An important part of "first-principles" materials calculations involves integrating over the occupied electron states, the so-called "band energy integration." This is the primary source of error in first-principles calculations of solids. Improving this integration would have a dramatic impact on computational simulations of metallic systems. The right half of the figure shows the "Brillouin zone," the periodic tile of the electron bands. The left half shows a sample band structure. Visualization is difficult because the bands are a multivalued, three-dimensional function. The shown function is a single-valued function with a cut-away to show the function variation as a function of position.
This solar eclipse image was secured on October 23, 2014 by Dr. Michael D. Joner. This observation was made at 4:05 PM MDT a couple of miles west of the BYU campus in Provo, Utah. In this near alignment of the Earth, Moon, and Sun only about 50% of the solar photosphere was blocked by the disk of the Moon as viewed from Provo. The result was a partial solar eclipse. The large group of sunspots near the center of the Sun has been cataloged as AR 2192. This is the largest active region seen during the current solar cycle. The dark central spot is significantly larger than the Earth. The entire sunspot complex is more than 100,000 km across.
The small black spot projected on the Sun just above the foreground clouds in Provo is caused by the planet Venus as it transits for the last time this century. The transits of Venus come in pairs separated by eight years that only occur after a period of 105 or 122 years without a transit visible from the Earth. If you missed this event, the next opportunity will be in December of 2117. Finding the transit of an Earth sized planet across a stellar photosphere was the primary mission of the Kepler spacecraft as it searched for extrasolar planets up through August 2013. The difficulty of this mission is apparent when you note the tiny fraction of the Sun's light that is blocked by the transit of a planet the size of Venus.
This image was taken with a DSLR at the West Mountain Observatory about an hour before sunrise on 4 April 2015 by Dr. Michael Joner. Near the center of the constellation of Sagittarius is a bright star that was not seen just a few weeks earlier. This new naked eye star was discovered on March 15, 2015 in survey images taken in Australia. Spectroscopic observations secured the next night confirmed that this is a classical nova, and it was named Nova Sagittarii 2015 No. 2. A classical nova is a binary system where a white-dwarf star collects gas from a close companion star so that the material flows onto the surface of the white dwarf. As the material builds up on the white dwarf, the bottom layers become hot and dense so that they ignite in a runaway hydrogen-fusion reaction which blasts the shell off into space and causes a temporary increase in luminosity by a factor of 50,000 or more. Unlike supernovae that destroy the progenitor star, novae are recurrent events. It is estimated that about 40 novae occur in the Milky Way each year, and about ten of these are visible from Earth. This nova is expected to fade away in a month or two and return to a luminosity close to what it was before this outburst.
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
22 Feb, Today
23 Feb, Thursday
Mark Transtrum et al. recently published an article titled "Theoretical estimates of maximum fields in superconducting resonant radio frequency cavities: stability theory, disorder, and laminates" in Superconductor Science and Technology. Click on the image above to read it.
Almost Three Tails for Comet Encke : How can a comet have three tails? Normally, a comet has two tails: an ion tail of charged particles emitted by the comet and pushed out by the wind from the Sun, and a dust tail of small debris that orbits behind the comet but is also pushed out, to some degree, by the solar wind....
This photograph and Description come from NASA's Astronomy Picture of the Day web site.