The irreducible representations (IRs) of the parent symmetry of a system provide a symmetry-motivated parameter set for describing any periodic or aperiodic distortion. The IRs of complete crystallographic space groups and their extensions to (3+d)-dimensional superspace, including all special and non-special k-vectors, commensurate and incommensurate, have now been exhaustively tabulated for the first time. Photo (Wikipedia): Table Mountain, Capetown, South Africa.
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
The anisotropic x-ray diffuse scattering pattern surrounding this Bragg reflection from La1.8Sr2.2Mn2O7 at 125 K provides evidence that Jahn-Teller polarons (football-shaped lattice distortions that follow hopping electrons from site to site) play a role in this material's exotic phase transition from paramagnetic insulator to ferromagnetic metal. This data was used to perform a quantitative three-dimensional structural analysis of transient polaronic distortions.
This image from the BYU 0.9-m telescope looks out along the plane of our Milky Way Galaxy toward the constellation Cygnus the Swan. Called the Tulip Nebula, the glowing cloud of interstellar gas and dust is also listed in the 1959 catalog by astronomer Stewart Sharpless as Sh2-101. This nebula is about 8,000 light-years away from the solar system. The nebula shown here is a composite image that maps emission from sulfur, hydrogen, and oxygen atoms into red, green, and blue colors. Energy from the hot O-type star HDE 227018 ionizes atoms in this region so that we see a faint glow from the Tulip Nebula. HDE 227018 is seen near the blue arc at center of the image. This appeared as the NASA Astronomy Picture of the Day on July 26, 2012. Image Credit & Copyright: Michael Joner, David Laney (West Mountain Observatory, BYU); Processing - Robert Gendler
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Brian Thornock, Timothy Leishman, Brian Anderson, and James Esplin recently published an article titled "Effects of simultaneous sound arrivals on direction-of-arrival estimates of the polar energy time curve" in Applied Acoustics. Click on the image above to read it.
NGC 2442: Galaxy in Volans: Distorted galaxy NGC 2442 can be found in the southern constellation of the flying fish, (Piscis) Volans. Located about 50 million light-years away, the galaxy's two spiral arms extending from a pronounced central bar have a hook-like appearance in wide-field images....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.