archive: SETI Physics News Update.247

SETI Physics News Update.247

Larry Klaes ( lklaes@bbn.com )
Tue, 11 May 1999 08:20:57 -0400

>Date: Mon, 10 May 1999 14:22:39 -0400 (EDT)
>From: AIP listserver <physnews@aip.org>
>To: physnews-mailing@aip.org
>Subject: update.247
>
>PHYSICS NEWS UPDATE
>The American Institute of Physics Bulletin of Physics News
>Number 427 May 10, 1999 by Phillip F. Schewe and Ben Stein
>
>WATCHING PACEMAKERS FORM IN A PETRI DISH. The
>bandleaders of biological systems, pacemakers are cells or groups
>of cells capable of generating regularly repeating activity on their
>own or in response to outside signals. In humans, roughly 5000
>cells in the sinoatrial node, located in the right roof of the atrium,
>generate the signals that regulate the rhythmic contractions of the
>heart. In efforts that may improve understanding of how natural
>pacemakers form and provide steady signals, researchers at
>Technion University in Israel (Yoav Soen, yoav@technion.ac.il)
>excised muscle cells and connective tissue (fibroblasts) from the
>ventricles of rats. Spreading these cells on a petri dish under the
>proper conditions caused the cells to proliferate, move around and
>eventually form a hardy network of fibers after 1-3 weeks. Using a
>CCD camera and real-time computer processing , the researchers
>detected rhythmic contractions in the cells. They also noticed
>rhythm disorders, such as alternations between irregular and
>regular rates of contraction. This suggested to them that one or
>more pacemakers had formed within the network. While in-vitro
>pacemaker activity has been observed before, the Technion optical
>technique is the first that monitors the cells noninvasively and
>continuously long enough to watch a cell network evolve and form
>a pacemaker system. Although the cell network is very different
>from a biological heart, it can provide insights into how its
>structure and density affects the development of a pacemaker.
>(Soen et al., Physical Review Letters, 26 April; figure at
>www.aip.org/physnews/graphics)
>
>CONTROLLING STOCHASTIC RESONANCE. In some
>systems, such as radio receivers, turning up the volume in order to
>hear a faint signal amidst much noise usually only results in
>turning up the noise as well. However, in other systems increasing
>the amount of ambient noise actually enhances (up to a certain
>point) the signal-to-noise ratio through a complicated nonlinear
>cooperation between the system and detector. This effect, known
>to operate in neurons, lasers, and tunnel diodes, is called stochastic
>resonance: the noise fluctuations might be stochastic (meaning
>totally random) but the detection of a desired signal can be
>maximized by tuning the noise. Now, researchers at Georgia Tech
>(Bill Ditto, 404-894-5216, wditto@acl.gatech.edu) have not only
>adjusted the noise knob to advantage but also the detector
>threshold. This can make the signal-to-noise ratio even better, with
>a bearing on the study of how sensory systems such as touch or
>hearing can pick out faint signals. Conversely the extra control
>mechanism can be used to undo the stochastic resonance effect,
>which just might be a desirable step in, for example, military
>applications (jamming) or in the suppression of unwanted
>interactions between electromagnetic radiation and biological
>tissue. (Gammaitoni et al., Physical Review Letters, tent. 31 May.)
>
>FERMI QUESTIONS, named for the Enrico Fermi who reveled in
>the exercise, are problems that call upon the art of approximation.
>Example: How many liters of water are drunk in the US per year?
>Answer---10^11 liters (250 x 10^6 people times 1.5 liters of water
>per day times 365 days). How long would it take to walk the
>distance between Earth and Moon? 10^4 days (2.4 x 10^5 miles
>divided by 24 miles/day). The number of postage stamps covering
>a football field? 10^7 (stamp area of 4 cm^2 over a field of 100 x
>50 m^2). (The Physics Teacher magazine, May 1999; contact
>columnist Karen Bouffard, at kbouff@aol.com.)
>