A suggested procedure for resolving an anomaly in least-squares data analysis known as Peelle's Pertinent Puzzle'' and the general implications for nuclear data evaluation

Modern nuclear-data evaluation methodology is based largely on statistical inference, with the least-squares technique being chosen most often to generate best estimates for physical quantities and their uncertainties. It has been observed that those least-squares evaluations which employ covariance matrices based on absolute errors that are derived directly from the reported experimental data often tend to produce results which appear to be too low. This anomaly is discussed briefly in this report, and a procedure for resolving it is suggested. The method involves employing data uncertainties which are derived from errors expressed in percent. These percent errors are used, in conjunction with reasonable a priori estimates for the quantities to be evaluated, to derive the covariance matrices which are required for applications of the least-squares procedure. This approach appears to lead to more rational weighting of the experimental data and, thus, to more realistic evaluated results than are obtained when the errors are based on the actual data. The procedure is very straightforward when only one parameter must be estimated. However, for those evaluation exercises involving more than one parameter, this technique demands that a priori estimates be provided at the outset for all of the parameters in question. Then, the least-squares method is applied iteratively to produce a sequence of sets of estimated values which are anticipated to convergence toward a particular set of parameters which one then designates as the best'' evaluated results from the exercise. It is found that convergence usually occurs very rapidly when the a priori estimates approximate the final solution reasonably well

Seismic responses of a pool-type fast reactor with different core support designs

In designing the core support system for a pool-type fast reactor, there are many issues which must be considered in order to achieve an optimum and balanced design. These issues include safety, reliability, as well as costs. Several design options are possible to support the reactor core. Different core support options yield different frequency ranges and responses. Seismic responses of a large pool-type fast reactor incorporated with different core support designs have been investigated. 4 refs., 3 figs

Dynamic analysis of the EBR-II plant with the DSNP-ND simulation package

Development and initial testing have been completed for a special version of the DSNP simulation language software package, DSNP-ND, which simulates EBR-II based on the models of the primary system components used in the NATDEMO program. Preliminary results are included for a comparison with an original NATDEMO prediction for the SHRT-45 transient. 7 refs

Contact-impact simulations on massively parallel SIMD supercomputers

The implementation of explicit finite element methods with contact-impact on massively parallel SIMD computers is described. The basic parallel finite element algorithm employs an exchange process which minimizes interprocessor communication at the expense of redundant computations and storage. The contact-impact algorithm is based on the pinball method in which compatibility is enforced by preventing interpenetration on spheres embedded in elements adjacent to surfaces. The enhancements to the pinball algorithm include a parallel assembled surface normal algorithm and a parallel detection of interpenetrating pairs. Some timings with and without contact-impact are given

Strategies for mimicking the primary events of bacterial photosynthesis: Structure, function, and mechanism

Some of the possible implications of the photochemistry of photosynthesis for artificial systems are presented. A major aspect of this paper involves the special conditions required to prevent the undesirable charge recombination via the excited triplet state of the primary donor. If a multi-jump model is operative in the primary events of photosynthesis, then artificial model systems are relatively easy to synthesize. Such systems prevent back reactions via a series of downhill chemical reactions. Each downhill step in energy results in an increase in charge separation distance. The annihilation reactions, even to the less energetic triplet state, involve intermediate states uphill in energy and consequently are greatly diminished. However, if superexchange is a correct explanation of photosynthesis, then model systems have not been developed that properly mimic the natural process. In particular, the triplet back reaction can occur due to the lack of any thermal activation barrier. In nature this downhill back reaction appears to be prevented by carefully balancing the energetics using four molecules in the electron transport system. If this is the case, artificial photosynthesis would also require fine tuning of the coupling and energetics with three or four molecules making duplication more difficult to achieve. 10 refs

BEAM TESTS OF THE 12 MHz RFQ RIB INJECTOR FOR ATLAS

Abstract Beam tests of the ANL 12 MHz Radio-Frequency Quadruple (RFQ), designed for use as the initial element of an injector system for radioactive beams into the existing ATLAS accelerators, are in progress. Recent highvoltage tests of the RFQ without beam achieved the design intervane voltage of 100 kV CW,enabling beam tests with A/q as large as 132 using beams from the ANI., Physics Division 4 MV Dynamitron accelerator facility. Although the RFQ was designed for bunched beams, initial tests have been performed with unbunched beams. Experiments with stable, unbunched beams of singlycharged '32Xeand %r measured the output beam energy distribution as a function of the RFQ operating voltage. The observed energies are in excellent agreement with numerical beam simulations