2,943 research outputs found
Intracellular pH regulation in isolated trout gill mitochondrion-rich (MR) cell subtypes: Evidence for Na\u3csup\u3e+\u3c/sup\u3e/H\u3csup\u3e+\u3c/sup\u3e activity
We have studied intracellular pH (pHi) recovery in isolated trout gill mitochondrion-rich (MR) cells following acidification by the NH4Cl pre-pulse technique. Within a mixed MR cell population, one cell type displayed Na+-independent pHi recovery while the other cell type lacked a Na+-independent pHi recovery. Cells displaying Na+ independent recovery exhibited a significantly higher buffering capacity compared to cells lacking Na+-independent pHi recovery. Cells displaying Na+ independent recovery were identified as PNA+ (peanut lectin agluttinin binding) MR cells while those unable to recover were identified as PNA- (non-peanut lectin agluttinin binding) MR cells. Therefore, recovery from acidification in the absence of Na+ provides a direct functional marker for PNA+ and PNA- MR cells. Re-addition of Na+ to acidified cells resulted in a transient pHi recovery in both cell types. This event was abolished by amiloride (500 ΌM) but it was insensitive to phenamil (50 ΌM). The phorbol ester PMA (1 ΌM) potentiated the Na+ induced pHi recovery suggesting that activation by PKC is required for continuous Na+/H+ exchanger activity in trout gill MR cells. This study is the first functional description of pHi recovery in lectin-identified trout gill MR cells and provides insight into a putative cellular signaling mechanism that may control pHi regulation in the gill epithelium. © 2009 Elsevier Inc. All rights reserved
A Test of Pre-Main Sequence Evolutionary Models Across the Stellar/Substellar Boundary Based on Spectra of the Young Quadruple GG Tau
We present spatially separated optical spectra of the components of the young
hierarchical quadruple GG Tau. Spectra of GG Tau Aa and Ab (separation 0".25 ~
35 AU) were obtained with the Faint Object Spectrograph aboard the Hubble Space
Telescope. Spectra of GG Tau Ba and Bb (separation 1".48 ~ 207 AU) were
obtained with both the HIRES and the LRIS spectrographs on the W. M. Keck
telescopes. The components of this mini-cluster, which span a wide range in
spectral type (K7 - M7), are used to test both evolutionary models and the
temperature scale for very young, low mass stars under the assumption of coeval
formation. Of the evolutionary models tested, those of Baraffe et al. (1998,
A&A, 337, 403) yield the most consistent ages when combined with a temperature
scale intermediate between that of dwarfs and giants. The version of the
Baraffe et al. models computed with a mixing length nearly twice the pressure
scale height is of particular interest as it predicts masses for GG Tau Aa and
Ab that are in agreement with their dynamical mass estimate.
Using this evolutionary model and a coeval (at 1.5 Myrs) temperature scale,
we find that the coldest component of the GG Tau system, GG Tau Bb, is
substellar with a mass of 0.044 +/- 0.006 Msun. This brown dwarf companion is
especially intriguing as it shows signatures of accretion, although this
accretion is not likely to alter its mass significantly. GG Tau Bb is currently
the lowest mass, spectroscopically confirmed companion to a T Tauri star, and
is one of the coldest, lowest mass T Tauri objects in the Taurus-Auriga star
forming region.Comment: 25 pages, 6 figures, accepted for publication in The Astrophysical
Journa
The Structure of IR Luminous Galaxies at 100 Microns
We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.Comment: 8 tables, 23 figure
Gene expression differences during the heterogeneous progression of peripheral atherosclerosis in familial hypercholesterolemic swine
Intergenerational Education: The significance of 'reciprocity' and 'place'
In this article, the case is made for greater clarity in the definition of intergenerational practice and intergenerational education. Theoretically, the effects of all-age reciprocity and the significance of attending to 'place' are explored. Taken together, they help point to what is distinctive about the scope and purpose of intergenerational education. The author argues that any intergenerational practice must always involve an educative element that is focused, at least in part, on the on-going reciprocal production of new relations between generations through the way challenges are purposefully responded to in some specific place
Noise Kernel and Stress Energy Bi-Tensor of Quantum Fields in Hot Flat Space and Gaussian Approximation in the Optical Schwarzschild Metric
Continuing our investigation of the regularization of the noise kernel in
curved spacetimes [N. G. Phillips and B. L. Hu, Phys. Rev. D {\bf 63}, 104001
(2001)] we adopt the modified point separation scheme for the class of optical
spacetimes using the Gaussian approximation for the Green functions a la
Bekenstein-Parker-Page. In the first example we derive the regularized noise
kernel for a thermal field in flat space. It is useful for black hole
nucleation considerations. In the second example of an optical Schwarzschild
spacetime we obtain a finite expression for the noise kernel at the horizon and
recover the hot flat space result at infinity. Knowledge of the noise kernel is
essential for studying issues related to black hole horizon fluctuations and
Hawking radiation backreaction. We show that the Gaussian approximated Green
function which works surprisingly well for the stress tensor at the
Schwarzschild horizon produces significant error in the noise kernel there. We
identify the failure as occurring at the fourth covariant derivative order.Comment: 21 pages, RevTeX
Light Element Depletion in Contracting Brown Dwarfs and Pre--Main-Sequence Stars
We present an analytic calculation of the thermonuclear depletion of the
light elements lithium, beryllium, and boron in fully convective, low-mass
stars. Under the presumption that the pre--main-sequence star is always fully
mixed during contraction, we find that the burning of these rare light elements
can be computed analytically, even when the star is degenerate. Using the
effective temperature as a free parameter, we constrain the properties of
low-mass stars from observational data, independently of the uncertainties
associated with modeling their atmospheres and convection. Our analytic
solution explains the dependence of the age at a given level of elemental
depletion on the stellar effective temperature, nuclear cross sections, and
chemical composition. Most importantly, our results allow observers to
translate lithium non-detections in young cluster members into a
model-independent minimum age for that cluster. Using this procedure, we have
found lower limits to the ages of the Pleiades (100 Myr) and Alpha Persei (60
Myr) clusters. Recent experimental work on the low energy resonance in the
^10B(p,\alpha)^7Be reaction has greatly enhanced estimates of the destruction
rate of ^10B, making it possible for stars with M>0.1 M_sun to deplete both
^10B and ^11B before reaching the main sequence. Moreover, there is an
interesting range of masses, 0.085 M_sun < M < 0.13 M_sun, where boron
depletion occurs on the main sequence in less than a Hubble time, providing a
potential ``clock'' for dating low-mass stars.Comment: 34 pages, including 6 figures; Accepted to Ap
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