PHYSICS NEWS UPDATE -- Number 846 November 12, 2007 by Phillip F. Schewe

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 846 November 12, 2007 by Phillip F. Schewe
www.aip.org/pnu

THE HIGHEST-ENERGY COSMIC RAYS probably come from the cores of active
galactic nuclei (AGN), where super massive black holes are thought to
supply vast energy for flinging the rays across the cosmos. This is
the conclusion reached by scientists who operate the Pierre Auger
Observatory in Argentina. This gigantic array of detectors spread
across 3000 sq. km of terrain, looks for one thing: cosmic ray
showers. These arise when extremely energetic particles strike our
atmosphere, spawning a gush of secondary particles. Many of the rays
come from inside our own Milky Way, especially from our sun, but many
others come from far away. Of most interest are the highest-energy
showers, with energies above 10^19 electron volts, far higher than any
particle energy that can be produced in terrestrial accelerators. The
origin of such potent physical artifacts offers physicists a tool for
studying the most violent events in the universe. To arrive at Earth
most cosmic rays will have crossed a great deal of intergalactic space,
where magnetic fields can deflect them from their starting
trajectories. But for the highest-energy rays, the magnetic fields
can*t exert as much influence, and consequently the starting point for
the cosmic rays can be traced with some confidence. This allowed the
Auger scientists to assert that the premier cosmic rays were not coming
uniformly from all directions but rather preferentially from galaxies
with active cores, where the engine for particle acceleration was
probably black holes of enormous size. The very largest of cosmic ray
showers, those with an energy higher than 57 EeV (1EeV equals 10^18
eV), correlated pretty well with known AGN*s. (Science, 9 November
2007)

BREATHING EXERCISES FOR ENZYMES. A new model of proteins seeks to
explain how enzymes extract energy form their vicinity and put it to
use in regulating cell chemistry. Enzymes are huge protein molecules
that play a crucial role in catalyzing chemical reactions among other
molecules or atoms by lowering the energy barrier that would otherwise
keep the reaction from happening. Enzymes can therefore be considered
as energy-processing chemical-reaction-facilitating machines. They are
usually large, typically containing thousands of heavy (non-hydrogen)
atoms, but of these only a few dozen atoms actually participate in the
catalytic process. Addressing this important issue, a team of
scientists at the Ecole Normale Superieure (Lyon, France) and the Ecole
Polytechnique Federale de Lausanne (Switzerland) have concentrated on
modeling the behavior of the stiff parts of the enzyme since they
believe that some of the energy used in carrying out the catalytic task
is stored not just as chemical energy (in the form of adenosine
triphosphate, or ATP, the all-purpose *food* of cells) but also as
mechanical energy in the form of a waggling or *breathing* motion in
the stiffer parts of the enzyme. Extending this research to proteins
in general, Yves-Henri Sanejouand (yves-henri.sanejouand@xxxxxxxxxxx,
33-04-72-72-8870) says that he and his colleagues would like to
scrutinize in more detail the nonlinear process by which some proteins
catch and store thermal energy from their environment and also how
chemical energy can be turned into mechanical energy, such as in muscle
contraction. (Juanico et al., Physical Review Letters, upcoming
article;)

DIGITAL DROPLET SORTING. A new microfluidic lab-on-a-chip setup forms
tiny droplets, passes them through a pair of electrodes which can
perform an identification of the droplets, passes them through a second
pair which gives them a charge, and then through a third pair which
sorts the drops according to their properties. Basically the charge
imparted to the droplet is proportional to the droplet size, and the
charge is gauged by the effect it has when passing through the first
set of capacitor electrodes. Scientists at the Hong Kong University of
Science and Technology form a supply of drops moving in a microchannel
by having the fluid of interest (in one channel) merge with a running
rivulet of oil (silicon or sunflower oil) in a second channel (see the
figure at http://www.aip.org/png/2007/290.htm). By regulating the flow
rate of the fluid and the oil, droplets of many sizes and rates can be
formed. The Hong Kong Scientists currently can look at droplets
smaller than a pico-liter (10^-12 liter) in size with a capacitive
sensitivity of a pico-Farad (10^-12 F). The detection rate right now
is about 10,000 drops per second, which is already pretty high.
According to one of the researchers, Weijia Wen (phwen@xxxxxx), this
capacitance-based detection rate is better than that can be
accomplished with optical means (such as with a CCD camera), and the
capacitance method is intrinsically cheaper than the optical
equivalent. In the Hong Kong approach the detection and the sorting
are both performed electrostatically: sorting happens when an electric
field sends the higher-charged drops into one channel, and the
lesser-charged drops into another channel. In this way nano- or
micro-particles can be sorted digitally. The goal is to furnish a
useful digitally-controlled bio-chemical chip for performing various
experiments with nano-liter volumes of reactants or biological
samples. (Niu et al., Biomicrofluidics, Oct-Dec 2007; lab website at
www.phys.ust.hk/phwen)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
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Physics News Update appears approximately once a week.
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