778 research outputs found
Development of 2 underseat energy absorbers for application to crashworthy passenger seats for general aviation aircraft
This report presents the methodology and results of a program conducted to develop two underseat energy absorber (E/A) concepts for application to nonadjustable crashworthy passenger seats for general aviation aircraft. One concept utilizes an inflated air bag, and the other, a convoluted sheet metal bellows. Prototypes of both were designed, built, and tested. Both concepts demonstrated the necessary features of an energy absorber (load-limiter); however, the air bag concept is particularly encouraging because of its light weight. Several seat frame concepts also were investigated as a means of resisting longitudinal and lateral loads and of guiding the primary vertical stroke of the underseat energy absorber. Further development of a seat system design using the underseat energy absorbers is recommended because they provide greatly enhanced crash survivability as compared with existing general aviation aircraft seats
On the Stellar Kinematics and Mass of the Virgo Ultra-Diffuse Galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultra-diffuse
galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager
(KCWI). We confirm VCC 1287's association both with the Virgo cluster and its
globular cluster (GC) system, measuring a recessional velocity of $1116 \pm 2\
\mathrm{km\ s^{-1}}19 \pm 6\
\mathrm{km\ s^{-1}}1.11^{+0.81}_{-0.81}
\times 10^{9} \ \mathrm{M_{\odot}}13^{+11}_{-11}$)
within the half light radius (4.4 kpc). This places VCC 1287 slightly above the
well established relation for normal galaxies, with a higher mass to light
ratio for its dynamical mass than normal galaxies. We use our dynamical mass,
and an estimate of GC system richness, to place VCC 1287 on the GC number --
dynamical mass relation, finding good agreement with a sample of normal
galaxies. Based on a total halo mass derived from GC counts, we then infer that
VCC 1287 likely resides in a cored or low concentration dark matter halo. Based
on the comparison of our measurements to predictions from simulations, we find
that strong stellar feedback and/or tidal effects are plausibly the dominant
mechanisms in the formation of VCC 1287. Finally, we compare our measurement of
the dynamical mass with those for other UDGs. These dynamical mass estimates
suggest relatively massive halos and a failed galaxy origin for at least some
UDGs.Comment: 13 pages, 10 figures with an additional 5 pages and 5 figures in
appendices. Accepted for publication in MNRAS. v2: with small updates from
publication formatting and a minor plotting fix for Fig. 1
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Beach Nourishment Impacts on Bacteriological Water Quality and Phytoplankton Bloom Dynamics
Keck Spectroscopy of the Coma Cluster Ultra-Diffuse Galaxy Y358: Dynamical Mass in a Wider Context
We examine ultra-diffuse galaxies (UDGs) and their relation to non-UDGs in
mass-radius-luminosity space. We begin by publishing Keck/KCWI spectroscopy for
the Coma cluster UDG Y358, for which we measure both a recessional velocity and
velocity dispersion. Our recessional velocity confirms association with the
Coma cluster and Y358's status as a UDG. From our velocity dispersion (19
3 km s) we calculate a dynamical mass within the half-light radius which
provides evidence for a core in Y358's dark matter halo. We compare this
dynamical mass, along with those for globular cluster (GC)-rich/-poor UDGs in
the literature, to mass profiles for isolated, gas-rich UDGs and UDGs in the
NIHAO/FIRE simulations. We find GC-poor UDGs have dynamical masses similar to
isolated, gas-rich UDGs, suggesting an evolutionary pathway may exist between
the two. Conversely, GC-rich UDGs have dynamical masses too massive to be
easily explained as the evolution of the isolated, gas-rich UDGs. The simulated
UDGs match the dynamical masses of the GC-rich UDGs. However, once compared in
stellar mass -- halo mass space, the FIRE/NIHAO simulated UDGs do not match the
halo masses of either the isolated, gas-rich UDGs or the GC-rich UDGs at the
same stellar mass. Finally, we supplement our data for Y358 with other UDGs
that have measured velocity dispersions in the literature. We compare this
sample to a wide range of non-UDGs in mass-radius-luminosity space, finding
UDGs have a similar locus to non-UDGs of similar luminosity with the primary
difference being their larger half-light radii.Comment: 16 pages, 9 figures, accepted for publication in MNRA
On the stellar kinematics and mass of the Virgo ultradiffuse galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultradiffuse galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager (KCWI). We confirm VCC 1287\u27s association both with the Virgo cluster and its globular cluster (GC) system, measuring a recessional velocity of 1116 ± 2 km s-1. We measure a stellar velocity dispersion (19 ± 6 km s-1) and infer both a dynamical mass () and mass-To-light ratio (M/L) () within the half-light radius (4.4 kpc). This places VCC 1287 slightly above the well-established relation for normal galaxies, with a higher M/L for its dynamical mass than normal galaxies. We use our dynamical mass, and an estimate of GC system richness, to place VCC 1287 on the GC number-dynamical mass relation, finding good agreement with a sample of normal galaxies. Based on a total halo mass derived from GC counts, we then infer that VCC 1287 likely resides in a cored or low-concentration dark matter halo. Based on the comparison of our measurements to predictions from simulations, we find that strong stellar feedback and/or tidal effects are plausibly the dominant mechanisms in the formation of VCC 1287. Finally, we compare our measurement of the dynamical mass with those for other UDGs. These dynamical mass estimates suggest relatively massive haloes and a failed galaxy origin for at least some UDGs
Attributing variations of temporal and spatial groundwater recharge: a statistical analysis of climatic and non-climatic factors
This paper demonstrated the benefits of statistical methods when investigating the climatic and non-climatic drivers responsible for variations in groundwater recharge with a series of up to 43 years of annual recharge for 426 bores in South-East South Australia. We identified the factors influencing groundwater recharge based on 71 climatic metrics and 13 non-climatic metrics (including groundwater abstraction). The results showed: 1) Rainfall during April to October was the most important variable influencing recharge temporal variation, with its decline identified as the most significant factor related to recharge reduction; 2) In contrast, a negative correlation between rainfall during December to February (DJF) and annual groundwater recharge was found. This suggests that a seasonal shift in rainfall (such as decreasing rainfall during April to October and an increase during DJF) can result in a decline in recharge even when the annual rainfall remains unchanged; 3) The length of wet spells (consecutive rain days) and increasing PET were additional significant predictors for recharge temporal variation. It demonstrated that a simple empirical relationship (such as recharge as a fixed percentage of rainfall) is not a reliable estimation of renewable groundwater resources under changing climatic conditions; 4) There is a statistically significant spatial correlation between mean groundwater depth and recharge, and this implies that a reduction in rainfall can lead to a positive feedback loop of declining recharge and water level; 5) Spatially the most statistically significant factors influencing groundwater recharge were soil types and land attributes. The findings of this study can identify which stressors should be included when investigating the impact of climate change on groundwater recharge
Stellar velocity dispersion and dynamical mass of the ultra diffuse galaxy NGC 5846_UDG1 from the keck cosmic web imager
The ultra diffuse galaxy in the NGC 5846 group (NGC 5846 UDG1) was shown to have a large number of globular cluster (GC) candidates from deep imaging as part of the VEGAS survey. Recently, Muller et al. published a velocity dispersion, based ¨ on a dozen of its GCs. Within their quoted uncertainties, the resulting dynamical mass allowed for either a dark matter free or a dark-matter-dominated galaxy. Here, we present spectra from KCWI that reconfirms membership of the NGC 5846 group and reveals a stellar velocity dispersion for UDG1 of σ GC = 17 ± 2 km s−1. Our dynamical mass, with a reduced uncertainty, indicates a very high contribution of dark matter within the effective radius. We also derive an enclosed mass from the locations and motions of the GCs using the tracer mass estimator, finding a similar mass inferred from our stellar velocity dispersion. We find no evidence that the galaxy is rotating and is thus likely pressure supported. The number of confirmed GCs, and the total number inferred for the system (∼45), suggests a total halo mass of ∼2 × 1011 M. A cored mass profile is favoured when compared to our dynamical mass. Given its stellar mass of 1.1 × 108 M, NGC 5846 UDG1 appears to be an ultra diffuse galaxy with a dwarf-like stellar mass and an overly massive halo
The large-scale structure of globular clusters in the NGC 1052 group
Prompted by the many controversial claims involving the NGC 1052 group,
including that it hosts two dark matter-free galaxies with overluminous and
monochromatic globular cluster (GC) systems, here we map out the large-scale
structure (LSS) of GCs over the entire group. To recover the LSS, we use
archival optical CFHT imaging data. We recover two GC density maps, one based
on universal photometric properties of GCs from simple stellar population
models, and one based on the properties of spectroscopically confirmed GCs in
DF2 and DF4 (the two dwarf galaxies with overluminous GC populations). Both
selection methods reveal overdensities around the massive galaxies in the
group, as well as around NGC 1052 itself, that are coincident with the
positions of previously identified stellar streams and tidal features. No
intragroup GCs are found connecting these structures to any of the dwarf
galaxies. We find, however, two other dwarfs in the group hosting GC systems.
These include RCP32 with 2 GCs with ages equivalent to the GCs around NGC 1052,
and DF9 with 3 GCs with ages similar to the GCs around DF2 and DF4. We conclude
that the GC distribution in the group does not strongly support any formation
scenario in particular. It favours, nonetheless, scenarios relying on
galaxy-galaxy interactions and on the coeval formation of GCs around the
DM-free dwarf galaxies. These may include the recently proposed bullet-dwarf
formation, as well as high-redshift tidal dwarf galaxy models.Comment: Accepted for publication in MNRAS. 11 pages, 5 figures, 2 table
The epsilon Chamaeleontis young stellar group and the characterization of sparse stellar clusters
We present the outcomes of a Chandra X-ray Observatory snapshot study of five
nearby Herbig Ae/Be (HAeBe) stars which are kinematically linked with the
Oph-Sco-Cen Association (OSCA). Optical photometric and spectroscopic followup
was conducted for the HD 104237 field. The principal result is the discovery of
a compact group of pre-main sequence (PMS) stars associated with HD 104237 and
its codistant, comoving B9 neighbor epsilon Chamaeleontis AB. We name the group
after the most massive member. The group has five confirmed stellar systems
ranging from spectral type B9-M5, including a remarkably high degree of
multiplicity for HD 104237 itself. The HD 104237 system is at least a quintet
with four low mass PMS companions in nonhierarchical orbits within a projected
separation of 1500 AU of the HAeBe primary. Two of the low-mass members of the
group are actively accreting classical T Tauri stars. The Chandra observations
also increase the census of companions for two of the other four HAeBe stars,
HD 141569 and HD 150193, and identify several additional new members of the
OSCA.
We discuss this work in light of several theoretical issues: the origin of
X-rays from HAeBe stars; the uneventful dynamical history of the
high-multiplicity HD 104237 system; and the origin of the epsilon Cha group and
other OSCA outlying groups in the context of turbulent giant molecular clouds.
Together with the similar eta Cha cluster, we paint a portrait of sparse
stellar clusters dominated by intermediate-mass stars 5-10 Myr after their
formation.Comment: Accepted for publication in the Astrophysical Journal. 32 pages and 7
figure
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