SSRL Science Highlights Archive

Approximately 1,600 scientists visit SSRL annually to conduct experiments in broad disciplines including life sciences, materials, environmental science, and accelerator physics. Science highlights featured here and in our monthly newsletter, Headlines, increase the visibility of user science as well as the important contribution of SSRL in facilitating basic and applied scientific research. Many of these scientific highlights have been included in reports to funding agencies and have been picked up by other media. Users are strongly encouraged to contact us when exciting results are about to be published. We can work with users and the SLAC Office of Communication to develop the story and to communicate user research findings to a much broader audience. Visit SSRL Publications for a list of the hundreds of SSRL-related scientific papers published annually. Contact us to add your most recent publications to this collection.

August 2002
Kaspar P. Locher, Allen T. Lee, Douglas C. Rees, Caltech
Figure 1.

Transport proteins, embedded in lipid membranes, facilitate the import of nutrients into cells or the release of toxic products into the surrounding medium. The largest and arguably the most important family of membrane transport proteins are the ABC transporters. They are ubiquitous in biology and power the translocation of substrates across the membrane, often against a concentration gradient, by hydrolyzing ATP (Higgins, 1992). 

Macromolecular Crystallography
BL9-2
July 2002
Figure 1.

In the well-known Greek legend the touch of King Midas would convert anything to metallic gold. Recently, a team working at SSRL lead by Professor Jorge Gardea-Torresdey from the University of Texas at El Paso have shown that ordinary alfalfa plants can accumulate very small particles (nanoparticles) of metallic gold (1). The best-known materials that contain nanoparticles of metallic gold are gold colloids. These lack the familiar metallic luster, but show bright colors which range from red, violet or blue, depending upon the size of the nanoparticles (2,3). 

X-ray Absorption Spectroscopy
BL7-3
June 2002
M. Cornacchia (SSRL), H.-D. Nuhn (SSRL), C. Pellegrini (UCLA)
Figure 1.

Advances in accelerator technology and in the theoretical understanding of collective instabilities and production of coherent radiation, have been the driving forces of the progress toward brighter synchrotron radiation sources, with scientific applications developing in response to the availability of new sources. The rate of improvement in source capability has been tremendous: for 30 years x-ray source brightness has been increasing exponentially with a doubling time of about 10 months. A modern synchrotron source is eleven orders of magnitude brighter than a 1960s laboratory x-ray source. Seldom, if ever, in history (perhaps only in the field of visible laser optics and colliders for high energy physics) has a scientific discipline seen its tools change so dramatically within the active life of a single generation of scientists.

May 2002
David L. Clark, Los Alamos National Laboratory
Figure 1.

The Rocky Flats Environmental Technology Site (RFETS) is an environmental cleanup site located about 16 miles northwest of downtown Denver (Fig 1).  Two decades of routine monitoring have shown that the environment around RFETS is contaminated with actinide elements (U, Pu, Am) from site operations, [1] and RFETS has been designated by the U.S. Environmental Protection Agency (EPA) as a Superfund cleanup site.  Until December 1989, the Rocky Flats Plant made components for nuclear weapons using various radioactive and hazardous materials, including plutonium, uranium and beryllium. Nearly 40 years of nuclear weapons production left behind a legacy of contaminated facilities, soils, and ground water.  More than 2.5 million people live within a 50 mile radius of the site; 300,000 of those live in the Rocky Flats watershed.

BL11-2
April 2002
Thiang Yian Wong, Robert Schwarzenbacher, Robert C. Liddington
Figure 1.

Anthrax Toxin is a major virulence factor in the infectious disease, Anthrax (1). This toxin is produced by Bacillus anthracis, which is an encapsulated, spore-forming, rod-shaped bacterium. Inhalation anthrax, the most deadly form, is contracted through breathing spores. Once spores germinate within cells of the immune system called macrophages (2), bacterial cells are released into the bloodstream. There they proliferate rapidly and secrete Anthrax Toxin, ultimately leading to septic shock and death. Although antibiotics may be used to kill the bacteria, the level of toxin has often become so high in the bloodstream that removing the bacteria alone is not sufficient to prevent death.

Macromolecular Crystallography
BL7-1, BL9-1
March 2002
Satish C. B. Myneni, Department of Geosciences, Princeton University, Princeton, NJ 08544
Figure 1.

When we think of chlorine, we often relate it to the salt used in food preparation, chloride in the oceans, chlorine gas from swimming pools, and gaseous chlorofluorocarbons that have close links to the depletion of stratospheric ozone. We rarely think of thousands of chlorinated hydrocarbons that exist in the natural systems, several of which are highly toxic to humans (1). The C-Cl bond, common to all organo-Cl compounds, is strong and gives high stability to organo-Cl compounds. For this reason, several organo-Cl compounds have been synthesized and used extensively for years in agricultural and industrial applications.

BL6-2
February 2002
Magnus Sandström, Farideh Jalilehvand, Ingmar Persson, Ulrik Gelius, Patrick Frank
Figure 1.

The famous 17th-century Swedish warship Vasa has been on display in the Vasa Museum since 1990 (Figure 1). The Vasa sank on its maiden voyage in 1628, and was recovered in 1961 after 333 years in the cold brackish water of Stockholm harbor. After extensive conservation treatment, the oaken Vasa appeared in good condition (1). However, high acidity and a rapid spread of sulfate salts and elemental sulfur were recently observed on many wooden surfaces. A research team led by Prof. Magnus Sandström, University of Stockholm, have approached the problem by using X-ray absorption near edge spectroscopy (XANES) at the sulfur K-edge. 

BL6-2
January 2002
I. J. Pickering, G. N. George
Figure 1.

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 (S2-) to sulfate (SO42-). Many of these organisms can store elemental sulfur (S0) in "globules" for use when food is in short supply (Fig. 1). The chemical nature of the sulfur in these globules has been an enigma since they were first described as far back as 1887 (1); 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 α-sulfur.

X-ray Absorption Spectroscopy
BL6-2
December 2001
J. Stöhr, H. Ohldag, J. Lüning

Computer hard drives and other advanced electronic devices depend on layered stacks of magnetic and non-magnetic materials, but researchers don't fully understand why such layered materials exhibit new properties that cannot be predicted from the properties of the individual layers. In a recent publication a team working at SSRL and the ALS describes new methods, based on x-ray spectroscopy and x-ray microscopy, that reveal the magnetic structures at the boundaries between these layers. Their data show that the boundaries are not as clean as previously assumed but a new ultrathin interface layer may be formed by a chemical reaction. The thickness of the interfacial layer is found to change with temperature and this change can be directly correlated with the magnetic properties of the multilayer stack. The work provides the first magnetic images of a buried interface and gives direct experimental evidence for the existence and long-assumed importance of interfacial magnetic spins.

BL10-1
November 2001
Alexis S. Templeton, Thomas P. Trainor, Gordon E. Brown, Jr.
Figure 1.

Sorption reactions on particle surfaces can dramatically affect the speciation, cycling and bioavailability of essential micronutrients (i.e. PO43-, Cu, Zn etc.) and toxic metals and metalloids (i.e. Pb, Hg, Se, As) in soils and aquatic environments. Considerable attention has been focused on understanding metal sorption reactions at a molecular/mechanistic level and the effects of metal concentration, pH, ionic strength, and complexing ligands on the ways in which metal ions bind to the surfaces of common mineral phases such as Fe-, Mn- and Al-(hydr)oxides and clays. However, a significant fraction of mineral surfaces in natural environments are extensively colonized by microbial organisms, which can also be potent sorbents for metals due to the large number of reactive functional groups that decorate the cell walls and outer membranes of bacterial surfaces. 

X-ray Absorption Spectroscopy
BL6-2

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