1,656 research outputs found
KIC 4247791: A SB4 system with two eclipsing binaries (2EBs)
KIC 4247791 is an eclipsing binary observed by the Kepler satellite mission.
We wish to determine the nature of its components and in particular the origin
of a shallow dip in its Kepler light curve that previous investigations have
been unable to explain in a unique way. We analyze newly obtained
high-resolution spectra of the star using synthetic spectra based on atmosphere
models, derive the radial velocities of the stellar components from
cross-correlation with a synthetic template, and calculate the orbital
solution. We use the JKTEBOP program to model the Kepler light curve of KIC
4247791. We find KIC 4247791 to be a SB4 star. The radial velocity variations
of its four components can be explained by two separate eclipsing binaries. In
contradiction to previous photometric findings, we show that the observed
composite spectrum as well as the derived masses of all four of its components
correspond to spectral type F. The observed small dip in the light curve is not
caused by a transit-like phenomenon but by the eclipses of the second binary
system. We find evidence that KIC 4247791 might belong to the very rare
hierarchical SB4 systems with two eclipsing binaries.Comment: 6 pages, 8 figures, 2 table
Planetary systems around close binary stars: the case of the very dusty, Sun-like, spectroscopic binary BD+20 307
Field star BD+20 307 is the dustiest known main sequence star, based on the
fraction of its bolometric luminosity, 4%, that is emitted at infrared
wavelengths. The particles that carry this large IR luminosity are unusually
warm, comparable to the temperature of the zodiacal dust in the solar system,
and their existence is likely to be a consequence of a fairly recent collision
of large objects such as planets or planetary embryos. Thus, the age of BD+20
307 is potentially of interest in constraining the era of terrestrial planet
formation. The present project was initiated with an attempt to derive this age
using the Chandra X-ray Observatory to measure the X-ray flux of BD+20 307 in
conjunction with extensive photometric and spectroscopic monitoring
observations from Fairborn Observatory. However, the recent realization that
BD+20 307 is a short period, double-line, spectroscopic binary whose components
have very different lithium abundances, vitiates standard methods of age
determination. We find the system to be metal-poor; this, combined with its
measured lithium abundances, indicates that BD+20 307 may be several to many
Gyr old. BD+20 307 affords astronomy a rare peek into a mature planetary system
in orbit around a close binary star (because such systems are not amenable to
study by the precision radial velocity technique).Comment: accepted for ApJ, December 10, 200
The visual orbits of the spectroscopic binaries HD 6118 and HD 27483 from the Palomar Testbed Interferometer
We present optical interferometric observations of two double-lined
spectroscopic binaries, HD 6118 and HD 27483, taken with the Palomar Testbed
Interferometer (PTI) in the K band. HD 6118 is one of the most eccentric
spectroscopic binaries and HD 27483 a spectroscopic binary in the Hyades open
cluster. The data collected with PTI in 2001-2002 allow us to determine
astrometric orbits and when combined with the radial velocity measurements
derive all physical parameters of the systems. The masses of the components are
2.65 +/- 0.27 M_Sun and 2.36 +/- 0.24 M_Sun for HD 6118 and 1.38 +/- 0.13 M_Sun
and 1.39 +/- 0.13 M_Sun for HD 27483. The apparent semi-major axis of HD 27483
is only 1.2 mas making it the closest binary successfully observed with an
optical interferometer.Comment: submitted to Ap
Valve interstitial cells induce donor-specific T-cell anergy
AbstractObjectives: Valve allografts produce an immune response, which can influence their performance. The exact role of the interaction between recipient T cells and the different cellular components of the donor valve in stimulating an immune response is not known. Therefore the T-cell response to valve endothelial and interstitial cells was investigated in vitro. Methods: Valve endothelial and interstitial cells were characterized for cell-surface molecules before and after interferon γ treatment by means of a panel of specific monoclonal antibodies and flow cytometry. The proliferative response of highly purified T lymphocytes was used to assess the immunogenicity of cultured valve endothelial and interstitial cells. This was further investigated by using a 2-step tolerance-induction protocol. Results: Valve endothelial and interstitial cells express similar levels of human leukocyte antigens and adhesion and costimulatory molecules, which are either induced or upregulated after interferon γ treatment. T-cell responses to endothelial cells were detected after interferon γ treatment, but responses to interferon γ–treated interstitial cells were not detected. This lack of response resulted in the induction of T-cell anergy, which was reversed by the presence of the costimulatory molecule B7-1. Conclusions: Although valve endothelial and interstitial cells express a similar range of cell-surface molecules, it is only the endothelial cells that are immunogenic. In addition, we have shown that these 2 cell types interact in a donorspecific manner to orchestrate the immune response and therefore may have clinical relevance in the allogeneic response of the heart valve recipients.J Thorac Cardiovasc Surg 2001;122:129-3
Multi-Line Geometry of Qubit-Qutrit and Higher-Order Pauli Operators
The commutation relations of the generalized Pauli operators of a
qubit-qutrit system are discussed in the newly established graph-theoretic and
finite-geometrical settings. The dual of the Pauli graph of this system is
found to be isomorphic to the projective line over the product ring Z2xZ3. A
"peculiar" feature in comparison with two-qubits is that two distinct
points/operators can be joined by more than one line. The multi-line property
is shown to be also present in the graphs/geometries characterizing two-qutrit
and three-qubit Pauli operators' space and surmised to be exhibited by any
other higher-level quantum system.Comment: 8 pages, 6 figures. International Journal of Theoretical Physics
(2007) accept\'
Biomass production chamber air analysis of wheat study (BWT931)
NASA's Controlled Ecological Life Support System (CELSS) biomass production chamber at John F. Kennedy Space Center provides a test bed for bioregenerative studies using plants to provide food, oxygen, carbon dioxide removal, and potable water to humans during long term space travel. Growing plants in enclosed environments has brought about concerns regarding the level of volatile organic compounds (VOC's) emitted from plants and the construction materials that make up the plant growth chambers. In such closed systems, the potential exists for some VOC's to reach toxic levels and lead to poor plant growth, plant death, or health problems for human inhabitants. This study characterized the air in an enclosed environment in which wheat cv. Yocora Rojo was grown. Ninty-four whole air samples were analyzed by gas chromatography/mass spectrometry throughout the eighty-four day planting. VOC emissions from plants and materials were characterized and quantified
Testing Rotational Mixing Predictions with New Boron Abundances in Main Sequence B-type Stars
(Abridged) New boron abundances for seven main-sequence B-type stars are
determined from HST STIS spectroscopy around the BIII 2066A line. Boron
abundances provide a unique and critical test of stellar evolution models that
include rotational mixing since boron is destroyed in the surface layers of
stars through shallow mixing long before other elements are mixed from the
stellar interior through deep mixing. Boron abundances range from 12+log(B/H) =
1.0 to 2.2. The boron abundances are compared to the published values of their
stellar nitrogen abundances (all have 12+log(N/H) < 7.8, i.e., they do not show
significant CNO-mixing) and to their host cluster ages (4 to 16 Myr) to
investigate the predictions from models of massive star evolution with
rotational mixing effects (Heger & Langer 2000). Only three stars (out of 34)
deviate from the model predictions, including HD36591, HD205021, and HD30836.
These three stars suggest that rotational mixing could be more efficient than
currently modelled at the highest rotation rates.Comment: 10 figures, 7 tables; accepted for publication in the Astrophysical
Journa
Palynofacies and geochemical analyses of the Upper Cretaceous–Eocene succession, western Sirte Basin, Libya:Palaeoenvironmental interpretation and implications for hydrocarbon generation potential
Characterisation of Peste Des Petits Ruminants Disease in Pastoralist Flocks in Ngorongoro District of Northern Tanzania and Bluetongue Virus Co-Infection
Peste des petits ruminants (PPR) disease was first confirmed in Tanzania in 2008 in sheep and goats in Ngorongoro District, northern Tanzania, and is now endemic in this area. This study aimed to characterise PPR disease in pastoralist small ruminant flocks in Ngorongoro District. During June 2015, 33 PPR-like disease reports were investigated in different parts of the district, using semi-structured interviews, clinical examinations, PPR virus rapid detection test (PPRV-RDT), and laboratory analysis. Ten flocks were confirmed as PPRV infected by PPRV-RDT and/or real-time reverse transcription-polymerase chain reaction (RT-qPCR), and two flocks were co-infected with bluetongue virus (BTV), confirmed by RT-qPCR. Phylogenetic analysis of six partial N gene sequences showed that the PPR viruses clustered with recent lineage III Tanzanian viruses, and grouped with Ugandan, Kenyan and Democratic Republic of Congo isolates. No PPR-like disease was reported in wildlife. There was considerable variation in clinical syndromes between flocks: some showed a full range of PPR signs, while others were predominantly respiratory, diarrhoea, or oro-nasal syndromes, which were associated with different local disease names (olodua—a term for rinderpest, olkipiei—lung disease, oloirobi—fever, enkorotik—diarrhoea). BTV co-infection was associated with severe oro-nasal lesions. This clinical variability makes the field diagnosis of PPR challenging, highlighting the importance of access to pen-side antigen tests and multiplex assays to support improved surveillance and targeting of control activities for PPR eradication
Unusual magnetic-field dependence of partially frustrated triangular ordering in manganese tricyanomethanide
Manganese tricyanomethanide, Mn[C(CN)3]2, consists of two interpenetrating
three-dimensional rutile-like networks. In each network, the tridentate C(CN)3-
anion gives rise to superexchange interactions between the Mn2+ ions (S=5/2)
that can be mapped onto the "row model" for partially frustrated triangular
magnets. We present heat capacity measurements that reveal a phase transition
at T_N = 1.18K, indicative of magnetic ordering. The zero-field magnetically
ordered structure was solved from neutron powder diffraction data taken between
0.04 and 1.2 K. It consists of an incommensurate spiral with a temperature
independent propagation vector Q=(2Q 0 0)=(+/-0.622 0 0), where different signs
relate to the two different networks. This corresponds to (+/-0.311 +/-0.311 0)
in a quasi-hexagonal representation. The ordered moment mu=3.3mu_B is about 2/3
of the full Mn2+ moment. From the values of T_N and Q, the exchange parameters
J/k = 0.15 K and J'/J = 0.749 are estimated. The magnetic-field dependence of
the intensity of the Bragg reflection, measured for external fields
H||Q, indicates the presence of three different magnetic phases. We associate
them with the incommensurate spiral (H < 13.5 kOe), an intermediate phase (13.5
kOe 16 kOe)
proposed for related compounds. For increasing fields, Q continuously
approaches the value 1/3, corresponding to the commensurate magnetic structure
of the fully frustrated triangular lattice. This value is reached at H_c = 19
kOe. At this point, the field-dependence reverses and Q adopts a value of 0.327
at 26 kOe, the highest field applied in the experiment. Except for H_c, the
magnetic ordering is incommensurate in all three magnetic phases of
Mn[C(CN)3]2.Comment: accepted for publication in J. Phys.: Condens. Matte
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