Determination of the Fundamental Frequencies of Fluorochloro-Derivatives of Ethane and Its Application to Calculate Ideal Gas Heat Capacities

Quantum mechanical calculations for all fluorochloro-derivatives of ethane were performed. It was shown that the B3LYP/cc-pVDZ density functional method and single-point MP2/cc-pVTZ calculations lead to an accuracy of the molecular data that is sufficient for prediction of ideal gas heat capacities. Finally, reliable experimental heat capacity data reveal that an uncertainty of the heat capacity calculations of ±1.5% or less is achieved.     

An analytical and experimental study of the performance of Markovrandom fields applied to textured images using small samples

We investigate to what extent textures can be distinguished using conditional Markov fields and small samples. We establish that the least square (LS) estimator is the only reasonable choice for this task, and we prove its asymptotic consistency and normality for a general class of random fields that includes Gaussian Markov fields as a special case. The performance of this estimator when applied to textured images of real surfaces is poor if small boxes are used (20x20 or less). We investigate the nature of this problem by comparing the behavior predicted by the rigorous theory to the one that has been experimentally observed. Our analysis reveals that 20x20 samples contain enough information to distinguish between the textures in our experiments and that the poor performance mentioned above should be attributed to the fact that conditional Markov fields do not provide accurate models for textured images of many real surfaces. A more general model that exploits more efficiently the information contained in small samples is also suggested.     

Studies of core disruptive accidents and licensing aspects of fast breeder reactors

This paper discusses the role of the core disruptive accident (CDA) in the safety evaluations and licensing of Liquid Metal Fast Breeder Reactors (LMFBR). Parametric studies of transient overpower (TOP) accidents based on calculations for SNR-300 using the HOPE computer code are presented. Major uncertainties in TOP analysis are identified and discussed with emphasis on the need for reliable fuel failure criteria. A series of calculations illustrating the possible behavior of the U.S. LMFBR demonstration plant following a loss-of-flow (LOF) accident without scram using the SAS-IIIA computer code are described. It is shown that for a beginning of life (BOL) core and end of equilibrium cycle (EOEC) core, the reactivity effects from sodium voiding and clad motion can lead to further sustained reactivity additions from subsequent fuel motion and FCI driven sodium voiding. In these calculations we have used the fuel enthalpy criterion which predicts clad failure around the core midplane. For the EOEC case these effects can add sufficient reactivity to take the system above prompt-critical (LOF driven TOP) and into hydrodynamic disassembly. For the BOL case the sodium void may not be sufficient to bring the system near sustained prompt-critical. However, clad motion appears to be effective in raising the reactivity to prompt-criticality. These results are based on clad failure dynamics modeling in SAS-IIIA. Further work is needed in the area of fuel-clad behavior under severe transients before definitive conclusions can be drawn regarding the applicability of current clad failure models at high clad temperatures (>1000°C). The potential significance of a new concept in CDA analysis called the “transition phase” is briefly mentioned.     

Ideal-gas properties of new refrigerants from quantum mechanical ab initio calculations

Theoretical predictions of ideal-gas properties from molecular data such as structure, vibrational frequencies, and the barrier of internal rotation are compared to recent experimental data on heat capacities of new refrigerants. It is demonstrated that the required molecular data can be obtained from quantum-mechanical ab initio calculations with sufficient accuracy to provide heat capacities with an accuracy of ±2%. Further improvement of the approach appears feasible. This is of great practical significance, since molecular data obtained from experimental spectra tend to be inaccurate for systems of technical interest with somewhat larger molecules, like the new refrigerants.     

Feature extraction for texture discrimination via random fieldmodels with random spatial interaction

In this paper, we attack the problem of distinguishing textured images of real surfaces using small samples. We first analyze experimental data that results from applying ordinary conditional Markov fields. In the face of the disappointing performance of these models, we introduce a random field with spatial interaction that is itself a random variable (usually referred to as a random field in a random environment). For this class of models, we establish the power spectrum and the autocorrelation function as well-defined quantities, and we devise a scheme for the estimation of related parameters. The new set of features that resulted from this approach was applied to real images. Accurate discrimination was observed even for boxes of size 10x16.     

Vibrational Frequencies and Ideal Gas Heat Capacities of Fluorochloro-Derivatives of Methane as Calculated from Quantum Mechanical Methods

In a previous paper various quantum mechanical methods were applied to difluoromethane in order to find a suitable path to accurate ideal gas heat capacities. Now, these calculations are extended to all fluorochloro-derivatives of methane. Reliable experimental heat capacity data reveal that the combination of quantum mechanics and statistical thermodynamics facilitates a prediction of ideal gas heat capacities with an accuracy of ±1% and better. This is very close to the range of accuracy, which is observed for the best experimental zero pressure heat capacity data from different sources of the literature.     

Structural superplasticity of a fine-grained and rapidly solidified ultra-high carbon-alloy tool steel X 245 VCr 10 5

The fine-grained ultra-high carbon-alloy tool steel X 245 VCr 10 5, containing large volume fractions of special vanadium and chromium carbides within a ferritic solid solution matrix has been produced by rapid solidification – meltatomization – and powder metallurgical techniques. This steel exhibits structural superplasticity in the temperature regime from 900 to 1150°C at initial strain rates of about ?? = 10^?3 s^?1. High strain-rate sensitivity parameters of m > 0.4 and uniform tensile elongations up to 950% were recorded. The dominant deformation mechanism in the superplastic region is grain-boundary sliding accommodated by lattice diffusion. The failure of superplastically strained samples is caused by interlinkages of cavities at matrix/carbide interfaces.