3,122 research outputs found
An evaluation of contractor projected and actual costs
GSFC contractors with cost-plus contracts provide cost estimates for each of the next four quarters on a quarterly basis. Actual expenditures over a two-year period were compared to the estimates, and the data were sorted in different ways to answer several questions and give quantification to observations, such as how much does the accuracy of estimates degrade as they are made further into the future? Are estimates made for small dollar amounts more accurate than for large dollar estimates? Other government agencies and private companies with cost-plus contracts may be interested in this analysis as potential methods of contract management for their organizations. It provides them with the different methods one organization is beginning to use to control costs
Invariant Measures on Stationary Bratteli Diagrams
We study dynamical systems acting on the path space of a stationary
(non-simple) Bratteli diagram. For such systems we explicitly describe all
ergodic probability measures invariant with respect to the tail equivalence
relation (or the Vershik map). These measures are completely described by the
incidence matrix of the diagram. Since such diagrams correspond to substitution
dynamical systems, this description gives an algorithm for finding invariant
probability measures for aperiodic non-minimal substitution systems. Several
corollaries of these results are obtained. In particular, we show that the
invariant measures are not mixing and give a criterion for a complex number to
be an eigenvalue for the Vershik map.Comment: 40 pages. Exposition is reworke
Gas gun shock experiments with single-pulse x-ray phase contrast imaging and diffraction at the Advanced Photon Source
The highly transient nature of shock loading and pronounced microstructure
effects on dynamic materials response call for {\it in situ}, temporally and
spatially resolved, x-ray-based diagnostics. Third-generation synchrotron x-ray
sources are advantageous for x-ray phase contrast imaging (PCI) and diffraction
under dynamic loading, due to their high photon energy, high photon fluxes,
high coherency, and high pulse repetition rates. The feasibility of bulk-scale
gas gun shock experiments with dynamic x-ray PCI and diffraction measurements
was investigated at the beamline 32ID-B of the Advanced Photon Source. The
x-ray beam characteristics, experimental setup, x-ray diagnostics, and static
and dynamic test results are described. We demonstrate ultrafast, multiframe,
single-pulse PCI measurements with unprecedented temporal (100 ps) and
spatial (2 m) resolutions for bulk-scale shock experiments, as well
as single-pulse dynamic Laue diffraction. The results not only substantiate the
potential of synchrotron-based experiments for addressing a variety of shock
physics problems, but also allow us to identify the technical challenges
related to image detection, x-ray source, and dynamic loading
Pre-Equilibrium Calculations of Backward-Angle Proton Spectra
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Comment on Breakup Densities of Hot Nuclei
In [1,2]the observed decrease in spectral peak energies of IMFs emitted from
hot nuclei was interpreted in terms of a breakup density that decreased with
increasing energy. Subsequently, Raduta et al. [3] performed MMM simulations
that showed decreasing spectral peaks could be obtained at constant density. In
this letter we examine this apparent inconsistency.Comment: 9 pages, 2 figures, 1 tabl
Search for Rare Natural Decay Modes from 228-Th
This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440
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