1,709 research outputs found
The statistics of multi-planet systems
We describe statistical methods for measuring the exoplanet multiplicity
function - the fraction of host stars containing a given number of planets -
from transit and radial-velocity surveys. The analysis is based on the
approximation of separability - that the distribution of planetary parameters
in an n-planet system is the product of identical 1-planet distributions. We
review the evidence that separability is a valid approximation for exoplanets.
We show how to relate the observable multiplicity function in surveys with
similar host-star populations but different sensitivities. We also show how to
correct for geometrical selection effects to derive the multiplicity function
from transit surveys if the distribution of relative inclinations is known.
Applying these tools to the Kepler transit survey and radial-velocity surveys,
we find that (i) the Kepler data alone do not constrain the mean inclination of
multi-planet systems; even spherical distributions are allowed by the data but
only if a small fraction of host stars contain large planet populations (> 30);
(ii) comparing the Kepler and radial-velocity surveys shows that the mean
inclination of multi-planet systems lies in the range 0-5 degrees; (iii) the
multiplicity function of the Kepler planets is not well-determined by the
present data.Comment: 34 pages, 10 figure
Recombinant expression and functional analysis of proteases from Streptococcus pneumoniae, Bacillus anthracis, and Yersinia pestis
<p>Abstract</p> <p>Background</p> <p>Uncharacterized proteases naturally expressed by bacterial pathogens represents important topic in infectious disease research, because these enzymes may have critical roles in pathogenicity and cell physiology. It has been observed that cloning, expression and purification of proteases often fail due to their catalytic functions which, in turn, cause toxicity in the <it>E. coli </it>heterologous host.</p> <p>Results</p> <p>In order to address this problem systematically, a modified pipeline of our high-throughput protein expression and purification platform was developed. This included the use of a specific <it>E. coli </it>strain, BL21(DE3) pLysS to tightly control the expression of recombinant proteins and various expression vectors encoding fusion proteins to enhance recombinant protein solubility. Proteases fused to large fusion protein domains, maltosebinding protein (MBP), SP-MBP which contains signal peptide at the N-terminus of MBP, disulfide oxidoreductase (DsbA) and Glutathione S-transferase (GST) improved expression and solubility of proteases. Overall, 86.1% of selected protease genes including hypothetical proteins were expressed and purified using a combination of five different expression vectors. To detect novel proteolytic activities, zymography and fluorescence-based assays were performed and the protease activities of more than 46% of purified proteases and 40% of hypothetical proteins that were predicted to be proteases were confirmed.</p> <p>Conclusions</p> <p>Multiple expression vectors, employing distinct fusion tags in a high throughput pipeline increased overall success rates in expression, solubility and purification of proteases. The combinatorial functional analysis of the purified proteases using fluorescence assays and zymography confirmed their function.</p
Radial Velocity Prospects Current and Future: A White Paper Report prepared by the Study Analysis Group 8 for the Exoplanet Program Analysis Group (ExoPAG)
[Abridged] The Study Analysis Group 8 of the NASA Exoplanet Analysis Group
was convened to assess the current capabilities and the future potential of the
precise radial velocity (PRV) method to advance the NASA goal to "search for
planetary bodies and Earth-like planets in orbit around other stars.: (U.S.
National Space Policy, June 28, 2010). PRVs complement other exoplanet
detection methods, for example offering a direct path to obtaining the bulk
density and thus the structure and composition of transiting exoplanets. Our
analysis builds upon previous community input, including the ExoPlanet
Community Report chapter on radial velocities in 2008, the 2010 Decadal Survey
of Astronomy, the Penn State Precise Radial Velocities Workshop response to the
Decadal Survey in 2010, and the NSF Portfolio Review in 2012. The
radial-velocity detection of exoplanets is strongly endorsed by both the Astro
2010 Decadal Survey "New Worlds, New Horizons" and the NSF Portfolio Review,
and the community has recommended robust investment in PRVs. The demands on
telescope time for the above mission support, especially for systems of small
planets, will exceed the number of nights available using instruments now in
operation by a factor of at least several for TESS alone. Pushing down towards
true Earth twins will require more photons (i.e. larger telescopes), more
stable spectrographs than are currently available, better calibration, and
better correction for stellar jitter. We outline four hypothetical situations
for PRV work necessary to meet NASA mission exoplanet science objectives.Comment: ExoPAG SAG 8 final report, 112 pages, fixed author name onl
Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: II. omicron Draconis, a Candidate for Recent Low-Mass Companion Ingestion
To measure the stellar and orbital properties of the metal-poor RS CVn binary
o Draconis (o Dra), we directly detect the companion using interferometric
observations obtained with the Michigan InfraRed Combiner at Georgia State
University's Center for High Angular Resolution Astronomy (CHARA) Array. The
H-band flux ratio between the primary and secondary stars is the highest
confirmed flux ratio (370 +/- 40) observed with long-baseline optical
interferometry. These detections are combined with radial velocity data of both
the primary and secondary stars, including new data obtained with the
Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the
Fred Lawrence Whipple Observatory and the 2-m Tennessee State University
Automated Spectroscopic Telescope at Fairborn Observatory. We determine an
orbit from which we find model-independent masses and ages of the components
(M_A = 1.35 +\- 0.05 M_Sun, M_B = 0.99 +\- 0.02 M_Sun, system age = 3.0 -\+ 0.5
Gyr). An average of a 23-year light curve of o Dra from the Tennessee State
University Automated Photometric Telescope folded over the orbital period newly
reveals eclipses and the quasi-sinusoidal signature of ellipsoidal variations.
The modeled light curve for our system's stellar and orbital parameters confirm
these ellipsoidal variations due to the primary star partially filling its
Roche lobe potential, suggesting most of the photometric variations are not due
to stellar activity (starspots). Measuring gravity darkening from the average
light curve gives a best-fit of beta = 0.07 +\- 0.03, a value consistent with
conventional theory for convective envelope stars. The primary star also
exhibits an anomalously short rotation period, which, when taken with other
system parameters, suggests the star likely engulfed a low-mass companion that
had recently spun-up the star.Comment: 14 pages, 13 figures, Accepted to Ap
The Evolution of Wide Binary Stars
We study the orbital evolution of wide binary stars in the solar neighborhood
due to gravitational perturbations from passing stars. We include the effects
of the Galactic tidal field and continue to follow the stars after they become
unbound. For a wide variety of initial semi-major axes and formation times, we
find that the number density (stars per unit logarithmic interval in projected
separation) exhibits a minimum at a few times the Jacobi radius r_J, which
equals 1.7 pc for a binary of solar-mass stars. The density peak interior to
this minimum arises from the primordial distribution of bound binaries, and the
exterior density, which peaks at \sim 100--300 pc separation, arises from
formerly bound binaries that are slowly drifting apart. The exterior peak gives
rise to a significant long-range correlation in the positions and velocities of
disk stars that should be detectable in large astrometric surveys such as GAIA
that can measure accurate three-dimensional distances and velocities.Comment: 36 pages, 9 figures, accepted by MNRAS, typos correcte
The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses
We present spatially and spectrally resolved Atacama Large
Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the
pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of
the CO and CO =2-1 transitions permits a measurement of
the total stellar mass in this system, , and the
circum-triple disk inclination, . Optical spectra spanning
a 35 year period were used to derive new radial velocities and, coupled with a
spectroscopic disentangling technique, revealed that the A and B components of
GW Ori form a double-lined spectroscopic binary with a day
period; a tertiary companion orbits that inner pair with a day
period. Combining the results from the ALMA data and the optical spectra with
three epochs of astrometry in the literature, we constrain the individual
stellar masses in the system (,
, ) and
find strong evidence that at least one (and likely both) stellar orbital planes
are misaligned with the disk plane by as much as . A -band light
curve spanning 30 years reveals several new 30 day eclipse events
0.1-0.7~mag in depth and a 0.2 mag sinusoidal oscillation that is clearly
phased with the AB-C orbital period. Taken together, these features suggest
that the A-B pair may be partially obscured by material in the inner disk as
the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude
that stellar evolutionary models are consistent with our measurements of the
masses and basic photospheric properties if the GW Ori system is 1 Myr
old.Comment: 26 pages, 15 figures, accepted to Ap
A Multi-Institutional Partnership Catalyzing the Commercialization of Medical Devices and Biotechnology Products.
The commercialization of medical devices and biotechnology products is characterized by high failure rates and long development lead times particularly among start-up enterprises. To increase the success rate of these high-risk ventures, the University of Massachusetts Lowell (UML) and University of Massachusetts Medical School (UMMS) partnered to create key academic support centers with programs to accelerate entrepreneurship and innovation in this industry. In 2008, UML and UMMS founded the Massachusetts Medical Device Development Center (M2D2), which is a business and technology incubator that provides business planning, product prototyping, laboratory services, access to clinical testing, and ecosystem networking to medical device and biotech startup firms. M2D2 has three physical locations that encompass approximately 40,000 square feet. Recently, M2D2 leveraged these resources to expand into new areas such as health security, point of care technologies for heart, lung, blood, and sleep disorders, and rapid diagnostics to detect SARS-CoV-2. Since its inception, M2D2 has vetted approximately 260 medical device and biotech start-up companies for inclusion in its programs and provided active support to more than 80 firms. This manuscript describes how two UMass campuses leveraged institutional, state, and Federal resources to create a thriving entrepreneurial environment for medical device and biotech companies
Binary Contamination in the SEGUE sample: Effects on SSPP Determinations of Stellar Atmospheric Parameters
Using numerical modeling and a grid of synthetic spectra, we examine the
effects that unresolved binaries have on the determination of various stellar
atmospheric parameters for SEGUE targets measured using the SEGUE Stellar
Parameter Pipeline (SSPP). To model undetected binaries that may be in the
SEGUE sample, we use a variety of mass distributions for the primary and
secondary stars in conjunction with empirically determined relationships for
orbital parameters to determine the fraction of G-K dwarf stars, as defined by
SDSS color cuts, that will be blended with a secondary companion. We focus on
the G-K dwarf sample in SEGUE as it records the history of chemical enrichment
in our galaxy. To determine the effect of the secondary on the spectroscopic
parameters, we synthesize a grid of model spectra from 3275 to 7850 K (~0.1 to
1.0 \msun) and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using
TurboSpectrum. We analyze both "infinite" signal-to-noise ratio (S/N) models
and degraded versions, at median S/N of 50, 25 and 10. By running individual
and combined spectra (representing the binaries) through the SSPP, we determine
that ~10% of the blended G-K dwarf pairs with S/N>=25 will have their
atmospheric parameter determinations, in particular temperature and
metallicity, noticeably affected by the presence of an undetected secondary. To
account for the additional uncertainty from binary contamination at a S/N~10,
uncertainties of ~140 K and ~0.17 dex in [Fe/H] must be added in quadrature to
the published uncertainties of the SSPP. (Abridged)Comment: 68 pages, 20 figures, 9 table
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