97 research outputs found
Some Performance Characteristics of Subsurface Gravel Wetlands for Stormwater Management
Subsurface gravel wetlands were originally purposed for wastewater treatment and more recently have been used for stormwater treatment as a green infrastructure technology. Systems are sized to hold the water quality volume above, and drain within 24â48 hours. Design guidance follows static sizing principles with very little hydraulic calculations, which has left a gap in hydraulic performance data. Data from 12 years of field monitoring of various systems constructed in the northeast United States is presented. These systems include fully-sized as well as undersized (hold less that the water quality volume). Hydraulics are controlled by a restrictive outlet. At the same time, this outlet also creates the wetland characteristics of the system. Pollutant removal efficiencies for common stormwater pollutants are some of the highest for green infrastructure systems, with a significant component being microbially-mediated in the low dissolved oxygen gravel layers.
This is a book chapter published by the American Society of Civil Engineers in World Environmental and Water Resources Congress 2020: Emerging and Innovative Technologies and International Perspectives in 2020, available online: https://doi.org/10.1061/978078448294
Characterization of Titanium Alloys Produced by Electron Beam Directed Energy Deposition
Functionally graded materials offer the potential to improve structural efficiency by allowing the material composition and/or microstructural features to spatially vary within a component. Additive manufacturing techniques enable the fabrication of such graded materials and structures. While examining several titanium alloys, this paper focuses on Ti-8Al-1Er as it has a unique microstructure that is only feasible when produced by rapid solidification methods like electron beam directed energy deposition, an additive manufacturing process. The results show that, when mixed, Ti-8Al-1Er and commercially-pure titanium uniformly mix at various ratios and the resultant static tensile properties of the mixed alloys behave according to rule-of-mixtures. At discontinuous interfaces between Ti-8Al-1Er and commercially-pure titanium, the crack growth behavior progresses smoothly across the discontinuity as the crack transitions from one crack growth regime into another. Studies on monolithic samples shows the mechanisms of damage in the Ti-8Al-1Er; specifically, that strain localization occurs near grain boundaries of high mis-orientation on the microscale and that twinning and dislocation density is concentrated near erbia-strengthening particles (Er2O3) on the nanoscale
Rotation Distributions around the Kraft Break with TESS and Kepler: The Influences of Age, Metallicity, and Binarity
Stellar rotation is a complex function of mass, metallicity, and age and can
be altered by binarity. To understand the importance of these parameters in
main sequence stars, we have assembled a sample of observations that spans a
range of these parameters using a combination of observations from The
Transiting Exoplanet Survey Satellite (TESS) and the Kepler Space Telescope. We
find that while we can measure rotation periods and identify other classes of
stellar variability (e.g., pulsations) from TESS lightcurves, instrument
systematics prevent the detection of rotation signals longer than the TESS
orbital period of 13.7 days. Due to this detection limit, we also utilize
rotation periods constrained using rotational velocities measured by the APOGEE
spectroscopic survey and radii estimated using the Gaia mission for both TESS
and Kepler stars. From these rotation periods, we 1) find we can track
rotational evolution along discrete mass tracks as a function of stellar age,
2) find we are unable to recover trends between rotation and metallicity that
were observed by previous studies, and 3) note that our sample reveals that
wide binary companions do not affect rotation, while close binary companions
cause stars to exhibit more rapid rotation than single stars.Comment: 19 pages, 13 figures, Accepted for publication in the Astrophysical
Journa
The Asymptotic distribution of circles in the orbits of Kleinian groups
Let P be a locally finite circle packing in the plane invariant under a
non-elementary Kleinian group Gamma and with finitely many Gamma-orbits. When
Gamma is geometrically finite, we construct an explicit Borel measure on the
plane which describes the asymptotic distribution of small circles in P,
assuming that either the critical exponent of Gamma is strictly bigger than 1
or P does not contain an infinite bouquet of tangent circles glued at a
parabolic fixed point of Gamma. Our construction also works for P invariant
under a geometrically infinite group Gamma, provided Gamma admits a finite
Bowen-Margulis-Sullivan measure and the Gamma-skinning size of P is finite.
Some concrete circle packings to which our result applies include Apollonian
circle packings, Sierpinski curves,
Schottky dances, etc.Comment: 31 pages, 8 figures. Final version. To appear in Inventiones Mat
Asymptotic channels and gauge transformations of the time-dependent Dirac equation for extremely relativistic heavy-ion collisions
We discuss the two-center, time-dependent Dirac equation describing the
dynamics of an electron during a peripheral, relativistic heavy-ion collision
at extreme energies. We derive a factored form, which is exact in the
high-energy limit, for the asymptotic channel solutions of the Dirac equation,
and elucidate their close connection with gauge transformations which transform
the dynamics into a representation in which the interaction between the
electron and a distant ion is of short range. We describe the implications of
this relationship for solving the time-dependent Dirac equation for extremely
relativistic collisions.Comment: 12 pages, RevTeX, 2 figures, submitted to PR
Critical Review of Theoretical Models for Anomalous Effects (Cold Fusion) in Deuterated Metals
We briefly summarize the reported anomalous effects in deuterated metals at
ambient temperature, commonly known as "Cold Fusion" (CF), with an emphasis on
important experiments as well as the theoretical basis for the opposition to
interpreting them as cold fusion. Then we critically examine more than 25
theoretical models for CF, including unusual nuclear and exotic chemical
hypotheses. We conclude that they do not explain the data.Comment: 51 pages, 4 Figure
TESS Asteroseismology of Mensae: Benchmark Ages for a G7 Dwarf and its M-dwarf Companion
Asteroseismology of bright stars has become increasingly important as a
method to determine fundamental properties (in particular ages) of stars. The
Kepler Space Telescope initiated a revolution by detecting oscillations in more
than 500 main-sequence and subgiant stars. However, most Kepler stars are
faint, and therefore have limited constraints from independent methods such as
long-baseline interferometry. Here, we present the discovery of solar-like
oscillations in Men A, a naked-eye (V=5.1) G7 dwarf in TESS's Southern
Continuous Viewing Zone. Using a combination of astrometry, spectroscopy, and
asteroseismology, we precisely characterize the solar analog alpha Men A (Teff
= 5569 +/- 62 K, R = 0.960 +/- 0.016 Rsun, M = 0.964 +/- 0.045 Msun). To
characterize the fully convective M dwarf companion, we derive empirical
relations to estimate mass, radius, and temperature given the absolute Gaia
magnitude and metallicity, yielding M = 0.169 +/- 0.006, R = 0.19 +/- 0.01 and
Teff = 3054 +/- 44 K. Our asteroseismic age of 6.2 +/- 1.4 (stat) +/- 0.6 (sys)
Gyr for the primary places Men B within a small population of M dwarfs
with precisely measured ages. We combined multiple ground-based spectroscopy
surveys to reveal an activity cycle of 13.1 +/- 1.1 years, a period similar to
that observed in the Sun. We used different gyrochronology models with the
asteroseismic age to estimate a rotation period of ~30 days for the primary.
Alpha Men A is now the closest (d=10pc) solar analog with a precise
asteroseismic age from space-based photometry, making it a prime target for
next-generation direct imaging missions searching for true Earth analogs.Comment: Accepted to The Astrophysical Journal; 15 pages, 10 figure
Kepler-102: Masses and Compositions for a Super-Earth and Sub-Neptune Orbiting an Active Star
Kepler-102 : masses and compositions for a super-Earth and sub-Neptune orbiting an active star
Funding: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant No. 1842402. C.L.B., L.W., and D.H. acknowledge support from National Aeronautics and Space Administration (grant No. 80NSSC19K0597) issued through the Astrophysics Data Analysis Program. D.H. also acknowledges support from the Alfred P. Sloan Foundation. K.R. acknowledges support from the UK STFC via grant No. ST/V000594/1. E.G. acknowledges support from NASA grant No. 80NSSC20K0957 (Exoplanets Research Program).Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the solar system. Kepler-102, which consists of five tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using RVs. Previous work found a high density for Kepler-102d, suggesting a composition similar to that of Mercury, while Kepler-102e was found to have a density typical of sub-Neptune size planets; however, Kepler-102 is an active star, which can interfere with RV mass measurements. To better measure the mass of these two planets, we obtained 111 new RVs using Keck/HIRES and Telescopio Nazionale Galileo/HARPS-N and modeled Kepler-102's activity using quasiperiodic Gaussian process regression. For Kepler-102d, we report a mass upper limit Md < 5.3 Mâ (95% confidence), a best-fit mass Md = 2.5 ± 1.4 Mâ, and a density Ïd = 5.6 ± 3.2 g cmâ3, which is consistent with a rocky composition similar in density to the Earth. For Kepler-102e we report a mass Me = 4.7 ± 1.7 Mâ and a density Ïe = 1.8 ± 0.7 g cmâ3. These measurements suggest that Kepler-102e has a rocky core with a thick gaseous envelope comprising 2%â4% of the planet mass and 16%â50% of its radius. Our study is yet another demonstration that accounting for stellar activity in stars with clear rotation signals can yield more accurate planet masses, enabling a more realistic interpretation of planet interiors.Publisher PDFPeer reviewe
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