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
If you missed your chance to see the transit of Mercury on May 9, 2016, you only need to wait a few years to get another chance. While Venus transits are rare and occur about twice in a century, Mercury will transit the Sun 14 times in this century. The next such event will occur on November 11, 2019. Mercury is the tiny black dot seen just below the center of the picture. The larger sunspot group seen just above the center of the picture is cataloged as AR 2542. This picture was taken in Provo by Professor Michael 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.
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Joseph Moody et al. recently published an article titled "Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010" in Astronomy & Astrophysics. Click on the image above to read it.
IC 5067 in the Pelican Nebula: The prominent ridge of emission featured in this sharp, colorful skyscape is cataloged as IC 5067. Part of a larger emission nebula with a distinctive shape, popularly called The Pelican Nebula, the ridge spans about 10 light-years following the curve of the cosmic pelican's head and neck....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.