238 research outputs found

    Unusual chemical compositions of noctilucent-cloud particle nuclei

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    Two sounding rocket payloads were launched from the ESRO range in Sweden during a noctilucent cloud display. Large numbers of submicron particles were collected, most of which appear to be made up of a high density material coated with a low density material. Typical electron micrographs are shown. Particle chemical compositions have been measured by use of dispersive X-ray analysis equipment attached to an electron microscope and have revealed that most of the high density particle nuclei have atomic weights greater than iron

    Possible evidence of ablation on cosmic dust particles

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    Scanning electron micrographic studies on trapped particles collected shortly after the Leonid meteor shower exhibit surface ablation and spherical formation

    S-149 micrometeorite collection experiment

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    There are no author-identified significant results in this report

    Evolutionary and Physical Properties of Meteoroids

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    Astrophysical models for meteoroid formation and stellar and planetary evolutions are developed from simulation composition studies

    The Survival of Microorganisms in Space. Further Rocket and Balloon Borne Exposure Experiments

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    Rocket and balloon borne exposure experiments on survival of microorganisms in space environmen

    Image-orthicon spectra of Geminids in 1969

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    The spectra of 25 meteors, recorded with an image orthicon technique in December 1969, are studied in relation to similar records made in August of the same year. Of 19 Geminid meteors in the absolute visual magnitude range 0 to +2, only one showed any evidence of the forbidden line of oxygen at 5577 A, while all Perseid meteors recorded in August exhibited the oxygen line, a result of the large difference in geocentric velocity between the two showers. Atoms identified in faint Geminid meteors include neutral iron, magnesium, calcium and sodium. The molecular bands of nitrogen are also observed

    An unusual meteor spectrum

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    An extraordinary spectrum of a meteor at a velocity of about 18.5 + or - 1.0 km/s was observed with an image orthicon camera. The radiant of the meteor was at an altitude of about 49 deg. It was first seen showing a yellow red continuous spectrum alone at a height of 137 + or - 8 km which is ascribed to the first positive group of nitrogen bands. After the meteor had descended to 116 + or - 6 km above sea level it brightened rapidly from its previous threshold brightness into a uniform continuum, the D-line of neutral sodium appeared, and at height 105 + or - 5 km all the other lines of the spectrum also appeared. The continuum remained dominant to the end. Water of hydration and entrained carbon flakes of characteristic dimension about 0.2 micron or less are proposed as constituents of the meteoroid to explain these phenomena

    Onset of criticality and transport in a driven diffusive system

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    We study transport properties in a slowly driven diffusive system where the transport is externally controlled by a parameter pp. Three types of behavior are found: For p<p′p<p' the system is not conducting at all. For intermediate pp a finite fraction of the external excitations propagate through the system. Third, in the regime p>pcp>p_c the system becomes completely conducting. For all p>p′p>p' the system exhibits self-organized critical behavior. In the middle of this regime, at pcp_c, the system undergoes a continuous phase transition described by critical exponents.Comment: 4 latex/revtex pages; 4 figure

    Bostonia. Volume 16

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    Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
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