The picture above depicts an crystal structure first observed in Pt-Ti in the 1950s. The structure has an unusual stoichiometry of 8:1 and has only been observed in materials that are rich in platinum, palladium, or nickel. If this structure forms in these materials and can significantly increase their strength. By a tour de force approach using BYU's supercomputer, we predict that this phase will be stable in 36 previously unsuspected systems.
Seven students, one postdoc, and four faculty attended the 174th Meeting of the ASA in New Orleans, LA from Dec. 4-8, 2017, including chairing 4 sessions and presenting 12 talks.
Experimentally and computationally, the structure of Pt–Cu at 1:3 stoichiometry has a convoluted history. The L1_3 structure has been predicted to occur in binary alloy systems, but has not been linked to experimental observations. Using a combination of electron diffraction, synchrotron X-ray powder diffraction, and Monte Carlo simulations, we found that this phase is present in the Cu–Pt system at 1:3 stoichiometry. We also find that the 4-atom, fcc superstructure L13 is equivalent to the large 32-atom orthorhombic superstructure reported in older literature, resolving much of the confusion surrounding this composition. Monte Carlo simulations confirm the formation of a large cubic superstructure at high temperatures, and its eventual transformation to the L1_3 structure at lower temperature, but also provide evidence of other transitional orderings.
Wave-like modulations with non-lattice periodicities accompany a variety of important physical phenomena (e.g. magnetism and superconductivity). Though such a material is not properly crystalline in three dimensions, it does have a regular crystal lattice in a higher dimensional superspace. The superspace symmetry groups in (3+1), (3+2) and (3+3) dimensions have now been exhaustively tabulated, which will make it easier to solve modulated structure and understand their properties.
This image was secured just after the end of evening twilight on a clear April night from the West Mountain Observatory. The view is looking west past the domes housing the two smaller research telescopes at the observatory. The thin crescent Moon is also illuminated by reflected light from the Earth that is known as earthshine. Higher in the sky, the bright 'star' is actually the planet Venus. In between the two, the 'V' shaped group of stars in the constellation of Taurus is in reality the nearby open cluster known as the Hyades. Photo credit: Dr. Michael D. Joner
20 Mar, Today
21 Mar, Wednesday
Joseph Moody, Eric Hintz, Mike Joner, Peter Roming, and Maureen Hintz recently published an article titled "Point and Compact Hα Sources in the Interior of M33" in Astronomical Journal. Click on the image above to read it.
Chicagohenge: Equinox in an Aligned City : Sometimes, in a way, Chicago is like a modern Stonehenge. The way is east to west, and the time is today. Today, and every equinox, the Sun will set exactly to the west, everywhere on Earth....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.