170 research outputs found
Development of Low Density Titanium Alloys for Structural Applications
In this report the results of a program designed to reduce the density of titanium by adding magnesium are presented. Because these two elements are immiscible under conventional ingot metallurgy techniques, two specialized powder metallurgy methods namely, mechanical alloying (MA) and physical vapor deposition (PVD) were implemented. The mechanical alloying experiments were done both at the University of Idaho and at the Defense Research Agency in UK. Since titanium is reactive with interstitial elements, a secondary goal of this research was to correlate solubility extensions with interstitial contamination content, especially oxygen and nitrogen. MA was carried out in SPEX 8000 shaker mils and different milling containers were utilized to control the level of contamination. Results showed that solubilities of Mg in Ti were obtained up to 28 at.% (16.4 wt. %) Mg in Ti for Ti-39.6 at. % (25 wt. %) Mg alloys, which greatly exceed those obtained under equilibrium conditions. This reflects a density reduction of approximately 26 %. Contamination of oxygen and nitrogen seemed to increase the solubility of magnesium in titanium in some cases; however, we were not able to make a clear correlation between contamination levels with solubilities. Work at the DRA has emphasized optimization of present PVD equipment, specifically composition and temperature control. Preliminary PVD data has shown Ti-Mg deposits have successfully been made up to 2 mm thick and that solubility extensions were achieved. The potential for density reduction of titanium by alloying with magnesium has been demonstrated; however, this work has only scratched the surface of the development of such low density alloys. Much research is needed before such alloys could be implemented into industry. Further funding is required in order to optimize the MA/PVD processes including contamination control, determination of optimal alloy compositions, microstructure development, and mechanical property determination
Discovery and Validation of a High-Density sub-Neptune from the K2 Mission
We report the discovery of BD+20594b, a high density sub-Neptune exoplanet,
made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission,
ground-based radial velocity follow-up from HARPS and high resolution lucky and
adaptive optics imaging obtained using AstraLux and MagAO, respectively. The
host star is a bright (, ), slightly metal poor
([Fe/H] dex) solar analogue located at pc
from Earth, for which we find a radius of
and a mass of . A joint analysis of the
K2 photometry and HARPS radial velocities reveal that the planet is in a
day orbit around its host star, has a radius of
, and a mass of .
Although the data at hand puts the planet in the region of the mass-radius
diagram where we could expect planets with a pure rock (i.e. magnesium
silicate) composition using two-layer models (i.e., between rock/iron and
rock/ice compositions), we discuss more realistic three-layer composition
models which can explain the high density of the discovered exoplanet. The fact
that the planet lies in the boundary between "possibly rocky" and "non-rocky"
exoplanets, makes it an interesting planet for future RV follow-up.Comment: 12 pages, 11 figures. Accepted for publication in Ap
ALMA Discovery of a Disk around the Planetary-Mass Companion Sr 12 C
We report an Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum detection of the accretion disk around SR 12 c, an ∼11 M Jup planetary-mass companion (PMC) orbiting its host binary at 980 au. This is the first submillimeter detection of a circumplanetary disk around a wide PMC. The disk has a flux density of 127 ± 14 μJy and is not resolved by the ∼0.″1 beam, so the dust disk radius is likely less than 5 au and can be much smaller if the dust continuum is optically thick. If, however, the dust emission is optically thin, then the SR 12 c disk has a comparable dust mass to the circumplanetary disk around PDS 70 c but is about five times lower than that of the ∼12 M Jup free-floating OTS 44. This suggests that disks around bound and unbound planetary-mass objects can span a wide range of masses. The gas mass estimated with an accretion rate of 10-11 M ⊙ yr-1 implies a gas-to-dust ratio higher than 100. If cloud absorption is not significant, a nondetection of 12CO(3-2) implies a compact gas disk around SR 12 c. Future sensitive observations may detect more PMC disks at 0.88 mm flux densities of ≲ 100 μJy
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
Improved Orbital Constraints and H Photometric Monitoring of the Directly Imaged Protoplanet Analog HD 142527 B
Companions embedded in the cavities of transitional circumstellar disks have
been observed to exhibit excess luminosity at H, an indication that
they are actively accreting. We report 5 years (2013-2018) of monitoring of the
position and H excess luminosity of the embedded, accreting low-mass
stellar companion HD 142527 B from the MagAO/VisAO instrument. We use pyklip, a
python implementation of the Karhounen-Loeve Image Processing algorithm, to
detect the companion. Using pyklip forward modeling, we constrain the relative
astrometry to precision and achieve sufficient photometric
precision ( error) to detect changes in the H
contrast of the companion over time. In order to accurately determine the
relative astrometry of the companion, we conduct an astrometric calibration of
the MagAO/VisAO camera against 20 years of Keck/NIRC2 images of the Trapezium
cluster. We demonstrate agreement of our VisAO astrometry with other published
positions for HD 142527 B, and use orbitize! to generate a posterior
distribution of orbits fit to the relative astrometry of HD 142527 B. Our data
suggest that the companion is close to periastron passage, on an orbit
significantly misinclined with respect to both the wide circumbinary disk and
the recently observed inner disk encircling HD 142527 A. We translate observed
H-alpha contrasts for HD 142527 B into mass accretion rate estimates on the
order of . Photometric
variation in the H-alpha excess of the companion suggests that the accretion
rate onto the companion is variable. This work represents a significant step
towards observing accretion-driven variability onto protoplanets, such as PDS
70 b\&c.Comment: Accepted to the Astronomical Journal. 32 pages, 16 figures, 8 tables,
4 appendice
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Elementary particle interactions
This report discusses freon bubble chamber experiments exposed to {mu}{sup +} and neutrinos, photon-proton interactions; shower counter simulations; SLD detectors at the Stanford Linear Collider, and the detectors at the Superconducting Super Collider; elementary particle interactions; physical properties of dielectric materials used in High Energy Physics detectors; and Nuclear Physics. (LSP
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Genetic diversity at the Dhn3 locus in Turkish Hordeum spontaneum populations with comparative structural analyses
We analysed Hordeum spontaneum accessions from 21 different locations to understand the genetic diversity of HsDhn3 alleles and effects of single base mutations on the intrinsically disordered structure of the resulting polypeptide (HsDHN3). HsDHN3 was found to be YSK2-type with a low-frequency 6-aa deletion in the beginning of Exon 1. There is relatively high diversity in the intron region of HsDhn3 compared to the two exon regions. We have found subtle differences in K segments led to changes in amino acids chemical properties. Predictions for protein interaction profiles suggest the presence of a protein-binding site in HsDHN3 that coincides with the K1 segment. Comparison of DHN3 to closely related cereals showed that all of them contain a nuclear localization signal sequence flanking to the K1 segment and a novel conserved region located between the S and K1 segments [E(D/T)DGMGGR]. We found that H. vulgare, H. spontaneum, and Triticum urartu DHN3s have a greater number of phosphorylation sites for protein kinase C than other cereal species, which may be related to stress adaptation. Our results show that the nature and extent of mutations in the conserved segments of K1 and K2 are likely to be key factors in protection of cells
The formation of very wide binaries during the star cluster dissolution phase
Over the past few decades, numerous wide (>1000 au) binaries in the Galactic
field and halo have been discovered. Their existence cannot be explained by the
process of star formation or by dynamical interactions in the field, and their
origin has long been a mystery. We explain the origin of these wide binaries by
formation during the dissolution phase of young star clusters: an initially
unbound pair of stars may form a binary when their distance in phase-space is
small. Using N-body simulations, we find that the resulting wide binary
fraction in the semi-major axis range 1000 au - 0.1 pc for individual clusters
is 1-30%, depending on the initial conditions. The existence of numerous wide
binaries in the field is consistent with observational evidence that most
clusters start out with a large degree of substructure. The wide binary
fraction decreases strongly with increasing cluster mass, and the semi-major
axis of the newly formed binaries is determined by the initial cluster size.
The resulting eccentricity distribution is thermal, and the mass ratio
distribution is consistent with gravitationally-focused random pairing. As a
large fraction of the stars form in primordial binaries, we predict that a
large number of the observed 'wide binaries' are in fact triple or quadruple
systems. By integrating over the initial cluster mass distribution, we predict
a binary fraction of a few per cent in the semi-major axis range 1000 au - 0.1
pc in the Galactic field, which is smaller than the observed wide binary
fraction. However, this discrepancy may be solved when we consider a broad
range of cluster morphologies.Comment: 14 pages, 12 figures, accepted by MNRA
The Giant Accreting Protoplanet Survey (GAPlanetS) -- Results from a Six Year Campaign to Image Accreting Protoplanets
Accreting protoplanets represent a window into planet formation processes. We
report H{\alpha} differential imaging results from the deepest and most
comprehensive accreting protoplanet survey to date, acquired with the Magellan
Adaptive Optics (MagAO) system's VisAO camera. The fourteen transitional disks
targeted are ideal candidates for protoplanet discovery due to their wide,
heavily depleted central cavities, wealth of non-axisymmetric circumstellar
disk features evocative of ongoing planet formation, and ongoing stellar
accretion. To address the twin challenges of morphological complexity in the
target systems and PSF instability, we develop novel approaches for frame
selection and optimization of the Karhounen-Loeve Image Processing algorithm
pyKLIP. We detect one new candidate protoplanet, CS Cha "c", at a separation of
75mas and a {\Delta}mag of 5.1 and robustly recover the HD142527 B and HD100453
B low mass stellar companions across multiple epochs. Though we cannot rule out
a substantial scattered light contribution to its emission, we also recover
LkCa 15 b. Its presence inside of the cleared disk cavity and consistency with
a forward-modeled point source suggest that it remains a viable protoplanet
candidate. The protoplanet PDS 70 c was marginally recovered under our
conservative general methodology. However, through targeted optimization in
H{\alpha} imagery, we tentatively recover PDS 70 c in three epochs and PDS 70 b
in one epoch. Of the many other previously-reported companions and companion
candidates around objects in the sample, we do not recover any additional
robust candidates. However, lack of recovery at moderate H{\alpha} contrast
does not rule out the presence of protoplanets at these locations, and we
report limiting H{\alpha} contrasts in such cases.Comment: Accepted for publication in A
Further Search for the Two-Photon Production of the Glueball Candidate
The CLEOII detector at the Cornell e+ e- storage ring CESR has been used to
search for the two-photon production of the decaying into pi+ pi-.
No evidence for a signal is found in data corresponding to an integrated
luminosity of 4.77/fb and a 95% CL upper limit on of 2.5 eV is set. If this result is combined with the BES Collaboration's
measurement of in radiative decay, a 95% CL
lower limit on the stickiness of the of 73 is obtained. If the
recent CLEO result for \Gamma_{two-photon} * BR{\K_S K_S} is combined with
the present result, the stickiness of the is found to be larger
than 102 at the 95% CL. These results for the stickiness (the ratio of the
probabilities for two-gluon coupling and two-photon coupling) provide further
support for a substantial neutral parton content in the .Comment: 8 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
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