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In this issue:
Road Header Finds Teeth as it Chews
Safety Today: Honey Bee or Yellow Jacket?
symmetry: The Hottest Citation

SLAC Today

Tuesday - May 29, 2007

Road Header Finds Teeth as it Chews

LCLS Conventional Facilities Manager David Saenz holds the shark tooth found during LCLS construction.
(Click on image for larger version.)

The insatiable road header, plying its way under SLAC as it burrows out tunnels for the Linac Coherent Light Source (LCLS), has discovered in its diet a little more than sandstone. In April, crews working the early stages of the Access Tunnel behind the Collider Hall noticed among the spoils an ancient shark tooth, believed by paleontologists to be more than 10 million years old.

Shark teeth are plentiful in the soils of SLAC, a fact initially made apparent during the original excavation for the linear accelerator in the 1960s. The tooth found by crews last April probably belonged to a member of the Mako sharks genus Isurus.

In mid-May, SLAC environmental expert Helen Nuckolls presented a group of tunnel workers with samples of fossil specimens that crews might find while digging. Adele Panofsky, Susan Witebsky and Nuckolls later accompanied construction managers into the tunnel to examine the exposed rock face. (A short video of their exploration is available online. View with Real Media Player.) Panofsky's paleontological experience at SLAC extends back to the early excavations when a nearly complete Paleoparadoxia skeleton was unearthed in what is now the Research Yard. Curiously, several Isurus shark teeth were also found between the animal's rib bones, although paleontologists are uncertain what that may imply. A reconstruction of the Paleoparadoxia skeleton now resides in the SLAC Visitor Center.

(Column - Safety Today)

Honey Bee or
Yellow Jacket?

A honey bee (left) and yellow jacket. (Click on image for larger version.)

Beware deer, ticks, snakes, skunks, bobcats, black widow spiders and feral cats, says the SLAC safety guide. The omission of bees may seem like an oversight at first, but according to resident bee expert and Engineering Physicist Dieter Walz, it is not.

The local honey bees found outside the A&E Building (Building 41) and on the Computer Center (Building 50) are European honey bees (Apis mellifera), according to Walz. This species is content to buzz along its busy way, foraging for nectar and pollen, while ignoring those walking in and out of buildings. Honey bees are even protected on Stanford University grounds. Walz has observed the oak tree colony in front of A&E since the building's construction in 1964. There they are thriving, despite attempts to remove them by filling the tree's cavities with cement.

Walz guesses the colony might be about 12 to 15 thousand bees strong in early spring; a modest number for a species whose colonies can grow to 65 or even 70 thousand when given enough space and properly managed. Most every spring, when the colony reaches a certain critical size, the old queen and about half of the bees swarm out into the world to start a new colony creating an impressive, thick cloud.

But before leaving, the bees gorge themselves on stored honey to the point that they are no longer able to sting, making the swarm completely harmless. This is when pictures are taken of beekeepers with "beards of bees," Walz says.

Yellow jackets (Vespula pennsylvanica), on the other hand, are a more aggressive insect that also makes its home on the SLAC site. These are carnivorous wasps that seek out meat at barbecues, and may sting anything standing between them and their meals. The two can be distinguished by their bodies. Honey bees, which seek out sweets instead of meat, are hairy while yellow jackets are longer with a smooth, shiny abdomen.

"If a bee-like insect is coming after your hamburger, it is a yellow jacket," says Walz. "Either share your meal or move elsewhere, do not challenge them."

But be careful, some people are allergic to the venom in bee and yellow jacket stings. Bees lose their stinger and can only sting once, but yellow jackets, like other wasps, can sting multiple times. If you know you are allergic or experience allergic symptoms after being stung by one of these insects, seek medical attention. The medical office is inside the A&E Building in room 135.

If you become aware of a problem yellow jacket nest, please contact Conventional and Experimental Facilities at x8901 or the Safety Service Desk at x4554.

The Hottest Citation

The article at the top of the spires lists of the most-cited articles in high-energy physics is, as always, the Review of Particle Physics (RPP), a compendium of experimental data and reviews put out by the Particle Data Group. This highly useful work is cited whenever the author of a paper refers to standard experimental results, and it gets more than 1,000 citations every year.

Just as physicists often look at spires' lists as a measure of which papers are "hot" at a given moment, librarians and journal publishers, in evaluating journals, look at something called the impact factor. It's based on the number of articles published in a journal in a two-year span and the number of citations those articles received in the following year. Impact factors, like other ranking systems based on article citations, may be pilloried as useless or vaunted as convenient measures of quality. In reality they are somewhere in between, and the RPP provides a good example of some subtle effects.

The RPP is run in one of the major particle physics journals every two years, although it isn't submitted, reviewed, or edited like a typical journal article. Because the RPP gets more than 1000 citations a year, any journal in which it appears in gets a big but temporary lift in its impact factor.

In Physics Letters B, for example, 10% of the 10,000 citations received in 2005 were to the RPP. The resulting boost in impact factor from 4.5 to 5 was based on nothing more than the Particle Data Group's decision to publish the review in the journal that year. For this reason, among others, the group rotates the publication of the book among several journals, and the RPP effect, while pronounced in each year, does get spread around. In 2003 and 2004 the Physical Review D impact factor was boosted by about 5% due to the RPP, in 2005 and 2006 Physics Letters B saw a 10% rise, and for 2007 and 2008, we can expect the Journal of Physics G to see a near doubling of its impact factor due to the RPP.

While physicists generally nod their heads in agreement when they see the RPP at the top of spires' lists, confirming that the Particle Data Group's efforts are quite useful, journal publishers and librarians who don't know about the RPP may wonder at the strange cycle of bumps in impact factors for the journals of particle physics.

The latest edition of symmetry is now online.

Safety Firsts & Seconds

Due to the holiday, Safety Firsts and Seconds will return next week.

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