15,060 research outputs found
An electrochemical study of the corrosion behavior of primer coated 2219-T87 aluminum
The corrosion behavior for 2219-T87 aluminum coated with various primers, including those used for the external tank and solid rocket boosters of the Space Shuttle Transportation System, were investigated using electrochemical techniques. Corrosion potential time, polarization resistance time, electrical resistance time, and corrosion rate time measurements were all investigated. It was found that electrical resistance time and corrosion rate time measurement were most useful for studying the corrosion behavior of painted aluminum. Electrical resistance time determination give useful information concerning the porosity of paint films, while corrosion rate time curves give important information concerning overall corrosion rates and corrosion mechanisms. In general, the corrosion rate time curves all exhibited at least one peak during the 30 day test period, which was attributed, according to the proposed mechanisms, to the onset of the hydrogen evolution reaction and the beginning of destruction of the protective properties of the paint film
Galvanic coupling between D6AC steel, 6061-T6 aluminum, Inconel 718 and graphite-epoxy composite material: Corrosion occurrence and prevention
The effects of galvanic coupling between D6AC steel, 6061-T6 aluminum, Inconel 718, and graphite-epoxy composite material (G/E) in 3.5% NaCl were studied. Measurements of corrosion potentials, galvanic currents and corrosion rates of the bare metals using weight-loss methods served to establish the need for corrosion protection in cases where D6AC steel and 6061-T6 aluminum are galvanically coupled to G/E in salt water while Inconel 718 was shown to be compatible with G/E. Six tests were made to study corrosion protective methods for eliminating galvanic corrosion in the cases of D6AC steel and 6061-T6 aluminum coupled to G/E. These results indicate that, when the G/E is completely coated with paint or a paint/polyurethane resin combination, satisfactory protection of the D6AC steel is achieved with either a coat of zinc-rich primer or a primer/topcoat combination. Likewise, satisfactory corrosion protection of the aluminum is achieved by coating it with an epoxy coating system
Quasi-exact-solution of the Generalized Exe Jahn-Teller Hamiltonian
We consider the solution of a generalized Exe Jahn-Teller Hamiltonian in the
context of quasi-exactly solvable spectral problems. This Hamiltonian is
expressed in terms of the generators of the osp(2,2) Lie algebra. Analytical
expressions are obtained for eigenstates and eigenvalues. The solutions lead to
a number of earlier results discussed in the literature. However, our approach
renders a new understanding of ``exact isolated'' solutions
Effects of weld heat on the protective properties of conversion coatings
Welding temperature effects on protective properties of chromate conversion coating for Saturn 5 tan
Evaluation of several corrosion protective coating systems on aluminum
A study of several protective coating systems for use on aluminum in seawater/seacoast environments was conducted to review the developments made on protective coatings since early in the Space Shuttle program and to perform comparative studies on these coatings to determine their effectiveness for providing corrosion protection during exposure to seawater/seacoast environments. Panels of 2219-T87 aluminum were coated with 21 different systems and exposed to a 5 percent salt spray for 4000 hr. Application properties, adhesion measurements, heat resistance and corrosion protection were evaluated. For comparative studies, the presently specified Bostik epoxy system used on the SRB structures was included. Results of these tests indicate four systems with outstanding performance and four additional systems with protection almost as good. These systems are based on a chromated pretreatment, a chromate epoxy primer, and a polyurethane topcoat. Consideration for one of these systems should be included for those applications where superior corrosion protection for aluminum surfaces is required
The investigation of vertebral injury sustained during aircrew ejection. Phase 2a - Basic science experimental design and investigation of dynamic characteristics of vertebral columns considered as an engineering structure Annual report, 1 Nov. 1966 - 31 Oct. 1967
Dynamic strength studies on human vertebrae for correlation with data on effects of forcible ejection from disabled aircraf
Interpretation of the angular dependence of the de Haas-van Alphen effect in MgB_2
We present detailed results for the amplitude and field dependence of the de
Haas-van Alphen (dHvA) signal arising from the electron-like sheet of
Fermi surface in MgB_2. Our data and analysis show that the dip in dHvA
amplitude when the field is close to the basal plane is caused by a beat
between two very similar dHvA frequencies and not a spin-zero effect as
previously assumed. Our results imply that the Stoner enhancement factors in
MgB_2 are small on both the Sigma and Pi sheets.Comment: 4 pages with figures. Submitted to PR
Study of a small solar probe /sunblazer/. part ii- spacecraft and payload design progress report, jul. 1, 1964 - jun. 30, 1965
Design considerations for Sunblazer solar probe and payloa
An examination of the effects of self-regulatory focus on the perception of the media richness: the case of email
Communication is a key element in organizations’ business success. The media richness theory and the channel expansion theory are two of the most influential theories regarding the selection and use of communication media in organizations; however, literature has focused little on the effects of self-regulation by managers and employees in these theories. To analyze these topics, this study develops an empirical investigation by gathering data from 600 managers and employees using a questionnaire. The results suggest that the perception of media richness is positively affected when the individual shows a promotion focus or strategy.Peer ReviewedPostprint (author’s final draft
Peierls transition in the quantum spin-Peierls model
We use the density matrix renormalization group method to investigate the
role of longitudinal quantized phonons on the Peierls transition in the
spin-Peierls model. For both the XY and Heisenberg spin-Peierls model we show
that the staggered phonon order parameter scales as (and the
dimerized bond order scales as ) as (where
is the electron-phonon interaction). This result is true for both linear and
cyclic chains. Thus, we conclude that the Peierls transition occurs at
in these models. Moreover, for the XY spin-Peierls model we show
that the quantum predictions for the bond order follow the classical prediction
as a function of inverse chain size for small . We therefore conclude
that the zero phase transition is of the mean-field type
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