2,848 research outputs found
Unified Geostatistical Modeling for Data Fusion and Spatial Heteroskedasticity with R Package ramps
This article illustrates usage of the ramps R package, which implements the reparameterized and marginalized posterior sampling (RAMPS) algorithm for complex Bayesian geostatistical models. The RAMPS methodology allows joint modeling of areal and point-source data arising from the same underlying spatial process. A reparametrization of variance parameters facilitates slice sampling based on simplexes, which can be useful in general when multiple variances are present. Prediction at arbitrary points can be made, which is critical in applications where maps are needed. Our implementation takes advantage of sparse matrix operations in the Matrix package and can provide substantial savings in computing time for large datasets. A user-friendly interface, similar to the nlme mixed effects models package, enables users to analyze datasets with little programming effort. Support is provided for numerous spatial and spatiotemporal correlation structures, user-defined correlation structures, and non-spatial random effects. The package features are illustrated via a synthetic dataset of spatially correlated observation distributed across the state of Iowa, USA.
Microwave state transfer and adiabatic dynamics of magnetically trapped polar molecules
Cold and ultracold polar molecules with nonzero electronic angular momentum
are of great interest for studies in quantum chemistry and control,
investigations of novel quantum systems, and precision measurement. However, in
mixed electric and magnetic fields, these molecules are generically subject to
a large set of avoided crossings among their Zeeman sublevels; in magnetic
traps, these crossings lead to distorted potentials and trap loss from electric
bias fields. We have characterized these crossings in OH by
microwave-transferring trapped OH molecules from the upper |f; M = +3/2> parity
state to the lower |e; +3/2> state and observing their trap dynamics under an
applied electric bias field. Our observations are very well described by a
simple Landau-Zener model, yielding insight to the rich spectra and dynamics of
polar radicals in mixed external fields.Comment: 5 pages, 4 figures plus supplementary materia
The aerobraking space transfer vehicle
With the advent of the Space Station and the proposed Geosynchronous Operation Support Center (GeoShack) in the early 21st century, the need for a cost effective, reusable orbital transport vehicle has arisen. This transport vehicle will be used in conjunction with the Space Shuttle, the Space Station, and GeoShack. The vehicle will transfer mission crew and payloads between low earth and geosynchronous orbits with minimal cost. Recent technological advances in thermal protection systems such as those employed in the Space Shuttle have made it possible to incorporate and aerobrake on the transfer vehicle to further reduce transport costs. The research and final design configuration of the aerospace senior design team from VPISU, working in conjunction with NASA, are presented. The topic of aerobraking and focuses on the evolution of an Aerobraking Space Transfer Vehicle (ASTV), is addressed
Low-energy molecular collisions in a permanent magnetic trap
Cold, neutral hydroxyl radicals are Stark decelerated and confined within a
magnetic trap consisting of two permanent ring magnets. The OH molecules are
trapped in the ro-vibrational ground state at a density of
cm and temperature of 70 mK. Collisions between the trapped OH sample
and supersonic beams of atomic He and molecular D are observed and
absolute collision cross sections measured. The He--OH and D--OH
center-of-mass collision energies are tuned from 60 cm to 230 cm
and 145 cm to 510 cm, respectively, yielding evidence of reduced
He--OH inelastic cross sections at energies below 84 cm, the OH ground
rotational level spacing.Comment: 4 pages, 4 figure
Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant
We report precise measurements of ground-state, -doublet microwave
transitions in the hydroxyl radical molecule (OH). Utilizing slow, cold
molecules produced by a Stark decelerator we have improved over the precision
of the previous best measurement by twenty-five-fold for the F' = 2 F = 2
transition, yielding (1 667 358 996 4) Hz, and by ten-fold for the F' = 1
F = 1 transition, yielding (1 665 401 803 12) Hz. Comparing these
laboratory frequencies to those from OH megamasers in interstellar space will
allow a sensitivity of 1 ppm for over
years.Comment: This version corrects minor typos in the Zeeman shift discussio
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