Publications by authors named "Nicholas Hartley"
Laser-driven dynamic compression experiments of plastic materials have found surprisingly fast formation of nanodiamonds (ND) via X-ray probing. This mechanism is relevant for planetary models, but could also open efficient synthesis routes for tailored NDs. We investigate the release mechanics of compressed NDs by molecular dynamics simulation of the isotropic expansion of finite size diamond from different P-T states.
View Article and Find Full Text PDFPhonon scattering in metals is one of the most fundamental processes in materials science. However, understanding such processes has remained challenging and requires detailed information on interactions between phonons and electrons. We use an ultrafast electron diffuse scattering technique to resolve the nonequilibrium phonon dynamics in femtosecond-laser-excited tungsten in both time and momentum.
View Article and Find Full Text PDFStudies of laser-heated materials on femtosecond timescales have shown that the interatomic potential can be perturbed at sufficiently high laser intensities. For gold, it has been postulated to undergo a strong stiffening leading to an increase of the phonon energies, known as phonon hardening. Despite efforts to investigate this behavior, only measurements at low absorbed energy density have been performed, for which the interpretation of the experimental data remains ambiguous.
View Article and Find Full Text PDFIntense x-ray pulses can cause the non-thermal structural transformation of diamond. At the SACLA XFEL facility, pump x-ray pulses triggered this phase transition, and probe x-ray pulses produced diffraction patterns. Time delays were observed from 0 to 250 fs, and the x-ray dose varied from 0.
View Article and Find Full Text PDFExtreme conditions inside ice giants such as Uranus and Neptune can result in peculiar chemistry and structural transitions, e.g., the precipitation of diamonds or superionic water, as so far experimentally observed only for pure C─H and HO systems, respectively.
View Article and Find Full Text PDFArticle Synopsis
- Meteorites contain high-pressure minerals formed from past hypervelocity collisions between asteroids, which were thought to result from larger, kilometer-sized impacts.
- This study introduces a new transformation mechanism for creating ringwoodite, a common high-pressure mineral, from shock-compressed olivine crystals using a powerful laser and advanced imaging techniques.
- The findings suggest that smaller asteroids can also produce high-pressure minerals during collisions, indicating that even unshocked meteorites may show evidence of past high-pressure conditions.
Article Synopsis
- Understanding fracture phenomena at high strain rates is crucial for various scientific fields, including applied science, technology, and fundamental science like geology and laser interactions.
- Successful research in this area requires detailed analysis at multiple scales, from atomic to macroscopic, which has typically been done through large-scale simulations.
- Recent advancements using a combination of high-power laser and femtosecond x-ray probes have allowed for real-time monitoring of these dynamic fracture processes in tantalum, revealing critical data related to spallation and stress responses in materials.
Predictors of discharge destination for 234 patients admitted to a combined geriatric medicine/old age psychiatry unit.
Int J Geriatr Psychiatry
September 2008
Objective: To examine the factors that predicted discharge destinations of all patients admitted to a combined geriatric medicine/old age psychiatry unit over a 4-year period.
Method: Data regarding discharge destinations, active medical problems and demographics of 234 patients admitted to the unit were analysed using non-parametric bivariate correlation and logistic regression analysis.
Results: Independence for activities of daily living (ADL) was the key predictor of discharge destination.