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Accelerating scientific discovery through computation and visualization
No full textThe rate of scientific discovery can be accelerated through computation and visualization. This acceleration results from the synergy of expertise, computing tools, and hardware for enabling highperformance computation, information science, and visualization that is provided by a team of computation and visualization scientists collaborating in a peer-to-peer effort with the research scientists. In the context of this discussion, high performance refers to capabilities beyond the current state of the art in desktop computing. To be effective in this arena, a team comprising a critical mass of talent, parallel computing techniques, visualization algorithms, advanced visualization hardware, and a recurring investment is required to stay beyond the desktop capabilities. This article describes, through examples, how the Scientific Applications and Visualization Group (SAVG) at NIST has utilized high performance parallel computing and visualization to accelerate condensate modeling, (2) fluid flow in porous materials and in other complex geometries, (3) flows in suspensions, (4) x-ray absorption, (5) dielectric breakdown modeling, and (6) dendritic growth in alloys
GAMS5
No full textThe construction of the double-crystal gamma-spectrometer GAMS5 was finished recently and the instrument is now operational. Measurements with double flat crystals were carried out and we will report here on the progress concerning the characteristics of the spectrometer
Low-spin states from decay studies in the mass 80 region
No full textNeutron-deficient nuclei in the mass 80 region are known to exhibit strongly deformed ground states deduced mainly from yrast-state properties measured in-beam via heavy-ion fusion-evaporation reactions. Vibrational excitations and non-yrast states as well as their interplay with the observed rotational collectivity have been less studied to date within this mass region. Thus, several beta-decay experiments have been performed to populate low-spin states in the neutron-deficient Y-80.84 and Sr-80.84 nuclei. An overview of excited 0(+) states in Sr and Kr nuclei is given and conclusions about shape evolution at low-spins are presented. In general, the non-yrast states in even-even Sr nuclei show mainly vibration-like collectivity which evolves to rotational behavior with increasing spin and decreasing neutron number
Applications of high-precision gamma-spectroscopy papers presented at the July 1998 Workshop at the University of Notre Dame - Preface
No full textPossible advantages of a robust evaluation of comparisons
No full textMean values, traditionally used as a location parameter in the analysis of intercomparisons, are known to lack stability against the effect of ""outliers"". It is therefore proposed to replace (or complement) them by the use of medians, which have better statistical ""robustness"". An estimate for the corresponding uncertainty is derived and the procedure is illustrated by a numerical example. The simplicity of the suggested robust approach should favor its practical use in a number of metrological applications
An auto-focusing method in a microscopic testbed for optical discs
No full textAn auto-focusing method in a digital image system is demonstrated that uses a standard deviation of pixel gray levels as a feedback signal. In this system, an optical microscope and a charge coupled device (CCD) camera are used to create clear pit images of optical discs. A dynamic focusing scheme is designed in the system-control software, which is able to eliminate environmental disturbances and other noises so that a fast and stable focus can be achieved. The method shows an excellent focusing accuracy. The performance and possible applications of this method are discussed. The test results for optical discs are given in this paper
An approach to combining results from multiple methods motivated by the ISO GUM
No full textThe problem of determining a consensus value and its uncertainty from the results of multiple methods or laboratories is discussed. Desirable criteria of a solution are presented. A solution motivated by the ISO Guide to the Expression of Uncertainty in Measurement (ISO GUM) is introduced and applied in a detailed worked example. A Bayesian hierarchical model motivated by the proposed solution is presented and compared to the solution
Secondary gamma transitions in 159-Gd after neutron capture at isolated resonances
No full textThe 158-Gd(n,gamma)159-Gd reaction was studied at 12 isolated neutron resonances by the TOF method at the IBR-30 Fast Pulse Reactor at JINR Dubna. Totally 15 secondary gamma transitions in 159-Gd were recorded in the range from 450 keV to 750 keV. Of these, six previously unseen transitions were placed on the established 159-Gd level scheme. The depopulation of strongly populated levels at 507.7 keV and 558.2 keV (the head and the first excited members of band 1/2(-)[521]) was observed for the first time. It was shown that the observed 507.7 keV gamma line, masked by the annihilation peak, originates from an unresolved doubler of transitions from the 507.7 keV level to the ground state and from the 558.2 keV level to the level at 50.7 keV. The 507.7 keV level decays exclusively to the ground state, while the 558.2 keV level decays via two transitions with a branching ratio that agrees well with the prediction according to Alaga's rule
The GRID technique: Current status and new trends
No full textIn the GRID technique one measures Doppler-broadened line profiles of gamma transitions using the high resolution crystal spectrometers GAMS, which are installed at the high flux reactor of the ILL Grenoble. One of the essential applications of this technique is the measurement of nuclear state lifetimes. In the present contribution the precision and the principal limits of the technique are discussed
Simulations of gamma cascades and modelling atomic collision chains
No full textA new method for simulation of nuclear gamma cascades by the Monte Carlo technique is described. It makes it possible to generate artificially individual events of the gamma-cascade decay of neutron capturing states in heavy nuclei. For the purpose of determination of lifetimes of nuclear levels by the GRID method the previously developed Mean Free Path Approach for modelling atomic collisions and their interplay with cascades has been generalized. Examples of the use of this generalization for determination of lifetimes of selected Sm-150 and Gd-158 levels are given and discussed