138,415 research outputs found
The nonperturbative closed string tachyon vacuum to high level
We compute the action of closed bosonic string field theory at quartic order
with fields up to level ten. After level four, the value of the potential at
the minimum starts oscillating around a nonzero negative value, in contrast
with the proposition made in [5]. We try a different truncation scheme in which
the value of the potential converges faster with the level. By extrapolating
these values, we are able to give a rather precise value for the depth of the
potential.Comment: 24 pages. v2: typos corrected, clarified extrapolation in scheme B,
and added extrapolated tachyon and dilaton vev's at the end of Section
Determination of load sequence effects on the degradation and failure of composite materials
A theoretical model was established to predict the fatigue behavior of composite materials, with emphasis placed on predictions of the degradation of residual strength and residual stiffness during fatigue cycling. The model parameters were evaluated from three test series including static strength fatigue life and residual strength tests. The tests were applied to two graphite/epoxy laminates. Load sequence effects were emphasized for both laminates and the predicted results agreed quite well with subsequent verification tests. Dynamic as well as static stiffness reduction data were collected by use of a PDP11-03 computer, which performed quite satisfactorily and permitted the recording of a substantial amount of dynamic stiffness reduction data
NASA Langley Research Center HBCU/OMU program: 1990 student support survey
The results of a survey of students who are receiving support through the Historically Black Colleges and Universities and Other Minority Universities are given. Information is given on the race, sex, ethnic distribution, grade point average distribution, and target degree distribution
Statistical characterization of the fatigue behavior of composite lamina
A theoretical model was developed to predict statistically the effects of constant and variable amplitude fatigue loadings on the residual strength and fatigue life of composite lamina. The parameters in the model were established from the results of a series of static tensile tests and a fatigue scan and a number of verification tests were performed. Abstracts for two other papers on the effect of load sequence on the statistical fatigue of composites are also presented
Xenon fluorides show potential as fluorinating agents
Xenon fluorides permit the controlled addition of fluorine across an olefinic double bond. They provide a series of fluorinating agents that permit ready separation from the product at a high purity. The reactions may be carried out in the vapor phase
Multipole analysis for pion photoproduction with MAID and a dynamical models
Results of new analysis of pion photoproduction data obtained with Dynamical
and MAID models are presentedComment: 5 pages, 1 figure, talk given at the NSTAR2001 Workshop, Mainz,
Germany, March 7-10, 200
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