404 research outputs found
Akari Observations of Brown Dwarfs. II CO2 as Probe of Carbon and Oxygen Abundances in Brown Dwarfs
Recent observations with the infrared astronomical satellite AKARI have shown
that the CO2 bands at 4.2 micron in three brown dwarfs are much stronger than
expected from the unified cloudy model (UCM) based on recent solar C & O
abundances. This result has been a puzzle, but we now find that this is simply
an abundance effect: We show that these strong CO2 bands can be explained with
the UCMs based on the classical C & O abundances (log Ac and log Ao), which are
about 0.2 dex larger compared to the recent values. Since three other brown
dwarfs could be well interpreted with the recent solar C & O abundances, we
require at least two model sequences based on the different chemical
compositions to interpret all the AKARI spectra. The reason for this is that
the CO2 band is especially sensitive to C & O abundances, since the CO2
abundance depends approximately on AcAo^2 --- the cube of C & O abundances. For
this reason, even low resolution spectra of very cool dwarfs, especially of CO2
cannot be understood unless a model with proper abundances is applied. For the
same reason, CO2 is an excellent indicator of C & O abundances, and we can now
estimate C & O abundances of brown dwarfs: Three out of six brown dwarfs
observed with AKARI should have high C & O abundances similar to the classical
solar values (e.g. logAc = 8.60 and logAo = 8.92), but the other three may have
low C & O abundances similar to the recent solar values (e.g. logAc = 8.39 and
logAo = 8.69). This result implies that three out of six brown dwarfs are
highly metal rich relative to the Sun if the recent solar C & O abundances are
correct.Comment: 12 pages, 6 figures, To appear in ApJ June 20 issu
Functionally Distinct Subsets of CD1d-restricted Natural Killer T Cells Revealed by CD1d Tetramer Staining
CD1d-restricted natural killer (NK)T cells are known to potently secrete T helper (Th)1 and Th2 cytokines and to mediate cytolysis, but it is unclear how these contrasting functional activities are regulated. Using lipid antigenβloaded CD1d tetramers, we have distinguished two subsets of CD1d-restricted T cells in fresh peripheral blood that differ in cytokine production and cytotoxic activation. One subset, which was CD4β, selectively produced the Th1 cytokines interferon Ξ³ and tumor necrosis factor Ξ±, and expressed NKG2d, a marker associated with cytolysis of microbially infected and neoplastic cells. This subset up-regulated perforin after exposure to interleukin (IL)-2 or IL-12. In contrast, CD4+ CD1d-restricted NKT cells potently produced both Th1 and Th2 cytokines, up-regulated perforin in response to stimulation by phorbol myristate acetate and ionomycin but not IL-2 or IL-12, and could be induced to express CD95L. Further, for both CD1d-restricted NKT cell subsets, we found that antigenic stimulation induced cytokine production but not perforin expression, whereas exposure to inflammatory factors enhanced perforin expression but did not stimulate cytokine production. These results show that the various activities of CD1d-restricted T cells in tumor rejection, autoimmune disease, and microbial infections could result from activation of functionally distinct subsets, and that inflammatory and antigenic stimuli may influence different effector functions
FRET probe for detecting two mutations in one EGFR mRNA
Technologies for visualizing and tracking RNA are essential in molecular biology, including in disease-related fields. In this study, we propose a novel probe set (DAt-probe and T-probe) that simultaneously detects two mutations in the same RNA using fluorescence resonance energy transfer (FRET). The DAt-probe carrying the fluorophore Atto488 and the quencher Dabcyl were used to detect a cancer mutation (exon19del), and the T-probe carrying the fluorophore Tamra was used to detect drug resistance mutations (T790M) in epidermal growth factor receptor (EGFR) mRNA. These probes were designed to induce FRET when both mutations were present in the mRNA. Gel electrophoresis confirmed that the two probes could efficiently bind to the mutant mRNA. We measured the FRET ratios using wild-type and double-mutant RNAs and found a significant difference between them. Even in living cells, the FRET probe could visualize mutant RNA. As a result, we conclude that this probe set provides a method for detecting two mutations in the single EGFR mRNA via FRET
Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
We report a detection of water in emission in the spectrum of the M2
supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer
(SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO
Archives. The emission first appears in the 6 micron region (nu2 fundamental)
and then in the 40 micron region (pure rotation lines) despite the rather
strong dust emission. The intensity ratios of the emission features are far
from those of the optically thin gaseous emission. Instead, we could reproduce
the major observed emission features by an optically thick water sphere of the
inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) =
3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near
infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission
provides strong constraints on the nature of water in the early M supergiant
stars, and especially its origin in the outer atmosphere is confirmed against
other models such as the large convective cell model. We finally confirm that
the early M supergiant star is surrounded by a huge optically thick sphere of
the warm water vapor, which may be referred to as MOLsphere for simplicity.
Thus, the outer atmosphere of M supergiant stars should have a complicated
hierarchical and/or hybrid structure with at least three major constituents
including the warm MOLsphere (T about 1.0E+3K) together with the previously
known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope
(T about 1.0E+2K).Comment: 14 pages, 5 postscript figures, to appear in ApJ
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