252 research outputs found
Can Sodium Abundances of A-Type Stars Be Reliably Determined from Na I 5890/5896 Lines?
An extensive non-LTE abundance analysis based on Na I 5890/5896 doublet lines
was carried out for a large unbiased sample of ~120 A-type main-sequence stars
(including 23 Hyades stars) covering a wide v_e sin i range of ~10--300 km/s,
with an aim to examine whether the Na abundances in such A dwarfs can be
reliably established from these strong Na I D lines. The resulting abundances
([Na/H]_{58}), which were obtained by applying the T_eff-dependent
microturbulent velocities of \xi ~2--4 km/s with a peak at T_eff ~ 8000 K
(typical for A stars), turned out generally negative with a large diversity
(from ~-1 to ~0), while showing a sign of v_e sin i-dependence (decreasing
toward higher rotation). However, the reality of this apparently subsolar trend
is very questionable, since these [Na/H]_{58} are systematically lower by
~0.3--0.6 dex than more reliable [Na/H]_{61} (derived from weak Na I 6154/6161
lines for sharp-line stars). Considering the large \xi-sensitivity of the
abundances derived from these saturated Na I D lines, we regard that
[Na/H]_{58} must have been erroneously underestimated, suspecting that the
conventional \xi values are improperly too large at least for such strong
high-forming Na I 5890/5896 lines, presumably due to the depth-dependence of
\xi decreasing with height. The nature of atmospheric turbulent velocity field
in mid-to-late A stars would have to be more investigated before we can
determine reliable sodium abundances from these strong resonance D lines.Comment: 14 pages, 8 figures, accepted for publication in Publ. Astron. Soc.
Japan, Vol. 61, No. 5 (2009
Hydrogen-bonded multilayer of pH-responsive polymeric micelles with tannic acid for surface drug delivery
We report the design of a platform for the delivery of hydrophobic drugs conjugated to block copolymer micelles via pH-responsive linkage that are assembled within hydrogen-bonded polymer multilayer thin films.close465
Antibacterial and antibiofilm activity of Abroma augusta stabilized silver (Ag) nanoparticles against drug-resistant clinical pathogens
Infectious diseases remain among the most pressing concerns for human health. This issue has grown even more complex with the emergence of multidrug-resistant (MDR) bacteria. To address bacterial infections, nanoparticles have emerged as a promising avenue, offering the potential to target bacteria at multiple levels and effectively eliminate them. In this study, silver nanoparticles (AA-AgNPs) were synthesized using the leaf extract of a medicinal plant, Abroma augusta. The synthesis method is straightforward, safe, cost-effective, and environment friendly, utilizing the leaf extract of this Ayurvedic herb. The UV-vis absorbance peak at 424Â nm indicated the formation of AA-AgNPs, with the involvement of numerous functional groups in the synthesis and stabilization of the particles. AA-AgNPs exhibited robust antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). The MIC values of AA-AgNPs ranged from 8 to 32Â ÎŒg/mL. Electron microscopic examination of the interaction of AA-AgNPs with the test bacterial pathogens showed a deleterious impact on bacterial morphology, resulting from membrane rupture and leakage of intracellular components. AA-AgNPs also demonstrated a dose-dependent effect in curtailing biofilm formation below inhibitory doses. Overall, this study highlights the potential of AA-AgNPs in the successful inhibition of both the growth and biofilms of MRSA and VRE bacteria. Following studies on toxicity and dose optimization, such AgNPs could be developed into effective medical remedies against infections
How Many Sentinel Lymph Nodes Are Enough for Accurate Axillary Staging in T1-2 Breast Cancer?
Purpose: During a sentinel lymph node biopsy (SLNB) for breast cancer, the appropriate number of sentinel lymph nodes (SLNs) to be removed for accurate axillary staging is still controversial. We hypothesized that there might be an optimal threshold number of SLNs. We investigated how many SLNs should be removed to achieve an acceptable accuracy and ensure minimal morbidity. Methods: We reviewed data of 328 patients with invasive breast cancer who underwent SLNB followed by complete level I and II axillary dissection between January 2004 and December 2005. The false negative rate (FNR) and accuracy of SLNB according to the number of removed SLNs were evaluated. Results: The mean number of SLNs removed was 3.0 (range, 1-14), and that of total retrieved axillary lymph nodes was 17.5 (range, 10-40). In total, 111 (33.8%) patients had positive nodes on the permanent pathological report. Among them, 12 patients had negative SLNs
Hybrid star HD 81817 accompanied by brown dwarf or substellar companion
HD 81817 is known as a hybrid star. Hybrid stars have both cool stellar wind
properties and Ultraviolet (UV) or even X-ray emission features of highly
ionized atoms in their spectra. A white dwarf companion has been suggested as
the source of UV or X-ray features. HD 81817 has been observed since 2004 as a
part of a radial velocity (RV) survey program to search for exoplanets around K
giant stars using the Bohyunsan Observatory Echelle Spectrograph at the 1.8 m
telescope of Bohyunsan Optical Astronomy Observatory in Korea. We obtained 85
RV measurements between 2004 and 2019 for HD 81817 and found two periodic RV
variations. The amplitudes of RV variations are around 200 m s^-1, which are
significantly lower than that expected from a closely orbiting white dwarf
companion. Photometric data and relevant spectral lines were also analyzed to
help determine the origin of the periodic RV variations. We conclude that
627.4-day RV variations are caused by intrinsic stellar activities such as
long-term pulsations or rotational modulations of surface activities based on
H{\alpha} equivalent width (EW) variations of a similar period. On the other
hand, 1047.1-day periodic RV variations are likely to be caused by a brown
dwarf or substellar companion, which is corroborated by a recent GAIA proper
motion anomaly for HD 81817. The Keplerian fit yields a minimum mass of 27.1
M_Jup, a semimajor axis of 3.3 AU, and an eccentricity of 0.17 for the stellar
mass of 4.3 M_sun for HD 81817. The inferred mass puts HD 81817 b in the brown
dwarf desert
Microlensing Detections of Planets in Binary Stellar Systems
We demonstrate that microlensing can be used for detecting planets in binary
stellar systems. This is possible because in the geometry of planetary binary
systems where the planet orbits one of the binary component and the other
binary star is located at a large distance, both planet and secondary companion
produce perturbations at a common region around the planet-hosting binary star
and thus the signatures of both planet and binary companion can be detected in
the light curves of high-magnification lensing events. We find that identifying
planets in binary systems is optimized when the secondary is located in a
certain range which depends on the type of the planet. The proposed method can
detect planets with masses down to one tenth of the Jupiter mass in binaries
with separations <~ 100 AU. These ranges of planet mass and binary separation
are not covered by other methods and thus microlensing would be able to make
the planetary binary sample richer.Comment: 5 pages, two figures in JPG forma
- âŠ