| Topic: |
Science > Physics |
| User: |
"Robert Karl Stonjek" |
| Date: |
13 Apr 2006 08:59:56 PM |
| Object: |
ScienceMag - Editors Choices |
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ScienceMag - Editors Choices
http://www.sciencemag.org/content/vol312/issue5771/twil.dtl
Posted by
Robert Karl Stonjek
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SPACE POLICY: A Line in the Sky
Where does airspace end and outer space begin? Space exploration has =
proceeded for nearly 50 years without a clear answer, but the increased =
use of spacecraft and satellites by many nations has spurred calls to =
define the boundary precisely. Harris and Harris argue that =
international law should establish a boundary based on the vertical =
distance from Earth's surface, rather than on more complicated =
functional criteria that could change as technology evolves. They note =
that airspace is heavily regulated and comes under the jurisdiction of =
sovereign nations, who have the authority to restrict airplane flight =
above their territories. In contrast, outer space is considered to be a =
public realm--described in the Outer Space Treaty as "the province of =
all mankind"--and an orbiting object is accountable to its owners and =
not to the countries beneath it. At the moment, orbiting satellites can =
be used to observe any country, whereas aircraft can be prohibited from =
doing so legally. Moreover, modern satellites can image the ground with =
meter-scale resolution, yielding pictures as sharp as those captured by =
a spy plane operating in airspace. A vertical boundary definition would =
promote discussion of the policy issues arising from technological =
progress. -- JB
Space Policy 22, 3 (2006).
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ASTROPHYSICS: Galactic Flapping
The Milky Way's flattened disk contains vast reservoirs of hydrogen =
gas. Near the edges, the disk consists mostly of hydrogen, with few =
stars. Radio astronomical observations have revealed warping at these =
edges, as in a dish or saddle. Weinberg and Blitz modeled this warping =
phenomenon using perturbation theory calculations. Their results =
attribute the shape to tidal effects induced by motions of the Milky =
Way's small neighboring galaxies, the Large and Small Magellanic Clouds. =
As these satellite galaxies move in orbital loops around the Milky Way, =
they create trailing wakes in the Milky Way's halo of surrounding dark =
matter. These wakes in turn can cause the outer edges of the Milky Way's =
lightweight gas disk to bend and flap like a flag in the breeze. The =
model describes a dynamic disk, which continually changes its shape as =
the clouds move along their orbits. The authors further suggest that =
warp observations offer a useful constraint for determining dark matter =
distributions. -- JB
Astrophys. J. 641, L33 (2006).
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CHEMISTRY: THF Up Close
Although molecules in the liquid state are in constant random motion, =
they appear to adopt specific average configurations that account for =
such properties as heat capacity and solvation. Insight into these =
configurations has come mainly from theoretical simulations, whose =
accuracy is gauged by the extent to which bulk properties are correctly =
predicted. The pentagonal (CH2)4O tetrahydrofuran (THF) is a widely used =
solvent in organic synthesis because of its relatively high polarity in =
the absence of hydrogen bonding capacity.
Bowron et al. have taken advantage of progress in neutron scattering =
technology to probe the molecular structure of liquid THF at room =
temperature directly. Because neutrons are scattered preferentially by =
protons, the authors refined their analysis by comparing spectra of =
protiated and deuterated THF, as well as a 1:1 mixture of the =
isotopomers. Computer modeling of the data revealed a propensity for =
T-shaped interaction geometries, in which adjacent molecules were =
oriented edge to face. This arrangement leads to 2.5-=C5 diameter void =
spaces, which may account for the solvent's capacity to harbor free =
electrons. -- JSY
J. Am. Chem. Soc. 128, 10.1021/ja0583057 (2006).
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APPLIED PHYSICS: Optical Sifting
The separation and sorting of micrometer-scale particles by size, =
shape, optical properties, or some combination thereof is necessary in a =
broad range of applications, from fundamental lab-on-chip studies to the =
filtering of colloids for materials synthesis. The available techniques =
tend to rely on the precisely controlled microfluidic flow of particles =
through a separator.
Ric=E1rdez-Vargas et al. present a simple alternative method, based on =
reconfigurable patterns of light, that eliminates the need for a =
microfluidic system. Two interfering laser beams form a periodic =
potential energy landscape, resembling a washboard, in the liquid layer =
suspending the polydisperse sample of particles. The spatial periodicity =
of the fringes is varied to accommodate particles of different sizes. By =
modulating one of the laser beams with a sawtooth signal that directs an =
interferometer mirror, the authors effectively vibrate the potential =
landscape from side to side. This jiggling motion is sufficient to =
separate particles that are 1 to 5 m in diameter by size: the larger =
ones are driven in one direction and the smaller ones in the opposite =
direction. Moreover, particles of similar size but different optical =
refractive index (such as latex and silica) can be separated by varying =
the intensity of the light. -- ISO
Appl. Phys. Lett. 88, 121116 (2006).
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<DIV>ScienceMag - Editors Choices<BR><A=20
href=3D"http://www.sciencemag.org/content/vol312/issue5771/twil.dtl">http=
://www.sciencemag.org/content/vol312/issue5771/twil.dtl</A></DIV>
<DIV><BR>Posted by<BR>Robert Karl Stonjek</DIV>
<DIV> </DIV>
<DIV>--------------------------------------------------------------------=
------------</DIV>
<DIV> </DIV>
<DIV>SPACE POLICY: A Line in the Sky<BR> Where does airspace end =
and outer=20
space begin? Space exploration has proceeded for nearly 50 years without =
a clear=20
answer, but the increased use of spacecraft and satellites by many =
nations has=20
spurred calls to define the boundary precisely. Harris and Harris argue =
that=20
international law should establish a boundary based on the vertical =
distance=20
from Earth's surface, rather than on more complicated functional =
criteria that=20
could change as technology evolves. They note that airspace is heavily =
regulated=20
and comes under the jurisdiction of sovereign nations, who have the =
authority to=20
restrict airplane flight above their territories. In contrast, outer =
space is=20
considered to be a public realm--described in the Outer Space Treaty as =
"the=20
province of all mankind"--and an orbiting object is accountable to its =
owners=20
and not to the countries beneath it. At the moment, orbiting satellites =
can be=20
used to observe any country, whereas aircraft can be prohibited from =
doing so=20
legally. Moreover, modern satellites can image the ground with =
meter-scale=20
resolution, yielding pictures as sharp as those captured by a spy plane=20
operating in airspace. A vertical boundary definition would promote =
discussion=20
of the policy issues arising from technological progress. -- JB<BR>Space =
Policy=20
22, 3 (2006).</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>--------------------------------------------------------------------=
------------</DIV>
<DIV> </DIV>
<DIV>ASTROPHYSICS: Galactic Flapping<BR> The Milky Way's flattened =
disk=20
contains vast reservoirs of hydrogen gas. Near the edges, the disk =
consists=20
mostly of hydrogen, with few stars. Radio astronomical observations have =
revealed warping at these edges, as in a dish or saddle. Weinberg and =
Blitz=20
modeled this warping phenomenon using perturbation theory calculations. =
Their=20
results attribute the shape to tidal effects induced by motions of the =
Milky=20
Way's small neighboring galaxies, the Large and Small Magellanic Clouds. =
As=20
these satellite galaxies move in orbital loops around the Milky Way, =
they create=20
trailing wakes in the Milky Way's halo of surrounding dark matter. These =
wakes=20
in turn can cause the outer edges of the Milky Way's lightweight gas =
disk to=20
bend and flap like a flag in the breeze. The model describes a dynamic =
disk,=20
which continually changes its shape as the clouds move along their =
orbits. The=20
authors further suggest that warp observations offer a useful constraint =
for=20
determining dark matter distributions. -- JB<BR>Astrophys. J. 641, L33=20
(2006).</DIV>
<DIV> </DIV>
<DIV>--------------------------------------------------------------------=
------------</DIV>
<DIV> </DIV>
<DIV>CHEMISTRY: THF Up Close<BR> Although molecules in the liquid =
state are=20
in constant random motion, they appear to adopt specific average =
configurations=20
that account for such properties as heat capacity and solvation. Insight =
into=20
these configurations has come mainly from theoretical simulations, whose =
accuracy is gauged by the extent to which bulk properties are correctly=20
predicted. The pentagonal (CH2)4O tetrahydrofuran (THF) is a widely used =
solvent=20
in organic synthesis because of its relatively high polarity in the =
absence of=20
hydrogen bonding capacity.<BR>Bowron et al. have taken advantage of =
progress in=20
neutron scattering technology to probe the molecular structure of liquid =
THF at=20
room temperature directly. Because neutrons are scattered preferentially =
by=20
protons, the authors refined their analysis by comparing spectra of =
protiated=20
and deuterated THF, as well as a 1:1 mixture of the isotopomers. =
Computer=20
modeling of the data revealed a propensity for T-shaped interaction =
geometries,=20
in which adjacent molecules were oriented edge to face. This arrangement =
leads=20
to 2.5-=C5 diameter void spaces, which may account for the solvent's =
capacity to=20
harbor free electrons. -- JSY</DIV>
<DIV> </DIV>
<DIV>J. Am. Chem. Soc. 128, 10.1021/ja0583057 (2006).</DIV>
<DIV> </DIV>
<DIV>--------------------------------------------------------------------=
------------</DIV>
<DIV> </DIV>
<DIV>APPLIED PHYSICS: Optical Sifting<BR> The separation and =
sorting of=20
micrometer-scale particles by size, shape, optical properties, or some=20
combination thereof is necessary in a broad range of applications, from=20
fundamental lab-on-chip studies to the filtering of colloids for =
materials=20
synthesis. The available techniques tend to rely on the precisely =
controlled=20
microfluidic flow of particles through a separator.<BR>Ric=E1rdez-Vargas =
et al.=20
present a simple alternative method, based on reconfigurable patterns of =
light,=20
that eliminates the need for a microfluidic system. Two interfering =
laser beams=20
form a periodic potential energy landscape, resembling a washboard, in =
the=20
liquid layer suspending the polydisperse sample of particles. The =
spatial=20
periodicity of the fringes is varied to accommodate particles of =
different=20
sizes. By modulating one of the laser beams with a sawtooth signal that =
directs=20
an interferometer mirror, the authors effectively vibrate the potential=20
landscape from side to side. This jiggling motion is sufficient to =
separate=20
particles that are 1 to 5 m in diameter by size: the larger ones are =
driven in=20
one direction and the smaller ones in the opposite direction. Moreover,=20
particles of similar size but different optical refractive index (such =
as latex=20
and silica) can be separated by varying the intensity of the light. -- =
ISO</DIV>
<DIV> </DIV>
<DIV>Appl. Phys. Lett. 88, 121116 (2006).<BR></DIV></BODY></HTML>
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