PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 637 May 14, 2003   by Phillip F. Schewe, Ben Stein, and James Riordon

PLASMA WAKEFIELDS ACCELERATE POSITRONS.  An experiment conducted at SLAC
features a number of firsts: the first time positrons
have been accelerated by the plasma wakefield method (for background, see
http://www.aip.org/enews/physnews/1998/split/pnu385-2
.htm ); the first time wakefield acceleration has been achieved with
meter-size plasmas (previous efforts have taken place in 1
0 cm cells); and the first to operate under realistic accelerator
conditions (in this case a 30-GeV beam of positrons).  In thi
s UCLA/SLAC/USC collaboration, positron bursts are sent into a
1.4-meter-long chamber filled with a lithium plasma.  The first
two-thirds of the burst sets up powerful electric fields in the plasma
which then serve to accelerate the trailing one-third of
 the b
urst to higher energy.  The boosted positrons increased their energy by
about 80 MeV over a length of 1.4 m, for an acceleratio
n gradient of about 50 MeV/m.  This is comparable to the best acceleration
that can be accomplished with conventional RF techni
ques in which electrons or positrons are taken up to higher energies by
soaking up radio energy coupled  into the beam pipe.  B
ut the wakefield researchers expect that the gradient can be enhanced a
hundredfold to 5 GeV/m if the size of the beam pulses c
an be shrunk by a factor of 10.  According to Chan Joshi of UCLA  (contact
Chan Joshi, joshi{at}ee.ucla.edu, 310-825-7279) the wak
efield approach may not be fully mature by the time the next
electron-positron collider is built, but its benefit could be test
ed by
 installing two plasma accelerator sections, one for positrons and one for
electrons, just before the interaction point for som
e final energy boosting in an existing collider.  (Blue et al., Physical
Review Letters, upcoming article)

TURNING BUBBLES INTO MICROSCOPIC SYRINGES through the use of sound has been
experimentally shown by researchers in the Netherla
nds (Claus-Dieter Ohl, University of Twente, 011-31-53-489-5604.
c.d.ohl{at}tn.utwente.nl), demonstrating a potential method for i
njecting drugs and genes into specific regions of a patient's body.  Taking
high-speed microscopic photographs, the researchers
 revealed that even bubbles much smaller than the thickness of a human hair
could transform into a needle-like tube, delivering
 a billionth of a millionth of a gallon of liquid.  While this
sub-nanofluidic volume seems very small, it is more than enough
to transfer large molecules (such as DNA and most drugs) into desired cells
for medical therapy.
In their experiment, the researchers start with a room-temperature
container of water that was slightly "degassed," or had some
 oxygen gas removed from it.  Inside the water container, they create tiny
bubbles between 7 and 55 microns in size.  Next, the
y broadcast high-intensity ultrasound into the liquid, creating supersonic
disturbances known as shock waves.  Slamming against
 the microscopic bubbles and squeezing them into needle-like shapes, the
shock waves also introduce small amounts of surroundin
g liquid into the bubble. The liquid shoots through the bubble at very high
speed, punctures its opposite end, and continues ou
tside as a high-speed stream of fluid resembling a syringe.  Based on the
speed of the flow, the researchers expect that this l
iquid
 stream could easily penetrate a nearby cell membrane.  Dissolved drugs or
genetic material surrounding specially designed micr
obubbles could therefore be injected into targeted cells. Long suspected
but now confirmed, the acoustically driven metamorphos
is of bubbles into micro-syringes could someday become a useful medical
tool.  (Ohl and Ikink, Physical Review Letters, upcomin
g).
While this work aims to inject material deeply into living cells, other
U-Twente researchers have just introduced a new acousti
c method for manipulating cells: they devised a "sonoporation"
technique which uses gently oscillating bubbles attached to a su
rface to deform or even puncture cell membranes (Marmottant and
Hilgenfeldt, Nature, 8 May 2003).

FIRST-YEAR PHYSICS GRADUATE STUDENTS are on the rise at US universities, a
new AIP study shows.  The number of first-year physi
cs/astronomy students for the year 2000 (2697) was some 5% higher than the
recent low in 1997.  (In still more recent numbers f
or 2002, about to be published, the number of first year grad students is
some 15% higher than in 1997.)  In the 1999/2000 begi
nning-grad cohort, foreign students (52%) outnumber US students (48%). 
Chinese students (25%) make up the largest single inter
national component, with Eastern European students accounting for 22%, up
from about 5% in the early 1980s.  Women constitute 1
9% of the 1999/2000 first-year physics grad students and 29% in astronomy. 
Age is a factor: about 64% of the foreign students
were 2
4 or older when they began physics grad school, whereas the number for US
students is 41%.  What kind of employment do these st
udents hope for?  A majority indicated their long-term desire was an
academic job.  ("Graduate Student Report: First-Year Stude
nts in 1999 and 2000," prepared by the Statistical Research Center,
AIP; www.aip.org/statistics, contact Patrick J. Mulvey, 301
-209-3070.)

***********
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