Previous Editions__________________________________________________________________________SSRL Headlines Vol. 10, No. 10 April, 2010__________________________________________________________________________
Contents of this Issue:
A group led by John Peters of Montana State University used SSRL Beam Lines 9-1
and 9-2 to solve the crystal structure of a green algae [FeFe]-hydrogenase
enzyme. They used an intermediate form of the enzyme to acquire information
about the mechanism of enzyme assembly and maturation. Their 1.97 Å
structure revealed a positively charged channel linked to the [4Fe-4S]
subcluster site, while the 2Fe subcluster was absent. The authors propose a
stepwise mechanism in which the [4Fe-4S] subcluster is assembled first and then
the 2Fe cluster is assembled and inserted through the channel, which collapses
and disappears in the mature enzyme. This mechanism is similar to that seen in
nitrogenase, which transforms nitrogen gas into ammonia, suggesting an
evolutionary link.
The researchers suggest that knowledge obtained from this structure can inform
efforts to engineer better hydrogenases, ultimately leading to more
cost-effective renewable energy sources, such as hydrogen fuel cells. This work
was published on April 25 on the Nature website.
To learn more about this research see the full scientific highlight
A group of researchers led by Zhi-Xun Shen of Photon Science at SLAC and
Applied Physics, Stanford University explored the behavior of electrons in a
high-temperature superconducting material. They used SSRL Beam Line 5-4 for
angle-resolved photoemission spectroscopy (ARPES) experiments at a variety of
temperatures spanning the normal state, the pseudogap state, and the
superconducting state. They were surprised to find that the electrons in the
pseudogap state do not pair at all. Instead, they saw the tendency of electrons
traveling in a density wave. The pseudogap state is not predominantly composed
of electron pairs ready to take on Cooper pair properties but of an electronic
state that probably competes with superconducting pairing by consuming
electrons otherwise available for pairing.
Given their surprising findings, the researchers conclude that room temperature
superconductivity, if it can exist, may rely on a different electronic behavior
than what was previously assumed. They are currently working on understanding
the nature of the density wave they observed and its effects on the underlying
high-temperature superconductivity. This research was published online on April
4 by Nature Physics.
To learn more about this research see the full scientific
highlight
A collaboration between SIMES, SSRL, the University of Houston and the Argonne
and Oak Ridge National Labs has provided a fundamental understanding of a
method used to increase the reactivity of platinum so that 80% less needs to be
used for the same power generation. Using so much less platinum would allow a
dramatic reduction in fuel cell cost. To accomplish this, the University of
Houston research group of Peter Strasser reacted platinum with copper, then
partially removed the copper, in a process called dealloying, leaving the
platinum in a different configuration. The SSRL research groups of Anders
Nilsson, Hiro Ogasawara and Mike Toney analyzed the structure of the dealloying
materials at SSRL Beam Lines 2-1, 4-2 and 13-2; this revealed that the
increased reactivity was due to lattice strain between the platinum atoms.
Because of decreased spacing of atoms at the surface, the platinum creates
weaker connections to the oxygen atom products and thus has better reaction
rate.
The researchers plan to test other processes that alter platinum structure,
aiming to further optimize its reactivity and reduce the amount required for
fuel cell use. This research brings us a step closer to making a green energy
alternative affordable. This study was published on April 25, 2010 online and
will appear in the June issue of Nature Chemistry.
P. Strasser, S. Koh, T. Anniyev, J. Greeley, K. More, C. Yu, Z. Liu, S. Kaya,
D. Nordlund, H. Ogasawara, M.F. Toney and A. Nilsson, "Lattice-strain Control
of the Activity in Dealloyed Core-shell Fuel Cell Catalysts", Nat. Chem.
(2010) doi: 10.1038/nchem.623
SLAC Press Release:
http://home.slac.stanford.edu/pressreleases/2010/20100426.htm
On Thursday, April 8 the SPEAR3 booster klystron, which had been in operation
since the injector was first commissioned in 1990, failed. Testing to diagnose
the problem was completed later that evening, and the klystron was replaced in
just 14 hours starting the following day. After removing the failed tube, it
was determined that the problem was due to water leaking into the oil tank
causing breakdown at high voltage. Fortunately, there was a spare klystron
available, last used to power the SPEAR RF cavity in 2003 during the final days
of SPEAR2 operation. Cathode thermal processing began immediately after
installation. The tube required over two days of thermal processing before it
was feasible to raise the cathode heater to full power. High voltage testing
began Monday morning which caused the vacuum pressure to rise to an
unacceptable level requiring further cathode processing. A second HVPS was
implemented to raise the voltage to the allowable limit to speed up the
processing as much as possible. By Tuesday morning the vacuum pressure had
dropped to acceptable levels and full voltage was applied on the tube.
Operations staff were able to establish booster beam and inject into SPEAR3 a
few hours later. Replacing the klystron required prompt assistance in strong
coordination from numerous staff across many SLAC departments who are
gratefully acknowledged. Additional appreciation is extended to those who gave
up most their accelerator physics time on April 19-20 for user operations to
make up some of the lost beam time, and to the SSRL staff who accommodated
this late change in schedule.
Dr. Michel van der Rest, Director General for the Synchrotron SOLEIL, the
third-generation synchrotron facility in Saint-Aubin, France, visited SSRL on
April 20. Having a life science background and career, Dr.
van der Rest's visit focused in particular on the SSRL Structural Molecular
Biology program, including beam lines, facilities and science. A beam line
tour included the microfocus Beam Line 12-2 with the newly installed PILATUS 6M
detector for macromolecular crystallography, the biological small-angle
scattering beam line 4-2, the biological XAS Beam Line 9-3, and the microXAS
imaging Beam Line 2-3.
In the Panofsky Auditorium, Tuesday evening, May 25 at 7:30 p.m., diamondoids
researcher Jeremy Dahl of the Stanford Institute for Materials and Energy
Science (SIMES) will present a public lecture, "Ultimate Atomic Bling." Dahl
will discuss the discovery of these nano-size diamonds and highlight current
SLAC/Stanford research into their applications in electronics and medicine. The
talk is free and open to all. http://www2.slac.stanford.edu/lectures/default.asp?id=home
Register for the SSRL SRXRS School to be hosted by SSRL at SLAC June 1-3, 2010.
This school will provide a practical users' guide to planning and conducting
scattering measurements at SSRL beam lines. The school will cover important
techniques, including surface and thin-film scattering, powder diffraction,
in-situ x-ray scattering, and amorphous materials. It will cover topics
that
are not commonly addressed in text books or class lectures, but are typically
obtained only through on-the-experiment training. Modern synchrotron-based
x-ray scattering techniques offer the ability to probe nano- and atomic-scale
structures and order/disorder relationships that critically govern the
properties of advanced technological and environmental materials. Good planning
and a working knowledge of beam lines, in addition to techniques, are keys to
conducting successful SR-XRS measurements. The goal of the school is to provide
this knowledge.
Register at:
https://www-ssrl.slac.stanford.edu/conferences/workshops/srxas2010/
Over 500 abstracts have been submitted and more than 450 delegates from ~30
countries are expected to participate in the upcoming VUVX2010 conference July
11-16. If you wish to attend, please note that the early registration
deadline is May 14. There will be an increased registration fee after that
date. For those who have submitted abstracts, notification of the type and date
of presentation will be sent by May 7 at the latest.
http://www.vuvx2010.ca
John Bozek (SLAC/LCLS) is organizing the Ultrafast Vacuum Ultraviolet & X-ray
Physics Workshop, July 19-21 at SLAC, which is a satellite meeting of VUVX2010.
Invited speakers will present the current state-of-the-art of FELs and
laser-based ultrafast VUV/soft x-ray sources along with key new scientific
discoveries. Participants will be given the opportunity to present their
results in a poster session, with a few contributions selected to give brief
oral presentations at the meeting. The location of the meeting will allow
participants the opportunity to tour the electron and photon beam paths of the
LCLS on July 21. For more information please see the conference web site at:
http://www.vuvx2010.ca/showcontent.aspx?MenuID=672
New X-ray/VUV proposals are due June 1 for beam time starting in fall 2010.
Please note that our current experimental run ends July 26, 2010. We plan to
resume user operations in late November or the beginning of December 2010.
Macromolecular Crystallography proposals are due July 1 for beam time starting
in fall 2010.
In this next call for proposals, the world's research community is invited to
submit scientific proposals for experiments to be carried out ~March-June 2011.
During this period, the AMO, SXR, XPP and CXI instruments will be operational.
We have demonstrated FEL operations over the energy range 540 eV to 10 keV, and
we expect to be able to offer an energy down to 520 eV with the LCLS
fundamental for the Spring 2011 run. Typically, the LCLS delivers about 2 mJ
per pulse in the fundamental. Further, LCLS will deliver photons up to 20 keV
from a second harmonic afterburner but reduced by roughly an order of magnitude
in photon number. The pulse length can be tuned from 70-300 fs. Additionally,
shorter pulses (10-40 fs) with reduced pulse energy are also available. The
maximum repetition rate of the x-ray flashes is expected to be 120 Hz. For more
information, see http://lcls.slac.stanford.edu/Article.aspx?article_id=178
__________________________________________________________________________
SSRL Headlines is published electronically monthly to inform SSRL users,
sponsors and other interested people about happenings at SSRL. SSRL is a
national synchrotron user facility operated by Stanford University for the
U.S. Department of Energy Office of Basic Energy
Sciences. Additional support for
the structural biology program is provided by
the DOE
Office of Biological and Environmental Research, the NIH
National Center for Research Resources and the NIH Institute for General Medical
Sciences. Additional information about
SSRL and its operation and schedules is available from the SSRL WWW
site.
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