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Sulfur is essential for all life, but it plays a particularly central role in the metabolism of many anaerobic microorganisms. Prominent among these are the sulfide-oxidizing bacteria that oxidize sulfide to sulfate. Many of these organisms can store elemental sulfur in "globules" for use when food is in short supply. The chemical nature of the sulfur in these globules has been an enigma since they were first described as far back as 1887; all known forms (or allotropes) of elemental sulfur are solid at room temperature, but globule sulfur has been described as "liquid", and it apparently has a low density - 1.3 compared to 2.1 for the common yellow allotrope alpha-sulfur. Various exotic forms of sulfur have been proposed to explain these properties, including micelles (small bubble-like structures) formed from long-chain polythionates, but all of these deductions have been based upon indirect evidence (for example, the density was estimated by flotation of intact cells), and many questions remained. Using X-ray absorption spectroscopy at the sulfur K-edge recorded on SSRL's Beam Line 6-2, Ingrid Pickering, Graham George and Eileen Yu (SSRL) together with co-workers from Arizona State University, University of British Columbia, and ExxonMobil Research and Engineering Co. have resolved this long-standing conundrum and the results are described in a recent publication.
More information regarding this research, including the reference to
the publication in Biochemistry can be found at:
In conjunction with a visit to Stanford University and discussions with Stanford President John Hennessy on January 17, 2002, Catalonian President Jordi Pujol visited SSRL to gain a better insight into the broad range of scientific research conducted at a synchrotron radiation facility. Following an overview presentation given by SSRL Deputy Director Jo Stöhr, President Pujol was given a tour of the SSRL experimental hall. At BL9-2, staff scientist Ana Gonzales described how high energy x-rays are used in the determination of 3-D protein structures. Katharina Baur then introduced him to a research effort currently underway on BL6-2 involving trace impurity analysis on semiconductor surfaces and its importance to the semiconductor industry. Other delegates joining the tour included, Pujol's Deputy Minister of Education, Ramon Farre; Minister of Industry and Commerce, Antoni Subira; Minister of Universities, Technology and R&D, Andreu Mas-Colell and Science Advisor and Physics Professor Ramon Pascual. Relevant to plans for construction of a Catalonian synchrotron facility by 2006, the group learned that SSRL attracts scientists from more than 200 institutions and has become a nucleus for national and international collaborations involving pharmaceutical design, environmental monitoring and detection of impurities in high-tech materials - among many others.
As users should be aware, plans and preparations for SPEAR3 have been underway at SSRL for several years. Users will not have access to SSRL beam lines during the installation and commissioning of this third generation light source, which is scheduled from approximately April 2003 through January 2004. A subcommittee of the SSRL Users' Organization has been formed to represent users' issues related to the shutdown and to suggest ways that SSRL may be able to mitigate the resulting loss of beam time to users. The subcommittee members include Uwe Bergmann, Corwin Booth, Paul Foster, Lipika Basumallick, Ben Bostic, Nicholas Pingatore and Vittal Yachandra.
The SSRL Users' Organization Executive Committee has scheduled their
next meeting on Friday, March 15, from 10:30 a.m.-12:30 p.m. The
meeting will be held in the Orange Conference Room, which is located in
the SLAC Central Lab Building 40 (adjacent to the SLAC cafeteria). The
agenda includes a SPEAR3 update as well as a presentation on beam line
development. All interested SSRL users are invited and encouraged to
attend. If there are other issues that users would like to bring to the
attention of the Users' Organization, please feel free to contact anyone
on the Executive Committee. A listing of the SSRLUO-EC members, agenda
and site map can be found at:
Despite a forward-looking focus on SPEAR3 and future developments such as the Linac Coherent Light Source (LCLS), we want to take this opportunity to mark an important anniversary - it has now been 10 years since the injector synchrotron complex was commissioned and SPEAR became a fully dedicated synchrotron radiation source.
In 1992 we reported that 26 beam line stations served 280 experiments from 130 different principal investigators. In all, 550 experimenters came to SSRL during the experimental run that spanned from February 17 - September 7, 1992. In comparison, during the most recent experimental run ending July 3, 2001, 776 individual experiments were scheduled across 32 beam line stations and approximately 900 users came to the facility to run these experiments. The dedicated injector, with its reliable operation and "on demand" injection was one of the main underpinning factors in vastly improving SPEAR beam time delivery and performance that contributed to this strong growth. We thank both the staff who managed the project so efficiently and the DOE Office of Basic Energy Sciences for providing the funding.
Non-coincidentally, several SSRL staff members, including Dave Calloway, Ian Evans, Chris Hoover, Craig Haggart, Thomas Nguyen and Howard Page, were recently honored at a SLAC Service Awards program for employees who had completed 10 years of service during 2001. Jonathan Dorfan, SLAC Director, congratulated the honorees for their contributions and presented each with a service pin and a gift. While 10 years of service for these individuals or any other SSRL staffers cannot be easily summed up, we do know that Ian, SSRL's Safety Officer, has reviewed upwards of 5,290 experiments for safety concerns during his tenure, and Dave, Chris, Craig, Thomas and Howard, members of the behind-the-scenes Accelerator Operations group responsible for keeping beam in SPEAR, have steered a lot of beam and logged in thousands of shift reports.
The last two weeks of 2001 were marked by the closure of Beam Line 2 for vacuum reasons. During the December 10-11 Accelerator Physics period the BL2 moveable mask was being cycled normally when a leak in the bellows that allows the vertical motion of this water-cooled copper mask occurred. The initial indications were that BL2 tripped closed on a vacuum fault with a subsequent SPEAR vacuum fault. Vacuum personnel immediately mobilized and the Accelerator Physics program was terminated to find the source of the leak. It was at this time that the leak was isolated to the BL2 mask bellows. A temporary repair was effected by spraying the bellows with a vacuum sealant. Since further cycling of the bellows would almost certainly have reopened the leak and vented SPEAR, the decision was made to leave the beam line closed until more permanent repairs could be made.
Minimizing the impact on users on other lines and bringing BL2 back up as soon as possible required that we be in a position to replace the bellows at the beginning of the 2001 Holiday shutdown, basically giving the lab two weeks to prepare. This would allow the Holiday shutdown period to be used for pumping the quadrant of SPEAR that had to be vented. Building a new mask in two weeks time seemed out of the question so we removed an unused mask from Beam Line 7 and modified it to fit Beam Line 2. The Accelerator Department managed to finish preparations with two days to spare and the beam was shut down early on Friday, December 21, for installation. Since this is a part of the Machine and Personnel Protection Systems (PPS), SSRL staff were required to come in between Christmas and New Year's Day to certify proper operation of the mask. BL2 was then opened for operation on January 2 along with all the other beam lines. Initial lifetimes were degraded but the normal lifetimes were recovered after the first 24 hours of operation with beam.
As we find news highlights that involve research done at SSRL or other items, we will provide links (or citations if not available on line) in SSRL HEADLINES where we feel that these articles will be of interest to the SSRL community, our users or our sponsoring agencies. Please let us know if you become aware of any "news" that can be highlighted in this section.