123,843 research outputs found
The effect of hyperthermia on the radiation response of crypt cells in mouse jejunum
The effect of hyperthermia and/or gamma-radiation on the survival of intestinal crypt cells was studied in BDF sub 1 mice using a microcolony assay. Hyperthermia treatments, which in themselves caused no detectable cell lethality, inhibited the capacity of crypt cells to repair sublethal radiation damage. In addition, heat applied either before or after single radiation exposures potentiated lethal damage to crypt cells; the degree of enhancement was dependent on the time interval between treatments. At the levels of heating employed, DNA synthesis in the intestinal epithelium was significantly reduced immediately following exposure, but returned rapidly to normal levels. No further disturbances in cellular kinetics were observed for up to 10 days after heating
Relationship of mechanical characteristics and microstructural features to the time-dependent edge notch sensitivity of inconel 718 sheet
Time-dependent notch sensitivity of Inconel 718 sheet was observed at 900 F to 1200 F (482 - 649 C). It occurred when edge-notched specimens were loaded below the yield strength and smooth specimen tests showed that small amounts of creep consumed large rupture life fractions. The severity of the notch sensitivity was reduced by decreasing the solution temperature, increasing the time and/or temperature of aging and increasing the test temperature to 1400 F (760 C). Elimination of time-dependent notch sensitivity correlated with a change in dislocation motion mechanism from shearing to by-passing precipitate particles
Fabrication process of a high temperature polymer matrix engine duct
The process that was used in the molding of an advanced composite outer by-pass duct planned for the F404 engine is discussed. This duct was developed as a potential replacement for the existing titanium duct in order to reduce both the weight and cost of the duct. The composite duct is now going into the manufacturing technology portion of the program. The duct is fabricated using graphite cloth impregnated with the PMR-15 matrix system
Static and dynamic helicopter airframe analysis with NASTRAN
The use of NASTRAN at Bell Helicopter Company for structural static and dynamic analysis of a helicopter airframe is described. Analysis of airframe internal loads, main rotor isolation systems, and airframe vibration is discussed. The use of each rigid format for these types of analysis is summarized. Suggested improvements to NASTRAN to increase its effectiveness in performing helicopter airframe analysis are given
Decay channels and charmonium mass-shifts
The discovery in the last few years of the and states of the
extended charmonium family has highlighted the importance of the closeness of
decay channels to an understanding of these mesons. We aid this debate by
illustrating a simple calculational procedure for including the effect of open
and nearby closed channels.Comment: 4 pages, 2 figures Revised version: (1) corrected 2 typos in Table
II, (2) additional text in penultimate paragraph to clarify the calculation
of mass-shifts for and . We thank colleagues for pointing
out confusing wording of previous tex
Testing An Identification Algorithm for Extragalactic OB Associations Using a Galactic Sample
We have used a Galactic sample of OB stars and associations to test the
performance of an automatic grouping algorithm designed to identify
extragalactic OB associations. The algorithm identifies the known Galactic OB
associations correctly when the search radius (78 pc) is defined by the
observed stellar surface density. Galactic OB associations identified with a 78
pc search radius have diameters that are 3 times larger than OB
associations identified with a 22 pc search radius in M33. Applying the smaller
search radius to the Galactic data matches both the sizes and the number of
member stars between the two galaxies quite well. Thus, we argue that this and
similar algorithms should be used with a constant physical search radius,
rather than one which varies with the stellar surface density. Such an approach
would allow the identification of differences in the giant molecular cloud
populations and star formation efficiency under most circumstances.Comment: accepted to AJ; 16 pages, aas latex, 9 postscript figures; available
at http://www.physics.mcmaster.ca/Wilson_Preprints/index.htm
Features controlling the early stages of creep deformation of Waspaloy
A model has been presented for describing primary and second stage creep. General equations were derived for the amount and time of primary creep. It was shown how the model can be used to extrapolate creep data. Applicability of the model was demonstrated for Waspaloy with gamma prime particle sizes from 75 - 1000 A creep tested in the temperature range 1000 - 1400 F (538 - 760 C). Equations were developed showing the dependence of creep parameters on dislocation mechanism, gamma prime volume fraction and size
Sensitivity of the creep-rupture properties of nickel-base superalloy sheet to sharp edge-notches in the temperature range of 1000 deg F - 1400 deg F
Edge notch sensitivity in thin sheet nickel alloys under stress at high temperature
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