Text 769, 85 rader
Skriven 2006-03-30 19:25:24 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 771
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PHYSICS NEWS UPDATE
                                        
The American Institute of Physics Bulletin of Physics News
Number 771   March 29, 2006  by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi
        
BLACK HOLE MERGER MOVIE.  Accurate calculations of the gravitational
waveforms emitted during the collision of black holes can now be
made.  A new computer study of how a pair of black holes, circling
each other, disturbs the surrounding space and sends huge gusts of
gravitational waves outwards, should greatly benefit the
experimental search for those waves with detectors like LIGO and
LISA.  The relative difficulty of computer modeling of complicated
physical behavior depends partly on the system in question and on
the equations that describe the forces at work.  To describe the
complicated configuration of charges and currents, one uses
Maxwell's equations to determine the forces at work.  In the case of
black-hole binaries, the equations are those from Albert Einstein's
theory of general relativity.  Black holes encapsulate the ultimate
in gravitational forces, and this presents difficulties for
computations attempting to model behavior nearby.  Nevertheless,
some physicists at the University of Texas at Brownsville have now
derived an algorithm that not only produces accurate estimates of
the gravity waves of the inspiraling black holes, even over the
short time intervals leading up to the final merger, but also is
easily implemented on computers (see figures and movie at
www.aip.org/png/2006/256.htm ).  "The importance of this work,"
says Carlos Lousto, one of the authors of the new study, "is that it
gives an accurate prediction to the gravitational wave
observatories, such as LIGO, of what they are going to observe."
The new results are part of a larger study of numerical relativity
carried out at the University of Texas, work referred to as the
Lazarus Project
(http://www.phys.utb.edu/numrel/research_dir/lazarus.html ).
(Campanelli, Lousto, Marronetti, and Zlochower; Physical Review
Letters, 24 March 2006; contact information, lousto@phys.utb.edu,
956-882-6651)

A SUBMERSIBLE HOLOGRAPHIC MICROSCOPE.    A new device allows
scientists to form 3D images of tiny marine organisms at depths as
great as 100 m. The device allows the recording of behavioral
characteristics of zooplankton and other marine organisms in their
natural environment without having to bring specimens  to the
surface for examination. Scientists at Dalhousie University in
Halifax, Canada, used the hologram arrangement originally invented
by Denis Gabor: light from a laser is focused on a pinhole that acts
as a point source of light if the size of the hole is comparable to
the wavelength of light. The spherical waves that emanate from the
pinhole illuminate a sample of sea water.  Waves scattered by
objects in the sea water then combine at the chip of a CCD camera
with un-scattered waves (the reference wave) from the pin hole to
form a digitized  interference pattern or hologram. The digital
holograms are then sent to a computer where they are digitally
reconstructed with specially developed software to provide images of
the objects. The Dalhousie researchers packaged their holography
apparatus in such a way that the laser and digital camera parts are
in separate watertight containers, while the object plane is left
open (see figure at http://www.aip.org/png/2006/255.htm ). One
difficulty was to get container windows of optical quality that are
thin enough for high resolution imaging but thick enough to resist
sea pressure. The new submersible microscope can also record the
trajectories of organisms in the sample volume so that movies of the
swimming characteristics of micron size marine organisms can easily
be produced.  Holograms with1024 x 1024 pixels can be recorded at 7
to 10 frames/s. This requires a large bandwidth for data
transmission to a surface vessel and was accomplished with water
tight Ethernet cables. Imaging volumes can be several cubic
centimeters depending on the desired resolution. The Gabor geometry
allowed the Dalhousie researchers to design a very simple instrument
capable of wavelength limited resolution of marine organisms in
their natural environment. Past generations of submersible
holographic microscopes  had lower resolution, weighed several tons,
had to be deployed from large ships, and used high-resolution film
as the hologram recording medium. This meant that only a small
number of holograms could be recorded. In contrast, the Dalhousie
instrument only weighs 20 kg, can be deployed from small boats or
even pleasure vessels, and can record thousands of holograms in a
few minutes so that the motion of aquatic organisms can be captured
in detail.  (Jericho et al., Review of Scientific Instruments,
upcoming article; contact M.H. Jericho, Dalhousie University,
jericho@fizz.phys.dal.ca, and also the Universidad Nacional de
Columbia)

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 * Origin: Big Bang (1:106/2000.7)