12,865 research outputs found
Geodetic Earth Orbiting Satellite /GEOS-C/, Applications Technology Satellite /ATS-F/ tracking experiment
Design analysis of GEOS-C/ATS-F tracking experimen
Development of sputtered techniques for thrust chambers, task 1
Filler materials proposed for use in the sputter fabrication regeneratively cooled thrust chambers were evaluated. Low melting castable alloys, CERROBEND. CERROCAST, and CERROTRU, slurry applied SERMETEL 481 and flame-sprayed aluminum were investigated as filler materials. Sputter deposition from a cylindrical cathode inverted magnestron was used to apply an OFHC copper closeout layer to filled OFHC copper ribbed-wall cylindrical substrates. The sputtered closeout layer structure was evaluated with respect to filler material contamination, predeposition machining and finishing operations, and deposition parameters. The application of aluminum by flame-spraying resulted in excessiver filler porosity. Though the outgassing from this porosity was found to be detrimental to the closeout layer structure, bond strengths in excess of 10,500 psi were achieved. Removal of the aluminum from the grooves was readily accomplished by leaching in a 7.0 molar solution of sodium hydroxide at 353 K. Of the other filler materials evaluated, CERROTRU was found to be the most suitable material with respect to completely filling the ribbed-wall cylinders and vacuum system compatibility. However, bond contamination resulted in low closeout layer bond strength with the CERROTRU filler. CERROBEND, CERROCAST, and SERMETEL 481 were found to be unacceptable as filler materials
Development of sputtered techniques for thrust chambers
Techniques and materials were developed and evaluated for the fabrication and coating of advanced, long life, regeneratively cooled thrust chambers. Materials were analyzed as fillers for sputter application of OFHC copper as a closeout layer to channeled inner structures; of the materials evaluated, aluminum was found to provide the highest bond strength and to be the most desirable for chamber fabrication. The structures and properties were investigated of thick sputtered OFHC copper, 0.15 Zr-Cu, Al2O3,-Cu, and SiC-Cu. Layered structures of OFHC copper and 0.15 Zr-Cu were investigated as means of improving chamber inner wall fatigue life. The evaluation of sputtered Ti-5Al-2.5Sn, NASA IIb-11, aluminum and Al2O3-Al alloys as high strength chamber outer jackets was performed. Techniques for refurbishing degraded thrust chambers with OFHC copper and coating thrust chambers with protective ZrO2 and graded ZrO2-copper thermal barrier coatings were developed
Dynamic Model and Phase Transitions for Liquid Helium
This article presents a phenomenological dynamic phase transition theory --
modeling and analysis -- for superfluids. As we know, although the
time-dependent Ginzburg-Landau model has been successfully used in
superconductivity, and the classical Ginzburg-Landau free energy is still
poorly applicable to liquid helium in a quantitative sense. The study in this
article is based on 1) a new dynamic classification scheme of phase
transitions, 2) new time-dependent Ginzburg-Landau models for general
equilibrium transitions, and 3) the general dynamic transition theory. The
results in this article predict the existence of a unstable region H, where
both solid and liquid He II states appear randomly depending on fluctuations
and the existence of a switch point M on the lambda-curve, where the
transitions changes types
Hamiltonian systems with symmetry, coadjoint orbits and plasma physics
The symplectic and Poisson structures on reduced phase spaces are reviewed, including the symplectic structure on coadjoint orbits of a Lie group and the Lie-Poisson structure on the dual of a Lie algebra. These results are
applied to plasma physics. We show in three steps how the Maxwell-Vlasov equations for a collisionless plasma can be written in Hamiltonian form relative to a certain Poisson bracket. First, the Poisson-Vlasov equations are shown
to be in Hamiltonian form relative to the Lie-Poisson bracket on the dual of the (nite dimensional) Lie algebra of innitesimal canonical transformations. Then we write Maxwell's equations in Hamiltonian form using the canonical
symplectic structure on the phase space of the electromagnetic elds, regarded as a gauge theory. In the last step we couple these two systems via the reduction
procedure for interacting systems. We also show that two other standard models in plasma physics, ideal MHD and two-
uid electrodynamics, can be written in Hamiltonian form using similar group theoretic techniques
Gravity anomaly detection: Apollo/Soyuz
The Goddard Apollo-Soyuz Geodynamics Experiment is described. It was performed to demonstrate the feasibility of tracking and recovering high frequency components of the earth's gravity field by utilizing a synchronous orbiting tracking station such as ATS-6. Gravity anomalies of 5 MGLS or larger having wavelengths of 300 to 1000 kilometers on the earth's surface are important for geologic studies of the upper layers of the earth's crust. Short wavelength Earth's gravity anomalies were detected from space. Two prime areas of data collection were selected for the experiment: (1) the center of the African continent and (2) the Indian Ocean Depression centered at 5% north latitude and 75% east longitude. Preliminary results show that the detectability objective of the experiment was met in both areas as well as at several additional anomalous areas around the globe. Gravity anomalies of the Karakoram and Himalayan mountain ranges, ocean trenches, as well as the Diamantina Depth, can be seen. Maps outlining the anomalies discovered are shown
Raman Scattered He II 6545 Line in the Symbiotic Star V1016 Cygni
We present a spectrum of the symbiotic star V1016 Cyg observed with the 3.6 m
Canada-France-Hawaii Telescope, in order to illustrate a method to measure the
covering factor of the neutral scattering region around the giant component
with respect to the hot emission region around the white dwarf component. In
the spectrum, we find broad wings around H and a broad emission feature
around 6545 that is blended with the [N II] 6548 line.
These two features are proposed to be formed by Raman scattering by atomic
hydrogen, where the incident radiation is proposed to be UV continuum radiation
around Ly in the former case and He II 1025 emission line
arising from transitions for the latter feature. We remove the
H wings by a template Raman scattering wing profile and subtract the [N
II] 6548 line using the 3 times stronger [N II] 6583
feature in order to isolate the He II Raman scattered 6545 \AA line. We obtain
the flux ratio of the He II 6560 emission
line and the 6545 \AA feature for V1016 Cyg. Under the assumption that the He
II emission from this object is isotropic, this ratio is converted to the ratio
of the number of the incident photons and that
of the scattered photons. This implies that the scattering region with H I
column density covers 17 per cent of the
emission region. By combining the presumed binary period yrs of this
system we infer that a significant fraction of the slow stellar wind from the
Mira component is ionized and that the scattering region around the Mira
extends a few tens of AU, which is closely associated with the mass loss
process of the Mira component.Comment: 12 pages, 6 figures, accepted for publication in Ap
Two-State Migration of DNA in a structured Microchannel
DNA migration in topologically structured microchannels with periodic
cavities is investigated experimentally and with Brownian dynamics simulations
of a simple bead-spring model. The results are in very good agreement with one
another. In particular, the experimentally observed migration order of Lambda-
and T2-DNA molecules is reproduced by the simulations. The simulation data
indicate that the mobility may depend on the chain length in a nonmonotonic way
at high electric fields. This is found to be the signature of a nonequilibrium
phase transition between two different migration states, a slow one and a fast
one, which can also be observed experimentally under appropriate conditions.Comment: Revised edition corresponding to the comments by the referees,
submitted to Physical Review
Variational Calculations of the Nucleus Structure in a 3 Model Using a Deep Potential with Forbidden States
The energy spectrum of the nucleus with and
is investigated in the framework of the multicluster dynamical model
by using a deep -potential with forbidden states in the S and D
waves. A very high sensitivity of the compact ground and first excited
states energy levels to the description of the two-body forbidden states wave
functions has been estabilished. It is shown also that the chosen method of
orthogonalizing pseudopotentials yields convergent results for the energies of
the excited and states of the nucleus with a
well developed cluster like structure
Influence of correlations on molecular recognition
The influence of the patchiness and correlations in the distribution of
hydrophobic and polar residues at the interface between two rigid biomolecules
on their recognition ability is investigated in idealised coarse-grained
lattice models. A general two-stage approach is utilised where an ensemble of
probe molecules is designed first and the recognition ability of the probe
ensemble is related to the free energy of association with both the target
molecule and a different rival molecule in a second step. The influence of
correlation effects are investigated using numerical Monte Carlo techniques and
mean field methods. Correlations lead to different optimum characteristic
lengths of the hydrophobic and polar patches for the mutual design of the two
biomolecules on the one hand and their recognition ability in the presence of
other molecules on the other hand.Comment: 15 pages, 5 figure
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