1,526 research outputs found
Avidity enhancement of L-selectin bonds by flow: shear-promoted rotation of leukocytes turn labile bonds into functional tethers
L-selectin is a key lectin essential for leukocyte capture and rolling on vessel walls. Functional adhesion of L-selectin requires a minimal threshold of hydrodynamic shear. Using high temporal resolution videomicroscopy, we now report that L-selectin engages its ligands through exceptionally labile adhesive bonds (tethers) even below this shear threshold. These tethers share a lifetime of 4 ms on distinct physiological ligands, two orders of magnitude shorter than the lifetime of the P-selectin–PSGL-1 bond. Below threshold shear, tether duration is not shortened by elevated shear stresses. However, above the shear threshold, selectin tethers undergo 14-fold stabilization by shear-driven leukocyte transport. Notably, the cytoplasmic tail of L-selectin contributes to this stabilization only above the shear threshold. These properties are not shared by P-selectin– or VLA-4–mediated tethers. L-selectin tethers appear adapted to undergo rapid avidity enhancement by cellular transport, a specialized mechanism not used by any other known adhesion receptor
p-forms on d-spherical tessellations
The spectral properties of p-forms on the fundamental domains of regular
tesselations of the d-dimensional sphere are discussed. The degeneracies for
all ranks, p, are organised into a double Poincare series which is explicitly
determined. In the particular case of coexact forms of rank (d-1)/2, for odd d,
it is shown that the heat--kernel expansion terminates with the constant term,
which equals (-1)^{p+1}/2 and that the boundary terms also vanish, all as
expected. As an example of the double domain construction, it is shown that the
degeneracies on the sphere are given by adding the absolute and relative
degeneracies on the hemisphere, again as anticipated. The eta invariant on a
fundamental domain is computed to be irrational. The spectral counting function
is calculated and the accumulated degeneracy give exactly. A generalised
Weyl-Polya conjecture for p-forms is suggested and verified.Comment: 23 pages. Section on the counting function adde
Molecular gas in high-velocity clouds: revisited scenario
We report a new search for 12CO(1-0) emission in high-velocity clouds (HVCs)
performed with the IRAM 30 m telescope. This search was motivated by the recent
detection of cold dust emission in the HVCs of Complex C. Despite a spatial
resolution which is three times better and sensitivity twice as good compared
to previous studies, no CO emission is detected in the HVCs of Complex C down
to a best 5 sigma limit of 0.16 K km/s at a 22'' resolution. The CO emission
non-detection does not provide any evidence in favor of large amounts of
molecular gas in these HVCs and hence in favor of the infrared findings. We
discuss different configurations which, however, allow us to reconcile the
negative CO result with the presence of molecular gas and cold dust emission.
H2 column densities higher than our detection limit, N(H2) = 3x10^{19} cm^{-2},
are expected to be confined in very small and dense clumps with 20 times
smaller sizes than the 0.5 pc clumps resolved in our observations according to
the results obtained in cirrus clouds, and might thus still be highly diluted.
As a consequence, the inter-clump gas at the 1 pc scale has a volume density
lower than 20 cm^{-3} and already appears as too diffuse to excite the CO
molecules. The observed physical conditions in the HVCs of Complex C also play
an important role against CO emission detection. It has been shown that the
CO-to-H2 conversion factor in low metallicity media is 60 times higher than at
the solar metallicity, leading for a given H2 column density to a 60 times
weaker integrated CO intensity. And the very low dust temperature estimated in
these HVCs implies the possible presence of gas cold enough (< 20 K) to cause
CO condensation onto dust grains under interstellar medium pressure conditions
and thus CO depletion in gas-phase observations.Comment: 9 pages, 4 figures, Accepted for publication in A&
Climate-informed stochastic hydrological modeling: Incorporating decadal-scale variability using paleo data
A hierarchical framework for incorporating modes of climate variability into stochastic simulations of hydrological data is developed, termed the climate-informed multi-time scale stochastic (CIMSS) framework. A case study on two catchments in eastern Australia illustrates this framework. To develop an identifiable model characterizing long-term variability for the first level of the hierarchy, paleoclimate proxies, and instrumental indices describing the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO) are analyzed. A new paleo IPO-PDO time series dating back 440 yr is produced, combining seven IPO-PDO paleo sources using an objective smoothing procedure to fit low-pass filters to individual records. The paleo data analysis indicates that wet/dry IPO-PDO states have a broad range of run lengths, with 90% between 3 and 33 yr and a mean of 15 yr. The Markov chain model, previously used to simulate oscillating wet/dry climate states, is found to underestimate the probability of wet/dry periods >5 yr, and is rejected in favor of a gamma distribution for simulating the run lengths of the wet/dry IPO-PDO states. For the second level of the hierarchy, a seasonal rainfall model is conditioned on the simulated IPO-PDO state. The model is able to replicate observed statistics such as seasonal and multiyear accumulated rainfall distributions and interannual autocorrelations. Mean seasonal rainfall in the IPO-PDO dry states is found to be 15%-28% lower than the wet state at the case study sites. In comparison, an annual lag-one autoregressive model is unable to adequately capture the observed rainfall distribution within separate IPO-PDO states. Copyright © 2011 by the American Geophysical Union.Benjamin J. Henley, Mark A. Thyer, George Kuczera and Stewart W. Frank
Climate-informed stochastic hydrological modeling: Incorporating decadal-scale variability using paleo data
A hierarchical framework for incorporating modes of climate variability into stochastic simulations of hydrological data is developed, termed the climate-informed multi-time scale stochastic (CIMSS) framework. A case study on two catchments in eastern Australia illustrates this framework. To develop an identifiable model characterizing long-term variability for the first level of the hierarchy, paleoclimate proxies, and instrumental indices describing the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO) are analyzed. A new paleo IPO-PDO time series dating back 440 yr is produced, combining seven IPO-PDO paleo sources using an objective smoothing procedure to fit low-pass filters to individual records. The paleo data analysis indicates that wet/dry IPO-PDO states have a broad range of run lengths, with 90% between 3 and 33 yr and a mean of 15 yr. The Markov chain model, previously used to simulate oscillating wet/dry climate states, is found to underestimate the probability of wet/dry periods >5 yr, and is rejected in favor of a gamma distribution for simulating the run lengths of the wet/dry IPO-PDO states. For the second level of the hierarchy, a seasonal rainfall model is conditioned on the simulated IPO-PDO state. The model is able to replicate observed statistics such as seasonal and multiyear accumulated rainfall distributions and interannual autocorrelations. Mean seasonal rainfall in the IPO-PDO dry states is found to be 15%-28% lower than the wet state at the case study sites. In comparison, an annual lag-one autoregressive model is unable to adequately capture the observed rainfall distribution within separate IPO-PDO states. Copyright © 2011 by the American Geophysical Union.Benjamin J. Henley, Mark A. Thyer, George Kuczera and Stewart W. Frank
Numerical simulations on the relative importance of starbursts and AGN in ultra-luminous infrared galaxies
We investigate the relative importance of starbursts and AGN in nuclear
activities of ultra-luminous infrared galaxies (ULIRGs) based on chemodynamical
simulations combined with spectrophotometric synthesis codes. We numerically
investigate both the gas accretion rates (m_acc) onto super massive black holes
(SMBHs) and the star formation rates (m_sf) in ULIRGs formed by gas-rich galaxy
mergers and thereby discuss what powers ULIRGs. Our principal results, which
can be tested against observations, are as follows. (1) ULIRGs powered by AGN
can be formed by major merging between luminous, gas-rich disk galaxies with
prominent bulges containing SMBHs, owing to the efficient gas fuelling m_acc >
1 M_sun/yr of the SMBH. AGN in these ULIRGs can be surrounded by compact
poststarburst stellar populations (e.g., A-type stars). (2) ULIRGs powered by
starbursts with m_sf ~ 100 M_sun/yr can be formed by merging between gas-rich
disk galaxies with small bulges having the bulge-to-disk-ratio (f_b) as small
as 0.1. (3) The relative importance of starbursts and AGN can depend on
physical properties of merger progenitor disks, such as f_b, gas mass fraction,
and total masses. For example, more massive galaxy mergers are more likely to
become AGN-dominated ULIRGs. (4) For most models, major mergers can become
ULIRGs, powered either by starbursts or by AGN, only when the two bulges
finally merge. Interacting disk galaxies can become ULIRGs with well separated
two cores (> 20kpc) at their pericenter when they are very massive and have
small bulges. (5) Irrespective of the choice of model, interacting/merging
galaxies show the highest accretion rates onto the central SMBHs, and the
resultant rapid growth of the SMBHs occur when their star formation rates are
very high.Comment: 18 pages, 15 figures (f1.jpg for color figure of figure 1), accepted
in MNRA
Interstellar gas within pc of Sgr A
We seek to obtain a coherent and realistic three-dimensional picture of the
interstellar gas out to about 10 pc of the dynamical center of our Galaxy,
which is supposed to be at Sgr A. We review the existing observational
studies on the different gaseous components that have been identified near Sgr
A, and retain all the information relating to their spatial configuration
and/or physical state. Based on the collected information, we propose a
three-dimensional representation of the interstellar gas, which describes each
component in terms of both its precise location and morphology and its
thermodynamic properties. The interstellar gas near Sgr A can represented
by five basic components, which are, by order of increasing size: (1) a central
cavity with roughly equal amounts of warm ionized and atomic gases, (2) a ring
of mainly molecular gas, (3) a supernova remnant filled with hot ionized gas,
(4) a radio halo of warm ionized gas and relativistic particles, and (5) a belt
of massive molecular clouds. While the halo gas fills of the
studied volume, the molecular components enclose of the
interstellar mass.Comment: 21 pages, 7 figure
EpiChIP: gene-by-gene quantification of epigenetic modification levels
The combination of chromatin immunoprecipitation with next-generation sequencing technology (ChIP-seq) is a powerful and increasingly popular method for mapping protein–DNA interactions in a genome-wide fashion. The conventional way of analyzing this data is to identify sequencing peaks along the chromosomes that are significantly higher than the read background. For histone modifications and other epigenetic marks, it is often preferable to find a characteristic region of enrichment in sequencing reads relative to gene annotations. For instance, many histone modifications are typically enriched around transcription start sites. Calculating the optimal window that describes this enrichment allows one to quantify modification levels for each individual gene. Using data sets for the H3K9/14ac histone modification in Th cells and an accompanying IgG control, we present an analysis strategy that alternates between single gene and global data distribution levels and allows a clear distinction between experimental background and signal. Curve fitting permits false discovery rate-based classification of genes as modified versus unmodified. We have developed a software package called EpiChIP that carries out this type of analysis, including integration with and visualization of gene expression data
Morphological and kinematical analysis of the double-barred galaxy NGC3504 using ALMA CO (2–1) data
This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.00650.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic ofKorea), in cooperationwith theRepublic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The authors are grateful to Krajnovi ' c et al. for the Kinemetry code. The authors thank the referee, Prof. JeffreyKenney, for valuable comments and suggestions that improved this paper. The authors also thank the support of the Astronomical Data Center of the National Astronomical Observatory of Japan, and Anthony Moraghan for assistance on the computational facilities and resources at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA). DE acknowledges support from a Beatriz Galindo senior fellowship (BG20/00224) from the SpanishMinistry of Science and Innovation. YTW wishes to thank Dr. Yu-Nung Su and Dr. Sheng-Yuan Liu for hosting her visit at ASIAA in 2020.We present results obtained from ALMA CO (2–1) data of the double-barred galaxy NGC3504.With three times higher angular
resolution (∼0.
8) than previous studies, our observations reveal an inner molecular gas bar, a nuclear ring, and four inner spiral
arm-like structures in the central 1-kpc region. Furthermore, the CO emission is clearly aligned with the two dust lanes in the
outer bar region, with differences in shape and intensity between them. The total molecular gas mass in the observed region (50
arcsec×57 arcsec) is estimated to be∼3.1 × 109M , which is 17 per cent of the stellarmass.We used the Kinemetry package to
fit the velocity field and found that circular motion strongly dominates at R = 0.3–0.8 kpc, but radial motion becomes important
at R < 0.3 kpc and R = 1.0–2.5 kpc, which is expected due to the presence of the inner and outer bars. Finally, assuming that the
gas moves along the dust lanes in the bar rotating frame, we derived the pattern speed of the outer bar to be 18 ± 5 kms−1 kpc−1,
the average streaming velocities on each of the two dust lanes to be 165 and 221 km s−1, and the total mass inflow rate along
the dust lanes to be 12M yr−1. Our results give a new example of an inner gas bar within a gas-rich double-barred galaxy and
suggest that the formation of double-barred galaxies could be associated with the existence of such gas structures.Spanish Government BG20/0022
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