2,595 research outputs found
A study of high-altitude manned research aircraft employing strut-braced wings of high-aspect-ratio
The effect of increased wing aspect ratio of subsonic aircraft on configurations with and without strut bracing. Results indicate that an optimum cantilever configuration, with a wing aspect ratio of approximately 26, has a 19% improvement in cruise range when compared to a baseline concept with a wing aspect ratio of approximately 10. An optimum strut braced configuration, with a wing aspect ratio of approximately 28, has a 31% improvment in cruise range when compared to the same baseline concept. This improvement is mainly due to the estimated reduction in wing weight resulting from use of lifting struts. All configurations assume the same mission payload and fuel. The drag characteristics of the wings are enhanced with the use of laminar flow airfoils. A method for determining the extent of attainable natural laminar flow, and methods for preliminary structural design and for aerodynamic analysis of wings lifting struts are presented
Remote clocks linked by a fully calibrated two-way timing link
Fully calibrated two-way time transfers between the U.S. Naval Observatory (USNO) and the U.S. Naval Observatory Time Service Substation (NOTSS) have become operational. The calibration method employed was the co-located Earth station method. Results concerning timing, stability, comparison of two-way and Global Positioning System (GPS) timing links, and remote clock contribution to local time scale computation will be presented
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy
The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions
Population of neutron unbound states via two-proton knockout reactions
The two-proton knockout reaction 9Be(26Ne,O2p) was used to explore excited
unbound states of 23O and 24O. In 23O a state at an excitation energy of
2.79(13) MeV was observed. There was no conclusive evidence for the population
of excited states in 24O.Comment: 6 pages, 3 figures, Proc. 9th Int. Spring Seminar on Nucl. Phys.
Changing Facets of Nuclear Structure, May 20-34, 200
Energy distributions from three-body decaying many-body resonances
We compute energy distributions of three particles emerging from decaying
many-body resonances. We reproduce the measured energy distributions from
decays of two archetypal states chosen as the lowest and
-resonances in C populated in -decays. These states are
dominated by sequential, through the Be ground state, and direct decays,
respectively. These decay mechanisms are reflected in the ``dynamic'' evolution
from small, cluster or shell-model states, to large distances, where the
coordinate or momentum space continuum wavefunctions are accurately computed.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review
Letter
Search for unbound 15Be states in the 3n+12Be channel
15Be is expected to have low-lying 3/2+ and 5/2+ states. A first search did
not observe the 3/2+ [A. Spyrou et al., Phys. Rev. C 84, 044309 (2011)],
however, a resonance in 15Be was populated in a second attempt and determined
to be unbound with respect to 14Be by 1.8(1) MeV with a tentative spin-parity
assignment of 5/2+ [J. Snyder et al., Phys. Rev. C 88, 031303(R) (2013)].
Search for the predicted 15Be 3/2+ state in the three-neutron decay channel. A
two-proton removal reaction from a 55 MeV/u 17C beam was used to populate
neutron-unbound states in 15Be. The two-, three-, and four-body decay energies
of the 12Be + neutron(s) detected in coincidence were reconstructed using
invariant mass spectroscopy. Monte Carlo simulations were performed to extract
the resonance and decay properties from the observed spectra. The low-energy
regions of the decay energy spectra can be described with the first excited
unbound state of 14Be (E_x=1.54 MeV, E_r=0.28 MeV). Including a state in 15Be
that decays through the first excited 14Be state slightly improves the fit at
higher energies though the cross section is small. A 15Be component is not
needed to describe the data. If the 3/2+ state in 15Be is populated, the decay
by three-neutron emission through 14Be is weak, less than or equal to 11% up to
4 MeV. In the best fit, 15Be is unbound with respect to 12Be by 1.4 MeV
(unbound with respect to $14Be by 2.66 MeV) with a strength of 7%.Comment: 6 pages, 5 figures, accepted in Physical Review
Three-body correlations in the ground-state decay of 26O
Background: Theoretical calculations have shown that the energy and angular
correlations in the three-body decay of the two-neutron unbound O26 can provide
information on the ground-state wave function, which has been predicted to have
a dineutron configuration and 2n halo structure.
Purpose: To use the experimentally measured three-body correlations to gain
insight into the properties of O26, including the decay mechanism and
ground-state resonance energy.
Method: O26 was produced in a one-proton knockout reaction from F27 and the
O24+n+n decay products were measured using the MoNA-Sweeper setup. The
three-body correlations from the O26 ground-state resonance decay were
extracted. The experimental results were compared to Monte Carlo simulations in
which the resonance energy and decay mechanism were varied.
Results: The measured three-body correlations were well reproduced by the
Monte Carlo simulations but were not sensitive to the decay mechanism due to
the experimental resolutions. However, the three-body correlations were found
to be sensitive to the resonance energy of O26. A 1{\sigma} upper limit of 53
keV was extracted for the ground-state resonance energy of O26.
Conclusions: Future attempts to measure the three-body correlations from the
ground-state decay of O26 will be very challenging due to the need for a
precise measurement of the O24 momentum at the reaction point in the target
Exploring Neutron-Rich Oxygen Isotopes with MoNA
The Modular Neutron Array (MoNA) was used in conjunction with a large-gap
dipole magnet (Sweeper) to measure neutron-unbound states in oxygen isotopes
close to the neutron dripline. While no excited states were observed in 24O, a
resonance at 45(2) keV above the neutron separation energy was observed in 23O.Comment: 6 pages, 4 Figures, submitted to Proc. Int. Conf. on Proton Emitting
Nuclei and Related Topics, PROCON0
Development of a new laser Doppler velocimeter for the Ames High Reynolds Channel No. 2
A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. 2 is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to position the laser beams in the channel flow. Techniques used to seed the flow with 0.5-micron-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy
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