3,907 research outputs found
Measurement of the lowest millimetre-wave transition frequency of the CH radical
The CH radical offers a sensitive way to test the hypothesis that fundamental
constants measured on earth may differ from those observed in other parts of
the universe. The starting point for such a comparison is to have accurate
laboratory frequencies. Here we measure the frequency of the lowest
millimetre-wave transition of CH, near 535 GHz, with an accuracy of 0.6 kHz.
This improves the uncertainty by roughly two orders of magnitude over previous
determinations and opens the way for sensitive new tests of varying constants.Comment: 5 pages, 5 figure
Advanced thermoplastic resins, phase 1
Eight thermoplastic polyimide resin systems were evaluated as composite matrix materials. Two resins were selected for more extensive mechanical testing and both were versions of LaRC-TPI (Langley Research Center - Thermoplastic Polyimide). One resin was made with LaRC-TPI and contained 2 weight percent of a di(amic acid) dopant as a melt flow aid. The second system was a 1:1 slurry of semicrystalline LaRC-TPI powder in a polyimidesulfone resin diglyme solution. The LaRC-TPI powder melts during processing and increases the melt flow of the resin. Testing included dynamic mechanical analysis, tension and compression testing, and compression-after-impact testing. The test results demonstrated that the LaRC-TPI resins have very good properties compared to other thermoplastics, and that they are promising matrix materials for advanced composite structures
Vibrational branching ratios and hyperfine structure of BH and its suitability for laser cooling
The simple structure of the BH molecule makes it an excellent candidate for
direct laser cooling. We measure the branching ratios for the decay of the
state to vibrational levels of the ground state, , and find that they are exceedingly favourable for laser
cooling. We verify that the branching ratio for the spin-forbidden transition
to the intermediate state is inconsequentially small. We
measure the frequency of the lowest rotational transition of the X state, and
the hyperfine structure in the relevant levels of both the X and A states, and
determine the nuclear electric quadrupole and magnetic dipole coupling
constants. Our results show that, with a relatively simple laser cooling
scheme, a Zeeman slower and magneto-optical trap can be used to cool, slow and
trap BH molecules.Comment: 7 pages, 5 figures. Updated analysis of A state hyperfine structure
and other minor revision
A Multidisciplinary Approach to Mixer-Ejector Analysis and Design
The design of an engine for a civil supersonic aircraft presents a difficult multidisciplinary problem to propulsion system engineers. There are numerous competing requirements for the engine, such as to be efficient during cruise while yet quiet enough at takeoff to meet airport noise regulations. The use of mixer-ejector nozzles presents one possible solution to this challenge. However, designing a mixer-ejector which will successfully address both of these concerns is a difficult proposition. Presented in this paper is an integrated multidisciplinary approach to the analysis and design of these systems. A process that uses several low-fidelity tools to evaluate both the performance and acoustics of mixer-ejectors nozzles is described. This process is further expanded to include system-level modeling of engines and aircraft to determine the effects on mission performance and noise near airports. The overall process is developed in the OpenMDAO framework currently being developed by NASA. From the developed process, sample results are given for a notional mixer-ejector design, thereby demonstrating the capabilities of the method
A high quality, efficiently coupled microwave cavity for trapping cold molecules
We characterize a Fabry-Perot microwave cavity designed for trapping atoms
and molecules at the antinode of a microwave field. The cavity is fed from a
waveguide through a small coupling hole. Focussing on the compact resonant
modes of the cavity, we measure how the electric field profile, the cavity
quality factor, and the coupling efficiency, depend on the radius of the
coupling hole. We measure how the quality factor depends on the temperature of
the mirrors in the range from 77 to 293K. The presence of the coupling hole
slightly changes the profile of the mode, leading to increased diffraction
losses around the edges of the mirrors and a small reduction in quality factor.
We find the hole size that maximizes the intra-cavity electric field. We
develop an analytical theory of the aperture-coupled cavity that agrees well
with our measurements, with small deviations due to enhanced diffraction
losses. We find excellent agreement between our measurements and
finite-difference time-domain simulations of the cavity.Comment: 16 pages, 8 figure
Characterization of a cryogenic beam source for atoms and molecules
We present a combined experimental and theoretical study of beam formation
from a cryogenic buffer gas cell. Atoms and molecules are loaded into the cell
by laser ablation of a target, and are cooled and swept out of the cell by a
flow of cold helium. We study the thermalization and flow dynamics inside the
cell and measure how the speed, temperature, divergence and extraction
efficiency of the beam are influenced by the helium flow. We use a finite
element model to simulate the flow dynamics and use the predictions of this
model to interpret our experimental results.Comment: 10 pages, 14 figure
Preliminary experimental results for a cryogenic brush seal configuration
Preliminary fluid nitrogen flow data are reported for a five-brush, ceramic-coated-rub-runner brush seal system, where the brushes and the rub runner were placed at each end of a centrally pressurized multifunction tester ('back-to-back' set of brushes) and tested at rotor speeds of 0, 10, 18, and 22.5 krpm. After testing, both the brushes and the ceramic-coated rub runner appeared pristine. The coating withstood both the thermomechanical and dynamic loadings with minor wear track scarring. The bristle tips showed some indication of material shearing (smearing) wear. The Ergun porous flow equation was applied to the brush seal data. The Ergun relation, which required heuristic information to characterize the coefficients, fit the gaseous data but was in poor agreement with the fluid results. The brush seal exit conditions were two phase. Two-phase, choked-flow design charts were applied but required one data point at each rotor speed to define the (C(sub f)A x Constant) flow and area coefficients. Reasonable agreement between prediction and data was found, as expected, but such methods are not to be construed as two-phase-flow brush seal analyses
A search for varying fundamental constants using Hz-level frequency measurements of cold CH molecules
Many modern theories predict that the fundamental constants depend on time,
position, or the local density of matter. We develop a spectroscopic method for
pulsed beams of cold molecules, and use it to measure the frequencies of
microwave transitions in CH with accuracy down to 3 Hz. By comparing these
frequencies with those measured from sources of CH in the Milky Way, we test
the hypothesis that fundamental constants may differ between the high and low
density environments of the Earth and the interstellar medium. For the fine
structure constant we find \Delta\alpha/\alpha = (0.3 +/- 1.1)*10^{-7}, the
strongest limit to date on such a variation of \alpha. For the
electron-to-proton mass ratio we find \Delta\mu/\mu = (-0.7 +/- 2.2) * 10^{-7}.
We suggest how dedicated astrophysical measurements can improve these
constraints further and can also constrain temporal variation of the constants.Comment: 8 pages, 3 figure
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