4,232 research outputs found
Line Ratios Reveal N2H+ Emission Originates Above the Midplane in TW Hydrae
Line ratios for different transitions of the same molecule have long been
used as a probe of gas temperature. Here we use ALMA observations of the N2H+
J~=~1-0 and J~=~4-3 lines in the protoplanetary disk around TW Hya to derive
the temperature at which these lines emit. We find an averaged temperature of
39~K with a one sigma uncertainty of 2~K for the radial range 0.8-2'',
significantly warmer than the expected midplane temperature beyond 0.5'' in
this disk. We conclude that the N2H+ emission in TW Hya is not emitting from
near the midplane, but rather from higher in the disk, in a region likely
bounded by processes such as photodissociation or chemical reprocessing of CO
and N2 rather than freeze out.Comment: Accepted for publication in ApJ Letters, 5 pages, 1 figur
Field Interpretation of Latitude and Longitude in Arkansas: A Portable Coordinate Projection
Two- and three-dimensional coordinate systems are fundamental to most quantitative mapping applications. The Geodetic, Universal Transverse Mercator (UTM),and State Plane systems have traditional roles in various science, surveying, and government agency engineering applications. The coordinates of three-dimensional Geodetic system are latitude, longitude, and height above ellipsoid (HAE).Because of its ability to cope with the intrinsically three dimensional character of the earth\u27s surface, the Geodetic system is capable of supporting precise relative positioning and very high accuracy computations of distance between any two positions on or near the earth\u27s surface. The two-dimensional UTMand State Plane systems are extremely useful for the local horizontal positioning and scaling required for paper maps of county-size land areas. In the two plane systems, horizontal distance computation is a very straightforward application of the distance formula (analytic geometry) based on the Pythagorean theorem. Although precision line- and geodesic- distance formulas based on geodetic coordinates are more complex, useful horizontal distance estimates are easily derived from the latitudes and longitudes of two positions. This paper examines this premise for Arkansas. The approach to estimating horizontal distances utilizes an application of the distance formula in conjunction with an assumed constant distance/unit latitude of 30.8 m (arc sec) 1.Alinear regression equation is used to represent distance/unit longitude as a function of latitude in Arkansas. The approximation math is extremely simple, and the process as a whole is equivalent to a portable coordinate projection
Coreset Clustering on Small Quantum Computers
Many quantum algorithms for machine learning require access to classical data
in superposition. However, for many natural data sets and algorithms, the
overhead required to load the data set in superposition can erase any potential
quantum speedup over classical algorithms. Recent work by Harrow introduces a
new paradigm in hybrid quantum-classical computing to address this issue,
relying on coresets to minimize the data loading overhead of quantum
algorithms. We investigate using this paradigm to perform -means clustering
on near-term quantum computers, by casting it as a QAOA optimization instance
over a small coreset. We compare the performance of this approach to classical
-means clustering both numerically and experimentally on IBM Q hardware. We
are able to find data sets where coresets work well relative to random sampling
and where QAOA could potentially outperform standard -means on a coreset.
However, finding data sets where both coresets and QAOA work well--which is
necessary for a quantum advantage over -means on the entire data
set--appears to be challenging
The 1.06 micrometer wideband laser modulator: Fabrication and life testing
The design, fabrication, testing and delivery of an optical modulator which will operate with a mode-locked Nd:YAG laser at 1.06 micrometers were performed. The system transfers data at a nominal rate of 400 Mbps. This wideband laser modulator can transmit either Pulse Gated Binary Modulation (PGBM) or Pulse Polarization Binary Modulation (PPBM) formats. The laser beam enters the modulator and passes through both crystals; approximately 1% of the transmitted beam is split from the main beam and analyzed for the AEC signal; the remaining part of the beam exits the modulator. The delivered modulator when initially aligned and integrated with laser and electronics performed very well. The optical transmission was 69.5%. The static extinction ratio was 69:1. A 1000 hour life test was conducted with the delivered modulator. A 63 bit pseudorandom code signal was used as a driver input. At the conclusion of the life test the modulator optical transmission was 71.5% and the static extinction ratio 65:1
Changes in Soil Chemistry Beneath Exposed Poultry House Pads and Manure Storage Areas
Concerns about nitrates in private drinking water supplies in the older poultry growing areas of Arkansas prompted soil and water testing in the early 1990\u27s. Exposed poultry house pads were recognized as a potential source of nitrates in the groundwater. Soils beneath nine different poultry house pads in five counties were sampled in 10-30 cm increments to bedrock or to a maximum sampling depth of 90 cm. The nine sites had been exposed to natural weathering conditions ranging from never to for more than 20 years. Routine soil tests were conducted by the University of Arkansas Soil Testing Lab at Marianna according to standard methods (Mehlich III extractant). The relatively immobile elements P, Ca, Mg, Fe, Mn, Cu, and Zn were mainly concentrated in the upper part of the soil profiles (0-30 cm). The more leachable NO3-N, K, and SO4-S were generally found throughout the soil profile. Sodium was found in high concentrations throughout the soil profile at two sites. This study shows that nitrate-N, potassium, and sulfate-S from exposed poultry house pads and manure storage areas have the potential of leaching into groundwater. The other eight elements tested do not pose a threat of leaching, but are possible surface water contaminants
On the methanol emission detection in the TW Hya disc: the role of grain surface chemistry and non-LTE excitation
The recent detection of gas-phase methanol (CHOH) lines in the disc of TW
Hya by Walsh et al. provided the first observational constraints on the complex
O-bearing organic content in protoplanetary discs. The emission has a ring-like
morphology, with a peak at au and an inferred column density of
cm. A low CHOH fractional abundance of (with respect to H) is derived, depending on the
assumed vertical location of the CHOH molecular layer. In this study, we
use a thermo-chemical model of the TW Hya disc, coupled with the ALCHEMIC
gas-grain chemical model, assuming laboratory-motivated, fast diffusivities of
the surface molecules to interpret the CHOH detection. Based on this disc
model, we performed radiative transfer calculations with the LIME code and
simulations of the observations with the CASA simulator. We found that our
model allows to reproduce the observations well. The CHOH emission in our
model appears as a ring with radius of au. Synthetic and observed line
flux densities are equal within the rms noise level of observations. The
synthetic CHOH spectra calculated assuming local thermodynamic equilibrium
(LTE) can differ by up to a factor of 3.5 from the non-LTE spectra. For the
strongest lines, the differences between LTE and non-LTE flux densities are
very small and practically negligible. Variations in the diffusivity of the
surface molecules can lead to variations of the CHOH abundance and,
therefore, line flux densities by an order of magnitude.Comment: Accepted for publication in MNRAS, 8 pages, 8 figure
Missing Data in Discrete Time State-Space Modeling of Ecological Momentary Assessment Data: A Monte-Carlo Study of Imputation Methods
When using ecological momentary assessment data (EMA), missing data is
pervasive as participant attrition is a common issue. Thus, any EMA study must
have a missing data plan. In this paper, we discuss missingness in time series
analysis and the appropriate way to handle missing data when the data is
modeled as a discrete time continuous measure state-space model. We found that
Missing Completely At Random, Missing At Random, and Time-dependent Missing At
Random data have less bias and variability than Autoregressive Time-dependent
Missing At Random and Missing Not At Random. The Kalman filter excelled at
handling missing data. Contrary to the literature, we found that, with either
default package settings or a lag-1 imputation model, multiple imputation
struggled to recover the parameters
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