Validation of Electromagnetic Showers in CORSIKA 8

The air shower simulation code CORSIKA has served as a key part of the simulation chain for numerous astroparticle physics experiments over the past decades. Due to retirement of the original developers and the increasingly difficult maintenance of the monolithic Fortran code of CORSIKA, a new air shower simulation framework has been developed over the course of the last years in C++, called CORSIKA 8. Besides the hadronic and muonic component, the electromagnetic component is one of the key constituents of an air shower. The cascade producing the electromagnetic component of an air shower is driven by bremsstrahlung and photoproduction of electron-positron pairs. At ultrahigh energies or in media with high densities, the bremsstrahlung and pair production processes are suppressed by the Landau-Pomeranchuk-Migdal (LPM) effect, which leads to more elongated showers compared to showers without the LPM suppression. Furthermore, photons at higher energies can produce muon pairs or interact hadronically with nucleons in the target medium, producing a muon component in electromagnetic air showers. In this contribution, we compare electromagnetic showers simulated with the latest Fortran version of CORSIKA and CORSIKA 8, which uses the library PROPOSAL for the electromagnetic component. While earlier validations of CORSIKA 8 electromagnetic showers focused on showers of lower energy, the recent implementation of the LPM effect, photo pair production of muons, and of photohadronic interactions allows now to make a physics-complete comparison also at high energies.Comment: Proceedings of the 38th International Cosmic Ray Conference (ICRC) in Nagoya, Japa

Transcriptional transactivation by selected short random peptides attached to lexA-GFP fusion proteins

BACKGROUND: Transcriptional transactivation is a process with remarkable tolerance for sequence diversity and structural geometry. In studies of the features that constitute transactivating functions, acidity has remained one of the most common characteristics observed among native activation domains and activator peptides. RESULTS: We performed a deliberate search of random peptide libraries for peptides capable of conferring transcriptional transactivation on the lexA DNA binding domain. Two libraries, one composed of C-terminal fusions, the other of peptide insertions within the green fluorescent protein structure, were used. We show that (i) peptide sequences other than C-terminal fusions can confer transactivation; (ii) though acidic activator peptides are more common, charge neutral and basic peptides can function as activators; and (iii) peptides as short as 11 amino acids behave in a modular fashion. CONCLUSIONS: These results support the recruitment model of transcriptional activation and, combined with other studies, suggest the possibility of using activator peptides in a variety of applications, including drug development work

Functional Comparison of Induced Pluripotent Stem Cell- and Blood-Derived GPIIbIIIa Deficient Platelets

Human induced pluripotent stem cells (hiPSCs) represent a versatile tool to model genetic diseases and are a potential source for cell transfusion therapies. However, it remains elusive to which extent patient-specific hiPSC-derived cells functionally resemble their native counterparts. Here, we generated a hiPSC model of the primary platelet disease Glanzmann thrombasthenia (GT), characterized by dysfunction of the integrin receptor GPIIbIIIa, and compared side-by-side healthy and diseased hiPSC-derived platelets with peripheral blood platelets. Both GT-hiPSC-derived platelets and their peripheral blood equivalents showed absence of membrane expression of GPIIbIIIa, a reduction of PAC-1 binding, surface spreading and adherence to fibrinogen. We demonstrated that GT-hiPSC-derived platelets recapitulate molecular and functional aspects of the disease and show comparable behavior to their native counterparts encouraging the further use of hiPSC-based disease models as well as the transition towards a clinical application

Book Reviews

With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino ‘track’ events from the Northern Hemisphere, while the second analysis uses 2 years of ‘cascade’ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than $10^{28}$ s at 90% CL for dark matter masses above 10 TeV