772 research outputs found
Agricultural atlas of Missouri : maps illustrating the state, its people, forests, soils, climate, use of land, types, size and number of farms, distribution of crops, distribution of livestock, agricultural values, agricultural industries
Cover title
HST Observations of Heavy Elements in Metal-Poor Galactic Halo Stars
We present new abundance determinations of neutron-capture elements Ge, Zr,
Os, Ir, and Pt in a sample of 11 metal-poor (-3.1 <= [Fe/H] <= -1.6) Galactic
halo giant stars, based on Hubble Space Telescope UV and Keck I optical
high-resolution spectroscopy. The stellar sample is dominated by r-process-rich
stars such as the well-studied CS 22892-052 and bd+173248, but also includes
the r-process-poor, bright giant HD 122563. Our results demonstrate that
abundances of the 3rd r-process peak elements Os, Ir and Pt in these metal-poor
halo stars are very well-correlated among themselves, and with the abundances
of the canonical r-process element Eu (determined in other studies), thus
arguing for a common origin or site for r-process nucleosynthesis of heavier
(Z>56) elements. However, the large (and correlated) scatters of
[Eu,Os,Ir,Pt/Fe] suggests that the heaviest neutron-capture r-process elements
are not formed in all supernovae. In contrast, the Ge abundances of all program
stars track their Fe abundances, very well. An explosive process on iron-peak
nuclei (e.g., the alpha-rich freeze-out in supernovae), rather than neutron
capture, appears to have been the dominant synthesis mechanism for this element
at low metallicities -- Ge abundances seem completely uncorrelated with Eu.Comment: 35 pages, 5 tables, 7 figures; To appear in the Astrophysical Journa
The Rise of the s-Process in the Galaxy
From newly-obtained high-resolution, high signal-to-noise ratio spectra the
abundances of the elements La and Eu have been determined over the stellar
metallicity range -3<[Fe/H]<+0.3 in 159 giant and dwarf stars. Lanthanum is
predominantly made by the s-process in the solar system, while Eu owes most of
its solar system abundance to the r-process. The changing ratio of these
elements in stars over a wide metallicity range traces the changing
contributions of these two processes to the Galactic abundance mix. Large
s-process abundances can be the result of mass transfer from very evolved
stars, so to identify these cases, we also report carbon abundances in our
metal-poor stars. Results indicate that the s-process may be active as early as
[Fe/H]=-2.6, alalthough we also find that some stars as metal-rich as [Fe/H]=-1
show no strong indication of s-process enrichment. There is a significant
spread in the level of s-process enrichment even at solar metallicity.Comment: 64 pages, 15 figures; ApJ 2004 in pres
RACE-OC Project: Rotation and variability in the epsilon Chamaeleontis, Octans, and Argus stellar associations
We aim at determining the rotational and magnetic-related activity properties
of stars at different stages of evolution. We focus our attention primarily on
members of young stellar associations of known ages. Specifically, we extend
our previous analysis in Paper I (Messina et al. 2010, A&A 520, A15) to 3
additional young stellar associations beyond 100 pc and with ages in the range
6-40 Myr: epsilon Chamaeleontis (~6 Myr), Octans (~20 Myr), and Argus (~40
Myr). Additional rotational data of eta Chamaeleontis and IC2391 clusters are
also considered. Rotational periods were determined from photometric
time-series data obtained by the All Sky Automated Survey (ASAS) and the Wide
Angle Search for Planets (SuperWASP) archives. With the present study we have
completed the analysis of the rotational properties of the late-type members of
all known young loose associations in the solar neighborhood. Considering also
the results of Paper I, we have derived the rotation periods of 241 targets:
171 confirmed, 44 likely, 26 uncertain. The period of the remaining 50 stars
known to be part of loose associations still remains unknown. This rotation
period catalogue, and specifically the new information presented in this paper
at ~6, 20, and 40 Myr, contributes significantly to a better observational
description of the angular momentum evolution of young stars.Comment: Accepted by Astronomy & Astrophysics. Onlines figures will be
available at CD
Rossiter-McLaughlin Effect Measurements for WASP-16, WASP-25 and WASP-31
We present new measurements of the Rossiter-McLaughlin (RM) effect for three
WASP planetary systems, WASP-16, WASP-25 and WASP-31, from a combined analysis
of their complete sets of photometric and spectroscopic data. We find a low
amplitude RM effect for WASP-16 (Teff = 5700 \pm 150K), suggesting that the
star is a slow rotator and thus of an advanced age, and obtain a projected
alignment angle of lambda = -4.2 degrees +11.0 -13.9. For WASP-25 (Teff =
5750\pm100K) we detect a projected spin-orbit angle of lambda = 14.6 degrees
\pm6.7. WASP-31 (Teff = 6300\pm100K) is found to be well-aligned, with a
projected spin-orbit angle of lambda = 2.8degrees \pm3.1. A circular orbit is
consistent with the data for all three systems, in agreement with their
respective discovery papers. We consider the results for these systems in the
context of the ensemble of RM measurements made to date. We find that whilst
WASP-16 fits the hypothesis of Winn et al. (2010) that 'cool' stars (Teff <
6250K) are preferentially aligned, WASP-31 has little impact on the proposed
trend. We bring the total distribution of the true spin-orbit alignment angle,
psi, up to date, noting that recent results have improved the agreement with
the theory of Fabrycky & Tremaine (2007) at mid-range angles. We also suggest a
new test for judging misalignment using the Bayesian Information Criterion,
according to which WASP-25 b's orbit should be considered to be aligned.Comment: 20 pages, 14 tables, 10 figures. Accepted to MNRA
Recommended from our members
Transport of DNA within cohesin involves clamping on top of engaged heads by Scc2 and entrapment within the ring by Scc3.
In addition to extruding DNA loops, cohesin entraps within its SMC-kleisin ring (S-K) individual DNAs during G1 and sister DNAs during S-phase. All three activities require related hook-shaped proteins called Scc2 and Scc3. Using thiol-specific crosslinking we provide rigorous proof of entrapment activity in vitro. Scc2 alone promotes entrapment of DNAs in the E-S and E-K compartments, between ATP-bound engaged heads and the SMC hinge and associated kleisin, respectively. This does not require ATP hydrolysis nor is it accompanied by entrapment within S-K rings, which is a slower process requiring Scc3. Cryo-EM reveals that DNAs transported into E-S/E-K compartments are 'clamped' in a sub-compartment created by Scc2's association with engaged heads whose coiled coils are folded around their elbow. We suggest that clamping may be a recurrent feature of cohesin complexes active in loop extrusion and that this conformation precedes the S-K entrapment required for sister chromatid cohesion
AutoSpill is a principled framework that simplifies the analysis of multichromatic flow cytometry data.
Compensating in flow cytometry is an unavoidable challenge in the data analysis of fluorescence-based flow cytometry. Even the advent of spectral cytometry cannot circumvent the spillover problem, with spectral unmixing an intrinsic part of such systems. The calculation of spillover coefficients from single-color controls has remained essentially unchanged since its inception, and is increasingly limited in its ability to deal with high-parameter flow cytometry. Here, we present AutoSpill, an alternative method for calculating spillover coefficients. The approach combines automated gating of cells, calculation of an initial spillover matrix based on robust linear regression, and iterative refinement to reduce error. Moreover, autofluorescence can be compensated out, by processing it as an endogenous dye in an unstained control. AutoSpill uses single-color controls and is compatible with common flow cytometry software. AutoSpill allows simpler and more robust workflows, while reducing the magnitude of compensation errors in high-parameter flow cytometry
The cohesin ring uses its hinge to organize DNA using non-topological as well as topological mechanisms
As predicted by the notion that sister chromatid cohesion is mediated by entrapment of sister DNAs inside cohesin rings, there is perfect correlation between co-entrapment of circular minichromosomes and sister chromatid cohesion. In most cells where cohesin loads without conferring cohesion, it does so by entrapment of individual DNAs. However, cohesin with a hinge domain whose positively charged lumen is neutralized loads and moves along chromatin despite failing to entrap DNAs. Thus, cohesin engages chromatin in non-topological, as well as topological, manners. Since hinge mutations, but not Smc-kleisin fusions, abolish entrapment, DNAs may enter cohesin rings through hinge opening. Mutation of three highly conserved lysine residues inside the Smc1 moiety of Smc1/3 hinges abolishes all loading without affecting cohesinâs recruitment to CEN loading sites or its ability to hydrolyze ATP. We suggest that loading and translocation are mediated by conformational changes in cohesinâs hinge driven by cycles of ATP hydrolysis
- âŠ