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In this issue:
Faster than a Speeding Bubble
The Search for Dark Matter in the form of WIMPs and the CDMS Experiments
SLAC to Experience Computing Outage
Performance Evaluation Training Sessions

SLAC Today

Monday - April 21, 2008

X-ray scattering images (above) and corresponding 3D depictions (below) of nucleation events, or "bubbles," forming in the semiconductor Indium Antimonide in the first instances after being hit with a laser pulse.

Faster than a Speeding Bubble

What do melting chocolate and bubbles in a champagne glass have in common? Besides being treats one might sample at a sophisticated soiree, they are both handy examples of first-order phase transitions in which a material transforms from one phase to another—that is, atoms changing from an orderly arrangement into a more chaotic arrangement.

Now, in an experiment led by Aaron Lindenberg, an international collaboration of scientists has uncovered new clues about the first instants of that process. The results are published in the April 4 edition of Physical Review Letters.

"We did not at all expect to see what we saw," said Lindenberg, "although in the aftermath we can go back and realize perhaps we should have. What's amazing about the process is that it spans such a huge range of time scales."

The process of melting, or in the case of champagne, of bubbling, has long been of interest to scientists. Phase transitions take place in the tiniest fraction of a second. In the case of Indium Antimonide (InSb), a semiconductor used by scientists to study such processes, the first steps in melting take a few hundred femtoseconds, a quadrillionth of a second. But no one knew what happened after that.  Read more...

Colloquium Monday

The Search for Dark Matter in the form of WIMPs and the CDMS Experiments

Observations of galaxies, superclusters, distant supernovae, and the cosmic microwave background radiation, tell us that about 85% of the matter in the universe is not made of ordinary atoms. Deciphering the nature of this dark matter is of central importance for cosmology, astrophysics, and high-energy particle physics. A leading hypothesis is that this dark matter is comprised of Weakly Interacting Massive Particles, (WIMPs), that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our Milky Way may be detectable via scattering from atomic nuclei in a terrestrial detector. The lightest supersymmetric particle (LSP) is an excellent WIMP candidate and is within reach for many models of supersymmetry for both the LHC and direct detection experiments over the next five years, providing a deep complementarity.

In this afternoon's colloquium, Stanford's Blas Cabrera will discuss the Cryogenic Dark Matter Search (CDMS) Collaboration, which has pioneered the use of low temperature phonon-mediated detectors to detect the rare scattering of WIMPs on nuclei and distinguish them from backgrounds. Cabrera will describe this powerful technology, which is operating deep underground in the Soudan mine in Minnesota, and compare this approach with new noble liquid techniques that have made recent advances. CDMS II is at the sensitivity frontier for WIMP searches, and its reach is projected to grow by a factor of three by the end of 2008. Cabrera will also describe the new SuperCDMS 25 kilogram experiment, which is partially approved and which will increase sensitivity by an additional factor of 15 by the end of 2012.

The colloquium takes place at 4:15 p.m. in Panofsky Auditorium. All are invited to attend.

Learn more...

SLAC to Experience Computing Outage:
April 26 and 27

Nearly all central computer services at SLAC will be shut down over the weekend of April 26-27, as part of Scientific Computing and Computing Services' (SCCS) efforts to make the computer center more earthquake-ready and to provide new power sources for future expansion.

The shutdown will begin at 5:00 p.m. Friday, with all services restored by 7:00 a.m. Monday.

Although nearly all central computer services will be down, a few systems will have limited service through the weekend, said SCCS Assistant Director Chuck Boeheim. Office computers will maintain internet connectivity, and Microsoft Exchange e-mail services (including Microsoft Outlook and imap) will be available for most of the weekend. Unix e-mail will be down throughout the weekend, however. Outside visitors to the SLAC web will receive a webpage notifying them of the expected duration of the outage.

Turning off your workstation before leaving on Friday will minimize problems. If residual difficulties occur Monday morning, SCCS recommends rebooting the workstation before reporting problems.

The outage will allow SCCS to install new power distribution units on the second-floor of Building 50 in preparation for moving many of the servers to new seismically sound flooring. The project is part of ongoing earthquake upgrades in the Computing Building.

Performance Evaluation Training Sessions

This time of year, managers and supervisors are preparing performance evaluations for their direct reports. Reviews for the period May 1, 2007 – April 30, 2008 are due to Human Resources (Attention Claudia Ransom, MS 11) by May 31, 2008 for non-bargaining unit employees and June 30, 2008 for bargaining unit employees.

The Training and Development Office will hold three training sessions on the performance evaluation process and will assist supervisors with any questions.

Supervisors are encouraged to attend one of the following training sessions:

Tuesday, April 22
   9:00 a.m. – 11:00 a.m.
   Building 40, Orange Room
Wednesday, April 23
   1:00 p.m. – 3:00 p.m.
   Building 48 (ROB),
   Redwood Room
Monday, April 28
   10:00 a.m. – noon
   Building 40, Orange Room

In the meantime, if anyone needs help with performance evaluations, please contact Carmella Huser at x2358 or Barry Webb at x2355.


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