6,151 research outputs found
Regulation of AQP0 water permeability is enhanced by cooperativity.
Aquaporin 0 (AQP0), essential for lens clarity, is a tetrameric protein composed of four identical monomers, each of which has its own water pore. The water permeability of AQP0 expressed in Xenopus laevis oocytes can be approximately doubled by changes in calcium concentration or pH. Although each monomer pore functions as a water channel, under certain conditions the pores act cooperatively. In other words, the tetramer is the functional unit. In this paper, we show that changes in external pH and calcium can induce an increase in water permeability that exhibits either a positive cooperativity switch-like increase in water permeability or an increase in water permeability in which each monomer acts independently and additively. Because the concentrations of calcium and hydrogen ions increase toward the center of the lens, a concentration signal could trigger a regulatory change in AQP0 water permeability. It thus seems plausible that the cooperative modes of water permeability regulation by AQP0 tetramers mediated by decreased pH and elevated calcium are the physiologically important ones in the living lens
On the HI-Hole and AGB Stellar Population of the Sagittarius Dwarf Irregular Galaxy
Using two HST/ACS data-sets that are separated by ~2 years has allowed us to
derive the relative proper-motion for the Sagittarius dwarf irregular (SagDIG)
and reduce the heavy foreground Galactic contamination. The proper-motion
decontaminated SagDIG catalog provides a much clearer view of the young
red-supergiant and intermediate-age asymptotic giant branch populations. We
report the identification of 3 Milky Way carbon-rich dwarf stars, probably
belonging to the thin disk, and pointing to the high incidence of this class at
low Galactic latitudes. A sub-group of 4 oxygen-rich candidate stars depicts a
faint, red extension of the well-defined SagDIG carbon-rich sequence. The
origin of these oxygen-rich candidate stars remains unclear, reflecting the
uncertainty in the ratio of carbon/oxygen rich stars. SagDIG is also a gas-rich
galaxy characterized by a single large cavity in the gas disk (HI-hole), which
is offset by ~360 pc from the optical centre of the galaxy. We nonetheless
investigate the stellar feedback hypothesis by comparing the proper-motion
cleaned stellar populations within the HI-hole with appropriately selected
comparison regions, having higher HI densities external to the hole. The
comparison shows no significant differences. In particular, the centre of the
HI-hole (and the comparison regions) lack stellar populations younger than ~400
Myr, which are otherwise abundant in the inner body of the galaxy. We conclude
that there is no convincing evidence that the SagDIG HI-hole is the result of
stellar feedback, and that gravitational and thermal instabilities in the gas
are the most likely mechanism for its formation.Comment: Accepted for publication in A&A, 11 pages, 6 jpeg figure
Mass production of volume phase holographic gratings for the VIRUS spectrograph array
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) is a baseline
array of 150 copies of a simple, fiber-fed integral field spectrograph that
will be deployed on the Hobby-Eberly Telescope (HET). VIRUS is the first
optical astronomical instrument to be replicated on an industrial scale, and
represents a relatively inexpensive solution for carrying out large-area
spectroscopic surveys, such as the HET Dark Energy Experiment (HETDEX). Each
spectrograph contains a volume phase holographic (VPH) grating with a 138 mm
diameter clear aperture as its dispersing element. The instrument utilizes the
grating in first-order for 350-550 nm. Including witness samples, a suite of
170 VPH gratings has been mass produced for VIRUS. Here, we present the design
of the VIRUS VPH gratings and a discussion of their mass production. We
additionally present the design and functionality of a custom apparatus that
has been used to rapidly test the first-order diffraction efficiency of the
gratings for various discrete wavelengths within the VIRUS spectral range. This
device has been used to perform both in-situ tests to monitor the effects of
adjustments to the production prescription as well as to carry out the final
acceptance tests of the gratings' diffraction efficiency. Finally, we present
the as-built performance results for the entire suite of VPH gratings.Comment: 16 pages, 11 figures, 2 tables. To be published in Proc. SPIE, 2014,
"Advances in Optical and Mechanical Technologies for Telescopes and
Instrumentation", 9151-53. The work presented in this article follows from
arXiv:1207:448
Evolutionary calculations of phase separation in crystallizing white dwarf stars
We present an exploration of the significance of Carbon/Oxygen phase
separation in white dwarf stars in the context of self-consistent evolutionary
calculations. Because phase separation can potentially increase the calculated
ages of the oldest white dwarfs, it can affect the age of the Galactic disk as
derived from the downturn in the white dwarf luminosity function. We find that
the largest possible increase in ages due to phase separation is 1.5 Gyr, with
a most likely value of approximately 0.6 Gyr, depending on the parameters of
our white dwarf models.
The most important factors influencing the size of this delay are the total
stellar mass, the initial composition profile, and the phase diagram assumed
for crystallization. We find a maximum age delay in models with masses of 0.6
solar masses, which is near the peak in the observed white dwarf mass
distribution. We find that varying the opacities (via the metallicity) has
little effect on the calculated age delays.
In the context of Galactic evolution, age estimates for the oldest Galactic
globular clusters range from 11.5 to 16 Gyr, and depend on a variety of
parameters. In addition, a 4 to 6 Gyr delay is expected between the formation
of the globular clusters and that of the Galactic thin disk, while the observed
white dwarf luminosity function gives an age estimate for the thin disk of 9.5
+/-1.0 Gyr, without including the effect of phase separation. Using the above
numbers, we see that phase separation could add between 0 to 3 Gyr to the white
dwarf ages and still be consistent with the overall picture of Galaxy
formation. Our calculated maximum value of 1.5 Gyr fits within these bounds, as
does our best guess value of 0.6 Gyr.Comment: 13 total pages, 8 figures, 3 tables, accepted for publication in the
Astrophysical Journal on May 25, 199
Mode identification of Pulsating White Dwarfs using the HST
We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV
stars G226-29 and G185-32, and for the pulsating DBV star PG1351+489 with the
Hubble Space Telescope Faint Object Spectrograph, to compare the ultraviolet to
the optical pulsation amplitude and determine the pulsation indices. We find
that for essentially all observed pulsation modes, the amplitude rises to the
ultraviolet as the theoretical models predict for l=1 non-radial g-modes. We do
not find any pulsation mode visible only in the ultraviolet, nor any modes
whose phase flips by 180 degrees; in the ultraviolet, as would be expected if
high l pulsations were excited. We find one periodicity in the light curve of
G185-32, at 141 s, which does not fit theoretical models for the change of
amplitude with wavelength of g-mode pulsations.Comment: Accepted for publication in the Astrophysical Journal, Aug 200
Genetic variation in wood properties of mid-rotation age Eucalyptus globoidea
Background: Eucalyptus globoidea Blakely produces ground-durable (Class 2) and stiff wood and has the potential to be
grown in New Zealand to supply high-value environmentally-friendly timber for use as posts in the agricultural sector
and stiff veneers for the LVL industry. The New Zealand Dryland Forests Initiative (NZDFI) has established a breeding
programme for this species. The objective of this study was to identify trees with superior wood properties for commercial
propagation enabling the establishment of a domestic plantation resource of ground-durable timber.
Methods: The genetic variation in wood properties at mid-rotation age (8-year-old) of 141 E. globoidea families was
assessed for the following traits: heartwood diameter, diameter under bark at ~0.5 m height, combined sapwood diameter,
heartwood collapse, sapwood collapse, standing tree acoustic velocity and extractive content in the heartwood. Families
were ranked and genotypes with large heartwood diameter, high extractive content and stiffness as well as low collapse
were identified.
Results: Heartwood diameter (h2
= 0.51) and extractive content (h2
= 1.16) showed good heritability, which in combination
with high variation are promising traits for a breeding programme. The high heritability for extractive content indicated
a closer relatedness within the population than the assumption of unrelated families of half-siblings. The unfavourable
correlation between the heartwood diameter and extractive content (genetic correlation (rg
) = −0.45) indicated that a
compromise is required for simultaneous improvement of both traits. Heritability estimates for heartwood collapse
(h2 = 0.30) and acoustic velocity (h2 = 0.36) were moderate.
Conclusions: Genetic selection for wood quality traits of E. globoidea is practically feasible. Superior individuals with
above average performance for multiple traits were present in the breeding populations, however, this was dependent on
the intended end use of the timber
Enhanced root-to-shoot translocation of cadmium in the hyperaccumulating ecotype of Sedum alfredii
Sedum alfredii (Crasulaceae) is the only known Cd-hyperaccumulating species that are not in the Brassica family; the mechanism of Cd hyperaccumulation in this plant is, however, little understood. Here, a combination of radioactive techniques, metabolic inhibitors, and fluorescence imaging was used to contrast Cd uptake and translocation between a hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of S. alfredii. The Km of 109Cd influx into roots was similar in both ecotypes, while the Vmax was 2-fold higher in the HE. Significant inhibition of Cd uptake by low temperature or metabolic inhibitors was observed in the HE, whereas the effect was less pronounced in the NHE. 109Cd influx into roots was also significantly decreased by high Ca in both ecotypes. The rate of root-to-shoot translocation of 109Cd in the HE was >10 times higher when compared with the NHE, and shoots of the HE accumulated dramatically higher 109Cd concentrations those of the NHE. The addition of the metabolic inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) resulted in a significant reduction in Cd contents in the shoots of the HE, and in the roots of the NHE. Cd was distributed preferentially to the root cylinder of the HE but not the NHE, and there was a 3–5 times higher Cd concentration in xylem sap of the HE in contrast to the NHE. These results illustrate that a greatly enhanced rate of root-to-shoot translocation, possibly as a result of enhanced xylem loading, rather than differences in the rate of root uptake, was the pivotal process expressed in the Cd hyperaccumulator HE S. alfredii
C-reactive Protein and Temperament: An Instrumental Variable Analysis
BACKGROUND:
Temperament is associated with circulating inflammatory biomarkers, such as C-reactive protein (CRP), which has been associated with various health conditions, including depression. This study aims to investigate whether genetic disposition for increased circulating CRP concentration may influence temperament over the life-course.
METHODS:
Using a longitudinal cohort that began in 1980—the Cardiovascular Risk in Young Finns Study (YFS)—we included 920 participants (59.8% female) aged 3–12 years old at baseline (childhood), and the same participants again at ages 30–39 years old (adulthood) in this study. We used both ordinary least-squares regression (OLS linear regression) and instrumental variable (IV) regression to assess associations between CRP concentration and temperament dimensions (negative emotionality, activity, and sociability). To represent genetically determined risk for increase in circulating CRP concentration, we calculated a weighted genetic risk score (GRS) which reflects risk for increased circulating CRP concentration.
RESULTS:
In OLS linear regression analyses, we found that increased circulating CRP concentration in childhood was associated with slightly higher scores for sociability in childhood (19% increase, CI = 7–32%) and adulthood (13% increase, CI = 2–27%), and lower activity scores in adulthood (15% decrease, CI = 3–25%). For all IV regressions, there were no apparent associations between GRS and temperament in either childhood or adulthood (all p>0.3). The Durbin-Wu-Hausman test for endogeneity produced p-values (all>0.05) that suggest there is no evidence for disagreement between the OLS and IV estimates.
CONCLUSIONS:
We found no clear evidence for an association of GRS for elevated CRP with childhood or adulthood emotionality, activity, or sociability, although circulating CRP was associated with some of these traits
Nonclassical effects in a driven atoms/cavity system in the presence of arbitrary driving field and dephasing
We investigate the photon statistics of light transmitted from a driven
optical cavity containing one or two atoms interacting with a single mode of
the cavity field. We treat arbitrary driving fields with emphasis on departure
from previous weak field results. In addition effects of dephasing due to
atomic transit through the cavity mode are included using two different models.
We find that both models show the nonclassical correlations are quite sensitive
to dephasing. The effect of multiple atoms on the system dynamics is
investigated by placing two atoms in the cavity mode at different positions,
therefore having different coupling strengths.Comment: 8 pages, 10 figures, minor typographical errors corrected, submitted
to Phys Rev
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