Thursday - August 16, 2007
SLAC Today is
available online at:
http://today.slac.stanford.edu
In this issue:
Photons on the Half Shell
Science Today: The Shortest Flux Variations Detected from Active Galactic Nuclei
Cataloguing Program Continues Full Steam
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Thursday - August 16, 2007 |
Aaron Lindenberg (left) with Haidan Wen, who designed the optical layout used to create terahertz pulses.
Photons on the Half ShellIn the realm of ultra-fast science, there's a region where photons of light can be made to dance only half steps. Here, advances in laser science are letting researchers tinker with the behavior light in an entirely new way. "It's a really new regime for studying materials properties," said Aaron Lindenberg of SLAC's PULSE Center and the Stanford Materials Science and Engineering Department. "We’re just learning how to create such intense fields in this relatively simple way." Lindenberg's team is pioneering a technique that creates highly intense beams of low-energy infrared photons, separated into extremely short pulses lasting less than a trillionth of a second (one picosecond). These "terahertz fields" show promise as a powerful tool for manipulating matter at the atomic level. Read more... |
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 The Shortest Flux Variations Detected from Active Galactic Nuclei
An Active Galactic Nucleus (AGN) is a compact region at the centre of a galaxy that can outshine some or all the electromagnetic radiation of the host galaxy by up to three orders of magnitude. The ultimate energy source of those objects is commonly believed to be the release of gravitational potential energy of matter from an accretion disk surrounding a super-massive black hole (10 million to 100 billion times the mass of the Sun). Although this general model has won broad support, discussion on the detailed emission processes underlying the broadband spectral energy distribution of AGNs is still ongoing. The observation of fast flux variations can potentially bring important information from the innermost regions of the AGN in a rather model-independent way. The most extreme flux variations have been observed in so-called blazars: AGNs containing jets of plasma moving at relativistic speed towards the observer. Although blazars comprise only several percent of the overall AGN population, they largely dominate the high-energy extragalactic sky. This is because most of the non-thermal power, which arises from relativistic jets that are narrowly beamed and boosted in the forward direction, is emitted in the gamma-ray band, whereas the presumably nearly-isotropic emission from the accretion disk is most luminous at optical, UV, and X-ray energies. Therefore, the study of the variable gamma-ray emission of blazars can potentially bring key data for the understanding of the working principle of the still rather unknown AGNs. Recently, the MAGIC and the HESS instruments (Imaging Atmospheric Cherenkov Telescopes, IACT, for gamma-ray observation of the northern and southern hemisphere, respectively) recorded the fastest ever-detected flux variations from blazars. (Related papers about these blazars, Markarian 501 and PKS2155-304, are currently in publication and can be accessed via the links below.) Assuming the emission comes from a spherical blob in the jet, these observations imply that the source's radius is less than about 0.6 δ astronomical units (an AU is an astronomical unit, or the mean distance between the Earth and the Sun, about 150 million kilometers), where δ is the Doppler factor of the source. Since the central engine of these objects is believed to be a super-massive black hole (with a mass about one billion times the mass of the sun), the most natural and smallest rule to measure distance in those systems is the Schwarzchild radius which defines the horizon of the black hole. |
Cataloguing Program Continues Full Steam
Since May, the Conventional and Experimental Facilities (CEF) department has enlisted the help of several summer students to collect maintenance equipment data for the new computerized maintenance management system (CMMS) called FAMIS. A previous SLAC Today article outlined how summer student Ryan Auer and temporary employee Maria Aguaristi were collecting and cataloguing heating ventilating air conditioning (HVAC) equipment data to input to the system. Since then, the cataloguing project has continued with great success and the CEF department has reviewed the Previous Maintenance (PM) program, which will utilize the new CMMS system. The cataloguing of equipment has continued in full force. Auer has scoured every building searching for HVAC equipment, completing the massive undertaking during the first week of August and cataloging over 2,200 pieces of equipment. Augmenting Auer's search is summer student Pascal Bui from Andrew Hill High School, San Jose, who is cataloguing cryogenic equipment and validating site vehicle information. Since mid-June, Bui has collected data on cryogenic pressure valves, trailer truck-sized pressure vessels, and other heavy equipment such as forklifts. Bui carries a tablet PC into which he inputs the equipment data. "The tablet PC really helps out a lot," said Bui, who has catalogued 385 pieces of equipment so far. "It's very easy to use and I can input the data quickly." "We're trying to catalogue as many pieces of equipment as possible with our summer students," said Bachant. "When they leave, the cataloguing will be continued by each department following the same process used by the summer students. It's proven to be a success." In addition to Ryan and Pascal, two graduate students from the National Consortium for Graduate Degrees for Minorities in Engineering (GEM) joined CEF. Since June, they have examined CEF's PM Program from every possible angle. Marcus Bellamy, who will attend graduate school at Georgia Tech next year, investigated how PMs are carried out in the field. Willie Montgomery, from the University of Arkansas, focused on the overall scope of the PM program, proposing a solution toward a more effective system for planning and implementing maintenance. "Our comprehensive assessment indicates that the current PM program is more reactive than proactive. We're trying to help change that by providing concrete recommendations and a plan of action," said Montgomery. And while SLAC is benefiting from their engineering expertise, both Bellamy and Montgomery are benefiting from their work. "It's been a great real-life experience," said Bellamy. "We've been able to see how different departments are run from technicians' offices to human relations." "We've been extremely lucky to have such bright and wonderful students in our group this year. They’ve each made a unique contribution to the CMMS project. I will miss them," said Leslie Bachant. |
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