Latest PhysicsWeb Summaries

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Veneto Nanotech Launches the 2nd Edition of Nanochallenge Enter your
nanotechnology business plan to Nanochallenge 2006 and you could win the
grand prize of Euro 300,000. The competition seeks commercially viable
business plans for innovative start-ups to produce and commercialize
products and services in the nanotechnology industry. Find out more at
http://www.nanochallenge.com/nc/files/index.cfm?id_rst=259

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News

General relativity reveals its secrets (Apr 19)
http://physicsweb.org/article/news/10/4/8
Einstein's general theory of relativity might be over 90 years old, but
it is only recently that many of its implications can be explored thanks
to advances in computing power. This is because its complex nonlinear
equations -- which describe how space--time is curved by matter and
therefore how matter moves in a gravitational field -- cannot be solved
exactly, even for the simplest situations.

Metals protect Milky Way from gamma-ray bursts (Apr 20)
http://physicsweb.org/article/news/10/4/9
Do you lie awake at night worrying that life on Earth might one day be
destroyed by a blast of gamma radiation from space? Then don't, because
a team of astronomers in the US has calculated that the probability of
such an event occurring in our galaxy is virtually zero. Krzysztof
Stanek and colleagues at Ohio State University say that gamma-ray bursts
-- the most powerful explosions in the universe after the big bang --
only tend to occur in small, misshapen "metal-poor" galaxies. Our Milky
Way is safe since it is a large spiral galaxy that contains lots of
heavy elements (astro-ph/0604113).

Google unearths physics gems (Apr 21)
http://physicsweb.org/article/news/10/4/10
Google could be a good way of measuring the "impact" of a particular
scientific paper and might even be used to replace traditional citation
indices, according to a new statistical analysis by physicists in the
US. The researchers have found that the Google PageRank algorithm, which
measures the relative importance of Web pages, can provide a systematic
way to find important papers. The technique also uncovers scientific
"gems" -- top papers overlooked by conventional searches
(physics/0604130).

PHYSICS NEWS UPDATE

     
The American Institute of Physics Bulletin of Physics News
Number 774  April 19, 2006  by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi
  
INDICATIONS OF A CHANGE IN THE PROTON-TO-ELECTRON MASS RATIO have
shown up in comparisons of the spectra of hydrogen gas as recorded
in a lab with spectra of light coming from hydrogen clouds at the
distance of quasars.  This is another of those tests of so-called
physical constants that might not be absolutely constant.  For
example, the steadiness of the fine structure constant (denoted by
the letter alpha), defined as the square of the electron's charge
divided by the speed of light times Planck's constant, has been in
dispute (http://www.aip.org/pnu/1999/split/pnu410-1.htm ).  Some
tests say it's changing, others say it isn't.  This is an
important
issue since alpha sets the overall strength of the electromagnetic
force, the force that holds atoms together.  Similarly, the
proton-to-electron mass ratio (denoted by the letter mu) figures in
setting the scale of the strong nuclear force.   There is at present
no explanation why the proton's mass should be 1836 times that of
the electron's.  The new search for a varying mu was carried out by
Wim Ubachs of the Vrije Universiteit Amsterdam.  He and his
colleagues approach their task by studying hydrogen gas in the lab,
performing ultra-high-resolution spectroscopy in the
difficult-to-access extreme-ultraviolet range. This data is compared
to accurate observations of absorption spectra of distant hydrogen
(which absorbs light from even more distant quasars) as recorded
with the European Southern Observatory (ESO) in Chile.  The
astronomical hydrogen is essentially hydrogen as it was 12 billion
years ago, so one can seek hints of a changing value for mu.  Why
the comparison?  Because the position of a particular spectral line
depends on the value of mu; locate the spectral line accurately
(that is, its wavelength) and you can infer a value for mu.   In
this way, the researchers report that they see evidence that mu has
decreased by 0.002% over those 12 billion years. According to Ubachs
(wimu@nat.vu.nl, www.nat.vu.nl/~wimu ), the statistical confidence
of his spectroscopic comparison is at the level of 3.5 standard
deviations. (Reinhold et al., Physical Review Letters, 21 April
2006, laser website at www.nat.vu.nl/~laser )

NUCLEAR QUANTUM OPTICS.  Normally the atomic realm, characterized by
an energy scale of electron volts or less, is very much removed from
the nuclear realm, where energy levels are measured in thousands and
millions of eV.  Some laser interactions in nuclei can be achieved
indirectly by using light to create plasmas, whose secondary
particles either interact with nuclei or, in a tertiary step,
produce gamma rays which then influence nuclear states.  Scientists
at the Max-Planck-Institut fur Kernphysik have now studied how
present and future x-ray laser facilities will make possible direct
laser intervention in the nucleus and how this will open up a new
branch of quantum optics.  X-ray sources such as the TESLA device at
the DESY lab in Hamburg will not only deliver high-intensity,
high-energy beams but will, at least partially, consist of coherent
(laserlike) radiation.  One doesn't need coherent light to excite a
nucleus, but coherence can be important in exercising greater
control over optical phenomena analogous to those in atomic
systems.  Examples include exciting a complete population inversion
of the target nuclei or even producing some kind of nuclear
"electromagnetically induced transparency."  One of the
researchers,
Thomas Burvenich (buervenich@fias.uni-frankfurt.de), says that an
additional benefit of nuclear quantum optics will be the direct
measurement of specific nuclear facts, such as nuclear dipole
moments and the energy levels of nuclei.  (Burvenich et al.,
Physical Review Letters, 14 April 2006;  lab website at
http://www.mpi-hd.mpg.de/keitel/evers/  )

Latest PhysicsWeb Summaries

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Veneto Nanotech Launches the 2nd Edition of Nanochallenge Enter your
nanotechnology business plan to Nanochallenge 2006 and you could win the
grand prize of Euro 300,000. The competition seeks commercially viable
business plans for innovative start-ups to produce and commercialize
products and services in the nanotechnology industry. Find out more at
http://www.nanochallenge.com/nc/files/index.cfm?id_rst=259

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News

Physics goes to the movies (Apr 11)
http://physicsweb.org/article/news/10/4/5
The popularity of a particular film largely depends on word-of-mouth
recommendations according to a new study by statistical physicists in
the US and Chile. César Hidalgo of the University of Notre Dame and
colleagues have also developed a quantitative indicator of a film's
quality, which they say could be used by film producers and studios to
estimate the commercial value of a movie (New J. Phys. 8 52).

Fermilab probes matter-antimatter transitions (Apr 12)
http://physicsweb.org/article/news/10/4/6
The international CDF collaboration at Fermilab has made the most
precise measurement to date of the extremely rapid transitions between
matter and antimatter. The experiment has found that certain B mesons
spontaneously turn into their own antiparticle equivalents -- anti-B
mesons -- and back again at a rate of three trillion times per second.
The result agrees well with the Standard Model of particle physics and
confirms yet again the existence of CP violation -- the reason why there
is more matter than antimatter in the universe.

Putting equilibrium on hold (Apr 13)
http://physicsweb.org/article/news/10/4/7
Physicists in the US have made the first gas that never reaches
equilibrium. David Weiss and colleagues at Penn State University
performed their experiment with a one-dimensional Bose gas of ultracold
rubidium atoms. According to the team, the gas behaves like a "quantum
Newton's cradle" -- the atomic equivalent of the popular desk toy that
has five steel balls suspended from strings in a straight line. The work
could help us better understand the behaviour of many-particle systems
and even be used in practical applications like ultrasenstive force
detectors (Nature 440 900).


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PHYSICS NEWS UPDATE

     
The American Institute of Physics Bulletin of Physics News
Number 773  April 12, 2006  by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi
  
SHARPER FOCUSING OF HARD X RAYS has been achieved with a device
developed at Argonne National Lab.  Because of their high energy, x
rays are hard to focus: they can be reflected from a surface but
only at a glancing angle (less than a tenth of a degree); they can
be
refracted but the index of refraction is very close to 1, so that
making efficient lenses becomes a problem; and they can be
diffracted, but the thick, variable pitch grating required for
focusing is tricky to achieve.  The Argonne device is of the
diffraction type, and it consists of a stack of alternating layers
of metal and silicon, made by depositing progressively thicker
layers (see figure at http://www.aip.org/png/2006/258.htm ).  When
the x rays fall on such a structure, nearly edge-on, what they see
is a grating pattern (called a linear zone plate) consisting of a
sort of bar-code pattern. The Argonne device succeeds so well in
focusing x rays because the position of the zones can be controlled
to within nanometer tolerances through the deposition process, and
the depth of the zones that the x rays experience can be made
arbitrarily long---microns long---by merely cutting a thicker
section of the multilayer wafer.  In tests so far, one of these zone
plates, very slightly tilted to the x rays coming out of a
synchrotron source, has focused 20-keV x rays to a line only 30 nm
wide, better than previously possible.  According to Argonne
researcher Brian Stephenson (stephenson@anl.gov, 630-252-3214), an
ideal version of this kind of x-ray lens, which they call a
Multilayer Laue Lens (MLL), should be able to focus x rays to a spot
of 1 nm or less.  The likely uses for a better x-ray lens are in
full-field microscopy (making a magnified x-ray image of a sample)
or in scanning probe microscopy (by scanning the beam across a
sample).  (Kang et al., Physical Review Letters, 31 March 2006)

NANO-EARTHQUAKES: ACOUSTIC WAVES EXCITE ARTIFICIAL MOLECULES.  By
absorbing photons from a laser, an atom can be excited to any of
various discrete energy levels allowed by quantum mechanics.  What
about artificial atoms?  A quantum dot, created by the same
lithographic methods used to prepare electronic chips, is nearly a
zero-dimensional zone of semiconducting material; as with electrons
inside atoms, electrons inside the confinement of a quantum dot will
also possess only a restricted menu of allowed energies.  The same
is true for a pair of quantum dots 200 nm apart; with just the right
voltage applied, electrons can tunnel from one dot to the other.  In
fact, an electron, considered as a spread-out quantum wave
phenomenon, can be considered to reside in both dots at the same
time, a property which makes the quantum-dot "molecule"
potentially
useful for carrying out quantum computing operations.
Now, a group of scientists have been able to probe, and to change,
the quantum energy states of a double quantum dot with sound waves,
or more particularly surface acoustic waves excited in the substrate
supporting the dots.  The acoustic waves, less than1 nm in
amplitude, ripple through the surface for distances as long as
hundreds of microns as a sort of nano-earthquake, are created
through the process of piezoelectricity; a small voltage is sent
into a series of tiny electrodes painted onto the surface.  This
excites the faint acoustic waves (see figure at
http://www.aip.org/png/2006/259.htm ).  The acoustic-dot
arrangement, mediated by the delicate interactions between electrons
and phonons, can work in both directions: the quantum dots can be
used to monitor the acoustic waves (which, because of their tiny
energy, are otherwise difficult to detect) or the acoustic waves can
be used to interrogate the electronic status of the dots, which
makes possible the aforesaid quantum-information applications.  The
researchers involved work at the University of Twente and the Delft
University of Technology (Netherlands), NTT Corporation, Tokyo
Institute of Technology, and University of Tokyo (Japan), and Jilin
University (China).  (Naber et al., Physical Review Letters, April 7
2006; contact Wouter Naber, W.J.M.Naber@utwente.nl) 

Latest PhysicsWeb Summaries

----------------------------------------------------------------------

Veneto Nanotech Launches the 2nd Edition of Nanochallenge Enter your
nanotechnology business plan to Nanochallenge 2006 and you could win the
grand prize of Euro 300,000. The competition seeks commercially viable
business plans for innovative start-ups to produce and commercialize
products and services in the nanotechnology industry. Find out more at
http://www.nanochallenge.com/nc/files/index.cfm?id_rst=259

----------------------------------------------------------------------

News

Solitons show up in uranium (Apr 4)
http://physicsweb.org/article/news/10/4/1
Scientists have observed highly localized solitary vibrations, or
solitons, in a three-dimensional solid for the first time. The solitons
exist in crystals of uranium heated to temperatures of 450K. Although
they were predicted to exist in 3D solids some 20 years ago, conclusive
evidence for them has never been obtained until now (Phys. Rev. Lett. 96
125501).

A new look for bifocals (Apr 5)
http://physicsweb.org/article/news/10/4/2
Do you wear bifocal spectacles and get frustrated at having to move your
gaze between the upper and lower lenses as you switch from far to near
vision? If so, help could soon be at hand thanks to a new lens developed
by optical scientists in the US. It consists of a layer of liquid
crystal sandwiched between two glass surfaces, the focusing power of
which can be changed by altering the voltage applied to the lens.
Although the lens has to be manually switched on and off to change
focus, the researchers say the work could lead to lenses that
automatically adjust their focus depending on where the user is looking
(Proc. Natl. Acad. Sci. to be published).

Spray-on silicon makes its debut (Apr 7)
http://physicsweb.org/article/news/10/4/3
Researchers in Japan have unveiled a new way to make silicon-based
microelectronic devices. The method involves depositing silicon directly
onto a substrate from solution and overcomes some of the problems
associated with traditional silicon-processing lithographic techniques,
such as using sophisticated clean rooms and expensive vacuum equipment.
The researchers say the technique could lead to a way of making large,
flexible displays using "ink-jet" technology (Nature 440 783).

Water drops bounce into action (Apr 7)
http://physicsweb.org/article/news/10/4/4
What happens if you let a drop of water fall gently onto a
water-repelling surface? Physicists in France and the Netherlands who
tried the experiment were surprised by what they saw. They found that a
violent, ultra-fine jet of water emerges from the drop, moving at up to
40 times the drop's initial impact speed. The researchers believe the
unusual behaviour is caused by the collapse of an air cavity that is
created when the drop deforms as it hits the surface. The finding could
have a bearing on industrial applications in which liquids are coated on
to surfaces, such as insecticides being sprayed onto crops or in ink-jet
printing (Phys. Rev. Lett. 96 124501).

Fossil Called Missing Link From Sea to Land Animals - New York Times

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Understanding Evolution
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"Scientists have discovered fossils of a 375-million-year-old fish, a large scaly creature not seen before, that they say is a long-sought missing link in the evolution of some fishes from water to a life walking on four limbs on land.

In two reports today in the journal Nature, a team of scientists led by Neil H. Shubin of the University of Chicago say they have uncovered several well-preserved skeletons of the fossil fish in sediments of former streambeds in the Canadian Arctic, 600 miles from the North Pole.The skeletons have the fins, scales and other attributes of a giant fish, four to nine feet long. But on closer examination, the scientists found telling anatomical traits of a transitional creature, a fish that is still a fish but has changes that anticipate the emergence of land animals — and is thus a predecessor of amphibians, reptiles and dinosaurs, mammals and eventually humans.

In the fishes' forward fins, the scientists found evidence of limbs in the making. There are the beginnings of digits, proto-wrists, elbows and shoulders. The fish also had a flat skull resembling a crocodile's, a neck, ribs and other parts that were similar to four-legged land animals known as tetrapods."

There cna be no argument that this is a transitional fossil - removing one of the arguments used by anti-scientific "creationists." This article, by John Noble Wilford, is a commendable piece of science journalism - rather than trying to "find the other side" of evolution, he presents the evidence that exists. As Larry Krauss has recently stated, there is no other side to evolution.

Read more at www.nytimes.com/2006/04... (free registration required)

Liquid Flowing Uphill to Cool Chips, Entangled Photon Holes, Sunlight from LED

Related Resources
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Elsewhere on the Web
Extensive Visuals and Explanations of Leidenfrost Experiments
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LIQUID FLOWING UPHILL; MIGHT BE USED TO COOL CHIPS. In a phenomenon known as the "Leidenfrost effect," water droplets can perform a dance in which they glide in random directions on a cushion of vapor that forms between the droplets and a hot surface. Now, a US-Australia collaboration (Heiner Linke, University of Oregon, linke@uoregon.edu) shows that these droplets can be steered in a selected direction by placing them on a sawtooth-shaped surface.
Heating the surface to temperatures above the boiling point of water creates a cushion of vapor on which the droplet floats. The researchers think that the jagged sawtooth surface, acting as a sort of ratchet, redirects the flow of vapor, creating a force that moves the droplet in a preferred direction. The droplets travel rapidly over distances of up to a meter and can even be made to move up inclines. This striking method for pumping a liquid occurs for many different liquids (including nitrogen, acetone, methanol, ethanol and water) over a wide temperature range (from - 196 to + 151 C).
A practical application of this phenomenon might be to cool off hot computer processors. In a concept the researchers plan to test, waste heat in a computer would activate a pump moving a stream of liquid past the processor to cool it off. Such a pump for coolants would need no additional power, have no moving parts, and would spring into action only when needed, when the processor gets warm. (Linke et al., Physical Review Letters, upcoming;)

ENTANGLED PHOTON HOLES. In some semiconductor devices, such as light-emitting diodes, an applied voltage can dislodge electrons from some atoms, leaving behind a hole which behaves in some situations as if it were a positively charged particle in its own right. A "current" of holes can move through the material and the holes can recombine later with electrons to produce light. In very loose analogy, James Franson (Johns Hopkins) suggests that photonic holes might be created; a photon hole, to give one example, would be a place in an otherwise intense laser-beam wavefront where a photon had been removed (by passing the laser beam through vapor, forinstance). Not only can there be photon holes, Franson (443-778-6226, james.franson@jhuapl.edu) suggests, but the holes can be entangled, meaning that their quantum properties would be correlated, even if far apart from each other. Such entangled photon-holes would be able to propagate through optical fibers just as well as entangled photons, but might be even more robust against the decoherence (the undoing of the quantum correlations) that plagues present efforts to establish quantum information schemes.

Franson expects to do put his idea to experimental test in the next few months. (Physical Review Letters, 10 March 2006)

SUNLIGHT ON A CHIP. A new LED design employs a handy combination of light and phosphors to produce light whose color spectrum is not so different from that of sunlight. Light emitting diodes (LEDs) convert electricity into light very efficiently, and are increasingly the preferred design for niche applications like traffic and automobile brake lights. To really make an impression in the lighting world, however, a device must be able to produce room light. And to do this one needs a softer, whiter, more color balanced illumination. The advent of blue-light LEDs, used in conjunction with red and green LEDs, helped a lot. But producing LED light efficiently at blue, red, and yellow wavelengths is still relatively expensive, and an alternative approach is to use phosphors to artificially achieve the desired balance, by turning blue into yellow light. Scientists at the National Institute for Materials Science and at the Sharp Corporation (in Japan) have now achieved a highly efficient, tunable white light with an improved yellow-producing phosphor. Their light yield is 55 lumens per watt, about twice as bright as commercially available products operating in the same degree of whiteness. (Xie et al., Applied Physics Letters, 6 March 2006; contact Rong-Jun Xie, xie.rong-jun@nims.go.jp)

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PHYSICS NEWS UPDATE
     
The American Institute of Physics Bulletin of Physics News
Number 772  April 5, 2006  by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi