3,680 research outputs found
The attitude control of a satellite in an elliptic orbit
Attitude control system for satellite in elliptical orbit calculated by linear equations and computer simulatio
Minimum-fuel Attitude Control of a Rigid Body in Orbit by an Extended Method of Steepest-descent
Minimum fuel control of spacecraft in orbit using extended method of steepest descen
Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
We present a study of the prevalence, strength, and kinematics of ultraviolet
FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected
from the DEEP2 survey. We find FeII* emission in composite spectra assembled on
the basis of different galaxy properties, indicating that FeII* emission is
prevalent at z = 1. In these composites, FeII* emission is observed at roughly
the systemic velocity. At z = 1, we find that the strength of FeII* emission is
most strongly modulated by dust attenuation, and is additionally correlated
with redshift, star-formation rate, and [OII] equivalent width, such that
systems at higher redshifts with lower dust levels, lower star-formation rates,
and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII
emission in at least 15% of the individual spectra and we find that objects
showing stronger MgII emission have higher specific star-formation rates,
smaller [OII] linewidths, larger [OII] equivalent widths, lower dust
attenuations, and lower stellar masses than the sample as a whole. MgII
emission strength exhibits the strongest correlation with specific
star-formation rate, although we find evidence that dust attenuation and
stellar mass also play roles in the regulation of MgII emission. Future
integral field unit observations of the spatial extent of FeII* and MgII
emission in galaxies with high specific star-formation rates, low dust
attenuations, and low stellar masses will be important for probing the
morphology of circumgalactic gas.Comment: 29 pages, 22 figures, 2 tables; accepted to Ap
New Image Statistics for Detecting Disturbed Galaxy Morphologies at High Redshift
Testing theories of hierarchical structure formation requires estimating the
distribution of galaxy morphologies and its change with redshift. One aspect of
this investigation involves identifying galaxies with disturbed morphologies
(e.g., merging galaxies). This is often done by summarizing galaxy images
using, e.g., the CAS and Gini-M20 statistics of Conselice (2003) and Lotz et
al. (2004), respectively, and associating particular statistic values with
disturbance. We introduce three statistics that enhance detection of disturbed
morphologies at high-redshift (z ~ 2): the multi-mode (M), intensity (I), and
deviation (D) statistics. We show their effectiveness by training a
machine-learning classifier, random forest, using 1,639 galaxies observed in
the H band by the Hubble Space Telescope WFC3, galaxies that had been
previously classified by eye by the CANDELS collaboration (Grogin et al. 2011,
Koekemoer et al. 2011). We find that the MID statistics (and the A statistic of
Conselice 2003) are the most useful for identifying disturbed morphologies.
We also explore whether human annotators are useful for identifying disturbed
morphologies. We demonstrate that they show limited ability to detect
disturbance at high redshift, and that increasing their number beyond
approximately 10 does not provably yield better classification performance. We
propose a simulation-based model-fitting algorithm that mitigates these issues
by bypassing annotation.Comment: 15 pages, 14 figures, accepted for publication in MNRA
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Matrix modification for enhancing the transport properties of the human cartilage endplate to improve disc nutrition.
Poor solute transport through the cartilage endplate (CEP) impairs disc nutrition and could be a key factor that limits the success of intradiscal biologic therapies. Here we demonstrate that treating the CEP with matrix metalloproteinase-8 (MMP-8) reduces the matrix constituents that impede solute uptake and thereby improves nutrient diffusion. Human CEP tissues harvested from four fresh cadaveric lumbar spines (age range: 38-66 years old) were treated with MMP-8. Treatment caused a dose-dependent reduction in sGAG, localized reductions to the amount of collagen, and alterations to collagen structure. These matrix modifications corresponded with 16-24% increases in the uptake of a small solute (376 Da). Interestingly, the effects of MMP-8 treatment depended on the extent of non-enzymatic glycation: treated CEPs with high concentrations of advanced glycation end products (AGEs) exhibited the lowest uptake compared to treated CEPs with low concentrations of AGEs. Moreover, AGE concentrations were donor-specific, and the donor tissues with the highest AGE concentrations appeared to have lower uptake than would be expected based on the initial amounts of collagen and sGAG. Finally, increasing solute uptake in the CEP improved cell viability inside diffusion chambers, which supports the nutritional relevance of enhancing the transport properties of the CEP. Taken together, our results provide new insights and in vitro proof-of-concept for a treatment approach that could improve disc nutrition for biologic therapy: specifically, matrix reduction by MMP-8 can enhance solute uptake and nutrient diffusion through the CEP, and AGE concentration appears to be an important, patient-specific factor that influences the efficacy of this approach
Star Clusters in Virgo and Fornax Dwarf Irregular Galaxies
We present the results of a search for clusters in dwarf irregular galaxies
in the Virgo and Fornax Cluster using HST WFPC2 snapshot data. The galaxy
sample includes 28 galaxies, 11 of which are confirmed members of the Virgo and
Fornax clusters. In the 11 confirmed members, we detect 237 cluster candidates
and determine their V magnitudes, V-I colors and core radii. After statistical
subtraction of background galaxies and foreground stars, most of the cluster
candidates have V-I colors of -0.2 and 1.4, V magnitudes lying between 20 and
25th magnitude and core radii between 0 and 6 pc. Using H-alpha observations,
we find that 26% of the blue cluster candidates are most likely HII regions.
The rest of the cluster candidates are most likely massive (>10^4 Msol) young
and old clusters. A comparison between the red cluster candidates in our sample
and the Milky Way globular clusters shows that they have similar luminosity
distributions, but that the red cluster candidates typically have larger core
radii. Assuming that the red cluster candidates are in fact globular clusters,
we derive specific frequencies (S_N) ranging from ~0-9 for the galaxies.
Although the values are uncertain, seven of the galaxies appear to have
specific frequencies greater than 2. These values are more typical of
ellipticals and nucleated dwarf ellipticals than they are of spirals or Local
Group dwarf irregulars.Comment: 46 pages, 14 figures, 3 tables, accepted by AJ. Higher quality PS
version of entire paper available at
http://www.astro.washington.edu/seth/dirr_gcs.htm
Antlia Dwarf Galaxy: Distance, quantitative morphology and recent formation history via statistical field correction
We apply a statistical field correction technique originally designed to
determine membership of high redshift galaxy clusters to Hubble Space Telescope
imaging of the Antlia Dwarf Galaxy; a galaxy at the very edge of the Local
Group. Using the tip of the red giant branch standard candle method coupled
with a simple Sobel edge detection filter we find a new distance to Antlia of
1.31 +/- 0.03 Mpc. For the first time for a Local Group Member, we compute the
concentration, asymmetry and clumpiness (CAS) quantitative morphology
parameters for Antlia from the distribution of resolved stars in the HST/ACS
field, corrected with a new method for contaminants and complement these
parameters with the Gini coefficient (G) and the second order moment of the
brightest 20 per cent of the flux (M_20). We show that it is a classic dwarf
elliptical (C = 2.0, A = 0.063, S = 0.077, G = 0.39 and M_20 = -1.17 in the
F814W band), but has an appreciable blue stellar population at its core,
confirming on-going star-formation. The values of asymmetry and clumpiness, as
well as Gini and M_20 are consistent with an undisturbed galaxy. Although our
analysis suggests that Antlia may not be tidally influenced by NGC 3109 it does
not necessarily preclude such interaction.Comment: Accepted for publication in MNRA
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