Picosecond
magnetization
dynamics
by Art Robinson
The data rate in modern disk drives will
soon surpass 1 GHz. Subnanosecond magnetic-field pulses like
those of a write head initiate magnetization precession, a
gyroscopic motion of the magnetization around an applied field
(like a wobbling top). An ALS–Stanford–Berlin
group has used a new time-resolved x-ray photoemission imaging
technique to resolve the motion of magnetic vortices, peculiar
magnetic structures that appear in micron-size magnetic patterns,
in response to an excitation field pulse. Analysis of the
observed gyrating trajectory of the core on such short time
scales suggests the precession is induced by a handedness
or chirality in the magnetization pattern, thereby demonstrating
that handedness plays an important role in the dynamics of
microscopic magnets. Full
story.
Publication about this research: S.-B.
Choe, Y. Acremann, A. Scholl, A. Bauer, A. Doran, J. Stöhr,
and H.A. Padmore, "Vortex-driven magnetization dynamics,"
Science 304, 420 (2004).
Contact: Andreas Scholl, A_Scholl@lbl.gov
Spin-resolved
photoelectron
spectroscopy
by Giorgio Turri
Inner-shell electrons, localized on a
single atom, are sensitive site-specific probes of the molecular
environment, unlike valence electrons, which can be delocalized
over the whole molecule. Binding energies of inner-shell electrons
for an atom vary depending on the electron density around
that atom modified by the electron-donating and -withdrawing
properties of the surrounding atoms. Furthermore, the molecule's
geometry can remove the degeneracy of inner-shell electrons,
separating them depending on the orientation of their orbitals
within the molecule. Such phenomena do not occur in atoms,
and hence the investigation of inner-shell photoionization
in molecules is considerably more complex. At ALS Beamline
10.0.1, a group of scientists has, for the first time, used
spin-resolved photoelectron spectroscopy to study molecular
effects on the inner-shell electrons of two simple sulfur-containing
molecules, carbonyl sulfide and hydrogen sulfide. The authors
show that this technique is very sensitive to molecular environment
in the selected cases by comparing with previous atomic results.
Full
story.
Publication about this research: G. Turri,
G. Snell, B. Langer, M. Martins, E. Kukk, S.E. Canton, R.C.
Bilodeau, N. Cherepkov, J.D. Bozek, A.L. Kilcoyne, and N.
Berrah, "Probing the molecular environment using spin-resolved
photoelectron spectroscopy," Phys. Rev. Lett.
92, 013001 (2004).
Contact: Nora Berrah, berrah@wmich.edu
Nerve growth
factor
gets good reception
by Bruce Balfour
In a breakthrough that can now be directly
applied to drug design for treating neurodegenerative conditions
such as Alzheimer's disease or spinal cord injuries, researchers
from Stanford University have discovered a critical step in
the mechanism for reproducing nerve growth factor (NGF). One
of the most important molecules in the nervous system, nerve
growth factor and its other neurotrophin family members control
the development of the nervous system in the embryo and the
maintenance of nervous tissue and neural transmission in the
adult. The researchers used the ALS to obtain the three-dimensional
x-ray crystallography structure of a complex of NGF bound
to a p75 cell surface receptor, demonstrating the mechanism
for receptor activation that has eluded the drug companies
for many years. Full
story.
Publication about this research: X. He
and K.C. Garcia, "Structure of Nerve Growth Factor Complexed
with the Shared Neurotrophin Receptor p75," Science
304, 870 (2004).
Contact: K. Christopher Garcia, kcgarcia@stanford.edu
Users' Meeting:
Record crowd puts
bright face on stormy weather
by Art Robinson
 It's
not exactly Russian roulette, but scheduling October events
outdoors is not risk-free, even in usually sunny California.
An overflow crowd of more than 400 registered users, ALS staff,
and vendors enjoyed a full indoor program featuring science
highlights and workshops spread over two and a half days starting
October 18. However, a major storm, heralding the onset of
the San Francisco Bay Area rainy season, posed a few weather
challenges for the events on the ALS patio, including a flooded
exhibit tent that necessitated an early exit by the 28 vendors
(a record number) present on Tuesday morning.
Users' Executive Committee chair Dennis
Lindle (Univ. of Nevada, Las Vegas) started the meeting off
with a warm welcome to new Berkeley Lab Director Stephen Chu.
Coming from a laser-based science background, Chu confessed
he was not yet intimately familiar with the ALS but was already
hearing that it is one of the best facilities for users to
do great science. Acting ALS Director Janos Kirz followed
Chu by introducing a surprise guest: Daniel Chemla, who is
on extended medical leave from his normal duties as ALS Director
while recovering from major surgery.
Janos continued with an overview of the
ALS, starting with a nod of appreciation to division deputies
Ben Feinberg, Neville Smith, and Jim Krupnick for keeping
the facility on track in  Daniel's
absence and bringing him up to speed soon after his June arrival
at the ALS. He emphasized the need for continuous attention
to safety in the face of the continuing rapid growth in the
user count, summarized several accelerator improvements and
new beamlines, and took a look at the future. Coming up in
Feburary 2005 is a major Department of Energy (DOE) review
of the ALS, which will also include a presentation of the
new ALS strategic plan now being constructed based on an upgrade
to higher brightness by means of top-off operation, advanced
insertion devices, and specialized beamlines. Janos' talk
is available online in PowerPoint
(21 MB) or PDF
(36 MB) formats.
ALS operation is funded by the DOE Office
of Basic Energy Sciences (BES), so the annual "View from
Washington" by DOE Associate Director for BES, Pat Dehmer,
is always eagerly anticipated. Like Janos, she emphasized
the seriousness of safety, calling attention to recent stand
downs at other labs that resulted from laser and electrical
mishaps and pointedly noted that the same could happen at
the ALS. Regarding the budget outlook, fiscal year 2005 is
uncertain, as Congress has not finished its actions, and after
that there is likely to be pressure on the budget.
In other Monday morning presentations,
Uwe Arp (NIST) described lightsources.org,
a Web site to be launched in early 2005 that will be a one-stop-shopping
venue for a broad audience for news and information about
light sources. Michael Lubell (Director of Public Affairs,
American Physical Society) spoke of the need to emphasize
what science can do for the country in order to preserve support
for science in the coming budget climate. And Dennis Lindle
conducted a town hall meeting on the strategic planning process
that has been under way at the ALS. Monday afternoon sessions
were devoted to new science at the ALS and Tuesday was dedicated
to a set of 10 workshops. Consult the Users'
Meeting Web site for details.
Franz Himpsel addresses attendees
of
the "Nanoscience at Synchrotrons" workshop.
By Tuesday evening, the elements were
calmed sufficiently for everyone to enjoy a well-prepared
BBQ dinner under an open-air tent on the ALS patio. After
dinner, user meeting program co-chair Corie Ralston (Berkeley
Lab Physical Biosciences Division) hosted the user award session.
Mandana Veiseh (Univ. of Washington) won the student poster
award for her poster titled "Direct Bacterial Detection
by Single-Cell-Based Sensors and Synchrotron FTIR Spectromicroscopy."
James Holton (Physical Biosciences Division) took home the
Tim Renner User Service Award for "friendly and tireless
support of users and for implementation of his ELVES program
that optimizes the usage of beamtime." Klaus Halbach's
widow Ruth presented the Klaus Halbach Award for Innovative
Instrumentation at the ALS to Frank Ogletree (Materials Sciences
Division), Hendrik Bluhm (Chemical Sciences Division), Zahid
Hussain (ALS), and Miquel Salmeron (Materials Sciences Division)
for "the development of a photoelectron spectrometer
that operates in ambient gas pressures of up to tens of Torr."
And the David A. Shirley Award for Outstanding Scientific
Achievement at the ALS went to Andrea Cavalleri (Materials
Sciences Division) for "pioneering ultrafast x-ray experiments
on the metal-insulator transition."
Award winners line up for photos with
program co-chairs
Corie Ralston (4th from left) and Keith Jackson (far right).
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