5,448 research outputs found

    A photon-counting photodiode array detector for far ultraviolet (FUV) astronomy

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    A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location

    Characterizing upward lightning with and without a terrestrial gamma-ray flash

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    We compare two observations of gamma-rays before, during, and after lightning flashes initiated by upward leaders from a tower during low-altitude winter thunderstorms on the western coast of Honshu, Japan. While the two leaders appear similar, one produced a terrestrial gamma-ray flash (TGF) so bright that it paralyzed the gamma-ray detectors while it was occurring, and could be observed only via the weaker flux of neutrons created in its wake, while the other produced no detectable TGF gamma-rays at all. The ratio between the indirectly derived gamma-ray fluence for the TGF and the 95% confidence gamma-ray upper limit for the gamma-ray quiet flash is a factor of 1Ă—1071\times10^7. With the only two observations of this type providing such dramatically different results -- a TGF probably as bright as those seen from space and a powerful upper limit -- we recognize that weak, sub-luminous TGFs in this situation are probably not common, and we quantify this conclusion. While the gamma-ray quiet flash appeared to have a faster leader and more powerful initial continuous current pulse than the flash that produced a TGF, the TGF-producing flash occurred during a weak gamma-ray "glow", while the gamma-ray quiet flash did not, implying a higher electric field aloft when the TGF was produced. We suggest that the field in the high-field region approached by a leader may be more important for whether a TGF is produced than the characteristics of the leader itself.Comment: 21 pages, 6 figures, accepted for publication by the Journal of Geophysical Research - Atmosphere

    1 May 1913 property agreement

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    Agreement between G. M. D. Bowers, W. W. Colson, and B. R. Colson to hold Dixieland Park land for Theophilus Brown Larimore. The one-page typewritten document is dated 1 May 1913

    Satisfaction of Mortgage

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    Satisfaction of Mortgage between J. J. Freeze to G. M. D. Bowers and B. R. Colson. The document is dated 11 April 1914

    [Unsigned agreement to hold land unchanged for Larimore]

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    Unsigned agreement on Our Florida Friend letterhead where G. M. D. Bowers, W. W. Colson, and B. R. Colson agree to hold land for Theophilus Brown Larimore unchanged. The agreement is one-page typewritten and dated 1 May 1913

    The Lemaitre-Schwarzschild Problem Revisited

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    The Lemaitre and Schwarzschild analytical solutions for a relativistic spherical body of constant density are linked together through the use of the Weyl quadratic invariant. The critical radius for gravitational collapse of an incompressible fluid is shown to vary continuously from 9/8 of the Schwarzschild radius to the Schwarzschild radius itself while the internal pressures become locally anisotropic.Comment: Final version as accepted by GR&G (to appear in vol. 34, september 2002

    Effective gluon interactions in the Colour Superconductive Phase of two flavor QCD

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    The gluon self-energies and dispersion laws in the color superconducting phase of QCD with two massless flavors are calculated using the effective theory near the Fermi surface. These quantities are calculated at zero temperature for all the eight gluons, those of the remaining SU(2) color group and those corresponding to the broken generators. The construction of the effective interaction is completed with the one loop calculation of the three- and four-point gluon interactions.Comment: LaTeX, p 17, 4 figures. Final version to be published in Phys. Lett. B. Several corrections have been done and some point clarifie
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