2,874 research outputs found
Ongoing astrometric microlensing events from VVV and Gaia
6 pages, 2 figures, accepted MNRAS LettersWe extend predictive microlensing event searches using the Vista Variables in the Via Lactea survey and the second Gaia data release. We identify two events with maxima in 2019 that require urgent follow-up. First, we predict that the nearby M2 dwarf L 338-152 will align with a background source with a closest approach of mas on 2019 November d. This will cause a peak astrometric shift and photometric amplification of the background source of mas and mmag respectively. This event should be astrometrically detectable by both the Hubble Space Telescope (HST) and the Spectro-Polarimetric High-contrast Exoplanet Research instrument on the Very Large Telescope. Secondly, we predict the likely K dwarf NLTT 45128 will lens a background source with a closest approach of mas on 2019 September d. This will produce a peak astrometric shift of mas. NLTT 45128 is only 3.6 magnitudes brighter than the background source which makes it an excellent candidate for follow-up with HST. Characterisation of these signals will allow direct gravitational masses to be inferred for both L 338-152 and NLTT 45128 with an estimated precision of and per cent respectively.Peer reviewedFinal Published versio
A Direct Stellar Metallicity Determination in the Disk of the Maser Galaxy NGC4258
We present the first direct determination of a stellar metallicity in the
spiral galaxy NGC4258 (D=7.6 Mpc) based on the quantitative analysis of a
low-resolution (~5 AE) Keck LRIS spectrum of a blue supergiant star located in
its disk. A determination of stellar metallicity in this galaxy is important
for the absolute calibration of the Cepheid Period-Luminosity relation as an
anchor for the extragalactic distance scale and for a better characterization
of its dependence as a function of abundance. We find a value 0.2 dex lower
than solar metallicity at a galactocentric distance of 8.7 kpc, in agreement
with recent HII region studies using the weak forbidden auroral oxygen line at
4363 AE. We determine the effective stellar temperature, gravity, luminosity
and line-of-sight extinction of the blue supergiant being studied. We show that
it fits well on the flux-weighted gravity--luminosity relation (FGLR),
strengthening the potential of this method as a new extragalactic distance
indicator.Comment: Accepted for publication by ApJ Letters, 5 pages, 5 figure
Fracture in teeth—a diagnostic for inferring bite force and tooth function
Teeth are brittle and highly susceptible to cracking. We propose that observations of such cracking can be used as a diagnostic tool for predicting bite force and inferring tooth function in living and fossil mammals. Laboratory tests on model tooth structures and extracted human teeth in simulated biting identify the principal fracture modes in enamel. Examination of museum specimens reveals the presence of similar fractures in a wide range of vertebrates, suggesting that cracks extended during ingestion or mastication. The use of ‘fracture mechanics’ from materials engineering provides elegant relations for quantifying critical bite forces in terms of characteristic tooth size and enamel thickness. The role of enamel microstructure in determining how cracks initiate and propagate within the enamel (and beyond) is discussed. The picture emerges of teeth as damage-tolerant structures, full of internal weaknesses and defects and yet able to contain the expansion of seemingly precarious cracks and fissures within the enamel shell. How the findings impact on dietary pressures forms an undercurrent of the study
Improving Navy MPTE Studies with Model-Driven Big Data
The goal of this research was to improve upon the ability of OPNAV N1 analysts to quickly and efficiently obtain experiment-based information from their computational models. The enhanced information will enable N1’s analysts to better support Navy leadership in resource and policy decisions that shape the future Navy and help it retain and develop its most talented Sailors. This project built on previous collaborations with N1 using data farming to enhance the information gleaned from their Navy talent management models, such as the Officer Strategic Analysis Model (OSAM) model, the Production Resource Optimization (PRO) model, and the Navy Total Force Strength Model (NTFSM). During this research period, (1) Ensign William Desousa (2015) investigated the behavior of economic inputs in NTFSM; (2) Lieutenant Peter Bazalaki (2016) used the new data farming capabilities we developed in OSAM to investigate Surface Warfare Officer (SWO) inventory across a breadth of possibilities; and (3) Lieutenant Allison Hogarth (2016) built, tested, and demonstrated a user interface in Excel that enables users of the PRO model to automatically execute a sophisticated design of experiments—the tool that enables this new capability is known as Production Resource Optimization Model With Experimental Design (PROMWED). In addition to working with the student-officers, the faculty supporting this project performed an empirical study of statistical software packages that may provide better understanding of the high-dimensional behavior of manpower models in the future (Erickson, Ankenman, & Sanchez 2016).Naval Research ProgramPrepared for Topic Sponsor: OPNAV N1; Research POC Name: Mr. Ian AndersoNPS-N16-N154-
HI intensity mapping with FAST
We discuss the detectability of large-scale HI intensity fluctuations using
the FAST telescope. We present forecasts for the accuracy of measuring the
Baryonic Acoustic Oscillations and constraining the properties of dark energy.
The FAST -beam L-band receivers (-- GHz) can provide
constraints on the matter power spectrum and dark energy equation of state
parameters () that are comparable to the BINGO and CHIME
experiments. For one year of integration time we find that the optimal survey
area is . However, observing with larger frequency coverage
at higher redshift (-- GHz) improves the projected errorbars on the
HI power spectrum by more than confidence level. The combined
constraints from FAST, CHIME, BINGO and Planck CMB observations can provide
reliable, stringent constraints on the dark energy equation of state.Comment: 7 pages, 3 figures, submitted to "Frontiers in Radio Astronomy and
FAST Early Sciences Symposium 2015" conference proceedin
Frequent grazing by sheep reduced caucasian clover cover and rhizome mass in ryegrass pasture
The responses of hexaploid caucasian clover
(Trifolium ambiguum) to four contrasting grazing
regimes were compared with those of white clover
(T. repens) in an endophytic (Neotyphodium lolii)
hybrid ryegrass pasture on a fertile lowland site.
After 2 years, frequent grazing (set stocking) by
sheep reduced caucasian clover cover to 10%
compared with 25.5% in infrequent grazing
(rotational grazing) treatments (mean spelling time
25 days). Similarly, frequent grazing reduced
caucasian clover rhizome plus root dry weight (780
kg DM/ha when sampled to 100 mm depth in
frequently grazed plots, compared with 3220 kg
DM/ha for infrequent). Under frequent grazing
treatments, mean white clover cover was 21%,
under infrequent hard grazing it was 26% and under
lax infrequent grazing it was 14%. The reduction
in ryegrass tiller population from 5720/m² in the
infrequently and laxly grazed treatments to 4150/
m² in the frequently hard grazed pastures indicated
the severity of that hard grazed treatment. These
results show that in lowland ryegrass pastures on
high fertility sites, the stoloniferous growth form
of white clover may be superior to the rhizomatous
strategy of caucasian clover when grazing by sheep
is frequent throughout spring, summer and autumn
Personality traits, sex and food abundance shape space use in an arboreal mammal
Animal space use is affected by spatio-temporal variation in food availability and/or population density and varies among individuals. This inter-individual variation in spacing behaviour can be further influenced by sex, body condition, social dominance, and by the animal’s personality. We used capture-mark-recapture and radio-tracking to examine the relationship between space use and personality in Eurasian red squirrels (Sciurus vulgaris) in three conifer forests in the Italian Alps. We further explored to what extent this was influenced by changes in food abundance and/or population density. Measures of an individual’s trappability and trap diversity had high repeatability and were used in a Principal Component Analysis to obtain a single personality score representing a boldness-exploration tendency. Males increased home-range size with low food abundance and low female density, independent of their personality. However, bolder males used larger core-areas that overlapped less with other males than shy ones, suggesting different resource (food, partners) utilization strategies among personality types. For females, space use-personality relationships varied with food abundance, and bolder females used larger home ranges than shy ones at low female density, but the trend was opposite at high female density. Females’ intrasexual core-area overlap was negatively related to body mass, with no effect of personality. We conclude that relationships between personality traits and space use in free-ranging squirrels varied with sex, and were further influenced by spatio-temporal fluctuations in food availability. Moreover, different personality types (bold-explorative vs. shy) seemed to adopt different space-use strategies to increase access to food and/or partners. © 2021, The Author(s).Ministero dell’Istruzione, dell’Università e della RicercaOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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