity and dense knots agree with
abundance determinations for other PNe with [WR]-type CSPNe. We suggest that
the densest knots inside NGC 2371 are the oldest structures, remnant of a dense
equatorial structure, whilst the main nebular shell and outer lobes resulted
from a latter ejection that ended the stellar evolution. The analysis of
position-velocity diagrams produced from our high-quality spectra suggests that
NGC 2371 has a bipolar shape with each lobe presenting a double-structure
protruding from a barrel-like central region. The analysis of the spectra of WD
0722295 results in similar stellar parameters as previously reported. We
corroborate that the spectral sub-type corresponds with a [WO1] type.Comment: 15 pages, 12 figures, 5 tables; accepted to MNRA
Electronic properties of mono-substituted tetraferrocenyl porphyrins in solution and on a gold surface: Assessment of the influencing factors for photoelectrochemical applications
Two unsymmetric meso-tetraferrocenyl-containing porphyrins of general formula Fc3(FcCOR)Por (Fc=ferrocenyl, R=CH3 or (CH2)5Br, Por=porphyrin) were prepared and characterized by a variety of spectroscopic methods, whereas their redox properties were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches. The mixed-valence [Fc3(FcCOR)Por]n+ (n=1,3) were investigated using spectroelectrochemical as well as chemical oxidation methods and corroborated with density functional theory (DFT) calculations. Inter-valence charge-transfer (IVCT) transitions in [Fc3(FcCOR)Por]+ were analyzed, and the resulting data matched closely previously reported complexes and were assigned as RobinâDay classâ
II mixed-valence compounds. Self-assembled monolayers (SAMs) of a thioacetyl derivative (Fc3(FcCO(CH2)5SCOCH3)Por) were also prepared and characterized. Photoelectrochemical properties of SAMs in different electrolyte systems were investigated by electrochemical techniques and photocurrent generation experiments, showing that the choice of electrolyte is critical for efficiency of redox-active SAMs
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