41,243 research outputs found
No warmup crystal oscillator
During warmup, crystal oscillators often show a frequency offset as large as 1 part in 10 to the 5th power. If timing information is transferred to the oscillator and then the oscillator is allowed to warmup, a timing error greater than 1 millisecond will occur. For many applications, it is unsuitable to wait for the oscillator to warmup. For medium accuracy timing requirements where overall accuracies in the order of 1 millisecond are required, a no warmup crystal concept was developed. The concept utilizes two crystal oscillator, used sequentially to avoid using a crystal oscillator for timing much higher frequency accuracy once warmed up. The accuracy achieved with practical TCXOs at initial start over a range of temperatures is discussed. A second design utilizing two oven controlled oscillators is also discussed
Resolution changes in lithium-drifted silicon semiconductor detectors irradiated with 0.5, 1.0, 2.0, and 3.0 MeV electrons
Electron irradiation effect on resolution of lithium-drifted silicon semiconductor detector
Computed structures of polyimides model compounds
Using a semi-empirical approach, a computer study was made of 8 model compounds of polyimides. The compounds represent subunits from which NASA Langley Research Center has successfully synthesized polymers for aerospace high performance material application, including one of the most promising, LARC-TPI polymer. Three-dimensional graphic display as well as important molecular structure data pertaining to these 8 compounds are obtained
Pion-mass dependence of three-nucleon observables
We use an effective field theory (EFT) which contains only short-range
interactions to study the dependence of a variety of three-nucleon observables
on the pion mass. The pion-mass dependence of input quantities in our
``pionless'' EFT is obtained from a recent chiral EFT calculation. To the order
we work at, these quantities are the 1S0 scattering length and effective range,
the deuteron binding energy, the 3S1 effective range, and the binding energy of
one three-nucleon bound state. The chiral EFT input we use has the inverse 3S1
and 1S0 scattering lengths vanishing at mpi_c=197.8577 MeV. At this
``critical'' pion mass, the triton has infinitely many excited states with an
accumulation point at the three-nucleon threshold. We compute the binding
energies of these states up to next-to-next-to-leading order in the pionless
EFT and study the convergence pattern of the EFT in the vicinity of the
critical pion mass. Furthermore, we use the pionless EFT to predict how doublet
and quartet nd scattering lengths depend on mpi in the region between the
physical pion mass and mpi=mpi_c.Comment: 24 pages, 9 figure
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
Gust alleviation system to improve ride comfort of light airplanes
System consists of movable auxiliary aerodynamic sensors mounted on fuselage and connected to trailing-edge flaps by rigid mechanical linkages. System achieves alleviation by reducing lift-curve slope of airplane to such a small value that gust-induced angles of attack will result in small changes in lift
DNA adducts in human tissues: biomarkers of exposure to carcinogens in tobacco smoke.
Tobacco smoking causes millions of cancer deaths annually. Tobacco smoke is a complex mixture of thousands of chemicals including many known animal carcinogens. Because many carcinogens from DNA adducts in target animal or human tissues, the detection of the formation of adducts using such methods as postlabeling, immunoassay, fluorescence spectroscopy, and mass spectrometry is a means of monitoring human exposure to tobacco carcinogens. Smokers are at increased risk of cancer in many organs, and studies have revealed either specific adducts related to smoking or increased levels of adducts in the lung, bronchus, larynx, bladder, cervix, and oral mucosa of smokers. In a limited number of studies, the adducts and the carcinogens responsible for them have been identified. Some studies have demonstrated higher levels of adducts in the white blood cells of smokers, while other studies indicate other sources of genotoxic agents, including diet, can contribute to the DNA damage observed in these cells
A solar spectroscopic absolute abundance of argon from RESIK
Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at 3.949
Angstroms and 3.733 Angstroms respectively with the RESIK X-ray spectrometer on
the CORONAS-F spacecraft, together with temperatures and emission measures from
the two channels of GOES, have been analyzed to obtain the abundance of Ar in
flare plasmas in the solar corona. The line fluxes per unit emission measure
show a temperature dependence like that predicted from theory, and lead to
spectroscopically determined values for the absolute Ar abundance, A(Ar) = 6.44
pm 0.07 (Ar XVII) and 6.49 pm 0.16 (Ar XVIII) which are in agreement to within
uncertainties. The weighted mean is 6.45 pm 0.06, which is between two recent
compilations of the solar Ar abundance and suggest that the photospheric and
coronal abundances of Ar are very similar.Comment: 4 figure
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