SETI update.437

Larry Klaes (
Fri, 02 Jul 1999 16:14:19 -0400

>Date: Fri, 2 Jul 1999 10:50:52 -0400 (EDT)
>From: AIP listserver <>
>Subject: update.437
>The American Institute of Physics Bulletin of Physics News
>Number 437 July 2, 1999 by Phillip F. Schewe and Ben Stein
>Interstellar matter formed in a supernova has been discovered on
>Earth now for the first time. Light coming to Earth from distant
>supernovas is recorded all the time. Likewise, a dozen or so
>neutrinos from nearby Supernova 1987A have been detected. But
>atoms from supernovas are a different matter. In a sense, all the
>heavy atoms on Earth have been processed through or created in
>supernovas long ago and far away. But now comes evidence of
>atoms from a supernova that may have been deposited here only a
>few million years ago. An interdisciplinary team of German
>scientists from the Technical University of Munich (Gunther
>Korschinek, 011-49-89-289-14257, >Korschinek, 011-49-89-289-14257, korschin@physik.tu-
>, the Max-Planck Institute (Garching), and the
>University of Kiel have identified radioactive iron-60 atoms in an
>ocean sediment layer from a seafloor site in the South Pacific.
>First, several sediment layers were dated, and only then were
>samples scrutinized with accelerator mass spectroscopy, needed to
>spot the faintly-present iron. The half-life of Fe-60 (only 1.5
>million years), the levels detected in the sample, and the lack of
>terrestrial sources point to a relatively nearby and recent supernova
>as the origin. How recent? Several million years. How close? An
>estimated 90-180 light years. If the supernova had been any closer
>than this, it might have had an impact on Earth's climate. The
>researchers believe traces of the Fe-60 layer (like the iridium layer
>that signaled the coming of a dinosaur-killing meteor 65 million
>years ago) should be found worldwide but have not yet been able
>to search for it. (K. Knie et al., Physical Review Letters, 5 July
>In organic light emitting devices (OLEDs) electrical energy
>injected onto a host molecule is often transferred to luminescent
>"guest" molecules which then light up. Using this approach,
>OLEDs have been fabricated to emit colors ranging from violet to
>the near infrared and have been incorporated into displays already
>on the market. So far OLED researchers have concentrated on
>maximizing fluorescent emission of light. Fluorescent OLEDs use
>a process whereby the energy transfer occurs between a singlet-
>state (total spin of zero) host molecule and a singlet-state guest
>molecule. Phosphorescent OLEDs, by contrast, transfer energy
>from a triplet-state (total spin value of one) host to a triplet-state
>guest, which subsequently emits the energy as light.
>Phosphorescence is inherently a slower and less efficient process,
>but triplet states constitute the majority of electrically excited
>states, so putting them to
>work can increase the overall luminescence. This is exactly what
>scientists at Princeton (Stephen Forrest,
>,609-258-4532) and the University of
>California have now done. Using both singlet and triplet states for
>producing green light, they have achieved quantum efficiencies
>(photons out divided by electrons in) of up to 8% and power
>efficiencies (optical power out divided by electrical power in) of up
>to 30 lumens/Watt. These high efficiencies are unprecedented and
>may have a great impact on display technology. (Baldo et al.,
>Applied Physics Letters, 5 July 1999).
>out by the Soudan-2 detector, located deep in a Minnesota mine
>and built originally to look for proton decay. To be exact, Soudan
>records muons produced by incoming cosmic rays hitting the
>atmosphere. The muon imaging process clearly senses the shadow
>cast by the passing Moon, which temporarily blocks cosmic rays
>coming from that position in the sky. (Science, 18 June.)

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