2,459 research outputs found
The role of inhibitory G proteins and regulators of G protein signaling in the in vivo control of heart rate and predisposition to cardiac arrhythmias
Inhibitory heterotrimeric G proteins and the control of heart rate. The activation of cell signaling pathways involving inhibitory heterotrimeric G proteins acts to slow the heart rate via modulation of ion channels. A large number of Regulators of G protein signalings (RGSs) can act as GTPase accelerating proteins to inhibitory G proteins and thus it is important to understand the network of RGS\G-protein interaction. We will review our recent findings on in vivo heart rate control in mice with global genetic deletion of various inhibitory G protein alpha subunits. We will discuss potential central and peripheral contributions to the phenotype and the controversies in the literature
What Does Clustering Tell Us About the Buildup of the Red Sequence?
We analyze the clustering of red and blue galaxies from four samples spanning
a redshift range of 0.4<z<2.0 to test the various scenarios by which galaxies
evolve onto the red sequence. The data are taken from the UKIDSS Ultra Deep
Survey, DEEP2, and COMBO-17. The use of clustering allows us to determine what
fraction of the red sequence is made up of central galaxies and satellite
galaxies. At all redshifts, including z=0, the data are consistent with ~60% of
satellite galaxies being red or quenched, implying that ~1/3 of the red
sequence is comprised of satellite galaxies. More than three-fourths of red
satellite galaxies were moved to the red sequence after they were accreted onto
a larger halo. The constant fraction of satellite galaxies that are red yields
a quenching time for satellite galaxies that depends on redshift in the same
way as halo dynamical times; t_Q ~ (1+z)^{-1.5}. In three of the four samples,
the data favor a model in which red central galaxies are a random sample of all
central galaxies; there is no preferred halo mass scale at which galaxies make
the transition from star-forming to red and dead. The large errors on the
fourth sample inhibit any conclusions. Theoretical models in which star
formation is quenched above a critical halo mass are excluded by these data. A
scenario in which mergers create red central galaxies imparts a weaker
correlation between halo mass and central galaxy color, but even the merger
scenario creates tension with red galaxy clustering at redshifts above 0.5.
These results suggest that the mechanism by which central galaxies become red
evolves from z=0.5 to z=0.Comment: 18 emulateapj pages, 13 figures. submitted to Ap
Star Formation Quenching Timescale of Central Galaxies in a Hierarchical Universe
Central galaxies make up the majority of the galaxy population, including the
majority of the quiescent population at . Thus, the mechanism(s) responsible for quenching
central galaxies plays a crucial role in galaxy evolution as whole. We combine
a high resolution cosmological -body simulation with observed evolutionary
trends of the "star formation main sequence," quiescent fraction, and stellar
mass function at to construct a model that statistically tracks the
star formation histories and quenching of central galaxies. Comparing this
model to the distribution of central galaxy star formation rates in a group
catalog of the SDSS Data Release 7, we constrain the timescales over which
physical processes cease star formation in central galaxies. Over the stellar
mass range to we infer quenching
e-folding times that span to with more massive
central galaxies quenching faster. For , this implies a total migration time of from the star formation main sequence to quiescence. Compared
to satellites, central galaxies take longer to quench
their star formation, suggesting that different mechanisms are responsible for
quenching centrals versus satellites. Finally, the central galaxy quenching
timescale we infer provides key constraints for proposed star formation
quenching mechanisms. Our timescale is generally consistent with gas depletion
timescales predicted by quenching through strangulation. However, the exact
physical mechanism(s) responsible for this still remain unclear.Comment: 16 pages, 11 figure
Rates of hillslope lowering in the Badlands of North Dakota
Measurements in a small drainage basin in the Little Missouri Badlands of western North Dakota indicate an average rate of hillslope lowering by slopewash of 0.41 inch per year on the west-facing hillslopes underlain by the Sentinel Butte Formation, 0.14 inch per year on the southwest-facing hillslopes underlain by the Tongue River Formation, and 0.11 inch per year on the northeast-facing hillslopes underlain by the Tongue River Formation. Soil creep occurs mainly on the Tongue River Formation and is mostly restricted to the northeast-facing hillslopes where the average rate of soil creep parallel to the hillslope surface is 0.23 inch per year in the upper 2.5 inches of surficial sediment. Erosion perpendicular to the face of seepage steps is 0.29 inch per year.
The Sentinel Butte Formation has a lower rate of infiltration and percolation, which results in a higher rate of surface runoff than on the Tongue River Formation. This in part causes the higher rates of lowering of the hillslope by slopewash on the Sentinel Butte Formation than on the Tongue River Formation.
The lowering of the hillslopes by slopewash contributes 99.9 percent of the 43,000 cubic feet of sediment per year from the hillslopes in the study areas. Comparison of the hillslope sediment yield with the rates of valley-bottom deposition from June to July 1969 indicates that approximately 62 percent of the hillslope sediment left the drainage basin
Time and soil development on lateral moraines, Martin River Glacier, south-central Alaska
During the summer of 1966, eighteen soil profiles on a series of 21 lateral moraines, were studied to ascertain the relationship of time to soil development. The moraines are located on Charlotte Ridge on the south margin of the Martin River Glacier in south-central Alaska. The elevation of the highest moraine is approximately fifteen hundred feet and is located 800 feet above the present level of the glacier.
To determine the direct effect of time on soil formation, the remaining soil forming factors were kept constant; the soil pits were located so that relief, exposure, and vegetation of the sites were as similar as possible. Till, rich in variable amounts of basalt, granodiorite and metamorphic rock, composed the moraine sediment. The climate of the region is cool maritime but microclimatic differences may be important for the ridge as a whole.
Field results indicate that a mature podzolic soil has developed on the upper 14 moraines, whereas the lower 7 moraines are characterized by a regosol. Samples of the soil horizons were collected for laboratory analysis.
The analyses for total carbon, carbonate carbon, organic carbon, nitrogen and particle-size distribution support the field descriptions and also confirm the major difference in soil development between the fourteenth and fifteenth moraines.
Lateral variation of the soil profiles along single moraines is minor. The increase in the abundance of cobbles in the till of the older moraines sharply increases the permeability of the till, thus increasing the depth of the soil profile. This variability in cobble distribution is the main factor affecting the minor soil profile differences on the older moraines.
No absolute date of formation exists for the older moraines, but tree-ring analysis indicates that the youngest two moraines formed in 1910 and 1700-1800, respectively. A core of a large spruce tree immediately upslope from the 1700-1800 year old moraine indicated the tree was at least 407 years old. But, the core penetrated only about half-way to the center of the tree revealing a probable age of about 800 years. Any further conclusion on the age of the older moraine must wait until datable material is found in the moraine sediment.
The study of the relationship of time to soil development on the till of Charlotte Ridge indicates a significant time interval between the fourteenth and fifteenth moraines. Other significant differences in age or a gradational sequence in age of the 21 moraines is not apparent from the analysis of the soil development
Galaxy evolution in groups and clusters: satellite star formation histories and quenching timescales in a hierarchical Universe
Satellite galaxies in groups and clusters are more likely to have low star
formation rates (SFR) and lie on the red-sequence than central (field)
galaxies. Using galaxy group/cluster catalogs from SDSS DR7, together with a
cosmological N-body simulation to track satellite orbits, we examine the star
formation histories and quenching timescales of satellites of M_star > 5 x 10^9
M_sun at z=0. We first explore satellite infall histories: group preprocessing
and ejected orbits are critical aspects of satellite evolution, and properly
accounting for these, satellite infall typically occurred at z~0.5, or ~5 Gyr
ago. To obtain accurate initial conditions for the SFRs of satellites at their
time of first infall, we construct an empirical parametrization for the
evolution of central galaxy SFRs and quiescent fractions. With this, we
constrain the importance and efficiency of satellite quenching as a function of
satellite and host halo mass, finding that satellite quenching is the dominant
process for building up all quiescent galaxies at M_star < 10^10 M_sun. We then
constrain satellite star formation histories, finding a 'delayed-then-rapid'
quenching scenario: satellite SFRs evolve unaffected for 2-4 Gyr after infall,
after which star formation quenches rapidly, with an e-folding time of < 0.8
Gyr. These quenching timescales are shorter for more massive satellites but do
not depend on host halo mass: the observed increase in satellite quiescent
fraction with halo mass arises simply because of satellites quenching in a
lower mass group prior to infall (group preprocessing), which is responsible
for up to half of quenched satellites in massive clusters. Because of the long
time delay before quenching starts, satellites experience significant stellar
mass growth after infall, nearly identical to central galaxies. This fact
provides key physical insight into the subhalo abundance matching method.Comment: 25 pages, 13 figures. Accepted for publication in MNRAS, matches
published versio
Where do "red and dead" early-type void galaxies come from?
Void regions of the Universe offer a special environment for studying
cosmology and galaxy formation, which may expose weaknesses in our
understanding of these phenomena. Although galaxies in voids are observed to be
predominately gas rich, star forming and blue, a sub-population of bright red
void galaxies can also be found, whose star formation was shut down long ago.
Are the same processes that quench star formation in denser regions of the
Universe also at work in voids?
We compare the luminosity function of void galaxies in the 2dF Galaxy
Redshift Survey, to those from a galaxy formation model built on the Millennium
Simulation. We show that a global star formation suppression mechanism in the
form of low luminosity "radio mode" AGN heating is sufficient to reproduce the
observed population of void early-types. Radio mode heating is environment
independent other than its dependence on dark matter halo mass, where, above a
critical mass threshold of approximately M_vir~10^12.5 M_sun, gas cooling onto
the galaxy is suppressed and star formation subsequently fades. In the
Millennium Simulation, the void halo mass function is shifted with respect to
denser environments, but still maintains a high mass tail above this critical
threshold. In such void halos, radio mode heating remains efficient and red
galaxies are found; collectively these galaxies match the observed space
density without any modification to the model. Consequently, galaxies living in
vastly different large-scale environments but hosted by halos of similar mass
are predicted to have similar properties, consistent with observations.Comment: 6 pages, 3 figures, accepted MNRA
Foam rigidized inflatable structural assemblies
An inflatable and rigidizable structure for use as a habitat or a load bearing structure is disclosed. The structure consists of an outer wall and an inner wall defining a containment member and a bladder. The bladder is pressurized to erect the structure from an initially collapsed state. The containment member is subsequently injected with rigidizable fluid through an arrangement of injection ports. Exhaust gases from the curing rigidizable fluid are vented through an arrangement of exhaust ports. The rate of erection can be controlled by frictional engagement with a container or by using a tether. A method for fabricating a tubular structure is disclosed
Cosmological Constraints from Galaxy Clustering and the Mass-to-Number Ratio of Galaxy Clusters
We place constraints on the average density (Omega_m) and clustering
amplitude (sigma_8) of matter using a combination of two measurements from the
Sloan Digital Sky Survey: the galaxy two-point correlation function, w_p, and
the mass-to-galaxy-number ratio within galaxy clusters, M/N, analogous to
cluster M/L ratios. Our w_p measurements are obtained from DR7 while the sample
of clusters is the maxBCG sample, with cluster masses derived from weak
gravitational lensing. We construct non-linear galaxy bias models using the
Halo Occupation Distribution (HOD) to fit both w_p and M/N for different
cosmological parameters. HOD models that match the same two-point clustering
predict different numbers of galaxies in massive halos when Omega_m or sigma_8
is varied, thereby breaking the degeneracy between cosmology and bias. We
demonstrate that this technique yields constraints that are consistent and
competitive with current results from cluster abundance studies, even though
this technique does not use abundance information. Using w_p and M/N alone, we
find Omega_m^0.5*sigma_8=0.465+/-0.026, with individual constraints of
Omega_m=0.29+/-0.03 and sigma_8=0.85+/-0.06. Combined with current CMB data,
these constraints are Omega_m=0.290+/-0.016 and sigma_8=0.826+/-0.020. All
errors are 1-sigma. The systematic uncertainties that the M/N technique are
most sensitive to are the amplitude of the bias function of dark matter halos
and the possibility of redshift evolution between the SDSS Main sample and the
maxBCG sample. Our derived constraints are insensitive to the current level of
uncertainties in the halo mass function and in the mass-richness relation of
clusters and its scatter, making the M/N technique complementary to cluster
abundances as a method for constraining cosmology with future galaxy surveys.Comment: 23 pages, submitted to Ap
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