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In this issue:
The Shape of Things to Come
Science Today: The Many Sides of Cells
Scheduled Computing Outages: When and Why?

SLAC Today

Thursday - July 26, 2007

George Doucas of Oxford University checks on the array of cylindrical detectors that measure the shape of electron bunches produced for the End Station A test beam.

The Shape of Things to Come

When you pack 16 billion electrons into a space smaller than the head of pin, things get crowded in unpredictable ways.

Within a 300-micron-long footprint, the shape of an electron bunch can vary tremendously, and has a big effect on the collision of particles. For example, the electrons—and their negative charge—might congregate at one end of the bunch, or they might scatter evenly throughout, or they might clump together to make randomly placed peaks and valleys.

At the proposed International Linear Collider, researchers will need to know the shape of the bunch to calculate how much it was deflected just before striking an oncoming bunch of positrons. Instrumentation to measure bunch shape is being developed by a group from Oxford University and was tested again earlier this month at the test beam in End Station A.  Read more...

(Daily Column - Science Today)

The Many Sides of Cells

(Image - Sro7p protein)
Structure of the Sro7p protein involved in cellular polarization.

The mechanics of a basic cellular process found in most living organisms, including humans, is less of a mystery, thanks to work done in part by Douglas Hattendorf at the Stanford Synchrotron Radiation Laboratory (SSRL). The team of researchers, led by Bill Weis of the Stanford University School of Medicine, solved the structure of a protein that assists in the developmental process of cellular polarization, which gives cells the ability to perform specific biological functions. 

Polarization occurs in most living cells, and is a feature whereby different sides of individual cells are made up of membranes of differing composition that perform different functions. Epithelial cells in the lining of the gut, for example, possess membranes that absorb nutrients on one side and membranes that connect to other cells on the other side. Special surface proteins determine the composition and function of these differing membranes. The current study sheds light on how these surface proteins find their way to the proper membrane of a cell.

Within a cell, pockets called vesicles deliver proteins to the various surface membranes, fusing with the membrane to deliver its cargo. The mechanism behind how vesicles discriminate between the membranes—fusing with some but not with others—has been mostly a mystery. Read more...

Scheduled Computing Outages: When
and Why?

Keeping SLAC's Windows servers current with the latest software updates comes with a small price: once a month the servers must be shut down for a few hours while the latest security packages, service packs, and hotfixes are installed. The scheduled outages, the Wednesday following the third Tuesday each month, coincide with regular releases of Microsoft updates.

"After Microsoft tests their updates and releases them to their customers, we do our own extensive testing," said Jean-Raymond Pierre, Windows Infrastructure Manager for SLAC's Scientific Computing and Computing Services (SCCS). "We make every effort to minimize any problems these updates could have on the lab."

On the second Tuesday of every month, known as "patch Tuesday," Microsoft publicly releases security updates that have undergone extensive internal testing. These updates are installed on a small number of Windows systems at SLAC within 24 hours to look for any adverse effects.

At the same time, desktop updates are released with an installation deadline of Tuesday at 3:00 AM. If users wish to avoid having their systems reboot automatically at that time, they may install the updates at their convenience by double clicking the update icon in the lower right corner of their screen. Any system that has not been patched by the deadline will immediately be updated and rebooted.

The following Wednesday evening, beginning at 6:00 PM, the SCCS group installs updates on the Windows servers, thereby completing the patch cycle. Read more...

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