| ALS Colloquium:
Birgeneau
on liquid crystal gels
On March 2, the ALS was extremely pleased
and honored that Robert Birgeneau, Chancellor of the University
of California, Berkeley, took time out from his busy schedule
to present the first ALS Colloquium of the year on "Liquid
Crystal Gels: A New and Novel State of Matter." Chancellor
Birgeneau's research involves the use of neutron and x-ray
scattering techniques to probe the phase and phase-transition
behavior of novel states of matter such as one- and two-dimensional
quantum magnets, liquid crystals, physisorbed and chemisorbed
surface monolayers, graphite intercalates, highly disordered
magnets, and lamellar CuO2 superconductors. In
this colloquium, Birgeneau discussed how thermodynamic and
synchrotron studies of liquid crystal gels can elucidate the
fundamental physics of this and other exotic states of matter.
Berkeley Chancellor Robert Birgeneau
presents the first ALS Colloquium of 2006.
Before coming to Berkeley, Birgeneau
served four years as president of the University of Toronto.
He was also Dean of the School of Science at the Massachusetts
Institute of Technology and a Member of Technical Staff at
Bell Laboratories from 1968 to 1975. He is a foreign associate
of the National Academy of Sciences, has received many awards
for teaching and research, and is one of the most cited physicists
in the world for his work on the fundamental properties of
materials. No stranger to the ALS, he chaired a Department
of Energy review committee whose "Birgeneau/Shen Report"
was very critical of the ALS, but which resulted in beneficial
changes that have ultimately led to the emrgence of the ALS
as a model of how a synchrotron facilty should be run.
DNA-binding mechanism
in prokaryotic
partition complex formation
The faithful inheritance of genetic information,
essential for all organisms, requires accurate movement and
positioning of replicated DNA to daughter cells during cell
division. In cells without distinct nuclei (prokaryotes),
this process, called partition or segregation, is mediated
by par systems. The prototype system of prokaryotic
partition is the Escherichia coli P1 plasmid par
system, which consists of a centromere site (parS)
on the plasmid DNA and two proteins, ParA and ParB. The initial
formation of the so-called partition complex between ParB
and the centromere is a critical step in partition. To understand
the DNA-binding mechanism utilized by ParB, Schumacher and
Funnell determined crystal structures of the C-terminal region
of ParB, known as ParB(142-333), bound to centromere sites.
Full
story.
Publication about this research: M.A.
Schumacher and B.E. Funnell, "Structures of ParB bound
to DNA reveal mechanism of partition complex formation,"
Nature 438, 516 (2005).
Contact: Maria Schumacher, maschuma@mdanderson.org
Tuning of the
metal–insulator transition
via alkali adsorption
Turning a material from an insulator
to a metal, or vice versa, by light irradiation, exposure
to electric or magnetic fields, or applying small changes
in temperature, pressure, or doping—such intriguing
control of a material's electronic properties is possible
by exploiting strongly interacting or "correlated"
electrons. Now a team of researchers from the University of
Kiel in Germany and the ALS has found a novel, surprising
way to continuously transform a layered metallic transition-metal
compound, TaS2, into an insulator. Using angle-resolved
photoemission spectroscopy (ARPES), they have demonstrated
that adsorption of an alkali onto this material's surface
gradually makes it more insulating, although in general, alkali
adsorption should lead to more metallic behavior, as alkali
atoms easily give away their loosely bound outermost electron.
Full
story.
Publication about this research: K. Rossnagel,
H. Koh, E. Rotenberg, N.V. Smith, and L. Kipp, "Continuous
tuning of electronic correlations by alkali adsorption on
layered 1T-TaS2," Phys. Rev. Lett. 95,
126403 (2005).
Contact: Kai Rossnagel, rossnagel@physik.uni-kiel.de
Long-range validity
of threshold laws
in inner-shell photodetachment
A threshold law describes the dependence of a reaction yield
near a reaction threshold. It is also a signature of the physical
forces involved in the reaction, so the agreement of an observed
threshold behavior with a threshold law or a departure from
it can be a sensitive probe into how well the reaction physics
is understood. A collaboration from Western Michigan University,
the ALS, and Denison University has now shown that the threshold
laws for inner-shell photodetachment of negative ions are
not only obeyed but can extend over a much wider energy range
than theory had predicted. Full
story.
Publications about this research: R.C. Bilodeau, J.D. Bozek,
N.D. Gibson, C.W. Walter, G.D. Ackerman, I. Dumitriu, and
N. Berrah, "Inner-shell photodetachment thresholds: Unexpected
long-range validity of the Wigner law," Phys. Rev.
Lett. 95, 083001 (2005); R.C. Bilodeau,
N.D. Gibson, J.D. Bozek, C.W. Walter, G.D. Ackerman, P. Andersson,
J.G. Heredia, M. Perri, and N. Berrah, "High-charge-state
formation following inner-shell photodetachment from S–,"
Phys. Rev A 72, 050701(R) (2005);
R.C. Bilodeau, J.D. Bozek, G.D. Ackerman, A. Aguilar, and
N. Berrah, "Photodetachment of He– near
the 1s threshold: Absolute cross-section measurements and
postcollision interactions," Phys. Rev. A 73,
034701 (2006).
Berkeley Lab
Division Review
of ALS held this month
On March 8–9, the ALS underwent
a Berkeley Lab division review conducted by a panel of experts
from industry, academia, and other national laboratories.
Such periodic reviews of scientific programs, management,
and strategic direction are required of all Berkeley Lab divisions,
and this was the fourth such review of the ALS since it became
a stand-alone laboratory division in 1997. John Hemminger
(Univ. of California, Irvine) chaired the review committee.
Other committee members were Juan-Carlos Campuzano (Univ.
of Illinois), Hans Coufal (IBM-Almaden Research Center), Gabrielle
Long (Argonne National Laboratory), Peter Moore (Yale Univ.),
and James Murphy (Brookhaven National Laboratory).
Berkeley Lab Director Steve Chu and Deputy
Director Graham Fleming welcomed the committee members in
a closed session at the start of the first day. Acting ALS
Director Janos Kirz then began with an overview of division
developments, including positive budget news and progress
toward finding a new director. ALS Deputy Director Ben Feinberg
then briefed the panel on recent safety issues and on the
division's proactive response. David Robin (Division Deputy
for Operations and Accelerator Development) followed with
an update on the transition to top-off mode and other facility
upgrades. ALS Scientific Director Neville Smith gave an overview
of exciting scientific developments, followed by more detailed
scientific highlights presented by Craig Taatjes (Sandia National
Laboratories) on flame chemistry and Z.X. Shen (Stanford Univ.)
on strongly correlated materials. Steve Kevan (Univ. of Oregon)
and Eli Rotenberg (Scientific Support Group) addressed strategic
plans for Sector 7—coherent scattering/microscopy (COSMIC)
and nanoARPES (MAESTRO), respectively. David Attwood reported
on activities at the Center for X-Ray Optics, and Paul Adams
reported on macromolecular crystallography programs. The agenda
also included ample time for one-on-one discussions with user
representatives, poster presentations on the experiment floor,
and question-and-answer sessions with ALS management.
Contact: Neville Smith, NVSmith@lbl.gov
UEC Corner: Notes
from the Users'
Executive Committee
by Clemens Heske
 Dear
ALS users: The past few weeks have been busy for the UEC—among
other things, we have met with the ALS management and the
ALS Division Review Committee, worked on the procedure for
unscheduled shutdowns, helped to optimize the upcoming beam-time
schedule, prepared activities to educate public figures about
the importance of the research conducted at the ALS and other
synchrotron and neutron sources, prepared a revised version
of the ALS User Association Charter, and continued with the
preparation of the ALS Users' Meeting in October. For all
these activities, it is important to have as much input from
ALS users as possible. Please, let any member of the UEC know
of concerns, issues, or joyous occasions that are associated
with your activities at the ALS.
As a reminder: the 2006 ALS Users' Meeting
will be held October 9–11, 2006, at Berkeley Lab. We
are currently soliciting suggestions for workshop topics—they
could include areas of current activity at the ALS, fields
that will be "hot" a few years down the road, etc.
Workshops on areas of mutual interest can also be conducted
jointly with the Stanford Synchrotron Radiation Laboratory's
Users' Meeting. Please send suggestions for workshop topics
to Elke Arenholz (EArenholz@lbl.gov)
and Hendrik Ohldag (HOhldag@lbl.gov)
and indicate whether you would be interested in organizing
the workshop. Thank you for your help—the ALS UEC is
looking forward to a productive Users' Meeting in October!
Contact: Clemens Heske, heske@unlv.nevada.edu
Office space
at a premium during
replacement of Bldg. 10
 Last
month Acting ALS Director Janos Kirz shared the exciting news
that we have received funding to begin planning for the demolition
of Building 10 in anticipation of the subsequent construction
of a new User Support Building. We are now dealing with the
realities associated with this exciting news and are making
plans to relocate the occupants and functions of Building
10 to other areas for the duration of the project.
Owing to the already tight space constraints
around the ALS complex, space will become ever more valuable,
and we will have less space available to assign to guests
and students. We ask for your patience and understanding in
regards to the availability of office space until the completion
of the User Support Building.
Contact: Steve Rossi, SLRossi@lbl.gov |
