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Digitale Medien

Measuring Seeing from Solar Scintillometry and the Spectral Ratio Technique (2000)

Goode, P.R. ; Wang, H. ; Marquette, W.H. ; [weitere]

Springer

Solar physics 195 (2000), S. 421-431

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract In principle, the optical transfer function can be described by a single parameter, the Fried parameter r 0, which reveals the net effect of the turbulence along the line of sight. We present measurements of the Fried parameter obtained from the spectral ratio technique and compare them to data from solar scintillometry and from angle-of-arrival fluctuations. The measurements were performed at the Big Bear Solar Observatory (BBSO) in 1997 and 1998 – before and after a series of steps were taken to reduce dome seeing. The results show that the dome seeing was considerably reduced and now approaches the seeing conditions measured outside the dome. The Fried parameter as measured by the spectral ratio technique now frequently exceeds r 0=10 cm at our lake site observatory. Accounting for the remaining dome and window seeing, the scintillometer and the angle-of-arrival data imply the potential for an r 0〉20 cm for BBSO during days of good seeing.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1005285314970

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Digitale Medien

An analysis of the business characteristics of adopters and non‐adopters of World Wide Web technology (2000)

Goode, Sigi ; Stevens, Kenneth

Springer

Information technology and management 1 (2000), S. 129-154

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ISSN: 1573-7667

Schlagwort(e): World Wide Web ; adoption ; business size ; business age ; IT experience ; industry

Quelle: Springer Online Journal Archives 1860-2000

Thema: Informatik

Notizen: Abstract The World Wide Web has received considerable media attention in recent times. Little is known concerning the technology’s appeal for commercial applications, and the topic deserves investigation. This study aims to analyze the differences between adopter and non‐adopter businesses according to their organizational characteristics. Six characteristics consistently associated with the adoption of technology, business size, age, industry, use of an IT support unit and IT budget, and degree of technology experience, are selected from the literature. A sample of 245 adopter businesses is gathered using on‐line directories and “keyword” searches of the World Wide Web. A sample of 245 non‐adopter businesses is obtained from the state business telephone directory. The study finds a number of interesting associations. No significant relationship is found between business size and World Wide Web adoption. Adopters tend to be younger yet more experienced with technology than non‐adopters. Businesses that made use of IT budgets and IT support units also tended to be adopters, however adoption did not rely on the existence of these two factors. The study raises a number of additional findings that are of interest but are not directly related to this work. These findings merit further research.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1019112722593

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Extreme-Ultraviolet Flare Loop Emissions in an Eruptive Event (2000)

Qiu, Jiong ; Wang, Haimin ; Chae, Jongchul ; [weitere]

Springer

Solar physics 194 (2000), S. 269-283

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The TRACE/BBSO joint campaign on 27 September 1998 observed an eruptive flare event which lasted for half an hour. The observation covered several ultraviolet (UV) and extreme-ultraviolet (EUV) lines and Hα center and off-band emissions with very high spatial resolution. We find the EUV emissions in different stages of the flare display different characteristics. (1) During the `pre-flare' phase, when the SXR output was weak, we observed simultaneous impulsive HXR peak at 25–100 keV and strong EUV emission. (2) In the impulsive phase, when Hα, UV and SXR emissions were rising to the maxima, the EUV emission was very weak. (3) During the main phase, when SXR emission was decaying, a peak in the EUV emission was observed which was substantially delayed by 7 min compared to emissions from other wavelengths. Based on our observations, we propose that the `pre-flare' phase in this event was a separate energy release process rather than a mere pre-cursor of the flare, and it is likely that the `pre-flare' EUV emission was due to weak in situ heating of low-lying coronal loops. The mechanism of the EUV emission in the main phase is investigated. It is suggested that the delayed EUV emission may come from cooling of SXR loops.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1005283023336

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High-Resolution Hα Observations of Proper Motion in NOAA 8668: Evidence for Filament Mass Injection by Chromospheric Reconnection (2000)

Chae, Jongchul ; Denker, Carsten ; Spirock, Tom J. ; [weitere]

Springer

Solar physics 195 (2000), S. 333-346

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract There have been two different kinds of explanations for the source of cool material in prominences or filaments: coronal condensations from above and cool plasma injections from below. In this paper, we present observational results which support filament mass injection by chromospheric reconnection. The observations of an active filament in the active region NOAA 8668 were performed on 17 August 1999 at a wavelength of Hα−0.6 Å using the 65 cm vacuum reflector, a Zeiss Hα birefringent filter, and a 12-bit SMD digital camera of Big Bear Solar Observatory. The best image was selected every 12 s for an hour based on a frame selection algorithm. All the images were then co-aligned and corrected for local distortion due to the seeing. The time-lapse movie of the data shows that the filament was undergoing ceaseless motion. The Hα flow field has been determined as a function of time using local correlation tracking. Time-averaged flow patterns usually trace local magnetic field lines, as inferred from Hα fibrils and line-of-sight magnetograms. An interesting finding is a transient flow field in a system of small Hα loops, some of which merge into the filament. The flow is associated with a cancelling magnetic feature which is located at one end of the loop system. Initially a diverging flow with speeds below 10 km s−1 is visible at the flux cancellation site. The flow is soon directed along the loops and accelerated up to 40 km s−1 in a few minutes. Some part of the plasma flow then merges into and moves along the filament. This kind of transient flow takes place several times during the observations. Our results clearly demonstrate that reconnection in the photosphere and chromosphere is a likely way to supply cool material to a filament, as well as re-organizing the magnetic field configuration, and, hence, is important in the formation of filaments.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1005242832293

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