4 research outputs found
The HiSPARC experiment
The High School Project on Astrophysics Research with Cosmics (HiSPARC) is a
large extensive air shower (EAS) array with detection stations throughout the
Netherlands, United Kingdom, Denmark and Namibia. HiSPARC is a collaboration of
universities, scientific institutes and high schools. The majority of detection
stations is hosted by high schools. A HiSPARC station consists of two or four
scintillators placed inside roof boxes on top of a building. The measured
response of a detector to single incoming muons agrees well with GEANT4
simulations. The response of a station to EASs agrees with simulations as well.
A four-scintillator station was integrated in the KASCADE experiment and was
used to determine the accuracy of the shower direction reconstruction. Using
simulations, the trigger efficiency of a station to detect a shower as function
of both distance to the shower core and zenith angle was determined. The
HiSPARC experiment is taking data since 2003. The number of stations (~140 in
2019) still increases. The project demonstrates that its approach is viable for
educational purposes and that scientific data can be obtained in a
collaboration with high school students and teachers.Comment: Accepted for publication in NIM
DNA damage in transcribed genes induces apoptosis via the JNK pathway and the JNK-phosphatase MKP-1
The nucleotide excision repair (NER) system consists of two subpathways, global genome repair (GGR) and transcription-coupled repair (TCR), which exhibit distinct functions in the cellular response to genotoxic stress. Defects in TCR result in prolonged UV light-induced stalling of RNA polymerase II and hypersensitivity to apoptosis induced by UV and certain chemotherapeutic drugs. Here, we show that low doses of UV trigger delayed activation of the stress-induced MAPkinase JNK and its proapoptotic targets c-Jun and ATF-3 in TCR-deficient primary human fibroblasts from Xeroderma Pigmentosum (XP) and Cockayne syndrome (CS) patients. This delayed activation of the JNK pathway is not observed in GGR-deficient TCR-proficient XP cells, is independent of functional p53, and is established through repression of the JNK-phosphatase MKP-1 rather than by activation of the JNK kinases MKK4 and 7. Enzymatic reversal of UV-induced cyclobutane pyrimidine dimers (CPDs) by CPD photolyase abrogated JNK activation, MKP-1 repression, and apoptosis in TCR-deficient XPA cells. Ectopic expression of MKP-1 inhibited DNA-damage-induced JNK activity and apoptosis. These results identify both MKP-1 and JNK as sensors and downstream effectors of persistent DNA damage in transcribed genes and suggest a link between the JNK pathway and UV-induced stalling of RNApol II.Oncogene advance online publication, 25 July 2005; doi:10.1038/sj.onc.1208875
Spin density matrix elements in exclusive electroproduction on and targets at 27.5 GeV beam energy
Spin Density Matrix Elements (SDMEs) describing the angular distribution of
exclusive rho^0 electroproduction and decay are determined in the HERMES
experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium
targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal
polarization of the beam are extracted in the kinematic region 1 GeV^2 < Q^2 <
7 GeV^2, 3.0 GeV < W < 6.3 GeV, and -t < 0.4 GeV^2. Within the given
experimental uncertainties, a hierarchy of relative sizes of helicity
amplitudes is observed. Kinematic dependences of all SDMEs on Q^2 and t are
presented, as well as the longitudinal-to-transverse rho^0 electroproduction
cross section ratio as a function of Q^2. A small but statistically significant
deviation from the hypothesis of s-channel helicity conservation is observed.
An indication is seen of a contribution of unnatural-parity-exchange
amplitudes; these amplitudes are naturally generated with a quark-exchange
mechanism.Comment: 41 pages, 20 figures, 16 table; revised version corrects small typos,
text clarified on 6 pages, two references added and new data added to figure
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