PHYSICS NEWS UPDATE -- Number 713 December 27, 2004 by Phillip F. Schewe, Ben Stein
From: Sam Wormley (swormley1_at_mchsi.com)
Date: 12/27/04
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Date: Mon, 27 Dec 2004 23:12:48 GMT
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 713 December 27, 2004 by Phillip F. Schewe, Ben Stein
WHY DO HEART ATTACKS OCCUR MOST FREQUENTLY BETWEEN 9 AND 11 AM?
Studying five healthy volunteers for 10-day periods in pioneering
efforts to ultimately answer this question, a collaboration of
Boston University physicists and Harvard physiologists has found
evidence that the body's circadian clock (a part of the brain that
regulates daily biological activities) influences patterns in the
heart's "interbeat intervals," the lengths of time between
successive heartbeats. At around 10AM for all the healthy
individuals, the values of successive interbeat intervals displayed
increased signs of randomness, statistically resembling that seen in
previous studies of individuals with heart disease. In their
studies, the researchers took special care to isolate the effects of
a person's internal circadian clock (which has a 24.2-hour rhythm,
marked by a regular rise and fall of body temperature) from the
effects of behavior (such as physical activity and a person's
wake/sleep time) or external stimuli (such as the rising or setting
of the sun). Towards these ends, the researchers made sure to
"desynchronize" the individuals' internal body clocks from these
other factors by keeping the volunteers in a dimly lit room and by
varying their sleep and wake times from day to day while keeping
activity levels relatively constant.
The researchers next plan to explore how an individual's behavior
may interact with the circadian clock to influence the correlations
in interbeat intervals. The researchers have not yet studied
patients with heart disease and are far from being able to make
clinical recommendations. However, their further research may obtain
insights into the underlying causes of increased cardiac risk and
could lead to improved therapy, such as more appropriately timed
medication to coincide with phases of the body clock. (Hu et al.,
Proceedings of the National Academy of Sciences, December 28, 2004;
contact Plamen Ch. Ivanov, Boston University, 617-353-3891,
plamen@argento.bu.edu; Steven Shea, Harvard Medical School,
617-732-5013, sshea@hms.harvard.edu)
A PEA-SIZED MAGNETOMETER can do the job of much bigger units, and
measure magnetic fields with a sensitivity of 50 pico-tesla.
Researchers at NIST exploit the fact that rubidium atoms possess
quantum levels whose energies will depend on the ambient magnetic
field. By encapsulating a tiny portion of atoms in a cell and
making precision measurements of laser light traveling through the
atoms, a field reading can be made. All of this is packaged in only
about 12 cubic millimeters. Furthermore, the device can be
manufactured in large batches through lithographic means. For
geophysical applications, such as for detecting underwater or
underground iron objects such as pipelines, tanks, and shipwrecks,
the device's tiny power consumption, compact size, and low price
should move it ahead of several existing magnetometer designs with a
few more years of development work. (Schwindt et al., Applied
Physics Letters, 27 December 2004; contact Peter Schwindt,
schwindt@boulder.nist.gov, 303-497-7969; lab website at
www.boulder.nist.gov/timefreq/ofm/smallclock/CSAM.htm )
DNA STRETCHING CROSS-STREAM. A new experiment shows that in
specially engineered fluid flows typical of coating processes,
single DNA molecules can sometimes enter into a kind of flow
instability in which the DNA orients itself perpendicular to the
plane of the flow. The
experiment, conducted at Rice University by Matteo Pasquali and
Rajat Duggal, was part of a broader study of how polymer molecules
behave in moving fluids, a subject pertinent to many biological and
technological research areas, such as inkjet printing, paper
coating, the movement of air in lung alveoli, and DNA arrays.
Studying polymers in complex fluid flows is difficult because single
polymers are hard to resolve (being typically only 10-100 nm in
size) and because polymers can influence each other and the flow
itself even at very low concentration (down to few parts per
million). That's why DNA (above 10 microns in contour length) was
chosen and why the DNA was kept "ultradilute," so that it would not
influence the flow and that only DNA molecule is visible at a time.
In the Rice experiment, a dilute suspension of DNA in water
thickened by sugar is taken up by a rotating drum which moves past a
glass knife edge. In this way a thin slice of solution can be moved
as if on a conveyor belt past a lens. The lens focuses a blue-green
light on the DNA and picks up green-yellow light emitted by the
previously fluorescently-stained DNA molecules. The resulting
30-frame-per-second film clearly can image
individual DNAs at a time with a spatial resolution of 250 nm (the
thickness of the molecule cannot be resolved but its length can
be). The researchers had expected that in the complex flow (a flow
in which the velocity of the fluid varies across the width of the
channel) the DNA
would deploy itself with the flow rather than at right angles.
Indeed, this happened at the lowest drum rotation speeds; the
direction of stretching changed once the drum speed became high
enough to induce ripples on the surface of the liquid moving past
the glass knife. (Journal of Rheology, July/August 2004)
***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.
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