149 research outputs found
Calculations of the Far-Wing Line Profiles of Sodium and Potassium in the Atmospheres of Substellar-Mass Objects
At the low temperatures achieved in cool brown dwarf and hot giant planet
atmospheres, the less refractory neutral alkali metals assume an
uncharacteristically prominent role in spectrum formation. In particular, the
wings of the Na-D (5890 \AA) and K I (7700 \AA) resonance lines come to define
the continuum and dominate the spectrum of T dwarfs from 0.4 to 1.0 \mic.
Whereas in standard stellar atmospheres the strengths and shapes of the wings
of atomic spectral lines are rarely needed beyond 25 \AA of a line center, in
brown dwarfs the far wings of the Na and K resonance lines out to 1000's of \AA
detunings are important. Using standard quantum chemical codes and the Unified
Franck-Condon model for line profiles in the quasi-static limit, we calculate
the interaction potentials and the wing line shapes for the dominant Na and K
resonance lines in H- and helium-rich atmospheres. Our theory has natural
absorption profile cutoffs, has no free parameters, and is readily adapted to
spectral synthesis calculations for stars, brown dwarfs, and planets with
effective temperatures below 2000 Kelvin.Comment: 14 pages, Latex, 7 figures in JPEG format, accepted for publication
in the Astrophysical Journa
The Near-Infrared and Optical Spectra of Methane Dwarfs and Brown Dwarfs
We identify the pressure--broadened red wings of the saturated potassium
resonance lines at 7700 \AA as the source of anomalous absorption seen in the
near-infrared spectra of Gliese 229B and, by extension, of methane dwarfs in
general. This conclusion is supported by the recent work of Tsuji {\it et al.}
1999, though unlike them we find that dust need not be invoked to explain the
spectra of methane dwarfs shortward of 1 micron. We find that a combination of
enhanced alkali abundances due to rainout and a more realistic non-Lorentzian
theory of resonant line shapes may be all that is needed to properly account
for these spectra from 0.5 to 1.0 microns. The WFPC2 measurement of Gliese
229B is also consistent with this theory. Furthermore, a combination of the
blue wings of this K I resonance doublet, the red wings of the Na D lines at
5890 \AA, and, perhaps, the Li I line at 6708 \AA can explain in a natural way
the observed WFPC2 band flux of Gliese 229B. Hence, we conclude that the
neutral alkali metals play a central role in the near-infrared and optical
spectra of methane dwarfs and that their lines have the potential to provide
crucial diagnostics of brown dwarfs. We speculate on the systematics of the
near-infrared and optical spectra of methane dwarfs, for a given mass and
composition, that stems from the progressive burial with decreasing \teff of
the alkali metal atoms to larger pressures and depths.Comment: Revised and accepted to Ap.J. volume 531, March 1, 2000, also
available at http://jupiter.as.arizona.edu/~burrows/papers/BMS.p
Mechanisms of necroptosis in T cells
In caspase 8-deficient mouse T cells, necroptosis occurs via a Ripk3- and Ripk1-dependent pathway independent of autophagy and programmed necrosis
Influence of pH on Ca2+ current and its control of electrical and Ca2+ signaling in ventricular myocytes
Modulation of L-type Ca2+ current (ICa,L) by H+ ions in cardiac myocytes is controversial, with widely discrepant responses reported. The pH sensitivity of ICa,L was investigated (whole cell voltage clamp) while measuring intracellular Ca2+ (Ca2+i) or pHi (epifluorescence microscopy) in rabbit and guinea pig ventricular myocytes. Selectively reducing extracellular or intracellular pH (pHo 6.5 and pHi 6.7) had opposite effects on ICa,L gating, shifting the steady-state activation and inactivation curves to the right and left, respectively, along the voltage axis. At low pHo, this decreased ICa,L, whereas at low pHi, it increased ICa,L at clamp potentials negative to 0 mV, although the current decreased at more positive potentials. When Ca2+i was buffered with BAPTA, the stimulatory effect of low pHi was even more marked, with essentially no inhibition. We conclude that extracellular H+ ions inhibit whereas intracellular H+ ions can stimulate ICa,L. Low pHi and pHo effects on ICa,L were additive, tending to cancel when appropriately combined. They persisted after inhibition of calmodulin kinase II (with KN-93). Effects are consistent with H+ ion screening of fixed negative charge at the sarcolemma, with additional channel block by H+o and Ca2+i. Action potential duration (APD) was also strongly H+ sensitive, being shortened by low pHo, but lengthened by low pHi, caused mainly by H+-induced changes in late Ca2+ entry through the L-type Ca2+ channel. Kinetic analyses of pH-sensitive channel gating, when combined with whole cell modeling, successfully predicted the APD changes, plus many of the accompanying changes in Ca2+ signaling. We conclude that the pHi-versus-pHo control of ICa,L will exert a major influence on electrical and Ca2+-dependent signaling during acid–base disturbances in the heart
Cellular IAPs inhibit a cryptic CD95-induced cell death by limiting RIP1 kinase recruitment
cIAPs keep RIP1 from getting to the DISC complex and complex II; when cIAPs are repressed, signaling is modulated by the cFLIP isoform
From hope to hope:the experience of older Chinese people with advanced cancer
In our study that explored the current end-of-life care provision for Chinese older people with advanced/terminal cancer, hope emerged as a significant aspect of coping with their condition. Drawing on data from in-depth interviews with a group of older people, their family carers and health professionals, this article explores participants’ constructions of hope in terms of what they were hoping for, how their hopes helped them cope with their illness and what sociocultural resources they drew on to build and sustain these hopes. While acknowledging similarities to Western studies of hope in terminal illness, this article identifies significant divergences in terms of the impact of different sociocultural values and their implications for clinical practice in light of an unfavourable health care environment for patients with advanced cancer and a social support system sustained mainly by Chinese families. It argues that hope represents an important resource for coping with terminal illness among these patients
The Theory of Brown Dwarfs and Extrasolar Giant Planets
Straddling the traditional realms of the planets and the stars, objects below
the edge of the main sequence have such unique properties, and are being
discovered in such quantities, that one can rightly claim that a new field at
the interface of planetary science and and astronomy is being born. In this
review, we explore the essential elements of the theory of brown dwarfs and
giant planets, as well as of the new spectroscopic classes L and T. To this
end, we describe their evolution, spectra, atmospheric compositions, chemistry,
physics, and nuclear phases and explain the basic systematics of
substellar-mass objects across three orders of magnitude in both mass and age
and a factor of 30 in effective temperature. Moreover, we discuss the
distinctive features of those extrasolar giant planets that are irradiated by a
central primary, in particular their reflection spectra, albedos, and transits.
Aspects of the latest theory of Jupiter and Saturn are also presented.
Throughout, we highlight the effects of condensates, clouds, molecular
abundances, and molecular/atomic opacities in brown dwarf and giant planet
atmospheres and summarize the resulting spectral diagnostics. Where possible,
the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for
publication in the Reviews of Modern Physics. 30 figures are color. Most of
the figures are in GIF format to reduce the overall size. The full version
with figures can also be found at:
http://jupiter.as.arizona.edu/~burrows/papers/rm
Book Review: The Qing Opening to the Ocean: Chinese Maritime Policies, 1684–1757, written by Zhao Gang. Honolulu: Univ. of Hawai’i Press, 2013. viii + 272 pp.
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