RESUMEN
Transition metal carbides find widespread use throughout industry due to their high strength and resilience under extreme conditions. However, they remain largely limited to compounds formed from the early d-block elements, since the mid-to-late transition metals do not form thermodynamically stable carbides. We report here the high-pressure bulk synthesis of large single crystals of a novel metastable manganese carbide compound, MnCx (P63/mmc), which adopts the anti-NiAs-type structure with significant substoichiometry at the carbon sites. We demonstrate how synthesis pressure modulates the carbon loading, with ~40 % occupancy being achieved at 9.9â GPa.
RESUMEN
Spin-orbit coupling enables the realization of topologically nontrivial ground states. As spin-orbit coupling increases with increasing atomic number, compounds featuring heavy elements, such as lead, offer a pathway toward creating new topologically nontrivial materials. By employing a high-pressure flux synthesis method, we synthesized single crystals of Ni3Pb2, the first structurally characterized bulk binary phase in the Ni-Pb system. Combining experimental and theoretical techniques, we examined structure and bonding in Ni3Pb2, revealing the impact of chemical substitutions on electronic structure features of importance for controlling topological behavior. From these results, we determined that Ni3Pb2 completes a series of structurally related transition-metal-heavy main group intermetallic materials that exhibit diverse electronic structures, opening a platform for synthetically tunable topologically nontrivial materials.
RESUMEN
A new experimental system to measure elastic wave velocities in samples in situ under extreme conditions of pressure and temperature in a multi-anvil apparatus has been installed at Beamline 6-BM-B of the Advanced Photon Source at Argonne National Laboratory. This system allows for measurement of acoustic velocities via ultrasonic interferometry, and makes use of the synchrotron beam to measure sample densities via X-ray diffraction and sample lengths using X-radiographic imaging. This system is fully integrated into the automated software controls of the beamline and is capable of collecting robust data on elastic wave travel times in less than 1 s, which is an improvement of more than one to two orders of magnitude over existing systems. Moreover, this fast data collection time has been shown to have no effect on the obtained travel time results. This allows for more careful study of time-dependent phenomena with tighter snapshots in time of processes that would otherwise be lost or averaged out in other acoustic measurement systems.
RESUMEN
A new multi-anvil deformation apparatus, based on the widely used 6-8 split-cylinder, geometry, has been developed which is capable of deformation experiments at pressures in excess of 18 GPa at room temperature. In 6-8 (Kawai-type) devices eight cubic anvils are used to compress the sample assembly. In our new apparatus two of the eight cubes which sit along the split-cylinder axis have been replaced by hexagonal cross section anvils. Combining these anvils hexagonal-anvils with secondary differential actuators incorporated into the load frame, for the first time, enables the 6-8 multi-anvil apparatus to be used for controlled strain-rate deformation experiments to high strains. Testing of the design, both with and without synchrotron-X-rays, has demonstrated the Deformation T-Cup (DT-Cup) is capable of deforming 1-2 mm long samples to over 55% strain at high temperatures and pressures. To date the apparatus has been calibrated to, and deformed at, 18.8 GPa and deformation experiments performed in conjunction with synchrotron X-rays at confining pressures up to 10 GPa at 800 °C .
RESUMEN
PURPOSE: Dosimetry using film, CR, electronic portal imaging, or other 2D detectors requires calibration of the raw image data to obtain dose. Typically, a series of known doses are given to the detector, the raw signal for each dose is obtained, and a calibration curve is created. This calibration curve is then applied to the measured raw signals to convert them to dose. With the advent of IMRT, film dosimetry for quality assurance has become a routine and labor intensive part of the physicist's day. The process of calibrating the film or other 2D detector takes time and additional film or images for performing the calibration, and comes with its own source of errors. This article studies a new methodology for the relative dose calibration of 2D imaging detectors especially useful for IMRT QA, which relies on the treatment plan dose image to provide the dose information which is paired with the raw QA image data after registration of the two images (plan-based calibration). METHODS: Validation of the accuracy and robustness of the method is performed on ten IMRT cases performed using EDR2 film with conventional and plan-based calibration. Also, for each of the ten cases, a 5 mm registration error was introduced and the Gamma analysis was reevaluated. In addition, synthetic image tests were performed to test the limits of the method. The Gamma analysis is used as a measure of dosimetric agreement between plan and film for the clinical cases and a dose difference metric for the synthetic cases. RESULTS: The QA image calibrated by the plan-based method was found to more accurately match the treatment plan doses than the conventionally calibrated films and also to reveal dose errors more effectively when a registration error was introduced. When synthetic acquired images were systematically studied, localized and randomly placed dose errors were correctly identified without excessive falsely passing or falsely failing pixels, unless the errors were concentrated in a majority of pixels in a contiguous narrow dose band. Irregularities seen in the calibration curve expose these errors. CONCLUSIONS: The plan-based calibration method was found to be an accurate, efficient procedure, capable of detecting IMRT QA relative dosimetry errors as well as, or better than conventional calibration methods.
