Internet:Historie und Technik

Das Internet - oft als "Netz der Netze" bezeichnet - hat in den letzten Jahren ein rasantes Wachstum hinter sich. Häufig wird der Begriff Internet mit dem Internet-Dienst World Wide Web gleichgesetzt, ohne hier die notwendige Differenzierung vorzunehmen, denn das Internet ist weit mehr als nur ein Medium zur Verwaltung von World-Wide-Web-Seiten. Dienste wie FTP, E-Mail und NetNews verzeichnen auch drei Jahrzehnte nach den ersten Internet- Versuchen stetig zunehmende Benutzerzahlen. Um die Diskussion um das Internet konzeptionell zu untermauern, wird in diesem Artikel die historische Entwicklung, die zur Bildung des Internet in seiner heutigen Form führte, beschrieben sowie der technische Hintergrund und die Organisation des weltweiten Datennetzes näher erläutert. Daran anschließend werden einige Entwicklungen erläutert, welche die zukünftige Entwicklung des Internet beeinflussen werden.<br/

Der Lösungsbeitrag von Metadatenmodellen beim Vergleich von Workflowmanagementsystemen

Die DV-gestützte Prozeßabwicklung mittels Workflowmanagementsystemen erlaubt die Auslagerung der Ablaufsteuerung aus Anwendungssystemen. Mittlerweile ist eine Vielzahl an Systemen mit unterschiedlicher Entwicklungsgeschichte (Dokumentenmanagement, Vorgangssteuerung etc.) verfügbar. Damit stellt sich das Problem der Auswahl eines bedarfsgerechten Workflowmanagementsystems. Im Rahmen dieses Arbeitsberichts soll der diesbezügliche Lösungsbeitrag des Vergleichs der Metadatenmodelle von Workflowmanagementsystemen evaluiert werden. Nach allgemeinen Ausführungen zur Metamodellierung werden hierzu exemplarisch die Metadatenmodelle für die Workflowmanagementsysteme WorkParty (SNI) und FlowMark (IBM) skizziert und verglichen.<br/

Searching for a Stochastic Background of Gravitational Waves with LIGO

The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed the fourth science run, S4, with significantly improved interferometer sensitivities with respect to previous runs. Using data acquired during this science run, we place a limit on the amplitude of a stochastic background of gravitational waves. For a frequency independent spectrum, the new limit is $\Omega_{\rm GW} < 6.5 \times 10^{-5}$. This is currently the most sensitive result in the frequency range 51-150 Hz, with a factor of 13 improvement over the previous LIGO result. We discuss complementarity of the new result with other constraints on a stochastic background of gravitational waves, and we investigate implications of the new result for different models of this background.Comment: 37 pages, 16 figure

Search of S3 LIGO data for gravitational wave signals from spinning black hole and neutron star binary inspirals

We report on the methods and results of the first dedicated search for gravitational waves emitted during the inspiral of compact binaries with spinning component bodies. We analyze 788 hours of data collected during the third science run (S3) of the LIGO detectors. We searched for binary systems using a detection template family designed specially to capture the effects of the spin-induced precession of the orbital plane. We present details of the techniques developed to enable this search for spin-modulated gravitational waves, highlighting the differences between this and other recent searches for binaries with non-spinning components. The template bank we employed was found to yield high matches with our spin-modulated target waveform for binaries with masses in the asymmetric range 1.0 Msol < m1 < 3.0 Msol and 12.0 Msol < m2 < 20.0 Msol which is where we would expect the spin of the binary's components to have significant effect. We find that our search of S3 LIGO data had good sensitivity to binaries in the Milky Way and to a small fraction of binaries in M31 and M33 with masses in the range 1.0 Msol < m1, m2 < 20.0 Msol. No gravitational wave signals were identified during this search. Assuming a binary population with spinning components and Gaussian distribution of masses representing a prototypical neutron star - black hole system with m1 ~ 1.35 Msol and m2 ~ 5 Msol, we calculate the 90%-confidence upper limit on the rate of coalescence of these systems to be 15.9 yr^-1 L_10^-1, where L_10 is 10^10 times the blue light luminosity of the Sun.Comment: 18 pages, 8 figure

Upper limits on gravitational wave emission from 78 radio pulsars

We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors. The data from both runs have been combined coherently to maximize sensitivity. For the first time, pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is 2.6×10-25 for PSR J1603-7202, and the equatorial ellipticity of PSR J2124–3358 is less than 10-6. Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times greater than the fiducial spin-down limit