2,434 research outputs found
Centaur propellant acquisition system study
A study was performed to determine the desirability of replacing the hydrogen peroxide settling system on the Centaur D-1S with a capillary acquisition system. A comprehensive screening was performed to select the most promising capillary device fluid acquisition, thermal conditioning, and fabrication techniques. Refillable start baskets and bypass feed start tanks were selected for detailed design. Critical analysis areas were settling and refilling, start sequence development with an initially dry boost pump, and cooling the fluid delivered to the boost pump in order to provide necessary net position suction head (NPSH). Design drawings were prepared for the start basket and start tank concepts for both LO2 and LH2 tanks. System comparisons indicated that the start baskets using wicking for thermal conditioning, and thermal subcooling for boost pump NPSH, are the most desirable systems for future development
Dipole excitation and geometry of borromean nuclei
We analyze the Coulomb breakup cross sections of Li and He nuclei
using a three-body model with a density-dependent contact interaction. We show
that the concentration of the B(E1) strength near the threshold can be well
reproduced with this model. With the help of the calculated B(E1) value, we
extract the root-mean-square (rms) distance between the core nucleus and the
center of mass of two valence neutrons without resorting to the sum rule, which
may suffer from unphysical Pauli forbidden transitions. Together with the
empirical rms distance between the neutrons obtained from the matter radius
study and also from the three-body correlation study in the break-up reaction,
we convert these rms distances to the mean opening angle between the valence
neutrons from the core nucleus. We find that the obtained mean opening angles
in Li and He agree with the three-body model predictions.Comment: 4 pages, 4 eps figure
Cryogenic zero-gravity prototype vent system
Design, fabrication, and tests of prototype cryogenic zero-gravity heat exchanger vent syste
Filling of orbital fluid management systems
A study was performed with three objectives: (1) analyze fluid management system fill under orbital conditions; (2) determine what experimentation is needed; and (3) develop an experimental program. The fluid management system was a 1.06m (41.7 in) diameter pressure vessel with screen channel device. Analyses were conducted using liquid hydrogen and N2O4. The influence of helium and autogenous pressurization systems was considered. Analyses showed that fluid management system fill will be more difficult with a cryogen than with an earth storable. The key to a successful fill with cryogens is in devising techniques for filling without vent liquid, and removing trapped vapor from the screen device at tank fill completion. This will be accomplished with prechill, fill, and vapor condensation processes. Refill will require a vent and purge process, to dilute the residual helium, prior to introducing liquid. Neither prechill, chill, nor purge processes will be required for earth storables
Capillary acquisition devices for high-performance vehicles: Executive summary
Technology areas critical to the development of cryogenic capillary devices were studied. Passive cooling of capillary devices was investigated with an analytical and experimental study of wicking flow. Capillary device refilling with settled fluid was studied using an analytical and experimental program that resulted in successful correlation of a versatile computer program with test data. The program was used to predict Centaur D-1S LO2 and LH2 start basket refilling. Comparisons were made between the baseline Centaur D-1S propellant feed system and feed system alternatives including systems using capillary devices. The preferred concepts from the Centaur D-1S study were examined for APOTV and POTV vehicles for delivery and round trip transfer of payloads between LEO and GEO. Mission profiles were determined to provide propellant usage timelines and the payload partials were defined
Centaur Propellant Thermal Conditioning Study
A wicking investigation revealed that passive thermal conditioning was feasible and provided considerable weight advantage over active systems using throttled vent fluid in a Centaur D-1s launch vehicle. Experimental wicking correlations were obtained using empirical revisions to the analytical flow model. Thermal subcoolers were evaluated parametrically as a function of tank pressure and NPSP. Results showed that the RL10 category I engine was the best candidate for boost pump replacement and the option showing the lowest weight penalty employed passively cooled acquisition devices, thermal subcoolers, dry ducts between burns and pumping of subcooler coolant back into the tank. A mixing correlation was identified for sizing the thermodynamic vent system mixer. Worst case mixing requirements were determined by surveying Centaur D-1T, D-1S, IUS, and space tug vehicles. Vent system sizing was based upon worst case requirements. Thermodynamic vent system/mixer weights were determined for each vehicle
On the Divergence Phenomenon in Hermite–Fejér Interpolation
AbstractGeneralizing results of L. Brutman and I. Gopengauz (1999, Constr. Approx.15, 611–617), we show that for any nonconstant entire function f and any interpolation scheme on [−1, 1], the associated Hermite–Fejér interpolating polynomials diverge on any infinite subset of C\[−1, 1]. Moreover, it turns out that even for the locally uniform convergence on the open interval ]−1, 1[ it is necessary that the interpolation scheme converges to the arcsine distribution
Self-consistent Green's functions calculation of the nucleon mean-free path
The extension of Green's functions techniques to the complex energy plane
provides access to fully dressed quasi-particle properties from a microscopic
perspective. Using self-consistent ladder self-energies, we find both spectra
and lifetimes of such quasi-particles in nuclear matter. With a consistent
choice of the group velocity, the nucleon mean-free path can be computed. Our
results indicate that, for energies above 50 MeV at densities close to
saturation, a nucleon has a mean-free path of 4 to 5 femtometers.Comment: 5 pages, 4 figures. Minor changes, bibliography corrected. Accepted
version in Phys. Rev. Let
Fano Lineshapes Revisited: Symmetric Photoionization Peaks from Pure Continuum Excitation
In a photoionization spectrum in which there is no excitation of the discrete
states, but only the underlying continuum, we have observed resonances which
appear as symmetric peaks, not the commonly expected window resonances.
Furthermore, since the excitation to the unperturbed continuum vanishes, the
cross section expected from Fano's configuration interaction theory is
identically zero. This shortcoming is removed by the explicit introduction of
the phase shifted continuum, which demonstrates that the shape of a resonance,
by itself, provides no information about the relative excitation amplitudes to
the discrete state and the continuum.Comment: 4 pages, 3 figure
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