8,308 research outputs found
Approximations to the Bayes estimate for a quantal assay with simple exponential tolerance distribution
Approximations to Bayes estimate for quantal assay with simple exponential tolerance distributio
Estimation for a Simple Exponential Model
Methods of parameter estimation for exponential model arising in epidemiological studies and biological assa
Measuring Electric Fields From Surface Contaminants with Neutral Atoms
In this paper we demonstrate a technique of utilizing magnetically trapped
neutral Rb-87 atoms to measure the magnitude and direction of stray electric
fields emanating from surface contaminants. We apply an alternating external
electric field that adds to (or subtracts from) the stray field in such a way
as to resonantly drive the trapped atoms into a mechanical dipole oscillation.
The growth rate of the oscillation's amplitude provides information about the
magnitude and sign of the stray field gradient. Using this measurement
technique, we are able to reconstruct the vector electric field produced by
surface contaminants. In addition, we can accurately measure the electric
fields generated from adsorbed atoms purposely placed onto the surface and
account for their systematic effects, which can plague a precision
surface-force measurement. We show that baking the substrate can reduce the
electric fields emanating from adsorbate, and that the mechanism for reduction
is likely surface diffusion, not desorption.Comment: 7 pages, 6 figures, published in Physical Review
The Structure Of The Accretion Disk In The ADC Source 4U 1822-371
The low-mass X-ray binary (LMXB) 4U 1822-371 has an accretion disk corona (ADC) that scatters X-ray photons from the inner disk and neutron star out of the line of sight. It has a high orbital inclination and the secondary star eclipses the disk and ADC. We have obtained new time-resolved UV spectrograms and V- and I-band photometry of 4U 1822-371. The large quadratic term in our new optical eclipse ephemeris confirms that the system has an extremely high rate of mass transfer and mass accretion. The C IV lambda lambda = 1548 - 1550 angstrom emission line has a half width of similar to 4400 km/s, indicating a strong, high velocity wind is being driven off the accretion disk. Near the disk the wind is optically thick in UV, V, and J and the eclipse analysis shows that in V and J the optically thick wind extends nearly to the outer edge of the disk. The ADC must also extend vertically to a height equal to approximately half the disk radius.Astronom
Interactive multi-mode blade impact analysis
The theoretical methodology used in developing an analysis for the response of turbine engine fan blades subjected to soft-body (bird) impacts is reported, and the computer program developed using this methodology as its basis is described. This computer program is an outgrowth of two programs that were previously developed for the purpose of studying problems of a similar nature (a 3-mode beam impact analysis and a multi-mode beam impact analysis). The present program utilizes an improved missile model that is interactively coupled with blade motion which is more consistent with actual observations. It takes into account local deformation at the impact area, blade camber effects, and the spreading of the impacted missile mass on the blade surface. In addition, it accommodates plate-type mode shapes. The analysis capability in this computer program represents a significant improvement in the development of the methodology for evaluating potential fan blade materials and designs with regard to foreign object impact resistance
Recent Experiments with Bose-Condensed Gases at JILA
We consider a binary mixture of two overlapping Bose-Einstein condensates in
two different hyperfine states of \Rb87 with nearly identical magnetic moments.
Such a system has been simply realized through application of radiofrequency
and microwave radiation which drives a two-photon transition between the two
states. The nearly identical magnetic moments afford a high degree of spatial
overlap, permitting a variety of new experiments. We discuss some of the
conditions under which the magnetic moments are identical, with particular
emphasis placed on the requirements for a time-averaged orbiting potential
(TOP) magnetic trap.Comment: 9 pages, 5 figures; corrected post-publication editio
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Feasibility of Using 2,3,3,3-Tetrafluoropropene (R1234yf) as a Solvent for Solid–Liquid Extraction of Biopharmaceuticals
Tetrafluoropropene (R1234yf) is the most likely replacement for tetrafluoroethane (R134a), a widely used refrigerant, propellant, and solvent, characterized by a very high global warming potential. In this study, solvation properties of R1234yf were studied experimentally and computationally for solubility of artemisinin, a precursor to the important biopharmaceutical API, and extraction of artemisinin from biomass. R1234yf was shown to be a poorer solvent than R134a for artemisinin. COSMO-RS calculations of solvation in R1234yf suggest that the decrease in performance is likely due to entropic effects. However, R1234yf was effectively used in solid–liquid extraction of Artemisia annua. The new solvent has shown an increased selectivity to the target metabolite artemisinin. This should allow for design of more selective separation processes based on the new solvent molecule with a low global warming potential of 4 relative to CO2.This work was funded under iCON feasibility projects scheme of EPSRC “Centre for Continuous Manufacturing (CMAC)”, EP/IO33459/1. We acknowledge past funding from Medicine for Malaria Ventures for HPLC instrument and funding by University of Cambridge for the LCMS system
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