Michael Schilling

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For the first time an excess of photons above an energy threshold of 730 GeV from the giant radio galaxy M 87 has been measured at a significance level above 4σ. The data have been taken during the years 1998 and 1999 with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes. The excess of 107.4±26.8 events above 730 GeV corresponds(More)
A sample of 54 selected Active Galactic Nuclei (AGN) has been observed with the HEGRA stereoscopic system of Cherenkov Telescopes between 1996 and 2002 in the TeV energy regime. The observations were motivated by the positive results obtained for Mkn 421 and Mkn 501. The distances of the selected objects vary over a large range of redshifts between z =(More)
Immobilized metal affinity chromatography (IMAC) based on Fe (3+) or Ga (3+) chelation is the most widely employed technique for the enrichment of phosphopeptides from biological samples prior to mass spectrometric analysis. An IMAC resin geared mainly toward phosphoprotein enrichment, Pro-Q Diamond, has been assessed for its utility in phosphopeptide(More)
For the first time, we report a miniaturized approach for isotachophoresis employing the technique of free-flow electrophoresis. Using a micromachined separation chamber with a volume of 200 nL, a sample mixture of fluorescein, eosin G, and acetylsalicylic acid was separated, stacked, and concentrated in less than a minute. Additionally, an isotachophoretic(More)
The Crab Nebula has been observed by the HEGRA (High-Energy GammaRay Astronomy) stereoscopic system of imaging air Čerenkov telescopes (IACTs) for a total of about 200 hrs during two observational campaigns: from September 1997 to March 1998 and from August 1998 to April 1999. The recent detailed studies of system performance give an energy threshold and an(More)
A novel electrospray interface is presented which induces an electric field by dielectric polarization through a non-conductive barrier. Therefore, a square-wave high-voltage signal is applied. This technique allows mass spectrometric measurements in the positive as well as in the negative mass spectrometry mode without changing the polarity of the(More)
The mechanism which leads to a dielectric barrier electrospray (DB-ES) was investigated by measurements of the electrical current. It comprises several components, namely, the displacement current, currents which are initiated by electromagnetic transmission, an ion current inside the capillary, which is responsible for the built-up of the potential at the(More)
The mechanism of the previously published technique of dielectric barrier electrospray ionization (DB-ESI) was investigated in more detail. Two independent current signals occurring during the DB-ESI could be explained and allocated to sub-processes. The modulated shape of the HV signal, the applied frequency as well as the inner diameter of the emitter(More)
The parameters influencing the combination of the dielectric barrier electrospray (DB-ES) with an ion trap mass spectrometer are investigated. Two approaches are presented: the application of different polarity cycles in the DB electrospray high voltage signal and the triggering of it to an output signal received by the mass spectrometer. Both approaches(More)
The HEGRA system of imaging air Cherenkov telescopes has been used to observe the BL Lac object H1426+428 (z = 0.129) for 217.5 hours in 2002. In this data set alone, the source is detected at a confidence level of 5.3 σ, confirming this object as a TeV source. The overall flux level during the observations in 2002 is found to be a factor of ≈ 2.5 lower(More)