Peter von Ballmoos

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The clonogenic growth inhibition, the cell cycle dependence of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine (NHAC) cytotoxicity and the capability to induce apoptosis in ara-C-sensitive and -resistant HL-60 cells were investigated and compared with arabinofuranosylcytosine (ara-C). In the clonogenic assay with sensitive HL-60 cells, ara-C was slightly(More)
We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately ∼ 95% of the celestial sphere. Within the exposed sky area, 511 keV line emission is significantly detected towards the galactic bulge region and, at a very low level,(More)
We present a measurement of the sky distribution of positronium (Ps) annihilation continuum emission obtained with the SPI spectrometer on board ESA's INTEGRAL observatory. The only sky region from which significant Ps continuum emission is detected is the Galactic bulge. The Ps continuum emission is circularly symmetric about the Galactic centre, with an(More)
With the aim of analysing the relative importance of sugar supply and nitrogen nutrition for the regulation of sulphate assimilation, the regulation of adenosine 5'-phosphosulphate reductase (APR), a key enzyme of sulphate reduction in plants, was studied. Glucose feeding experiments with Arabidopsis thaliana cultivated with and without a nitrogen source(More)
Gamma-ray line radiation at 511 keV is the signature of electron-positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles(More)
The Gamma-Ray Imager (GRI) is a novel mission concept that will provide an unprecedented sensitivity leap in the soft gamma-ray domain by using for the first time a focusing lens built of Laue diffracting crystals. The lens will cover an energy band from 200-1300 keV with an effective area reaching 600 cm 2. It will be complemented by a single reflection(More)
The imaging spectrometer SPI on board ESA's INTEGRAL observatory provides us with an unprecedented view of positron annihilation in our Galaxy. The first sky maps in the 511 keV annihilation line and in the positronium continuum from SPI showed a puzzling concentration of annihilation radiation in the Galactic bulge region. By now, more than twice as many(More)
During its first year in orbit the INTEGRAL observatory performed deep exposures of the Galac-tic Center region and scanning observations of the Galactic plane. We report on the status of our analysis of the positron annihilation radiation from the 4 th Galactic quadrant with the spectrometer SPI, focus-ing on the sky distribution of the 511 keV line(More)
Phase Fresnel lenses have the same imaging properties as zone plates, but with the possibility of concentrating all of the incident power into the primary focus, increasing the maximum theoretical efficiency from 11% to close to 100%. For X-rays, and in particular for gamma-rays, large, diffraction-limited phase Fresnel lenses can be made relatively easily.(More)
Crystals are the elementary constituents of Laue lenses, an emerging technology which could allow the realization of a space borne telescope 10 to 100 times more sensitive than existing ones in the 100 keV-1.5 MeV energy range. This study addresses the current endeavor to the development of efficient crystals for the realization of a Laue lens. In the(More)