RESUMO
Despite the widespread use of silicon in modern technology, its peculiar thermal expansion is not well understood. Adapting harmonic phonons to the specific volume at temperature, the quasiharmonic approximation, has become accepted for simulating the thermal expansion, but has given ambiguous interpretations for microscopic mechanisms. To test atomistic mechanisms, we performed inelastic neutron scattering experiments from 100 K to 1,500 K on a single crystal of silicon to measure the changes in phonon frequencies. Our state-of-the-art ab initio calculations, which fully account for phonon anharmonicity and nuclear quantum effects, reproduced the measured shifts of individual phonons with temperature, whereas quasiharmonic shifts were mostly of the wrong sign. Surprisingly, the accepted quasiharmonic model was found to predict the thermal expansion owing to a large cancellation of contributions from individual phonons.
RESUMO
OBJECTIVE: To extensively test the functional integrity of the PAPNET Testing System, a computer-assisted cervical smear rescreening device, to ensure performance and reliability. STUDY DESIGN: Various system and subsystem testing methodologies were used to verify that the PAPNET Scanning Station performed according to specifications. Using synthetic and biologic slides, proper operation of the system in its intended use environment was verified. An automated system test was employed to demonstrate the ability of the system to detect cytologic abnormality. Several tests were performed throughout the production process and normal operation to ensure subsystem operations. RESULTS: The testing methodologies were shown to provide accurate measurements of scanning performance. CONCLUSION: Methodical testing and implementation of technologic enhancements ensure system performance and reliability. When used with microscopy, PAPNET testing provides the means to improve the accuracy of cervical cytology.
